• Adobe After Effects

  Masking footage with keyed alpha channel

  Posted by Tim Swiss on December 20, 2011 at 5:43 pm

  Hey guys,
  I’m bringing animated files from Photoshop into After Effects and comping them into footage.

  The animations are white line drawings exported with a premultiplied alpha channel-black. I then used the Shift Channels filter to mask the black. This method is detailed here:
  https://www.motion-graphics-exchange.com/after-effects/Removing-black-or-white-from-layer-footage-deMult-unMult/4987ec1b94c7e

  Once I’ve done this layer masks can’t be applied to the animation layer. If I disable the Shift Channels filter the layer mask works fine.

  Is there another method for keying out the alpha that will allow me to also use layer masks?

  Darby Edelen replied 14 years, 8 months ago 3 Members · 2 Replies
• 2 Replies

• 

  John Cuevas

  December 20, 2011 at 6:33 pm

  Apply your effects first. Now choose your layer and under “Layer” choose precompose “shift+cntl+c”(PC), now you can apply your mask.

  Another method would be to create a layer(solid) over your effected layer, add a mask to that layer and change your effected layers Track Matte to alpha.

  Johnny Cuevas, Editor
  Thinkck.com

  “I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
  —THOMAS EDISON on inventing the light bulb.
• 

  Darby Edelen

  December 21, 2011 at 11:25 am

  The “Set Matte” effect should work for you.

  Darby Edelen

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