Performance And Memory; Memory Usage; Chapter 20: Performance And Memory - Adobe AFTER EFFECTS 7.0 Manual

Chapter 20: Performance and memory

Memory

Memory usage

Memory requirements for viewing and rendering increase with the resolution of the composition frame, the memory
requirement of the most memory-intensive layer in the composition, and the size of the project file.
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.
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:
•
You use a larger source image.
•
You add a mask.
•
You use certain blending modes or effects, especially those that involve multiple layers.
•
You apply certain output options, such as 3:2 pulldown, cropping, and stretching.
•
You add 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.
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, follow procedures in this section to free memory or reduce
the memory requirements of your 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
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.
636
), the number
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