In this paper we present a simple algorithm for computing the degree of convexity of a convex polyomino, defined as the smallest integer k such that any two cells of P can be joined by a monotone path inside P with at most k changes of direction. We show how it can be used to obtain an efficient algorithm for computing all k-convex polyominoes of size n. More precisely, such an algorithm uses space O(n) and runs in constant amortized time