    // Copyright (C) 2008  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #include <sstream>
    #include <string>
    #include <cstdlib>
    #include <ctime>
    #include <dlib/pixel.h>
    #include <dlib/array2d.h>
    #include <dlib/image_transforms.h>
    #include <dlib/image_io.h>
    #include <dlib/matrix.h>
    #include <dlib/rand.h>

    #include "tester.h"

    namespace
    {
        using namespace test;
        using namespace dlib;
        using namespace std;

        logger dlog("test.image");

        void image_test (
        )
        /*!
            ensures
                - runs tests on pixel objects and functions for compliance with the specs
        !*/
        {

            print_spinner();

            array2d<unsigned char> img1, img2;

            img1.set_size(100,100);

            assign_all_pixels(img1,7);

            assign_image(img2, img1);

            DLIB_TEST_MSG(img1.nr() == 100 && img1.nc() == 100 &&
                         img2.nr() == 100 && img2.nc() == 100,"");

            for (long r = 0; r < img1.nr(); ++r)
            {
                for (long c = 0; c < img1.nc(); ++c)
                {
                    DLIB_TEST(img1[r][c] == 7);
                    DLIB_TEST(img2[r][c] == 7);
                }
            }

            img2.clear();
            DLIB_TEST(img2.size() == 0);
            DLIB_TEST(img2.nr() == 0);
            DLIB_TEST(img2.nc() == 0);
            assign_image(img2, mat(img1));

            DLIB_TEST_MSG(img1.nr() == 100 && img1.nc() == 100 &&
                         img2.nr() == 100 && img2.nc() == 100,"");

            for (long r = 0; r < img1.nr(); ++r)
            {
                for (long c = 0; c < img1.nc(); ++c)
                {
                    DLIB_TEST(img1[r][c] == 7);
                    DLIB_TEST(img2[r][c] == 7);
                }
            }

            threshold_image(img1, img2, 4);

            for (long r = 0; r < img1.nr(); ++r)
            {
                for (long c = 0; c < img1.nc(); ++c)
                {
                    DLIB_TEST(img1[r][c] == 7);
                    DLIB_TEST(img2[r][c] == on_pixel);
                }
            }

            {
                array2d<hsi_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].h = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].s = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].i = static_cast<unsigned char>(r*14 + c + 3);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                istringstream sin(sout.str());

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_dng(img, sin);

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c].h == r*14 + c + 1);
                        DLIB_TEST(img[r][c].s == r*14 + c + 2);
                        DLIB_TEST(img[r][c].i == r*14 + c + 3);
                    }
                }
            }

            {
                array2d<rgb_alpha_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                        img[r][c].alpha = static_cast<unsigned char>(r*14 + c + 4);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                istringstream sin(sout.str());

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_dng(img, sin);

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c].red == r*14 + c + 1);
                        DLIB_TEST(img[r][c].green == r*14 + c + 2);
                        DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        DLIB_TEST(img[r][c].alpha == r*14 + c + 4);
                    }
                }
            }

    #ifdef DLIB_PNG_SUPPORT
            {
                array2d<rgb_alpha_pixel> img;
                array2d<rgb_pixel> img2, img3;
                img.set_size(14,15);
                img2.set_size(img.nr(),img.nc());
                img3.set_size(img.nr(),img.nc());
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                        img[r][c].alpha = static_cast<unsigned char>(r*14 + c + 4);
                    }
                }

                save_png(img, "test.png");

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_png(img, "test.png");

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                assign_all_pixels(img2, 255);
                assign_all_pixels(img3, 0);
                load_png(img2, "test.png");
                assign_image(img3, img);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c].red == r*14 + c + 1);
                        DLIB_TEST(img[r][c].green == r*14 + c + 2);
                        DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        DLIB_TEST(img[r][c].alpha == r*14 + c + 4);

                        DLIB_TEST(img2[r][c].red == img3[r][c].red);
                        DLIB_TEST(img2[r][c].green == img3[r][c].green);
                        DLIB_TEST(img2[r][c].blue == img3[r][c].blue);
                    }
                }
            }
    #endif // DLIB_PNG_SUPPORT

            {
                array2d<rgb_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                save_bmp(img, sout);
                save_dng(img, sout);
                save_bmp(img, sout);
                istringstream sin(sout.str());

                for (int i  = 0; i < 2; ++i)
                {
                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_dng(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c].red == r*14 + c + 1);
                            DLIB_TEST(img[r][c].green == r*14 + c + 2);
                            DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        }
                    }

                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_bmp(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST_MSG(img[r][c].red == r*14 + c + 1, "got " << (int)img[r][c].red << "  but expected " << r*14 + c + 1);
                            DLIB_TEST(img[r][c].green == r*14 + c + 2);
                            DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        }
                    }
                }
            }
            {
                array2d<bgr_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                save_bmp(img, sout);
                save_dng(img, sout);
                save_bmp(img, sout);
                istringstream sin(sout.str());

                for (int i  = 0; i < 2; ++i)
                {
                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_dng(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c].red == r*14 + c + 1);
                            DLIB_TEST(img[r][c].green == r*14 + c + 2);
                            DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        }
                    }

                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_bmp(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST_MSG(img[r][c].red == r*14 + c + 1, "got " << (int)img[r][c].red << "  but expected " << r*14 + c + 1);
                            DLIB_TEST(img[r][c].green == r*14 + c + 2);
                            DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                        }
                    }
                }
            }

    #ifdef DLIB_PNG_SUPPORT
            {
                array2d<rgb_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                    }
                }

                save_png(img, "test.png");

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_png(img, "test.png");

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c].red == r*14 + c + 1);
                        DLIB_TEST(img[r][c].green == r*14 + c + 2);
                        DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                    }
                }
            }
            {
                array2d<bgr_pixel> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c].red = static_cast<unsigned char>(r*14 + c + 1);
                        img[r][c].green = static_cast<unsigned char>(r*14 + c + 2);
                        img[r][c].blue = static_cast<unsigned char>(r*14 + c + 3);
                    }
                }

                save_png(img, "test.png");

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_png(img, "test.png");

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c].red == r*14 + c + 1);
                        DLIB_TEST(img[r][c].green == r*14 + c + 2);
                        DLIB_TEST(img[r][c].blue == r*14 + c + 3);
                    }
                }
            }
    #endif // DLIB_PNG_SUPPORT

            {
                array2d<unsigned short> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c] = static_cast<unsigned short>(r*14 + c + 0xF0);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                istringstream sin(sout.str());

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_dng(img, sin);

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c] == r*14 + c + 0xF0);
                    }
                }
            }

    #ifdef DLIB_PNG_SUPPORT
            {
                array2d<unsigned short> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c] = static_cast<unsigned short>(r*14 + c + 0xF0);
                    }
                }

                save_png(img, "test.png");

