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Activity Forums Adobe After Effects Rendering alpha channel

  • Rendering alpha channel

    Posted by Joakim Dalfors on July 28, 2007 at 7:46 pm

    Hi!

    I recently watched Steve Holmes in the Total Training AE Pro Features suggest to use generate fill effect with a white color and render that to a separate file to use as a luma matte.
    So far I just used the alpha only option in the render settings to render such a file.
    Does anyone know what the difference between theese methods (if any) would be and why you would prefer one over the other.

    Joakim Dalfors replied 18 years, 9 months ago 3 Members · 5 Replies
  • 5 Replies
  • Darby Edelen

    July 28, 2007 at 10:52 pm

    [jodal] “Does anyone know what the difference between theese methods (if any) would be and why you would prefer one over the other.”

    I think it’s a matter of personal preference, as well as what you need the alpha information for. Sometimes I prefer to use the Channel > Set Matte operation when I’m taking the alpha information from the layer’s (or another layer’s) luma values. There are dozens of ways to get the result you want, it’s just a matter of what you like to do.

    Darby Edelen
    DVD Menu Artist
    Left Coast Digital
    Aptos, CA

  • Steve Roberts

    July 29, 2007 at 1:24 am

    It depends on how you’re going to use the thing in an NLE later on. Does the NLE prefer luma mattes or alpha mattes?:

  • Joakim Dalfors

    July 29, 2007 at 7:18 am

    I’ll use it in both Premiere Pro and AE and I use the luma matte option in both cases.
    Just to clarify, in both methods I mentioned above I end up with a separate greyscale luma matte file (i.e I do not render RGB+alpha in the same file) to which (together with the “color version file”) I apply the track matte option in AE and PPro on to get the desired transparency. To my untrained eye they both seems to give the same result so I was just curious why one would go through the trouble of “filling with white” to get a matte-file when there is an option to render the alpha channel directly as the matte-file?

  • Steve Roberts

    July 30, 2007 at 4:25 pm

    I really don’t know. Some guys have their own familiar workflow. Or maybe he didn’t know about the “render alpha only” option. Hard to say. I’d just render the alpha.

  • Joakim Dalfors

    July 30, 2007 at 6:07 pm

    OK.
    Then I’ll continue render the alpha.

    Thanks for the input.

    best regards
    Joakim

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