How Analog Video Signals Are Measured
Analog video is measured using IRE units. (IRE originally stood for Institute of
Radio Engineers, which has since merged into the modern IEEE organization; the
measurement is a video-specific unit of voltage.) One IRE is 7.143 millivolts, but it’s easier
to remember that an analog video signal has a range of 1 volt, which spans 140 IRE
units. Synchronization pulses, which are necessary for an analog television broadcast,
are located between –40 and 0 IRE.
PAL and Japanese NTSC systems have luma (or Y´) values between 0 IRE (black)
and 100 IRE (white), although higher values are possible. Signals above 100 IRE are
considered illegal for broadcast. North American NTSC systems set black at 7.5 IRE.
This extra 7.5 IRE is called setup or pedestal (because it pushes the entire image higher
on the waveform monitor).