AU2020351524A1

AU2020351524A1 - In-loop filter-based image encoding/decoding method and apparatus

Info

Publication number: AU2020351524A1
Application number: AU2020351524A
Authority: AU
Inventors: Ki Baek Kim
Original assignee: B1 Institute of Image Technology Inc
Current assignee: B1 Institute of Image Technology Inc
Priority date: 2019-09-18
Filing date: 2020-09-10
Publication date: 2022-05-12
Also published as: US20240098262A1; US11039134B2; US20220248008A1; US11343496B2; US11876961B2; US20210250582A1; EP4033767A4; KR20220061207A; CA3151453A1; US20210084296A1; CN114424576A; EP4033767A1

Abstract

An image encoding/decoding method and apparatus of the present invention may divide one picture into a plurality of division units, determine whether or not to perform filtering on a boundary of a current division unit, and perform filtering on the boundary of the current division unit in response to the determination.

Description

DESCRIPTION IN-LOOP FILTER-BASED IMAGE ENCODING/DECODING METHOD AND APPARATUS TECHNICAL FIELD

[0001] The present invention relates to an image

encoding/decoding method and apparatus.

BACKGROUND ART

[0002] Recently, demand for high-resolution and high-quality

images such as High Definition (HD) images and Ultra High

Definition (UHD) images is increasing in various application

fields, and accordingly, high-efficiency image compression

techniques are being discussed.

[0003] For image compression technology, various technologies

such as inter prediction technology that predicts pixel value

included in the current picture from a picture before or after the

current picture using image compression technology, intra

prediction technology that predicts pixel value included in the

current picture by using pixel information in the current picture,

an entropy encoding technology that allocates a short code to a

value with a high frequency of appearance and a long code to a

value with a low frequency of appearance, exist, and by using such

the image compression technology, image data can be effectively compressed and transmitted or stored.

DISCLOSURE TECHNICAL PROBLEM

[0004] An object of the present invention is to provide a method

and apparatus for dividing a picture into a predetermined division

unit.

[0005] An object of the present invention is to provide a method

and apparatus for adaptively performing filtering on a boundary of

a division unit.

[0006] An object of the present invention is to provide a method

and apparatus for applying an improved deblocking filter.

TECHNICAL SOLUTION

[0007] The video decoding method and apparatus according to the

present invention may divide one picture into a plurality of

division units, determine whether to perform filtering on a

boundary of a current division unit based on a predetermined flag,

and perform filtering on the boundary of the current division unit

in response to the determination.

[0008] In the video decoding method and apparatus according to

the present invention, the division unit may include at least one

of a sub picture, a slice, or a tile.

[0009] In the video decoding method and apparatus according to

the present invention, the flag may include at least one of a first

flag indicating whether filtering is performed on a boundary of a

division unit within the one picture or a second flag indicating

whether filtering is performed on the boundary of the current

division unit in the one picture.

[0010] In the video decoding method and apparatus according to

the present invention, when the first flag is a first value, it

may not be restricted so that filtering is not performed on the

boundary of the division unit within the one picture, and when the

first flag is a second value, the restriction on the boundary of

the division unit within the picture may not be imposed.

[0011] In the video decoding method and apparatus according to

the present invention, when the second flag is the first value, it

may be restricted so that filtering is not performed on the

boundary of the current division unit, and when the second flag is

the second value, filtering may be allowed to be performed on the

boundary of the current division unit.

[0012] In the video decoding method and apparatus according to

the present invention, the second flag may be decoded only when it

is not restricted so that filtering is not performed on the

boundary of the division unit within the one picture according to

the first flag.

[0013] In the video decoding method and apparatus according to the present invention, whether to perform filtering on the boundary of the current division unit may be determined by further considering a third flag indicating whether filtering is performed on a boundary of a neighboring division unit adjacent to the current block unit.

[0014] In the video decoding method and apparatus according to

the present invention, a position of the neighboring division unit

may be determined based on whether the boundary of the current

division unit is a vertical boundary or a horizontal boundary.

[0015] In the video decoding method and apparatus according to

the present invention, the step of performing the filtering may

comprise, specifying a block boundary for deblocking filtering,

deriving a decision value for the block boundary, determining a

filter type for the deblocking filtering based on the decision

value, and performing filtering on the block boundary based on the

filter type.

[0016] The video encoding method and apparatus according to the

present invention may divide one picture into a plurality of

division units, determine whether to perform filtering on a

boundary of a current division unit, and perform filtering on the

boundary of the current division unit in response to the

determination.

[0017] In the video encoding method and apparatus according to

the present invention, the division unit may include at least one of a sub picture, a slice, or a tile.

[0018] In the video encoding method and apparatus according to

the present invention, the step of determining whether to perform

filtering on the boundary of the current division unit may comprise,

encoding at least one of a first flag indicating whether filtering

is performed on a boundary of a division unit within the one

picture or a second flag indicating whether filtering is performed

on the boundary of the current division unit in the one picture.

[0019] In the video encoding method and apparatus according to

the present invention, when it is determined that filtering is

restricted not to be performed on the boundary of the division

unit within the one picture, the first flag may be encoded as a

first value, and when it is determined that the restriction is not

imposed on the boundary of the division unit within the picture,

the first flag may be encoded as a second value.

[0020] In the video encoding method and apparatus according to

the present invention, when it is determined that filtering is

restricted not to be performed on the boundary of the current

division unit, the second flag may be encoded as the first value,

and when it is determined that filtering is allowed to be performed

on the boundary of the current division unit, the second flag may

be encoded as the second value.

[0021] In the video encoding method and apparatus according to

the present invention, the second flag may be encoded only when it is not restricted so that filtering is not performed on the boundary of the division unit within the one picture.

[0022] In the video encoding method and apparatus according to

the present invention, whether to perform filtering on the boundary

of the current division unit may be determined by further

considering a third flag indicating whether filtering is performed

on a boundary of a neighboring division unit adjacent to the

current block unit.

[0023] In the video encoding method and apparatus according to

the present invention, a position of the neighboring division unit

may be determined based on whether the boundary of the current

division unit is a vertical boundary or a horizontal boundary.

[0024] In the video encoding method and apparatus according to

the present invention, wherein the step of performing the filtering

comprises, specifying a block boundary for deblocking filtering,

deriving a decision value for the block boundary, determining a

filter type for the deblocking filtering based on the decision

value, and performing filtering on the block boundary based on the

filter type.

ADVANTAGEOUS EFFECTS

[0025] According to the present invention, encoding/decoding

efficiency can be improved by dividing one picture into various division units.

[0026] According to the present invention, encoding/decoding

efficiency can be improved by adaptively performing filtering on

the boundary of the division unit.

[0027] According to the present invention, image quality can be

improved by applying an improved deblocking filter to a

reconstructed image.

DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a block diagram showing an image encoding

apparatus according to an embodiment of the present invention.

[0029] FIG. 2 is a block diagram showing an image decoding

apparatus according to an embodiment of the present invention.

[0030] FIG. 3 to 6 illustrate a method of dividing one picture

into one or more division units according to the present disclosure.

[0031] FIG. 7 illustrates a method of performing filtering based

on a predetermined flag according to the present disclosure.

[0032] FIG. 8 to 15 illustrate a method of determining whether

filtering is performed on a boundary of a division unit based on

one or more flags according to the present disclosure.

[0033] FIG. 16 illustrates a method of applying a deblocking

filter according to the present disclosure.

BEST MODE FOR INVENTION

[0034] An image decoding method and apparatus of the present

invention may divide one picture into a plurality of division units,

determine whether to perform filtering on a boundary of a current

division unit based on a predetermined flag, and perform filtering

on the boundary of the current division unit in response to the

determination.

[0035] In the image decoding method and apparatus of the present

invention, the division unit may include at least one of a sub

picture, a slice, or a tile.

[0036] In the image decoding method and apparatus of the present

invention, the flag may include at least one of a first flag

indicating whether filtering is performed on a boundary of a

division unit within the one picture or a second flag indicating

whether filtering is performed on the boundary of the current

division unit in the one picture.

[0037] In the image decoding method and apparatus of the present

invention, when the first flag is a first value, it may be

restricted so that filtering is not performed on the boundary of

the division unit within the one picture, and when the first flag

is a second value, the restriction on the boundary of the division

unit within the picture may not be imposed.

[0038] In the image decoding method and apparatus of the present

invention, when the second flag is the first value, it may be restricted so that filtering is not performed on the boundary of the current division unit, and when the second flag is the second value, filtering may be performed on the boundary of the current division unit.

