Determining regions when performing intra block copying

In general, techniques are described for performing an intra block copying process to code video data. A video decoding device that includes a memory and one or more processors may perform the techniques. The memory may be configured to store a current block of a picture. The processors may be configured to perform an intra block copying process to decode the current block using a prediction block that is from a same slice or a same tile as that in which the coded current block resides, the prediction block restricted to be within a search region that only includes the same slice or the same tile as that in which the coded current block resides.

TECHNICAL FIELD

This disclosure relates to video coding, and more particularly to techniques for predicting video data.

BACKGROUND

Video compression techniques include spatial prediction and/or temporal prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video picture or slice may be partitioned into blocks. Each block can be further partitioned. Blocks in an intra-coded (I) picture or slice are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture or slice. Blocks in an inter-coded (P or B) picture or slice may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or slice or temporal prediction with respect to reference samples in other reference pictures. Spatial or temporal prediction results in a predictive block for a block to be coded. Residual data represents pixel differences between the original block to be coded and the predictive block.

An inter-coded block is encoded according to an offset vector that points to a block of reference samples forming the predictive block, and the residual data indicating the difference between the coded block and the predictive block. An intra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain, resulting in residual transform coefficients, which then may be quantized.

SUMMARY

Techniques of this disclosure generally relate to searching techniques in a video coding process and, more specifically, to searching techniques used for an intra-block copying operation of the video coding process.

In one aspect, a method of decoding video data comprises performing an intra block copying process to decode a current block of a picture using a prediction block that is from a same slice or a same tile as that in which the coded current block resides, the prediction block restricted to be within a search region that only includes the same slice or the same tile as that in which the coded current block resides.

In another aspect, a method of encoding video data comprises performing an intra block copying process to code a current block of a picture such that pixels from a different slice or a different tile than that in which the current block resides are not included in a search region used in the intra block copying process.

In another aspect, a video decoding device comprises a memory configured to store a current block of a picture, and one or more processors configured to perform an intra block copying process to decode the current block using a prediction block that is from a same slice or a same tile as that in which the coded current block resides, the prediction block restricted to be within a search region that only includes the same slice or the same tile as that in which the coded current block resides.

In another aspect, a video encoding device comprises a memory configured to store a current block of a picture, and one or more processors configured to perform an intra block copying process to encode the current block such that pixels from a different slice or a different tile than that in which the current block resides are not included in a region used when performing the intra block copying process.

In another aspect, a method of encoding video data comprises performing an intra block copying process with respect to a current block of a picture such that pixels from a different slice or different tile than that in which the current block resides are not used when performing the intra block copying process, and encoding the current block after performing the intra block copying process.

In another aspect, a device comprises one or more processors configured to perform an intra block copying process with respect to a current block of a picture such that pixels from a different slice or different tile than that in which the current block resides are not used when performing the intra block copying process, and encode the current block after performing the intra block copying process.

In another aspect, a device comprises means for performing an intra block copying process with respect to a current block of a picture such that pixels from a different slice or different tile than that in which the current block resides are not used when performing the intra block copying process, and means for encoding the current block after performing the intra block copying process.

In another aspect, a method comprises determining a region of a picture when performing an intra block copying process for a current block of the picture, restricting a size of a offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture, identifying the prediction block within the determined region based on the restricted size of the offset vector, and coding the current block based on the identified prediction block.

In another aspect, a device comprises one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture, restrict a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture, identify the prediction block within the determined region based on the restricted size of the offset vector, and code the current block based on the identified prediction block.

In another aspect, a device comprises means for determining a region of a picture when performing an intra block copying process for a current block of the picture, means for restricting a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture, means for identifying the prediction block within the determined region based on the restricted size of the offset vector, and means for coding the current block based on the identified prediction block.

In another aspect, a non-transitory computer-readable storage medium has stored thereon instruction that, when executed, cause one or more processors to determine a region of a picture when performing an intra block copying process for a current block of the picture, restrict a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture, identify the prediction block within the determined region based on the restricted size of the offset vector, and code the current block based on the identified prediction block.

In another aspect, a method comprises determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture, identifying a prediction block within the determined region, and coding the current block based on the identified prediction block.

In another aspect, a device comprises one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

In another aspect, a device comprises means for determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture, means for identifying a prediction block within the determined region, and means for coding the current block based on the identified prediction block.

In another aspect, a non-transitory computer-readable storage medium having stored thereon instruction that, when executed, cause one or more processors to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

In another aspect, a method comprises determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture, identify a prediction block within the determined region, and coding the current block based on the identified prediction block.

In another aspect, a device comprises one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

In another aspect, a device comprises means for determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture, means for identifying a prediction block within the determined region, and means for coding the current block based on the identified prediction block.

In another aspect, a non-transitory computer-readable storage medium has stored thereon instruction that, when executed, cause one or more processors to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

In another aspect, a method comprises determining one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and decoding the encoded version of the current block of the picture based on the one or more syntax elements.

In another aspect, a device comprises one or more processors configured to determine one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and decode the encoded version of the current block of the picture based on the one or more syntax elements.

In another aspect, a device comprises means for determining one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and means for decoding the encoded version of the current block of the picture based on the one or more syntax elements.

In another aspect, a non-transitory computer-readable storage medium has stored thereon instructions that, when executed, cause one or more processors to determine one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and decode the encoded version of the current block of the picture based on the one or more syntax elements.

DETAILED DESCRIPTION

Aspects of this disclosure generally relate to video coding and compression. In some examples, the techniques may be related to a High Efficiency Video Coding (HEVC) Range Extension, in which color spaces other than YCbCr 4:2:0 may be supported. The techniques may also relate to an HEVC screen contents coding extension to HEVC. More information for the screen contents coding extension of HEVC can be found in the document of the Visual Coding group of ITU-T Q6/16 and ISO/IEC/JTC1/SC29/WG11, entitled “Joint Call for Proposals for Coding of Screen Content,” presented in the 17 Jan. 2014 meeting at San Jose, Calif. and available at: http://www.itu.int/en/ITU-T/studygroups/com16/video/Documents/CfP-HEVC-coding-screen-content.pdf.

