Photoshop CS5: 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 your image to an inkjet printer. Unlike printing to an inkjet printer, where your images gets converted from RGB to CMYK during the printing process, a commercial offset press usually requires you to convert your image to CMYK before it's printed. In this section, you'll learn the very specific steps you need to follow to preserve your 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.

Note

Inkjet printers spray their ink from a print head directly onto a page. An offset press, however, transfers, or offsets, ink from an image on a plate onto a rubber blanket and then onto a page—which is why commercial printing presses are called "offset presses."

Commercial offset presses are huge, noisy, ink-filled metal beasts. As you learned back in Chapter 5 (CMYK Channels), they split your 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 your final image. If the cylinders aren't aligned properly, you'll see faint traces of one or more colors peeking outside the edges of your image, making it look blurry (this blurriness ...