static BufferedImage testBlockOptimizedIntMatrix(BufferedImage img default shootScreen2()) {
  int blockShift = 3;
  BlockOptimizedIntMatrix m = new(img.getWidth(), img.getHeight(), blockShift);
  copyMatrix(imageToMatrix(img), m);
  print("Size before opt=", deepObjectSize(m));
  m.optimize();
  print("Size after opt=", deepObjectSize(m));
  assertSameImage(img, matrixToImage(m));
  ret img;
}