POV-Ray : Newsgroups : povray.beta-test.binaries : Radiosity POV 3.6 vs. 3.7 vs. MCPov : Re: Radiosity POV 3.6 vs. 3.7 vs. MCPov Server Time
23 Feb 2024 20:41:12 EST (-0500)
  Re: Radiosity POV 3.6 vs. 3.7 vs. MCPov  
From: Ive
Date: 19 Jan 2009 04:22:31
Message: <49744657@news.povray.org>
clipka wrote:
> Ive <"ive### [at] lilysoftorg"> wrote:
>> I have no explanation why the reflection in the mirror looks different
>> in the MCPov version. And in fact it makes me quite unhappy, it looks
>> somewhat desaturated.
> 
> Hum... maybe max trace level issues of sorts...?
>

Hmm, maybe. But shouldn't be max_trace_level of 8 be enough? It's just 
camera -> mirror -> rug. And the rug is not reflective.


>>> - The 3.6.1 shot looks rather dark; I attribute this to the windows and flaws in
>>> POV 3.6 radiosity: When gathering deep-recursion samples, POV 3.6 effectively
>>> just traced a single level, so I guess it will not make it through the windows.
>>> All 3rd-bounce samples will probably be pitch black, and possibly even the
>>> 2nd-bounce ones.
>>>
>> In fact there is NO window "glass", there is just empty space ;)
> 
> Hum again... okay, so there is no spoon...
> 
> If the scene is just radiosity-lit, and materials are defined deliberately to be
> identical, then the only thing I can think of that could cause a significant
> bias to any particular color (like, for example, black) is POV-Ray giving up on
> some rays due to max trace level, ADC bailout or similar (i.e. recursion depth
> in case of radiosity) - in which cases POV will invariably use pitch black as
> substitute.
> 
> So the way a version of POV "counts" recursion depth might make a difference
> regarding how much black is mixed in.
> 
> Does a significant portion of surfaces in your shot have reflective components?
>

All woods have a small amount of blurred reflection to get highlights. 
In the original 2002 version also the floor tiles where slightly 
reflective but I have disabled the floor reflection for this test 
render. The original version also used more complicated layered textures 
   for the walls, and this new renders do use simplified texture there.
The layered textures caused some strange artifacts in the 2002 render 
and where the main reason I gave up at this time.


> 
>>> - The 3.7 shot indeed looks weird - but this weirdness look distinctively
>>> familiar: "Ambient" immediately comes to mind.
>> Nope. All materials do use ambient 0 in the finish statement and no
>> default include files are used where something else might be specified.
> 
> That's perfectly weird. In all tests shots, I have never seen such effects. Note
> that the white tiles do not only "bleed" onto the walls - they themselves look
> overly bright.
> 
> Something gets a >1 term into it somewhere.
> 
> Again: Does a significant portion of surfaces in your shot have reflective
> components?
> 
> Assuming for now that the tiles are partially reflective - is the sum of their
> "reflection" and "diffuse" values possibly >1?

Nope. I would never do this ;) (And I have always double checked in the 
SDL source files to really make sure my answers and description is 
correct.) The color AND diffuse values are alwayxs <= 1. And, as 
mentioned, for the new renders NO reflection for the floor.


> Note that this breaks the law of conservation of energy. This is not an issue in
> classically-lit POV scenes, because of the strict separation between "images"
> and "light sources"; however, in radiosity scenes it can become dramatic.
> 

I know, I really do.

> I can imagine that MCPov *might* handle such situations automatically as a side
> effect of its design. However, I'm quite sure standard POV does not.
> 
> 
> Just to make sure: We are talking about 3.7.0.beta.30-rad1, right?
> 

Yes, 3.7.0.beta.30-rad1 from Chris' zip file, exactly.


I have attached a version with higher quality settings (and about 5h 
render time):

radiosity {
     pretrace_start 8/image_width
     pretrace_end   2/image_width
     count 800
     error_bound 0.4
     nearest_count 1
     low_error_factor 0.5
     recursion_limit 3
     brightness 1
}


And also a version where the radiosity block is just commented out (and 
no other changes are made). As expected, everything is pitch black 
except the sky and reflective parts of the scene where the sky gets 
reflected.

I really hate it to say so, but I think there is something weird going 
on with the radiosity calculation.

-Ive


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