mental ray For Maya Beta with NVIDIA

We are now beta testing Pi-ray, our exciting new version 3.14 of mental ray, within Maya 2016, in a private mental ray For Maya beta test. If you are interested, please email, with your beta test request. Please state your company, how you use mental ray, and your machine configuration. In addition to registering in our forum, you need to have Maya 2016 and the mental ray for Maya 2016 plugin installed before installing the beta plugin.

The following image is rendered with the latest global illumination (GI) algorithm in 3.14. Enter the beta test to find out some great things about the latest GI.


Using Modern Materials and Lights in Maya 2016

In this third post in a series on mental ray for Maya 2016 Render Settings, we assume you are familiar with the concepts presented in the introductory post and the second post on adjusting quality.

Modern Materials and Lights

We recommend physically-based materials and lights to fit a modern workflow. In this post, we focus mostly on the materials, and we will follow-up with more posts on lights. These materials are designed to work more compatibly with unified sampling, and the simpler UI quality controls. They provide the flexibility of balance in adjusting global vs. local sampling quality controls.


The Layering (MILA) material not only provides better compatibility with unified sampling and quality controls, but it also provides simple passes which can help you to adjust the quality settings.

For example, this interior scene using mila materials clearly demonstrates the difference between direct and indirect lighting. The left picture has no indirect diffuse lighting as it is turned off in the Render Setting Quality tab, and the right picture has Indirect Diffuse (GI) Mode turned On with a depth of 4. Note that the 2 pictures below are organized in a gallery, so that if you click on them, you can see a larger version. Click on x upper left to get back to this page.

The direct lighting quality is controlled with Lighting Quality, while the indirect quality is controlled with Indirect Diffuse Quality when Indirect Diffuse (GI) Mode is On.

quality_tab_samplesIf using mila_materials, we can easily turn on the direct_diffuse and the indirect_diffuse passes in the Scene tab under Camera>Passes.


Then, we can see the relationship between the pass results with respect to their quality. Note again that the 4 pictures below are organized in a gallery, so that if you click on them, you can see a larger version, and step through each with a right, left arrow.

Below we increase the Indirect Diffuse (GI) Quality to reduce noise in that pass.

Adjusting (MILA) Material Quality

Use the (MILA) Material Quality to address noise caused by the material sampling.  For the layering library (MILA) materials with either glossy reflection/transmission or scatter components, the Material Quality controls the number of samples, ie the outgoing rays split out from the interaction of the material with an incoming ray. In a sense, this is the indirect quality aside from the indirect diffuse, i.e., the indirect glossy and scatter components.

When Advanced Settings are on, we provide separate Glossy Quality and Scatter Quality controls in case the noise differs significantly between these components. Note that the material quality settings are relative, so controlling Material Quality will continue to control both glossy and scatter quality.  The material quality is multiplied by glossy or scatter quality to determine a quality for each respective component, with all defaults at 1.0.

When Advanced Settings are on, we also see Glossy and Scatter Quality
When Advanced Settings are on, we also see Glossy and Scatter Quality under Material Quality

Note that the passes for indirect glossy/specular and scatter directly correlate in quality to these settings.

Increasing Glossy Quality

Increasing Scatter Quality


Scene Settings Shared across Materials

Note that for the MILA shaders, we provide quality settings by scene. In other words, all the materials in the scene share the settings. This makes it easier to control in a typical scene with many materials, rather than per-shader. It also allows the renderer implementation to optimize better.

Besides quality, we have several other useful render settings that are shared by the mila materials. They are in the Scene tab in the Materials section.

Layering (MILA)


Reducing very high dynamic range results

MILA Clamp Output

Clamps the output of mila_material. This is an enable, for using the clamp level. If off, light transports through the scene in the most physically-accurate way, though with high dynamic range lighting, more quality may be required. The default is off.

MILA Clamp Level

The level used for clamping, typically between 1 and 10, based on desired output.

Understanding internal reflection

When making a material to model colored glass, not only do transmission paths inside the glass need to be colored, but also, if one of those paths reflect inside the glass again (internal reflection), it should be colored. Depending on your scene, this may be more or less subtle of an effect visually.

A material with a reflection component could be on the outside or the inside, so the max distance parameter for a reflection component needs information as to whether it is modeling physically-correct internal reflection, or modeling the legacy max distance render trick for the external reflections. We recommend using colored max distance primarily for internal reflection, when combined with a transmission component, and therefore, make this the default.

MILA Use Max Distance Inside

Use the max distance for reflection internally for colored glass. On is the default. If off, the max distance is used for external reflections, those bouncing off the outside of an object, instead of internal reflections.

Scatter look adjustment

Modern rendering uses more quantities that depend on scene units, such as the distance to scatter with mila_scatter. In the Materials section of the Scene tab, we provide a global scaling factor for scatter distances.

MILA Scatter Scale

The MILA Scatter Scale is very convenient for re-using materials across different size scenes. It multiplies by the local scale control, if exposed, in the (MILA) scatter component. Below we show how increasing the scale makes the scatter pass look more like the diffuse pass, with less and less scattering.

For practically good results the scatter pass should look barely noticeable when mixed in with all the other passes.

Layering complexity not a significant performance factor

At SIGGRAPH 2015, I noticed how many users were still concerned that the number of layers in a material may affect performance. For modern materials, such as MILA and MDL, this should not be of concern. The elemental component structure provides the renderer with this ability. The material can either be selectively sampled or flattenend for a single minimal BSDF representation, and as the depth of a ray increases, more optimizations can occur.


