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Can someone confirm this please?
"Anders K." <and### [at] f2s com> wrote in message
news:3c1168c5$1@news.povray.org...
> I have a white plane that is half transparent (rgbt <1, 1, 1, 1/2>), and a
> sphere on top of the plane that casts a shadow on it. I was then looking
at
> the alpha channel with GIMP's color picker tool. On the part of the plane
> that's in the light, the alpha value is 186 (= the gamma-corrected version
> of 1/2), as it should be. However, on the part of the plane that's in
> shadow, the alpha value is 127, the *non*-gamma corrected version of 1/2!
>
> Here's a simplified version of my scene that demonstrates the problem.
>
> // +ft +ua
> global_settings { assumed_gamma 1.0 }
> camera { orthographic location 10*z look_at 0 up y right 4/3*x }
> light_source { <-10, 10, 20> color rgb 1 }
> plane {
> z, 0 pigment { rgbt <1, 1, 1, 1/2> }
> finish { diffuse 1 ambient 0 brilliance 0 }
> }
> sphere { <0, 0, 5/16>, 5/16 pigment { rgb <1, 0, 0> } }
>
> The "finish" line on the plane makes the plane pure white in the light,
and
> pure black in shadow. If you comment out this line, the alpha value in the
> light becomes 147, while the alpha value in the shadow remains 127. It
> should be 186 in both cases.
>
> If the assumed_gamma 1.0 line is commented out, the alpha value in both
the
> light and the shadow is 127, as it should be (since there is no gamma
> correction). So this definately has something to do with gamma correction,
> but I don't see why it would. Shouldn't the color values only be
> gamma-corrected at the very end, as part of writing the image file output?
> Anyway, this bug should hopefully be easy to track down.
>
> POV-Ray 3.5 beta 8, Windows 98, Athlon 700, 256 MB
>
> Anders
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