[0039] In the image decoding method and apparatus of the present

invention, the second flag may be decoded only when it is not

restricted so that filtering is not performed on the boundary of

the division unit within the one picture according to the first

flag.

[0040] In the image decoding method and apparatus of the present

invention, whether to perform filtering on the boundary of the

current division unit may be determined by further considering a

third flag indicating whether filtering is performed on a boundary

of a neighboring division unit adjacent to the current block unit.

[0041] In the image decoding method and apparatus of the present

invention, a position of the neighboring division unit may be

determined based on whether the boundary of the current division

unit is a vertical boundary or a horizontal boundary.

[0042] In the image decoding method and apparatus of the present

invention, performing the filtering may comprise specifying a

block boundary for deblocking filtering, deriving a decision value

for the block boundary, determining a filter type for the

deblocking filtering based on the decision value, and performing

the filtering on the block boundary based on the filter type.

[0043] An image encoding method and apparatus of the present

invention may divide one picture into a plurality of division units,

determine whether to perform filtering on a boundary of a current

division unit, and perform filtering on the boundary of the current

division unit in response to the determination.

[0044] In the image encoding method and apparatus of the present

invention, the division unit may include at least one of a sub

picture, a slice, or a tile.

[0045] In the image encoding method and apparatus of the present

invention, determining whether to perform filtering on the

boundary of the current division unit may comprise encoding at

least one of a first flag indicating whether filtering is performed

on a boundary of a division unit within the one picture or a second

flag indicating whether filtering is performed on the boundary of

the current division unit in the one picture.

[0046] In the image encoding method and apparatus of the present

invention, when it is determined that filtering is restricted not

to be performed on the boundary of the division unit within the

one picture, the first flag may be encoded as a first value, and

when it is determined that the restriction is not imposed on the

boundary of the division unit within the picture, the first flag

may be encoded as a second value,

[0047] In the image encoding method and apparatus of the present

invention, when it is determined that filtering is restricted not to be performed on the boundary of the current division unit, the second flag may be encoded as the first value, and when it is determined that filtering is allowed to be performed on the boundary of the current division unit, the second flag may be encoded as the second value.

[0048] In the image encoding method and apparatus of the present

invention, the second flag may be encoded only when it is not

restricted so that filtering is not performed on the boundary of

the division unit within the one picture.

[0049] In the image encoding method and apparatus of the present

invention, whether to perform filtering on the boundary of the

current division unit may be determined by further considering a

third flag indicating whether filtering is performed on a boundary

of a neighboring division unit adjacent to the current block unit.

[0050] In the image encoding method and apparatus of the present

invention, a position of the neighboring division unit may be

determined based on whether the boundary of the current division

unit is a vertical boundary or a horizontal boundary.

[0051] In the image encoding method and apparatus of the present

invention, performing the filtering may comprise specifying a

block boundary for deblocking filtering, deriving a decision value

for the block boundary, determining a filter type for the

deblocking filtering based on the decision value, and performing

the filtering on the block boundary based on the filter type.

MODE FOR INVENTION

[0052] In the present invention, various modifications may be

made and various embodiments may be provided, and specific

embodiments will be illustrated in the drawings and described in

detail in the detailed description. However, this is not intended

to limit the present invention to a specific embodiment, it should

be understood to include all changes, equivalents, and substitutes

included in the idea and scope of the present invention. In

describing each drawing, similar reference numerals have been used

for similar elements.

[0053] Terms such as first and second may be used to describe

various components, but the components should not be limited by

the terms. These terms are used only for the purpose of

distinguishing one component from another component. For example,

without departing from the scope of the present invention, a first

component may be referred to as a second component, and similarly,

a second component may be referred to as a first component. The

term and/or includes a combination of a plurality of related listed

items or any of a plurality of related listed items.

[0054] When a component is referred to as being "connected" or

"connected" to another component, it may be directly connected or

connected to the another component, but it should be understood

that other component may exist in the middle. On the other hand,

when a component is referred to as being "directly connected" or

"directly connected" to another component, it should be understood

that there is no other component in the middle.

[0055] The terms used in the present application are only used to

describe specific embodiments, and are not intended to limit the

present invention. Singular expressions include plural expressions

unless the context clearly indicates otherwise. In the present

application, terms such as "comprise" or "have" are intended to

designate the presence of features, numbers, steps, actions,

components, parts, or combinations thereof described in the

specification, but one or more other features. It should be

understood that the presence or addition of elements or numbers,

steps, actions, components, parts, or combinations thereof, does

not preclude in advance.

[0056] Hereinafter, preferred embodiments of the present

invention will be described in more detail with reference to the

accompanying drawings. Hereinafter, the same reference numerals

are used for the same elements in the drawings, and duplicate

descriptions for the same elements are omitted.

[0057]

[0058] FIG. 1 is a block diagram showing an image encoding

apparatus according to an embodiment of the present invention.

[0059] Referring to FIG. 1, the image encoding apparatus 100 may

include a picture division unit 110, a prediction unit 120, 125,

a transform unit 130, a quantization unit 135, a rearrangement unit 160, and an entropy encoding unit 165, an inverse quantization unit 140, an inverse transform unit 145, a filter unit 150, and a memory 155.

[0060] Each of the components shown in FIG. 1 is independently

shown to represent different characteristic functions in an image

encoding apparatus, and does not mean that each component is formed

of separate hardware or a single software component. That is, each

constituent part is listed and included as a respective constituent

part for convenience of explanation, and at least two constituent

parts of each constituent part are combined to form one constituent

part, or one constituent part may be divided into a plurality of

constituent parts to perform a function. Integrated embodiments

and separate embodiments of the components are also included in

the scope of the present invention unless departing from the

essence of the present invention.

[0061] In addition, some of the components may not be essential

components that perform essential functions in the present

invention, but may be optional components only for improving

performance. The present invention may be implemented by including

only components essential to implement the essence of the present

invention excluding components used for performance improvement,

and a structure including only essential components excluding

optional components used for performance improvement may be also

included in the scope of the present invention.

[0062] The picture division unit 110 may divide the input picture

into at least one processing unit. In this case, the processing

unit may be a prediction unit (PU), a transform unit (TU), or a

coding unit (CU) . The picture division unit 110 may encode the

picture by dividing into a combination of a plurality of coding

units, prediction units, and transform units, and selecting the

combination of a coding unit, a prediction unit, and a

transformation unit based on a predetermined criterion (for

example, a cost function).

[0063] For example, one picture may be divided into a plurality

of coding units. In order to split the coding units in a picture,

a recursive tree structure such as a quad tree structure may be

used, and a coding unit that is split into other coding unit based

on one image or the largest coding unit as a root may be divided

with as many child nodes as the number of divided coding units.

Coding units that are no longer split according to certain

restrictions become leaf nodes. That is, when it is assumed that

only square splitting is possible for one coding unit, one coding

unit may be split into up to four different coding units.

[0064] Hereinafter, in an embodiment of the present invention, a

coding unit may be used as a meaning of a unit that performs

encoding, or may be used as a meaning of a unit that performs

decoding.

[0065] The prediction unit may be obtained by dividing one coding unit into at least one square or non-square shape of the same size.

One coding unit may be divided such that one prediction unit of

prediction units has a different shape and/or size from another

prediction unit.

[0066] When a prediction unit that performs intra prediction based

on a coding unit is not a minimum coding unit, intra prediction

may be performed without dividing into a plurality of NxN

prediction units.

[0067] The prediction units 120 and 125 may include an inter

prediction unit 120 that performs inter prediction, and an intra

prediction unit 125 that performs intra prediction. Whether to use

inter prediction or intra prediction for a prediction unit may be

determined, and specific information (e.g., intra prediction mode,

motion vector, reference picture, etc.) according to each

prediction method may be determined. In this case, a processing

unit in which prediction is performed may be different from a

processing unit in which a prediction method and specific content

are determined. For example, a prediction method and a prediction

mode are determined in a prediction unit, and prediction may be

performed in a transformation unit. The residual value (residual

block) between the generated prediction block and the original

block may be input to the transform unit 130. In addition,

prediction mode information, motion vector information, and the

like used for prediction may be encoded by the entropy encoding unit 165 together with the residual value and transmitted to the decoder. In the case of using a specific encoding mode, it is possible to encode an original block as it is and transmit it to a decoder without generating a prediction block through the prediction units 120 and 125.

[0068] The inter prediction unit 120 may predict a prediction

unit based on information of at least one of a previous picture or

a subsequent picture of the current picture, and in some cases,

predict a prediction unit based on information of some regions,

which encoding has been completed, in the current picture. The

inter prediction unit 120 may include a reference picture

interpolation unit, a motion prediction unit, and a motion

compensation unit.

