Definition: Moire is an unsightly interference pattern that appears on images that have been scanned from a previously printed source such as a newspaper, magazine, or book. Moire appears as a checkered or herringbone type of pattern. (Continued below...)
The pattern is a result of the halftone screen process used in modern printing where patterns of small dots are overlayed to produce color and shading. Typically moire patterns from newspaper scans are the worst, compared to magazines, cards, brochures, and books. Scanning photos printed on textured paper can also produce a moire-like pattern, and though it is usually not as severe, the same removal methods can be used for both types of patterns.
Most scanning software offers a built-in descreen option to correct this problem before passing the image to your editing software. However, if your scanner does not have a descreen option, or if you don't like the results, there are several methods you can use to remove moire patterns in image editing software. One simple solution that often works well is to place the image on the scanner bed at a slight angle, then rotate to the proper position in your graphics software.
When removing moire patterns always work at 100% magnification in your editing software. Displaying an image at other magnification levels can sometimes result in visual distortion that could be mistaken as moire, but it actually has to do with the way the pixels are interpolated for screen display and will not appear in the printed image or at 100% zoom.
It's also worth noting that when you scan images from printed sources, they are very likely to be copyrighted. Be sure you have secured proper permissions before scanning from such sources.
The image on the left shows a moire pattern scanned from a newspaper. The image on the right shows moire pattern scanned from a high-quality textbook. Notice how the newspaper moire pattern is much more severe due to the lower line screen used in newspaper printing.
Also Known As: dots, checkered pattern, herringbone pattern, halftone screen, interference
Alternate Spellings: moiré
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Explanation of Moire patterns from scantips.com.