Apple Final Cut Pro 7 - Manual (Page 1318)

• Both: With this option turned on, red zebra stripes indicate both areas of the frame
with luma above 100 percent and areas of the frame with illegal chroma values. If zebra
stripes appear, a yellow exclamation point icon also appears, indicating that there are
levels that are too hot.
Tip: The Excess Chroma and Both options are especially useful when using one of the
color correction filters. They warn you if you’re raising the chroma of a clip to levels
that are unacceptable for broadcast.
Using the Broadcast Safe Filter
The Broadcast Safe filter provides a quick way to reduce luma and chroma levels that
exceed the broadcast limits for NTSC, PAL, and HD video.
The easiest way to use the Broadcast Safe filter is by choosing one of the presets in the
filter’s Luma/Chroma Mode pop-up menu. The presets provide varying degrees of luma
and chroma limiting depending on the tolerance of your broadcast facility. For more
precise control, you can use the Custom preset to manually adjust the luma and chroma
saturation limits. You can also use the RGB Limiting controls to ensure that your video
levels are acceptable when converted to RGB color (for example, when your video is
displayed on a CRT monitor).
Clamping and Clipping
The Broadcast Safe filter and the RGB Limit filter (see “Using the RGB Limit Filter” ) use
clamping to adjust all values above or below a certain threshold to the threshold level.
Clamping creates a waveform whose top or bottom appears flat, or clipped.
Clipping usually refers to signals that have been negatively affected by in-camera
underexposure or overexposure, color space conversion, or improper use of color
correction tools. When you shoot video, you should control your exposure to avoid
clipping. It’s best to start with a signal that doesn’t have clipping and then clamp extreme
levels as needed using a color correction filter.
1318 Chapter 78 Measuring and Setting Video Levels