Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
  • H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
  • H04N19/174—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a slice, e.g. a line of blocks or a group of blocks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/80—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation
  • H04N19/82—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation involving filtering within a prediction loop
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
  • H04N19/117—Filters, e.g. for pre-processing or post-processing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
  • H04N19/136—Incoming video signal characteristics or properties
  • H04N19/14—Coding unit complexity, e.g. amount of activity or edge presence estimation

Definitions

• This disclosure relates to video coding and, more particularly, to techniques for deblocking coded blocks of video data.
• a video slice (e.g., a video frame or a portion of a video frame) may be partitioned into video blocks, which may also be referred to as treeblocks, coding units (CUs) and/or coding nodes.
• Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture.
• Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures.
• Pictures may be referred to as frames, and reference pictures may be referred to a reference pictures.
• this disclosure describes techniques for deblocking coded blocks of video data, e.g., transform units (TUs), coding units (CUs), or prediction units (PUs).
• Block-based video coding techniques can sometimes lead to "blockiness" artifacts, where boundaries or edges between individually coded blocks can be perceived. Such artifacts can arise when blocks are coded at different quality levels.
• An amount of quantization applied to a block (as indicated by a quantization parameter (QP)) can directly impact the quality of the block. Therefore, deblocking techniques typically take account of the QP of the block, e.g., when determining whether to deblock an edge of the block and how to deblock the edge.
• QP quantization parameter
• the techniques of this disclosure may improve deblocking functions applied to such edges (e.g., reducing the appearance of an edge) and, more particularly, may improve the deblocking functions applied to the chrominance components at a common edge shared by two blocks of video data.
• a video coder e.g., a video encoder or video decoder
• the video coder determines a strength for a deblocking filter for the common edge based on the chrominance quantization parameter. Because the video decoder determined the chrominance quantization parameter for the edge based on the chrominance
• the strength of the deblocking filter may be more appropriate for the quality levels of the chrominance components of the two blocks of video data that share the common edge.
• a method for processing video data comprises decoding a first block of video data and a second block of video data, wherein the first block of video data and the second block of video data share a common edge, and determining a first luminance quantization parameter for the first block of video data and a second luminance quantization parameter for the second block of video data.
• the method further comprises, for each of one or more chrominance components, determining a chrominance quantization parameter offset value and, for each of the one or more chrominance components, calculating a chrominance quantization parameter for the edge based on the first luminance quantization parameter for the first block of video data, the second luminance quantization parameter for the second block of video data, and the chrominance quantization parameter offset value for the chrominance component.
• the method further comprises, for each of the one or more chrominance components, determining a strength for a deblocking filter for the common edge based on the chrominance quantization parameter for the chrominance component and, for each of the one or more chrominance components, applying the deblocking filter according to the determined strength to deblock the common edge.
• an apparatus for processing video data comprises a video coder configured to decode a first block of video data and a second block of video data, wherein the first block of video data and the second block of video data share a common edge, and determine a first luminance quantization parameter for the first block of video data and a second luminance quantization parameter for the second block of video data.
• the video coder is further configured to, for each of one or more chrominance components, determine a chrominance quantization parameter offset value and, for each of the one or more chrominance components, calculate a chrominance quantization parameter for the edge based on the first luminance quantization parameter for the first block of video data, the second luminance quantization parameter for the second block of video data, and the chrominance quantization parameter offset value for the chrominance component.
• the video coder is further configured to, for each of the one or more chrominance components, determine a strength for a deblocking filter for the common edge based on the chrominance quantization parameter for the chrominance component and, for each of the one or more chrominance components, apply the deblocking filter according to the determined strength to deblock the common edge.
• an apparatus for processing video data comprises means for decoding a first block of video data and a second block of video data, wherein the first block of video data and the second block of video data share a common edge, and means for determining a first luminance quantization parameter for the first block of video data and a second luminance quantization parameter for the second block of video data.
• the apparatus further comprises means for, for each of one or more chrominance components, determining a chrominance quantization parameter offset value, and means for, for each of the one or more chrominance components, calculating a chrominance quantization parameter for the edge based on the first luminance quantization parameter for the first block of video data, the second luminance quantization parameter for the second block of video data, and the chrominance quantization parameter offset value for the chrominance component.
• the apparatus further comprises means for, for each of the one or more chrominance components, determining a strength for a deblocking filter for the common edge based on the chrominance quantization parameter for the chrominance component, and means for, for each of the one or more chrominance components, applying the deblocking filter according to the determined strength to deblock the common edge.
• the instructions further cause the processor to, for each of the one or more chrominance components, determine a strength for a deblocking filter for the common edge based on the chrominance quantization parameter for the chrominance component and, for each of the one or more chrominance components, apply the deblocking filter according to the determined strength to deblock the common edge.
• FIG. 1 is a block diagram illustrating an example video encoding and decoding system that may utilize techniques for deblocking edges between video blocks.
• FIG. 2 is a block diagram illustrating an example of a video encoder that may implement techniques for deblocking edges between video blocks.
• FIG. 3 is a block diagram illustrating an example of a video decoder that may implement techniques for deblocking an edge between video blocks.
• FIG. 5 is a conceptual diagram illustrating an edge formed by two neighboring video blocks.
• Video coders such as video encoders and video decoders, are generally configured to code individual pictures of a sequence of pictures using either spatial prediction (or intra-prediction) or temporal prediction (or inter-prediction). More particularly, video coders may predict blocks of a picture using intra-prediction or inter- prediction. Video coders may code residual values for the blocks, where the residual values correspond to pixel-by-pixel differences between a predicted block and an original (that is, uncoded) block. Video coders may transform a residual block to convert values of the residual block from a pixel domain to a frequency domain.
• block-based coding in this manner may lead to blockiness artifacts between blocks of the picture. That is, after dividing a frame into blocks, coding the blocks, and then decoding the blocks, perceptible artifacts at edges between the blocks may occur. Therefore, video coders may perform various deblocking procedures to remove the blockiness artifacts.
• video encoders may encode video data of a frame, then
• Such deblocking filtering performed by a video coding device, such as a video encoder or video decoder, prior to storing the decoded video data for use as reference data is generally referred to as "in-loop" filtering.
• a video encoder or decoder may perform the deblocking within a video loop.
• Video encoders may begin with receiving raw video data, encoding the video data, decoding the encoded video data, deblocking the decoded video data, and storing deblocked pictures in a reference picture memory.
• Video decoders may be configured to decode received video data, and then apply the same deblocking filters as was applied by the encoder to the decoded video data.
• Video decoders may deblock decoded video data for purposes of displaying the video data, e.g., to a user of a device including the decoder, as well as for use as reference video for subsequent video data to be decoded, e.g., for storage in a reference picture memory.
