GB2599433A

GB2599433A - Data encoding and decoding

Info

Publication number: GB2599433A
Application number: GB2015633.7A
Authority: GB
Inventors: Mark Keating Stephen; James Sharman Karl; Richard Browne Adrian
Original assignee: Sony Group Corp
Current assignee: Sony Group Corp
Priority date: 2020-10-02
Filing date: 2020-10-02
Publication date: 2022-04-06
Also published as: GB202015633D0

Abstract

A method for encoding data values of a 4:4:4 format video signal comprises selecting 1300 a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first data values representing a current block of a primary video component channel. A second spatial processing operation is selected 1310, from a second set of one or more candidate spatial processing operations in the first set including at least the selected first spatial processing operation, for spatially processing second data values representing the current block of video component channels other than the primary video component channel. The first and second video data values are processed according to the selected first and second spatial processing operations. The primary component may be a luminance component and the other components may be colour difference components or chrominance components. The spatial processing operations may be a transform or a transform skip. The second set may be the same as the first set, may contain the operation selected for the primary component as well as an additional predetermined operation, or may only contain the operation selected for the primary component. A corresponding decoding method and corresponding apparatuses are also claimed.

Description

DATA ENCODING AND DECODING

BACKGROUND Field

This disclosure relates to data encoding and decoding.

Description of Related Art

The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, is neither expressly or impliedly admitted as

prior art against the present disclosure.

There are several systems, such as video or image data encoding and decoding systems which involve transforming video data into a frequency domain representation, quantising the frequency domain coefficients and then applying some form of entropy encoding to the quantised coefficients. This can achieve compression of the video data. A corresponding decoding or decompression technique is applied to recover a reconstructed version of the original video data.

SUMMARY

The present disclosure addresses or mitigates problems arising from this processing. The present disclosure provides a video data encoding method for encoding video data values of a 4:4:4 format video signal, the method comprising: selecting a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.

The present disclosure also provides a video data decoding method for decoding video data values of a 4:4:4 format encoded input video signal, the method comprising: selecting a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.

The present disclosure also provides computer software which, when executed by a computer, causes the computer to perform such methods, a non-transitory machine-readable storage medium which stores such computer software.

The present disclosure also provides a video data encoding apparatus for encoding video data values of a 4:4:4 format video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.

The present disclosure also provides a video data decoding apparatus for decoding video data values of a 4:4:4 format encoded input video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.

The present disclosure also provides video data capture, transmission, display and/or storage apparatus comprising such apparatus.

Further respective aspects and features of the present disclosure are defined in the appended claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the present technology.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure 1 schematically illustrates an audio/video (AN) data transmission and reception system using video data compression and decompression; Figure 2 schematically illustrates a video display system using video data 15 decompression; Figure 3 schematically illustrates an audio/video storage system using video data compression and decompression; Figure 4 schematically illustrates a video camera using video data compression; Figures 5 and 6 schematically illustrate storage media; Figure 7 provides a schematic overview of a video data compression and decompression apparatus; Figure 8 schematically illustrates a predictor; Figures 9a and 9b schematically illustrates control of a frequency transformation / inverse transformation operation; Figure 10 schematically illustrates at least a part of control circuitry; and Figures 11 to 15 are schematic flowcharts representing respective methods.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, Figures 1-4 are provided to give schematic illustrations of apparatus or systems making use of the compression and/or decompression apparatus to be described below in connection with embodiments of the present technology.

All of the data compression and/or decompression apparatus to be described below may be implemented in hardware, in software running on a general-purpose data processing apparatus such as a general-purpose computer, as programmable hardware such as an application specific integrated circuit (ASIC) or field programmable gate array (FPGA) or as combinations of these. In cases where the embodiments are implemented by software and/or firmware, it will be appreciated that such software and/or firmware, and non-transitory data storage media by which such software and/or firmware are stored or otherwise provided, are considered as embodiments of the present technology.

Figure 1 schematically illustrates an audio/video data transmission and reception system using video data compression and decompression. In this example, the data values to be encoded or decoded represent image data.

An input audio/video signal 10 is supplied to a video data compression apparatus 20 which compresses at least the video component of the audio/video signal 10 for transmission along a transmission route 30 such as a cable, an optical fibre, a wireless link or the like. The compressed signal is processed by a decompression apparatus 40 to provide an output audio/video signal 50 For the return path, a compression apparatus 60 compresses an audio/video signal for transmission along the transmission route 30 to a decompression apparatus 70.

The compression apparatus 20 and decompression apparatus 70 can therefore form one node of a transmission link. The decompression apparatus 40 and decompression apparatus 60 can form another node of the transmission link. Of course, in instances where the transmission link is uni-directional, only one of the nodes would require a compression apparatus and the other node would only require a decompression apparatus.

Figure 2 schematically illustrates a video display system using video data decompression. In particular, a compressed audio/video signal 100 is processed by a decompression apparatus 110 to provide a decompressed signal which can be displayed on a display 120. The decompression apparatus 110 could be implemented as an integral part of the display 120, for example being provided within the same casing as the display device. Alternatively, the decompression apparatus 110 maybe provided as (for example) a so-called set top box (STB), noting that the expression "set-top" does not imply a requirement for the box to be sited in any particular orientation or position with respect to the display 120; it is simply a term used in the art to indicate a device which is connectable to a display as a peripheral device.

Figure 3 schematically illustrates an audio/video storage system using video data compression and decompression. An input audio/video signal 130 is supplied to a compression apparatus 140 which generates a compressed signal for storing by a store device 150 such as a magnetic disk device, an optical disk device, a magnetic tape device, a solid state storage device such as a semiconductor memory or other storage device. For replay, compressed data is read from the storage device 150 and passed to a decompression apparatus 160 for decompression to provide an output audio/video signal 170.

It will be appreciated that the compressed or encoded signal, and a storage medium such as a machine-readable non-transitory storage medium, storing that signal, are considered as embodiments of the present technology.

Figure 4 schematically illustrates a video camera using video data compression. In Figure 4, an image capture device 180, such as a charge coupled device (CCD) image sensor and associated control and read-out electronics, generates a video signal which is passed to a compression apparatus 190. A microphone (or plural microphones) 200 generates an audio signal to be passed to the compression apparatus 190. The compression apparatus 190 generates a compressed audio/video signal 210 to be stored and/or transmitted (shown generically as a schematic stage 220).

