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.

 

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

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