/*********************************************************/
/*   program 12: alpha filter composite                  */
/*********************************************************/

#define  MAX    255
#define  XSIZE  640
#define  YSIZE  480

unsigned char *fgr,*fgg,*fgb;
unsigned char *bgr,*bgg,*bgb;
unsigned char *or,*og,*ob;
unsigned char *m;

main()
  {
  long  int  x,y;
  long  int  r,g,b,a;

  /* allocate input, output and matte memory buffers */
  fgr = (unsigned char *) malloc (XSIZE*YSIZE);
  fgg = (unsigned char *) malloc (XSIZE*YSIZE);
  fgb = (unsigned char *) malloc (XSIZE*YSIZE);
  bgr = (unsigned char *) malloc (XSIZE*YSIZE);
  bgg = (unsigned char *) malloc (XSIZE*YSIZE);
  bgb = (unsigned char *) malloc (XSIZE*YSIZE);
  or  = (unsigned char *) malloc (XSIZE*YSIZE);
  og  = (unsigned char *) malloc (XSIZE*YSIZE);
  ob  = (unsigned char *) malloc (XSIZE*YSIZE);
  m   = (unsigned char *) malloc (XSIZE*YSIZE);

/* 
  Read the foreground, background, and matte images.
*/
  read_image("hands",fgr,fgg,fgb);
  read_image("mountain",bgr,bgg,bgb);
  read_image_matte("hands_matte",m);

/* 
  Perform alpha filter for each pixel.
*/
  for (y = 0; y < YSIZE; y = y++)
    {
    for (x = 0; x < XSIZE; x = x++)
      {
/* 
  Calculate alpha value (which is simply inverse of matte).
*/
      a = MAX - (long)m[(y*XSIZE)+x];

/* 
  Calculate composite rgb values.
*/
      r = ((long)fgr[(y*XSIZE)+x] * a) + ((long)bgr[(y*XSIZE)+x] * (MAX - a));
      g = ((long)fgg[(y*XSIZE)+x] * a) + ((long)bgg[(y*XSIZE)+x] * (MAX - a));
      b = ((long)fgb[(y*XSIZE)+x] * a) + ((long)bgb[(y*XSIZE)+x] * (MAX - a));

/* 
  Normalize composite to 8-bit values and save.
*/
      or[(y*XSIZE)+x] = (unsigned char)(r / (MAX + 1));
      og[(y*XSIZE)+x] = (unsigned char)(g / (MAX + 1));
      ob[(y*XSIZE)+x] = (unsigned char)(b / (MAX + 1));
      }
    }

/* 
  Write the composite output image.
*/
  write_image("output",or,og,ob);

/* 
  Free memory buffers.
*/
  free(fgr);
  free(fgg);
  free(fgb);
  free(bgr);
  free(bgg);
  free(bgb);
  free(or);
  free(og);
  free(ob);
  free(m);
}