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112 Chapter 17: Rendering
The presets affect the following sett ings:
•InitialFGPointDensity
•RaysperFGPoint
•InterpolateOverNum.FGPoints
The preset settings are defined in the text file
mentalray_fg_presets.ini,foundinthe\plugcfg
folder in the program installation. You can mod ify
the existing presets and add new ones by editing
this file.
Basic group
Enable Final Gather—When on, the mental ray
renderer uses final gathering (page 3–940) to
improve the quality of global illumination.
Default=off.
Tip: Without final gathering, global i l lumination
can appear to be p atchy. 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 w hite, 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—Amultiplierforthe
densit y of final gather points. Increasing this value
increasesthedensity(andthusthequantity)of
final gather points in the image. The points will
thereforebecloserandmorenumerous. 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 il lumination
less noisy, but also increases rendering time.
Default=250.
Note: In previous versions of the software, this
parameterwasnamed“Samples”anduseda
higher default va lue.
Inter polate Over Num. FG Points—This parameter,
which replaces the radius sett ings found prev iously
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 B ounces—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 Reflect ions 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 automatical ly
raised to the Diffuse Bounces value in the MI
output file, but this is not reflected in the 3ds Max
interface.
Note: When Global Illumination (page 3–106) is
on, changing this setting has no effect.
Weigh t—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 diff u se b ounces"
(value=1.0). Default=1.0.
Final Gather Ma p group
These controls tell mental ray how to ca lculate the
final gather map for indirect illumination. The
map uses the FGM file format (page 3–937).
Read/Wr ite File—When on, the mental ray renderer
saves the fina l gather map to the specified FGM
file, if it do esn’t already exist. If the file exists,
mental ray loads it and uses the map data it
contains instead of generating a new one.