The rehabilitation of gamma

Copyright © 2000-01-16 Charles Poynton


Gamma characterizes the reproduction of tone scale in an imaging system. Gamma summarizes, in a single numerical parameter, the nonlinear relationship between code value - in an 8-bit system, from 0 through 255 - and luminance. Nearly all image coding systems are nonlinear, and so involve values of gamma different from unity.

Owing to poor understanding of tone scale reproduction, and to misconceptions about nonlinear coding, gamma has acquired a terrible reputation in computer graphics and image processing. In addition, the world-wide web suffers from poor reproduction of grayscale and color images, due to poor handling of nonlinear image coding. This paper aims to make gamma respectable again.

I presented this paper at the SPIE/IS&T Conference in San Jose, Calif., Jan. 26-30, 1998. The paper is published in the Proceedings of that conference, Rogowitz ,B. E.,l and T. N. Pappas (eds.), Human Vision and Electronic Imaging III, Proceedings of SPIE 3299, 232-249 (Bellingham, Wash.: SPIE, 1998).

See also: Gamma FAQ - Frequently-Asked Questions about Gamma;
GammaFQA - Frequently-questioned answers about gamma.


I must confess to having been uneducated in the proper definition and use of the term intensity when I wrote this article. I have edited the article to bring it into conformance with correct usage. If you have a copy of the conference proceedings, or if you obtained a copy of this paper prior to 2000-01-16, please replace that copy with the version provided here.

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