In this fourth post in a series on mental ray for Maya 2016 Render Settings, we follow up on the Using Modern Materials and Lights post with more detail on the new Physical Area Light.

Where to find the new Physical Area Light

Note the new mental ray section. All lights below the line are mental ray lights.

Convenient Creation of Maya Area Light

The Physical Area Light is a Maya Area Light set up using the mila_light shader, for best operation with Layering (MILA) materials.

By default, the settings are as follows:

• Physically-based falloff (Light Decay is Quadratic)
• Shapes supported by mental ray (Light Shape Type is Rectangle)
• Intensity connected to the mila_light
• Color connected to the mila_light, supporting textures

Scene scale matters

The Physical Area Light has physically-based falloff (Light Decay is Quadratic) so the intensity of the light compared to the scene scale matters. It is the number one reason we find when troubleshooting a physically-based scene that renders black or dark. Take the following example.

A default polygon plane is created on the default grid.

The plane is scaled up to the size of the default grid.

A Physical Area Light is created and moved to 4 units above the plane.

Then rendered, noting that the default intensity of the light is 100.

Now the light is  moved to 10 units above the plane.

Rendered. And barely lighting this  plane, so more than that requires more light intensity.

Also, the size of  the area light matters.

A flashlight can light up a baseball, but it cannot light up a baseball field. This kind of thinking has to start informing your lighting decisions. But once you get used to it, it may actually help you work more efficiently to produce realistic lighting results.

Lighting Quality

With Light Importance Sampling (LIS) on, the area light Samples settings are ignored, and quality of direct lighting can be more easily controlled with the Lighting Quality setting in the Quality tab of the Render Settings. This is especially useful for scenes with many lights.

Using textures

Because the Physical Area light automatically uses the texture-able mila_light shader, one can set the input for the light Color with a Maya File node. By the way, we also updated the physical_light to be able to use textures, but now the mila_light is preferred, as it will evolve with the physical area light.

Example using an HDR textured rectangular area light. The intensity multiplier scales the values whether they are HDR or LDR. It’s just a multiply of whatever the texture returns. In other words, the texture is not normalized before multiplication.

Spot edge falloff

The physical area light defaults to use a point light output pattern over the surface area of the light. In order to use a more spot-like falloff for the edges of the area, we need to adjust the area light. To do this, change the light type of your  Physical Area Light from Area Light to Spot Light. It is still a Physical Area Light because it uses the light shape. The mila_light shader remains hooked up to the  color and the intensity.

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 mental-ray-beta@nvidia.com, 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.

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.

Materials

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.

If 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.

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.

Lights

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.

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.

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.