    /* pngrtran.c - transforms the data in a row for PNG readers
     *
     * Last changed in libpng 1.6.4 [August 21, 2013]
     * Copyright (c) 1998-2013 Glenn Randers-Pehrson
     * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
     * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
     *
     * This code is released under the libpng license.
     * For conditions of distribution and use, see the disclaimer
     * and license in png.h
     *
     * This file contains functions optionally called by an application
     * in order to tell libpng how to handle data when reading a PNG.
     * Transformations that are used in both reading and writing are
     * in pngtrans.c.
     */

    #include "pngpriv.h"

    #ifdef PNG_READ_SUPPORTED

    /* Set the action on getting a CRC error for an ancillary or critical chunk. */
    void PNGAPI
    png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
    {
       png_debug(1, "in png_set_crc_action");

       if (png_ptr == NULL)
          return;

       /* Tell libpng how we react to CRC errors in critical chunks */
       switch (crit_action)
       {
          case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
             break;

          case PNG_CRC_WARN_USE:                               /* Warn/use data */
             png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
             png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
             break;

          case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
             png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
             png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                               PNG_FLAG_CRC_CRITICAL_IGNORE;
             break;

          case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
             png_warning(png_ptr,
                "Can't discard critical data on CRC error");
          case PNG_CRC_ERROR_QUIT:                                /* Error/quit */

          case PNG_CRC_DEFAULT:
          default:
             png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
             break;
       }

       /* Tell libpng how we react to CRC errors in ancillary chunks */
       switch (ancil_action)
       {
          case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
             break;

          case PNG_CRC_WARN_USE:                              /* Warn/use data */
             png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
             png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
             break;

          case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
             png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
             png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                               PNG_FLAG_CRC_ANCILLARY_NOWARN;
             break;

          case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
             png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
             png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
             break;

          case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */

          case PNG_CRC_DEFAULT:
          default:
             png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
             break;
       }
    }

    #ifdef PNG_READ_TRANSFORMS_SUPPORTED
    /* Is it OK to set a transformation now?  Only if png_start_read_image or
     * png_read_update_info have not been called.  It is not necessary for the IHDR
     * to have been read in all cases, the parameter allows for this check too.
     */
    static int
    png_rtran_ok(png_structrp png_ptr, int need_IHDR)
    {
       if (png_ptr != NULL)
       {
          if (png_ptr->flags & PNG_FLAG_ROW_INIT)
             png_app_error(png_ptr,
                "invalid after png_start_read_image or png_read_update_info");

          else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
             png_app_error(png_ptr, "invalid before the PNG header has been read");

          else
          {
             /* Turn on failure to initialize correctly for all transforms. */
             png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;

             return 1; /* Ok */
          }
       }

       return 0; /* no png_error possible! */
    }
    #endif

    #ifdef PNG_READ_BACKGROUND_SUPPORTED
    /* Handle alpha and tRNS via a background color */
    void PNGFAPI
    png_set_background_fixed(png_structrp png_ptr,
        png_const_color_16p background_color, int background_gamma_code,
        int need_expand, png_fixed_point background_gamma)
    {
       png_debug(1, "in png_set_background_fixed");

       if (!png_rtran_ok(png_ptr, 0) || background_color == NULL)
          return;

       if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
       {
          png_warning(png_ptr, "Application must supply a known background gamma");
          return;
       }

       png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
       png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;

       png_ptr->background = *background_color;
       png_ptr->background_gamma = background_gamma;
       png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
       if (need_expand)
          png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
       else
          png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
    }

    #  ifdef PNG_FLOATING_POINT_SUPPORTED
    void PNGAPI
    png_set_background(png_structrp png_ptr,
        png_const_color_16p background_color, int background_gamma_code,
        int need_expand, double background_gamma)
    {
       png_set_background_fixed(png_ptr, background_color, background_gamma_code,
          need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
    }
    #  endif  /* FLOATING_POINT */
    #endif /* READ_BACKGROUND */

    /* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
     * one that pngrtran does first (scale) happens.  This is necessary to allow the
     * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
     */
    #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
    void PNGAPI
    png_set_scale_16(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_scale_16");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= PNG_SCALE_16_TO_8;
    }
    #endif

    #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
    /* Chop 16-bit depth files to 8-bit depth */
    void PNGAPI
    png_set_strip_16(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_strip_16");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= PNG_16_TO_8;
    }
    #endif

    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
    void PNGAPI
    png_set_strip_alpha(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_strip_alpha");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= PNG_STRIP_ALPHA;
    }
    #endif

    #if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
    static png_fixed_point
    translate_gamma_flags(png_structrp png_ptr, png_fixed_point output_gamma,
       int is_screen)
    {
       /* Check for flag values.  The main reason for having the old Mac value as a
        * flag is that it is pretty near impossible to work out what the correct
        * value is from Apple documentation - a working Mac system is needed to
        * discover the value!
        */
       if (output_gamma == PNG_DEFAULT_sRGB ||
          output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
       {
          /* If there is no sRGB support this just sets the gamma to the standard
           * sRGB value.  (This is a side effect of using this function!)
           */
    #     ifdef PNG_READ_sRGB_SUPPORTED
             png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
    #     else
             PNG_UNUSED(png_ptr)
    #     endif
          if (is_screen)
             output_gamma = PNG_GAMMA_sRGB;
          else
             output_gamma = PNG_GAMMA_sRGB_INVERSE;
       }

       else if (output_gamma == PNG_GAMMA_MAC_18 ||
          output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
       {
          if (is_screen)
             output_gamma = PNG_GAMMA_MAC_OLD;
          else
             output_gamma = PNG_GAMMA_MAC_INVERSE;
       }

       return output_gamma;
    }

    #  ifdef PNG_FLOATING_POINT_SUPPORTED
    static png_fixed_point
    convert_gamma_value(png_structrp png_ptr, double output_gamma)
    {
       /* The following silently ignores cases where fixed point (times 100,000)
        * gamma values are passed to the floating point API.  This is safe and it
        * means the fixed point constants work just fine with the floating point
        * API.  The alternative would just lead to undetected errors and spurious
        * bug reports.  Negative values fail inside the _fixed API unless they
        * correspond to the flag values.
        */
       if (output_gamma > 0 && output_gamma < 128)
          output_gamma *= PNG_FP_1;

       /* This preserves -1 and -2 exactly: */
       output_gamma = floor(output_gamma + .5);

       if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
          png_fixed_error(png_ptr, "gamma value");

       return (png_fixed_point)output_gamma;
    }
    #  endif
    #endif /* READ_ALPHA_MODE || READ_GAMMA */

    #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
    void PNGFAPI
    png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
       png_fixed_point output_gamma)
    {
       int compose = 0;
       png_fixed_point file_gamma;

       png_debug(1, "in png_set_alpha_mode");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);

       /* Validate the value to ensure it is in a reasonable range. The value
        * is expected to be 1 or greater, but this range test allows for some
        * viewing correction values.  The intent is to weed out users of this API
        * who use the inverse of the gamma value accidentally!  Since some of these
        * values are reasonable this may have to be changed.
        */
       if (output_gamma < 70000 || output_gamma > 300000)
          png_error(png_ptr, "output gamma out of expected range");

       /* The default file gamma is the inverse of the output gamma; the output
        * gamma may be changed below so get the file value first:
        */
       file_gamma = png_reciprocal(output_gamma);

       /* There are really 8 possibilities here, composed of any combination
        * of:
        *
        *    premultiply the color channels
        *    do not encode non-opaque pixels
        *    encode the alpha as well as the color channels
        *
        * The differences disappear if the input/output ('screen') gamma is 1.0,
        * because then the encoding is a no-op and there is only the choice of
        * premultiplying the color channels or not.
        *
        * png_set_alpha_mode and png_set_background interact because both use
        * png_compose to do the work.  Calling both is only useful when
        * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
        * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
        */
       switch (mode)
       {
          case PNG_ALPHA_PNG:        /* default: png standard */
             /* No compose, but it may be set by png_set_background! */
             png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
             png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
             break;

          case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
             compose = 1;
             png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
             png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
             /* The output is linear: */
             output_gamma = PNG_FP_1;
             break;

          case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
             compose = 1;
             png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
             png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
             /* output_gamma records the encoding of opaque pixels! */
             break;

          case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
             compose = 1;
             png_ptr->transformations |= PNG_ENCODE_ALPHA;
             png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
             break;

          default:
             png_error(png_ptr, "invalid alpha mode");
       }

       /* Only set the default gamma if the file gamma has not been set (this has
        * the side effect that the gamma in a second call to png_set_alpha_mode will
        * be ignored.)
        */
       if (png_ptr->colorspace.gamma == 0)
       {
          png_ptr->colorspace.gamma = file_gamma;
          png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
       }

       /* But always set the output gamma: */
       png_ptr->screen_gamma = output_gamma;

       /* Finally, if pre-multiplying, set the background fields to achieve the
        * desired result.
        */
       if (compose)
       {
          /* And obtain alpha pre-multiplication by composing on black: */
          memset(&png_ptr->background, 0, (sizeof png_ptr->background));
          png_ptr->background_gamma = png_ptr->colorspace.gamma; /* just in case */
          png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
          png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;

          if (png_ptr->transformations & PNG_COMPOSE)
             png_error(png_ptr,
                "conflicting calls to set alpha mode and background");

          png_ptr->transformations |= PNG_COMPOSE;
       }
    }

    #  ifdef PNG_FLOATING_POINT_SUPPORTED
    void PNGAPI
    png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
    {
       png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
          output_gamma));
    }
    #  endif
    #endif

    #ifdef PNG_READ_QUANTIZE_SUPPORTED
    /* Dither file to 8-bit.  Supply a palette, the current number
     * of elements in the palette, the maximum number of elements
     * allowed, and a histogram if possible.  If the current number
     * of colors is greater then the maximum number, the palette will be
     * modified to fit in the maximum number.  "full_quantize" indicates
     * whether we need a quantizing cube set up for RGB images, or if we
     * simply are reducing the number of colors in a paletted image.
     */

    typedef struct png_dsort_struct
    {
       struct png_dsort_struct * next;
       png_byte left;
       png_byte right;
    } png_dsort;
    typedef png_dsort *   png_dsortp;
    typedef png_dsort * * png_dsortpp;

    void PNGAPI
    png_set_quantize(png_structrp png_ptr, png_colorp palette,
        int num_palette, int maximum_colors, png_const_uint_16p histogram,
        int full_quantize)
    {
       png_debug(1, "in png_set_quantize");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= PNG_QUANTIZE;

       if (!full_quantize)
       {
          int i;

          png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
              (png_uint_32)(num_palette * (sizeof (png_byte))));
          for (i = 0; i < num_palette; i++)
             png_ptr->quantize_index[i] = (png_byte)i;
       }

       if (num_palette > maximum_colors)
       {
          if (histogram != NULL)
          {
             /* This is easy enough, just throw out the least used colors.
              * Perhaps not the best solution, but good enough.
              */

             int i;

             /* Initialize an array to sort colors */
             png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
                 (png_uint_32)(num_palette * (sizeof (png_byte))));

             /* Initialize the quantize_sort array */
             for (i = 0; i < num_palette; i++)
                png_ptr->quantize_sort[i] = (png_byte)i;

             /* Find the least used palette entries by starting a
              * bubble sort, and running it until we have sorted
              * out enough colors.  Note that we don't care about
              * sorting all the colors, just finding which are
              * least used.
              */

             for (i = num_palette - 1; i >= maximum_colors; i--)
             {
                int done; /* To stop early if the list is pre-sorted */
                int j;

                done = 1;
                for (j = 0; j < i; j++)
                {
                   if (histogram[png_ptr->quantize_sort[j]]
                       < histogram[png_ptr->quantize_sort[j + 1]])
                   {
                      png_byte t;

                      t = png_ptr->quantize_sort[j];
                      png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
                      png_ptr->quantize_sort[j + 1] = t;
                      done = 0;
                   }
                }

                if (done)
                   break;
             }

             /* Swap the palette around, and set up a table, if necessary */
             if (full_quantize)
             {
                int j = num_palette;

                /* Put all the useful colors within the max, but don't
                 * move the others.
                 */
                for (i = 0; i < maximum_colors; i++)
                {
                   if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                   {
                      do
                         j--;
                      while ((int)png_ptr->quantize_sort[j] >= maximum_colors);

                      palette[i] = palette[j];
                   }
                }
             }
             else
             {
                int j = num_palette;

                /* Move all the used colors inside the max limit, and
                 * develop a translation table.
                 */
                for (i = 0; i < maximum_colors; i++)
                {
                   /* Only move the colors we need to */
                   if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                   {
                      png_color tmp_color;

                      do
                         j--;
                      while ((int)png_ptr->quantize_sort[j] >= maximum_colors);

                      tmp_color = palette[j];
                      palette[j] = palette[i];
                      palette[i] = tmp_color;
                      /* Indicate where the color went */
                      png_ptr->quantize_index[j] = (png_byte)i;
                      png_ptr->quantize_index[i] = (png_byte)j;
                   }
                }

                /* Find closest color for those colors we are not using */
                for (i = 0; i < num_palette; i++)
                {
                   if ((int)png_ptr->quantize_index[i] >= maximum_colors)
                   {
                      int min_d, k, min_k, d_index;

                      /* Find the closest color to one we threw out */
                      d_index = png_ptr->quantize_index[i];
                      min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                      for (k = 1, min_k = 0; k < maximum_colors; k++)
                      {
                         int d;

                         d = PNG_COLOR_DIST(palette[d_index], palette[k]);

                         if (d < min_d)
                         {
                            min_d = d;
                            min_k = k;
                         }
                      }
                      /* Point to closest color */
                      png_ptr->quantize_index[i] = (png_byte)min_k;
                   }
                }
             }
             png_free(png_ptr, png_ptr->quantize_sort);
             png_ptr->quantize_sort = NULL;
          }
          else
          {
             /* This is much harder to do simply (and quickly).  Perhaps
              * we need to go through a median cut routine, but those
              * don't always behave themselves with only a few colors
              * as input.  So we will just find the closest two colors,
              * and throw out one of them (chosen somewhat randomly).
              * [We don't understand this at all, so if someone wants to
              *  work on improving it, be our guest - AED, GRP]
              */
             int i;
             int max_d;
             int num_new_palette;
             png_dsortp t;
             png_dsortpp hash;

             t = NULL;

             /* Initialize palette index arrays */
             png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
                 (png_uint_32)(num_palette * (sizeof (png_byte))));
             png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
                 (png_uint_32)(num_palette * (sizeof (png_byte))));

             /* Initialize the sort array */
             for (i = 0; i < num_palette; i++)
             {
                png_ptr->index_to_palette[i] = (png_byte)i;
                png_ptr->palette_to_index[i] = (png_byte)i;
             }

             hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
                 (sizeof (png_dsortp))));

             num_new_palette = num_palette;

             /* Initial wild guess at how far apart the farthest pixel
              * pair we will be eliminating will be.  Larger
              * numbers mean more areas will be allocated, Smaller
              * numbers run the risk of not saving enough data, and
              * having to do this all over again.
              *
              * I have not done extensive checking on this number.
              */
             max_d = 96;

             while (num_new_palette > maximum_colors)
             {
                for (i = 0; i < num_new_palette - 1; i++)
                {
                   int j;

                   for (j = i + 1; j < num_new_palette; j++)
                   {
                      int d;

                      d = PNG_COLOR_DIST(palette[i], palette[j]);

                      if (d <= max_d)
                      {

                         t = (png_dsortp)png_malloc_warn(png_ptr,
                             (png_uint_32)(sizeof (png_dsort)));

                         if (t == NULL)
                             break;

