You'll see exactly the same thing if you take a photo of an orange, then 
load it into your favourite paint program and gamma correct it.

Gamma effectively adjusts the brightness of the midtones and leaves 0 and 1 
in the same place, so if your orange colour is <1,0.5,0> then with 
assumed_gamma it will look more like <1,.73,0>, which is 
<1,pow(0.5,1/2.2),0> because your monitor gamma is probably 2.2ish.

If you want to pick a colour in a paint program and have it look the same in 
pov then you need to gamma correct it from your monitor's gamma space (the 
space you picked it in) into the assumed_gamma space you've told pov to work 
in. Usually that means applying pow(<colour>, 2.2) to it.

Personally I find it's just easier to always work with assumed_gamma 1 
turned on, and pick numbers in pov that look right, and forget about gamma 
space altogether.

-- 
Tek
http://evilsuperbrain.com


"Ard" <ard### [at] waikatoacnz> wrote in message 
news:web.4373fd35d28cb00fed802ab30@news.povray.org...
> The Gods of non-linearity are having fun with me today.  No wonder the 
> 19th
> century was so good for art: they didn't have gamma to contend with.
>
> Attached is my render of the following scene, with an inset of what 
> happens
> when I remove the assumed_gamma.  The scene is so simple that I'm sure I
> haven't done anything stupid.  Haven't I?  Surely, an orange sphere should
> be orange?
>
> I get similar results with no .ini file, and an .ini file containing
> "display_gamma 2.5" (which is what, in theory, I should be using).  Is
> something broken in my install?
>
> Please help.
>
>
> #include "colors.inc"
>
> global_settings {
>  assumed_gamma 1
> }
> plane {  y, -2 texture { pigment { checker colour Green colour Yellow} }}
> light_source { -10*z colour White}
> camera { location -3*z look_at 0 }
> sphere {0, 1
>  texture {pigment {Orange}}  // Did I say "banana"?  Nooooooooo.
> }
>
>
>


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