"Tek" <tek### [at] evilsuperbraincom> wrote in message 
news:46542d56$1@news.povray.org...
> "St." <dot### [at] dotcom> wrote in message news:464c7fdb$1@news.povray.org...
>>
>>  That's all there is apart from Wings models and some PovTree's. As it is 
>> now, the scene looks quite good and I'm happy with it, I'm just not 
>> getting the assumed_gamma thing. It's confusing me because it should 
>> either be 2.2 or 1 (from what I've read). FWIW, nearly all of my images 
>> over the last two years use a low assumed_gamma. Where am I going wrong 
>> with this?
>
> assumed_gamma should be 1 for the best simulation of light. Povray will 
> gamma correct the image from the "assumed" gamma to the "actual" gamma 
> which is stored in one of it's ini files. The ini file value is 2.2 so if 
> you want no gamma correction use the (default) assumed_gamma 2.2. But, 
> light by definition has linear gamma, whereas monitors have non-linear 
> gamma (50% grey is not half the brightness of white on a monitor), so 
> assumed_gamma 1 tells pov to do all it's maths as if they have a gamma of 
> 1, then to implicitly correct that to a gamma of 2.2 for the image. It's 
> VERY counter intuitive!

     Hmm, now I get it, thanks Tek, I think I'll leave it at 1 from now on 
and use Sam' trick too.


>
> I've tried your source with a simple scene and I can't get any blue. 
> assumed_gamma won't be the cause, it will just be adjusting the brightness 
> of the error. Has anything in the scene got negative colour values? e.g. 
> negative ambient light?

    No, not a negative ambient light, but my ground texture is negative, 
would that also create that blue in combination with the fog? I'll have a 
play and see what happens.

      ~Steve~


>
> -- 
> Tek
> http://evilsuperbrain.com
>
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>

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