static ImageSurface test_AbstractFastRegions_fastMode() {
  set flag FastRegions_debug.
  //var imgBin = randomImage2B(2);
  var imgBin = new Image2B(2, 2, new byte[] { 0x0a });
  var img = new Hi15Image(imgBin);
  var r1 = FastRegions_Hi15Image(img);
  var regions1 = r1!;
  print("fastMode");
  var r2 = FastRegions_Hi15Image(img).fastMode(true);
  var regions2 = r2!;
  print(pixels := sfu(imgBin.pixels));
  printStruct(regionMatrix := r1.regionMatrix);
  printStruct(regionMatrix := r2.regionMatrix);
  var left = mergeBufferedImagesVertically(allToBufferedImage(map regionToBWImage(regions1)));
  var right = mergeBufferedImagesVertically(allToBufferedImage(map regionToBWImage(regions2)));
  ret zoomedPixelatedImageSurface(mergeBufferedImagesHorizontally(toBufferedImage(img), left, right));
}