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sclass MakeMaskCorrelationMatrix is MakesBufferedImage {
  settable long[][] imagesH;
  settable long[][] imagesW;
  
  // size w()*h(), every entry is a pixel diff count
  gettable int[] matrix;
  
  int w() { ret imagesH.length; }
  int h() { ret imagesW.length; }
  
  int maxPixelDiff() { ret l(first(imagesW))*64; }
  
  run {
    int w = w(), h = h();
    var matrix = this.matrix = new int[w*h];
    int i = 0;
    for y to h: {
      long[] imageH = imagesH[y];
      for x to w:
        matrix[i++] = countDifferingBits(imageH, imagesW[x]);
    }
  }
  
  FloatBWImage get() {
    if (matrix == null) run();
    int w = w(), h = h();
    float max = maxPixelDiff();
    ret floatBWImageFromFunction(w, h,
      (x, y) -> 1f-matrix[y*w+x]/max);
  }
  
  public BufferedImage getBufferedImage() { ret toBufferedImage (get()); }
}