HEVC is a video coding standard that was recently developed by the Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T WP3/16 and ISO/IEC JTC 1/SC 29/WG 11. The Range Extension of HEVC includes extending video coding for color spaces other than YCbCr 4:2:0, such as YCbCr 4:2:2, YCbCr 4:4:4, and RGB.

For example, the luma and chroma components of pixels in a coding unit (CU) or transform unit (TU) may be coded in different sub-sampling formats. In an example, the luma and chroma components of a pixel may be coded in a 4:2:0 format. In a 4:2:0 pixel format, for every 2×2 block of pixels, there are four luma components and 2 chroma components (e.g., 1 Cr chroma component and 1 Cb chroma component). As such, in a 2×2 block of pixels, the chroma components are sampled at ½ horizontal resolution and ½ vertical resolution. In a 4:2:2 pixel format, for every 2×2 block of pixels, there are four luma components and 4 chroma components (e.g., 2 Cr chroma components and 2 Cb chroma components). As such, for a 4:2:2 format, the chroma components are sampled at one-half (½) horizontal resolution and full vertical resolution. The 4:4:4 pixel format involves no sub-sampling of chroma components. That is, for a 2×2 block of pixels, there are four luma components, four Cr components, and four Cb components. In an RGB format, the number of red samples, the number of green samples and the number of blue samples are typically equal.

For many applications, such as remote desktop, remote gaming, wireless displays, automotive infotainment, and cloud computing to provide a few examples, the video contents in these applications are usually combinations of natural content, text, artificial graphics and the like. In test and artificial graphics regions, repeated patterns (such as characters, icons, and symbols to provide a few examples) often exist. Intra block copying (BC) may be characterized as a dedicated process that can enable removal of this kind of redundancy, thereby potentially improving the intra-frame coding efficiency as reported in JCT-VC N0256. Intra BC was adopted in the HEVC Range Extension (and has since been proposed to be moved to the Screen Contents Coding extension of HEVC noted above). The techniques described in this disclosure may provide for search region restriction in intra BC, as discussed in further detail below. The search region restriction techniques described in this disclosure may promote more robust video coding in that the search is restricted to the current slice/tile in which the current block resides rather than a different slice/tile, which may be lost or corrupted during transmission and thereby unavailable for use in reconstructing the current block.

FIG. 1is a block diagram illustrating an example video encoding and decoding system10that may utilize techniques for filtering video data. As shown inFIG. 1, system10includes a source device12that provides encoded video data to be decoded at a later time by a destination device14. In particular, source device12provides the video data to destination device14via a computer-readable medium16. Source device12and destination device14may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device12and destination device14may be equipped for wireless communication.

In some examples, encoded data may be output from output interface22to a storage device. Similarly, encoded data may be accessed from the storage device by input interface. The storage device may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device12.

Destination device14may access stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device14. Example file servers include a web server (e.g., for a website), an FTP server, network attached storage (NAS) devices, or a local disk drive. Destination device14may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof.

In the example ofFIG. 1, source device12includes video source18, video encoder20, and output interface22. Destination device14includes input interface28, video decoder30, and display device32. In accordance with this disclosure, video encoder20of source device12may be configured to apply the techniques for performing transformation in video coding. In other examples, a source device and a destination device may include other components or arrangements. For example, source device12may receive video data from an external video source18, such as an external camera. Likewise, destination device14may interface with an external display device, rather than including an integrated display device.

The illustrated system10ofFIG. 1is merely one example. Techniques for performing intra BC in video coding may be performed by any digital video encoding and/or decoding device. Although generally the techniques of this disclosure are performed by a video encoding device, the techniques may also be performed by a video codec. Moreover, the techniques of this disclosure may also be performed by a video preprocessor. Source device12and destination device14are merely examples of such coding devices in which source device12generates coded video data for transmission to destination device14. In some examples, devices12,14may operate in a substantially symmetrical manner such that each of devices12,14include video encoding and decoding components. Hence, system10may support one-way or two-way video transmission between video devices12,14, e.g., for video streaming, video playback, video broadcasting, or video telephony.

Video source18of source device12may include a video capture device, such as a video camera, a video archive containing previously captured video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source18may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In some cases, if video source18is a video camera, source device12and destination device14may form so-called camera phones or video phones. As mentioned above, however, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications. In each case, the captured, pre-captured, or computer-generated video may be encoded by video encoder20. The encoded video information may then be output by output interface22onto a computer-readable medium16.

Input interface28of destination device14receives information from computer-readable medium16. The information of computer-readable medium16may include syntax information defined by video encoder20, which is also used by video decoder30, that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., GOPs. Display device32displays the decoded video data to a user, and may comprise any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

This disclosure may generally refer to video encoder20“signaling” certain information to another device, such as video decoder30. It should be understood, however, that video encoder20may signal information by associating certain syntax elements with various encoded portions of video data. That is, video encoder20may “signal” data by storing certain syntax elements to headers of various encoded portions of video data. In some cases, such syntax elements may be encoded and stored (e.g., stored to storage device24) prior to being received and decoded by video decoder30. Thus, the term “signaling” may generally refer to the communication of syntax or other data for decoding compressed video data, whether such communication occurs in real- or near-real-time or over a span of time, such as might occur when storing syntax elements to a medium at the time of encoding, which then may be retrieved by a decoding device at any time after being stored to this medium.

Video encoder20and video decoder30may operate according to a video compression standard, such as the ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. The ITU-T H.264/MPEG-4 (AVC) standard was formulated by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG) as the product of a collective partnership known as the Joint Video Team (JVT). In some aspects, the techniques described in this disclosure may be applied to devices that generally conform to the H.264 standard. The H.264 standard is described in ITU-T Recommendation H.264, Advanced Video Coding for generic audiovisual services, by the ITU-T Study Group, and dated March 2005, which may be referred to herein as the H.264 standard or H.264 specification, or the H.264/AVC standard or specification. Other examples of video compression standards include MPEG-2 and ITU-T H.263.

While the techniques of this disclosure are not limited to any particular coding standard, the techniques may be relevant to the HEVC standard. The HEVC standardization efforts are based on a model of a video coding device referred to as the HEVC Test Model (HM). The HM presumes several additional capabilities of video coding devices relative to existing devices according to, e.g., ITU-T H.264/AVC. For example, whereas H.264 provides nine intra-prediction encoding modes, the HM may provide as many as thirty-five intra-prediction encoding modes.

