Contents || Index
12/12/2003

Gamma

‘Gamma’ is a type of contrast adjustment that keeps black as black, white as white, but makes a non linear transition between the two. Gamma can be used to make shadows less deep, or highlights less washed out. As far as Lispix is concerned, it affects the display of the images, but not their pixel values, for example, gamma adjustment on an image will not affect how the threshold tool works, nor change blob statistics.


For Lispix, the value of gamma is the exponent applied to the pixel value to get the light intensity. If gamma is less than unity, the curve is convex down and most of the image appears brighter. Photoshop seems to use the inverse value. In any event, both Lispix and Photoshop brighten the image by moving the appropriate slider to the left, and the gamma range for both programs is 0.1 – 10.0.