Data encoding and decoding

Abstract

A data encoding method is provided, the method comprising the steps of: acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a 4:4:4 format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream. A data encoding apparatus is also provided. Furthermore, a corresponding data decoding method and data decoding apparatus is also provided.

Description

[0001] DATA ENCODING AND DECODING

[0002] BACKGROUND

[0003] Field

[0004] This disclosure relates to data encoding and decoding. of Related Art

[0005] 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.

[0006] 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.

[0007] Efficient encoding and decoding of video content is required in applications such as entertainment or communication. However, in recent years, there has been demand for efficient encoding and decoding of video content in a new range of applications. In some of the new applications - such as computer-vision systems, security systems, or the like - the reconstructed video data may not necessarily be viewed by a person. Instead, the reconstructed video data may be used for machine tasks (such as object detection or object tracking).

[0008] There is a desire to improve coding for machine consumption of reconstructed (decoded) video.

[0009] It is an aim of the present disclosure to address these issues. SUMMARY

[0010] Aspects of the present disclosure are defined by the appended claims.

[0011] Further respective aspects and features of the present disclosure are defined in the appended claims.

[0012] In accordance with embodiments of the disclosure, improvements in coding for machine consumption of decoded video can be achieved. Indeed, improved performance can be achieved when decoded video data is used for machine tasks in accordance with embodiments of the disclosure.

[0013] 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

[0014] 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:

[0015] Figure 1 schematically illustrates an audio / video (A / V) data transmission and reception system using video data compression and decompression;

[0016] Figure 2 schematically illustrates a video display system using video data decompression;

[0017] Figure 3 schematically illustrates an audio / video storage system using video data compression and decompression;

[0018] Figure 4 schematically illustrates a video camera using video data compression;

[0019] Figures 5 and 6 schematically illustrate storage media;

[0020] Figure 7 provides a schematic overview of a video data compression and decompression apparatus;

[0021] Figure 8 schematically illustrates a predictor;

[0022] Figure 9 schematically illustrates an example data encoding method;

[0023] Figure 10 schematically illustrates chroma subsampling;

[0024] Figure 11 schematically illustrates a conversion process;

[0025] Figure 12 schematically illustrates a conversion process;

[0026] Figure 13 schematically illustrates an example data encoding apparatus;

[0027] Figure 14 schematically illustrates an example data decoding method;

[0028] Figure 15 schematically illustrates a conversion process;

[0029] Figure 16 schematically illustrates a conversion process;

[0030] Figure 17 schematically illustrates an example data decoding apparatus.

[0031] Figure 18 schematically illustrates an example situation.

[0032] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Figure 7 provides a schematic overview of a video or image data compression and decompression apparatus, for encoding and / or decoding image data representing one or more images.

[0046] 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.

[0047] 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 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The remainder of the apparatus acting as an encoder (to encode the residual or difference image) will now be described.

[0052] The residual image data 330 is supplied to a transform unit or circuitry 340 which generates a discrete cosine transform (DCT) representation of blocks or regions of the residual image data. The DCT 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.

[0053] 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.

[0054] The output of the transform unit 340, which is to say (in an example), a set of DCT coefficients for each transformed block of image data, is supplied to a quantiser 350. Various quantisation techniques are known in the field of video data compression, ranging from a simple multiplication by a quantisation scaling factor through to the application of complicated lookup tables under the control of a quantisation parameter. The general aim is twofold. Firstly, the quantisation process reduces the number of possible values of the transformed data. Secondly, the quantisation process can increase the likelihood that values of the transformed data are zero. Both of these can make the entropy encoding process, to be described below, work more efficiently in generating small amounts of compressed video data.

[0055] A data scanning process is applied by a scan unit 360. The purpose of the scanning process is to reorder the quantised transformed data so as to gather as many as possible of the non-zero quantised transformed coefficients together, and of course therefore to gather as many as possible of the zero-valued coefficients together. These features can allow so- called run-length coding or similar techniques to be applied efficiently. So, the scanning process involves selecting coefficients from the quantised transformed data, and in particular from a block of coefficients corresponding to a block of image data which has been transformed and quantised, according to a "scanning order" so that (a) all of the coefficients are selected once as part of the scan, and (b) the scan tends to provide the desired reordering. One example scanning order which can tend to give useful results is a diagonal order such as a so-called up-right diagonal scanning order.

[0056] The scanning order can be different, as between transform-skip blocks and transform blocks (blocks which have undergone at least one spatial frequency transformation).

[0057] 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.

[0058] 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 transformskipped or the like, provides a compressed output video signal 380.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Figure 8 schematically illustrates the generation of predicted images, and in particular the operation of the image predictor 320.

[0067] There are two basic modes of prediction carried out by the image predictor 320: so- called intra-image prediction and so-called inter-image, or motion-compensated (MC), prediction. At the encoder side, each involves detecting a prediction direction in respect of a current block to be predicted, and generating a predicted block of samples according to other samples (in the same (intra) or another (inter) image). By virtue of the units 310 or 450, the difference between the predicted block and the actual block is encoded or applied so as to encode or decode the block respectively.

[0068] (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).

[0069] Intra-image prediction bases a prediction of the content of a block or region of the image on data from within the same image. This corresponds to so-called l-frame 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] The processing applied to the signal 460 will now be described.

[0077] 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.

[0078] 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.

[0079] 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 I decompression system may be used. The stored images may be passed to an interpolation filter 580 which generates a higher resolution version of the stored images; in this example, intermediate samples (sub-samples) are generated such that the resolution of the interpolated image is output by the interpolation filter 580 is 4 times (in each dimension) that of the images stored in the image stores 570 for the luminance channel of 4:2:0 and 8 times (in each dimension) that of the images stored in the image stores 570 for the chrominance channels of 4:2:0. The interpolated images are passed as an input to the motion estimator 550 and also to the motion compensated predictor 540.

[0080] 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.

[0081] 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 (in at least the present examples) that each sample of an image is allocated to one, and only one, such block or region.

