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Changing white background to alpha
Fairly new to AE, (and the concept of alpha, for that matter) and I just can’t figure this out. I’m sure it’s simple: I have a black, moving video element set over a white background, basically an inverted grayscale image– in a quicktime file. I want to turn the white background to alpha so I just have the black element sitting in space, which I can convert to .flv while keeping the alpha channel (need to send this element to a web designer). Using any kind of key is producing really strange results, and basically not getting anything close to a legitimate key at all… is there any simple way to convert the white backround to an alpha channel? Much thanks.
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5 Replies
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1. add black moving square footage to comp as “grey square layer”
2. add color correction->curves effect to black moving square footage
3. invert the two dot points in curve channel so that moving square is brightest
4. add difference matte to same footage below curve effect and set view final output, diff layer grey square, change only tolerance slider, not the softness or blurs!
5. mode silhouelette alpha
6. double check your results with transparency button in comp window that looks like a checkerboard and lay a solid beneath footage to see checkerboard transparency alpha working successfully! delete solid after confirming alpha channel working.
7. export with uncompressed codecnote.Adobe Flash recognizes only premultiplied alpha channels. Ask what he wants.
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Or you could duplicate your layer and set the bottom one to Inverted Luma Matte. If your object turn out semi-transparent, add Levels to the top layer and push the outside triangles inward.
Joey Foreman
Editor/Animator
Nowhere Productions, Athens, GA -
Thanks guys, it worked perfectly… oddly enough, after four hours of frustration, when I finally tried opening the footage in a different comoposition with exactly the same settings, keying worked perfectly… but your solutions worked out much better than a key.
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Delete the BG layer altogether?
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You can also try:
1)Channel>Invert
2)Channel>Channel Combiner (from:Max RGB To:Alpha not inverted)
3)Channel>Remove Color Matting (Background Color:pure black)
4)Channel>InvertThis is a variation on the “unmult without third party plugin” technique seen elsewhere here on the cow. That works for ‘effect on black’ images, this for ‘effect on white’ images.
sorry about the late post.
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