The techniques to be described below relate primarily to video data compression and decompression. It will be appreciated that many existing techniques may be used for audio data compression in conjunction with the video data compression techniques which will be described, to generate a compressed audio/video signal. Accordingly, a separate discussion of audio data compression will not be provided. It will also be appreciated that the data rate associated with video data, in particular broadcast quality video data, is generally very much higher than the data rate associated with audio data (whether compressed or uncompressed). It will therefore be appreciated that uncompressed audio data could accompany compressed video data to form a compressed audio/video signal. It will further be appreciated that although the present examples (shown in Figures 1-4) relate to audio/video data, the techniques to be described below can find use in a system which simply deals with (that is to say, compresses, decompresses, stores, displays and/or transmits) video data. That is to say, the embodiments can apply to video data compression without necessarily having any associated audio data handling at all.

Figure 4 therefore provides an example of a video capture apparatus comprising an image sensor and an encoding apparatus of the type to be discussed below. Figure 2 therefore provides an example of a decoding apparatus of the type to be discussed below and a display to which the decoded images are output.

A combination of Figure 2 and 4 may provide a video capture apparatus comprising an image sensor 180 and encoding apparatus 190, decoding apparatus 110 and a display 120 to which the decoded images are output.

Figures 5 and 6 schematically illustrate storage media, which store (for example) the compressed data generated by the apparatus 20, 60, the compressed data input to the apparatus 110 or the storage media or stages 150, 220. Figure 5 schematically illustrates a disc storage medium such as a magnetic or optical disc, and Figure 6 schematically illustrates a solid state storage medium such as a flash memory. Note that Figures 5 and 6 can also provide examples of non-transitory machine-readable storage media which store computer software which, when executed by a computer, causes the computer to carry out one or more of the methods to be discussed below.

Therefore, the above arrangements provide examples of video storage, capture, transmission or reception apparatuses embodying any of the present techniques.

Figure 7 provides a schematic overview of a video or image data compression and decompression apparatus, for encoding and/or decoding image data representing one or more images.

A controller 343 controls the overall operation of the apparatus and, in particular when referring to a compression mode, controls a trial encoding processes by acting as a selector to select various modes of operation such as block sizes and shapes, and whether the video data is to be encoded losslessly or otherwise. The controller is considered to form part of the image encoder or image decoder (as the case may be). Successive images of an input video signal 300 are supplied to an adder 310 and to an image predictor 320. The image predictor 320 will be described below in more detail with reference to Figure 8. The image encoder or decoder (as the case may be) plus the intra-image predictor of Figure 8 may use features from the apparatus of Figure 7. This does not mean that the image encoder or decoder necessarily requires every feature of Figure 7 however.

The adder 310 in fact performs a subtraction (negative addition) operation, in that it receives the input video signal 300 on a "+" input and the output of the image predictor 320 on a "-" input, so that the predicted image is subtracted from the input image. The result is to generate a so-called residual image signal 330 representing the difference between the actual and predicted images.

One reason why a residual image signal is generated is as follows. The data coding techniques to be described, that is to say the techniques which will be applied to the residual image signal, tend to work more efficiently when there is less "energy" in the image to be encoded. Here, the term "efficiently" refers to the generation of a small amount of encoded data; for a particular image quality level, it is desirable (and considered "efficient") to generate as little data as is practicably possible. The reference to "energy" in the residual image relates to the amount of information contained in the residual image. If the predicted image were to be identical to the real image, the difference between the two (that is to say, the residual image) would contain zero information (zero energy) and would be very easy to encode into a small amount of encoded data. In general, if the prediction process can be made to work reasonably well such that the predicted image content is similar to the image content to be encoded, the expectation is that the residual image data will contain less information (less energy) than the input image and so will be easier to encode into a small amount of encoded data.

Therefore, encoding (using the adder 310) involves predicting an image region for an image to be encoded; and generating a residual image region dependent upon the difference between the predicted image region and a corresponding region of the image to be encoded. In connection with the techniques to be discussed below, the ordered array of data values comprises data values of a representation of the residual image region. Decoding involves predicting an image region for an image to be decoded; generating a residual image region indicative of differences between the predicted image region and a corresponding region of the image to be decoded; in which the ordered array of data values comprises data values of a representation of the residual image region; and combining the predicted image region and the residual image region.

The remainder of the apparatus acting as an encoder (to encode the residual or difference image) will now be described.

The residual image data 330 is supplied to a transform unit or circuitry 340 which generates a discrete cosine transform (DOT) representation of blocks or regions of the residual image data. The DOT technique itself is well known and will not be described in detail here. Note also that the use of DCT is only illustrative of one example arrangement. Other transforms which might be used include, for example, the discrete sine transform (DST). A transform could also comprise a sequence or cascade of individual transforms, such as an arrangement in which one transform is followed (whether directly or not) by another transform. The choice of transform may be determined explicitly and/or be dependent upon side information used to configure the encoder and decoder. In other examples a so-called "transform-skip" mode can selectively be used in which no transform is applied.

Therefore, in examples, an encoding and/or decoding method comprises predicting an image region for an image to be encoded; and generating a residual image region dependent upon the difference between the predicted image region and a corresponding region of the image to be encoded; in which the ordered array of data values (to be discussed below) comprises data values of a representation of the residual image region.

The output of the transform unit 340, which is to say On an example), a set of DOT coefficients for each transformed block of image data, is supplied to a quantiser 350. Various quantisation techniques are known in the field of video data compression, ranging from a simple multiplication by a quantisation scaling factor through to the application of complicated lookup tables under the control of a quantisation parameter. The general aim is twofold. Firstly, the quantisation process reduces the number of possible values of the transformed data. Secondly, the quantisation process can increase the likelihood that values of the transformed data are zero. Both of these can make the entropy encoding process, to be described below, work more efficiently in generating small amounts of compressed video data.

