    /* pngread.c - read a PNG file
     *
     * Last changed in libpng 1.6.1 [March 28, 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 routines that an application calls directly to
     * read a PNG file or stream.
     */

    #include "pngpriv.h"
    #if defined(PNG_SIMPLIFIED_READ_SUPPORTED) && defined(PNG_STDIO_SUPPORTED)
    #  include <errno.h>
    #endif

    #ifdef PNG_READ_SUPPORTED

    /* Create a PNG structure for reading, and allocate any memory needed. */
    PNG_FUNCTION(png_structp,PNGAPI
    png_create_read_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
        png_error_ptr error_fn, png_error_ptr warn_fn),PNG_ALLOCATED)
    {
    #ifndef PNG_USER_MEM_SUPPORTED
       png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
          error_fn, warn_fn, NULL, NULL, NULL);
    #else
       return png_create_read_struct_2(user_png_ver, error_ptr, error_fn,
           warn_fn, NULL, NULL, NULL);
    }

    /* Alternate create PNG structure for reading, and allocate any memory
     * needed.
     */
    PNG_FUNCTION(png_structp,PNGAPI
    png_create_read_struct_2,(png_const_charp user_png_ver, png_voidp error_ptr,
        png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
        png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
    {
       png_structp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
          error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);
    #endif /* PNG_USER_MEM_SUPPORTED */

       if (png_ptr != NULL)
       {
          png_ptr->mode = PNG_IS_READ_STRUCT;

          /* Added in libpng-1.6.0; this can be used to detect a read structure if
           * required (it will be zero in a write structure.)
           */
    #     ifdef PNG_SEQUENTIAL_READ_SUPPORTED
             png_ptr->IDAT_read_size = PNG_IDAT_READ_SIZE;
    #     endif

    #     ifdef PNG_BENIGN_READ_ERRORS_SUPPORTED
             png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;

             /* In stable builds only warn if an application error can be completely
              * handled.
              */
    #        if PNG_LIBPNG_BUILD_BASE_TYPE >= PNG_LIBPNG_BUILD_RC
                png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;
    #        endif
    #     endif

          /* TODO: delay this, it can be done in png_init_io (if the app doesn't
           * do it itself) avoiding setting the default function if it is not
           * required.
           */
          png_set_read_fn(png_ptr, NULL, NULL);
       }

       return png_ptr;
    }

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    /* Read the information before the actual image data.  This has been
     * changed in v0.90 to allow reading a file that already has the magic
     * bytes read from the stream.  You can tell libpng how many bytes have
     * been read from the beginning of the stream (up to the maximum of 8)
     * via png_set_sig_bytes(), and we will only check the remaining bytes
     * here.  The application can then have access to the signature bytes we
     * read if it is determined that this isn't a valid PNG file.
     */
    void PNGAPI
    png_read_info(png_structrp png_ptr, png_inforp info_ptr)
    {
    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
       int keep;
    #endif

       png_debug(1, "in png_read_info");

       if (png_ptr == NULL || info_ptr == NULL)
          return;

       /* Read and check the PNG file signature. */
       png_read_sig(png_ptr, info_ptr);

       for (;;)
       {
          png_uint_32 length = png_read_chunk_header(png_ptr);
          png_uint_32 chunk_name = png_ptr->chunk_name;

          /* IDAT logic needs to happen here to simplify getting the two flags
           * right.
           */
          if (chunk_name == png_IDAT)
          {
             if (!(png_ptr->mode & PNG_HAVE_IHDR))
                png_chunk_error(png_ptr, "Missing IHDR before IDAT");

             else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
                 !(png_ptr->mode & PNG_HAVE_PLTE))
                png_chunk_error(png_ptr, "Missing PLTE before IDAT");

             else if (png_ptr->mode & PNG_AFTER_IDAT)
                png_chunk_benign_error(png_ptr, "Too many IDATs found");

             png_ptr->mode |= PNG_HAVE_IDAT;
          }

          else if (png_ptr->mode & PNG_HAVE_IDAT)
             png_ptr->mode |= PNG_AFTER_IDAT;

          /* This should be a binary subdivision search or a hash for
           * matching the chunk name rather than a linear search.
           */
          if (chunk_name == png_IHDR)
             png_handle_IHDR(png_ptr, info_ptr, length);

          else if (chunk_name == png_IEND)
             png_handle_IEND(png_ptr, info_ptr, length);

    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
          else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
          {
             png_handle_unknown(png_ptr, info_ptr, length, keep);

             if (chunk_name == png_PLTE)
                png_ptr->mode |= PNG_HAVE_PLTE;

             else if (chunk_name == png_IDAT)
             {
                png_ptr->idat_size = 0; /* It has been consumed */
                break;
             }
          }
    #endif
          else if (chunk_name == png_PLTE)
             png_handle_PLTE(png_ptr, info_ptr, length);

          else if (chunk_name == png_IDAT)
          {
             png_ptr->idat_size = length;
             break;
          }

    #ifdef PNG_READ_bKGD_SUPPORTED
          else if (chunk_name == png_bKGD)
             png_handle_bKGD(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_cHRM_SUPPORTED
          else if (chunk_name == png_cHRM)
             png_handle_cHRM(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_gAMA_SUPPORTED
          else if (chunk_name == png_gAMA)
             png_handle_gAMA(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_hIST_SUPPORTED
          else if (chunk_name == png_hIST)
             png_handle_hIST(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_oFFs_SUPPORTED
          else if (chunk_name == png_oFFs)
             png_handle_oFFs(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_pCAL_SUPPORTED
          else if (chunk_name == png_pCAL)
             png_handle_pCAL(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sCAL_SUPPORTED
          else if (chunk_name == png_sCAL)
             png_handle_sCAL(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_pHYs_SUPPORTED
          else if (chunk_name == png_pHYs)
             png_handle_pHYs(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sBIT_SUPPORTED
          else if (chunk_name == png_sBIT)
             png_handle_sBIT(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sRGB_SUPPORTED
          else if (chunk_name == png_sRGB)
             png_handle_sRGB(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_iCCP_SUPPORTED
          else if (chunk_name == png_iCCP)
             png_handle_iCCP(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sPLT_SUPPORTED
          else if (chunk_name == png_sPLT)
             png_handle_sPLT(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tEXt_SUPPORTED
          else if (chunk_name == png_tEXt)
             png_handle_tEXt(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tIME_SUPPORTED
          else if (chunk_name == png_tIME)
             png_handle_tIME(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tRNS_SUPPORTED
          else if (chunk_name == png_tRNS)
             png_handle_tRNS(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_zTXt_SUPPORTED
          else if (chunk_name == png_zTXt)
             png_handle_zTXt(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_iTXt_SUPPORTED
          else if (chunk_name == png_iTXt)
             png_handle_iTXt(png_ptr, info_ptr, length);
    #endif

          else
             png_handle_unknown(png_ptr, info_ptr, length,
                PNG_HANDLE_CHUNK_AS_DEFAULT);
       }
    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    /* Optional call to update the users info_ptr structure */
    void PNGAPI
    png_read_update_info(png_structrp png_ptr, png_inforp info_ptr)
    {
       png_debug(1, "in png_read_update_info");

       if (png_ptr != NULL)
       {
          if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
          {
             png_read_start_row(png_ptr);

    #        ifdef PNG_READ_TRANSFORMS_SUPPORTED
                png_read_transform_info(png_ptr, info_ptr);
    #        else
                PNG_UNUSED(info_ptr)
    #        endif
          }

          /* New in 1.6.0 this avoids the bug of doing the initializations twice */
          else
             png_app_error(png_ptr,
                "png_read_update_info/png_start_read_image: duplicate call");
       }
    }

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    /* Initialize palette, background, etc, after transformations
     * are set, but before any reading takes place.  This allows
     * the user to obtain a gamma-corrected palette, for example.
     * If the user doesn't call this, we will do it ourselves.
     */
    void PNGAPI
    png_start_read_image(png_structrp png_ptr)
    {
       png_debug(1, "in png_start_read_image");

       if (png_ptr != NULL)
       {
          if ((png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
             png_read_start_row(png_ptr);

          /* New in 1.6.0 this avoids the bug of doing the initializations twice */
          else
             png_app_error(png_ptr,
                "png_start_read_image/png_read_update_info: duplicate call");
       }
    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    void PNGAPI
    png_read_row(png_structrp png_ptr, png_bytep row, png_bytep dsp_row)
    {
       png_row_info row_info;

       if (png_ptr == NULL)
          return;

       png_debug2(1, "in png_read_row (row %lu, pass %d)",
           (unsigned long)png_ptr->row_number, png_ptr->pass);

       /* png_read_start_row sets the information (in particular iwidth) for this
        * interlace pass.
        */
       if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
          png_read_start_row(png_ptr);

       /* 1.5.6: row_info moved out of png_struct to a local here. */
       row_info.width = png_ptr->iwidth; /* NOTE: width of current interlaced row */
       row_info.color_type = png_ptr->color_type;
       row_info.bit_depth = png_ptr->bit_depth;
       row_info.channels = png_ptr->channels;
       row_info.pixel_depth = png_ptr->pixel_depth;
       row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);

       if (png_ptr->row_number == 0 && png_ptr->pass == 0)
       {
       /* Check for transforms that have been set but were defined out */
    #if defined(PNG_WRITE_INVERT_SUPPORTED) && !defined(PNG_READ_INVERT_SUPPORTED)
       if (png_ptr->transformations & PNG_INVERT_MONO)
          png_warning(png_ptr, "PNG_READ_INVERT_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_FILLER_SUPPORTED) && !defined(PNG_READ_FILLER_SUPPORTED)
       if (png_ptr->transformations & PNG_FILLER)
          png_warning(png_ptr, "PNG_READ_FILLER_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \
        !defined(PNG_READ_PACKSWAP_SUPPORTED)
       if (png_ptr->transformations & PNG_PACKSWAP)
          png_warning(png_ptr, "PNG_READ_PACKSWAP_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_PACK_SUPPORTED) && !defined(PNG_READ_PACK_SUPPORTED)
       if (png_ptr->transformations & PNG_PACK)
          png_warning(png_ptr, "PNG_READ_PACK_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_SHIFT_SUPPORTED) && !defined(PNG_READ_SHIFT_SUPPORTED)
       if (png_ptr->transformations & PNG_SHIFT)
          png_warning(png_ptr, "PNG_READ_SHIFT_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_BGR_SUPPORTED) && !defined(PNG_READ_BGR_SUPPORTED)
       if (png_ptr->transformations & PNG_BGR)
          png_warning(png_ptr, "PNG_READ_BGR_SUPPORTED is not defined");
    #endif

    #if defined(PNG_WRITE_SWAP_SUPPORTED) && !defined(PNG_READ_SWAP_SUPPORTED)
       if (png_ptr->transformations & PNG_SWAP_BYTES)
          png_warning(png_ptr, "PNG_READ_SWAP_SUPPORTED is not defined");
    #endif
       }

    #ifdef PNG_READ_INTERLACING_SUPPORTED
       /* If interlaced and we do not need a new row, combine row and return.
        * Notice that the pixels we have from previous rows have been transformed
        * already; we can only combine like with like (transformed or
        * untransformed) and, because of the libpng API for interlaced images, this
        * means we must transform before de-interlacing.
        */
       if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
       {
          switch (png_ptr->pass)
          {
             case 0:
                if (png_ptr->row_number & 0x07)
                {
                   if (dsp_row != NULL)
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);
                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             case 1:
                if ((png_ptr->row_number & 0x07) || png_ptr->width < 5)
                {
                   if (dsp_row != NULL)
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);

                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             case 2:
                if ((png_ptr->row_number & 0x07) != 4)
                {
                   if (dsp_row != NULL && (png_ptr->row_number & 4))
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);

                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             case 3:
                if ((png_ptr->row_number & 3) || png_ptr->width < 3)
                {
                   if (dsp_row != NULL)
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);

                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             case 4:
                if ((png_ptr->row_number & 3) != 2)
                {
                   if (dsp_row != NULL && (png_ptr->row_number & 2))
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);

                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             case 5:
                if ((png_ptr->row_number & 1) || png_ptr->width < 2)
                {
                   if (dsp_row != NULL)
                      png_combine_row(png_ptr, dsp_row, 1/*display*/);

                   png_read_finish_row(png_ptr);
                   return;
                }
                break;

             default:
             case 6:
                if (!(png_ptr->row_number & 1))
                {
                   png_read_finish_row(png_ptr);
                   return;
                }
                break;
          }
       }
    #endif

       if (!(png_ptr->mode & PNG_HAVE_IDAT))
          png_error(png_ptr, "Invalid attempt to read row data");

       /* Fill the row with IDAT data: */
       png_read_IDAT_data(png_ptr, png_ptr->row_buf, row_info.rowbytes + 1);

       if (png_ptr->row_buf[0] > PNG_FILTER_VALUE_NONE)
       {
          if (png_ptr->row_buf[0] < PNG_FILTER_VALUE_LAST)
             png_read_filter_row(png_ptr, &row_info, png_ptr->row_buf + 1,
                png_ptr->prev_row + 1, png_ptr->row_buf[0]);
          else
             png_error(png_ptr, "bad adaptive filter value");
       }

       /* libpng 1.5.6: the following line was copying png_ptr->rowbytes before
        * 1.5.6, while the buffer really is this big in current versions of libpng
        * it may not be in the future, so this was changed just to copy the
        * interlaced count:
        */
       memcpy(png_ptr->prev_row, png_ptr->row_buf, row_info.rowbytes + 1);

    #ifdef PNG_MNG_FEATURES_SUPPORTED
       if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) &&
           (png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING))
       {
          /* Intrapixel differencing */
          png_do_read_intrapixel(&row_info, png_ptr->row_buf + 1);
       }
    #endif

    #ifdef PNG_READ_TRANSFORMS_SUPPORTED
       if (png_ptr->transformations)
          png_do_read_transformations(png_ptr, &row_info);
    #endif

       /* The transformed pixel depth should match the depth now in row_info. */
       if (png_ptr->transformed_pixel_depth == 0)
       {
          png_ptr->transformed_pixel_depth = row_info.pixel_depth;
          if (row_info.pixel_depth > png_ptr->maximum_pixel_depth)
             png_error(png_ptr, "sequential row overflow");
       }

       else if (png_ptr->transformed_pixel_depth != row_info.pixel_depth)
          png_error(png_ptr, "internal sequential row size calculation error");

    #ifdef PNG_READ_INTERLACING_SUPPORTED
       /* Blow up interlaced rows to full size */
       if (png_ptr->interlaced &&
          (png_ptr->transformations & PNG_INTERLACE))
       {
          if (png_ptr->pass < 6)
             png_do_read_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass,
                png_ptr->transformations);

          if (dsp_row != NULL)
             png_combine_row(png_ptr, dsp_row, 1/*display*/);

          if (row != NULL)
             png_combine_row(png_ptr, row, 0/*row*/);
       }

       else
    #endif
       {
          if (row != NULL)
             png_combine_row(png_ptr, row, -1/*ignored*/);

          if (dsp_row != NULL)
             png_combine_row(png_ptr, dsp_row, -1/*ignored*/);
       }
       png_read_finish_row(png_ptr);

       if (png_ptr->read_row_fn != NULL)
          (*(png_ptr->read_row_fn))(png_ptr, png_ptr->row_number, png_ptr->pass);

