/*********************************************************/
/*   program 5: histogram collection                     */
/*********************************************************/

#define  MAX    256
#define  XSIZE  640
#define  YSIZE  480

unsigned char *ir,*ig,*ib;
unsigned char *or,*og,*ob;

main()
  {
  long  int  i,x,y;
  long  int  maxr, maxg, maxb;
  long  int  hr[MAX], hg[MAX], hb[MAX];

  /* allocate input and histogram image memory buffers */
  ir = (unsigned char *) malloc (XSIZE*YSIZE);
  ig = (unsigned char *) malloc (XSIZE*YSIZE);
  ib = (unsigned char *) malloc (XSIZE*YSIZE);
  or = (unsigned char *) malloc (MAX*MAX);
  og = (unsigned char *) malloc (MAX*MAX);
  ob = (unsigned char *) malloc (MAX*MAX);

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

  /* be sure histogram collection bins start at zero */
  for (i = 0; i < MAX; i++)
    {
    hr[i] = 0;
    hg[i] = 0;
    hb[i] = 0;
    }

  /* collect histogram data for each color plane */
  for (y = 0; y < YSIZE; y++)
    {
    for (x = 0; x < XSIZE; x++)
      {
      hr[ir[(y*XSIZE)+x]]++;
      hg[ig[(y*XSIZE)+x]]++;
      hb[ib[(y*XSIZE)+x]]++;
      }
    }

  /* find maximum bin value of each color plane */
  maxr = 0;
  maxg = 0;
  maxb = 0;
  for (i = 0; i < MAX; i++)
    {
    if (hr[i] > maxr) maxr = hr[i];
    if (hg[i] > maxg) maxg = hg[i];
    if (hb[i] > maxb) maxb = hb[i];
    }

  /* normalize all bins to maximum */
  for (x = 0; x < MAX; x++)
    {
    hr[x] = hr[x] * (MAX - 1) / maxr;
    hg[x] = hg[x] * (MAX - 1) / maxg;
    hb[x] = hb[x] * (MAX - 1) / maxb;
    }

  /* generate rgb histogram image */
  for (x = 0; x < MAX; x++)
    {
    for (y = (MAX - 1); y >= 0; y--)
      {
      /* draw red line */
      if (y > hr[x])
        or[((MAX-y-1)*MAX)+x] = 0x00;
      else
        or[((MAX-y-1)*MAX)+x] = 0xff;

      /* draw green line */
      if (y > hg[x])
        og[((MAX-y-1)*MAX)+x] = 0x00;
      else
        og[((MAX-y-1)*MAX)+x] = 0xff;

      /* draw blue line */
      if (y > hb[x])
        ob[((MAX-y-1)*MAX)+x] = 0x00;
      else
        ob[((MAX-y-1)*MAX)+x] = 0xff;
      }
    }

  /* write the output image */
  write_image("histo",or,og,ob);

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