• Adobe After Effects

  AE mask question

  Posted by Yoshiko Tanaka on July 17, 2006 at 2:10 am

  Hi,

  I have two movie clips and I want to use of one as a mask for the other clip. There are actually identical clips which are a 3D Car in a city driving. The only difference is that one already has the car being painted with solid red. I just want to knock off the backgroung of the movie and hoping to find a way to use one clip as a mask.

  Here is the movie on the top layer and trying to use it as mask layer.

  https://jalapeno.netfirms.com/3Dciity3_red.html

  And this movie at the bottom layer and I want to knock off the background and leaving only the car running.

  https://jalapeno.netfirms.com/3Dciity3.html

  By now i know how to use regular mask but using clips as mask is totally new to me and just can;t figure this out….

  If anyone knows this please let me kno. many man thanks.

  Yoshiko

  Lars Bunch replied 19 years, 9 months ago 3 Members · 2 Replies
• 2 Replies

• 

  Steve Roberts

  July 17, 2006 at 3:42 am

  Search the AE Help for “track matte”.
• 

  Lars Bunch

  July 17, 2006 at 7:13 am

  Hi,

  You can’t use one image to directly mask the other without doing a few things first, but since the painted out car seems to have been painted out with a single discrete color of red, you can fairly easily use a keying program to select only that color of red.

  I tested the following in AE 7 and it worked adequately. If you are using another version of AE, the effects may be in different catagories.

  Place your footage with the car painted out in a comp. Apply the following effects to the layer with the painted out car… Keying>Color Key or Keylight if you’ve got it. Select the solid red color to create an alpha. You will have to tweak the edge thining and feathering to your tastes.

  The problem here is that your alpha gets rid of the car but not the background. Apply the Channels>Invert effect to this layer and set it to “Alpha”

  Create a new comp and drop both the unmasked car footage and the masked car COMP into the new comp. Make sure the masked car comp is in the layer directly above the unmasked car footage.
  Set the unmasked layer to use the masked layer as an “Alpha Matte”

  This should mask out the car so you have no background.

  I hope this does what you need.

  Lars

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