Stochastic moire

Hello all,

I run across an interesting case of moire the other day at work. We had to print boxes for a customer that was selling loud speakers. Loud speakers, as you might imagine, have pretty much a halftone pattern on themselves, which is usually grey.

We tried outputting the job with AM screening and we got terrible moire. We figured we had to try FM screening, since it is known for eliminating moire since the dots are randomly dispersed within the addressability grid. Well, we got somewhat less of moire, but there was still there.

It is a case of subject moire, or moire that is embedded in the digital file, due to the halftone pattern of the digital camera's CCD sensor. Hence, since it is on the digital file and not on the halftone screen of the printed sheet, the moire is much less likely -if ever- to go away.

What we tried to do and got successful was to increase the resolution both of the RIP and of the digital file. We figured that a more detailed addressability grid and higher pixel definition would generate FM dots that are more dispersed, thus reducing the likelihood of moire. It worked!

-D

PS. Foveon X3 sensors offer a distinct advantage in avoiding subject moire in the captured image. Check it out: http://www.foveon.com/article.php?a=69 and for a more technical reading: http://www.foveon.com/files/FrequencyResponse.pdf.