WO2019244719A1

WO2019244719A1 - Systems and methods for performing affine motion compensation prediction for coding of video data

Info

Publication number: WO2019244719A1
Application number: PCT/JP2019/023131
Authority: WO
Inventors: Weijia Zhu; Byeongdoo CHOI; Kiran Mukesh MISRA; Christopher Andrew Segall
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2018-06-18
Filing date: 2019-06-11
Publication date: 2019-12-26
Anticipated expiration: 2020-12-18

Abstract

This disclosure relates to video coding and more particularly to techniques for performing motion compensation. According to an aspect of an invention, control points (mv0, mv1 and mv2) for a video block are determined by comparing a function of one or more motion vector candidates (mvA to mvG) to a threshold value. Moreover, the control points determine motion vector fields for sub-blocks within the video block and a motion compensation process based on the motion vector fields is performed.

Description

SYSTEMS AND METHODS FOR PERFORMING AFFINE MOTION COMPENSATION PREDICTION FOR CODING OF VIDEO DATA

This disclosure relates to video coding and more particularly to techniques for performing motion compensation for coding video data.

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265, December 2016, which is incorporated by reference, and referred to herein as ITU-T H.265. Extensions and improvements for ITU-T H.265 are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) have commenced standardization of video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model 7 (JEM 7), Algorithm Description of Joint Exploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which is incorporated by reference herein, describes coding features under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. It should be noted that the coding features of JEM 7 are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM 7 and implementations of JEM reference software. Further, in response to a “Joint Call for Proposals on Video Compression with Capabilities beyond HEVC,” jointly issued by VCEG and MPEG, multiple descriptions of video coding were proposed by various groups at the 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 April 2018, San Diego, CA.

Video compression techniques enable data requirements for storing and transmitting video data to be reduced. Video compression techniques may reduce data requirements by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of frames within a video sequence, a frame within a group of frames, slices within a frame, coding tree units (e.g., macroblocks) within a slice, coding blocks within a coding tree unit, etc.). Intra prediction coding techniques (e.g., intra-picture (spatial)) and inter prediction techniques (i.e., inter-picture (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, motion vectors, and block vectors). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in a compliant bitstream.

In one example, a method of performing motion compensation comprises determining control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, determining motion vector fields for sub-blocks within the video block based on the determined control points, and performing a motion compensation process based on the determined motion vector fields.

FIG. 1 is a block diagram illustrating an example of a system that may be configured to encode and decode video data according to one or more techniques of this disclosure. FIG. 2 is a conceptual diagram illustrating a quad tree binary tree partitioning in accordance with one or more techniques of this disclosure. FIG. 3 is a conceptual diagram illustrating an example of candidate control motion vectors in accordance with one or more techniques of this disclosure. FIG. 4A is a conceptual diagram illustrating an example of deriving control motion vectors in accordance with one or more techniques of this disclosure. FIG. 4B is a conceptual diagram illustrating an example of deriving control motion vectors in accordance with one or more techniques of this disclosure. FIG. 5 is a conceptual diagram illustrating an example of deriving motion vector fields in accordance with one or more techniques of this disclosure. FIG. 6 is a conceptual diagram illustrating an example of control motion vectors in accordance with one or more techniques of this disclosure. FIG. 7 is a conceptual diagram illustrating an example of deriving control motion vectors in accordance with one or more techniques of this disclosure. FIG. 8 is a block diagram illustrating an example of a video encoder that may be configured to encode video data according to one or more techniques of this disclosure. FIG. 9 is a conceptual diagram illustrating an example of dividing a video block into regions for purposed of performing affine motion compensation prediction according to one or more techniques of this disclosure. FIG. 10 is a conceptual diagram illustrating an example of deriving control motion vectors in according to one or more techniques of this disclosure. FIG. 11 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure.

In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for performing affine motion compensation prediction for coding of video data. It should be noted that although techniques of this disclosure are described with respect to ITU-T H.264, ITU-T H.265, and JEM, the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H.265 and JEM. Thus, reference to ITU-T H.264, ITU-T H.265, and/or JEM is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein is for descriptive purposes and should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.

In one example, a device for video coding comprises one or more processors configured to determine control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, determine motion vector fields for sub-blocks within the video block based on the determined control points, and perform a motion compensation process based on the determined motion vector fields.

In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to determine control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, determine motion vector fields for sub-blocks within the video block based on the determined control points, and perform a motion compensation process based on the determined motion vector fields.

In one example, an apparatus comprises means for determining control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, means for determining motion vector fields for sub-blocks within the video block based on the determined control points, and means for performing a motion compensation process based on the determined motion vector fields.

