WO2020003257A1 - Boundary filtering for sub-block - Google Patents

Abstract

Devices, systems and methods for boundary filtering for sub-block based prediction are described. Partitioning a block can result in discontinuities between adjacent sub-blocks that may introduce some undesirable high-frequency energy in the residual signal, which can deteriorate the performance of subsequent transform coding. Implementations of the disclosed technology can reduce the effect of the discontinuities. In a representative aspect, a method for video coding includes partitioning a block of video data into multiple sub-blocks, filtering, using a set of filter taps/coefficients, boundary samples of at least one sub-block of the multiple sub-blocks to generate filtered boundary samples, and perform prediction of the block of video data using the filtered boundary samples.

Description

BOUNDARY FILTERING FOR SUB-BLOCK

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Under the applicable patent law and/or rules pursuant to the Paris Convention, this application is made to timely claim the priority to and benefit of International Patent Application No. PCT/CN2018/093634, filed on June 29, 2018. For all purposes under the U.S. law, the entire disclosure of the International Patent Application No. PCT/CN2018/093634 is

incorporated by reference as part of the disclosure of this patent document.

TECHNICAL FIELD

[0002] This patent document is directed generally to image and video coding technologies.

BACKGROUND

[0003] Motion compensation is a technique in video processing to predict a frame in a video, given the previous and/or future frames by accounting for motion of the camera and/or objects in the video. Motion compensation can be used in the encoding and decoding of video data for video compression.

SUMMARY

[0004] Devices, systems and methods related to boundary filtering for sub-block based prediction for image and video coding are described.

[0005] In one representative aspect, the disclosed technology may be used to provide a method for video encoding that includes partitioning a current block of video data into multiple sub-blocks, generating a prediction sub-block for at least one sub-block of the multiple sub blocks, filtering, using a set of filter coefficients, boundary samples of the prediction sub-block of the at least one sub-block to generate filtered boundary samples, and determining a final prediction block of the current block of video data using the filtered boundary samples.

[0006] In another representative aspect, the disclosed technology may be used to provide a method for video decoding that includes filtering, using a set of filter coefficients, boundary samples of a prediction sub-block to generate filtered boundary samples. The prediction sub block is generated for at least one sub-block of multiple sub-blocks of a current video block. The method also includes performing prediction of the current video block of video data using the filtered boundary samples and reconstructing the current video block using the prediction.

[0007] In another representative aspect, a device that is configured or operable to perform the above-described method is disclosed. The device may include a processor that is programmed to implement this method.

[0008] In another representative aspect, a video encoder apparatus may implement a method as described herein. In another representative aspect, a video decoder apparatus may implement a method as described herein.

[0009] In yet another representative aspect, the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.

[0010] The above and other aspects and features of the disclosed technology are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 shows an example of sub-block based prediction of video processing.

[0012] FIG. 2 shows an example of a simplified affine motion model.

[0013] FIG. 3 shows an example of an affine motion vector field (MVT) per sub-block.

[0014] FIG. 4 shows an example of motion prediction using the alternative temporal motion vector prediction (ATMVP) algorithm for a coding unit (CU).

[0015] FIG. 5 shows an example of a coding unit (CU) with sub-blocks and neighboring blocks used by the spatial-temporal motion vector prediction (STMVP) algorithm.

[0016] FIG. 6 shows an example of an optical flow trajectory used by the bi-directional optical flow (BIO) algorithm.

[0017] FIG. 7A shows an example snapshot of using of the bi-directional optical flow (BIO) algorithm without block extensions.

[0018] FIG. 7B shows another example snapshot of using of the BIO algorithm without block extensions.

[0019] FIG. 8 shows an example of bilateral matching in the frame-rate up conversion (FRUC) algorithm.

[0020] FIG. 9 shows an example of template matching in the FRUC algorithm.

[0021] FIG. 10A shows an example of boundaries of sub-blocks that can be filtered in accordance with one or more embodiments of the present technology. [0022] FIG. 10B shows another example of boundaries of sub-blocks that can be filtered in accordance with one or more embodiments of the present technology.

[0023] FIG. 11 A shows an example of prediction samples to be filtered in accordance with one or more embodiments of the present technology.

[0024] FIG. 11B shows another example of prediction samples to be filtered in accordance with one or more embodiments of the present technology.

[0025] FIG. 12A shows an example of neighboring samples to be used for filtering a sample in accordance with one or more embodiments of the present technology.

[0026] FIG. 12B shows another example of neighboring samples to be used for filtering a sample in accordance with one or more embodiments of the present technology.

[0027] FIG. 12C shows yet another example of neighboring samples to be used for filtering a sample in accordance with one or more embodiments of the present technology.

[0028] FIG. 13 A shows a flowchart of an example method for video encoding in accordance with the disclosed technology.

[0029] FIG. 13B shows a flowchart of an example method for video decoding in accordance with the disclosed technology.

[0030] FIG. 14 shows a flowchart of an example method for video coding in accordance with the disclosed technology.

[0031] FIG. 15 is a block diagram illustrating an example encoding apparatus that can be utilized to implement various portions of the presently disclosed technology.

[0032] FIG. 16 is a block diagram illustrating an example encoding apparatus that can be utilized to implement various portions of the presently disclosed technology.

[0033] FIG. 17 is a block diagram illustrating an example of the architecture for a computer system or other control device that can be utilized to implement various portions of the presently disclosed technology.

[0034] FIG. 18 shows a block diagram of an example embodiment of a mobile device that can be utilized to implement various portions of the presently disclosed technology.

DETAILED DESCRIPTION

[0035] Due to the increasing demand of higher resolution video, video coding methods and techniques are ubiquitous in modern technology. Video codecs typically include an electronic circuit or software that compresses or decompresses digital video, and are continually being improved to provide higher coding efficiency. A video codec converts uncompressed video to a compressed format or vice versa. There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency). The compressed format usually conforms to a standard video compression specification, e.g., the High Efficiency Video Coding (HEVC) standard (also known as H.265 or MPEG-H Part 2), the Versatile Video Coding standard to be finalized, or other current and/or future video coding standards.

