{'fraction_non_alphanumeric': 0.020833333333333332, 'fraction_numerical': 0.003205128205128205, 'mean_word_length': 4.8915094339622645, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Background Restitution In An Astronomical Image Using An Histogram Of Local Contrast

A fast algorithm is presented in this paper to restore non uniform background in astronomical images with starlike or contrasted objects. The digitized image is divided into adjacent squares of equal area of (2n x 2n)pixels. A definition of the local contrast measure is given. For a fixed area the histogram of local contrast measures is established for the whole image. The influence of image characteristics (background structure, extended sources, starlike objects, film defects, etc...) on the shape of this histogram is discussed. It is shown that a threshold may be found on this histogram to select the background areas. From these areas we are able to determine the background level over the entire image. Some typical astronomical applications show that the background is estimated with accuracy and that film defects may be removed without damage. With this algorithm, and unlike the median algorithm, the restored background is not biased even in the neighborhood of the removed objects. However, sharp edges in the background itself are smoothed. Experience shows that this algorithm is easy to use; it has been implemented on a 16 bit minicomputer.