The details of one or more examples are set forth in the accompanying drawings and the description below. Unless explicitly stated otherwise, components and functions are optional and may be combined or subdivided, and operations may vary in sequence or may be combined or subdivided. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Video content typically includes video sequences comprised of a series of frames. A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may include a plurality of slices or tiles, where a slice or tile includes a plurality of video blocks. As used herein, the term video block may generally refer to an area of a picture including one or more video components, or may more specifically refer to the largest array of pixel/sample values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, the term current video block may refer to an area of a picture being encoded or decoded. A video block may be defined as an array of pixel values (also referred to as samples) that may be predictively coded. Video blocks may be ordered according to a scan pattern (e.g., a raster scan). A video encoder may perform predictive encoding on video blocks and sub-divisions thereof. Video blocks and sub-divisions thereof may be referred to as nodes. ITU-T H.264 specifies a macroblock including 16x16 luma samples. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU) structure where a picture may be split into CTUs of equal size and each CTU may include Coding Tree Blocks (CTB) having 16x16, 32x32, or 64x64 luma samples. In ITU-T H.265, the CTBs of a CTU may be partitioned into Coding Blocks (CB) according to a corresponding quadtree block structure. According to ITU-T H.265, one luma CB together with two corresponding chroma CBs (e.g., Cr and Cb chroma components) and associated syntax elements are referred to as a coding unit (CU). In ITU-T H.265, a minimum allowed size of a CB may be signaled. In ITU-T H.265, the smallest minimum allowed size of a luma CB is 8x8 luma samples. A CU is associated with a prediction unit (PU) structure defining one or more prediction units (PU) for the CU, where a PU is associated with corresponding reference samples. That is, in ITU-T H.265, the decision to code a picture area using intra prediction or inter prediction is made at the CU level. In ITU-T H.265, a PU may include luma and chroma prediction blocks (PBs), where square PBs are supported for intra prediction and rectangular PBs are supported for inter prediction. Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) may associate PUs with corresponding reference samples.

JEM specifies a CTU having a maximum size of 256x256 luma samples. In JEM, CTUs may be further partitioned according a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree structure. In JEM, the binary tree structure enables quadtree leaf nodes to be divided vertically or horizontally. FIG. 2 illustrates an example of a CTU (e.g., a CTU having a size of 128x128 luma samples) being partitioned into quadtree leaf nodes and quadtree leaf nodes being further partitioned according to a binary tree. That is, in FIG. 2 dashed lines indicate binary tree partitions. Thus, the binary tree structure in JEM enables square and rectangular leaf nodes, where each leaf node includes a Coding Block (CB) for each component of video data. In JEM, CBs may be used for prediction without any further partitioning. Further, in JEM, luma and chroma components may have separate QTBT structures. That is, chroma CBs may be independent of luma partitioning. In JEM, separate QTBT structures are enabled for slices of video data coded using intra prediction techniques.

A video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a CU with respect to the number of luma samples included in a CU. For example, for the 4:2:0 format, the sampling rate for the luma component is twice that of the chroma components for both the horizontal and vertical directions. As a result, for a CU formatted according to the 4:2:0 format, the width and height of an array of samples for the luma component are twice that of each array of samples for the chroma components. As described above, a CU is typically defined according to the number of horizontal and vertical luma samples. Thus, a 16x16 CU formatted according to the 4:2:0 sample format includes 16x16 samples of luma components and 8x8 samples for each chroma component. Similarly, for a CU formatted according to the 4:2:2 format, the width of an array of samples for the luma component is twice that of the width of an array of samples for each chroma component, but the height of the array of samples for the luma component is equal to the height of an array of samples for each chroma component. Further, for a CU formatted according to the 4:4:4 format, an array of samples for the luma component has the same width and height as an array of samples for each chroma component.

The difference between sample values included in a current CU, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. Residual data may include respective arrays of difference values corresponding to each component of video data (e.g., luma (Y) and chroma (Cb and Cr). Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to pixel difference values to generate transform coefficients. It should be noted that in ITU-T H.265, CUs may be further sub-divided into Transform Units (TUs). That is, in ITU-T H.265, an array of pixel difference values may be sub-divided for purposes of generating transform coefficients (e.g., four 8x8 transforms may be applied to a 16x16 array of residual values), for each component of video data, such sub-divisions may be referred to as Transform Blocks (TBs). Currently in JEM, when a QTBT partitioning structure is used, residual values corresponding to a CB are used to generate transform coefficients without further partitioning. That is, in JEM a QTBT leaf node may be analogous to both a PB and TB in ITU-T H.265. Thus, JEM enables rectangular CB predictions for intra and inter predictions. Further, in JEM, a core transform and a subsequent secondary transforms may be applied (in the encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed. Further, in JEM, whether a secondary transform is applied to generate transform coefficients may be dependent on a prediction mode.

A quantization process may be performed on transform coefficients. Quantization essentially scales transform coefficients in order to vary the amount of data required to represent a group of transform coefficients. Quantization may include division of transform coefficients by a quantization scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Quantized transform coefficients may be referred to as coefficient level values. Inverse quantization (or “dequantization”) may include multiplication of coefficient level values by the quantization scaling factor. It should be noted that as used herein the term quantization process in some instances may refer to division by a scaling factor to generate level values and multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases.

