GB2601184A

GB2601184A - Image data encoding and decoding

Info

Publication number: GB2601184A
Application number: GB2018388.5A
Authority: GB
Inventors: James Sharman Karl; Richard Browne Adrian; Mark Keating Stephen
Original assignee: Sony Group Corp
Current assignee: Sony Group Corp
Priority date: 2020-11-23
Filing date: 2020-11-23
Publication date: 2022-05-25
Also published as: GB202018388D0

Abstract

A method of encoding image data comprises: generating a respective base encoding parameter applicable to each independently decodable image region; generating a block of coefficients from image data representing a block of a given independently decodable image region; quantising the block of coefficients depending upon a quantisation parameter applicable to that block; and generating and encoding a respective set of quantised data items. The encoding step comprises: encoding a given quantised data item by a first encoding technique, comprising encoding a series of zero or more data sets, each representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter and quantisation parameter applicable to the given block of coefficients; and encoding any remaining value of the given data item, being an amount by which the data item exceeds a maximum value which can be encoded by the first technique, by a second, different encoding technique. The second technique comprises encoding an escape code (first portion, non-unary coded second portion) having a second portion length, in bits, in which aspect(s) of the second encoding technique including at least the second portion length depend upon the region encoding parameter.

Description

IMAGE DATA ENCODING AND DECODING

BACKGROUND Field

This disclosure relates to image 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.

In some examples, the entropy encoding process can involve generating one or more "data sets" (such as a significance map, a greater than one map, a greater than two map and/or other data sets) to describe a block of coefficients, with any excess values which cannot be encoded by the significance maps alone being encoded as so-called escape values. The coding of an escape value can On some examples) be performed by generating a first portion (for example, a unary or truncated unary coded portion such as a prefix) and a non-unary coded second portion (such as a suffix) having a length, in bits, dependent upon a region encoding parameter value.

SUMMARY

The present disclosure addresses or mitigates problems arising from this processing. The present disclosure provides a method of encoding image data representing an image, the method comprising: generating a respective base encoding parameter applicable to each independently decodable image region of the image; generating a block of coefficients from image data representing a block of a given independently decodable image region; quantising the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoding the set of quantised data items derived from a given block of coefficients; in which the encoding step comprises: encoding a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quanfisafion parameter applicable to the given block of coefficients; and encoding any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

The present disclosure also provides an encoded data signal generated by the method defined above. This may in turn be embodied by a non-transitory machine-readable storage medium which stores such an encoded data signal.

The present disclosure also provides a method of decoding image data representing an image, the method comprising: detecting, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoding a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoding step comprises: decoding a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quanfisation parameter applicable to the given block of coefficients; and decoding any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quantising the set of quantised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.

The methods defined above may be embodied as computer software which, when executed by a computer, causes the computer to perform such a method. Such computer software may be embodied by a non-transitory machine-readable storage medium which stores such computer software.

The present disclosure also provides apparatus for encoding image data representing an image, the apparatus comprising: circuitry configured to generate a respective base encoding parameter applicable to each independently decodable image region of the image; circuitry configured to generate a block of coefficients from image data representing a block of a given independently decodable image region; quantisation circuitry configured to quantise the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoder circuitry configured to encode the set of quantised data items derived from a given block of coefficients; in which the encoder circuitry is configured: to encode a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and to encode any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

The present disclosure also provides apparatus for decoding image data representing an image, the method comprising: circuitry to detect, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoder circuitry to decode a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoder circuitry is configured: to decode a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quantisation parameter applicable to the given block of coefficients; and to decode any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quantisation circuitry configured to inverse quantise the set of quantised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.

The present disclosure also provides video data capture, transmission, display and/or storage apparatus comprising any of the apparatus defined above.

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 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; Figure 9 schematically illustrates a transform-skip mode; Figures 10a, 10b, lla and llb schematically illustrate respective scanning directions; Figure 12 schematically illustrates some aspects of an encoder; Figure 13 schematically illustrates some aspects of a decoder; and Figures 14 to 17 are schematic flowcharts illustrating 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 20 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 quanfiser 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 upright 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 10- 20% 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 On 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).

I ntra-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 kframe encoding in other video compression techniques. In contrast to l-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 (ii) 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 On 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-skip mode Figure 9 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 the schematic bypass path 900 in Figure 9, the transform unit 340 On the encoding path) and the inverse transform unit 430 On the decoding path of the encoding side or in a decoder) 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, DCT, 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.

Figures 10a and 11 a schematically illustrate respective scanning directions, with Figure 10a providing an example applicable to a 4x4 transform-skip block and Figure 11a providing an example applicable to a so-called transform block, which is to say a block for which transform-skip mode was not enabled and so the block has undergone a spatial frequency transform (or more than one frequency transform) by the transform unit 340 during encoding.

Referring to Figure 10a, in the case of transform-skip blocks, the scan order is in this example a diagonal order from the top left ("1") to lower right ("16"). In contrast, as shown in Figure 11a, in the case of a transform block (as an example of an encoding block) the scan order is a diagonal order from the lower right to top left. Note that the scan order in use makes little substantive difference to the techniques to be discussed below other than in terms of which coefficients or samples are available "already encoded" or "already decoded" for use in the derivation of encoding parameters for subsequent samples or coefficients.

