1. A method implemented by a computing device, the method comprising: calculating, for candidate croppings of a scene, scores indicative of a boundary simplicity for each of the candidate croppings, including: ranking the candidate croppings according to values derived for the candidate croppings that indicate a complexity of the scene along a boundary of a candidate cropping, and calculating the scores indicative of the boundary simplicity as normalized scores for the candidate croppings based on the ranking; and choosing one or more croppings from the candidate croppings based, at least in part, on the scores calculated for the candidate croppings that are indicative of the boundary simplicity.