Wednesday, August 31, 2005


"Trapping" is an obscure but interesting part of the pre-press process. When a color picture is printed using four colors of ink (cyan, magenta, yellow and black, or CMYK), each color is put down on the paper via a separate pass through the press. If the paper lines up perfectly with each pass, all the colors align and you get perfect registration. Very often, though, if you look at four-color printing closely enough, you can see that the inks are just a bit off. You'll see a colored halo on one side, or colors slopping out of their black boundaries, or a gap where colors don't meet up.

Good registration (left) and bad (right)

Trapping helps minimize registration problems by spreading out the non-black colors a few pixels so that, even if registration is a little bit off, they still have some "wiggle room" to fit and overlap as intended. With Photoshop, trapping is as easy as pushing a button (I can't imagine how anyone did it pre-digitally, or whether they bothered at all). Coincidentally, a private cartoonists' board I frequent just had a long discussion about trapping.

That discussion came in handy when I got word late last week that the printer wasn't happy with my color registration. It wasn't coming out right. Not lining up. Within half a second I realized the problem: no trapping. When I submitted my final image files to Abrams they were trapless. Trap-free. Bereft of trap. My trapping had shuffled off this mortal coil, run down the curtain, and joined the choir invisible. The subject never came up and I never thought to ask. My bad.

So I spent a few hours this morning speedily trapping the 26 color pages scattered throughout Mom's Cancer. I envisioned the overseas printer tapping his toe, glancing nervously at his watch, paying overtime while the presses waited in idle silence for my upload.

Assuming my trapping worked, I should have first proofs to review in a few days. Next book, I'm hiring a high school kid to take care of this.

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