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Thread: Antialiasing alpha-channel

  1. #1
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    Question Antialiasing alpha-channel

    Hi!

    I'm currently working on an ident for a national TV-company(Norway). I'm rendering in layers and composite everything in Combustion. The alpha-channels doesn't seam to be antialiased . How can I antialias the alpha-channels so that the the edge of each object look smooth. Is there a function in lightwave that does this or do i HAVE to use the "remove white matte"-function in photoshop? I have tried to save as png/tiff/tga. They all s***ed!

    Example:

    The red background is only there to illustrate the unantialiased edges better...

    Lars
    Last edited by larserik; 05-15-2003 at 04:26 AM.

  2. #2
    Super Member Red_Oddity's Avatar
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    I think those are the edges of a premultiplied alpha...try clicking on your footage (either in the Footage Library or in the composite it is in, click on the Source panel in you Footage Control tab, and set the Alpha to Premultiplied with (the background color you used in LW).

  3. #3
    obfuscated SDK hacker Lightwolf's Avatar
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    Red_Oddity is right.
    Next time, render in front of black, that tends to cause less problem in compositing.

  4. #4
    Yes, surely looks like that. If the problem remains you will have to re-render your anim with extra alpha output or use fader alpha mode.

    Mylenium
    [Pour Mylène, ange sur terre]

  5. #5
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    Red_oddity: Great! The "Premultiplied with" function worked perfectly.

    Lightwolf: What if the background of the whole composite is white or another bright color. Is it still preferable to use black as the background color in lightwave?

    Mylenium: I havn't used lightwave for a while... What if I choose to save ONLY the alpha, does it render any faster? What does the fader aplha mode actually do? Does it blur the alpha mask?

    Thanx for all replies this far!!

  6. #6
    obfuscated SDK hacker Lightwolf's Avatar
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    larserik:
    Well, technically yes.
    Premultiplied means, that in the semi-transparent borders (of the image/alpha channel), the colours are stored already multiplied with the alpha.
    Let's say you have a red image, rgb: 255,0,0
    At the edges, the alpha is 50% -> 128.
    The red image would be 128, 0, 0 (255 * 50%) at that place.
    Alpha 25% -> 64, 0, 0
    Alpha 75% -> 196, 0, 0

    This is much easier for the compositing tool, since it only has to add values when merging.

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