/*********************************************************/
/*   program 28: program 1 rewrite                       */
/*********************************************************/

#include "sys/file.h"
#include "math.h"

main(argc,argv)
short int argc;                  /* number of arguments */
char      *argv[];               /* argument values */
  {
  unsigned char *ir,*ig,*ib;
  unsigned char *or,*og,*ob;
  long  int  x,y;
  long  int  fpi,fpo;
  long  int  xsize,ysize;
  long  int  planes;
  long  int  sgi_type;
  long  int  depth;
  float      scale;
  char       in_file[256],out_file[256];

  if (argc < 4)
    {
    printf("Usage: prog28 <in_file> <out_file> <depth>\n");
    }
  else
    {
    sscanf(argv[1],"%s",in_file);
    sscanf(argv[2],"%s",out_file);
    sscanf(argv[3],"%d",&depth);

    if ((depth < 1) || (depth > 7))
      {
      printf("invalid depth request: %d\n",depth);
      }
    else
      {
      /* open the input image file */
      fpi = open(in_file,O_RDONLY);
      if (fpi <= 0)
        {
        printf("cannot open input file: %s\n",in_file);
        }
      else
        {
        /* read the input image file header */
        read_sgi_header(fpi,&xsize,&ysize,&planes,&sgi_type);

        /* allocate input and output memory buffers */
        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 input image data */
        read_sgi_data(fpi,xsize,ysize,planes,sgi_type,ir,ig,ib);
        close(fpi);

        /* calculate the scale factor that will reduce 8-bit values
            (0-255, inclusive) to evenly spaced values of 0-255 for
            the requested depth resolution. */
        /* example: if depth = 2, values are 0, 85, 171, and 255 */
        scale = 255.0 / (powf (2.0, (float)depth) - 1.0);

        /* reduce depth resolution by generating new 8-bit pixel values */
        for (y = 0; y < ysize; y = y++)
          {
          for (x = 0; x < xsize; x = x++)
            {
            or[(y*xsize)+x] = (ir[(y*xsize)+x] >> (8 - depth)) * scale;
            og[(y*xsize)+x] = (ig[(y*xsize)+x] >> (8 - depth)) * scale;
            ob[(y*xsize)+x] = (ib[(y*xsize)+x] >> (8 - depth)) * scale;
            }
          }

        /* create and open the output image file */
        fpo = open(out_file,O_WRONLY|O_CREAT|O_TRUNC,0666);
        if (fpo <= 0)
          {
          printf("cannot open input file: %s\n",in_file);
          }
        else
          {
          /* write the output image */
          write_sgi_header(fpo,xsize,ysize,planes,sgi_type);
          write_sgi_data(fpo,xsize,ysize,planes,or,og,ob,sgi_type);
          close(fpo);
          }

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