/*
  Sampe code uses JPEG library.
  This program reads a jpeg image, converts to a B/W image, and writes to a RAS image.

  Project files : jpeg2ras.c + rasio.c 
  JPEG library can be obtained from http://www.ijg.org
*/

#include <stdio.h>
#include <stdlib.h>
#include "jpeglib.h"



unsigned char **cpicalloc(int, int);
unsigned char **process(unsigned char **, int, int);
void write_raster_file(char *,unsigned char **,int, int); 


extern swabb; 

main()
{
  FILE *jpegin, *jpegout;
  char file_name[50];
  unsigned char **pic,  **out_pic;
  int width, height, row_stride;
  struct jpeg_decompress_struct cinfo;
  struct jpeg_error_mgr jerr;
  
  
  // Open an image file 
  sprintf(file_name, "%s.jpg", "testimg");               
  if((jpegin = fopen(file_name, "rb")) == NULL){
    fprintf(stderr, "cannot open %s\n", file_name);
    return 0;
  }


  cinfo.err = jpeg_std_error(&jerr);     
  jpeg_create_decompress(&cinfo);
  jpeg_stdio_src(&cinfo, jpegin);
  (void) jpeg_read_header(&cinfo, TRUE);        // read header
  (void) jpeg_start_decompress(&cinfo);         // decompressing  
  row_stride = cinfo.output_width * cinfo.output_components;   

  width = cinfo.output_width;
  height = cinfo.output_height;

  pic = cpicalloc(cinfo.output_height, cinfo.output_width*3);           // allocate a buffer for the input jpeg color(RGB 3 channels) image 
  out_pic = cpicalloc(cinfo.output_height, cinfo.output_width);         // allocare a buffer fot the output sunraster B/W image  

  while (cinfo.output_scanline < cinfo.output_height) {
    (void) jpeg_read_scanlines(&cinfo, &pic[cinfo.output_scanline], 1);      // read the jpeg image 
  }

  (void) jpeg_finish_decompress(&cinfo);                                         
  jpeg_destroy_decompress(&cinfo);
  fclose(jpegin);


  /* Processing (conver to a B/W picture) */
  out_pic = process(pic, cinfo.output_height, cinfo.output_width);           // processs the original image   



  sprintf(file_name, "%s.ras", "output");
  if((jpegout = fopen(file_name, "wb")) == NULL){                            // open another file for writing the sunraster 
    fprintf(stderr, "cannot open %s\n", file_name);
    return 0;
  }

  // write to a sunraster file 

  swabb = 1;                                                                 // set the swabb flag to 1, Don't forget  
  write_raster_file( file_name, out_pic, height, width);                     // write sunraster buffer to the image file  


  return 1; 

}


unsigned char **cpicalloc( int row, int col) 
{
  int i;
  unsigned char **p;
  
  p = (unsigned char **) calloc(row,sizeof(unsigned char *));
  if(!p){
    fprintf(stderr,"memory allocation error\n");
    exit(1);
  }
  for(i=0;i<row;i++){
    p[i] = (unsigned char *) calloc(col,sizeof(unsigned char));
    if(!p[i]){
      fprintf(stderr,"memory allocation error\n");
      exit(1);
    }
  }
  return p;
}




unsigned char **process(unsigned char **pic, int height, int width)
{
  int i, j;
  unsigned char **out_pic;

  out_pic = cpicalloc(height, width);

  for(i=0; i<height; i++){
    for(j=0; j<width; j++)
      out_pic[i][j] = (unsigned char) ((double)pic[i][3*j]*0.13+ (double)pic[i][3*j+1]*0.62 + (double)pic[i][3*j+2]*0.25);    // convert to a B/W image (B*0.13+G*0.62+R*0.25)  
     
  }

  return out_pic;
}