[0036] Sub-block based prediction is first introduced into the video coding standard by the High Efficiency Video Coding (HEVC) standard. With sub-block based prediction, a block, such as a Coding Unit (CU) or a Prediction Unit (PU), is divided into several non-overlapped sub blocks. Different sub-blocks may be assigned different motion information, such as reference index or motion vector (MV), and motion compensation (MC) is performed individually for each sub-block. FIG. 1 shows an example of sub-block based prediction.

[0037] Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H.265) and future standards to improve runtime performance. Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments (and/or implementations) to the respective sections only.

1. Examples of sub-block based prediction

[0038] Future video coding technologies are explored using a reference software known as the Joint Exploration Model (JEM). In JEM, sub-block based prediction is adopted in several coding tools, such as affine prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), bi-directional optical flow (BIO), Frame- Rate Up Conversion (FRUC), Locally Adaptive Motion Vector Resolution (LAMVR),

Overlapped Block Motion Compensation (OBMC), Local Illumination Compensation (LIC), and Decoder-side Motion Vector Refinement (DMVR).

1.1 Examples of affine prediction

[0039] In HEVC, only a translation motion model is applied for motion compensation prediction (MCP). However, the camera and objects may have many kinds of motion, e.g. zoom in/out, rotation, perspective motions, and/or other irregular motions. JEM, on the other hand, applies a simplified affine transform motion compensation prediction. FIG. 2 shows an example of an affine motion field of a block 200 described by two control point motion vectors Vo and Vi. The motion vector field (MVF) of the block 200 can be described by the following equation:

[0041] As shown in FIG. 2, (vox, vo_y) is motion vector of the top-left corner control point, and (vix, viy) is motion vector of the top-right corner control point. To simplify the motion compensation prediction, sub-block based affine transform prediction can be applied. The sub block size MxN is derived as follows:

[0043] Here, MvPre is the motion vector fraction accuracy (e.g., 1/16 in JEM). (v_2x, v_2y) is motion vector of the bottom-left control point, calculated according to Eq. (1). M and N can be adjusted downward if necessary to make it a divisor of w and h, respectively.

[0044] FIG. 3 shows an example of affine MVF per sub-block for a block 300. To derive motion vector of each MxN sub-block, the motion vector of the center sample of each sub-block can be calculated according to Eq. (1), and rounded to the motion vector fraction accuracy (e.g., 1/16 in JEM). Then the motion compensation interpolation filters can be applied to generate the prediction of each sub-block with derived motion vector. After the MCP, the high accuracy motion vector of each sub-block is rounded and saved as the same accuracy as the normal motion vector.

1.2 Examples of alternative temporal motion vector prediction (ATMVP)

[0045] In the ATMVP method, the temporal motion vector prediction (TMVP) method is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from blocks smaller than the current CU.

[0046] FIG. 4 shows an example of ATMVP motion prediction process for a CU 400. The ATMVP method predicts the motion vectors of the sub-CUs 401 within a CU 400 in two steps. The first step is to identify the corresponding block 451 in a reference picture 450 with a temporal vector. The reference picture 450 is also referred to as the motion source picture. The second step is to split the current CU 400 into sub-CUs 401 and obtain the motion vectors as well as the reference indices of each sub-CU from the block corresponding to each sub-CU.

[0047] In the first step, a reference picture 450 and the corresponding block is determined by the motion information of the spatial neighboring blocks of the current CU 400. To avoid the repetitive scanning process of neighboring blocks, the first merge candidate in the merge candidate list of the current CU 400 is used. The first available motion vector as well as its associated reference index are set to be the temporal vector and the index to the motion source picture. This way, the corresponding block may be more accurately identified, compared with TMVP, wherein the corresponding block (sometimes called collocated block) is always in a bottom-right or center position relative to the current CU.

[0048] In the second step, a corresponding block of the sub-CU 451 is identified by the temporal vector in the motion source picture 450, by adding to the coordinate of the current CU the temporal vector. For each sub-CU, the motion information of its corresponding block (e.g., the smallest motion grid that covers the center sample) is used to derive the motion information for the sub-CU. After the motion information of a corresponding NxN block is identified, it is converted to the motion vectors and reference indices of the current sub-CU, in the same way as TMVP of HEVC, wherein motion scaling and other procedures apply. For example, the decoder checks whether the low-delay condition (e.g. the POCs of all reference pictures of the current picture are smaller than the POC of the current picture) is fulfilled and possibly uses motion vector MVx (e.g., the motion vector corresponding to reference picture list X) to predict motion vector MVy (e.g., with X being equal to 0 or 1 and Y being equal to l-X) for each sub-CU.

1.3 Examples of spatial-temporal motion vector prediction (STMVP)

[0049] In the STMVP method, the motion vectors of the sub-CUs are derived recursively, following raster scan order. FIG. 5 shows an example of one CU with four sub-blocks and neighboring blocks. Consider an 8x8 CU 500 that includes four 4x4 sub-CUs A (501), B (502),

C (503), and D (504). The neighboring 4x4 blocks in the current frame are labelled as a (511), b (512), c (513), and d (514).

[0050] The motion derivation for sub-CU A starts by identifying its two spatial neighbors. The first neighbor is the NxN block above sub-CU A 501 (block c 513). If this block c (513) is not available or is intra coded the other NxN blocks above sub-CU A (501) are checked (from left to right, starting at block c 513). The second neighbor is a block to the left of the sub-CU A 501 (block b 512). If block b (512) is not available or is intra coded other blocks to the left of sub-CU A 501 are checked (from top to bottom, staring at block b 512). The motion information obtained from the neighboring blocks for each list is scaled to the first reference frame for a given list. Next, temporal motion vector predictor (TMVP) of sub-block A 501 is derived by following the same procedure of TMVP derivation as specified in HEVC. The motion information of the collocated block at block D 504 is fetched and scaled accordingly. Finally, after retrieving and scaling the motion information, all available motion vectors are averaged separately for each reference list. The averaged motion vector is assigned as the motion vector of the current sub-CU.

