That’s a moiré
Moirés—the distracting wavy patterns that sometimes appear in printed images—can cause big problems on press. Subject moirés appear when the image that is reproduced includes grid or line patterns that clash with the pattern of the halftone dots on conventional ruled screens. Other types of moirés include screen angle moirés and scan moirés. Moirés can often be prevented by using stochastic screens.
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Ed #11 Print It
Image Credit: James Schnepf
