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4K to 1080 Aliasing issue

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Greg Cohan
4K to 1080 Aliasing issue
on Nov 5, 2015 at 7:21:07 pm

Cross posting from Avid forum.

Working on a series were we shot 4K Drone footage (UHD H.264 codec). Work flow as follows

AMA link 4k. Transcode to DNX HQ. Transcode to DNX LB

Drag LB into Offline project and Edit with.

Relink to HQ for online in 1080p Project.

DNx HQ and LB are introducing major aliasing on it's intial transcode.

Same results on Offline Mac Pro 10.9.5 MC 8.31 and PC Online Symphony 8.4.1 (Nitris DX box)

Any Ideas?


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Eric Santiago
Re: 4K to 1080 Aliasing issue
on Nov 7, 2015 at 3:16:41 am

could it be that the image itself is too sharp?

Ive read workflows where they add a slight blur.

but not due to scaling down.


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Greg Cohan
Re: 4K to 1080 Aliasing issue
on Nov 9, 2015 at 5:28:19 pm

Yeah it behaves like the but has something to do with the downconversion avid is doing from 4k size to 1080.

The simple solution we have been doing is just adding a very slight blur. But it does not appease the "why can't I solve this problem" part of me.

In additional tests I can can eliminate the issue by slightly altering the flex frame on the clip but it means resizing someone I don't want to resize.


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Greg Cohan
Re: 4K to 1080 Aliasing issue
on Nov 10, 2015 at 9:30:27 pm

Just to update here.
This is up I have come up with so far.

This footage is shoot on an Inspire DJI drone. This camera only shoots TrueP and not Psf.

Not sure why yet but When I transcode UDH DnxHR SQ 23.98p (any variety really) then play back in full raster downscaled in 1080p 23.98 project I get interlace errors.

If I go to video output tool and switch output from PsF to TrueP. Then the errors go away. Doesn't really help me because I have to output PsF but it at least points to the issue somewhere in there.

greg


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