dlib C++ Library - jpeg_loader.cpp

    // Copyright (C) 2010  Davis E. King (davis@dlib.net), Nils Labugt
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_JPEG_LOADER_CPp_
    #define DLIB_JPEG_LOADER_CPp_

    // only do anything with this file if DLIB_JPEG_SUPPORT is defined
    #ifdef DLIB_JPEG_SUPPORT

    #include "../array2d.h"
    #include "../pixel.h"
    #include "../dir_nav.h"
    #include "jpeg_loader.h"
    #include <stdio.h>
    #ifdef DLIB_JPEG_STATIC
    #   include "../external/libjpeg/jpeglib.h"
    #else
    #   include <jpeglib.h>
    #endif
    #include <sstream>
    #include <setjmp.h>

    namespace dlib
    {

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

        jpeg_loader::
        jpeg_loader( const char* filename ) : height_( 0 ), width_( 0 ), output_components_(0)
        {
            read_image( check_file( filename ), NULL, 0L );
        }

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

        jpeg_loader::
        jpeg_loader( const std::string& filename ) : height_( 0 ), width_( 0 ), output_components_(0)
        {
            read_image( check_file( filename.c_str() ), NULL, 0L );
        }

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

        jpeg_loader::
        jpeg_loader( const dlib::file& f ) : height_( 0 ), width_( 0 ), output_components_(0)
        {
            read_image( check_file( f.full_name().c_str() ), NULL, 0L );
        }

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

        jpeg_loader::
        jpeg_loader( const unsigned char* imgbuffer, size_t imgbuffersize ) : height_( 0 ), width_( 0 ), output_components_(0)
        {
            read_image( NULL, imgbuffer, imgbuffersize );
        }

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

        bool jpeg_loader::is_gray() const
        {
            return (output_components_ == 1);
        }

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

        bool jpeg_loader::is_rgb() const
        {
            return (output_components_ == 3);
        }

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

        bool jpeg_loader::is_rgba() const
        {
            return (output_components_ == 4);
        }

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

        long jpeg_loader::nr() const
        {
            return static_cast<long>(height_);
        }

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

        long jpeg_loader::nc() const
        {
            return static_cast<long>(width_);
        }

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

        struct jpeg_loader_error_mgr
        {
            jpeg_error_mgr pub;    /* "public" fields */
            jmp_buf setjmp_buffer;  /* for return to caller */
            char jpegLastErrorMsg[JMSG_LENGTH_MAX];
        };

        void jpeg_loader_error_exit (j_common_ptr cinfo)
        {
            /* cinfo->err really points to a jpeg_loader_error_mgr struct, so coerce pointer */
            jpeg_loader_error_mgr* myerr = (jpeg_loader_error_mgr*) cinfo->err;

            /* Create the message */
            ( *( cinfo->err->format_message ) ) ( cinfo, myerr->jpegLastErrorMsg );

            /* Return control to the setjmp point */
            longjmp(myerr->setjmp_buffer, 1);
        }

    // ----------------------------------------------------------------------------------------
        FILE * jpeg_loader::check_file( const char* filename )
        {
          if ( filename == NULL )
          {
              throw image_load_error("jpeg_loader: invalid filename, it is NULL");
          }
          FILE *fp = fopen( filename, "rb" );
          if ( !fp )
          {
              throw image_load_error(std::string("jpeg_loader: unable to open file ") + filename);
          }
          return fp;
        }

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

        void jpeg_loader::read_image( FILE * file, const unsigned char* imgbuffer, size_t imgbuffersize )
        {

            jpeg_decompress_struct cinfo;
            jpeg_loader_error_mgr jerr;

            cinfo.err = jpeg_std_error(&jerr.pub);

            jerr.pub.error_exit = jpeg_loader_error_exit;

            /* Establish the setjmp return context for my_error_exit to use. */
            if (setjmp(jerr.setjmp_buffer))
            {
                /* If we get here, the JPEG code has signaled an error.
                 * We need to clean up the JPEG object, and return.
                 */
                jpeg_destroy_decompress(&cinfo);
                if (file != NULL) fclose(file);
                throw image_load_error(std::string("jpeg_loader: error while loading image: ") + jerr.jpegLastErrorMsg);
            }

            jpeg_create_decompress(&cinfo);

            if (file != NULL) jpeg_stdio_src(&cinfo, file);
            else if (imgbuffer != NULL) jpeg_mem_src(&cinfo, (unsigned char*)imgbuffer, imgbuffersize);
            else throw image_load_error(std::string("jpeg_loader: no valid image source"));

            jpeg_read_header(&cinfo, TRUE);

            jpeg_start_decompress(&cinfo);

            height_ = cinfo.output_height;
            width_ = cinfo.output_width;
            output_components_ = cinfo.output_components;

            if (output_components_ != 1 &&
                output_components_ != 3 &&
                output_components_ != 4)
            {
                if (file != NULL) fclose(file);
                jpeg_destroy_decompress(&cinfo);
                std::ostringstream sout;
                sout << "jpeg_loader: Unsupported number of colors (" << output_components_ << ") in image";
                throw image_load_error(sout.str());
            }

            std::vector<unsigned char*> rows;
            rows.resize(height_);

            // size the image buffer
            data.resize(height_*width_*output_components_);

            // setup pointers to each row
            for (size_t i = 0; i < rows.size(); ++i)
                rows[i] = &data[i*width_*output_components_];

            // read the data into the buffer
            while (cinfo.output_scanline < cinfo.output_height)
            {
                jpeg_read_scanlines(&cinfo, &rows[cinfo.output_scanline], 100);
            }

            jpeg_finish_decompress(&cinfo);
            jpeg_destroy_decompress(&cinfo);

            if (file != NULL) fclose(file);
        }

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

    }

    #endif // DLIB_JPEG_SUPPORT

    #endif // DLIB_JPEG_LOADER_CPp_