Chromatic aberration - alpha mask? is there a way to apply chromatic aberration(with the vanilla lens disortion node) on the edges of an alpha mask image? or is it bound to the standard elipse shape and only works from edges of the image to the center? Is it possible to work around this if I make my own chromatic aberration node group? 

all help and tips are greatly appreciated.
You could use a grayscale image connected to a displacement node to create distortion, and then offset the color channels as a form of chromatic aberration.


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Or a different variation of the same idea, but using the greyscale image to displace each one of the color channels of an image with different values:


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A different example of the same: