Cauchy B Coeff might produce wrong results?

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Silverwing
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Cauchy B Coeff might produce wrong results?

Post by Silverwing » Sun Nov 15, 2015 1:45 am

Hi there,

I just rendered my glass scene again over night (17h) with a little dispersion.
However the Result is not giving me what I have expected.

Render algorithm was MLT-BiDir but it looks the same in Pathtracing-BiDir.

The Renderer was Indigo fo Cinema 4D 3.8.26.2
Cauchy B Coeff was 0.005
Indigo_Glass_Cauchy_Test.jpg

Here is the original render. Same Material but without the Cauchy B Coeff
It looks more natural (is not brighter then the background).
Also notice the silhouette of the glass thickens inside the glass is much more pronounced with the Cauchy B material.
Indigo_Glass_Test.jpg
Cheers,
Raphael
Last edited by Silverwing on Mon Nov 16, 2015 4:31 am, edited 1 time in total.
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zeitmeister
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Re: Cauchy B Coeff might broduce wrong results?

Post by zeitmeister » Sun Nov 15, 2015 4:34 am

This is strange and definately shouldn't look that way. Did you check your scene scale?


Cheers, zeiti
Cheers, David



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Re: Cauchy B Coeff might broduce wrong results?

Post by contegufo » Sun Nov 15, 2015 5:48 am

Hi

The scene was lit by an environment map?
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Silverwing
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Re: Cauchy B Coeff might broduce wrong results?

Post by Silverwing » Sun Nov 15, 2015 7:49 am

zeitmeister wrote:This is strange and definately shouldn't look that way. Did you check your scene scale?
Cheers, zeiti
The Scene scale should match real world. I´m not sure if it fits exactly because I do not know exactly what scale is exported by cindigo. But at least in C4D everything is in scale.
zeitmeister wrote:This is strange and definately shouldn't look that way. Did you check your scene scale?
Cheers, zeiti
Yes the scene is lit entirely by a HDRI 360° map.
I should mention that this is the result of a linear output. (Untonemapped EXR)

It looks perfect with Cauchy B set to 0.

Cheers,
Raphael
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Re: Cauchy B Coeff might broduce wrong results?

Post by thesquirell » Sun Nov 15, 2015 11:55 pm

Dear Raphael,

Cindigo will export in scale which is chosen in Render Setting, Enviroment, Scene scale. I think it just takes the numbers from the scene and it just takes them as they are, without conversion. But I am not sure about that. To avoid all the confusion about the scale etc. I make sure my project settings say the same scene scale as Scene scale in cindigo's render setting, which is the same as unit display in C4D's preferences. Play safe! :D

Would love to hear how this develops. Never had any problem with CBC before.

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Re: Cauchy B Coeff might broduce wrong results?

Post by zeitmeister » Mon Nov 16, 2015 12:48 am

What Happens if you use the cindigo version before? And does it come correctly of you use a coefficient of 0.001?


Cheers, zeiti
Cheers, David



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Re: Cauchy B Coeff might broduce wrong results?

Post by Oscar J » Mon Nov 16, 2015 2:10 am

Oh my. Though Indigo at least had its basics right. :(

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Re: Cauchy B Coeff might broduce wrong results?

Post by OnoSendai » Mon Nov 16, 2015 2:21 am

Hi, send over the scene, I'll take a look (eventually).

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Re: Cauchy B Coeff might produce wrong results?

Post by Silverwing » Mon Nov 16, 2015 4:56 am

thesquirell wrote:Dear Raphael,

Cindigo will export in scale which is chosen in Render Setting, Enviroment, Scene scale. I think it just takes the numbers from the scene and it just takes them as they are, without conversion. But I am not sure about that. To avoid all the confusion about the scale etc. I make sure my project settings say the same scene scale as Scene scale in cindigo's render setting, which is the same as unit display in C4D's preferences. Play safe! :D
Would love to hear how this develops. Never had any problem with CBC before.
Yes that´s what I have been doing too. I checked the scene scale with the apperture. Whrong translations end up with the wrong DOF. So if the DOF is way to strong or not there with a Apperture 3.5 you know there is something off the scale.

I have set the Scale to mm within C4D and within the Exporter.
I changed it to cm and to m just to see if it makes a difference. But unfortunately it does not. Cauchy B always has that magenta tint.
zeitmeister wrote:What Happens if you use the cindigo version before? And does it come correctly of you use a coefficient of 0.001?
Cheers, zeiti
No I have not checked yet. Maybe I should.
I have instead exported it to the latest Indigo standalone v3.8.29

I added some pictures:
Indigo_No_Cauchy.jpg
Picture with Cauchy B at 0
Indigo_Chauchy.jpg
Picture with Cauchy B at 0.00001
I will upload the scene later.

Cheers,
Raphael
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Silverwing
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Re: Cauchy B Coeff might produce wrong results?

Post by Silverwing » Wed Nov 18, 2015 12:40 am

As Promised here´s the scene.
I hope this *.pigs file works!

If not just write me a line!

GLASS-SCENE

Cheers,
Raphael
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Re: Cauchy B Coeff might produce wrong results?

Post by OnoSendai » Wed Nov 18, 2015 1:39 am

Thank Sliverwing.
Looks like it's a problem with the combination of dispersion (single wavelength rendering), and non-post-process aperture diffraction.
Easy workaround - use post-process aperture diffraction only (or turn it off).

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Re: Cauchy B Coeff might produce wrong results?

Post by Silverwing » Thu Nov 19, 2015 12:28 am

OnoSendai wrote:Thank Sliverwing.
Looks like it's a problem with the combination of dispersion (single wavelength rendering), and non-post-process aperture diffraction.
Easy workaround - use post-process aperture diffraction only (or turn it off).
Oh such an easy fix. Thanks a lot for having a look at the scene!
Much appreciated!

Cheers,
Raphael
You don´t dream in cryo.

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Silverwing
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Re: Cauchy B Coeff might produce wrong results?

Post by Silverwing » Fri Nov 20, 2015 1:07 am

Sorry for being so picky.
Yes the Aperture Fix got rid of the coloring. But I still get this stange "Artifact" in the rendering with Chauchy B Coeff. The Silhouette of the glass gets much more pronounced (Marked Green). I think there is something off!

P.s. I used the old colored rendering for comparison. The test with the Aperture fix only gets rid of the color!
Glass_Comparison_01.jpg
Cheers,
Raphael
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Re: Cauchy B Coeff might produce wrong results?

Post by OnoSendai » Fri Nov 20, 2015 1:37 am

That's no problem for being picky, good spotting :)
There's a known issue/limitation with the dispersion code that I should probably fix. It's to do with the computation of the fresnel reflection term and the actual (waveelength-dependent) IOR for the wavelength as opposed to the base wavelength.

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Re: Cauchy B Coeff might produce wrong results?

Post by galinette » Fri Nov 20, 2015 6:29 am

What if you increase cauchy B to a value such as 0.005?
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