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Colors turning illegal after encoding (chroma-subsampling?)

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Gregoire Verweijen
Colors turning illegal after encoding (chroma-subsampling?)
on Jan 13, 2016 at 1:54:57 pm

Hi Guys,

I have this strange issue which I haven't been able to solve yet..

Its about an broadcast delivery that keeps getting rejected by one specific broadcaster in the Netherlands. They are known for being extremely picky when it comes to delivery specs. (All other broadcasters have accepted my broadcast file)

Little background:
We have to deliver according to the 'Spot specification' which means we deliver a MXF file with an XDCAM HD422 codec (OP1a)

The errorreport we got from the broadcaster signals an 'MB Size exceeds limit.' error. "Which probably means there are illegal colors" as I have been told by the engineer at the broadcaster.

So I've been looking at the scopes and found the following.

Source is a motiongraphic (apple animation) RGB luma en chrome are within broadcast limits. (I cant check out-of-gamut colors as I dont have a diamond-scope)

As soon as I convert it to a broadcast file I looks like colors turn illegal in the chroma-subsampling phase during encoding. the edges of the white graphic have values higher than 1.

I cant seem to get rid of these artifacts. I even tried to make a ProresHD 422 first (which results in artifacts above white) than clip these values in resolve.
when I play out a ProresHQ these artifacts are back again..

Any suggestions/experiance on how to tackle this issue?

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MIke Guidotti
Re: Colors turning illegal after encoding (chroma-subsampling?)
on Jan 20, 2016 at 9:18:15 pm

[Gregoire Verweijen] "As soon as I convert it to a broadcast file"

First off what are you "converting it to a broadcast file" with? From your description I conjecture that your problem is happening in the encode phase of your workflow.

Also is the "spot specification" dictated by the broadcaster that has the problem with your files or a third party?

Also, there is nothing wrong with an engineer having quality control standards and sticking to their guns. I wish there were more of us.

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