[0082] As explained in the Background, there is a desire to improve coding of video for machine consumption (i.e. video for which the decoded video will be used to perform machine based tasks). Machine consumption of video has applications in security, computer vision, medical environments, surgical environments and the like. Indeed, the different situations to which machine consumption of video may be applied are ever increasing. Video coded for human consumption has certain optimizations which are targeted for the specific peculiarities and limitations of human vision. A computer (or machine) does not have the same limitations as a human. Therefore, certain coding optimizations used for video for human consumption may not necessarily be advantageous when performed for video for machine consumption.

[0083] Accordingly, a data encoding method and apparatus and a data decoding method and apparatus are provided in accordance with embodiments of the disclosure in order to address these issues (in addition to those reasons explained in the Background).

[0084] Example Method

[0085] Consider, now, Figure 9 of the present disclosure. Figure 9 of the present disclosure illustrates an example encoding method.

[0086] The example encoding method of Figure 9 starts at step S900 and proceeds to step S902.

[0087] In step S902, the method comprises acquiring a block of image data. The block of image data is a block of image data to be encoded. In examples, the block of image data may correspond to a transform unit, a coding unit, a prediction unit, a slice or a picture, a subpicture or a tile.

[0088] In examples, the block of image data may correspond to one or more determined portions of a picture. In examples, a determined portion of a picture may include a Region of Interest (Rol). In examples, a Rol may be determined by an auxiliary device (such as a radar, an infrared sensor, or any other suitable type of sensing device). The auxiliary device may determine the region of interest based, for example, on an approximate location of an object, a previous location of an object or the like. In this case, the auxiliary device may then compute the dimensions of the ROI; the method may then be applied to this ROI within a current frame. The position and / or the dimension of the ROI may change on a frame to frame basis (as explained in more detail later).

[0089] Then, in step S904, the method comprises selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing. In examples, a flag may comprise one or more bits. In examples, the flag may indicate one or more additional adaptations in addition to indicating that the block of image data should be prepared for machine processing. The flag may be interpreted differently in different scenarios. As an example, the flag may be dependent upon one or more other preexisting flags; the flag may only exist when another flag is set to indicate a certain processing mode. Indeed, it will be appreciated that generally the bitstream will contain certain parameters indicating width, height, chroma format and the like. If these parameters are not in accordance with the required final output (e.g. because of re-sampling in the encoder) than a flag may be used in order to indicate what the final output format should be or what resampling must be applied in order to obtain data with the final output format, for example.

[0090] In examples, the flag be applied for some frames and then not applied and then reapplied. In other words, the flag can be used in order to indicate that a frame should be prepared for machine processing on a frame by frame basis. In examples, absence of a flag in the bit stream - or setting the flag to a predetermined value such as zero may - indicate that the process should not be applied to a given block of image data.

[0091] In step S906, the method comprises converting the block of image data. In particular, the method comprises converting the block of image data to a 4:4:4 format on the basis of the flag.

[0092] Then, in step S908, the method comprises encoding the converted block of image data in order to generate the encoded data stream.

[0093] The method proceeds to, and ends with, step S910.

[0094] Accordingly, in the example method of Figure 9 of the present disclosure, a flag is selectively encoded when an encoded data stream corresponding to the block of image data should be prepared for machine processing. This flag can be used to signal to a decoding side process that one or more certain processes have been applied on the encoded side when encoding the block of image data. As the flag is selectively encoded when the image data should be prepared for machine processing, this enables an adaptation of the encoding process to be made when the video will be used for machine processing. As such, it is possible to optimize the encoding for this situation.

[0095] In this way, improvements in coding for machine consumption of decoded video can be achieved. Indeed, improved performance can be achieved when decoded video data is used for machine tasks.

[0096] In particular, the inventors have realized that machine tasks (such as object detection or tracking) work better with 4:4:4 data than, say, 4:2:0 data. In part this is because machine vision systems do not have the same limitations as human vision. Converting the block of image data to a 4:4:4 format provides the same resolution to both the luma and chroma components of an image. Machine tasks work better in this situation. However, use of 4:4:4 data may not necessarily be the most efficient when the video is for human consumption. Human vision is typically much more sensitive to variations in brightness than variations in colour. Accordingly, when the video is for human consumption, improvements in coding efficiency can be achieved by devoting more bandwidth to luma than chroma (e.g. by using 4:2:0 or 4:2:2 data). The ability to signal the optimization which is used when encoding the data by selectively encoding the flag in step S904 thus enables improvements in coding for machine consumption of decoded video to be achieved, while retaining coding efficiency when encoding video for human consumption. Therefore, in examples, parallel encoding for human and machine use may be performed. In this situation, a full encoding may be performed for a human vision channel, while a second, lower bit-rate machine vision encoding could be used for a machine vision channel. In some examples, the encoding for the human video channel may be applied to the entire image (as a human will likely look at the entire image) while encoding for the machine vision channel may be performed only for a certain image block (e.g. a certain region within the image) of interest for the machine (as the machine may only perform a certain task, e.g. object recognition, on a certain portion of the image). In other words, in examples, when it is determined that a certain image block should be prepared for machine processing, that image block may be encoded using an encoding method of the present disclosure and, in parallel, that image block may be encoded using a full encoding process (for human vision). All other image blocks may be encoded using a full encoding process (for human vision).

[0097] Such a parallel encoding may be advantageous in certain situations. For example, a parallel encoding process may be advantageous when encoded video is to be sent to different places; this may include a first destination, such as a display device, which will be used for human vision and a second destination, such as a host processor, which will be used for machine vision. This enables a lower bit-rate machine vision channel to be provided (which is optimized for machine processing tasks) while also enabling a human to view the video content in a desired format for human vision. Such a parallel encoding may also be advantageous when the coded video data is to be sent to a storage. Consider an example of a security system, where video data from one or more security cameras is captured and stored in a storage. The video data from the one or more security cameras may be processed by a machine (e.g. to perform object recognition to identify a person). On the other hand, the video from the one or more security cameras may also be viewed by a person (e.g. a security guard reviewing the footage from the security cameras). In this situation, it may be advantageous to provide a small, fast-access storage which stores video which has been prepared for machine processing is used for machine processing and a larger, slower-access storage, which stores video which has been prepared for human viewing. However, it will be appreciated that parallel encoding is not necessarily required in accordance with embodiments of the disclosure. In examples, each image block may be encoded depending on whether or not it will be used for machine processing. In examples, only image blocks which will be used for machine processing may be encoded (in accordance with an encoding method of the present disclosure). Furthermore, while parallel encoding has been discussed, in examples, an encoding for the human vision channel and an encoding for the machine vision channel may take place sequentially.

