Apple Final Cut Pro 7 - Manual (Page 1332)

When Should You Use Color Bars?
Analog devices always need to be calibrated and adjusted, even if only by minute degrees.
This is because heat, age, noise, cable length, and many other factors subtly affect the
voltage of an analog electronic video signal, which affects the brightness and color of
the video image. Color bars provide a reference signal you can use to calibrate the output
levels of an analog device.
Using Color Bars to Adjust Brightness and Color
Broadcast video professionals use color bars to calibrate the output of analog video
devices such as:
• Playback VTRs used for capturing analog video into your editing system
• Your video editing system’s video interface analog output (for output to analog video)
• Playback VTRs used for dubbing tapes to VHS
Typically, 30 to 60 seconds of color bars is recorded at the beginning of each new
videotape shot in the field. Color bars from a professional camcorder are used to calibrate
the on-location video monitor used to watch what’s being shot, so that adjustments for
brightness or color temperature made to the camcorder are made accurately. Later, the
color bars recorded at the head of each source tape are used to calibrate the clip settings
in Final Cut Pro. If you don’t have color bars on your tape, see
“Adjusting Capture Settings
on Source Tapes Without Color Bars.”
Each source tape should be individually calibrated because tapes from various camcorders
may have slightly different settings, and because even a single camcorder may have
fluctuated slightly over the course of the production.
Calibrating Video Monitors with Color Bars
Videographers don’t rely on the viewfinder of a camcorder to adjust the image being
recorded. Viewfinders and camcorder LCD displays are often too small and have color
fidelity that’s too inaccurate to ensure proper focus, brightness, and color adjustments.
Instead, a properly calibrated video monitor can be set up on location to monitor the
video during shooting.
Similarly, editors and broadcast designers shouldn’t rely on an uncalibrated monitor when
making crucial adjustments to the color and brightness of their movie footage. Instead,
it’s important to use a calibrated broadcast monitor to ensure that any adjustments made
to exposure and color quality are accurate.
Monitors are calibrated using SMPTE standard color bars. Brightness and contrast are
often adjusted by eye, using the color bars onscreen. Adjusting chroma and phase involves
using the “blue only” button found on professional video monitors. This calibration should
be done to all monitors in use, whether they’re in the field or in the editing room.
1332 Chapter 78 Measuring and Setting Video Levels