• Adobe After Effects

  AHOY there expression-eers

  Posted by Moog Gravett on November 2, 2006 at 11:56 am

  ahem – sorry about the nautical intro there – one of the pitfally of living to near the sea I think.

  I’m after a little help. Obviously.

  What I’m trying to do (in AE 6.5) is link the scale and opacity of an element to its rotation.
  I have (for example) a piece of video rotating in 3D space around it’s Y axis, and want it to be larger when close to the camera, and smaller when further away. also i’d like its opacity to react in a similar manner.

  Any ideas from you clever folks out there ?

  Cheers and… Yarrrrrrrrr-ha-haaaaa

  Moog
  Video Editor

  http://www.kuju.com | http://www.singstargame.com | http://www.Perculiana.com

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  Mike Clasby replied 19 years, 6 months ago 3 Members · 2 Replies
• 2 Replies

• 

  Tyler Paul

  November 2, 2006 at 1:40 pm

  Well, the rotation is based on 360 degrees, scale and opacity is 100.

  100 divided by 360 is .27

  Use that as your multiplier and you shouldn’t have any problems
• 

  Mike Clasby

  November 2, 2006 at 7:40 pm

  Here’s how to link Opacity and Scale to Y Rotation and Interpolate the results. Take you 3D layer and hit the s, t , and r to expose the Scale, Opacity and Rotation.

  Now for Opacity, ALt Click the Opacity Stopwatch, then drag the Pickwhip (looks like @) to the Y Rotation, it gives you this expression:

  rotationY

  But like you said, the opacity it 100% at 100 degrees rotation or larger,
  You need to Interpolate the values, here is that standard interpolation expression:

  linear (rotationY, 0,360, 0,100)

  This says as the Y Rotation varies from 0 to 360 degrees, make the opacity go from 0 to 100%.

  linear (rotationY, 0,360, 20,100)

  This changes the resulting Opacity to 20% minimum value.

  The only trouble is that if you make more then 1 rotation the opacity will be 100% at all values greater then 360 degrees so to stretch the Opacity from 0 to 100 over 4 rotations (360 x 4 = 1440) you’d need this linear interpolation:

  linear (rotationY, 0,1440, 0,100)

  When you do the same Pickwhip for Scale you get this expression:

  temp = rotationY;
  [temp, temp, temp]

  Linear Interpolation gives you this:

  temp = linear (rotationY, 0,360, 0,100);
  [temp, temp, temp]

  I didn’t quite understand about the camera, because the layer will automatically appear larger as the camera gets closer.

  Also there are other types of Interpolation, click the triangle next to the Pickwhip and then Interpolation and you’ll see the form for Ease, EaseIn and EaseOut.

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