    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    /* Read one or more rows of image data.  If the image is interlaced,
     * and png_set_interlace_handling() has been called, the rows need to
     * contain the contents of the rows from the previous pass.  If the
     * image has alpha or transparency, and png_handle_alpha()[*] has been
     * called, the rows contents must be initialized to the contents of the
     * screen.
     *
     * "row" holds the actual image, and pixels are placed in it
     * as they arrive.  If the image is displayed after each pass, it will
     * appear to "sparkle" in.  "display_row" can be used to display a
     * "chunky" progressive image, with finer detail added as it becomes
     * available.  If you do not want this "chunky" display, you may pass
     * NULL for display_row.  If you do not want the sparkle display, and
     * you have not called png_handle_alpha(), you may pass NULL for rows.
     * If you have called png_handle_alpha(), and the image has either an
     * alpha channel or a transparency chunk, you must provide a buffer for
     * rows.  In this case, you do not have to provide a display_row buffer
     * also, but you may.  If the image is not interlaced, or if you have
     * not called png_set_interlace_handling(), the display_row buffer will
     * be ignored, so pass NULL to it.
     *
     * [*] png_handle_alpha() does not exist yet, as of this version of libpng
     */

    void PNGAPI
    png_read_rows(png_structrp png_ptr, png_bytepp row,
        png_bytepp display_row, png_uint_32 num_rows)
    {
       png_uint_32 i;
       png_bytepp rp;
       png_bytepp dp;

       png_debug(1, "in png_read_rows");

       if (png_ptr == NULL)
          return;

       rp = row;
       dp = display_row;
       if (rp != NULL && dp != NULL)
          for (i = 0; i < num_rows; i++)
          {
             png_bytep rptr = *rp++;
             png_bytep dptr = *dp++;

             png_read_row(png_ptr, rptr, dptr);
          }

       else if (rp != NULL)
          for (i = 0; i < num_rows; i++)
          {
             png_bytep rptr = *rp;
             png_read_row(png_ptr, rptr, NULL);
             rp++;
          }

       else if (dp != NULL)
          for (i = 0; i < num_rows; i++)
          {
             png_bytep dptr = *dp;
             png_read_row(png_ptr, NULL, dptr);
             dp++;
          }
    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    /* Read the entire image.  If the image has an alpha channel or a tRNS
     * chunk, and you have called png_handle_alpha()[*], you will need to
     * initialize the image to the current image that PNG will be overlaying.
     * We set the num_rows again here, in case it was incorrectly set in
     * png_read_start_row() by a call to png_read_update_info() or
     * png_start_read_image() if png_set_interlace_handling() wasn't called
     * prior to either of these functions like it should have been.  You can
     * only call this function once.  If you desire to have an image for
     * each pass of a interlaced image, use png_read_rows() instead.
     *
     * [*] png_handle_alpha() does not exist yet, as of this version of libpng
     */
    void PNGAPI
    png_read_image(png_structrp png_ptr, png_bytepp image)
    {
       png_uint_32 i, image_height;
       int pass, j;
       png_bytepp rp;

       png_debug(1, "in png_read_image");

       if (png_ptr == NULL)
          return;

    #ifdef PNG_READ_INTERLACING_SUPPORTED
       if (!(png_ptr->flags & PNG_FLAG_ROW_INIT))
       {
          pass = png_set_interlace_handling(png_ptr);
          /* And make sure transforms are initialized. */
          png_start_read_image(png_ptr);
       }
       else
       {
          if (png_ptr->interlaced && !(png_ptr->transformations & PNG_INTERLACE))
          {
             /* Caller called png_start_read_image or png_read_update_info without
              * first turning on the PNG_INTERLACE transform.  We can fix this here,
              * but the caller should do it!
              */
             png_warning(png_ptr, "Interlace handling should be turned on when "
                "using png_read_image");
             /* Make sure this is set correctly */
             png_ptr->num_rows = png_ptr->height;
          }

          /* Obtain the pass number, which also turns on the PNG_INTERLACE flag in
           * the above error case.
           */
          pass = png_set_interlace_handling(png_ptr);
       }
    #else
       if (png_ptr->interlaced)
          png_error(png_ptr,
              "Cannot read interlaced image -- interlace handler disabled");

       pass = 1;
    #endif

       image_height=png_ptr->height;

       for (j = 0; j < pass; j++)
       {
          rp = image;
          for (i = 0; i < image_height; i++)
          {
             png_read_row(png_ptr, *rp, NULL);
             rp++;
          }
       }
    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    /* Read the end of the PNG file.  Will not read past the end of the
     * file, will verify the end is accurate, and will read any comments
     * or time information at the end of the file, if info is not NULL.
     */
    void PNGAPI
    png_read_end(png_structrp png_ptr, png_inforp info_ptr)
    {
    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
       int keep;
    #endif

       png_debug(1, "in png_read_end");

       if (png_ptr == NULL)
          return;

       /* If png_read_end is called in the middle of reading the rows there may
        * still be pending IDAT data and an owned zstream.  Deal with this here.
        */
    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
       if (!png_chunk_unknown_handling(png_ptr, png_IDAT))
    #endif
          png_read_finish_IDAT(png_ptr);

    #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
       /* Report invalid palette index; added at libng-1.5.10 */
       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
          png_ptr->num_palette_max > png_ptr->num_palette)
         png_benign_error(png_ptr, "Read palette index exceeding num_palette");
    #endif

       do
       {
          png_uint_32 length = png_read_chunk_header(png_ptr);
          png_uint_32 chunk_name = png_ptr->chunk_name;

          if (chunk_name == png_IHDR)
             png_handle_IHDR(png_ptr, info_ptr, length);

          else if (chunk_name == png_IEND)
             png_handle_IEND(png_ptr, info_ptr, length);

    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
          else if ((keep = png_chunk_unknown_handling(png_ptr, chunk_name)) != 0)
          {
             if (chunk_name == png_IDAT)
             {
                if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
                   png_benign_error(png_ptr, "Too many IDATs found");
             }
             png_handle_unknown(png_ptr, info_ptr, length, keep);
             if (chunk_name == png_PLTE)
                png_ptr->mode |= PNG_HAVE_PLTE;
          }
    #endif

          else if (chunk_name == png_IDAT)
          {
             /* Zero length IDATs are legal after the last IDAT has been
              * read, but not after other chunks have been read.
              */
             if ((length > 0) || (png_ptr->mode & PNG_HAVE_CHUNK_AFTER_IDAT))
                png_benign_error(png_ptr, "Too many IDATs found");

             png_crc_finish(png_ptr, length);
          }
          else if (chunk_name == png_PLTE)
             png_handle_PLTE(png_ptr, info_ptr, length);

    #ifdef PNG_READ_bKGD_SUPPORTED
          else if (chunk_name == png_bKGD)
             png_handle_bKGD(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_cHRM_SUPPORTED
          else if (chunk_name == png_cHRM)
             png_handle_cHRM(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_gAMA_SUPPORTED
          else if (chunk_name == png_gAMA)
             png_handle_gAMA(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_hIST_SUPPORTED
          else if (chunk_name == png_hIST)
             png_handle_hIST(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_oFFs_SUPPORTED
          else if (chunk_name == png_oFFs)
             png_handle_oFFs(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_pCAL_SUPPORTED
          else if (chunk_name == png_pCAL)
             png_handle_pCAL(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sCAL_SUPPORTED
          else if (chunk_name == png_sCAL)
             png_handle_sCAL(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_pHYs_SUPPORTED
          else if (chunk_name == png_pHYs)
             png_handle_pHYs(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sBIT_SUPPORTED
          else if (chunk_name == png_sBIT)
             png_handle_sBIT(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sRGB_SUPPORTED
          else if (chunk_name == png_sRGB)
             png_handle_sRGB(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_iCCP_SUPPORTED
          else if (chunk_name == png_iCCP)
             png_handle_iCCP(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_sPLT_SUPPORTED
          else if (chunk_name == png_sPLT)
             png_handle_sPLT(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tEXt_SUPPORTED
          else if (chunk_name == png_tEXt)
             png_handle_tEXt(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tIME_SUPPORTED
          else if (chunk_name == png_tIME)
             png_handle_tIME(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_tRNS_SUPPORTED
          else if (chunk_name == png_tRNS)
             png_handle_tRNS(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_zTXt_SUPPORTED
          else if (chunk_name == png_zTXt)
             png_handle_zTXt(png_ptr, info_ptr, length);
    #endif

    #ifdef PNG_READ_iTXt_SUPPORTED
          else if (chunk_name == png_iTXt)
             png_handle_iTXt(png_ptr, info_ptr, length);
    #endif

          else
             png_handle_unknown(png_ptr, info_ptr, length,
                PNG_HANDLE_CHUNK_AS_DEFAULT);
       } while (!(png_ptr->mode & PNG_HAVE_IEND));
    }
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    /* Free all memory used in the read struct */
    static void
    png_read_destroy(png_structrp png_ptr)
    {
       png_debug(1, "in png_read_destroy");

    #ifdef PNG_READ_GAMMA_SUPPORTED
       png_destroy_gamma_table(png_ptr);
    #endif

       png_free(png_ptr, png_ptr->big_row_buf);
       png_free(png_ptr, png_ptr->big_prev_row);
       png_free(png_ptr, png_ptr->read_buffer);

    #ifdef PNG_READ_QUANTIZE_SUPPORTED
       png_free(png_ptr, png_ptr->palette_lookup);
       png_free(png_ptr, png_ptr->quantize_index);
    #endif

       if (png_ptr->free_me & PNG_FREE_PLTE)
          png_zfree(png_ptr, png_ptr->palette);
       png_ptr->free_me &= ~PNG_FREE_PLTE;

    #if defined(PNG_tRNS_SUPPORTED) || \
        defined(PNG_READ_EXPAND_SUPPORTED) || defined(PNG_READ_BACKGROUND_SUPPORTED)
       if (png_ptr->free_me & PNG_FREE_TRNS)
          png_free(png_ptr, png_ptr->trans_alpha);
       png_ptr->free_me &= ~PNG_FREE_TRNS;
    #endif

       inflateEnd(&png_ptr->zstream);

    #ifdef PNG_PROGRESSIVE_READ_SUPPORTED
       png_free(png_ptr, png_ptr->save_buffer);
    #endif

    #if defined(PNG_STORE_UNKNOWN_CHUNKS_SUPPORTED) &&\
       defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
       png_free(png_ptr, png_ptr->unknown_chunk.data);
    #endif

    #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
       png_free(png_ptr, png_ptr->chunk_list);
    #endif

       /* NOTE: the 'setjmp' buffer may still be allocated and the memory and error
        * callbacks are still set at this point.  They are required to complete the
        * destruction of the png_struct itself.
        */
    }

    /* Free all memory used by the read */
    void PNGAPI
    png_destroy_read_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr,
        png_infopp end_info_ptr_ptr)
    {
       png_structrp png_ptr = NULL;

       png_debug(1, "in png_destroy_read_struct");

       if (png_ptr_ptr != NULL)
          png_ptr = *png_ptr_ptr;

       if (png_ptr == NULL)
          return;

       /* libpng 1.6.0: use the API to destroy info structs to ensure consistent
        * behavior.  Prior to 1.6.0 libpng did extra 'info' destruction in this API.
        * The extra was, apparently, unnecessary yet this hides memory leak bugs.
        */
       png_destroy_info_struct(png_ptr, end_info_ptr_ptr);
       png_destroy_info_struct(png_ptr, info_ptr_ptr);

       *png_ptr_ptr = NULL;
       png_read_destroy(png_ptr);
       png_destroy_png_struct(png_ptr);
    }

    void PNGAPI
    png_set_read_status_fn(png_structrp png_ptr, png_read_status_ptr read_row_fn)
    {
       if (png_ptr == NULL)
          return;

       png_ptr->read_row_fn = read_row_fn;
    }

    #ifdef PNG_SEQUENTIAL_READ_SUPPORTED
    #ifdef PNG_INFO_IMAGE_SUPPORTED
    void PNGAPI
    png_read_png(png_structrp png_ptr, png_inforp info_ptr,
                               int transforms,
                               voidp params)
    {
       int row;

       if (png_ptr == NULL || info_ptr == NULL)
          return;

       /* png_read_info() gives us all of the information from the
        * PNG file before the first IDAT (image data chunk).
        */
       png_read_info(png_ptr, info_ptr);
       if (info_ptr->height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
          png_error(png_ptr, "Image is too high to process with png_read_png()");

       /* -------------- image transformations start here ------------------- */

    #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
       /* Tell libpng to strip 16-bit/color files down to 8 bits per color.
        */
       if (transforms & PNG_TRANSFORM_SCALE_16)
       {
         /* Added at libpng-1.5.4. "strip_16" produces the same result that it
          * did in earlier versions, while "scale_16" is now more accurate.
          */
          png_set_scale_16(png_ptr);
       }
    #endif

    #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
       /* If both SCALE and STRIP are required pngrtran will effectively cancel the
        * latter by doing SCALE first.  This is ok and allows apps not to check for
        * which is supported to get the right answer.
        */
       if (transforms & PNG_TRANSFORM_STRIP_16)
          png_set_strip_16(png_ptr);
    #endif

    #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
       /* Strip alpha bytes from the input data without combining with
        * the background (not recommended).
        */
       if (transforms & PNG_TRANSFORM_STRIP_ALPHA)
          png_set_strip_alpha(png_ptr);
    #endif

    #if defined(PNG_READ_PACK_SUPPORTED) && !defined(PNG_READ_EXPAND_SUPPORTED)
       /* Extract multiple pixels with bit depths of 1, 2, or 4 from a single
        * byte into separate bytes (useful for paletted and grayscale images).
        */
       if (transforms & PNG_TRANSFORM_PACKING)
          png_set_packing(png_ptr);
    #endif

    #ifdef PNG_READ_PACKSWAP_SUPPORTED
       /* Change the order of packed pixels to least significant bit first
        * (not useful if you are using png_set_packing).
        */
       if (transforms & PNG_TRANSFORM_PACKSWAP)
          png_set_packswap(png_ptr);
    #endif

    #ifdef PNG_READ_EXPAND_SUPPORTED
       /* Expand paletted colors into true RGB triplets
        * Expand grayscale images to full 8 bits from 1, 2, or 4 bits/pixel
        * Expand paletted or RGB images with transparency to full alpha
        * channels so the data will be available as RGBA quartets.
        */
       if (transforms & PNG_TRANSFORM_EXPAND)
          if ((png_ptr->bit_depth < 8) ||
              (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ||
              (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS)))
             png_set_expand(png_ptr);
    #endif

       /* We don't handle background color or gamma transformation or quantizing.
        */

