Data encoding and decoding

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;

deriving a luminance motion vector for a prediction unit; and

independently deriving one or more chrominance motion vectors for the derived prediction unit, wherein

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, and

the same ×R horizontal and ×S vertical interpolation filters are used in respect of 4:2:0 input video data and 4:2:2 input video data.

2. The method according to claim 1 , wherein, in respect of input video data in a 4:2:2 format, M=2 and N=1.

3. The method according to claim 2 , wherein, in respect of input video data in a 4:2:2 format, the interpolated chrominance prediction unit has a height in samples twice that of a 4:2:0 format prediction unit interpolated using the same ×R and ×S interpolation filters.

4. The method according to claim 1 , wherein P=4.

5. The method according to claim 1 , wherein Q=4.

6. The method according to claim 1 , wherein at least one of R and S is equal to 2 or more.

7. The method according to claim 1 , further comprising applying the ×R horizontal and ×S vertical interpolation filter to the luminance components of the stored image.

8. The method according to claim 1 , wherein the method being also is further operable in respect of 4:4:4 video data, P and Q being the same for operation of the method in respect of 4:2:0, 4:2:2 and 4:4:4 video data and the same ×R horizontal and ×S vertical interpolation filters being used in respect of 4:2:0, 4:2:2 and 4:4:4 video data.

9. A video coding method operable in respect of 4:2:0 and 4:2:2 video data using inter-image prediction to encode 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, 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;

detecting inter-image motion between a current image and the interpolated samples accessed in respect of one or more stored images so as to generate motion vectors between a prediction unit of the current image and areas of the one or more preceding images;

deriving a luminance motion vector for a prediction unit; and

independently deriving one or more chrominance motion vectors for the derived prediction unit, wherein

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, and

the same ×R horizontal and ×S vertical interpolation filters are used in respect of 4:2:0 input video data and 4:2:2 input video data.

10. A video decoding apparatus 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 apparatus comprising:

an image store configured to store one or more images preceding a current image; and

circuitry configured to

access 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 apparatus in respect of 4:2:0 and 4:2:2 video data;

derive a luminance motion vector for a prediction unit;

independently derive one or more chrominance motion vectors for the derived prediction unit; and

in which the circuitry is configured:

apply 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 to use, 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, wherein

the same ×R horizontal and ×S vertical interpolation filters are used in respect of 4:2:0 input video data and 4:2:2 input video data.

11. A video coding apparatus operable in respect of 4:2:0 and 4:2:2 video data using inter-image prediction to encode 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 apparatus comprising:

an image store configured to store one or more images preceding a current image;

circuitry configured to access interpolated samples of a higher resolution version of prediction units of the stored images, 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 apparatus in respect of 4:2:0 and 4:2:2 video data; and

a detector configured to detect inter-image motion between a current image and the interpolated samples accessed in respect of one or more stored images so as to generate motion vectors between a prediction unit of the current image and areas of the one or more preceding images, wherein

in which the circuitry is further configured to

derive a luminance motion vector for a prediction unit;

independently derive one or more chrominance motion vectors for the derived prediction unit; and

apply 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 to use, 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, and

the same ×R horizontal and ×S vertical interpolation filters are used in respect of 4:2:0 input video data and 4:2:2 input video data.

12. A video capture, display, transmission, reception and/or or storage apparatus comprising the video coding apparatus according to claim 11 .

13. A video capture, display, transmission, reception and/or or storage apparatus comprising the video decoding apparatus according to claim 10 .

14. A video reception apparatus comprising:

the video decoding apparatus according to claim 10 ; and

a display configured to output the decoded video data.

15. A video capture apparatus comprising:

the video coding apparatus according to claim 11 ; and

a memory that stores the input video data.