• Adobe After Effects Expressions

  linking luminace value to scale

  Posted by Criis Daw on March 16, 2010 at 5:12 pm

  Hi can anyone help me please.

  I am trying to create an expression where the luminace value of a layer dictates the z scale value of a precomp above it. I want it to work like a displacement map so the precomps scale at different values depending on the luminosity of the displacement image.

  I need to know how to write an expression that will determine what point of the displacment map to take the value from.

  Make sense ?

  Hope some one can help

  Cheers

  Dan Ebberts replied 15 years, 6 months ago 3 Members · 13 Replies
• 13 Replies

• 

  Dan Ebberts

  March 16, 2010 at 5:24 pm

  Something like this should work:

  minScale = 0;
  maxScale = 100;
  L = thisComp.layer(“displacement image”);
  sampleSize = 1;
  point = L.fromWorld(toWorld(anchorPoint));
  sample = L.sampleImage(point,[sampleSize,sampleSize]/2,true,time);
  lightness = rgbToHsl(sample)[2];
  s = linear(lightness,0,1,minScale,maxScale);
  [s,s]

  Dan
• 

  Criis Daw

  March 16, 2010 at 5:29 pm

  Thanks Dan,

  I think i can get my head round it. Did you just write that ?
  I am very impressed…
• 

  Dan Ebberts

  March 16, 2010 at 5:34 pm

  I did. But I’ve had a lot of practice…. 🙂

  Dan
• 

  Criis Daw

  March 16, 2010 at 5:41 pm

  well its working….

  but the x and y are scaling and the z remaining the same. Its the reverse I am after.
  I am tying to work it out but ……
• 

  Dan Ebberts

  March 16, 2010 at 5:45 pm

  Sorry – that’s what I get for reading too fast. Try this:

  minScale = 0;
  maxScale = 100;
  L = thisComp.layer(“displacement image”);
  sampleSize = 1;
  point = L.fromWorld(toWorld(anchorPoint));
  sample = L.sampleImage(point,[sampleSize,sampleSize]/2,true,time);
  lightness = rgbToHsl(sample)[2];
  s = linear(lightness,0,1,minScale,maxScale);
  [value[0],value[1],s]

  Dan
• 

  Criis Daw

  March 16, 2010 at 5:53 pm

  Thanks i worked it out !
  well almost .

  i changed the last line to

  [50,50,s]

  and typed in suitable x,y values (50) and it works like i want.

  what does the command (value) meam / make it do ?

  thanks for your help.
• 

  Dan Ebberts

  March 16, 2010 at 5:59 pm

  value just retrieves the pre-expression, keyframed (or static) value. So if you set the scale of the layer to 50%, both versions should give you the same result.

  Dan
• 

  Criis Daw

  March 16, 2010 at 6:04 pm

  thanks for your help

  little by little I am getting better at them.

  I can even more or less understand the body of the one you sent me. Its a bit like learning a foreign language. Reading often comes more easily than speaking (well correctly at least) .

  again many thanks

  Chris
• 

  Anton Arkh

  August 19, 2010 at 1:19 pm

  Hello! I am a complete novice when it comes to expressions, so I have no idea how to create anything more complex than a wiggle expression.

  How easy is it to adapt this code that Dan wrote to a lens flare brightness? I have a black/white image that I want to use as a mask, so when the Flare Center is over the white area, the Flare Brightness goes up, when its over black, it’s at 0%

  Thank you very much in advance!
• 

  Dan Ebberts

  August 19, 2010 at 5:43 pm

  This should work:

  
minBrightness = 0;
maxBrightness = 100;
L = thisComp.layer("your mask image");
sampleSize = 1;
point = L.fromWorld(toWorld(effect("Lens Flare")("Flare Center")));
sample = L.sampleImage(point,[sampleSize,sampleSize]/2,true,time);
lightness = rgbToHsl(sample)[2];
linear(lightness,0,1,minBrightness,maxBrightness);


  Dan

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