[Tig] Luminance measuring procedure

[Michel Lapointe]

Good evening,

I am quite familiar with video  signal evaluation using regular waveform 
line display, but we have now started evaluating digital video (digibetas 
and HDcams) by relying on the scopes Y-Pb-Pr displays. When using this 
display to check for luminance exceeding 100%, should I use "no filter" mode 
or "low pass " filter mode,  like on a regular waveform ?
Question emerged when running some video material through a clipper to make 
it conform to luminance broadcast limits. Signal that showed proper clipping 
when looking at it on a waveform 2 line display still showed  levels beyond 
100% when looking at the Y, Pb Pr display in flat mode. When looking at the 
actual pixel data, the Y component actually showed the effect of the clipper 
bringing the Y signal below 700 mv. But the scope Y display kept showing 
signal spikes going way overboard. It obviously disappear when I switch the 
display to "low Pass",  but I am still wondering what is it I am seeing and 
measuring.

Michel Lapointe
NFB Montreal