Analog-X is right, I'm pretty sure you can do this using "Actions" in PhotoShop - you can then use the Batch function to do thousands in the blink of an eye.  Our technical demonstrator just showed us how to do it the other day - especially helpful for removing the background on simple animations.

You might need to look through the frames afterwards to ensure that a small area hasn't got enclosed and thus missed by the action as originally set up - but it's so much quicker than doing it by hand for each frame.

Maybe thousands is a slight exageration, but I was impressed but this ability.

Measure your mind's height
by the shade it casts.
Robert Browning (Paracelsus)

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