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_png(img, "test.png");

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c] == r*14 + c + 0xF0);
                    }
                }
            }
    #endif // DLIB_PNG_SUPPORT

            {
                array2d<unsigned char> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c] = static_cast<unsigned char>(r*14 + c*111);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                save_bmp(img, sout);
                save_dng(img, sout);
                save_bmp(img, sout);
                istringstream sin(sout.str());

                for (int i = 0; i < 2; ++i)
                {
                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_dng(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c] == static_cast<unsigned char>(r*14 + c*111));
                        }
                    }

                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_bmp(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c] == static_cast<unsigned char>(r*14 + c*111));
                        }
                    }
                }
            }

    #ifdef DLIB_PNG_SUPPORT
            {
                array2d<unsigned char> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c] = static_cast<unsigned char>(r*14 + c);
                    }
                }

                save_png(img, "test.png");

                img.clear();
                DLIB_TEST(img.nr() == 0);
                DLIB_TEST(img.nc() == 0);

                load_png(img, "test.png");

                DLIB_TEST(img.nr() == 14);
                DLIB_TEST(img.nc() == 15);

                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        DLIB_TEST(img[r][c] == r*14 + c);
                    }
                }

            }
    #endif // DLIB_PNG_SUPPORT

            {
                // in this test we will only assign pixel values that can be
                // represented with 8 bits even though we are using a wider pixel type.
                array2d<unsigned short> img;
                img.set_size(14,15);
                for (long r = 0; r < 14; ++r)
                {
                    for (long c = 0; c < 15; ++c)
                    {
                        img[r][c] = static_cast<unsigned char>(r*14 + c);
                    }
                }

                ostringstream sout;
                save_dng(img, sout);
                save_bmp(img, sout);
                save_dng(img, sout);
                save_bmp(img, sout);
                istringstream sin(sout.str());

                for (int i = 0; i < 2; ++i)
                {
                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_dng(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c] == r*14 + c);
                        }
                    }

                    img.clear();
                    DLIB_TEST(img.nr() == 0);
                    DLIB_TEST(img.nc() == 0);

                    load_bmp(img, sin);

                    DLIB_TEST(img.nr() == 14);
                    DLIB_TEST(img.nc() == 15);

                    for (long r = 0; r < 14; ++r)
                    {
                        for (long c = 0; c < 15; ++c)
                        {
                            DLIB_TEST(img[r][c] == r*14 + c);
                        }
                    }
                }
            }

            {
                array2d<unsigned short> img1;
                array2d<unsigned char> img2;
                img1.set_size(10,10);
                assign_all_pixels(img1, 0);

                img1[5][5] = 10000;
                img1[7][7] = 10000;

                equalize_histogram(img1, img2);

                for (long r = 0; r < img1.nr(); ++r)
                {
                    for (long c = 0; c < img2.nc(); ++c)
                    {
                        if ((r == 5 && c == 5) ||
                            (r == 7 && c == 7))
                        {
                            DLIB_TEST(img2[r][c] == 255);
                        }
                        else
                        {
                            DLIB_TEST(img2[r][c] == 0);
                        }
                    }
                }

            }

            {
                array2d<unsigned char> img;
                img.set_size(10,10);
                assign_all_pixels(img, 0);

                assign_border_pixels(img, 2,2, 4);

                DLIB_TEST(zeros_matrix<unsigned char>(6,6) == subm(mat(img), rectangle(2,2,7,7)));
                DLIB_TEST(uniform_matrix<unsigned char>(1,10, 4) == rowm(mat(img), 0));
                DLIB_TEST(uniform_matrix<unsigned char>(1,10, 4) == rowm(mat(img), 1));
                DLIB_TEST(uniform_matrix<unsigned char>(1,10, 4) == rowm(mat(img), 8));
                DLIB_TEST(uniform_matrix<unsigned char>(1,10, 4) == rowm(mat(img), 9));

                DLIB_TEST(uniform_matrix<unsigned char>(10,1, 4) == colm(mat(img), 0));
                DLIB_TEST(uniform_matrix<unsigned char>(10,1, 4) == colm(mat(img), 1));
                DLIB_TEST(uniform_matrix<unsigned char>(10,1, 4) == colm(mat(img), 8));
                DLIB_TEST(uniform_matrix<unsigned char>(10,1, 4) == colm(mat(img), 9));

                assign_border_pixels(img, 7, 7, 5);
                DLIB_TEST(uniform_matrix<unsigned char>(10,10, 5) == mat(img));
                assign_border_pixels(img, 37, 47, 5);
                DLIB_TEST(uniform_matrix<unsigned char>(10,10, 5) == mat(img));
            }

            {
                array2d<unsigned char> img;
                img.set_size(11,11);
                assign_all_pixels(img, 0);

                assign_border_pixels(img, 2,2, 4);

                DLIB_TEST(zeros_matrix<unsigned char>(7,7) == subm(mat(img), rectangle(2,2,8,8)));
                DLIB_TEST(uniform_matrix<unsigned char>(1,11, 4) == rowm(mat(img), 0));
                DLIB_TEST(uniform_matrix<unsigned char>(1,11, 4) == rowm(mat(img), 1));
                DLIB_TEST(uniform_matrix<unsigned char>(1,11, 4) == rowm(mat(img), 9));
                DLIB_TEST(uniform_matrix<unsigned char>(1,11, 4) == rowm(mat(img), 10));

                DLIB_TEST(uniform_matrix<unsigned char>(11,1, 4) == colm(mat(img), 0));
                DLIB_TEST(uniform_matrix<unsigned char>(11,1, 4) == colm(mat(img), 1));
                DLIB_TEST(uniform_matrix<unsigned char>(11,1, 4) == colm(mat(img), 9));
                DLIB_TEST(uniform_matrix<unsigned char>(11,1, 4) == colm(mat(img), 10));

                assign_border_pixels(img, 7, 7, 5);
                DLIB_TEST(uniform_matrix<unsigned char>(11,11, 5) == mat(img));
                assign_border_pixels(img, 70, 57, 5);
                DLIB_TEST(uniform_matrix<unsigned char>(11,11, 5) == mat(img));
            }

        }

        template <typename T, typename pixel_type>
        void test_integral_image (
        )
        {
            dlib::rand rnd;

            array2d<pixel_type> img;
            integral_image_generic<T> int_img;

            int_img.load(img);
            DLIB_TEST(int_img.nr() == 0);
            DLIB_TEST(int_img.nc() == 0);

