1. A video decoding method operable in respect of 4:2:0 and 4:2:2 video data using inter-image prediction to decode input video data in which each chrominance component has 1/Mth of the horizontal resolution of the luminance component and 1/Nth of the vertical resolution of the luminance component, where M and N are integers equal to 1 or more which depend upon the subsampling format of the video data, the method comprising: storing one or more images preceding a current image; accessing interpolated samples of a higher resolution version of prediction units of the stored images so as to generate a motion compensated prediction of a prediction unit of the current image with respect to an area represented by the interpolated samples pointed to by a respective motion vector, the luminance component of the interpolated samples of a prediction unit having a horizontal resolution P times that of the corresponding portion of the stored image and a vertical resolution Q times that of the corresponding portion of the stored image, where P and Q are integers greater than 1 and are the same for operation of the method in respect of 4:2:0 and 4:2:2 video data; in which the step of accessing interpolated samples comprises: applying a ×R horizontal and ×S vertical interpolation filter to the chrominance components of a stored image, where R is equal to (U×M×P) and S is equal to (V×N×Q), U and V being integers equal to 1 or more; and using, as samples to be accessed, only every Uth sample horizontally and every Vth sample vertically, so that the interpolated chrominance samples have a resolution of MP×NQ.