A data scanning process is applied by a scan unit 360. The purpose of the scanning process is to reorder the quantised transformed data so as to gather as many as possible of the non-zero quantised transformed coefficients together, and of course therefore to gather as many as possible of the zero-valued coefficients together. These features can allow so-called run-length coding or similar techniques to be applied efficiently. So, the scanning process involves selecting coefficients from the quantised transformed data, and in particular from a block of coefficients corresponding to a block of image data which has been transformed and quantised, according to a "scanning order" so that (a) all of the coefficients are selected once as part of the scan, and (b) the scan tends to provide the desired reordering. One example scanning order which can tend to give useful results is a diagonal order such as a so-called up-right diagonal scanning order.

The scanning order can be different, as between transform-skip blocks and transform blocks (blocks which have undergone at least one spatial frequency transformation).

The scanned coefficients are then passed to an entropy encoder (EE) 370. Again, various types of entropy encoding may be used. Two examples are variants of the so-called CABAC (Context Adaptive Binary Arithmetic Coding) system and variants of the so-called CAVLC (Context Adaptive Variable-Length Coding) system. In general terms, CABAC is considered to provide a better efficiency, and in some studies has been shown to provide a 1020% reduction in the quantity of encoded output data for a comparable image quality compared to CAVLC. However, CAVLC is considered to represent a much lower level of complexity (in terms of its implementation) than CABAC. Note that the scanning process and the entropy encoding process are shown as separate processes, but in fact can be combined or treated together. That is to say, the reading of data into the entropy encoder can take place in the scan order. Corresponding considerations apply to the respective inverse processes to be described below.

The output of the entropy encoder 370, along with additional data (mentioned above and/or discussed below), for example defining the manner in which the predictor 320 generated the predicted image, whether the compressed data was transformed or transform-skipped or the like, provides a compressed output video signal 380.

However, a return path 390 is also provided because the operation of the predictor 320 itself depends upon a decompressed version of the compressed output data.

The reason for this feature is as follows. At the appropriate stage in the decompression process (to be described below) a decompressed version of the residual data is generated. This decompressed residual data has to be added to a predicted image to generate an output image (because the original residual data was the difference between the input image and a predicted image). In order that this process is comparable, as between the compression side and the decompression side, the predicted images generated by the predictor 320 should be the same during the compression process and during the decompression process. Of course, at decompression, the apparatus does not have access to the original input images, but only to the decompressed images. Therefore, at compression, the predictor 320 bases its prediction (at least, for inter-image encoding) on decompressed versions of the compressed images.

The entropy encoding process carried out by the entropy encoder 370 is considered (in at least some examples) to be "lossless", which is to say that it can be reversed to arrive at exactly the same data which was first supplied to the entropy encoder 370. So, in such examples the return path can be implemented before the entropy encoding stage. Indeed, the scanning process carried out by the scan unit 360 is also considered lossless, so in the present embodiment the return path 390 is from the output of the quantiser 350 to the input of a complimentary inverse quantiser 420. In instances where loss or potential loss is introduced by a stage, that stage (and its inverse) may be included in the feedback loop formed by the return path. For example, the entropy encoding stage can at least in principle be made lossy, for example by techniques in which bits are encoded within parity information. In such an instance, the entropy encoding and decoding should form part of the feedback loop.

In general terms, an entropy decoder 410, the reverse scan unit 400, an inverse quantiser 420 and an inverse transform unit or circuitry 430 provide the respective inverse functions of the entropy encoder 370, the scan unit 360, the quantiser 350 and the transform unit 340. For now, the discussion will continue through the compression process; the process to decompress an input compressed video signal will be discussed separately below.

In the compression process, the scanned coefficients are passed by the return path 390 from the quantiser 350 to the inverse quantiser 420 which carries out the inverse operation of the scan unit 360. An inverse quantisation and inverse transformation process are carried out by the units 420, 430 to generate a compressed-decompressed residual image signal 440.

The image signal 440 is added, at an adder 450, to the output of the predictor 320 to generate a reconstructed output image 460 (although this may be subject to so-called loop filtering and/or other filtering before being output -see below). This forms one input to the image predictor 320, as will be described below.

Turning now to the decoding process applied to decompress a received compressed video signal 470, the signal is supplied to the entropy decoder 410 and from there to the chain of the reverse scan unit 400, the inverse quantiser 420 and the inverse transform unit 430 before being added to the output of the image predictor 320 by the adder 450. So, at the decoder side, the decoder reconstructs a version of the residual image and then applies this (by the adder 450) to the predicted version of the image (on a block by block basis) so as to decode each block. In straightforward terms, the output 460 of the adder 450 forms the output decompressed video signal 480 (subject to the filtering processes discussed below). In practice, further filtering may optionally be applied (for example, by a loop filter 565 shown in Figure 8 but omitted from Figure 7 for clarity of the higher level diagram of Figure 7) before the signal is output.

The apparatus of Figures 7 and 8 can act as a compression (encoding) apparatus or a decompression (decoding) apparatus. The functions of the two types of apparatus substantially overlap. The scan unit 360 and entropy encoder 370 are not used in a decompression mode, and the operation of the predictor 320 (which will be described in detail below) and other units follow mode and parameter information contained in the received compressed bit-stream rather than generating such information themselves.

Figure 8 schematically illustrates the generation of predicted images, and in particular the operation of the image predictor 320.

There are two basic modes of prediction carried out by the image predictor 320: so-called intra-image prediction and so-called inter-image, or motion-compensated (MC), prediction. At the encoder side, each involves detecting a prediction direction in respect of a current block to be predicted, and generating a predicted block of samples according to other samples (in the same (intra) or another (inter) image). By virtue of the units 310 or 450, the difference between the predicted block and the actual block is encoded or applied so as to encode or decode the block respectively.

(At the decoder, or at the reverse decoding side of the encoder, the detection of a prediction direction may be in response to data associated with the encoded data by the encoder, indicating which direction was used at the encoder. Or the detection may be in response to the same factors as those on which the decision was made at the encoder). Intra-image prediction bases a prediction of the content of a block or region of the image on data from within the same image. This corresponds to so-called I-frame encoding in other video compression techniques. In contrast to I-frame encoding, however, which involves encoding the whole image by intra-encoding, in the present embodiments the choice between intra-and inter-encoding can be made on a block-by-block basis, though in other embodiments the choice is still made on an image-by-image basis.

