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Removing 'background colour' from video

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Joshua Harris
Removing 'background colour' from video
on Jun 14, 2011 at 9:11:04 pm

I've been given some animation footage with a white background which I'm looking to give an alpha channel so that only the animation shows over another video. the catch is that the footage is just black and white line drawing, and the inside of the characters etc is also white. so I just want to remove the white on the outside of the characters, like so:



You can imagine it would be quite easy with a tool like the Magic Wand Tool from Photoshop. But i need it for video. Any ideas? Or perhaps help me with an easy way to batch process the video through photoshop with the magic wand tool? (though that doesnt seem like it would be possible because each frame would need its own 'click' to know what colour to remove.


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Dave LaRonde
Re: Removing 'background colour' from video
on Jun 14, 2011 at 9:16:53 pm

Try AE 10's Rotobrush; it can do what you want. But DO NOT try to use it intuitively -- you'll hose yourself. There are resources that can help: go to AE's online help, do a search for rotobrush, and you'll find 'em.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Kevin Camp
Re: Removing 'background colour' from video
on Jun 14, 2011 at 9:21:38 pm

to create the alpha you can use an effect like channel combiner, set 'from' to luminance and 'to' to alpha and choose 'invert;

to clean the white edges add the remove color matting effect and set it to white.

then, to fill the areas back in, you could try adding the paint bucket effect. it will give you a fill point that you can position in the area that you want to fill. try setting the fill selector to alpha only, and set the color to white. you can duplicate the paint bucket effect for every part that you want to re-fill with white, just change the fill points.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Joshua Harris
Re: Removing 'background colour' from video
on Jun 14, 2011 at 9:43:55 pm

Thanks for your help guys but neither worked. The channel combiner seemed to do nothing than what a luma key would do and still was removing the white from the inside of the characters.

The Rotobrush would definitely work if my footage didnt move so much. The animation moves very fast and so the effect can't work out what to rotoscope.

Thanks though!


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Dave LaRonde
Re: Removing 'background colour' from video
on Jun 14, 2011 at 9:49:54 pm

[Joshua Harris] "The channel combiner seemed to do nothing than what a luma key would do and still was removing the white from the inside of the characters."

Uh-huh. Did you notice the second part of Kevin's response about using the paint bucket to fill in the empty bits? If your footage moves as fast as you say, you may have to split the layer, reapply the fill, and repeat as necessary.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Kevin Camp
Re: Removing 'background colour' from video
on Jun 14, 2011 at 9:50:04 pm

[Joshua Harris] "The channel combiner seemed to do nothing than what a luma key would do and still was removing the white from the inside of the characters"

yep, that's what it should do.

then you'll need to 'fill' the areas that need to be filled with the paint bucket effect. you can apply that effect to the same layer after channel combiner (or other luma key effect). if the area(s) are moving around, then you'll need to animate the fill point(s).

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Kevin Camp
Re: Removing 'background colour' from video
on Jun 14, 2011 at 10:25:28 pm

depending on how much 're-filling' is needed, it may be easier to use the paint bucket effect to 'fill' the outer area.

then you can then choose to 'invert fill' and set the blending mode (in the paint bucket effect) to stencil alpha and then add cc composite to composite the original with the new alpha.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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John Cuevas
Re: Removing 'background colour' from video
on Jun 15, 2011 at 2:08:12 pm

Actually it would be very easy to do in Photoshop. I'm not familiar with using Photoshop with video files or animations, so I would first bring the file into AE and create a tif sequence.

Now create an action in photoshop with the magic wand. Find some place in your sequence that doesn't have the animation(say in one of the corners), choose that area, hit delete and you should be good to go.

If it happens that the animation drifts into your seletion area, you may need to repeat the process a few times.

Johnny Cuevas, Editor


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