The potato-peeling problem (also known as convex skull) is a fundamental computational geometry problem that consist in finding the largest convex shape inside a given polygon. The fastest algorithm to date runs in O(n 8 ) time for a polygon with n vertices that may have holes. In this paper, we consider a digital version of the problem.where conv(K) denotes the convex hull of K. Given a set S of n lattice points, we present polynomial time algorithms for the problems of finding the largest digital convex subset K of S (digital potato-peeling problem) and the largest union of two digital convex subsets of S. The two algorithms take roughly O(n 3 ) and O(n 9 ) time, respectively. We also show that those algorithms provide an approximation to the continuous versions.