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.

This is the first in a series of posts on mental ray for Maya 2016 Render Settings

Introduction

We significantly changed the mental ray for Maya 2016 Render Settings User Interface (UI) in order to reduce time spent adjusting renders. The defaults aim for no-fuss rendering of the most frequently used and up-to-date features. Of specific note, our newest Global Illumination (GI) mode significantly increases ease-of-use and productivity.

We provide almost everything a user needs here within this UI. For example, a user should not have to type in string options anymore.

Goals

Members of both NVIDIA ARC and Autodesk, including UI designers and developers, collaborated to make this change significant. As stated in the Maya 2016 documentation for mental ray Render Settings, we aim to:

• Enable complete rendering without requirement to adjust or enable most settings. The defaults should enable the most frequently used features.
• Increase ease-of-use when adjusting settings to control for optimization and quality.
• Provide single global controls to reduce repetitive and potentially error-inducing settings across scene elements.

We also want to retain the flexibility of mental ray for production users. So we provide an Advanced Settings option on each of the new tabs. We hide less frequently used features in favor of a cleaner, more productive and simpler control for basic workflow. This leads users of all levels to what is fundamentally important to control.

Render Settings Tabs

We re-organized the mental ray Render Settings into four main tabs:

The Quality tab contains quality settings for controlling sampling. By using quality settings, instead of sample counts, we take advantage of better optimization schemes internally. We also believe it will be conceptually easier, once the community gets familiar with this style of control.

The Scene tab contains shared settings across scene elements, such as camera settings that should be applied to all renderable cameras. This is where we provide the new simplified mental ray Passes.

The Configuration tab contains settings that are more likely to be used across Maya sessions, and how a user likes to work with the scene. For example, the interactive rendering control for progressive rendering depends on a machine’s resources.

The Diagnostics tab contains settings that help a user with problem solving, or identification of areas for optimization.

Quality Settings

Here, we provide an overview of how to adjust your scenes with the new UI, suggesting our recommended practice.

For new scenes, use the Overall Quality setting in the Sampling section as the primary control for speed vs. quality. It is located at the top of the Quality tab.This controls samples across a scene. Samples are not fixed per pixel. Rather, they vary in density per pixel region. More samples are taken in each region until the quality is matched.

In the next section, we provide detail to better understand how to adjust quality beyond the Overall Quality setting. With better understanding, we hope you can more quickly achieve your desired results. 

Understanding more about quality adjustment

Here, we introduce the concept of global vs. local sampling. This concept is key to adjusting quality now and in the future, as rendering technology evolves.

The Overall Quality setting is a global setting that controls samples across a scene. Each sample starts a ray traced from the camera out into the scene. In essence, we sample the scene from the eye (E). Below, we show an eye ray (in green) over a work by Albrecht Dürer.

When an eye ray intersects an object, the eye ray may split into several samples. We will call those the local samples, in contrast to the global samples, because they are local to each eye ray. Below, we show a diffuse distribution of local samples split out for diffuse reflection.

We separate the local samples into two categories at an intersection point: the samples used for lights and the samples used for materials.

For materials, the sample directions depend on the type of surface at the intersection point. For example, above a diffuse surface creates samples in the hemisphere above the intersection point. Because these samples tend to hit objects, it represents indirect light.

For lighting, the samples are taken from all visible lights in the scene. Below, we see a single light sample for the same intersection point. There could be more light samples depending on number and size of lights. Light samples represent direct light.

Traditionally, lights were only those elements specified explicitly as lights in the scene, and they had no size. However, as rendering implementations evolved, so did lights, from point to area lights, and now, emissive objects. Also, consider the light from an environment. Environments convert automatically into light sources by enabling environment light emission. When enabled, we provide a separate quality control for the environment lighting.Note that it is grayed out when not enabled. Furthermore, now one can create such a light more directly. See for example Create > Lights > Environment Image (IBL).

Similarly, we provide a separate control for indirect diffuse (GI) quality in materials, even though it is conceptually a part of material quality.As global illumination techniques have evolved considerably, so have the ways to control these techniques. Yet, the Indirect Diffuse Quality applies to any Indirect Diffuse (GI) Mode selected, and to any material used.

In our next mental ray for Maya 2016 Render Settings post, we provide more details and examples for Adjusting Quality.