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ProRes 422 banding/dithering issue at discrete IRE levels

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Danny Thompson
ProRes 422 banding/dithering issue at discrete IRE levels
on Aug 28, 2012 at 2:48:04 pm

I'm having an issue with ProRes 422 producing banding at certain IRE levels. I am producing some test reels for my studio and in the process I have noticed this banding in grey tones. The issue is apparent in 4444 as well.

The sequence is 24N 1920x1080, encoded as 422 HQ. I've uploaded the export, as well as the fcp file:

In this ProRes 422 file I see the banding at a handful of specific IRE values: 10, 21, 46, 49, 82, and 85. In the FCP file I have a sequence, "temp CC3W grade", with some stacked color corrector filters to exaggerate the pattern. The banding has a very distinct dither pattern, which looks like this (levels adjusted to show the pattern). Some other tests in which the hue or saturation are keyframed display this issue too.

This issue has appeared at other points in time as well in non-testing situations: Apple Color's Broadcast Safe plugin (which we no longer use) and in DaVinci with grades that limit the white point. It is evident from this testing that the issue is likely due to problems with ProRes itself.

I have attempted tweaking a lot of different variables: white point rendering, motion quality, and YUV bit depth. I have tried a handful of other codecs which don't show it, but 422 is the chosen master format at my studio so a solution that allows us to continue using 422 would be ideal.

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