Kenneth nous apporta ses lumieres en ce 09/08/2006 03:57:
> Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
>> Hi Ken:
>>
>>    It's seems not that bad to me, but indeed it can be better. First, to
>> control the color spill, just use gray_threshold.
> 
> Sorry, I may have described things the wrong way.  In my scene, it *seems*
> that there should be MORE color spill onto the ceiling, from the
> saturated-color walls. But then again, the tall (distant) box shape seems
> to show quite good color spill from the red wall.  So perhaps I'm looking
> for an effect that really shouldn't be there. Difficult to tell!
> 
>> For more defined
>> shadows, error_bound should be lower and nearest count perhaps higher.
> 
> Yes, I'm beginning to understand that a lower error_bound value "breaks up"
> (and distorts) the ray-created color "patches" into smaller and smaller
> pieces, which would seem to be more accurate. (Smoothing out those many
> patches has proven difficult for me, though. As I understand things, a
> higher count is then needed.) A higher nearest_count DOES radically improve
> things--but from what I've seen, it appears to make shadows less defined,
> sort of smoothing them out. Am I mistaken about that? Is it interacting
> with "something else" that I should change?
> 
>> In the other hand, I don't think you need more than 2 bounces, 3 at
>> most (recursion_limit).
> 
> I'm still trying to understand this "bounce" idea. But you're right, higher
> recursion_limit values seem to have less and less of an effect. I've
> settled on 3. Is it correct to assume that the more bounces, the more the
> various radiosity-created colors in the scene blend together and become
> MORE muted? If so, it sounds like something to be avoided (?) As you can
> see, I'm really struggling with these concepts!
>>    Hope this helps...
> 
> Yes indeed! Thanks.
> 
> Ken W.
> 
> 
> 
A high recursion_limit can be good if you want light to spill into somewhat 
distant or convoluted areas that would otherwise remain unlit. You are correct 
in your observation about diminishing effect with higher recursion_limit. It's a 
normal effect. It diminish acording to the diffuse value of the surfaces and on 
the colour of those. If you bounce upon a pure red surface, then on a pure green 
or blue one, there is no light left as the first returns only red and the second 
returns only green or blue that they don't receive.

-- 
Alain
-------------------------------------------------
An idea is not responsible for the people who believe in it.

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Kenneth nous apporta ses lumieres en ce 09/08/2006 04:48:
> Hi, Alain, thanks for posting these tips. I do have some questions (of
> course!):
> 
> Alain <ele### [at] netscapenet> wrote:
> 
>> Default to 1. It's a multiplicator for the returned radiosity samples. Without
>> this, your scene would be almost all black.
> 
> For some not-yet-understandable reason (perhaps because the light_sphere is
> so small)  I HAD to pump the brightness up, otherwise the scene was just
> way too dark. But this surely interacts with other values, so perhaps it
> should be lowered, and some other things adjusted.
Increase the ambient value of the "light", you can also increase the RGB value 
beyong 1. You are not limited to values from 0 to 1.
> 
>> Shifting this "may" help you getting rid of some artefacts near corners like
>> dark spots along inside corners.
> 
> Shifting it up ot down?  Is it better to use a higher value for this or a
> lower value?
Equivalent. You only want the pretrace sampling to shift place so that they miss 
the problem pixels. It's also advisable to move the camera a very small amount, 
like +/-0.000001 unit.
> 
>> Lowering this may enable you to use more relaxed settings elswhere, possibly
>> lending to somewhat shorter render times.
> 
> I'll try that.  Lower values do produce a drastic difference in smoothing
> things out. But does a lower value also make subtle artifacts more visible
> and
> pronounced? It seems to, but my eyes may be playing tricks on me.
> 
>> This puts a cap on the brightness. Not importent in your case as you apparently
>> don't have any object with a brightness larger than 1.
> 
> I'm a bit fuzzy on this: Does it control the brightness of rays shot from
> the light source, or the brightness of BOUNCED rays? Or both?? I thought it
Both if you use a high ambient "light" in place of a regulat light_source.
> would keep any area of the scene from exceeding a certain brightness, but
> that doesn't seem so; I can easily "wash out" areas of the scene closest to
> the light sphere if I'm not careful. So, I don't really understand what
> max_sample does.
This "wash out" is due to oversaturation. It appens when the (incident light * 
brightness * diffuse) leads to RGB values greater than 1. Those values are taken 
"as is" during calculations, then clipped to 1 in the final image.
> 
>> 1/20 the default of 0.5.
> 
> Sorry, I don't understand that. Explain?
Half of 0.5 is 0.25. 1/20 if 0.5 is 0.025.
Your specified error_bound of 0.9 gets lowered to 0.0225 during the last 
pretrace step. That's prety small.
> 
>> Why? Default to "on". Only relevant if you do multi-pass or distributed render.
> 
> I've found that the quality gets better with it off--at least in this
> particular scene. It's a subtle difference, but it's there.
Good reason.
>> You may try lowering brightness to 1 and bump up the pigment or ambient of the
>> small ambient light sphere.
> 
> Yes, that does help. I'll work with the idea.
> 
> Ken W.
> 
> 


-- 
Alain
-------------------------------------------------
How many of you believe in psycho-kinesis? Raise my hand...

