Top left shows an image of the star that was only corrected for bad pixels. Only the first quadrant of the detector is shown because this is where the star was put in this exposure. The top right figure is the same image with identical colourbar length but after a mean background subtraction. The figure on the bottom is additionally smoothed with a Gaussian filter to reduce the pixel noise and has a narrower colourbar emphasize the inhomogeneous residual background structure.