I was checking for stuck pixels and dirt on the sensor. I took some photos of a plain ceiling. ISO 200, It was fairly dark so f/6.3, 0.625 secs. The 12-40 lens was set to 40mm, manual focus and the focus was set as close as possible to make the image as blurred as possible. Here is the photo - nothing special to see YET. Now using any image processing program that does levels, set the black to the bottom of the histogram and the white to the top of the histogram, then drag the middle point to just below the white - and you get this... These shapes are created within the camera, they are not there in reality. I could understand regular shapes that correspond to sensor design, but I cannot explain these curves. Any ideas?