In the case of larger blocks, a similar scan order can be used, or sub-blocks of (for example) 4x4 coefficients such as sub-TUs can be scanned as shown, with a predetermined pattern being used to scan each sub-block in order.

In general terms, the blocks of samples or coefficients may be considered as groups of data values (or, once encoded, groups of encoded data values), each having an associated encoding order (in other words, the scan order as illustrated by the examples of Figures 10a and 11a).

Referring to Figures 10b and 11 b, in at least some examples of processing to be discussed below, reference is made to samples or coefficients (which may for convenience be referred to below by the single generic term "coefficients" even in the case of transform-skip blocks) which have been encoded or decoded before encoding or decoding of a given coefficient 1000, 1100. In the case of transform-skip, the previously handled coefficients relevant to at least some of the techniques discussed below will be coefficients in a predetermined grouping or pattern as shown in shaded form (one box for each coefficient), which are above and left of the given coefficient 1000. In the case of non-transform-skip operation, a similar predetermined pattern or grouping is used but here the previously handled coefficients relevant to at least some of the techniques discussed below are coefficients (shown shaded) below and to the right of the given coefficient 1100. As mentioned, these coefficients will be referred to by at least some techniques below. If any coefficient in the relevant shaded group is unavailable, for example because it would fall into another block or a not-yet encoded or not-yet-decoded block, that coefficient is simply omitted from the respective process and where necessary, the result of the process may be normalised to the reduced number of coefficients. (For example, normalisation is relevant to a process deriving a mean of the shaded coefficients but is not relevant to a process detecting a maximum or minimum of the shaded coefficients).

Data sets and escape codes In example arrangements, the entropy encoding stage (for example, performed by the entropy encoder 370, with the inverse process being performed by the entropy decoder 410) involves encoding the scanned quantized transform coefficients (with the scan applied by the scan unit 360 being accorded to the examples shown in Figures 10 and 11 for transform-skip and transform blocks respectively).

The entropy encoding is arranged to encode the values as zero or more so-called data sets along with escape codes for remaining values not encoded by the data sets. In examples, one or more data sets are used. The number of data sets to be used can be predetermined; or can be established by header or parameter data such as data contained in a video, sequence or picture parameter set; or in response to prevailing encoding attributes, options or other features. Whichever technique is used for selecting the number of data sets, an equivalent procedure is performed at both the encoder and the decoder sides. Generally, when fewer than all of the available datasets discussed below are included, those which are used are selected in the order shown (so, an example configuration might be to use the significance map and the GT1 flag only).

Examples of the data sets may include zero or more data sets selected from the list consisting of, the following, and (in examples) encoded in a predetermined data set order: a significance data set indicating whether a data item is non-zero; one or more greater-than-n data sets indicating whether a given data item is greater than a respective value of n; a parity data set indicating a value of a least significant bit of a data item.

To generate the data sets, the data values to be encoded are handled in the encoding order (for example the scan order). The data sets generated in respect of a block of samples such as a 4x4 block or a 4x4 (or other) sub-portion of a larger block are selectable as zero or more of a group of candidate data sets (which is to say, the data sets could be capable of being enabled, just not enabled for a particular coefficient or sub-TU or other block or group), where the group of candidate data sets may include one or more of: * Significance map (Sig) which indicates the position of so-called "significant" coefficients or samples, which is to say non-zero coefficients or samples. A significance flag indicating a non-zero value is coded for each coefficient position in the block.

* greater than 1 flag (GT1) which indicates whether the absolute value is greater than 1 for each significant coefficient. In some examples for a 4x4 block, the flag is sent only for the first 8 significant coefficients in the encoding order; in other examples, it can be sent for each significant coefficient. In other examples the GT1 flag is always sent if the significance flag is sent.

* "Value & 1" flag or parity flag is effectively the least significant bit (LSB) at this stage (where & signifies a logical AND operation).

* greater than 2 flag (012) which indicates if the coefficient absolute value is greater than 2 up to and including the first coefficient in the scanning order with this property.

Note that the flag is sent only for coefficients larger than 1 as indicated by the GT1 flag.

In some examples, after the occurrence of the first coefficient which is greater than 2 in the scanning order, the GT2 flag is not further sent. However, in at least some of the present examples being discussed, the GT2 flag may be sent at each calculated occurrence or at least up to a particular number of occurrences per coefficient for a sub-TU (such as up to four occurrences, the number of allowable occurrences being selectable for a sub-TU as discussed below).

In some examples, for Non-TS operation, the 0T2 flag is coded whenever the GT1 flag is set. The limit of 4 applies to TS and may be applied up to 4 times to each coefficient or until it is not set. Thus if the first G12 flag is not set then the value is 1 or 2 (depending on parity), if the first is set and the second is not set the value is 3 or 4, and if the first two are set by the third is not the value is 5 or 6 and so on.