Quantized transform coefficients are coded into a bitstream. Quantized transform coefficients and syntax elements (e.g., syntax elements indicating a coding structure for a video block) may be entropy coded according to an entropy coding technique. Examples of entropy coding techniques include content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), and the like. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data at a video decoder. An entropy coding process may include performing a binarization on syntax elements. Binarization refers to the process of converting a value of a syntax value into a series of one or more bits. These bits may be referred to as “bins.” Binarization is a lossless process and may include one or a combination of the following coding techniques: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding. For example, binarization may include representing the integer value of 5 for a syntax element as 00000101 using an 8-bit fixed length binarization technique or representing the integer value of 5 as 11110 using a unary coding binarization technique. As used herein each of the terms fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding may refer to general implementations of these techniques and/or more specific implementations of these coding techniques. For example, a Golomb-Rice coding implementation may be specifically defined according to a video coding standard, for example, ITU-T H.265. An entropy coding process further includes coding bin values using lossless data compression algorithms. In the example of a CABAC, for a particular bin, a context model may be selected from a set of available context models associated with the bin. In some examples, a context model may be selected based on a previous bin and/or values of previous syntax elements. A context model may identify the probability of a bin having a particular value. For instance, a context model may indicate a 0.7 probability of coding a 0-valued bin. After selecting an available context model, a CABAC entropy encoder may arithmetically code a bin based on the identified context model. The context model may be updated based on the value of a coded bin. The context model may be updated based on an associated variable stored with the context, e.g., adaptation window size, number of bins coded using the context. It should be noted, that according to ITU-T H.265, a CABAC entropy encoder may be implemented, such that some syntax elements may be entropy encoded using arithmetic encoding without the usage of an explicitly assigned context model, such coding may be referred to as bypass coding.

As described above, intra prediction data or inter prediction data may associate an area of a picture (e.g., a PB or a CB) with corresponding reference samples. For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode (predMode: 0), a DC (i.e., flat overall averaging) prediction mode (predMode: 1), and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode (predMode: 0), a DC prediction mode (predMode: 1), and 65 angular prediction modes (predMode: 2-66). It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.

For inter prediction coding, a previously decoded picture, i.e., a reference picture, is determined and a motion vector (MV) identifies samples in the reference picture. For example, a current video block may be predicted using reference sample values located in one or more previously coded picture(s) and a motion vector is used to indicate the location of the reference block relative to the current video block. A motion vector may describe, for example, a horizontal displacement component of the motion vector (i.e., MVx), a vertical displacement component of the motion vector (i.e., MVy), and a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision). In ITU-T H.265, a motion vector is represented at 1/4-pixel precision. Previously decoded pictures, which may include pictures output before or after a current picture, may be organized into one or more to reference pictures lists and identified using a reference picture index value. Further, in inter prediction coding, uni-prediction refers to generating a prediction using sample values from a single reference picture and bi-prediction refers to generating a prediction using respective sample values from two reference pictures. That is, in uni-prediction, a single reference picture and corresponding motion vector are used to generate a prediction for a current video block and in bi-prediction, a first reference picture and corresponding first motion vector and a second reference picture and corresponding second motion vector are used to generate a prediction for a current video block. In bi-prediction, respective sample values are combined (e.g., added, rounded, and clipped, or averaged according to weights) to generate a prediction. In ITU-T H.265, pictures and slices are classified based on which types of prediction modes may be utilized for encoding video blocks thereof. That is, for slices having a B type (i.e., a B slice), bi-prediction, uni-prediction, and intra prediction modes may be utilized, for slices having a P type (i.e., a P slice), uni-prediction, and intra prediction modes may be utilized, and for slices having an I type (i.e., an I slice), only intra prediction modes may be utilized. As described above, reference pictures are identified through reference indices. In ITU-T H.265, for a P slice, there is a single reference picture list, RefPicList0 and for a B slice, there is a second independent reference picture list, RefPicList1, in addition to RefPicList0. It should be noted that for uni-prediction in a B slice, one of RefPicList0 or RefPicList1 may be used to generate a prediction. Further, it should be noted that in ITU-T H.265, during the decoding process, at the onset of decoding a picture, reference picture list(s) are generated from previously decoded picture stored in a decoded picture buffer (DPB).

Further, a coding standard, such as, for example ITU-T H.265, may support motion vector prediction. Motion vector prediction enables the value of a motion vector to be derived based on another motion vector. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, JEM supports advanced temporal motion vector prediction (ATMVP) and Spatial-temporal motion vector prediction (STMVP). ITU-T H.265 supports two modes for motion vector prediction: a merge mode and so-called Advanced Motion Vector Prediction (AMVP). In ITU-T H.265, for both the merge mode and the AMVP for a current PB, a set of candidate blocks is derived. Both a video encoder and video decoder perform the same process to derive a set of candidates. Thus, for a current video block, the same set of candidates is generated during encoding and decoding. A candidate block includes a video block having associated motion information from which motion information used to generate a prediction for a current video block can be derived. For the merge mode in ITU-T H.265, all motion information (i.e., motion vector displacement values, reference picture indices, and reference picture lists) associated with a selected candidate is inherited as the motion information for the current PB. That is, at a video encoder, a candidate block is selected from the derived set of candidates and an index value included in the bitstream indicates the selected candidate and thus, indicates the motion information for the current PB. For AMVP in ITU-T H.265, the motion vector information for the selected candidate is used as a motion vector predictor (MVP) for the motion vector of the current PB. That is, at a video encoder, a candidate block is selected from the derived set of candidates and an index value indicating the selected candidate and a delta value (i.e., a motion vector delta (MVD)) indicating the difference between the motion vector predictor and the motion vector for the current PB are included in the bitstream. Further, for AMVP in ITU-T H.265, syntax elements identifying a reference picture are included in the bitstream.