    #ifdef PNG_READ_INVERT_SUPPORTED
       /* Invert monochrome files to have 0 as white and 1 as black
        */
       if (transforms & PNG_TRANSFORM_INVERT_MONO)
          png_set_invert_mono(png_ptr);
    #endif

    #ifdef PNG_READ_SHIFT_SUPPORTED
       /* If you want to shift the pixel values from the range [0,255] or
        * [0,65535] to the original [0,7] or [0,31], or whatever range the
        * colors were originally in:
        */
       if ((transforms & PNG_TRANSFORM_SHIFT)
           && png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT))
       {
          png_color_8p sig_bit;

          png_get_sBIT(png_ptr, info_ptr, &sig_bit);
          png_set_shift(png_ptr, sig_bit);
       }
    #endif

    #ifdef PNG_READ_BGR_SUPPORTED
       /* Flip the RGB pixels to BGR (or RGBA to BGRA) */
       if (transforms & PNG_TRANSFORM_BGR)
          png_set_bgr(png_ptr);
    #endif

    #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
       /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
       if (transforms & PNG_TRANSFORM_SWAP_ALPHA)
          png_set_swap_alpha(png_ptr);
    #endif

    #ifdef PNG_READ_SWAP_SUPPORTED
       /* Swap bytes of 16-bit files to least significant byte first */
       if (transforms & PNG_TRANSFORM_SWAP_ENDIAN)
          png_set_swap(png_ptr);
    #endif

    /* Added at libpng-1.2.41 */
    #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
       /* Invert the alpha channel from opacity to transparency */
       if (transforms & PNG_TRANSFORM_INVERT_ALPHA)
          png_set_invert_alpha(png_ptr);
    #endif

    /* Added at libpng-1.2.41 */
    #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
       /* Expand grayscale image to RGB */
       if (transforms & PNG_TRANSFORM_GRAY_TO_RGB)
          png_set_gray_to_rgb(png_ptr);
    #endif

    /* Added at libpng-1.5.4 */
    #ifdef PNG_READ_EXPAND_16_SUPPORTED
       if (transforms & PNG_TRANSFORM_EXPAND_16)
          png_set_expand_16(png_ptr);
    #endif

       /* We don't handle adding filler bytes */

       /* We use png_read_image and rely on that for interlace handling, but we also
        * call png_read_update_info therefore must turn on interlace handling now:
        */
       (void)png_set_interlace_handling(png_ptr);

       /* Optional call to gamma correct and add the background to the palette
        * and update info structure.  REQUIRED if you are expecting libpng to
        * update the palette for you (i.e., you selected such a transform above).
        */
       png_read_update_info(png_ptr, info_ptr);

       /* -------------- image transformations end here ------------------- */

       png_free_data(png_ptr, info_ptr, PNG_FREE_ROWS, 0);
       if (info_ptr->row_pointers == NULL)
       {
          png_uint_32 iptr;

          info_ptr->row_pointers = (png_bytepp)png_malloc(png_ptr,
              info_ptr->height * (sizeof (png_bytep)));
          for (iptr=0; iptr<info_ptr->height; iptr++)
             info_ptr->row_pointers[iptr] = NULL;

          info_ptr->free_me |= PNG_FREE_ROWS;

          for (row = 0; row < (int)info_ptr->height; row++)
             info_ptr->row_pointers[row] = (png_bytep)png_malloc(png_ptr,
                png_get_rowbytes(png_ptr, info_ptr));
       }

       png_read_image(png_ptr, info_ptr->row_pointers);
       info_ptr->valid |= PNG_INFO_IDAT;

       /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
       png_read_end(png_ptr, info_ptr);

       PNG_UNUSED(transforms)   /* Quiet compiler warnings */
       PNG_UNUSED(params)

    }
    #endif /* PNG_INFO_IMAGE_SUPPORTED */
    #endif /* PNG_SEQUENTIAL_READ_SUPPORTED */

    #ifdef PNG_SIMPLIFIED_READ_SUPPORTED
    /* SIMPLIFIED READ
     *
     * This code currently relies on the sequential reader, though it could easily
     * be made to work with the progressive one.
     */
    /* Arguments to png_image_finish_read: */

    /* Encoding of PNG data (used by the color-map code) */
    /* TODO: change these, dang, ANSI-C reserves the 'E' namespace. */
    #  define E_NOTSET  0 /* File encoding not yet known */
    #  define E_sRGB    1 /* 8-bit encoded to sRGB gamma */
    #  define E_LINEAR  2 /* 16-bit linear: not encoded, NOT pre-multiplied! */
    #  define E_FILE    3 /* 8-bit encoded to file gamma, not sRGB or linear */
    #  define E_LINEAR8 4 /* 8-bit linear: only from a file value */

    /* Color-map processing: after libpng has run on the PNG image further
     * processing may be needed to conver the data to color-map indicies.
     */
    #define PNG_CMAP_NONE      0
    #define PNG_CMAP_GA        1 /* Process GA data to a color-map with alpha */
    #define PNG_CMAP_TRANS     2 /* Process GA data to a background index */
    #define PNG_CMAP_RGB       3 /* Process RGB data */
    #define PNG_CMAP_RGB_ALPHA 4 /* Process RGBA data */

    /* The following document where the background is for each processing case. */
    #define PNG_CMAP_NONE_BACKGROUND      256
    #define PNG_CMAP_GA_BACKGROUND        231
    #define PNG_CMAP_TRANS_BACKGROUND     254
    #define PNG_CMAP_RGB_BACKGROUND       256
    #define PNG_CMAP_RGB_ALPHA_BACKGROUND 216

    typedef struct
    {
       /* Arguments: */
       png_imagep image;
       png_voidp  buffer;
       png_int_32 row_stride;
       png_voidp  colormap;
       png_const_colorp background;
       /* Local variables: */
       png_voidp       local_row;
       png_voidp       first_row;
       ptrdiff_t       row_bytes;           /* step between rows */
       int             file_encoding;       /* E_ values above */
       png_fixed_point gamma_to_linear;     /* For E_FILE, reciprocal of gamma */
       int             colormap_processing; /* PNG_CMAP_ values above */
    } png_image_read_control;

    /* Do all the *safe* initialization - 'safe' means that png_error won't be
     * called, so setting up the jmp_buf is not required.  This means that anything
     * called from here must *not* call png_malloc - it has to call png_malloc_warn
     * instead so that control is returned safely back to this routine.
     */
    static int
    png_image_read_init(png_imagep image)
    {
       if (image->opaque == NULL)
       {
          png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, image,
              png_safe_error, png_safe_warning);

          /* And set the rest of the structure to NULL to ensure that the various
           * fields are consistent.
           */
          memset(image, 0, (sizeof *image));
          image->version = PNG_IMAGE_VERSION;

          if (png_ptr != NULL)
          {
             png_infop info_ptr = png_create_info_struct(png_ptr);

             if (info_ptr != NULL)
             {
                png_controlp control = png_voidcast(png_controlp,
                   png_malloc_warn(png_ptr, (sizeof *control)));

                if (control != NULL)
                {
                   memset(control, 0, (sizeof *control));

                   control->png_ptr = png_ptr;
                   control->info_ptr = info_ptr;
                   control->for_write = 0;

                   image->opaque = control;
                   return 1;
                }

                /* Error clean up */
                png_destroy_info_struct(png_ptr, &info_ptr);
             }

             png_destroy_read_struct(&png_ptr, NULL, NULL);
          }

          return png_image_error(image, "png_image_read: out of memory");
       }

       return png_image_error(image, "png_image_read: opaque pointer not NULL");
    }

    /* Utility to find the base format of a PNG file from a png_struct. */
    static png_uint_32
    png_image_format(png_structrp png_ptr)
    {
       png_uint_32 format = 0;

       if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
          format |= PNG_FORMAT_FLAG_COLOR;

       if (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)
          format |= PNG_FORMAT_FLAG_ALPHA;

       /* Use png_ptr here, not info_ptr, because by examination png_handle_tRNS
        * sets the png_struct fields; that's all we are interested in here.  The
        * precise interaction with an app call to png_set_tRNS and PNG file reading
        * is unclear.
        */
       else if (png_ptr->num_trans > 0)
          format |= PNG_FORMAT_FLAG_ALPHA;

       if (png_ptr->bit_depth == 16)
          format |= PNG_FORMAT_FLAG_LINEAR;

       if (png_ptr->color_type & PNG_COLOR_MASK_PALETTE)
          format |= PNG_FORMAT_FLAG_COLORMAP;

       return format;
    }

    /* Is the given gamma significantly different from sRGB?  The test is the same
     * one used in pngrtran.c when deciding whether to do gamma correction.  The
     * arithmetic optimizes the division by using the fact that the inverse of the
     * file sRGB gamma is 2.2
     */
    static int
    png_gamma_not_sRGB(png_fixed_point g)
    {
       if (g < PNG_FP_1)
       {
          /* An uninitialized gamma is assumed to be sRGB for the simplified API. */
          if (g == 0)
             return 0;

          return png_gamma_significant((g * 11 + 2)/5 /* i.e. *2.2, rounded */);
       }

       return 1;
    }

    /* Do the main body of a 'png_image_begin_read' function; read the PNG file
     * header and fill in all the information.  This is executed in a safe context,
     * unlike the init routine above.
     */
    static int
    png_image_read_header(png_voidp argument)
    {
       png_imagep image = png_voidcast(png_imagep, argument);
       png_structrp png_ptr = image->opaque->png_ptr;
       png_inforp info_ptr = image->opaque->info_ptr;

       png_set_benign_errors(png_ptr, 1/*warn*/);
       png_read_info(png_ptr, info_ptr);

       /* Do this the fast way; just read directly out of png_struct. */
       image->width = png_ptr->width;
       image->height = png_ptr->height;

       {
          png_uint_32 format = png_image_format(png_ptr);

          image->format = format;

    #ifdef PNG_COLORSPACE_SUPPORTED
          /* Does the colorspace match sRGB?  If there is no color endpoint
           * (colorant) information assume yes, otherwise require the
           * 'ENDPOINTS_MATCHE_sRGB' colorspace flag to have been set.  If the
           * colorspace has been determined to be invalid ignore it.
           */
          if ((format & PNG_FORMAT_FLAG_COLOR) != 0 && ((png_ptr->colorspace.flags
             & (PNG_COLORSPACE_HAVE_ENDPOINTS|PNG_COLORSPACE_ENDPOINTS_MATCH_sRGB|
                PNG_COLORSPACE_INVALID)) == PNG_COLORSPACE_HAVE_ENDPOINTS))
             image->flags |= PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
    #endif
       }

       /* We need the maximum number of entries regardless of the format the
        * application sets here.
        */
       {
          png_uint_32 cmap_entries;

          switch (png_ptr->color_type)
          {
             case PNG_COLOR_TYPE_GRAY:
                cmap_entries = 1U << png_ptr->bit_depth;
                break;

             case PNG_COLOR_TYPE_PALETTE:
                cmap_entries = png_ptr->num_palette;
                break;

             default:
                cmap_entries = 256;
                break;
          }

          if (cmap_entries > 256)
             cmap_entries = 256;

          image->colormap_entries = cmap_entries;
       }

       return 1;
    }

    #ifdef PNG_STDIO_SUPPORTED
    int PNGAPI
    png_image_begin_read_from_stdio(png_imagep image, FILE* file)
    {
       if (image != NULL && image->version == PNG_IMAGE_VERSION)
       {
          if (file != NULL)
          {
             if (png_image_read_init(image))
             {
                /* This is slightly evil, but png_init_io doesn't do anything other
                 * than this and we haven't changed the standard IO functions so
                 * this saves a 'safe' function.
                 */
                image->opaque->png_ptr->io_ptr = file;
                return png_safe_execute(image, png_image_read_header, image);
             }
          }

          else
             return png_image_error(image,
                "png_image_begin_read_from_stdio: invalid argument");
       }

       else if (image != NULL)
          return png_image_error(image,
             "png_image_begin_read_from_stdio: incorrect PNG_IMAGE_VERSION");

       return 0;
    }

    int PNGAPI
    png_image_begin_read_from_file(png_imagep image, const char *file_name)
    {
       if (image != NULL && image->version == PNG_IMAGE_VERSION)
       {
          if (file_name != NULL)
          {
             FILE *fp = fopen(file_name, "rb");

             if (fp != NULL)
             {
                if (png_image_read_init(image))
                {
                   image->opaque->png_ptr->io_ptr = fp;
                   image->opaque->owned_file = 1;
                   return png_safe_execute(image, png_image_read_header, image);
                }

                /* Clean up: just the opened file. */
                (void)fclose(fp);
             }

             else
                return png_image_error(image, strerror(errno));
          }

          else
             return png_image_error(image,
                "png_image_begin_read_from_file: invalid argument");
       }

       else if (image != NULL)
          return png_image_error(image,
             "png_image_begin_read_from_file: incorrect PNG_IMAGE_VERSION");

       return 0;
    }
    #endif /* PNG_STDIO_SUPPORTED */

    static void PNGCBAPI
    png_image_memory_read(png_structp png_ptr, png_bytep out, png_size_t need)
    {
       if (png_ptr != NULL)
       {
          png_imagep image = png_voidcast(png_imagep, png_ptr->io_ptr);
          if (image != NULL)
          {
             png_controlp cp = image->opaque;
             if (cp != NULL)
             {
                png_const_bytep memory = cp->memory;
                png_size_t size = cp->size;

                if (memory != NULL && size >= need)
                {
                   memcpy(out, memory, need);
                   cp->memory = memory + need;
                   cp->size = size - need;
                   return;
                }

                png_error(png_ptr, "read beyond end of data");
             }
          }

          png_error(png_ptr, "invalid memory read");
       }
    }

    int PNGAPI png_image_begin_read_from_memory(png_imagep image,
       png_const_voidp memory, png_size_t size)
    {
       if (image != NULL && image->version == PNG_IMAGE_VERSION)
       {
          if (memory != NULL && size > 0)
          {
             if (png_image_read_init(image))
             {
                /* Now set the IO functions to read from the memory buffer and
                 * store it into io_ptr.  Again do this in-place to avoid calling a
                 * libpng function that requires error handling.
                 */
                image->opaque->memory = png_voidcast(png_const_bytep, memory);
                image->opaque->size = size;
                image->opaque->png_ptr->io_ptr = image;
                image->opaque->png_ptr->read_data_fn = png_image_memory_read;

                return png_safe_execute(image, png_image_read_header, image);
             }
          }

          else
             return png_image_error(image,
                "png_image_begin_read_from_memory: invalid argument");
       }

       else if (image != NULL)
          return png_image_error(image,
             "png_image_begin_read_from_memory: incorrect PNG_IMAGE_VERSION");

       return 0;
    }

    /* Utility function to skip chunks that are not used by the simplified image
     * read functions and an appropriate macro to call it.
     */
    #ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
    static void
    png_image_skip_unused_chunks(png_structrp png_ptr)
    {
       /* Prepare the reader to ignore all recognized chunks whose data will not
        * be used, i.e., all chunks recognized by libpng except for those
        * involved in basic image reading:
        *
        *    IHDR, PLTE, IDAT, IEND
        *
        * Or image data handling:
        *
        *    tRNS, bKGD, gAMA, cHRM, sRGB, iCCP and sBIT.
        *
        * This provides a small performance improvement and eliminates any
        * potential vulnerability to security problems in the unused chunks.
        */
       {
             static PNG_CONST png_byte chunks_to_process[] = {
                98,  75,  71,  68, '\0',  /* bKGD */
                99,  72,  82,  77, '\0',  /* cHRM */
               103,  65,  77,  65, '\0',  /* gAMA */
               105,  67,  67,  80, '\0',  /* iCCP */
               115,  66,  73,  84, '\0',  /* sBIT */
               115,  82,  71,  66, '\0',  /* sRGB */
               };