[0069] The reference picture interpolation unit may receive

reference picture information from the memory 155 and generate

pixel information of an integer pixel or less in the reference

picture. In the case of a luma pixel, a DCT-based 8-tap

interpolation filter (DCT-based interpolation filter) having

different filter coefficients may be used to generate pixel

information of an integer pixel or less in units of a 1/4 pixels.

In case of a chroma signal, a DCT-based 4-tap interpolation filter

(DCT-based interpolation filter) having different filter

coefficients may be used to generate pixel information of an

integer pixel or less in units of 1/8 pixels.

[0070] The motion prediction unit may perform motion prediction

based on the reference picture interpolated by the reference

picture interpolation unit. As a method for calculating the motion

vector, various methods such as Full Search-based Block Matching

Algorithm (FBMA), Three Step Search (TSS), and New Three-Step

Search Algorithm (NTS) may be used. The motion vector may have a

motion vector value in units of 1/2 or 1/4 pixels based on the

interpolated pixels. The motion prediction unit may predict a

current prediction unit by differently using a motion prediction

method. Various methods such as a skip method, a merge method, an

AMVP (Advanced Motion Vector Prediction) method, and an intra block

copy method may be used as the motion prediction method.

[0071] The intra prediction unit 125 may generate a prediction

unit based on reference pixel information around a current block,

which is pixel information in a current picture. When the

neighboring block of the current prediction unit is a block that

performs inter prediction and the reference pixel is a pixel that

performs inter prediction, the reference pixel included in the

block that performs inter prediction may be used by replacing it

with reference pixel information of a block that performs intra

prediction around it. That is, when the reference pixel is not

available, the unavailable reference pixel information may be used

by replacing with at least one reference pixel among the available

reference pixels.

[0072] In intra prediction, the prediction mode may have a

directional prediction mode in which reference pixel information

is used according to a prediction direction and a non-directional

mode in which directional information is not used when prediction

is performed. A mode for predicting luma information and a mode

for predicting chroma information may be different, and intra

prediction mode information or predicted luma signal information

used to predict luma information may be used to predict chroma

information.

[0073] When the size of the prediction unit and the size of the

transformation unit are the same when performing intra prediction,

intra prediction for the prediction unit may be performed based on

a pixel on the left, a pixel on the above left, and a pixel on the

above of the prediction unit. However, when the size of the

prediction unit and the size of the transformation unit are

different when performing intra prediction, intra prediction may

be performed using a reference pixel based on the transformation

unit. Also, intra prediction using N x N splitting may be used for

only the minimum coding unit.

[0074] The intra prediction method may generate a prediction block

after applying an AIS (Adaptive Intra Smoothing) filter to a

reference pixel according to a prediction mode. The types of AIS

filters applied to the reference pixels may be different. In order

to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When predicting the prediction mode of the current prediction unit using the mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit are the same, information indicating that the prediction mode of the current prediction unit and the neighboring prediction units are the same may be transmitted using predetermined flag information, and if the prediction modes of the current prediction unit and the neighboring prediction units are different, entropy encoding may be performed to encode prediction mode information of the current block.

[0075] In addition, a residual block including residual

information that is a difference value between the prediction unit

that performs prediction based on the prediction units generated

by the prediction units 120 and 125 and the original block of the

prediction unit may be generated. The generated residual block may

be input to the transform unit 130.

[0076] The transform unit 130 may transform a residual block

including residual information between a prediction unit generated

by the prediction units 120 and 125 and the original block by using

the transform method such as DCT (Discrete Cosine Transform), DST

(Discrete Sine Transform), and KLT. Whether DCT, DST, or KLT is applied to transform the residual block may be determined based on intra prediction mode information of a prediction unit used to generate the residual block.

[0077] The quantization unit 135 may quantize values transformed

to the frequency domain by the transform unit 130. The quantization

coefficient may vary depending on the block or the importance of

the image. The value calculated by the quantization unit 135 may

be provided to the inverse quantization unit 140 and the

rearrangement unit 160.

[0078] The rearrangement unit 160 may perform the rearrangement

of the coefficient value for the quantized residual value.

[0079] The rearrangement unit 160 may change coefficients of 2

dimensional block form into 1-dimensional vector form through a

coefficient scanning method. For example, the rearrangement unit

160 may change into a 1-dimensional vector form by scanning from

a DC coefficient to a coefficient in a high frequency region

according to a Zig-Zag Scan method. Depending on the size of the

transform unit and the intra prediction mode, a vertical scan of

scanning coefficients of two-dimensional block form in a column

direction and a horizontal scan of scanning coefficients of two

dimensional block form in a row direction may be used instead of

a zig-zag scan. That is, depending on the size of the transform

unit and the intra prediction mode, it may be determined which one

of a zigzag scan, a vertical scan, and a horizontal scan is used.

[0080] The entropy encoding unit 165 may perform entropy-encoding

based on values calculated by the rearrangement unit 160. Various

encoding methods, such as exponential Golomb, CAVLC (Context

Adaptive Variable Length Coding), and CABAC (Context-Adaptive

Binary Arithmetic Coding), may be used for entropy-encoding.

[0081] The entropy encoder 165 may encode various information,

such as residual value coefficient information, block type

information, prediction mode information, division unit

information, prediction unit information, transmission unit

information, motion vector information, reference frame

information, block interpolation information, filtering

information, etc.

[0082] The entropy encoder 165 may entropy-encode a coefficient

value of a coding unit input from the reordering unit 160.

[0083] The inverse quantization unit 140 and the inverse transform

unit 145 inverse-quantize the values quantized by the quantization

unit 135 and inverse-transform the values transformed by the

transform unit 130. The reconstructed block may be generated by

combining the residual value generated by the inverse quantization

unit 140 and the inverse transform unit 145 with the prediction

unit predicted through the motion estimation unit, the motion

compensation unit, and the intra prediction unit included in the

prediction units 120 and 125.

[0084] The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

[0085] The deblocking filter may remove block distortion caused

by boundary between blocks in the reconstructed picture. In order

to determine whether to perform deblocking, it may be determined

whether to apply the deblocking filter to the current block based

on the pixels included in several columns or rows included in the

block. When applying a deblocking filter to a block, a strong

filter or a weak filter may be applied according to the required

deblocking filtering strength. In addition, in applying the

deblocking filter, horizontal filtering and vertical filtering may

be processed in parallel when performing vertical filtering and

horizontal filtering.

[0086] The offset correction unit may correct an offset from the

original image in units of pixels for the deblocking-filtered image.

In order to perform offset correction for a specific picture, after

classifying the pixels included in the image into a certain number

of regions and determining the region to which the offset is

applied, a method of applying the offset to the region offset or

a method of applying the offset by considering edge information of

each pixel may be used.

[0087] ALF (Adaptive Loop Filtering) may be performed based on a

value obtained by comparing a filtered reconstructed image with an

original image. After classifying the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined to perform filtering differently for each group.

Information related to whether to apply ALF may be transmitted for

each coding unit (CU) of a luma signal, and a shape and filter

coefficient of an ALF filter to be applied may vary according to

each block. In addition, the same type (fixed type) ALF filter may

be applied regardless of the characteristics of the block to be

applied.

[0088] The memory 155 may store the reconstructed block or picture

output from the filter unit 150, and the stored reconstructed block

or picture may be provided to the prediction units 120 and 125

when performing inter prediction.

[0089]

[0090] FIG. 2 is a block diagram showing an image decoding

apparatus according to an embodiment of the present invention.

[0091] Referring to FIG. 2, the image decoder 200 may include an

entropy decoding unit 210, a rearrangement unit 215, an inverse

quantization unit 220, an inverse transform unit 225, a prediction

unit 230, 235, and a filter unit 240, a memory 245.

[0092] When an image bitstream is input from the image encoder,

the input bitstream may be decoded in a procedure opposite to that

of the image encoder.

[0093] The entropy decoding unit 210 may perform entropy-decoding

in a procedure opposite to that performed by entropy-encoding in the entropy encoding unit of the image encoder. For example, various methods corresponding to the method performed in the image encoder such as Exponential Golomb (CAVLC), Context-Adaptive

Variable Length Coding (CAVLC), and Context-Adaptive Binary

Arithmetic Coding (CABAC) may be applied.

[0094] The entropy decoding unit 210 may decode information

related to intra prediction and inter prediction performed by the

encoder.