                         t->next = hash[d];
                         t->left = (png_byte)i;
                         t->right = (png_byte)j;
                         hash[d] = t;
                      }
                   }
                   if (t == NULL)
                      break;
                }

                if (t != NULL)
                for (i = 0; i <= max_d; i++)
                {
                   if (hash[i] != NULL)
                   {
                      png_dsortp p;

                      for (p = hash[i]; p; p = p->next)
                      {
                         if ((int)png_ptr->index_to_palette[p->left]
                             < num_new_palette &&
                             (int)png_ptr->index_to_palette[p->right]
                             < num_new_palette)
                         {
                            int j, next_j;

                            if (num_new_palette & 0x01)
                            {
                               j = p->left;
                               next_j = p->right;
                            }
                            else
                            {
                               j = p->right;
                               next_j = p->left;
                            }

                            num_new_palette--;
                            palette[png_ptr->index_to_palette[j]]
                                = palette[num_new_palette];
                            if (!full_quantize)
                            {
                               int k;

                               for (k = 0; k < num_palette; k++)
                               {
                                  if (png_ptr->quantize_index[k] ==
                                      png_ptr->index_to_palette[j])
                                     png_ptr->quantize_index[k] =
                                         png_ptr->index_to_palette[next_j];

                                  if ((int)png_ptr->quantize_index[k] ==
                                      num_new_palette)
                                     png_ptr->quantize_index[k] =
                                         png_ptr->index_to_palette[j];
                               }
                            }

                            png_ptr->index_to_palette[png_ptr->palette_to_index
                                [num_new_palette]] = png_ptr->index_to_palette[j];

                            png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
                                = png_ptr->palette_to_index[num_new_palette];

                            png_ptr->index_to_palette[j] =
                                (png_byte)num_new_palette;

                            png_ptr->palette_to_index[num_new_palette] =
                                (png_byte)j;
                         }
                         if (num_new_palette <= maximum_colors)
                            break;
                      }
                      if (num_new_palette <= maximum_colors)
                         break;
                   }
                }

                for (i = 0; i < 769; i++)
                {
                   if (hash[i] != NULL)
                   {
                      png_dsortp p = hash[i];
                      while (p)
                      {
                         t = p->next;
                         png_free(png_ptr, p);
                         p = t;
                      }
                   }
                   hash[i] = 0;
                }
                max_d += 96;
             }
             png_free(png_ptr, hash);
             png_free(png_ptr, png_ptr->palette_to_index);
             png_free(png_ptr, png_ptr->index_to_palette);
             png_ptr->palette_to_index = NULL;
             png_ptr->index_to_palette = NULL;
          }
          num_palette = maximum_colors;
       }
       if (png_ptr->palette == NULL)
       {
          png_ptr->palette = palette;
       }
       png_ptr->num_palette = (png_uint_16)num_palette;

       if (full_quantize)
       {
          int i;
          png_bytep distance;
          int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
              PNG_QUANTIZE_BLUE_BITS;
          int num_red = (1 << PNG_QUANTIZE_RED_BITS);
          int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
          int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
          png_size_t num_entries = ((png_size_t)1 << total_bits);

          png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
              (png_uint_32)(num_entries * (sizeof (png_byte))));

          distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
              (sizeof (png_byte))));

          memset(distance, 0xff, num_entries * (sizeof (png_byte)));

          for (i = 0; i < num_palette; i++)
          {
             int ir, ig, ib;
             int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
             int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
             int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));

             for (ir = 0; ir < num_red; ir++)
             {
                /* int dr = abs(ir - r); */
                int dr = ((ir > r) ? ir - r : r - ir);
                int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
                    PNG_QUANTIZE_GREEN_BITS));

                for (ig = 0; ig < num_green; ig++)
                {
                   /* int dg = abs(ig - g); */
                   int dg = ((ig > g) ? ig - g : g - ig);
                   int dt = dr + dg;
                   int dm = ((dr > dg) ? dr : dg);
                   int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);

                   for (ib = 0; ib < num_blue; ib++)
                   {
                      int d_index = index_g | ib;
                      /* int db = abs(ib - b); */
                      int db = ((ib > b) ? ib - b : b - ib);
                      int dmax = ((dm > db) ? dm : db);
                      int d = dmax + dt + db;

                      if (d < (int)distance[d_index])
                      {
                         distance[d_index] = (png_byte)d;
                         png_ptr->palette_lookup[d_index] = (png_byte)i;
                      }
                   }
                }
             }
          }

          png_free(png_ptr, distance);
       }
    }
    #endif /* PNG_READ_QUANTIZE_SUPPORTED */

    #ifdef PNG_READ_GAMMA_SUPPORTED
    void PNGFAPI
    png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
       png_fixed_point file_gamma)
    {
       png_debug(1, "in png_set_gamma_fixed");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       /* New in libpng-1.5.4 - reserve particular negative values as flags. */
       scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
       file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);

       /* Checking the gamma values for being >0 was added in 1.5.4 along with the
        * premultiplied alpha support; this actually hides an undocumented feature
        * of the previous implementation which allowed gamma processing to be
        * disabled in background handling.  There is no evidence (so far) that this
        * was being used; however, png_set_background itself accepted and must still
        * accept '0' for the gamma value it takes, because it isn't always used.
        *
        * Since this is an API change (albeit a very minor one that removes an
        * undocumented API feature) the following checks were only enabled in
        * libpng-1.6.0.
        */
       if (file_gamma <= 0)
          png_error(png_ptr, "invalid file gamma in png_set_gamma");

       if (scrn_gamma <= 0)
          png_error(png_ptr, "invalid screen gamma in png_set_gamma");

       /* Set the gamma values unconditionally - this overrides the value in the PNG
        * file if a gAMA chunk was present.  png_set_alpha_mode provides a
        * different, easier, way to default the file gamma.
        */
       png_ptr->colorspace.gamma = file_gamma;
       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
       png_ptr->screen_gamma = scrn_gamma;
    }

    #  ifdef PNG_FLOATING_POINT_SUPPORTED
    void PNGAPI
    png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
    {
       png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
          convert_gamma_value(png_ptr, file_gamma));
    }
    #  endif /* FLOATING_POINT_SUPPORTED */
    #endif /* READ_GAMMA */

    #ifdef PNG_READ_EXPAND_SUPPORTED
    /* Expand paletted images to RGB, expand grayscale images of
     * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
     * to alpha channels.
     */
    void PNGAPI
    png_set_expand(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_expand");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    }

    /* GRR 19990627:  the following three functions currently are identical
     *  to png_set_expand().  However, it is entirely reasonable that someone
     *  might wish to expand an indexed image to RGB but *not* expand a single,
     *  fully transparent palette entry to a full alpha channel--perhaps instead
     *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
     *  the transparent color with a particular RGB value, or drop tRNS entirely.
     *  IOW, a future version of the library may make the transformations flag
     *  a bit more fine-grained, with separate bits for each of these three
     *  functions.
     *
     *  More to the point, these functions make it obvious what libpng will be
     *  doing, whereas "expand" can (and does) mean any number of things.
     *
     *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
     *  to expand only the sample depth but not to expand the tRNS to alpha
     *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
     */

    /* Expand paletted images to RGB. */
    void PNGAPI
    png_set_palette_to_rgb(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_palette_to_rgb");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    }

    /* Expand grayscale images of less than 8-bit depth to 8 bits. */
    void PNGAPI
    png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_expand_gray_1_2_4_to_8");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= PNG_EXPAND;
    }

    /* Expand tRNS chunks to alpha channels. */
    void PNGAPI
    png_set_tRNS_to_alpha(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_tRNS_to_alpha");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
    }
    #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */

    #ifdef PNG_READ_EXPAND_16_SUPPORTED
    /* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
     * it may not work correctly.)
     */
    void PNGAPI
    png_set_expand_16(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_expand_16");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
    }
    #endif

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    void PNGAPI
    png_set_gray_to_rgb(png_structrp png_ptr)
    {
       png_debug(1, "in png_set_gray_to_rgb");

       if (!png_rtran_ok(png_ptr, 0))
          return;

       /* Because rgb must be 8 bits or more: */
       png_set_expand_gray_1_2_4_to_8(png_ptr);
       png_ptr->transformations |= PNG_GRAY_TO_RGB;
    }
    #endif

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    void PNGFAPI
    png_set_rgb_to_gray_fixed(png_structrp png_ptr, int error_action,
        png_fixed_point red, png_fixed_point green)
    {
       png_debug(1, "in png_set_rgb_to_gray");

       /* Need the IHDR here because of the check on color_type below. */
       /* TODO: fix this */
       if (!png_rtran_ok(png_ptr, 1))
          return;

       switch(error_action)
       {
          case PNG_ERROR_ACTION_NONE:
             png_ptr->transformations |= PNG_RGB_TO_GRAY;
             break;

          case PNG_ERROR_ACTION_WARN:
             png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
             break;

          case PNG_ERROR_ACTION_ERROR:
             png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
             break;

          default:
             png_error(png_ptr, "invalid error action to rgb_to_gray");
             break;
       }

       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
    #ifdef PNG_READ_EXPAND_SUPPORTED
          png_ptr->transformations |= PNG_EXPAND;
    #else
       {
          /* Make this an error in 1.6 because otherwise the application may assume
           * that it just worked and get a memory overwrite.
           */
          png_error(png_ptr,
            "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");

          /* png_ptr->transformations &= ~PNG_RGB_TO_GRAY; */
       }
    #endif
       {
          if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
          {
             png_uint_16 red_int, green_int;

             /* NOTE: this calculation does not round, but this behavior is retained
              * for consistency, the inaccuracy is very small.  The code here always
              * overwrites the coefficients, regardless of whether they have been
              * defaulted or set already.
              */
             red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
             green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);

             png_ptr->rgb_to_gray_red_coeff   = red_int;
             png_ptr->rgb_to_gray_green_coeff = green_int;
             png_ptr->rgb_to_gray_coefficients_set = 1;
          }

          else
          {
             if (red >= 0 && green >= 0)
                png_app_warning(png_ptr,
                   "ignoring out of range rgb_to_gray coefficients");

             /* Use the defaults, from the cHRM chunk if set, else the historical
              * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
              * png_do_rgb_to_gray for more discussion of the values.  In this case
              * the coefficients are not marked as 'set' and are not overwritten if
              * something has already provided a default.
              */
             if (png_ptr->rgb_to_gray_red_coeff == 0 &&
                png_ptr->rgb_to_gray_green_coeff == 0)
             {
                png_ptr->rgb_to_gray_red_coeff   = 6968;
                png_ptr->rgb_to_gray_green_coeff = 23434;
                /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
             }
          }
       }
    }

    #ifdef PNG_FLOATING_POINT_SUPPORTED
    /* Convert a RGB image to a grayscale of the same width.  This allows us,
     * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
     */

    void PNGAPI
    png_set_rgb_to_gray(png_structrp png_ptr, int error_action, double red,
       double green)
    {
       png_set_rgb_to_gray_fixed(png_ptr, error_action,
          png_fixed(png_ptr, red, "rgb to gray red coefficient"),
          png_fixed(png_ptr, green, "rgb to gray green coefficient"));
    }
    #endif /* FLOATING POINT */

    #endif /* RGB_TO_GRAY */

    #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
        defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
    void PNGAPI
    png_set_read_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
        read_user_transform_fn)
    {
       png_debug(1, "in png_set_read_user_transform_fn");

    #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
       png_ptr->transformations |= PNG_USER_TRANSFORM;
       png_ptr->read_user_transform_fn = read_user_transform_fn;
    #endif
    }
    #endif

    #ifdef PNG_READ_TRANSFORMS_SUPPORTED
    #ifdef PNG_READ_GAMMA_SUPPORTED
    /* In the case of gamma transformations only do transformations on images where
     * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
     * slows things down slightly, and also needlessly introduces small errors.
     */
    static int /* PRIVATE */
    png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
    {
       /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
        * correction as a difference of the overall transform from 1.0
        *
        * We want to compare the threshold with s*f - 1, if we get
        * overflow here it is because of wacky gamma values so we
        * turn on processing anyway.
        */
       png_fixed_point gtest;
       return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
           png_gamma_significant(gtest);
    }
    #endif

    /* Initialize everything needed for the read.  This includes modifying
     * the palette.
     */

    /*For the moment 'png_init_palette_transformations' and
     * 'png_init_rgb_transformations' only do some flag canceling optimizations.
     * The intent is that these two routines should have palette or rgb operations
     * extracted from 'png_init_read_transformations'.
     */
    static void /* PRIVATE */
    png_init_palette_transformations(png_structrp png_ptr)
    {
       /* Called to handle the (input) palette case.  In png_do_read_transformations
        * the first step is to expand the palette if requested, so this code must
        * take care to only make changes that are invariant with respect to the
        * palette expansion, or only do them if there is no expansion.
        *
        * STRIP_ALPHA has already been handled in the caller (by setting num_trans
        * to 0.)
        */
       int input_has_alpha = 0;
       int input_has_transparency = 0;

       if (png_ptr->num_trans > 0)
       {
          int i;

          /* Ignore if all the entries are opaque (unlikely!) */
          for (i=0; i<png_ptr->num_trans; ++i)
          {
             if (png_ptr->trans_alpha[i] == 255)
                continue;
             else if (png_ptr->trans_alpha[i] == 0)
                input_has_transparency = 1;
             else
             {
                input_has_transparency = 1;
                input_has_alpha = 1;
                break;
             }
          }
       }

       /* If no alpha we can optimize. */
       if (!input_has_alpha)
       {
          /* Any alpha means background and associative alpha processing is
           * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
           * and ENCODE_ALPHA are irrelevant.
           */
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;

          if (!input_has_transparency)
             png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
       }

    #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
       /* png_set_background handling - deals with the complexity of whether the
        * background color is in the file format or the screen format in the case
        * where an 'expand' will happen.
        */

       /* The following code cannot be entered in the alpha pre-multiplication case
        * because PNG_BACKGROUND_EXPAND is cancelled below.
        */
       if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
           (png_ptr->transformations & PNG_EXPAND))
       {
          {
             png_ptr->background.red   =
                 png_ptr->palette[png_ptr->background.index].red;
             png_ptr->background.green =
                 png_ptr->palette[png_ptr->background.index].green;
             png_ptr->background.blue  =
                 png_ptr->palette[png_ptr->background.index].blue;

    #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
            if (png_ptr->transformations & PNG_INVERT_ALPHA)
            {
               if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
               {
                  /* Invert the alpha channel (in tRNS) unless the pixels are
                   * going to be expanded, in which case leave it for later
                   */
                  int i, istop = png_ptr->num_trans;

                  for (i=0; i<istop; i++)
                     png_ptr->trans_alpha[i] = (png_byte)(255 -
                        png_ptr->trans_alpha[i]);
               }
            }
    #endif /* PNG_READ_INVERT_ALPHA_SUPPORTED */
          }
       } /* background expand and (therefore) no alpha association. */
    #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
    }

    static void /* PRIVATE */
    png_init_rgb_transformations(png_structrp png_ptr)
    {
       /* Added to libpng-1.5.4: check the color type to determine whether there
        * is any alpha or transparency in the image and simply cancel the
        * background and alpha mode stuff if there isn't.
        */
       int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
       int input_has_transparency = png_ptr->num_trans > 0;

       /* If no alpha we can optimize. */
       if (!input_has_alpha)
       {
          /* Any alpha means background and associative alpha processing is
           * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
           * and ENCODE_ALPHA are irrelevant.
           */
    #     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
             png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
             png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
    #     endif

          if (!input_has_transparency)
             png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
       }

    #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
       /* png_set_background handling - deals with the complexity of whether the
        * background color is in the file format or the screen format in the case
        * where an 'expand' will happen.
        */

