Photoshop CC: The Missing Manual

Printing on a Commercial Offset Press

If you prepare artwork for stuff that’s printed using a commercial offset printing press (magazines, product packaging, newspapers, and so on), you’ve got loads more to worry about than if you’re sending an image to an inkjet printer. Unlike printing to an inkjet printer, where your images get converted from RGB to CMYK during the printing process, a commercial offset press usually requires you to convert the image to CMYK before it’s printed. This section explains the very specific steps you need to follow to preserve an image’s color when you convert it to CMYK. But before you dive too deeply into color-mode conversion, you need to understand a bit more about how offset presses work.

Commercial offset presses are huge, noisy, ink-filled metal beasts. An inkjet printer sprays ink from a print head directly onto a page, whereas an offset press transfers, or offsets, ink from an image on a plate onto a rubber blanket and then onto a page. As you learned back in Chapter 6, offset presses split an image’s four CMYK channels into individual color separations, which are loaded onto big cylinders aligned so that all four colors are printed, one on top of another, to form the final image. If these cylinders aren’t aligned properly, you’ll see faint traces of one or more colors peeking outside the edges of the image, making it look blurry (this blurriness is called being “out of registration”).

Instead of the dyes used by inkjet printers, commercial offset ...