Removing Moiré Patterns From Images

The following excerpt is taken from Real World Scanning and Halftones by Glenn Fleishman, David Blatner, and Steve Roth:

"Moiré ("mwah-RAY") patterns are caused by our eyes' perception of straight lines and repeating patterns. Anytime you overlay a bunch of straight lines or grids on top of each other, you have the opportunity for moiré patterns. One grid, all by its lonesome, never has a problem with these patterns. It's when you have two or more overlaid on each other that the wires in your perceptual system get crossed, and these little gremlins start to appear."

Moiré patterns occur when scanning copying an original that is comprised of a halftone. Moiré is a form of digital artifact that occurs when two regular patterns intersect to form a new pattern. Because the new pattern is always more coarse that the two original patterns, the appearance will change as a function of screen frequency and angle. Typically, the finer of the two originals patterns are the easier it is to see the Moiré. Lower frequency halftone screens are less prone to visible Moiré.

Moiré can occur while viewing scanned halftones on a monitor screen, because the monitor has a certain screen frequency, which may or may not be in alignment with the screen frequency and angle of the original image.

Suggestions for removing moiré patterns:

• If your image contains a halftone, make sure you are NOT using Text Mode. If legibility of the the text is important, and good reproduction of any pictures is also needed, consider using Mixed Text & Halftones.
• Decrease the Sharpen control slightly. See Adjusting Sharpness.
• Rotate the original slightly on the Document Glass.
• Scan/Copy at the highest possible resolution capable by the system.
• Wherever possible, scan/copy continuous tone images (for example, photographs) only. If there is no continuous tone original available, scan/copy the halftoned image as a last resort.
• When submitting a print job, you may need to select a different halftone.

TIP: If you have programmed and run a job, and received unexpected results, ensure that the system-wide settings are all set back to their defaults by clicking <Clear All> or <Reset> in the user interface. Then proceed to do job programming pertinent to your job.