           /* Ignore unknown chunks and all other chunks except for the
            * IHDR, PLTE, tRNS, IDAT, and IEND chunks.
            */
           png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_NEVER,
             NULL, -1);

           /* But do not ignore image data handling chunks */
           png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_AS_DEFAULT,
             chunks_to_process, (sizeof chunks_to_process)/5);
        }
    }

    #  define PNG_SKIP_CHUNKS(p) png_image_skip_unused_chunks(p)
    #else
    #  define PNG_SKIP_CHUNKS(p) ((void)0)
    #endif /* PNG_HANDLE_AS_UNKNOWN_SUPPORTED */

    /* The following macro gives the exact rounded answer for all values in the
     * range 0..255 (it actually divides by 51.2, but the rounding still generates
     * the correct numbers 0..5
     */
    #define PNG_DIV51(v8) (((v8) * 5 + 130) >> 8)

    /* Utility functions to make particular color-maps */
    static void
    set_file_encoding(png_image_read_control *display)
    {
       png_fixed_point g = display->image->opaque->png_ptr->colorspace.gamma;
       if (png_gamma_significant(g))
       {
          if (png_gamma_not_sRGB(g))
          {
             display->file_encoding = E_FILE;
             display->gamma_to_linear = png_reciprocal(g);
          }

          else
             display->file_encoding = E_sRGB;
       }

       else
          display->file_encoding = E_LINEAR8;
    }

    static unsigned int
    decode_gamma(png_image_read_control *display, png_uint_32 value, int encoding)
    {
       if (encoding == E_FILE) /* double check */
          encoding = display->file_encoding;

       if (encoding == E_NOTSET) /* must be the file encoding */
       {
          set_file_encoding(display);
          encoding = display->file_encoding;
       }

       switch (encoding)
       {
          case E_FILE:
             value = png_gamma_16bit_correct(value*257, display->gamma_to_linear);
             break;

          case E_sRGB:
             value = png_sRGB_table[value];
             break;

          case E_LINEAR:
             break;

          case E_LINEAR8:
             value *= 257;
             break;

          default:
             png_error(display->image->opaque->png_ptr,
                "unexpected encoding (internal error)");
             break;
       }

       return value;
    }

    static png_uint_32
    png_colormap_compose(png_image_read_control *display,
       png_uint_32 foreground, int foreground_encoding, png_uint_32 alpha,
       png_uint_32 background, int encoding)
    {
       /* The file value is composed on the background, the background has the given
        * encoding and so does the result, the file is encoded with E_FILE and the
        * file and alpha are 8-bit values.  The (output) encoding will always be
        * E_LINEAR or E_sRGB.
        */
       png_uint_32 f = decode_gamma(display, foreground, foreground_encoding);
       png_uint_32 b = decode_gamma(display, background, encoding);

       /* The alpha is always an 8-bit value (it comes from the palette), the value
        * scaled by 255 is what PNG_sRGB_FROM_LINEAR requires.
        */
       f = f * alpha + b * (255-alpha);

       if (encoding == E_LINEAR)
       {
          /* Scale to 65535; divide by 255, approximately (in fact this is extremely
           * accurate, it divides by 255.00000005937181414556, with no overflow.)
           */
          f *= 257; /* Now scaled by 65535 */
          f += f >> 16;
          f = (f+32768) >> 16;
       }

       else /* E_sRGB */
          f = PNG_sRGB_FROM_LINEAR(f);

       return f;
    }

    /* NOTE: E_LINEAR values to this routine must be 16-bit, but E_FILE values must
     * be 8-bit.
     */
    static void
    png_create_colormap_entry(png_image_read_control *display,
       png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,
       png_uint_32 alpha, int encoding)
    {
       png_imagep image = display->image;
       const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) ?
          E_LINEAR : E_sRGB;
       const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
          (red != green || green != blue);

       if (ip > 255)
          png_error(image->opaque->png_ptr, "color-map index out of range");

       /* Update the cache with whether the file gamma is significantly different
        * from sRGB.
        */
       if (encoding == E_FILE)
       {
          if (display->file_encoding == E_NOTSET)
             set_file_encoding(display);

          /* Note that the cached value may be E_FILE too, but if it is then the
           * gamma_to_linear member has been set.
           */
          encoding = display->file_encoding;
       }

       if (encoding == E_FILE)
       {
          png_fixed_point g = display->gamma_to_linear;

          red = png_gamma_16bit_correct(red*257, g);
          green = png_gamma_16bit_correct(green*257, g);
          blue = png_gamma_16bit_correct(blue*257, g);

          if (convert_to_Y || output_encoding == E_LINEAR)
          {
             alpha *= 257;
             encoding = E_LINEAR;
          }

          else
          {
             red = PNG_sRGB_FROM_LINEAR(red * 255);
             green = PNG_sRGB_FROM_LINEAR(green * 255);
             blue = PNG_sRGB_FROM_LINEAR(blue * 255);
             encoding = E_sRGB;
          }
       }

       else if (encoding == E_LINEAR8)
       {
          /* This encoding occurs quite frequently in test cases because PngSuite
           * includes a gAMA 1.0 chunk with most images.
           */
          red *= 257;
          green *= 257;
          blue *= 257;
          alpha *= 257;
          encoding = E_LINEAR;
       }

       else if (encoding == E_sRGB && (convert_to_Y || output_encoding == E_LINEAR))
       {
          /* The values are 8-bit sRGB values, but must be converted to 16-bit
           * linear.
           */
          red = png_sRGB_table[red];
          green = png_sRGB_table[green];
          blue = png_sRGB_table[blue];
          alpha *= 257;
          encoding = E_LINEAR;
       }

       /* This is set if the color isn't gray but the output is. */
       if (encoding == E_LINEAR)
       {
          if (convert_to_Y)
          {
             /* NOTE: these values are copied from png_do_rgb_to_gray */
             png_uint_32 y = (png_uint_32)6968 * red  + (png_uint_32)23434 * green +
                (png_uint_32)2366 * blue;

             if (output_encoding == E_LINEAR)
                y = (y + 16384) >> 15;

             else
             {
                /* y is scaled by 32768, we need it scaled by 255: */
                y = (y + 128) >> 8;
                y *= 255;
                y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
                encoding = E_sRGB;
             }

             blue = red = green = y;
          }

          else if (output_encoding == E_sRGB)
          {
             red = PNG_sRGB_FROM_LINEAR(red * 255);
             green = PNG_sRGB_FROM_LINEAR(green * 255);
             blue = PNG_sRGB_FROM_LINEAR(blue * 255);
             alpha = PNG_DIV257(alpha);
             encoding = E_sRGB;
          }
       }

       if (encoding != output_encoding)
          png_error(image->opaque->png_ptr, "bad encoding (internal error)");

       /* Store the value. */
       {
    #     ifdef PNG_FORMAT_BGR_SUPPORTED
             const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
                (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
    #     else
    #        define afirst 0
    #     endif
    #     ifdef PNG_FORMAT_BGR_SUPPORTED
             const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) ? 2 : 0;
    #     else
    #        define bgr 0
    #     endif

          if (output_encoding == E_LINEAR)
          {
             png_uint_16p entry = png_voidcast(png_uint_16p, display->colormap);

             entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

             /* The linear 16-bit values must be pre-multiplied by the alpha channel
              * value, if less than 65535 (this is, effectively, composite on black
              * if the alpha channel is removed.)
              */
             switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
             {
                case 4:
                   entry[afirst ? 0 : 3] = (png_uint_16)alpha;
                   /* FALL THROUGH */

                case 3:
                   if (alpha < 65535)
                   {
                      if (alpha > 0)
                      {
                         blue = (blue * alpha + 32767U)/65535U;
                         green = (green * alpha + 32767U)/65535U;
                         red = (red * alpha + 32767U)/65535U;
                      }

                      else
                         red = green = blue = 0;
                   }
                   entry[afirst + (2 ^ bgr)] = (png_uint_16)blue;
                   entry[afirst + 1] = (png_uint_16)green;
                   entry[afirst + bgr] = (png_uint_16)red;
                   break;

                case 2:
                   entry[1 ^ afirst] = (png_uint_16)alpha;
                   /* FALL THROUGH */

                case 1:
                   if (alpha < 65535)
                   {
                      if (alpha > 0)
                         green = (green * alpha + 32767U)/65535U;

                      else
                         green = 0;
                   }
                   entry[afirst] = (png_uint_16)green;
                   break;

                default:
                   break;
             }
          }

          else /* output encoding is E_sRGB */
          {
             png_bytep entry = png_voidcast(png_bytep, display->colormap);

             entry += ip * PNG_IMAGE_SAMPLE_CHANNELS(image->format);

             switch (PNG_IMAGE_SAMPLE_CHANNELS(image->format))
             {
                case 4:
                   entry[afirst ? 0 : 3] = (png_byte)alpha;
                case 3:
                   entry[afirst + (2 ^ bgr)] = (png_byte)blue;
                   entry[afirst + 1] = (png_byte)green;
                   entry[afirst + bgr] = (png_byte)red;
                   break;

                case 2:
                   entry[1 ^ afirst] = (png_byte)alpha;
                case 1:
                   entry[afirst] = (png_byte)green;
                   break;

                default:
                   break;
             }
          }

    #     ifdef afirst
    #        undef afirst
    #     endif
    #     ifdef bgr
    #        undef bgr
    #     endif
       }
    }

    static int
    make_gray_file_colormap(png_image_read_control *display)
    {
       unsigned int i;

       for (i=0; i<256; ++i)
          png_create_colormap_entry(display, i, i, i, i, 255, E_FILE);

       return i;
    }

    static int
    make_gray_colormap(png_image_read_control *display)
    {
       unsigned int i;

       for (i=0; i<256; ++i)
          png_create_colormap_entry(display, i, i, i, i, 255, E_sRGB);

       return i;
    }
    #define PNG_GRAY_COLORMAP_ENTRIES 256

    static int
    make_ga_colormap(png_image_read_control *display)
    {
       unsigned int i, a;

       /* Alpha is retained, the output will be a color-map with entries
        * selected by six levels of alpha.  One transparent entry, 6 gray
        * levels for all the intermediate alpha values, leaving 230 entries
        * for the opaque grays.  The color-map entries are the six values
        * [0..5]*51, the GA processing uses PNG_DIV51(value) to find the
        * relevant entry.
        *
        * if (alpha > 229) // opaque
        * {
        *    // The 231 entries are selected to make the math below work:
        *    base = 0;
        *    entry = (231 * gray + 128) >> 8;
        * }
        * else if (alpha < 26) // transparent
        * {
        *    base = 231;
        *    entry = 0;
        * }
        * else // partially opaque
        * {
        *    base = 226 + 6 * PNG_DIV51(alpha);
        *    entry = PNG_DIV51(gray);
        * }
        */
       i = 0;
       while (i < 231)
       {
          unsigned int gray = (i * 256 + 115) / 231;
          png_create_colormap_entry(display, i++, gray, gray, gray, 255, E_sRGB);
       }

       /* 255 is used here for the component values for consistency with the code
        * that undoes premultiplication in pngwrite.c.
        */
       png_create_colormap_entry(display, i++, 255, 255, 255, 0, E_sRGB);

       for (a=1; a<5; ++a)
       {
          unsigned int g;

          for (g=0; g<6; ++g)
             png_create_colormap_entry(display, i++, g*51, g*51, g*51, a*51,
                E_sRGB);
       }

       return i;
    }

    #define PNG_GA_COLORMAP_ENTRIES 256

    static int
    make_rgb_colormap(png_image_read_control *display)
    {
       unsigned int i, r;

       /* Build a 6x6x6 opaque RGB cube */
       for (i=r=0; r<6; ++r)
       {
          unsigned int g;

          for (g=0; g<6; ++g)
          {
             unsigned int b;

             for (b=0; b<6; ++b)
                png_create_colormap_entry(display, i++, r*51, g*51, b*51, 255,
                   E_sRGB);
          }
       }

       return i;
    }

    #define PNG_RGB_COLORMAP_ENTRIES 216

    /* Return a palette index to the above palette given three 8-bit sRGB values. */
    #define PNG_RGB_INDEX(r,g,b) \
       ((png_byte)(6 * (6 * PNG_DIV51(r) + PNG_DIV51(g)) + PNG_DIV51(b)))

    static int
    png_image_read_colormap(png_voidp argument)
    {
       png_image_read_control *display =
          png_voidcast(png_image_read_control*, argument);
       const png_imagep image = display->image;

       const png_structrp png_ptr = image->opaque->png_ptr;
       const png_uint_32 output_format = image->format;
       const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) ?
          E_LINEAR : E_sRGB;

       unsigned int cmap_entries;
       unsigned int output_processing;        /* Output processing option */
       unsigned int data_encoding = E_NOTSET; /* Encoding libpng must produce */

       /* Background information; the background color and the index of this color
        * in the color-map if it exists (else 256).
        */
       unsigned int background_index = 256;
       png_uint_32 back_r, back_g, back_b;

       /* Flags to accumulate things that need to be done to the input. */
       int expand_tRNS = 0;

       /* Exclude the NYI feature of compositing onto a color-mapped buffer; it is
        * very difficult to do, the results look awful, and it is difficult to see
        * what possible use it is because the application can't control the
        * color-map.
        */
       if (((png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0 ||
             png_ptr->num_trans > 0) /* alpha in input */ &&
          ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0) /* no alpha in output */)
       {
          if (output_encoding == E_LINEAR) /* compose on black */
             back_b = back_g = back_r = 0;

          else if (display->background == NULL /* no way to remove it */)
             png_error(png_ptr,
                "a background color must be supplied to remove alpha/transparency");

          /* Get a copy of the background color (this avoids repeating the checks
           * below.)  The encoding is 8-bit sRGB or 16-bit linear, depending on the
           * output format.
           */
          else
          {
             back_g = display->background->green;
             if (output_format & PNG_FORMAT_FLAG_COLOR)
             {
                back_r = display->background->red;
                back_b = display->background->blue;
             }
             else
                back_b = back_r = back_g;
          }
       }

       else if (output_encoding == E_LINEAR)
          back_b = back_r = back_g = 65535;

       else
          back_b = back_r = back_g = 255;