* Coefficient sign which is provided for the significant coefficients. The absolute coefficient value (ABS(COEFF)) is modified in response to each coding pass of the above arrangement and the modified value is used in the next pass. The modification is: * At the generation of the significance map, subtract 1; * At the generation of the GT1 map, subtract 1; * At the generation of the value & 1 flag, divide by 2.

This provides an example in which, when one or more data sets are selected, encoding by a first technique comprises modifying the data value after encoding by a given data set to account for values which can be encoded by that data set.

In other words, a coefficient for which one GT2 flag has been generated in fact has a minimum value of 4, as shown in the following example in which each data set is shown in turn, with the following column indicating a remaining value (Val) to be encoded after the modification mentioned above: Val (i/p) Sig Val Gt1 Val Val&1 Val Gt2 0 0 1 1 0 0 2 1 1 1 0 0 0 0 3 1 2 1 1 1 0 0 4 1 3 1 2 0 1 1 1 4 1 3 1 1 1 6 1 5 1 4 0 2 1 Escape codes Escape codes are used to encode the remaining absolute level, which is to say level information which has not been encoded by the data sets outlined above. Because of the effective subtraction of 4 discussed above, in an arrangement in which one G12 flag is always sent when it is applicable, the remaining absolute level needs to be encoded only for "coeff -4". Where more than one GT2 flag is sent for a coefficient, the offset is increased to represent the increasing contribution to the value represented by each successive GT2 flag.

The remaining absolute level is encoded by an escape code, for example, comprising a first portion and a non-unary coded second portion. The second portion may have a length, in bits, dependent on (for example, equal to) a region encoding parameter value defined by a so-called Rice parameter.

Such an arrangement may be referred to as a Golomb-Rice code in which a value to be encoded is considered as two portions (the first and second portions mentioned above). The first portion is the result of the division of the value to be encoded by M, where M = 2b, and the second portion is the remainder, for example b least significant bits of the value to be encoded. In the discussion provided here, the parameter b applicable to a particular block or region is referred to as the region encoding parameter. It is also referred to as the Rice parameter. Note that one or more aspects of the encoding! decoding technique for escape codes including at least the second portion length are dependent upon the region encoding parameter. In examples, the first portion is also (as discussed above) dependent upon the region encoding parameter.

In examples, the quotient or first portion is encoded using unary coding and is followed by the remainder encoded using, for example, truncated binary encoding. Note that if M = 1, then this coding is equivalent to unary coding.

In example embodiments the first portion is a prefix and the second portion is a suffix. For example, the first portion may comprise a unary encoded value. For example, the first portion may comprise a truncated unary value. Note however that the terms "first" and "second" are simply identifiers and do not necessarily imply any requirement for the first portion to precede the second portion in an encoding or transmission order.

The generation of escape codes using Rice parameters is discussed in "Versatile Video Coding Editorial Refinements on Draft 10", Bross et al, Joint Video Experts Team, 20th meeting, October 2020, JVET-T2001-v1, the contents of which are hereby incorporated by reference.

In the case that a remaining value is too large to be entirely represented by an escape code (which is to say, the value is larger than the maximum value which can be represented by an escape code using the prevailing parameters including the Rice parameter), a further type of code (an escape-escape code) may be provided in addition or instead, for example being encoded using exponential-Golomb-order-k coding. In exponential Golomb order-k codes, a number to be encoded is split into a variable length unary-encoded prefix and a variable length suffix. The number of suffix bits = prefix_length + k. Here, prefix_length is once again the number of is in the unary code, and k is also an aspect dependent upon (for example, equal to) the prevailing Rice parameter or region encoding parameter.

Provision of Rice parameter -previous proposal A previous proposal is entitled "AHG12: Slice based Rice parameter selection for transform skip residual coding", Jhu et al, Joint Video Experts Team, 20th meeting, October 2020 (JVET-T0089), the contents of which are hereby incorporated in the present description by reference. In this proposal, the Rice parameter may be signalled (at least for some transform skip blocks) in a slice header. The signalling is selectable, in that a control flag may be signalled in the sequence parameter set to indicate whether such Rice parameter signalling is enabled or disabled. When such signalling is disabled, a default Rice parameter such as 1 is used for the whole of the transform skip slice.

Provision of Rice parameter in example embodiments -overview The present arrangement also provides for the signalling of a Rice parameter to be used for a slice, but differs in a number of significant ways from the proposal discussed above.

The present disclosure recognises that within a slice, the quantisation parameter (OP) may not in fact be constant across the entire slice. So, while a base parameter or a slice OP may be defined and in at least some examples communicated from the encoder side to the decoder side, in practical embodiments it is entirely possible for some blocks to deviate from the use of the slice OP. This is significant to the present discussion because the OP actually used affects the size or magnitude of the resulting quantised coefficients. Smaller magnitude coefficient values imply that a lower Rice parameter may be more appropriate. In example embodiments, it is possible to achieve coding efficiency gains if the Rice parameter actually used is allowed to vary from the slice Rice parameter discussed above, for example in response to variations in the OP actually being used.

