interface IImageRegion<Img extends WidthAndHeight> {
  // get whole image that the region refers to
  public default Img image() { null; }
  
  // smallest rectangle that all of the region's pixels are contained in
  public Rect bounds();
  
  public int numberOfPixels();
  public Pt firstPixel();
  public Iterator<Pt> pixelIterator();
  public bool contains(int x, int y);
}