Adobe PHOTOSHOP 5.0 User Manual page 79

Specifying a halftone screen for a Bitmap-
mode image
The Halftone Screen option in the Bitmap dialog
box lets you convert a grayscale image to simulated
halftone dots.
Important: The halftone screen becomes part of the
image. If you print the image on a halftone printer,
it will print with the halftone screen you choose here
plus that of the printer. On some printers, the result
probably will be a moiré pattern in the image.
To specify the halftone screen for a Bitmap-mode
image:
Choose Image > Mode > Bitmap.
1
Click Halftone Screen; then click OK.
2
3 For Frequency, enter a value for the screen
frequency, and choose a unit of measurement.
Values can range from 1 to 999 for lines per inch
and from 0.400 to 400 for lines per centimeter. You
can enter decimal values.
The screen frequency specifies the ruling of the
halftone screen in lines per inch (lpi). The
frequency depends on the paper stock and type of
press used for printing. Newspapers commonly
use an 85-line screen. Magazines use higher
resolution screens, such as 133 lpi and 150 lpi.
Check with your print shop for correct screen
frequencies.
4 Enter a value for the screen angle in degrees
from –180 to +180.
The screen angle refers to the orientation of the
screen. Continuous-tone and black-and-white
halftone screens commonly use a 45 angle.
5 For Shape, choose the dot shape you want.
6 Click OK.
Original grayscale image, and Halftone Screen conversion:
53 lpi, 45 ª angle, round dot
You can save and reuse halftone screen settings by
using the Save and Load buttons in the Halftone
Screen dialog box.
Additional bitmap conversion options
Like the Halftone Screen option, the other bitmap
conversion options determine the quality of the
Bitmap-mode image.
50% Threshold Converts pixels with gray values
above the middle gray level (128) to white and
below to black. The result is a very high-contrast,
black-and-white representation of the image.
Converts an image by organizing
Pattern Dither
the gray levels into geometric configurations of
black-and-white dots.
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