Adobe After Effects CS4 - Manual (Page 234)

228 USING AFTER EFFECTS CS4
Animation and keyframes
Last updated 12/21/2009
When motion blur is enabled for a composition and the Timeline panel is zoomed in so that you can see individual
frames, a light gray region around the current-time indicator indicates the shutter phase and shutter angle. The width
of the column shows the shutter angle, and the offset of the column shows the shutter phase. This visual indication
shows how individual frames are sampled to calculate motion blur within this composition.
You can apply motion blur to masks. See “ Apply motion blur to a mask ” on page 332.
You can use motion blur when you animate a layer—for example, moving a layer of text across the screen. You cannot
add motion blur to motion that already exists within a layer by means of the Motion Blur layer switch and Enable
Motion Blur composition switch.
If you want to smooth live-action video to which you assigned a frame rate much lower or higher than the original, use
frame blending, not motion blur.
More Help topics
“ Frame blending ” on page 253
“ Render settings ” on page 697
“ Effects overview and resources ” on page 388
Motion blur settings in the Advanced tab of Composition Settings
Samples Per Frame The minimum number of samples. This minimum is the number of samples used for frames for
which After Effects is not able to determine an adaptive sampling rate based on layer motion. This sample rate is used
for 3D layers and shape layers.
Adaptive Sample Limit The maximum number of samples.
Shutter Angle The shutter angle is measured in degrees, simulating the exposure allowed by a rotating shutter. The
shutter angle uses the footage frame rate to determine the simulated exposure, which affects the amount of motion
blur. For example, entering 90° (25% of 360°) for 24-fps footage creates an effective exposure of 1/96 of a second (25%
of 1/24 of a second). Entering 1° applies almost no motion blur, and entering 720° applies a large amount of blur.
Shutter Phase The shutter phase is also measured in degrees. It defines an offset that determines when the shutter
opens relative to the beginning of a frame. Adjusting this value can help if an object with motion blur applied appears
to lag behind the position of the object without motion blur applied.
A Shutter Phase value that is -1/2 of the Shutter Angle value is best for a layer that is composited on top of another
using motion tracking data. (For example, Shutter Phase = -90, Shutter Angle = 180.) This setting combination causes
a blur that is centered on the original object.
Additional resources about motion blur
Mark Christiansen explains some of the concepts surrounding motion blur, shutter speed, and shutter angle on the
ProVideo Coalition website .
Trish and Chris Meyer provide instructions on the ProVideo Coalition website for shooting footage and using motion
blur to smooth motion.
Andrew Kramer provides a video tutorial on his Video Copilot website in which he demonstrates the advantages of
using 32bpc color with motion blur. (See “ Color depth and high dynamic range color ” on page 274.)
The ReelSmart Motion Blur effect from RE:Vision Effects analyzes motion from frame to frame within a layer and uses
this information to add motion blur to motion within the layer. For information, see the
RE:Vision Effects website .
To achieve a result similar to the result of ReelSmart Motion Blur, apply the Timewarp effect, set Speed to 100, enable
motion blur within the effect, and use the manual shutter control features to adjust the motion blur.