Adobe After Effects CS3 - Manual (Page 43)

AFTER EFFECTS CS3
User Guide
38
After Effects renders each frame of a composition one layer at a time. For this reason, the memory requirement of
each individual layer is more important than the duration of the composition or the number of layers in the compo-
sition. The memory requirement for a composition is equivalent to the memory requirement for the most memory-
intensive single layer in the composition. For example, it generally takes less memory to render 30 layers at NTSC
resolution than 2 layers at motion-picture film resolution.
Note: If the Render Multiple Frames Simultaneously option is selected, each background copy of the After Effects appli-
cation renders one frame at a time.
When a layer includes a composition as a source item, everything in that composition must be rendered before the
next layer is rendered.
The memory requirements of a layer increase under the following circumstances:
• Using a larger source image
• Enabling color management
• Adding a mask
• Adding per-character 3D properties
• Using certain blending modes, layer styles, or effects, especially those involving multiple layers
• Applying certain output options, such as 3:2 pulldown, cropping, and stretching
• Adding shadows or depth-of-field effects
If you have no problems viewing each frame of a full-resolution, best-quality preview of a composition, then you
have enough memory to render the composition. Rendering a composition into a movie takes no more memory than
displaying it on-screen with the same settings.
Occasionally, After Effects may display an alert message indicating that it requires more memory to display or render
a composition. If you receive an out-of-memory alert, free memory or reduce the memory requirements of the most
memory-intensive layers, and then try again.
Free memory immediately with one or more of the commands in the Edit > Purge menu.
After Effects requires a contiguous block of memory to store each frame; it cannot store a frame in pieces in
fragmented memory.
Use the following formula to determine the number of megabytes required to store one uncompressed frame at full
resolution:
(height in pixels) x (width in pixels) x (number of bits per channel) / 2,097,152
Note: The value 2,097,152 is a conversion factor that accounts for the number of bytes per megabyte (2
20 ), the number
of bits per byte (8), and the number of channels per pixel (4).
For example, a DV NTSC frame in an 8-bpc project requires 1.3 megabytes, and a D1/DV PAL frame in an 8-bpc
project requires 1.6 megabytes, whereas a 1080i60 DVCPRO HD frame in a 32-bpc project requires 21.1 megabytes.