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Keying...Scratchy Footage

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Max Jackson
Keying...Scratchy Footage
on Feb 7, 2011 at 9:29:16 pm

Hi CC,

I call it scratchy as I am not exactly sure why it looks the way it does.

For some reason the motion of the green and the hand have like...meshed and splintered somehow. So in keying it it looks rather...odd.

It's moving rather fast, motion blur or not, so it probably doesn't really matter, but in a still frame it looks rather bizarre.





I was wondering if anybody has run into this or known ways around it. ?


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Tudor "Ted" Jelescu
Re: Keying...Scratchy Footage
on Feb 7, 2011 at 10:01:42 pm

To be direct, it's called bad footage, probably some sort of DV variation. So, either re-shoot with a higher quality camera, or bite the bullet and do the roto. There are some plugins out there that "clean out" DV artefacts, but I'm not convinced that they can help much.

Tudor "Ted" Jelescu
Senior VFX Artist


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Todd Kopriva
Re: Keying...Scratchy Footage
on Feb 7, 2011 at 10:21:28 pm

Yuck.

At least part of your issue appears to be that you haven't dealt properly with the fields in this interlaced footage. Be sure to separate fields.

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Todd Kopriva, Adobe Systems Incorporated
Technical Support for professional video software
After Effects Help & Support
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Max Jackson
Re: Keying...Scratchy Footage
on Feb 7, 2011 at 11:27:41 pm

Cool, that's what I thought. I'm actually practicing this at home. However, if I were on the job, I'd want to know what to tell the client in good faith.

Thanks Ted!


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Spencer Tweed
Re: Keying...Scratchy Footage
on Feb 8, 2011 at 9:51:47 pm

This isn't a field problem, it is a compression problem. Whenever our editor exports files for me DNxHD it looks exactly like this (no matter the resolution). The last project that I keyed we shot 4:2:2 and it still had this issue. All I did to fix it was had the editor export 1:1 out of Avid and it vanished (woohoo!).

I realize that you probably don't have an Avid bay in your home, but you could still look into the compression. You may not have to re-shoot this!

- Spencer


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Max Jackson
Re: Keying...Scratchy Footage
on Feb 8, 2011 at 10:55:17 pm

Wow! That's great info Spencer. Next time I see it, I can tell the client to have the previous editor who sent it to us to export 1:1 ratio (Not quite sure what that means, but good to know).

But I'm curious, if it does this, why do people use it? Or further when would one NOT use DNxHD to create this field glitch appear?


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Spencer Tweed
Re: Keying...Scratchy Footage
on Feb 9, 2011 at 12:17:34 am

It is really just a codec thing. 1:1 is basically uncompressed, while DNxHD isn't. One other area that this thing can come in is when the footage is imported into Avid. Avid can either link to footage (which is called AMA) - this is what After Effects does - or Avid can import and transcode footage. If you transcode the footage you would usually convert to MXF of the like. During this process you can get these artifacts - so make sure that you either get the source footage, or if this is impossible then make sure that at no point the footage gets compressed - in other words don't just check your export settings, you also need to check your import.

Here is a frame of that project I was talking about, showing only the red channel:



- Spencer


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Max Jackson
Re: Keying...Scratchy Footage
on Feb 9, 2011 at 12:23:13 am

Awesome, cool. I figured that 1:1 is what you put in is what you get out, but wasn't sure.

Cool, if I see this I'll know to explain it as compression artifacts and that the footage needs to be rendered uncompressed.

That's really great to know! Thanks Spencer!


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Spencer Tweed
Re: Keying...Scratchy Footage
on Feb 9, 2011 at 3:39:51 am

No problem!

And you are right about the 1:1 thing.

- Spencer


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