[FFmpeg-user] Numerical histogram output for checking typical broadcast ranges (16-235)

tim nicholson nichot20 at yahoo.com
Mon May 18 08:28:52 CEST 2015

On 17/05/15 13:05, Carl Eugen Hoyos wrote:
> Christoph Gerstbauer <christophgerstbauer <at> gmail.com> writes:
>>> do you realise that valid (specification-compliant) 
>>> broadcast-range video may contain values < 16 and > 235?
>> Hello Carl, no, I don´t.
>> Can you explain this to me?
>> I always thought that SD broadcast levels has to 
>> be >16 and <235.
> I cannot explain the relevant specifications (and I 
> don't even know where to find them) to you but to the 
> best of my knowledge:
> Just as "MPEG constant bitrate" does not mean constant 
> frame size, so a stream containing video frames of 
> different sizes is not necessarily "variable bitrate", 
> you cannot judge a video stream as being non-"broadcast 
> level" just because it contains values < 16 or > 235.

I would say a broadcast signal could quite reasonably contain values  <
16 or > 235, that is the point of such values, it allows for
over/undershoot transients resulting from analogue to digital
conversion, or filtering.

What you could reasonably say is that a broadcast signal to Rec601 or
709 etc has its black and white points defined at those values, and that
anything outside that range should only be a transient, which those
specs allow to be preserved in the interests of avoiding distortion.

> Carl Eugen
> [..]

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