In general, the working model of the HM describes that a video picture may be divided into a sequence of treeblocks or largest coding units (LCU) that include both luma and chroma samples. Syntax data within a bitstream may define a size for the LCU, which is a largest coding unit in terms of the number of pixels. A slice includes a number of consecutive coding tree units (CTUs). Each of the CTUs may comprise a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks. In a monochrome picture or a picture that have three separate color planes, a CTU may comprise a single coding tree block and syntax structures used to code the samples of the coding tree block.”

A video picture may be partitioned into one or more slices. Each treeblock may be split into coding units (CUs) according to a quadtree. In general, a quadtree data structure includes one node per CU, with a root node corresponding to the treeblock. If a CU is split into four sub-CUs, the node corresponding to the CU includes four leaf nodes, each of which corresponds to one of the sub-CUs. A CU may comprise a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array and a Cr sample array, and syntax structures used to code the samples of the coding blocks. In a monochrome picture or a picture that have three separate color planes, a CU may comprise a single coding block and syntax structures used to code the samples of the coding block. A coding block is an N×N block of samples.

Each node of the quadtree data structure may provide syntax data for the corresponding CU. For example, a node in the quadtree may include a split flag, indicating whether the CU corresponding to the node is split into sub-CUs. Syntax elements for a CU may be defined recursively, and may depend on whether the CU is split into sub-CUs. If a CU is not split further, it is referred as a leaf-CU. In this disclosure, four sub-CUs of a leaf-CU will also be referred to as leaf-CUs even if there is no explicit splitting of the original leaf-CU. For example, if a CU at 16×16 size is not split further, the four 8×8 sub-CUs will also be referred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, except that a CU does not have a size distinction. For example, a treeblock may be split into four child nodes (also referred to as sub-CUs), and each child node may in turn be a parent node and be split into another four child nodes. A final, unsplit child node, referred to as a leaf node of the quadtree, comprises a coding node, also referred to as a leaf-CU. Syntax data associated with a coded bitstream may define a maximum number of times a treeblock may be split, referred to as a maximum CU depth, and may also define a minimum size of the coding nodes. Accordingly, a bitstream may also define a smallest coding unit (SCU). This disclosure uses the term “block” to refer to any of a CU, PU, or TU, in the context of HEVC, or similar data structures in the context of other standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transform units (TUs) associated with the coding node. A size of the CU corresponds to a size of the coding node and must be square in shape. The size of the CU may range from 8×8 pixels up to the size of the treeblock with a maximum of 64×64 pixels or greater. Each CU may contain one or more PUs and one or more TUs.

In general, a PU represents a spatial area corresponding to all or a portion of the corresponding CU, and may include data for retrieving a reference sample for the PU. Moreover, a PU includes data related to prediction. For example, when the PU is intra-mode encoded, data for the PU may be included in a residual quadtree (RQT), which may include data describing an intra-prediction mode for a TU corresponding to the PU. As another example, when the PU is inter-mode encoded, the PU may include data defining one or more motion vectors for the PU. A prediction block may be a rectangular (i.e., square or non-square) block of samples on which the same prediction is applied. A PU of a CU may comprise a prediction block of luma samples, two corresponding prediction blocks of chroma samples of a picture, and syntax structures used to predict the prediction block samples. In a monochrome picture or a picture that have three separate color planes, a PU may comprise a single prediction block and syntax structures used to predict the prediction block samples.

TUs may include coefficients in the transform domain following application of a transform, e.g., a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data. The residual data may correspond to pixel differences between pixels of the unencoded picture and prediction values corresponding to the PUs. Video encoder20may form the TUs including the residual data for the CU, and then transform the TUs to produce transform coefficients for the CU. A transform block may be a rectangular block of samples on which the same transform is applied. A transform unit (TU) of a CU may comprise a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples. In a monochrome picture or a picture that have three separate color planes, a TU may comprise a single transform block and syntax structures used to transform the transform block samples.

Following transformation, video encoder20may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the coefficients, providing further compression. The quantization process may reduce the bit depth associated with some or all of the coefficients. For example, an n-bit value may be rounded down to an m-bit value during quantization, where n is greater than m.

Video encoder20may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) coefficients at the front of the array and to place lower energy (and therefore higher frequency) coefficients at the back of the array. In some examples, video encoder20may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector that can be entropy encoded. In other examples, video encoder20may perform an adaptive scan.

After scanning the quantized transform coefficients to form a one-dimensional vector, video encoder20may entropy encode the one-dimensional vector, e.g., according to context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), Probability Interval Partitioning Entropy (PIPE) coding or another entropy encoding methodology. Video encoder20may also entropy encode syntax elements associated with the encoded video data for use by video decoder30in decoding the video data.

Video encoder20may further send syntax data, such as block-based syntax data, picture-based syntax data, and group of pictures (GOP)-based syntax data, to video decoder30, e.g., in a picture header, a block header, a slice header, or a GOP header. The GOP syntax data may describe a number of pictures in the respective GOP, and the picture syntax data may indicate an encoding/prediction mode used to encode the corresponding picture.

Video decoder30, upon obtaining the coded video data, may perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder20. For example, video decoder30may obtain an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from video encoder20. Video decoder30may reconstruct the original, unencoded video sequence using the data contained in the bitstream.

Many applications, such as remote desktop, remote gaming, wireless displays, automotive infotainment, cloud computing, or the like, are becoming routine in daily personal lives. Video content in these applications are typically combinations of natural content, text, artificial graphics, and the like. In text and artificial graphics, region of the content may include repeated patterns (such as characters, icons, and symbols to provide a few examples) often exist. Intra block copying (BC) is a dedicated technique that enables removal of this kind of redundancy, thereby potentially improving the intra-frame coding efficiency as reported in JCT-VC N0256. At a recent JCT-VC meeting, intra BC was adopted in the HEVC Range Extension standard (which has since been moved to the Screen Contents Coding extension of HEVC, as noted above). As illustrated in more detail in the example ofFIG. 6, for a current coding unit (CU)140under intra BC, video encoder20may obtain a prediction signal142(which may also be referred to as a “prediction block”) from an already reconstructed region144in the same frame. In some instances, video encoder20may encode the offset or displacement vector146(which may also be referred to by the misnomer “motion vector”), which indicates the position of the prediction signal142displaced from the current CU140, together with the residue signal.

