HP QMS 1660E manual setgray

Gamma

Correction,

Halftones, and

Screens

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 overall midrange contrast while blacks (shadows) and whites (high- lights) keep their original values. Gamma correction sets grayscale values specified through the PostScript setgray operator to your printer’s gray-scale values.

Gamma correction is linked to print resolution. The main benefit of gamma correction is that it improves the print quality of a scanned image by improving halftoning at a given resolution. To get the best gray-scale PostScript image at any resolution, gamma correction should be turned on.

You can set gamma correction through PS Executive or through the Administration/Emulations/PostScript/Gamma Correction menu

Menu	Administration/Emulations/PostScript/Gamma Correction
Choices	No—Don’t use gamma correction
	Yes—Use gamma correction
Default	No
Notes	Gamma correction is automatically adjusted when printer
	resolution is changed.
	Gamma correction applies only to PostScript images.
	Gamma correction has no affect when the printer is set to
	1200x1200 dpi resolution.
	If turning on gamma correction doesn’t yield a suitable gray-
	scale image for your needs, set a specific gamma correction
	value through your drawing application or through the
	PostScript settransfer operator. (See your drawing application
	documentation and the PostScript Language Reference
	Manual for more information.)

Additional Technical Information 5-7