Rendering Setting up physically based rendering

There are two types of rendering in PBR, micropolygon rendering and raytracing. Micropolygon physically based rendering, like micropolygon rendering, decouple the Min Ray Samples from the Pixel Samples, allowing different numbers of motion blur from raytracing samples.

Micropolygon rendering uses the maximum of the Min/Max Ray Samples samples to determine the number of antialiasing samples per micropolygon. Raytracing uses Pixel Samples to do all of these things.

The following in an example of micropolygon PBR with Pixel Samples set to 4×4 and Min Ray Samples set to 16:

The following in an example of raytraced PBR with Pixel Samples set to 4×4:

One of the features of micropolygon rendering is that shading is dragged with the object as it moves. This has the desirable side effect of blurring out noise from the low sampling rate.

See the Render Quality and Performance help for more information.

Micropolygon renderer does not generally allow shading to be occluded on a per-pixel basis; however, ray tracing does. Mantra will perform occlusion culling to eliminate volumes that are hidden by a fully opaque surface, but if that surface is partly transparent or it is not solid across many tiles this optimization is likely to fail. The reason for this is that normally micropolygon or microvolume grids cover many pixels (often several tiles), so all those tiles would need to be fully occluded for the volume shading to be avoided.

To enable path tracing of longer paths using physically based rendering, you must increase the Diffuse Limit parameter on the PBR sub-tab in the parameter editor of the mantra output driver. Increasing the number of diffuse bounces will slow down the render and increase the amount of noise, so you might have to increase the number of samples to achieve a higher quality render.

Caching indirect lighting to a photon map requires the addition of an Indirect Light to the scene.

Managing a renderer that uses photon maps can be a little more complex than simply using PBR with extra diffuse bounces. Here’s a checklist to verify that the photon maps are being generated accurately and that your render is running as efficiently as possible. These steps assume that you are using the Physically Based Rendering Rendering Engine.

1. Create an Indirect Light using either the GI Light shelf tool or by using the tab menu to create an Indirect Light.

2. In the Render View, perform an initial render. Verify that the photon map generation progress is reported at the top of the IPR viewer before the image is rendered.

3. On the Indirect Light object, change the Light Type to Direct Global Photon Map. This setting can be used during interactive renders to verify that the photon map has been generated correctly and is a reasonable approximation for the diffuse lighting in the scene.

4. If the render appears to have large blocks of constant illumination, increase the Photon Count until the quality reaches an acceptable level.

5. Switch between Direct Global Photon Map and Indirect Global Photon Map to see the quality difference between rendering the photons directly and using them for indirect lighting. If enough photons exist in the scene, the overall light level for each render should be roughly the same.

6. If you notice some artifacts in corners, increase the Prefilter Samples or try increasing the Photon Distance Threshold. Increasing the number of samples may require you to go back and increase the Photon Count to sharpen the photon map result.

If you use PBR, you don’t have to do anything else to see caustics. Use the Caustic Light tool on the Lights and Cameras shelf tab to add indirect light to the scene with the correct options. This tool adds an environment light using caustic photon maps, causing other lights in the scene to cast caustic reflections/refractions.

By default, when you place an indirect light using the Caustic Light tool, you have to turn off Prefilter Photon Map and increase the Filter Samples to 100 to get it to work correctly. Also, make sure you have a reflective/refractive material in the scene, such as the glass default shader.

Deep raster planes are exported by the pathtracer shader for PBR. The default PBR shader supports a number of export variables. Exports that are available as light exports can be exported either on a per-light basis or as a combination for all lights. To specify a per-light value, use the light name in the deep raster parameters. To specify a sum over all lights, leave the light name blank. The same variable name is used for both the light and combination export. However, you should name the deep raster planes differently.

If you have white speckles in your image, you can try to fix it by limiting the number of color contributions a pixel will accept.

On the output driver Properties tab, add the mantra9.0/render/Color Limit property (see properties for information on how to add properties).

Decreasing this value is a bit of a hack: it can eliminate white speckles by clamping the amount of color contributed to each pixel, but it thereby darkens the image overall, and decreases the accuracy by truncating color contributions instead of distributing them equally.