sclass AOA_CompareImagesToProtos implements Steppable {
  new Map<S, BWImage> images;
  new Map<S, BWImage> protos;
  
  new AllOnAll<S> allOnAll;
  new Map<S, Scored<S>> bestProtoForImage;
  new Map<S, Scored<S>> bestImageForProto;
  
  void addImages(Map<S, BWImage> images) {
    putAll(this.images, images);
    for (S id : keys(images)) allOnAll.newA(id);
  }
  
  void addProtos(Map<S, BWImage> protos) {
    putAll(this.protos, protos);
    for (S id : keys(protos)) allOnAll.newB(id);
  }
  
  public bool step() {
    PairS p = allOnAll.next();
    if (p == null) false;
    BWImage img1 = images.get(p.a);
    BWImage img2 = protos.get(p.b);
    Scored<S> bestProto = bestProtoForImage.get(p.a);
    float sim = bwImageSimilarityResized(img1, img2, score(bestProto));
    scoredMapPut(bestProtoForImage, p.a, p.b, sim);
    scoredMapPut(bestImageForProto, p.b, p.a, sim);
    true;
  }
  
  Map<S, Double> scoresForProtos() {
    ret mapValues doubleScore(bestImageForProto);
  }
}