Adobe PHOTOSHOP 6.0 Manual page 390

CHAPTER 14
380
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.
Halftone screen with black ink.
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
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(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.
To define the screen attributes:
Choose File > Print Options.
1
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.