In ITU-T H.265, a set of candidate blocks may be derived from spatial neighboring blocks, and temporal blocks. Further, generated (or default) motion information may be used for motion vector prediction. In ITU-T H.265, whether motion information used for motion vector prediction of a current PB includes motion information associated with spatial neighboring blocks, motion information associated with temporal blocks, or generated motion information is dependent on the number of candidates to be included in a set, whether temporal motion vector prediction is enabled, the availability of blocks, and/or whether motion information associated with blocks is redundant. For the merge mode in ITU-T H.265, a maximum number of candidates that may be included in a set of candidate blocks may be set and signaled by a video encoder and may be up to five. Further, a video encoder may disable the use of temporal motion vector candidates (e.g., in order to reduce the amount memory resources needed to store motion information at a video decoder) and signal whether the use of temporal motion vector candidates is enabled or disabled for a picture. For AMVP in ITU-T H.265, the derivation of the set of candidates includes adding one of a left candidate and one of an above candidate to the set based on their availability. That is, the first available left candidate and the first available above candidate are added to the set. When the left candidate and the above candidate have redundant motion vector components, one redundant candidate is removed from the set. If the number of candidates included in the set is less than two, and temporal motion vector prediction is enabled, the temporal candidate (Temp) is included in the set. In cases where the number of available spatial candidates (after pruning) and temporal candidate included in the set is less than two, a zero value motion vector is included in the set in order to fill the set.

With respect to the equations used herein, the following arithmetic operators may be used:

Further, the following mathematical functions may be used:

Further, the following relational operators may be applied:

Another example of inter prediction includes so-called affine motion compensation prediction. JEM supports an implementation of affine motion compensation prediction. The techniques described herein may be generally applicable to affine motion compensation prediction implementations. Affine motion compensation prediction techniques may be particularly useful for coding a video sequence including rotational motion (as opposed to translation motion). For a current CU, or other video block, (e.g., a CB or the like) of video data, affine motion prediction techniques determine one or more control motion vectors, (e.g., control motion vectors v0 and v1), which may be referred to as control points for a current CU and generate so-called motion vector fields (MVFs) for sub-blocks within the CU using the control points. MVFs are used to perform motion compensation, i.e., generate a predictive block of video data for each sub-block. It should be noted that control points and MVFs may be initially calculated and updated (i.e., recalculated) during affine motion compensation prediction. JEM provides two modes for affine motion compensation prediction: a AF_INTER mode and a AF_MERGE mode.

In JEM for CUs with both a width and a height larger than 8, the AF_INTER mode may be applied. In the AF_INTER mode, an initial top-left control motion vector, v0, and an initial top-right control motion vector, v1, are determined based on a candidate list of motion vectors, where the candidate list of motion vectors may include motion vectors of neighboring blocks of video data. FIG. 3 illustrates the spatial location of candidate control motion vectors A, B, and C which may be selected for control motion vector v0 and the spatial location of candidate control motion vectors D and E which may be selected for control motion vector v1. That is, for a control motion vector pair (v0,v1), for v0, a motion vector may be selected from the candidate set {v_A, v_B, v_C}, and for v1, a motion vector may be selected from the candidate set {v_D, v_E}. The motion vectors selected from the candidate set {v_A, v_B, v_C}, and the candidate set {v_D, v_E} may be referred to as a control point motion vector prediction (CPMVP). Index values are included in the bitstream to indicate the CPMVPs. After the CPMVPs are selected, affine motion estimation is applied, as described in further detail below, and the control point motion vector (CPMV) is found. Then the difference of the CPMV and the CPMVP is signaled in the bitstream.

In the AF_MERGE mode in JEM, for a current block, a check of reconstructed neighboring video blocks is performed to determine if any of the neighboring blocks were coded using affine motion compensation prediction. The neighboring blocks which are checked are illustrated in FIG. 4A as A (left), B (above), C (above right), D (left bottom), and E (above left). In JEM, the check is performed in the following order: left, above, above right, left bottom, and above left block and the first neighboring block coded using affine motion compensation prediction is selected. As described in further detail below, a neighboring block coded using affine motion compensation includes a top-left control motion vector, a top-right control motion vector, a bottom-left control motion vector, and a bottom-right control motion vector. The top-left control motion vector, the top-right control motion vector, and the bottom-left control motion vector of the first neighboring block coded using affine motion compensation are used to generate an initial top-left control motion vector, v0, and an initial top-right control motion vector, v1, for the current CU. For example, referring to FIG. 4B, FIG. 4B, illustrates an example where the left neighboring block (A) is coded using affine motion compensation and the associated top-left control motion vector, a top-right control motion vector, and a bottom-left control motion vector of the left neighboring block are respectively illustrated as v₂, v₃, and v₄.

As described above, in affine motion compensation prediction techniques, based on the control motion vectors, MVFs may be determined for sub-blocks within the CU. JEM provides where the motion vector fields are generated based on the following equations:

JEM further provides where a M×N sub-block size is derived according to the following equations:

It should be noted that M and N should be adjusted downward if necessary to make it a divisor of w and h, respectively, i.e., each sub block should have same width and height.

