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# Any other difference matte options?

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 Any other difference matte options? on Jan 3, 2013 at 10:04:58 pm

I know how unreliable difference mattes are, but wondered if there was any other option other than the built in After Effects effect? Something like Keylight that allows fine tuning?

thanks!

 Re: Any other difference matte options?on Jan 3, 2013 at 11:43:46 pm

Depending on what you need, you might look into Boris Motion Key [link] -- it uses optical flow to figure out which pixels are moving and which ones are not to remove moving objects.

You may be able to use this in conjunction with your original footage to generate a more useful difference matte (though I suspect it will still require a little manipulation).

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events

 Re: Any other difference matte options?on Jan 4, 2013 at 11:53:56 am

Depending on what you need, you might look into Boris Motion Key [link] -- it uses optical flow to figure out which pixels are moving and which ones are not to remove moving objects.

Walter, I searched for the meaning of Optical Flow but found it difficult to understand as the explanation was some complex maths equations.

You stated that Boris Motion Key uses optical flow. Is it an advantage? If yes then why?

Any explanation would be of great help.

Vishesh Arora
3D and Motion Graphics Artist
Films Rajendra

Blog:
http://digieffects.wordpress.com

Demo Reel(3D):

 Re: Any other difference matte options?on Jan 4, 2013 at 3:06:53 pm

[Vishesh Arora] "Walter, I searched for the meaning of Optical Flow but found it difficult to understand as the explanation was some complex maths equations. "

The gist of optical flow in this context is for the application to figure out the shape and motion of objects in the scene by analyzing a series of frames. By tracking specific features and/or pixels over time and seeing how they move from one frame to the next, the system can make guess at the structure and movement of the objects themselves.

[Vishesh Arora] "You stated that Boris Motion Key uses optical flow. Is it an advantage? If yes then why?"

Optical flow is the method by which Boris Motion Key determines what is part of a moving object and what is not, which in turn allows is to identify the pixels of moving (foreground) objects to remove, and the pixels of static (background) objects to replace them with.

Without some method to determine what is moving and what is not, Motion Key wouldn't be possible.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events

 Re: Any other difference matte options?on Jan 5, 2013 at 5:47:00 am

I got it. Thanks for the explanation Walter.

Vishesh Arora
3D and Motion Graphics Artist
Films Rajendra

Blog:
http://digieffects.wordpress.com

Demo Reel(3D):

 Re: Any other difference matte options?on Jan 5, 2013 at 2:18:02 pm

I've never used optical flow with keying before but I doubt it would work. It's used to restore a background, not a foreground. There's feathers and blurs all over the place. just a note, mocha has a new replace function too.

or my favorite:
3 separate linear color keys all layered normal with the key color set to pure white.
one using chroma
one using hue
one using rgb
this can remove and key pretty much anything including banding with smart blurs. Works better than plugins.