IBM 1725 SLS - Manual (Page 130)

Using Gamma
Correction
QMS 1725 SLS Print System User's Guide 4-4
tion. To get the best gray-scale PostScript image at any resolution,
gamma correction should be turned on.
Terms
Several terms related to gamma correction are explained in this sec-
tion to help you better understand the gamma correction concept.
Gray Levels
Gray levels are a progressive series of gray tones between black and
white. Gray levels are obtained by varying the ratio of black to white
dots. The number of gray levels depends on printer resolution and
screen frequency.
Halftone
A halftone is a printed copy of a scanned image as a set of tiny,
evenly spaced spots of variable diameter that, when printed, visually
blur together to appear as shades of gray. Your QMS 1725 SLS Print
System creates halftone cells by mapping each gray level onto a col-
lection of dots.
Factors that influence the quality of a halftone are
n Device resolution of the printer
n Screen frequency of the halftone
n Quality of the scan
n Diameter of the laser beam
Changing print resolution from 300x300 dpi to 600x600 dpi smooths
the resulting spots. In addition, because each spot is represented by
a wider range of dots, a greater number of gray levels is possible. The
laser beam is part of the print engine, so it’s not a factor you can
adjust.
Screen Frequency
Screen frequency is the number of lines of dots that compose each
inch of a halftone screen. The screen frequency of a halftone deter-