This article appeared in the September/October 2002 issue of PT. To purchase this issue and receive this and other valuable articles in this issue, CLICK HERE: Ship within the U.S. | Ship outside the U.S.

When dealing with digital cameras and digital images, users often talk about aliasing and moiré fringes. But what is aliasing? In this article, I’ll explain the causes of aliasing in digital imagery, look at reasons why aliasing is found only in digital (and not photographic) images, and share several methods to reduce aliasing in digital photography. I’ll even show how aliasing artifacts can sometimes be useful.

Aliasing occurs in images that contain a fine, repetitive pattern, e.g. a fence, bicycle spokes or a patterned tie. Aliasing, also called moiré fringing, is readily recognized as a strange pattern in areas of the image that contain fine detail. Information in the original scene is corrupted by the digital camera system, and appears as a jumble of colors that distort this part of the picture.

Why does aliasing occur in CCD-based digital cameras? CCDs are a fantastic image sensor—cheap, efficient and of high resolution. However, CCD pixels are arranged in a regular array. This regular, equi-spaced pixel configuration is the cause of the problem since the regular repeat of the CCD pixels interferes with the regular pattern of the incident image.

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