ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O B-Observatory O O O O O O O O O O O O O O O O O O O O O O O O
tokens: there is no over-exposure on the QS. Figure A.7 shows the CC constructed for the extreme exposure problems considered. The green, blue, and red curves display the imposed relation, the measured QS CLV, and the standardized linear relation, respectively. For all the data, our method allows calculating the NSB accurately enough so that the obtained CLV reproduces the imposed relation for almost the whole range of QS values. In particular, the maximum unsigned relative difference between the imposed CC and the one recovered by the method is less than 0.005. The accuracy drops slightly for the last point at the limb and only for the cases of severe under-exposure, rising to 0.017. Subset 4: Different disc sizes with linear CC without inhomogeneities in the image The photographic plates from different observatories have different sizes. Even among the images of the same archive there are variations due to changes of the spectroheliograph and of the photographic plates. The digitization affects the number of pixels covered by the disc as well. The disc size is also affected by the seasonal variation of the Sun–Earth distance. Therefore, this subset was created to test the efficiency of the proposed method when applied to datasets that have a different disc size. We selected 10 Rome/PSPT images covering the period 2000–2014 and re-sampled them, so that each was represented in the form of solar images with 10 different radii between 100 and 550 pixels. The range of radii was defined to include the sampling present in most available datasets, however the upper limit was dictated by the number of pixels covered by the disc on Rome/PSPT observations. Subset 4 consists of 100 images. Figure A.8 shows the relative differences between the images derived with our method and the original Rome/PSPT data. Panels a) and b) refer to values of NSB, while panels c) and d) refer to values of contrast images, each (coloured) box for a different image of subset 4. In each panel, rows (columns) show values derived from different observations (imposed radii). The relative difference between the retrieved NSB (SB) and imposed background decreases with increasing radius of the disc; the maximum unsigned difference measured is 0.03 (0.007) for the images with the smallest radius, average difference is , and maximum of rms difference is 0.004 (0.001). The relative difference between the contrast image derived with our method and the original data reaches up to 0.056; the average differences are ; the rms differences are . Fig. A.8 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