To derive a motion vector of each M×N sub-block, the motion vector of a center sample of each sub-block is calculated according to the MVF_1 equations and rounded to 1/16 fraction accuracy. Then motion compensation interpolation filters described in JEM are applied to generate the prediction of each sub-block with derived motion vector. FIG. 5 is a conceptual diagram illustrating an example of deriving motion vector fields in accordance with one or more techniques of this disclosure. In the example illustrated in FIG. 5, for a 16x16 CB of video data, for each 4x4 sub-block (i.e., M = 4 and N = 4), respective motion vector fields (i.e., MVF_(x,y)) are generated. Further, control point motion vectors v₁, v₂, v₃, and v₄ are illustrated.

It should be noted that in J0021, unlike in JEM there is no separate merge mode for affine. A merge candidate in the merge candidate list can be an affine merge candidate or a normal merge candidate. For each adjacent or non-adjacent spatial neighboring block, an affine merge candidate is derived from the affine model as in JEM. The candidate construction process starts with generating four non-affine spatial merge candidates (left, top, top-right, left-bottom), and followed by up to four affine merge candidates if the corresponding spatial neighboring blocks are coded in affine mode. For top-left spatial neighboring block and each non-adjacent spatial neighboring block an affine merge candidate from a spatial neighboring block is inserted into the merge candidate list after the normal merge candidate from that neighboring block has been inserted.

In the implementations of affine motion compensation prediction in JEM and J0021 may be less than ideal. According to the techniques herein various techniques for deriving, indicating, and using control points to generate MVFs are described.

FIG. 1 is a block diagram illustrating an example of a system that may be configured to code (i.e., encode and/or decode) video data according to one or more techniques of this disclosure. System 100 represents an example of a system that may reconstruct video data according to one or more techniques of this disclosure. As illustrated in FIG. 1, system 100 includes source device 102, communications medium 110, and destination device 120. In the example illustrated in FIG. 1, source device 102 may include any device configured to encode video data and transmit encoded video data to communications medium 110. Destination device 120 may include any device configured to receive encoded video data via communications medium 110 and to decode encoded video data. Source device 102 and/or destination device 120 may include computing devices equipped for wired and/or wireless communications and may include set top boxes, digital video recorders, televisions, desktop, laptop, or tablet computers, gaming consoles, mobile devices, including, for example, “smart” phones, cellular telephones, personal gaming devices, and medical imagining devices.

Communications medium 110 may include any combination of wireless and wired communication media, and/or storage devices. Communications medium 110 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium 110 may include one or more networks. For example, communications medium 110 may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.

Referring again to FIG. 1, source device 102 includes video source 104, video encoder 106, and interface 108. Video source 104 may include any device configured to capture and/or store video data. For example, video source 104 may include a video camera and a storage device operably coupled thereto. Video encoder 106 may include any device configured to receive video data and generate a compliant bitstream representing the video data. A compliant bitstream may refer to a bitstream that a video decoder can receive and reproduce video data therefrom. Aspects of a compliant bitstream may be defined according to a video coding standard. When generating a compliant bitstream, video encoder 106 may compress video data. Compression may be lossy (discernible or indiscernible) or lossless. Interface 108 may include any device configured to receive a compliant video bitstream and transmit and/or store the compliant video bitstream to a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can send and/or receive information. Further, interface 108 may include a computer system interface that may enable a compliant video bitstream to be stored on a storage device. For example, interface 108 may include a chipset supporting Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect Express (PCIe) bus protocols, proprietary bus protocols, Universal Serial Bus (USB) protocols, I2C, or any other logical and physical structure that may be used to interconnect peer devices.

Referring again to FIG. 1, destination device 120 includes interface 122, video decoder 124, and display 126. Interface 122 may include any device configured to receive a compliant video bitstream from a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can receive and/or send information. Further, interface 122 may include a computer system interface enabling a compliant video bitstream to be retrieved from a storage device. For example, interface 122 may include a chipset supporting PCI and PCIe bus protocols, proprietary bus protocols, USB protocols, I2C, or any other logical and physical structure that may be used to interconnect peer devices. Video decoder 124 may include any device configured to receive a compliant bitstream and/or acceptable variations thereof and reproduce video data therefrom. Display 126 may include any device configured to display video data. Display 126 may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display 126 may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in FIG. 1, video decoder 124 is described as outputting data to display 126, video decoder 124 may be configured to output video data to various types of devices and/or sub-components thereof. For example, video decoder 124 may be configured to output video data to any communication medium, as described herein.

FIG. 8 is a block diagram illustrating an example of video encoder 200 that may implement the techniques for encoding video data described herein. It should be noted that although example video encoder 200 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video encoder 200 and/or sub-components thereof to a particular hardware or software architecture. Functions of video encoder 200 may be realized using any combination of hardware, firmware, and/or software implementations. In one example, video encoder 200 may be configured to encode video data according to the techniques described herein. Video encoder 200 may perform intra prediction coding and inter prediction coding of picture areas, and, as such, may be referred to as a hybrid video encoder. In the example illustrated in FIG. 8, video encoder 200 receives source video blocks. In some examples, source video blocks may include areas of picture that has been divided according to a coding structure. For example, source video data may include macroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalent coding unit. In some examples, video encoder may be configured to perform additional sub-divisions of source video blocks. It should be noted that the techniques described herein are generally applicable to video coding, regardless of how source video data is partitioned prior to and/or during encoding. In the example illustrated in FIG. 8, video encoder 200 includes summer 202, transform coefficient generator 204, coefficient quantization unit 206, inverse quantization/transform processing unit 208, summer 210, intra prediction processing unit 212, inter prediction processing unit 214, filter unit 216, and entropy encoding unit 218. As illustrated in FIG. 8, video encoder 200 receives source video blocks and outputs a bitstream.

