Graphics Reference
In-Depth Information
Audio Clips
- IFF, MP3, WAVE.
Project Composition Files
- AEP, PRPROJ, PPJ.
Each of these files has attributes that should be addressed as they are
imported, before they are used in your project.
Alpha Channel - The Embedded Mask Layer
Many of the media formats described previously can have more than just the
visual data included, they can have additional Channels or Embedded Data that
After Effects uses for proper layering and other unique effects. Perhaps the
most common extension is the Alpha Channel - the image's embedded mask.
All too often, a well-designed animation is ruined when its Alpha Channel is
misused.
The Alpha is an additional channel of visual data (in addition to the RGB or
CMYK color channels for print) that has a range of luminosity from black to
white. Usually a full value of white indicates the RGB image will be seen
completely when layered atop another background item, whereas a gray level
Alpha allows both the background and the RGB image layers to mix together.
Black will prevent any
of the foreground
RGB image from
being seen, making
the background fully
viewable.
Notice the image at
right. It's composed
of two images: the
foreground robot with
its Alpha, and the
background stage.
The foreground layer
shows the RGB image
data with the Alpha
Channel separated beneath. The white areas in the Alpha create a mask that
blocks the background from being seen (it creates a hole in the background for
the robot to fill), while the black areas allow the background to be seen.
