I've had a course in Computer-Graphics this Semester, and
got all excited about all the kind of approaches and ideas
that there are in order to render an image.

Anyways, the last session was about global illumination,
local vs global lighting techniques etc. This got me started
in understanding the technique of POV-Ray in detail...

The basic idea: Create several passes to generate the
different effects. So, one pass for gathering detailed and
blotchy radiosity data. This is later loaded and smoothened
by using a higher error_bound when loading as compared
to when saving.
Another pass for gathering the photons. Since these stay
unaffected of everything all the time when loaded, I could
gather photons in one pass, and load them, even without
the lightsource, a special criteria when combining pure
radiosity lighting with photons.

So, I've just made successive experiments: pure radiosity,
with no lightsource. Then, photons (since POV's radiosity
doesn't do light reflection/refraction very detailed), but these
were loaded into the radiosity scene, no lightsource present.
Finally, lightsource AND photons. For testing purposes,
I've sometimes calculated the radiosity samples with photons,
sometimes without, to look for differences.

Anyways, I've noticed that photons DO make a difference,
but its very small, but it DOES take longer to generate the
radiosity data. So unless there's heavy "photonizing", its
not really needed.
Additionally, it might be of interest to know that using
actual lightsources gives sharper shadows (though using
area-lights to get soft shadows is a must for realistic lighting,
somewhat paradox). BUT, it must be said that shadows
produced by pure radiosity lighting are VERY soft.
Lightsources also generate specular highlights, which are
hard to come by with pure rad-lighting. Using reflection
values with high exponents does the job, but slows down
the entire raytracing of the final pass (should be switched
off when gathering radiosity data).

I just thought I'd share these few images. I've got some dozens
more (most of em in 320x240) and will likely create a new
page on my website which'll cover the experiments and obtained
results.

Also note that outdoor scenes will most likely require different
setups, but I've found this very entertaining and educating. Expect
some of my next images to be Radiosity-Filled. :-)

Regards,
Tim

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights



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Attachments:
Download '1_rad_r2b1p1_largeAA.jpg' (24 KB) Download '3_rad_r2b1p1_largeAA.jpg' (26 KB) Download '4_rad_r2b2p1_g00_largeAA.jpg' (25 KB)

Preview of image '1_rad_r2b1p1_largeAA.jpg'

Preview of image '3_rad_r2b1p1_largeAA.jpg'

Preview of image '4_rad_r2b2p1_g00_largeAA.jpg'

What images show what? I have three here, but I don't know which one is
supposed to show radiosity and/or photons....

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Oh, ok. All of them have photons.

There is one image where the glowing box
throws a shadow on the ceiling. That's
lightsource and radiosity combined.

There are two images where the glowing box
doesn't have a shadow. The one with the
VERY smooth shadows is pure radiosity,
with photons loaded AFTER the radiosity
was generated.
The other image is almost the same setup,
but the glowing box has a no_shadow-tag,
and uses a lightsource.

Note that the last image (lightsource+no_shadow)
uses a different brightness value, its .5 compared
to the others using 1.25.

The results are VERY different when using no_shadow
or not.

Which one do you like best?

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


> What images show what? I have three here, but I don't know which one is
> supposed to show radiosity and/or photons....
>
>


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> All of them have photons
That's too bad! I'd like to do the same with radiosity as one would normally
do with photons. Addiotionally I would be really happy if media would with
ambient light-sources into account: no light source, but just a(n) object(s)
with high ambient value, using radiosity.


I like 4_rad_r2b2p1_g00_largeAA best. It has no light bleeding at the bottom
of the triangle (see 1_rad_r2b1p1_largeAA), and the light source doesn't
reflect the wall colors (3_rad_r2b1p1_largeAA).

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> That's too bad! I'd like to do the same with radiosity as one would
normally
> do with photons. Addiotionally I would be really happy if media would with
> ambient light-sources into account: no light source, but just a(n)
object(s)
> with high ambient value, using radiosity.

I've attached an image showing how the first pass using radiosity
looks like: its rather blotchy and patchy. Notice though that we do
get a little refracted/reflected light underneath the sphere.
Still, radiosity is more of a diffuse reflection function, than photons,
which does specular reflection. They both complement each other
pretty well, and you shouldn't attempt doing photon effects with
pure radiosity unless you've got waaaay too much time on your
hands. But I guess its far from practical.
AFAIR someone had posted a reflecting torus, where radiosity
was used to create that light-focussed effect which occurs on the
inside of that obect. I'm not too sure who did it, and when though.
Still, it shows that it IS possible if you're desperate.

About that media interaction: I'll just make some tests. AFAIK
"media on" in the radiosity statement should take care of that,
but I hadn't experimented with that yet. I'll notify in this thread.


> I like 4_rad_r2b2p1_g00_largeAA best. It has no light bleeding at the
bottom
> of the triangle (see 1_rad_r2b1p1_largeAA), and the light source doesn't
> reflect the wall colors (3_rad_r2b1p1_largeAA).

Thanks for the feedback. Yeah, a shadowing lightsource doesn't
look too good. But IMHO, the lightbleeding may be a desired
effect when using radiosity, and it may be toned down using
gray_threshold.

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights



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Well, here's the pic I've forgotten to attach...
Notie that all those artifacts get smoothened
out later when using a higher error_bound.

Anyways, I've also found the thread the with radiosity
I mentioned earlier:
http://news.povray.org/povray.binaries.images/29501/


-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights



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Attachments:
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Preview of image '1_rad_r1b0p0_largeAA.jpg'

Scattering media doesn't take ambient lightsources
from radiosity calculations into account. After reading
the docs carefully I should have expected that, as it
says

6.11.11.2.9 Media and Radiosity
Radiosity estimation can be affected by media.

It doesn't say that its vice versa.

But its always better to experiment and find out
yourself...


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> which does specular reflection. They both complement each other
> pretty well, and you shouldn't attempt doing photon effects with
> pure radiosity unless you've got waaaay too much time on your
> hands. But I guess its far from practical.
> AFAIR someone had posted a reflecting torus, where radiosity
> was used to create that light-focussed effect which occurs on the
> inside of that obect. I'm not too sure who did it, and when though.
> Still, it shows that it IS possible if you're desperate.

I did, and actually it shows that it is NOT possible to get decent caustics
using pure radiosity.  It would be possible if you could use more samples
for radiosity though.

cu!
--
ZK AKA SaD
http://www.povplace.be.tf
"Use the instrumentpanel, Luke!"

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I stand corrected. Then, at least, it is theoretically
possible. But in theory, what isn't? :-)


-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


>
> I did, and actually it shows that it is NOT possible to get decent
caustics
> using pure radiosity.  It would be possible if you could use more samples
> for radiosity though.
>
> cu!



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ratiosity will take media into account with "media on". But what about the
other way around: media taking ambient light sources or diffused light into
account?

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