Black Levels and your field monitor

ccroo

ccroo

Well-known member
Dear Folks:

This issue is really getting to me.

How many people put a proc amp between their camera and their field monitor while shooting? Apparently if you don't the 7.5 IRE difference in black level between the digital and analog standard makes NTSC color bars and your field monitor an unreliable tool for controlling your image -- on the set and in post.

It seems that shooting with this issue in mind is not a part of our DV shooting culture. Or is it?

Raoul
 
Re: Black Levels and your field monitor

If you follow the instructions on the link to John Jackman's "Great DV" site I provided in the other thread regarding setup, you should be able to calibrate your monitor properly without a proc amp.

I agree that this setup issue is frustrating, and honestly, just when I thought I understood it, thanks to the Adam Wilt info, I stumbled across a thread discussing setup in the Apple FCP forums (http://discussions.info.apple.com/WebX?14@146.ZbyNa38amn2.3@.689309db), where filter creator Graeme Nattress claims that you don't need setup at all and can just calibrate your monitor to bars with your black level at 0, which doesn't really make much sense to me.

Adding to my new confusion on the issue is this: if you calibrate your monitor to NTSC bars, with setup, then your actual DV footage will still have blacks at 0, so if you color-correct to the monitor, with 7.5 setup, and your image is just as you want it, it'll display just right on NTSC tvs, but your DV footage would be too dark, wouldn't it?

Aaarrrrggghhhh!!!
 
Re: Black Levels and your field monitor

More on this...

I'm thinking the idea is we ignore setup as an issue and work with the zero IRE digital signal our equipment produces. We set color bars normally on our field monitor (using the bars generated by the DVX) and later on our studio monitor (using bars from the NLE). When we make a DVD and play it on a regular television the DVD player will add setup, changing our black levels BUT the television itself has been set to show things correctly with black levels at 7.5 IRE so the correction is accomodated and blacks look as we shot them.

Please find holes in this. I don't purport to be correct, just searching.

Raoul
 
Re: Black Levels and your field monitor

The way I understand it, the NTSC bars are designed specifically to calibrate a monitor to a video signal where setup is at 7.5, so using them to calibrate a monitor to black level zero wouldn't work; if you calibrated to zero in post, your image when played back on a properly calibrated NTSC tv, with black level at 7.5, would be too bright.

Frankly, given that analog's a dying format anyway, we in the U.S. should just join the rest of the world in using a black level of zero and dispense with setup entirely. It would make things much easier.

In the meantime, of course, we must struggle to fully comprehend the issue. :)

Found another interesting read regarding the subject here:

http://www.signvideo.com/dv-black-level-dvd-7.5-ire-0-ntsc-part-2.htm
 
NTSC bars are for calibration, and as they're digital, they're neither 0IRE or 7.5IRE, but have their blacks correctly at code 16. As long as you calibrate the whole chain to your bars from your NLE, and through to your monitor, then you won't have a problem. Basically, you just pretend you're in Japan if your deck or camera doesn't add analogue setup on it's outputs.

Graeme
 
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