In the present examples, it is also recognised that there is no need to restrict the signalling of the Rice parameter to transform skip blocks (transform skip residual coding or TSRC) but in fact the signalling of the Rice parameter can be used for non-TS or regular residual coding (RRC) blocks.

In some examples, a variation delta_Rice from the slice Rice parameter may be defined as follows: delta_Rice = -delta_QP / 6 where: delta_QP = local_QP -slice_QP; localQP is the OP value actually in use for the current block; and slice_QP is the slice OP value.

In other examples, rather than using this formula the encoder or decoder could use a look-up table to vary the Rice parameter. Such a table could be indexed by, for example, delta_QP, with the table containing, for example, values of delta_Rice, for example being limited to a valid index range. For example: delta_Rice = delta_rice_table [localQP -sliceQP] In other examples, where local_QP, or at least delta_QP, depends on one or more block attributes X, Y..., the present arrangement could be implemented by a look-up table for delta_Rice indexed by one or more of the attributes X, Y...

delta_Rice = delta_rice_table [X, Y...] The negative sign in the formula for delta_Rice implies that a harsher quantisation (higher OP value) corresponds to a lower Rice parameter. The divisor of 6 is an example arrangement based upon a previously proposed relationship between bit depth and OP such that for an increase of 1 bit in bit depth, a change of 6 is applied to the minimum OP to be used.

A Rice parameter for use in connection with the current block, local_Rice, may then be defined as follows: local_Rice = Max (0, slice_Rice + (scaling_factor* delta_Rice)) Here, the function "Max" returns the numerically higher of its arguments. The value of zero therefore represents a minimum value of local_Rice. A different minimum value, such as 1, may be used instead. The selection of the minimum value can be empirical. However, as a general discussion, the choice of a minimum of 0 or 1 (or perhaps >1) can depend on the expected distribution of values. Using a Rice parameter of 0 is considered more appropriate when the number of non-zero values is small, as a Rice parameter of 0 is more appropriate for coding zero. Thus for data which are almost all zero but with a few larger values, 0 would be appropriate whilst a different distribution with mostly small but non-zero coefficients would benefit from a non-zero minimum Rice parameter.

A scaling factor of 1 (that is to say, no scaling) may be applied as scaling_factor or alternatively a non-unity positive scaling factor may be used.

As an example (with scaling factor of 1): slice_QP = -30, local_QP = -12, slice_Rice = 5 delta_QP = -12 -(-30) = 18 delta_Rice = -18 / 6 = -3 local_Rice = Max(0, 5 + -3) = 2 As well as (or indeed instead of) a minimum value, a maximum value (greater than the minimum value if one is in use) could be applied. So while in some examples the generation of the region encoding parameter is subject to a predetermined minimum region encoding parameter, in general, the generation of the region encoding parameter is subject to a predetermined allowable range of region encoding parameters.

This provides an example of generating a region encoding parameter (local_Rice) in response to the base encoding parameter (slice_Rice) applicable to the given independently decodable image region and the quantisation parameter (local OP) applicable to the given block of coefficients. For example, a difference could be detected between local_QP and slice_QP, though in other examples a ratio or other relationship could be used, or a look-up table could be used. For example, local_Rice could be generated as a difference from slice_Rice, though in other examples a ratio or other relationship between local_Rice and slice_Rice could be generated, or once again a look-up table could be used.

Therefore, example arrangements involve selectively applying a variation to the base encoding parameter (slice_Rice) generated for and applicable to the given independently decodable image region, the variation being dependent upon a difference between the quantisation parameter local_QP and the respective base quantisation parameter slice_QP applicable to the given independently decodable image region.

In turn, the block quantisation parameter local_QP may be generated in response to the base quantisation parameter slice_QP generated for and applicable to the given independently decodable image region and one or more attributes of the block of coefficients.

Example attributes upon which local_QP may depend An example arrangement for the derivation of OP is discussed in section 8.7.1 of "Versatile Video Coding Editorial Refinements on Draft 10", Bross et al, Joint Video Experts Team, 20th meeting, October 2020, JVET-12001-v1, the contents of which are hereby incorporated by reference.

According to these examples, localQP may differ from slice_QP for any one or more of at least the following reasons: (a) whether one or more encoding options of a predetermined list of encoding options are enabled for the block of coefficients. For example, the so-called ACT (adaptive colour transform) tool, when enabled, introduces OP modifications of (-5, +1, +3) for the three colour components. In other examples, when so-called dual tree operation is enabled (rather than single tree), OP values applicable to chrominance blocks may be changed.

(b) a colour channel represented by the block of coefficients. In addition to the examples given under (a) above, a parameter chromaQPoffset, indicating a difference to be applied to the OP for chroma blocks may be signalled in the picture parameter set. Other offsets can also be set in the slice header.

