Light Transport Simulation with Vertex Connection and Merging
(or How to combine bidirectional path tracing with progressive photon mapping and get the best out of it)
A comparison of our new progressive vertex connection and merging (VCM) algorithm against bidirectional path tracing
(BPT) and stochastic progressive photon mapping (PPM) after 30 minutes of rendering. BPT fails to reproduce the reflected caustics produced by
the vase, while PPM has difficulties handling the illumination coming from the room seen in the mirror. Our new VCM algorithm automatically
computes a good mixture of sampling techniques from BPT and PPM to robustly capture the entire illumination in the scene. The rightmost
column shows the relative contributions of the BPT and PPM techniques to the VCM image in false color.
(Compare large images in individual tabs.)
Developing robust light transport simulation algorithms that are
capable of dealing with arbitrary input scenes remains an elusive
challenge. Although efficient global illumination algorithms exist,
an acceptable approximation error in a reasonable amount of time is
usually only achieved for specific types of input scenes. To address
this problem, we present a reformulation of the photon mapping
as a bidirectional path sampling technique for Monte Carlo light
transport simulation. The benefit of our new formulation is twofold.
First, it makes it possible, for the first time, to explain in a formal
manner the relative efficiency of photon mapping and bidirectional
path tracing, which have so far been considered conceptually incompatible
solutions to the light transport problem. Second, it allows
for a seamless integration of the two methods into a more robust
combined rendering algorithm via multiple importance sampling.
A progressive version of this algorithm is consistent and efficiently
handles a wide variety of lighting conditions, ranging from direct
illumination, diffuse and glossy inter-reflections, to specular-diffuse-specular
light transport. Our analysis shows that this algorithm
inherits the high asymptotic performance from bidirectional path
tracing for most light path types, while benefiting from the efficiency
of photon mapping for specular-diffuse-specular lighting effects.
Iliyan Georgiev, Jaroslav Křivánek, Tomáš Davidovič, and Philipp Slusallek.
Light Transport Simulation with Vertex Connection and Merging.
ACM Trans. Graph. (SIGGRAPH Asia 2012) 31, 6 (2012) ... DOI | BibTeX
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