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Ms. Masucci and Chroma



Anne Masucci wrote 

*	" My first question is, has anyone used a lightning display for
color correction, and if so, do you prefer it to the "traditional"
vector and waveform, and why?  Also, how do I know when I have illegal
chroma in the video? Is is when the color goes outside the boxes?"

As I understand it, Lightning Displays can show INVALID chroma - Chroma
that lies outside the component chromaticity envelope.
Vectorscopes can display chroma that is ILLEGAL - Chroma that is outside
the parameters of the coded system i.e. PAL or NTSC

Can anyone tell me how US colourists calibrate their vectorscopes using
only 75% SMPTE bars ? Is there still a limit to how much chroma can
tolerated on the broadcast sytem ? I have never seen an NTSC vectorscope
with a 100% graticule.

Anne continues:
*	"Speaking of illegal chroma, this leads me to my next question.  So
far,
      I've had three different answers on this one.  Maybe someone can
give me
      the diffinitive answer.  When looking at the vector, when is the
chroma
      illegal?  I always thought it is illegal when it goes beyond the
little
      boxes.  Then I was told that chroma is illegal if it goes outside
the
      circle."

Anne see my question above. If you calibrate your vectorscope with SMPTE
bars with 75% Chroma then the chroma can go outside the boxes but you
have no measurement of value - it's more than 75% - you can't say how
much more. If you have Bars direct from your Telecine what levels are
they and what are you measuring them with ?


*	"Today I was told that chroma is illegal if it goes outside the
      big boxes (which, of course, are outside the little ones).  (Like
my
      technical terms?)  I also go by the rule that if chroma goes
beyond
      120ire on the waveform monitor, then it is illegal too."

Could someone advise what overall NTSC levels are permissible ?
No black below 7.5 IRE - No white over 100 IRE - OK that covers
Luminance in NTSC. 
But what about Chroma levels ?




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