persistable sclass G22PixelSplitMasks<A> is IG22OptimizedMasksHolder<MultiSet<A>> {
  replace Mask with IG22Mask<MultiSet<A>>.
  
  settable Pt splitPixel;
  settable IG22MasksHolder<MultiSet<A>> darkHolder;
  settable IG22MasksHolder<MultiSet<A>> brightHolder;
  
  public L<Mask> masks() {
    ret new ConcatOnDemandList(
      darkHolder.masks(),
      brightHolder.masks());
  }
  
  public L<IG22MasksHolder<MultiSet<A>>> subHolders() {
    ret ll(darkHolder, brightHolder);
  }
  
  public void transformSubHolders(IF1<IG22MasksHolder<MultiSet<A>>> f) {
    darkHolder = f.get(darkHolder);
    brightHolder = f.get(brightHolder);
  }
  
  public PStackComputable<Void> findSimilarMasks(
    Image2B maskImage, ProbabilisticList<Mask> outList) {
    ret new FindSimilarMasks<A>(maskImage, outList);
  }

  record noeq FindSimilarMasks<A>(Image2B maskImage,
    ProbabilisticList<Mask> outList) extends PStackComputableWithStep<Void> {
    bool brightBranch;
    
    void step(IPStack stack) {
      if (step == 0) {
        ++step;
        bool bright = isMaskBright(maskImage);
        double p = 0.9;
        stack.probabilisticOptions(this, ll(
          withProbability(p,   self -> self.brightBranch = bright),
          withProbability(1-p, self -> self.brightBranch = !bright)));
      } else {
        (brightBranch ? brightHolder : darkHolder).findSimilarMasks(maskImage, outList);
        stack.ret();
      }
    }
  }
  
  // Does the mask belong in darkHolder or brightHolder?
  bool isMaskBright(Image2B maskImage) {
    ret maskImage.getBoolPixel(splitPixel);
  }
  
  !include early #1035854 // Masks holder Include
}