static ItIt<ParameterizedSegmenter> chessOCR_varySegmenterGain(ParameterizedSegmenter baseSegmenter, O... _) {
  optPar float minGain = 1f;
  optPar float maxGain = 10f;
  optPar float gainStep = 1f;
  
  ret mapI(floatIota(minGain, maxGain, gainStep), gain -> {
    ParameterizedSegmenter seg = baseSegmenter.clone();
    seg.dc_gain = gain;
    ret seg;
  });
}