1. A method for encoding an image signal comprising motion information, the method comprising: selecting a motion vector from a set of at least three candidate vectors, for at least one current block of a current image to be encoded, wherein selecting comprises: a step of determining an optimal selection subset, containing a part of said candidate vectors, a step of selecting said motion vector from among the vectors of said optimal selection subset, and a step of inserting into said signal a piece of information on designation of the motion vector selected among the vectors of said optimal selection subset.