[0095] The rearrangement unit 215 may perform rearrangement of

the bitstream entropy-decoded by the entropy decoding unit 210

based on a rearrangement method of the encoding unit. The

coefficients of a 1-dimensional vector form may be rearranged into

coefficients of a 2-dimensional block form again. The rearrangement

unit 215 may perform reordering through a method of receiving

information related to coefficient scanning performed by the

encoder and performing reverse scanning based on the scanning order

performed by the corresponding encoder.

[0096] The inverse quantization unit 220 may perform inverse

quantization based on the quantization parameter provided by the

encoder and the coefficients of the rearranged block.

[0097] The inverse transform unit 225 may perform inverse

transform, that is, inverse DCT, inverse DST, and inverse KLT,

corresponding to transforms performed by the transform unit, that

is, DCT, DST, and KLT for the quantization results performed by the image encoder. The inverse transform may be performed based on the transmission unit determined by the image encoder. In the inverse transform unit 225 of the image decoder, a transform method

(for example, DCT, DST, KLT) may be selectively performed according

to a plurality of information such as a prediction method, a size

of a current block, and a prediction direction.

[0098] The prediction units 230 and 235 may generate a prediction

block based on prediction block generation related information

provided by the entropy decoding unit 210 and previously decoded

block or picture information provided by the memory 245.

[0099] As described above, when a size of the prediction unit and

a size of the transform unit are the same in performing intra

prediction in the same manner as in the image encoder, the intra

prediction of the prediction unit may be performed based on pixels

located on the left, the top-left and the top of the prediction

unit. However, when the size of the prediction unit and the size

of the transform unit are different in performing intra prediction,

the intra prediction may be performed using a reference pixel based

on the transform unit. In addition, the intra prediction using NxN

division may be used only for the minimum coding unit.

[0100] The prediction units 230 and 235 may include a prediction

unit determination unit, an inter prediction unit, and an intra

prediction unit. The prediction unit determination unit may

receive various information from the entropy decoding unit 210 such as prediction unit information, prediction mode information of an intra prediction method, and motion prediction related information of an inter prediction method, classify the prediction unit from the current coding unit, and determine whether the prediction unit performs inter prediction or intra prediction. The inter prediction unit 230 may perform inter prediction for a current prediction unit based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit, by using information required for inter prediction of the current prediction unit provided by the image encoder. Alternatively, inter prediction may be performed based on information on a partial region previously-reconstructed in the current picture including the current prediction unit.

[0101] In order to perform inter prediction, a motion prediction

method of a prediction unit included in a coding unit may be

determined among a skip mode, a merge mode, an AMVP mode, and an

intra block copy mode.

[0102] The intra prediction unit 235 may generate a prediction

block based on pixel information in the current picture. When the

prediction unit is a prediction unit that has performed intra

prediction, intra prediction may be performed based on intra

prediction mode information of a prediction unit provided by an

image encoder. The intra prediction unit 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolation unit, and a DC filter. The AIS filter is a part that performs filtering on the reference pixel of the current block and may be applied by determining whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on a reference pixel of a current block by using prediction mode and AIS filter information of a prediction unit provided by an image encoder. When the prediction mode of the current block is a mode that does not perform AIS filtering, the

AIS filter may not be applied.

[0103] When the prediction mode of the prediction unit is the

prediction unit that performs intra prediction based on the pixel

value obtained by interpolating the reference pixel, the reference

pixel interpolation unit may interpolate the reference pixel to

generate a reference pixel of an integer pixel or less. When the

prediction mode of the current prediction unit is a prediction

mode in which a prediction block is generated without interpolating

a reference pixel, the reference pixel may not be interpolated.

The DC filter may generate a prediction block through filtering

when the prediction mode of the current block is the DC mode.

[0104] The reconstructed block or picture may be provided to the

filter unit 240. The filter unit 240 may include a deblocking

filter, an offset correction unit, and an ALF.

[0105] Information about whether a deblocking filter is applied to a corresponding block or picture and information about whether a strong filter is applied or a weak filter is applied in applying the deblocking filter may be provided from a video encoder. In the deblocking filter of the video decoder, information related to the deblocking filter provided by the video encoder may be provided, and the video decoder may perform deblocking filtering on the corresponding block.

[0106] The offset correction unit may perform offset correction

on the reconstructed image based on a type of offset correction

and offset value information applied to the image during encoding.

[0107] ALF may be applied to a coding unit based on information

on whether to apply ALF, ALF coefficient information, and the like,

provided by an encoder. This ALF information may be provided from

a specific parameter set.

[0108] The memory 245 may store the reconstructed picture or block

so that it can be used as a reference picture or a reference block,

and may also provide the reconstructed picture to an output unit.

[0109] As described above, in an embodiment of the present

invention, for convenience of description, a coding unit is used

as a coding unit, but it may be a unit that performs not only

encoding but also decoding.

[0110]

[0111] FIG. 3 to 6 illustrate a method of dividing one picture

into one or more division units according to the present disclosure.

[0112] One picture may be divided into division units pre-defined

in the encoding/decoding apparatus. Here, the pre-defined division

unit may include at least one of a sub picture, a slice, a tile,

or a brick.

[0113] Specifically, one picture may be divided into one or more

tile rows or one or more tile columns. In this case, the tile may

mean a group of blocks covering a predetermined rectangular area

in the picture. Here, the block may mean a coding tree block

(largest coding block). Coding tree blocks belonging to one tile

may be scanned based on a raster scan order.

[0114] Tiles may be divided into one or more bricks. Bricks may

be composed of blocks in rows or columns of tiles. That is, the

division into bricks may be performed only in either a vertical

direction or a horizontal direction. However, the present

invention is not limited thereto, and one tile may be divided into

a plurality of bricks based on one or more vertical lines and one

or more horizontal lines. Brick may be a sub-concept of a tile,

and may be called a sub-tile.

[0115] One slice may include one or more tiles. Alternatively,

one slice may include one or more bricks. Alternatively, one slice

may be defined as one or more coding tree block rows (CTU rows) in

a tile. Alternatively, one slice may be defined as one or more

coding tree block columns (CTU columns) within a tile. That is,

one tile may be set as one slice, and one tile may be composed of a plurality of slices. When one tile is divided into a plurality of slices, the division may be limited to be performed only in the horizontal direction. In this case, the vertical boundary of the slice may coincide with the vertical boundary of the tile, but the horizontal boundary of the slice is not same with the horizontal boundary of the tile, but rather may coincide with the horizontal boundary of the coding tree block in the tile. On the other hand, the division may be limited to be performed only in the vertical direction.

[0116] The encoding/decoding apparatus may define a plurality of

splitting modes for a slice. For example, the segmentation mode

may include at least one of a raster-scan mode and a rectangular

slice mode. In the case of the raster-scan mode, one slice may

include a series of tiles (or blocks, bricks) according to the

raster scan order. In the case of the rectangular slice mode, one

slice may include a plurality of tiles forming a rectangular area,

or may include one or more rows (or columns) of coding tree blocks

in one tile forming a rectangular area.

[0117] The information on the split mode of the slice may be

explicitly encoded by an encoding device and signaled to a decoding

device, or may be implicitly determined by an encoding/decoding

device. For example, a flag indicating whether it is a rectangular

slice mode may be signaled. When the flag is a first value, a

raster-scan mode may be used, and when the flag is a second value, a rectangular slice mode may be used. The flag may be signaled at at least one level of a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), or a picture header (PH).

[0118] As described above, one slice may be configured in a

rectangular unit including one or more blocks, bricks, or tiles,

and the location and size information of the slice may be expressed

in the corresponding unit.

[0119] The sub picture may include one or more slices. Here, the

slice may cover a rectangular area within one picture. That is,

the boundary of the sub picture may always coincide with the slice

boundary, and the vertical boundary of the sub picture may always

coincide with the vertical boundary of the tile. All coding tree

blocks (CTUs) belonging to one sub picture may belong to the same

tile. All coding tree blocks belonging to one tile may belong to

the same sub picture.

[0120] In the present invention, a picture may be composed of one

or more sub pictures, a sub picture may be composed of one or more

slices, tiles, or bricks, a slice may be composed of one or more

tiles or bricks, and a tile may be composed of one or more bricks.

It is described on the assumption that it can be configured, but

is not limited thereto. That is, as described above, one tile may

be composed of one or more slices.

[0121] The division unit may be composed of an integer number of blocks, but is not limited thereto and may be composed of a decimal number instead of an integer number. That is, when it is not composed of an integer number of blocks, at least one division unit may be composed of sub-blocks. FIG. 3 illustrates an example of slice division according to a raster-scan mode. Referring to

FIG. 3, it may be seen that it is composed of 18 x 12 blocks (each

column and row), 12 tiles, and 3 slices. Here, the slice may be

regarded as an example of a group of blocks or tiles according to

a predetermined scan (raster scan).

