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Broadcast safe question

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Mark Woods
Broadcast safe question
on Dec 28, 2011 at 9:27:59 pm

How essential is it that 8-bit digital video prepared for broadcast be in the 16-235 range? I was under the impression that this was mandatory, however the default broadcast safe filter in my editing software has various degrees of strictness and it is set to clamp at 105% (around 246-247) by default. I downloaded a professional broadcast safe filter suite, tried various settings and noticed that it put the luma between 1 and 254. I also checked some clips I'd previously sent to broadcast that were broadcast safe by eye using the scopes and discovered that a couple of pixels were slightly out (e.g. 15 instead of 16) that was too small to notice by eye. These were not rejected by QC and went out to broadcast with no problems.

So is there some leeway in the luma values that can be broadcast? Is 16-235 a target but not necessarily a rule? I know 0 and 255 are reserved values but is 1-254 fair game?


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Andrew Rendell
Re: Broadcast safe question
on Dec 29, 2011 at 11:47:21 am

Broadcasters frequently use clippers in their broadcasting chain so that they don't broadcast unsafe levels. (N.B. I wouldn't rely on that as it seems to be rather mixed across different broadcasters).

So in theory you could get away with delivering material with unsafe levels, but I'd ask the following questions:

If you deliver material that isn't safe and the levels are clipped, that has an effect on the way pictures look, so are you happy for your programme to be visually degraded in that way?

Broadcasters generally specify safe levels, so if you deliver material that isn't "safe" you're giving them the power to either withhold payment or charge you for correcting the levels before broadcast. Is that a situation you'd be happy to be in?

Personally, safe levels are just one of many things that I want to have right out of a sense of professional pride/responsibility.


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Mark Woods
Re: Broadcast safe question
on Dec 29, 2011 at 6:17:36 pm

I think you may be misunderstanding my question. I do take a pride in my work and I now have the ability to analyze it at a pixel level and detect discrepancies. It was upon analyzing old work that I discovered some pixels were slightly out (15 instead of 16) that was too subtle to show up on the scopes.

My primary question is if 16-235 is absolute, what is the point of the various strictness settings on the Broadcast Safe filter? Why is FCP's set to 105% by default? And why did neither of the ones I tested clip the out of range pixels I couldn't see on the scopes?


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Bouke Vahl
Re: Broadcast safe question
on Jan 1, 2012 at 2:48:00 pm

It may have to do with not bothering you with too much detail.
A small glowing reflection can clip without a noticable effect in the final image.
If something is 'default' in FCP, it does not make it 'good', nor 'industry standard'.
In the end, it does not matter what you do nor how you do it, as long as you end up with something you are satisfied with. And it helps to know what it will look like in broadcast.
(for that reason my client monitor was driven composit untill a few years ago)

So, you can happily set the tools to 100% and ignore small peaks, at least you know where to look for potential problems.

hth,

Bouke

http://www.videotoolshed.com/
smart tools for video pros


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Mark Woods
Re: Broadcast safe question
on Jan 2, 2012 at 7:07:33 am

Thanks Bouke. That makes sense.

It also just occurred to me that FCP may not be sampling every single pixel in order to calculate the waveform. That would explain how minor problems managed to slip through.


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