For an image portion to encode an initial set of motion information predictors is obtained (S502). It is tested (S512) whether the number (N) of motion information predictors in the initial set is lower than a target number (Nmax) and, if so, one or more motion information predictors are added (S516) to the initial set to generate a set of motion information predictors having controlled diversity. The motion information predictors of the initial set are actual motion information predictors, having motion vectors obtained from image portions of the image being encoded or of a reference image, and potential motion information predictors for addition include one or more further such actual motion information predictors and also include one or more virtual motion information predictors not having motion vectors obtained from image portions of said image being encoded or of a reference image. A motion information predictor for the image portion to encode is selected from the generated set of motion information predictors.