Thank you for the explanation - it surely beats wikipedia.

>> Or, better put, is the left or right side of your image "correct"?
>
> As you can see (or /should/ see, unless your display an/or your image 
> viewing software is /totally/ screwed up), the left side shows a checkered 
> plane, but the reflection on the sphere does not. Can this possibly be 
> correct?

I was referring to luminance, not to the reflection in the sphere. The 
brightness of the sky is very different, too. I meant: what is more correct 
(related to the sky) - luminence on the left or right?

Of course reflection on the left makes more sense than on the right. Is this 
a gamma-related problem or is this an error in povray?

I am having lots of problems with gamma correction on my system. At least 
there are a lot of iffy things.

Contrary to what has been posted here, my video card's driver seems to do 
some gamma correction (Nvidea). At least I can do a some gamma correcting in 
the setup. However, it is a lot of voodoo: I don't know for sure what is 
corrected and when. I really don't see any difference.

Now, I am using Corel quite a lot. Corel has a lot of colour correcting, 
too. I downloaded the proper colour-management system files for my monitor 
and my printer, respectively, but the printed result did not look much like 
the screen. The PDF-file I sent to my printer (I mean the real one, the guy 
who doesn't bother printing anything below 1000 copies ;-) did look like 
neither my printout, nor the screen.

So I did trash all colour-correcting. All set to "ignore" - from video card 
driver to Corel to printer profile and printer driver. And behold: now I get 
on my printer what I see on my TFT and the guys at the printing press 
produce something that comes close enough to what I want.

So I am a bit distrustful of colour correction, especially when it is stored 
as a kind of optional parameter in the image-file, like in PNG. Depending on 
the respective viewer / editor, gamma correction in PNG is either ignored or 
applied. If it is applied, one only can hope it is applied correctly. This 
really is a problem. Do you know which browsers support PNG 
gamma-correction?

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