2008

Maximum Num. Photons per Sample Sets how many photons are used to
shade the volume. Default=100.
Maximum Sampling Radius When the check box is on, the spinner sets the
size of photons. When off, each photon is calculated to be one-tenth the size
of the scene extents on page 7919 . Default: check box=off; value=1.0.
This spinner is unavailable if the check box is turned off.
Photon Map group
These controls tell mental ray how to calculate the photon map for indirect
illumination.
NOTE If you've specified a photon map here, mental ray continues to use that
map instead of generating a new one. To cause the photon map file to be rebuilt,
delete the existing file.
Read/Write File When on, if the specified photon map (
PMAP on page 7897
) file does not yet exist, mental ray generates a new map file when rendering.
If the specified file does exist, mental ray loads and uses the file.
This option becomes available after you click Browse (“...”) and provide a
name for the PMAP file.
... [browse] Click to display a file selector dialog, which lets you specify a
name and path for the photon map (PMAP) file. This automatically turns on
Read/Write File.
[file name] When you have used the [...] button to specify a photon map
file, this field displays its name and path.
Delete File Click to delete the current PMAP file.
Trace Depth group
The Trace Depth controls are similar to those for calculating reflections and
refractions, but they refer to the photons used by caustics and global
illumination, rather than to rays used in diffuse reflection and refraction.
Max. Depth Limits the combination of reflection and refraction. Reflection
and refraction of a photon 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 photon can be reflected twice and refracted once,
or vice versa, but it can’t be reflected and refracted four times. Default=5.
6102 | Chapter 18 Rendering