Side-Channel Blur Effect?

is there a side-channel-blur effect, e.g. the size of the blur is set by the color of a pixels channel, so you can have lets say alpha=0.0->blur=0, alpha = 1.0 -> blur at this pixel=maximum set?

Or do I have to code it myself?

PS: sorry for the stupid theme selection, i didnt get the chance to enter my own themes.