The Metropolis light transport is a SIGGRAPH 1997 paper by Eric Veach and Leonidas J. Guibas, describing an application of a variant of the Monte Carlo method called the MetropolisHastings algorithm to the rendering equation for generating images from detailed physical descriptions of three dimensional scenes.
The procedure constructs paths from the eye to a light source using bidirectional path tracing, then constructs slight modifications to the path. Some careful statistical calculation (the Metropolis algorithm) is used to compute the appropriate distribution of brightness over the image. This procedure has the advantage, relative to bidirectional path tracing, that once a path has been found from light to eye, the algorithm can then explore nearby paths; thus difficulttofind light paths can be explored more thoroughly with the same number of simulated photons. Metropolis Light Transport is an unbiased method that converges to a solution of the rendering equation quicker than other unbiased algorithms, Path tracing and Bidirectional Path Tracing.
In short, the algorithm generates a path and stores the paths 'nodes' in a list. It can then modify the path by adding extra nodes and creating a new light path. While creating this new path, the algorithm decides how many new 'nodes' to add and whether or not these new nodes will actually create a new path.
