In article <40329903@news.povray.org>,
 "Gilles Tran" <gitran_nospam_@wanadoo.fr> wrote:

> To be honest, after reading the docs over and over and reading many
> discussions in these groups, I'm still unable to understand what are the
> "right" gamma settings for a given computer, and the fact that the gamma
> test doesn't seem to work on flat screens adds to my confusion :(

assumed_gamma should be 1 for new scenes. Display_Gamma should be the 
gamma of the display your image will be viewed on. LCD displays have an 
S-shaped response curve, the power curve used to approximate the 
response of CRT displays doesn't work well at all on them, but I think 
the system usually maps it to either a CRT response curve or a linear 
(gamma 1) function. I don't have any technical references for this, it 
just seems to match the behavior I've seen.

The gamma actually used to correct things is Display_Gamma/assumed_gamma.
If assumed_gamma is 1, that is just Display_Gamma, otherwise it corrects 
the colors for a scene designed on a machine with a display gamma of 
assumed_gamma, but without any gamma correction. Maybe this will make it 
clearer:

Say you make a scene on a machine with gamma of G1. When you do this, 
the version of POV you use doesn't support gamma correction, so you just 
choose the colors to look right, essentially encoding the gamma into the 
scene itself.
Years later, you dig up the scene in some archives and render it. It was 
designed for a display with a different gamma, and doesn't turn out 
right, so you add an assumed_gamma statement with the gamma of your old 
machine. The scene now renders correctly.

New scenes should just use assumed_gamma 1, to use the display gamma of 
the machine the scene is being rendered on.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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