saving rgb char* into jpeg image using libjpeg

0
votes

I am trying to save an rgb bytearray into a jpg file.

I followed instructions in this page and here is my code

//rgb is the image
//rgb->imageData is char* to the rgb data
//rgb->imageSize is the image size which is 640*480*3

struct jpeg_compress_struct cinfo;
  struct jpeg_error_mgr jerr;

  /* this is a pointer to one row of image data */
  FILE *outfile = fopen( "file.jpeg", "wb" );

  cinfo.err = jpeg_std_error( &jerr );
  jpeg_create_compress(&cinfo);
  jpeg_stdio_dest(&cinfo, outfile);

  /* Setting the parameters of the output file here */
  cinfo.image_width = 640;//width;
  cinfo.image_height = 480;//height;
  cinfo.input_components = 3;
  cinfo.in_color_space = JCS_RGB;

  jpeg_set_defaults( &cinfo );
  /* Now do the compression .. */
  jpeg_start_compress( &cinfo, TRUE );

  JSAMPROW buffer;
  for(int i=0;i<rgb->imageSize;i+=640)
  {
      memcpy(buffer,
             (JSAMPROW)rgb->imageData+i,
             640);//segmentation fault here
      jpeg_write_scanlines( &cinfo, &buffer, 1 );
  }
  jpeg_finish_compress( &cinfo );
  jpeg_destroy_compress( &cinfo );
  fclose( outfile );

I am getting a segmentation fault, and when trying buffer = rgb->image data i got a libjpeg error that too much scanlines and nothing is written into the file, what is wrong with my code ??

I can find a bunch of libjpeg examples online but I can't find memory to memory (char* to char*) example.

I have a secondary question: I have a very optimized YUV to rgb function , is it good to convert YUV(more compressed) image into RGB (not compressed) and then convert RGB to jpeg ?? or only use YUV to Jpeg in libjpeg ??

2
cjpegrgbdecodelibjpeg

2 Answers

0
votes

How is the type JSAMPROW declared?. Try this:

memcpy(&buffer, (JSAMPROW)rgb->imageData+i, 640);
0
votes

try this instead of for loop:



    while (cinfo.next_scanline < cinfo.image_height) {
        JSAMPLE *row = rgb->imageData + 3 * cinfo.image_width * cinfo.next_scanline;
        jpeg_write_scanlines(&cinfo, &row, 1);
    }