Apple Color 1.0 - Manual (Page 30)

30 Chapter 1 Color Correction Basics
Luma
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.
Note: Unadjusted super-white levels will be clamped by the Broadcast Safe settings if
they’re turned on with their default settings, such that pixels in the image with luma
above 100 percent will be set to 100 percent.
What Is Setup
Beginning colorists sometimes confuse the black level of digital video with setup.
Setup refers to the black level of an analog video signal and is only an issue with
analog video. 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´C
B
C
R
black level simply remains at the
appropriate digital value corresponding to the bit depth of the video signal
(represented by 0 percent on a video scope).
Black
0% luminance 100% 109%
White
Superwhite