Search found 21 matches

by citadel
Tue May 23, 2017 11:26 am
Forum: General Development
Topic: Multi-wavelength free path sampling using ratio tracking
Replies: 7
Views: 1507

Re: Multi-wavelength free path sampling using ratio tracking

Actually, I'm most concerned with figure 11 in Karl's paper, which is a cumulus cloud with albedo = 1, and forward scattering g = 0.877. For some data, such as my binary checkerboard volume, delta tracking seems to outperform ratio tracking, as it skips most of the sigma_t queries when transmittance...
by citadel
Mon May 22, 2017 8:16 am
Forum: General Development
Topic: Multi-wavelength free path sampling using ratio tracking
Replies: 7
Views: 1507

Re: Multi-wavelength free path sampling using ratio tracking

After more tests I still find some bias in the image. Maybe it's also necessary to also consider the compensation for passtrough rays that leave the volume. Or just use an infinite medium to compare. ps. I just worked out a compensation for passthrough rays. Seems to match multichannel and blue chan...
by citadel
Sun May 21, 2017 11:22 pm
Forum: General Development
Topic: Multi-wavelength free path sampling using ratio tracking
Replies: 7
Views: 1507

Re: Multi-wavelength free path sampling using ratio tracking

OK, now I get it what you meant with the code :roll: . I write it down in case someone else wonders. compensation.png And I took some time to pick up my old volumetric path tracer, improved it with the fancy stuff (hosted here, https://github.com/RNG65536/volpath ), and did some comparisons. It may ...
by citadel
Fri May 12, 2017 2:57 pm
Forum: General Development
Topic: Multi-wavelength free path sampling using ratio tracking
Replies: 7
Views: 1507

Re: Multi-wavelength free path sampling using ratio tracking

Residual ratio tracking is very promising, but I wonder how it's used for evaluating multiple scattering? Specifically, how to apply it to sample a free length? I only figured out how to apply it to estimate transmittance for direct illumination. As far as I remember, high variance for high albedo d...
by citadel
Sat May 07, 2016 3:05 pm
Forum: General Development
Topic: Regarding directional dipole
Replies: 4
Views: 1690

Re: Regarding directional dipole

Tonemapped using Reinhard '05 Dynamic Range Reduction Inspired by Photoreceptor Physiology

tonemapped_dipole.jpg
tonemapped_dipole.jpg (218 KiB) Viewed 1558 times


tonemapped_dirpole.jpg
tonemapped_dirpole.jpg (211.5 KiB) Viewed 1558 times
by citadel
Fri May 06, 2016 6:17 am
Forum: General Development
Topic: Regarding directional dipole
Replies: 4
Views: 1690

Re: Regarding directional dipole

Comparing using the XYZ dragon model (up to down, dipole, dirpole and vpt):
compare_dragon.jpg
compare_dragon.jpg (882.55 KiB) Viewed 1632 times


Mitsuba in (almost) the same setting:
mts_ref.jpg
mts_ref.jpg (312.31 KiB) Viewed 1632 times
by citadel
Fri May 06, 2016 5:48 am
Forum: General Development
Topic: Regarding directional dipole
Replies: 4
Views: 1690

Re: Regarding directional dipole

If I remember correctly, the dirpole model includes single scattering, so in theory its result should be closer to the path traced reference. Can you actually please post that reference here for completeness? You're right, the directional solution has included single scattering. I had some problem ...
by citadel
Wed May 04, 2016 7:57 pm
Forum: General Development
Topic: A question about BSSRDF generalized to rough surface
Replies: 3
Views: 1616

Re: A question about BSSRDF generalized to rough surface

Have yet to read that paper. But PBRT has a good explanation on that matter. BTW, 1/pi is a like a normalization factor as in BRDF. 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...
by citadel
Wed May 04, 2016 7:38 pm
Forum: General Development
Topic: Regarding directional dipole
Replies: 4
Views: 1690

Regarding directional dipole

Following the shader code from http://people.compute.dtu.dk/jerf/code/dirsss/, I have compared bssrdf using dipole (Jensen'01) and dirpole (Hachisuka'15), cdipole.jpg cdirpole.jpg Both are sufficiently converged using a very small solid angle threshold(<0.25^2 sr) for hierarchical integration. The p...
by citadel
Thu Apr 09, 2015 4:52 pm
Forum: General Development
Topic: Out-Scattering problem
Replies: 6
Views: 2504

Re: Out-Scattering problem

You may take a look at this, http://www.cs.cornell.edu/Courses/cs6630/2012sp/notes/09volpath.pdf if you are doing path tracing. But I don't see how you can "ignore" out-scattering, since it does not contribute in the spherical integration of the radiative transfer equation, but only works ...

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