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RSMB: How to create this effect

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Will MacNeil
RSMB: How to create this effect
on Apr 25, 2007 at 12:08:57 pm

Hi, I've been asked to create a shot like this:

A presenter is doing a piece to camera on a busy street or at a train station or anywhere a lot of people are bustling about. To enhance the sense of hustle and bustle, I want to add a heavy motion blur effect to everything except the presenter. I know this is a fairly popular effect right now, but I've never really thought how to do it.

I originally planned to shoot this in three passes and comp everything together like this:

1) Clean background - locked off
2) Presenter piece to camera - locked off
3) People moving about - locked off

Then I would add RSMB to the people moving shot, possibly speeding it up beforehand. I would use shots 1 and 2 to create a difference matte to comp my presenter into the blurred shot.

The problem I now face is that it will probably be impossible to get a clean background without someone moving around.

So my question is: Can I shoot this as a regular peice to camera with all the people moving in front of and behind the presenter and add the motion blur to the whole shot? I'm guessing that since the presenter is only moving a little (basically just talking) he won't really blur. And if I needed to I could always matte out his face from the blur.

Would this give me a significant amount of blur? Can anyone think of another way to do it?

Many thanks,


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Pierre Jasmin
Re: RSMB: How to create this effect
on Apr 25, 2007 at 8:25:28 pm

One simple thing that can help you is that RSMB PRO supports an FG/BG separation matte allowing you loke that to apply different Motion Blur amounts to the two regions. (remember that matte is 0 or 1, is just a coverage that split the effect to FG or BG)

Another idea if you roto the guy anyway is to precomp the MB and use some way to average multiple frames - SmoothKit Frame Accumulate for example on that layer. If the presenter becomes too soft (so you decide you need a matte anyway), if you do a mix of frame blend and MB, you could for the precomp'd MB pass just render the BG in RSMB (these are modes in the Display Menu) using that same matte. Then so the character matte gets MB you render him FG1 only as a separate layer OVER the layer you Frame Average (which will then have full pixels everywhere - note when you render BG only it should put pixels that come from elsewhere then the presenter so if he is in different color then the rest it won't look weird).


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Will MacNeil
Re: RSMB: How to create this effect
on Apr 27, 2007 at 2:46:11 pm

Thanks Pierre. I had forgotten that the matte option in RSMB works before the motion blur is calculated. This should help alot.

Unfortunately, I working in Shake and it appears that SmoothKit is not available for this. But I think I can find another way to create some frame averaging.

Thanks alot.


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