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FresnelReflectance / IOR of Satin, Velvet


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#1 lipsryme   Members   -  Reputation: 1052

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Posted 17 June 2014 - 06:32 AM

I'm currently fiddling around with a cloth shader and am wondering (since I couldn't find anything on this) what the IOR or fresnel reflectance of a fabric like satin is ?

It does seem to me that it has a highly glossy surface and is not in the usual F(0°) range of 0.2- 0.3 (linear) as other insulators are...

Does anyone have some information on this ? Or is it something that I might just have to fake using a higher FresnelReflectance because its such a complex material ?



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#2 ikarth   Members   -  Reputation: 447

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Posted 17 June 2014 - 08:23 AM

Satin is anisotropic, which basically means that the reflectance changes depending on the direction, so the highlights look stretched, and the lighting changes as you rotate it. 

 

More than you ever wanted to know about rendering anisotropic surfaces:

http://www.neilblevins.com/cg_education/satin/satin.htm

 

http://books.google.com/books?id=H5UVcCYSbXcC&pg=PA64&lpg=PA64&dq=anisotropic+satin&source=bl&ots=NhxUK3BRa0&sig=gbxdQHUF0b2cyiA2nf_EB1_8e00&hl=en&sa=X&ei=SU2gU5njOoKHqgb7qoKYAQ&ved=0CHQQ6AEwDQ#v=onepage&q=anisotropic%20satin&f=false

 

http://research.microsoft.com/en-us/um/people/xtong/aniso_release.pdf

 

http://people.csail.mit.edu/addy/research/brdf/

 

ftp://ftp.sgi.com/opengl/contrib/blythe/advanced99/notes/node154.html

 

http://www.pernroth.nu/lightandmaterials/

 

http://www.blenderguru.com/tutorials/introduction-to-anisotropic-shading/#.U6BO3fldV8E



#3 Chris_F   Members   -  Reputation: 2469

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Posted 17 June 2014 - 09:03 AM


Satin is anisotropic, which basically means that the reflectance changes depending on the direction, so the highlights look stretched, and the lighting changes as you rotate it.

 

You need more than simply the right IOR and anisotropy to get satin right. You can either fake it till you make it or you can look into cloth specific BRDFs. For faking it you could try Cook-Torrance (Beckmann, GGX) with a roughness value > 1.



#4 lipsryme   Members   -  Reputation: 1052

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Posted 17 June 2014 - 09:06 AM

I'm already using a cloth brdf by ashikhmin and it already looks quite nice but I was wondering if the reflection strength shouldn't be much stronger.






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