• the encoders and decoders can be synchronized, such that deblocking does not introduce error for subsequently coded video data using the deblocked video data for reference.
• HEVC High Efficiency Video Coding
• the upcoming standard is also referred to as H.265.
• the HEVC standard may also be referred to as ISO/IEC 23008-HEVC, which is intended to be the standard number for the delivered version of HEVC.
• the standardization efforts are based on a model of a video coding device referred to as the HEVC Test Model (HM).
• HM presumes several capabilities of video coding devices over devices according to, previous coding standards, such as ITU-T H.264/AVC. For example, whereas H.264 provides nine intra-prediction encoding modes, HM provides as many as thirty-five intra-prediction encoding modes.
• HEVC Working Draft 6 A recent working Draft (WD) of HEVC, referred to as “HEVC Working Draft 6” or “WD6,” is described in document JCTVC-H1003, Bross et al, "High-Efficiency Video Coding (HEVC) text specification draft 6," Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 8th Meeting: San Jose, California, USA, Feb. 2012, which is incorporated herein by reference in its entirety, and which as of October 1, 2012, is downloadable from:
• the proposed HEVC standard includes signaling respective offset values for the quantization parameters (QP) that are used for coding the chrominance components Cr and Cb. More particularly, according to the proposed HEVC standard specifies cb qp offset and cr qp offset syntax elements that are signaled in the picture parameter set (PPS).
• QP quantization parameters
• PPS picture parameter set
• the syntax elements cb qp offset and cr qp offset are examples of chrominance quantization parameter offset values that, for the respective chrominance component, specify an offset relative to the luminance QP, and may be used by a video coder to determine the respective chrominance QP (e.g., QP'cb and QP'cr) for a video block from a luminance QP (e.g., QP' Y ) for the video block.
• the proposed HEVC standard specifies that video coders may process chrominance components with a deblocking filter.
• the video coders may process an edge between two video blocks, P and Q, when at least one of these video blocks is intra-coded.
• the video coder typically looks up the tc parameter in a table based on the a chrominance QP of the edge for that component, e.g., QPc,Cr or QPc,cb for the Cr and Cb components, respectively.
• the tc parameter may determine the strength of the deblocking filter, and the video coder may apply the tc parameter in a clipping operation of the chrominance filter.
• the proposed HEVC standard specifies chrominance quantization parameter offset values, and the use of such values to determine chrominance QP parameters for blocks of video data
• the offset between luminance and chrominance QPs for blocks with a common edge may not be considered when configuring a chrominance component deblocking filter for the edge.
• the chrominance QP for edge i.e., the chrominance QP used to configure the chrominance component deblocking filter for the edge, may be determined based on the luminance QPs for the video blocks sharing the edge alone, without considering a chrominance quantization parameter offset values.
• the chrominance QP offset values are not considered. Because the offset values may be large, the video coder may apply deblocking filters with a less than ideal deblocking strength to the chrominance components.
• the techniques of this disclosure may improve deblocking functions applied to such edges, and may thereby reduce the appearance of the edge. More particularly, the techniques of this disclosure may improve the deblocking functions applied to the chrominance components at a common edge shared by two blocks of video data.
• a video coder e.g., a video encoder or video decoder, may calculate a chrominance QP for the edge between two blocks of video data not only based on the luminance QPs for the two blocks of video data, but also based on a chrominance QP offset value.
• a video decoder may, according to the techniques of this disclosure, determine the chrominance QP for the edge based on the chrominance QP offset value, the strength of the deblocking filter, e.g., the value of the tc parameter, may be more appropriate for the quality levels of the chrominance components of the two blocks of video data that share the common edge.
• FIG. 1 is a block diagram illustrating an example video encoding and decoding system 10 that may utilize techniques for deblocking an edge between video blocks.
• system 10 includes a source device 12 that provides encoded video data to be decoded at a later time by a destination device 14.
• source device 12 provides the video data to destination device 14 via a computer-readable medium 16.
• Source device 12 and destination device 14 may 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.
• source device 12 and destination device 14 may be equipped for wireless communication.
• computer-readable medium 16 may comprise a wireless communication channel.
• encoded data may be output from output interface 22 to a storage device.
• encoded data may be accessed from the storage device by input interface 28.
• 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.
• the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device 12. Destination device 14 may 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 device 14.
• 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 device 14 may 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.
• the techniques of this disclosure which concern deblocking edges between video blocks, are not necessarily limited to wireless applications or settings.
• the techniques may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.
• system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.
• the illustrated system 10 of FIG. 1 is merely one example. Techniques for deblocking edges between video blocks may be performed by any digital video encoding and/or decoding device. Moreover, the techniques of this disclosure may also be performed by a video preprocessor.
• Source device 12 and destination device 14 are merely examples of such coding devices in which source device 12 generates coded video data for transmission to destination device 14.
• devices 12, 14 may operate in a substantially symmetrical manner such that each of devices 12, 14 include video encoding and decoding components.
• system 10 may support oneway or two-way video transmission between video devices 12, 14, e.g., for video streaming, video playback, video broadcasting, or video telephony.
• Video source 18 of source device 12 may 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.
• video source 18 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video.
• source device 12 and destination device 14 may form so-called camera phones or video phones.
• the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications.
• the captured, pre-captured, or computer-generated video may be encoded by video encoder 20.
• the encoded video information may then be output by output interface 22 onto a computer- readable medium 16.
• Input interface 28 of destination device 14 receives information from computer- readable medium 16.
• the information of computer-readable medium 16 may include syntax information defined by video encoder 20, which is also used by video decoder 30, that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., GOPs.
• Display device 32 displays 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.
• CTR cathode ray tube
• LCD liquid crystal display
• plasma display e.g., a plasma display
• OLED organic light emitting diode
• Video encoder 20 and video decoder 30 may operate according to a video compression standard, such as the forthcoming ITU-T High Efficiency Video Coding (HEVC) standard, also referred to as "H.265.”
• Video encoder 20 and video decoder 30 may conform to the High Efficiency Video Coding Test Model (HM).
• HM High Efficiency Video Coding Test Model
• the techniques of this disclosure are not limited to any particular coding standard.
• Other examples include MPEG-2 and ITU-T H.263, and ITU-T H.264/AVC (Advanced Video Coding).
• video encoder 20 and video decoder 30 may each be integrated with an audio encoder and decoder, and may include appropriate MUX-DEMUX units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP).
• MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP).
• 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).
• JVT Joint Video Team
• 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.
• the Joint Video Team (JVT) continues to work on extensions to H.264/MPEG-4 AVC.
• Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), wireless communication devices that include a video coding device, such as encoder or decoder, discrete logic, software, hardware, firmware or any combinations thereof.
• DSPs digital signal processors
• ASICs application specific integrated circuits
• FPGAs field programmable gate arrays
• wireless communication devices that include a video coding device, such as encoder or decoder, discrete logic, software, hardware, firmware or any combinations thereof.
• Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective camera, computer, mobile device, subscriber device, broadcast device, set-top box, server, or the like.
• Each node of the quadtree data structure may provide syntax data for the corresponding CU.
• 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.
• 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 16x16 size is not split further, the four 8x8 sub-CUs will also be referred to as leaf-CUs although the 16x16 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.
• 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.
• 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.
• a bitstream may also define a smallest coding unit (SCU).
• SCU smallest coding unit
• 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 8x8 pixels up to the size of the treeblock with a maximum of 64x64 pixels or greater.
• Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may describe, for example, partitioning of the CU into one or more PUs.
• the HEVC standard allows for transformations according to TUs, which may be different for different CUs.
• the TUs are typically sized based on the size of PUs within a given CU defined for a partitioned LCU, although this may not always be the case.
• the TUs are typically the same size or smaller than the PUs.
• residual samples corresponding to a CU may be subdivided into smaller units using a quadtree structure known as "residual quad tree" (RQT).
• RQT residual quadtree structure
• the leaf nodes of the RQT may be referred to as transform units (TUs).
• Pixel difference values associated with the TUs may be transformed to produce transform coefficients, which may be quantized.
• a leaf-CU may include one or more prediction units (PUs).
• 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.
• 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.
• RQT residual quadtree
• the PU may include data defining one or more motion vectors for the PU.
• the data defining the motion vector for a PU may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a resolution for the motion vector (e.g., one-quarter pixel precision or one-eighth pixel precision), a reference picture to which the motion vector points, and/or a reference picture list (e.g., List 0, List 1, or List C) for the motion vector.
• a horizontal component of the motion vector e.g., a vertical component of the motion vector
• a resolution for the motion vector e.g., one-quarter pixel precision or one-eighth pixel precision
• a reference picture to which the motion vector points e.g., List 0, List 1, or List C
• a leaf-CU having one or more PUs may also include one or more transform units (TUs).
• the transform units may be specified using an RQT (also referred to as a TU quadtree structure), as discussed above.
• RQT also referred to as a TU quadtree structure
• a split flag may indicate whether a leaf-CU is split into four transform units. Then, each transform unit may be split further into further sub-TUs. When a TU is not split further, it may be referred to as a leaf-TU.
• all the leaf-TUs belonging to a leaf-CU share the same intra prediction mode. That is, the same intra-prediction mode is generally applied to calculate predicted values for all TUs of a leaf-CU.
• a video encoder may calculate a residual value for each leaf-TU using the intra prediction mode, as a difference between the portion of the CU corresponding to the TU and the original block.
• a TU is not necessarily limited to the size of a PU. Thus, TUs may be larger or smaller than a PU.
• a PU may be collocated with a corresponding leaf- TU for the same CU.
• the maximum size of a leaf-TU may correspond to the size of the corresponding leaf-CU.
• TUs of leaf-CUs may also be associated with respective quadtree data structures, referred to as residual quadtrees (RQTs). That is, a leaf-CU may include a quadtree indicating how the leaf-CU is partitioned into TUs.
• the root node of a TU quadtree generally corresponds to a leaf-CU, while the root node of a CU quadtree generally corresponds to a treeblock (or LCU).
• TUs of the RQT that are not split are referred to as leaf-TUs.
• this disclosure uses the terms CU and TU to refer to leaf-CU and leaf-TU, respectively, unless noted otherwise.
• a video sequence typically includes a series of video frames or pictures.
• a group of pictures generally comprises a series of one or more of the video pictures.
• a GOP may include syntax data in a header of the GOP, a header of one or more of the pictures, or elsewhere, that describes a number of pictures included in the GOP.
• Each slice of a picture may include slice syntax data that describes an encoding mode for the respective slice.
• Video encoder 20 typically operates on video blocks within individual video slices in order to encode the video data.
• a video block may correspond to a coding node within a CU.
• the video blocks may have fixed or varying sizes, and may differ in size according to a specified coding standard.
• the HM supports prediction in various PU sizes. Assuming that the size of a particular CU is 2Nx2N, the HM supports intra-prediction in PU sizes of 2Nx2N or NxN, and inter-prediction in symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, or NxN. The HM also supports asymmetric partitioning for inter-prediction in PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N. In asymmetric partitioning, one direction of a CU is not partitioned, while the other direction is partitioned into 25% and 75%.
• 2NxnU refers to a 2Nx2N CU that is partitioned horizontally with a 2Nx0.5N PU on top and a 2Nxl .5N PU on bottom.
• NxN and N by N may be used interchangeably to refer to the pixel dimensions of a video block in terms of vertical and horizontal dimensions, e.g., 16x16 pixels or 16 by 16 pixels.
• an NxN block generally has N pixels in a vertical direction and N pixels in a horizontal direction, where N represents a nonnegative integer value.
• the pixels in a block may be arranged in rows and columns.
• blocks need not necessarily have the same number of pixels in the horizontal direction as in the vertical direction.
• blocks may comprise NxM pixels, where M is not necessarily equal to N.
• video encoder 20 may calculate residual data for the TUs of the CU.
• the PUs may comprise syntax data describing a method or mode of generating predictive pixel data in the spatial domain (also referred to as the pixel domain) and the TUs may comprise 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 encoder 20 may form the TUs including the residual data for the CU, and then transform the TUs to produce transform coefficients for the CU.
• video encoder 20 may 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.
• the video encoder may 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.
• video encoder 20 may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector that can be entropy encoded.
• video encoder 20 may perform an adaptive scan.
• video encoder 20 may 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 encoder 20 may also entropy encode syntax elements associated with the encoded video data for use by video decoder 30 in decoding the video data.
• video encoder 20 may assign a context within a context model to a symbol to be transmitted.
• the context may relate to, for example, whether neighboring values of the symbol are non-zero or not.
• video encoder 20 may select a variable length code for a symbol to be transmitted.
• Codewords in VLC may be constructed such that relatively shorter codes correspond to more probable symbols, while longer codes correspond to less probable symbols. In this way, the use of VLC may achieve a bit savings over, for example, using equal- length codewords for each symbol to be transmitted.
• the probability determination may be based on a context assigned to the symbol.
• video encoder 20 may decode encoded pictures, e.g., by inverse quantizing and inverse transforming residual data, and combine the residual data with prediction data. In this manner, video encoder 20 can simulate the decoding process performed by video decoder 30. Both video encoder 20 and video decoder 30, therefore, will have access to substantially the same decoded pictures for use in inter- picture prediction.
