Adobe After Effects CS3 - Manual (Page 239)

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Chapter 9: Color
Color basics
Set the color depth
Color depth (or bit depth) is the number of bits per channel (bpc) used to represent the color of a pixel. The more bits
for each RGB channel (red, green, and blue), the more colors can be represented.
In After Effects, you can work in 8-bpc, 16-bpc, or 32-bpc color.
In addition to bit depth, a separate characteristic of the numbers used to represent pixel values is whether the
numbers are integers or floating-point numbers. Floating-point numbers can represent a larger range of numbers
with the same number of bits. In After Effects, 32-bpc pixel values are floating-point values.
8-bpc pixels can have values for each color channel from 0 (black) to 255 (pure color). 16-bpc pixels can have values
for each color channel from 0 (black) to 32,768 (pure color). If all three color channels have the maximum, pure-
color value, the result is white. 32-bpc pixels can have values under 0.0 and values over 1.0 (pure color); this means
that 32-bpc color in After Effects is also high dynamic range (HDR) color. HDR values can be much brighter than
white. (See “High dynamic range color” on page 235.)
Glow effect and Gaussian Blur effect applied to image in 32-bpc project (left) and 16-bpc project (right)
Set the project color depth to 32 bpc to work with HDR footage or to work with over-range values—values above 1.0
(white) that aren’t supported in 8- or 16-bpc mode. Over-range values preserve the intensity of highlights, which is
just as useful for synthetic effects such as lights, blurs, and glows as it is for working with HDR footage. The headroom
provided by working in 32 bpc prevents many kinds of data loss during operations from color correction to color
profile conversion. Even if you’re using 8-bpc footage and are creating movies in 8-bpc formats, you can obtain better
results by having the project color depth set to 16 or 32 bpc. Working in a higher bit depth provides higher precision
for calculations and greatly reduces quantization artifacts, such as banding in gradients.
Because 16-bpc frames use half the memory of 32-bpc frames, rendering previews in a 16-bpc project is faster, and
RAM previews can be longer than in a 32-bpc project. 8-bpc frames use even less memory, but the tradeoff between
quality and performance can be quite visible in some images at a project color depth of 8 bpc.
• Alt-click (Windows) or Option-click (Mac OS) the Project Settings button in the Project panel.
• Choose File > Project Settings or click the Project Settings button in the Project panel, and choose a color depth
from the Depth menu.