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How Offset Printing Works
When you prepare a project, such as a brochure, poster, book, and so on, for commercial printing, you need to work with a commercial printer and possibly a service bureau.Traditionally, a service bureau uses your prepared Photoshop files to either print the image with a high-resolution printer, giving you camera-ready output, or (more likely) images the files onto film. If you get camera-ready output, the commercial printer uses a camera or scanner to capture the output and create film.However, because many graphic artists have the ability to save files on transportable large storage media, such as writable CD-ROMs, Zip drives, and removable storage media, the artists skip the serv-ice bureau entirely, cutting out the intermediate step of film or camera-ready output. Instead, they go directly to the commercial printer with their files. Many commercial printers work with Photoshop, so files saved in the native Photoshop PSD format are usually acceptable. However, some printers may prefer to use encapsulated PostScript (EPS) files.The commercial printer takes any of these media — camera-ready output, film, or computer files — and uses them to make printing plates. Printing plates are usually made out of acid-etched metal. If your project uses more than one color, one plate is created for each color. The plates are put on large rollers on a printing press by the press operator, a pressman. The pressman uses registration marks to make sure that all the plates are exactly aligned so that the colors line up. He or she then runs the press. As the rollers rotate, the plates are dipped in ink. The inked plate is then rolled across paper, transferring the ink to the paper.After the ink dries, the paper is trimmed and folded as necessary, using crop marks as guides. The print job is then stapled or bound, depending upon the number of pages. The completed print job is packed into boxes and shipped to you.
Many commercial printers and service bureaus use Photoshop, so they may ask for regular Photoshop PSD files. To ensure that your files work for the printer or service bureau, talk to them first. They’ll tell you what printer to specify, which printer’s marks to select, and any other specialized output settings that should be used. If this is too much for you to deal with, many printers and service bureaus will even take your completed Photoshop files and perform any conversions or add the necessary output settings for you.
