// 0xRRGGBB
static int rawRGBDiff(int a, int b) {
  int r1 = (a >> 16) & 0xFF;
  int g1 = (a >> 8) & 0xFF;
  int b1 = a & 0xFF;
  int r2 = (b >> 16) & 0xFF;
  int g2 = (b >> 8) & 0xFF;
  int b2 = b & 0xFF;
  ret Math.abs(r1-r2) + Math.abs(g1-g2) + Math.abs(b1-b2);
}