Adobe 23101335 User Guide - Page 390

380 CHAPTER 14 Printing (Photoshop) screens. Setting the screens at different angles ensures that the dots placed by the four screens blend to look like continuous color and do not produce moiré patterns. Halftone screens consist of dots that control how much ink is deposited at a specific location on-press. Varying their size and density creates the illusion of variations of gray or continuous color. For a process color image, four halftone screens are used: cyan, magenta, yellow, and black-one for each ink used in the printing process. 450 00 (a PostScript imagesetter, for example) should be set to the correct density limit, and your processor should be properly calibrated; otherwise, results can be unpredictable. Before creating your halftone screens, check with your print shop for preferred frequency, angle, and dot settings. (Use the default angle settings unless your print shop specifies changes.) Important: Some output devices ignore the screen frequency and angle attributes you set in Photoshop. When printing custom halftone screens, it is advisable to save the image in EPS format, which embeds custom halftone screen settings in the file. In many (but not all) cases, the halftone screen settings in the EPS file will override the printer's default halftone screens. Halftone screen with black ink. 1050 900 750 450 00 Halftone screens with process ink at different screen angles; correctly registered dots form rosettes. In traditional print production, a halftone is produced by placing a halftone screen between a piece of film and the image and then exposing the film. In Photoshop, you specify the halftone screen attributes just before producing the film or paper output. For best results, your output device To define the screen attributes: 1 Choose File > Print Options. 2 Select Show More Options, choose Output from the pop-up menu, and click Screen. 3 In the Halftone Screens dialog box, choose whether to generate your own screen settings: • Deselect Use Printer's Default Screens to choose your own screen settings. • Select Use Printer's Default Screens to use the default halftone screen built into the printer. Photoshop then ignores the specifications in the Halftone Screens dialog box when it generates the halftone screens. 4 For a grayscale halftone, enter a screen frequency from 1 to 999.999, and choose a unit of measurement. Enter a screen angle from -180 to +180 degrees.