Colour-coded relative differences between the images retrieved by applying our method to images of subset 4 and the underlying original, undegraded Rome/PSPT images. Each box (with a given colour) corresponds to a different synthetic image; row (column) shows results derived from a given Rome/PSPT observation (imposed radius). Note the different scale of the colour code, as represented by the corresponding colour bars. a) Mean relative and b) rms difference between the NSB and the imposed background within a given subfigure, c) mean relative and d) rms difference between the retrieved contrast image and the original data. The values are given for disc positions within 0.98 R.