# dlib C++ Library - load_image.h

    // Copyright (C) 2011  Davis E. King (davis@dlib.net), Nils Labugt, Changjiang Yang (yangcha@leidos.com)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_LOAd_IMAGE_Hh_
    #define DLIB_LOAd_IMAGE_Hh_

    #include "load_image_abstract.h"
    #include "../string.h"
    #include "png_loader.h"
    #include "jpeg_loader.h"
    #include "webp_loader.h"
    #include "image_loader.h"
    #include <fstream>
    #include <sstream>
    #ifdef DLIB_GIF_SUPPORT
    #include <gif_lib.h>
    #endif

    namespace dlib
    {
        namespace image_file_type
        {
            enum type
            {
                BMP,
                JPG,
                PNG,
                DNG,
                GIF,
                WEBP,
                UNKNOWN
            };

            inline type read_type(const std::string& file_name)
            {
                std::ifstream file(file_name.c_str(), std::ios::in|std::ios::binary);
                if (!file)
                    throw image_load_error("Unable to open file: " + file_name);

                char buffer[13];
                file.read((char*)buffer, 12);
                buffer[12] = 0;

                // Determine the true image type using link:
                // http://en.wikipedia.org/wiki/List_of_file_signatures
                static const char *pngHeader = "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A";

                if (memcmp(buffer, pngHeader, strlen(pngHeader)) == 0)
                    return PNG;
                else if(buffer[0]=='\xff' && buffer[1]=='\xd8' && buffer[2]=='\xff')
                    return JPG;
                else if(buffer[0]=='B' && buffer[1]=='M')
                    return BMP;
                else if(buffer[0]=='D' && buffer[1]=='N' && buffer[2] == 'G')
                    return DNG;
                else if(buffer[0]=='G' && buffer[1]=='I' && buffer[2] == 'F')
                    return GIF;
                else if(buffer[0]=='R' && buffer[1]=='I' && buffer[2] == 'F' && buffer[3] == 'F' &&
                        buffer[8]=='W' && buffer[9]=='E' && buffer[10] == 'B' && buffer[11] == 'P')
                    return WEBP;

                return UNKNOWN;
            }
        }

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

    // handle the differences in API between libgif v5 and older.
    #if defined(GIFLIB_MAJOR) && GIFLIB_MAJOR >= 5
    #define DLIB_GIFLIB_HANDLE_DIFF_VERSIONS ,0
    #else
    #define DLIB_GIFLIB_HANDLE_DIFF_VERSIONS
    #endif

        template <typename image_type>
        void load_image (
            image_type& image,
            const std::string& file_name
        )
        {
            const image_file_type::type im_type = image_file_type::read_type(file_name);
            switch (im_type)
            {
                case image_file_type::BMP: load_bmp(image, file_name); return;
                case image_file_type::DNG: load_dng(image, file_name); return;
    #ifdef DLIB_PNG_SUPPORT
                case image_file_type::PNG: load_png(image, file_name); return;
    #endif
    #ifdef DLIB_JPEG_SUPPORT
                case image_file_type::JPG: load_jpeg(image, file_name); return;
    #endif
    #ifdef DLIB_WEBP_SUPPORT
                case image_file_type::WEBP: load_webp(image, file_name); return;
    #endif
    #ifdef DLIB_GIF_SUPPORT
                case image_file_type::GIF:
                {
                    image_view<image_type> img(image);
                    GifFileType* gif = DGifOpenFileName(file_name.c_str() DLIB_GIFLIB_HANDLE_DIFF_VERSIONS);
                    try
                    {
                        if (gif == 0) throw image_load_error("Couldn't open file " + file_name);
                        if (DGifSlurp(gif) != GIF_OK)
                            throw image_load_error("Error reading from " + file_name);

                        if (gif->ImageCount != 1)   throw image_load_error("Dlib only supports reading GIF files containing one image.");
                        if (gif->SavedImages == 0)  throw image_load_error("Unsupported GIF format 1.");

                        ColorMapObject* cmo=gif->SColorMap?gif->SColorMap:gif->SavedImages->ImageDesc.ColorMap;

                        if (cmo==0)                                             throw image_load_error("Unsupported GIF format 2.");
                        if (cmo->Colors == 0)                                   throw image_load_error("Unsupported GIF format 3.");
                        if (gif->SavedImages->ImageDesc.Width != gif->SWidth)   throw image_load_error("Unsupported GIF format 4.");
                        if (gif->SavedImages->ImageDesc.Height != gif->SHeight) throw image_load_error("Unsupported GIF format 5.");
                        if (gif->SavedImages->RasterBits == 0)                  throw image_load_error("Unsupported GIF format 6.");
                        if (gif->Image.Top != 0)                                throw image_load_error("Unsupported GIF format 7.");
                        if (gif->Image.Left != 0)                               throw image_load_error("Unsupported GIF format 8.");

