IRE measuring & setting to or from 0 or 7.5 IRE

[xbox360]

Hi how can I measure the black level of a video in IRE ? then how can I convert that black level only to 0 or 7.5 IRE & leave the rest to be minimum 7.5 IRE ?

As far as I know, For a RGB range of 0 to 255, this will give an IRE range of 40 to 140.

[FlimsyFeet]

First I'd say this is not really an Avisynth question. IRE is used to measure composite video signals so to measure you would need something like an waveform monitor to look at the waveform from a colourbar test pattern and see if your "pedestal" is at 0.285V (0 IRE) or 0.339V (7.5 IRE). See http://en.wikipedia.org/wiki/IRE_%28unit%29

I don't understand the second part of your question, are you talking about using devices that output NTSC-J on a US display or vice versa?

RGB 0 to 255 (PC range) is equivalent to 7.5 to 100 IRE in the US, or 0 to 100 IRE in Japan and Europe. Also for YUV video the Y range would be 16 to 235 (TV scale).

But it's more complicated than that, because composite video has lumiance and chroma mixed together, some colours can make the signal higher than peak video (i.e. above 100 IRE). For example saturated yellows may cause problems displaying on analogue TVs. I don't know exactly how you work out IRE form RGB or YUV values, but there's some stuff on it here:
http://www.mediachance.com/dvdlab/Helppro/ntsc.htm
and Trevlacs VirtualDub plugin to show "hot pixels" here:
http://www.trevlac.us/colorCorrection/

Is "NTSC safe" even relevant anymore in this age of digital video?