In the example illustrated in FIG. 8, video encoder 200 may generate residual data by subtracting a predictive video block from a source video block. Summer 202 represents a component configured to perform this subtraction operation. In one example, the subtraction of video blocks occurs in the pixel domain. Transform coefficient generator 204 applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block or sub-divisions thereof (e.g., four 8x8 transforms may be applied to a 16x16 array of residual values) to produce a set of residual transform coefficients. Transform coefficient generator 204 may be configured to perform any and all combinations of the transforms included in the family of discrete trigonometric transforms. Transform coefficient generator 204 may output transform coefficients to coefficient quantization unit 206.

Coefficient quantization unit 206 may be configured to perform quantization of the transform coefficients. As described above, the degree of quantization may be modified by adjusting a quantization scaling factor which may be determined by quantization parameters. Coefficient quantization unit 206 may be further configured to determine quantization values and output QP data that may be used by a video decoder to reconstruct a quantization parameter (and thus a quantization scaling factor) to perform inverse quantization during video decoding. For example, signaled QP data may include QP delta values. In ITU-T H.265, the degree of quantization applied to a set of transform coefficients may depend on slice level parameters, parameters inherited from a previous coding unit, and/or optionally signaled CU level delta values.

As illustrated in FIG. 8, quantized transform coefficients are output to inverse quantization/transform processing unit 208. Inverse quantization/transform processing unit 208 may be configured to apply an inverse quantization and/or an inverse transformation to generate reconstructed residual data. As illustrated in FIG. 8, at summer 210, reconstructed residual data may be added to a predictive video block. In this manner, an encoded video block may be reconstructed and the resulting reconstructed video block may be used to evaluate the encoding quality for a given quality for a given prediction, transformation type, and/or level of quantization. Video encoder 200 may be configured to perform multiple coding passes (e.g., perform encoding while varying one or more coding parameters). The rate-distortion of a bitstream or other system parameters may be optimized based on evaluation of reconstructed video blocks. Further, reconstructed video blocks may be stored and used as reference for predicting subsequent blocks.

As described above, a video block may be coded using an intra prediction. Intra prediction processing unit 212 may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit 212 may be configured to evaluate a frame and/or an area thereof and determine an intra prediction mode to use to encode a current block. As illustrated in FIG. 8, intra prediction processing unit 212 outputs intra prediction data (e.g., syntax elements) to filter unit 216 and entropy encoding unit 218. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode (predMode: 0), a DC (i.e., flat overall averaging) prediction mode (predMode: 1), and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode (predMode: 0), a DC prediction mode (predMode: 1), and 65 angular prediction modes (predMode: 2-66). It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes. Further, in some examples, a prediction for a chroma component may be inferred from an intra prediction for a luma prediction mode.

Inter prediction processing unit 214 may be configured to perform inter prediction coding for a current video block. Inter prediction processing unit 214 may be configured to generate a predictive block using the motion prediction data. For example, inter prediction processing unit 214 may locate a predictive video block within a frame buffer (not shown in FIG. 8). Inter prediction processing unit 214 may output motion prediction data for a calculated motion vector to filter unit 216 and entropy encoding unit 218. Inter prediction processing unit 214 may be configured to receive source video blocks and calculate a motion vector for PUs, or the like, of a video block. A motion vector may indicate the displacement of a PU, or the like, of a video block within a current video frame relative to a predictive block within a reference frame. Inter prediction coding may use one or more reference pictures. Further, motion prediction may be uni-predictive (use one motion vector) or bi-predictive (use two motion vectors). Inter prediction processing unit 214 may be configured to select a predictive block by calculating a pixel difference determined by, for example, sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. A motion vector and associated data 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), a prediction direction and/or a reference picture index value. Further, a coding standard, such as, for example ITU-T H.265, may support motion vector prediction. Motion vector prediction enables a motion vector to be specified using motion vectors of neighboring blocks. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, JEM supports advanced temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), and advanced motion vector resolution (AMVR) mode. It should be noted that inter prediction processing unit 214 may further be configured to apply one or more interpolation filters to calculate sub-integer pixel values for use in motion estimation.

