Suppression of moiré patterns in scanned halftone images

Moiré patterns often appear in the image obtained from scanning an image printed on a magazine or a newspaper. The patterns do not exist in the original printing but come from alias sampling of screened halftone pictures. A strategy to design a moiré suppression scanning procedure is proposed. Fourier analysis is presented for both the screening and the scanning processes, from which a formula is derived to calculate a special scanning resolution, called moiré controlling scanning resolution. With the moiré scanning resolution, an input halftone image is scanned and the moiré signals can be confined in programmed frequency areas. After filtering out the signals in those areas, the original can be restored. Some useful spatial filters for this purpose are designed. Experimental results are shown to demonstrate the feasibility of the proposed approach. ( 1998 Elsevier Science B.V. All rights reserved.