Master Thesis - Computer Graphics and Visualization - TU Delft

Unbiased Rendering 2.9 Metropolis Light Transport
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Figure 2.7: Lai Lens mutation of a path of the form ESDSDL. The mutation starts at the
eye. Further path vertices are mutated backwards until an explicit connection can be made.
Diffuse vertices are connected directly to specular vertices while extending the path.
vertex. The mutation is then extended through one specular bounce. Finally, the first diffuse
vertex is explicitly connected to the eye to complete the mutation.
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Figure 2.8: Caustic mutation of a path of the form EDSDL. The mutation starts at the
second diffuse vertex from the eye. All preceding vertices are perturbed forward and an
explicit connection to the eye is made.
When using more advanced camera models with a finite aperture lens, both mutations
should also perturb the eye vertex x0 itself. For simple models such as the pinhole camera,
there is only one valid x0, so perturbing x0 is not necessary. Aside from these perturbation
mutations, Veach also proposed mutations that substitute any subpath by a completely new
subpath of possibly different length and signature, using bidirectional mutations [52]. We
will not discuss these mutations here, and direct the interested reader to the original paper on
Metropolis light transport [52]. Because the original paper is found to be difficult to understand
by many people trying to implement the Metropolis Light Transport algorithm, Cline
presented a comprehensive tutorial on Metropolis Light Transport and its implementation
[10].
For more details on generating lens and caustic mutations and evaluating their acceptance
probability, see appendix F.
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