“…The scanned or copied image is usually in halftone format no matter how meticulous and sensitive the sensor is, because the document is printed in halftoning format finally. So far, there are many halftoning schemes [1,2,8,9,12,13,15,16,18,24,28] and inverse halftoning schemes [3,5,6,10,14,21,22,27,29] have been proposed.…”