POV-Ray : Newsgroups : povray.binaries.images : any ideas what these black patches are.. Server Time
2 Aug 2024 02:28:48 EDT (-0400)
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From: s day
Subject: Re: any ideas what these black patches are..
Date: 14 Mar 2008 18:20:01
Message: <web.47db079dd387c8866ba4aa160@news.povray.org>
"Sven Littkowski" <sven [] jamaica-focus [] com> wrote:
> Hmmm.... All this guessing...
>
> S. Day, my suggestion is, that you publish the entire scene code and related
> graphics and INI files. This would allow us, to have some persons working on
> your scene to find out where the problem is.
>
> Once we can try and try again, you should get soon an exact answer. I hope,
> this suggestion is okay for you. Once the black holes are fixed, your scene
> will become a beautiful scene.


Hi,

The scene code is on the povcomp site for all to use:

http://www.povcomp.com/entries/199.php

Just paste the radiosity settings from the first post into the file. The strange
thing is the only settings I changed from the previous render (which worked fine
at lower resolutions) were

error_bound from 0.1 to 0.08
recursion_limit from 2 to 5
count from 200 to 500
brightness from 0.9 to 0.8

Of these I guess error_bound is the most likely to cause the problem but I am
still not sure if it coulde be related to the resolution.. I should have an
idea by Monday morning.

Anyway, anyone who wants to try rendering this is OK with me (I hope you have a
spare PC and plenty of time though... but then if you are used to POV patience
is something of a necessity ;-)

Sean


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From: Tim Attwood
Subject: Re: any ideas what these black patches are..
Date: 15 Mar 2008 01:51:53
Message: <47db7209@news.povray.org>
> The scene code is on the povcomp site for all to use:

sky_sphere ...

The radiosity engine only uses rays that travel finite
distances, sky_sphere and background are both an
infinite distance.  When a radiosity ray "leaks" thru
a seam, and then goes infinite, that ray is considered
pure black, which affects previous bounces of the
ray, coloring them black as well. Higher quality
settings means there are more rays to leak thru.

You should use a large inverted sphere for sky
in radiosity scenes, that way there will be no infinite
rays at all. That should reduce the artifacts.


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From: Thomas de Groot
Subject: Re: any ideas what these black patches are..
Date: 15 Mar 2008 03:11:06
Message: <47db849a$1@news.povray.org>
"s.day" <s.d### [at] uelacuk> schreef in bericht 
news:web.47db059fd387c8866ba4aa160@news.povray.org...
>
> I have had similar issues to you but find rendering at 50% of the final
> width/height to usually be acceptable (although comparissons may show that
> rendering with 50% the radiosity quality at the correct resolution will be 
> just
> as good..).
I think that you can try less than 50% and get good results. The only thing 
probably is that some more radiosity has to be calculated in the second 
pass, but that might be compensated somewhat by a higher trace resolution in 
the first..

>
> I do not really understand the radiosity settings very well I have a rough 
> idea
> of how most of them work but tend to resort to trial and error more than
> educated guessing..
>
Yes, I understand what you mean. I am slowly getting understanding of it, 
but experimentation remains dominant.

Thomas


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From: s day
Subject: Re: any ideas what these black patches are..
Date: 15 Mar 2008 04:15:00
Message: <web.47db935ed387c8866ba4aa160@news.povray.org>
"Tim Attwood" <tim### [at] comcastnet> wrote:
> > The scene code is on the povcomp site for all to use:
>
> sky_sphere ...
>
> The radiosity engine only uses rays that travel finite
> distances, sky_sphere and background are both an
> infinite distance.  When a radiosity ray "leaks" thru
> a seam, and then goes infinite, that ray is considered
> pure black, which affects previous bounces of the
> ray, coloring them black as well. Higher quality
> settings means there are more rays to leak thru.
>
> You should use a large inverted sphere for sky
> in radiosity scenes, that way there will be no infinite
> rays at all. That should reduce the artifacts.


Hi Tim,

That's something I did not know, not completely sure it is affecting this image
as some of the black patches are on areas I am pretty confident do not have any
seam's but as I created this over 3 years ago (was povcomp really that long ago)
I don't remember too much about it.

I will wait to see how the current render is when it gets past the pretrace
stages and if I still have the black patches will give this a go. I think I
will try some experiments with this anyway without all the objects in the scene
to see if I can find out a bit sooner..

Sean


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From: s day
Subject: Re: any ideas what these black patches are..
Date: 17 Mar 2008 07:25:00
Message: <web.47de6242d387c8867eb3d110@news.povray.org>
The mystery deepens.. The machine I was running this render on crashed over the
weekend (not sure of the reason for the crash), but it had (just) done enough
of the render to see that the patches were still present (and may have been
even worse).

This was with the following radiosity settings:

    pretrace_start 0.08
    pretrace_end   0.01
    count 1000
    nearest_count 20
    error_bound 0.2
    recursion_limit 4
    low_error_factor .9
    gray_threshold 0
    minimum_reuse 0.015
    brightness 0.8
    adc_bailout 0.01/2

I am now wondering if this is a problem with the machine I am using for the
render (maybe a dodgy memory chip issue which would explain the crash), I think
I will try stripping the radiosity settings back to something really basic that
should not cause any issues (and will be much quicker) then see how that goes.

