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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Transcoding Artifacting

G

Greg Gelber

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We have transcoded a 4k 1080/23.97 files down to 720x486/30 and on the clips with bright lit areas, we are getting artifacts. We tried it at 1080/29.97 and although not as noticable, the artifacting is still there. It's hard to see in this image but to us, it shows up as layers of banding where shadows are created. So as the host moves, so do the bands. Any clues? Off the top of my head, I don't remeber my Redcine settings but they were set to what we thought were the "best" settings. We just heard about bayer and I don't know what it was set at. Has anyone seen this before?
 
What codec are you using and what program is doing the down conversion to SD? It's not a trival thing to go from 4k 12 bit RGB into 8 bit YUV. This means you are cross converting between not only RGB to YUV, but also, reducing the color information substantially. I would recommend converting from 4k to 10 bit ProRes as an intermediate step, then down convert in a good scaling program. Check each step incrementally to see where and when the color banding appears. 12 bit RGB 4k into 8 bit YUV SD in one single step will very likely cause the problems that you are seeing.
 
Originally the files were made using the "animation" codec but since then, we have also tried Avid DNxHD codec and uncompressed 10 bit. Again, the artifacting was reduced but still there. In a typical situation, we could possibly "live with it" but this is a spot for a major do-it-yourself warehouse. Will ProRes be better than uncompressed and if we care so much about the "quality" of the images, how does debayer play into the issue and and what setting should we try?
 
The issue may be in the RGB to YUV conversion from the RED Tools to your HD output format. This has come up a few times before and we are looking into what might be the cause. Going to an uncompressed format eliminates any compression issues, so the color space conversion may be the culprit.

Michael
 
Greg,

What program are you using to do the conversion?
 
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