sclass BWHistogram {
  IBWImage image; // optional
  int[] data; // pixel count for each brightness from 0 to 255
  int nPixels; // sum of pixel count
  
  *(BWImage *image) {
    nPixels = area(image);
    data = bwImageHistogramArray(image);
  }
  
  toString { ret "BWHistogram of " + nPixels(nPixels); }
}