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; wherein said step of determining an optimal selection subset comprises the following sub-steps: comparing at least two first candidates vectors, delivering a piece of information on proximity between said first candidate vectors, capable of taking a first value indicating that said first candidate vectors are identical or proximate according to a predetermined criterion, and a second value indicating that said first candidate vectors are not identical or proximate according to said predetermined criterion; if said information on proximity takes said first value, building said optimal selection subset with one of said first candidate vectors and at least one second candidate vector, distinct from said first candidate vectors; and if said information on proximity takes said second value, building said optimal selection subset with said first candidate vectors.