Motion-compensated prediction is an example of inter-image prediction and makes use of motion information which attempts to define the source, in another adjacent or nearby image, of image detail to be encoded in the current image. Accordingly, in an ideal example, the contents of a block of image data in the predicted image can be encoded very simply as a reference (a motion vector) pointing to a corresponding block at the same or a slightly different position in an adjacent image.

A technique known as "block copy" prediction is in some respects a hybrid of the two, as it uses a vector to indicate a block of samples at a position displaced from the currently predicted block within the same image, which should be copied to form the currently predicted block.

Returning to Figure 8, two image prediction arrangements (corresponding to intra-and inter-image prediction) are shown, the results of which are selected by a multiplexer 500 under the control of a mode signal 510 (for example, from the controller 343) so as to provide blocks of the predicted image for supply to the adders 310 and 450. The choice is made in dependence upon which selection gives the lowest "energy" (which, as discussed above, may be considered as information content requiring encoding), and the choice is signalled to the decoder within the encoded output data-stream. Image energy, in this context, can be detected, for example, by carrying out a trial subtraction of an area of the two versions of the predicted image from the input image, squaring each pixel value of the difference image, summing the squared values, and identifying which of the two versions gives rise to the lower mean squared value of the difference image relating to that image area. In other examples, a trial encoding can be carried out for each selection or potential selection, with a choice then being made according to the cost of each potential selection in terms of one or both of the number of bits required for encoding and distortion to the picture.

The actual prediction, in the intra-encoding system, is made on the basis of image blocks received as part of the signal 460 (as filtered by loop filtering; see below), which is to say, the prediction is based upon encoded-decoded image blocks in order that exactly the same prediction can be made at a decompression apparatus. However, data can be derived from the input video signal 300 by an intra-mode selector 520 to control the operation of the intra-image predictor 530.

For inter-image prediction, a motion compensated (MC) predictor 540 uses motion information such as motion vectors derived by a motion estimator 550 from the input video signal 300. Those motion vectors are applied to a processed version of the reconstructed image 460 by the motion compensated predictor 540 to generate blocks of the inter-image prediction.

Accordingly, the units 530 and 540 (operating with the estimator 550) each act as detectors to detect a prediction direction in respect of a current block to be predicted, and as a generator to generate a predicted block of samples (forming part of the prediction passed to the units 310 and 450) according to other samples defined by the prediction direction.

The processing applied to the signal 460 will now be described.

Firstly, the signal may be filtered by a so-called loop filter 565. Various types of loop filters may be used. One technique involves applying a "deblocking" filter to remove or at least tend to reduce the effects of the block-based processing carried out by the transform unit 340 and subsequent operations. A further technique involving applying a so-called sample adaptive offset (SAO) filter may also be used. In general terms, in a sample adaptive offset filter, filter parameter data (derived at the encoder and communicated to the decoder) defines one or more offset amounts to be selectively combined with a given intermediate video sample (a sample of the signal 460) by the sample adaptive offset filter in dependence upon a value of:(i) the given intermediate video sample; or 00 one or more intermediate video samples having a predetermined spatial relationship to the given intermediate video sample.

Also, an adaptive loop filter is optionally applied using coefficients derived by processing the reconstructed signal 460 and the input video signal 300. The adaptive loop filter is a type of filter which, using known techniques, applies adaptive filter coefficients to the data to be filtered. That is to say, the filter coefficients can vary in dependence upon various factors. Data defining which filter coefficients to use is included as part of the encoded output data-stream.

The filtered output from the loop filter unit 565 in fact forms the output video signal 480 when the apparatus is operating as a decompression apparatus. It is also buffered in one or more image or frame stores 570; the storage of successive images is a requirement of motion compensated prediction processing, and in particular the generation of motion vectors. To save on storage requirements, the stored images in the image stores 570 may be held in a compressed form and then decompressed for use in generating motion vectors. For this particular purpose, any known compression / decompression system may be used. The stored images may be passed to an interpolation filter 580 which generates a higher resolution version of the stored images; in this example, intermediate samples (sub-samples) are generated such that the resolution of the interpolated image is output by the interpolation filter 580 is 4 times (in each dimension) that of the images stored in the image stores 570 for the luminance channel of 4:2:0 and 8 times (in each dimension) that of the images stored in the image stores 570 for the chrominance channels of 4:2:0. The interpolated images are passed as an input to the motion estimator 550 and also to the motion compensated predictor 540.

The way in which an image is partitioned for compression processing will now be described. At a basic level, an image to be compressed is considered as an array of blocks or regions of samples. The splitting of an image into such blocks or regions can be carried out by a decision tree, such as that described in SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS Infrastructure of audio-visual services -Coding of moving video High efficiency video coding Recommendation ITU-T H.265 12/2016. Also: High Efficiency Video Coding (HEVC) algorithms and Architectures, Editors: Madhukar Budagavi, Gary J. Sullivan, Vivienne Sze; chapter 3; ISBN 978-3-319-06894-7; 2014 which are incorporated herein in their respective entireties by reference.

In some examples, the resulting blocks or regions have sizes and, in some cases, shapes which, by virtue of the decision tree, can generally follow the disposition of image features within the image. This in itself can allow for an improved encoding efficiency because samples representing or following similar image features would tend to be grouped together by such an arrangement. In some examples, square blocks or regions of different sizes (such as 4x4 samples up to, say, 64x64 or larger blocks) are available for selection. In other example arrangements, blocks or regions of different shapes such as rectangular blocks or arrays (for example, vertically or horizontally oriented) can be used. Other non-square and non-rectangular blocks are envisaged. The result of the division of the image into such blocks or regions is On at least the present examples) that each sample of an image is allocated to one, and only one, such block or region.

Transform Process and Transform Skip Figure 9a schematically illustrates control of a spatial processing operation performed at the encoder side.

In particular, Figure 9a schematically illustrates a so-called transform-skip mode. In this mode, blocks of samples, for example rectangular encoding blocks or arrays of samples such as so-called transform units (TUs) are assigned a transform-skip' mode indicator, for example by a part of the functionality of the controller 343. When the transform-skip indicator is set, as shown by schematic selection of a schematic bypass path 900 in Figure 9, the transform unit 340 On the encoding path) and the inverse transform unit 430 (in the decoding path of the encoding side; see Figure 9b) is bypassed so that no spatial frequency transform is applied to the samples in that particular block.

