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Rotobrush loses track on simple edge...

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ethan galloRotobrush loses track on simple edge...
by on Aug 16, 2011 at 8:47:04 pm

I apologize if this is already discussed somewhere. I haven't stumbled across it if it does. I'm rotobrushing out a grayish background in an interview. The subject is barely moving so it's a pretty easy deal. Brush it, let it crunch away and then adjust the parameters after. However for some reason the rotobrush is having a hard time following the edge of the subject's jaw and ear. Said facial features aren't overexposed. All subjects were lit to roughly the same exposure on the face. Other people in other interviews with the same light setup and same background that were shot literally 20 minutes after this guy are having no problem with the edge tracking.

Any thoughts on how I might be able to adjust the rotobrush to better perform in such a scenario. As of now, I'm going through very closely and modifying the selection when it gets off track. And mind you it doesn't go way off of the edge either, it just barely goes off track which looks all warpy when a white solid is put underneath the layer for a white background effect. Like I said, other people in identical setup look like the pure white background was actually shot there, but not this one guy. Curious eh?


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steve agriosiRe: Rotobrush loses track on simple edge...
by on Aug 16, 2011 at 9:45:48 pm

since we have no reference frame to check, pls tell if this part of your shot is a stationary camera result or not.
A hand held camera i guess could make this harder.
For every shot u used a fixed focal length/ follow focus? ?
Also the motion blur depending of each moving person might be different so this might be a reason as well.
So your goal is to mask-remove the background, or just to put some light/color control for it?
If u need to pull out some matte, and your camera was static, u may try to use difference matte filter. [ in case u have any clean plate for the background ]

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ethan galloRe: Rotobrush loses track on simple edge...
by on Aug 17, 2011 at 2:53:19 am

It's a med/cu stationary shot. The subject shifts his head slightly from time to time but only by an inch or so. Focus never changes. The goal is to remove the background and replace with a matte. This is part of 8 or 9 different people on the same background. The others look b-e-a-utiful, it's just something about this guy's jaw and ear that the rotobrush doesnt seem to like. Like I said it's shot on a light gray/whiteish background. The client wanted it on a pure white one so AE was the logical choice to change this after the fact. There is great separation/ edge definition between the subject and background so it is odd that it is having trouble. On all of the other subjects the background removal/replacement looks seamless, it's just this one guy, so I was wondering if there were any suggestions to modify settings for the rotobrush tool that might combat this issue.

Ethan Gallo-

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steve agriosiRe: Rotobrush loses track on simple edge...
by on Aug 17, 2011 at 11:38:14 am

sounds really strange.
I assume u already tried to pick even smaller portions with the green brush, but again i don't think rotobrush is the ideal solution for a long clip.
I remember i had a similar issue time ago.
I had to split my 30sec shot into 3x10sec pieces.
For some reason it was easier for rotobrush.
I also tried to convert my original video file [ H.264 mov ]
Dealing on tif files is always better.

I'm not sure if it's a matter of rototbrush settings.
But apart of difference matte I'd recommend some keying.
Color range can really do a good job for a raw basic matte.
then u can try to repair the edges details with some luma keyer for the hair.
U can use a smarter keyer 4 some skin tones for the rest.
I think a good combination of different keyers would do the trick.
If you like upload some sec. as an image sequence and I'll try to make a template AE project for you.
It's sounds tricky and I'd really wanna try this.
let me know what plugins u have installed so my aep can follow ur setup.

U can post your footage link here for me:

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