Further, as described above, JEM and J0021 support an affine motion compensation prediction implementations. Inter prediction processing unit 214 may be configured to perform inter prediction coding according to the techniques described in JEM and J0021. Further, inter prediction processing unit 214 may be configured to perform inter prediction coding according to one or more of the techniques described herein. For example, inter prediction processing unit 214 may be configured to perform affine motion compensation prediction according to one or more techniques described herein. As described above, in JEM, the derivation of control points may be less than ideal. In particular, for a CU, the distance a top left and a top right control point may be relatively large. That is, w, the width of the CU may be relatively large in some cases. In such cases, calculation of MVFs based on these control points may lead to less than ideal predictions. In one example, according to the techniques herein, a current CU may be partitioned into several sub-regions for purposes of generating motion vector control points. That is, each sub-region may be associated with its own motion vector control points. Further, in one example, partitions can be considered as a further partition for affine motion compensation prediction. That is, affine motion compensation prediction may be performed on a sub-region by sub-region basis and MVFs of the sub-block in a sub-region can be derived by using the motion vector control points corresponding to the current sub-region. In one example, sub-regions may include a square region or a rectangle region inside a CU. In one example, the size of a sub-region may be dependent on one or more of a slice type (e.g., whether the current slice is a P-Slice or a B-Slice), the CU size, the level of quantization of the CU (which may be determined from a quantization parameter (QP) value). FIG. 9 illustrates an example where a current CU is divided into region 1 and region 2 for purposes of performing affine motion compensation prediction. In the example illustrated in FIG. 9, region 1 uses the v0 and v1 as CPMVPs and region 2 uses the v1 and v2 CPMVPs.

As described above, in JEM, according to the MVF_1 equations described above, the affine mode implementation in JEM only uses the left top corner control point and right top corner to calculate all MVFs inside a CU. In one example, according to the techniques herein, a left top corner control point and a left bottom corner control point may be used to calculate initial MVFs for all sub-blocks inside the CU.

In one example the following equations (MVF_2) may be used to calculate the initial MVFs when using the left top corner point and left bottom corner point:

As described above, in JEM, in the AF_INTER mode, v0 a motion vector may be selected from the candidate set {v_A, v_B, v_C}, and for v1 a motion vector may be selected from the candidate set {v_D, v_E}, where v_A, v_B, v_C, v_D, and v_E are included in the current picture. In one example, according to the techniques herein, a temporal motion vector prediction (TMVP) can be considered as a CPMVP. For example, in one example, v_A, v_B, v_C, v_D, and v_E may be included in a previously decoded picture. In one example, a flag may be used for each candidate of v_A, v_B, v_C, v_D, and v_E to indicate whether the candidate is a spatial candidate or a temporal candidate.

Further, as described above, in the AF_INTER mode index values are included in the bitstream to indicate the CPMVPs. In one example, according to the techniques herein, the CPMVPs may be derived independently by a video encoder and video decoder using a predefined process. That is, a video decoder may determine a selected candidate implicitly. Referring to FIG. 10, a value LT may be derived from the motion vectors corresponding to video blocks A, B, and C. Further, a value LB may be derived from the motion vectors corresponding to video blocks F and G and a value RT may be derived from the motion vectors corresponding to video blocks D and E. Each of LT, LB, and RT may be referred to as corner control points. In one example, LT, LB, and RT may be derived as follows, where A, B, C, D, E, F, and G refer to motion vectors associated with the corresponding spatial candidate and threshold0, threshold1, and threshold2, are threshold values which may be predefined, signaled, and/or determined based on coding and/or video properties:

It should be noted that according to the derivation of LT, LB, and RT above, outliers are removed and an average value is determined for remaining motion vector candidates. Further, it should be noted that LT, LB, and RT have a motion vector data type. Once corner control points LT, LB, and RT are calculated, the motion vector of top-middle CU (TM in FIG. 10) and the motion vector of left-middle CU (LM in FIG. 10) can be compared with the corner control point. If TM or LM is considerably different from LT, LB, and RT, then the current CU is partitioned into two regions. In one example, the partition of the current CU into sub-regions may be as follows, where threshold3 is a threshold value which may be predefined, signaled, and/or determined based on coding and/or video properties:

It should be noted that in other examples, a CU may be split in other ways. For example, a CU may be split asymmetrically (e.g., at 1/3 of its height or width). In one example, other statistical properties of A, B, C, D, E, F, and G may be used to determine how partitioning is performed. For example, outliers may be identified by comparing values to a variance of a set of motion vectors.

In this manner video encoder 200 represents an example of a device configured to determine control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, determine motion vector fields for sub-blocks within the video block based on the determined control points, and perform a motion compensation process based on the determined motion vector fields.

Referring again to FIG. 8, filter unit 216 receives reconstructed video blocks and coding parameters and outputs modified reconstructed video data. Filter unit 216 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering. SAO filtering is a non-linear amplitude mapping that may be used to improve reconstruction by adding an offset to reconstructed video data. It should be noted that as illustrated in FIG. 8, intra prediction processing unit 212 and inter prediction processing unit 214 may receive modified reconstructed video block via filter unit 216. Entropy encoding unit 218 receives quantized transform coefficients and predictive syntax data (i.e., intra prediction data, motion prediction data, QP data, etc.). It should be noted that in some examples, coefficient quantization unit 206 may perform a scan of a matrix including quantized transform coefficients before the coefficients are output to entropy encoding unit 218. In other examples, entropy encoding unit 218 may perform a scan. Entropy encoding unit 218 may be configured to perform entropy encoding according to one or more of the techniques described herein. Entropy encoding unit 218 may be configured to output a compliant bitstream, i.e., a bitstream that a video decoder can receive and reproduce video data therefrom.