Guo et al., “INTRA-PREDICTION FROM A PREDICTIVE BLOCK,” U.S. application Ser. No. 14/309,730 filed Jun. 19, 2014 (hereinafter, the “'730 patent application,” and provided as Appendix 1 in U.S. Provisional Application Ser. No. 61/926,177) described an extension of Intra BC to PUs and TUs, motion vector signaling for Intra BC, interaction of Intra BC with deblocking/SAO, an interpolation filter for Intra BC, signaling of Intra_bc_flag, and similar techniques. Pang et al., “PARTIAL INTRA BLOCK COPYING,” U.S. Provisional Application Ser. No. 61/891,291, filed Oct. 15, 2013 (hereinafter, the “'291 provisional application,” and provided in U.S. Provisional Application Ser. No. 61/926,177 as Appendix 2), describes an extension of Intra BC to a situation where only a prediction block is not completely reconstructed.

In JCT-VC N0256, the search region may be restricted to be in the reconstructed area of a coded tree unit (CTU) to the left of the current CTU potentially without in-loop filtering. However, because of the possible interaction with other components, the restriction proposed in JCT-VC N0256 may not be enough for the coding units (CUs) of the current CTU at boundaries of slices/tiles/frames. For example, when multiple slices are allowed for a picture and the prediction block is from a different slice, the current CU (which is another way of referring to a video block) coded with intra BC mode may not be correctly decoded. Also, as another example, when the offset vector points to a position that is out of a current picture (meaning that the search region extends beyond the bounds of the picture) and no padding scheme is pre-defined, then the CU coded with the intra BC mode may not be correctly decoded as well.

In accordance with various aspects of the techniques described in this disclosure, video encoder20may determine a search region that can be used for Intra BC such that this region is inside the same slice/tile in which the current CU resides. For example, with this restriction, when the possible search region is set to be the reconstructed area of the left CTU and current CTU as in JCT-VC N0256 (which refers to this region as the “intended region”), the left CTU may be used only when this left CTU is in the same slice/tile as that of the current CTU. In other words, when the left CTU and the current CTU are in different slices/tiles, the video encoder20may only determine that the current CTU without in-loop filtering is used for Intra BC. In this respect, video encoder20may be configured to perform the intra block copying process to encode a current block of a picture such that pixels from a different slice or a different tile than that in which the current block resides are excluded from a search region used for the intra block copying process.

In some examples, the pixels included in the region (also referred to herein as the “search region”) have not been processed using any in-loop filters. Application of in-loop filters to the search region may result in increased residual and/or differences between the prediction block and the current CU to which the intra block copying process is performed. By foregoing or disabling the typical application of in-loop filtering to the pixels (or a block of pixels) of the search region, the techniques may promote more efficient encoding through application of the intra block copying process in that less bits may be required to represent the current CU to which the intra block copying process is performed.

In yet other examples where the current block to which the intra block copying processes is applied is a PU/TU, the techniques may provide a configuration for video encoder20that further restricts the application of the intra block copying process. Video encoder20may, when the current block is a PU/TU of a current CU, apply the intra block copying process such that not only is the search region restricted to the same slice and tile as that in which the current PU/TU resides but also restricted such that any other PU/TU's of the current CU are not included in the search region. This second restriction with regard to excluding other PU/TU's of the current CU from the search region may promote parallel processing of PU/TU's for the current CU. In other words, video encoder20may process multiple PU/TU's of the same CU at the same time, which as a result would the PU/TU's of the same CU as being within a search region for the other PU/TU's of the same CU. Video encoder20may promote this same CU restriction so as to facilitate parallel processing at video encoder30. In this manner, the techniques may promote more efficient and reliable application of the intra-block copying process by video encoder20.

The techniques may also enable a configuration of video decoder30generally reciprocal to that described above with respect to video encoder20. In this respect, video decoder30may be configured to perform an intra block copying process to decode a coded current block of a picture using a prediction block that is from a same slice or a same tile as that in which the coded current block resides. In some examples, the prediction block has, as noted above when discussing video encoder20, not been processed using any in-loop filtering. Moreover, when the coded current block is one or more of a coded current prediction unit (PU) or a coded current transform unit (TU) of a coded current coding unit (CU), the prediction block may not overlap the coded current CU.

FIG. 2is a block diagram illustrating an example of a video encoder20that may use techniques for transformation as described in this disclosure. The video encoder20will be described in the context of HEVC coding for purposes of illustration, but without limitation of this disclosure as to other coding standards.

In the example ofFIG. 2, video encoder20includes mode select unit40, reference picture memory64, summer50, transform processing unit52, quantization unit54, and entropy encoding unit56. Mode select unit40, in turn, includes motion compensation unit44, motion estimation unit42, intra-prediction unit46, and partition unit48. For video block reconstruction, video encoder20also includes inverse quantization unit58, inverse transform processing unit60, summer62, and filtering unit66.

During the encoding process, video encoder20receives a video picture or slice to be coded. The picture or slice may be divided into multiple video blocks. Motion estimation unit42and motion compensation unit44perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference pictures to provide temporal compression. Intra-prediction unit46may alternatively perform intra-predictive coding of the received video block relative to one or more neighboring blocks in the same picture or slice as the block to be coded to provide spatial compression. Video encoder20may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

Moreover, partition unit48may partition blocks of video data into sub-blocks, based on evaluation of previous partitioning schemes in previous coding passes. For example, partition unit48may initially partition a picture or slice into LCUs, and partition each of the LCUs into sub-CUs based on rate-distortion analysis (e.g., rate-distortion optimization). Mode select unit40may further produce a quadtree data structure indicative of partitioning of an LCU into sub-CUs. Leaf-node CUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit40may select one of the coding modes, intra or inter, e.g., based on error results, and provides the resulting intra- or inter-coded block to summer50to generate residual block data and to summer62to reconstruct the encoded block for use as a reference picture. Mode select unit40also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit56. The techniques of this disclosure may be applied in response to mode select unit40implementing an intra-block copy mode.

