9

142 Chapter 17: Rendering
Wa rning: If you use Exclude, make sure the Effect ID and
G-Buffer ID parameters are n ot turned on. These modes
do not provide good results when used in combination.
Ve locity El ement Pa r amet er s
Rollout
Main toolbar > Render Scene button > Render Scene
dialog > Render Elements panel > Render Elements
rollout>Addbutton>RenderElementsdialog>Add
Velocity element to the elements list (or highlight an
existing Velocity element in the list).
Rendering menu > Render > Render Scene dial og >
Render Elements panel > Render Elements rollout > Add
button > Render Elements dialog > Add Velocity eleme nt
to the elements list (or highlight an existing Velocity
element in the list).
The Velocity element generates a rendering that
contains information about the motion of objects
in the frame. You can use the Velocity rendering to
generate motion blur when you use a composition
application such as Combustion or Flame. There
are plug-ins for compositors that generate motion
blur; for example, those created by RE:Vision
Effects, Inc.
The advantages of rendering a Velocity element are
that the composition application m ight g ive you
finer control over the motion blur than 3ds Max
does; you can render a “beauty” frame that does
not contain motion blur; and the Velocity element
is quicker to render than using one of the 3ds Max
motion-blur effects.
Another use of the Velocity element is to re-time
clips rendered in 3D. There are specia lized
applications that allow you to re-time an image
sequence, using velocity data to generate more
accurate inbetween frames.
In the Velocity rendering, the motion information
is saved as RGB color information:.red saves
movement on the X axis, green save s Y-axis
movement, a nd blue saves Z-axis movement,
relative to the plane of the rendered frame.
The mental ray renderer supports this element, but
the men tal ray Motion Blur camera effect must be
turned off. Also, some mental ray materials do not
support render elements.
Controls on the element’s rollout let you improve
the precision of the motion data sav ed in the
rendering. See the procedure, following.
Procedure
To r ender a vel ocity el ement for a n ani mati on
sequence:
1.
On the Render Scene dialog > Render Elements
panel > Render Elements rollout, click Add.
In the Render Elements dialog that appears,
highlight Velocity, and then click OK.
2. Highlight the Velocity element in the Elem ent
Rendering list.
3. On the Velocity Element Parameters rollout,
turn on Update, then render several test frames.
(Choose frames where object velocity appears
to be the greatest.)
4. After each test frame, make a note of the
Maximum Velocity value. If you need to do
so, enter the largest of these values as the
Maximum Velocity to use.
Having a spec ific Maximum Velocity value will
give you more accurate velocity data.
5. Turn off Update.
NowtheMaximumVelocitywillremain
constan t.
6. Render the animation.
Interfa ce
Maximum Velocity—Enter a Maximum Velocity
value based on the result collected by Update.