8

Matte/Shadow Material 1395
Inter face
Matte group
Opaque Alpha—Determines w hether or not the
matte material appears in the alpha chann el. If
you turn off Opaque Alpha, the matte object will
not make an alpha channel, and the image can be
used for compositing, just as if t here are no matte
objects in the scene. Default=off.
Atmosphere group
Theseoptionsdeterminewhetherfogeffectsare
appliedtothemattesurfaces,andhowtheyare
applied.
Apply Atmospher e—Turns the fogging of matte
objects on and off.
When applying fog, you can choose between two
different methods. You can either apply fog as if
the matte surface is at an infinite distance from the
camera or you can apply it as if the matte surface is
actually at that point on the object being shaded.
In other words, y ou can apply the fog to the matte
surfaceineither2Dor3D.Thefollowingcontrols
determine how this is applied:
At B ack ground Depth—This is the 2D method. The
scanline renderer (page 3–1100) fogs the scene,
and then renders its shadows. In this case, the
shadows won’t be lightened by the fog. If you want
to lighten the shadows, you need to turn up the
shadow brightness.
At Obj ect Depth—This is the 3D method. The
renderer first renders the shadows, and then
fogs the scene. Since this varies the amount of
fog over t he 3D matte surface, the generated
matte/a lpha channels don’t blend per fectly into
thebackground.UseAtObjectDepthwhenthe
matte object is meant to be a 3D object in the scene
that the 2D background represents.
Shadow group
This group determines whether the m atte surfaces
receive shadows that are cast upon them, and how
they receive them.
Receive Shadows—Renders shadows on the matte
surfaces. Default=on.
Affect Alpha—When on, shadows cast on a matte
material are applied to the alpha channel. This lets
you render bitmaps with alpha channels that you
can composite later. Default=on.
Affect Alpha is available only when Opaque Alpha
(in the Matte group box) is turned off.
When Affect Alpha is on, the higher the Shadow
Brightness value, the more transparent the shadow,
allowing the background to show through more,
and making the shadow appear brighter.
Shadow Br ightness—Sets shadow brightness . At
0.5, the shadows w ill not be attenuated on the
matte surface; at 1.0, the shadows are brightened
to the color of the matte surface; and at 0.0 they
are darkened to completely obliterate the matte
surface.
Co lor—Displays a Color Selector (page 1–157)
to let you choose the color of the shadow.
Default=black.