[0122] FIG. 4 illustrates an example of slice division according

to a rectangular slice mode. Referring to FIG. 4, it may be seen

that it is composed of 18 x 12 blocks, 24 tiles, and 9 slices.

Here, 24 tiles may be represented by 6 tile columns and 4 tile

rows.

[0123] FIG. 5 illustrates an example in which one picture is

divided into a plurality of tiles and rectangular slices. Referring

to FIG. 5, one picture may be composed of 11 bricks, 4 tiles (2

tile columns and 2 tile rows), and 4 slices.

[0124] FIG. 6 illustrates an example of dividing one picture into

a plurality of sub pictures. Referring to FIG. 6, one picture may

consist of 18 tiles. Here, 4x4 blocks on the left (i.e., 16 CTUs)

may constitute one tile, and 2x4 blocks on the right (i.e., 8 CTUs)

may constitute one tile. Also, like a tile on the left, one tile

may be one sub picture (or slice), and like a tile on the right, one tile may be composed of two sub pictures (or slices).

[0125] Table 1 shows examples of division or configuration

information on a sub picture according to the present disclosure,

and encoding control information (e.g., information on whether to

apply an in-loop filter to a boundary, etc.).

[0126] [Table 1]

subpicspresent flag if(subpicspresent flag){ max subpics minus subpicgridcolwidth-minus1 subpicgrid row heightminus1 for( i = 0; i < NumSubPicGridRows; i-) for(j = 0; j <NumSubPicGridCols; j+-) subpicgrid idx[ i][ j ] for(i=0;i <= NumSubPics;i ){ subpictreated aspic flag[i] loopfilter_across_subpic enabled-flag[ i] } }

[0127] In Table 1, subpics present flag means whether a sub

picture is supported, and when the sub picture is supported (when

1), information on the number of sub pictures (maxsubpicminus1)

or information width or height (subpic grid-col-width-minus1,

subpicgridrowheightminus1) of the sub picture may be generated.

At this time, length information such as width and height may be

expressed as it is (e.g., in units of 1 pixel) or may be expressed

as multiple, exponent, etc. of a predetermined unit/constant (e.g.,

integers such as 2, 4, 8, 16, 32, 64, 128, etc., or maximum encoding unit, minimum coding unit, maximum transform unit, minimum transform unit, etc.).

[0128] Here, based on the width and height of the picture, and

the width and height (equal length) of each sub picture, how many

sub pictures exist in the picture in units of columns and rows

(NumSubPicGridRows, NumSubPicGridCols) may be derived. In addition,

how many sub pictures are in the picture (NumSubPics) may be

derived.

[0129] The above example assumes that the width or height of each

sub picture is uniform, but it may also be possible when at least

one of the width or height of each sub picture is not uniform.

Therefore, a flag specifying whether all sub pictures constituting

one picture have the same size may be used.

[0130] When all sub pictures do not have the same size according

to the flag, position information of each sub picture and size

information of each sub picture may be encoded/decoded. On the

other hand, when all sub pictures have the same size according to

the flag, size information may be encoded/decoded only for the

first sub picture.

[0131] Information on how many sub pictures exist in a column or

row unit in a picture may be generated, and information on the

width or height of each sub picture may be individually generated.

[0132] After sub pictures are partitioned in units of columns and

rows, an index of each sub picture may be allocated. In the implicit case, indexes may be allocated based on a predetermined scan order (raster scan, etc.) (e.g., 0, 1, 2, etc. indexes are allocated to the left->right of the first sub picture row), but explicitly index information each sub picture (subpicgrid-idx) may be generated.

[0133] In the case of a sub picture, it may be determined whether

to set as a picture (subpictreatedaspic_flag) during a decoding

process excluding an in-loop filtering operation. This may operate

in relation to whether a sub picture can be considered as one

independent picture (when the flag is 1) in processing such as a

reference picture list for inter prediction.

[0134] It is possible to determine whether to set all sub pictures

within a picture as pictures (one flag is applied in common), or

it is possible to determine whether to individually set them as

pictures (a plurality of flags are applied individually). Here, a

plurality of individual flags may be encoded/decoded for each sub

picture only when a restriction that all sub pictures are treated

as pictures according to one flag applied in common is not imposed.

[0135] In addition, loopfiter-acrosssubpicenabledflag[i] may

determine whether to perform the filtering operation across the

boundary of the i-th sub picture. If it is 1, it is performed

across, if it is 0, it is not performed.

[0136] Here, the part related to

loopfitler across subpicenabledflag may be applied in the same/similar manner not only in the case of the syntax element but also in the example of processing the boundary of various division units described later.

[0137]

[0138] The area located at the boundary of the picture cannot be

referred or filtered because there is no data outside the picture.

That is, the area located inside a picture may be referred to or

may be filtered.

[0139] On the other hand, even inside a picture, it can be divided

into in units of such as sub pictures, slices, tiles, bricks, etc.,

and in the case of some division units, whether to refer to regions

adjacent to both sides of the boundary of different division units,

whether to apply filtering, and the like may be adaptively

determined.

[0140] Here, whether to cross-reference both regions adjacent to

the boundary may be determined by explicit information or may be

implicitly determined.

[0141] Here, whether to perform boundary filtering (e.g., an in

loop filter or an inside loop filter, De-blocking filter, SAO, ALF,

etc.) may be determined by explicit information or implicitly

determined.

[0142] For example, in the case of some units A, cross-reference

for encoding/decoding between division units may be possible, and

filtering may be performed on a boundary of the division unit. For example, in the case of some units B, cross-referencing for encoding/decoding between division units may be prohibited, and filtering cannot be performed on the boundary of division units.

For example, in the case of some units C, cross-reference for

encoding/decoding between division units may be prohibited, and

filtering may be performed on a boundary of the division unit. For

example, in the case of some units D, cross-reference for

encoding/decoding between division units may be possible, and

whether to perform filtering at a boundary of the division unit

may be determined based on predetermined flag information. For

example, in the case of some units (E), whether to cross-reference

for encoding/decoding between division units may be determined

based on predetermined flag information, and whether to perform

filtering on the boundary of division units may be determined based

on predetermined flag information.

[0143] The A to E division units may correspond to at least one

of the above-described sub picture, slice, tile, or brick. For

example, all of the division units A to E may be sub pictures,

tiles, or slices. Alternatively, some of the A to E division units

may be sub pictures, and the rest may be slices or tiles.

Alternatively, some of the A to E division units may be slices and

the rest may be tiles.

[0144]

[0145] FIG. 7 illustrates a method of performing filtering based on a predetermined flag according to the present disclosure.

[0146] Referring to FIG. 7, one picture may be divided into a

plurality of division units (5700).

[0147] The division unit may be at least one of the aforementioned

sub picture, slice, tile, and brick. For example, one picture may

be divided into a plurality of sub pictures. Of course, one picture

may be additionally divided into a plurality of slices and/or tiles

in addition to the sub picture. Since the division unit is the

same as described above, a detailed description will be omitted

here.

[0148] Referring to FIG. 7, it may be determined whether to

perform filtering on a boundary of a division unit based on a

predetermined flag (S710).

[0149] For convenience of explanation, it is assumed that the

division unit in the present disclosure is a sub picture. However,

the present disclosure is not limited thereto, and the present

disclosure may be applied same/similarly to the boundary of a slice,

tile, or brick. In addition, filtering in the present disclosure

may mean in-loop filtering applied to a reconstructed picture, and

a filter for the in-loop filtering may include at least one of a

deblocking filter (DF), a sample adaptive offset (SAO), or an

adaptive loop filter (ALF).

[0150] The division unit may be supported for purposes such as

parallel processing and partial decoding.

[0151] Therefore, when the encoding/decoding of each division

unit is finished, whether to perform filtering at a boundary

between division units or filtering at a boundary of division unit

(e.g., in-loop filter) may be determined implicitly or explicitly.

[0152] Specifically, a flag indicating whether to perform

filtering on the boundary of the division unit may be used. Here,

the flag may be implicitly determined in a higher unit including

a plurality of division units, or may be explicitly encoded/decoded.

The higher unit may mean a picture or may mean a unit composed of

only some of the division units constituting the picture.

