// threshold 0.75 + Cubed distance from black 3.0 + blur + min 3",
static BWImage chessOCR_piecePreprocessing_1(BufferedImage img) {
  ret bwAutoCrop(bwImageTo2Bit(0.75f,
    img_cubedDistanceFromColor_withGain(rgbBlack(), 3.0,
      blurFilterBufferedImage(
        minFilterBufferedImage(3,
          img)))));
}