       /* Default the input file gamma if required - this is necessary because
        * libpng assumes that if no gamma information is present the data is in the
        * output format, but the simplified API deduces the gamma from the input
        * format.
        */
       if ((png_ptr->colorspace.flags & PNG_COLORSPACE_HAVE_GAMMA) == 0)
       {
          /* Do this directly, not using the png_colorspace functions, to ensure
           * that it happens even if the colorspace is invalid (though probably if
           * it is the setting will be ignored)  Note that the same thing can be
           * achieved at the application interface with png_set_gAMA.
           */
          if (png_ptr->bit_depth == 16 &&
             (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
             png_ptr->colorspace.gamma = PNG_GAMMA_LINEAR;

          else
             png_ptr->colorspace.gamma = PNG_GAMMA_sRGB_INVERSE;

          png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
       }

       /* Decide what to do based on the PNG color type of the input data.  The
        * utility function png_create_colormap_entry deals with most aspects of the
        * output transformations; this code works out how to produce bytes of
        * color-map entries from the original format.
        */
       switch (png_ptr->color_type)
       {
          case PNG_COLOR_TYPE_GRAY:
             if (png_ptr->bit_depth <= 8)
             {
                /* There at most 256 colors in the output, regardless of
                 * transparency.
                 */
                unsigned int step, i, val, trans = 256/*ignore*/, back_alpha = 0;

                cmap_entries = 1U << png_ptr->bit_depth;
                if (cmap_entries > image->colormap_entries)
                   png_error(png_ptr, "gray[8] color-map: too few entries");

                step = 255 / (cmap_entries - 1);
                output_processing = PNG_CMAP_NONE;

                /* If there is a tRNS chunk then this either selects a transparent
                 * value or, if the output has no alpha, the background color.
                 */
                if (png_ptr->num_trans > 0)
                {
                   trans = png_ptr->trans_color.gray;

                   if ((output_format & PNG_FORMAT_FLAG_ALPHA) == 0)
                      back_alpha = output_encoding == E_LINEAR ? 65535 : 255;
                }

                /* png_create_colormap_entry just takes an RGBA and writes the
                 * corresponding color-map entry using the format from 'image',
                 * including the required conversion to sRGB or linear as
                 * appropriate.  The input values are always either sRGB (if the
                 * gamma correction flag is 0) or 0..255 scaled file encoded values
                 * (if the function must gamma correct them).
                 */
                for (i=val=0; i<cmap_entries; ++i, val += step)
                {
                   /* 'i' is a file value.  While this will result in duplicated
                    * entries for 8-bit non-sRGB encoded files it is necessary to
                    * have non-gamma corrected values to do tRNS handling.
                    */
                   if (i != trans)
                      png_create_colormap_entry(display, i, val, val, val, 255,
                         E_FILE/*8-bit with file gamma*/);

                   /* Else this entry is transparent.  The colors don't matter if
                    * there is an alpha channel (back_alpha == 0), but it does no
                    * harm to pass them in; the values are not set above so this
                    * passes in white.
                    *
                    * NOTE: this preserves the full precision of the application
                    * supplied background color when it is used.
                    */
                   else
                      png_create_colormap_entry(display, i, back_r, back_g, back_b,
                         back_alpha, output_encoding);
                }

                /* We need libpng to preserve the original encoding. */
                data_encoding = E_FILE;

                /* The rows from libpng, while technically gray values, are now also
                 * color-map indicies; however, they may need to be expanded to 1
                 * byte per pixel.  This is what png_set_packing does (i.e., it
                 * unpacks the bit values into bytes.)
                 */
                if (png_ptr->bit_depth < 8)
                   png_set_packing(png_ptr);
             }

             else /* bit depth is 16 */
             {
                /* The 16-bit input values can be converted directly to 8-bit gamma
                 * encoded values; however, if a tRNS chunk is present 257 color-map
                 * entries are required.  This means that the extra entry requires
                 * special processing; add an alpha channel, sacrifice gray level
                 * 254 and convert transparent (alpha==0) entries to that.
                 *
                 * Use libpng to chop the data to 8 bits.  Convert it to sRGB at the
                 * same time to minimize quality loss.  If a tRNS chunk is present
                 * this means libpng must handle it too; otherwise it is impossible
                 * to do the exact match on the 16-bit value.
                 *
                 * If the output has no alpha channel *and* the background color is
                 * gray then it is possible to let libpng handle the substitution by
                 * ensuring that the corresponding gray level matches the background
                 * color exactly.
                 */
                data_encoding = E_sRGB;

                if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                   png_error(png_ptr, "gray[16] color-map: too few entries");

                cmap_entries = make_gray_colormap(display);

                if (png_ptr->num_trans > 0)
                {
                   unsigned int back_alpha;

                   if (output_format & PNG_FORMAT_FLAG_ALPHA)
                      back_alpha = 0;

                   else
                   {
                      if (back_r == back_g && back_g == back_b)
                      {
                         /* Background is gray; no special processing will be
                          * required.
                          */
                         png_color_16 c;
                         png_uint_32 gray = back_g;

                         if (output_encoding == E_LINEAR)
                         {
                            gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                            /* And make sure the corresponding palette entry
                             * matches.
                             */
                            png_create_colormap_entry(display, gray, back_g, back_g,
                               back_g, 65535, E_LINEAR);
                         }

                         /* The background passed to libpng, however, must be the
                          * sRGB value.
                          */
                         c.index = 0; /*unused*/
                         c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                         /* NOTE: does this work without expanding tRNS to alpha?
                          * It should be the color->gray case below apparently
                          * doesn't.
                          */
                         png_set_background_fixed(png_ptr, &c,
                            PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                            0/*gamma: not used*/);

                         output_processing = PNG_CMAP_NONE;
                         break;
                      }

                      back_alpha = output_encoding == E_LINEAR ? 65535 : 255;
                   }

                   /* output_processing means that the libpng-processed row will be
                    * 8-bit GA and it has to be processing to single byte color-map
                    * values.  Entry 254 is replaced by either a completely
                    * transparent entry or by the background color at full
                    * precision (and the background color is not a simple gray leve
                    * in this case.)
                    */
                   expand_tRNS = 1;
                   output_processing = PNG_CMAP_TRANS;
                   background_index = 254;

                   /* And set (overwrite) color-map entry 254 to the actual
                    * background color at full precision.
                    */
                   png_create_colormap_entry(display, 254, back_r, back_g, back_b,
                      back_alpha, output_encoding);
                }

                else
                   output_processing = PNG_CMAP_NONE;
             }
             break;

          case PNG_COLOR_TYPE_GRAY_ALPHA:
             /* 8-bit or 16-bit PNG with two channels - gray and alpha.  A minimum
              * of 65536 combinations.  If, however, the alpha channel is to be
              * removed there are only 256 possibilities if the background is gray.
              * (Otherwise there is a subset of the 65536 possibilities defined by
              * the triangle between black, white and the background color.)
              *
              * Reduce 16-bit files to 8-bit and sRGB encode the result.  No need to
              * worry about tRNS matching - tRNS is ignored if there is an alpha
              * channel.
              */
             data_encoding = E_sRGB;

             if (output_format & PNG_FORMAT_FLAG_ALPHA)
             {
                if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                   png_error(png_ptr, "gray+alpha color-map: too few entries");

                cmap_entries = make_ga_colormap(display);

                background_index = PNG_CMAP_GA_BACKGROUND;
                output_processing = PNG_CMAP_GA;
             }

             else /* alpha is removed */
             {
                /* Alpha must be removed as the PNG data is processed when the
                 * background is a color because the G and A channels are
                 * independent and the vector addition (non-parallel vectors) is a
                 * 2-D problem.
                 *
                 * This can be reduced to the same algorithm as above by making a
                 * colormap containing gray levels (for the opaque grays), a
                 * background entry (for a transparent pixel) and a set of four six
                 * level color values, one set for each intermediate alpha value.
                 * See the comments in make_ga_colormap for how this works in the
                 * per-pixel processing.
                 *
                 * If the background is gray, however, we only need a 256 entry gray
                 * level color map.  It is sufficient to make the entry generated
                 * for the background color be exactly the color specified.
                 */
                if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0 ||
                   (back_r == back_g && back_g == back_b))
                {
                   /* Background is gray; no special processing will be required. */
                   png_color_16 c;
                   png_uint_32 gray = back_g;

                   if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                      png_error(png_ptr, "gray-alpha color-map: too few entries");

                   cmap_entries = make_gray_colormap(display);

                   if (output_encoding == E_LINEAR)
                   {
                      gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                      /* And make sure the corresponding palette entry matches. */
                      png_create_colormap_entry(display, gray, back_g, back_g,
                         back_g, 65535, E_LINEAR);
                   }

                   /* The background passed to libpng, however, must be the sRGB
                    * value.
                    */
                   c.index = 0; /*unused*/
                   c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                   png_set_background_fixed(png_ptr, &c,
                      PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                      0/*gamma: not used*/);

                   output_processing = PNG_CMAP_NONE;
                }

                else
                {
                   png_uint_32 i, a;

                   /* This is the same as png_make_ga_colormap, above, except that
                    * the entries are all opaque.
                    */
                   if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                      png_error(png_ptr, "ga-alpha color-map: too few entries");

                   i = 0;
                   while (i < 231)
                   {
                      png_uint_32 gray = (i * 256 + 115) / 231;
                      png_create_colormap_entry(display, i++, gray, gray, gray,
                         255, E_sRGB);
                   }

                   /* NOTE: this preserves the full precision of the application
                    * background color.
                    */
                   background_index = i;
                   png_create_colormap_entry(display, i++, back_r, back_g, back_b,
                      output_encoding == E_LINEAR ? 65535U : 255U, output_encoding);

                   /* For non-opaque input composite on the sRGB background - this
                    * requires inverting the encoding for each component.  The input
                    * is still converted to the sRGB encoding because this is a
                    * reasonable approximate to the logarithmic curve of human
                    * visual sensitivity, at least over the narrow range which PNG
                    * represents.  Consequently 'G' is always sRGB encoded, while
                    * 'A' is linear.  We need the linear background colors.
                    */
                   if (output_encoding == E_sRGB) /* else already linear */
                   {
                      /* This may produce a value not exactly matching the
                       * background, but that's ok because these numbers are only
                       * used when alpha != 0
                       */
                      back_r = png_sRGB_table[back_r];
                      back_g = png_sRGB_table[back_g];
                      back_b = png_sRGB_table[back_b];
                   }

                   for (a=1; a<5; ++a)
                   {
                      unsigned int g;

                      /* PNG_sRGB_FROM_LINEAR expects a 16-bit linear value scaled
                       * by an 8-bit alpha value (0..255).
                       */
                      png_uint_32 alpha = 51 * a;
                      png_uint_32 back_rx = (255-alpha) * back_r;
                      png_uint_32 back_gx = (255-alpha) * back_g;
                      png_uint_32 back_bx = (255-alpha) * back_b;

                      for (g=0; g<6; ++g)
                      {
                         png_uint_32 gray = png_sRGB_table[g*51] * alpha;

                         png_create_colormap_entry(display, i++,
                            PNG_sRGB_FROM_LINEAR(gray + back_rx),
                            PNG_sRGB_FROM_LINEAR(gray + back_gx),
                            PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, E_sRGB);
                      }
                   }

                   cmap_entries = i;
                   output_processing = PNG_CMAP_GA;
                }
             }
             break;

          case PNG_COLOR_TYPE_RGB:
          case PNG_COLOR_TYPE_RGB_ALPHA:
             /* Exclude the case where the output is gray; we can always handle this
              * with the cases above.
              */
             if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0)
             {
                /* The color-map will be grayscale, so we may as well convert the
                 * input RGB values to a simple grayscale and use the grayscale
                 * code above.
                 *
                 * NOTE: calling this apparently damages the recognition of the
                 * transparent color in background color handling; call
                 * png_set_tRNS_to_alpha before png_set_background_fixed.
                 */
                png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE, -1,
                   -1);
                data_encoding = E_sRGB;

                /* The output will now be one or two 8-bit gray or gray+alpha
                 * channels.  The more complex case arises when the input has alpha.
                 */
                if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                   png_ptr->num_trans > 0) &&
                   (output_format & PNG_FORMAT_FLAG_ALPHA) != 0)
                {
                   /* Both input and output have an alpha channel, so no background
                    * processing is required; just map the GA bytes to the right
                    * color-map entry.
                    */
                   expand_tRNS = 1;

                   if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                      png_error(png_ptr, "rgb[ga] color-map: too few entries");

                   cmap_entries = make_ga_colormap(display);
                   background_index = PNG_CMAP_GA_BACKGROUND;
                   output_processing = PNG_CMAP_GA;
                }

                else
                {
                   /* Either the input or the output has no alpha channel, so there
                    * will be no non-opaque pixels in the color-map; it will just be
                    * grayscale.
                    */
                   if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                      png_error(png_ptr, "rgb[gray] color-map: too few entries");

                   /* Ideally this code would use libpng to do the gamma correction,
                    * but if an input alpha channel is to be removed we will hit the
                    * libpng bug in gamma+compose+rgb-to-gray (the double gamma
                    * correction bug).  Fix this by dropping the gamma correction in
                    * this case and doing it in the palette; this will result in
                    * duplicate palette entries, but that's better than the
                    * alternative of double gamma correction.
                    */
                   if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                      png_ptr->num_trans > 0) &&
                      png_gamma_not_sRGB(png_ptr->colorspace.gamma))
                   {
                      cmap_entries = make_gray_file_colormap(display);
                      data_encoding = E_FILE;
                   }

                   else
                      cmap_entries = make_gray_colormap(display);

                   /* But if the input has alpha or transparency it must be removed
                    */
                   if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                      png_ptr->num_trans > 0)
                   {
                      png_color_16 c;
                      png_uint_32 gray = back_g;

                      /* We need to ensure that the application background exists in
                       * the colormap and that completely transparent pixels map to
                       * it.  Achieve this simply by ensuring that the entry
                       * selected for the background really is the background color.
                       */
                      if (data_encoding == E_FILE) /* from the fixup above */
                      {
                         /* The app supplied a gray which is in output_encoding, we
                          * need to convert it to a value of the input (E_FILE)
                          * encoding then set this palette entry to the required
                          * output encoding.
                          */
                         if (output_encoding == E_sRGB)
                            gray = png_sRGB_table[gray]; /* now E_LINEAR */

                         gray = PNG_DIV257(png_gamma_16bit_correct(gray,
                            png_ptr->colorspace.gamma)); /* now E_FILE */

                         /* And make sure the corresponding palette entry contains
                          * exactly the required sRGB value.
                          */
                         png_create_colormap_entry(display, gray, back_g, back_g,
                            back_g, 0/*unused*/, output_encoding);
                      }

                      else if (output_encoding == E_LINEAR)
                      {
                         gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                         /* And make sure the corresponding palette entry matches.
                          */
                         png_create_colormap_entry(display, gray, back_g, back_g,
                            back_g, 0/*unused*/, E_LINEAR);
                      }

                      /* The background passed to libpng, however, must be the
                       * output (normally sRGB) value.
                       */
                      c.index = 0; /*unused*/
                      c.gray = c.red = c.green = c.blue = (png_uint_16)gray;

