static IIntegralImage scaledIntegralImage(IIntegralImage img, int w) {
  ret scaledIntegralImage(img, w, iround(w*img.getHeight()/(double) img.getWidth()));
}

static IIntegralImage scaledIntegralImage(IIntegralImage img, int w, int h) {
  ret new IIntegralImage {
    int w1 = img.getWidth(), h1 = img.getHeight();
    double factorX = doubleRatio(w1, w);
    double factorY = doubleRatio(h1, h);
    double areaCorrection = 1/(factorX*factorY);
    
    public int getWidth() { ret w; }
    public int getHeight() { ret h; }
    
    // get value for 1 channel
    // normal range [0; pixelCount*256)
    // TODO: test
    public double getIntegralValue(int x, int y, int channel) {
      double x2 = (x+1)*factorX-1;
      double y2 = (y+1)*factorY-1;
      double val = img.getIntegralValue(x2, y2, channel);
      ifdef scaledIntegralImage_debug
        printVars scaledIntegralImage(+x, +y, +x2, +y2, +val, val2 := val*areaCorrection);
      endifdef
      ret val*areaCorrection;
    }
  };
}

Began life as a copy of #1027206