It used to be the case (and sometimes still is) that, when you prepared a document for a commercial printer, you would convert the images to the CMYK color mode before you inserted them into a page-layout document and certainly before you fired them off to the printing company. However, that process is changing because an increasing number of print shops now use digital presses.
Most digital presses work just like laser printers or copiers; they use electrostatic charges to transfer images from cylinders to the print surface. Like commercial offset presses, digital presses are primarily CMYK printers, but they use powdered toners instead of inks (which is why they can’t print spot colors). Some digital presses, like the Kodak NexPress, actually do offer toner spot-color printing, but they’re limited to very specific colors like red, green, or blue. And rather than being used for special objects like logos, these additional spot colors typically expand the gamut of the CMYK toners, much like light cyan and light magenta do in inkjet printers.
Because of these quirks, you have to perform some special steps if your project is headed for a digital printer. The following sections explain how to prepare various types of images for a run on a digital press.