                      /* NOTE: the following is apparently a bug in libpng. Without
                       * it the transparent color recognition in
                       * png_set_background_fixed seems to go wrong.
                       */
                      expand_tRNS = 1;
                      png_set_background_fixed(png_ptr, &c,
                         PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                         0/*gamma: not used*/);
                   }

                   output_processing = PNG_CMAP_NONE;
                }
             }

             else /* output is color */
             {
                /* We could use png_quantize here so long as there is no transparent
                 * color or alpha; png_quantize ignores alpha.  Easier overall just
                 * to do it once and using PNG_DIV51 on the 6x6x6 reduced RGB cube.
                 * Consequently we always want libpng to produce sRGB data.
                 */
                data_encoding = E_sRGB;

                /* Is there any transparency or alpha? */
                if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                   png_ptr->num_trans > 0)
                {
                   /* Is there alpha in the output too?  If so all four channels are
                    * processed into a special RGB cube with alpha support.
                    */
                   if (output_format & PNG_FORMAT_FLAG_ALPHA)
                   {
                      png_uint_32 r;

                      if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
                         png_error(png_ptr, "rgb+alpha color-map: too few entries");

                      cmap_entries = make_rgb_colormap(display);

                      /* Add a transparent entry. */
                      png_create_colormap_entry(display, cmap_entries, 255, 255,
                         255, 0, E_sRGB);

                      /* This is stored as the background index for the processing
                       * algorithm.
                       */
                      background_index = cmap_entries++;

                      /* Add 27 r,g,b entries each with alpha 0.5. */
                      for (r=0; r<256; r = (r << 1) | 0x7f)
                      {
                         png_uint_32 g;

                         for (g=0; g<256; g = (g << 1) | 0x7f)
                         {
                            png_uint_32 b;

                            /* This generates components with the values 0, 127 and
                             * 255
                             */
                            for (b=0; b<256; b = (b << 1) | 0x7f)
                               png_create_colormap_entry(display, cmap_entries++,
                                  r, g, b, 128, E_sRGB);
                         }
                      }

                      expand_tRNS = 1;
                      output_processing = PNG_CMAP_RGB_ALPHA;
                   }

                   else
                   {
                      /* Alpha/transparency must be removed.  The background must
                       * exist in the color map (achieved by setting adding it after
                       * the 666 color-map).  If the standard processing code will
                       * pick up this entry automatically that's all that is
                       * required; libpng can be called to do the background
                       * processing.
                       */
                      unsigned int sample_size =
                         PNG_IMAGE_SAMPLE_SIZE(output_format);
                      png_uint_32 r, g, b; /* sRGB background */

                      if (PNG_RGB_COLORMAP_ENTRIES+1+27 > image->colormap_entries)
                         png_error(png_ptr, "rgb-alpha color-map: too few entries");

                      cmap_entries = make_rgb_colormap(display);

                      png_create_colormap_entry(display, cmap_entries, back_r,
                            back_g, back_b, 0/*unused*/, output_encoding);

                      if (output_encoding == E_LINEAR)
                      {
                         r = PNG_sRGB_FROM_LINEAR(back_r * 255);
                         g = PNG_sRGB_FROM_LINEAR(back_g * 255);
                         b = PNG_sRGB_FROM_LINEAR(back_b * 255);
                      }

                      else
                      {
                         r = back_r;
                         g = back_g;
                         b = back_g;
                      }

                      /* Compare the newly-created color-map entry with the one the
                       * PNG_CMAP_RGB algorithm will use.  If the two entries don't
                       * match, add the new one and set this as the background
                       * index.
                       */
                      if (memcmp((png_const_bytep)display->colormap +
                            sample_size * cmap_entries,
                         (png_const_bytep)display->colormap +
                            sample_size * PNG_RGB_INDEX(r,g,b),
                         sample_size) != 0)
                      {
                         /* The background color must be added. */
                         background_index = cmap_entries++;

                         /* Add 27 r,g,b entries each with created by composing with
                          * the background at alpha 0.5.
                          */
                         for (r=0; r<256; r = (r << 1) | 0x7f)
                         {
                            for (g=0; g<256; g = (g << 1) | 0x7f)
                            {
                               /* This generates components with the values 0, 127
                                * and 255
                                */
                               for (b=0; b<256; b = (b << 1) | 0x7f)
                                  png_create_colormap_entry(display, cmap_entries++,
                                     png_colormap_compose(display, r, E_sRGB, 128,
                                        back_r, output_encoding),
                                     png_colormap_compose(display, g, E_sRGB, 128,
                                        back_g, output_encoding),
                                     png_colormap_compose(display, b, E_sRGB, 128,
                                        back_b, output_encoding),
                                     0/*unused*/, output_encoding);
                            }
                         }

                         expand_tRNS = 1;
                         output_processing = PNG_CMAP_RGB_ALPHA;
                      }

                      else /* background color is in the standard color-map */
                      {
                         png_color_16 c;

                         c.index = 0; /*unused*/
                         c.red = (png_uint_16)back_r;
                         c.gray = c.green = (png_uint_16)back_g;
                         c.blue = (png_uint_16)back_b;

                         png_set_background_fixed(png_ptr, &c,
                            PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                            0/*gamma: not used*/);

                         output_processing = PNG_CMAP_RGB;
                      }
                   }
                }

                else /* no alpha or transparency in the input */
                {
                   /* Alpha in the output is irrelevant, simply map the opaque input
                    * pixels to the 6x6x6 color-map.
                    */
                   if (PNG_RGB_COLORMAP_ENTRIES > image->colormap_entries)
                      png_error(png_ptr, "rgb color-map: too few entries");

                   cmap_entries = make_rgb_colormap(display);
                   output_processing = PNG_CMAP_RGB;
                }
             }
             break;

          case PNG_COLOR_TYPE_PALETTE:
             /* It's already got a color-map.  It may be necessary to eliminate the
              * tRNS entries though.
              */
             {
                unsigned int num_trans = png_ptr->num_trans;
                png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
                png_const_colorp colormap = png_ptr->palette;
                const int do_background = trans != NULL &&
                   (output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
                unsigned int i;

                /* Just in case: */
                if (trans == NULL)
                   num_trans = 0;

                output_processing = PNG_CMAP_NONE;
                data_encoding = E_FILE; /* Don't change from color-map indicies */
                cmap_entries = png_ptr->num_palette;
                if (cmap_entries > 256)
                   cmap_entries = 256;

                if (cmap_entries > image->colormap_entries)
                   png_error(png_ptr, "palette color-map: too few entries");

                for (i=0; i < cmap_entries; ++i)
                {
                   if (do_background && i < num_trans && trans[i] < 255)
                   {
                      if (trans[i] == 0)
                         png_create_colormap_entry(display, i, back_r, back_g,
                            back_b, 0, output_encoding);

                      else
                      {
                         /* Must compose the PNG file color in the color-map entry
                          * on the sRGB color in 'back'.
                          */
                         png_create_colormap_entry(display, i,
                            png_colormap_compose(display, colormap[i].red, E_FILE,
                               trans[i], back_r, output_encoding),
                            png_colormap_compose(display, colormap[i].green, E_FILE,
                               trans[i], back_g, output_encoding),
                            png_colormap_compose(display, colormap[i].blue, E_FILE,
                               trans[i], back_b, output_encoding),
                            output_encoding == E_LINEAR ? trans[i] * 257U :
                               trans[i],
                            output_encoding);
                      }
                   }

                   else
                      png_create_colormap_entry(display, i, colormap[i].red,
                         colormap[i].green, colormap[i].blue,
                         i < num_trans ? trans[i] : 255U, E_FILE/*8-bit*/);
                }

                /* The PNG data may have indicies packed in fewer than 8 bits, it
                 * must be expanded if so.
                 */
                if (png_ptr->bit_depth < 8)
                   png_set_packing(png_ptr);
             }
             break;

          default:
             png_error(png_ptr, "invalid PNG color type");
             /*NOT REACHED*/
             break;
       }

       /* Now deal with the output processing */
       if (expand_tRNS && png_ptr->num_trans > 0 &&
          (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) == 0)
          png_set_tRNS_to_alpha(png_ptr);

       switch (data_encoding)
       {
          default:
             png_error(png_ptr, "bad data option (internal error)");
             break;

          case E_sRGB:
             /* Change to 8-bit sRGB */
             png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
             /* FALL THROUGH */

          case E_FILE:
             if (png_ptr->bit_depth > 8)
                png_set_scale_16(png_ptr);
             break;
       }

       if (cmap_entries > 256 || cmap_entries > image->colormap_entries)
          png_error(png_ptr, "color map overflow (BAD internal error)");

       image->colormap_entries = cmap_entries;

       /* Double check using the recorded background index */
       switch (output_processing)
       {
          case PNG_CMAP_NONE:
             if (background_index != PNG_CMAP_NONE_BACKGROUND)
                goto bad_background;
             break;

          case PNG_CMAP_GA:
             if (background_index != PNG_CMAP_GA_BACKGROUND)
                goto bad_background;
             break;

          case PNG_CMAP_TRANS:
             if (background_index >= cmap_entries ||
                background_index != PNG_CMAP_TRANS_BACKGROUND)
                goto bad_background;
             break;

          case PNG_CMAP_RGB:
             if (background_index != PNG_CMAP_RGB_BACKGROUND)
                goto bad_background;
             break;

          case PNG_CMAP_RGB_ALPHA:
             if (background_index != PNG_CMAP_RGB_ALPHA_BACKGROUND)
                goto bad_background;
             break;

          default:
             png_error(png_ptr, "bad processing option (internal error)");

          bad_background:
             png_error(png_ptr, "bad background index (internal error)");
       }

       display->colormap_processing = output_processing;

       return 1/*ok*/;
    }

    /* The final part of the color-map read called from png_image_finish_read. */
    static int
    png_image_read_and_map(png_voidp argument)
    {
       png_image_read_control *display = png_voidcast(png_image_read_control*,
          argument);
       png_imagep image = display->image;
       png_structrp png_ptr = image->opaque->png_ptr;
       int passes;

       /* Called when the libpng data must be transformed into the color-mapped
        * form.  There is a local row buffer in display->local and this routine must
        * do the interlace handling.
        */
       switch (png_ptr->interlaced)
       {
          case PNG_INTERLACE_NONE:
             passes = 1;
             break;

          case PNG_INTERLACE_ADAM7:
             passes = PNG_INTERLACE_ADAM7_PASSES;
             break;

          default:
             passes = 0;
             png_error(png_ptr, "unknown interlace type");
       }

       {
          png_uint_32  height = image->height;
          png_uint_32  width = image->width;
          int          proc = display->colormap_processing;
          png_bytep    first_row = png_voidcast(png_bytep, display->first_row);
          ptrdiff_t    step_row = display->row_bytes;
          int pass;

          for (pass = 0; pass < passes; ++pass)
          {
             unsigned int     startx, stepx, stepy;
             png_uint_32      y;

             if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
             {
                /* The row may be empty for a short image: */
                if (PNG_PASS_COLS(width, pass) == 0)
                   continue;

                startx = PNG_PASS_START_COL(pass);
                stepx = PNG_PASS_COL_OFFSET(pass);
                y = PNG_PASS_START_ROW(pass);
                stepy = PNG_PASS_ROW_OFFSET(pass);
             }

             else
             {
                y = 0;
                startx = 0;
                stepx = stepy = 1;
             }

             for (; y<height; y += stepy)
             {
                png_bytep inrow = png_voidcast(png_bytep, display->local_row);
                png_bytep outrow = first_row + y * step_row;
                png_const_bytep end_row = outrow + width;

                /* Read read the libpng data into the temporary buffer. */
                png_read_row(png_ptr, inrow, NULL);

                /* Now process the row according to the processing option, note
                 * that the caller verifies that the format of the libpng output
                 * data is as required.
                 */
                outrow += startx;
                switch (proc)
                {
                   case PNG_CMAP_GA:
                      for (; outrow < end_row; outrow += stepx)
                      {
                         /* The data is always in the PNG order */
                         unsigned int gray = *inrow++;
                         unsigned int alpha = *inrow++;
                         unsigned int entry;

                         /* NOTE: this code is copied as a comment in
                          * make_ga_colormap above.  Please update the
                          * comment if you change this code!
                          */
                         if (alpha > 229) /* opaque */
                         {
                            entry = (231 * gray + 128) >> 8;
                         }
                         else if (alpha < 26) /* transparent */
                         {
                            entry = 231;
                         }
                         else /* partially opaque */
                         {
                            entry = 226 + 6 * PNG_DIV51(alpha) + PNG_DIV51(gray);
                         }

                         *outrow = (png_byte)entry;
                      }
                      break;

                   case PNG_CMAP_TRANS:
                      for (; outrow < end_row; outrow += stepx)
                      {
                         png_byte gray = *inrow++;
                         png_byte alpha = *inrow++;

                         if (alpha == 0)
                            *outrow = PNG_CMAP_TRANS_BACKGROUND;

                         else if (gray != PNG_CMAP_TRANS_BACKGROUND)
                            *outrow = gray;

                         else
                            *outrow = (png_byte)(PNG_CMAP_TRANS_BACKGROUND+1);
                      }
                      break;

                   case PNG_CMAP_RGB:
                      for (; outrow < end_row; outrow += stepx)
                      {
                         *outrow = PNG_RGB_INDEX(inrow[0], inrow[1], inrow[2]);
                         inrow += 3;
                      }
                      break;

                   case PNG_CMAP_RGB_ALPHA:
                      for (; outrow < end_row; outrow += stepx)
                      {
                         unsigned int alpha = inrow[3];

                         /* Because the alpha entries only hold alpha==0.5 values
                          * split the processing at alpha==0.25 (64) and 0.75
                          * (196).
                          */

                         if (alpha >= 196)
                            *outrow = PNG_RGB_INDEX(inrow[0], inrow[1],
                               inrow[2]);

                         else if (alpha < 64)
                            *outrow = PNG_CMAP_RGB_ALPHA_BACKGROUND;

                         else
                         {
                            /* Likewise there are three entries for each of r, g
                             * and b.  We could select the entry by popcount on
                             * the top two bits on those architectures that
                             * support it, this is what the code below does,
                             * crudely.
                             */
                            unsigned int back_i = PNG_CMAP_RGB_ALPHA_BACKGROUND+1;

                            /* Here are how the values map:
                             *
                             * 0x00 .. 0x3f -> 0
                             * 0x40 .. 0xbf -> 1
                             * 0xc0 .. 0xff -> 2
                             *
                             * So, as above with the explicit alpha checks, the
                             * breakpoints are at 64 and 196.
                             */
                            if (inrow[0] & 0x80) back_i += 9; /* red */
                            if (inrow[0] & 0x40) back_i += 9;
                            if (inrow[0] & 0x80) back_i += 3; /* green */
                            if (inrow[0] & 0x40) back_i += 3;
                            if (inrow[0] & 0x80) back_i += 1; /* blue */
                            if (inrow[0] & 0x40) back_i += 1;

