Sigma?

General questions about Indigo, the scene format, rendering etc...
neo0.
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Sigma?

Post by neo0. » Tue Dec 15, 2009 9:00 am

What is back scattering? How does it affect the material?

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lycium
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Re: Sigma?

Post by lycium » Tue Dec 15, 2009 9:47 am

the roughness of the surface, basically more backscattering == flatter looking.

for more information and examples, google "oren nayar" and check the first hit.

Soup
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Re: Sigma?

Post by Soup » Wed Dec 16, 2009 10:05 am

I found this in the Technical manual the other day:
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sigma.jpg
Example of sigma levels
sigma.jpg (84.15 KiB) Viewed 3987 times

neo0.
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Re: Sigma?

Post by neo0. » Wed Dec 16, 2009 2:21 pm

Nice, but the images are a bit small for their complexity..

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Borgleader
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Re: Sigma?

Post by Borgleader » Wed Dec 16, 2009 5:06 pm

benn hired a mercenary to kill my sig...

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Polinalkrimizei
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Re: Sigma?

Post by Polinalkrimizei » Wed Dec 16, 2009 5:59 pm

The above pictures make no sense to me. Sigma = 0 in the wikipedia article looks like Sigma = 1 in the technical manual. According to wikipedia, a higher value for sigma makes the model look more flat, but with indigo it looks flattest with the lowest sigma setting.
Is it just me? :lol: Or did something get mixed up?

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Borgleader
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Re: Sigma?

Post by Borgleader » Wed Dec 16, 2009 6:33 pm

Polinalkrimizei wrote:The above pictures make no sense to me. Sigma = 0 in the wikipedia article looks like Sigma = 1 in the technical manual. According to wikipedia, a higher value for sigma makes the model look more flat, but with indigo it looks flattest with the lowest sigma setting.
Is it just me? :lol: Or did something get mixed up?
Is it possible ono somehow implemented the function...backwards?
benn hired a mercenary to kill my sig...

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OnoSendai
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Re: Sigma?

Post by OnoSendai » Wed Dec 16, 2009 6:41 pm

Polinalkrimizei wrote:The above pictures make no sense to me. Sigma = 0 in the wikipedia article looks like Sigma = 1 in the technical manual. According to wikipedia, a higher value for sigma makes the model look more flat, but with indigo it looks flattest with the lowest sigma setting.
Is it just me? :lol: Or did something get mixed up?
It just depends where the light comes from - sigma increases backscattering.

neo0.
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Re: Sigma?

Post by neo0. » Wed Dec 16, 2009 7:56 pm

Could someone please describe back scattering for the well... unitiated?

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lycium
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Re: Sigma?

Post by lycium » Wed Dec 16, 2009 8:43 pm

Polinalkrimizei wrote:The above pictures make no sense to me. Sigma = 0 in the wikipedia article looks like Sigma = 1 in the technical manual. According to wikipedia, a higher value for sigma makes the model look more flat, but with indigo it looks flattest with the lowest sigma setting.
Is it just me? :lol: Or did something get mixed up?
i got the same impression; the wiki images are in line with my expectations.

anyone wanna render some spheres? :)

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fused
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Re: Sigma?

Post by fused » Wed Dec 16, 2009 9:08 pm

like the wikipedia image. 0, 0.1, 0.3
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sigma.jpg
sigma.jpg (26.28 KiB) Viewed 3883 times

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CTZn
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Re: Sigma?

Post by CTZn » Wed Dec 16, 2009 9:48 pm

I wasn't either under the same impression than you, polin and lyc. Higher sigma seems to darken the surface, however if you observe closer you can see that the dark rim edges are also fading away, see below.

I'm fine with the actual implementation :)
Attachments
ON_test.jpg
diffuse - 0.0 - 0.2 - 0.5 - 1.0
ON_test.jpg (58.29 KiB) Viewed 3859 times
obsolete asset

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PureSpider
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Re: Sigma?

Post by PureSpider » Wed Dec 16, 2009 11:09 pm

While on the "topic"...
Can the Torrance-Sparrow model for Phong be implemented, Ono?
Or is it too much of a hassle?

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Polinalkrimizei
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Re: Sigma?

Post by Polinalkrimizei » Wed Dec 16, 2009 11:42 pm

Thanks for the clarification guys.
CTZn, your image made it pretty clear and now I think I got it! :wink:

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Zom-B
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Re: Sigma?

Post by Zom-B » Thu Dec 17, 2009 1:23 am

clearly visible the higher the sigma the darker the material gets!

This is something I never understood... :oops:



(About my old Statue render on the top... simply drag & Drop the image into a new Firefox Tab to see it in Full size Neo, the forum scales images down!)
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