I assume you mean "connected-component labeling" with union-find as the underlying "manage the sets" algorithm? If not, a link would be helpful.

What I mean could be described that way, but I'm not sure if you mean the same thing. Just in case, I elicited an implementation from Opus 5.5. I have carefully verified that this implementation implements what I mean: http://canonical.org/~kragen/sw/union-find-components.html