1.4 Examples of bi-directional optical flow (BIO)

[0051] Motion estimation can be performed from either one reference picture (also known as uni-prediction) or from two reference pictures (also known as bi-prediction). The bi-directional optical flow (BIO) method is a sample- wise motion refinement performed on top of block- wise motion compensation for bi-prediction. In some implementations, the sample-level motion refinement does not use signaling.

[0052] Let

be the luma value from reference k (k= 0, 1) after block motion compensation, and dl^(k) / dx , dl^(k) / dy are horizontal and vertical components of the /^(k) gradient, respectively. Assuming the optical flow is valid, the motion vector field ( v_x , v_y) is given by:

[0053] dl^/dt+v_x dl^/dx+v_y dl^/dy = 0. Eq. (3)

[0054] Combining this optical flow equation with Hermite interpolation for the motion trajectory of each sample results in a unique third-order polynomial that matches both the function values 7® and dl^(k) / dx , dl^(k) / dy derivatives at the ends. The value of this polynomial at t= 0 is the BIO prediction:

[0056] FIG. 6 shows an example optical flow trajectory in the Bi-directional Optical flow (BIO) method. Here, t₀ and t_c denote the distances to the reference frames. Distances t₀ and t_c are calculated based on POC for Refo and Refi: To=POC(current) - POC(Refo), ti= POC(Refi) - POC(current). If both predictions come from the same time direction (either both from the past or both from the future) then the signs are different (e.g., t₀ t_c < 0). In this case, BIO is applied if the prediction is not from the same time moment (e.g., t₀ ¹ t^. Both referenced regions have non-zero motion (e.g., MVx₀, MVy₀, MVx₁, MVy₁ ¹ 0) and the block motion vectors are proportional to the time distance (e.g., MVx₀/MVx₁ = MVy₀/MVy₁

[0057] The motion vector field ( v_x , v_y) is determined by minimizing the difference

D between values in points A and B. FIGS. 7A-7B show an example of intersection of motion trajectory and reference frame planes. Model uses only first linear term of a local Taylor expansion for D:

[0059] All values in the above equation depend on the sample location, denoted as (i', ). Assuming the motion is consistent in the local surrounding area, D can be minimized inside the (2M+l)x(2M+l) square window W centered on the currently predicted point (i,y), where M is equal to 2:

[0060] (v ,v = argmin åD² [;',/] Eq. (6) v*’^vy [i’J n

[0061] For this optimization problem, the JEM uses a simplified approach making first a minimization in the vertical direction and then in the horizontal direction. This results in the following:

[0062] v_x = (s_x + r) > m? clip? (— thBIO , thBIO,— ^Ss ) : 0 Eq. (7)

[0066] In order to avoid division by zero or a very small value, regularization parameters r and m can be introduced in Eq. (7) and Eq. (8), where:

[0067] r = 500 4^d_8 Eq. (10)

[0068] m = 700 4 d'—8 Eq. (11) [0069] Here, d is bit depth of the video samples.

[0070] In order to keep the memory access for BIO the same as for regular bi-predictive motion compensation, all prediction and gradients values, 7®, 57® /dx , 57® /5y, are calculated for positions inside the current block. FIG. 7 A shows an example of access positions outside of a block 700. As shown in FIG. 7A, in Eq. (9), (2M+l)x(2M+l) square window W centered in currently predicted point on a boundary of predicted block needs to accesses positions outside of the block. In the JEM, values of 7®, 57®/ dx , 5/®/ dy outside of the block are set to be equal to the nearest available value inside the block. For example, this can be implemented as a padding area 701, as shown in FIG. 7B.

[0071] With BIO, it is possible that the motion field can be refined for each sample. To reduce the computational complexity, a block-based design of BIO is used in the JEM. The motion refinement can be calculated based on a 4x4 block. In the block-based BIO, the values of Sn in Eq. (9) of all samples in a 4x4 block can be aggregated, and then the aggregated values of s_n in are used to derived BIO motion vectors offset for the 4x4 block. More specifically, the following formula can used for block-based BIO derivation:

[0073] Here, bk denotes the set of samples belonging to the k-th 4x4 block of the predicted block sn in Eq (7) and Eq (8) are replaced by ((s_n,bk) » 4 ) to derive the associated motion vector offsets.

[0074] In JEM, BIO is only invoked for the luma component.

1.5 Examples of frame-rate up conversion (FRUC)

[0075] A FRUC flag can be signaled for a CU when its merge flag is true. When the FRUC flag is false, a merge index can be signaled and the regular merge mode is used. When the FRUC flag is true, an additional FRUC mode flag can be signaled to indicate which method (e.g., bilateral matching or template matching) is to be used to derive motion information for the block.

[0076] At the encoder side, the decision on whether using FRUC merge mode for a CU is based on RD cost selection as done for normal merge candidate. For example, multiple matching modes (e.g., bilateral matching and template matching) are checked for a CU by using RD cost selection. The one leading to the minimal cost is further compared to other CU modes. If a FRUC matching mode is the most efficient one, FRUC flag is set to true for the CU and the related matching mode is used.

[0077] Typically, motion derivation process in FRUC merge mode has two steps: a CU-level motion search is first performed, then followed by a Sub-CU level motion refinement. At CU level, an initial motion vector is derived for the whole CU based on bilateral matching or template matching. First, a list of MV candidates is generated and the candidate that leads to the minimum matching cost is selected as the starting point for further CU level refinement. Then a local search based on bilateral matching or template matching around the starting point is performed. The MV results in the minimum matching cost is taken as the MV for the whole CU. Subsequently, the motion information is further refined at sub-CU level with the derived CU motion vectors as the starting points.

[0078] For example, the following derivation process is performed for a W X H CU motion information derivation. At the first stage, MV for the whole W x H CU is derived. At the second stage, the CU is further split into M x M sub-CUs. The value of M is calculated as in (16), D is a predefined splitting depth which is set to 3 by default in the JEM. Then the MV for each sub-CU is derived.

