diff --git a/src/mtsgui/resources/docs.xml b/src/mtsgui/resources/docs.xml index 1bc04460..c71e78c4 100644 --- a/src/mtsgui/resources/docs.xml +++ b/src/mtsgui/resources/docs.xml @@ -72,7 +72,7 @@ leads to 14x(2*14)=392 samples - Quality setting (\kappa in the [Tabellion et al.] paper). + Quality setting ("kappa" in the [Tabellion et al.] paper). A value of 1 should be adequate in most cases. @@ -196,10 +196,10 @@ - Extended path tracer -- uses multiple importance sampling to combine - two sampling strategies, namely BSDF and luminaire sampling. This class also - supports volumetric absorption, but does not attempt to solve the - full radiative transfer equation (see volpath if this is needed). + This integrator implements a basic path tracer with multiple importance sampling and is a good + default choice when there is no strong reason to prefer another method. + It does not account for participating media, such as fog or smoke—see + the volumetric path tracer if this is needed. @@ -395,7 +395,7 @@ when rendering scenes involving depth-of-field, motion blur, and glossy reflections.

Note that this integrator ignores the sampler - configuration---hence, the usual steps of choosing a sample generator and a desired + configuration—hence, the usual steps of choosing a sample generator and a desired number of samples per pixel are not necessary. As with PPM, once started, the rendering process continues indefinitely until it is manually stopped.

@@ -437,7 +437,7 @@ are explicitly represented by surfaces in the scene so that they can be intersected by random walks started at emitters.

-

Bidirectional path tracing is a relatively "heavy" rendering technique---for +

Bidirectional path tracing is a relatively "heavy" rendering technique—for the same number of samples per pixel, it is easily 3-4 times slower than regular path tracing. However, it usually makes up for this by producing considerably lower-variance radiance estimates (i.e. the output images have less noise).

@@ -586,11 +586,27 @@ - Veach-style Metropolis Light Transport implementation with support for - bidirectional mutations, lens perturbations, caustic perturbations and - multi-chain perturbations. Several optimizations are also implemented, namely - separate direct illumination, two-stage MLT, and importance sampling of - mutation strategies. For details, see the respective parameter descriptions. +

Metropolis Light Transport (MLT) is a seminal rendering technique proposed by Veach and + Guibas, which applies the Metropolis-Hastings + algorithm to the path-space formulation of light transport. + Please refer to the PSSMLT documentation for a general description of MLT-type + algorithms and a list of caveats that also apply to this plugin.

+ +

Like PSSMLT, this integrator explores the space of light paths, + searching with preference for those that carry a significant amount of + energy from an emitter to the sensor. The main difference is that PSSMLT + does this exploration by piggybacking on another rendering technique and + "manipulating" the random number stream that drives it, whereas MLT does + not use such an indirection: it operates directly on the actual light + paths.

+ +

This means that the algorithm has access to considerably more + information about the problem to be solved, which allows it to perform a + directed exploration of certain classes of light paths. The main downside + is that the implementation is rather complex, which may make it more + susceptible to unforeseen problems. Mitsuba reproduces the full MLT + algorithm except for the lens subpath mutation. In addition, the plugin also provides the + manifold perturbation proposed by Jakob and Marschner.

 Specifies the longest path depth in the generated output image (where -1 @@ -598,26 +614,24 @@ 2 will lead to single-bounce (direct-only) illumination, and so on. - When separateDirect is set to true, this parameter can - be used to specify the samples per pixel used to render the - direct component. Should be a power of two (otherwise, it will be - rounded to the next one). When set to zero or less, the - direct illumination component will be hidden, which is useful - for analyzing the component rendered by MLT. + By default, this plugin renders the direct illumination component + separately using an optimized direct illumination sampling strategy + that uses low-discrepancy number sequences for superior performance + (in other words, it is not rendered by MLT). This + parameter specifies the number of samples allocated to that method. To + force MLT to be responsible for the direct illumination + component as well, set this parameter to -1. - - This setting can be very useful to reduce noise in dark regions - of the image: it activates two-stage MLT, where a nested MLT renderer - first creates a tiny version of the output image. In a second pass, - the full version is then rendered, while making use of information - about the image-space luminance distribution found in the first - pass. Two-stage MLT is very useful in making the noise characteristics - more uniform over time image -- specifically, since MLT tends to get - stuck in very bright regions at the cost of the remainder of the image. + + Use two-stage MLT? Please see the documentation for details. - Number of samples used to estimate the total luminance - received by the camera's sensor. + MLT-type algorithms create output images that are only + relative The algorithm can e.g. determine that a certain pixel + is approximately twice as bright as another one, but the absolute + scale is unknown. To recover it, this plugin computes + the average luminance arriving at the sensor by generating a + number of samples. Selectively enable/disable the bidirectional mutation @@ -635,27 +649,34 @@ Selectively enable/disable the manifold perturbation - Manifold perturbation: probability factor ("lambda") - - - If set to a nonzero value, the rendering process will automatically be stopped after this many seconds. + Probability factor ("lambda") of the manifold perturbation - Energy redistribution path tracing as proposed by Cline et al. +

Energy Redistribution Path Tracing (ERPT) by Cline et al. + combines Path Tracing with the perturbation strategies of Metropolis Light Transport.

+ +

An initial set of seed paths is generated using a standard bidirectional + path tracer, and for each one, a MLT-style Markov Chain is subsequently started + and executed for some number of steps. + This has the effect of redistributing the energy of the individual samples + over a larger area, hence the name of this method.

+ +

This plugin shares all the perturbation strategies of the MLT plugin, and + the same rules for selecting them apply. In contrast to the original + paper by Cline et al., the Mitsuba implementation uses a bidirectional + (rather than an unidirectional) bidirectional path tracer to create seed paths. + Also, since they add bias to the output, this plugin does not use the image + post-processing filters proposed by the authors.

 Specifies the longest path depth in the generated output image (where -1 corresponds to ∞). A value of 1 will only render directly visible light sources. 2 will lead to single-bounce (direct-only) illumination, and so on. - - Specifies the minimum path depth, after which the implementation will start to use the - "russian roulette" path termination criterion (set to -1 to disable). - Specifies the number of Markov Chains that, on average, are started per pixel @@ -668,12 +689,13 @@ Specifies the number of mutations to be performed in each Markov Chain - When separateDirect is set to true, this parameter can - be used to specify the samples per pixel used to render the - direct component. Should be a power of two (otherwise, it will be - rounded to the next one). When set to zero or less, the - direct illumination component will be hidden, which is useful - for analyzing the component rendered by MLT. + By default, this plugin renders the direct illumination component + separately using an optimized direct illumination sampling strategy + that uses low-discrepancy number sequences for superior performance + (in other words, it is not rendered by ERPT). This + parameter specifies the number of samples allocated to that method. To + force ERPT to be responsible for the direct illumination + component as well, set this parameter to -1. Number of samples used to estimate the average contribution of a @@ -695,22 +717,13 @@ Selectively enable/disable the manifold perturbation - Manifold perturbation: probability factor ("lambda") + Probability factor ("lambda") of the manifold perturbation + + + When creating seed paths, this parameter specifies the minimum path depth, after which the + implementation will start to use the + "russian roulette" path termination criterion (set to -1 to disable). - - - Base class of all participating media - - Base class of all participating media -- By default, the parameters are set to - the skim milk data from "A Practical Model for Subsurface scattering" (Jensen et al.) - - Scattering coefficient - Absorption coefficient - Scattering/absorption coefficient multiplier - can be used to convert these to world-space units. - - Specifies the phase function of the medium. If none is specified, - the default (isotropic) is chosen. -