Abstract: A method of encoding image data, including: frequency-transforming input image data to generate an array of frequency-transformed input image coefficients by a matrix-multiplication process, according to a maximum dynamic range of the transformed data and using transform matrices having a data precision; and selecting the maximum dynamic range and/or the data precision of the transform matrices according to the bit depth of the input image data.

Abstract: An image encoding apparatus comprises a selector configured to select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples; and an intra-image predictor configured to interpolate predicted samples of the current region with respect to one or more of a group of reference samples being samples decoded from previously encoded samples of the current image, the group of reference samples being selected in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples, in which the intra-image predictor is configured to apply an interpolation process to the group of reference samples in order to generate each predicted sample; in which the intra-image predictor is configured to

Abstract: A video data encoding method for encoding an array of video data values includes frequency-transforming the video data values according to a frequency transform, to generate an array of frequency-transformed values by a matrix-multiplication process using a transform matrix having a data precision greater than six bits.

Abstract: An image data encoding apparatus includes an entropy encoder configured to selectively encode data items representing image data by an encoding system selected from a context adaptive binary arithmetic coding (CABAC) encoding system and a bypass encoding system. The data items include (i) a first data item indicating whether a multi-direction linear model (MDLM) chroma mode applies to a current image region; and (ii) a second data item indicating a processing direction for operation of the MDLM chroma mode. The entropy encoder encodes instances of the first data item and instances of the second data item independently of the encoding of instances of the first data item.

Abstract: A method of data encoding input data values of a data set for encoding includes selecting one of a plurality of complementary sub-ranges of a set of code values according to the value of a current input data value, the set of code values being defined by a range variable, assigning the current input data value to a code value within the selected sub-range, modifying the set of code values in dependence upon the assigned code value and the size of the selected sub-range, detecting whether the range variable defining the set of code values is less than a predetermined minimum size and if so, successively increasing the range variable so as to increase the size of the set of code values until it has at least the predetermined minimum size and outputting an encoded data bit in response to each such size-increasing operation, and after encoding a group of input data values, setting the range variable to a value selected from a predetermined subset of available range variable values, each value in the subset having

Abstract: Apparatus comprises a data encoder configured to derive, from an array of sample values, sample range flags each indicative of whether one or more sample values of the array of sample values lie in a predetermined range of sample values, the data encoder being configured in a first encoding mode to encode the array of sample values, at least in part, by encoding the sample range flags to an output data stream; a predictor configured to predict the state of a group of the sample range flags for a given array of sample values, the group being at least a subset of the sample range flags; and a comparator configured to compare the predicted state of the group of sample range flags with the actual state of the respective sample range flags for the given array of sample values; the data encoder being configured, in response to the comparator, to encode the given array of samples values in a second encoding mode in which the encoder is configured to encode to the output data stream a predetermined number of indicato

Abstract: 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.

Abstract: An image decoding apparatus comprises a selector configured to select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples; and an intra-image predictor configured to derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples; in which, for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region.

Abstract: A video data encoding method for encoding an array of video data values includes frequency-transforming the video data values according to a frequency transform, to generate an array of frequency-transformed values by a matrix-multiplication process using a transform matrix having a data precision greater than six bits.

Abstract: A data encoding method comprises generating an ordered array of data values representing an image region and having an array order; deriving a quantization parameter indicating a quantization degree so that the ordered array of data values, when encoded using that quantization degree, meets one or more predetermined criteria; quantizing the data values using the derived quantization parameter to generate respective quantized values; detecting a number of non-zero quantized values; if no more than a threshold number of first values in the array order are non-zero, selecting a different quantization parameter and quantizing the data values using a quantization degree indicated by the selected different quantization parameter; and entropy encoding at least the non-zero quantized values.

Abstract: A method encoding data values of a data set, including: selecting one of plural complementary sub-ranges of a code values set according to a current input data value, the code values set defined by a range variable; assigning the current input data value to a code value within the selected sub-range; modifying the code values set depending on the assigned code value and size of the selected sub-range; detecting whether the range variable is less than a predetermined minimum size and if so, successively increasing the range variable to increase the code values set size to at least the predetermined minimum size; outputting an encoded data bit in response to each size-increasing operation; after encoding a group of input data values, setting the range variable to a value selected from a predetermined subset of available range variable values, each subset value having at least one least significant bit of zero.

