Gamma Correction Concept - QMS 1725E Reference

The following illustration shows the relationship between screen fre-
quency, gray levels, and print resolution. As the screen frequency
increases, the number of gray levels decreases.
Gray Levels
250
200
150
100
50
0
The number of gray levels that your printer can produce depends on
the screen frequency and the print resolution. The default value for
screen frequency using 600 dpi is 71 lpi. This typically allows 73 dif-
ferent levels of gray. The default value for screen frequency using 300
dpi is 53 lpi. This typically allows 33 different levels of gray.
You can change screen frequency through your application or by
using the PostScript setscreen operator. The QMS Crown Technical
Reference Manual contains information on setscreen.
The extra gray levels available through higher resolution provide a
smoother shift from the darkest black to very light grays while higher
resolution provides sharper image outlines.

Gamma Correction Concept

Often in scanned images, gray scaling may be too light or dark to
show details clearly. Using gamma correction on a gray-scale image
is similar to using a graphic equalizer on a home stereo; the range of
gray levels is adjusted for the best possible image. This sharpens
Additional Technical Information
300x300 dpi
600x600 dpi
201
129
73
51
33
19
42 53 71
Screen Frequency (lpi)
33
9
106
About Gamma
Correction
5-5