• video decoder 30 may perform a decoding process that is the inverse of the encoding process performed by video encoder. For example, video decoder 30 may perform entropy decoding using the inverse of the entropy encoding techniques used by video encoder to entropy encode the quantized video data. Video decoder 30 may further inverse quantize the video data using the inverse of the quantization techniques employed by video encoder 20, and may perform an inverse of the transformation used by video encoder 20 to produce the transform coefficients that quantized. Video decoder 30 may then apply the resulting residual blocks to adjacent reference blocks (intra-prediction) or reference blocks from another picture (inter- prediction) to produce the video block for eventual display. Video decoder 30 may be configured, instructed controlled or directed to perform the inverse of the various processes performed by video encoder 20 based on the syntax elements provided by video encoder 20 with the encoded video data in the bitstream received by video decoder 30.
• Deblocking may generally be performed following inverse quantization and inverse transformation of video data, whether performed “in loop” by video encoder 20 or video decoder 30, or for eventual display of the blocks of video data by video decoder 30.
• a deblocking process may be performed "in loop” in the sense that the deblocking filtered pictures may be used as reference pictures for subsequently coded pictures (e.g., pictures coded using inter-prediction).
• video encoder 20 and video decoder 30 may be configured according to the HEVC test model (HM).
• HM HEVC test model
• a video encoder or decoder configured in accordance with the HM may generally determine, for each edge separating two PUs or TUs, whether to apply a deblocking filter to deblock the edge.
• the video encoder or decoder configured according to the techniques of HM may be configured to determine whether to deblock an edge based on an analysis of one or more lines of pixels perpendicular to the edge, for example, a line of 8 pixels.
• the HM may determine whether to deblock the edge by examining four pixels to the left and four pixels to the right of the edge along a common line.
• the number of pixels selected generally corresponds to the smallest block for deblocking, for example 8x8 pixels.
• the line of pixels used for analysis may enter only two PUs or TUs, namely the PUs or TUs immediately to the left and to the right of an edge.
• the line of pixels used for analysis of whether to perform deblocking for an edge is also referred to as a set of support pixels, or simply "support.”
• Video encoder 20 and video decoder 30 are examples of video coders that may perform deblocking according to the techniques of this disclosure for deblocking the chrominance components at a common edge between first and second decoded blocks of video data.
• video encoder 20 and video decoder 30 may be configured to decode a first block of data and a second block of video data. Both the first and second blocks may share a common edge.
• video encoder 20 may encode the first block and the second block, which encoder 20 may later decode to generate a reference picture.
• video encoder 20 and/or video decoder 30 may determine a strength of a deblocking filter for deblocking the edge and, more particularly, for deblocking chrominance components, based at least in part on a chrominance quantization parameter offset value.
• cr qp offset and cb qp offset values in the computation of the QPc,Cr and QPc,cb values that are used to look up tc parameters for deblocking filtering the Cb and Cr chrominance components at an edge between two blocks of video data, as follows:
• QPc,Cr QpU ( (QP Y , P + QP Y ,Q + l)/2 + cr_qp_offset ) (2)
• QPc,cb QpUV ( (QPY,P + QPY,Q + l)/2 + cb_qp_offset ) (3)
• QpUV is a function, table, or the like that converts the luminance quantization parameter QP Y for a particular block of video data into the chrominance quantization parameters QP & or QPcb values for the video block for Cb and Cr, respectively.
• QPy,p and QP Y ,Q are the luminance quantization parameter values for the first and second blocks of video data (denoted P and Q), respectively.
• (QP Y , P + QP Y ,Q + l)/2 is the average of the luminance quantization parameter values for the first and second blocks of video data.
• the chrominance quantization parameter offset values for Cr and Cb are cr qp offset and cb qp offset, respectively.
• the chrominance quantization parameter offset values may apply to all blocks of video data in a picture, and may be signaled, e.g., by video encoder 20, in a picture parameter set (PPS).
• QPc,Cr and QPc,cb are examples of chrominance quantization parameter values (for Cr and Cb, respectively) for a common edge between two blocks of video data.
• Cr and Cb may refer to two different types of chrominance values, e.g., two different chrominance components of the video data.
• Cr and Cb may be generalized and represented by the value "C.”
• the techniques of this disclosure may be compatible with chrominance QP offset signaling methods proposed in the following JCT-VC proposal:
• the Xu proposal proposes the following techniques for signaling the QPc r and QPc b chroma quantization parameters as an alternative to the techniques described in HEVC WD6:
• the QP& and QPc b values are the chrominance quantization parameters for Cr and Cb, respectively, for a particular block of video data.
• Cb QP offset and Cr QP offset are the signalled chrominance quantization parameter offset values for Cr and Cb, respectively.
• Cb QP offset and Cr QP offset may apply to each block of video data in a picture and may be signaled in a PPS.
• the QPc,Cr and QPc,c b quantization parameter values for a common edge between two blocks that are used to look up tc parameters for deblocking filtering the Cb and Cr components may be computed according to the techniques of this disclosure as follows:
• QPc,cb Clip3(0, 51, QpUV ( (QP Y , P + QP Y , Q + l)/2 ) + cb_qp_offset ) (15)
• the techniques of this disclosure may be compatible with chrominance QP offset signaling methods proposed in the following JCT-VC proposal:
• the Sullivan proposal was adopted into the text of HEVC WD8.
• the modification of the HEVC standard based on the Sullivan proposal is related to the conversion table from luminance QP to chrominance QP, which is an example of QpUV in the equations herein.
• the range of values supported in the mapping of luminance QP to chrominance QP is extended.
• the variable QPcbr specifies the value of QPcb and QPc r and is given by Table 1 (QpUV) below.
• variable QPcb r is based on the index qPi.
• the index qPi in Table 1 corresponds to qPIcb for chrominance component Cb and qPI & for chrominance component C r .
• QpBdOffsetC is the value of a chrominance quantization parameter range offset. The value of QpBdOffsetC may be determined based on the bit depth of the chrominance components.
• the Sullivan proposal introduces slice-level chrominance QP offsets.
• the Sullivan proposal introduces slice qp delta cb and slice qp delta cr as slice-level chrominance QP offsets.
• cb qp offset and cr qp offset may be picture-level QP offsets that apply to all video blocks in a picture
• each of one or more slices in a picture may be associated with respective slice-level chrominance QP offsets that are associated with all video blocks in a particular slice.
• the slice-level chrominance QP offsets may be picture-level QP offsets that apply to all video blocks in a picture.
• chrominance QP offsets may be signaled, for example, in a slice header.
