AN ENCODER, A DECODER AND CORRESPONDING METHODS FOR INTER PREDICTION

A bidirectional optical flowing prediction method, comprising: obtaining an initial motion vector pair for a current block; obtaining a forward and a backward prediction block according to the forward motion vector and a backward prediction block according to the initial motion vector pair; calculating gradient parameters for a current sample in the current block; obtaining at least two sample optical flow parameters, comprising a first parameter and a second parameter, for the current sample based on the gradient parameters; obtain block optical flow parameters based on sample optical flow parameters of samples in the current block, one of the block optical flow parameters is obtained by an operation including multiplying a value of the first parameter and a value of a sign function of the second parameter, and the sign function is a piecewise function with at least three subintervals; and obtaining a prediction value of the current block.