       /* The following code cannot be entered in the alpha pre-multiplication case
        * because PNG_BACKGROUND_EXPAND is cancelled below.
        */
       if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
           (png_ptr->transformations & PNG_EXPAND) &&
           !(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
           /* i.e., GRAY or GRAY_ALPHA */
       {
          {
             /* Expand background and tRNS chunks */
             int gray = png_ptr->background.gray;
             int trans_gray = png_ptr->trans_color.gray;

             switch (png_ptr->bit_depth)
             {
                case 1:
                   gray *= 0xff;
                   trans_gray *= 0xff;
                   break;

                case 2:
                   gray *= 0x55;
                   trans_gray *= 0x55;
                   break;

                case 4:
                   gray *= 0x11;
                   trans_gray *= 0x11;
                   break;

                default:

                case 8:
                   /* FALL THROUGH (Already 8 bits) */

                case 16:
                   /* Already a full 16 bits */
                   break;
             }

             png_ptr->background.red = png_ptr->background.green =
                png_ptr->background.blue = (png_uint_16)gray;

             if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
             {
                png_ptr->trans_color.red = png_ptr->trans_color.green =
                   png_ptr->trans_color.blue = (png_uint_16)trans_gray;
             }
          }
       } /* background expand and (therefore) no alpha association. */
    #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
    }

    void /* PRIVATE */
    png_init_read_transformations(png_structrp png_ptr)
    {
       png_debug(1, "in png_init_read_transformations");

       /* This internal function is called from png_read_start_row in pngrutil.c
        * and it is called before the 'rowbytes' calculation is done, so the code
        * in here can change or update the transformations flags.
        *
        * First do updates that do not depend on the details of the PNG image data
        * being processed.
        */

    #ifdef PNG_READ_GAMMA_SUPPORTED
       /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
        * png_set_alpha_mode and this is another source for a default file gamma so
        * the test needs to be performed later - here.  In addition prior to 1.5.4
        * the tests were repeated for the PALETTE color type here - this is no
        * longer necessary (and doesn't seem to have been necessary before.)
        */
       {
          /* The following temporary indicates if overall gamma correction is
           * required.
           */
          int gamma_correction = 0;

          if (png_ptr->colorspace.gamma != 0) /* has been set */
          {
             if (png_ptr->screen_gamma != 0) /* screen set too */
                gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
                   png_ptr->screen_gamma);

             else
                /* Assume the output matches the input; a long time default behavior
                 * of libpng, although the standard has nothing to say about this.
                 */
                png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
          }

          else if (png_ptr->screen_gamma != 0)
             /* The converse - assume the file matches the screen, note that this
              * perhaps undesireable default can (from 1.5.4) be changed by calling
              * png_set_alpha_mode (even if the alpha handling mode isn't required
              * or isn't changed from the default.)
              */
             png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);

          else /* neither are set */
             /* Just in case the following prevents any processing - file and screen
              * are both assumed to be linear and there is no way to introduce a
              * third gamma value other than png_set_background with 'UNIQUE', and,
              * prior to 1.5.4
              */
             png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;

          /* We have a gamma value now. */
          png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;

          /* Now turn the gamma transformation on or off as appropriate.  Notice
           * that PNG_GAMMA just refers to the file->screen correction.  Alpha
           * composition may independently cause gamma correction because it needs
           * linear data (e.g. if the file has a gAMA chunk but the screen gamma
           * hasn't been specified.)  In any case this flag may get turned off in
           * the code immediately below if the transform can be handled outside the
           * row loop.
           */
          if (gamma_correction)
             png_ptr->transformations |= PNG_GAMMA;

          else
             png_ptr->transformations &= ~PNG_GAMMA;
       }
    #endif

       /* Certain transformations have the effect of preventing other
        * transformations that happen afterward in png_do_read_transformations,
        * resolve the interdependencies here.  From the code of
        * png_do_read_transformations the order is:
        *
        *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
        *  2) PNG_STRIP_ALPHA (if no compose)
        *  3) PNG_RGB_TO_GRAY
        *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
        *  5) PNG_COMPOSE
        *  6) PNG_GAMMA
        *  7) PNG_STRIP_ALPHA (if compose)
        *  8) PNG_ENCODE_ALPHA
        *  9) PNG_SCALE_16_TO_8
        * 10) PNG_16_TO_8
        * 11) PNG_QUANTIZE (converts to palette)
        * 12) PNG_EXPAND_16
        * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
        * 14) PNG_INVERT_MONO
        * 15) PNG_SHIFT
        * 16) PNG_PACK
        * 17) PNG_BGR
        * 18) PNG_PACKSWAP
        * 19) PNG_FILLER (includes PNG_ADD_ALPHA)
        * 20) PNG_INVERT_ALPHA
        * 21) PNG_SWAP_ALPHA
        * 22) PNG_SWAP_BYTES
        * 23) PNG_USER_TRANSFORM [must be last]
        */
    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
       if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
          !(png_ptr->transformations & PNG_COMPOSE))
       {
          /* Stripping the alpha channel happens immediately after the 'expand'
           * transformations, before all other transformation, so it cancels out
           * the alpha handling.  It has the side effect negating the effect of
           * PNG_EXPAND_tRNS too:
           */
          png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
             PNG_EXPAND_tRNS);
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;

          /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
           * so transparency information would remain just so long as it wasn't
           * expanded.  This produces unexpected API changes if the set of things
           * that do PNG_EXPAND_tRNS changes (perfectly possible given the
           * documentation - which says ask for what you want, accept what you
           * get.)  This makes the behavior consistent from 1.5.4:
           */
          png_ptr->num_trans = 0;
       }
    #endif /* STRIP_ALPHA supported, no COMPOSE */

    #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
       /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
        * settings will have no effect.
        */
       if (!png_gamma_significant(png_ptr->screen_gamma))
       {
          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
       }
    #endif

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
       /* Make sure the coefficients for the rgb to gray conversion are set
        * appropriately.
        */
       if (png_ptr->transformations & PNG_RGB_TO_GRAY)
          png_colorspace_set_rgb_coefficients(png_ptr);
    #endif

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
       /* Detect gray background and attempt to enable optimization for
        * gray --> RGB case.
        *
        * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
        * RGB_ALPHA (in which case need_expand is superfluous anyway), the
        * background color might actually be gray yet not be flagged as such.
        * This is not a problem for the current code, which uses
        * PNG_BACKGROUND_IS_GRAY only to decide when to do the
        * png_do_gray_to_rgb() transformation.
        *
        * TODO: this code needs to be revised to avoid the complexity and
        * interdependencies.  The color type of the background should be recorded in
        * png_set_background, along with the bit depth, then the code has a record
        * of exactly what color space the background is currently in.
        */
       if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
       {
          /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
           * the file was grayscale the background value is gray.
           */
          if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
             png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
       }

       else if (png_ptr->transformations & PNG_COMPOSE)
       {
          /* PNG_COMPOSE: png_set_background was called with need_expand false,
           * so the color is in the color space of the output or png_set_alpha_mode
           * was called and the color is black.  Ignore RGB_TO_GRAY because that
           * happens before GRAY_TO_RGB.
           */
          if (png_ptr->transformations & PNG_GRAY_TO_RGB)
          {
             if (png_ptr->background.red == png_ptr->background.green &&
                 png_ptr->background.red == png_ptr->background.blue)
             {
                png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
                png_ptr->background.gray = png_ptr->background.red;
             }
          }
       }
    #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
    #endif /* PNG_READ_GRAY_TO_RGB_SUPPORTED */

       /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
        * can be performed directly on the palette, and some (such as rgb to gray)
        * can be optimized inside the palette.  This is particularly true of the
        * composite (background and alpha) stuff, which can be pretty much all done
        * in the palette even if the result is expanded to RGB or gray afterward.
        *
        * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
        * earlier and the palette stuff is actually handled on the first row.  This
        * leads to the reported bug that the palette returned by png_get_PLTE is not
        * updated.
        */
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          png_init_palette_transformations(png_ptr);

       else
          png_init_rgb_transformations(png_ptr);

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
       defined(PNG_READ_EXPAND_16_SUPPORTED)
       if ((png_ptr->transformations & PNG_EXPAND_16) &&
          (png_ptr->transformations & PNG_COMPOSE) &&
          !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
          png_ptr->bit_depth != 16)
       {
          /* TODO: fix this.  Because the expand_16 operation is after the compose
           * handling the background color must be 8, not 16, bits deep, but the
           * application will supply a 16-bit value so reduce it here.
           *
           * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
           * present, so that case is ok (until do_expand_16 is moved.)
           *
           * NOTE: this discards the low 16 bits of the user supplied background
           * color, but until expand_16 works properly there is no choice!
           */
    #     define CHOP(x) (x)=((png_uint_16)PNG_DIV257(x))
          CHOP(png_ptr->background.red);
          CHOP(png_ptr->background.green);
          CHOP(png_ptr->background.blue);
          CHOP(png_ptr->background.gray);
    #     undef CHOP
       }
    #endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
       (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
       defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
       if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
          (png_ptr->transformations & PNG_COMPOSE) &&
          !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
          png_ptr->bit_depth == 16)
       {
          /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
           * component this will also happen after PNG_COMPOSE and so the background
           * color must be pre-expanded here.
           *
           * TODO: fix this too.
           */
          png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
          png_ptr->background.green =
             (png_uint_16)(png_ptr->background.green * 257);
          png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
          png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
       }
    #endif

       /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
        * background support (see the comments in scripts/pnglibconf.dfa), this
        * allows pre-multiplication of the alpha channel to be implemented as
        * compositing on black.  This is probably sub-optimal and has been done in
        * 1.5.4 betas simply to enable external critique and testing (i.e. to
        * implement the new API quickly, without lots of internal changes.)
        */

    #ifdef PNG_READ_GAMMA_SUPPORTED
    #  ifdef PNG_READ_BACKGROUND_SUPPORTED
          /* Includes ALPHA_MODE */
          png_ptr->background_1 = png_ptr->background;
    #  endif

       /* This needs to change - in the palette image case a whole set of tables are
        * built when it would be quicker to just calculate the correct value for
        * each palette entry directly.  Also, the test is too tricky - why check
        * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
        * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
        * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
        * the gamma tables will not be built even if composition is required on a
        * gamma encoded value.
        *
        * In 1.5.4 this is addressed below by an additional check on the individual
        * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
        * tables.
        */
       if ((png_ptr->transformations & PNG_GAMMA)
          || ((png_ptr->transformations & PNG_RGB_TO_GRAY)
             && (png_gamma_significant(png_ptr->colorspace.gamma) ||
                png_gamma_significant(png_ptr->screen_gamma)))
          || ((png_ptr->transformations & PNG_COMPOSE)
             && (png_gamma_significant(png_ptr->colorspace.gamma)
                || png_gamma_significant(png_ptr->screen_gamma)
    #  ifdef PNG_READ_BACKGROUND_SUPPORTED
                || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE
                   && png_gamma_significant(png_ptr->background_gamma))
    #  endif
          )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA)
             && png_gamma_significant(png_ptr->screen_gamma))
          )
       {
          png_build_gamma_table(png_ptr, png_ptr->bit_depth);

    #ifdef PNG_READ_BACKGROUND_SUPPORTED
          if (png_ptr->transformations & PNG_COMPOSE)
          {
             /* Issue a warning about this combination: because RGB_TO_GRAY is
              * optimized to do the gamma transform if present yet do_background has
              * to do the same thing if both options are set a
              * double-gamma-correction happens.  This is true in all versions of
              * libpng to date.
              */
             if (png_ptr->transformations & PNG_RGB_TO_GRAY)
                png_warning(png_ptr,
                   "libpng does not support gamma+background+rgb_to_gray");

             if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
             {
                /* We don't get to here unless there is a tRNS chunk with non-opaque
                 * entries - see the checking code at the start of this function.
                 */
                png_color back, back_1;
                png_colorp palette = png_ptr->palette;
                int num_palette = png_ptr->num_palette;
                int i;
                if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
                {

                   back.red = png_ptr->gamma_table[png_ptr->background.red];
                   back.green = png_ptr->gamma_table[png_ptr->background.green];
                   back.blue = png_ptr->gamma_table[png_ptr->background.blue];

                   back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
                   back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
                   back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
                }
                else
                {
                   png_fixed_point g, gs;

                   switch (png_ptr->background_gamma_type)
                   {
                      case PNG_BACKGROUND_GAMMA_SCREEN:
                         g = (png_ptr->screen_gamma);
                         gs = PNG_FP_1;
                         break;

                      case PNG_BACKGROUND_GAMMA_FILE:
                         g = png_reciprocal(png_ptr->colorspace.gamma);
                         gs = png_reciprocal2(png_ptr->colorspace.gamma,
                            png_ptr->screen_gamma);
                         break;

                      case PNG_BACKGROUND_GAMMA_UNIQUE:
                         g = png_reciprocal(png_ptr->background_gamma);
                         gs = png_reciprocal2(png_ptr->background_gamma,
                            png_ptr->screen_gamma);
                         break;
                      default:
                         g = PNG_FP_1;    /* back_1 */
                         gs = PNG_FP_1;   /* back */
                         break;
                   }

                   if (png_gamma_significant(gs))
                   {
                      back.red = png_gamma_8bit_correct(png_ptr->background.red,
                          gs);
                      back.green = png_gamma_8bit_correct(png_ptr->background.green,
                          gs);
                      back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                          gs);
                   }

                   else
                   {
                      back.red   = (png_byte)png_ptr->background.red;
                      back.green = (png_byte)png_ptr->background.green;
                      back.blue  = (png_byte)png_ptr->background.blue;
                   }

                   if (png_gamma_significant(g))
                   {
                      back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
                         g);
                      back_1.green = png_gamma_8bit_correct(
                         png_ptr->background.green, g);
                      back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                         g);
                   }

                   else
                   {
                      back_1.red   = (png_byte)png_ptr->background.red;
                      back_1.green = (png_byte)png_ptr->background.green;
                      back_1.blue  = (png_byte)png_ptr->background.blue;
                   }
                }

                for (i = 0; i < num_palette; i++)
                {
                   if (i < (int)png_ptr->num_trans &&
                       png_ptr->trans_alpha[i] != 0xff)
                   {
                      if (png_ptr->trans_alpha[i] == 0)
                      {
                         palette[i] = back;
                      }
                      else /* if (png_ptr->trans_alpha[i] != 0xff) */
                      {
                         png_byte v, w;

                         v = png_ptr->gamma_to_1[palette[i].red];
                         png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
                         palette[i].red = png_ptr->gamma_from_1[w];

                         v = png_ptr->gamma_to_1[palette[i].green];
                         png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
                         palette[i].green = png_ptr->gamma_from_1[w];

                         v = png_ptr->gamma_to_1[palette[i].blue];
                         png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
                         palette[i].blue = png_ptr->gamma_from_1[w];
                      }
                   }
                   else
                   {
                      palette[i].red = png_ptr->gamma_table[palette[i].red];
                      palette[i].green = png_ptr->gamma_table[palette[i].green];
                      palette[i].blue = png_ptr->gamma_table[palette[i].blue];
                   }
                }

                /* Prevent the transformations being done again.
                 *
                 * NOTE: this is highly dubious; it removes the transformations in
                 * place.  This seems inconsistent with the general treatment of the
                 * transformations elsewhere.
                 */
                png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
             } /* color_type == PNG_COLOR_TYPE_PALETTE */

