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6 Jul 2022 00:31:52 EDT (-0400)
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From: Chris R
Subject: Re: Impending Disaster
Date: 13 Feb 2022 23:20:00
Message: <web.6209d852941abfdda9cd79b35cc1b6e@news.povray.org>
"Chris R" <car### [at] comcastnet> wrote:
> Latest attempt at an indoor scene lit by sunlight from a window.  I ended up
> adding some extra lights for interest on the toys, too.
>
> This particular rendering was done with a pretty high anti-aliasing setting, but
> just the Radiosity_Fast setting for radiosity.  Even increasing it to
> Radiosity_IndoorLQ introduced terrible artifacts on all of my isosurfaces, and I
> haven't figured out how to eliminate them yet.
>
> The blocks, the plane, the train and tracks are all isosurfaces with wood
> pattern perturbations.  I experimented with a lot of combinations of low
> accuracy and high max_gradient, and used evaluation, but when I bump up the
> radiosity I end up with black splotches everywhere.  I may need to dig into the
> details of the radiosity settings to figure out how to tune them for a
> particular scene...
>
> -- Chris R.

I added a few more elements to the scene, including some haze, generated by the
smoke puffing out of the train engine.

For this run, here were my radiosity settings:
                pretrace_start 0.0625
                pretrace_end 0.0078125
                count 25
                nearest_count 5
                error_bound 0.25
                low_error_factor 0.3
                recursion_limit 2



-- Chris R.


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From: Chris R
Subject: Re: Impending Disaster
Date: 13 Feb 2022 23:25:00
Message: <web.6209d94e941abfdda9cd79b35cc1b6e@news.povray.org>
"Chris R" <car### [at] comcastnet> wrote:
> Latest attempt at an indoor scene lit by sunlight from a window.  I ended up
> adding some extra lights for interest on the toys, too.
>
> This particular rendering was done with a pretty high anti-aliasing setting, but
> just the Radiosity_Fast setting for radiosity.  Even increasing it to
> Radiosity_IndoorLQ introduced terrible artifacts on all of my isosurfaces, and I
> haven't figured out how to eliminate them yet.
>
> The blocks, the plane, the train and tracks are all isosurfaces with wood
> pattern perturbations.  I experimented with a lot of combinations of low
> accuracy and high max_gradient, and used evaluation, but when I bump up the
> radiosity I end up with black splotches everywhere.  I may need to dig into the
> details of the radiosity settings to figure out how to tune them for a
> particular scene...
>
> -- Chris R.

I tried a number of combinations of higher-quality radiosity settings and am
still getting artifacts; the higher the count and lower the error_bound the
worse the artifacts.  In the image below, I took the radiosity settings from
before and just cut the pretrace_end size in half.  As you can see, this
introduced a noticeable, but relatively small artifact on the robot's
glass-covered dial.  I am running again with these same settings, but adding a
maximum_reuse of 0.05 and a minimum_reuse of 0.005 to see if that makes the
artifact go away or makes it worse.


-- Chris R.


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From: Thomas de Groot
Subject: Re: Impending Disaster
Date: 14 Feb 2022 02:22:27
Message: <620a0333$1@news.povray.org>
For what it is worth, I generally use the following radiosity settings, 
to full satisfaction:

     pretrace_start     0.08
     pretrace_end       0.004
       count            100, 1000
       nearest_count    10, 5
       error_bound      1
       recursion_limit  2
       low_error_factor 0.3
       gray_threshold   0.0
       minimum_reuse    0.015
       maximum_reuse    0.1		
       brightness       1

       adc_bailout      0.01/2
       normal           on
       media            off
       always_sample    off

This is quite fast and I experience little or no artefacts. Note the 
dual (optional) parameters used for count and nearest_count. This can 
increase the quality of your render without slowing it down much. See 
the following page of the wiki: 
https://wiki.povray.org/content/Reference:Radiosity#count

You may also want to try stochastic rendering with, e.g., +am3 +a0.01 
+ac0.90 +r3. If you do that, change count to 10 all other radiosity 
settings remaining the same.

-- 
Thomas


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From: Chris R
Subject: Re: Impending Disaster
Date: 14 Feb 2022 22:45:00
Message: <web.620b2157941abfdda9cd79b35cc1b6e@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> For what it is worth, I generally use the following radiosity settings,
> to full satisfaction:
>
>      pretrace_start     0.08
>      pretrace_end       0.004
>        count            100, 1000
>        nearest_count    10, 5
>        error_bound      1
>        recursion_limit  2
>        low_error_factor 0.3
>        gray_threshold   0.0
>        minimum_reuse    0.015
>        maximum_reuse    0.1
>        brightness       1
>
>        adc_bailout      0.01/2
>        normal           on
>        media            off
>        always_sample    off
>
> This is quite fast and I experience little or no artefacts. Note the
> dual (optional) parameters used for count and nearest_count. This can
> increase the quality of your render without slowing it down much. See
> the following page of the wiki:
> https://wiki.povray.org/content/Reference:Radiosity#count
>
> You may also want to try stochastic rendering with, e.g., +am3 +a0.01
> +ac0.90 +r3. If you do that, change count to 10 all other radiosity
> settings remaining the same.
>
> --
> Thomas

Thanks, I tried these out and they seem to have worked pretty well.

-- Chris R.


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From: Thomas de Groot
Subject: Re: Impending Disaster
Date: 15 Feb 2022 02:08:58
Message: <620b518a$1@news.povray.org>
Op 15/02/2022 om 04:43 schreef Chris R:
> 
> Thanks, I tried these out and they seem to have worked pretty well.
> 
> -- Chris R.

Indeed. Looks pretty good. Most credit goes to Clipka and Alain I 
believe, not forgetting all those povers struggling and coming up with 
smart solutions. :-)

It is a fair basis from which tweaking can be done simply when necessary.

-- 
Thomas


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From: Kenneth
Subject: Re: Impending Disaster
Date: 16 Feb 2022 19:20:00
Message: <web.620d9410941abfdd4cef624e6e066e29@news.povray.org>
"Chris R" <car### [at] comcastnet> wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> > For what it is worth, I generally use the following radiosity settings,
> > to full satisfaction:
> > [snip]
> >
> > This is quite fast and I experience little or no artifacts. Note the
> > dual (optional) parameters used for count and nearest_count. This can
> > increase the quality of your render without slowing it down much.
>
> Thanks, I tried these out and they seem to have worked pretty well.
>

This does look much better.

About the 2-value count: In my own tests over the last six months, I have set
the 2nd value *really* high -- for example 700, 93271 (!) I have found that it
seems to smooth-out the distribution of the radiosity light patches, by
gathering them from many truly different random directions. (That's my rather
simplistic description of the process, anyway.) With a single-value count, those
directions/locations are still random-- to a degree-- but 'not quite random
enough', in my opinion; I have seen some subtle artifacts that look like
'harmonic bands' of rad patches on objects...like very subtle geometric bands or
stripes. Sorry that I can't be more descriptive, but it's an effect that the
higher 2nd count helps to eliminate.


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