Apple Color 1.5 - Manual (Page 30)

For more information about adjusting image contrast, see Contrast Adjustment Explained .
Luma Explained
Luma (which technically speaking is gamma-corrected luminance) describes the exposure
(lightness) of a video shot, from absolute black, through the distribution of gray tones,
all the way up to the brightest white. Luma can be separated from the color of an image.
In fact, if you desaturate an image completely, the grayscale image that remains is the
luma.
Luma is measured by Color as a digital percentage from 0 to 100, where 0 represents
absolute black and 100 represents absolute white. Color also supports super-white levels
(levels from 101 to 109 percent) if they exist in your shot. While super-white video levels
are not considered to be safe for broadcast, many cameras record video at these levels
anyway.
Black
0% luminance 100% 109%
White
Super-white
Note: Unadjusted super-white levels will be clamped by the Broadcast Safe settings (if
they’re turned on with their default settings), so that pixels in the image with luma above
100 percent will be set to 100 percent.
What Is Setup?
People often confuse the black level of digital video with setup. Setup refers to the
minimum black level assigned to specific analog video signals and is only an issue with
analog video output to the Beta SP tape format. If you are outputting to an analog tape
format using a third-party analog video interface, you should check the documentation
that came with that video interface to determine how to configure the video interface
for the North American standard for setup (7.5 IRE) or the Japanese standard (0 IRE).
Most vendors of analog video interfaces include a software control panel that allows
you to select which black level to use. Most vendors label this as “7.5 Setup” versus “0
Setup,” or in some cases “NTSC” versus “NTSC-J.”
Video sent digitally via SDI has no setup. The Y
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C
B
C
R
minimum black level for all digital
video signals is 0 percent, 0 IRE, or 0 millivolts, depending on how you’re monitoring
the signal.
30 Chapter 1 Color Correction Basics