POV-Ray : Newsgroups : povray.binaries.images : Radiosity and reflective glass : Re: Radiosity and reflective glass Server Time
18 Oct 2021 12:04:18 EDT (-0400)
  Re: Radiosity and reflective glass  
From: Alain Martel
Date: 16 Sep 2021 12:14:10
Message: <61436d52$1@news.povray.org>

> "Chris R" <car### [at] comcastnet> wrote:
>> As promised, here is the scene with max_sample set to 10.  The artifacts are
>> gone.  I also took the suggestion of using a 5x5 area light for the main indoor
>> light.
> 
> Hi Chris,
> 
> It did help.
> 
> After reading the docs here
> (http://www.povray.org/documentation/3.7.0/r3_4.html#r3_4_4_3_3_8) it would seem
> that the max_sample feature controls the intensity of reflected/refracted rays.
> It would appear that using it is similar to altering the brightness clamping of
> reflected and refracted caustics in Blender Cycles... The bright blotches that
> your scene was producing are probably analogous to the so-called "fireflies"
> that you get in renderers such as Cycles. When you clamp these values, a scene's
> lighting becomes a bit less realistic.
> 
> I can't think of any other good solution... You can't just add a no_radiosity
> flag to the offending objects, because then the lighting would probably be
> *really* unrealistic. And if you use a super-high count in the radiosity block,
> the scene would take forever to render... The only other option I can think of
> it to try Clipka's UberPOV to make use of the randomized radiosity samples (I
> think the keyword to enable it is called no_cache). But even then, your problem
> goes from blotches to sharp pixel-sized fireflies...
> 
> (For the record, I think most of the initial blotches you were seeing were cast
> from the brass objects.)
> 
> Sam
> 
An option would be to use the importance mechanism.

Use a large count value. Add a #default directive that include something 
like :
#declare PrettyHighCount = 10000000; // 10 millions
#declare Intended_count = 150;
#default {... radiosity{importance Intended_count/PrettyHighCount}}

Then, in the description of the bright objects, add :
radiosity{importance 1}

In other not quite as bright objects, you can set the importance to 
something else, like 0.1.

That allow a lot of samples to be taken in the vicinity of the bright 
objects, while using a reasonable sampling density for the rest of the 
scene. That greatly reduce the rendering time.
Need version 3.7, work better in version 3.8.


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