             /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
             else /* color_type != PNG_COLOR_TYPE_PALETTE */
             {
                int gs_sig, g_sig;
                png_fixed_point g = PNG_FP_1;  /* Correction to linear */
                png_fixed_point gs = PNG_FP_1; /* Correction to screen */

                switch (png_ptr->background_gamma_type)
                {
                   case PNG_BACKGROUND_GAMMA_SCREEN:
                      g = png_ptr->screen_gamma;
                      /* gs = PNG_FP_1; */
                      break;

                   case PNG_BACKGROUND_GAMMA_FILE:
                      g = png_reciprocal(png_ptr->colorspace.gamma);
                      gs = png_reciprocal2(png_ptr->colorspace.gamma,
                         png_ptr->screen_gamma);
                      break;

                   case PNG_BACKGROUND_GAMMA_UNIQUE:
                      g = png_reciprocal(png_ptr->background_gamma);
                      gs = png_reciprocal2(png_ptr->background_gamma,
                          png_ptr->screen_gamma);
                      break;

                   default:
                      png_error(png_ptr, "invalid background gamma type");
                }

                g_sig = png_gamma_significant(g);
                gs_sig = png_gamma_significant(gs);

                if (g_sig)
                   png_ptr->background_1.gray = png_gamma_correct(png_ptr,
                       png_ptr->background.gray, g);

                if (gs_sig)
                   png_ptr->background.gray = png_gamma_correct(png_ptr,
                       png_ptr->background.gray, gs);

                if ((png_ptr->background.red != png_ptr->background.green) ||
                    (png_ptr->background.red != png_ptr->background.blue) ||
                    (png_ptr->background.red != png_ptr->background.gray))
                {
                   /* RGB or RGBA with color background */
                   if (g_sig)
                   {
                      png_ptr->background_1.red = png_gamma_correct(png_ptr,
                          png_ptr->background.red, g);

                      png_ptr->background_1.green = png_gamma_correct(png_ptr,
                          png_ptr->background.green, g);

                      png_ptr->background_1.blue = png_gamma_correct(png_ptr,
                          png_ptr->background.blue, g);
                   }

                   if (gs_sig)
                   {
                      png_ptr->background.red = png_gamma_correct(png_ptr,
                          png_ptr->background.red, gs);

                      png_ptr->background.green = png_gamma_correct(png_ptr,
                          png_ptr->background.green, gs);

                      png_ptr->background.blue = png_gamma_correct(png_ptr,
                          png_ptr->background.blue, gs);
                   }
                }

                else
                {
                   /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
                   png_ptr->background_1.red = png_ptr->background_1.green
                       = png_ptr->background_1.blue = png_ptr->background_1.gray;

                   png_ptr->background.red = png_ptr->background.green
                       = png_ptr->background.blue = png_ptr->background.gray;
                }

                /* The background is now in screen gamma: */
                png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
             } /* color_type != PNG_COLOR_TYPE_PALETTE */
          }/* png_ptr->transformations & PNG_BACKGROUND */

          else
          /* Transformation does not include PNG_BACKGROUND */
    #endif /* PNG_READ_BACKGROUND_SUPPORTED */
          if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
             /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
             && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
             (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
    #endif
             )
          {
             png_colorp palette = png_ptr->palette;
             int num_palette = png_ptr->num_palette;
             int i;

             /* NOTE: there are other transformations that should probably be in
              * here too.
              */
             for (i = 0; i < num_palette; i++)
             {
                palette[i].red = png_ptr->gamma_table[palette[i].red];
                palette[i].green = png_ptr->gamma_table[palette[i].green];
                palette[i].blue = png_ptr->gamma_table[palette[i].blue];
             }

             /* Done the gamma correction. */
             png_ptr->transformations &= ~PNG_GAMMA;
          } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
       }
    #ifdef PNG_READ_BACKGROUND_SUPPORTED
       else
    #endif
    #endif /* PNG_READ_GAMMA_SUPPORTED */

    #ifdef PNG_READ_BACKGROUND_SUPPORTED
       /* No GAMMA transformation (see the hanging else 4 lines above) */
       if ((png_ptr->transformations & PNG_COMPOSE) &&
           (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
       {
          int i;
          int istop = (int)png_ptr->num_trans;
          png_color back;
          png_colorp palette = png_ptr->palette;

          back.red   = (png_byte)png_ptr->background.red;
          back.green = (png_byte)png_ptr->background.green;
          back.blue  = (png_byte)png_ptr->background.blue;

          for (i = 0; i < istop; i++)
          {
             if (png_ptr->trans_alpha[i] == 0)
             {
                palette[i] = back;
             }

             else if (png_ptr->trans_alpha[i] != 0xff)
             {
                /* The png_composite() macro is defined in png.h */
                png_composite(palette[i].red, palette[i].red,
                    png_ptr->trans_alpha[i], back.red);

                png_composite(palette[i].green, palette[i].green,
                    png_ptr->trans_alpha[i], back.green);

                png_composite(palette[i].blue, palette[i].blue,
                    png_ptr->trans_alpha[i], back.blue);
             }
          }

          png_ptr->transformations &= ~PNG_COMPOSE;
       }
    #endif /* PNG_READ_BACKGROUND_SUPPORTED */

    #ifdef PNG_READ_SHIFT_SUPPORTED
       if ((png_ptr->transformations & PNG_SHIFT) &&
          !(png_ptr->transformations & PNG_EXPAND) &&
           (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
       {
          int i;
          int istop = png_ptr->num_palette;
          int shift = 8 - png_ptr->sig_bit.red;

          png_ptr->transformations &= ~PNG_SHIFT;

          /* significant bits can be in the range 1 to 7 for a meaninful result, if
           * the number of significant bits is 0 then no shift is done (this is an
           * error condition which is silently ignored.)
           */
          if (shift > 0 && shift < 8)
             for (i=0; i<istop; ++i)
             {
                int component = png_ptr->palette[i].red;

                component >>= shift;
                png_ptr->palette[i].red = (png_byte)component;
             }

          shift = 8 - png_ptr->sig_bit.green;
          if (shift > 0 && shift < 8)
             for (i=0; i<istop; ++i)
             {
                int component = png_ptr->palette[i].green;

                component >>= shift;
                png_ptr->palette[i].green = (png_byte)component;
             }

          shift = 8 - png_ptr->sig_bit.blue;
          if (shift > 0 && shift < 8)
             for (i=0; i<istop; ++i)
             {
                int component = png_ptr->palette[i].blue;

                component >>= shift;
                png_ptr->palette[i].blue = (png_byte)component;
             }
       }
    #endif  /* PNG_READ_SHIFT_SUPPORTED */
    }

    /* Modify the info structure to reflect the transformations.  The
     * info should be updated so a PNG file could be written with it,
     * assuming the transformations result in valid PNG data.
     */
    void /* PRIVATE */
    png_read_transform_info(png_structrp png_ptr, png_inforp info_ptr)
    {
       png_debug(1, "in png_read_transform_info");

    #ifdef PNG_READ_EXPAND_SUPPORTED
       if (png_ptr->transformations & PNG_EXPAND)
       {
          if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          {
             /* This check must match what actually happens in
              * png_do_expand_palette; if it ever checks the tRNS chunk to see if
              * it is all opaque we must do the same (at present it does not.)
              */
             if (png_ptr->num_trans > 0)
                info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;

             else
                info_ptr->color_type = PNG_COLOR_TYPE_RGB;

             info_ptr->bit_depth = 8;
             info_ptr->num_trans = 0;
          }
          else
          {
             if (png_ptr->num_trans)
             {
                if (png_ptr->transformations & PNG_EXPAND_tRNS)
                   info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
             }
             if (info_ptr->bit_depth < 8)
                info_ptr->bit_depth = 8;

             info_ptr->num_trans = 0;
          }
       }
    #endif

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
       defined(PNG_READ_ALPHA_MODE_SUPPORTED)
       /* The following is almost certainly wrong unless the background value is in
        * the screen space!
        */
       if (png_ptr->transformations & PNG_COMPOSE)
          info_ptr->background = png_ptr->background;
    #endif

    #ifdef PNG_READ_GAMMA_SUPPORTED
       /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
        * however it seems that the code in png_init_read_transformations, which has
        * been called before this from png_read_update_info->png_read_start_row
        * sometimes does the gamma transform and cancels the flag.
        *
        * TODO: this looks wrong; the info_ptr should end up with a gamma equal to
        * the screen_gamma value.  The following probably results in weirdness if
        * the info_ptr is used by the app after the rows have been read.
        */
       info_ptr->colorspace.gamma = png_ptr->colorspace.gamma;
    #endif

       if (info_ptr->bit_depth == 16)
       {
    #  ifdef PNG_READ_16BIT_SUPPORTED
    #     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
             if (png_ptr->transformations & PNG_SCALE_16_TO_8)
                info_ptr->bit_depth = 8;
    #     endif

    #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
             if (png_ptr->transformations & PNG_16_TO_8)
                info_ptr->bit_depth = 8;
    #     endif

    #  else
          /* No 16 bit support: force chopping 16-bit input down to 8, in this case
           * the app program can chose if both APIs are available by setting the
           * correct scaling to use.
           */
    #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
             /* For compatibility with previous versions use the strip method by
              * default.  This code works because if PNG_SCALE_16_TO_8 is already
              * set the code below will do that in preference to the chop.
              */
             png_ptr->transformations |= PNG_16_TO_8;
             info_ptr->bit_depth = 8;
    #     else

    #        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
                png_ptr->transformations |= PNG_SCALE_16_TO_8;
                info_ptr->bit_depth = 8;
    #        else

                CONFIGURATION ERROR: you must enable at least one 16 to 8 method
    #        endif
    #    endif
    #endif /* !READ_16BIT_SUPPORTED */
       }

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
       if (png_ptr->transformations & PNG_GRAY_TO_RGB)
          info_ptr->color_type = (png_byte)(info_ptr->color_type |
             PNG_COLOR_MASK_COLOR);
    #endif

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
       if (png_ptr->transformations & PNG_RGB_TO_GRAY)
          info_ptr->color_type = (png_byte)(info_ptr->color_type &
             ~PNG_COLOR_MASK_COLOR);
    #endif

    #ifdef PNG_READ_QUANTIZE_SUPPORTED
       if (png_ptr->transformations & PNG_QUANTIZE)
       {
          if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
              (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
              png_ptr->palette_lookup && info_ptr->bit_depth == 8)
          {
             info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
          }
       }
    #endif

    #ifdef PNG_READ_EXPAND_16_SUPPORTED
       if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
          info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
       {
          info_ptr->bit_depth = 16;
       }
    #endif

    #ifdef PNG_READ_PACK_SUPPORTED
       if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
          info_ptr->bit_depth = 8;
    #endif

       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
          info_ptr->channels = 1;

       else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
          info_ptr->channels = 3;

       else
          info_ptr->channels = 1;

    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
       if (png_ptr->transformations & PNG_STRIP_ALPHA)
       {
          info_ptr->color_type = (png_byte)(info_ptr->color_type &
             ~PNG_COLOR_MASK_ALPHA);
          info_ptr->num_trans = 0;
       }
    #endif

       if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
          info_ptr->channels++;

    #ifdef PNG_READ_FILLER_SUPPORTED
       /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
       if ((png_ptr->transformations & PNG_FILLER) &&
           ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
           (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
       {
          info_ptr->channels++;
          /* If adding a true alpha channel not just filler */
          if (png_ptr->transformations & PNG_ADD_ALPHA)
             info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
       }
    #endif

    #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
    defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
       if (png_ptr->transformations & PNG_USER_TRANSFORM)
       {
          if (info_ptr->bit_depth < png_ptr->user_transform_depth)
             info_ptr->bit_depth = png_ptr->user_transform_depth;

          if (info_ptr->channels < png_ptr->user_transform_channels)
             info_ptr->channels = png_ptr->user_transform_channels;
       }
    #endif

       info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
           info_ptr->bit_depth);

       info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);

       /* Adding in 1.5.4: cache the above value in png_struct so that we can later
        * check in png_rowbytes that the user buffer won't get overwritten.  Note
        * that the field is not always set - if png_read_update_info isn't called
        * the application has to either not do any transforms or get the calculation
        * right itself.
        */
       png_ptr->info_rowbytes = info_ptr->rowbytes;

    #ifndef PNG_READ_EXPAND_SUPPORTED
       if (png_ptr)
          return;
    #endif
    }

    /* Transform the row.  The order of transformations is significant,
     * and is very touchy.  If you add a transformation, take care to
     * decide how it fits in with the other transformations here.
     */
    void /* PRIVATE */
    png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
    {
       png_debug(1, "in png_do_read_transformations");

       if (png_ptr->row_buf == NULL)
       {
          /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
           * error is incredibly rare and incredibly easy to debug without this
           * information.
           */
          png_error(png_ptr, "NULL row buffer");
       }

       /* The following is debugging; prior to 1.5.4 the code was never compiled in;
        * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
        * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.6 the new flag is set only for
        * all transformations, however in practice the ROW_INIT always gets done on
        * demand, if necessary.
        */
       if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
          !(png_ptr->flags & PNG_FLAG_ROW_INIT))
       {
          /* Application has failed to call either png_read_start_image() or
           * png_read_update_info() after setting transforms that expand pixels.
           * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
           */
          png_error(png_ptr, "Uninitialized row");
       }

    #ifdef PNG_READ_EXPAND_SUPPORTED
       if (png_ptr->transformations & PNG_EXPAND)
       {
          if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
          {
             png_do_expand_palette(row_info, png_ptr->row_buf + 1,
                 png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
          }

          else
          {
             if (png_ptr->num_trans &&
                 (png_ptr->transformations & PNG_EXPAND_tRNS))
                png_do_expand(row_info, png_ptr->row_buf + 1,
                    &(png_ptr->trans_color));

             else
                png_do_expand(row_info, png_ptr->row_buf + 1,
                    NULL);
          }
       }
    #endif

    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
       if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
          !(png_ptr->transformations & PNG_COMPOSE) &&
          (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
          row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
          png_do_strip_channel(row_info, png_ptr->row_buf + 1,
             0 /* at_start == false, because SWAP_ALPHA happens later */);
    #endif

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
       if (png_ptr->transformations & PNG_RGB_TO_GRAY)
       {
          int rgb_error =
              png_do_rgb_to_gray(png_ptr, row_info,
                  png_ptr->row_buf + 1);

          if (rgb_error)
          {
             png_ptr->rgb_to_gray_status=1;
             if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
                 PNG_RGB_TO_GRAY_WARN)
                png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");

             if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
                 PNG_RGB_TO_GRAY_ERR)
                png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
          }
       }
    #endif

    /* From Andreas Dilger e-mail to png-implement, 26 March 1998:
     *
     *   In most cases, the "simple transparency" should be done prior to doing
     *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
     *   pixel is transparent.  You would also need to make sure that the
     *   transparency information is upgraded to RGB.
     *
     *   To summarize, the current flow is:
     *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
     *                                   with background "in place" if transparent,
     *                                   convert to RGB if necessary
     *   - Gray + alpha -> composite with gray background and remove alpha bytes,
     *                                   convert to RGB if necessary
     *
     *   To support RGB backgrounds for gray images we need:
     *   - Gray + simple transparency -> convert to RGB + simple transparency,
     *                                   compare 3 or 6 bytes and composite with
     *                                   background "in place" if transparent
     *                                   (3x compare/pixel compared to doing
     *                                   composite with gray bkgrnd)
     *   - Gray + alpha -> convert to RGB + alpha, composite with background and
     *                                   remove alpha bytes (3x float
     *                                   operations/pixel compared with composite
     *                                   on gray background)
     *
     *  Greg's change will do this.  The reason it wasn't done before is for
     *  performance, as this increases the per-pixel operations.  If we would check
     *  in advance if the background was gray or RGB, and position the gray-to-RGB
     *  transform appropriately, then it would save a lot of work/time.
     */

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
       /* If gray -> RGB, do so now only if background is non-gray; else do later
        * for performance reasons
        */
       if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
           !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
          png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
    #endif

    #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
       defined(PNG_READ_ALPHA_MODE_SUPPORTED)
       if (png_ptr->transformations & PNG_COMPOSE)
          png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
    #endif