            // make 5 random images
            for (int i = 0; i < 5; ++i)
            {
                print_spinner();
                img.set_size(rnd.get_random_16bit_number()%200+1, rnd.get_random_16bit_number()%200+1);

                for (long r = 0; r < img.nr(); ++r)
                {
                    for (long c = 0; c < img.nc(); ++c)
                    {
                        img[r][c] = (int)rnd.get_random_8bit_number() - 100;
                    }
                }

                int_img.load(img);
                DLIB_TEST(int_img.nr() == img.nr());
                DLIB_TEST(int_img.nc() == img.nc());

                // make 200 random rectangles
                for (int j = 0; j < 500; ++j)
                {
                    point p1(rnd.get_random_32bit_number()%img.nc(), rnd.get_random_32bit_number()%img.nr());
                    point p2(rnd.get_random_32bit_number()%img.nc(), rnd.get_random_32bit_number()%img.nr());
                    rectangle rect(p1,p2);
                    DLIB_TEST(int_img.get_sum_of_area(rect) == sum(subm(matrix_cast<T>(mat(img)), rect)));
                    rect = rectangle(p1,p1);
                    DLIB_TEST(int_img.get_sum_of_area(rect) == sum(subm(matrix_cast<T>(mat(img)), rect)));
                }

            }

        }

        void test_filtering2(int nr, int nc, dlib::rand& rnd)
        {
            print_spinner();
            dlog << LINFO << "test_filtering2(): " << nr << "  " << nc;
            array2d<float> img(302,301);
            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    img[r][c] = rnd.get_random_gaussian();
                }
            }
            matrix<float> filt = matrix_cast<float>(randm(nr,nc,rnd));

            matrix<float> out = xcorr_same(mat(img),filt);
            matrix<float> out2 = subm(conv(mat(img),flip(filt)), filt.nr()/2, filt.nc()/2, img.nr(), img.nc());
            // make sure xcorr_same does exactly what the docs say it should.
            DLIB_TEST(max(abs(out-out2)) < 1e-7);

            // Now compare the filtering functions to xcorr_same to make sure everything does
            // filtering in the same way.
            array2d<float> imout(img.nr(), img.nc());
            assign_all_pixels(imout, 10);
            rectangle rect = spatially_filter_image(img, imout, filt);
            border_enumerator be(get_rect(imout),rect);
            while (be.move_next())
            {
                DLIB_TEST(imout[be.element().y()][be.element().x()] == 0)
            }
            DLIB_TEST_MSG(max(abs(subm(mat(imout),rect) - subm(out,rect))) < 1e-5, max(abs(subm(mat(imout),rect) - subm(out,rect))));

            assign_all_pixels(imout, 10);
            out = 10;
            rect = spatially_filter_image(img, imout, filt,2,true,true);
            be = border_enumerator(get_rect(imout),rect);
            while (be.move_next())
            {
                DLIB_TEST(imout[be.element().y()][be.element().x()] == 10)
            }
            out += abs(xcorr_same(mat(img),filt)/2);
            DLIB_TEST(max(abs(subm(mat(imout),rect) - subm(out,rect))) < 1e-7);

            assign_all_pixels(imout, -10);
            out = -10;
            rect = spatially_filter_image(img, imout, filt,2,false,true);
            be = border_enumerator(get_rect(imout),rect);
            while (be.move_next())
            {
                DLIB_TEST(imout[be.element().y()][be.element().x()] == -10)
            }
            out += xcorr_same(mat(img),filt)/2;
            DLIB_TEST_MSG(max(abs(subm(mat(imout),rect) - subm(out,rect))) < 1e-5, max(abs(subm(mat(imout),rect) - subm(out,rect))));

            matrix<float> row_filt = matrix_cast<float>(randm(nc,1,rnd));
            matrix<float> col_filt = matrix_cast<float>(randm(nr,1,rnd));
            assign_all_pixels(imout, 10);
            rect = spatially_filter_image_separable(img, imout, row_filt, col_filt);
            out = xcorr_same(tmp(xcorr_same(mat(img),trans(row_filt))), col_filt);
            DLIB_TEST_MSG(max(abs(subm(mat(imout),rect) - subm(out,rect))) < 1e-5, max(abs(subm(mat(imout),rect) - subm(out,rect))));

            be = border_enumerator(get_rect(imout),rect);
            while (be.move_next())
            {
                DLIB_TEST(imout[be.element().y()][be.element().x()] == 0);
            }

            assign_all_pixels(imout, 10);
            out = 10;
            rect = spatially_filter_image_separable(img, imout, row_filt, col_filt,2,true,true);
            out += abs(xcorr_same(tmp(xcorr_same(mat(img),trans(row_filt))), col_filt)/2);
            DLIB_TEST_MSG(max(abs(subm(mat(imout),rect) - subm(out,rect))) < 1e-7,
                max(abs(subm(mat(imout),rect) - subm(out,rect))));

            be = border_enumerator(get_rect(imout),rect);
            while (be.move_next())
            {
                DLIB_TEST(imout[be.element().y()][be.element().x()] == 10);
            }

        }

        template <typename T>
        void test_filtering(bool use_abs, unsigned long scale )
        {
            print_spinner();
            dlog << LINFO << "test_filtering(" << use_abs << "," << scale << ")";
            array2d<T> img, img2, img3;
            img.set_size(10,11);

            assign_all_pixels(img, 10);

            matrix<int,3,5> filter2;
            filter2 = 1,1,1,1,1,
                      1,1,1,1,1,
                      1,1,1,1,1;

            assign_all_pixels(img2,3);
            rectangle brect = spatially_filter_image(img, img2, filter2);
            DLIB_TEST(brect == shrink_rect(get_rect(img), filter2.nc()/2, filter2.nr()/2));

            const rectangle rect(2,1,img.nc()-3,img.nr()-2);

            for (long r = 0; r<img2.nr(); ++r)
            {
                for (long c = 0; c<img2.nc(); ++c)
                {
                    if (rect.contains(c,r))
                    {
                        DLIB_TEST_MSG(img2[r][c] == 150, (int)img2[r][c]);
                    }
                    else
                    {
                        DLIB_TEST_MSG(img2[r][c] == 0,(int)img2[r][c]);
                    }
                }
            }

            assign_all_pixels(img2,3);
            assign_all_pixels(img3,3);
            brect = spatially_filter_image(img, img2, filter2);
            DLIB_TEST(brect == shrink_rect(get_rect(img), filter2.nc()/2, filter2.nr()/2));

            matrix<int,1,5> row_filter;
            matrix<int,1,3> col_filter;

            row_filter = 1,1,1,1,1;
            col_filter = 1,1,1;

            spatially_filter_image_separable(img, img3, row_filter, col_filter);

            DLIB_TEST(mat(img2) == mat(img3));

            dlib::rand  rnd;

            for (int i = 0; i < 30; ++i)
            {
                for (long r = 0; r < img.nr(); ++r)
                {
                    for (long c = 0; c < img.nc(); ++c)
                    {
                        img[r][c] = rnd.get_random_8bit_number();
                    }
                }

                row_filter(0) = ((int)rnd.get_random_8bit_number() - 100)/10;
                row_filter(1) = ((int)rnd.get_random_8bit_number() - 100)/10;
                row_filter(2) = ((int)rnd.get_random_8bit_number() - 100)/10;
                row_filter(3) = ((int)rnd.get_random_8bit_number() - 100)/10;
                row_filter(4) = ((int)rnd.get_random_8bit_number() - 100)/10;
                col_filter(0) = ((int)rnd.get_random_8bit_number() - 100)/10;
                col_filter(1) = ((int)rnd.get_random_8bit_number() - 100)/10;
                col_filter(2) = ((int)rnd.get_random_8bit_number() - 100)/10;

                const matrix<int,3,5> filter = trans(col_filter)*row_filter;

                assign_all_pixels(img2,3);
                assign_all_pixels(img3,3);
                // Just make sure both filtering methods give the same results.
                rectangle brect1, brect2;
                brect1 = spatially_filter_image(img, img2, filter, scale, use_abs);
                brect2 = spatially_filter_image_separable(img, img3, row_filter, col_filter, scale, use_abs);
                DLIB_TEST(mat(img2) == mat(img3));

                DLIB_TEST(brect1 == shrink_rect(get_rect(img), filter.nc()/2, filter.nr()/2));
                DLIB_TEST(brect1 == brect2);
            }

            {
                array2d<int> img, img2;
                img.set_size(3,4);

                matrix<int> filter(3,3);
                filter = 1;
                assign_all_pixels(img,-1);

                spatially_filter_image(img,img2,filter);

                DLIB_TEST(img2[0][0] == 0);
                DLIB_TEST(img2[0][1] == 0);
                DLIB_TEST(img2[0][2] == 0);
                DLIB_TEST(img2[0][3] == 0);

                DLIB_TEST(img2[1][0] == 0);
                DLIB_TEST(img2[1][1] == -9);
                DLIB_TEST(img2[1][2] == -9);
                DLIB_TEST(img2[1][3] == 0);

                DLIB_TEST(img2[2][0] == 0);
                DLIB_TEST(img2[2][1] == 0);
                DLIB_TEST(img2[2][2] == 0);
                DLIB_TEST(img2[2][3] == 0);

                assign_all_pixels(img,-1);

                spatially_filter_image(img,img2,filter,2,true);

                DLIB_TEST(img2[0][0] == 0);
                DLIB_TEST(img2[0][1] == 0);
                DLIB_TEST(img2[0][2] == 0);
                DLIB_TEST(img2[0][3] == 0);

                DLIB_TEST(img2[1][0] == 0);
                DLIB_TEST(img2[1][1] == 4);
                DLIB_TEST(img2[1][2] == 4);
                DLIB_TEST(img2[1][3] == 0);

                DLIB_TEST(img2[2][0] == 0);
                DLIB_TEST(img2[2][1] == 0);
                DLIB_TEST(img2[2][2] == 0);
                DLIB_TEST(img2[2][3] == 0);

                matrix<int> rowf(3,1), colf(3,1);
                rowf = 1;
                colf = 1;
                assign_all_pixels(img,-1);

                spatially_filter_image_separable(img,img2,rowf,colf);
                DLIB_TEST(img2[0][0] == 0);
                DLIB_TEST(img2[0][1] == 0);
                DLIB_TEST(img2[0][2] == 0);
                DLIB_TEST(img2[0][3] == 0);

                DLIB_TEST(img2[1][0] == 0);
                DLIB_TEST(img2[1][1] == -9);
                DLIB_TEST(img2[1][2] == -9);
                DLIB_TEST(img2[1][3] == 0);

                DLIB_TEST(img2[2][0] == 0);
                DLIB_TEST(img2[2][1] == 0);
                DLIB_TEST(img2[2][2] == 0);
                DLIB_TEST(img2[2][3] == 0);

                spatially_filter_image_separable(img,img2,rowf,colf,1,true);
                DLIB_TEST(img2[0][0] == 0);
                DLIB_TEST(img2[0][1] == 0);
                DLIB_TEST(img2[0][2] == 0);
                DLIB_TEST(img2[0][3] == 0);

                DLIB_TEST(img2[1][0] == 0);
                DLIB_TEST(img2[1][1] == 9);
                DLIB_TEST(img2[1][2] == 9);
                DLIB_TEST(img2[1][3] == 0);

                DLIB_TEST(img2[2][0] == 0);
                DLIB_TEST(img2[2][1] == 0);
                DLIB_TEST(img2[2][2] == 0);
                DLIB_TEST(img2[2][3] == 0);

                assign_all_pixels(img2, 3);
                spatially_filter_image_separable(img,img2,rowf,colf,1,true, true);
                DLIB_TEST(img2[0][0] == 3);
                DLIB_TEST(img2[0][1] == 3);
                DLIB_TEST(img2[0][2] == 3);
                DLIB_TEST(img2[0][3] == 3);

                DLIB_TEST(img2[1][0] == 3);
                DLIB_TEST_MSG(img2[1][1] == 9+3, img2[1][1] );
                DLIB_TEST(img2[1][2] == 9+3);
                DLIB_TEST(img2[1][3] == 3);

                DLIB_TEST(img2[2][0] == 3);
                DLIB_TEST(img2[2][1] == 3);
                DLIB_TEST(img2[2][2] == 3);
                DLIB_TEST(img2[2][3] == 3);
            }
            {
                array2d<double> img, img2;
                img.set_size(3,4);

                matrix<double> filter(3,3);
                filter = 1;
                assign_all_pixels(img,-1);

                spatially_filter_image(img,img2,filter,2);

                DLIB_TEST(img2[0][0] == 0);
                DLIB_TEST(img2[0][1] == 0);
                DLIB_TEST(img2[0][2] == 0);
                DLIB_TEST(img2[0][3] == 0);

                DLIB_TEST(img2[1][0] == 0);
                DLIB_TEST(std::abs(img2[1][1] -  -4.5) < 1e-14);
                DLIB_TEST(std::abs(img2[1][2] -  -4.5) < 1e-14);
                DLIB_TEST(img2[1][3] == 0);

                DLIB_TEST(img2[2][0] == 0);
                DLIB_TEST(img2[2][1] == 0);
                DLIB_TEST(img2[2][2] == 0);
                DLIB_TEST(img2[2][3] == 0);

            }
            {
                array2d<double> img, img2;
                img.set_size(3,4);
                img2.set_size(3,4);
                assign_all_pixels(img2, 8);

                matrix<double> filter(3,3);
                filter = 1;
                assign_all_pixels(img,-1);

                spatially_filter_image(img,img2,filter,2, false, true);