[0080] FIG. 8 shows an example of bilateral matching used in the Frame-Rate Up

Conversion (FRUC) method. The bilateral matching is used to derive motion information of the current CU by finding the closest match between two blocks along the motion trajectory of the current CU (800) in two different reference pictures (810, 811). Under the assumption of continuous motion trajectory, the motion vectors MV0 (801) and MV1 (802) pointing to the two reference blocks are proportional to the temporal distances, e.g., TD0 (803) and TD1 (804), between the current picture and the two reference pictures. In some embodiments, when the current picture 800 is temporally between the two reference pictures (810, 811) and the temporal distance from the current picture to the two reference pictures is the same, the bilateral matching becomes mirror based bi-directional MV.

[0081] FIG. 9 shows an example of template matching used in the Frame-Rate Up Conversion (FRUC) method. Template matching can be used to derive motion information of the current CU 900 by finding the closest match between a template (e.g., top and/or left neighboring blocks of the current CU) in the current picture and a block (e.g., same size to the template) in a reference picture 910. Except the aforementioned FRUC merge mode, the template matching can also be applied to AMVP mode. In both JEM and HEVC, AMVP has two candidates. With the template matching method, a new candidate can be derived. If the newly derived candidate by template matching is different to the first existing AMVP candidate, it is inserted at the very beginning of the AMVP candidate list and then the list size is set to two (e.g., by removing the second existing AMVP candidate). When applied to AMVP mode, only CU level search is applied.

1.6 Examples of MV derived for MC in chroma components

[0082] In an example, the HEVC standard defines how to derive the MV used for MC in chroma components (noted as mvC) from the MV used for MC in the luma component (noted as mv). Generally speaking, mvC is calculated as inv multiplying a factor, which relies on the color format, such as 4:2:0 or 4:2:2.

2. Boundary filtering in sub-block based prediction

[0083] In some existing implementations, sub-block based prediction is used since it is usually more accurate than the whole block prediction because it can partition a block into more parts with their own MVs. However, the partitioning may result in discontinuities between two adjacent sub-blocks along their boundary. The discontinuities may introduce some undesirable high-frequency energy in the residual signal, which can deteriorate the performance of subsequent transform coding.

[0084] The use of boundary filtering for sub-block based prediction to improve video coding efficiency (e.g., to reduce the discontinuities at the sub-block boundaries) and enhance both existing and future video coding standards is elucidated in the following examples described for various implementations. In the following examples, which should not be construed to be limiting, the width and height of the current block for a component are noted as W and H respectively, the width and height of the sub-block assigned to the component are noted as w and h respectively.

[0085] Example 1. The prediction samples along the boundaries of sub-blocks partitioned by the sub-block based prediction are filtered before being used to determine a prediction block of the current block.

[0086] (a) In one example, the boundaries only include the inner boundaries (e.g., the boundaries between sub-blocks) as shown in the example in FIG. 10A. The shaded regions cover the samples along the boundaries.

[0087] (b) In one example, the boundaries include both the inner boundaries and the outer boundaries (e.g., the boundaries between sub-blocks and other blocks already coded or decoded) as shown in the example in FIG. 10B. The shaded regions cover the samples along the boundaries.

[0088] (c) In one example, there can be N (N>=0) columns of prediction samples along a vertical boundary and M (M>=0) rows of prediction samples along a horizontal boundary being filtered. FIGS. 11 A and 11B show examples of prediction samples for M=N=2.

[0089] (i) In one example, M and/or N depend on the width and height of the sub block; e.g., M=N=2 if the sub-block’s shape is 4x4; M=N=4 if the sub-block’s shape is 8x8.

[0090] (ii) In one example, M and/or N depend on color component. For example,

M=N=2 for the luma component; and M=N=l for the chroma components.

[0091] (iii) In one example, M and/or N depend on the location of the boundary.

For example, M=N=2 if the boundary is between the sub-block and a coded/decoded

neighboring block; and M=N=l if the boundary is between two sub-blocks

[0092] (iv) In one example, M and/or N may depend on the location of the sub block. Alternatively, it may depend on how many neighboring blocks are coded/decoded and/or how many prediction blocks of neighboring blocks are available.

[0093] (v) In one example, M and N are signaled from the encoder to the decoder.

For example, M and N can be signaled in Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice header, Coding Tree Unit (CTU) or Coding Unit (CU).

[0094] Example 2 The filtering on a prediction sample along the boundary of a sub-block can rely on neighboring prediction samples. If the boundary is an outer boundary, i.e., it is between a sub-block and a coded/decoded neighboring block, the filtering can also rely on reconstructed samples of the coded/decoded neighboring block.

[0095] Example 3 When a sample along the boundary of a sub-block is filtered, the filtered sample is calculated as the output of a filter applying on several relied neighboring samples (in one example, including the filtered sample itself). These“relied neighboring” samples include both adjacent samples and non-adjacent samples covered by the filter range. In a formulation form, x' = {

a(k), where x(k) are neighboring samples and a(k) are filtering taps.

[0096] (a) In one example, the relied neighboring samples are in the same row of the sample to be filtered if the boundary is vertical. For example, as shown in FIG. 12A, the relied neighboring samples include qO, pO, and pl, where pO is the sample to be filtered.

[0097] (b) In one example, the relied neighboring samples are in the same column of the sample to be filtered if the boundary is horizontal. For example, as shown in FIG. 12B, the relied neighboring samples include pl, pO, qO, where pO is the sample to be filtered.

[0098] (c) In one example, the relied neighboring samples can be in a 2-D area instead of a l-D line. For example, as shown in FIG. 12C, the relied neighboring samples include 3x3 area around pO, where pO is the sample to be filtered.

[0099] (d) In one example, the selection of relied neighboring samples depends on the width and height of the sub-block.

[00100] (e) In one example, the selection of relied neighboring samples depends on color component.

[00101] (f) In one example, the selection of relied neighboring samples depends on the location of the boundary.

[00102] (g) In one example, the selection of relied neighboring samples is signaled from the encoder to the decoder. For example, the selection can be signaled in Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice header, Coding Tree Unit (CTU) or Coding Unit (CU).

[00103] Example 4 The filter taps/coefficients and/or filter support can be predefined.