• a video coder may use both the slice-level chrominance QP offsets and the picture-level chrominance QP offsets to determine the chrominance QP values (e.g., QPc r and QPcb) for a video block from the luminance QP value for the video block.
• QpUV is a function or a table used by a video coder for converting a luminance quantization parameter QPy into chrominance quantization parameter values QPc r or QPcb- QpUV may also be implemented by mathematical equations and/or conditions. In one example, clipping may be applied before looking up the tc parameters in the QpUV table.
• slice qp delta cb from one of the slices. From which slice to take the slice-level chrominance quantization parameter offset values may be predetermined, or signaled by video encoder 20. In one example, the values of slice qp delta cr and
• slice qp delta cb may be taken from the slice containing block Q.
• a video coder may determine the slice-level QP offset value to be an average or other mathematical combination of the respective slice level QP offset values for the two slices.
• a video coder may compute the QPc,Cr and QPc,cb values that are used to look up tc parameters for deblocking filtering the Cb and Cr components as follows:
• slice qp delta cr Q are the Cr component QP offsets for the slices including video blocks P and Q, respectively.
• slice qp delta cb P and slice qp delta cb Q are the Cb component QP offsets for slices including P and Q, respectively.
• equation 8 may be modified as follows:
• QPccr Clip3(0, 51 , (QP Y , P + QP Y , Q + l)/2 + (24)
• slice-level chrominance QP offsets may be added to the picture-level chrominance QP offsets of the seven remaining equations described above with respect to Method A* and Method B*. For the sake of brevity, each of the equations is not reproduced herein.
• a video coder may compute the chrominance quantization parameter values for the edge, e.g., QPc,Cr and QPc,cb, that are used to look up tc parameters for deblocking filtering the Cb and Cr components as follows:
• QPc,cb ( QpUV ( QP Y , P + cb qp offset + slice_qp_delta_cb_p) (26)
• QPy,p and QP Y ,Q are the respective luminance QP values of the first and second video blocks (denoted P and Q) that share the common edge.
• the 4:2:2 and 4:4:4 formats may be included in future HEVC extensions.
• the cb qp offset and cr qp offset syntax elements in the PPS and/or the slice-level chrominance QP offsets may be used to determine the value of QPc,cr and QPc,cb- QPc,Cr and QPc,cb may be used to look up tc parameters for deblocking filtering the Cb and Cr components.
• a determination whether to include PPS and/or slice- level chrominance offsets when configuring a deblocking filter may be dependent on a color format.
• QPc,Cr and QPc,c b may be made dependent on the color format.
• PPS and/or slice-level chrominance offsets may be included when configuring deblocking filtering 4:2:2 and/or 4:4:4 chrominance components.
• the HEVC high-level syntax parameter chroma format idc included in the Sequence Parameter Set (SPS) determines the chroma format. Therefore, the inclusion of the PPS- and/or slice-level chroma QP offsets to determine the QPc,c r and QPc,c b values may be made dependent on the chroma format idc syntax element. Further, the inclusion of the PPS- and/or slice-level chrominance QP offsets to determine the QPc,Cr and QPc,c b values may be made dependent on a profile and/or level for the video data included in the blocks of video data that share the common edge.
• SPS Sequence Parameter Set
• Video encoder 20 and video decoder 30 each may implement any of the techniques described herein for deblocking filtering of chrominance components at a common edge between two blocks of video data.
• video encoder 20 and video decoder 30 may each employ any of the example equations discussed above to determine a chrominance QP value for the edge, which in turn may be used to determine a strength of a deblocking filter, e.g., a t c value, for a chrominance component.
• Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable encoder or decoder circuitry, as applicable, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic circuitry, software, hardware, firmware or any combinations thereof.
• DSPs digital signal processors
• ASICs application specific integrated circuits
• FPGAs field programmable gate arrays
• Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined video encoder/decoder (CODEC).
• An apparatus including video encoder 20 and/or video decoder 30 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.
• FIG. 2 is a block diagram illustrating an example of video encoder 20 that may implement techniques for deblocking edges between video blocks.
• Video encoder 20 may perform intra- and inter-coding of blocks within video frames, including CUs, or sub-CUs of CUs.
• Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame.
• Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames of a video sequence.
• Intra-mode may refer to any of several spatial based compression modes and inter-modes such as uni-directional prediction (P-mode) or bidirectional prediction (B-mode) may refer to any of several temporal-based compression modes.
• I-mode may refer to any of several spatial based compression modes and inter-modes such as uni-directional prediction (P-mode) or bidirectional prediction (B-mode) may refer to any of several temporal-based compression modes.
• components for inter-mode encoding are depicted in FIG. 2, it
• video encoder 20 receives a current video block within a video frame to be encoded.
• video encoder 20 includes mode select unit 40, reference picture memory 64, summer 50, transform processing unit 52, quantization unit 54, entropy encoding unit 56, and deblocker 66.
• Mode select unit 40 includes motion compensation unit 44, motion estimation unit 42, intra- prediction unit 46, and partition unit 48.
• video encoder 20 also includes inverse quantization unit 58, inverse transform unit 60, and summer 62.
• video encoder 20 includes deblocker 66 that selectively filters the output of summer 62.
• deblocker 66 receives reconstructed video data from summer 62, which corresponds to predictive data received from either motion compensation unit 44 or intra-prediction unit 46, added to inverse quantized and inverse transformed residual data.
• deblocker 66 receives decoded blocks of video data, e.g., CUs of an LCU and/or LCUs of a slice or frame.
• deblocker 66 selectively filters the blocks of video data to remove blockiness artifacts. Deblocker 66 is described in greater detail below.
• video encoder 20 receives a video frame or slice to be coded.
• the frame or slice may be divided into multiple video blocks.
• Motion estimation unit 42 and motion compensation unit 44 perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal compression.
• An intra prediction unit may also perform intra- predictive coding of the received video block relative to one or more neighboring blocks in the same frame or slice as the block to be coded to provide spatial compression.
• Video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.
• partition unit 48 may partition blocks of video data into sub-blocks, based on evaluation of previous partitioning schemes in previous coding passes. For example, partition unit 48 may initially partition a frame 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 unit 40 may 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 unit 40 may 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 summer 50 to generate residual block data and to summer 62 to reconstruct the encoded block for use as a reference picture. Mode select unit 40 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit 56.
• Motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.
• Motion estimation performed by motion estimation unit 42, 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 frame or picture relative to a predictive block within a reference picture (or other coded unit) relative to the current block being coded within the current frame (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.
• video encoder 20 may calculate values for sub-integer pixel positions of reference pictures stored in reference picture memory 64. For example, video encoder 20 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.
• Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture.