                DLIB_TEST(img2[0][0] == 8);
                DLIB_TEST(img2[0][1] == 8);
                DLIB_TEST(img2[0][2] == 8);
                DLIB_TEST(img2[0][3] == 8);

                DLIB_TEST(img2[1][0] == 8);
                DLIB_TEST(std::abs(img2[1][1] -  -4.5 - 8) < 1e-14);
                DLIB_TEST(std::abs(img2[1][2] -  -4.5 - 8) < 1e-14);
                DLIB_TEST(img2[1][3] == 8);

                DLIB_TEST(img2[2][0] == 8);
                DLIB_TEST(img2[2][1] == 8);
                DLIB_TEST(img2[2][2] == 8);
                DLIB_TEST(img2[2][3] == 8);

            }
        }

        void test_zero_border_pixels(
        )
        {
            array2d<unsigned char> img;
            img.set_size(4,5);

            assign_all_pixels(img, 1);
            zero_border_pixels(img, 2,1);

            DLIB_TEST(img[0][0] == 0);
            DLIB_TEST(img[1][0] == 0);
            DLIB_TEST(img[2][0] == 0);
            DLIB_TEST(img[3][0] == 0);
            DLIB_TEST(img[0][1] == 0);
            DLIB_TEST(img[1][1] == 0);
            DLIB_TEST(img[2][1] == 0);
            DLIB_TEST(img[3][1] == 0);

            DLIB_TEST(img[0][3] == 0);
            DLIB_TEST(img[1][3] == 0);
            DLIB_TEST(img[2][3] == 0);
            DLIB_TEST(img[3][3] == 0);
            DLIB_TEST(img[0][4] == 0);
            DLIB_TEST(img[1][4] == 0);
            DLIB_TEST(img[2][4] == 0);
            DLIB_TEST(img[3][4] == 0);

            DLIB_TEST(img[0][2] == 0);
            DLIB_TEST(img[3][2] == 0);

            DLIB_TEST(img[1][2] == 1);
            DLIB_TEST(img[2][2] == 1);

            rectangle rect = get_rect(img);
            rect.left()+=2;
            rect.top()+=1;
            rect.right()-=2;
            rect.bottom()-=1;
            assign_all_pixels(img, 1);
            zero_border_pixels(img, rect);

            DLIB_TEST(img[0][0] == 0);
            DLIB_TEST(img[1][0] == 0);
            DLIB_TEST(img[2][0] == 0);
            DLIB_TEST(img[3][0] == 0);
            DLIB_TEST(img[0][1] == 0);
            DLIB_TEST(img[1][1] == 0);
            DLIB_TEST(img[2][1] == 0);
            DLIB_TEST(img[3][1] == 0);

            DLIB_TEST(img[0][3] == 0);
            DLIB_TEST(img[1][3] == 0);
            DLIB_TEST(img[2][3] == 0);
            DLIB_TEST(img[3][3] == 0);
            DLIB_TEST(img[0][4] == 0);
            DLIB_TEST(img[1][4] == 0);
            DLIB_TEST(img[2][4] == 0);
            DLIB_TEST(img[3][4] == 0);

            DLIB_TEST(img[0][2] == 0);
            DLIB_TEST(img[3][2] == 0);

            DLIB_TEST(img[1][2] == 1);
            DLIB_TEST(img[2][2] == 1);

            rect.right()+=1;
            assign_all_pixels(img, 1);
            zero_border_pixels(img, rect);
            DLIB_TEST(img[0][0] == 0);
            DLIB_TEST(img[1][0] == 0);
            DLIB_TEST(img[2][0] == 0);
            DLIB_TEST(img[3][0] == 0);
            DLIB_TEST(img[0][1] == 0);
            DLIB_TEST(img[1][1] == 0);
            DLIB_TEST(img[2][1] == 0);
            DLIB_TEST(img[3][1] == 0);

            DLIB_TEST(img[0][3] == 0);
            DLIB_TEST(img[1][3] == 1);
            DLIB_TEST(img[2][3] == 1);
            DLIB_TEST(img[3][3] == 0);
            DLIB_TEST(img[0][4] == 0);
            DLIB_TEST(img[1][4] == 0);
            DLIB_TEST(img[2][4] == 0);
            DLIB_TEST(img[3][4] == 0);

            DLIB_TEST(img[0][2] == 0);
            DLIB_TEST(img[3][2] == 0);

            DLIB_TEST(img[1][2] == 1);
            DLIB_TEST(img[2][2] == 1);
        }

        void test_label_connected_blobs()
        {
            array2d<unsigned char> img;
            img.set_size(400,401);

            assign_all_pixels(img,0);

            rectangle rect1, rect2, rect3;

            rect1 = centered_rect(99,120, 50,70);
            rect2 = centered_rect(199,80, 34,68);
            rect3 = centered_rect(249,180, 120,78);

            fill_rect(img, rect1, 255);
            fill_rect(img, rect2, 255);
            fill_rect(img, rect3, 255);

            array2d<unsigned char> labels;
            unsigned long num;
            num = label_connected_blobs(img,
                                        zero_pixels_are_background(),
                                        neighbors_8(),
                                        connected_if_both_not_zero(),
                                        labels);

            DLIB_TEST(num == 4);
            DLIB_TEST(labels.nr() == img.nr());
            DLIB_TEST(labels.nc() == img.nc());

            const unsigned char l1 = labels[rect1.top()][rect1.left()];
            const unsigned char l2 = labels[rect2.top()][rect2.left()];
            const unsigned char l3 = labels[rect3.top()][rect3.left()];

            DLIB_TEST(l1 != 0 && l2 != 0 && l3 != 0);
            DLIB_TEST(l1 != l2 && l1 != l3 && l2 != l3);

            for (long r = 0; r < labels.nr(); ++r)
            {
                for (long c = 0; c < labels.nc(); ++c)
                {
                    if (rect1.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l1);
                    }
                    else if (rect2.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l2);
                    }
                    else if (rect3.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l3);
                    }
                    else
                    {
                        DLIB_TEST(labels[r][c] == 0);
                    }
                }
            }
        }

        void test_label_connected_blobs2()
        {
            array2d<unsigned char> img;
            img.set_size(400,401);

            assign_all_pixels(img,0);

            rectangle rect1, rect2, rect3;

            rect1 = centered_rect(99,120, 50,70);
            rect2 = centered_rect(199,80, 34,68);
            rect3 = centered_rect(249,180, 120,78);

            fill_rect(img, rect1, 255);
            fill_rect(img, rect2, 253);
            fill_rect(img, rect3, 255);

            array2d<unsigned char> labels;
            unsigned long num;
            num = label_connected_blobs(img,
                                        nothing_is_background(),
                                        neighbors_4(),
                                        connected_if_equal(),
                                        labels);