[00104] (a) The filter taps/coefficients can be the same for the vertical filtering and the horizontal filtering. For example, and as shown in FIGS. 12A and 12B, pO’ = (3 xp0+q0+2)»2, where pO’ is the filtered sample.

[00105] (b) The filter taps/coefficients can be the same for symmetric samples around the boundary. For example, and as shown in FIGS. 12A and 12B, the coefficient for the target sample pO is 3, and the coefficient for the neighboring sample qO is 1 : pO’ = (3xp0+q0+2)»2. The coefficient for the target sample qO is 3, and the coefficient for the neighboring sample pO is 1 : q0’= (3xq0+p0+2)»2.

[00106] (c) The filter taps/coefficients can depend on the distance between the sample to be filtered and the boundary. For example, and as shown in FIGS. 12A and 12B, rq’ =

(3xp0+q0+2)»2 and pl’= (6xpl+p0+q0+4)»3.

[00107] (d) In one example, filter taps/coefficients depend on the width and height of the sub-block.

[00108] (e) In one example, filter taps/coefficients depend on color component.

[00109] (f) In one example, and as shown in FIG. 12C, filter taps/coefficients depend on the location of the boundary/sub-block.

[00110] Example 5 Indications of the filter taps/coefficients and/or filter support can be signaled from the encoder to the decoder, such as in Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS), Slice header, Coding Tree Unit (CTU) or Coding Unit (CU).

[00111] Example 6 The boundary filtering can be Finite Impulse Response (FIR) filtering or Infinite Impulse Response (HR) filtering.

[00112] Example 7 Filtering process may be done in a given order, such as all vertical boundaries firstly, followed by all horizontal boundaries or vice versa.

[00113] (a) Alternatively, filtering process may be applied according to the sub-block scanning order (e.g., raster scan order of sub-blocks). For each sub-block, the vertical boundary may be firstly filtered, followed by the horizontal boundary, or vice versa.

[00114] (b) In one example, all the neighboring samples to filter a sample should be fetched before they are filtered. In other words, the filtering process is applied to unfiltered samples.

[00115] (c) In one example, some or all of the neighboring samples to filter a sample are fetched after they are filtered.

[00116] (i) In one example, all the vertical boundaries are filtered first, then the horizontal boundaries are filtered, with neighboring samples already filtered in the vertical boundary filtering.

[00117] (ii) In one example, all the horizontal boundaries are filtered first, then the vertical boundaries are filtered, with neighboring samples already filtered in the horizontal boundary filtering. [00118] Example 8. The boundary filtering may depend on some coded information of the current coding block or coded/decoded neighboring blocks.

[00119] (a) The coding information includes MV, quantization parameter (QP), intra prediction mode, inter-prediction direction, merge mode or AMVP mode, and so on.

[00120] (b) In one example, filtering is enabled/disabled adaptively for each sub-block.

When a sub-block and its horizonal/vertical adjacent block have similar motion information (e.g., if they have same reference pictures and the absolute motion vector component difference on each reference picture is smaller than 1 integer pixel), the corresponding horizonal/vertical boundary filtering is disabled for the sub-block.

[00121] Example 9 The de-blocking filtering approach can be applied to the boundary filtering for sub-blocks, assuming all sub-blocks have non-zero or zero residual value. In this case, the de-blocking filtering is applied on prediction samples, instead of the reconstructed samples.

[00122] (a) Alternatively, the de-blocking filtering can be applied to both the prediction samples and the reconstructed samples.

[00123] Example 10. It should be noted that it is allowed to filter partial of samples along the boundaries, and not filter the remaining samples along the boundaries.

[00124] (a) Filtering or not filtering may be decided in an implicit way.

[00125] (b) In one example, the rule for deblocking filter enabbng/disabling for

PU/TU/CU boundaries may be utilized to determine a sample located at the sub-block boundary should be filtered or not.

[00126] (c) In one example, the rule to determine a sample located at the sub-block boundary should be filtered or not may depend on block shape/size/coded mode/reconstructed samples/prediction samples values.

[00127] Example 11. When there is at least one sub-block is coded with bi-prediction, the filtering process may be applied twice for each of the intermediate prediction block

corresponding to a reference picture list.

[00128] (a) Alternatively, filtering is applied to the final prediction block.

[00129] (b) Similarly, for multi hypothesis coding, either performing filtering for each intermediate prediction block or performing filtering for the final prediction block may be used.

[00130] Example 12 The proposed methods may be applied to certain color components. [00131] (a) In one example, only luma blocks may enable the proposed methods.

[00132] (b) The proposed methods may be applied to certain block sizes/shapes, and/or certain sub-block sizes.

[00133] (c) The proposed methods may be applied to certain coding tools, such as alternative temporal motion vector prediction (ATMVP) and/or affine prediction.

[00134] The examples described above may be incorporated in the context of the methods described below, e.g., method 1300, which may be implemented at a video decoder and/or video encoder.

[00135] FIG. 13A shows a flowchart of an example method 1300 for video encoding. The method 1300 includes, at operation 1302, partitioning a current block of video data into multiple sub-blocks. The method 1300 includes, at operation 1304, generating a prediction sub-block for at least one sub-block of the multiple sub-blocks. The method 1300 includes, at operation 1306, filtering, using a set of filter coefficients, boundary samples of the prediction sub-block of the at least one sub-block to generate filtered boundary samples. The method 1300 includes, at operation 1308, determining a final prediction block of the current block of video data using the filtered boundary samples.

[00136] FIG. 13B shows a flowchart of an example method 1350 for video decoding. The method 1350 includes, at operation 1352, filtering, using a set of filter coefficients, boundary samples of a prediction sub-block to generate filtered boundary samples. The prediction sub block is generated for at least one sub-block of multiple sub-blocks of a current video block. The method 1350 includes, at operation 1354, performing prediction of the current video block of video data using the filtered boundary samples. The method 1350 also includes, at operation 1356, reconstructing the current video block using the prediction.

[00137] In some embodiments of both the encoding and decoding methods, the prediction sub-block is generated by performing bi-prediction using two references, and the filtering comprises filtering at least one intermediate prediction block of the bi-prediction. In some embodiments, the filtering comprises de-blocking filtering, and wherein the at least one sub block comprises a non-zero or zero residual value.

