Am 05.12.2016 um 06:42 schrieb omniverse:
> Alain <kua### [at] videotronca> wrote:

>>> "omniverse" <omn### [at] charternet> wrote:
>>>
>>> Specular highlights used for Ivory_M and Ebony_M material/texture/finish are
>>> probably too bright unless used in conjunction with fresnel, a feature of
>>> current unofficial 3.7.1.1-alpha versions.
>>>
>>
>> Why does those finishes have any emission at all? Emission is only if
>> you want a texture to actually glow, even if it's a very dim glow.
>> Beter remove all emission everywhere, or set it at zero everywhere.
> 
> Well, considering radiosity eliminates ambient lighting I just use a tiny bit of
> emission to try and avoid any totally black areas. And also for a while now I've
> been keeping ambient to much lower levels than the default 0.1 for non-radiosity
> scenes, sometimes ambient 0 in lieu of a very low emission for the kind of
> ambient lighting.

But avoiding completely black areas _is_ radiosity's _job_ (when it is
enabled).

In this manner it differs fundamentally from ambient occlusion, which
reduces the brightness of an image, especially where surfaces are close
together. Radiosity, in contrast, brightens up things, especially where
surfaces are far apart -- but it also does add some brightness to nooks
and crannies.

If you still see completely black areas, this can mean one of two (well,
maybe three) things:

(A) You have set `recursion_limit` too low. I'd recommend 1 or 2 for
wide open outdoor scenes, but 2 or 3 for indoor scenes. Add another
level if your scene has no conventional light sources and is illuminated
exclusively from sky spheres, emissive materials or emissive media.

(B) Your light sources are too bright and your materials too dark.
Without radiosity this cancels out and you'll never be able to notice,
but when radiosity enters the picture this makes nooks and crannies darker.

(C Using a high assumed_gamma will also cause nooks and crannies to look
darker, because the gamma's overall darkening effect is most pronounced
for very dark tones.)


An additional note to (A): When reaching the recursion limit, the
radiosity algorithm currently presumes everything to be pitch black;
i.e. if `recursion_limit 2` is set, the algorithm will pretend that
light rays can't bounce around between diffuse surfaces more than twice.
This has the effect that using a low recustion limit makes the entire
image a tad darker than would be realistic (the most realistic setting
would be infinity, but that's not realistically computable... pun intended).

I have plans in my drawer to extend the radiosity algorithm, and make it
respect "ambient" again -- but only once it reaches the recursion limit.
This should have the effect of brightening up the scene just enough to
approximately compensate for the lack of infinite recursion (provided
"ambient" is set to a reasonable value).

I might also add an ambient occlusion mode to the mix: If enabled, an
incomplete recursion step would be made, querying only distance
information, and using that to simply darken the effective "ambient"
component.

But that's future plans, so nobody hold their breath please...

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