Unacceptable Moire' distortion may result when images that include periodic structures such as halftone dots are scanned. In the frequency domain, Moire' patterns are the result of visible aliased frequencies. In the spatial domain, the aliased frequency components correspond to cyclic changes in the size of halftone dots which are visible as periodic "beat" patterns. Moire' formation depends on the following factors: (1) halftone screen frequency, (2) scan frequency, (3) angle between the scan direction and the halftone screen, (4) the scanner aperture size and shape, (5) quantization errors from the thresholding operation, (6) scanner and printer noise, and (7) ink flow on paper during printing. This paper analyzes the visibility of Moire' patterns in terms of these factors. Moreover, the paper describes an approach to reduce the visibility of Moire' patterns by manipulating the Moire' formation factors directly rather than by post-scan processing. Computer simulated, and actual scan images are presented to illustrate the approach.

Date Published: 25 October 1988
PDF: 12 pages
Proc. SPIE 1001, Visual Communications and Image Processing '88: Third in a Series, (25 October 1988);

Published in SPIE Proceedings Vol. 1001:
Visual Communications and Image Processing '88: Third in a Series
T. Russell Hsing, Editor(s)