            DLIB_TEST(num == 5);
            DLIB_TEST(labels.nr() == img.nr());
            DLIB_TEST(labels.nc() == img.nc());

            const unsigned char l0 = labels[0][0];
            const unsigned char l1 = labels[rect1.top()][rect1.left()];
            const unsigned char l2 = labels[rect2.top()][rect2.left()];
            const unsigned char l3 = labels[rect3.top()][rect3.left()];

            DLIB_TEST(l0 != 0 && l1 != 0 && l2 != 0 && l3 != 0);
            DLIB_TEST(l1 != l2 && l1 != l3 && l2 != l3 &&
                      l0 != l1 && l0 != l2 && l0 != l3);

            for (long r = 0; r < labels.nr(); ++r)
            {
                for (long c = 0; c < labels.nc(); ++c)
                {
                    if (rect1.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l1);
                    }
                    else if (rect2.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l2);
                    }
                    else if (rect3.contains(c,r))
                    {
                        DLIB_TEST(labels[r][c] == l3);
                    }
                    else
                    {
                        DLIB_TEST(labels[r][c] == l0);
                    }
                }
            }
        }

    // ----------------------------------------------------------------------------------------

        template <
            typename in_image_type,
            typename out_image_type
            >
        void downsample_image (
            const unsigned long downsample,
            const in_image_type& in_img,
            out_image_type& out_img,
            bool add_to
        )
        {
            out_img.set_size((in_img.nr()+downsample-1)/downsample,
                             (in_img.nc()+downsample-1)/downsample);

            for (long r = 0; r < out_img.nr(); ++r)
            {
                for (long c = 0; c < out_img.nc(); ++c)
                {
                    if (add_to)
                        out_img[r][c] += in_img[r*downsample][c*downsample];
                    else
                        out_img[r][c] = in_img[r*downsample][c*downsample];
                }
            }
        }

        template <
            typename in_image_type,
            typename out_image_type,
            typename EXP1,
            typename EXP2,
            typename T
            >
        void test_spatially_filter_image_separable_down_simple (
            const unsigned long downsample,
            const in_image_type& in_img,
            out_image_type& out_img,
            const matrix_exp<EXP1>& row_filter,
            const matrix_exp<EXP2>& col_filter,
            T scale,
            bool use_abs = false,
            bool add_to = false
        )
        {
            out_image_type temp;
            spatially_filter_image_separable(in_img, temp, row_filter, col_filter, scale, use_abs, false);
            downsample_image(downsample, temp, out_img, add_to);
        }

        template <unsigned long downsample>
        void test_downsampled_filtering_helper(long row_filt_size, long col_filt_size)
        {
            print_spinner();
            dlog << LTRACE << "***********************************";
            dlog << LTRACE << "downsample: " << downsample;
            dlog << LTRACE << "row_filt_size: "<< row_filt_size;
            dlog << LTRACE << "col_filt_size: "<< col_filt_size;
            dlib::rand rnd;
            array2d<int> out1, out2;
            for (long nr = 0; nr < 3; ++nr)
            {
                for (long nc = 0; nc < 3; ++nc)
                {
                    dlog << LTRACE << "nr: "<< nr;
                    dlog << LTRACE << "nc: "<< nc;
                    array2d<unsigned char> img(25+nr,25+nc);
                    for (int k = 0; k < 5; ++k)
                    {
                        for (long r = 0; r < img.nr(); ++r)
                        {
                            for (long c = 0; c < img.nc(); ++c)
                            {
                                img[r][c] = rnd.get_random_8bit_number();
                            }
                        }

                        matrix<int,0,1> row_filter(row_filt_size);
                        matrix<int,0,1> col_filter(col_filt_size);

                        row_filter = matrix_cast<int>(10*randm(row_filt_size,1, rnd));
                        col_filter = matrix_cast<int>(10*randm(col_filt_size,1, rnd));

                        row_filter -= 3;
                        col_filter -= 3;

                        test_spatially_filter_image_separable_down_simple(downsample, img, out1, row_filter, col_filter,1 );
                        spatially_filter_image_separable_down(downsample, img, out2, row_filter, col_filter);

                        DLIB_TEST(get_rect(out1) == get_rect(out2));
                        DLIB_TEST(mat(out1) == mat(out2));

                        test_spatially_filter_image_separable_down_simple(downsample, img, out1, row_filter, col_filter,3, true, true );
                        spatially_filter_image_separable_down(downsample, img, out2, row_filter, col_filter, 3, true, true);

                        DLIB_TEST(get_rect(out1) == get_rect(out2));
                        DLIB_TEST(mat(out1) == mat(out2));

                    }
                }
            }
        }

        void test_downsampled_filtering()
        {
            test_downsampled_filtering_helper<1>(5,5);
            test_downsampled_filtering_helper<2>(5,5);
            test_downsampled_filtering_helper<3>(5,5);
            test_downsampled_filtering_helper<1>(3,5);
            test_downsampled_filtering_helper<2>(3,5);
            test_downsampled_filtering_helper<3>(3,5);
            test_downsampled_filtering_helper<1>(5,3);
            test_downsampled_filtering_helper<2>(5,3);
            test_downsampled_filtering_helper<3>(5,3);

            test_downsampled_filtering_helper<1>(3,3);
            test_downsampled_filtering_helper<2>(3,3);
            test_downsampled_filtering_helper<3>(3,3);

            test_downsampled_filtering_helper<1>(1,1);
            test_downsampled_filtering_helper<2>(1,1);
            test_downsampled_filtering_helper<3>(1,1);

        }

    // ----------------------------------------------------------------------------------------

        template <typename T>
        void test_segment_image()
        {
            print_spinner();
            array2d<T> img(100,100);
            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    if (c < 50 || r < 50)
                        assign_pixel(img[r][c], 0);
                    else
                        assign_pixel(img[r][c], 255);
                }
            }

            array2d<unsigned long> out;
            segment_image(img, out);

            DLIB_TEST(get_rect(img) == get_rect(out));
            const unsigned long v1 = out[0][0];
            const unsigned long v2 = out[90][90];

            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    if (c < 50 || r < 50)
                    {
                        DLIB_TEST(out[r][c] == v1);
                    }
                    else
                    {
                        DLIB_TEST(out[r][c] == v2);
                    }
                }
            }
        }

    // ----------------------------------------------------------------------------------------

        template <typename T>
        void test_dng_floats(double scale)
        {
            dlog << LINFO << "in test_dng_floats";
            print_spinner();
            array2d<T> img(100,101);

            dlib::rand rnd;
            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    T val = rnd.get_random_double()*scale;
                    img[r][c] = val;

