Moiré Patterns and Proofing

If you are under the misconception that you can check to see whether a moiré pattern is going to be a problem by viewing a proof—think again! Unless the proof is printed on the same output device, using the same screen as your final print, the interaction of previous and current screens will not be the same. If your proof is printed on an ink-jet proofer, or other proofing device that uses FM (stochastic) screens, any potential pattern—moiré or other—will be masked by the random dot placement inherent in FM screens. Therefore, if your final print is produced with a standard AM halftone dot screen featuring regularly spaced halftone dots, your final output may be a big surprise! If your proofing device uses an AM type of dot, you will likely see a moiré pattern on the proof but it will not be identical to the one produced during the final printing process unless the dot generation mechanism is indeed the same. This is why it is so critical to identify and remove screen patterns prior to going to press. Heck, even some image patterns such as herringbone patterns in cloth can create moiré on output. If you have any doubts about a pattern you recognize in an image, send in a test image to your printer so they can review and maybe even print it on the cut off side of another job, to evaluate the moiré potential. When in doubt, consult!