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Chroma key waving lines

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Mickey PowerChroma key waving lines
by on Mar 25, 2012 at 7:52:45 am

Some greenscreened footage supplied to me was shot years ago on DV CAM, I just found out, and has been captured as Apple prores.

It seems to be incredibly noisy and while I can get a reasonable key off it, adjusting the edge thinning and softening I get these waving lines along the interviewee's outline.

I've tried the FCP 7 chroma keys, the Motion 4 chroma key, even downloaded the Boris trial chroma key and still I get the wavy lines.

Any ideas are welcome. I'm hoping the footage archive can recapture in the original DVCAM to see if that will make a difference.

Mickey


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Neil PatienceRe: Chroma key waving lines
by on Mar 25, 2012 at 6:08:18 pm

You may have a fundamental problem trying to key material that has been originated on DVCam.
Both DV and DVCam use 4:1:1 chroma subsampling and although DVcam usually has s slightly better picture quality than DV, as the cameras and lenses are a little better quality the 4:1:1 signal makes keying poor.
Recapturing from the original may help a little but broadly there is not enough colour information to provide a clean key with that format.

best wishes
Neil
http://www.patience.tv


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Phil HoppesRe: Chroma key waving lines
by on Mar 26, 2012 at 12:42:03 pm

If you know someone who has Nuke (I do) there is a trick for dealing with chroma sub sampled data. You feed your original track into a colorspace node and break it into YUV data, or in the case of Nuke it is YCbCr. Your Luma in now on the red channel and your color is on the green and blue channels. Take and put a blur on just the green and blue channels. Now put in another colorspace node and convert YUV back to linear. You will find that when you key you have a lot more edge data in your color space and you can get a much cleaner key. It does not really require Nuke but a compositor that can break your RGB to YUV and then add selected blur to just the color and put YUV back to RGB. Not 100% sure if this will fix your problem but it is worth a shot.


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Simon UbsdellRe: Chroma key waving lines
by on Mar 26, 2012 at 1:51:06 pm

[Phil Hoppes] "If you know someone who has Nuke (I do) there is a trick for dealing with chroma sub sampled data. You feed your original track into a colorspace node and break it into YUV data, or in the case of Nuke it is YCbCr. Your Luma in now on the red channel and your color is on the green and blue channels."

You can of course achieve this in the much more humbly priced Conduit. And yes, it's a good keying tip if you have access to any nodal compositor.

Simon Ubsdell
http://www.tokyo-uk.com


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Shawn MillerRe: Chroma key waving lines
by on Mar 28, 2012 at 12:27:14 am

[Simon Ubsdell]"You can of course achieve this in the much more humbly priced Conduit. And yes, it's a good keying tip if you have access to any nodal compositor."

Or... if you don't have access to a node based compositor, but do have After Effects, you can use the Channel Combiner to convert from RGB to YUV, then use two instances of Channel Blur (one for blue one for green) and then use another instance of Channel Combiner to convert back to RGB from YUV. :-)

FWIW, I do like Conduit as well. I'm hoping to see it come back to Windows some day.

Thanks,

Shawn



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Simon UbsdellRe: Chroma key waving lines
by on Mar 28, 2012 at 8:00:15 am

[Shawn Miller] "Or... if you don't have access to a node based compositor, but do have After Effects, you can use the Channel Combiner to convert from RGB to YUV, then use two instances of Channel Blur (one for blue one for green) and then use another instance of Channel Combiner to convert back to RGB from YUV. :-)"

Good point - should have thought of that. It's just that I'd rather poke my eye out with a sharp stick than do this stuff in AE ;-)

Simon Ubsdell
http://www.tokyo-uk.com


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Shawn MillerRe: Chroma key waving lines
by on Mar 28, 2012 at 5:56:38 pm

[Simon Ubsdell] "Good point - should have thought of that. It's just that I'd rather poke my eye out with a sharp stick than do this stuff in AE ;-)"

Fair enough. I wonder if this can be done in Blender... I haven't tried it, but I know it now has node based compositing built in.

Shawn



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