"Bruno Cabasson" <bru### [at] cabassoncom> wrote:
>
> Besides, real atmosphere is a very complex thing, not easy to model, and
> real clouds are also quite complex and there are many kinds of them, each one having
a specific behaviour with light.


In fact, for a fully automatic volumn(cloud) renderer, it is not so different
between different kind of cloud. The main difference of them is the height, and
the shape(density map), and the average density(because a dense cloud needs more
multiple scattering)

ice droplets and liquid water droplets have different phase function when
scatters light. but for a dense media(if light from sun light source collide
many times in the cloud) the difference of the final appearance is small.
And because water droplets almost never absorb light, represent the albedo of
cloud almost 1.0( between visible wavelength range), so it is seldom eliminated
in cloud, a light beam can collide hundred of times in a heavy cloud. You can
see this:
http://news.povray.org/povray.binaries.utilities/message/%3Cweb.5bec15ae87bb2a51c8edf6b30%40news.povray.org%3E/#%3Cweb.
5bec15ae87bb2a51c8edf6b30%40news.povray.org%3E

This is the power(sp-radiance) at different level scattering output quantity.
Maybe you can say the most of it still concentrated at first level. But this is
an image contains a white cloud on the center, and the blue sky the other. It is
 the average sp-radiance on the whole image. If look at the cloud separately,
the multiple scattering part is the dominate.

And I attach a comparison. The image contains three images I rendered one year
ago but should be the same (or similar) condition. They are 1 level, 3 level,
and 27 level scattering renders.
(up to down.)






"Bruno Cabasson" <bru### [at] cabassoncom> wrote:


> the rest is the same values, except the sun power and the parmeters for the fog
> media. Colors are obtained automatically thanks to media, mainly the atmosphere
> with rayleigh scattering.
>
> Regards

When I watch this I guess you use scattering "extinction" not 1, because if you
use correct extinction 1 and lacks of multiple scattering, your clouds
is impossible so white. finally you use 0.25. When I use POV-Ray rendering
cloud, I always find I need use filled lights or additional emission.

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