Apple Final Cut Pro 5 - Manual (Page 325)

324 Part IV Logging, Capturing, and Importing
If possible, you should aim to use a Y´C
B
C
R
codec throughout the entire
postproduction process.
For more information about managing luma and chroma levels, see Volume III,
Chapter 20, “Color Correcting Clips.” For more information about video processing, see
Volume III, Chapter 24, “Rendering.”
How Analog Video Levels Are Measured
Analog video equipment measures signals using IRE units, a video-specific unit of
voltage. IRE originally stood for Institute of Radio Engineers, which has since merged
into the modern IEEE organization. One IRE is 7.143 milliVolts, but it’s easier to
remember that an analog video signal has a range of 1 volt, which spans 140 IRE units
(–40 to 0 is for sync pulses; 0 to 100 is for picture information).
The picture information in an analog signal is measured between 0 and 100 IRE,
although higher values are possible. Synchronization pulses, which are necessary for an
analog television broadcast, are located between –40 and 0 IRE. The sharp voltage
difference between sync pulses (located at –40 IRE) and the video picture information
(starting at 0 or 7.5 IRE for black) is important to make sure that low picture information
isn’t accidentally confused as a sync pulse, which would cause video lines to draw on
screen at the wrong time. In all cases, if you are working on video destined for analog
broadcast, the absolute white value of your analog signal should never exceed 100 IRE.
Note: When analog video is digitized, only the picture information is recorded. The
sync pulses are ignored because digital video has its own method of synchronization. If
digital video signals are converted back to analog signals, new sync pulses are added at
that point.