Abstract: A method decoding a data values set includes: decoding a first portion of each data value from one or more data sets; decoding a second portion depending on integer bits of data values not fully encoded by the data sets, and, if a data value has not been fully decoded by first and second portions, decoding a remaining third portion of the data value; detecting, for a subset of the data values, (i) instances of data values for which a third portion has been encoded and would still have been required had a higher value of n been used, and (ii) instances of data values for which a second portion has been encoded but the value of n was such that the data value could have been fully encoded by first and second portions using a lower value of n; and varying n for use in subsequent data values.

Abstract: Apparatus comprises an image data encoder to encode a current image region of an image, the image data encoder being operable in at least two modes of operation; a controller to control a mode of operation of the image data encoder in dependence upon the encoded data for the current image region meeting a predetermined criterion; and prediction circuitry configured to predict, from one or more properties of one or more image regions other than the current image region, whether the encoded data for the current image region will meet the predetermined criterion.

Abstract: A method encoding image data including: encoding the image data by an inter-image predictor in which a block of one or more samples of a current image is predicted from a reference block of samples located at one of a number of candidate block positions in a reference image; and selectively applying a constrained inter-image prediction mode in which, in comparison to an inter-image prediction mode for the encoding, one or both of the number of candidate block positions and the number of candidate reference images is reduced.

Abstract: Image data encoding and/or decoding apparatus comprises an inter-image predictor configured to predict samples of a current image region, of a plurality of regions of an image in a sequence of images, with respect to a reference image region of another, reference, image of the sequence of images, according to a direction vector indicating a spatial displacement of the reference image region from the current image region;an interpolation filter configured to generate the predicted samples of the current image region by spatial interpolation of samples of the reference image region, at least in instances where the direction vector indicates a spatial displacement of a non-integer number of samples, in which the interpolation filter is configured to operate according to a set of filter parameters each defining the spatial frequency response of a set of filters providing interpolation at a spatial displacement resolution of 1/m sample, where m is an integer greater than one; and a filter response selector configu

Abstract: A data encoding method comprises generating an ordered array of data values representing an image region and having an array order; deriving a quantization parameter indicating a quantization degree so that the ordered array of data values, when encoded using that quantization degree, meets one or more predetermined criteria; quantizing the data values using the derived quantization parameter to generate respective quantized values; detecting a number of non-zero quantized values; if no more than a threshold number of first values in the array order are non-zero, selecting a different quantization parameter and quantizing the data values using a quantization degree indicated by the selected different quantization parameter; and entropy encoding at least the non-zero quantized values.

Abstract: 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.

Abstract: An image encoding apparatus comprises a selector configured to select a prediction operation, for prediction of samples of a current region of a current image with respect to one or more of a group of reference samples, from a set of candidate prediction operations, at least some of which define, as an intra-image prediction operation, a prediction direction between a current sample to be predicted and a group of reference samples in the same image; and an intra-image predictor configured to derive predicted samples of a current image region from reference samples of the same image in response to selection, by the selector, of an intra-image prediction operation for the current image region; in which: the current region comprises at least a subset of a current coding tree unit (CTU) in an array of CTUs; the group of references samples is disposed, with respect to the current image region at one or more predetermined sides of the current image region; and the selector is configured to inhibit the selection of

Abstract: Apparatus comprises video data decoder circuitry configured to decode an input video data stream, the video data decoder being responsive to parameter data associated with the input video data stream, the parameter data indicating a profile selected from a plurality of profiles, each profile defining a decoding attribute comprising one or more of a bit depth and a chrominance subsampling format; detector circuitry configured to detect constraint data associated with the input video data stream, the constraint data defining a difference between a decoding attribute applicable to the input video data stream and the decoding attribute defined by the profile indicated by the parameter data, in which the constraint data is configured to indicate a zero difference of the decoding attribute by a zero value of the constraint data; and control circuitry configured to control the video data decoder to decode the input video data stream to generate a decoded video data stream having a decoding attribute defined by the e

Abstract: An image encoding apparatus comprises a selector configured to select, from a set of candidate prediction operations each defining at least a prediction direction, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples; an intra-image predictor configured to derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and a reference position amongst the reference samples; in which, for at least some of the candidate prediction operations, the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region; a detector configured to detect whether samples corresponding to any of the two or more par