A video coding or decoding method 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, comprises: storing one or more images preceding a current image; interpolating a higher resolution version of prediction units of the stored images so that the luminance component of an interpolated prediction unit has 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; detecting inter-image motion between a current image and the one or more interpolated 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; and generating a motion compensated prediction of the prediction unit of the current image with respect to an area of an interpolated stored image pointed to by a respective motion vector; in which the interpolating step comprises: applying a ?R horizontal and ?S vertical interpolation filter to the chrominance components of a stored image to generate an interpolated chrominance prediction unit, 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 subsampling the interpolated chrominance prediction unit, such that its horizontal resolution is divided by a factor of U and its vertical resolution is divided by a factor of V, thereby resulting in a block of MP?NQ samples.

A video coding or decoding method in which luminance and chrominance samples are predicted from other respective reference samples according to a prediction direction associated with a current sample to be predicted, the chrominance samples having a lower horizontal and/or vertical sampling rate than the luminance samples so that the ratio of luminance horizontal resolution to chrominance horizontal resolution is different than the ratio of luminance vertical resolution to chrominance vertical resolution, so that a block of luminance samples has a different aspect ratio to a corresponding block of chrominance samples, the method including: detecting a first prediction direction defined in relation to a first grid of a first aspect ratio in respect of a set of current samples to be predicted; and applying a direction mapping to the prediction direction to generate a second prediction direction defined in relation to a second grid of a different aspect ratio.

A video coding or decoding method operable to generate blocks of quantized spatial frequency data by quantizing the video data according to a selected quantization step size and a matrix of data modifying the quantization step size for use at different respective block positions within an ordered block of samples, the method being operable with respect to at least two different chrominance subsampling formats, and includes for at least one of the chrominance subsampling formats, defining one or more quantization matrices as one or more predetermined modifications with respect to one or more reference quantization matrices defined for a reference one of the chrominance subsampling formats.

Decoding corresponding to a first array of quantized coefficients including an NM array corresponding to a first block and data corresponding to a second array including an NM array corresponding to a second block. Deriving a first array of orthogonal transform coefficients from the first array of quantized coefficients by using at least a first quantization matrix of an NM array of elements, and derives a second array of orthogonal transform coefficients from the second array of by using at least a second quantization matrix of an NM array of elements. Performing inverse orthogonal transform on the first array of orthogonal transform coefficients to generate a PQ array of pixels of first prediction residuals, and performs inverse orthogonal transform on the second array of orthogonal transform coefficients to generate an NM array of pixels of second prediction residuals.

Decoding corresponding to a first array of quantized coefficients including an NM array corresponding to a first block and data corresponding to a second array including an NM array corresponding to a second block. Deriving a first array of orthogonal transform coefficients from the first array of quantized coefficients by using at least a first quantization matrix of an NM array of elements, and derives a second array of orthogonal transform coefficients from the second array of by using at least a second quantization matrix of an NM array of elements. Performing inverse orthogonal transform on the first array of orthogonal transform coefficients to generate a PQ array of pixels of first prediction residuals, and performs inverse orthogonal transform on the second array of orthogonal transform coefficients to generate an NM array of pixels of second prediction residuals.

Decoding corresponding to a first array of quantized coefficients including an NM array corresponding to a first block and data corresponding to a second array including an NM array corresponding to a second block. Deriving a first array of orthogonal transform coefficients from the first array of quantized coefficients by using at least a first quantization matrix of an NM array of elements, and derives a second array of orthogonal transform coefficients from the second array of by using at least a second quantization matrix of an NM array of elements. Performing inverse orthogonal transform on the first array of orthogonal transform coefficients to generate a PQ array of pixels of first prediction residuals, and performs inverse orthogonal transform on the second array of orthogonal transform coefficients to generate an NM array of pixels of second prediction residuals.

Decoding corresponding to a first array of quantized coefficients including an NM array corresponding to a first block and data corresponding to a second array including an NM array corresponding to a second block. Deriving a first array of orthogonal transform coefficients from the first array of quantized coefficients by using at least a first quantization matrix of an NM array of elements, and derives a second array of orthogonal transform coefficients from the second array of by using at least a second quantization matrix of an NM array of elements. Performing inverse orthogonal transform on the first array of orthogonal transform coefficients to generate a PQ array of pixels of first prediction residuals, and performs inverse orthogonal transform on the second array of orthogonal transform coefficients to generate an NM array of pixels of second prediction residuals.

Decoding corresponding to a first array of quantized coefficients including an NM array corresponding to a first block and data corresponding to a second array including an NM array corresponding to a second block. Deriving a first array of orthogonal transform coefficients from the first array of quantized coefficients by using at least a first quantization matrix of an NM array of elements, and derives a second array of orthogonal transform coefficients from the second array of by using at least a second quantization matrix of an NM array of elements. Performing inverse orthogonal transform on the first array of orthogonal transform coefficients to generate a PQ array of pixels of first prediction residuals, and performs inverse orthogonal transform on the second array of orthogonal transform coefficients to generate an NM array of pixels of second prediction residuals.

A video coding or decoding method in which luminance and chrominance samples in a 4:4:4 format or a 4:2:2 format are predicted from other respective samples according to a prediction direction associated with blocks of samples to be predicted; comprises detecting a prediction direction in respect of a current block to be predicted; generating a predicted block of chrominance samples according to other chrominance samples defined by the prediction direction; if the detected prediction direction is substantially vertical, filtering the left column of samples in the predicted block of chrominance samples, or if the detected prediction direction is substantially horizontal, filtering the top row of samples in the predicted block of chrominance samples; and encoding a difference between the filtered predicted chrominance block and the actual chrominance block or applying a decoded difference to the filtered predicted chrominance block so as to encode or decode the block respectively.

A method of coding 4:2:2 or 4:4:4 video data comprises predicting luminance and/or chrominance samples of an image from other respective reference samples derived from the same image according to a prediction mode associated with a sample to be predicted, the prediction mode being selected for each of a plurality of blocks of samples, from a set of two or more candidate prediction modes; detecting differences between the samples and the respective predicted samples; selecting a frequency-separation transform from two or more candidate frequency separation transforms according to the prediction mode associated with a current block of samples using a mapping between transform and prediction mode, the mapping between different, as between chrominance and luminance samples, for at least the 4:4:4: format; and encoding the detected differences by frequency-separating the differences, using the selected frequency-separation transform.