Suppression of moire patterns in scanned halftone images by double scans with grid movements

Abstract

Moire patterns often appear in images obtained from scanning printings on magazines or newspapers. The patterns do not exist in the original printings but come from alias sampling of the screened halftone pictures. A new method of scanning is proposed to suppress the moire patterns. First, the Fourier analyses of both screening and scanning are presented, from which the new moire suppression scanning method is derived. The method employs a double-scan process. In the second scan, the scan position is shifted by half of the sampling grid distance of the first scan in either or both of the horizontal and vertical directions. Then by averaging the images of the two scans, most of the moire fringes can be removed. Some experimental results are shown to demonstrate the feasibility of the proposed approach. (C) 1997 Published by Elsevier Science B.V.