The invention relates to an image processor configured to: receive an image, take area-specific samples (11) of the image information of the area and calculate (12) a reference value (REF) on the basis of the samples; store into a memory (16) or to transmit (17) the reference value (REF) calculated for an area and the area identifier (ALUE) area-specifically; check (13) whether the reference value (REF) obtained as a result of the calculation and the image information (INF) corresponding to it have already been stored in the memory (16) or transmitted (15); and to store into the memory (16) or to transmit (15) the calculated reference value (REF) and the corresponding image information (INF), if the reference value (REF) and the corresponding image information (INF) have not been stored into the memory or transmitted previously.