The transform-skip mode is selectable by the controller 343, alongside a possible selection of DOT, DST or another transform mode, in dependence upon properties of the block in question, properties of nearby blocks, trial (full or partial) encodings or the like. Generally, the aim of the selection algorithm executed by the controller 343 is to improve the efficiency of the encoding of the block in question.

In some previously proposed example arrangements, transform-skip mode was restricted to 4x4 block sizes or smaller. In more recent examples, this restriction has been relaxed and the transform-skip mode can be selectively applied to larger blocks. The transform-skip mode can be applied to a TU even when the TU is actually processed as multiple (smaller) sub-TUs.

Further aspects represented by Figure 9a include the controller 343 selecting frequency transformations for use by the unit 340. In the present examples a so-called MTS (multiple transform set) arrangement is used. This allows the selection, for use in connection with (for example) a particular coding unit or other block, a transform skip mode; or a default or predetermined spatial processing operation; or another spatial processing operation. Various transformations may be used as candidate spatial processing operations for selection by this technique. These can include for example the following, as defined by ISO/IEC JTC1/S029/WG11 document N17055 (Algorithm Description of Joint Exploration Test Model 7), the contents of which are hereby incorporated into this description by reference: Transform Type Basis function Ta, 1, j=0, 1,..., N-1 OCT-II (TE * i * (21 ± 1))

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where coo = -11 i = 0 ( 1 i # 0 Ti(j)= coo co s 2N DCT-V T1(j) rAr"1), \II j = 0 =NI2 W2 1 cos N 1 j # 0 \F i = 0 where coo = At, co, = 1 I # 0 DCT-VIII 4 IT * (2i + 1) -(2 j + 1) Q)=4 2N + 1 4N + 2 DST-I Tt(j) 2 it. * (i + 1) -(j +1)) sin ( N +1 N + 1 DST-VII Tt(j) 4 TT * (2i + 1) * (j + 1)) sin 2N + 1 2N + 1 Of these, DCT-V and DST-I are not applicable in at least some example embodiments. The transformations in the list (except for OCT-V and DST-I in some examples) form candidate spatial processing operations for selection by the controller 343 in connection with (for example) a CU to be encoded. They may be selectable as pairs for horizontal and vertical application respectively; in such arrangements the selection may be indicated as A x B where A is a transformation to be applied horizontally and B is to be applied vertically. The corresponding inverse transform to be discussed below may also be referred to in shorthand as A x B but would in fact represent the application of A' (inverse A) horizontally and B-1 (inverse B) vertically. In these examples, such a pair would represent a "candidate spatial processing operation" selectable by the controller 343 for application by the transform unit 340. Examples of such candidate spatial processing operations On the notation "Ax B" discussed above) may include: * none (transform skip, or TS) * OCT-I I x DCT-I I * DST-VII x DST-VII * DCT-VIII x DST-VII * DST-VII x OCT-VIII * DCT-VIII x DCT-VIII These (including transform skip as listed) are examples of spatial processing operations.

A so-called default or predetermined spatial processing operation may be defined. An example default transformation is DCT-II x DCT-II but any of the transformation operations may serve as the default. This can assist in coding efficiency in that a potentially smaller code can be used to indicate the use of the default spatial processing operation. Example coding strategies may include the following: * a one bit flag to indicate whether TS is in use (for example, 0 = no, 1 = TS) if this flag = 0, or in other words TS is not in use: * a one bit flag to indicate whether MTS is in use or the default transformation is in use (for example: 0 = default [DCT-II x DCT-II]; 1 = another selection) if this flag is 1, or in other words a selection other than the default is in use: * a two bit flag to indicate the particular selection (for example 00 = DST-VII x DST-VII; 01 = DCT-VIII x DST-VII; 10 = DST-VII x DCT-VIII; 11 = DCT-VIII x DCT-VIII) Therefore, if the first flag indicates TS mode, the other two flags are not required. If TS mode is not in use but the second flag indicates that the default transformation is to be used, the remaining two bits of the final flag are not required.

Selection of the spatial processing operation for a given CU or other block is handled by the controller 343, for example by using a series of trial encodings of at least a subset of the CU according to at least a subset of the encoding process or using a technique to predict the outcome of the trial encodings. For example a so-called "cost function" may be evaluated, for example indicating a balance, for each of the transformations under test, between factors such as encoding efficiency (or output data quantity) and encoding quality (for example, noise or errors introduced by the encoding). The detection or prediction of output data quantity can be sensitive to the data used to encode flags to indicate the different transformations, Amongst the transformations under test (for example, by a trial encoder 1000, Figure 10, forming part of or under the control of the controller 343), a selection is made (for example by a selector 1010, again forming part of or under the control of the controller 343), for example according to the best outcome in terms of the respective detected or predicted cost functions. The selected transformation is communicated to the transform unit 340 and also to circuitry 920 (which may form part of or be under the control of the controller 343) acting as a flag data encoder to encode the flags discussed above to (or to be associated with) the output data stream 930 from the encoder. The broken line 910 indicates schematically that other parts of the process may take place between the operations carried out by the units 340, 920.

In carrying out these actions, the controller 343 may be responsive to input information such as current encoding parameters (for example, which may allow or exclude one or both of TS and MTS as selectable options) and/or a current prediction mode.

In the present examples, the video data to be encoded represents a 4:4:4 format video signal.

In previously proposed arrangements, the full range of choices of MTS was available only to a primary component channel (such as luminance or Y in a YUV system, or green or G in a GBR (green blue red) representation). The other two channels, other than the primary channel, were restricted to either using TS or the default transform DCT-II x DCT-II. However, in 4:4:4 video there are just as many chrominance samples (or B, R) samples as luminance (or G) samples, so there is a potential benefit in allowing a wider range of choices for spatially processing the U,V (B,R) channels in this arrangement. Having said this, the present techniques to be described are potentially applicable to other video formats such as 4:2:2 and 4:2:0 video formats.

