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75% bars

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Adam Swaab
75% bars
on Sep 14, 2005 at 6:20:01 pm

**Duplicate post in After Effects Forum**

Hi,

I've been asked to deliver a spot using 75% bars as my limit for chroma/luminance. Normally, I just deliver with the after effects broadcast filter on top of everything, knocking my spot down to 110 IRE, and there are no problems. We gave them (the network) a test this way, and they said it was too hot.

So, I have no idea what I should be setting my colors/whites at for 75% IRE. Can anyone explain this in layman's terms and tell me what settings I should be using?

Thanks!
Adam


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tony salgado
Re: 75% bars
on Sep 15, 2005 at 5:16:59 pm




Adam,


75% bars refer to saturation when bars are viewed on a vectorscope.

Vectorscopes can be set to display either 100% or 75% saturation.

75% bars are a standard primarily due to NTSC transmission issues with 100% saturation.


You can verify which saturation level your bars are by checking the levels on a vectorscope.




Tony Salgado


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Frank Otto
Re: 75% bars
on Sep 16, 2005 at 9:18:52 am

[tony salgado] "75% bars refer to saturation when bars are viewed on a vectorscope."


No it does not.


Color Bars are always 100 percent saturated. The 75% refers to amplitude.

To repeat: The number refers to the amplitude of RGB into the encoder. One hundred percent color bars put an undue strain on transmission systems in that the subcarrier peaks for yellow (which sits atop the highest luminance value) go to 130 IRE. Blue, the lowest in brightness has subcarrier that sinks below blanking. But the math for 75% amplitude color bars works out to a signal that reached to just 100 IRE for the positive peaks of the subcarrier signal for both yellow and cyan.





Cheers,

Frank Otto



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tony salgado
Re: 75% bars
on Sep 16, 2005 at 3:19:26 pm



Yes Frank you are correct,


I will use the proper term amplitude not saturation.



Tony Salgado


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glenn chan
Re: 75% bars
on Sep 18, 2005 at 5:30:27 am

Frank, is it 130IRE or 133IRE? (I see 133 everywhere.)


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Doug
Re: 75% bars
by
on Sep 19, 2005 at 11:38:12 pm

hehehe....all this discussion and I once worked with an engineer who swore time and time again that color bars are worthless, they don't tell you anything. Until the day our then-owner saw a spot on air that was so hot the video was tearing....it looked good on the editing monitors....and since the owner was the one that conceived the spot he took it personally. The next day we had a waveform monitor and vectorscope installed in the edit bay, the first ever for that station. (And the one in master control was hooked up and checked as well).

Doug


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