dlib C++ Library - save_png.h

    // Copyright (C) 2011  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_SAVE_PnG_Hh_
    #define DLIB_SAVE_PnG_Hh_

    #include <vector>
    #include <string>
    #include <fstream>
    #include <functional>
    #include "save_png_abstract.h"
    #include "image_saver.h"
    #include "../array2d.h"
    #include "../pixel.h"
    #include "../matrix/matrix_exp.h"
    #include "../image_transforms/assign_image.h"

    namespace dlib
    {

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

        namespace impl
        {
            enum png_type
            {
                png_type_rgb,
                png_type_rgb_alpha,
                png_type_gray,
            };

            void impl_save_png (
                std::function<void(const char*, std::size_t)> clb,
                std::vector<unsigned char*>& row_pointers,
                const long width,
                const png_type type,
                const int bit_depth,
                const bool swap_rgb = false
            );

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

            template <
              class image_type
            >
            void save_png(
                const image_type& img_,
                std::function<void(const char*, std::size_t)> clb
            )
            {
                const_image_view<image_type> img(img_);

                // make sure requires clause is not broken
                DLIB_CASSERT(img.size() != 0,
                    "\t save_png()"
                    << "\n\t You can't save an empty image as a PNG"
                    );

    #ifndef DLIB_PNG_SUPPORT
                    /* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                        You are getting this error because you are trying to use save_png()
                        but you haven't defined DLIB_PNG_SUPPORT.  You must do so to use
                        this function.   You must also make sure you set your build environment
                        to link against the libpng library.
                    !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!*/
                    COMPILE_TIME_ASSERT(sizeof(image_type) == 0);
    #else
                std::vector<unsigned char*> row_pointers(img.nr());
                using pixel_type = pixel_type_t<image_type>;

                if (std::is_same<rgb_pixel,pixel_type>::value)
                {
                    for (unsigned long i = 0; i < row_pointers.size(); ++i)
                        row_pointers[i] = (unsigned char*)(&img[i][0]);

                    impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_rgb, 8);
                }
                else if (std::is_same<bgr_pixel,pixel_type>::value)
                {
                    for (unsigned long i = 0; i < row_pointers.size(); ++i)
                        row_pointers[i] = (unsigned char*)(&img[i][0]);

                    impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_rgb, 8, true);
                }
                else if (std::is_same<rgb_alpha_pixel,pixel_type>::value)
                {
                    for (unsigned long i = 0; i < row_pointers.size(); ++i)
                        row_pointers[i] = (unsigned char*)(&img[i][0]);

                    impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_rgb_alpha, 8);
                }
                else if (pixel_traits<pixel_type>::lab || pixel_traits<pixel_type>::hsi || pixel_traits<pixel_type>::rgb)
                {
                    // convert from Lab or HSI to RGB (Or potentially RGB pixels that aren't laid out as R G B)
                    array2d<rgb_pixel> temp_img;
                    assign_image(temp_img, img_);
                    for (unsigned long i = 0; i < row_pointers.size(); ++i)
                        row_pointers[i] = (unsigned char*)(&temp_img[i][0]);

                    impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_rgb, 8);
                }
                else if (pixel_traits<pixel_type>::rgb_alpha)
                {
                    // convert from RGBA pixels that aren't laid out as R G B A
                    array2d<rgb_alpha_pixel> temp_img;
                    assign_image(temp_img, img_);
                    for (unsigned long i = 0; i < row_pointers.size(); ++i)
                        row_pointers[i] = (unsigned char*)(&temp_img[i][0]);

                    impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_rgb_alpha, 8);
                }
                else // this is supposed to be grayscale
                {
                    DLIB_CASSERT(pixel_traits<pixel_type>::grayscale, "impossible condition detected");

                    if (pixel_traits<pixel_type>::is_unsigned && sizeof(pixel_type) == 1)
                    {
                        for (unsigned long i = 0; i < row_pointers.size(); ++i)
                            row_pointers[i] = (unsigned char*)(&img[i][0]);

                        impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_gray, 8);
                    }
                    else if (pixel_traits<pixel_type>::is_unsigned && sizeof(pixel_type) == 2)
                    {
                        for (unsigned long i = 0; i < row_pointers.size(); ++i)
                            row_pointers[i] = (unsigned char*)(&img[i][0]);

                        impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_gray, 16);
                    }
                    else
                    {
                        // convert from whatever this is to 16bit grayscale
                        array2d<dlib::uint16> temp_img;
                        assign_image(temp_img, img_);
                        for (unsigned long i = 0; i < row_pointers.size(); ++i)
                            row_pointers[i] = (unsigned char*)(&temp_img[i][0]);

                        impl::impl_save_png(std::move(clb), row_pointers, img.nc(), impl::png_type_gray, 16);
                    }
                }
    #endif
            }
        }

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

        template <
          class image_type
        >
        void save_png (
            const image_type& img,
            std::ostream& out
        )
        {
            impl::save_png (
                img,
                [&out](const char* data, std::size_t ndata) {
                    out.write(data, ndata);
                }
            );
        }

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

        template <
          class image_type
        >
        void save_png (
            const image_type& img,
            const std::string& file_name
        )
        {
            std::ofstream out(file_name, std::ios::binary);
            save_png(img, out);
        }

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

        template <
          class image_type,
          class Byte,
          class Alloc
        >
        void save_png (
            const image_type& img,
            std::vector<Byte, Alloc>& buf
        )
        {
            static_assert(is_byte<Byte>::value, "Byte must be char, int8_t or uint8_t");
            impl::save_png (
                img,
                [&buf](const char* data, std::size_t ndata) {
                    buf.insert(end(buf), data, data + ndata);
                }
            );
        }

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

        template <
          class T, long NR, long NC, class MM, class L,
          class Output
        >
        void save_png (
            const matrix<T,NR,NC,MM,L>& img,
            Output&& out
        )
        {
            save_png(make_image_view(img), std::forward<Output>(out));
        }

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

        template <
          class EXP,
          class Output
        >
        void save_png (
            const matrix_exp<EXP>& img,
            Output&& out
        )
        {
            array2d<typename EXP::type> temp;
            assign_image(temp, img);
            save_png(temp, std::forward<Output>(out));
        }

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

    }

    #ifdef NO_MAKEFILE
    #include "save_png.cpp"
    #endif

    #endif // DLIB_SAVE_PnG_Hh_