[0098] In examples, certain segments of a picture (a part of a picture) may be required for a machine processing task, while other segments of the picture are not required for machine processing tasks. For example, a segment of a picture may include a certain Rol within the picture. In examples, the Rol may include a certain region of the picture that the machine is currently interested in (i.e. a region on which the machine will perform machine processing). In examples, the Rol may include a subset of the picture (such as, for example, a region in which a certain object was previously detected). Therefore, the method may comprise selectively encoding the flag when the encoded data stream corresponding to the block of image data should be prepared for machine processing, where the block of image data includes a certain Rol within a picture. On the other hand, image blocks not included within this Rol may be processed for human vision (e.g. without the conversion process of the present disclosure). Thus, different image blocks within a same picture may be encoded differently depending on whether or not they will be used for machine processing tasks.

[0099] In some examples, a certain block of image data may be used for both machine processing tasks and human vision. This may include an example where a machine performs a certain machine task on image data (e.g. object detection) while, at the same time, the image data is provided to a human for visualisation.

[0100] In examples, the method may comprise selectively encoding the flag when the encoded data stream corresponding to the block of image data should be prepared for machine processing on the basis of a determination that the encoded image data will be processed for machine tasks. In examples, the determination may be made on the basis of indication information, the indication information indicating that the encoded image data will be processed for machine tasks.

[0101] In examples, the indication information may be received from an external device. For example, a user may provide information indicating that the encoded data will be processed for machine tasks using a user input device. This information may then be used during the encoding process, to set the flag and perform the corresponding encoding process.

[0102] In examples, the determination may be made on the basis of a source of the image data. The source of the image data may include a type of device which captures the image data. For example, consider a situation where image data is received from an image capture device forming part of a security system. In a security system, a machine may process the image data in order to perform object tracking or objection recognition tasks, for example. This may include recognising or tracking a person within the image. Therefore, a determination may be made, based on information such as the type of the image capture device, that the encoded data may be used or processed for machine tasks.

[0103] In examples, the determination may be made on the basis of a destination of the encoded data stream. For example, when the encoded data stream is to be sent to a device such as a visual display device, it can be determined that the video will be consumed by a human (e.g. by the human watching the video on the visual display device). On the other hand, if the encoded data stream is to be sent to a server or processing system, then it can be determined that the video will be consumed by a machine (e.g. by the machine performing machine tasks on the video). Therefore, the determination may be made on the basis of a destination of the encoded data stream. Consider, now, an example situation whereby embodiments of the disclosure are applied to an automotive camera. The automotive camera may be used as part of a vision system for a vehicle (e.g. as part of an autonomous vehicle, for example). In this example situation, the automotive camera may perform video processing in order to encode the image data it acquires. Then, this encoded data stream may be transmitted (or otherwise sent) to a host computer of the vehicle. Since the data is encoded before it is sent to the host computer of the vehicle, it is possible to limit or reduce the amount of data which has to be sent to the host computer. The host computer may then decode the data which has been received and perform a machine task on this data. Furthermore, since the data for the host computer has been prepared for machine processing, improved performance can be achieved when the coded video data is used for machine tasks

[0104] In some examples, the determination may further include a determination as to whether one or more constraints apply to the block of image data. If one or more constraints apply to the block of image data, then the encoding apparatus may determine not to selectively encode the flag even when an encoded data stream corresponding to the block of image data will be used for machine processing. In examples, the constraint may include that a block of image data corresponds to a masked portion of an image.

[0105] When image data is for machine processing - and not for human consumption - a determination may be made to apply a mask to a certain region of the image, if that image does not contain any information which is necessary for a task to be performed by the machine. This can improve the performance of the machine processing task and reduce the amount of data which has to be coded. In examples, if a block of image data corresponds to a masked portion of an image, then it may be determined that certain optimizations for machine processing (including conversion) should not be applied to that image block and as such, the encoding apparatus may determine not to selectively encode the flag even when an encoded data stream corresponding to the block of image data will be used for machine processing.

[0106] The determination can be made on a block by block basis (enabling conversion of, or changes to, the chroma format on a block by block basis). In this situation, the flag can be selectively set individually for each image block. This further improves the optimizations which can be performed. More generally, in examples, a Rol may be determined for a current frame and a determination may be made to convert the format of the Rol by resampling of luma and / or chroma when it is determined that the Rol should be prepared for machine processing.

[0107] In accordance with the present disclosure, the flag can be used in order to indicate to the decoding process (described in more detail later) whether certain adaptations and optimizations have been performed when encoding the video data (such that the video data is optimized for machine processing).

[0108] In examples, the flag may include a binary flag. For example, by selectively encoding the value of the flag to equal 1 , the encoding process may signal that the optimizations for machine processing have been performed. On the other hand, by setting the value of the flag equal to 0, the encoding process may signal that the optimizations for machine processing have not been performed. In examples, the presence of the flag itself may be used in order to indicate whether or not the optimizations for machine processing have been performed. For example, if the flag is not present, then it can be determined that the optimizations for machine vision have not been performed.

[0109] In examples, the flag may also be used in order to indicate a type of optimization which has been performed. For example, the flag may indicate a conversion process applied to the block of image data. Different types of conversion processes which are applied to the image data are described in more detail later. However, it will be appreciated that the flag may indicate the manner by which the block of image data has been converted to the 4:4:4 format by the encoder, for example.

[0110] Thus, according to embodiments of the disclosure, a data encoding method is provided, the method comprising the steps of acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a 4:4:4 format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream.

[0111] Conversion

[0112] As noted with reference to Figure 9 of the present disclosure, in examples the method comprises converting the block of image data to a 4:4:4 format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream. Consider, now, Figure 10 of the present disclosure. Figure 10 schematically illustrates chroma subsampling.

