persistable sclass G22GhostImage is IBWImage {

  int w, h;

  public int getWidth() { ret w; }

  public int getHeight() { ret h; }

  // number of images averaged

  int imageCount;

  // array contains raw sum over images

  // (1 for white pixel, 0 for black pixel)

  int[] pixels;

  *(L<Image2B> maskImages) {

    imageCount = l(maskImages);

    if (imageCount == 0) ret;

    var img = first(maskImages);

    w = img.w(); h = img.h();

    pixels = sumOfBinaryImages(maskImages);

  }

  public float getFloatPixel(int x, int y) {

    ret imageCount == 0 ? 0.5f : floatRatio(pixels[y*w+x], imageCount);

  }

  FloatBWImage toFloatBWImage() {

    float[] floatPixels = new[pixels.length];

    if (imageCount == 0)

      fillArray(floatPixels, 0.5f);

    else

      for i over pixels:

        floatPixels[i] = floatRatio(pixels[i], imageCount);

    ret new FloatBWImage(w, h, floatPixels);

  }

  public BufferedImage getBufferedImage() {

    ret toFloatBWImage().getBufferedImage();

  }

  FloatBWImage certaintyImage() {

    ret preciseCertaintyImage(this);

  }

  simplyCached double certainty() {

    if (imageCount == 0) ret 0;

    double sum = 0;

    int n = pixels.length;

    for i to n:

      sum += g22pixelCertainty(doubleRatio(pixels[i], imageCount));

    ret sum/(w*h);

  }

  G22GhostImage minus(G22GhostImage img) {

    new G22GhostImage ghost;

    ghost.w = w; ghost.h = h;

    ghost.imageCount = imageCount-img.imageCount;

    ghost.pixels = intArray_minus(pixels, img.pixels);

    ret ghost;

  }

}