Preventing Illegal Broadcast Levels
Broadcast facilities have limits on the maximum values of luma and chroma that are
allowable for broadcast. If a video exceeds these limits, distortion can appear in the
form of colors bleeding into one another, the whites and blacks of your program
washing out, or the picture signal bleeding into the audio signal and causing audible
distortion. In all these cases, exceeding standard signal levels can result in
unacceptable transmission quality.
For this reason, as you are performing color correction on clips in your edited
sequence, you need to make sure that the luma and chroma levels of your video stay
within the parameters referred to as broadcast-legal, or acceptable for broadcast. It is
easy to inadvertently push the levels of clips in your sequence too high, so it’s
important to use Final Cut Pro scopes and range-checking options to make sure that
the luma and chroma levels you set stay legal.
Color Correction and Video Quality Control
If your program has been accepted for broadcast, you can usually get a set of
guidelines specifying the broadcaster’s criteria for a legal video signal. The Corporation
for Public Broadcasting has a frequently cited set of guidelines for defining what levels
of luma and chroma are acceptable for broadcast. You will probably be in the clear with
most broadcasters if your program adheres to these guidelines, since they are fairly
conservative. Other broadcast companies publish their own guidelines.
Displaying Excess Luma and Chroma Levels
in the Viewer and Canvas
The Final Cut Pro range-checking options (in the Range Check submenu of the View
menu) allow you to enable zebra striping in the Viewer and Canvas to immediately warn
you of areas of your clip’s image that may stray outside the broadcast-legal range.
Zebra stripes appear as animated diagonal “marching lines” that are superimposed over
illegal areas in your picture or areas that are very near the broadcast-legal limits.
Additional icons are displayed to warn you about luma or chroma levels that fall
outside the legal range for broadcast.