[0113] The top panel of Figure 10 illustrates a typical 4:2:2 chroma subsampling format. In this 4:2:2 chroma format, the two chroma components are sampled at half the horizontal sample rate of luma; this means that the horizontal chroma resolution is halved. Owing to certain peculiarities and limitations of human vision, a reduction in the resolution of the chroma component can provide an efficient way of optimizing video when the video is for human consumption; human vision is more sensitive to changes in brightness than in colour. However, as has been explained, machine vision is not subject to these same limitations as human vision. Therefore, video for machine consumption is better optimized when the video is in a 4:4:4 format.

[0114] There are two options when converting data of a 4:2:2 chroma subsampling format to a 4:4:4 format. The first of these is to downscale the resolution of the luma component such that it matches the resolution of the chroma component. The other is to upscale the resolution of the chroma component such that it matches the resolution of the chroma component. Both of these options provide data having the same sampling rate (and resolution) across the luma and chroma components and thus both of these options result in data having a 4:4:4 format. However, the resolution of the resultant image will be different in each case.

[0115] Take the second panel of Figure 10 of the present disclosure as an example. In this situation, source data of a 4:2:2 format (such as the data shown in the first panel of Figure 10) has been converted to data having a 4:4:4 format by conversion. In particular, in this example, the conversion process which has been applied comprises downsampling a luma component of the video data to match a resolution of a chroma component of the video data.

[0116] As can be seen in the second panel of Figure 10, the luma and chroma component after conversion have the same resolution. Accordingly, the data is in a 4:4:4 format. However, the resolution of the image has been reduced, since the luma component has been downsampled to the resolution of the chroma component. If, for example, the source video was 1920x1080 4:2:2 data then, after conversion, the resultant data may be 960x540 4:4:4 data. Therefore, reducing the resolution of the luma component to match the resolution of the chroma component (by downsampling the luma component) will reduce the resolution of the image.

[0117] On the other hand, an option is to convert the source data to a 4:4:4 format by upsampling the chroma component. Take the third panel of Figure 10 as an example. Here, the source image having a 4:2:2 format (as illustrated in Figure 10) is converted to the 4:4:4 format by upsampling of the chroma component such that the resolution of the chroma component matches the resolution of the luma component of the video data. As can be seen in the third panel of Figure 10, the luma and chroma component after conversion have the same resolution. Accordingly, the data is in a 4:4:4 format. However, the resolution of the image has been maintained at the level of the luma component of the image. In particular, it will be appreciated that upsampling chroma will generally increase bit-rates (unless the resolution of the image is subsequently reduced after conversion). If, for example, the source video was 1920x1080 4:2:2 data then, after conversion, the resultant data may be 1920x1080 4:4:4 data.

[0118] The example conversion processes described with reference to Figure 10 of the present disclosure have been described in an example situation whereby the source data has a 4:2:2 format. However, it will be appreciated that the present disclosure is not particularly limited in this regard. More generally, the source data may have any format including, for example, a 4:2:2 data format or a 4:0:0 data format.

[0119] As has been explained, coding in the 4:4:4 format can give a benefit of improved performance when decoded video data is used for machine tasks in accordance with embodiments of the disclosure. Indeed, coding in the 4:4:4 format can give a benefit in terms of BD-rate when decoded video data is used for machine tasks. In this context, the BD-rate is a rate based on bit rate and task performance. Task performance reflects how well a machine can perform a given task using the coded video content. For example, in the context of object detection, task performance indicates how well a machine can correctly identify an object in the coded video content.

[0120] Therefore, embodiments of the disclosure comprise selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing and converting the block of image data to a 4:4:4 format on the basis of the flag. In examples, the conversion can comprise downsampling the luma component of the image block (block of image data). In examples, the conversion can comprise upsampling the chorma component of the image block (block of image data).

[0121] While the above described example has been described with reference to a situation of converting to a 4:4:4 format, it will be appreciated that the present disclosure is not particularly limited in this regard. Indeed, in examples, a data encoding method may be provided, the method comprising the steps of: acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a new format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream.

[0122] The new format is a format other than the current format of the block of image data. In examples, as has been explained, this new format may be a 4:4:4 format. However, in other examples, the new format may be a 4:2:2 format. As an example, the data may currently be of a 4:2:0 format. In this case, the embodiments of the disclosure may be used in order to convert the data to a 4:2:2 format when it is determined that the block of image data should be prepared for machine processing. In other words, more generally, embodiments of the disclosure can be used in order to selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing and convert the block of image data to a new format on the basis of the flag, wherein the new format is a format other than the current format of the block of image data and is a format which is particularly suited for machine processing.

[0123] Encoding

[0124] As explained with reference to Figure 9 of the present disclosure, once the block of image data has been converted, the method comprises encoding the converted block of image data in order to generate the encoded data stream.

[0125] It has been shown that coding in reduced resolution can give a benefit in terms of BD- rate in the context of machine consumption of coded video content. Again, in this context, the BD-rate is a rate based on bit rate and task performance. Task performance reflects how well a machine can perform a given task using the coded video content. For example, in the context of object detection, task performance indicates how well a machine can correctly identify an object in the coded video content.

[0126] Therefore, when the flag is selectively encoded (when the encoded data stream corresponding to the block of image data should be prepared for machine processing) the block of image data should be encoded at reduced resolution in order to further improve coding performance (that is, in order to achieve further improvements in the BD-rate).

[0127] However, in the present disclosure, the type of encoding process applied may also depend upon the conversion process which has been applied in order to convert the data to the 4:4:4 format. That is, in examples, the resolution of the block of image data may have already been reduced by the conversion process which has been performed on the block of image data. In these examples, a further reduction of the resolution of the image may not necessarily provide any further optimization of the BD-rate in the context of machine consumption of the coded video.

[0128] Consider, now, Figure 11 of the present disclosure. Figure 11 schematically illustrates a conversion process in accordance with embodiments of the disclosure.

[0129] In this example, the source image data which is received (i.e. the block of image data to be encoded) is image data having a 4:2:2 data format. However, the block of image data may also be an image having an alternative format such as a 4:2:0 data format, for example.

