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4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline

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Fabio Huchant
4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline
on Mar 13, 2019 at 1:46:34 pm

Hi guys,

I've got an issue with premiere.

I have a green screen shot in 4K, mxf format from a Sony Z150. Due to the lack of lights, i shot at 12db.

So I removed the greend with ultra key, seems nice. I also corrected the colors with lumetri. Seems fine.

But ! When I export to h264 4K, it take so much time that I feel like there is something wrong going on. And also, when I play the exported video, I've got a lot of artifacts and even a green screen shadow that did not appeared before the export (and you can't see that in alpha channel ou color channel preview).

I tried at 10 mpbs vbr 1 pass, 10/12 mpbs vbr 2 pass, now I'm trying to export HEVC at 25 mbps...

Any ideas why ?

Thanks in advance,
Fabio


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Todd Perchert
Re: 4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline
on Mar 13, 2019 at 8:55:07 pm

Did you do a preview render to see if there was noise that you can't really notice in a still frame? Sounds like it could be low light noise that became visible when you boosted the levels. Some codecs, especially h264 don't do low light well - at all. I'd be interested in seeing a before/after stills. Before all your keying and color correction, and after your render.
TC


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Jon Doughtie
Re: 4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline
on Mar 14, 2019 at 10:58:01 am

When it is a "less than ideal" green screen comp, I still prefer to do those in After Effects and render them out. I know Ultra Key is available for the timeline and does a great job for many keys. But, for me, taking the time in AE still gets the best results.

System:
Dell Precision T7600 (x2)
Win 7 64-bit
32GB RAM
Adobe CC 2017.1 (as of 8/2017)
256GB SSD system drive
4 internal media drives RAID 5
Typically cutting short form from UHD MP4, HD MP4, and HD P2 MXF.


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Mark Suszko
Re: 4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline
on Mar 15, 2019 at 2:15:59 pm

Something I might do with a problematic greenscreen job is to not bother trying to do it in just one step, but to first "re-generate" the green background, by adjusting the levels and brightness/ saturation to make the key work, without regard to what it's doing to the look of the subjects.

The point is to only worry about the matte, and to re-composite that matte with a fresh background. The new background for that first key attempt is... a pure generated green or blue, depends on needs of the job. Then what we're doing is imitating an old-fashioned optical printer, layering a composite of the new matte over the untreated original footage, to generate the actual chromakey. I have saved a couple of janky keying jobs this way in the past.


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Todd Perchert
Re: 4K export quality pretty bad -> artifacts from green screen that couldn't be seen in the timeline
on Mar 15, 2019 at 2:37:58 pm

Good tips Mark! I've done similar to poorly lit green screen in the past. AE has much better tools for dealing with these sort of problems.


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