                    // Lets the float_details object while we are here doing this stuff.
                    float_details temp = val;
                    T val2 = temp;
                    // for the same type we should exactly reproduce the value (unless
                    // it's long double and then maybe it's slightly different).
                    if (is_same_type<T,long double>::value)
                    {
                        DLIB_TEST(std::abs(val2-val) < scale*std::numeric_limits<T>::epsilon());
                    }
                    else
                    {
                        DLIB_TEST(val2 == val);
                    }

                    float valf = temp;
                    double vald = temp;
                    long double vall = temp;

                    DLIB_TEST(std::abs(valf-val) < scale*std::numeric_limits<float>::epsilon());
                    DLIB_TEST(std::abs(vald-val) < scale*std::numeric_limits<double>::epsilon());
                    DLIB_TEST(std::abs(vall-val) < scale*std::numeric_limits<long double>::epsilon());
                }
            }

            ostringstream sout;
            save_dng(img, sout);
            istringstream sin;

            array2d<float> img1;
            array2d<double> img2;
            array2d<long double> img3;

            sin.clear(); sin.str(sout.str());
            load_dng(img1, sin);

            sin.clear(); sin.str(sout.str());
            load_dng(img2, sin);

            sin.clear(); sin.str(sout.str());
            load_dng(img3, sin);

            DLIB_TEST(img.nr() == img1.nr());
            DLIB_TEST(img.nr() == img2.nr());
            DLIB_TEST(img.nr() == img3.nr());
            DLIB_TEST(img.nc() == img1.nc());
            DLIB_TEST(img.nc() == img2.nc());
            DLIB_TEST(img.nc() == img3.nc());

            DLIB_TEST(max(abs(mat(img) - matrix_cast<T>(mat(img1)))) < scale*std::numeric_limits<float>::epsilon());
            DLIB_TEST(max(abs(mat(img) - matrix_cast<T>(mat(img2)))) < scale*std::numeric_limits<double>::epsilon());
            DLIB_TEST(max(abs(mat(img) - matrix_cast<T>(mat(img3)))) < scale*std::numeric_limits<long double>::epsilon());
        }

        void test_dng_float_int()
        {
            dlog << LINFO << "in test_dng_float_int";
            print_spinner();

            array2d<uint16> img;
            assign_image(img, gaussian_randm(101,100)*10000);

            ostringstream sout;
            save_dng(img, sout);
            istringstream sin(sout.str());
            array2d<double> img2;
            load_dng(img2, sin);
            sout.clear(); sout.str("");

            save_dng(img2, sout);
            sin.clear(); sin.str(sout.str());
            array2d<uint16> img3;
            load_dng(img3, sin);

            // this whole thing should have been totally lossless.
            DLIB_TEST(mat(img) == mat(img3));
        }

    // ----------------------------------------------------------------------------------------

        template <typename T>
        void test_filtering_center (
            dlib::rand& rnd
        )
        {
            array2d<T> img(rnd.get_random_32bit_number()%100+1,
                rnd.get_random_32bit_number()%100+1);
            matrix<T> filt(rnd.get_random_32bit_number()%10+1,
                rnd.get_random_32bit_number()%10+1);

            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    img[r][c] = rnd.get_random_32bit_number()%100;
                }
            }
            for (long r = 0; r < filt.nr(); ++r)
            {
                for (long c = 0; c < filt.nc(); ++c)
                {
                    filt(r,c) = rnd.get_random_32bit_number()%100;
                }
            }

            array2d<T> out;
            const rectangle area = spatially_filter_image(img, out, filt);

            for (long r = 0; r < out.nr(); ++r)
            {
                for (long c = 0; c < out.nc(); ++c)
                {
                    const rectangle rect = centered_rect(point(c,r), filt.nc(), filt.nr());
                    if (get_rect(out).contains(rect))
                    {
                        T val = sum(pointwise_multiply(filt, subm(mat(img),rect)));
                        DLIB_TEST_MSG(val == out[r][c],"err: " << val-out[r][c]);
                        DLIB_TEST(area.contains(point(c,r)));
                    }
                    else
                    {
                        DLIB_TEST(!area.contains(point(c,r)));
                    }
                }
            }
        }

        template <typename T>
        void test_separable_filtering_center (
            dlib::rand& rnd
        )
        {
            array2d<T> img(rnd.get_random_32bit_number()%100+1,
                rnd.get_random_32bit_number()%100+1);
            matrix<T,1,0> row_filt(rnd.get_random_32bit_number()%10+1);
            matrix<T,0,1> col_filt(rnd.get_random_32bit_number()%10+1);

            for (long r = 0; r < img.nr(); ++r)
            {
                for (long c = 0; c < img.nc(); ++c)
                {
                    img[r][c] = rnd.get_random_32bit_number()%10;
                }
            }
            for (long r = 0; r < row_filt.size(); ++r)
            {
                row_filt(r) = rnd.get_random_32bit_number()%10;
            }
            for (long r = 0; r < col_filt.size(); ++r)
            {
                col_filt(r) = rnd.get_random_32bit_number()%10;
            }

            array2d<T> out;
            const rectangle area = spatially_filter_image_separable(img, out, row_filt, col_filt);

            for (long r = 0; r < out.nr(); ++r)
            {
                for (long c = 0; c < out.nc(); ++c)
                {
                    const rectangle rect = centered_rect(point(c,r), row_filt.size(), col_filt.size());
                    if (get_rect(out).contains(rect))
                    {
                        T val = sum(pointwise_multiply(col_filt*row_filt, subm(mat(img),rect)));
                        DLIB_TEST_MSG(val == out[r][c],"err: " << val-out[r][c]);

                        DLIB_TEST(area.contains(point(c,r)));
                    }
                    else
                    {
                        DLIB_TEST(!area.contains(point(c,r)));
                    }
                }
            }
        }