                            *outrow = (png_byte)back_i;
                         }

                         inrow += 4;
                      }
                      break;

                   default:
                      break;
                }
             }
          }
       }

       return 1;
    }

    static int
    png_image_read_colormapped(png_voidp argument)
    {
       png_image_read_control *display = png_voidcast(png_image_read_control*,
          argument);
       png_imagep image = display->image;
       png_controlp control = image->opaque;
       png_structrp png_ptr = control->png_ptr;
       png_inforp info_ptr = control->info_ptr;

       int passes = 0; /* As a flag */

       PNG_SKIP_CHUNKS(png_ptr);

       /* Update the 'info' structure and make sure the result is as required; first
        * make sure to turn on the interlace handling if it will be required
        * (because it can't be turned on *after* the call to png_read_update_info!)
        */
       if (display->colormap_processing == PNG_CMAP_NONE)
          passes = png_set_interlace_handling(png_ptr);

       png_read_update_info(png_ptr, info_ptr);

       /* The expected output can be deduced from the colormap_processing option. */
       switch (display->colormap_processing)
       {
          case PNG_CMAP_NONE:
             /* Output must be one channel and one byte per pixel, the output
              * encoding can be anything.
              */
             if ((info_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
                info_ptr->color_type == PNG_COLOR_TYPE_GRAY) &&
                info_ptr->bit_depth == 8)
                break;

             goto bad_output;

          case PNG_CMAP_TRANS:
          case PNG_CMAP_GA:
             /* Output must be two channels and the 'G' one must be sRGB, the latter
              * can be checked with an exact number because it should have been set
              * to this number above!
              */
             if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
                info_ptr->bit_depth == 8 &&
                png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
                image->colormap_entries == 256)
                break;

             goto bad_output;

          case PNG_CMAP_RGB:
             /* Output must be 8-bit sRGB encoded RGB */
             if (info_ptr->color_type == PNG_COLOR_TYPE_RGB &&
                info_ptr->bit_depth == 8 &&
                png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
                image->colormap_entries == 216)
                break;

             goto bad_output;

          case PNG_CMAP_RGB_ALPHA:
             /* Output must be 8-bit sRGB encoded RGBA */
             if (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
                info_ptr->bit_depth == 8 &&
                png_ptr->screen_gamma == PNG_GAMMA_sRGB &&
                image->colormap_entries == 244 /* 216 + 1 + 27 */)
                break;

             /* goto bad_output; */
             /* FALL THROUGH */

          default:
          bad_output:
             png_error(png_ptr, "bad color-map processing (internal error)");
       }

       /* Now read the rows.  Do this here if it is possible to read directly into
        * the output buffer, otherwise allocate a local row buffer of the maximum
        * size libpng requires and call the relevant processing routine safely.
        */
       {
          png_voidp first_row = display->buffer;
          ptrdiff_t row_bytes = display->row_stride;

          /* The following expression is designed to work correctly whether it gives
           * a signed or an unsigned result.
           */
          if (row_bytes < 0)
          {
             char *ptr = png_voidcast(char*, first_row);
             ptr += (image->height-1) * (-row_bytes);
             first_row = png_voidcast(png_voidp, ptr);
          }

          display->first_row = first_row;
          display->row_bytes = row_bytes;
       }

       if (passes == 0)
       {
          int result;
          png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

          display->local_row = row;
          result = png_safe_execute(image, png_image_read_and_map, display);
          display->local_row = NULL;
          png_free(png_ptr, row);

          return result;
       }

       else
       {
          png_alloc_size_t row_bytes = display->row_bytes;

          while (--passes >= 0)
          {
             png_uint_32      y = image->height;
             png_bytep        row = png_voidcast(png_bytep, display->first_row);

             while (y-- > 0)
             {
                png_read_row(png_ptr, row, NULL);
                row += row_bytes;
             }
          }

          return 1;
       }
    }

    /* Just the row reading part of png_image_read. */
    static int
    png_image_read_composite(png_voidp argument)
    {
       png_image_read_control *display = png_voidcast(png_image_read_control*,
          argument);
       png_imagep image = display->image;
       png_structrp png_ptr = image->opaque->png_ptr;
       int passes;

       switch (png_ptr->interlaced)
       {
          case PNG_INTERLACE_NONE:
             passes = 1;
             break;

          case PNG_INTERLACE_ADAM7:
             passes = PNG_INTERLACE_ADAM7_PASSES;
             break;

          default:
             passes = 0;
             png_error(png_ptr, "unknown interlace type");
       }

       {
          png_uint_32  height = image->height;
          png_uint_32  width = image->width;
          ptrdiff_t    step_row = display->row_bytes;
          unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) ? 3 : 1;
          int pass;

          for (pass = 0; pass < passes; ++pass)
          {
             unsigned int     startx, stepx, stepy;
             png_uint_32      y;

             if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
             {
                /* The row may be empty for a short image: */
                if (PNG_PASS_COLS(width, pass) == 0)
                   continue;

                startx = PNG_PASS_START_COL(pass) * channels;
                stepx = PNG_PASS_COL_OFFSET(pass) * channels;
                y = PNG_PASS_START_ROW(pass);
                stepy = PNG_PASS_ROW_OFFSET(pass);
             }

             else
             {
                y = 0;
                startx = 0;
                stepx = channels;
                stepy = 1;
             }

             for (; y<height; y += stepy)
             {
                png_bytep inrow = png_voidcast(png_bytep, display->local_row);
                png_bytep outrow;
                png_const_bytep end_row;

                /* Read the row, which is packed: */
                png_read_row(png_ptr, inrow, NULL);

                outrow = png_voidcast(png_bytep, display->first_row);
                outrow += y * step_row;
                end_row = outrow + width * channels;

                /* Now do the composition on each pixel in this row. */
                outrow += startx;
                for (; outrow < end_row; outrow += stepx)
                {
                   png_byte alpha = inrow[channels];

                   if (alpha > 0) /* else no change to the output */
                   {
                      unsigned int c;

                      for (c=0; c<channels; ++c)
                      {
                         png_uint_32 component = inrow[c];

                         if (alpha < 255) /* else just use component */
                         {
                            /* This is PNG_OPTIMIZED_ALPHA, the component value
                             * is a linear 8-bit value.  Combine this with the
                             * current outrow[c] value which is sRGB encoded.
                             * Arithmetic here is 16-bits to preserve the output
                             * values correctly.
                             */
                            component *= 257*255; /* =65535 */
                            component += (255-alpha)*png_sRGB_table[outrow[c]];

                            /* So 'component' is scaled by 255*65535 and is
                             * therefore appropriate for the sRGB to linear
                             * conversion table.
                             */
                            component = PNG_sRGB_FROM_LINEAR(component);
                         }

                         outrow[c] = (png_byte)component;
                      }
                   }

                   inrow += channels+1; /* components and alpha channel */
                }
             }
          }
       }

       return 1;
    }

    /* The do_local_background case; called when all the following transforms are to
     * be done:
     *
     * PNG_RGB_TO_GRAY
     * PNG_COMPOSITE
     * PNG_GAMMA
     *
     * This is a work-round for the fact that both the PNG_RGB_TO_GRAY and
     * PNG_COMPOSITE code performs gamma correction, so we get double gamma
     * correction.  The fix-up is to prevent the PNG_COMPOSITE operation happening
     * inside libpng, so this routine sees an 8 or 16-bit gray+alpha row and handles
     * the removal or pre-multiplication of the alpha channel.
     */
    static int
    png_image_read_background(png_voidp argument)
    {
       png_image_read_control *display = png_voidcast(png_image_read_control*,
          argument);
       png_imagep image = display->image;
       png_structrp png_ptr = image->opaque->png_ptr;
       png_inforp info_ptr = image->opaque->info_ptr;
       png_uint_32 height = image->height;
       png_uint_32 width = image->width;
       int pass, passes;

       /* Double check the convoluted logic below.  We expect to get here with
        * libpng doing rgb to gray and gamma correction but background processing
        * left to the png_image_read_background function.  The rows libpng produce
        * might be 8 or 16-bit but should always have two channels; gray plus alpha.
        */
       if ((png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
          png_error(png_ptr, "lost rgb to gray");

       if ((png_ptr->transformations & PNG_COMPOSE) != 0)
          png_error(png_ptr, "unexpected compose");

       if (png_get_channels(png_ptr, info_ptr) != 2)
          png_error(png_ptr, "lost/gained channels");

       /* Expect the 8-bit case to always remove the alpha channel */
       if ((image->format & PNG_FORMAT_FLAG_LINEAR) == 0 &&
          (image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
          png_error(png_ptr, "unexpected 8-bit transformation");

       switch (png_ptr->interlaced)
       {
          case PNG_INTERLACE_NONE:
             passes = 1;
             break;

          case PNG_INTERLACE_ADAM7:
             passes = PNG_INTERLACE_ADAM7_PASSES;
             break;

          default:
             passes = 0;
             png_error(png_ptr, "unknown interlace type");
       }

       switch (png_get_bit_depth(png_ptr, info_ptr))
       {
          default:
             png_error(png_ptr, "unexpected bit depth");
             break;

          case 8:
             /* 8-bit sRGB gray values with an alpha channel; the alpha channel is
              * to be removed by composing on a background: either the row if
              * display->background is NULL or display->background->green if not.
              * Unlike the code above ALPHA_OPTIMIZED has *not* been done.
              */
             {
                png_bytep first_row = png_voidcast(png_bytep, display->first_row);
                ptrdiff_t step_row = display->row_bytes;

                for (pass = 0; pass < passes; ++pass)
                {
                   png_bytep        row = png_voidcast(png_bytep,
                                                       display->first_row);
                   unsigned int     startx, stepx, stepy;
                   png_uint_32      y;

                   if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
                   {
                      /* The row may be empty for a short image: */
                      if (PNG_PASS_COLS(width, pass) == 0)
                         continue;

                      startx = PNG_PASS_START_COL(pass);
                      stepx = PNG_PASS_COL_OFFSET(pass);
                      y = PNG_PASS_START_ROW(pass);
                      stepy = PNG_PASS_ROW_OFFSET(pass);
                   }

                   else
                   {
                      y = 0;
                      startx = 0;
                      stepx = stepy = 1;
                   }

                   if (display->background == NULL)
                   {
                      for (; y<height; y += stepy)
                      {
                         png_bytep inrow = png_voidcast(png_bytep,
                            display->local_row);
                         png_bytep outrow = first_row + y * step_row;
                         png_const_bytep end_row = outrow + width;

                         /* Read the row, which is packed: */
                         png_read_row(png_ptr, inrow, NULL);

                         /* Now do the composition on each pixel in this row. */
                         outrow += startx;
                         for (; outrow < end_row; outrow += stepx)
                         {
                            png_byte alpha = inrow[1];

                            if (alpha > 0) /* else no change to the output */
                            {
                               png_uint_32 component = inrow[0];

                               if (alpha < 255) /* else just use component */
                               {
                                  /* Since PNG_OPTIMIZED_ALPHA was not set it is
                                   * necessary to invert the sRGB transfer
                                   * function and multiply the alpha out.
                                   */
                                  component = png_sRGB_table[component] * alpha;
                                  component += png_sRGB_table[outrow[0]] *
                                     (255-alpha);
                                  component = PNG_sRGB_FROM_LINEAR(component);
                               }

                               outrow[0] = (png_byte)component;
                            }

                            inrow += 2; /* gray and alpha channel */
                         }
                      }
                   }

                   else /* constant background value */
                   {
                      png_byte background8 = display->background->green;
                      png_uint_16 background = png_sRGB_table[background8];

                      for (; y<height; y += stepy)
                      {
                         png_bytep inrow = png_voidcast(png_bytep,
                            display->local_row);
                         png_bytep outrow = first_row + y * step_row;
                         png_const_bytep end_row = outrow + width;

                         /* Read the row, which is packed: */
                         png_read_row(png_ptr, inrow, NULL);

                         /* Now do the composition on each pixel in this row. */
                         outrow += startx;
                         for (; outrow < end_row; outrow += stepx)
                         {
                            png_byte alpha = inrow[1];

                            if (alpha > 0) /* else use background */
                            {
                               png_uint_32 component = inrow[0];

                               if (alpha < 255) /* else just use component */
                               {
                                  component = png_sRGB_table[component] * alpha;
                                  component += background * (255-alpha);
                                  component = PNG_sRGB_FROM_LINEAR(component);
                               }

                               outrow[0] = (png_byte)component;
                            }

                            else
                               outrow[0] = background8;

                            inrow += 2; /* gray and alpha channel */
                         }

                         row += display->row_bytes;
                      }
                   }
                }
             }
             break;

          case 16:
             /* 16-bit linear with pre-multiplied alpha; the pre-multiplication must
              * still be done and, maybe, the alpha channel removed.  This code also
              * handles the alpha-first option.
              */
             {
                png_uint_16p first_row = png_voidcast(png_uint_16p,
                   display->first_row);
                /* The division by two is safe because the caller passed in a
                 * stride which was multiplied by 2 (below) to get row_bytes.
                 */
                ptrdiff_t    step_row = display->row_bytes / 2;
                int preserve_alpha = (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
                unsigned int outchannels = 1+preserve_alpha;
                int swap_alpha = 0;

                if (preserve_alpha && (image->format & PNG_FORMAT_FLAG_AFIRST))
                   swap_alpha = 1;

                for (pass = 0; pass < passes; ++pass)
                {
                   unsigned int     startx, stepx, stepy;
                   png_uint_32      y;

                   /* The 'x' start and step are adjusted to output components here.
                    */
                   if (png_ptr->interlaced == PNG_INTERLACE_ADAM7)
                   {
                      /* The row may be empty for a short image: */
                      if (PNG_PASS_COLS(width, pass) == 0)
                         continue;

                      startx = PNG_PASS_START_COL(pass) * outchannels;
                      stepx = PNG_PASS_COL_OFFSET(pass) * outchannels;
                      y = PNG_PASS_START_ROW(pass);
                      stepy = PNG_PASS_ROW_OFFSET(pass);
                   }

                   else
                   {
                      y = 0;
                      startx = 0;
                      stepx = outchannels;
                      stepy = 1;
                   }

                   for (; y<height; y += stepy)
                   {
                      png_const_uint_16p inrow;
                      png_uint_16p outrow = first_row + y*step_row;
                      png_uint_16p end_row = outrow + width * outchannels;

                      /* Read the row, which is packed: */
                      png_read_row(png_ptr, png_voidcast(png_bytep,
                         display->local_row), NULL);
                      inrow = png_voidcast(png_const_uint_16p, display->local_row);

                      /* Now do the pre-multiplication on each pixel in this row.
                       */
                      outrow += startx;
                      for (; outrow < end_row; outrow += stepx)
                      {
                         png_uint_32 component = inrow[0];
                         png_uint_16 alpha = inrow[1];

                         if (alpha > 0) /* else 0 */
                         {
                            if (alpha < 65535) /* else just use component */
                            {
                               component *= alpha;
                               component += 32767;
                               component /= 65535;
                            }
                         }

                         else
                            component = 0;

                         outrow[swap_alpha] = (png_uint_16)component;
                         if (preserve_alpha)
                            outrow[1 ^ swap_alpha] = alpha;

