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98 Chapter 17: Rendering
Samples per Pixel group
Set the minimum and maximum sample rate.
Mi nimum—Sets the minimum sample rate. The
value represents t he number of samples per pixel.
Avaluegreaterthanorequalto1indicatesthat
one or more samples are computed per pixel.
A fractional value indicates that one sample is
computed for every N pixels (for example, 1/4
computes a minimum of one sample for every four
pixels). Default=1/4.
Maximum—Sets the maximum sample rate. If
neighboring samples find a difference in contr ast
that exceeds the cont rast limit, the area containing
the contrast is subdivided to the depth specified by
Maximum. Default=4.
The values of the Minimum and Maximum lists
are "locked" together so that the value of Minimum
can’t exceed the value of Maximum.
Filter group
Filter ty pe—Determines how multiple samples
are combined into a single pixel value. Can be
set to Box, Gauss, Triangle, Mitchell, or Lanczos.
Default=Box.
Tip: For most scenes the Mitchell filter gives the
best results.
• Boxfilter:Sumsallsamplesinthefilterarea
w ith equal weig ht. This is the quickest sampling
method.
• Gauss fi lter: Weig hts the samples using a Gauss
(bell) curve centered on the pixel.
• Triangle filter: Weights the samples using a
pyramid centered on the pixel.
• Mitchell filter: Weights the samples using a
curve (steeper than Gauss) centered on the
pixel.
• Lanczos filter: Weights the samples using a
curve (steeper than Gauss) centered on the
pixel, diminishing the effect of samples at the
edge of the filter area.
Width and Height—Specify the size of the filtered
area. Increasing the value of Width and Height
can soften the image, however it will increase
rendering time.
Default=Depends on the Filter type you choose:
• Box filter: Width=1.0, Height=1.0
• Gauss filter: Width= 3 .0, Height=3.0
• Triangle filter: Width=2.0, Height=2.0
• Mitchell filter: Width=4.0, Height=4.0
• Lanczos filter: Width=4.0, Height=4.0
Contrast group
These controls set the contrast values used as
thresholds to control sampling. Spatial contrast
applies to each still image. Temporal contrast
applies to
motion blur (page 3–88) .
Spatial—If neighboring samples in a frame differ
by more than this color, the mental ray renderer
does recursive supersampling (that is, more than
onesampleperpixel),uptothedepthspecifiedby
Maximum, above. Increasing the Spatial contrast
values decreases the amount of sampling done,
and c an speed the rendering of a scene at the cost
of image quality.
•
R, G, B—Specify the threshold values for the
red, green, and blue components of samples.
These values are normalized, and range
from 0.0 to 1.0, where 0.0 indicates the color
component is fully unsaturated (black, or 0 in
eight-bit encoding) and 1.0 indicates the color
component is fully saturated (white, or 255 in
eight-bit encoding). Default=(0.051, 0.051,
0.051).
•
A—Specifies the threshold value for the
alpha component of samples. This value
is normalized, and ranges from 0.0 (fully
transparent, or 0 in eight-bit encoding) to 1.0