zebra IRE Question

[Are Pilskog]

Hi
I've looked around for this question. Hope someone can help me.

I am used to zebra in % where 100 % is overexposed (no information captured).

In Red One the zebra is presented in IRE. What is IRE, and how do I calculate the corresponding zebra prosent value?

Thanks!

Are

 

[Tanner Stauss]

I would like to revamp this post because I have the exact same question. But looks like we got 2 months and no answers on this one. Someone knows...

I'm going to also post the same question somewhere else to hopefully get an answer.

 

[Daniel S Williams]

from wikipedia.
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 zero voltage value during the blanking period. The sync pulse is normally 40 IRE below the zero value, so, peak to peak, an all white signal should be equal to 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.

 

[Tanner Stauss]

ok, I kind of get it now. So if 140 IRE is equal to all white, theoretically that should be 100% on a zebra percent scale, right? But we can only set the IRE to a maximum 108, that would put 108 around 75% white. How can we a setting closer to the 90-100% range?

 

[Daniel S Williams]

100 ire is the NTSC legal brightest white