The examples are applicable to arrangements in which the primary video component channel is a luminance channel and the video component channels other than the primary video component channel comprise respective colour difference channels, or to arrangements in which the primary video component channel is a green channel and the video component channels other than the primary video component channel comprise blue and red channels.

A different approach for use in connection with at least 4:4:4 format video signals will be discussed below with reference to Figures 11-15.

In the decoding path of the encoder, the same outcomes selected by the controller 343 are applied to the inverse transform unit 430.

At a decoder, however, an arrangement such as that shown schematically in Figure 9b may be used. Here, rather than conducting any trial encodings or the like, the information present as flags or similar data in or associated with the received encoded data stream 940 is used to control the selection of TS, MTS, the default transformation or the like. A flag data decoder 950, being part of or under the control of the controller 343, decodes the flags from the data stream 940 and provides information to the controller 343 to control the operation of the inverse transform unit 430 to perform TS (using the bypass route 900) or a selected transform operation.

The broken line 960 indicates schematically that other parts of the process may take place between the operations carried out by the units 950, 430.

Various options for implementation in connection with at least 4:4:4 video will now be discussed with reference to schematic flowcharts of Figures 11-13. These options all assume that a selection amongst TS, default, MTS is implemented for the primary component channel (such as Y or G), as represented by a common first step 1100, 1200, 1300 of Figures 11-13.

The reference to "non-primary channels" is to video component channels other than the primary video component channel, which is to say U,V in a YUV representation or B,R in a GBR representation.

The units 340 / 430 are arranged to spatially process the first and second video data values according to the respective selected first and second spatial processing operations.

The following examples concern selecting a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels.

In various options discussed below, the examples also involve selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel.

Option A: non-primary channels use same as primary channel A schematic step 1110 represents the re-use for both of the non-primary channels of the same spatial processing operation as that selected (at the step 1100) for the primary channel.

In this case, there is no need for further signalling or flags, and a step 1120 can simply encode whatever flags are required (for example, using the format discussed above) to indicate the selection made for the primary channel.

Note that in this case, each of the non-primary channels may (individually or collectively, which is to say that the two may or may not be constrained to adopt the same approach) select TS as an alternative to the spatial processing operation selected for the primary channel. This provides an example in which first and second sets of candidate spatial processing operations comprise a transform skip operation.

This provides an example in which the second set of candidate spatial processing operations comprises only the selected first spatial processing operation and one other predetermined spatial processing operation (for example, TS).

In examples in which the constraint is simply to the selection of the primary channel, then the second set of candidate spatial processing operations may comprise only the selected first spatial processing operation.

Option B: non-primary channels may use primary channel selection or default (such as DCT-II x DCT-II) A schematic step 1110 represents a further selection step, for example by trial encodings carried out by the trial encoder 1000, to select whether to re-use for one or both of the non-primary channels (individually or collectively) the same spatial processing operation as that selected (at the step 1100) for the primary channel, or to use the default DOT-II x DCT-II operation.

In this case, further signalling or flags may be used. A step 1120 can encode whatever flags are required (for example, using the format discussed above) to indicate the selection made for the primary channel, and then a flag (which may be a one bit flag) to indicate the selection for the non-primary channels (for example: 0 = default; 1 = same as primary channel).

If the selection for the primary channel is the default operation then there is no need for any signalling of that selection. In this instance, simply the "not using TS" flag would be used for either or both of the non-primary channels.

Note that this selection can be made for the two non-primary channels collectively, which is to say the same decision applies to both (and only a single one-bit additional flag is needed), or it can be made individually for the two non-primary channels, in which case a one bit flag may be used for each.

Note that once again, in this case, each of the non-primary channels may (individually or collectively) select TS as an alternative to the spatial processing operation selected for the primary channel and the default operation.

Option C: non-primary channels may each select from all available operations (TS, default, MIS options) This selection is made as multiple trial encoding or similar processes at a schematic step 1310, one process in connection with each video component channel. At a schematic step 1320, a full set of flags is provided for each video component channel to indicate the operation selected for each channel.

In other examples, the selection could be constrained to be the same for the two non-primary channels, in which case flag data is required only for the primary channel (one set) and the non-primary channels (one set), or different selections could be allowed. Option C provides an example in which a second set of candidate spatial processing operations available to non-primary channels comprises all of the candidate spatial processing operations of the first set of candidate spatial processing operations (available to the primary channel).

Encoding the Selections In example arrangements, indicator data is encoded to indicate at least the selected first and second spatial processing operations.

The encoding system as set out above may be used for the Y or G (primary) channels.

In the case of the B, R or U, V channels, then if they are constrained to follow the same selection as one another then only one set of signalling (per pair of non-primary channels, per block) needs to be sent. Otherwise, if the two non-primary channels are able to select individually then signalling or flags are provided for each such non-primary channel, per block.

An example of signalling for the pair of non-primary channels or for each non-primary channel is summarised below. This assumes that TS is freely selectable in each case (which is to say, selectable independently of the selection made for the primary channel); if not then the IS flag may be omitted.

Option A: * a one bit flag to indicate whether TS is in use (for example, 0 = no, 1 = TS) if this flag = 0, or in other words TS is not in use.

Note that if TS is not set then the selection for the non-primary channels is assumed to be identical to that for the primary channel, so no signalling of the actual selection is required. Option B: * a one bit flag to indicate whether TS is in use (for example, 0 = no, 1 = TS) if this flag = 0, or in other words TS is not in use: * a one bit flag which may be omitted if the default transform is selected (or if TS is in use), or instead set to the use of the primary channel's selection.

Options A and B provide examples in which the first set of candidate spatial processing operations comprises a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; and encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of the first transformation operation as the second transformation operation.

Option C: * a one bit flag to indicate whether TS is in use (for example, 0 = no, 1 = TS) if this flag = 0, or in other words TS is not in use: * a one bit flag to indicate whether MTS is in use or the default transformation is in use (for example: 0 = default [DCT-II x DCT-I I]; 1 = another selection) if this flag is 1, or in other words a selection other than the default is in use: * a two bit flag to indicate the particular selection (for example 00 = DST-VI I x DST-VII; 01 = DCT-VIII x DST-VII; 10 = DST-VII x DCT-VIII; 11 = DCT-VIII x DCT-VIII) In other examples for option C, a shorter flag or flag set could indicate for a non-primary channel that "notwithstanding the full or wider choice available to this channel (options B or C), the (independent) selection for the channel is the same as that of the primary channel".

