/*********************************************************/
/*   program 7: apply flat field correction              */
/*********************************************************/

#define  XSIZE  1280
#define  YSIZE  960

short int *ff;
long  int  scale,val;
unsigned char *ir,*ig,*ib;
unsigned char *or,*og,*ob;

main()
  {
  long  int  x,y;

  /* allocate input and output memory buffers */
  ff  = (short int *) malloc (2*XSIZE*YSIZE);
  ir = (unsigned char *) malloc (XSIZE*YSIZE);
  ig = (unsigned char *) malloc (XSIZE*YSIZE);
  ib = (unsigned char *) malloc (XSIZE*YSIZE);
  or = (unsigned char *) malloc (XSIZE*YSIZE);
  og = (unsigned char *) malloc (XSIZE*YSIZE);
  ob = (unsigned char *) malloc (XSIZE*YSIZE);

  /* read the 16-bit flat field correction image */
  read_image16("ffcorrect",ff);

  /* read the uncorrected field rgb input image */
  read_image("input",ir,ig,ib);

  /* correct the rgb image */
  for (y = 0; y < YSIZE; y++)
    {
    for (x = 0; x < XSIZE; x++)
      {
      /* correct red plane */
      scale = ((long)ir[(y*XSIZE)+x] * (long)ff[(y*XSIZE)+x]) >> 12;
      val = (long)ir[(y*XSIZE)+x] - scale;
        or[(y*XSIZE)+x] = (unsigned int)val;
        if (val <   0) or[(y*XSIZE)+x] = 0;
        if (val > 255) or[(y*XSIZE)+x] = 255;

      /* correct green plane */
      scale = ((long)ig[(y*XSIZE)+x] * (long)ff[(y*XSIZE)+x]) >> 12;
      val = (long)ig[(y*XSIZE)+x] - scale;
        og[(y*XSIZE)+x] = (unsigned int)val;
        if (val <   0) og[(y*XSIZE)+x] = 0;
        if (val > 255) og[(y*XSIZE)+x] = 255;

      /* correct blue plane */
      scale = ((long)ib[(y*XSIZE)+x] * (long)ff[(y*XSIZE)+x]) >> 12;
      val = (long)ib[(y*XSIZE)+x] - scale;
        ob[(y*XSIZE)+x] = (unsigned int)val;
        if (val <   0) ob[(y*XSIZE)+x] = 0;
        if (val > 255) ob[(y*XSIZE)+x] = 255;
      }
    }

  /* write the corrected field rgb output image */
  write_image("output",or,or,or);

  /* free memory buffers */
  free (ff);
  free (ir);
  free (ig);
  free (ib);
  free (or);
  free (og);
  free (ob);
}