Colour-coded relative differences between the images retrieved by applying our method to images of subset 7 and the underlying original, undegraded Rome/PSPT images. Each box corresponds to a different observation. Each row (column) of boxes shows results derived from a given observation identified by the year in which it was recorded (imposed CLV, numbered as in Fig. A.13). 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 for all images, 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.