[Radiance-general] Color appearance and color temperature

Fri, 08 Feb 2002 13:55:02 +0200

Thank you, this was very helpful.
But it apparently means that only the latest Unix releases will have the 
new feature?

The von Kries transform seems to be a linear matrix transform. Is there any 
way to perform such arbitrary (user defined 3x3 matrix) transforms on 
Radiance images? If not, would it be possible to have such a thing some 
day?... It could be suitable for various tasks and experiments with images.

Regards,
Markku N.

At 10:35 2002-02-07 -0800, you wrote:
>>Does anybody know tools that might help in tuning chromaticity (color
>>temperature) adaptation for Radiance renderings? [...]
>One of the new features in Radiance 3.4 is a von Kries white-point 
>transform built into the -p option of pcond (and other programs).  This 
>transform does a reasonable job of simulating the apparent colors under a 
>different illuminant, and is an improvement over the straight color 
>transform that was used previously.  However, when you have a mixture of 
>illuminants in your rendered scene, there is no accepted adaptation 
>transform for such a condition.  A number of researchers have worked on 
>this problem, and no one has proposed a workable solution to my 
>knowledge.  The best you can do is pick an average of the illuminants that 
>seems right for the part of the scene you are viewing.
>
>The issue of white balance is separate from the issue of spectral 
>rendering, but as long as we're on the topic, one of the things people 
>have requested over the years is a means for full spectral rendering in 
>Radiance.  As it turns out, this is difficult for the very silly reason 
>that all the materials and patterns have arguments whose count would 
>change with the number of spectral samples.  Choosing anything other than 
>three samples will make Radiance input files incompatible with the 
>change.  In hindsight, it would have been much better to do things the way 
>I did them in the Material and Geometry Format (MGF), which separates 
>color into its own entity, with a number of different ways to specify it.
>
>Be that as it may, it is possible to obtain accurate spectral renderings 
>of a scene with a single illuminant, provided you precompute the adjusted 
>RGB color of the surfaces using a technique I described in my most recent 
>paper at the Color Imaging Conference.  You can get a PDF copy of the 
>paper through the link below if you want to read about the details.
>
>-Greg
>
>http://viz.cs.berkeley.edu/gwlarson/papers.html
>
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Markku_Norvasuo
Technical_Research_Centre_of_Finland