                        img.set_size(gif->SHeight, gif->SWidth);
                        unsigned char* raster = gif->SavedImages->RasterBits;
                        GifColorType* colormap = cmo->Colors;
                        if (gif->Image.Interlace)
                        {
                            const long interlaced_offset[] = { 0, 4, 2, 1 };
                            const long interlaced_jumps[] = { 8, 8, 4, 2 };
                            for (int i = 0; i < 4; ++i)
                            {
                                for (long r = interlaced_offset[i]; r < img.nr(); r += interlaced_jumps[i])
                                {
                                    for (long c = 0; c < img.nc(); ++c)
                                    {
                                        if (*raster >= cmo->ColorCount)
                                            throw image_load_error("Invalid GIF color value");
                                        rgb_pixel p;
                                        p.red = colormap[*raster].Red;
                                        p.green = colormap[*raster].Green;
                                        p.blue = colormap[*raster].Blue;
                                        assign_pixel(img[r][c], p);
                                        ++raster;
                                    }
                                }
                            }
                        }
                        else
                        {
                            for (long r = 0; r < img.nr(); ++r)
                            {
                                for (long c = 0; c < img.nc(); ++c)
                                {
                                    if (*raster >= cmo->ColorCount)
                                        throw image_load_error("Invalid GIF color value");
                                    rgb_pixel p;
                                    p.red = colormap[*raster].Red;
                                    p.green = colormap[*raster].Green;
                                    p.blue = colormap[*raster].Blue;
                                    assign_pixel(img[r][c], p);
                                    ++raster;
                                }
                            }
                        }
                        DGifCloseFile(gif DLIB_GIFLIB_HANDLE_DIFF_VERSIONS);
                    }
                    catch(...)
                    {
                        if (gif)
                            DGifCloseFile(gif DLIB_GIFLIB_HANDLE_DIFF_VERSIONS);
                        throw;
                    }
                    return;
                }
    #endif
                default:  ;
            }

            if (im_type == image_file_type::JPG)
            {
                std::ostringstream sout;
                sout << "Unable to load image in file " + file_name + ".\n" +
                        "You must #define DLIB_JPEG_SUPPORT and link to libjpeg to read JPEG files.\n" +
                        "Do this by following the instructions at http://dlib.net/compile.html.\n\n";
    #ifdef _MSC_VER
                sout << "Note that you must cause DLIB_JPEG_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, add it to the C/C++->Preprocessor->Preprocessor Definitions\n";
                sout << "field in Visual Studio's Property Pages window so it takes effect for your entire application.";
    #else
                sout << "Note that you must cause DLIB_JPEG_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, use a compiler switch like -DDLIB_JPEG_SUPPORT\n";
                sout << "so it takes effect for your entire application.";
    #endif
                throw image_load_error(sout.str());
            }
            else if (im_type == image_file_type::PNG)
            {
                std::ostringstream sout;
                sout << "Unable to load image in file " + file_name + ".\n" +
                        "You must #define DLIB_PNG_SUPPORT and link to libpng to read PNG files.\n" +
                        "Do this by following the instructions at http://dlib.net/compile.html.\n\n";
    #ifdef _MSC_VER
                sout << "Note that you must cause DLIB_PNG_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, add it to the C/C++->Preprocessor->Preprocessor Definitions\n";
                sout << "field in Visual Studio's Property Pages window so it takes effect for your entire application.\n";
    #else
                sout << "Note that you must cause DLIB_PNG_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, use a compiler switch like -DDLIB_PNG_SUPPORT\n";
                sout << "so it takes effect for your entire application.";
    #endif
                throw image_load_error(sout.str());
            }
            else if (im_type == image_file_type::GIF)
            {
                std::ostringstream sout;
                sout << "Unable to load image in file " + file_name + ".\n" +
                        "You must #define DLIB_GIF_SUPPORT and link to libgif to read GIF files.\n\n";
    #ifdef _MSC_VER
                sout << "Note that you must cause DLIB_GIF_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, add it to the C/C++->Preprocessor->Preprocessor Definitions\n";
                sout << "field in Visual Studio's Property Pages window so it takes effect for your entire application.\n";
    #else
                sout << "Note that you must cause DLIB_GIF_SUPPORT to be defined for your entire project.\n";
                sout << "So don't #define it in one file. Instead, use a compiler switch like -DDLIB_GIF_SUPPORT\n";
                sout << "so it takes effect for your entire application.";
    #endif
                throw image_load_error(sout.str());
            }
            else
            {
                throw image_load_error("Unknown image file format: Unable to load image in file " + file_name);
            }
        }

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

    }

    #endif // DLIB_LOAd_IMAGE_Hh_