Motion estimation unit42and motion compensation unit44may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation unit42, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a PU of a video block within a current video picture relative to a predictive block within a reference picture (or other coded unit) relative to the current block being coded within the current picture (or other coded unit). A predictive block is a block that is found to closely match the block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. In some examples, video encoder20may calculate values for sub-integer pixel positions of reference pictures stored in reference picture memory64. For example, video encoder20may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation unit42may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.

Motion compensation, performed by motion compensation unit44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit42. Again, motion estimation unit42and motion compensation unit44may be functionally integrated, in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation unit44may locate the predictive block to which the motion vector points in one of the reference picture lists. Summer50forms a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values, as discussed below. In general, motion estimation unit42performs motion estimation relative to luma components, and motion compensation unit44uses motion vectors calculated based on the luma components for both chroma components and luma components. Mode select unit40may also generate syntax elements associated with the video blocks and the video slice for use by video decoder30in decoding the video blocks of the video slice.

Intra-prediction unit46may intra-predict a current block, as an alternative to the inter-prediction performed by motion estimation unit42and motion compensation unit44, as described above. In particular, intra-prediction unit46may determine an intra-prediction mode to use to encode a current block. In some examples, intra-prediction unit46may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction unit46(or mode select unit40, in some examples) may select an appropriate intra-prediction mode to use from the tested modes.

For example, intra-prediction unit46may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (that is, a number of bits) used to produce the encoded block. Intra-prediction unit46may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

Video encoder20forms a residual video block by subtracting the prediction data from mode select unit40from the original video block being coded. Summer50represents the component or components that perform this subtraction operation.

Transform processing unit52applies a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform, to the residual block, producing a video block comprising residual transform coefficient values. Transform processing unit52may perform other transforms which are conceptually similar to DCT. Wavelet transforms, integer transforms, sub-band transforms or other types of transforms could also be used. In any case, transform processing unit52applies the transform to the residual block, producing a block of residual transform coefficients. The transform may convert the residual information from a pixel value domain to a transform domain, such as a frequency domain.

Following quantization, entropy encoding unit56entropy codes the quantized transform coefficients. For example, entropy encoding unit56may perform context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy coding technique. In the case of context-based entropy coding, context may be based on neighboring blocks. Following the entropy coding by entropy encoding unit56, the encoded bitstream may be transmitted to another device (e.g., video decoder30) or archived for later transmission or retrieval.

Inverse quantization unit58and inverse transform processing unit60apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block.

Filtering unit66may perform a variety of filtering processes. For example, filtering unit66may perform deblocking That is, filtering unit66may receive a plurality of reconstructed video blocks forming a slice or a frame of reconstructed video and filter block boundaries to remove blockiness artifacts from a slice or frame. In one example, filtering unit66evaluates the so-called “boundary strength” of a video block. Based on the boundary strength of a video block, edge pixels of a video block may be filtered with respect to edge pixels of an adjacent video block such that the transition from one video block are more difficult for a viewer to perceive.

In some instances, the variables used by a deblocking filter may be derived from reconstructed video blocks without a comparison of reconstructed video blocks to the original source video blocks. Thus, video encoder20and video decoder30(FIG. 3) may each be programmed to perform the same deblocking process on reconstructed video blocks with minimal additional information regarding the original video frame coded into the bitstream. However, in some cases, filtering unit66may include syntax elements in the bitstream to indicate whether deblocking should be performed and/or whether one of a particular type of deblocking modes should be performed.

In accordance with various aspects of the techniques described in this disclosure, video encoder20and, more specifically, intra prediction unit46of video encoder20may perform an intra block copying process to encode a current block of a picture such that pixels from a different slice or different tile than that in which the current block resides are not included in a regions used when performing the intra block copying process. More specifically, when performing the intra block copying process, the intra prediction unit46may be configured to determine a region of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides, identify a prediction block within the determined region, and encode the current block based on the identified prediction block.

In some examples, the pixels included in the region have not been processed using any in-loop filters for the reasons noted above. In these examples, the techniques may configure video encoder20such that filtering unit66is disabled and does not apply any in-loop filters to the search region.

In yet other examples where the current block to which the intra block copying processes is applied is a PU/TU, the techniques may provide a configuration for intra prediction unit46that further restricts the application of the intra block copying process. Intra prediction unit46may, when the current block is a PU/TU of a current CU, apply the intra block copying process such that not only is the search region restricted to the same slice and tile as that in which the current PU/TU resides but also restricted such that any other PU/TU's of the current CU are not included in the search region.

That is, the prediction block in the reconstructed region may, in these and other examples, be restricted such that this prediction block cannot overlap with the current CU. In other words, since the current CU is not in the reconstructed region in some instances, the whole prediction block should be in the reconstructed region. By ensuring this prediction block is the reconstructed region, mismatching between video encoder20and decoder30may be avoided when Intra BC mode is used. It is also possible that only part of the prediction block is in the reconstructed region, and the remaining part which is not in the reconstructed region is obtained using predefined methods, such as padding, inpainting, etc.

When Intra BC is extended to PU/TU, as in the '730 patent application, for example, a 2N×2N CU can be divided into two 2N×N, two N×2N blocks, or four N×N blocks. Each of the blocks in the above mentioned cases are denoted as PU/TU, to align the terminology as in HEVC version 1. This disclosure proposes that the prediction block for a PU/TU should not overlap with a current CU, although part of the current CU might be available, meaning a prediction block for a PU/TU of the current CU should not contain any pixel that is within the current CU. Alternatively, the prediction block of a PU/TU of the current CU can be located at least partially (and in some cases, completely) within an already decoded and reconstructed PU/TU of the current CU.

Under the restriction described above, it is possible that the whole prediction block for the PU/TU is reconstructed. It is also possible that only part of the prediction block is in the reconstructed region, and the remaining part, which is not in the reconstructed region, is obtained using predefined methods, such as padding (for example, the methods in the '291 provisional application), inpainting, or other such predefined methods.

In this respect, intra block wherein performing the intra prediction unit46may be configured to determine the region of the picture such that the region does not include any block of the picture assigned to the different slice or the different tile than the slice or the tile in which the current block resides and identify a prediction block that resides at least partially within the determined region. Intra prediction unit46may then encode the current block based on the identified prediction block.

