Technical information

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.

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.

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

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