Improving morphological closing

I'm trying to make an image uniformly bright using a morphological closing operation, as a prelude to an adaptive threshold. My method is to divide each pixel in the image by the value of that pixel after the closing operation, then normalize: ``` Imgproc.GaussianBlur(sudokuImage, sudokuImage, new Size(5,5), 0); Mat kernel = Imgproc.getStructuringElement(Imgproc.MORPH_ELLIPSE, new Size(11,11)); Imgproc.morphologyEx(image, closedImage, Imgproc.MORPH_CLOSE, kernel); Core.divide(image, closedImage, image); Core.normalize(image, image, 0, 255, Core.NORM_MINMAX); ``` Here is the result: - Top left - original image - Top right - after Gaussian blur - Bottom left - result of the closing operation - Bottom right - final result I'd like the final image to be less washed-out, more like the image below (which was obtained using what looks like the same method in this post). How can I accomplish this?