Denying the Antecedent vs Improper Transposition

Affirming the Consequent and Commutation of Conditionals are logically similar, as they have the same form (affirming the consequent Q and therefore affirming P), but the latter phrase applies to conditional statements. Thus, while both being examples of fallacious modus ponens, at least I can tell when to use each.

This is not the case for Denying the Antecedent and Improper Transposition, though. They appear too similar for me to distinguish between them.

Denying the Antecedent presents like this: P implies Q. Not-P, therefore, not-Q. Invalid because P is not a necessary condition for Q. Got it.

Improper Transposition presents like this: If P, then Q. If not-P, then not-Q. 

Nowhere in the page description is it stated whether this applies to conditionals only or not (which helped me with the first two fallacies I mention). So are the two effectively the same and just context-dependent? Or is there another difference I've missed?