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CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?

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Dan Englund
CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 14, 2011 at 3:10:52 am

Hi everyone,

I am trying to use the Timewarp effect to slow down some footage with a fast moving object moving against a somewhat complex background which results in parts of the background moving with and being distorted by the foreground object as it moves across it when just the Timewarp effect is used. I have been searching for a possible work around to this problem for quite some time and I have found some discussions indicating that the problem can be fixed by using the Rotobrush tool to create a matte and somehow applying this to the Timewarp effect. However I have not been able to find a clear description on how this can be done and after many hours of attempting to fix my Timewarp errors using a rotobrush matte I have yet to have any success. Could anyone offer me some guidance on how this might be done?

Thanks!

Dan


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Roland R. Kahlenberg
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 15, 2011 at 12:47:55 am

Usually a Stabilization process is done instead of Timewarp - then Rotobrush if needed, then re-introduce the original movement (inverse stabilization). Then there is Mocha that works well for tracking and roto-ing

Why don't you post the shot so that we can have a better idea of your issues.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia.


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Dan Englund
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 15, 2011 at 3:19:52 pm

Hi Roland,

My post wasn't very clear, I am actually simply trying to slow a few shots down using timewarp (25% speed or so) and for the most part I am getting very good results but am running into problems when the skier is moving against the landing hill. Here is a video showing some of my footage that I would like to use timewarp on:



You can see the problem I am running into if you watch closely at 0:29 As you can see the white lines on the landing hill distort and sort of move with the skier as he passes over them and it seems to me that there must be some way of isolating the skier from the background in timewarp. The earlier shots from the side are the ones I really want to be able to slow down and with timewarp I get nearly perfect results except for the tendency of the background to distort with the skier.

Thanks for your help!

Dan


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Roland R. Kahlenberg
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 15, 2011 at 8:07:41 pm

Sorry Dan but I'm on the tail end of an 18-hour shift; coupled with the compression artefacts and my failing eyes, I can't see the issue you're alluding to.

I did however notice that the imagery at abouts :29 is much slower that the other parts of the video. Perhaps, you're pushing the limits of the plugin.

What you have, in its entirety looks great. May I humbly suggest that you re-think the challenge for the :29 part. Do take a look at Carl Larsen's excellent COW Tutorial - http://library.creativecow.net/articles/larsen_carl/analyzing_motion.php

Perhaps you may be inspired to dabble with the technique.

Cheers
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia.


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Dan Englund
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 16, 2011 at 3:13:06 pm

It is hard to see the problem I am running into in the video I posted, here is a quick clip that clearly shows the issue I am hoping to fix by using a matte. In the "effect controls" for timewarp there are 3 fields titled matte layer, matte channel, and warp layer that from what I can tell should allow me to somehow isolate the skier from the background using a matte. That tutorial you linked to is very cool, I think I will have to try something similar for some of these shots!

Thanks again for your help!

Dan


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Roland R. Kahlenberg
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 16, 2011 at 5:15:02 pm

Hi Dan, I was going to post this but I've got ridiculous deadlines and sorta forgot.

I was going to tell you to work the Timewarp effect in stages instead of using brute force, at one go. For example, instead of lowering playback by a factor of 10 at one go, do it in stages of say two with the first slowing down by a factor of 2 (or 5) and then a second time (perhaps with nesting or a rendered version) by a factor of 5 (or 2).

Oftentimes, such a strategy works well - with slowing down footage as well as with sharpening or blurring images with a more delectable result.

As for the matte thingies in Timewarp, although I've not messed about with them, I would assume that they would exclude areas of the footage from being affected by the Timewarp effect. This, me thinks may not work in your favor, with your specific case.

And yes, that's a cool tutorial from Carl Larsen. That was one of the first things that came to mind when I saw your footage.

Cheers
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia.


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Dan Englund
Re: CS5.5 Rotobrush with Timewarp to fix errors between foreground and background motion?
on Oct 16, 2011 at 7:34:21 pm

Good tip on working with timewarp in stages, I will have to play around with that. It seems I failed to include the clip that I referred to in my last post, here it is: http://reels.creativecow.net/film/timewarp


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