[0130] In this example, the encoding method comprises selectively encoding a flag when the encoded data stream corresponding to the block of image data should be prepared for machine processing and converting the block of image data to a 4:4:4 format on the basis of the flag. More specifically, converting the video data to 4:4:4 format comprises downsampling a luma component of the video data to match a resolution of a chroma component of the video data.

[0131] As the conversion process to convert the resolution of the video data to the 4:4:4 format comprises downsampling the luma component of the video data, the resolution of the block of image data is reduced by the conversion process (as has been described with reference to Figure 10 of the present disclosure).

[0132] Therefore, a further reduction of the resolution is not required during the encoding process in order to achieve improvements in the BD-rate. Rather, the encoding process may be performed without any further reduction of the resolution in order to generate the encoded data stream.

[0133] In examples, the encoding may be performed by an entropy encoder such as that which has been described with reference to the video or image data compression and decompression apparatus as described with reference to Figure 7.

[0134] Consider, now, Figure 12 of the present disclosure. Figure 12 schematically illustrates a conversion process in accordance with embodiments of the disclosure.

[0135] In this example, similar to Figure 11 of the present disclosure, the source image data which is received (i.e. the block of image data to be encoded) is image data having a 4:2:2 data format. Again, it will be appreciated that the present disclosure is not particularly limited in this regard and the block of image data may also be an image having an alternative format such as a 4:2:0 data format, for example.

[0136] In this example, the encoding method comprises selectively encoding a flag when the encoded data stream corresponding to the block of image data should be prepared for machine processing and converting the block of image data to a 4:4:4 format on the basis of the flag. More specifically, the method comprises converting the video data to 4:4:4 format comprises upsampling a chroma component of the video data to match a resolution of a luma component of the video data.

[0137] As the conversion process has not reduced the resolution of the image block, a further adaption of the encoding process should be performed in order to encode the image block with reduced resolution and achieve further improvements in the BD-rate.

[0138] In examples, the encoding process may be a lossy encoding in order to reduce the resolution of the coded data. Converting the block of image data to 4:4:4 before lossy encoding preserves more chorma details in the coded data.

[0139] The Versatile Video Coding standard has a feature referred to as reference picture resampling (RPR). RPR allows coding of certain frames at lower resolution. It is known from JVET-AH0130 that RPR can be used in order to code with reduced resolution and improve coding efficiency for machine consumption of decoded video.

[0140] In examples, RPR can be used in for coding frames at lower resolution with rescaling factors of 1.24x, 1.5x and 2. Ox, for example.

[0141] Accordingly, when the conversion process which is applied converts the data to the 4:4:4 format by upscaling the chroma component to match the resolution of the luma component, the encoding process may comprise an encoding process such as a reference picture resampling encoding process in order to encode the data with reduced resolution.

[0142] The value of the flag when selectively encoding the flag may be set accordingly in order to indicate to the decoding process the conversion process - and thus also the encoding process - which has been performed on the image block (the block of image data).

[0143] In examples, the flag may include a 2-bit flag indicating that a conversion has taken place and, furthermore, indicating what conversion has taken place (e.g. a luma downsample or a chroma upsample). In examples, the flag may include a 1-bit flag to indicate that a conversion has taken place (e.g. to a 4:4:4 format). Then, in examples, the method may comprise inferring from one or more other flags the type of conversion which has taken place (e.g. a luma downsample or a chroma upsample). In examples, the one or more other flags which can be used to infer the type of conversion which has taken place can include one or more flags related to the RPR. In examples, at least one of the required output format or the encoded format may be signalled to the decoder side. The decoder side may then determine that a conversion has taken place and the type of conversion which must be applied in order to reconstruct the image block.

[0144] As explained, improvements in the BD-rate can be obtained by coding the image block with reduced resolution when the decoded data will be used for machine processing. However, in addition, converting the data to the 4:4:4 data format prior to lossy encoding provides further improvements in the BD-rate when the decoded data will be used for machine processing. In particular, it is understood that converting to 4:4:4 before lossy encoding preserves more chroma details in the coded data which may be particularly advantageous for machine processing tasks. This is in contrast to coded video for human consumption, where human vision is more sensitive to luma.

[0145] Taking object detection as an example of a machine processing task, improvements in BD-rate can be observed across a range of testing samples when converting the data to 4:4:4. These improvements are achieved for both a situation of resolution reduction through the conversion process and resolution reduction through the encoding process (e.g. using RPR downsamling, for example). Moreover, these improvements are achieved above and beyond any improvement that can be achieved by merely encoding the video at reduced resolution (i.e. without a conversion process). That is, the conversion to 4:4:4 data itself leads to an improvement in the BD-rate, compared to - say - encoding 4:2:2 data at a lower resolution.

[0146] Accordingly, with the encoding process of the present disclosure, improved performance can be achieved when decoded video data is used for machine tasks in accordance with embodiments of the disclosure.

[0147] Encoding Apparatus

[0148] Consider, now, Figure 13 of the present disclosure. Figure 13 schematically illustrates an example data encoding apparatus.

[0149] The data encoding apparatus 1300 of Figure 13 comprises an acquiring unit 1302, a flag setting unit 1304, a converting unit 1306 and an encoding unit 1308.

[0150] The acquiring unit 1302 is configured to acquire a block of image data to be encoded.

[0151] The flag setting unit 1304 is configured to selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing.

[0152] The converting unit 1306 is configured to convert the block of image data to a 4:4:4 format on the basis of the flag.

[0153] Finally, the encoding unit 1308 is configured to encode the converted block of image data in order to generate the encoded data stream.

[0154] In examples, the data encoding apparatus 1300 may be a part of a video or image data compression and decompression apparatus as described with reference to Figure 7 of the present disclosure. In examples, the data encoding apparatus 1300 may be part of a video data capture, transmission, display and / or storage apparatus.

