Abstract

This arrangement comprises at least a processing block (2) provided with mean value calculating members for calculating for each picture element different mean background values (16, 18, 20), a contrast measuring member (22) for producing a deviation value between the mean values and the luminance L(i, j) of the picture element to be processed, a comparator (30) for producing the indication of the contrasting object by comparing the different deviation values to at least one predetermined threshold value and a background value assigning member (55) for assigning a background value for each picture element on the basis of said mean values. The mean value calculating members (16, 18, 20) are formed from first storing means (95, 82) for storing a previous value of the mean value calculated for the preceding picture element, second storage means for the background values already assigned (80, 90, 100) and add-subtract means (84, 86, 92, 102) for producing the mean value for each picture element from the mean value contained in the first storage means and the background values contained in the second storage means.