A method of using a computer processor for grouping prosthetic valve leaflets of an aggregate of prosthetic valve leaflets is provided. For each leaflet of the aggregate, in response to an image parameter of the leaflet, a leaflet-flexibility value is derived. At least some of the leaflets of the aggregate are designated into leaflet groups, based on similarity between the respective leaflet-flexibility value of each leaflet of the aggregate. For each of the designated leaflet groups, the flexibility value of each leaflet in the designated leaflet group is within the intra-group tolerance with respect to the leaflet-flexibility value of each other leaflet in the designated leaflet group. An indication of the designated leaflet groups is outputted. Other embodiments are also described.