Color management workflow in Adobe After Effects CS4
19
appendix a: color spaces and color
management
You’ve seen the term
color space
used extensively in this document. You probably now know that
color spaces provide a reference for how RGB numbers are meant to appear to the viewer. This
chapter provides more detailed information about color spaces and how they are used in color-
managed workflows, like the workflows outlined for After Effects CS4 in chapters 2-4.
device dependence
When you select RGB values in an Adobe application, like After Effects or Photoshop, you’re
specifying relative amounts of primary colors you want to use in the image or project. However,
defining an amount of primary color does not provide enough information to describe what this
value is supposed to look like to the viewer of that color. Let’s look at an example. Let’s create
some red. We want this color to be as red as possible, so we define a value of R=255 G=0 B=0 in
our file. We ask the application to provide maximum red and no green or blue. If the application
presents these values to your computer monitor without any adjustment, the monitor will show
its maximum red, and no green or blue. However, if you view the file with the 255,0,0 values on
another monitor, you may see different colors because the monitor may use different material in
the liquid crystal filters, or differs in the quality of light passing through the LCD filters. We see
different colors on two displays even though the encoding in the digital file is the same (255,0,0).
This is a case of device dependence. The color appearance of an RGB value is defined
by the combination of 1) color values and 2) device characteristics.
device independence — specifying color accurately
We know that simply specifying RGB values for our colors will not provide an accurate, unam-
biguous description of the color appearance of those values. Some color spaces, like CIE XYZ
and CIE L*a*b*, define colors using a reference to human vision — the Standard Observer. The
Standard Observer provides a standard understanding of how sensitive human eyes are to the
three primary colors: red, green, and blue. By using this reference to human vision, color spaces
like CIE XYZ and CIE L*a*b* are able to define colors using three values that correspond to a
specific color appearance. That’s very handy. In addition to the Standard Observer, CIE XYZ uses
an understanding of the light source used to view an object as well as the reflective or transmis-
sive qualities of an object. By understanding the qualities of these three elements that make up
human visual response, we are able to encode device-independent color values in the CIE XYZ
color space.
Figure 1 — Device-independent color using the CIE XYZ color space
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daylight (D65)
D50
tungsten
CIE XYZ
Characteristics of light
Characteristics of surface or filter
Characteristics of viewer