The techniques may also, in some examples, avoid the fetch of pixels outside the current slice/tile by limiting the range of a motion vector to be possibly smaller than the intended region. This can also be achieved by pixel padding (and the range of the motion vector can be relaxed to be the same as the intended region). “Pixel padding” may refer to adding and/or interpolating pixels that are not included in an original picture or slice. To be more specific, when a pixel is outside the current slice/tile, video encoder20may replaced the pixel outside the current frame by the value of the closest pixel that is in the available region. Such techniques may improve efficiency by limiting the amount of data that is retrieved from memory during coding.

In this respect, intra prediction unit46may be configured to determine a region of a picture when performing an intra block copying process for a current block of the picture and restricting a size of an offset vector identifying a location of a prediction block relative to the current block within the determined region such that the offset vector is unable to identify those blocks of the region that reside outside of the slice or the tile in which the current block resides. Intra prediction unit46may further be configured to identify a prediction block within the determined region based on the offset vector, and encoding the current block based on the identified prediction block.

Moreover, in these and other examples, intra prediction unit46may be configured to determine a region of a picture when performing an intra block copying process for a current block of the picture and, when the determined region extends beyond the slice or the tile in which the current block resides, padding the slice or the tile to generate a padded slice or a padded tile that is the same size as the determined region. Intra prediction unit46may then identify a prediction block within the determined region, and encode the current block based on the identified prediction block.

Alternatively, intra prediction unit46may be configured to determine the region of the picture such that the region does not include any block of the picture assigned to the different slice or the different tile than the slice or the tile in which the current block resides and does not require pixel padding to be performed with respect to the picture.

In accordance with various aspects of the techniques described in this disclosure, a flag, intrabc_across_tiles_enabled_flag, may be added at a parameter set level, such as a picture parameter set (PPS) or sequence parameter set (SPS) level. Video encoder20may set intrabc_across_tiles_enabled_flag equal to 1 to specify that a reconstructed area without in-loop filters from other tiles can be used for the prediction of the CUs with intra BC mode in current tile. Video encoder20may set the intrabc_across_tiles_enabled_flag equal to 0 so as to specify that only a reconstructed area without in-loop filters from the current tile can be used for the prediction of the CUs with Intra BC mode in current tile.

Similarly, another flag, intrabc_cross_slices_enabled_flag, may be added at a PPS/SPS level, where intrabc_cross_slices_enabled_flag equal to 1 specifies that reconstructed area without in-loop filters from other slices can be used for the prediction of the CUs with Intra BC mode in current slice. When intrabc_cross_slices_enabled_flag is equal to 0, the intrabc_cross_slices_enabled_flag specifies that only reconstructed areas without in-loop filters from the current slice can be used for the prediction of the CUs with Intra BC mode in current slice.

The techniques may, in this way, provide a configuration enabling entropy coding unit56to specify, in one or more of a picture parameter set or sequence parameter set included within a bitstream to which the coded current block is stored, an intrabc_across_tiles_enabled_flag syntax element indicating whether the region was determined such that the region does not include any block of the picture assigned to the different tile than the tile in which the current block resides.

Moreover, the techniques may provide a configuration enabling entropy coding unit56to specify, in one or more of a picture parameter set or sequence parameter set included within a bitstream to which the coded current block is stored, an intrabc_cross_slices_enabled_flag syntax element indicating whether the region was determined such that the region does not include any block of the picture assigned to the different slice than the slice in which the current block resides.

While a number of different aspects and examples of the techniques are described in this disclosure, the various aspects and examples of the techniques may be performed together or separately from one another. In other words, the techniques should not be limited strictly to the various aspects and examples described above, but may be used in combination or performed together and/or separately. In addition, while certain techniques may be ascribed to certain units of video encoder20(such as intra prediction unit46or entropy encoding unit56) it should be understood that one or more other units of video encoder20may also be responsible for carrying out such techniques.

FIG. 3is a block diagram illustrating an example of video decoder30that may implement techniques for transformation as described in this disclosure. Again, the video decoder30will be described in the context of HEVC coding for purposes of illustration, but without limitation of this disclosure as to other coding standards.

In the example ofFIG. 3, video decoder30includes an entropy decoding unit70, motion compensation unit72, intra prediction unit74, inverse quantization unit76, inverse transformation processing unit78, reference picture memory82, summer80, and filtering unit84.

During the decoding process, video decoder30receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from video encoder20. Entropy decoding unit70of video decoder30entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit70forwards the motion vectors to and other syntax elements to motion compensation unit72. Video decoder30may receive the syntax elements at the video slice level and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intra prediction unit74may generate prediction data for a video block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter-coded (i.e., B, P or GPB) slice, motion compensation unit72produces predictive blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit70. The predictive blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder30may construct the reference picture lists, List0and List1, using default construction techniques based on reference pictures stored in reference picture memory82.

Motion compensation unit72may also perform interpolation based on interpolation filters. Motion compensation unit72may use interpolation filters as used by video encoder20during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit72may determine the interpolation filters used by video encoder20from the received syntax elements and use the interpolation filters to produce predictive blocks.

Inverse quantization unit76inverse quantizes, i.e., de-quantizes, the quantized transform coefficients provided in the bitstream and decoded by entropy decoding unit70. The inverse quantization process may include use of a quantization parameter QPYcalculated by video decoder30for each video block in the video slice to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse transform processing unit78applies an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to produce residual blocks in the pixel domain. Video decoder30forms a decoded video block by summing the residual blocks from inverse transform processing unit78with the corresponding predictive blocks generated by motion compensation unit72. Summer80represents the component or components that perform this summation operation.

Filtering unit84may, in some examples, be configured similarly to filtering unit66of video encoder20(FIG. 2). For example, filtering unit84may be configured to perform deblocking, SAO, or other filtering operations when decoding and reconstructing video data from an encoded bitstream.

In some instances, video decoder30may perform one or more of the techniques described with respect to video encoder20above. For example, video decoder30may perform the techniques of this disclosure for performing intra BC. In some examples, video decoder30may obtain one or more syntax elements from an encoded bitstream, and perform the techniques of this disclosure based on such syntax elements.

For example, video decoder30may be configured to determine one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and decode the encoded version of the current block of the picture based on the one or more syntax elements.

