/* rawvga converts raspiraw VGA resolution .raw to .ppm/.pgm without dcraw

A) https://www.johndcook.com/blog/2009/08/24/algorithms-convert-color-grayscale
*/
#include <stdio.h>
#include <string.h>
#include <assert.h>

int  hdr=0x8000, siz=640*480*5/4, shl=4, col=0;
char M[2][2]={{'B','G'},{'G','R'}};
int  L[17] = { 1/*B*/, 0,0,0,0, 10/*G*/, 0,0,0,0,0,0,0,0,0,0, 3/*R*/}; /* A) */

void out(char C, unsigned char u) {
  unsigned U = u * (col ? 1 : L[C-'B']);  U <<= shl;  if (U>255) { U=255; } 

  if (col<1) {
    putchar(U);
  } else {
    switch (C) {
      case 'B': putchar(0); putchar(0); putchar(U); break;
      case 'G': putchar(0); putchar(U); putchar(0); break;
      case 'R': putchar(U); putchar(0); putchar(0); break;
    }
  }
}

int main(int argc, char *argv[]) {
  FILE *src; int i,j;

  if (argc!=3) { fprintf(stderr,"%s -C|-c|-g|-l file.raw\n",argv[0]); return(1); }

       if (strcasecmp(argv[1], "-c")==0) { printf("P6"); col=argv[1][1]-'b'; }
  else if (strcmp(argv[1], "-g")==0) { printf("P5"); L['G'-'B']=L['R'-'B']=1; }
  else if (strcmp(argv[1], "-l")==0) { printf("P5"); shl=1; }
  else { assert( !"-C|-c|-g|-l needed"); }

  assert( src = fopen(argv[2],"rb") );
  fseek(src,0,SEEK_END); if (ftell(src) != hdr+siz) { hdr=0; }
  assert(ftell(src) == hdr+siz); fseek(src, hdr, 0);

if (col>=0) {
  printf("\n640 480\n255\n");

  for(i=0; i<480; ++i) {
    for(j=0; j<640; ++j) {
      out(M[i%2][j%2], fgetc(src));  if (j%4 == 3) { fgetc(src); }
    }
  }
} else {
  unsigned char line[640/4*5], b, g, G, r, m;

  printf("\n320 240\n255\n");

  for(i=0; i<480; i+=2) {
    int ofs=0; 

    assert(640/4*5 == fread(line, 1, 640/4*5, src));

    for(j=0; j<640; j+=2) {
      b=line[j+ofs]; g=line[j+ofs+1];
      G=fgetc(src);  r=fgetc(src);
      m=(((unsigned)g)+G)>>1;
      out('?', r); out('?', m); out('?', b);
      if (j%4 == 2) { fgetc(src); ++ofs; }
    }
  }
}

  return fclose(src);
}