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"Samuel Benge" <stb### [at] hotmailcom> wrote:
>
> Hi Ken. Are you the same Ken who once ran a big list of graphics links?

Nope, never did. Sorry!
>
>
> If I may give you some settings I always use for radiosity. Try these alone...
>

I'll give them a whirl, and report back with the results.  Thanks.
>
> The error_bound should be low for better shadows. This is one of the most
> important settings. error_bound and count together should be modified
> before anything else.

Yes, I've been wondering about that.  It seems that count
ISN'T the FIRST  thing to modify (given defaults
for everything else.) Not much visual
difference between low and high values, without modifying other things "in
step" as well. Thanks for the tip.
>
> In addition to these things, you should use a bright, fading (fade_power 2)
> light inside the sphere instead of just making the sphere very bright. An
> area_light (with orient and circular flags added) works well for this. The
> sphere should be given the no_shadow flag to let the light shine through.

Alas, I was *hoping* I could light this scene realistically just by using a
pure, small ambient "light source," but I do understand that the radiosity
equations (and/or just the default values) were made to be used with
ACTUAL light sources. I may ultimately have to do as you suggest.  Haven't
given up yet, though! ;-)

Let me ask a very basic question:
1)  Is it ALWAYS better --that is, more realistic and of higher quality--to
use the highest count possible and a very low error_bound value? (Assuming
that the resulting l*o*n*g render time is unimportant.)

Ken W.

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> > Alain <ele### [at] netscapenet> wrote:

> >> Shifting this "may" help you getting rid of some artefacts near corners like
> >> dark spots along inside corners.
> >
> > Shifting it up ot down?  Is it better to use a higher value for this or a
> > lower value?
> Equivalent. You only want the pretrace sampling to shift place so that they miss
> the problem pixels. It's also advisable to move the camera a very small amount,
> like +/-0.000001 unit.

Do you mean, shifting the camera BETWEEN the pretrace steps? If so, how
is that done?

Ken W

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Kenneth nous apporta ses lumieres en ce 10/08/2006 17:18:
>>> Alain <ele### [at] netscapenet> wrote:
> 
>>>> Shifting this "may" help you getting rid of some artefacts near corners like
>>>> dark spots along inside corners.
>>> Shifting it up ot down?  Is it better to use a higher value for this or a
>>> lower value?
>> Equivalent. You only want the pretrace sampling to shift place so that they miss
>> the problem pixels. It's also advisable to move the camera a very small amount,
>> like +/-0.000001 unit.
> 
> Do you mean, shifting the camera BETWEEN the pretrace steps? If so, how
> is that done?
> 
> Ken W
> 
> 
Not during the pretrace. Before you start the rendering. There are some cases 
where a radiosity sampling falls exactly on an internal corner. In those cases, 
the sampling can look behind a wall for example, taking information from a 
totaly dark area, leading to dark spots along the corner.
Changing pretrace_start or moving the camera very slightly can cause the problem 
sampling to miss the critical points.

-- 
Alain
-------------------------------------------------
Wouldn't it be nice if whenever we messed up our life we could simply press 
'Ctrl Alt Delete' and start all over?

