Tim Nikias wrote:
> AFAIK: There are two parts: the assumed_gamma and the display_gamma.
> Assumed_gamma is used internally during the raytracing, which is the reason
> why it should be set to 1.0: so that the internal calculations are done in
> the correct, linear colorspace.
> Display_gamma is applied *after* the raytracing, and is meant to ensure that
> when *rendering* the image on different PCs with different gamma, the output
> *looks* the same.

That's not correct, the gamma correction is performed exactly as 
described in the docs, section 3.3.3.3.

> Now, as for making use of image-maps in assumed_gamma=1 and
> display_gamma=2.2 scenes, I'm wondering if it shouldn't be possible somehow
> to use functions to add an inverse gamma-correction to the image-map, so
> that even though POV-Ray gamma-corrects, the image-maps will look the same.
> I would have use for this for my next short, so maybe I'll have to tackle
> that problem some time in the future. Again, this would only take care to
> look proper on a certain system with specified gamma, but then again,
> everyone is working with *his* system as reference and just wants it to look
> the same on other's systems.

It's not quite as simple.  Applying a gamma modification to the color 
values when reading from the image will result in information loss (and 
possibly color banding etc.).  Applying them when evaluating the 
image_map will result in performance loss.  This does not mean an 
internal pre-processing feature for images could not be useful but it is 
not as straight away as it might seem.

And if such a feature is introduced in some way you will have to specify 
the gamma factor for the image in the scene.  It will not use the 
display_gamma settings for reading images (this would be completely mad 
since the gamma correction of the image has nothing to do with the 
target gamma of the render).

Christoph

-- 
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 31 Oct. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/

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