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And the diffuse Fresnel transmittance is no more than approximation to specular

Fresnel transmittance from all directions. From my experience it may give darker results

if you don't rather use specular Fresnel transmittance for each light sample.

Statistics: Posted by citadel — Wed May 04, 2016 7:57 pm

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I have compared bssrdf using dipole (Jensen'01) and dirpole (Hachisuka'15),

cdipole.jpgcdirpole.jpg

Both are sufficiently converged using a very small solid angle threshold(<0.25^2 sr) for hierarchical integration.

The problem is that dipole is noticeably darker than dirpole. And they both look quite far from volumetric path tracing.

But I have not tried single scattering, so the error may largely come from that.

Statistics: Posted by citadel — Wed May 04, 2016 7:38 pm

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Statistics: Posted by dr_eck — Mon May 02, 2016 8:43 pm

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I got the following if I substitute an ideal specular BTDF to the equation I posted.

substitute_ideal_specular.png

However this slightly differs from the original one.

(The latter Fresnel term is the same to F(eta, wo), therefore the problem is the fraction term contains cosines)

Statistics: Posted by shocker_0x15 — Sun May 01, 2016 10:57 am

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Now I try to implement SSS feature in my renderer using BSSRDF.

I have started with "A Practical Model for Subsurface Light Transport" and Donner's thesis "Towards Realistic Image Synthesis of Scattering Materials".

They say that the diffuse component of BSSRDF for smooth surface ( = ideal specular BTDF?) is

Sd_smooth.png

(Screen shot from the former material)

In Donner's thesis they generalize enclosing surface to rough surface, that is

Sd_rough.png

(Screen shot from the latter material)

I'm confused by the symbols used in the latter material.

So, I tried to rewrite what they say by myself.

Sd_rough_my_understanding.png

Here, integration domain H^2- means lower hemisphere (inside material) and I write the diffuse transmittance term by using BSDF(BTDF) instead of BRDF they used.

My understanding for this generalized BSSRDF process is

1. The first integration term represents a total energy entering a material over the interface due to a light coming from wi direction at xi

2. The term R converts the energy to radiant exitance at xo

3. By multiplying 1 /pi to the radiant exitance, we get radiance reaching to xo from any direction in lower hemisphere

4. The second integration term converts the radiance from lower hemisphere to outgoing radiance from xo in direction wo

Is something wrong in my understanding?

Thanks,

Statistics: Posted by shocker_0x15 — Sun May 01, 2016 10:53 am

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I have several materials here and I need accurate values for rendering.

Here are the materials that I want to analyse : https://i.materialise.com/3d-printing-m ... ifications

Is there some hardware/software that allow me to produce accurate analysis ?

Thx

Statistics: Posted by spectral — Fri Apr 29, 2016 10:12 am

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in order to importance sample the product of both the lambertian brdf and a spherical light source?

Statistics: Posted by Paleos — Tue Apr 26, 2016 11:13 pm

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Statistics: Posted by zsolnai — Mon Apr 11, 2016 11:24 pm

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http://jcgt.org/published/0005/01/02/

The second half of the paper describes a technique essentially the same as my OP, but in more formal terms. Really cool! Hopefully this approach will get more visibility now, and perhaps further research.

EDIT:

It seems I maybe got a little over-excited. I read the paper again more thoroughly, and the technique they present isn't quite the same. To converge to a consistent result, their approach requires multi-pass progressive rendering, whereas the approach in my OP works quite happily within a single pass. Nevertheless, the concepts are very similar! Variations on the same theme.

Statistics: Posted by cessen — Thu Mar 31, 2016 2:54 pm

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