    #ifdef PNG_READ_GAMMA_SUPPORTED
       if ((png_ptr->transformations & PNG_GAMMA) &&
    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
          /* Because RGB_TO_GRAY does the gamma transform. */
          !(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
    #endif
    #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
       defined(PNG_READ_ALPHA_MODE_SUPPORTED)
          /* Because PNG_COMPOSE does the gamma transform if there is something to
           * do (if there is an alpha channel or transparency.)
           */
           !((png_ptr->transformations & PNG_COMPOSE) &&
           ((png_ptr->num_trans != 0) ||
           (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
    #endif
          /* Because png_init_read_transformations transforms the palette, unless
           * RGB_TO_GRAY will do the transform.
           */
           (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
          png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
    #endif

    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
       if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
          (png_ptr->transformations & PNG_COMPOSE) &&
          (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
          row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
          png_do_strip_channel(row_info, png_ptr->row_buf + 1,
             0 /* at_start == false, because SWAP_ALPHA happens later */);
    #endif

    #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
       if ((png_ptr->transformations & PNG_ENCODE_ALPHA) &&
          (row_info->color_type & PNG_COLOR_MASK_ALPHA))
          png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
    #endif

    #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
       if (png_ptr->transformations & PNG_SCALE_16_TO_8)
          png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
       /* There is no harm in doing both of these because only one has any effect,
        * by putting the 'scale' option first if the app asks for scale (either by
        * calling the API or in a TRANSFORM flag) this is what happens.
        */
       if (png_ptr->transformations & PNG_16_TO_8)
          png_do_chop(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_QUANTIZE_SUPPORTED
       if (png_ptr->transformations & PNG_QUANTIZE)
       {
          png_do_quantize(row_info, png_ptr->row_buf + 1,
              png_ptr->palette_lookup, png_ptr->quantize_index);

          if (row_info->rowbytes == 0)
             png_error(png_ptr, "png_do_quantize returned rowbytes=0");
       }
    #endif /* PNG_READ_QUANTIZE_SUPPORTED */

    #ifdef PNG_READ_EXPAND_16_SUPPORTED
       /* Do the expansion now, after all the arithmetic has been done.  Notice
        * that previous transformations can handle the PNG_EXPAND_16 flag if this
        * is efficient (particularly true in the case of gamma correction, where
        * better accuracy results faster!)
        */
       if (png_ptr->transformations & PNG_EXPAND_16)
          png_do_expand_16(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
       /* NOTE: moved here in 1.5.4 (from much later in this list.) */
       if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
           (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
          png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_INVERT_SUPPORTED
       if (png_ptr->transformations & PNG_INVERT_MONO)
          png_do_invert(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_SHIFT_SUPPORTED
       if (png_ptr->transformations & PNG_SHIFT)
          png_do_unshift(row_info, png_ptr->row_buf + 1,
              &(png_ptr->shift));
    #endif

    #ifdef PNG_READ_PACK_SUPPORTED
       if (png_ptr->transformations & PNG_PACK)
          png_do_unpack(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
       /* Added at libpng-1.5.10 */
       if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
           png_ptr->num_palette_max >= 0)
          png_do_check_palette_indexes(png_ptr, row_info);
    #endif

    #ifdef PNG_READ_BGR_SUPPORTED
       if (png_ptr->transformations & PNG_BGR)
          png_do_bgr(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_PACKSWAP_SUPPORTED
       if (png_ptr->transformations & PNG_PACKSWAP)
          png_do_packswap(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_FILLER_SUPPORTED
       if (png_ptr->transformations & PNG_FILLER)
          png_do_read_filler(row_info, png_ptr->row_buf + 1,
              (png_uint_32)png_ptr->filler, png_ptr->flags);
    #endif

    #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
       if (png_ptr->transformations & PNG_INVERT_ALPHA)
          png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
       if (png_ptr->transformations & PNG_SWAP_ALPHA)
          png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_READ_16BIT_SUPPORTED
    #ifdef PNG_READ_SWAP_SUPPORTED
       if (png_ptr->transformations & PNG_SWAP_BYTES)
          png_do_swap(row_info, png_ptr->row_buf + 1);
    #endif
    #endif

    #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
       if (png_ptr->transformations & PNG_USER_TRANSFORM)
        {
          if (png_ptr->read_user_transform_fn != NULL)
             (*(png_ptr->read_user_transform_fn)) /* User read transform function */
                 (png_ptr,     /* png_ptr */
                 row_info,     /* row_info: */
                    /*  png_uint_32 width;       width of row */
                    /*  png_size_t rowbytes;     number of bytes in row */
                    /*  png_byte color_type;     color type of pixels */
                    /*  png_byte bit_depth;      bit depth of samples */
                    /*  png_byte channels;       number of channels (1-4) */
                    /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
                 png_ptr->row_buf + 1);    /* start of pixel data for row */
    #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
          if (png_ptr->user_transform_depth)
             row_info->bit_depth = png_ptr->user_transform_depth;

          if (png_ptr->user_transform_channels)
             row_info->channels = png_ptr->user_transform_channels;
    #endif
          row_info->pixel_depth = (png_byte)(row_info->bit_depth *
              row_info->channels);

          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
       }
    #endif
    }

    #ifdef PNG_READ_PACK_SUPPORTED
    /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
     * without changing the actual values.  Thus, if you had a row with
     * a bit depth of 1, you would end up with bytes that only contained
     * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
     * png_do_shift() after this.
     */
    void /* PRIVATE */
    png_do_unpack(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_unpack");

       if (row_info->bit_depth < 8)
       {
          png_uint_32 i;
          png_uint_32 row_width=row_info->width;

          switch (row_info->bit_depth)
          {
             case 1:
             {
                png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
                png_bytep dp = row + (png_size_t)row_width - 1;
                png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
                for (i = 0; i < row_width; i++)
                {
                   *dp = (png_byte)((*sp >> shift) & 0x01);

                   if (shift == 7)
                   {
                      shift = 0;
                      sp--;
                   }

                   else
                      shift++;

                   dp--;
                }
                break;
             }

             case 2:
             {

                png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
                png_bytep dp = row + (png_size_t)row_width - 1;
                png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                for (i = 0; i < row_width; i++)
                {
                   *dp = (png_byte)((*sp >> shift) & 0x03);

                   if (shift == 6)
                   {
                      shift = 0;
                      sp--;
                   }

                   else
                      shift += 2;

                   dp--;
                }
                break;
             }

             case 4:
             {
                png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
                png_bytep dp = row + (png_size_t)row_width - 1;
                png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
                for (i = 0; i < row_width; i++)
                {
                   *dp = (png_byte)((*sp >> shift) & 0x0f);

                   if (shift == 4)
                   {
                      shift = 0;
                      sp--;
                   }

                   else
                      shift = 4;

                   dp--;
                }
                break;
             }

             default:
                break;
          }
          row_info->bit_depth = 8;
          row_info->pixel_depth = (png_byte)(8 * row_info->channels);
          row_info->rowbytes = row_width * row_info->channels;
       }
    }
    #endif

    #ifdef PNG_READ_SHIFT_SUPPORTED
    /* Reverse the effects of png_do_shift.  This routine merely shifts the
     * pixels back to their significant bits values.  Thus, if you have
     * a row of bit depth 8, but only 5 are significant, this will shift
     * the values back to 0 through 31.
     */
    void /* PRIVATE */
    png_do_unshift(png_row_infop row_info, png_bytep row,
        png_const_color_8p sig_bits)
    {
       int color_type;

       png_debug(1, "in png_do_unshift");

       /* The palette case has already been handled in the _init routine. */
       color_type = row_info->color_type;

       if (color_type != PNG_COLOR_TYPE_PALETTE)
       {
          int shift[4];
          int channels = 0;
          int bit_depth = row_info->bit_depth;

          if (color_type & PNG_COLOR_MASK_COLOR)
          {
             shift[channels++] = bit_depth - sig_bits->red;
             shift[channels++] = bit_depth - sig_bits->green;
             shift[channels++] = bit_depth - sig_bits->blue;
          }

          else
          {
             shift[channels++] = bit_depth - sig_bits->gray;
          }

          if (color_type & PNG_COLOR_MASK_ALPHA)
          {
             shift[channels++] = bit_depth - sig_bits->alpha;
          }

          {
             int c, have_shift;

             for (c = have_shift = 0; c < channels; ++c)
             {
                /* A shift of more than the bit depth is an error condition but it
                 * gets ignored here.
                 */
                if (shift[c] <= 0 || shift[c] >= bit_depth)
                   shift[c] = 0;

                else
                   have_shift = 1;
             }

             if (!have_shift)
                return;
          }

          switch (bit_depth)
          {
             default:
             /* Must be 1bpp gray: should not be here! */
                /* NOTREACHED */
                break;

             case 2:
             /* Must be 2bpp gray */
             /* assert(channels == 1 && shift[0] == 1) */
             {
                png_bytep bp = row;
                png_bytep bp_end = bp + row_info->rowbytes;

                while (bp < bp_end)
                {
                   int b = (*bp >> 1) & 0x55;
                   *bp++ = (png_byte)b;
                }
                break;
             }

             case 4:
             /* Must be 4bpp gray */
             /* assert(channels == 1) */
             {
                png_bytep bp = row;
                png_bytep bp_end = bp + row_info->rowbytes;
                int gray_shift = shift[0];
                int mask =  0xf >> gray_shift;

                mask |= mask << 4;

                while (bp < bp_end)
                {
                   int b = (*bp >> gray_shift) & mask;
                   *bp++ = (png_byte)b;
                }
                break;
             }

             case 8:
             /* Single byte components, G, GA, RGB, RGBA */
             {
                png_bytep bp = row;
                png_bytep bp_end = bp + row_info->rowbytes;
                int channel = 0;

                while (bp < bp_end)
                {
                   int b = *bp >> shift[channel];
                   if (++channel >= channels)
                      channel = 0;
                   *bp++ = (png_byte)b;
                }
                break;
             }

    #ifdef PNG_READ_16BIT_SUPPORTED
             case 16:
             /* Double byte components, G, GA, RGB, RGBA */
             {
                png_bytep bp = row;
                png_bytep bp_end = bp + row_info->rowbytes;
                int channel = 0;

                while (bp < bp_end)
                {
                   int value = (bp[0] << 8) + bp[1];

                   value >>= shift[channel];
                   if (++channel >= channels)
                      channel = 0;
                   *bp++ = (png_byte)(value >> 8);
                   *bp++ = (png_byte)(value & 0xff);
                }
                break;
             }
    #endif
          }
       }
    }
    #endif

    #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
    /* Scale rows of bit depth 16 down to 8 accurately */
    void /* PRIVATE */
    png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_scale_16_to_8");

       if (row_info->bit_depth == 16)
       {
          png_bytep sp = row; /* source */
          png_bytep dp = row; /* destination */
          png_bytep ep = sp + row_info->rowbytes; /* end+1 */

          while (sp < ep)
          {
             /* The input is an array of 16 bit components, these must be scaled to
              * 8 bits each.  For a 16 bit value V the required value (from the PNG
              * specification) is:
              *
              *    (V * 255) / 65535
              *
              * This reduces to round(V / 257), or floor((V + 128.5)/257)
              *
              * Represent V as the two byte value vhi.vlo.  Make a guess that the
              * result is the top byte of V, vhi, then the correction to this value
              * is:
              *
              *    error = floor(((V-vhi.vhi) + 128.5) / 257)
              *          = floor(((vlo-vhi) + 128.5) / 257)
              *
              * This can be approximated using integer arithmetic (and a signed
              * shift):
              *
              *    error = (vlo-vhi+128) >> 8;
              *
              * The approximate differs from the exact answer only when (vlo-vhi) is
              * 128; it then gives a correction of +1 when the exact correction is
              * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
              * input values) is:
              *
              *    error = (vlo-vhi+128)*65535 >> 24;
              *
              * An alternative arithmetic calculation which also gives no errors is:
              *
              *    (V * 255 + 32895) >> 16
              */

             png_int_32 tmp = *sp++; /* must be signed! */
             tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
             *dp++ = (png_byte)tmp;
          }

          row_info->bit_depth = 8;
          row_info->pixel_depth = (png_byte)(8 * row_info->channels);
          row_info->rowbytes = row_info->width * row_info->channels;
       }
    }
    #endif

    #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
    void /* PRIVATE */
    /* Simply discard the low byte.  This was the default behavior prior
     * to libpng-1.5.4.
     */
    png_do_chop(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_chop");

       if (row_info->bit_depth == 16)
       {
          png_bytep sp = row; /* source */
          png_bytep dp = row; /* destination */
          png_bytep ep = sp + row_info->rowbytes; /* end+1 */

          while (sp < ep)
          {
             *dp++ = *sp;
             sp += 2; /* skip low byte */
          }

          row_info->bit_depth = 8;
          row_info->pixel_depth = (png_byte)(8 * row_info->channels);
          row_info->rowbytes = row_info->width * row_info->channels;
       }
    }
    #endif

    #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
    void /* PRIVATE */
    png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_read_swap_alpha");

       {
          png_uint_32 row_width = row_info->width;
          if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
          {
             /* This converts from RGBA to ARGB */
             if (row_info->bit_depth == 8)
             {
                png_bytep sp = row + row_info->rowbytes;
                png_bytep dp = sp;
                png_byte save;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   save = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = save;
                }
             }

    #ifdef PNG_READ_16BIT_SUPPORTED
             /* This converts from RRGGBBAA to AARRGGBB */
             else
             {
                png_bytep sp = row + row_info->rowbytes;
                png_bytep dp = sp;
                png_byte save[2];
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   save[0] = *(--sp);
                   save[1] = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = save[0];
                   *(--dp) = save[1];
                }
             }
    #endif
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
          {
             /* This converts from GA to AG */
             if (row_info->bit_depth == 8)
             {
                png_bytep sp = row + row_info->rowbytes;
                png_bytep dp = sp;
                png_byte save;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   save = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = save;
                }
             }

    #ifdef PNG_READ_16BIT_SUPPORTED
             /* This converts from GGAA to AAGG */
             else
             {
                png_bytep sp = row + row_info->rowbytes;
                png_bytep dp = sp;
                png_byte save[2];
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   save[0] = *(--sp);
                   save[1] = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = save[0];
                   *(--dp) = save[1];
                }
             }
    #endif
          }
       }
    }
    #endif

    #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
    void /* PRIVATE */
    png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
    {
       png_uint_32 row_width;
       png_debug(1, "in png_do_read_invert_alpha");

       row_width = row_info->width;
       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
       {
          if (row_info->bit_depth == 8)
          {
             /* This inverts the alpha channel in RGBA */
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_uint_32 i;

             for (i = 0; i < row_width; i++)
             {
                *(--dp) = (png_byte)(255 - *(--sp));

    /*          This does nothing:
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                We can replace it with:
    */
                sp-=3;
                dp=sp;
             }
          }

    #ifdef PNG_READ_16BIT_SUPPORTED
          /* This inverts the alpha channel in RRGGBBAA */
          else
          {
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_uint_32 i;

             for (i = 0; i < row_width; i++)
             {
                *(--dp) = (png_byte)(255 - *(--sp));
                *(--dp) = (png_byte)(255 - *(--sp));

    /*          This does nothing:
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
                We can replace it with:
    */
                sp-=6;
                dp=sp;
             }
          }
    #endif
       }
       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
       {
          if (row_info->bit_depth == 8)
          {
             /* This inverts the alpha channel in GA */
             png_bytep sp = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_uint_32 i;

             for (i = 0; i < row_width; i++)
             {
                *(--dp) = (png_byte)(255 - *(--sp));
                *(--dp) = *(--sp);
             }
          }

    #ifdef PNG_READ_16BIT_SUPPORTED
          else
          {
             /* This inverts the alpha channel in GGAA */
             png_bytep sp  = row + row_info->rowbytes;
             png_bytep dp = sp;
             png_uint_32 i;

             for (i = 0; i < row_width; i++)
             {
                *(--dp) = (png_byte)(255 - *(--sp));
                *(--dp) = (png_byte)(255 - *(--sp));
    /*
                *(--dp) = *(--sp);
                *(--dp) = *(--sp);
    */
                sp-=2;
                dp=sp;
             }
          }
    #endif
       }
    }
    #endif

