An image decoder, wherein the motion compensation is performed with half-pixel accuracy and uses bilinear interpolation to calculate intensity values of chrominance or luminance at points where no pixels actually exist in the reference image, the bilinear interpolation being performable using a positive rounding method and a negative rounding method; wherein the bilinear interpolation is performed using a rounding method specified by the rounding method information; wherein the rounding method information is included in coded information of the currently decoded image; and wherein the rounding method information is included in a header section of the coded information of the currently decoded image.