Alternatively, the flag may be implicitly determined for each

division unit, or may be explicitly encoded/decoded. Alternatively,

the flag may be implicitly determined for each boundary of the

division unit, or may be explicitly encoded/decoded. This will be

described in detail with reference to FIGS. 8 to 15.

[0153] Referring to FIG. 7, filtering may be performed on a

boundary of a division unit in response to the determination in

S710 (S720).

[0154] Specifically, at least one of a deblocking filter, a sample

adaptive offset, or an adaptive loop filter may be applied to the

boundary of the division unit. The above-described filters may be

sequentially applied according to a predetermined priority. For

example, after the deblocking filter is applied, a sample adaptive

offset may be applied. After the sample adaptive offset is applied, the adaptive loop filter may be applied. A method of applying the deblocking filter to the boundary of the division unit will be described in detail with reference to FIG. 16.

[0155]

[0156] FIG. 8 to 15 illustrate a method of determining whether

filtering is performed on a boundary of a division unit based on

one or more flags according to the present disclosure.

[0157] A flag for determining whether to perform filtering at the

boundary of the division unit may be supported for each type of

division unit. For example, at least one of a flag indicating

whether filtering is performed on the boundary of a sub picture

(loop_filteracross subpicenabled_flag, hereinafter referred to

as a first flag), a flag indicating whether filtering is performed

on the boundary of a slice (loop filter-across slices enabled flag,

hereinafter referred to as a second flag), a flag indicating

whether filtering is performed on the boundary of the tile

(loop filter across tiles enabled flag, hereinafter referred to

as a third flag), or a flag indicating whether filtering is

performed on the boundary of the brick

(loop filter across bricks enabled flag, hereinafter referred to

as a fourth flag) may be supported.

[0158] Alternatively, the encoding/decoding apparatus may support

only some of the aforementioned flags. For example, {the first

flag, the second flag, the third flag}, {the first flag, the second flag, the fourth flag}, {the second flag, the third flag, the fourth flag}, {the first flag , the second flag}, {the first flag, the third flag}, {the first flag, the fourth flag}, {the second flag, the third flag}, {the second flag, the fourth flag}, {the third flag , the fourth flag}, {the first flag}, {the second flag},

{the third flag}, or {the fourth flag} may be supported.

[0159] Also, all of the first to fourth flags described above may

be explicitly supported, or, some of the first to fourth flags may

be explicitly supported, and the others may be implicitly supported.

For example, one of the first to fourth flags may be explicitly

supported, and the other may be implicitly determined based on the

explicitly supported flag.

[0160] In an embodiment to be described later, for convenience of

description, the first to fourth flags will be referred to as

loop_filteracross enabled_flag. In addition, it is assumed that

the flag is supported when the corresponding division unit is

supported.

[0161] FIG. 8 illustrates an example in which a flag

(loop_filteracrossenabled_flag) is supported for one picture

including a plurality of division units.

[0162] Referring to Table 2, when the flag

(loopfilteracrossenabledflag) is a first value, filtering is

restricted not to be performed at the boundary of a division unit

in a picture, and when the flag is a second value, the restriction is not imposed on the boundary of the division unit. That is, when the flag is the second value, filtering on the boundary of the division unit within the picture may be performed or may not be performed.

[0163] In other words, when the flag is the first value, it may

mean that the boundary of the division unit is treated the same as

the boundary of the picture, and when the flag is the second value,

it may mean that the limitation that the boundary of the division

unit is treated the same as the boundary of the picture is not

imposed.

[0164] [Table 2]

loop filter across enabled flag

[0165] In FIG. 8, A to F denote a division unit, the presence of

an arrow as shown in the left drawing may mean that filtering

between the boundaries of the division unit can be performed, and

as shown in the right drawing, the absence of an arrow may mean

that filtering between the boundaries of is restricted not to be

performed. For convenience of explanation, it is assumed that each

division unit has a rectangular shape.

[0166] The above embodiment refers to a case where it is

determined whether to collectively perform filtering on a division

unit in a picture, regardless of a vertical relationship between division units.

[0167] FIG. 9 illustrates an example in which the flag is

individually supported in a higher unit of a division unit. That

is, based on the flag of the higher unit, it may be determined

whether to perform filtering on the boundary of the division unit

existing in the higher unit.

[0168] Referring to Table 3, a flag

(loop filter acrossenabled flag) may be encoded/decoded for each

higher unit. loopfilteracross enabledflag[i] may indicate

whether filtering is performed on the boundary of the division

unit within the i-th higher unit. For example, when the flag is a

first value, filtering is restricted not to be performed on the

boundary of the division unit within the higher unit, and when the

flag is a second value, the restriction is not imposed on the

boundary of the division unit within the higher unit. That is,

when the flag is the second value, filtering may or may not be

performed on the boundary of the division unit within the higher

unit.

[0169] Alternatively, when the flag is a first value, filtering

may not be performed on the boundary of the division unit within

the higher unit, and when the flag is the second value, filtering

may be performed on the boundary of the division unit within the

higher unit. This may mean that filtering may be performed on at

least one boundary of the division units within the higher unit, or filtering may be performed on the boundary of all division units belonging to the higher unit.

[0170] In this embodiment, one picture may be composed of a

plurality of higher units, and each higher unit may be composed of

a plurality of division units. For example, when the higher unit

is a sub picture, the division unit may be a tile, a slice, or a

brick. Alternatively, the higher unit may be defined as a group of

sub pictures having a smaller size than a picture, and in this

case, the division unit may be a sub picture, tile, slice, or

brick.

[0171] [Table 3]

for(i=0;i<NumUnits; i++) loopfilteracrossenabledflag [i]

[0172] The above embodiment refers to a case in which a flag for

determining whether to perform filtering on a boundary of a

division unit is supported in a higher unit defined as a group of

a predetermined division unit.

[0173] Referring to FIG. 9, one picture may be composed of two

higher units (i.e., a first higher unit composed of A to C and a

second higher unit composed of D to F).

[0174] In the first higher unit, it is the case in which the flag

indicating whether to perform filtering is 0, and in the second

higher unit, it is the case in which the flag indicating whether to perform filtering is 1. The boundary between the first higher unit and the division unit belonging to the second higher unit may or may not be filtered by a flag that determines whether to perform filtering of the higher unit.

[0175] FIG. 10 illustrates a case in which a flag

(loop_filteracrossenabled_flag) is supported for each division

unit constituting one picture.

[0176] This embodiment, unlike the embodiment of FIG. 9, is an

example of determining whether filtering is performed on the

boundary of each division unit. Thus, even if the syntax elements

are the same as in Table 2, their meanings may be different.

[0177] Referring to Table 4, a flag

(loopfilteracrossenabledflag) may be encoded/decoded for each

division unit. loop filter-across enabled flag[i] may indicate

whether filtering is performed on the boundary of the i-th division

unit in the picture.

[0178] For example, when the flag is a first value, filtering is

restricted so that no filtering is performed on the boundary of

the i-th division unit in the picture, and when the flag is a

second value, filtering may be performed on the boundary of the i

th division unit in the picture. That is, when the flag is the

second value, filtering may or may not be performed on the boundary

of the division unit within the picture.

[0179] Meanwhile, a flag for each division unit

(loopfilteracrossenabledflag[i]) may be selectively

encoded/decoded based on a flag (loop filter-across enabled flag)

for one picture. The flag for one picture is the same as described

in the embodiment of FIG. 8, and a detailed description will be

omitted.

[0180] For example, when filtering is restricted so that no

filtering is performed on a boundary of a division unit within a

picture according to a flag for one picture, the flag for each

division unit is not encoded/decoded. According to the flag for

the one picture, the flag for each of the division units may be

encoded/decoded only when the restriction is not imposed on the

boundary of the division unit.

[0181] Meanwhile, the flag for one picture and the flag for each

of the division units may be encoded/decoded at the same level.

Here, the same level may be any one of a video parameter set, a

sequence parameter set, or a picture parameter set.

[0182] [Table 4]

for(i=O;i<NumUnits; i++) loopfilteracrossenabledflag [i]

[0183] Referring to FIG. 10, based on a flag for each division

unit, filtering may be performed on a boundary of a corresponding

division unit as shown in the left drawing, and filtering may not

be performed on the boundary of a corresponding division unit as shown in the right drawing.

[0184] FIG. 11 illustrates a method of determining whether to

perform filtering according to a boundary position of a division

unit.

[0185] This embodiment relates to the embodiment of FIG. 9 or the

embodiment of FIG. 10 described above. When it is determined that

filtering is performed on the boundary of each division unit,

predetermined direction information to which filtering is applied

may be encoded/decoded.

