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Artifacting in ProRes HQ files (Resolve 8 and 9)

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John Gleim
Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 13, 2012 at 9:55:12 pm

I have some ProRes HQ footage shot on green screen. When I bring this footage into Resolve (either version 8 or 9) there seems to be extra artifacting added to it. The footage looks clean in Final Cut and Quicktime (7 and X). I also tried shutting off Perian, which had no effect. I took screen grabs at 100% size of the issue.

From Quicktime:


From Resolve (no grading applied):


You can easily see the problem along the outisde right edge of the jacket and were the jacket meets the white shirt. I know the reds are really hot at the outset, but I don't understand why QT/FCP are handling it ok. Is there some sort of image processing happening when the footage is brought in?

Thanks for your help.

John


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Juan Salvo
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 13, 2012 at 10:43:43 pm

Are you comparing a screen shot from the GUI of Resolve to screen shot from the GUI of QuickTime player? You should render out the shot then compare them both in the same app. THink you'll find the issue isn't there. THis is one of the reasons why we don't use the gui to evaluate an image.

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John Gleim
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 13, 2012 at 11:17:45 pm

Thanks for the response.

That screen shot was from the GUI, but it occurs in the rendered files as well. It was actually my compositor that noticed the artifacting.

Here is a screen shot from the file rendered out of Resolve:




I think I figured out a workaround. If I convert the ProRes HQ files to ProRes 4444, the artifacting goes away. (At least on my early test.)


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Juan Salvo
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 13, 2012 at 11:23:08 pm

Sounds like a difference in the chroma resampleing. ProRes HQ is 422... Resolve processes in 4:4:4 RGB... so the chroma has to be converted and resampled to 4:4:4.. qt is doing a bit of chroma smoothing which resolve is not. Interesting.

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John Gleim
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 13, 2012 at 11:40:53 pm

Gotcha. Just to show you the end result, here is a screengrab of the rendered out QT:



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Sascha Haber
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 14, 2012 at 6:32:33 am

I would suggest to convert to DPX and not ProRes to ProRes ..
And your compositor should start and you should grade afterwards IMHO :)

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John Gleim
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 14, 2012 at 2:28:27 pm

DPX is a good idea - thanks. Normally I would grade after the composite, but in this case the footage is being comp'd onto pure graphics, so I'm doing the grade first.

BTW I'm going to ICA training next month in LA!


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Jan Wassenberg
Re: Artifacting in ProRes HQ files (Resolve 8 and 9)
on Aug 15, 2012 at 7:57:05 am

Look like chroma subsampling is indeed the culprit here.
It is a viable technique on smoothly varying images because the eye is not as sensitive to chroma. However, here there is a high-contrast edge, so the artifacts are more likely to be perceived. Presumably ProRes is not going to any great effort to cleanly separate luminance and chrominance, so it's even more visible.

Using 444 is a good workaround.


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