• the reference picture may be selected from a first reference picture list (List 0) or a second reference picture list (List 1), each of which identify one or more reference pictures stored in reference picture memory 64.
• Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.
• Motion compensation performed by motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit 42. Again, motion estimation unit 42 and motion compensation unit 44 may be functionally integrated, in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the predictive block to which the motion vector points in one of the reference picture lists. Summer 50 forms 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 unit 42 performs motion estimation relative to luminance components, and motion
• compensation unit 44 uses motion vectors calculated based on the luminance
• Mode select unit 40 may also generate syntax elements associated with the video blocks and the video slice for use by video decoder 30 in decoding the video blocks of the video slice.
• Intra-prediction unit 46 may intra-predict a current block, as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44, as described above. In particular, intra-prediction unit 46 may determine an intra- prediction mode to use to encode a current block. In some examples, intra-prediction unit 46 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction unit 46 (or mode select unit 40, in some examples) may select an appropriate intra-prediction mode to use from the tested modes.
• intra-prediction unit 46 may 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 unit 46 may 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.
• intra-prediction unit 46 may provide information indicative of the selected intra-prediction mode for the block to entropy encoding unit 56.
• Entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode.
• Video encoder 20 may include in the transmitted bitstream configuration data, which may include a plurality of intra- prediction mode index tables and a plurality of modified intra-prediction mode index tables (also referred to as codeword mapping tables), definitions of encoding contexts for various blocks, and indications of a most probable intra-prediction mode, an intra- prediction mode index table, and a modified intra-prediction mode index table to use for each of the contexts.
• Video encoder 20 forms a residual video block by subtracting the prediction data from mode select unit 40 from the original video block being coded.
• Summer 50 represents the component or components that perform this subtraction operation.
• Transform processing unit 52 applies 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 unit 52 may 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.
• transform processing unit 52 applies 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.
• Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54.
• Quantization unit 54 quantizes the transform coefficients to further reduce bit rate.
• the quantization process may reduce the bit depth associated with some or all of the coefficients.
• the degree of quantization may be modified by adjusting a quantization parameter.
• quantization unit 54 may then perform a scan of the matrix including the quantized transform coefficients.
• entropy encoding unit 56 may perform the scan.
• entropy encoding unit 56 entropy codes the quantized transform coefficients.
• entropy encoding unit 56 may 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.
• context may be based on neighboring blocks.
• Inverse quantization unit 58 and inverse transform unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block.
• Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the frames of reference picture memory 64. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values for use in motion estimation.
• Summer 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reconstructed video block for storage in reference picture memory 64.
• video encoder 20 includes deblocker 66 that selectively filters the output of summer 62.
• Deblocker 66 performs any or all of the techniques of this disclosure to deblock the output of summer 62, that is, the reconstructed video blocks.
• the reconstructed video blocks, as filtered by deblocker 66, may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block to inter-code a block in a subsequently-coded picture.
• deblocker 66 receives reconstructed video data from summer 62, which corresponds to predictive data received from either motion compensation unit 44 or intra-prediction unit 46, added to inverse quantized and inverse transformed residual data.
• deblocker 66 receives decoded blocks of video data, e.g., CUs of an LCU, LCUs of a slice or frame, PUs of a CU, and/or TUs of a CU. In general, deblocker 66 selectively filters the blocks of video data.
• Deblocker 66 is generally configured to analyze pixels of two neighboring blocks (e.g., two CUs, PUs, or TUs) near an edge between the two blocks to determine whether to deblock the edge. More particularly, deblocker 66 may alter the values of the pixels near the edge when a high-frequency change in values is detected. Deblocker 66 may also be configured to perform any or all of the techniques of this disclosure.
• Deblocker 66 may include predefined adapted sets of support, or calculate adapted sets of support on the fly. Deblocker 66 may thereby avoid including nearby edges into the computation of the deblocking decisions or deblocking filtering, and to avoid filter result dependencies between nearby edges. Deblocker 66 may also skip support adaptation when narrow blocks on either or both sides of an edge under consideration for deblocking are perpendicular to the edge. When at least one narrow non-square partition or transform is parallel to the edge to be deblocked, deblocker 66 may adapt deblocking decision functions and/or deblocking filters to avoid
• deblocker 66 may compute QP c ,c r and QPc,cb values that are used to look up t c parameters for deblocking filtering according to the techniques described herein, e.g., according to any of the equations described above.
• deblocker 66 may calculate a chrominance QP value for a common edge between two blocks of video data by calculating an average of the first and second luminance QP values for the two video blocks, and applying the chrominance QP offset value to the average, e.g., as illustrated by equations 2, 3 and 8- 15.
• the two video blocks that share a common edge are located within different slices.
• the two video blocks may be associated with different slice-level QP offset values, e.g., different values for slice qp delta cr and slice qp delta cb.
• deblocker 66 may be configured to select the slice-level QP offset values for one of the blocks for application to determine the chrominance QP values for the edge according to the techniques described herein.
• deblocker 66 may be configured to average or otherwise combine the slice-level QP offset values for the two blocks to determine combined slice-level QP offset values, and may then apply the combined slice-level QP offset values to determine the chrominance QP values for the edge according to the techniques described herein.
• video encoder 20 of FIG. 2 represents an example of a video encoder configured, according to the techniques of this disclosure to determine a chrominance QP value for a common edge between two decoded blocks of video data based on a chrominance QP offset value, and determine a strength for a deblocking filter based on the chrominance QP value for the edge.
• FIG. 3 is a block diagram illustrating an example of video decoder 30, which decodes an encoded video sequence.
• video decoder 30 includes an entropy decoding unit 70, motion compensation unit 72, intra prediction unit 74, inverse quantization unit 76, inverse transformation unit 78, reference frame store 82, summer 80, and deblocker 84.
• Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 20 (FIG. 2).
• Motion compensation unit 72 may generate prediction data based on motion vectors received from entropy decoding unit 70.
• video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from video encoder 20.
• Entropy decoding unit 70 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra- prediction mode indicators, and other syntax elements.
• Entropy decoding unit 70 forwards the motion vectors to and other syntax elements to motion compensation unit 72.
• Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level.
• intra prediction unit 74 may 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 frame or picture.
• motion compensation unit 72 produces predictive blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 70.
• the predictive blocks may be produced from one of the reference pictures within one of the reference picture lists.
• Video decoder 30 may construct the reference picture lists, List 0 and List 1, using default construction techniques based on reference pictures stored in reference picture memory 92.
• Motion compensation unit 72 determines prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit 72 uses some of the received syntax elements to determine a prediction mode (e.g., intra- or inter- prediction) used to code the video blocks of the video slice, an inter-prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information to decode the video blocks in the current video slice.
