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clipka <ano### [at] anonymousorg> wrote:
> 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...
I can hold my breath forever... as long as no one is looking. ;)
I never use more than a recursion of 2 (of course I would be lying there),
mostly 1 or not set. So I still shy away from 3, from past experiences with
render time shock. Especially when impatiently experimenting on a scene.
Sounds like I was under the wrong impression, thinking already dark areas would
get darker still. I just figured that would be how it would be, as though
illumination drops. Ultimately to zero. I had thought in terms of a light fade
for radiosity, of sorts. Like a shadow + dark color = darker shadow, or
something along those lines of thinking.
So this means the current way radiosity works is only to brighten upward from a
certain threshold (the actual pigment color, or lack of any) and never go lower?
I always feel like the kid in school class who was daydreaming and not paying
attention. Oh yeah, I was that kid. LOL
Bob
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