Analysis and Reduction of Moire Patterns in Scanned Halftone Pictures

Abstract

In this dissertation we provide a

comprehensive theory for the formation of a

moire pattern in a sampled halftone image. We

explore techniques for restoring a sampled

halftone image with a moire pattern and

techniques for preventing a moire pattern when

a halftone picture is scanned. Specifically, we

study the frequency, phase, and spatial

geometry of a moire pattern. We observe and

explain the half period phase reversal

phenomenon that a moire pattern may exhibit.

As a case study, we examine the moire

patterns generated by a commercial scanner.

We propose three restoration methods,

including a notch filtering method, a simulation

method, and a relaxation method. We also

describe a moire prevention method, the

partial inverse Fourier transform method.

Finally, we propose a research agenda for

further investigation.