• a prediction mode e.g., intra- or inter- prediction
• an inter-prediction slice type e.g., B slice, P slice, or GPB slice
• construction information for one or more of the reference picture lists for the slice motion vectors for each inter-encoded video block of
• Motion compensation unit 72 may also perform interpolation based on interpolation filters. Motion compensation unit 72 may use interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 72 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.
• Inverse transform unit 78 applies 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.
• an inverse transform e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process
• video decoder 30 forms a decoded video block by summing the residual blocks from inverse transform unit 78 with the corresponding predictive blocks generated by motion compensation unit 82.
• Summer 80 represents the component or components that perform this summation operation.
• Deblocker 84 may be configured to perform any or all of the techniques of this disclosure to deblock the output of summer 80.
• Deblocker 84 may selectively deblock CUs, including TUs and PUs of CUs, received from summer 80 in accordance with any or all of the techniques of this disclosure.
• Deblocker 84 may conform substantially to deblocker 66 (FIG. 2), in that deblocker 84 may be configured to perform any or all of the techniques described with respect to de-b locker 66.
• the decoded video blocks in a given frame or picture, as filtered by deblocker 84, are then stored in reference picture memory 92, which stores reference pictures used for subsequent motion compensation.
• Reference picture memory 82 also stores decoded video for later presentation on a display device, such as display device 32 of FIG. 1.
• deblocker 84 may compute QPc,Cr and QPc,cb values that are used to look up tc parameters for deblocking filtering according to the techniques described herein, e.g., according to any of the equations described above.
• deblocker 84 may calculate a chrominance QP value for a common edge between two blocks of video data by calculating an average of the first and second luminance QP values for the two video blocks, and applying the chrominance QP offset value to the average, e.g., as illustrated by equations 2, 3 and 8-15.
• the chrominance QP offset value for a chrominance component may be a picture-level chrominance QP offset value, which may apply to all video blocks of a picture, and may be signaled in a PPS.
• deblocker 84 may additionally or alternatively determine a slice-level chrominance QP offset value for the chrominance component, which may apply to all video blocks in a given slice, and may be signaled in a slice-header.
• the slice-level chrominance QP offset may be applied in a manner similar to the picture-level chrominance QP offset value, e.g., by summation with the picture-level chrominance QP offset value and the average of the luminance QP values for the two blocks as illustrated by equations 20 and 21.
• the two video blocks that share a common edge are located within different slices.
• the two video blocks may be associated with different slice-level QP offset values, e.g., different values for slice qp delta cr and slice qp delta cb.
• deblocker 84 may be configured to select the slice-level QP offset values for one of the blocks for application to determine the chrominance QP values for the edge according to the techniques described herein.
• deblocker 84 may be configured to average or otherwise combine the slice-level QP offset values for the two blocks to determine combined slice-level QP offset values, and may then apply the combined slice-level QP offset values to determine the chrominance QP values for the edge according to the techniques described herein.
• video decoder 30 of FIG. 3 represents an example of a video decoder configured, according to the techniques of this disclosure, to determine a chrominance QP value for a common edge between two decoded blocks of video data based on a chrominance QP offset value, and determine a strength for a deblocking filter based on the chrominance QP value for the edge.
• FIG. 4 is a block diagram illustrating components of an example deblocker 90.
• deblocker 66 (FIG. 2) and deblocker 84 (FIG. 3) may include components substantially similar to those of deblocker 90.
• Other video coding devices such as video encoders, video decoders, video encoder/decoders (CODECs), and the like may also include components substantially similar to deblocker 90.
• Deblocker 90 may be implemented in hardware, software, or firmware. When implemented in software or firmware, corresponding hardware (such as one or more processors or processing units and memory for storing instructions for the software or firmware) may also be provided.
• deblocker 90 includes deblocking determination unit 94, support definitions 92, deblocking filtering unit 96, deblocking filter definitions 98, and edge locations data structure 95. Any or all of the components of deblocker 90 may be functionally integrated. The components of deblocker 90 are illustrated separately only for purposes of illustration.
• deblocker 90 receives data for decoded blocks, e.g., from a summation component, such as unit 62 (FIG. 2) or unit 80 (FIG. 3) that combines prediction data with residual data for the blocks.
• the data may further include an indication of how the blocks were predicted.
• deblocker 90 is configured to receive data including a decoded LCU and a CU quadtree for the LCU, where the CU quadtree describes how the LCU is partitioned into CUs and describes the prediction modes for leaf-node CUs.
• the data may also include information indicating partitioning of leaf-node CUs into PUs and TUs, which may further indicate whether the PUs are asymmetric motion partitions and/or whether the TUs are nonsquare quadtree transform (NSQT) partitions.
• NSP nonsquare quadtree transform
• a TU quadtree may indicate whether TUs are NSQT partitions and/or whether TUs correspond to asymmetric motion partition PUs.
• Deblocking determination unit 94 generally determines whether, for two neighboring blocks (for example, two CUs, PUs, or TUs), an edge between the two blocks should be deblocked. Deblocking determination unit 94 may determine locations of edges using edge locations data structure 95.
• Deblocking determination unit 94 may be configured to apply one or more deblocking determination functions to one or more sets of support, as defined by support definitions 92, to determine whether a particular edge between two blocks of video data should be deblocked. In some examples, however, deblocking determination unit 94 is configured to skip application of the deblocking determination functions to a particular edge or to adapt deblocking decision functions and/or deblocking filters for the particular edge.
• deblocker 90 may output the data for the blocks without altering the data. That is, the data may bypass deblocking filtering unit 96. As an example, deblocker 90 may determine that two blocks should not be filtered if they have overlapping sets of support for a de-blocking function and/or for a de-blocking function. On the other hand, when deblocking determination unit 94 determines that an edge should be deblocked, deblocking determination unit 94 may cause deblocking filtering unit 96 to filter values for pixels near the edge, to deblock the edge.
• Deblocker 90 may be configured to analyze lines of pixels perpendicular to and intersecting the respective edge segments to determine whether to deblock any or all of the edge segments, whether to apply a weak or strong filter to the edge segments to be deblocked, and widths of weak filters.
• deblocking determination unit 94 may be configured to make these various determinations (i.e., whether to deblock an edge segment, whether to apply a strong or weak filter to deblock the edge segment, and a width of a weak filter when a weak filter is selected) based at least in part on the deblocking parameters, e.g., ⁇ and t c .
• Support definitions 92 includes data defining the lines of pixels to be used to make these determinations.