In some instances, video decoder30may further be configured to, when determining the one or more syntax elements, determine an intrabc_across_tiles_enabled_flag indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

In some instances, video decoder30may further be configured to, when determining the one or more syntax elements, determine, in one or more of a picture parameter set or sequence parameter set, an intrabc_across_tiles_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

In some instances, video decoder30may further be configured to, when determining the one or more syntax elements, determine an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

In some instances, video decoder30may further be configured to, when determining the one or more syntax elements, determine, in one or more of a picture parameter set or sequence parameter set, an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

More specifically, the techniques may enable a configuration of intra prediction unit74of video decoder30that is generally reciprocal to that described above with respect to intra prediction unit46. In this respect, intra prediction unit74may be configured to perform an intra block copying process to decode a coded current block of a picture using a prediction block that is from a same slice or a same tile as that in which the coded current block resides.

In some examples, the prediction block has, as noted above when discussing intra prediction unit46, not been processed using any in-loop filtering. The techniques may, in this example, disable application of in-loop filters by filtering unit84to the identified prediction block (or possibly the pixels in the slice and/or tile as a whole).

Moreover, when the coded current block is one or more of a coded current prediction unit (PU) or a coded current transform unit (TU) of a coded current coding unit (CU), the prediction block may not overlap the coded current CU. Intra prediction unit74may be configured to generate an error when the prediction block overlaps the current CU in these instances, which may be handled in a number of different ways (e.g., by replacing the prediction block with a template block or replacing the prediction block with a block closest to the overlapping prediction block but that does not overlap the current CU).

Intra prediction unit74may further be configured to obtain an offset vector that identifies the prediction block within the same slice or the same tile as that in which the coded current block resides and obtain the prediction block based on a location of the coded current block and the offset vector. Typically, entropy decoding unit70parses the offset vector from the encoded video bitstream and provides this offset vector (after performing entropy decoding in some examples) to the intra prediction unit74. Intra prediction unit74may obtain the prediction block by accessing reference picture memory82(or an intermediate memory used to cache the current picture to be decoded). Intra prediction unit76may then decode the coded current block based on the prediction block.

Intra prediction unit74may, in some examples, be configured to obtain an offset vector that identifies the prediction block within the same slice or the same tile as that in which the coded current block resides, wherein a size of the offset vector has been restricted such that the offset vector is unable to identify a block outside of the same slice or the same tile in which the coded current block resides. Intra prediction unit74may then obtain the prediction block based on a location of the coded current block and the offset vector, and decode the coded current block based on the prediction block.

In some examples, the intra prediction unit74may obtain an offset vector that identifies the prediction block that resides partially within the same slice or the same tile as that in which the coded current block resides, and pad the slice or the tile to generate a padded slice or a padded tile that fills in a portion of the prediction block that resides outside of the slice or the tile. Intra prediction unit74may then obtain the prediction block based on a location of the coded current block and the offset vector, the prediction block including at least some portion of the padding, and decode the coded current block based on the prediction block.

In this respect, the techniques described in this disclosure may enable a video coder to perform a more efficient and reliable form of an intra block copying process that is resilient to loss of a slice and/or tile while also promoting coding efficiency. A video coder, as described in this disclosure, may refer to a video encoder or a video decoder. Similarly, a video coding unit may refer to a video encoder or a video decoder. Likewise, video coding may refer to video encoding or video decoding, as applicable.

FIG. 4is a flowchart illustrating exemplary operation of a video encoding device, such as video encoder20shown in the example ofFIG. 2, in performing the region restricted intra block coding techniques described in this disclosure. In the example ofFIG. 4, video encoder20receives a video picture or slice to be coded (100). The picture or slice may be divided into multiple video blocks. Motion estimation unit42and motion compensation unit44perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference pictures to provide temporal compression. Intra-prediction unit46may alternatively perform intra-predictive coding of the received video block relative to one or more neighboring blocks in the same picture or slice as the block to be coded to provide spatial compression. Video encoder20may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data. In this way, video encoder20may identify that application of an intra block copying process to a current block of a picture results in the most efficient way by which to code the current block.

In performing this intra block copying process, intra prediction unit46may first identify a search region in the video picture for a current block (e.g., CU) of the video picture such that the search region does not include pixels from a different slice or a different tile to which the current CU resides in accordance with the techniques described in this disclosure (102). Intra prediction unit46, after identifying the appropriate search region, may next determine a prediction block within the search region from which the current CU is to be predicted (104). Intra prediction unit46may perform this determination by accessing each block within the search region and determining the difference between each block and the current CU. Intra prediction unit46may determine the prediction block as the block that results in the least amount of residual or, in other words, smallest difference between the block and the current CU.

Intra prediction unit46may next determine an offset vector identifying the location of the selected block (which may be referred to as the “prediction block”) relative to the current CU. In this way, intra prediction unit46may determine the offset vector based on the prediction block and the current block (106). Intra prediction unit46may signal the offset vector to entropy encoding unit56, which entropy encodes the offset vector and adds the encoded offset vector to the bitstream. Intra prediction unit46may in this respect compute the residual as the difference between the prediction block and the current block (108) and then pass the residual as a residual block to the transform processing unit52.

Transform processing unit52applies a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform, to the residual block (110), producing a video block comprising residual transform coefficient values. Transform processing unit52may send the resulting transform coefficients to quantization unit54. Quantization unit54quantizes the transform coefficients to further reduce bit rate (112). Following quantization, entropy encoding unit56entropy codes (which refers to statistical lossless coding, as one example) the quantized transform coefficients (114) and store the entropy encoded quantized transform coefficients to the bitstream. This process iterates until all of the blocks of the video picture are encoded, although not all of the block may be encoded using an intra block copying process.

FIG. 5is a flowchart illustrating exemplary operation of a video decoding device, such as video decoder30shown in the example ofFIG. 3, in performing the region restricted intra block copying processing techniques described in this disclosure. Initially, video decoder30receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from video encoder20. Entropy decoding unit70of video decoder30entropy decodes the bitstream to generate quantized coefficients, and in the case of intra block copying, a corresponding an offset vector (122). Entropy decoding unit70forwards the quantized transform coefficients to inverse quantization unit76and the corresponding offset vector to intra prediction unit74.

