1. A method of encoding a sequence of digital images into a bitstream, at least one portion of an image being encoded by motion compensation with respect to a reference image portion, the method comprising: obtaining for an image portion to encode an initial set of motion information predictors; testing whether the number of motion information predictors in said initial set is lower than a target number and, if so, adding one or more motion information predictors to said initial set to generate a set of motion information predictors; and selecting a motion information predictor for said image portion to encode from the generated set of motion information predictors, wherein the motion information predictors of said initial set are actual motion information predictors, having motion vectors obtained from image portions of said 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.