Oops, forgot to say: "Good job!" I'll steal your code next time I need to 
gamma correct :)

-- 
Tek
http://evilsuperbrain.com


"Tek" <tek### [at] evilsuperbraincom> wrote in message 
news:439b6a95$1@news.povray.org...
> I've been adjusting my textures using a different trick: I filter the 
> texture over itself and over an opaque white surface, effectively raising 
> the colour to a power of 2, which isn't perfect gamma correction but it 
> suits my needs (the texture had to be filtered anyway for some effects I'm 
> doing).
>
> I was going to do it with functions like you have, but the pigment 
> definitions came out of poseray and I was too lazy to retype them all :)
>
> -- 
> Tek
> http://evilsuperbrain.com
>
> "Tim Nikias" <JUSTTHELOWERCASE:timISNOTnikias(at)gmx.netWARE> wrote in 
> message news:439b2aa2@news.povray.org...
>> (see thread "using assumed_gamma of 1.0... a discussion", located here:
>>
http://news.povray.org/povray.general/thread/%3Cweb.439a1b692d1f46002a1c213f0%40news.povray.org%3E/)
>>
>> Anyways. My experience is this: I have a nice image_map, I follow the 
>> docs
>> and supply assumed_gamma of 1.0 and have Display_Gamma properly set to 
>> 2.2,
>> and what happens? The image_maps turn out brighter than their source. 
>> Why?
>> Due to the internal gamma correction of POV-Ray.
>>
>> Personally, I'd like an image-map to look like it's source when its lit 
>> with
>> 100% white light (e.g. by applying finish{ambient 1 diffuse 0}), but the
>> gamma-correction prevents that. The image shows this. The upper-left 
>> corner
>> is the pure image-map in POV-Ray. The lower-left shows the original 
>> source.
>>
>> What's on the right side you ask? Well, the upper right is the image_map
>> "uncorrected", but passed through my gamma-correction macro using a gamma 
>> of
>> 1.0 (to show that it doesn't "harm" the image to pass through the macro).
>> The lower right is the uncorrected PNG version of the image. PNG comes 
>> with
>> internal gamma values, and POV-Ray makes proper use of them. The problem
>> lies within the usual floating point (in-)accuracy. If you take a closer
>> look at the ocean's horizon, you'll notice color-banding and
>> color-clipping-like effects. That's why I'd rather not use PNGs, at least
>> not if they're as dark as this source.
>>
>> Here's the macro:
>> #macro Gamma_Corrected(Image_Pigment,Gamma)
>>  #local Image_Function =
>>    function{
>>      pigment{Image_Pigment}
>>    }
>>  #declare Gamma_Corrected_Return=
>>  pigment{
>>    average pigment_map{
>>      [1 function{Image_Function(x,y,z).x} poly_wave Gamma color_map{[0 
>> rgb
>> 0][1 rgb 3*x]}]
>>      [1 function{Image_Function(x,y,z).y} poly_wave Gamma color_map{[0 
>> rgb
>> 0][1 rgb 3*y]}]
>>      [1 function{Image_Function(x,y,z).z} poly_wave Gamma color_map{[0 
>> rgb
>> 0][1 rgb 3*z]}]
>>    }
>>  }
>>  //Return value
>>  Gamma_Corrected_Return
>> #end
>>
>> All you do is #declare your image_map as a pigment and instead of 
>> applying
>> it directly onto your object, you pass it through the macro, like so:
>>
>> #declare Image_Map = pigment{image_map{sys "test.bmp"}}
>> box{-.5,.5 pigment{Gamma_Corrected(Image_Map,1.0)}
>>  finish{ambient 1 diffuse 0}
>> }
>>
>> I'll probably add this to my website some time soon, but wanted to get 
>> this
>> on the web for the ones joining the above-mentioned thread and wondering 
>> how
>> to do what they want to do. :-)
>>
>> Regards,
>> Tim
>>
>> -- 
>> aka "Tim Nikias v2.0"
>> Homepage: <http://www.nolights.de>
>>
>>
>>
>
>

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