    // ----------------------------------------------------------------------------------------

        void run_hough_test()
        {
            array2d<unsigned char> img(300,300);

            for (int k = -2; k <= 2; ++k)
            {
                print_spinner();
                running_stats<double> rs;
                array2d<int> himg;
                hough_transform ht(200+k);
                double angle1 = 0;
                double angle2 = 0;
                const int len = 90;
                // Draw a bunch of random lines, hough transform them, then make sure the hough
                // transform detects them accurately.
                for (int i = 0; i < 500; ++i)
                {
                    point cent = center(get_rect(img));
                    point arc = cent + point(len,0);
                    arc = rotate_point(cent, arc, angle1);

                    point l = arc + point(500,0);
                    point r = arc - point(500,0);
                    l = rotate_point(arc, l, angle2);
                    r = rotate_point(arc, r, angle2);

                    angle1 += pi/13;
                    angle2 += pi/40;

                    assign_all_pixels(img, 0);
                    draw_line(img, l, r, 255);
                    rectangle box = translate_rect(get_rect(ht),point(50,50));
                    ht(img, box, himg);

                    point p = max_point(mat(himg));
                    DLIB_TEST(himg[p.y()][p.x()] > 255*3);

                    l -= point(50,50);
                    r -= point(50,50);
                    std::pair<point,point> line = ht.get_line(p);
                    // make sure the best scoring hough point matches the line we drew.
                    double dist1 = distance_to_line(make_pair(l,r), line.first);
                    double dist2 = distance_to_line(make_pair(l,r), line.second);
                    //cout << "DIST1: " << dist1 << endl;
                    //cout << "DIST2: " << dist2 << endl;
                    rs.add(dist1);
                    rs.add(dist2);
                    DLIB_TEST(dist1 < 2.5);
                    DLIB_TEST(dist2 < 2.5);
                }
                //cout << "rs.mean(): " << rs.mean() << endl;
                DLIB_TEST(rs.mean() < 0.7);
            }
        }

    // ----------------------------------------------------------------------------------------

        void test_extract_image_chips()
        {
            dlib::rand rnd;

            // Make sure that cropping a white box out of a larger white image always produces an
            // exact white box.  This should catch any bad border effects from a messed up internal
            // cropping.
            for (int iter = 0; iter < 1000; ++iter)
            {
                print_spinner();
                const long nr = rnd.get_random_32bit_number()%100 + 1;
                const long nc = rnd.get_random_32bit_number()%100 + 1;
                const long size = rnd.get_random_32bit_number()%10000 + 4;
                const double angle = rnd.get_random_double() * pi;

                matrix<int> img(501,501), chip;
                img = 255;
                chip_details details(centered_rect(center(get_rect(img)),nr,nc), size, angle);
                extract_image_chip(img, details, chip);
                DLIB_TEST_MSG(max(abs(chip-255))==0,"nr: " << nr << "  nc: "<< nc << "  size: " << size << "  angle: " << angle
                    << " error: " << max(abs(chip-255)) );
            }

            {
                // Make sure that the interpolation in extract_image_chip() keeps stuff in the
                // right places.

                matrix<unsigned char> img(10,10), chip;
                img = 0;
                img(1,1) = 255;
                img(8,8) = 255;

                extract_image_chip(img, chip_details(get_rect(img), 9*9), chip);

                DLIB_TEST(chip(1,1) == 195);
                DLIB_TEST(chip(7,7) == 195);
                chip(1,1) -= 195;
                chip(7,7) -= 195;
                DLIB_TEST(sum(matrix_cast<int>(chip)) == 0);
            }

            // Test the rotation ability of extract_image_chip().  Do this by drawing a line and
            // then rotating it so it's horizontal.  Check that it worked correctly by hough
            // transforming it.
            hough_transform ht(151);
            matrix<unsigned char> img(300,300);
            for (int iter = 0; iter < 1000; ++iter)
            {
                print_spinner();
                img = 0;
                const int len = 9000;
                point cent = center(get_rect(img));
                point l = cent + point(len,0);
                point r = cent - point(len,0);
                const double angle = rnd.get_random_double()*pi*3;
                l = rotate_point(cent, l, angle);
                r = rotate_point(cent, r, angle);
                draw_line(img, l, r, 255);

                const long wsize = rnd.get_random_32bit_number()%350 + 150;

                matrix<unsigned char> temp;
                chip_details details(centered_rect(center(get_rect(img)), wsize,wsize),  chip_dims(ht.size(),ht.size()), angle);
                extract_image_chip(img, details, temp);

                matrix<long> tform;
                ht(temp, get_rect(temp), tform);
                std::pair<point,point> line = ht.get_line(max_point(tform));

                DLIB_TEST_MSG(line.first.y() == line.second.y()," wsize: " << wsize);
                DLIB_TEST(length(line.first-line.second) > 100);
                DLIB_TEST(length((line.first+line.second)/2.0 - center(get_rect(temp))) <= 1);
            }

        }

    // ----------------------------------------------------------------------------------------

        class image_tester : public tester
        {
        public:
            image_tester (
            ) :
                tester ("test_image",
                        "Runs tests on the image processing objects and functions.")
            {}

            void perform_test (
            )
            {
                image_test();
                run_hough_test();
                test_extract_image_chips();
                test_integral_image<long, unsigned char>();
                test_integral_image<double, int>();
                test_integral_image<long, unsigned char>();
                test_integral_image<double, float>();

                test_zero_border_pixels();

                test_filtering<unsigned char>(false,1);
                test_filtering<unsigned char>(true,1);
                test_filtering<unsigned char>(false,3);
                test_filtering<unsigned char>(true,3);
                test_filtering<int>(false,1);
                test_filtering<int>(true,1);
                test_filtering<int>(false,3);
                test_filtering<int>(true,3);

                test_label_connected_blobs();
                test_label_connected_blobs2();
                test_downsampled_filtering();

                test_segment_image<unsigned char>();
                test_segment_image<unsigned short>();
                test_segment_image<double>();
                test_segment_image<int>();
                test_segment_image<rgb_pixel>();
                test_segment_image<rgb_alpha_pixel>();

                test_dng_floats<float>(1);
                test_dng_floats<double>(1);
                test_dng_floats<long double>(1);
                test_dng_floats<float>(1e30);
                test_dng_floats<double>(1e30);
                test_dng_floats<long double>(1e30);

                test_dng_float_int();

                dlib::rand rnd;
                for (int i = 0; i < 10; ++i)
                {
                    // the spatial filtering stuff is the same as xcorr_same when the filter
                    // sizes are odd.
                    test_filtering2(3,3,rnd);
                    test_filtering2(5,5,rnd);
                    test_filtering2(7,7,rnd);
                }

                for (int i = 0; i < 100; ++i)
                    test_filtering_center<float>(rnd);
                for (int i = 0; i < 100; ++i)
                    test_filtering_center<int>(rnd);
                for (int i = 0; i < 100; ++i)
                    test_separable_filtering_center<int>(rnd);
                for (int i = 0; i < 100; ++i)
                    test_separable_filtering_center<float>(rnd);

                {
                    print_spinner();
                    matrix<unsigned char> img(40,80);
                    assign_all_pixels(img, 255);
                    skeleton(img);

                    DLIB_TEST(sum(matrix_cast<int>(mat(img)))/255 == 40);
                    draw_line(img, point(20,19), point(59,19), 00);
                    DLIB_TEST(sum(matrix_cast<int>(mat(img))) == 0);
                }
            }
        } a;

    }