                         inrow += 2; /* components and alpha channel */
                      }
                   }
                }
             }
             break;
       }

       return 1;
    }

    /* The guts of png_image_finish_read as a png_safe_execute callback. */
    static int
    png_image_read_direct(png_voidp argument)
    {
       png_image_read_control *display = png_voidcast(png_image_read_control*,
          argument);
       png_imagep image = display->image;
       png_structrp png_ptr = image->opaque->png_ptr;
       png_inforp info_ptr = image->opaque->info_ptr;

       png_uint_32 format = image->format;
       int linear = (format & PNG_FORMAT_FLAG_LINEAR) != 0;
       int do_local_compose = 0;
       int do_local_background = 0; /* to avoid double gamma correction bug */
       int passes = 0;

       /* Add transforms to ensure the correct output format is produced then check
        * that the required implementation support is there.  Always expand; always
        * need 8 bits minimum, no palette and expanded tRNS.
        */
       png_set_expand(png_ptr);

       /* Now check the format to see if it was modified. */
       {
          png_uint_32 base_format = png_image_format(png_ptr) &
             ~PNG_FORMAT_FLAG_COLORMAP /* removed by png_set_expand */;
          png_uint_32 change = format ^ base_format;
          png_fixed_point output_gamma;
          int mode; /* alpha mode */

          /* Do this first so that we have a record if rgb to gray is happening. */
          if (change & PNG_FORMAT_FLAG_COLOR)
          {
             /* gray<->color transformation required. */
             if (format & PNG_FORMAT_FLAG_COLOR)
                png_set_gray_to_rgb(png_ptr);

             else
             {
                /* libpng can't do both rgb to gray and
                 * background/pre-multiplication if there is also significant gamma
                 * correction, because both operations require linear colors and
                 * the code only supports one transform doing the gamma correction.
                 * Handle this by doing the pre-multiplication or background
                 * operation in this code, if necessary.
                 *
                 * TODO: fix this by rewriting pngrtran.c (!)
                 *
                 * For the moment (given that fixing this in pngrtran.c is an
                 * enormous change) 'do_local_background' is used to indicate that
                 * the problem exists.
                 */
                if (base_format & PNG_FORMAT_FLAG_ALPHA)
                   do_local_background = 1/*maybe*/;

                png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE,
                   PNG_RGB_TO_GRAY_DEFAULT, PNG_RGB_TO_GRAY_DEFAULT);
             }

             change &= ~PNG_FORMAT_FLAG_COLOR;
          }

          /* Set the gamma appropriately, linear for 16-bit input, sRGB otherwise.
           */
          {
             png_fixed_point input_gamma_default;

             if ((base_format & PNG_FORMAT_FLAG_LINEAR) &&
                (image->flags & PNG_IMAGE_FLAG_16BIT_sRGB) == 0)
                input_gamma_default = PNG_GAMMA_LINEAR;
             else
                input_gamma_default = PNG_DEFAULT_sRGB;

             /* Call png_set_alpha_mode to set the default for the input gamma; the
              * output gamma is set by a second call below.
              */
             png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, input_gamma_default);
          }

          if (linear)
          {
             /* If there *is* an alpha channel in the input it must be multiplied
              * out; use PNG_ALPHA_STANDARD, otherwise just use PNG_ALPHA_PNG.
              */
             if (base_format & PNG_FORMAT_FLAG_ALPHA)
                mode = PNG_ALPHA_STANDARD; /* associated alpha */

             else
                mode = PNG_ALPHA_PNG;

             output_gamma = PNG_GAMMA_LINEAR;
          }

          else
          {
             mode = PNG_ALPHA_PNG;
             output_gamma = PNG_DEFAULT_sRGB;
          }

          /* If 'do_local_background' is set check for the presence of gamma
           * correction; this is part of the work-round for the libpng bug
           * described above.
           *
           * TODO: fix libpng and remove this.
           */
          if (do_local_background)
          {
             png_fixed_point gtest;

             /* This is 'png_gamma_threshold' from pngrtran.c; the test used for
              * gamma correction, the screen gamma hasn't been set on png_struct
              * yet; it's set below.  png_struct::gamma, however, is set to the
              * final value.
              */
             if (png_muldiv(&gtest, output_gamma, png_ptr->colorspace.gamma,
                   PNG_FP_1) && !png_gamma_significant(gtest))
                do_local_background = 0;

             else if (mode == PNG_ALPHA_STANDARD)
             {
                do_local_background = 2/*required*/;
                mode = PNG_ALPHA_PNG; /* prevent libpng doing it */
             }

             /* else leave as 1 for the checks below */
          }

          /* If the bit-depth changes then handle that here. */
          if (change & PNG_FORMAT_FLAG_LINEAR)
          {
             if (linear /*16-bit output*/)
                png_set_expand_16(png_ptr);

             else /* 8-bit output */
                png_set_scale_16(png_ptr);

             change &= ~PNG_FORMAT_FLAG_LINEAR;
          }

          /* Now the background/alpha channel changes. */
          if (change & PNG_FORMAT_FLAG_ALPHA)
          {
             /* Removing an alpha channel requires composition for the 8-bit
              * formats; for the 16-bit it is already done, above, by the
              * pre-multiplication and the channel just needs to be stripped.
              */
             if (base_format & PNG_FORMAT_FLAG_ALPHA)
             {
                /* If RGB->gray is happening the alpha channel must be left and the
                 * operation completed locally.
                 *
                 * TODO: fix libpng and remove this.
                 */
                if (do_local_background)
                   do_local_background = 2/*required*/;

                /* 16-bit output: just remove the channel */
                else if (linear) /* compose on black (well, pre-multiply) */
                   png_set_strip_alpha(png_ptr);

                /* 8-bit output: do an appropriate compose */
                else if (display->background != NULL)
                {
                   png_color_16 c;

                   c.index = 0; /*unused*/
                   c.red = display->background->red;
                   c.green = display->background->green;
                   c.blue = display->background->blue;
                   c.gray = display->background->green;

                   /* This is always an 8-bit sRGB value, using the 'green' channel
                    * for gray is much better than calculating the luminance here;
                    * we can get off-by-one errors in that calculation relative to
                    * the app expectations and that will show up in transparent
                    * pixels.
                    */
                   png_set_background_fixed(png_ptr, &c,
                      PNG_BACKGROUND_GAMMA_SCREEN, 0/*need_expand*/,
                      0/*gamma: not used*/);
                }

                else /* compose on row: implemented below. */
                {
                   do_local_compose = 1;
                   /* This leaves the alpha channel in the output, so it has to be
                    * removed by the code below.  Set the encoding to the 'OPTIMIZE'
                    * one so the code only has to hack on the pixels that require
                    * composition.
                    */
                   mode = PNG_ALPHA_OPTIMIZED;
                }
             }

             else /* output needs an alpha channel */
             {
                /* This is tricky because it happens before the swap operation has
                 * been accomplished; however, the swap does *not* swap the added
                 * alpha channel (weird API), so it must be added in the correct
                 * place.
                 */
                png_uint_32 filler; /* opaque filler */
                int where;

                if (linear)
                   filler = 65535;

                else
                   filler = 255;

    #           ifdef PNG_FORMAT_AFIRST_SUPPORTED
                   if (format & PNG_FORMAT_FLAG_AFIRST)
                   {
                      where = PNG_FILLER_BEFORE;
                      change &= ~PNG_FORMAT_FLAG_AFIRST;
                   }

                   else
    #           endif
                   where = PNG_FILLER_AFTER;

                png_set_add_alpha(png_ptr, filler, where);
             }

             /* This stops the (irrelevant) call to swap_alpha below. */
             change &= ~PNG_FORMAT_FLAG_ALPHA;
          }

          /* Now set the alpha mode correctly; this is always done, even if there is
           * no alpha channel in either the input or the output because it correctly
           * sets the output gamma.
           */
          png_set_alpha_mode_fixed(png_ptr, mode, output_gamma);

    #     ifdef PNG_FORMAT_BGR_SUPPORTED
             if (change & PNG_FORMAT_FLAG_BGR)
             {
                /* Check only the output format; PNG is never BGR; don't do this if
                 * the output is gray, but fix up the 'format' value in that case.
                 */
                if (format & PNG_FORMAT_FLAG_COLOR)
                   png_set_bgr(png_ptr);

                else
                   format &= ~PNG_FORMAT_FLAG_BGR;

                change &= ~PNG_FORMAT_FLAG_BGR;
             }
    #     endif

    #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
             if (change & PNG_FORMAT_FLAG_AFIRST)
             {
                /* Only relevant if there is an alpha channel - it's particularly
                 * important to handle this correctly because do_local_compose may
                 * be set above and then libpng will keep the alpha channel for this
                 * code to remove.
                 */
                if (format & PNG_FORMAT_FLAG_ALPHA)
                {
                   /* Disable this if doing a local background,
                    * TODO: remove this when local background is no longer required.
                    */
                   if (do_local_background != 2)
                      png_set_swap_alpha(png_ptr);
                }

                else
                   format &= ~PNG_FORMAT_FLAG_AFIRST;

                change &= ~PNG_FORMAT_FLAG_AFIRST;
             }
    #     endif

          /* If the *output* is 16-bit then we need to check for a byte-swap on this
           * architecture.
           */
          if (linear)
          {
             PNG_CONST png_uint_16 le = 0x0001;

             if (*(png_const_bytep)&le)
                png_set_swap(png_ptr);
          }

          /* If change is not now 0 some transformation is missing - error out. */
          if (change)
             png_error(png_ptr, "png_read_image: unsupported transformation");
       }

       PNG_SKIP_CHUNKS(png_ptr);

       /* Update the 'info' structure and make sure the result is as required; first
        * make sure to turn on the interlace handling if it will be required
        * (because it can't be turned on *after* the call to png_read_update_info!)
        *
        * TODO: remove the do_local_background fixup below.
        */
       if (!do_local_compose && do_local_background != 2)
          passes = png_set_interlace_handling(png_ptr);

       png_read_update_info(png_ptr, info_ptr);

       {
          png_uint_32 info_format = 0;

          if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
             info_format |= PNG_FORMAT_FLAG_COLOR;

          if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
          {
             /* do_local_compose removes this channel below. */
             if (!do_local_compose)
             {
                /* do_local_background does the same if required. */
                if (do_local_background != 2 ||
                   (format & PNG_FORMAT_FLAG_ALPHA) != 0)
                   info_format |= PNG_FORMAT_FLAG_ALPHA;
             }
          }

          else if (do_local_compose) /* internal error */
             png_error(png_ptr, "png_image_read: alpha channel lost");

          if (info_ptr->bit_depth == 16)
             info_format |= PNG_FORMAT_FLAG_LINEAR;

    #     ifdef PNG_FORMAT_BGR_SUPPORTED
             if (png_ptr->transformations & PNG_BGR)
                info_format |= PNG_FORMAT_FLAG_BGR;
    #     endif

    #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
             if (do_local_background == 2)
             {
                if (format & PNG_FORMAT_FLAG_AFIRST)
                   info_format |= PNG_FORMAT_FLAG_AFIRST;
             }

             if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0 ||
                ((png_ptr->transformations & PNG_ADD_ALPHA) != 0 &&
                (png_ptr->flags & PNG_FLAG_FILLER_AFTER) == 0))
             {
                if (do_local_background == 2)
                   png_error(png_ptr, "unexpected alpha swap transformation");

                info_format |= PNG_FORMAT_FLAG_AFIRST;
             }
    #     endif

          /* This is actually an internal error. */
          if (info_format != format)
             png_error(png_ptr, "png_read_image: invalid transformations");
       }

       /* Now read the rows.  If do_local_compose is set then it is necessary to use
        * a local row buffer.  The output will be GA, RGBA or BGRA and must be
        * converted to G, RGB or BGR as appropriate.  The 'local_row' member of the
        * display acts as a flag.
        */
       {
          png_voidp first_row = display->buffer;
          ptrdiff_t row_bytes = display->row_stride;

          if (linear)
             row_bytes *= 2;

          /* The following expression is designed to work correctly whether it gives
           * a signed or an unsigned result.
           */
          if (row_bytes < 0)
          {
             char *ptr = png_voidcast(char*, first_row);
             ptr += (image->height-1) * (-row_bytes);
             first_row = png_voidcast(png_voidp, ptr);
          }

          display->first_row = first_row;
          display->row_bytes = row_bytes;
       }

       if (do_local_compose)
       {
          int result;
          png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

          display->local_row = row;
          result = png_safe_execute(image, png_image_read_composite, display);
          display->local_row = NULL;
          png_free(png_ptr, row);

          return result;
       }

       else if (do_local_background == 2)
       {
          int result;
          png_voidp row = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));

          display->local_row = row;
          result = png_safe_execute(image, png_image_read_background, display);
          display->local_row = NULL;
          png_free(png_ptr, row);

          return result;
       }

       else
       {
          png_alloc_size_t row_bytes = display->row_bytes;

          while (--passes >= 0)
          {
             png_uint_32      y = image->height;
             png_bytep        row = png_voidcast(png_bytep, display->first_row);

             while (y-- > 0)
             {
                png_read_row(png_ptr, row, NULL);
                row += row_bytes;
             }
          }

          return 1;
       }
    }

    int PNGAPI
    png_image_finish_read(png_imagep image, png_const_colorp background,
       void *buffer, png_int_32 row_stride, void *colormap)
    {
       if (image != NULL && image->version == PNG_IMAGE_VERSION)
       {
          png_uint_32 check;

          if (row_stride == 0)
             row_stride = PNG_IMAGE_ROW_STRIDE(*image);

          if (row_stride < 0)
             check = -row_stride;

          else
             check = row_stride;

          if (image->opaque != NULL && buffer != NULL &&
             check >= PNG_IMAGE_ROW_STRIDE(*image))
          {
             if ((image->format & PNG_FORMAT_FLAG_COLORMAP) == 0 ||
                (image->colormap_entries > 0 && colormap != NULL))
             {
                int result;
                png_image_read_control display;

                memset(&display, 0, (sizeof display));
                display.image = image;
                display.buffer = buffer;
                display.row_stride = row_stride;
                display.colormap = colormap;
                display.background = background;
                display.local_row = NULL;

                /* Choose the correct 'end' routine; for the color-map case all the
                 * setup has already been done.
                 */
                if (image->format & PNG_FORMAT_FLAG_COLORMAP)
                   result =
                      png_safe_execute(image, png_image_read_colormap, &display) &&
                      png_safe_execute(image, png_image_read_colormapped, &display);

                else
                   result =
                      png_safe_execute(image, png_image_read_direct, &display);

                png_image_free(image);
                return result;
             }

             else
                return png_image_error(image,
                   "png_image_finish_read[color-map]: no color-map");
          }

          else
             return png_image_error(image,
                "png_image_finish_read: invalid argument");
       }

       else if (image != NULL)
          return png_image_error(image,
             "png_image_finish_read: damaged PNG_IMAGE_VERSION");

       return 0;
    }

    #endif /* PNG_SIMPLIFIED_READ_SUPPORTED */
    #endif /* PNG_READ_SUPPORTED */