srecord noeq ImageDiffAsPNG(Rect r, byte[] pngData) is G2Drawable {
  public void drawOn(Graphics2D g) {
    var image = diffImage();
    if (image != null)
      g.drawImage(image, r.x, r.y, null);
  }
  
  BufferedImage diffImage() {
    ret imageFromBytes(pngData);
  }
  
  *(BufferedImage img1, BufferedImage img2) {
    this(ImageDifferenceAsTransparentOverlay(img1, img2));
  }
  
  *(ImageDifferenceAsTransparentOverlay diff) {
    r = diff.changedBounds();
    if (!empty(r))
      pngData = toPNG(clipBufferedImage(diff!, r));
  }
  
  bool isEmpty() { ret main empty(r); }
  
  toString {
    ret isEmpty() ? "No change"
      : "Changed area: " + r + ", png bytes: " + n2(l(pngData))
      + ", bits/pixel: " + formatDouble(bitsPerPixel(), 1);
  }
  
  double bitsPerPixel() {
    ret doubleRatio(l(pngData)*8L, area(r));
  }
}