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Kenneth nous apporta ses lumieres en ce 10/08/2006 16:18:
> "Samuel Benge" <stb### [at] hotmailcom> wrote:
>> Hi Ken. Are you the same Ken who once ran a big list of graphics links?
> 
> Nope, never did. Sorry!
>>
>> If I may give you some settings I always use for radiosity. Try these alone...
>>
> 
> I'll give them a whirl, and report back with the results.  Thanks.
>> The error_bound should be low for better shadows. This is one of the most
>> important settings. error_bound and count together should be modified
>> before anything else.
> 
> Yes, I've been wondering about that.  It seems that count
> ISN'T the FIRST  thing to modify (given defaults
> for everything else.) Not much visual
> difference between low and high values, without modifying other things "in
> step" as well. Thanks for the tip.
>> In addition to these things, you should use a bright, fading (fade_power 2)
>> light inside the sphere instead of just making the sphere very bright. An
>> area_light (with orient and circular flags added) works well for this. The
>> sphere should be given the no_shadow flag to let the light shine through.
> 
> Alas, I was *hoping* I could light this scene realistically just by using a
> pure, small ambient "light source," but I do understand that the radiosity
> equations (and/or just the default values) were made to be used with
> ACTUAL light sources. I may ultimately have to do as you suggest.  Haven't
> given up yet, though! ;-)
> 
> Let me ask a very basic question:
> 1)  Is it ALWAYS better --that is, more realistic and of higher quality--to
> use the highest count possible and a very low error_bound value? (Assuming
> that the resulting l*o*n*g render time is unimportant.)
> 
> Ken W.
> 
> 
> 
> 
> 
> 
You can have realy good lighting using only radiosity, but you get beter result 
if you use relatively large ambient lights.

-- 
Alain
-------------------------------------------------
Everybody should believe in something: I believe I'll have another drink.

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Kenneth wrote:
> Sorry, I may have described things the wrong way.  In my scene, it *seems*
> that there should be MORE color spill onto the ceiling, from the
> saturated-color walls. But then again, the tall (distant) box shape seems
> to show quite good color spill from the red wall.  So perhaps I'm looking
> for an effect that really shouldn't be there. Difficult to tell!

   Then I think you are expecting too much spill, more than normal for 
regular surfaces.

> [...] A higher nearest_count DOES radically improve
> things--but from what I've seen, it appears to make shadows less defined,
> sort of smoothing them out. Am I mistaken about that? Is it interacting
> with "something else" that I should change?

   Yes, with every other parameter!!! :) But I usually also raise 
error_bound and that compensates the effect.

> I'm still trying to understand this "bounce" idea. But you're right, higher
> recursion_limit values seem to have less and less of an effect. I've
> settled on 3. Is it correct to assume that the more bounces, the more the
> various radiosity-created colors in the scene blend together and become
> MORE muted? If so, it sounds like something to be avoided (?) As you can
> see, I'm really struggling with these concepts!

   The more bounces, more realistic is the radiosity, as in reality 
there are infinite bounces. But it's only useful with maze-like 
situations. I think you should only use the number of bounces needed 
just to light all the visible parts of the scene, no more.

--
Jaime

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Alain <ele### [at] netscapenet> wrote:

> You can have realy good lighting using only radiosity, but you get beter result
> if you use relatively large ambient lights.
>
> --

Yes, that has been my experience as well. Making my single ambient 1 light
just two or three times larger greatly improves the "realistic" look of the
bounced radiosity.  I think that I might be giving POV a somewhat *extreme
situation* to deal with, by making my single light sphere so small. In
"normal" radiosity scenes that I've done, using a sky_sphere
and several actual light sources, it is MUCH easier to get
good results.

Ken

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Kenneth nous apporta ses lumieres en ce 12/08/2006 17:28:
> Alain <ele### [at] netscapenet> wrote:
> 
>> You can have realy good lighting using only radiosity, but you get beter result
>> if you use relatively large ambient lights.
>>
>> --
> 
> Yes, that has been my experience as well. Making my single ambient 1 light
> just two or three times larger greatly improves the "realistic" look of the
> bounced radiosity.  I think that I might be giving POV a somewhat *extreme
> situation* to deal with, by making my single light sphere so small. In
> "normal" radiosity scenes that I've done, using a sky_sphere
> and several actual light sources, it is MUCH easier to get
> good results.
> 
> Ken
> 
> 
> 
> 
Small ambient light mean more chance for ALL samplings from any sampling area to 
miss it, resulting in dark patches in areas that should be lighted. If you rely 
on a small ambient light, you must use a high count value to increase your 
chance that any sampling will actualy hit that small object.

-- 
Alain
-------------------------------------------------
OFFICE ARITHMETIC
Smart boss + smart employee = profit
Smart boss + dumb employee = production
Dumb boss + smart employee = promotion
Dumb boss + dumb employee = overtime

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Alain <ele### [at] netscapenet> wrote:
> Kenneth nous apporta ses lumieres en ce 12/08/2006 17:28:
> > Alain <ele### [at] netscapenet> wrote:

> Small ambient light mean more chance for ALL samplings from any sampling area to
> miss it, resulting in dark patches in areas that should be lighted. If you rely
> on a small ambient light, you must use a high count value to increase your
> chance that any sampling will actualy hit that small object.

That's a good analysis of something quite important that I
didn't realize. Thanks!

Ken

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