(c) a quantisation parameter applicable to one or more previously encoded blocks of coefficients. Here, in some modes of operation, OP may be predicted using the OP derived in connection with previously encoded or decoded blocks. "Mien previously encoded blocks are used, in at least some examples a difference is signalled relative to them. This can be seen in equation 1110 of JVET-T2001-v1 cited above (see also equation 185). For chroma, a table index cu_chroma_qp_offset idx can be specified to derive the CuQp0ffsetCb/Cr/{CbCr} (equations 186-81. In addition for chroma, the calculated luma OP is converted via another table (which is designed so that for high QPs, all chroma information is not inadvertently lost), and then the various offsets are added (equations 1116-8).

Local_Rice could also be adjusted in response to one or both of the following: (d) block size; a larger block implies larger coefficient sizes. Therefore we might want to increase the local_Rice parameter when coding larger blocks (e.g. increase by 1 for blocks with at least 256 coefficients); (e) whether transform or transform-skip operation is in use; transform skip blocks typically have a different distribution of zero / non-zero coefficients and therefore a different Rice value may be appropriate. It might be appropriate to have a different minimum Rice value or allowable range for TS or non-TS blocks (as described above). Note also that transform skip blocks have a minimum OP level to apply. Same rule for "palette" mode. See "sps_min_qp_prime_ts" in JVET-T2001-v1, which forms sps_min_qp_prime_ts, which clips the OP value used during the dequanfizafion (see 430-2 for palette, and 1134 for transform skip) Example encoder operations Figure 12 schematically illustrates aspects of an encoding operation, and Figure 14 is a schematic flowchart provided to assist in the explanation of these operations.

In particular, the operation shown in Figure 12 refer to examples of the operations carried out by the units 340, 350, 360, 370, such that the input data at the top of Figure 12 represents the signal 330 of Figure 7 and the output at the bottom of Figure 12 represents the signal 380.

In a similar manner to Figure 7, either a frequency transform operation or a transform skip operation is performed by a unit 1200. Quantisation is handled by a unit 1210 and entropy encoding by units 1220, 1230, 1240. If in particular, the zero or more data sets are generated by the unit 1220; the unit 1230 detects whether there is any further not-yet-encoded value still to be encoded and, if so, escape values (and/or, if necessary, escape-escape codes) are encoded by the unit 1240 using a region encoding parameter defined by local_Rice.

An output unit 1250 generates the data output signal 380 as an output video data stream. Parameter generation for the quanfisation and entropy encoding operations is handled by a parameter generator 1260 which may be embodied as at least a part of the functionality of the controller 343.

The parameter generator is arranged to generate: * slice_Rice * slice_QP * localQP * local_Rice Of these, at least slice_Rice and slice_QP are communicated to the output stream, for example in the slice header. Note that in common with the previous proposal discussed above, the use of a slice_Rice value in the slice header may be enabled or disabled by a control flag, for example a flag in the sequence parameter set.

The question of whether local_QP is communicated using the output data stream depends on the particular manner by which local_QP is derived. In arrangements in which local_QP is derived by a process at the encoder side which is entirely repeatable at the decoder side, then there is no need to communicate local_QP using the data stream, as it can be generated identically at the decoder side. In other examples, local_QP may be communicated as between the encoder side and the decoder side, for example by block header data or the like.

The parameter generator 1260 generates local_Rice as a function of slice_Rice using any of the example techniques discussed above.

Referring to the flowchart of Figure 14, at a step 1400, the slice_Rice and slice_QP parameters are generated and, at a step 1410 are encoded to the slice header (assuming, as discussed above, that the encoding of slice_Rice is enabled by a control flag when one is used) At a step 1420, either a frequency transform or a transform skip operation is performed.

A step 1430 generates the localQP and local_Rice parameters and at a step 1440 the block is quantised using the local_QP quantisation parameter. Finally, at a step 1450, entropy encoding is performed using a region encoding parameter represented by the local_Rice parameter.

Therefore, in these examples, the step 1450 (as performed by the unit 1240) provides an example of encoding any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

Example decoder operations Figure 13 schematically illustrates aspects of a decoding operation, and Figure 15 is a schematic flowchart provided to assist in the explanation of these operations In particular, the operation shown in Figure 14 refer to examples of the operations carried out by the units 410, 400, 420, 430, such that the input data at the top of Figure 13 represents the signal 470 of Figure 7 and the output at the bottom of Figure 13 represents the signal 440.

A unit 1300 detects header data associated with the current slice and provides it to a parameter generator 1360 which, as discussed above, may be embodied as at least a part of the controller 343.

Entropy decoding is performed by units 1310, 1320, 1330, in that the unit 1310 decodes the zero or more data sets, the unit 1320 detects whether there is further data to be decoded as escape values (and/or, if necessary, escape-escape codes) and, if so, these are decoded by an escape value decoder (the unit 1330). Inverse quantisation is performed by an inverse quantisation 1340 and inverse frequency transform or transform skip operations are performed by a unit 1350.

Assuming that the communication of slice_Rice is enabled by a control flag, if in use, then the parameter generator 1360 receives from the header data detector 1300 at least: * slice_Rice * slice_QP and optionally (if communicated in this way, as discussed above): * localQP From these, the parameter generator 1360 generates local_Rice using any of the techniques described above. The parameter local_QP is provided to the inverse quantiser 1340 and the parameter local_Rice is provided to the escape value decoder 1330.