[0155] While the apparatus of Figure 13 of the present disclosure has been described as comprising a number of discrete units (namely, the acquiring unit 1302, the flag setting unit 1304, the converting unit 1306 and the encoding unit 1308) it will be appreciated that the present disclosure is not particularly limited in this regard. One or more of these discrete units of the data encoding apparatus may be combined as a single unit. On the other hand, a number of additional units not shown in Figure 13 may also be provided. More generally, the data encoding apparatus may comprise circuitry configured to perform the functions of the acquiring unit, the flag setting unit, the converting unit and the encoding unit.

[0156] Example Method

[0157] Consider, now, Figure 14 of the present disclosure. Figure 14 of the present disclosure illustrates an example decoding method. The example decoding method of Figure 14 may be used to decode data which has been encoded according to the encoding method of Figure 9 of the present disclosure, for example.

[0158] The example decoding method of Figure 14 starts at step S1400 and proceeds to step S1402. In step S1402, the method comprises acquiring an encoded data stream.

[0159] Then, in step S1404, the method comprises decoding the encoded data stream to generate a block of image data and, in step S1406, the method comprises converting the block of image data from a 4:4:4 format based on a flag in the encoded data stream. The flag indicates whether the encoded data stream has been prepared for machine processing by the encoder.

[0160] The method then proceeds to, and ends with, step S1408.

[0161] Accordingly, in the example method of Figure 14 of the present disclosure, a flag in the encoded data stream acquired by the decoder is used by the decoder in order to identify that the encoded data stream has been prepared for machine processing by the encoder. For example, the flag can be used, by the decoder, in order to identify that one or more certain processes have been applied to on the encoder side when encoding the block of image data.

[0162] For example, the flag may be used in order to indicate that a certain conversion or encoding process has been applied when encoding the video data. A corresponding process may then be required by the decoder in order to reconstruct the image block from the encoded data stream.

[0163] Consider, now, Figure 15 of the present disclosure. Figure 15 schematically illustrates a conversion process.

[0164] In this example, the decoder acquires an encoded data stream. The decoder then determines, based on a flag in the encoded data stream, whether the encoded data stream has been prepared for machine processing. In particular, in this example, the decoder can use the flag in order to determine a conversion and type of encoding which has been applied by the encoder when coding the encoded data stream.

[0165] In this example, the flag indicates that the image block corresponding to the encoded data stream has been converted to 4:4:4 data by donwsampling the luma component of the image prior to encoding. Accordingly, the decoder applies a decoding process to the encoded data stream to generate a block of image data having 4:4:4 data. Furthermore, a conversion is then applied to the data by the decoder. As the encoder applied a conversion to downsample the luma component to 4:4:4 data, the decoder applies a corresponding conversion process to upsample the luma component and return the image block to its source format (here, 4:2:2). Thus, the decoder adaptively changes the decoding process of the encoded data stream received from the encoder based on the flag which has been selectively encoded by the encoder. This enables the decoder to adapt to different encoding conditions such that certain optimizations can be made in the coding of data for machine consumption.

[0166] Consider, now, Figure 16 of the present disclosure. Figure 16 schematically illustrates a conversion process. In this example, the decoder acquires an encoded data stream. The decoder then determines, based on a flag in the encoded data stream, whether the encoded data stream has been prepared for machine processing. In particular, in this example, the decoder can use the flag in order to determine a conversion and type of encoding which has been applied by the encoder when coding the encoded data stream.

[0167] Indeed, in this example, the flag indicates that the image block corresponding to the encoded data stream has been converted to 4:4:4 data by upsampling the chroma component prior to encoding. Furthermore, as the conversion has been applied by upsampling of the chroma component, the flag may further indicate that the encoding process which has been applied has been made in order to reduce the resolution of the image data (using a reference picture resampling, for example). Thus, the decoder applies a decoding process to the encoded data stream to generate a block of image data having 4:4:4 data (here, the decoding process is a reference picture resampling decoding process). Then, a conversion process comprising downsampling of the chroma component is then applied by the decoder to return the image block to its source format (here, 4:2:2). Thus, the decoder adaptively changes the decoding process of the encoded data stream received from the encoder based on the flag which has been selectively encoded by the encoder. This enables the decoder to adapt to different encoding conditions such that certain optimizations can be made in the coding of data for machine consumption. Improvements in the coding performance (including improvements in the BD-rate) can therefore be achieved.

[0168] While the embodiments of the disclosure have been described with reference to an example situation that the encoded stream has been converted to 4:4:4 data (such that a conversion process has to be applied to this 4:4:4 data, by the decoder, in order to return the image block to its source format) it will be appreciated that the present disclosure is not particularly limited in this regard. In examples, the encoder may have converted the data to a so-called new format (being a format other than the source format) when it is determined that the image block should be prepared for machine processing. In examples, this new format may be a 4:2:2 format (e.g. in the case of converting from a 4:2:0 format to a 4:2:2 format). Accordingly, more generally, a data decoding method, the method comprising the steps of: acquiring an encoded data stream; decoding the encoded data stream to generate a block of image data and converting the block of image data from a new format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0169] Decoding Apparatus

[0170] Consider, now, Figure 17 of the present disclosure. Figure 17 schematically illustrates an example data decoding apparatus. The data decoding apparatus 1700 of Figure 17 comprises an acquiring unit 1702, a decoding unit 1704 and a converting unit 1706.

[0171] The acquiring unit 1702 is configured to acquire an encoded data stream. The encoded data stream may be an encoded data stream which has been produced by an encoding apparatus such as that described with reference to Figure 13 of the present disclosure, for example.

[0172] The decoding unit 1704 is configured to decode the encoded stream to generate a block of image data.

[0173] The converting unit 1704 is configured to convert the block of image data from a 4:4:4 format. The decoding unit 1704 and the converting unit 1706 may be configured to operate based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0174] In examples, the data decoding apparatus 1700 may be a part of a video or image data compression and decompression apparatus as described with reference to Figure 7 of the present disclosure. In examples, the data decoding apparatus 1700 may be a part of a video data capture, transmission, display and / or storage apparatus.

[0175] While the apparatus of Figure 17 of the present disclosure has been described as comprising a number of discrete units (namely, the acquiring unit 1702, the decoding unit 1704 and the converting unit 1706) it will be appreciated that the present disclosure is not particularly limited in this regard. One or more of these discrete units of the data decoding apparatus may be combined as a single unit. On the other hand, a number of additional units not shown in Figure 17 may also be provided. More generally, the data decoding apparatus may comprise circuitry configured to perform the functions of the acquiring unit 1702, the decoding unit 1704 and the converting unit 1706).

