Glow with Moving Objects Cuts Off at Frame Edge


Sometimes I apply a glow effect to a scene with items that are moving quickly on and off the screen. Depending on the size of the glow, the glow itself will disappear the moment the object goes off frame (even though you should still see some of the light emanating from it). Obviously this happens because once the item is off frame, the glow effect has nothing apply itself to.

When objects are moving fast, this creates a really noticeable effect as the glow halos just instantly vanish in a single frame (the frame the object moves off screen). This is not a desirable effect. I’ve been thinking of ways around it, but the best I’ve come up with so far is this:

Precompose the layer with the glow effect applied, increase the comp dimensions, then duplicate the layer, move it beneath the original, scale it up by about 2%, offset it by one frame, and repeat. So you’ll have a pyramid of layers with scales 100, 102, 104, 106, etc. Since they are offset by one frame, they don’t all disappear on the same frame and you get this look as though they are extended. Here’s a video example:

Unfortunately, this takes a bit longer to render and probably isn’t the best way. Does anybody else know a better way to do it? Is there a built-in effect in After Effects that can achieve something similar?

Remember, the key is that each scaled layer is a frame off from the previous. This is what creates the illusion of the moving object still going forward beyond the frame. Motion tile with mirror edges doesn’t work because it still vanishes in a single frame.