A method for decoding images of an image sequence comprising the following steps: storing a previously decoded image as a reference image; extracting motion vector information from input information to be decoded; and performing motion compensation using said motion vector information and said reference image for synthesising a prediction image, characterised by, when a currently decoded image is a P frame, extracting rounding method information consisting of one bit from a header section of the coded information of the currently decoded image, the rounding method information specifying either positive rounding or negative rounding; and performing pixel value interpolation for obtaining said prediction image by using a rounding method specified by the rounding method information; wherein the pixel value interpolation using said positive rounding is calculated according to the equations Ib = La + Lb + 1 / 2, Ic = La + Lc + 1 / 2, and Id = La + Lb + Lc + Ld + 2 / 4, and the pixel value interpolation using said negative rounding is calculated according to the equations Ib = La + Lb / 2, Ic = La + Lc / 2, and Id = La + Lb + Lc + Ld + 1 / 4, where La, Lb, Lc, and Ld are respectively the intensity values of a first pixel, a second pixel which is horizontally adjacent to said first pixel, a third pixel which is vertically adjacent to said first pixel, and a fourth pixel which is vertically adjacent to said second pixel and horizontally adjacent to said third pixel, and Ib, Ic and Id are respectively the interpolated intensity values of the middle point between said first and second pixel, the middle point between said first and third pixel, and the middle point between said first, second, third, and fourth pixel. storing a previously decoded image as a reference image; extracting motion vector information from input information to be decoded; and performing motion compensation using said motion vector information and said reference image for synthesising a prediction image, characterised by, when a currently decoded image is a P frame, extracting rounding method information consisting of one bit from a header section of the coded information of the currently decoded image, the rounding method information specifying either positive rounding or negative rounding; and performing pixel value interpolation for obtaining said prediction image by using a rounding method specified by the rounding method information; wherein the pixel value interpolation using said positive rounding is calculated according to the equations Ib = La + Lb + 1 / 2, Ic = La + Lc + 1 / 2, and Id = La + Lb + Lc + Ld + 2 / 4, and the pixel value interpolation using said negative rounding is calculated according to the equations Ib = La + Lb / 2, Ic = La + Lc / 2, and Id = La + Lb + Lc + Ld + 1 / 4, where La, Lb, Lc, and Ld are respectively the intensity values of a first pixel, a second pixel which is horizontally adjacent to said first pixel, a third pixel which is vertically adjacent to said first pixel, and a fourth pixel which is vertically adjacent to said second pixel and horizontally adjacent to said third pixel, and Ib, Ic and Id are respectively the interpolated intensity values of the middle point between said first and second pixel, the middle point between said first and third pixel, and the middle point between said first, second, third, and fourth pixel.