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Artifacting in ProRes HQ files (Resolve 8 and 9)
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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7 Replies
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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.
Colorist | Online Editor | Post Super | VFX Artist | BD Author
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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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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.
Colorist | Online Editor | Post Super | VFX Artist | BD Author
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Gotcha. Just to show you the end result, here is a screengrab of the rendered out QT:
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I would suggest to convert to DPX and not ProRes to ProRes ..
And your compositor should start and you should grade afterwards IMHO 🙂A slice of color…
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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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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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