• Deblocking filtering unit 96 retrieves definitions of deblocking filters from deblocking filter definitions 98 for edges to be deblocked, as indicated by deblocking determination unit 94. For edges between non-square blocks, deblocking filtering unit 96 may retrieve adapted deblocking filters from deblocking filter definitions 98, such that the filters do not cross additional boundaries. In general, filtering of an edge uses values of pixels from the neighborhood of a current edge to be deblocked. Therefore, both deblocking decision functions and deblocking filters may have a certain support region on both sides of an edge. By applying a deblocking filter to pixels in the neighborhood of an edge, deblocking filtering unit 96 may smooth the values of the pixels such that high frequency transitions near the edge are dampened. In this manner, application of deblocking filters to pixels near an edge may reduce blockiness artifacts near the edge.
• a video decoding device such as video encoder 20 or video decoder 30 of FIGS. 1-3, may include a deblocking unit conforming substantially to the example of deb locker 90.
• Video encoder 20 or video decoder 30 may be configured to apply a deblocking filter or function when a decision function indicates that a common edge between two blocks should be deblocked.
• deblocker 90 may compute QPc,Cr and QPc,cb values that are used to look up tc parameters for deblocking filtering according to the techniques described herein, e.g., according to any of the equations described above. As discussed above, the t c parameter may impact the strength of the deblocking filter applied by deb locker 90. In some examples, deblocker 90 may calculate a chrominance QP value for a common edge between two blocks of video data by calculating an average of the first and second luminance QP values for the two video blocks, and applying the chrominance QP offset value to the average, e.g., as illustrated by equations 2, 3 and 8-15.
• the chrominance QP offset value for a chrominance component may be a picture-level chrominance QP offset value, which may apply to all video blocks of a picture, and may be signaled in a PPS.
• deblocker 90 may additionally or alternatively determine a slice-level chrominance QP offset value for the chrominance component, which may apply to all video blocks in a given slice, and may be signaled in a slice-header.
• the slice-level chrominance QP offset may be applied in a manner similar to the picture-level chrominance QP offset value, e.g., by summation with the picture-level chrominance QP offset value and the average of the luminance QP values for the two blocks as illustrated by equations 20 and 21.
• the two video blocks that share a common edge are located within different slices.
• the two video blocks may be associated with different slice-level QP offset values, e.g., different values for slice qp delta cr and slice qp delta cb.
• deblocker 90 may be configured to select the slice-level QP offset values for one of the blocks for application to determine the chrominance QP values for the edge according to the techniques described herein.
• deblocker 90 may be configured to average or otherwise combine the slice-level QP offset values for the two blocks to determine combined slice-level QP offset values, and may then apply the combined slice-level QP offset values to determine the chrominance QP values for the edge according to the techniques described herein.
• FIG. 5 is a conceptual diagram illustrating an edge 104 formed by two neighboring blocks 100, 102.
• Blocks 100, 102 may correspond to blocks P and Q described above.
• FIG. 5 shows blocks 100, 102 in a side-by- side arrangement, it should be understood that above-and-below neighboring blocks may also form an edge that can be deblocked in accordance with the techniques of this disclosure.
• blocks 100, 102 are shown as being the same size, the neighboring blocks forming an edge are not necessarily the same size.
• Blocks 100, 102 may represent transform blocks of respective transform units (TUs). Accordingly, blocks 100, 102 may be associated with respective quantization parameter (QP) values. Additionally, blocks 100 and 102 may each include luminance components, as well as one or more chrominance components, e.g., Cr and Cb.
• QP quantization parameter
• a deblocker such as deblocker 66 (FIG. 2), deblocker 84 (FIG. 3), or deblocker 90 (FIG. 4) may be configured to determine a chrominance QP value (for each of one or more chrominance components) for deblocking edge 104 between blocks 100 and 102 based not only on the respective luminance QPs for blocks 100 and 102, but also on a chrominance QP offset value.
• the deblocker may apply the chrominance QP offset value to an average of the luminance QP values of blocks 100 and 102, e.g., according to any of equations 2, 3 and 8-15.
• the deblocker may then use the chrominance QP value for edge 104 for a particular chrominance component to determine the strength of the deblocking filter to apply to the edge for the particular chrominance component, e.g., to determine the t c value.
• blocks 100 and 102 may be included in different slices.
• blocks 100 and 102 may be associated with different slice-level QP offset values, e.g., different values for each of slice qp delta cr and slice qp delta cb.
• a deblocker may be configured to select the slice-level QP offset values associated with one of blocks 100 and 102 for application to determine the chrominance QP values for edge 104 according to the techniques described herein. In other examples, the deblocker may be configured to average or otherwise
• FIG. 6 is a flowchart illustrating an example method for performing deblocking during a video coding process in accordance with the techniques of this disclosure.
• the example method of FIG. 6 may be performed by a deblocker, such as deblocker 66 (FIG. 2), deblocker 84 (FIG. 3), or deblocker 90 (FIG. 4).
• the example method of FIG. 6 may be performed by a video coder, which may be a video encoder or a video decoder, such as video encoder 20 or video docoder 30 (FIGS. 1-3).
• the video coder may also determine a chrominance QP offset value for a particular one of one or more chrominance components of the video blocks, e.g., cr qp offset for the Cr component, or cb qp offset for the Cb component (114).
• the video coder calculates a chrominance QP value for the common edge between the first and second blocks based on the respective luminance QPs for the first and second blocks, as well as the chrominance QP offset value for the chrominance component (116).
• the video coder calculates the chrominance QP value for the common edge by averaging the luminance QP values for the two video blocks, and applying the chrominance QP offset value to the average.
• the video coder calculates the chrominance QP value for the common edge using any of the example equations 2, 3 and 8-15 discussed above.
• the video coder may then determine a strength of a deblocking filter to be applied to the common edge for the chrominance component, e.g., Cr or Cb, based on the chrominance QP value for edge that was calculated for the particular chrominance component (118).
• the determination of the strength of the deblocking filter may include determining the t c parameter value based on the chrominance QP value for edge that was calculated for the particular chrominance component.
• the video coder e.g., deblocker of the video coder, may then apply the deblocking filter with the determined strength to deblock the common edge between the first and second blocks (120).
• the method of FIG. 6 represents an example of a method including determining a chrominance QP value for a common edge between two decoded blocks of video data based on a chrominance QP offset value, and determining a strength for a deblocking filter based on the chrominance QP value for the edge.
• 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 on 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.
• 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.
• such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium.
• coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave are included in the definition of medium.
• DSL digital subscriber line
• computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media.
• Disk and disc 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.
• processors such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry.
• DSPs digital signal processors
• ASICs application specific integrated circuits
• FPGAs field programmable logic arrays
• the term "processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.
• the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.
• the techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set).
• IC integrated circuit
• a set of ICs e.g., a chip set.
• Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

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