These arrangements collectively provide examples in which the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of a predetermined transformation operation as the second transformation operation; and encoding indicator data of a third indicator data length greater than the second indicator data length to indicate selection of the second transformation operation to be other than the transform skip operation or the predetermined transformation operation.

Summary Methods

Figure 14 is a schematic flowchart illustrating a video data encoding method for encoding video data values of a video signal such as a 4:4:4 format video signal, the method comprising: selecting (at a step 1400) a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting (at a step 1410) a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing (at a step 1420) the first and second video data values according to the respective selected first and second spatial processing operations.

Figure 15 is a schematic flowchart illustrating a video data decoding method for decoding video data values of a video signal such as a 4:4:4 format encoded input video signal, the method comprising: selecting (at a step 1500) a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting (at a step 1510) a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing (at a step 1520) the first and second video data values according to the respective selected first and second spatial processing operations.

Summary Apparatus

Any one or more of the above encoding or decoding methods may be implemented by the apparatus of Figures 7 and/or 8 and/or 9 and/or 10. Such apparatus operating according to such a method provides an example of control circuitry 343 and frequency transformation circuitry 340/430.

Summary

In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Similarly, a data signal comprising coded data generated according to the methods discussed above (whether or not embodied on a non-transitory machine-readable medium) is also considered to represent an embodiment of the present disclosure.

It will be apparent that numerous modifications and variations of the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended clauses, the technology may be practised otherwise than as specifically described herein.

It will be appreciated that the above description for clarity has described embodiments with reference to different functional units, circuitry and/or processors. However, it will be apparent that any suitable distribution of functionality between different functional units, circuitry and/or processors may be used without detracting from the embodiments.

Described embodiments may be implemented in any suitable form including hardware, software, firmware or any combination of these. Described embodiments may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of any embodiment may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the disclosed embodiments may be implemented in a single unit or may be physically and functionally distributed between different units, circuitry and/or processors.

Although the present disclosure has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in any manner suitable to implement the technique.

Respective aspects and features are defined by the following numbered clauses: 1. A video data encoding method for encoding video data values of a video signal (such as 4:4:4 format video signal), or alternatively at least a 4:2:2 or 4:2:0 video signal, the method comprising: selecting a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.

2. The video data encoding method of clause 1, in which the first and second sets of candidate spatial processing operations comprise a transform skip operation.

3. The video data encoding method of clause 1, in which the second set of candidate spatial processing operations comprises all of the candidate spatial processing operations of the first set of candidate spatial processing operations.

4. The video data encoding method of clause 3, comprising: encoding indicator data to indicate at least the selected first and second spatial processing operations.

5. The video data encoding method of clause 4, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of a predetermined transformation operation as the second transformation operation; and encoding indicator data of a third indicator data length greater than the second indicator data length to indicate selection of the second transformation operation to be other than the transform skip operation or the predetermined transformation operation.

6. The video data encoding method of clause 1, in which the second set of candidate spatial processing operations comprises only the selected first spatial processing operation and one other predetermined spatial processing operation.

7. The video data encoding method of clause 6, comprising: encoding indicator data to indicate at least the selected first and second spatial processing operations.

8. The video data encoding method of clause 7, in which: the first set of candidate spatial processing operations comprises a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; and encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of the first transformation operation as the second transformation operation.

9. The video data encoding method of clause 1, in which the second set of candidate spatial processing operations comprises only the selected first spatial processing operation.

10. The video data encoding method of clause 9, comprising: encoding indicator data to indicate at least the selected first spatial processing operation.

11. The video data encoding method of any one of the preceding clauses, in which the primary video component channel is a luminance channel and the video component channels other than the primary video component channel comprise respective colour difference 15 channels.

12. The video data encoding method of any one of clauses 1 to 10, in which the primary video component channel is a green channel and the video component channels other than the primary video component channel comprise blue and red channels.

13. Computer software which, when executed by a computer, causes the computer to perform the method of any one of the preceding clauses.

14. A non-transitory machine-readable storage medium which stores the computer software of clause 13.

15. A video data decoding method for decoding video data values of an input encoded video signal (such as 4:4:4 format video signal), or alternatively at least a 4:2:2 or 4:2:0 video signal, the method comprising: selecting a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.

16. The video data decoding method of clause 15, in which the first and second sets of candidate spatial processing operations comprise a transform skip operation.

17. The video data decoding method of clause 15, in which: the second set of candidate spatial processing operations comprises all of the candidate spatial processing operations of the first set of candidate spatial processing operations; and the step of selecting a second spatial processing operation is responsive to indicator data associated with encoded input video signal indicating the second frequency transformation.

18. The video data decoding method of clause 17, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the indicator data indicating the first frequency transformation and the indicator data indicating the second frequency transformation each comprise: indicator data of a first indicator data length to indicate selection of the transform skip operation; indicator data of a second indicator data length greater than the first indicator data length to indicate selection of a predetermined transformation operation as the second transformation operation; or indicator data of a third indicator data length greater than the second indicator data length to indicate selection of the second transformation operation to be other than the transform skip operation or the predetermined transformation operation.

19. The video data decoding method of clause 15, in which: the second set of candidate spatial processing operations comprises only the selected first spatial processing operation and one other predetermined spatial processing operation; and the step of selecting a second spatial processing operation is responsive to indicator data associated with encoded input video signal indicating whether the second frequency transformation is the selected first spatial processing operation or the one other predetermined spatial processing operation.

20. The video data decoding method of clause 19, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the indicator data indicating the first frequency transformation and the indicator data indicating the second frequency transformation each comprise: indicator data of a first indicator data length to indicate selection of the transform skip operation; or indicator data of a second indicator data length greater than the first indicator data length to indicate selection of the first transformation operation as the second transformation operation.

21. The video data decoding method of clause 15, in which: the second set of candidate spatial processing operations comprises only the selected first spatial processing operation; and the step of selecting a second spatial processing operation comprises selecting the second frequency transformation to be the same as the first spatial processing operation.

