What is a moire pattern in printing?

A moire is an unwanted grid or wavy interference pattern that shows up when halftone dot screens overlap at the wrong angles, or when an already printed image is scanned and reprinted. It distracts from the artwork and signals a screening or source-file problem.

• Happens when dot screens clash at incorrect angles.
• Common when rescanning material that was already halftone printed.
• Prevented by using correct screen angles during output.
• Best avoided by supplying original vector or high-resolution art, not scans of prints.