"ingo" <ing### [at] homenl> wrote in message
news:Xns### [at] povrayorg...
> 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?

Don't know, but looking at the last line of the last paragraph of section
5.2.2.2 in the doc I see it says newer hardware could use Display_Gamma 1.0.
Having tried that just now since I have the ATI mobility 128, which must
certainly have gamma correction of some sort, and putting assumed_gamma 1.0
as recommended I get a perfectly good rendering.  So it was the visually
adjusted display gamma I had always set before which messed that idea up.  I
kept thinking display gamma had to be set manually by using the graphic
supplied in the doc.
Anyway, I'll be checking into this once again to find how the images end up.

Bob H.

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