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;

  }

}