[0176] Example Situation

[0177] The embodiments of the disclosure can be applied to a number of different situations. For example, embodiments of the disclosure can be applied to computer-vision systems, security systems or the like.

[0178] One example of a computer-vision system includes a computer-vision system used in a vehicle.

[0179] In recent years, there has been a rapid increase in the use of computer-vision systems for vehicles. This includes computer-vision systems used inside a vehicle (e.g. to sense a state within the vehicle (such as an occupancy level)) and computer-vision systems used outside the vehicle (e.g. to sense an environment outside the vehicle (such as a proximity of another vehicle)). Computer-vision systems may be used as part of autonomous, or semi- autonomous, vehicle control. Within such a computer-vision system, there may be a requirement to transfer video content between devices. Accordingly, efficient coding of video content is desired.

[0180] Consider the example of Figure 18 of the present disclosure. Figure 18 schematically illustrates an example situation. This situation is a situation where a computer vision system is used in the context of autonomous (or semi-autonomous) vehicle control.

[0181] In this example situation, a vehicle 1800 is travelling along a road 1802. The vehicle may be a vehicle such as a car. In this example, the car contains a computer vision system. The computer vision system of the car is provided in order to assist a driver of the vehicle in driving the car. Accordingly, in this example, the car is a semi-autonomous vehicle (where a driver is assisted, at least in part, in the control of the vehicle).

[0182] The car is following the road along a path P. However, from a current position of the car, it is not possible for an imaging device present on the car to obtain a clear image of the road ahead. That is, in this example, because of the curved nature of the road, it is not possible for an imaging device on the car to obtain a clear view of the road ahead (as the road ahead is obscured behind a bend in the road).

[0183] This may limit the effectiveness of the computer-vision system of the car and its ability to assist the driver in control of the car.

[0184] Accordingly, in this example, an additional external imaging device 1804 is provided. The external imaging device 1804 is provided, in this example, as part of a control tower. The control tower is located such that it can obtain an image of road after the bend. This means that the control tower can obtain a view of a portion of the road ahead which is not visible for oncoming vehicles (such as the car 1800).

[0185] The control tower may be communicatively coupled with the car. Accordingly, the control tower is able to transmit image data (including video data) to the car. The computervision system of the car 1800 can then use the image data received from the control tower in addition to the image data received from its own imaging device.

[0186] It will be appreciated that efficient transfer of the image data from the external imaging device 1804 of the control tower to the car 1800 is desired, in order that the image data from the external imaging device can be processed by the computer-vision system of the car 1800 to provide assistance to the driver of the car (e.g. to warn the driver of an oncoming vehicle which is obscured behind the bend in the road, for example).

[0187] Accordingly, each of the control tower and the car may include a data encoding and decoding apparatus as described with embodiments of the present disclosure. As the image data from the control tower will be used by the computer vision of the car, the control tower may selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; convert the block of image data to a 4:4:4 format on the basis of the flag; and encode the converted block of image data in order to generate the encoded data stream. In this way, the control tower may optimize the coding of the video content in order to improve coding performance when decoded video data is used by the computer-vision system of the car.

[0188] The example of Figure 18 describes one example situation to which the embodiments of the present disclosure can be applied. However, it will be appreciated that this is merely one such example situation to which the embodiments can be applied. More generally, embodiments of the disclosure can be applied to any situation whereby coded video data will be used for machine consumption tasks.

[0189] In addition, embodiments of the present disclosure are defined in accordance with the following numbered clauses:

[0190] 1) A data encoding method, the method comprising the steps of: acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a 4:4:4 format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream.

[0191] 2) The data encoding method according to clause 1 , wherein the flag indicates a conversion process applied to the block of image data.

[0192] 3) The data encoding method according to clause 1 or 2, wherein converting the video data to 4:4:4 format comprises downsampling a luma component of the video data to match a resolution of a chroma component of the video data.

[0193] 4) The data encoding method according to clause 1 or 2, wherein converting the video data to 4:4:4 format comprises upsampling a chroma component of the video data to match a resolution of a luma component of the video data.

[0194] 5) The data encoding method according to clause 4, wherein the encoding comprises a reference picture resampling encoding process.

[0195] 6) The data encoding method according to any preceding clause, wherein the block of image data corresponds to a transform unit, a coding unit, a prediction unit, a slice or a picture.

[0196] 7) The data encoding method according to any preceding clause, wherein the method comprises selectively encoding the flag based on a determination that the encoded image data will be processed for machine tasks. 8) The data encoding method according to clause 7, wherein the determination is made based on indication information received from an external device.

[0197] 9) The data encoding method according to clause 7 or 8, wherein, the determination that the encoded image data will be processed for machine tasks is made on a basis of a source or a destination of the image data.

[0198] 10) The data encoding method according any of clauses 7 to 9, wherein the determination further includes a determination as to whether one or more constraints apply to the block of image data.

[0199] 11) The data encoding method according to clause 10, wherein the constraint includes a constraint that the block of image data corresponds to a masked portion of an image.

[0200] 12) The data encoding method according to any preceding clause, wherein the machine processing includes at least one of object detection processing or object tracking processing.

[0201] 13) A data encoding apparatus, the apparatus comprising circuitry configured to: acquire a block of image data to be encoded; selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; convert the block of image data to a 4:4:4 format on the basis of the flag; and encode the converted block of image data in order to generate the encoded data stream.

[0202] 14) A data decoding method, the method comprising the steps of: acquiring an encoded data stream; decoding the encoded data stream to generate a block of image data and converting the block of image data from a 4:4:4 format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0203] 15) The data decoding method according to clause 14, wherein the flag indicates a conversion process applied to the block of image data during encoding.

[0204] 16) The data decoding method according to clause 14 or 15, wherein converting the video data from a 4:4:4 format comprises upsampling a luma component of the video data. 17) The data decoding method according to clause 14 or 15, wherein converting the video data from a 4:4:4 format comprises downsampling a chroma component of the video data.

