Final Gather Rollout (mental ray Renderer)

Preset—Provides a quick, easy solution for final gather. The default presets are: custom (the default choice), draft, low, medium, high, and very high. Available only when Enable Final Gather is on.

The presets affect the following settings:

The preset settings are defined in the text file mentalray_fg_presets.ini, found in the \plugcfg folder in the program installation. You can modify the existing presets and add new ones by editing this file.

Enable Final Gather—When on, the mental ray renderer uses final gathering to improve the quality of global illumination. Default=off.

Tip: Without final gathering, global illumination can appear to be patchy. But final gathering increases rendering time. Leave Final Gather off to preview the scene, then turn it on for the finished rendering. (Increasing the number of photons used to calculate global illumination can also improve global illumination.)

Multiplier/color swatch—Use these to control the intensity and color of the indirect light accumulated by final gathering. The defaults, 1.0 and white, produce physically correct rendering.

This is useful for adjusting the contribution of the final gather effect, thus improving the quality of an image.

Initial FG Point Density—A multiplier for the density of final gather points. Increasing this value increases the density (and thus the quantity) of final gather points in the image. The points will therefore be closer and more numerous. This parameter is useful for solving geometry problems; for example, near edges or corners. Default=1.0.

Rays per FG Point—Sets how many rays are used to compute indirect illumination in a final gather. Increasing this value makes global illumination less noisy, but also increases rendering time. Default=250.

Note: In previous versions of the software, this parameter was named “Samples” and used a higher default value.

Interpolate Over Num. FG Points—This parameter, which replaces the radius settings found previously in this group, controls the number of final gather points that are used for an image sample. It is useful for solving noise problems and getting smoother results.

Diffuse Bounces—Sets the number of times diffuse light bounces are calculated for a single diffuse ray, which the renderer casts for this purpose. Default=0.

Like Maximum Reflections and Maximum Refractions, this value is subject to the restriction of Max Depth. If you set Diffuse Bounces higher than Max Depth, the latter setting is automatically raised to the Diffuse Bounces value in the MI output file, but this is not reflected in the Autodesk VIZ interface.

Note: When Global Illumination is on, changing this setting has no effect.

Weight—Controls the relative contribution of the diffuse bounces to the final gather solution. The value scales from "using no diffuse bounces" (value=0.0) to "use full diffuse bounces" (value=1.0). Default=1.0.

These controls tell mental ray how to calculate the final gather map for indirect illumination. The map uses the FGM file format.

Read/Write File—When on, the mental ray renderer saves the final gather map to the specified FGM file, if it doesn't already exist. If the file exists, mental ray loads it and uses the map data it contains instead of generating a new one.

Read Only (FG Freeze)—Determines whether or not mental ray uses the final gather map file as is. When off, mental ray can add new final gather points if necessary. When on, mental ray uses only the data in the specified file, and does not generate any new final gather points. Available only when you've specified an FGM file. Default=off.

... [Browse]—Click to display a file selector dialog, which lets you specify a name for the final gather map (FGM) file, and the folder where it is saved.

[file name]—When you have used the Save button to specify a final gather map file, the name field displays its name and path.

Delete File—Click to delete the current FGM file.

Noise Filtering (Speckle Reduction)—Applies a median filter using neighboring final gather rays that are shot from the same point. This parameter lets you choose a value from a drop-down list. The options are None, Standard, High, Very High, and Extremely High. Default=Standard.

The practical effect of increasing Filter is to make the scene illumination smoother, at a cost of render time. However, increasing filtering can also make the illumination somewhat darker.

Note: In previous versions of the software, this parameter used a numeric value and was named “Filter.”

Draft Mode (No Precalculations)—When on, final gathering skips the precalculation phase. This results in a rendering with artifacts, but begins rendering more quickly, so it can useful when you want to do a series of trial renderings. Default=off.

Note: In previous versions of the software, this parameter was named “Preview (No Precalculations).”

The Trace Depth controls are similar to those for calculating reflections and refractions, but they refer to the light rays used by final gathering, rather than to rays used in diffuse reflection and refraction.

Max. Depth—Limits the combination of reflection and refraction. Reflection and refraction of a light ray stop when the total number of both equals the Maximum Depth setting. For example, if Maximum Depth equals 3 and the trace depths each equal 2, a ray can be reflected twice and refracted once, or vice versa, but it can’t be reflected and refracted four times. Default=5.

Max. Reflections—Sets the number of times a ray can be reflected. At 0, no reflection occurs. At 1, the ray can be reflected once only. At 2, the ray can be reflected twice, and so on. Default=5.

Max. Refractions—Sets the number of times a ray can be refracted. At 0, no refraction occurs. At 1, the ray can be refracted once only. At 2, the ray can be refracted twice, and so on. Default=5.

Use Falloff (Limits Ray Distance)—When on, uses the Start and Stop values to limit the length of light rays used for regathering. This can help improve regathering time, especially for scenes that are not fully enclosed by geometry. Default=off.

These settings provide access to the legacy method of final gather point interpolation.

Use Radius Interpolation Method—When on, makes the remaining controls in this group available. Also makes the Interpolate Over Num. FG Points check box unavailable, indicating that these controls override that setting.

Radius—When on, sets the maximum radius within which final gathering is applied. Reducing this value can improve quality at a cost of rendering time. If Radii In Pixels is off, the radius is specified in world units, and defaults to 10 percent of the maximum circumference of the scene. If Radii In Pixels is on, default=5.0 pixels.

If both Radii In Pixels and Radius are off, the maximum radius is the default value of 10 percent of the maximum scene radius, in world units.

Radii in Pixels—When on, the radii values are specified in pixels. When off, radii units depend on the value of the Radius toggle. Default=off.

Min. Radius—When on, sets the minimum radius within which final gathering must be used. Increasing this value can improve render quality but increase rendering time. Unavailable unless Radius is turned on. Default=0.0. If Radii In Pixels is on, default=0.5.