9

Precedence 997
parts, as opposed to the overall pose (page 3–996).
You can copy and paste postures. S ee Copy/Paste
Rollout (page 2–966).
Pr ecedence
Yo u c o n t r o l a n IK solution (page 3–955) by
setting joint precedence to determine which joints
contr ibute the most to the IK solution and which
joints contribute the least.
Joints with high precedence va lues are calculated
first, and, therefore, contribute more motion to the
IK solution. Joints with low precedence values are
calculatedlast,and,therefore,contributetheleast
motion to the I K solution.
Joints with equal precedence values are calculated
by their order in the hierarchy. Joints deep er in the
hierarchy (closer to the end effector) are calculated
first and joints closer to the root are calculated last.
Premultiplied Alpha
There are two methods of storing alpha in a
bitmap: premultiplied and nonpremultiplied.
To composite an image that is in nonpremultiplied
format, the alpha must be multiplied by each of
the R, G, and B channels before adding it to the
color of the background image. This provides the
correcttransparencyeffect,butitmustbedone
each ti me you composite. With premu ltiplied
alpha, you store the R, G, and B components w ith
the alpha already multiplied in, so compositing is
more efficient.
This is not the only reason that 3ds Max stores
images in the premultiplied format. When you
render an image, you typically want the edges of
the objects to be antialiased. This effect is achieved
by determining the f ractional coverage of pixels
ontheedgeoftheobject,andthenadjustingthe
alpha of the pixel to reflect this. For example, a
pixel that is 30% covered by the object will have an
alpha of 0.30.
To antialias the edges, the alpha must be
premultiplied to darken these edge pixels. (This is
equivalent to compositing the image over a black
image). So it is natural, in a sense, for rendered
images to have premult iplied alpha. If you do not
premultiply the alpha of a rendered image, then
just looking at the RGB you will see jaggies on the
edges of objects. You would need to composite it
against black using the alpha channel whenever
you wanted to display it.
Note: To control w hether or not the renderer
uses the env ironment map’s alpha channel in
creating the alpha for the rendered image, choose
Customize > Preferences > Rendering, and
thenturnonUseEnvironmentAlphainthe
Background Antialiasing group.
If U se Environment Alpha is turned off (the
default), the background receives an alpha value of
0 (completely transparent). If Use Environment
Alpha is turned on, the alpha of the resulting image
is a combination of the scene and background
image’s alpha channel. Also, when you render to
TGA files (page 3–633) with Pre-Multiplied Alpha
set to off, t urning on Use Environment Alpha
prevents incorrect results.
Tip: If you plan to composite objects in another
program such as Combustion or Photoshop,
render the objects against a black background.
Otherwise, a fringe of environment or background
color can appear around the objects.
Pr ocedur al Ma ps
Unlikeabitmap,whichisanimageproducedby
a fixed matrix of colored pixels like a mosaic, a
procedural map is generated by a mathematical
algorithm. Consequently, the types of cont rols
you might find for a procedural map w ill var y
depending on the capabilit ies of the procedure.