A method of determining encoding parameters for encoding, into a bitstream, a portion of an image of a video sequence, the image portion being encoded by motion compensation with respect to at least one reference image portion, the encoding parameters for encoding the image portion including a coding mode and a motion information predictor for predicting a motion vector of the image portion being encoded, the coding mode is selected from among at least a first coding mode in which a texture residual is not encoded and motion information is encoded using a set of motion information predictors and a second coding mode in which a texture residual may be encoded and motion information is encoded using a set of motion information predictors, the set of motion information predictors being the same for the first and the second coding modes, selection of the coding mode and the motion information predictor involving computing costs (607, 611, 706, 710, 806, 810, 906, 910) of encoding the image portion using motion information predictors of the set in the first and second coding modes and comparing computed costs (610, 613, 707, 713, 807, 813, 907, 912), the method comprising steps of: for each motion information predictor in the set of motion information predictors: computing the first-coding-mode cost and including the first-coding-mode cost in the comparison of costs; detecting when at least one condition (603, 609, 708, 803, 808, 908) relating to one or more motion information predictors of the set, or relating to one or more first-coding-mode and second-coding-mode costs (711, 811, 912) already computed, is met; and if it is detected that the condition is met, omitting the computing of the second-coding-mode cost, and otherwise carrying out the computing of the second-coding-mode cost and including the second-coding-mode cost in the comparing of costs; and wherein the at least one condition results in the computing of the second-coding-mode cost for at least one motion information predictor. for each motion information predictor in the set of motion information predictors: computing the first-coding-mode cost and including the first-coding-mode cost in the comparison of costs; detecting when at least one condition (603, 609, 708, 803, 808, 908) relating to one or more motion information predictors of the set, or relating to one or more first-coding-mode and second-coding-mode costs (711, 811, 912) already computed, is met; and if it is detected that the condition is met, computing the first-coding-mode cost and including the first-coding-mode cost in the comparison of costs; detecting when at least one condition (603, 609, 708, 803, 808, 908) relating to one or more motion information predictors of the set, or relating to one or more first-coding-mode and second-coding-mode costs (711, 811, 912) already computed, is met; and if it is detected that the condition is met, omitting the computing of the second-coding-mode cost, and otherwise carrying out the computing of the second-coding-mode cost and including the second-coding-mode cost in the comparing of costs; and wherein the at least one condition results in the computing of the second-coding-mode cost for at least one motion information predictor.