Francois Labreque <fla### [at] videotronca> wrote:

> I'm currently playing around with procedural clouds, but as soon as I
> add radiosity to my image, the undersides of the cloud pick up some of
> the green of the grassy field below.  Is there an easy way to get rid of
> it?

> The code is way too messy and embryonic to post.  I'm just looking for
> general ideas.

> Thanks in advance.

In questions of radiosity, I always go back to the source.  Ie, the real
world.  Why aren't clouds green in the real world?

Well, several answers that I can see (some which might be wrong).  First,
the ground isn't green over large sections, and the gathered light blends
out.  Also, the dynamic range of the sunlight is so much greater than the
ground that it just doesn't matter.  Finally, the dispersion is such that
the green doesn't get 'turned around' and come back to us on the ground.

The first is easy to fix.  Maybe you could add some bits off to the side out
of the view that color correct your image.  The second isn't, because pov's
dynamic range is limited, though perhaps a post-process color correction
could be done.

The final one requires tweaking the dispersion parameters (this assumes
you're using media) of the scattering so that the light doesn't come back.

I don't know if any of this will help, but it might give some ideas.

Geoff

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