    #ifdef PNG_READ_FILLER_SUPPORTED
    /* Add filler channel if we have RGB color */
    void /* PRIVATE */
    png_do_read_filler(png_row_infop row_info, png_bytep row,
        png_uint_32 filler, png_uint_32 flags)
    {
       png_uint_32 i;
       png_uint_32 row_width = row_info->width;

    #ifdef PNG_READ_16BIT_SUPPORTED
       png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
    #endif
       png_byte lo_filler = (png_byte)(filler & 0xff);

       png_debug(1, "in png_do_read_filler");

       if (
           row_info->color_type == PNG_COLOR_TYPE_GRAY)
       {
          if (row_info->bit_depth == 8)
          {
             if (flags & PNG_FLAG_FILLER_AFTER)
             {
                /* This changes the data from G to GX */
                png_bytep sp = row + (png_size_t)row_width;
                png_bytep dp =  sp + (png_size_t)row_width;
                for (i = 1; i < row_width; i++)
                {
                   *(--dp) = lo_filler;
                   *(--dp) = *(--sp);
                }
                *(--dp) = lo_filler;
                row_info->channels = 2;
                row_info->pixel_depth = 16;
                row_info->rowbytes = row_width * 2;
             }

             else
             {
                /* This changes the data from G to XG */
                png_bytep sp = row + (png_size_t)row_width;
                png_bytep dp = sp  + (png_size_t)row_width;
                for (i = 0; i < row_width; i++)
                {
                   *(--dp) = *(--sp);
                   *(--dp) = lo_filler;
                }
                row_info->channels = 2;
                row_info->pixel_depth = 16;
                row_info->rowbytes = row_width * 2;
             }
          }

    #ifdef PNG_READ_16BIT_SUPPORTED
          else if (row_info->bit_depth == 16)
          {
             if (flags & PNG_FLAG_FILLER_AFTER)
             {
                /* This changes the data from GG to GGXX */
                png_bytep sp = row + (png_size_t)row_width * 2;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 1; i < row_width; i++)
                {
                   *(--dp) = hi_filler;
                   *(--dp) = lo_filler;
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                }
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
                row_info->channels = 2;
                row_info->pixel_depth = 32;
                row_info->rowbytes = row_width * 4;
             }

             else
             {
                /* This changes the data from GG to XXGG */
                png_bytep sp = row + (png_size_t)row_width * 2;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 0; i < row_width; i++)
                {
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = hi_filler;
                   *(--dp) = lo_filler;
                }
                row_info->channels = 2;
                row_info->pixel_depth = 32;
                row_info->rowbytes = row_width * 4;
             }
          }
    #endif
       } /* COLOR_TYPE == GRAY */
       else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
       {
          if (row_info->bit_depth == 8)
          {
             if (flags & PNG_FLAG_FILLER_AFTER)
             {
                /* This changes the data from RGB to RGBX */
                png_bytep sp = row + (png_size_t)row_width * 3;
                png_bytep dp = sp  + (png_size_t)row_width;
                for (i = 1; i < row_width; i++)
                {
                   *(--dp) = lo_filler;
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                }
                *(--dp) = lo_filler;
                row_info->channels = 4;
                row_info->pixel_depth = 32;
                row_info->rowbytes = row_width * 4;
             }

             else
             {
                /* This changes the data from RGB to XRGB */
                png_bytep sp = row + (png_size_t)row_width * 3;
                png_bytep dp = sp + (png_size_t)row_width;
                for (i = 0; i < row_width; i++)
                {
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = lo_filler;
                }
                row_info->channels = 4;
                row_info->pixel_depth = 32;
                row_info->rowbytes = row_width * 4;
             }
          }

    #ifdef PNG_READ_16BIT_SUPPORTED
          else if (row_info->bit_depth == 16)
          {
             if (flags & PNG_FLAG_FILLER_AFTER)
             {
                /* This changes the data from RRGGBB to RRGGBBXX */
                png_bytep sp = row + (png_size_t)row_width * 6;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 1; i < row_width; i++)
                {
                   *(--dp) = hi_filler;
                   *(--dp) = lo_filler;
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                }
                *(--dp) = hi_filler;
                *(--dp) = lo_filler;
                row_info->channels = 4;
                row_info->pixel_depth = 64;
                row_info->rowbytes = row_width * 8;
             }

             else
             {
                /* This changes the data from RRGGBB to XXRRGGBB */
                png_bytep sp = row + (png_size_t)row_width * 6;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 0; i < row_width; i++)
                {
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = *(--sp);
                   *(--dp) = hi_filler;
                   *(--dp) = lo_filler;
                }

                row_info->channels = 4;
                row_info->pixel_depth = 64;
                row_info->rowbytes = row_width * 8;
             }
          }
    #endif
       } /* COLOR_TYPE == RGB */
    }
    #endif

    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
    /* Expand grayscale files to RGB, with or without alpha */
    void /* PRIVATE */
    png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
    {
       png_uint_32 i;
       png_uint_32 row_width = row_info->width;

       png_debug(1, "in png_do_gray_to_rgb");

       if (row_info->bit_depth >= 8 &&
           !(row_info->color_type & PNG_COLOR_MASK_COLOR))
       {
          if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
          {
             if (row_info->bit_depth == 8)
             {
                /* This changes G to RGB */
                png_bytep sp = row + (png_size_t)row_width - 1;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 0; i < row_width; i++)
                {
                   *(dp--) = *sp;
                   *(dp--) = *sp;
                   *(dp--) = *(sp--);
                }
             }

             else
             {
                /* This changes GG to RRGGBB */
                png_bytep sp = row + (png_size_t)row_width * 2 - 1;
                png_bytep dp = sp  + (png_size_t)row_width * 4;
                for (i = 0; i < row_width; i++)
                {
                   *(dp--) = *sp;
                   *(dp--) = *(sp - 1);
                   *(dp--) = *sp;
                   *(dp--) = *(sp - 1);
                   *(dp--) = *(sp--);
                   *(dp--) = *(sp--);
                }
             }
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
          {
             if (row_info->bit_depth == 8)
             {
                /* This changes GA to RGBA */
                png_bytep sp = row + (png_size_t)row_width * 2 - 1;
                png_bytep dp = sp  + (png_size_t)row_width * 2;
                for (i = 0; i < row_width; i++)
                {
                   *(dp--) = *(sp--);
                   *(dp--) = *sp;
                   *(dp--) = *sp;
                   *(dp--) = *(sp--);
                }
             }

             else
             {
                /* This changes GGAA to RRGGBBAA */
                png_bytep sp = row + (png_size_t)row_width * 4 - 1;
                png_bytep dp = sp  + (png_size_t)row_width * 4;
                for (i = 0; i < row_width; i++)
                {
                   *(dp--) = *(sp--);
                   *(dp--) = *(sp--);
                   *(dp--) = *sp;
                   *(dp--) = *(sp - 1);
                   *(dp--) = *sp;
                   *(dp--) = *(sp - 1);
                   *(dp--) = *(sp--);
                   *(dp--) = *(sp--);
                }
             }
          }
          row_info->channels = (png_byte)(row_info->channels + 2);
          row_info->color_type |= PNG_COLOR_MASK_COLOR;
          row_info->pixel_depth = (png_byte)(row_info->channels *
              row_info->bit_depth);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
    }
    #endif

    #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
    /* Reduce RGB files to grayscale, with or without alpha
     * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
     * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
     * versions dated 1998 through November 2002 have been archived at
     * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
     * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
     * Charles Poynton poynton at poynton.com
     *
     *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
     *
     *  which can be expressed with integers as
     *
     *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
     *
     * Poynton's current link (as of January 2003 through July 2011):
     * <http://www.poynton.com/notes/colour_and_gamma/>
     * has changed the numbers slightly:
     *
     *     Y = 0.2126*R + 0.7152*G + 0.0722*B
     *
     *  which can be expressed with integers as
     *
     *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
     *
     *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
     *  end point chromaticities and the D65 white point.  Depending on the
     *  precision used for the D65 white point this produces a variety of different
     *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
     *  used (0.3127,0.3290) the Y calculation would be:
     *
     *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
     *
     *  While this is correct the rounding results in an overflow for white, because
     *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
     *  libpng uses, instead, the closest non-overflowing approximation:
     *
     *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
     *
     *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
     *  (including an sRGB chunk) then the chromaticities are used to calculate the
     *  coefficients.  See the chunk handling in pngrutil.c for more information.
     *
     *  In all cases the calculation is to be done in a linear colorspace.  If no
     *  gamma information is available to correct the encoding of the original RGB
     *  values this results in an implicit assumption that the original PNG RGB
     *  values were linear.
     *
     *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
     *  the API takes just red and green coefficients the blue coefficient is
     *  calculated to make the sum 32768.  This will result in different rounding
     *  to that used above.
     */
    int /* PRIVATE */
    png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)

    {
       int rgb_error = 0;

       png_debug(1, "in png_do_rgb_to_gray");

       if (!(row_info->color_type & PNG_COLOR_MASK_PALETTE) &&
           (row_info->color_type & PNG_COLOR_MASK_COLOR))
       {
          PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
          PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
          PNG_CONST png_uint_32 bc = 32768 - rc - gc;
          PNG_CONST png_uint_32 row_width = row_info->width;
          PNG_CONST int have_alpha =
             (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;

          if (row_info->bit_depth == 8)
          {
    #ifdef PNG_READ_GAMMA_SUPPORTED
             /* Notice that gamma to/from 1 are not necessarily inverses (if
              * there is an overall gamma correction).  Prior to 1.5.5 this code
              * checked the linearized values for equality; this doesn't match
              * the documentation, the original values must be checked.
              */
             if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
             {
                png_bytep sp = row;
                png_bytep dp = row;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   png_byte red   = *(sp++);
                   png_byte green = *(sp++);
                   png_byte blue  = *(sp++);

                   if (red != green || red != blue)
                   {
                      red = png_ptr->gamma_to_1[red];
                      green = png_ptr->gamma_to_1[green];
                      blue = png_ptr->gamma_to_1[blue];

                      rgb_error |= 1;
                      *(dp++) = png_ptr->gamma_from_1[
                          (rc*red + gc*green + bc*blue + 16384)>>15];
                   }

                   else
                   {
                      /* If there is no overall correction the table will not be
                       * set.
                       */
                      if (png_ptr->gamma_table != NULL)
                         red = png_ptr->gamma_table[red];

                      *(dp++) = red;
                   }

                   if (have_alpha)
                      *(dp++) = *(sp++);
                }
             }
             else
    #endif
             {
                png_bytep sp = row;
                png_bytep dp = row;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   png_byte red   = *(sp++);
                   png_byte green = *(sp++);
                   png_byte blue  = *(sp++);

                   if (red != green || red != blue)
                   {
                      rgb_error |= 1;
                      /* NOTE: this is the historical approach which simply
                       * truncates the results.
                       */
                      *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
                   }

                   else
                      *(dp++) = red;

                   if (have_alpha)
                      *(dp++) = *(sp++);
                }
             }
          }

          else /* RGB bit_depth == 16 */
          {
    #ifdef PNG_READ_GAMMA_SUPPORTED
             if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
             {
                png_bytep sp = row;
                png_bytep dp = row;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 red, green, blue, w;

                   red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                   green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                   blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;

                   if (red == green && red == blue)
                   {
                      if (png_ptr->gamma_16_table != NULL)
                         w = png_ptr->gamma_16_table[(red&0xff)
                             >> png_ptr->gamma_shift][red>>8];

                      else
                         w = red;
                   }

                   else
                   {
                      png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
                          >> png_ptr->gamma_shift][red>>8];
                      png_uint_16 green_1 =
                          png_ptr->gamma_16_to_1[(green&0xff) >>
                          png_ptr->gamma_shift][green>>8];
                      png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
                          >> png_ptr->gamma_shift][blue>>8];
                      png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
                          + bc*blue_1 + 16384)>>15);
                      w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
                          png_ptr->gamma_shift][gray16 >> 8];
                      rgb_error |= 1;
                   }

                   *(dp++) = (png_byte)((w>>8) & 0xff);
                   *(dp++) = (png_byte)(w & 0xff);

                   if (have_alpha)
                   {
                      *(dp++) = *(sp++);
                      *(dp++) = *(sp++);
                   }
                }
             }
             else
    #endif
             {
                png_bytep sp = row;
                png_bytep dp = row;
                png_uint_32 i;

                for (i = 0; i < row_width; i++)
                {
                   png_uint_16 red, green, blue, gray16;

                   red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                   green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                   blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;

                   if (red != green || red != blue)
                      rgb_error |= 1;

                   /* From 1.5.5 in the 16 bit case do the accurate conversion even
                    * in the 'fast' case - this is because this is where the code
                    * ends up when handling linear 16 bit data.
                    */
                   gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
                      15);
                   *(dp++) = (png_byte)((gray16>>8) & 0xff);
                   *(dp++) = (png_byte)(gray16 & 0xff);

                   if (have_alpha)
                   {
                      *(dp++) = *(sp++);
                      *(dp++) = *(sp++);
                   }
                }
             }
          }

          row_info->channels = (png_byte)(row_info->channels - 2);
          row_info->color_type = (png_byte)(row_info->color_type &
              ~PNG_COLOR_MASK_COLOR);
          row_info->pixel_depth = (png_byte)(row_info->channels *
              row_info->bit_depth);
          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
       }
       return rgb_error;
    }
    #endif
    #endif /* PNG_READ_TRANSFORMS_SUPPORTED */

    #ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED
    /* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
     * large of png_color.  This lets grayscale images be treated as
     * paletted.  Most useful for gamma correction and simplification
     * of code.  This API is not used internally.
     */
    void PNGAPI
    png_build_grayscale_palette(int bit_depth, png_colorp palette)
    {
       int num_palette;
       int color_inc;
       int i;
       int v;

       png_debug(1, "in png_do_build_grayscale_palette");

       if (palette == NULL)
          return;

       switch (bit_depth)
       {
          case 1:
             num_palette = 2;
             color_inc = 0xff;
             break;

          case 2:
             num_palette = 4;
             color_inc = 0x55;
             break;

          case 4:
             num_palette = 16;
             color_inc = 0x11;
             break;

          case 8:
             num_palette = 256;
             color_inc = 1;
             break;

          default:
             num_palette = 0;
             color_inc = 0;
             break;
       }

       for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
       {
          palette[i].red = (png_byte)v;
          palette[i].green = (png_byte)v;
          palette[i].blue = (png_byte)v;
       }
    }
    #endif

    #ifdef PNG_READ_TRANSFORMS_SUPPORTED
    #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
       defined(PNG_READ_ALPHA_MODE_SUPPORTED)
    /* Replace any alpha or transparency with the supplied background color.
     * "background" is already in the screen gamma, while "background_1" is
     * at a gamma of 1.0.  Paletted files have already been taken care of.
     */
    void /* PRIVATE */
    png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
    {
    #ifdef PNG_READ_GAMMA_SUPPORTED
       png_const_bytep gamma_table = png_ptr->gamma_table;
       png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
       png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
       png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
       png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
       png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
       int gamma_shift = png_ptr->gamma_shift;
       int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
    #endif

       png_bytep sp;
       png_uint_32 i;
       png_uint_32 row_width = row_info->width;
       int shift;

       png_debug(1, "in png_do_compose");

       {
          switch (row_info->color_type)
          {
             case PNG_COLOR_TYPE_GRAY:
             {
                switch (row_info->bit_depth)
                {
                   case 1:
                   {
                      sp = row;
                      shift = 7;
                      for (i = 0; i < row_width; i++)
                      {
                         if ((png_uint_16)((*sp >> shift) & 0x01)
                            == png_ptr->trans_color.gray)
                         {
                            unsigned int tmp = *sp & (0x7f7f >> (7 - shift));
                            tmp |= png_ptr->background.gray << shift;
                            *sp = (png_byte)(tmp & 0xff);
                         }

