IRE (unit)

An IRE is a unit used in the measurement of composite video signals. Its name is derived from the initials of the Institute of Radio Engineers.

A value of 100 IRE was originally defined to be the range from black to white in a video signal. A value of 0 IRE corresponds to the voltage value of the signal during the blanking period. The sync pulse is normally 40 IRE below this 0 IRE value, so the total range covered from peak to trough of an all white signal would be 140 IRE.

The reason IRE is a relative measurement (percent) is because a video signal may be any amplitude. This unit is used in the ITU-R BT.470 which defines PAL, NTSC and SECAM.