This page provides information on the Global DMC rollout in the V-Ray tab of the Render Settings.

**Overview**

Monte Carlo (MC) sampling is a method for evaluating "blurry" values (anitaliasing, depth of field, indirect illumination, area lights, glossy reflections/refractions, translucency, motion blur, etc). V-Ray uses a variant of Monte Carlo sampling called Deterministic Monte Carlo (DMC).

The difference between pure Monte Carlo sampling and Deterministic Monte Carlo is that the first uses pseudo-random numbers which are different for each and every evaluation (and so re-rendering a single image will always produce slightly different results in the noise), while Deterministic Monte Carlo uses a pre-defined set of samples (possibly optimized to reduce the noise), which allows re-rendering an image to always produce the exact same result. By default, the Deterministic Monte Carlo method used by V-Ray is a modification of Schlick sampling, introduced by Christophe Schlick in [ 1 ] (see the References section below for more information).

Instead of having separate sampling methods for each of the blurry values, V-Ray has a single unified framework that determines how many and which exact samples are to be taken for a particular value, depending on the context in which that value is required. This framework is called the *DMC sampler*.

DMC parameters as well as material and light subdivs which are hidden from the UI can still be accessed via maxscript.

**UI Path**: ||Render Setup window|| > **V-Ray tab** > **Global DMC** rollout

Global DMC Rollout

Global DMC Rollout

The settings for the DMC sampler are located in the Global DMC rollout.

The actual number of samples for the DMC sampler's blurry values are determined by three factors:

- The subdivs value for a particular blurry effect. This is multiplied by the Global subdivs multiplier.
- The importance of the value (for example, dark glossy reflections can do with fewer samples than bright ones, since the effect of the reflection on the final result is smaller; distant area lights require fewer samples than closer ones, etc). Basing the number of samples allocated for a value on importance is called
*importance sampling*. - The variance (think "noise") of the samples taken for a particular value - if the samples are not very different from each other, then the value can do with fewer samples; if the samples are very different, then a larger number of them will be necessary to get a good result. This basically works by looking at the samples as they are computed one by one and deciding, after each new sample, if more samples are required. This technique is called
*early termination*or*adaptive sampling*.

More information is available in the Adaptive Sampling section.

**Parameters**

**Lock noise pattern** – When enabled, the sampling pattern is the same from frame to frame in an animation. Since this may be undesirable in some cases, you can disable this option to make the sampling pattern change with time. Note that re-rendering the same frame produces the same result in both cases.

**Blue noise sampling** – When enabled, reorders the DMC samples in screen space to produce a more pleasing result for low sample counts.

**References**

More information on deterministic Monte Carlo sampling for computer graphics can be found from the sources listed below.

[1] C. Schlick, **An Adaptive Sampling Technique for Multidimensional Integration by Ray Tracing**, in Second Eurographics Workshop on Rendering (Spain), 1991, pp. 48-56

* Describes deterministic MC sampling for antialiasing, motion blur, depth of field, area light sampling and glossy reflections. *

[2] K. Chiu, P. Shirley and C. Wang, **Multi-Jittered Sampling**, in Graphics Gems IV, 1994

*Describes a combination of jittered and N-rooks sampling for the purposes of computer graphics. *

[3] Masaki Aono and Ryutarou Ohbuchi, **Quasi-Monte Carlo Rendering with Adaptive Sampling**, IBM Tokyo Research Laboratory Technical Report RT0167, November 25, 1996, pp.1-5

An online version can be found at

http://www.kki.yamanashi.ac.jp/~ohbuchi/online_pubs/eg96_html/eg96.htm

*Describes an application of low discrepancy sequences to area light sampling and the global illumination problem. *

[4] M. Fajardo, **Monte Carlo Raytracing in Action**, in **State of the Art in Monte Carlo Ray Tracing for Realistic Image Synthesis**, SIGGRAPH 2001 Course 21, pp. 151-162;

An online version can be found at

http://cseweb.ucsd.edu/~viscomp/classes/cse274/wi18/readings/course29sig01.pdf

*Describes the ARNOLD renderer employing randomized quasi-Monte Carlo sampling using low discrepancy sequences for pixel sampling, global illumination, area light sampling, motion blur, depth of field, etc. *

[5] E. Veach, December, **Robust Monte Carlo Methods for Light Transport Simulation**, Ph. D. dissertation for Stanford University, 1997, pp. 58-65

An online version can be found at http://graphics.stanford.edu/papers/veach_thesis/

*Includes a description of low discrepancy sequences, quasi-Monte Carlo sampling and its application to solving the global illumination problem. *

[6] L. Szirmay-Kalos, **Importance Driven Quasi-Monte Carlo Walk Solution of the Rendering Equation**, Winter School of Computer Graphics Conf., 1998

An online version can be found at http://www.fsz.bme.hu/~szirmay/imp1_link.html

*Describes a two-pass method for solving the global illumination problem employing quasi-Monte Carlo sampling, as well as importance sampling using low discrepancy sequences.*