Here’s a version that uses binary search so is exponentially faster:

Note that it works best in 16 or 32 bpc for images that have a very small amount of opaque pixels ( < 0,4%)

// posterizeTime(0); // uncomment for still images
includeEffects = false;
l=thisLayer;
w=l.source.width;
h=l.source.height;
threshold = 0;
width_bits =…

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Here’s another method, that works more like the animation assistent:

Just keyframe your scale (I’m assuming 2D scales here) and apply this expression:

if (numKeys>2) {
    nk = nearestKey(time);
    prevKeyIndex = (1, nk.index - (nk.time>time ? 1 : 0))||1;
    nextKeyIndex = Math.min(numKeys, prevKeyIndex+1)||1;

    prevValue_X =…

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