[argyllcms] Writing self tests for gamma correction

  • From: Richard Hughes <hughsient@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 26 Feb 2013 16:38:11 +0000

Hi all,

I'm writing more platform tests, this time for gamma correction. The
whole "display gamma" being condensed into a single number is a thing
people cleverer than I have argued about for years, but I have a
simple question.

If a display is specified as "gamma 2.2", does that mean that the
XYZ->Y component follows a 2.2 curve, or has each RGB channel got it's
own gamma which is then averaged? If it's an RGB measurement we
calculate gamma with, how do we map from XYZ to RGB? Also, what
white-point would we use? All the "gamma checker" images decompose
this into sRGB gamma, but I'm not sure I get the logic why.

For my uncalibrated DreamColor, Y is pretty much exactly 2.2. For my
uncalibrated Thinkpad T510, my Y gamma is 2.7. Ouch.

Advice welcome, thanks.


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