Apple Color 1.0 - Manual (Page 329)

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Calibrating Your Monitor
When using analog devices, make sure they are calibrated for
accurate brightness and color so you can color correct your
video accurately.
About Color Bars
Color bars are an electronically generated video signal that meet very strict
specifications. Because the luma and chroma levels are standardized, you can use color
bars passing through different components of a video system to see how each device
is affecting the signal.
NTSC and PAL each have specific color bar standards, and even within NTSC and PAL
there are several standards. When you evaluate color bars on a video scope, it is
important to know which color bars standard you are measuring, or you may make
improper adjustments. “SMPTE bars” is a commonly used standard.
Calibrating Video Monitors With Color Bars
Editors and broadcast designers shouldn’t rely on an uncalibrated monitor when
making crucial adjustments to the color and brightness of their programs. Instead, it’s
important to use a calibrated broadcast monitor to ensure that any adjustments made
to exposure and color quality are accurate.
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.