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Kerkythea Rendering System • View topic - Specular Sampling Glitch
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Specular Sampling Glitch

Moderators: massimo, Avariant, Frederik, notareal, giannis, alvydas

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Fletch

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Post Tue Mar 08, 2011 7:28 pm

Specular Sampling Glitch

Here's what I'm talking about with the sampling glitch.
We thought it was with Fresnel, but it turns out that Ashikminh shader also has the issue.
Here's a test scene that reliably reproduces the error. I think it's important enough to mention, as I think fixing it will be to succeed in killing a major "bug" in KT. :D But more importantly, I think it will gain even more speed.

THE PROBLEM:
The RED PLASTIC CUBE is supposed to be a FLAT PLASTIC.
it's shininess is set to 10, but it's JUST AS SHINY as the SHINY PLASTIC yellow ball, which is set to 180 shininess.

When you change the RENDER SETTINGS from Lower settings to Higher settings, strange things start to happen with the specular reflections in the rendering. This effect is more noticeable or exaggerated when using the "patrick recommended standard plastic material" and it shows up as a circular effect. However, Chris determined that it's not due to the fresnel, it's just an issue with the specular sampling. I discovered when creating settings for Twilight that changing sampling DRASTICALLY effects results (and severely negatively effects render times)

Of course the sampling issue shows up in the shiny yellow plastic as well.
Attachments
SpecularGlitchTest.kzx
HERE'S THE KZX FILE!
(258.14 KiB) Downloaded 182 times
_0000_Low.jpg
_0001_Medium.jpg
_0002_High.jpg
_0003_Higher.jpg
_0004_Fine.jpg


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Fletch

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Post Tue Mar 08, 2011 9:04 pm

Chris came up with a work-around material that seems to hide or not display the bug as much, and as a result it renders faster in some cases, but in a strange way.

But most importantly, the strange circle in some render settings shown above doesn't show up. (see images and scene attached below.)
Attachments
SpecularGlitchTest-matfix.kzx
(257.27 KiB) Downloaded 178 times
_0004_low-matfix.jpg
_0003_Medium-matfix.jpg
_0002_High-matfix.jpg
_0001_Higher-matfix.jpg
_0000_fine-matfix.jpg


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Fletch

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Post Tue Mar 08, 2011 9:32 pm

Just out of curiosity - here's how it renders in Thea. :) (materials are obviously impossible to get exactly the same, but the flat red plastic is what I'm looking at in this view)

One thing I noticed is that where I expect to see a triangular shaped specular reflection on the yellow ball, even in thea it is not triangular.
Attachments
thea-fg.jpg


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notareal

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Post Wed Mar 09, 2011 4:27 pm

There is a little glossy roughness bug in Thea BSD. So if you used glossy based material, BSD result is not what it should be.
Thea Render and Kerkythea Rendering System, by Solid Iris Technologies
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Fletch

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Post Wed Mar 09, 2011 6:18 pm

no gloss.


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notareal

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Post Wed Mar 09, 2011 7:47 pm

Perhaps it's still the BSD roughness bug that affects. Smooth materials will need smaller blurred reflection subdivision than rough. Maybe 0-1 for smooth materials and for rough materials try a subdivision of 2 or 3.
Also material perceptual level should be in 5-10%

Can you post Thea scene, that you think is properly setup... Don't quite follow the logic of point lights / emitters and the Sun. Are both emitters and point lights meant to be used at the same time?
Thea Render and Kerkythea Rendering System, by Solid Iris Technologies
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notareal

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Post Wed Mar 09, 2011 7:57 pm

Maybe this is a better reference (Thea)...
Attachments
SpecularGlitchTest.pack.thea.zip
(349.15 KiB) Downloaded 177 times
SpecularGlitchTest_Thea.png
Thea Render and Kerkythea Rendering System, by Solid Iris Technologies
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Fletch

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Post Wed Mar 09, 2011 10:18 pm

Thanks Notareal, mucho better. I will look at it.
HOWEVER - IT'S COMPLETELY OFF TOPIC!!!!

We are not talking about Thea here, really, at all. We are talking about a bug in Kerky. :lol:


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Fletch

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Post Wed Mar 09, 2011 10:26 pm

wrong file?
mine looks diff. from yours.

30s seems like much too long a time for such a small scene to render well.
Can you get as good of a result but cut the render time in half?

how can you get the triangle to show but I can't?

yours rendered in 30s, here's mine below also - 12s. render.
Attachments
12s.jpg
my version
wrongfile.jpg
is this the wrong file?


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notareal

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Post Wed Mar 09, 2011 11:38 pm

Sorry for going off topic, but I was not the person who did make the first comparison on Thea. :P

I got a impression that you where stating that there is something wrong in Thea reflections - with is obviously incorrect at this case. Just scene setting need tuning.
It did render in 20 s with my i7 920, but now looking I used a internal build that might be a tiny bit faster that release RV :oops: With a little changes this did rendered in 12 sec, without a noticeable quality drop.

Did give a re-run with posted scene using release RV (with that posted scene) and it renders with triangle reflections. Looking the ISO setting, My posted file has 20, so you must have wrong file for some reason, it's not the same I did post.

Back to the topic, maybe this gives giannis some ideas where to look on...
Anyhow that "Fresnel" bug is fairly annoying in KT. It would be great, if it could be fixed.
Thea Render and Kerkythea Rendering System, by Solid Iris Technologies
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Fletch

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Post Thu Mar 10, 2011 2:21 am

1 - I wasn't implying there was something wrong with Thea, I was showing that, in fact, it's looking much better. (except that the triangular highlights were missing.)

2- :oops: I opened a scene named exactly like yours, but it was the wrong one.
I had to unzip your scene before I could see it in the open scene dialog in Thea, so now I opened it, I see what you did.
In order to get the triangle you needed to enable the area lights. you also changed roughness to 4 (from 10 like I had) for the yellow ball.

I have pointlights inside of a triangular shaped reflector, so it makes no sense to me that the reflections would not show that.


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notareal

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Post Thu Mar 10, 2011 5:14 pm

True, I think there is something related to roughness and point lights... But now I know how you planned to scene be rendered. Makes easier to do comparison.
Thea Render and Kerkythea Rendering System, by Solid Iris Technologies

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