static ImageSurface showImageWithGrayToBlackSlider(S name, final BufferedImage img) {
  final ImageSurface is = showImage(name, img);
  final SimpleLiveValue<Float> lv = floatLiveValue();
  
  Runnable update = r {
    BufferedImage img2 = cloneBufferedImage(img);
    float darkening = min(lv!, 0.99f);
    float factor = 1/(1-darkening);
    offset = -darkening*255;
    rgbContrastAndBrightness(factor, offset, img2);
    is.setImage(img2);
  };
  
  lv.onChange(update);
  addToWindowAndPack(is,
    withLabel("Darkening factor:", jLiveValueSliderZeroToOne(lv)));
  ret is;
}