I’ve been test-printing some pages with screentones, and had a few moments of horrible panic. Something that looked not at all bad when printed straight from Photoshop became hideously full of moire pattern when saved as a pdf and then printed. Actually, it was more a sort of allover argyle or plaid effect. I triple-checked all my settings, and everything — size, dpi, etc. — was being preserved. There was no compression or downsampling either. I searched through Sweatdrop’s useful forums, but didn’t find anything that helped this particular problem. Then, stricken with inspiration, or something rising from the subconscious I’d seen somewhere about a different technical problem that seemed related, I resaved the greyscale (grayscale to Americans) Photoshop page as a bitmap, and converted that to pdf. Hey presto, no moire. Well, not much. There’s one tone alone that has a little faint plaid pattern. At least now we know that it’s a problem with that particular tone, and not our entire technique. My guess is that Acrobat was, in effect, rescreening the toned page, generating the interference patterns.
On to the next problem.