                         if (!shift)
                         {
                            shift = 7;
                            sp++;
                         }

                         else
                            shift--;
                      }
                      break;
                   }

                   case 2:
                   {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                      if (gamma_table != NULL)
                      {
                         sp = row;
                         shift = 6;
                         for (i = 0; i < row_width; i++)
                         {
                            if ((png_uint_16)((*sp >> shift) & 0x03)
                                == png_ptr->trans_color.gray)
                            {
                               unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                               tmp |= png_ptr->background.gray << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            else
                            {
                               unsigned int p = (*sp >> shift) & 0x03;
                               unsigned int g = (gamma_table [p | (p << 2) |
                                   (p << 4) | (p << 6)] >> 6) & 0x03;
                               unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                               tmp |= g << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            if (!shift)
                            {
                               shift = 6;
                               sp++;
                            }

                            else
                               shift -= 2;
                         }
                      }

                      else
    #endif
                      {
                         sp = row;
                         shift = 6;
                         for (i = 0; i < row_width; i++)
                         {
                            if ((png_uint_16)((*sp >> shift) & 0x03)
                                == png_ptr->trans_color.gray)
                            {
                               unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                               tmp |= png_ptr->background.gray << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            if (!shift)
                            {
                               shift = 6;
                               sp++;
                            }

                            else
                               shift -= 2;
                         }
                      }
                      break;
                   }

                   case 4:
                   {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                      if (gamma_table != NULL)
                      {
                         sp = row;
                         shift = 4;
                         for (i = 0; i < row_width; i++)
                         {
                            if ((png_uint_16)((*sp >> shift) & 0x0f)
                                == png_ptr->trans_color.gray)
                            {
                               unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                               tmp |= png_ptr->background.gray << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            else
                            {
                               unsigned int p = (*sp >> shift) & 0x0f;
                               unsigned int g = (gamma_table[p | (p << 4)] >> 4) &
                                  0x0f;
                               unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                               tmp |= g << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            if (!shift)
                            {
                               shift = 4;
                               sp++;
                            }

                            else
                               shift -= 4;
                         }
                      }

                      else
    #endif
                      {
                         sp = row;
                         shift = 4;
                         for (i = 0; i < row_width; i++)
                         {
                            if ((png_uint_16)((*sp >> shift) & 0x0f)
                                == png_ptr->trans_color.gray)
                            {
                               unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                               tmp |= png_ptr->background.gray << shift;
                               *sp = (png_byte)(tmp & 0xff);
                            }

                            if (!shift)
                            {
                               shift = 4;
                               sp++;
                            }

                            else
                               shift -= 4;
                         }
                      }
                      break;
                   }

                   case 8:
                   {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                      if (gamma_table != NULL)
                      {
                         sp = row;
                         for (i = 0; i < row_width; i++, sp++)
                         {
                            if (*sp == png_ptr->trans_color.gray)
                               *sp = (png_byte)png_ptr->background.gray;

                            else
                               *sp = gamma_table[*sp];
                         }
                      }
                      else
    #endif
                      {
                         sp = row;
                         for (i = 0; i < row_width; i++, sp++)
                         {
                            if (*sp == png_ptr->trans_color.gray)
                               *sp = (png_byte)png_ptr->background.gray;
                         }
                      }
                      break;
                   }

                   case 16:
                   {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                      if (gamma_16 != NULL)
                      {
                         sp = row;
                         for (i = 0; i < row_width; i++, sp += 2)
                         {
                            png_uint_16 v;

                            v = (png_uint_16)(((*sp) << 8) + *(sp + 1));

                            if (v == png_ptr->trans_color.gray)
                            {
                               /* Background is already in screen gamma */
                               *sp = (png_byte)((png_ptr->background.gray >> 8)
                                    & 0xff);
                               *(sp + 1) = (png_byte)(png_ptr->background.gray
                                    & 0xff);
                            }

                            else
                            {
                               v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                               *sp = (png_byte)((v >> 8) & 0xff);
                               *(sp + 1) = (png_byte)(v & 0xff);
                            }
                         }
                      }
                      else
    #endif
                      {
                         sp = row;
                         for (i = 0; i < row_width; i++, sp += 2)
                         {
                            png_uint_16 v;

                            v = (png_uint_16)(((*sp) << 8) + *(sp + 1));

                            if (v == png_ptr->trans_color.gray)
                            {
                               *sp = (png_byte)((png_ptr->background.gray >> 8)
                                    & 0xff);
                               *(sp + 1) = (png_byte)(png_ptr->background.gray
                                    & 0xff);
                            }
                         }
                      }
                      break;
                   }

                   default:
                      break;
                }
                break;
             }

             case PNG_COLOR_TYPE_RGB:
             {
                if (row_info->bit_depth == 8)
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 3)
                      {
                         if (*sp == png_ptr->trans_color.red &&
                             *(sp + 1) == png_ptr->trans_color.green &&
                             *(sp + 2) == png_ptr->trans_color.blue)
                         {
                            *sp = (png_byte)png_ptr->background.red;
                            *(sp + 1) = (png_byte)png_ptr->background.green;
                            *(sp + 2) = (png_byte)png_ptr->background.blue;
                         }

                         else
                         {
                            *sp = gamma_table[*sp];
                            *(sp + 1) = gamma_table[*(sp + 1)];
                            *(sp + 2) = gamma_table[*(sp + 2)];
                         }
                      }
                   }
                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 3)
                      {
                         if (*sp == png_ptr->trans_color.red &&
                             *(sp + 1) == png_ptr->trans_color.green &&
                             *(sp + 2) == png_ptr->trans_color.blue)
                         {
                            *sp = (png_byte)png_ptr->background.red;
                            *(sp + 1) = (png_byte)png_ptr->background.green;
                            *(sp + 2) = (png_byte)png_ptr->background.blue;
                         }
                      }
                   }
                }
                else /* if (row_info->bit_depth == 16) */
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 6)
                      {
                         png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));

                         png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                             + *(sp + 3));

                         png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                             + *(sp + 5));

                         if (r == png_ptr->trans_color.red &&
                             g == png_ptr->trans_color.green &&
                             b == png_ptr->trans_color.blue)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                            *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                    & 0xff);
                            *(sp + 3) = (png_byte)(png_ptr->background.green
                                    & 0xff);
                            *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                    & 0xff);
                            *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                         }

                         else
                         {
                            png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);

                            v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                            *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 3) = (png_byte)(v & 0xff);

                            v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                            *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 5) = (png_byte)(v & 0xff);
                         }
                      }
                   }

                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 6)
                      {
                         png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));

                         png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                             + *(sp + 3));

                         png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                             + *(sp + 5));

                         if (r == png_ptr->trans_color.red &&
                             g == png_ptr->trans_color.green &&
                             b == png_ptr->trans_color.blue)
                         {
                            *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                            *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                    & 0xff);
                            *(sp + 3) = (png_byte)(png_ptr->background.green
                                    & 0xff);
                            *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                    & 0xff);
                            *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                         }
                      }
                   }
                }
                break;
             }

             case PNG_COLOR_TYPE_GRAY_ALPHA:
             {
                if (row_info->bit_depth == 8)
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                       gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 2)
                      {
                         png_uint_16 a = *(sp + 1);

                         if (a == 0xff)
                            *sp = gamma_table[*sp];

                         else if (a == 0)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)png_ptr->background.gray;
                         }

                         else
                         {
                            png_byte v, w;

                            v = gamma_to_1[*sp];
                            png_composite(w, v, a, png_ptr->background_1.gray);
                            if (!optimize)
                               w = gamma_from_1[w];
                            *sp = w;
                         }
                      }
                   }
                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 2)
                      {
                         png_byte a = *(sp + 1);

                         if (a == 0)
                            *sp = (png_byte)png_ptr->background.gray;

                         else if (a < 0xff)
                            png_composite(*sp, *sp, a, png_ptr->background.gray);
                      }
                   }
                }
                else /* if (png_ptr->bit_depth == 16) */
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                       gamma_16_to_1 != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 4)
                      {
                         png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                             + *(sp + 3));

                         if (a == (png_uint_16)0xffff)
                         {
                            png_uint_16 v;

                            v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);
                         }

                         else if (a == 0)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)((png_ptr->background.gray >> 8)
                                    & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                         }

                         else
                         {
                            png_uint_16 g, v, w;

                            g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                            png_composite_16(v, g, a, png_ptr->background_1.gray);
                            if (optimize)
                               w = v;
                            else
                               w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
                            *sp = (png_byte)((w >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(w & 0xff);
                         }
                      }
                   }
                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 4)
                      {
                         png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                             + *(sp + 3));

                         if (a == 0)
                         {
                            *sp = (png_byte)((png_ptr->background.gray >> 8)
                                    & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                         }

                         else if (a < 0xffff)
                         {
                            png_uint_16 g, v;

                            g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                            png_composite_16(v, g, a, png_ptr->background.gray);
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);
                         }
                      }
                   }
                }
                break;
             }

             case PNG_COLOR_TYPE_RGB_ALPHA:
             {
                if (row_info->bit_depth == 8)
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                       gamma_table != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 4)
                      {
                         png_byte a = *(sp + 3);

                         if (a == 0xff)
                         {
                            *sp = gamma_table[*sp];
                            *(sp + 1) = gamma_table[*(sp + 1)];
                            *(sp + 2) = gamma_table[*(sp + 2)];
                         }

                         else if (a == 0)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)png_ptr->background.red;
                            *(sp + 1) = (png_byte)png_ptr->background.green;
                            *(sp + 2) = (png_byte)png_ptr->background.blue;
                         }

                         else
                         {
                            png_byte v, w;

                            v = gamma_to_1[*sp];
                            png_composite(w, v, a, png_ptr->background_1.red);
                            if (!optimize) w = gamma_from_1[w];
                            *sp = w;

                            v = gamma_to_1[*(sp + 1)];
                            png_composite(w, v, a, png_ptr->background_1.green);
                            if (!optimize) w = gamma_from_1[w];
                            *(sp + 1) = w;

                            v = gamma_to_1[*(sp + 2)];
                            png_composite(w, v, a, png_ptr->background_1.blue);
                            if (!optimize) w = gamma_from_1[w];
                            *(sp + 2) = w;
                         }
                      }
                   }
                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 4)
                      {
                         png_byte a = *(sp + 3);

                         if (a == 0)
                         {
                            *sp = (png_byte)png_ptr->background.red;
                            *(sp + 1) = (png_byte)png_ptr->background.green;
                            *(sp + 2) = (png_byte)png_ptr->background.blue;
                         }

                         else if (a < 0xff)
                         {
                            png_composite(*sp, *sp, a, png_ptr->background.red);

                            png_composite(*(sp + 1), *(sp + 1), a,
                                png_ptr->background.green);

                            png_composite(*(sp + 2), *(sp + 2), a,
                                png_ptr->background.blue);
                         }
                      }
                   }
                }
                else /* if (row_info->bit_depth == 16) */
                {
    #ifdef PNG_READ_GAMMA_SUPPORTED
                   if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                       gamma_16_to_1 != NULL)
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 8)
                      {
                         png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                             << 8) + (png_uint_16)(*(sp + 7)));

                         if (a == (png_uint_16)0xffff)
                         {
                            png_uint_16 v;

                            v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);

                            v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                            *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 3) = (png_byte)(v & 0xff);

                            v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                            *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 5) = (png_byte)(v & 0xff);
                         }

                         else if (a == 0)
                         {
                            /* Background is already in screen gamma */
                            *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                            *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                    & 0xff);
                            *(sp + 3) = (png_byte)(png_ptr->background.green
                                    & 0xff);
                            *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                    & 0xff);
                            *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                         }

                         else
                         {
                            png_uint_16 v, w;

                            v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                            png_composite_16(w, v, a, png_ptr->background_1.red);
                            if (!optimize)
                               w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                    8];
                            *sp = (png_byte)((w >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(w & 0xff);

                            v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
                            png_composite_16(w, v, a, png_ptr->background_1.green);
                            if (!optimize)
                               w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                    8];

                            *(sp + 2) = (png_byte)((w >> 8) & 0xff);
                            *(sp + 3) = (png_byte)(w & 0xff);

                            v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
                            png_composite_16(w, v, a, png_ptr->background_1.blue);
                            if (!optimize)
                               w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                    8];

                            *(sp + 4) = (png_byte)((w >> 8) & 0xff);
                            *(sp + 5) = (png_byte)(w & 0xff);
                         }
                      }
                   }

                   else
    #endif
                   {
                      sp = row;
                      for (i = 0; i < row_width; i++, sp += 8)
                      {
                         png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                             << 8) + (png_uint_16)(*(sp + 7)));

                         if (a == 0)
                         {
                            *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                            *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                    & 0xff);
                            *(sp + 3) = (png_byte)(png_ptr->background.green
                                    & 0xff);
                            *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                    & 0xff);
                            *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                         }

                         else if (a < 0xffff)
                         {
                            png_uint_16 v;

                            png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                            png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                                + *(sp + 3));
                            png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                                + *(sp + 5));

                            png_composite_16(v, r, a, png_ptr->background.red);
                            *sp = (png_byte)((v >> 8) & 0xff);
                            *(sp + 1) = (png_byte)(v & 0xff);

                            png_composite_16(v, g, a, png_ptr->background.green);
                            *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 3) = (png_byte)(v & 0xff);

                            png_composite_16(v, b, a, png_ptr->background.blue);
                            *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                            *(sp + 5) = (png_byte)(v & 0xff);
                         }
                      }
                   }
                }
                break;
             }

             default:
                break;
          }
       }
    }
    #endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */

    #ifdef PNG_READ_GAMMA_SUPPORTED
    /* Gamma correct the image, avoiding the alpha channel.  Make sure
     * you do this after you deal with the transparency issue on grayscale
     * or RGB images. If your bit depth is 8, use gamma_table, if it
     * is 16, use gamma_16_table and gamma_shift.  Build these with
     * build_gamma_table().
     */
    void /* PRIVATE */
    png_do_gamma(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
    {
       png_const_bytep gamma_table = png_ptr->gamma_table;
       png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
       int gamma_shift = png_ptr->gamma_shift;

       png_bytep sp;
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;

       png_debug(1, "in png_do_gamma");

       if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
           (row_info->bit_depth == 16 && gamma_16_table != NULL)))
       {
          switch (row_info->color_type)
          {
             case PNG_COLOR_TYPE_RGB:
             {
                if (row_info->bit_depth == 8)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      *sp = gamma_table[*sp];
                      sp++;
                      *sp = gamma_table[*sp];
                      sp++;
                      *sp = gamma_table[*sp];
                      sp++;
                   }
                }

                else /* if (row_info->bit_depth == 16) */
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      png_uint_16 v;

                      v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;

                      v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;

                      v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;
                   }
                }
                break;
             }

             case PNG_COLOR_TYPE_RGB_ALPHA:
             {
                if (row_info->bit_depth == 8)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      *sp = gamma_table[*sp];
                      sp++;

                      *sp = gamma_table[*sp];
                      sp++;

                      *sp = gamma_table[*sp];
                      sp++;

                      sp++;
                   }
                }

                else /* if (row_info->bit_depth == 16) */
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;

                      v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;

                      v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 4;
                   }
                }
                break;
             }

             case PNG_COLOR_TYPE_GRAY_ALPHA:
             {
                if (row_info->bit_depth == 8)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      *sp = gamma_table[*sp];
                      sp += 2;
                   }
                }

                else /* if (row_info->bit_depth == 16) */
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 4;
                   }
                }
                break;
             }

             case PNG_COLOR_TYPE_GRAY:
             {
                if (row_info->bit_depth == 2)
                {
                   sp = row;
                   for (i = 0; i < row_width; i += 4)
                   {
                      int a = *sp & 0xc0;
                      int b = *sp & 0x30;
                      int c = *sp & 0x0c;
                      int d = *sp & 0x03;

