Thread: VirtualDub2
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Old 16th October 2018, 18:31   #672  |  Link
WorBry
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Join Date: Jan 2004
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@Shekh,

Question about YUV444 <-> YUV422 inter-conversion in VDub2.

I've been involved in some studies over on the BlackMagic Design DaVinci Resolve forum. There was concern about the degree of chroma loss seen when Uncompressed 10bit 422 sources are serially 'passed through' (i.e. no transforms applied) Resolve, which pointed to sub-optimal YUV422 chroma-sub-sampling. As you probably know Resolve uses it's own proprietary 'DaVinci YRGB' color-science for processing - the inner workings (algorithms) of which are not publicly known and one can only speculate based on observed behavior.

One of the forum members uploaded a couple of test clips that have proved very useful in gaining more insight. The 1080p clips (created with Natron) have a two-color checkerboard pattern. The size of the checkerboard blocks are exactly 5px wide/high, such that every second border will be placed in the middle of a color sub-sampled region. Here's a more complete explanation and the download links for the test clips - one ('Checker-444') in ProRes_4444 format and the other ('Checker'-422) in ProRes HQ (10bit 422) format:

https://forum.blackmagicdesign.com/v...=79163#p440425

I also have uncompressed v410 and v210 versions.

What has come to light is that when the Checker-422 (v210) is cycled through v410 in VDub2 (by which I mean encoding to v410 and then reconverting the export to v210) the pattern of results (as revealed by the Resolve Histogram and Parade scope profiles) is identical to that obtained when the 'Checker-422' clip is serially 'passed-through' Resolve.

https://imgur.com/nfUcnE4
https://forum.blackmagicdesign.com/v...art=50#p446976

Which suggests that they use the same chroma up-sampling and sub-sampling algorithms.

Sony (Magix) Vegas Pro 16 however appears to manage 422 chroma sub-sampling in a different way and one that, at face value, produces the more desirable outcome.

https://imgur.com/fCw4TvI

Could you shed some light on the specific algorithms used in VDub2 when inter-converting 10bit YUV-444 <-> YUV-422.

Thanks.
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Last edited by WorBry; 16th October 2018 at 18:50.
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