static long bwRawImageDiff_sameSize(MakesBWImage a, MakesBWImage b) {
  ret bwRawImageDiff_sameSize(a.getBWImage(), b.getBWImage());
}

static long bwRawImageDiff_sameSize(MakesBWImage a, BWImage b) {
  ret bwRawImageDiff_sameSize(a.getBWImage(), b);
}

static long bwRawImageDiff_sameSize(BWImage a, MakesBWImage b) {
  ret bwRawImageDiff_sameSize(a, b.getBWImage());
}

static long bwRawImageDiff_sameSize(BWImage a, BWImage b) {
  assertSameSize(a, b);
  int w = a.w(), h = a.h();
  byte[] pixels1 = a.pixels, pixels2 = b.pixels;
  int n = pixels1.length;
  
  long diff = 0;
  for i to n:
    diff += Math.abs(ubyteToInt(pixels1[i])-ubyteToInt(pixels2[i]));
  ret diff;
}