Jaroslav Křivánek

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)

Iliyan Georgiev
Saarland University
Intel VCI, Saarbruecken
Jaroslav Křivánek
Charles University in Prague
Faculty of Mathematics and Physics
Tomáš Davidovič
Saarland University
Intel VCI, Saarbruecken
Philipp Slusallek
Saarland University
Intel VCI & DFKI, Saarbruecken


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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