static BWImage blendBWImages(BWImage bi1, BWImage bi2) {
  ret blendBWImages(bi1, bi2, 0.5);
}

static BWImage blendBWImages(BWImage bi1, BWImage bi2, double weight2) {
  ret BWImage(blendBufferedImages(toBufferedImage(bi1), toBufferedImage(bi2), weight2));
}