Sean


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temp2.jpg


 

From: Thomas de Groot
Subject: Re: any ideas what these black patches are..
Date: 17 Mar 2008 08:10:25
Message: <47de6dc1$1@news.povray.org>
"s.day" <s.d### [at] uelacuk> schreef in bericht 
news:web.47de6242d387c8867eb3d110@news.povray.org...
>
> The mystery deepens.. The machine I was running this render on crashed 
> over the
> weekend (not sure of the reason for the crash), but it had (just) done 
> enough
> of the render to see that the patches were still present (and may have 
> been
> even worse).
>
> This was with the following radiosity settings:
>
>    pretrace_start 0.08
>    pretrace_end   0.01
>    count 1000
>    nearest_count 20
>    error_bound 0.2
>    recursion_limit 4
>    low_error_factor .9
>    gray_threshold 0
>    minimum_reuse 0.015
>    brightness 0.8
>    adc_bailout 0.01/2
>
> I am now wondering if this is a problem with the machine I am using for 
> the
> render (maybe a dodgy memory chip issue which would explain the crash), I 
> think
> I will try stripping the radiosity settings back to something really basic 
> that
> should not cause any issues (and will be much quicker) then see how that 
> goes.
>
This is strange indeed. I am wondering now if those artifacts are caused by 
radiosity... Have you had a mention of I-Stack Overflows reported in the 
statistics? Maybe max_intersections is too low?

OTOH, it looks a bit like a max_gradient problem, but if no isorfaces are 
used here... Neither max_trace.... And without reflective surfaces 
max_trace_level seems out of the question too...

Thomas


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From: s day
Subject: Re: any ideas what these black patches are..
Date: 17 Mar 2008 08:40:00
Message: <web.47de73e8d387c8867eb3d110@news.povray.org>
> This is strange indeed. I am wondering now if those artifacts are caused by
> radiosity... Have you had a mention of I-Stack Overflows reported in the
> statistics? Maybe max_intersections is too low?
>
> OTOH, it looks a bit like a max_gradient problem, but if no isorfaces are
> used here... Neither max_trace.... And without reflective surfaces
> max_trace_level seems out of the question too...
>
> Thomas

Hi Thomas,

Not sure about the max_intersections as the scene has not completed yet (it
crashed and now I have restarted it with lower quality radiosity settings but I
will look into this next).

However, I think I may have found the issue (although I am not sure yet and it
will require more test renders to check..) I inserted the basic radiosity
settings and re-rendered (wow! that was much quicker) the scene looks fine.
However, I noticed that the comment shows a value for nearest count of 1..10.
Now the documentation states that 20 is the highest possible value but on
Christoph's radiosity tutorial:

http://www.imagico.de/pov/radiosity01.html

He states 10 is the highest, obviously only one of these is correct and maybe
setting this too high is the cause.

I will do some tests to find out but am pretty sure I have used nearest_count=20
before without problems..

Sean


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From: Thomas de Groot
Subject: Re: any ideas what these black patches are..
Date: 17 Mar 2008 10:27:45
Message: <47de8df1@news.povray.org>
"s.day" <s.d### [at] uelacuk> schreef in bericht 
news:web.47de73e8d387c8867eb3d110@news.povray.org...
>
> I will do some tests to find out but am pretty sure I have used 
> nearest_count=20
> before without problems..
>

Sean,
20 should work fine, according to the docs. However, it certainly might up 
render time. I am not sure about that 10 on Christoph's site. Might be a 
typo, but it might also be a maximum Christoph considers as reasonable and 
within render time tolerance.
I am certainly curious to see the outcome of your experiments.

Thomas


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From: Alain
Subject: Re: any ideas what these black patches are..
Date: 17 Mar 2008 17:44:47
Message: <47def45f$1@news.povray.org>
s.day nous apporta ses lumieres en ce 2008/03/17 09:36:

> http://www.imagico.de/pov/radiosity01.html
> 
> He states 10 is the highest, obviously only one of these is correct and maybe
> setting this too high is the cause.
> 
> I will do some tests to find out but am pretty sure I have used nearest_count=20
> before without problems..
> 
> Sean
> 
In early MegaPOV radiosity implementations, nearest_count was limited to 10. The 
tutorial was originaly writen for those early specifications. It was edited for 
the POV-Ray radiosity in version 3.5, then updated for 3.6. Some details got 
forgotten.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you think it's a failing of the 
universe that the large software companies like Corel or Fractal Design do NOT 
export to POV primitives.
George Erhard


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From: Eero Ahonen
Subject: Re: any ideas what these black patches are..
Date: 18 Mar 2008 14:05:12
Message: <47e01268$1@news.povray.org>
s.day wrote:
> I forgot to add that the machine is only running XP 32 bit and 32 bit POV which
> is why I wondered if approaching the 2GB memory limit may be causing the
> problem.
> 
> Sean
> 

Start XP with /3GB -switch and it'll be able to allocate 3G for one process.

-- 
Eero "Aero" Ahonen
    http://www.zbxt.net
       aer### [at] removethiszbxtnetinvalid


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