Slime wrote:
>>Essentially this setting and a few
>>others should never have been in the scene file for this reason
> 
> I don't understand this (for assumed_gamma only).
> 
> I do understand that assumed_gamma was never meant to be used for adjusting
> the brightness of a scene.
> 
> However, I thought its purpose was to let the artist say, "when I made this
> image, I assumed the viewer had a gamma of x." That's an important
> assumption that affects the appearance of the colors the artist chose. In
> that way, it is strongly linked to the scene (and so should be stored in the
> scene file).

Well, yes and no.  You might know, the gamma factor POV-Ray uses internally 
is simply assumed-gamma divided by display-gamma.  So what assumed-gamma is 
really good for is tweaking display-gamma.  Of course, as you argue, that is 
specifically what it is designed for.  The main problem is that it is not 
what it gets used for.  To make proper use of it, you first need a proper 
display-gamma.  The chance that you have to tools (an external measurement 
device or a pre-calibrated screen) is extremely unlikely.  So you cannot get 
a truly accurate display-gamma.  Consequently, what do you do?  You tweak 
assumed-gamma because that is what you can easily change on a scene by scene 
basis.

So assumed-gamma makes sense, right? Wrong! ;-)  What you did with this use 
of assumed-gamma is exactly what it is not for because all you do is alter 
the brightness on a scene by scene basis, while still using the exact same 
display and display-gamma.  So, what you get is indeed some kind of 
brightness adjustment, but that isn't what assumed-gamma is for.  Yet, that 
is what you effectively used it for, without really doing so consciously.

So, if you think about it, what good is assumed-gamma for once you adjusted 
display-gamma to your screen?  Basically, nothing that has to do with gamma! 
:-)

Thus, while we still provide it mainly for backward compatibility as far as 
possible (you can render old scenes without changing your display-gamma), to 
adjust brightness we will provide a more flexible and more suitable mechanism.

I realise this is a huge change.  Still, it is one we had to make for a 
"better future".

	Thorsten

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