22. The video data decoding method of any one of clauses 15 to 21, in which the primary video component channel is a luminance channel and the video component channels other than the primary video component channel comprise respective colour difference channels.

23. The video data decoding method of any one of clauses 15 to 21, in which the primary video component channel is a green channel and the video component channels other than the primary video component channel comprise blue and red channels.

24. Computer software which, when executed by a computer, causes the computer to perform the method of any one of clauses 15 to 23 25. A non-transitory machine-readable storage medium which stores the computer software of clause 24.

26. A video data encoding apparatus for encoding video data values of a video signal (such as 4:4:4 format video signal), or alternatively at least a 4:2:2 or 4:2:0 video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.

27. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of clause 26.

28. A video data decoding apparatus for decoding video data values of an input encoded video signal (such as 4:4:4 format video signal), or alternatively at least a 4:2:2 or 4:2:0 video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.

29. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of clause 28.

Claims

CLAIMS1. A video data encoding method for encoding video data values of a 4:4:4 format video signal, the method comprising: selecting a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.
2. The video data encoding method of claim 1, in which the first and second sets of candidate spatial processing operations comprise a transform skip operation.
3. The video data encoding method of claim 1, in which the second set of candidate spatial processing operations comprises all of the candidate spatial processing operations of the first set of candidate spatial processing operations.
4. The video data encoding method of claim 3, comprising: encoding indicator data to indicate at least the selected first and second spatial processing operations.
5. The video data encoding method of claim 4, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of a predetermined transformation operation as the second transformation operation; and encoding indicator data of a third indicator data length greater than the second indicator data length to indicate selection of the second transformation operation to be other than the transform skip operation or the predetermined transformation operation
6. The video data encoding method of claim 1, in which the second set of candidate spatial processing operations comprises only the selected first spatial processing operation and one other predetermined spatial processing operation.
7. The video data encoding method of claim 6, comprising: encoding indicator data to indicate at least the selected first and second spatial processing operations.
8. The video data encoding method of claim 7, in which: the first set of candidate spatial processing operations comprises a transform skip operation; and the encoding step comprises: encoding indicator data of a first indicator data length to indicate selection of the transform skip operation; and encoding indicator data of a second indicator data length greater than the first indicator data length to indicate selection of the first transformation operation as the second transformation operation.
9. The video data encoding method of claim 1, in which the second set of candidate spatial processing operations comprises only the selected first spatial processing operation.
10. The video data encoding method of claim 9, comprising: encoding indicator data to indicate at least the selected first spatial processing operation.
11. The video data encoding method of claim 1, in which the primary video component channel is a luminance channel and the video component channels other than the primary video component channel comprise respective colour difference channels.
12. The video data encoding method of claim 1, in which the primary video component channel is a green channel and the video component channels other than the primary video component channel comprise blue and red channels.
13. Computer software which, when executed by a computer, causes the computer to perform the method of claim 1.
14. A non-transitory machine-readable storage medium which stores the computer software of claim 13.
15. A video data decoding method for decoding video data values of a 4:4:4 format encoded input video signal, the method comprising: selecting a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; selecting a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and spatially processing the first and second video data values according to the respective selected first and second spatial processing operations.
16. The video data decoding method of claim 15, in which the first and second sets of candidate spatial processing operations comprise a transform skip operation.
17. The video data decoding method of claim 15, in which: the second set of candidate spatial processing operations comprises all of the candidate spatial processing operations of the first set of candidate spatial processing operations; and the step of selecting a second spatial processing operation is responsive to indicator data associated with encoded input video signal indicating the second frequency transformation.
18. The video data decoding method of claim 17, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the indicator data indicating the first frequency transformation and the indicator data indicating the second frequency transformation each comprise: indicator data of a first indicator data length to indicate selection of the transform skip operation indicator data of a second indicator data length greater than the first indicator data length to indicate selection of a predetermined transformation operation as the second transformation operation; or indicator data of a third indicator data length greater than the second indicator data length to indicate selection of the second transformation operation to be other than the transform skip operation or the predetermined transformation operation.
19. The video data decoding method of claim 15, in which: the second set of candidate spatial processing operations comprises only the selected first spatial processing operation and one other predetermined spatial processing operation; and the step of selecting a second spatial processing operation is responsive to indicator data associated with encoded input video signal indicating whether the second frequency transformation is the selected first spatial processing operation or the one other predetermined spatial processing operation.
20. The video data decoding method of claim 19, in which: the first and second sets of candidate spatial processing operations comprise a transform skip operation; and the indicator data indicating the first frequency transformation and the indicator data indicating the second frequency transformation each comprise: indicator data of a first indicator data length to indicate selection of the transform skip operation; or indicator data of a second indicator data length greater than the first indicator data length to indicate selection of the first transformation operation as the second transformation operation.
21. The video data decoding method of claim 15, in which: the second set of candidate spatial processing operations comprises only the selected first spatial processing operation; and the step of selecting a second spatial processing operation comprises selecting the second frequency transformation to be the same as the first spatial processing operation.
22. The video data decoding method of claim 15, in which the primary video component channel is a luminance channel and the video component channels other than the primary video component channel comprise respective colour difference channels.
23. The video data decoding method of claim 15, in which the primary video component channel is a green channel and the video component channels other than the primary video component channel comprise blue and red channels.
24. Computer software which, when executed by a computer, causes the computer to perform the method of claim 15.
25. A non-transitory machine-readable storage medium which stores the computer software of claim 24.
26. A video data encoding apparatus for encoding video data values of a 4:4:4 format video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.
27. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of claim 26.
28. A video data decoding apparatus for decoding video data values of a 4:4:4 format encoded input video signal, the apparatus comprising: control circuitry configured to select a first spatial processing operation, in response to indicator data associated with encoded input video signal indicating the first spatial processing operation, from a first set of candidate spatial processing operations, for spatially processing first video data values representing a current block of a primary video component channel of a plurality of video component channels; and to select a second spatial processing operation, from a second set of one or more of the first set of candidate spatial processing operations including at least the selected first spatial processing operation, for spatially processing second video data values representing the current block of video component channels other than the primary video component channel; and frequency transformation circuitry configured to frequency-transform the first and second video data values according to the respective selected first and second spatial processing operations.
29. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of claim 28.