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#include <stdio.h>
#include <sys/types.h>

int main()  
{
  const int width=800, height=600;
  FILE *fp=NULL;
  int i,j;
  u_char col[3];

  // open binary file
  fp = fopen("output.ppm","wb");

  // print header
  fprintf (fp,"P6\n%d %d\n255\n",width,height);
 
  // create image values
  for (i=0; i<width; i++)
    for (j=0; j<width; j++)  {
      col[0] = (u_char) i-j;
      col[1] = (u_char) j-i;
      col[2] = (u_char) i+j;
      fwrite (col,3,1,fp);
    }
 
  // close file
  fclose(fp);

  return 0;
}