Final Gathering Workflow Overview
Defining final gathering in a scene is more straightforward than applying caustics or global illumination. Typically, all of the objects in a scene participate in final gathering calculations, so it’s less likely that you’ll want to limit the numbers of casters and receivers (although you can).
This section is an overview of the process of setting up a final gathering render. The options discussed in this section are discussed in greater detail in the rest of this chapter.
To create a final gathering effect
1. If necessary, specify which scene objects can cast final gathering rays, which objects are sampled by those rays, and/or which objects are invisible to final gathering rays. This is described in Setting Final Gathering Visibility Options.
2. Make sure that your scene contains at least one light with an Intensity value greater than 0.
3. Open the Render Manager and select the mental ray tab on the left side.
4. On the Optimization tab, make sure that Raytracing is selected for Primary Rays.
5. On the Final Gathering tab, select the Enable option to activate final gathering.
6. Select an Accuracy - Mode option to determine which parameters are displayed on this page and their default values. See Selecting a Final Gathering Mode for information.
7. Adjust the Accuracy values as described in Setting Accuracy Options.
8. If desired, activate the Falloff and set the Start and Stop values to limit the effect of distant objects on the final gathering calculation. See Setting the Final Gathering Falloff for information
9. If your scene contains transparent and/or reflective objects, set the Trace Depth settings to define the number of time final gathering rays are reflected and/or refracted, or bounced. See Setting the Final Gathering Trace Depth for information.
10. If desired, set the final gathering Map File options to use the map and specify its behavior. See Using the Final Gathering Map.
11. If you are rendering final gathering with global illumination, you may want to activate the Fast Lookup - Irradiance from Photon Map option. See Using Final Gathering with Global Illumination.
Final gathering is now rendered when you render your scene or draw a render region.
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You can activate the Visualize - Preview option to get an idea of what the calculated final gathering points look like in the rendered scene. When this option is selected, the final gathering points and color are displayed in the render region or render window before each frame is rendered. |
Fine-tuning the Final Gathering Effect
Use the following guidelines to adjust the final gathering settings.
• To set the effect, start with a low setting for Number of Rays such as 20 or 30. The effect is quite jagged, but you can tune it quickly.
For good quality renders, bring the value up to around 200-300. For the final render, you’ll rarely need to exceed a value of about 1000.
• As you fine-tune the effect, you may need to adjust the the Max Radius value to remove noise and artifacts.
- If you see high frequency noise (tiles, for example) in the rendered scene, increase the Number of Rays value and lower the Max Radius value.
- If you see low frequency noise (blotches) or flickering in animations, decrease the Max Radius value until the noise disappears. Keep in mind that lower values (below 1) give good results but do increase rendering time.
- If you can't get rid of scene artifacts, increase the Number of Rays value.
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