Auto-scale image to always fill composition when changing its position

Question

Hello,

I've been searching everywhere for this and haven't found how to do this.

What I'm trying to do is to have a composition that is for example 4k (3840 x 2160)

and to have a still image that I insert into my composition that's sometimes larger than the composition and sometimes smaller than the composition and varies in sizes like portrait, landscape and square images, regardless, I just need to create an expression on the image Scale property that will automatically fill the whole composition regardless of where I move the image.

Say that I animate the image position from point A to point B, I want the image to maintain a constant scale that fills the entire composition throughout the whole animation for the image.

Please help.

Thanks.

Dan Ebberts · Accepted Answer

Never mind the reply I just posted. This expression is exactly what I needed. Thank you Dan.

One more thing, what change can I make to the expression you suggested to have the image maintain the same scale?

If I animated the position of the image from point A to point B I suppose that a calculation needs to be made to get the scale of the image at the point that is further away from the center of the composition and keep that same scale throughout the whole animation.

I'm trying to figure out how to do that.

You could do something like this, but it will be slow if your comp is long. (You could always do Animation > Keyframe Assistant > Convert Expression to Keyframes once you're happy with the result.)

t = Math.max(inPoint,0);
maxS = 0;
while (t < thisComp.duration){
  p = position.valueAtTime(t);
  xScale = p[0] > thisComp.width/2 ? p[0]/(width/2) : (thisComp.width - p[0])/(width/2);
  yScale = p[1] > thisComp.height/2 ? p[1]/(height/2) : (thisComp.height - p[1])/(height/2);
  s = Math.max(xScale,yScale);
  maxS = Math.max(maxS,s);
  t += thisComp.frameDuration;
}
[maxS,maxS]*100

Dan Ebberts · Answer

Something like this will stretch (or shrink) your image layer, non-uniformly, so that the image is the same size as the comp:

[thisComp.width/width,thisComp.height/height]*100

I'm not sure if that's what you're asking for though...

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