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Photon and Final Gather maps can take a while to generate for a complicated scene, but once computed,
they can be saved and reloaded. These files are saved using the .pmap and .fgm extensions. To generate a
photon map, click the Generate Photon Map Now, or to generate a final gather map, click the Generate
Final Gather Map Now button.
Final Gather sends out rays to a scene that has computed caustics and global illumination already and com-
putes the light at that location. All these rays are then combined to produce a total lighting picture of the
scene and then blended to help fix any lighting abnormalities that may exist in the scene. The Samples
value determines how many rays are cast into the scene. The Final Gather lighting pass can then be saved to
a file after it is computed. Chapter 47: Rendering with mental ray
Rendering control
The core rendering settings for the mental ray renderer are contained within the Renderer panel of the
Render Scene dialog box, shown in Figure 47.10. Using these settings, you can increase the speed of the
renderer (at the expense of image quality).
FIGURE 47.10
The Renderer panel includes several rollouts of settings for controlling the mental ray renderer.

The Sampling settings are used to apply an anti-aliasing pass to the rendered image. These samples can be
filtered, and you can control the details of the contrast between the samples. The Bucket Width is the size
of the blocks that are identified and rendered. Smaller buckets do not take as long to render and provide
quicker feedback in the Render window.
The mental ray renderer uses several different algorithms, and you can specify which ones to ignore in
order to speed up the rendering cycle in the Rendering Algorithms rollout. If a needed algorithm is dis-
abled, the features that rely on that algorithm are skipped. You can also set the Trace Depth for Reflections
and Refractions and control the Raytrace Acceleration values.
When a preview render is rendered in the Rendered Frame Window while mental ray is enabled, an addi-
tional panel of options appears below the window as shown in Figure 47.11. The options on this panel let
you quickly adjust the precision value for the Antialiasing, Soft Shadows, Final Gather Precision, Reflection,
and Refraction settings. You also can speed the re-render by reusing the Geometry and Final Gather solu-
tions if they haven’t changed. The Render button lets you re-render the scene immediately.

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