Note that in an arrangement in which the number of datasets is adaptive, the parameter generator 1260 and/or the parameter generator 1360 can provide to the dataset generator 1220 or the dataset decoder 1310 as appropriate information defining the number of datasets to be used.

Referring to the schematic flowchart of Figure 15, at a step 1500 the parameters slice_Rice and slice_QP are detected from the slice header. At a step 1510, local_QP and local_Rice are generated. Entropy decoding is performed at a step 1520 using local_Rice. Inverse quantisation is performed at a step 1530 using local_QP, and inverse frequency transformation or transform skip is performed at a step 1540.

Therefore, the step 1520 (as performed by the unit 1330) provides an example of decoding any remaining value of the given quantised data item, the remaining value being an amount by which the given quanfised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

Independently decodable portions The examples above refer to slices. Other examples of independently decodable portions of an image include tiles. The terms "tile" and "slice" refer to independently decodable units and represent names in use at the priority date of the present application. In the case of a subsequent or other change of name, the arrangement is applicable to other such independently decodable units.

Therefore, in example arrangements, an independently decodable data unit or portion may be one of a picture, slice or tile.

Other potential uses of Rice parameter The techniques discussed above are not limited to the specific uses of the Rice parameter discussed above, namely the generation (encoding) or decoding of escape codes and/or, if necessary, escape-escape codes. If an encoder or a decoder uses the Rice parameter for any other purpose, or bases any other processing decision or derivation on it, then the same techniques may be used for the generation and communication of slice_Rice and local_Rice.

Summary Methods

Figure 16 is a schematic flowchart illustrating a method of encoding image data representing an image, the method comprising: generating (at a step 1600) a respective base encoding parameter applicable to each independently decodable image region of the image; generating (at a step 1610) a block of coefficients from image data representing a block of a given independently decodable image region; quantising (at a step 1620) the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoding (at a step 1630) the set of quantised data items derived from a given block of coefficients; in which the encoding step comprises: encoding (at a step 1640) a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; generating (at a step 1650) a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and encoding (at a step 1660) any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

Figure 17 is a schematic flowchart illustrating a method of decoding image data representing an image, the method comprising: detecting (at a step 1700), from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoding (at a step 1710) a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoding step comprises: decoding (at a step 1720) a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; generating (at a step 1730) a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quantisation parameter applicable to the given block of coefficients; and decoding (at a step 1740) any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quanfising (at a step 1750) the set of quantised data items to generate the block of coefficients in dependence upon the quanfisafion parameter applicable to that block of coefficients.

Any one or more of the above encoding methods may be implemented by the apparatus of Figures 7 and/or 8 and/or 12.

Any one or more of the above decoding methods may be implemented by the apparatus of Figures 7 and/or Band/or 13.

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 method of encoding image data representing an image, the method comprising: generating a respective base encoding parameter applicable to each independently decodable image region of the image; generating a block of coefficients from image data representing a block of a given independently decodable image region; quanfising the block of coefficients in dependence upon a quanfisation parameter applicable to that block of coefficients, to generate a respective set of quanfised data items; and encoding the set of quantised data items derived from a given block of coefficients; in which the encoding step comprises: encoding a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and encoding any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

2. The method of clause 1, comprising: generating a respective base quantisation parameter applicable to each independently decodable image region of the image.

3. The method of clause 2, in which the quanfising step comprises: generating the quantisation parameter in response to the base quantisation parameter applicable to the given independently decodable image region and one or more attributes of the block of coefficients.

4. The method of clause 3, in which the step of generating the region encoding parameter comprises: selectively applying a variation to the base encoding parameter applicable to the given independently decodable image region, the variation being dependent upon a difference between the quantisation parameter and the base quantisation parameter applicable to the given independently decodable image region.

5. The method of any one of the preceding clauses, in which the step of generating the region encoding parameter comprises generating the region encoding parameter subject to a predetermined allowable range of region encoding parameters.

6. The method of any one of clauses 3 to 5, in which the one or more attributes of the block of coefficients comprises one or more selected from the list consisting of: whether one or more encoding options of a predetermined list of encoding options are enabled for the block of coefficients; a colour channel represented by the block of coefficients; a quantisation parameter applicable to one or more previously encoded blocks of coefficients; block size of the block of coefficients; and whether transform or transform-skip operation is in use.

7. The method of any one of the preceding clauses, in which the zero or more data sets comprise zero or more data sets selected from the list consisting of: a significance data set indicating whether a data item is non-zero; one or more greater-than-n data sets indicating whether a given data item is greater than a respective value of n; a parity data set indicating a value of a least significant bit of a data item.

8. The method of clause 7, in which, when one or more data sets are selected, encoding by the first technique comprises modifying the data item after encoding by a given data set to account for values which can be encoded by that data set.

9. The method of clause 7 or clause 8, in which, when two or more data sets are selected, encoding by the first technique comprises encoding by the two or more data sets in a predetermined data set order.

10. The method of any one of the preceding clauses, in which the first encoding technique comprises encoding a series of one or more of the data sets.