                      *sp = (png_byte)(
                          ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
                          ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
                          ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
                          ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
                      sp++;
                   }
                }

                if (row_info->bit_depth == 4)
                {
                   sp = row;
                   for (i = 0; i < row_width; i += 2)
                   {
                      int msb = *sp & 0xf0;
                      int lsb = *sp & 0x0f;

                      *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
                          | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
                      sp++;
                   }
                }

                else if (row_info->bit_depth == 8)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      *sp = gamma_table[*sp];
                      sp++;
                   }
                }

                else if (row_info->bit_depth == 16)
                {
                   sp = row;
                   for (i = 0; i < row_width; i++)
                   {
                      png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                      *sp = (png_byte)((v >> 8) & 0xff);
                      *(sp + 1) = (png_byte)(v & 0xff);
                      sp += 2;
                   }
                }
                break;
             }

             default:
                break;
          }
       }
    }
    #endif

    #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
    /* Encode the alpha channel to the output gamma (the input channel is always
     * linear.)  Called only with color types that have an alpha channel.  Needs the
     * from_1 tables.
     */
    void /* PRIVATE */
    png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
    {
       png_uint_32 row_width = row_info->width;

       png_debug(1, "in png_do_encode_alpha");

       if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
       {
          if (row_info->bit_depth == 8)
          {
             PNG_CONST png_bytep table = png_ptr->gamma_from_1;

             if (table != NULL)
             {
                PNG_CONST int step =
                   (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;

                /* The alpha channel is the last component: */
                row += step - 1;

                for (; row_width > 0; --row_width, row += step)
                   *row = table[*row];

                return;
             }
          }

          else if (row_info->bit_depth == 16)
          {
             PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
             PNG_CONST int gamma_shift = png_ptr->gamma_shift;

             if (table != NULL)
             {
                PNG_CONST int step =
                   (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;

                /* The alpha channel is the last component: */
                row += step - 2;

                for (; row_width > 0; --row_width, row += step)
                {
                   png_uint_16 v;

                   v = table[*(row + 1) >> gamma_shift][*row];
                   *row = (png_byte)((v >> 8) & 0xff);
                   *(row + 1) = (png_byte)(v & 0xff);
                }

                return;
             }
          }
       }

       /* Only get to here if called with a weird row_info; no harm has been done,
        * so just issue a warning.
        */
       png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
    }
    #endif

    #ifdef PNG_READ_EXPAND_SUPPORTED
    /* Expands a palette row to an RGB or RGBA row depending
     * upon whether you supply trans and num_trans.
     */
    void /* PRIVATE */
    png_do_expand_palette(png_row_infop row_info, png_bytep row,
       png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
    {
       int shift, value;
       png_bytep sp, dp;
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;

       png_debug(1, "in png_do_expand_palette");

       if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
       {
          if (row_info->bit_depth < 8)
          {
             switch (row_info->bit_depth)
             {
                case 1:
                {
                   sp = row + (png_size_t)((row_width - 1) >> 3);
                   dp = row + (png_size_t)row_width - 1;
                   shift = 7 - (int)((row_width + 7) & 0x07);
                   for (i = 0; i < row_width; i++)
                   {
                      if ((*sp >> shift) & 0x01)
                         *dp = 1;

                      else
                         *dp = 0;

                      if (shift == 7)
                      {
                         shift = 0;
                         sp--;
                      }

                      else
                         shift++;

                      dp--;
                   }
                   break;
                }

                case 2:
                {
                   sp = row + (png_size_t)((row_width - 1) >> 2);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                   for (i = 0; i < row_width; i++)
                   {
                      value = (*sp >> shift) & 0x03;
                      *dp = (png_byte)value;
                      if (shift == 6)
                      {
                         shift = 0;
                         sp--;
                      }

                      else
                         shift += 2;

                      dp--;
                   }
                   break;
                }

                case 4:
                {
                   sp = row + (png_size_t)((row_width - 1) >> 1);
                   dp = row + (png_size_t)row_width - 1;
                   shift = (int)((row_width & 0x01) << 2);
                   for (i = 0; i < row_width; i++)
                   {
                      value = (*sp >> shift) & 0x0f;
                      *dp = (png_byte)value;
                      if (shift == 4)
                      {
                         shift = 0;
                         sp--;
                      }

                      else
                         shift += 4;

                      dp--;
                   }
                   break;
                }

                default:
                   break;
             }
             row_info->bit_depth = 8;
             row_info->pixel_depth = 8;
             row_info->rowbytes = row_width;
          }

          if (row_info->bit_depth == 8)
          {
             {
                if (num_trans > 0)
                {
                   sp = row + (png_size_t)row_width - 1;
                   dp = row + (png_size_t)(row_width << 2) - 1;

                   for (i = 0; i < row_width; i++)
                   {
                      if ((int)(*sp) >= num_trans)
                         *dp-- = 0xff;

                      else
                         *dp-- = trans_alpha[*sp];

                      *dp-- = palette[*sp].blue;
                      *dp-- = palette[*sp].green;
                      *dp-- = palette[*sp].red;
                      sp--;
                   }
                   row_info->bit_depth = 8;
                   row_info->pixel_depth = 32;
                   row_info->rowbytes = row_width * 4;
                   row_info->color_type = 6;
                   row_info->channels = 4;
                }

                else
                {
                   sp = row + (png_size_t)row_width - 1;
                   dp = row + (png_size_t)(row_width * 3) - 1;

                   for (i = 0; i < row_width; i++)
                   {
                      *dp-- = palette[*sp].blue;
                      *dp-- = palette[*sp].green;
                      *dp-- = palette[*sp].red;
                      sp--;
                   }

                   row_info->bit_depth = 8;
                   row_info->pixel_depth = 24;
                   row_info->rowbytes = row_width * 3;
                   row_info->color_type = 2;
                   row_info->channels = 3;
                }
             }
          }
       }
    }

    /* If the bit depth < 8, it is expanded to 8.  Also, if the already
     * expanded transparency value is supplied, an alpha channel is built.
     */
    void /* PRIVATE */
    png_do_expand(png_row_infop row_info, png_bytep row,
        png_const_color_16p trans_color)
    {
       int shift, value;
       png_bytep sp, dp;
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;

       png_debug(1, "in png_do_expand");

       {
          if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
          {
             unsigned int gray = trans_color ? trans_color->gray : 0;

             if (row_info->bit_depth < 8)
             {
                switch (row_info->bit_depth)
                {
                   case 1:
                   {
                      gray = (gray & 0x01) * 0xff;
                      sp = row + (png_size_t)((row_width - 1) >> 3);
                      dp = row + (png_size_t)row_width - 1;
                      shift = 7 - (int)((row_width + 7) & 0x07);
                      for (i = 0; i < row_width; i++)
                      {
                         if ((*sp >> shift) & 0x01)
                            *dp = 0xff;

                         else
                            *dp = 0;

                         if (shift == 7)
                         {
                            shift = 0;
                            sp--;
                         }

                         else
                            shift++;

                         dp--;
                      }
                      break;
                   }

                   case 2:
                   {
                      gray = (gray & 0x03) * 0x55;
                      sp = row + (png_size_t)((row_width - 1) >> 2);
                      dp = row + (png_size_t)row_width - 1;
                      shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                      for (i = 0; i < row_width; i++)
                      {
                         value = (*sp >> shift) & 0x03;
                         *dp = (png_byte)(value | (value << 2) | (value << 4) |
                            (value << 6));
                         if (shift == 6)
                         {
                            shift = 0;
                            sp--;
                         }

                         else
                            shift += 2;

                         dp--;
                      }
                      break;
                   }

                   case 4:
                   {
                      gray = (gray & 0x0f) * 0x11;
                      sp = row + (png_size_t)((row_width - 1) >> 1);
                      dp = row + (png_size_t)row_width - 1;
                      shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
                      for (i = 0; i < row_width; i++)
                      {
                         value = (*sp >> shift) & 0x0f;
                         *dp = (png_byte)(value | (value << 4));
                         if (shift == 4)
                         {
                            shift = 0;
                            sp--;
                         }

                         else
                            shift = 4;

                         dp--;
                      }
                      break;
                   }

                   default:
                      break;
                }

                row_info->bit_depth = 8;
                row_info->pixel_depth = 8;
                row_info->rowbytes = row_width;
             }

             if (trans_color != NULL)
             {
                if (row_info->bit_depth == 8)
                {
                   gray = gray & 0xff;
                   sp = row + (png_size_t)row_width - 1;
                   dp = row + (png_size_t)(row_width << 1) - 1;

                   for (i = 0; i < row_width; i++)
                   {
                      if (*sp == gray)
                         *dp-- = 0;

                      else
                         *dp-- = 0xff;

                      *dp-- = *sp--;
                   }
                }

                else if (row_info->bit_depth == 16)
                {
                   unsigned int gray_high = (gray >> 8) & 0xff;
                   unsigned int gray_low = gray & 0xff;
                   sp = row + row_info->rowbytes - 1;
                   dp = row + (row_info->rowbytes << 1) - 1;
                   for (i = 0; i < row_width; i++)
                   {
                      if (*(sp - 1) == gray_high && *(sp) == gray_low)
                      {
                         *dp-- = 0;
                         *dp-- = 0;
                      }

                      else
                      {
                         *dp-- = 0xff;
                         *dp-- = 0xff;
                      }

                      *dp-- = *sp--;
                      *dp-- = *sp--;
                   }
                }

                row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
                row_info->channels = 2;
                row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
                row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
                   row_width);
             }
          }
          else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_color)
          {
             if (row_info->bit_depth == 8)
             {
                png_byte red = (png_byte)(trans_color->red & 0xff);
                png_byte green = (png_byte)(trans_color->green & 0xff);
                png_byte blue = (png_byte)(trans_color->blue & 0xff);
                sp = row + (png_size_t)row_info->rowbytes - 1;
                dp = row + (png_size_t)(row_width << 2) - 1;
                for (i = 0; i < row_width; i++)
                {
                   if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
                      *dp-- = 0;

                   else
                      *dp-- = 0xff;

                   *dp-- = *sp--;
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                }
             }
             else if (row_info->bit_depth == 16)
             {
                png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
                png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
                png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
                png_byte red_low = (png_byte)(trans_color->red & 0xff);
                png_byte green_low = (png_byte)(trans_color->green & 0xff);
                png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
                sp = row + row_info->rowbytes - 1;
                dp = row + (png_size_t)(row_width << 3) - 1;
                for (i = 0; i < row_width; i++)
                {
                   if (*(sp - 5) == red_high &&
                       *(sp - 4) == red_low &&
                       *(sp - 3) == green_high &&
                       *(sp - 2) == green_low &&
                       *(sp - 1) == blue_high &&
                       *(sp    ) == blue_low)
                   {
                      *dp-- = 0;
                      *dp-- = 0;
                   }

                   else
                   {
                      *dp-- = 0xff;
                      *dp-- = 0xff;
                   }

                   *dp-- = *sp--;
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                   *dp-- = *sp--;
                }
             }
             row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
             row_info->channels = 4;
             row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
             row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
          }
       }
    }
    #endif

    #ifdef PNG_READ_EXPAND_16_SUPPORTED
    /* If the bit depth is 8 and the color type is not a palette type expand the
     * whole row to 16 bits.  Has no effect otherwise.
     */
    void /* PRIVATE */
    png_do_expand_16(png_row_infop row_info, png_bytep row)
    {
       if (row_info->bit_depth == 8 &&
          row_info->color_type != PNG_COLOR_TYPE_PALETTE)
       {
          /* The row have a sequence of bytes containing [0..255] and we need
           * to turn it into another row containing [0..65535], to do this we
           * calculate:
           *
           *  (input / 255) * 65535
           *
           *  Which happens to be exactly input * 257 and this can be achieved
           *  simply by byte replication in place (copying backwards).
           */
          png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
          png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
          while (dp > sp)
             dp[-2] = dp[-1] = *--sp, dp -= 2;

          row_info->rowbytes *= 2;
          row_info->bit_depth = 16;
          row_info->pixel_depth = (png_byte)(row_info->channels * 16);
       }
    }
    #endif

    #ifdef PNG_READ_QUANTIZE_SUPPORTED
    void /* PRIVATE */
    png_do_quantize(png_row_infop row_info, png_bytep row,
        png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
    {
       png_bytep sp, dp;
       png_uint_32 i;
       png_uint_32 row_width=row_info->width;

       png_debug(1, "in png_do_quantize");

       if (row_info->bit_depth == 8)
       {
          if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
          {
             int r, g, b, p;
             sp = row;
             dp = row;
             for (i = 0; i < row_width; i++)
             {
                r = *sp++;
                g = *sp++;
                b = *sp++;

                /* This looks real messy, but the compiler will reduce
                 * it down to a reasonable formula.  For example, with
                 * 5 bits per color, we get:
                 * p = (((r >> 3) & 0x1f) << 10) |
                 *    (((g >> 3) & 0x1f) << 5) |
                 *    ((b >> 3) & 0x1f);
                 */
                p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                    ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                    (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                    (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                    ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                    (PNG_QUANTIZE_BLUE_BITS)) |
                    ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                    ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));

                *dp++ = palette_lookup[p];
             }

             row_info->color_type = PNG_COLOR_TYPE_PALETTE;
             row_info->channels = 1;
             row_info->pixel_depth = row_info->bit_depth;
             row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
             palette_lookup != NULL)
          {
             int r, g, b, p;
             sp = row;
             dp = row;
             for (i = 0; i < row_width; i++)
             {
                r = *sp++;
                g = *sp++;
                b = *sp++;
                sp++;

                p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                    ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                    (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                    (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                    ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                    (PNG_QUANTIZE_BLUE_BITS)) |
                    ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                    ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));

                *dp++ = palette_lookup[p];
             }

             row_info->color_type = PNG_COLOR_TYPE_PALETTE;
             row_info->channels = 1;
             row_info->pixel_depth = row_info->bit_depth;
             row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
             quantize_lookup)
          {
             sp = row;

             for (i = 0; i < row_width; i++, sp++)
             {
                *sp = quantize_lookup[*sp];
             }
          }
       }
    }
    #endif /* PNG_READ_QUANTIZE_SUPPORTED */
    #endif /* PNG_READ_TRANSFORMS_SUPPORTED */

    #ifdef PNG_MNG_FEATURES_SUPPORTED
    /* Undoes intrapixel differencing  */
    void /* PRIVATE */
    png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_read_intrapixel");

       if (
           (row_info->color_type & PNG_COLOR_MASK_COLOR))
       {
          int bytes_per_pixel;
          png_uint_32 row_width = row_info->width;

          if (row_info->bit_depth == 8)
          {
             png_bytep rp;
             png_uint_32 i;

             if (row_info->color_type == PNG_COLOR_TYPE_RGB)
                bytes_per_pixel = 3;

             else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
                bytes_per_pixel = 4;

             else
                return;

             for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
             {
                *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
                *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
             }
          }
          else if (row_info->bit_depth == 16)
          {
             png_bytep rp;
             png_uint_32 i;

             if (row_info->color_type == PNG_COLOR_TYPE_RGB)
                bytes_per_pixel = 6;

             else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
                bytes_per_pixel = 8;

             else
                return;

             for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
             {
                png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
                png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
                png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
                png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
                png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
                *(rp    ) = (png_byte)((red >> 8) & 0xff);
                *(rp + 1) = (png_byte)(red & 0xff);
                *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
                *(rp + 5) = (png_byte)(blue & 0xff);
             }
          }
       }
    }
    #endif /* PNG_MNG_FEATURES_SUPPORTED */
    #endif /* PNG_READ_SUPPORTED */