What are Moiré Patterns?

Moiré Patterns in Scanned Images

A moiré effect or pattern is produced by superimposing a repetitive design, such as a grid or a series of circles, on the same or a different image. The combination of two like or similar images produces distortions in the form of waves or ripples across the altered image. In scanning, moiré patterns appear when published images such as newspapers or magazine pictures are scanned. Such images are printed by turning colors or gray tones into regular patterns of tiny dots set close together on the paper. This type of image is called a halftone. The conflict between the close pattern of dots in the halftone image and the regular pixels that make the scanned computer image often causes unwanted moiré distortions in scanned images.

Examples of Moiré Patterns in Scanned Images