[0186] Referring to Table 5, information on whether filtering is

performed on boundary at least one of left, right, top, or bottom

directions may be encoded/decoded. When a boundary of a specific

direction among the boundaries of a division unit coincides with

a boundary of a picture, encoding/decoding of information about

the corresponding direction may be omitted.

[0187] In this embodiment, a flag for determining whether to

perform filtering on a boundary in a specific direction is used,

and a flag for determining whether to perform filtering in unit of

a bundle in some directions (e.g., left+right, top+bottom,

left+right+top, etc.) may be used.

[0188] [Table 5] for( i= 0; i <NumUnits; i ++) loopfilteracrossenabledflag[i] if(loopfilter acrossenabled flag [i] { loopfilter leftboundaryflag[i] loop-filter-right boundary flag[i] loop filter top boundaryflag[i] loop_filterbottom boundaryflag[i] } }

[0189] Referring to FIG. 11, the left drawing shows a case in

which filtering is performed on the boundary in the omnidirectional

direction of the division unit (X). The central figure shows a

case in which filtering is performed only on the left and right

boundary of the division unit (x), and the right figure shows a

case where filtering is not performed on the boundary of the

division unit (X).

[0190] FIG. 12 and 13 illustrate a method of determining whether

to perform filtering on a boundary of a current division unit based

on a flag for a neighboring division unit.

[0191] This embodiment may be related to the embodiment of FIG.

described above. That is, whether to perform filtering on the

boundary of the current division unit may be determined by further

considering a flag for the neighboring division unit in addition

to the flag for the current division unit. When the boundary of

the current division unit is a vertical boundary, the neighboring division unit may mean a division unit adjacent to the left or right of the current division unit. When the boundary of the current division unit is a horizontal boundary, the neighboring division unit may mean a division unit adjacent to the top or bottom of the current division unit.

[0192] Referring to FIG. 12, it is assumed that filtering is

performed on the boundary in the division units of X and Y. Since

it is determined that filtering is performed on the boundary where

X and Y contact each other, filtering may be performed on the right

boundary of the division unit X (i.e., the left boundary of the

division unit Y).

[0193] Referring to FIG. 13, this is a case where it is determined

that filtering is not performed for only one of the division units

X and Y. That is, since the flag (loop filter-across enabled flag)

for the division unit X is 1, filtering may be performed on the

boundary of the division unit X. On the other hand, since the flag

(loop filter acrossenabled flag) for the division unit Y is 0,

filtering is not performed on the boundary of the division unit Y.

[0194] One of the reasons for filtering between division units is

to reduce deterioration between division units caused by

individual encoding/decoding between division units.

[0195] Thus, as in the above embodiment, filtering may be

performed on the boundary of one of the adjacent division regions

and filtering may not be performed on the boundary of the other division region.

[0196] Alternatively, if applying filtering only to the boundary

of one of the division regions may not be effective in removing

image quality deterioration, it may be determined not to perform

filtering on the boundary.

[0197] For example, when values of the flag for the division unit

X and the flag for the division unit Y are different from each

other, filtering may be performed on the boundary between the

division units X and Y, or it may be determined that filtering is

allowed.

[0198] For example, it is assumed that the left boundary of the

current block coincides with the left boundary of the current

division unit to which the current block belongs. In this case,

even if the flag for the current division unit is 0, if the flag

for the left division unit adjacent to the current division unit

is 1, filtering may be performed on the left boundary of the

current block.

[0199] Similarly, it is assumed that the top boundary of the

current block coincides with the top boundary of the current

division unit to which the current block belongs. In this case,

even if the flag for the current division unit is 0, if the flag

for the top division unit adjacent to the current division unit is

1, filtering may be performed on the top boundary of the current

block.

[0200] Alternatively, when the values of the flag for the division

unit X and the flag for the division unit Y are different from

each other, it may be determined that filtering is not performed

or filtering is not allowed at the boundary between the division

units X and Y.

[0201] For example, it is assumed that the left boundary of the

current block coincides with the left boundary of the current

division unit to which the current block belongs. In this case,

even if the flag for the current division unit is 1, if the flag

for the left division unit adjacent to the current division unit

is 0, filtering may not be performed on the left boundary of the

current block.

[0202] Similarly, it is assumed that the top boundary of the

current block coincides with the top boundary of the current

division unit to which the current block belongs. In this case,

even if the flag for the current division unit is 1, if the flag

for the top division unit adjacent to the current division unit is

, filtering may not be performed on the top boundary of the

current block.

[0203] FIG. 14 illustrates a case in which information indicating

whether to perform filtering is generated for each division unit

boundary.

[0204] Referring to FIG. 14, whether to perform filtering for

each division boundary line that divides or partitions division units A to F may be performed. If filtering is performed on the CO boundary, filtering may be performed on the A and B boundaries, and on the D and E boundary, otherwise, filtering may not be performed on the boundary.

[0205] The number or index of the CO, Cl, RO, etc. may be derived

by the division information or the partition information of the

division unit. Alternatively, information for explicitly

allocating information on the division unit boundary and an index

may be generated. As shown in the syntax elements of Table 6 below,

information for determining whether to perform filtering may be

generated at each division unit boundary (in this example, each

column or row) based on Num-units rows and Num-unit cols.

[0206] [Table 6]

for( i= 0; i<NumUnitRows; i++) { loopfllter across row [i] } for( i= 0; i<NumUnit_Cols; i ++) { loopfilteracrosscol [i] }

[0207] FIG. 15 illustrates another example in which information

indicating whether to perform filtering is generated for each

division unit boundary.

[0208] Referring to FIG. 15, whether to perform filtering for each division boundary line that divides or partitions division units A to F may be performed. The difference from the embodiment of FIG. 14 is that related information is generated for each divisional unit boundary, not for one column or row across the picture.

[0209] If filtering is performed on the LO boundary, filtering

may be performed on the A and B boundary, otherwise, filtering may

not be performed on the boundary.

[0210] The number or index of the CO, Cl, RO, etc. may be derived

by the division information or the division information of the

division unit. Alternatively, information for explicitly

allocating information on the division unit boundary and an index

may be generated. As in the syntax element of Table 7, information

for determining whether to perform filtering at each division unit

boundary may be generated based on Num-unit-boundary.

[0211] [Table 7]

for( i= 0; i <NumUnit-boundary; i ++) { loopfilter across [i] }

[0212] FIG. 16 illustrates a method of applying a deblocking

filter according to the present disclosure.

[0213] Referring to FIG. 16, a block boundary for deblocking

filtering (hereinafter, referred to as an edge) among block boundaries of a reconstructed picture may be specified (S1600).

[0214] The reconstructed picture may be partitioned into a

predetermined NxM sample grid. The NxM sample grid may mean a unit

in which deblocking filtering is performed. Here, N and M may be

4, 8, 16 or more integers. Each pixel grid may be defined for each

component type. For example, when the component type is a luminance

component, N and M may be set to 4, and when the component type is

a chrominance difference component, N and M may be set to 8.

Regardless of the component type, a fixed-size NxM pixel grid may

be used.

[0215] The edge is a block boundary positioned on an NxM sample

grid, and may include at least one of a boundary of a transform

block, a boundary of a prediction block, or a boundary of a sub

block.

[0216] Referring to FIG. 16, a decision value for the specified

edge may be derived (S1610).

[0217] In this embodiment, it is assumed that the edge type is a

vertical edge, and a 4x4 sample grid is applied. Based on the edge,

the left block and the right block will be referred to as P blocks

and Q blocks, respectively. The P block and the Q block are pre

reconstructed blocks, the Q block refers to a region in which

deblocking filtering is currently performed, and the P block may

refer to a block spatially adjacent to the Q block.

[0218] First, the decision value may be derived using a variable dSam for inducing the decision value. The variable dSam may be derived for at least one of a first pixel line or a fourth pixel line of the P block and the Q block. Hereinafter, dSam for the first pixel line (row) of the P block and Q block is referred to as dSamO, and dSam for the fourth pixel line (row) is referred to as dSam3.

[0219] When at least one of the following conditions is satisfied,

dSamO may be set to 1, otherwise, dSamO may be set to 0.

