sclass G22BurnIn {
  settable double alphaStep = 0.1;
  settable double tolerance = 0.1;
  settable double colorMorph = 0.1; // speed to update color within tolerance
  settable Color backgroundColor = Color.black;
  
  int toleranceSquaredInt;
  int w, h;
  int[] mask;
  
  // how much motion is there in the image overall? (0 to 1)
  double motionFactor = Double.NaN;
  
  void processFrame(BufferedImage frame) {
    toleranceSquaredInt = iround(sqr(tolerance*255)*3);
    
    int w = frame.getWidth(), h = frame.getHeight();
    if (mask == null || this.w != w || this.h != h) {
      this.w = w;
      this.h = h;
      this.mask = new int[w*h];
    }
    
    // We assume the frame has no transparency
    var gp = grabbableIntPixels_fastOrSlow(frame);
    int n = w*h, iMask = 0, iFrame = gp.offset;
    int[] pixels = gp.data;
    int[] mask = this.mask;
    
    for y to h: {
      for x to w: {
        int mpix = mask[iMask];
        int fcol = pixels[iFrame++] & 0xFFFFFF;
        if (mpix == 0)
          mpix = differentColor(mpix, fcol);
        else {
          int mcol = mpix & 0xFFFFFF;
          int diff = rgbDistanceSquaredInt(mcol, fcol);
          if (diff <= toleranceSquaredInt)
            mpix = sameColor(mpix, fcol);
          else
            mpix = differentColor(mpix, fcol);
        }
        mask[iMask++] = mpix;
      }
      
      iFrame += gp.scanlineStride-w;
    }
    
    motionFactor = Double.NaN;
  }
  
  bool isSameColor(int col1, int col2) {
    
    ret toleranceSquaredInt == 0
      ? col1 == col2
      : rgbDistanceSquaredInt(col1, col2) <= tolerance;
  }
  
  int sameColor(int mpix, int fcol) {
    double newAlpha = rgbAlphaZeroToOne(mpix)+alphaStep;
    int newColor = blendRGBInts(mpix, fcol, colorMorph);
    ret withAlpha(newAlpha, newColor);
  }
  
  int differentColor(int mpix, int fcol) {
    ret withAlpha(alphaStep, fcol);
  }
  
  BufferedImage stillImage aka image() {
    if (mask == null) null;
    var img = bufferedImage(w, h, mask);
    ret renderImageOnBackground(backgroundColor, img);
  }
  
  BufferedImage motionImage() {
    if (mask == null) null;
    int[] mask2 = pixelsWithInvertedAlpha(mask);
    var img = bufferedImage(w, h, mask2);
    ret renderImageOnBackground(backgroundColor, img);
  }
  
  BWImage motionDetectionImage() {
    ret BWImage(w, h, alphaChannelFromPixels(mask));
  }
  
  double motionFactor() {
    if (isNaN(motionFactor) && mask != null)
      motionFactor = 1-alphaChannelAverage(mask)/255.0;
    ret motionFactor;
  }
}