Es++ Class: JPGFileReader

 Es++ Class Library  Es++ Samples 

Source code

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 *  JPGFileReader.h
 *
 *****************************************************************************/


#pragma once

// See https://github.com/LuaDist/libjpeg/blob/master/example.c

#include <es++/JPGFile.h>

namespace Es {

class JPGFileReader :public JPGFile {
private:

  struct jpeg_decompress_struct cinfo;
  struct jpeg_error_mgr jerr;

  int width;
  int height;
  int depth;

  unsigned char* data;

public:
  JPGFileReader(const char* filename)
  :JPGFile(READER, filename),
  width(0),
  height(0),
  depth(0),
  data(NULL)
  {
    memset(&cinfo, 0, sizeof(cinfo));
    memset(&jerr,  0, sizeof(jerr));

    cinfo.err = jpeg_std_error(&jerr);

    jpeg_create_decompress(&cinfo);

    FILE* fp = getFP();
    jpeg_stdio_src(&cinfo,  fp);
  }

  ~JPGFileReader()
  {
    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);

    delete [] data;
    data = NULL;
  }

  int getImageWidth()
  {
    return width;
  }

  int getImageHeight()
  {
    return height;
  }

  int getDepth()
  {
    return depth;
  }

  unsigned char* getImageData()
  {
    return data;
  }

public:
  int read()
  {
    jpeg_read_header(&cinfo, TRUE);
    jpeg_start_decompress(&cinfo);

    width = cinfo.output_width;
    height = cinfo.output_height;
    printf("width %d height %d\n", width, height);

    data = new unsigned char [width*height*4];
    unsigned char* ptr = data;

    int row_stride = width * cinfo.output_components ;
    JSAMPARRAY pJpegBuffer = 
       (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, 
                   JPOOL_IMAGE, row_stride, 1);

    while (cinfo.output_scanline < cinfo.output_height) {
      unsigned char a,r,g,b;

      jpeg_read_scanlines(&cinfo, pJpegBuffer, 1);
      for (int x=0; x < width; x++) {
        a = 0; 
        r = pJpegBuffer[0][cinfo.output_components*x];

        if (cinfo.output_components>2) {
          g = pJpegBuffer[0][cinfo.output_components*x+1];
          b = pJpegBuffer[0][cinfo.output_components*x+2];
        } else {
          g = r;
          b = r;
        }
       *(ptr++) = b;
       *(ptr++) = g;
       *(ptr++) = r;
       *(ptr++) = a;
     }
   }

   depth = 32;
   return 0;
  }
};

}
 

Last modified: 27 July 2017

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