Use physically-based mental ray lights such as the Physical  Area or Environment lights. See Create>Lights>mental ray section


All lights in this section default to quadratic falloff for physically-based lighting, and compatibility with the modern techniques including Light Importance Sampling (LIS). With LIS, the Lighting Quality can be used for direct lighting quality.

In our next post, we will introduce the Physical Area Light, and in another post we will provide more detail for the Object Light, which is a special case of the Physical Area Light assigned to an object for emission. We will also provide a post on how to use the newly packaged Environment Lights.

NVIDIA vMaterials

The vMaterials are a collection of MDL materials designed for physically based rendering, representing real world materials. You can register for a free download here. vMaterials can be rendered with mental ray 3.13 as well as with any Iray plugin, such as NVIDIA® Iray® for Maya.



To use the vMaterials for rendering with mental ray for Maya 2016, you have to add the following definition to your Maya.env file (on Windows):

MI_MDL_PATH=C:\ProgramData\NVIDIA Corporation\mdl;C:\Users\<YourUsername>\Documents\mdl;

To find out how to apply the MDL materials in your scene, check our post on Using MDL with mental ray for Maya 2016.

Some materials are dependent on the scene unit and assume meter by default. You can either change the scene scale to meter or you can convert the scene unit dependent parameters. For example, the clarity parameter in the gem materials should be multiplied by 100 if the linear working unit is centimeter.

Note: mental ray 3.13 supports MDL v1.1 and the vMaterials are based on MDL v1.2.  Nevertheless, most materials are compatible and can be rendered with mental ray 3.13 out of the box.

Rendering Deep Images with mental ray in Maya 2016

Deep OpenEXR files allow to store a variable number of samples per pixel at different depth locations to aid advanced depth compositing workflows.

To render a Deep OpenEXR file with mental ray, open the Render Settings dialog and make sure that the image output format is set to “exr” in the Common tab:


In the Scene tab, enable the “Use Deep Image format” checkbox:


The  Deep OpenEXR file is written in multi-part, which means that files can contain a number of separate but related images. Each render pass gets its own part (i. e. direct_diffuse, indirect_diffuse).

In order to save memory during rendering, mental ray creates tiled Deep OpenEXR files. These files need to be converted to scanline for use in compositing applications like Nuke. This conversion can be performed using imf_copy, a command line tool that is part of your mental ray for Maya installation. It can be found in the bin directory. Call

imf_copy -s tiled-exr-file.exr scanline-exr-file.exr

to perform the conversion. Click on the image below to see a screenshot of the tool executed on a Windows system:


Please note that currently only z front is supported. This means that rendering deep volumes is not possible yet. Deep and flat data cannot be mixed in the same OpenEXR file.



mental ray for Maya 2016 SP2

mental ray for Maya 2016 SP2 is now available for download here or it is automatically installed by the Autodesk Application Manager.
It ships with mental ray which contains improvements for the BSP2 acceleration structure in certain cases, bug fixes for multi-host rendering and for some framebuffer handling issues. The release notes provide more details.

Several bugs were fixed in the mental ray for Maya translator, notably concerning undo when modifying simple mila_material parameters, satellite rendering issues, and a workflow improvement with regard to the new Create->Lights menu and Environment lights.

mental ray for Maya 2016 SP1

mental ray for Maya 2016 SP1 is now available for download here.
It ships with mental ray Both the mental ray core and the integration provide important fixes that we will list in this post.

MDL rendering: latest MDL fixes are incorporated into SP1.

The new version of the MILA layering shaders fixes various issues:

  • alpha channel computation for specular and glossy transmission
  • possible texturing artifacts if mila_light light shader was used
  • halo effect on specular highlight when using mila in IPR
  • possible black pixel artifacts / NaN warnings in custom curve layer weights
  • unknown tag access fatal if mila_specular_transmission was used in combination with irradiance particles or with the GI Next prototype
  • missing subsurface scattering effects behind refractions
  • possible issues with semi-transparent objects in segmented/sorted shadow modes
  • possible tile artifacts in particular with glossy reflection mix
  • VP2 display for mila is now also working for scenes created with Maya 2015

UV-tiling: There was a severe bug around uv-tiled textures and conversion to .map textures: the conversion to .map would sometimes be automatically triggered. This is fixed now. The conversion will only occur if ‘Use optimized textures (auto-conversion)’ is checked in the rendering preferences. (There is a known issue in this context: the button ‘Update optimized cache textures now’ only converts the first uv-tile of a uv-tile sequence. The others will be converted during the first rendering.)

Also, when you created two file texture nodes both referencing the same uv-tile sequence, this could lead to a crash with the previous version. This is now resolved.

There are also various performance improvements in the SP1 version:

  • Since Maya2016, the new shadow mode default is “shadow segments”. This mode supports all ray tracing effects including subsurface and volume scattering in contrast to the approximate, thus potentially faster “simple” shadows. With the latest mental ray, we have improved the performance of “shadow segments” on scenes with extremely high depth complexity.
  • Light Importance Sampling is now faster for scenes with a mixture of large and small are lights.
  • Mental ray render times with procedural shaders/textures (ocean, fractal, and so forth) are also improved.