[00138] In some embodiments of both the encoding and decoding methods, at least a first subset of the boundary samples is located along an inner boundary between two adjacent sub blocks in the block of video data. A second subset of the boundary samples is located along an outer boundary between one of the multiple sub-blocks of the block of video data and a second block of video data. The boundary samples may comprise a number of rows or columns of samples along a boundary. Either the encoding or decoding method can include determining the number of rows or columns of the boundary samples based on dimensions of at least one sub block, determining the number of rows or columns based on a color component of at least one sub-block, determining the number of rows or columns based on whether the boundary samples are located along the inner boundary or the outer boundary, determining the number of rows or columns based on a location of a sub-block in the block of video data, or determining the number of rows or columns based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

[00139] In some embodiments, filtering the boundary samples of the multiple sub-blocks comprises filtering a boundary sample by applying the set of filter coefficients to neighboring samples adjacent to the boundary sample. In some embodiments, the neighboring samples and the boundary sample are located in a same row or a same column. In some embodiments, the neighboring samples are in a two-dimensional area surrounding the boundary sample.

[00140] In some embodiments, either the encoding or decoding method can include selecting the neighboring samples based on dimensions of a corresponding sub-block, selecting the neighboring samples based on a color component of a corresponding sub-block, selecting the neighboring samples based on a location of the boundary sample, or selecting the neighboring samples based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

[00141] In some embodiments, the set of filter coefficients is same for horizontal filtering and vertical filtering. In some embodiments, the set of filter coefficients is same for symmetric samples around a boundary of a sub-block.

[00142] In some embodiments, either the encoding or decoding method can include determining the set of filter coefficients for the boundary sample based on a distance from the boundary sample to a corresponding boundary, determining the set of filter coefficients based on dimensions of at least one sub-block, determining the set of filter coefficients based on a color component of at least one sub-block, or determining the set of filter coefficients based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

[00143] In some embodiments, the filtering comprises finite impulse response (FIR) filtering or infinite impulse response (HR) filtering. In some embodiments, the filtering includes filtering, for each of the multiple sub-blocks, a set of boundary samples along vertical boundaries; and filtering, for each of the multiple sub-blocks, remaining boundary samples along horizontal boundaries after the set of boundary samples along vertical boundaries are filtered. The filtering of the multiple sub-blocks is performed according to a sub-block scanning order.

[00144] Alternatively, the filtering can include filtering, for each of the multiple sub-blocks, a set of boundary samples along horizontal boundaries; and filtering, for each of the multiple sub blocks, remaining boundary samples along vertical boundaries after the set of boundary samples along horizontal boundaries are filtered. The filtering of the multiple sub-blocks is performed according to a sub-block scanning order.

[00145] In some embodiments, the filtering includes filtering a set of boundary samples along vertical boundaries of all the multiple sub-blocks; and filtering, after the set of boundary samples along vertical boundaries are filtered, remaining boundary samples along horizontal boundaries of all the multiple sub-blocks.

[00146] Alternatively, the filtering includes filtering a set of boundary samples along horizontal boundaries of all the multiple sub-blocks; and filtering, after the set of boundary samples along horizontal boundaries are filtered, remaining boundary samples along vertical boundaries of all the multiple sub-blocks.

[00147] In some embodiments, the filtering is based on one or more properties of the block of video data or neighboring blocks of video data, wherein the one or more properties comprise a motion vector, a quantization parameter (QP), an intra-prediction mode, an inter-prediction direction, a merge mode or an advanced motion vector prediction (AMVP) mode. The filtering can be enabled or disabled adaptively for each of the multiple sub-blocks.

[00148] FIG. 14 shows a flowchart of an exemplary method for video coding. The method 1400 includes, at step 1410, partitioning a block of video data into multiple sub-blocks.

[00149] The method 1400 includes, at step 1420, filtering, using a set of filter

taps/coefficients, boundary samples of at least one sub-block of the multiple sub-blocks to generate filtered boundary samples. In some embodiments, the boundary of the at least one sub block is an inner boundary of the block of video data, and where the boundary samples comprises prediction samples from a neighboring sub-block of the multiple sub-blocks, as described in the context of FIG. 10A. In other embodiments, the boundary of the at least one sub block is an outer boundary of the block of video data, and where the boundary samples comprises reconstructed samples from a neighboring block of video data, as described in the context of FIG. 10B. In yet other embodiments, the set of filter taps/coefficients may be different for filtering different boundaries of the same or different sub-blocks (of the multiple sub-blocks). For example, a set of filters (e.g., a filter bank) may be used with distinct predetermined or adaptive filter taps/coefficients for each of the filters.

[00150] In some embodiments, and as described in the context of Example 3, the boundaries may be vertical or horizontal. For example, the boundary of the at least one sub-block includes a vertical boundary, and where a row index of each of the prediction samples is identical to a row index of each of the neighboring samples. For example, the boundary of the at least one sub block includes a horizontal boundary, and where a column index of each of the prediction samples is identical to a column index of each of the neighboring samples. For example, the neighboring samples includes samples with at least two different row indexes or at least two different column indexes, thereby forming a 2-dimensional area of samples.

[00151] In some embodiments, and as described in the context of Example 3, the selection of the neighboring samples may be based on dimensions of the at least one sub-block, a color component of the at least one sub-block, or a location of the boundary of the at least one sub block relative to the block of video data. In some embodiments, the selection of the neighboring samples is signaled in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

[00152] The method 1400 includes, at step 1430, perform prediction of the block of video data using the filtered boundary samples. In some embodiments, the filtered boundary samples may be the result of either finite impulse response (FIR) filtering or infinite impulse response (HR) filtering. In some embodiments, and as described in the context of Example 7, the filtering includes filtering the vertical boundaries before the horizontal boundaries, or vice versa. In some embodiments, the filtering may be based on one or more properties (e.g., a motion vector, a quantization parameter (QP), an intra-prediction mode, an inter-prediction direction, a merge mode or an advanced motion vector prediction (AMVP) mode) of the block of video data or neighboring blocks of video data. [00153] In some embodiments, and as described in the context of Example 4, the set of filter taps/coefficients may be based on a distance from the sample to the boundary of the at least one sub-block, dimensions of the at least one sub-block, or a color component of the at least one sub block. In some embodiments, the set of filter taps/coefficients may be signaled in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

[00154] In some embodiments, and as described in the context of Example 11, when the sub block is coded for bi-prediction, the filtering includes filtering each of the intermediate prediction blocks corresponding to a reference picture list.