Inverse quantization unit76dequantizes the quantized transform coefficients to obtain transform coefficients (124). Inverse transform processing unit78applies an inverse transform to the transform coefficients to obtain the residual block (126). Meanwhile, intra prediction unit74identifies a prediction block stored to reference picture memory82(or some other intermediate memory) based on the offset vector (128), providing this prediction block to summer80. Summer80sums the residual block with the prediction block to reconstruct or, in other words, decode the coded current block (130).

Certain aspects of this disclosure have been described with respect to the developing HEVC standard for purposes of illustration. However, the techniques described in this disclosure may be useful for other video coding processes, including other standard or proprietary video coding processes not yet developed.

In some examples, the techniques of this disclosure may relate to methods/devices/computer-readable media in accordance with one or more of the following clauses:

Clause 1. A method comprising:

determining a region of a picture when performing an intra block copying process for a current block of the picture;

restricting a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture;

identifying the prediction block within the determined region based on the restricted size of the offset vector; and

coding the current block based on the identified prediction block.

Clause 2. A device comprising:

one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture, restrict a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture, identify the prediction block within the determined region based on the restricted size of the offset vector, and code the current block based on the identified prediction block.

Clause 3. A device comprising:

means for determining a region of a picture when performing an intra block copying process for a current block of the picture;

means for restricting a size of a offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture;

means for identifying the prediction block within the determined region based on the restricted size of the offset vector; and

means for coding the current block based on the identified prediction block.

Clause 4. A non-transitory computer-readable storage medium having stored thereon instruction that, when executed, cause one or more processors to:

determine a region of a picture when performing an intra block copying process for a current block of the picture;

restrict a size of an offset vector identifying a location of a prediction block relative to the current block such that the offset vector only identifies those blocks of the region that reside within the picture;

identify the prediction block within the determined region based on the restricted size of the offset vector; and

code the current block based on the identified prediction block.

Clause 5. A method comprising:

determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture;

identifying a prediction block within the determined region; and

coding the current block based on the identified prediction block.

Clause 6. A device comprising:

one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

Clause 7. A device comprising:

means for determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture;

means for identifying a prediction block within the determined region; and

means for coding the current block based on the identified prediction block.

Clause 8. A non-transitory computer-readable storage medium having stored thereon instruction that, when executed, cause one or more processors to:

determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and does not require pixel padding to be performed with respect to the picture;

identify a prediction block within the determined region; and

code the current block based on the identified prediction block.

Clause 9. A method comprising:

determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture;

identifying a prediction block within the determined region; and

coding the current block based on the identified prediction block.

Clause 10. A device comprising:

one or more processors configured to determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture, identify a prediction block within the determined region, and code the current block based on the identified prediction block.

Clause 11. A device comprising:

means for determining a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture;

means for identifying a prediction block within the determined region; and

means for coding the current block based on the identified prediction block.

Clause 12. A non-transitory computer-readable storage medium having stored thereon instruction that, when executed, cause one or more processors to:

determine a region of a picture when performing an intra block copying process for a current block of the picture such that the region does not include any block of the picture assigned to a different slice or a different tile than a slice or a tile in which the current block resides and that does not extend beyond the picture;

identify a prediction block within the determined region; and

code the current block based on the identified prediction block.

Clause 13. A method comprising:

determining one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture; and

decoding the encoded version of the current block of the picture based on the one or more syntax elements.

Clause 14. The method of clause 13, wherein determining the one or more syntax elements comprises determining an intrabc_across_tiles_enabled_flag indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 15. The method of clause 13, wherein determining the one or more syntax elements comprises determining, in one or more of a picture parameter set or sequence parameter set, an intrabc_across_tiles_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 16. The method of clause 13, wherein determining the one or more syntax elements comprises determining an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 17. The method of clause 13, wherein determining the one or more syntax elements comprises determining, in one or more of a picture parameter set or sequence parameter set, an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 18. A device comprising:

one or more processors configured to determine one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture, and decode the encoded version of the current block of the picture based on the one or more syntax elements.

Clause 19. The device of clause 18, wherein the one or more processors are further configured to, when determining the one or more syntax elements, determine an intrabc_across_tiles_enabled_flag indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 20. The device of clause 18, wherein the one or more processors are further configured to, when determining the one or more syntax elements, determine, in one or more of a picture parameter set or sequence parameter set, an intrabc_across_tiles_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 21. The device of clause 18, wherein the one or more processors are further configured to, when determining the one or more syntax elements, determine an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 22. The device of clause 18, wherein the one or more processors are further configured to, when determining the one or more syntax elements, determine, in one or more of a picture parameter set or sequence parameter set, an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 23. A device comprising:

means for determining one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture; and

means for decoding the encoded version of the current block of the picture based on the one or more syntax elements.

Clause 24. The device of clause 23, wherein means for determining the one or more syntax elements comprises means for determining an intrabc_across_tiles_enabled_flag indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 25. The device of clause 23, wherein the means for determining the one or more syntax elements comprises means for determining, in one or more of a picture parameter set or sequence parameter set, an intrabc_across_tiles_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different tile than a tile in which the current block resides.

Clause 26. The device of clause 23, wherein the means for determining the one or more syntax elements comprises means for determining an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 27. The device of clause 23, wherein the means for determining the one or more syntax elements comprises means for determining, in one or more of a picture parameter set or sequence parameter set, an intrabc_cross_slices_enabled_flag syntax element indicating whether a region that was determined during application of the intra block copying process includes any block of the picture assigned to a different slice than a slice in which the current block resides.

Clause 28. A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to:

determine one or more syntax elements describing application of an intra block copying process to a current block of a picture to generate an encoded version of the current block of the picture; and

decode the encoded version of the current block of the picture based on the one or more syntax elements.

Clause 29. A method comprising coding video data in accordance with a restriction in which a prediction block for a block of video data is not permitted to overlap a current coding unit.

Clause 30. A method comprising coding video data comprising coding a block of a current coding unit of video data using a prediction block for the block, wherein the prediction block is located at least partially within an already coded block of the current CU.

Clause 31. The method of clause 30, wherein the prediction block is located completely within the current CU.

Clause 32. The method of any of clauses 29-31, further comprising reconstructing a first portion of the prediction block without reconstructing a second portion of the prediction block, wherein the first portion is different than the second portion.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol.

In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.