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

12. A non-transitory machine-readable storage medium which stores the computer software of clause 11.

13. An encoded data signal generated by the method of any one of the preceding clauses.

14. A non-transitory machine-readable storage medium which stores the encoded data signal of clause 13.

15. A method of decoding image data representing an image, the method comprising: detecting, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoding a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoding step comprises: decoding a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quanfisation parameter applicable to the given block of coefficients; and decoding any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quanfising the set of quanfised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.

16. The method of clause 15, comprising: detecting, from the parameter data associated with the image data, a respective base quantisation parameter applicable to each independently decodable image region of the image.

17. The method of clause 16, in which the inverse quantising step comprises: generating the quantisation parameter in response to the base quantisation parameter applicable to the given independently decodable image region and one or more attributes of the block of coefficients.

18. The method of clause 17, in which the step of generating the region encoding parameter comprises: selectively applying a variation to the base encoding parameter applicable to the given independently decodable image region, the variation being dependent upon a difference between the quantisation parameter and the base quantisation parameter applicable to the given independently decodable image region.

19. The method of any one of clauses 15 to 18, in which the step of generating the region encoding parameter comprises generating the region encoding parameter subject to a predetermined allowable range of region encoding parameters.

20. The method of clause 17 or clause 18, in which the one or more attributes of the block of coefficients comprises one or more selected from the list consisting of: whether one or more decoding options of a predetermined list of decoding options are enabled for the block of coefficients; a colour channel represented by the block of coefficients; a quantisation parameter applicable to one or more previously decoded blocks of coefficients; block size of the block of coefficients; and whether transform or transform-skip operation is in use.

21. The method of any one of clauses 15 to 20, in which the zero or more data sets comprise zero or more data sets selected from the list consisting of: a significance data set indicating whether a data item is non-zero; one or more greater-than-n data sets indicating whether a given data item is greater than a respective value of n; a parity data set indicating a value of a least significant bit of a data item.

22 The method of clause 21, in which, when one or more data sets are in use, decoding by the first technique comprises modifying the data item after decoding by a given data set to account for values which can be decoded from that data set.

23. The method of clause 21 or clause 22, in which, when two or more data sets are in use, decoding by the first technique comprises decoding the two or more data sets in a predetermined data set order.

24. The method of any one of clauses 15 to 23, in which the first encoding technique comprises decoding a series of one or more of the data sets.

25. Computer software which, when executed by a computer, causes the computer to perform the method of any one of clauses 15 to 24.

26. A non-transitory machine-readable storage medium which stores the computer software of clause 25.

27. Apparatus for encoding image data representing an image, the apparatus comprising: circuitry configured to generate a respective base encoding parameter applicable to each independently decodable image region of the image; circuitry configured to generate a block of coefficients from image data representing a block of a given independently decodable image region; quantisation circuitry configured to quantise the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoder circuitry configured to encode the set of quantised data items derived from a given block of coefficients; in which the encoder circuitry is configured: to encode a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and to encode any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.

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

29. Apparatus for decoding image data representing an image, the method comprising: circuitry to detect, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoder circuitry to decode a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoder circuitry is configured: to decode a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quantisation parameter applicable to the given block of coefficients; and to decode any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quantisation circuitry configured to inverse quantise the set of quantised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.

