sclass FloodFillBWImage extends FloodFill {
  IBWImage img;
  settable double tolerance = 1/8.0; // color tolerance pixel-to-pixel as fraction of 1
  
  *(IBWImage *img) { super(img.getWidth(), img.getHeight()); }
  
  bool isConnectable(Pt a, Pt b) {
    float brightnessA = img.getFloatPixel(a);
    float brightnessB = img.getFloatPixel(b);
    ret abs(brightnessA-brightnessB) <= tolerance;
  }
}