FIG. 11 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure. In one example, video decoder 400 may be configured to inter prediction techniques based on one or more of the techniques described above. It should be noted that video encoder 200 may signal syntax elements in a bitstream indicating coding parameters for reconstructed video data based on the inter prediction techniques described above. In this manner, video decoder 400 may receive a bitstream generated based on the techniques described above and perform a reciprocal coding process to generate reconstructed video data. In this manner video decoder 400 represents an example of a device configured to determine control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value, determine motion vector fields for sub-blocks within the video block based on the determined control points, and perform a motion compensation process based on the determined motion vector fields.

Video decoder 400 may be configured to perform intra prediction decoding and inter prediction decoding and, as such, may be referred to as a hybrid decoder. In the example illustrated in FIG. 11 video decoder 400 includes an entropy decoding unit 402, inverse quantization unit 404, inverse transform processing unit 406, intra prediction processing unit 408, inter prediction processing unit 410, summer 412, filter unit 414, reference buffer 416, and scaling unit 418. Video decoder 400 may be configured to decode video data in a manner consistent with a video encoding system, which may implement one or more aspects of a video coding standard. It should be noted that although example video decoder 400 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video decoder 400 and/or sub-components thereof to a particular hardware or software architecture. Functions of video decoder 400 may be realized using any combination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 11, entropy decoding unit 402 receives an entropy encoded bitstream. Entropy decoding unit 402 may be configured to decode syntax elements and quantized coefficients from the bitstream according to a process reciprocal to an entropy encoding process. Entropy decoding unit 402 may be configured to perform entropy decoding according any of the entropy coding techniques described above. Entropy decoding unit 402 may parse an encoded bitstream in a manner consistent with a video coding standard.

Referring again to FIG. 11, inverse quantization unit 404 receives quantized transform coefficients (i.e., level values) and quantization parameter data from entropy decoding unit 402. Quantization parameter data may include any and all combinations of delta QP values and/or quantization group size values and the like described above. Video decoder 400 and/or inverse quantization unit 404 may be configured to determine quantization values used for inverse quantization based on values signaled by a video encoder and/or through video properties and/or coding parameters. That is, inverse quantization unit 404 may operate in a reciprocal manner to coefficient quantization unit 206 described above. Inverse quantization unit 404 may be configured to apply an inverse quantization. Inverse transform processing unit 406 may be configured to perform an inverse transformation to generate reconstructed residual data. The techniques respectively performed by inverse quantization unit 404 and inverse transform processing unit 406 may be similar to techniques performed by inverse quantization/transform processing unit 208 described above. Inverse transform processing unit 406 may be configured to apply an inverse DCT, an inverse DST, an inverse integer transform, Non-Separable Secondary Transform (NSST), or a conceptually similar inverse transform processes to the transform coefficients in order to produce residual blocks in the pixel domain. Further, as described above, whether particular transform (or type of particular transform) is performed may be dependent on an intra prediction mode. As illustrated in FIG. 11, reconstructed residual data may be provided to summer 412. Summer 412 may add reconstructed residual data to a predictive video block and generate reconstructed video data. A predictive video block may be determined according to a predictive video technique (i.e., intra prediction and inter frame prediction).

Intra prediction processing unit 408 may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer 416. Reference buffer 416 may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. In one example, intra prediction processing unit 408 may reconstruct a video block using according to one or more of the intra prediction coding techniques describe herein. Inter prediction processing unit 410 may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer 416. Inter prediction processing unit 410 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit 410 may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block. Inter prediction processing unit 410 may be configured to perform inter prediction coding according to techniques described herein. For example, inter prediction processing unit 410 may perform inter prediction decoding in reciprocal manner to processes performed by inter prediction processing unit 214 as described above. Filter unit 414 may be configured to perform filtering on reconstructed video data according to the techniques described herein. For example, filter unit 414 may be configured to perform deblocking and/or SAO filtering, as described above with respect to filter unit 216 and filter unit 300. Further, it should be noted that in some examples, filter unit 414 may be configured to perform proprietary discretionary filter (e.g., visual enhancements). As illustrated in FIG. 11, a reconstructed video block may be output by video decoder 400.

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 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. 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.

By way of example, and not limitation, 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. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that 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, 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.

Instructions may be executed by one or more 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. Accordingly, 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. In addition, in some aspects, 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). 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.

Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples are within the scope of the following claims.

<Cross Reference>
This Nonprovisional application claims priority under 35 U.S.C. § 119 on provisional Application No. 62/686,179 on June 18, 2018, the entire contents of which are hereby incorporated by reference.

Claims

A method of performing motion compensation, the method comprising:
determining control points for a video block, wherein determining control points includes comparing a function of one or more motion vector candidates to a threshold value;
determining motion vector fields for sub-blocks within the video block based on the determined control points; and
performing a motion compensation process based on the determined motion vector fields.
The method of claim 1, wherein a function of one or more motion vector candidates includes the average of one or more motion vector candidates.
The method of claim 2, wherein determining control points for a video block includes determining a control point based on whether the average is greater than a threshold value.
A device for coding video data, the device comprising one or more processors configured to perform any and all combinations of the steps of claims 1-3.
The device of claim 4, wherein the device includes a video encoder.
The device of claim 4, wherein the device includes a video decoder.
A system comprising:
the device of claim 5; and
the device of claim 6.
An apparatus for coding video data, the apparatus comprising means for performing any and all combinations of the steps of claims 1-3.
A non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed, cause one or more processors of a device for coding video data to perform any and all combinations of the steps of claims 1-3.