Hello,
I read the recent paper on Spectral and Decomposition Tracking by Kutz et al.
http://drz.disneyresearch.com/~jnovak/p ... index.html
I want to use weighted tracking methods in my own toy path tracer.
Following the PBRT book pg 889, the incident radiance is composed of two terms: the radiance arriving from the distant hit point Tr*Lo and the inscattered radiance integrated along the viewing ray.
I evaluate only one of these terms probabilistically. The first, term if no collision was generated, otherwise there is a scattering or absorption even.
As per PBRT I need to weight Tr*Lo with the probability that no interaction takes place, i.e. the probability to hit the surface p_surf. Thus the estimator is Tr*Lo/p_surf.
However, I cannot figure out how to determine the weight Tr/p_surf.
So how is the inscattered radiance combined with the background?
I also took a brief look at Novak's Ratio Tracking paper but there I also failed to find an answer.
Cheers,
Weighted delta tracking question

 Posts: 62
 Joined: Sun Aug 19, 2012 3:24 pm
Re: Weighted delta tracking question
Hi,
In my understanding, T_r / p_surf becomes the weight computed by cumulatively multiplying the following single step weight:
as in the SD tracking paper.
If this is implemented by following PBRT's interface for example for GridDensityMedium::Sample(),
it returns the above weight if no interaction found, otherwise returns
, where w is the cumulative weight until this step.
In the conventional delta tracking,
P_n(x) = \mu_n(x) / \bar{\mu} (this leads the single step weight to 1.)
\bar{\mu} = \mu_a(x) + \mu_s(x) + \mu_n(x).
Therefore, this implementation matches the current PBRTv3's implementation.
In my understanding, T_r / p_surf becomes the weight computed by cumulatively multiplying the following single step weight:
as in the SD tracking paper.
If this is implemented by following PBRT's interface for example for GridDensityMedium::Sample(),
it returns the above weight if no interaction found, otherwise returns
, where w is the cumulative weight until this step.
In the conventional delta tracking,
P_n(x) = \mu_n(x) / \bar{\mu} (this leads the single step weight to 1.)
\bar{\mu} = \mu_a(x) + \mu_s(x) + \mu_n(x).
Therefore, this implementation matches the current PBRTv3's implementation.
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