Title page for ETD

Analysis and Reduction of Moire Patterns in Scanned Halftone Pictures

Xiangdong Liu

Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Approved

Dr. Roger Ehrich, Chair
Dr. Lynn Abbott
Dr. James Campbell
Dr. Lenwood Heath
Dr. Clifford Shaffer

May, 1996
Blacksburg, Virginia

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.

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