[0205] 18) The data decoding method according to clause 17, wherein the decoding comprises a reference picture resampling decoding.

[0206] 19) The data decoding method according to any of clauses 14 to 18, wherein the block of image data corresponds to a transform unit, a coding unit, a prediction unit, a slice or a picture.

[0207] 20) The data decoding method according to any of clauses 14 to 18, wherein the machine processing includes at least one of object detection processing or object tracking processing.

[0208] 21) A data decoding apparatus, the apparatus comprising circuitry configured to: acquiring an encoded data stream; decode the encoded data stream to generate a block of image data and converting the block of image data from a 4:4:4 format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0209] 22) An encoded data stream encoded by the data encoding method of any of clauses 1 to 12 or the data encoding apparatus of clause 13.

[0210] 23) Computer software which, when implemented by a computer, causes the computer to perform the data encoding method of any of clauses 1 to 12 or the data decoding method of any of clauses 14 to 20.

[0211] 24) A non-transitory computer readable storage medium which stores the computer software of clause 23.

[0212] 25) Video data capture, transmission, display and / or storage apparatus comprising the data encoding apparatus of clause 13 or the data decoding apparatus of clause 21 .

[0213] 26) A data encoding method, the method comprising the steps of: acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a new format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream.

[0214] 27) A data encoding apparatus, the apparatus comprising circuitry configured to: acquire a block of image data to be encoded; selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; convert the block of image data to a new format on the basis of the flag; and encode the converted block of image data in order to generate the encoded data stream.

[0215] 28) A data decoding method, the method comprising the steps of: acquiring an encoded data stream; decoding the encoded data stream to generate a block of image data and converting the block of image data from a new format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0216] 29) A data decoding apparatus, the apparatus comprising circuitry configured to: acquiring an encoded data stream; decode the encoded data stream to generate a block of image data and converting the block of image data from a new format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

[0217] 30) The method of clause 26 or 28, or the apparatus of clause 27 or 29, wherein the new format is a 4:2:2 format.

[0218] 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.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] Furthermore, in the present disclosure, the wording “in dependence upon” defines a relationship by which one value or parameter can be calculated from another value or parameter. That is, “A is calculated in dependence upon B” means that the value of B wholly or in part, directly or indirectly, contributes to a determination or calculation of A. Thus, when A is calculated in dependence upon B, A is at least in part based on a value of B or a value associated with B. Thus, the wording “in dependence upon” and “based on” may be used interchangeable within the present disclosure.

Claims

CLAIMS1. A data encoding method, the method comprising the steps of: acquiring a block of image data to be encoded; selectively encoding a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; converting the block of image data to a 4:4:4 format on the basis of the flag; and encoding the converted block of image data in order to generate the encoded data stream.

2. The data encoding method according to claim 1 , wherein the flag indicates a conversion process applied to the block of image data.

3. The data encoding method according to claim 1 , wherein converting the video data to 4:4:4 format comprises downsampling a luma component of the video data to match a resolution of a chroma component of the video data.

4. The data encoding method according to claim 1 , wherein converting the video data to 4:4:4 format comprises upsampling a chroma component of the video data to match a resolution of a luma component of the video data.

5. The data encoding method according to claim 4, wherein the encoding comprises a reference picture resampling encoding process.

6. The data encoding method according to claim 1, wherein the block of image data corresponds to a transform unit, a coding unit, a prediction unit, a slice or a picture.

7. The data encoding method according to claim 1 , wherein the method comprises selectively encoding the flag based on a determination that the encoded image data will be processed for machine tasks.

8. The data encoding method according to claim 7, wherein the determination is made based on indication information received from an external device.

9. The data encoding method according to claim 7, wherein, the determination that the encoded image data will be processed for machine tasks is made on a basis of a source or a destination of the image data.

10. The data encoding method according to claim 8, wherein the determination further includes a determination as to whether one or more constraints apply to the block of image data.

11. The data encoding method according to claim 10, wherein the constraint includes a constraint that the block of image data corresponds to a masked portion of an image.

12. The data encoding method according to claim 1, wherein the machine processing includes at least one of object detection processing or object tracking processing.

13. A data encoding apparatus, the apparatus comprising circuitry configured to: acquire a block of image data to be encoded; selectively encode a flag when an encoded data stream corresponding to the block of image data should be prepared for machine processing; convert the block of image data to a 4:4:4 format on the basis of the flag; and encode the converted block of image data in order to generate the encoded data stream.

14. A data decoding method, the method comprising the steps of: acquiring an encoded data stream; decoding the encoded data stream to generate a block of image data and converting the block of image data from a 4:4:4 format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

15. The data decoding method according to claim 14, wherein the flag indicates a conversion process applied to the block of image data during encoding.

16. The data decoding method according to claim 14, wherein converting the video data from a 4:4:4 format comprises upsampling a luma component of the video data.

17. The data decoding method according to claim 14, wherein converting the video data from a 4:4:4 format comprises downsampling a chroma component of the video data.

18. The data decoding method according to claim 17, wherein the decoding comprises a reference picture resampling decoding.

19. The data decoding method according to claim 14, wherein the block of image data corresponds to a transform unit, a coding unit, a prediction unit, a slice or a picture.

20. The data decoding method according to claim 14, wherein the machine processing includes at least one of object detection processing or object tracking processing.

21. A data decoding apparatus, the apparatus comprising circuitry configured to: acquiring an encoded data stream; decode the encoded data stream to generate a block of image data and converting the block of image data from a 4:4:4 format based on a flag in the encoded data stream, the flag indicating whether the encoded data stream has been prepared for machine processing.

22. An encoded data stream encoded by the data encoding method of claim 1 or the data encoding apparatus of claim 13.

23. Computer software which, when implemented by a computer, causes the computer to perform the data encoding method claim 1 or the data decoding method of claim 14.

24. A non-transitory computer readable storage medium which stores the computer software of claim 23.

25. Video data capture, transmission, display and / or storage apparatus comprising the data encoding apparatus of claim 13 or the data decoding apparatus of claim 21 .

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