An image decoding method includes decoding encoded image data to generate a decoded image signal including a luma signal and a chroma signal. The method further includes scaling, when a reference field is a bottom field while a current field is a top field for motion estimation and when the decoded image signal is in a format in which the number of chroma pixels is vertically different from the number of luma pixels, a chroma motion vector of the chroma signal by mv/2¼, where mv is a vertical component in a luma motion vector of the luma signal. The method also includes performing motion compensation of the decoded image signal using the scaled chroma motion vector.