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

Claims

CLAIMS1. A method of encoding image data representing an image, the method comprising: generating a respective base encoding parameter applicable to each independently decodable image region of the image; generating a block of coefficients from image data representing a block of a given independently decodable image region; quanfising the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoding the set of quantised data items derived from a given block of coefficients; in which the encoding step comprises: encoding a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and encoding any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.
2. The method of claim 1, comprising: generating a respective base quantisation parameter applicable to each independently decodable image region of the image
3. The method of claim 2, in which the quantising step comprises: generating the quantisation parameter in response to the base quantisation parameter applicable to the given independently decodable image region and one or more attributes of the block of coefficients.
4. The method of claim 3, in which the step of generating the region encoding parameter comprises: selectively applying a variation to the base encoding parameter applicable to the given independently decodable image region, the variation being dependent upon a difference between the quantisation parameter and the base quantisation parameter applicable to the given independently decodable image region.S
5. The method of claim 4, in which the step of generating the region encoding parameter comprises generating the region encoding parameter subject to a predetermined allowable range of region encoding parameters.
6. The method of claim 3, in which the one or more attributes of the block of coefficients comprises one or more selected from the list consisting of: whether one or more encoding options of a predetermined list of encoding options are enabled for the block of coefficients; a colour channel represented by the block of coefficients; a quantisation parameter applicable to one or more previously encoded blocks of coefficients; block size of the block of coefficients; and whether transform or transform-skip operation is in use.
7. The method of claim 1, in which the zero or more data sets comprise zero or more data sets selected from the list consisting of: a significance data set indicating whether a data item is non-zero; one or more greater-than-n data sets indicating whether a given data item is greater than a respective value of n; a parity data set indicating a value of a least significant bit of a data item.
8. The method of claim 7, in which, when one or more data sets are selected, encoding by the first technique comprises modifying the data item after encoding by a given data set to account for values which can be encoded by that data set.
9. The method of claim 7, in which, when two or more data sets are selected, encoding by the first technique comprises encoding by the two or more data sets in a predetermined data set order.
10. The method of claim 1, in which the first encoding technique comprises encoding a series of one or more of the data sets.
11. Computer software which, when executed by a computer, causes the computer to perform the method of claim 1.
12. A non-transitory machine-readable storage medium which stores the computer software of claim 11.
13. An encoded data signal generated by the method of claim 1.
14. A non-transitory machine-readable storage medium which stores the encoded data signal of claim 13.
15. A method of decoding image data representing an image, the method comprising: detecting, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoding a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoding step comprises: decoding a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; generating a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quantisation parameter applicable to the given block of coefficients; and decoding any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quantising the set of quantised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.
16. The method of claim 15, comprising: detecting, from the parameter data associated with the image data, a respective base quantisation parameter applicable to each independently decodable image region of the image.
17. The method of claim 16, in which the inverse quantising step comprises: generating the quantisation parameter in response to the base quantisation parameter applicable to the given independently decodable image region and one or more attributes of the block of coefficients.
18. The method of claim 17, in which the step of generating the region encoding parameter comprises: selectively applying a variation to the base encoding parameter applicable to the given independently decodable image region, the variation being dependent upon a difference between the quantisation parameter and the base quantisation parameter applicable to the given independently decodable image region.
19. The method of claim 18, in which the step of generating the region encoding parameter comprises generating the region encoding parameter subject to a predetermined allowable range of region encoding parameters.
20. The method of claim 17, in which the one or more attributes of the block of coefficients comprises one or more selected from the list consisting of: whether one or more decoding options of a predetermined list of decoding options are enabled for the block of coefficients; a colour channel represented by the block of coefficients; a quantisation parameter applicable to one or more previously decoded blocks of coefficients; block size of the block of coefficients; and whether transform or transform-skip operation is in use.
21. The method of claim 15, in which the zero or more data sets comprise zero or more data sets selected from the list consisting of: a significance data set indicating whether a data item is non-zero; one or more greater-than-n data sets indicating whether a given data item is greater than a respective value of n; a parity data set indicating a value of a least significant bit of a data item.
22 The method of claim 21, in which, when one or more data sets are in use, decoding by the first technique comprises modifying the data item after decoding by a given data set to account for values which can be decoded from that data set.
23. The method of claim 21, in which, when two or more data sets are in use, decoding by the first technique comprises decoding the two or more data sets in a predetermined data set order.
24. The method of claim 15, in which the first encoding technique comprises decoding a series of one or more of the data sets.
25. Computer software which, when executed by a computer, causes the computer to perform the method of claim 15.
26. A non-transitory machine-readable storage medium which stores the computer software of claim 25.
27. Apparatus for encoding image data representing an image, the apparatus comprising: circuitry configured to generate a respective base encoding parameter applicable to each independently decodable image region of the image; circuitry configured to generate a block of coefficients from image data representing a block of a given independently decodable image region; quantisation circuitry configured to quantise the block of coefficients in dependence upon a quantisation parameter applicable to that block of coefficients, to generate a respective set of quantised data items; and encoder circuitry configured to encode the set of quantised data items derived from a given block of coefficients; in which the encoder circuitry is configured: to encode a given quantised data item of the set of quantised data items by a first encoding technique, the first encoding technique comprising encoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and the quantisation parameter applicable to the given block of coefficients; and to encode any remaining value of the given data item, the remaining value being an amount by which the given data item exceeds a maximum value which can be encoded by the first encoding technique, by a second encoding technique different to the first encoding technique, in which the second encoding technique comprises encoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second encoding technique including at least the second portion length are dependent upon the region encoding parameter.
28. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of claim 27.
29. Apparatus for decoding image data representing an image, the method comprising: circuitry to detect, from parameter data associated with the image data, a respective base encoding parameter applicable to each independently decodable image region of the image; decoder circuitry to decode a set of quantised data items representing a given block of coefficients of a given independently decodable image region, in which the decoder circuitry is configured: to decode a given quantised data item of the set of quantised data items by a first decoding technique, the first encoding technique comprising decoding a series of zero or more data sets, each data set representing a respective range of data item values; to generate a region encoding parameter in response to the base encoding parameter applicable to the given independently decodable image region and a quantisation parameter applicable to the given block of coefficients; and to decode any remaining value of the given quantised data item, the remaining value being an amount by which the given quantised data item exceeds a maximum value which can be encoded by the first decoding technique, by a second decoding technique different to the first decoding technique, in which the second decoding technique comprises decoding an escape code comprising a first portion and a non-unary coded second portion having a second portion length, in bits, in which one or more aspects of the second decoding technique including at least the second portion length are dependent upon the region encoding parameter; and inverse quantisation circuitry configured to inverse quantise the set of quantised data items to generate the block of coefficients in dependence upon the quantisation parameter applicable to that block of coefficients.
30. Video data capture, transmission, display and/or storage apparatus comprising the apparatus of claim 29.