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.
Measuring and Setting Video Levels