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Optical Flow + Unwanted Random 'Predator' Effect

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james aldred
Optical Flow + Unwanted Random 'Predator' Effect
on Aug 3, 2009 at 2:28:24 pm

Hi

i've been using optical flow with a 50% success rate. at times, or during certain frames there is a 'predator movie' type effect surrounding the edges of the subject as it moves, a blurry watery like motion blur similar to the 'cloaked' predator in the movie.

is there an option or enhancement i'm missing, or does optical flow just work well when there's not so many textures in the background?

cheers.


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Noah Kadner
Re: Optical Flow + Unwanted Random 'Predator' Effect
on Aug 3, 2009 at 6:11:26 pm

It works best on very small portions of a shot with similar movement. So if you have a shot with a lot of different types of movement, cut it up. And be sure to export each slice and reimport as a new clip, otherwise the whole clip will be used to derive the analysis.

Noah

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james aldred
Re: Optical Flow + Unwanted Random 'Predator' Effect
on Aug 4, 2009 at 9:16:12 am

hi -

do you mean to say that the longer the clip the more likely it is this morph-blurring effect will happen? the shorter the clip the smoother the optical flow? or that it depends on the type of movement in shot?

i'm using the effect on people moving in a room, the quick turn of a head, flicking of hair etc. i did however see footage of optical flow used on an exploding car and that shot was mint.


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Noah Kadner
Re: Optical Flow + Unwanted Random 'Predator' Effect
on Aug 4, 2009 at 7:34:14 pm

I'm saying both actually. :) And to be honest it's not a miracle worker.

Noah

Check out my book: RED: The Ultimate Guide to Using the Revolutionary Camera!. Unlock the secrets of the 24p, HD and Final Cut Studio.
Now featuring the Sony EX1 Guidebook, Panasonic HVX200, and Panasonic DVX100.
http://www.callboxlive.com


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David Chai
Re: Optical Flow + Unwanted Random 'Predator' Effect
on Aug 12, 2009 at 10:45:08 pm

If you are using interlaced footage, make sure that it's interpreted correctly with the right fields before starting the optical flow analysis. Sometimes the footage is not interpreted on import and the calculations will be off. You can check the field ordering in the media tab, by selecting it and looking at the inspector under media, and see what the field ordering is. If the ordering is off. The optical flow analysis will be off.

Hope this helps,
David :D

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dc@davidchai.com
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