3. Example implementations of the disclosed technology

[00155] FIG. 15 is a block diagram illustrating an example encoding apparatus 1500 that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) method 1300 and method 1400. The encoding apparatus 1500 includes a quantizer 1505 for compressing input data bits. The encoding apparatus 1500 also includes a dequantizer 1515 so that data bits can be fed into memory 1525 and predictor 1520 to perform motion estimation. The encoding apparatus 1500 further includes a binary encoder 1530 to generated encoded binary codes.

[00156] FIG. 16 is a block diagram illustrating an example encoding apparatus 1600 that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) method 1300 and method 1400. The decoding apparatus 1600 includes a bindery decoder 1605 to decode the binary codes. The decoding apparatus 1600 also includes a dequantizer 1615 so that decoded data bits can be fed into memory 1625 and predictor 1620 to perform motion estimation on the decoding side.

[00157] FIG. 17 is a block diagram illustrating an example of the architecture for a computer system or other control device 1700 that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) method 1300 and method 1400. In FIG. 17, the computer system 1700 includes one or more processors 1705 and memory 1710 connected via an interconnect 1725. The interconnect 1725 may represent any one or more separate physical buses, point to point connections, or both, connected by appropriate bridges, adapters, or controllers. The interconnect 1725, therefore, may include, for example, a system bus, a Peripheral Component Interconnect (PCI) bus, a HyperTransport or industry standard architecture (ISA) bus, a small computer system interface (SCSI) bus, a universal serial bus (USB), IIC (I2C) bus, or an Institute of Electrical and Electronics Engineers (IEEE) standard 674 bus, sometimes referred to as“Firewire.”

[00158] The processor(s) 1705 may include central processing units (CPUs) to control the overall operation of, for example, the host computer. In certain embodiments, the processor(s) 1705 accomplish this by executing software or firmware stored in memory 1710. The processor(s) 1705 may be, or may include, one or more programmable general-purpose or special-purpose microprocessors, digital signal processors (DSPs), programmable controllers, application specific integrated circuits (ASICs), programmable logic devices (PLDs), or the like, or a combination of such devices.

[00159] The memory 1710 can be or include the main memory of the computer system. The memory 1710 represents any suitable form of random access memory (RAM), read-only memory (ROM), flash memory, or the like, or a combination of such devices. In use, the memory 1710 may contain, among other things, a set of machine instructions which, when executed by processor 1705, causes the processor 1705 to perform operations to implement embodiments of the presently disclosed technology.

[00160] Also connected to the processor(s) 1705 through the interconnect 1725 is a (optional) network adapter 1715. The network adapter 1715 provides the computer system 1700 with the ability to communicate with remote devices, such as the storage clients, and/or other storage servers, and may be, for example, an Ethernet adapter or Fiber Channel adapter.

[00161] FIG. 18 shows a block diagram of an example embodiment of a mobile device 1800 that can be utilized to implement various portions of the presently disclosed technology, including (but not limited to) method 1600. The mobile device 1800 can be a laptop, a smartphone, a tablet, a camcorder, or other types of devices that are capable of processing videos. The mobile device 1800 includes a processor or controller 1801 to process data, and memory 1802 in communication with the processor 1801 to store and/or buffer data. For example, the processor 1801 can include a central processing unit (CPU) or a microcontroller unit (MCU). In some implementations, the processor 1801 can include a field-programmable gate-array (FPGA). In some implementations, the mobile device 1800 includes or is in communication with a graphics processing unit (GPU), video processing unit (VPU) and/or wireless communications unit for various visual and/or communications data processing functions of the smartphone device. For example, the memory 1802 can include and store processor-executable code, which when executed by the processor 1801, configures the mobile device 1800 to perform various operations, e.g., such as receiving information, commands, and/or data, processing information and data, and transmitting or providing processed information/data to another device, such as an actuator or external display.

[00162] To support various functions of the mobile device 1800, the memory 1802 can store information and data, such as instructions, software, values, images, and other data processed or referenced by the processor 1801. For example, various types of Random Access Memory (RAM) devices, Read Only Memory (ROM) devices, Flash Memory devices, and other suitable storage media can be used to implement storage functions of the memory 1802. In some implementations, the mobile device 1800 includes an input/output (I/O) unit 1803 to interface the processor 1801 and/or memory 1802 to other modules, units or devices. For example, the I/O unit 1803 can interface the processor 1801 and memory 1802 with to utilize various types of wireless interfaces compatible with typical data communication standards, e.g., such as between the one or more computers in the cloud and the user device. In some implementations, the mobile device 1800 can interface with other devices using a wired connection via the I/O unit 1803. The mobile device 1800 can also interface with other external interfaces, such as data storage, and/or visual or audio display devices 1804, to retrieve and transfer data and information that can be processed by the processor, stored in the memory, or exhibited on an output unit of a display device 1804 or an external device. For example, the display device 1804 can display a video frame that includes a block (a CU, PU or TU) that applies the intra-block copy based on whether the block is encoded using a motion compensation algorithm, and in accordance with the disclosed technology.

[00163] In some embodiments, a video decoder apparatus may implement a method of sub block based prediction as described herein is used for video decoding. The various features of the method may be similar to the above-described method 1600.

[00164] In some embodiments, the video decoding methods may be implemented using a decoding apparatus that is implemented on a hardware platform as described with respect to FIG. 17 and FIG. 18.

[00165] From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed technology is not limited except as by the appended claims.

[00166] Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine- readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term“data processing unit” or“data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a

programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[00167] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code).

A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[00168] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[00169] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices.

Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[00170] It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example. As used herein, the singular forms“a”, “an” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Additionally, the use of“or” is intended to include“and/or”, unless the context clearly indicates otherwise.

[00171] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple

embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[00172] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[00173] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

CLAIMS What is claimed is:

1. A video encoding method, comprising:

partitioning a current block of video data into multiple sub-blocks;

generating a prediction sub-block for at least one sub-block of the multiple sub-blocks; filtering, using a set of filter coefficients, boundary samples of the prediction sub-block of the at least one sub-block to generate filtered boundary samples; and

determining a final prediction block of the current block of video data using the filtered boundary samples.

2. A video decoding method, comprising:

filtering, using a set of filter coefficients, boundary samples of a prediction sub-block to generate filtered boundary samples, wherein the prediction sub-block is generated for at least one sub-block of multiple sub-blocks of a current video block;

performing prediction of the current video block of video data using the filtered boundary samples; and

reconstructing the current video block using the prediction.

3. The method of claim 1 or 2, wherein the prediction sub-block is generated by performing bi-prediction using two references, and wherein the filtering comprises filtering at least one intermediate prediction block of the bi-prediction.

4. The method of any of claims 1 to 3, wherein the filtering comprises de-blocking filtering, and wherein the at least one sub-block comprises a non-zero or zero residual value.

5. The method of any of claims 1 to 4, wherein at least a first subset of the boundary samples is located along an inner boundary between two adjacent sub-blocks in the block of video data, and wherein a second subset of the boundary samples is located along an outer boundary between one of the multiple sub-blocks of the block of video data and a second block of video data.

6. The method of any of claims 1 to 5, wherein the boundary samples comprise a number of rows or columns of samples along a boundary.

7. The method of claim 6, comprising:

determining the number of rows or columns of the boundary samples based on dimensions of at least one sub-block.

8. The method of claim 6, comprising:

determining the number of rows or columns based on a color component of at least one sub-block.

9. The method of claim 6, comprising:

determining the number of rows or columns based on whether the boundary samples are located along the inner boundary or the outer boundary.

10. The method of claim 6, comprising:

determining the number of rows or columns based on a location of a sub-block in the block of video data.

11. The method of claim 6, comprising:

determining the number of rows or columns based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

12. The method of any of claims 1 to 11, wherein filtering the boundary samples of the multiple sub-blocks comprises:

filtering a boundary sample by applying the set of filter coefficients to neighboring samples adjacent to the boundary sample.

13. The method of claim 12, wherein the neighboring samples and the boundary sample are located in a same row or a same column.

14. The method of claim 12, wherein the neighboring samples are in a two-dimensional area surrounding the boundary sample.

15. The method of claim 12, comprising:

selecting the neighboring samples based on dimensions of a corresponding sub-block.

16. The method of claim 12, comprising:

selecting the neighboring samples based on a color component of a corresponding sub block.

17. The method of claim 12, comprising:

selecting the neighboring samples based on a location of the boundary sample.

18. The method of claim 12, comprising:

selecting the neighboring samples based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

19. The method of any of claims 1 to 18, wherein the set of filter coefficients is same for horizontal filtering and vertical filtering.

20. The method of any of claims 1 to 18, wherein the set of filter coefficients is same for symmetric samples around a boundary of a sub-block.

21. The method of any of claims 1 to 18, comprising:

determining the set of filter coefficients for the boundary sample based on a distance from the boundary sample to a corresponding boundary.

22. The method of any of claims 1 to 18, comprising:

determining the set of filter coefficients based on dimensions of at least one sub-block.

23. The method of any of claims 1 to 18, comprising:

determining the set of filter coefficients based on a color component of at least one sub block.

24. The method of any of claims 1 to 18, comprising:

determining the set of filter coefficients based on information in a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), a slice header, a coding tree unit (CTU) or a coding unit (CU).

25. The method of any of claims 1 to 24, wherein the filtering comprises finite impulse response (FIR) filtering or infinite impulse response (HR) filtering.

26. The method of any of claims 1 to 25, wherein the filtering comprises:

filtering, for each of the multiple sub-blocks, a set of boundary samples along vertical boundaries; and

filtering, for each of the multiple sub-blocks, remaining boundary samples along horizontal boundaries after the set of boundary samples along vertical boundaries are fdtered, wherein the filtering of the multiple sub-blocks is performed according to a sub-block scanning order.

27. The method of any of claims 1 to 25, wherein the filtering comprises:

filtering, for each of the multiple sub-blocks, a set of boundary samples along horizontal boundaries; and

filtering, for each of the multiple sub-blocks, remaining boundary samples along vertical boundaries after the set of boundary samples along horizontal boundaries are filtered,

wherein the filtering of the multiple sub-blocks is performed according to a sub-block scanning order.

28. The method of any of claims 1 to 25, wherein the filtering comprises: filtering a set of boundary samples along vertical boundaries of all the multiple sub blocks; and

filtering, after the set of boundary samples along vertical boundaries are filtered, remaining boundary samples along horizontal boundaries of all the multiple sub-blocks.

29. The method of any of claims 1 to 25, wherein the filtering comprises:

filtering a set of boundary samples along horizontal boundaries of all the multiple sub blocks; and

filtering, after the set of boundary samples along horizontal boundaries are filtered, remaining boundary samples along vertical boundaries of all the multiple sub-blocks.

30. The method of any of claims 1 to 29, wherein the filtering is based on one or more properties of the block of video data or neighboring blocks of video data, wherein the one or more properties comprise a motion vector, a quantization parameter (QP), an intra-prediction mode, an inter-prediction direction, a merge mode or an advanced motion vector prediction (AMVP) mode.

31. The method of any of claims 1 to 30, wherein the filtering is enabled or disabled adaptively for each of the multiple sub-blocks.

32. A video encoding apparatus comprising a processor configured to implement a method recited in any one of claims 1 and 3-31.

33. A video decoding apparatus comprising a processor configured to implement a method recited in any one of claims 2 to 31.

34. A computer program product stored on a non-transitory computer readable media, the computer program product including program code for carrying out the method in any one of claims 1 to 31.