Adobe PHOTOSHOP 5.0 User Manual page 344

336 CHAPTER 15
Printing
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
(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.
To define the screen attributes:
In Mac OS, choose Adobe Photoshop 5.0 from
1
the menu in the Page Setup dialog box.
Click Screens (Windows) or Screen (Mac OS).
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Choose whether to generate your own screen
3
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.
For a grayscale halftone, enter a screen
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frequency from 1 to 999.999 for Frequency, and
choose a unit of measurement. For Angle, enter a
screen angle from –180 to +180 degrees.
For a color separation, choose from the
5
following options:
To manually enter the screen frequency and
•
angle, choose a color of the screen for Ink, and
enter the frequency and angle; repeat for each
color separation.
To have Adobe Photoshop determine and enter
•
the best frequencies and angles for each screen,
click Auto. In the Auto Screens dialog box, enter
the resolution of the output device and the screen
frequency you intend to use; click OK. Photoshop
enters the values in the Halftone Screens dialog
box. Changing these values may result in moiré
patterns.
If you are using a high-resolution output device
•
equipped with PostScript Level 2 (or higher) or an
Emerald controller, make sure that the Use
Accurate Screens option is selected in the Auto
Screens dialog box (or in the Halftone Screens
dialog box if you're entering the values manually).
The Use Accurate Screen option lets the program
access the correct angles and halftone screen
frequencies for high-resolution output. If your
output device is not equipped with PostScript
Level 2 (or higher) or an Emerald controller, this
option has no effect.
For Shape, choose the dot shape you want. If
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you want all four screens to have the same dot
shape, select Use Same Shape For All Inks.
Choosing Custom from the Shape menu displays
the Custom Spot Function dialog box. You can
define your own dot shapes by entering
PostScript commands—useful for printing with
nonstandard halftone algorithms. For information
about using PostScript language commands, see
the PostScript Language Reference Manual
published by Addison-Wesley, or consult the
imagesetter's manufacturer.