in news:3baf6e49$1@news.povray.org Bob H. wrote:

> For PC systems, the most common display gamma is 2.2, while for
> scenes created on Macintosh systems should use a scene gamma of
> 1.8. Another gamma value that sometimes occurs in scenes is 1.0.
> 

 Guessing (as I used a pre 3.1 versions only for a week or two): going 
from version 2.2/3.0/3.1 a few things changed. In older versions you 
had to set the resulting gamma in the scene file. When a scene was 
designed on a Mac and renderd on a PC there had changes to be made to 
the scene file.

 In the current situation this is not needed anymore as display_gamma 
is set in the INI file, or defaults to the right value (at least 
for PC). assumed_gamma 1 just tells the system to use that 
display_gamma. final gamma = display_gamma/assumed_gamma, so 
assumed_gamma can be used to make small changes to the illumination of 
the scene, but in general it would be better to do it with the 
lightning sceme to prevent cross platform problems.

 As to the value to be written to the PNG file, shouldn't it be 
1/final_gamma instead of 1/display_gamma? Or is that one correction too 
much?


Ingo

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