[Radiance-general] estimating -av values, color

[Jack de Valpine]

Hi Lars,

Estimating ambient values is part science and part art as far as I have 
learned over the years. I don't think that I know of a situation where 
we have ever used a non neutral ambient value. I suppose if one were 
trying to more accurately account for certain kind of atmospheric shifts 
this might be a case to do this....?

Without knowing what your scene looks like (pictures help) it is 
difficult to help diagnose what is going on. My suscpicion though is 
that an ambient value of .5 .5 .5  may be too high for the given scene, 
thus the odd looking ("glowing") results. A very good option would be to 
use the "compamb" script that Greg wrote. This runs a pass on a small 
image using fairly high parameters and then does some calculations to 
come up with a good ambient value for the scene. This is pretty easy to 
use and does not take that long to return the results.

Note the av value affects the whole simulation not just the excluded 
objects.

-Jack

Lars O. Grobe wrote:

> Hi list,
>
> I have a question regarding the so-often given advice to use a neutral 
> -av setting. Why? Is it assumed that in general, the light conditions 
> in a building are like that? I have used a -av of .5 .5 .5 here, 
> together with -ae excluded objects (I wrote enough questions on that 
> topic ;-). This results in a strange image, as the calculated ambient 
> is redish, and the ambient-excluded objects appear very strange (like 
> blueish) because they are the only objects illuminated by this neutral 
> color. I can understand that if using -ab 0, setting a colored -av 
> would not make sense as ALL indirect illumination would be neutral than.
>
> So, am I right that in the case here (I use the -av settings only for 
> the -ae excluded objects in a scene that is rendered with -ab 2), 
> using a neutral value would be simply wrong and I have to use the 
> "measured" (from rview) radiance?
>
> TIA+CU Lars.
>
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