[0220] [Table 8]

condition

1 dqp < first threshold

2 (sp + sq) < second threshold

3 spq < third threshold

[0221] In Table 8, dpq may be derived based on at least one of a

first pixel value linearity dl of the first pixel line of the P

block or a second pixel value linearity d2 of the first pixel line

of the Q block. Here, the first pixel value linearity dl may be

derived using i pixels p belonging to the first pixel line of the

P block. The i may be 3, 4, 5, 6, 7 or more. The i pixels p may be

continuous pixels adjacent to each other, or may be non-contiguous

pixels separated by a predetermined interval. In this case, the

pixel p may be i pixels closest to the edge among the pixels of the first pixel line. Similarly, the second pixel value linearity d2 can be derived using j pixels q belonging to the first pixel line of the Q block. The j may be 3, 4, 5, 6, 7 or more. The j is set to the same value as the i, but is not limited thereto, and may be a value different from the i. The j pixels q may be contiguous pixels adjacent to each other, or may be non-contiguous pixels separated by a predetermined interval. In this case, the pixel q may be j pixels closest to the edge among the pixels of the first pixel line.

[0222] For example, when three pixels p and three pixels q are

used, the first pixel value linearity dl and the second pixel value

linearity d2 may be derived as in Equation 1 below.

[0223] [Equation 1]

[0224] dl =Abs(p2,0 -2 * pl,O+pO,O )

[0225] d2 = Abs( q2,0 - 2 *ql,O + qO,O )

[0226] Alternatively, when six pixels p and six pixels q are used,

the first pixel value linearity dl and the second pixel value

linearity d2 may be derived as in Equation 2 below.

[0227] [Equation 2]

[0228] dl=(Abs(p2,0-2*pl,O+pO,O)+Abs(p5,0-2*p 4 ,0+p 3 ,0)+1)>>1

[0229] d2= (Abs(q2,0-2* ql,O+qO,O)+Abs(q5,0-2* q4,0+q3,0)+1)>>1

[0230] In Table 8, sp may denote a first pixel value gradient v1

of a first pixel line of the block P, and sq may denote a second pixel value gradient v2 of a first pixel line of the Q block. Here, the first pixel value gradient v1 may be derived using m pixels p belonging to the first pixel line of the P block. The m may be 2,

3, 4, 5, 6, 7 or more. The m pixels p may be contiguous pixels

adjacent to each other, or may be non-contiguous pixels separated

by a predetermined interval. Alternatively, some of the m pixels

p may be contiguous pixels adjacent to each other, and the others

may be non-contiguous pixels separated by a predetermined interval.

Similarly, the second pixel value gradient v2 may be derived using

n pixels q belonging to the first pixel line of the Q block. The

n may be 2, 3, 4, 5, 6, 7 or more. The n is set to the same value

as m, but is not limited thereto, and may be a value different

from m. The n pixels q may be contiguous pixels adjacent to each

other, or may be non-contiguous pixels separated by a predetermined

interval. Alternatively, some of the n pixels q may be contiguous

pixels adjacent to each other, and the others may be non-contiguous

pixels separated by a predetermined interval.

[0231] For example, when two pixels p and two pixels q are used,

a first pixel value gradient v1 and a second pixel value gradient

v2 may be derived as in Equation 3 below.

[0232] [Equation 3]

[0233] vI = Abs( p3,0 - pO,O )

[0234] v2 = Abs( qO,O - q3,0 )

[0235] Alternatively, when six pixels p and six pixels q are used,

the first pixel value gradient v1 and the second pixel value

gradient v2 may be derived as in Equation 4 below.

[0236] [Equation 4]

[0237] v1=Abs(p3,0- p0,0)+Abs(p7,0- p6,0- p5,0+p4,0)

[0238] v2 = Abs( q0,0 - q3,0 ) + Abs( q4,0 - q5,0 - q6,0 + q7,0

)

[0239] The spq in Table 8 may be derived from the difference

between the pixel p0,0 and the pixel qO,0 adjacent to the edge.

[0240] The first and second thresholds of Table 8 may be derived

based on a predetermined parameter QP. Here, the QP may be

determined using at least one of a first quantization parameter of

the P block, a second quantization parameter of the Q block, or an

offset for inducing QP. The offset may be a value encoded and

signaled by an encoding device. For example, QP may be derived by

adding the offset to the average value of the first and second

quantization parameters. The third threshold of Table 8 may be

derived based on the above-described quantization parameter (QP)

and block boundary strength (BS). Here, the BS may be variably

determined in consideration of a prediction mode of a P/Q block,

an inter prediction mode, a presence or absence of a non-zero

transform coefficient, a difference in motion vectors, etc.

[0241] For example, when at least one prediction mode of the P

block and the Q block is an intra mode, the BS may be set to 2.

When at least one of the P blocks or the Q blocks is encoded in

the combined prediction mode, the BS may be set to 2. When at least

one of the P block or Q block includes a non-zero transform

coefficient, the BS may be set to 1. When the P block is coded in

an inter prediction mode different from the Q block (e.g., when

the P block is coded in the current picture reference mode and the

Q block is coded in the merge mode or AMVP mode), the BS may be

set to 1. When both the P block and the Q block are coded in the

current picture reference mode, and the difference between their

block vectors is greater than or equal to a predetermined threshold

difference, the BS may be set to 1. Here, the threshold difference

may be a fixed value (e.g., 4, 8, 16) pre-committed to the

encoding/decoding device.

[0242] Since dSam3 is derived using one or more pixels belonging

to the fourth pixel line through the same method as dSam described

above, a detailed description will be omitted.

[0243] A decision value may be derived based on the derived dSamO

and dSam3. For example, when both dSamO and dSam3 are 1, the

decision value may be set to a first value (e.g. 3), otherwise,

the decision value may be set to a second value (e.g., 1 or 2).

[0244] Referring to FIG. 16, a filter type of a deblocking filter

may be determined based on the derived decision value (S1620).

[0245] In the encoding/decoding apparatus, a plurality of filter

types having different filter lengths may be defined. As an example of the filter type, there may be a long filter having the longest filter length, a short filter having the shortest filter length, or one or more middle filters that are longer than the short filter and shorter than the long filter. The number of filter types defined in the encoding/decoding apparatus may be 2, 3, 4 or more.

[0246] For example, when the decision value is the first value,

the long filter may be used, and when the decision value is the

second value, the short filter may be used. Alternatively, when

the decision value is the first value, one of the long filter or

the middle filter may be selectively used, and when the decision

value is the second value, the short filter may be used.

Alternatively, when the decision value is the first value, the

long filter is used, and when the decision value is not the first

value, either the short filter or the middle filter may be

selectively used. In particular, when the decision value is 2, the

middle filter may be used, and when the decision value is 1, the

short filter may be used.

[0247] Referring to FIG. 16, filtering may be performed on an

edge of a reconstructed picture based on a deblocking filter

according to the determined filter type (S1630).

[0248] The deblocking filter may be applied to a plurality of

pixels located in both directions based on an edge and located in

the same pixel line. Here, a plurality of pixels to which the

deblocking filter is applied is referred to as a filtering region, and the length (or number of pixels) of the filtering region may be different for each filter type. The length of the filtering region may be interpreted as having the same meaning as the filter length of the aforementioned filter type. Alternatively, the length of the filtering region may mean a sum of the number of pixels to which the deblocking filter is applied in the P block and the number of pixels to which the deblocking filter is applied in the Q block.

[0249] In this embodiment, it is assumed that three filter types,

that is, the long filter, the middle filter, and the short filter,

are defined in an encoding/decoding apparatus, and a deblocking

filtering method for each filter type will be described. However,

the present disclosure is not limited thereto, and only the long

filter and the middle filter may be defined, only the long filter

and the short filter may be defined, or only the middle filter and

the short filter may be defined.

[0250] 1. In case of long filter-based deblocking filtering

[0251] For convenience of explanation, it is assumed that the

edge type is a vertical edge, and the currently filtered pixel

(hereinafter, the current pixel q) belongs to the Q block unless

otherwise stated. The filtered pixel fq may be derived through a

weighted average of a first reference value and a second reference

value.

[0252] Here, the first reference value may be derived using all or part of the pixels in the filtering area to which the current pixel q belongs. Here, the length (or number of pixels) of the filtering region may be an integer of 8, 10, 12, 14 or more. Some pixels in the filtering area may belong to the P block and the other pixels may belong to the Q block. For example, when the length of the filtering region is 10, 5 pixels may belong to the

P block and 5 pixels may belong to the Q block. Alternatively, 3

pixels may belong to the P block and 7 pixels may belong to the Q

block. Conversely, 7 pixels may belong to the P block and 3 pixels

may belong to the Q block. In other words, the long filter-based

deblocking filtering may be performed symmetrically or

asymmetrically on the P block and the Q block.

[0253] Regardless of the location of the current pixel q, all

pixels belonging to the same filtering area may share one and the

same first reference value. That is, the same first reference value

may be used regardless of whether the currently filtered pixel is

located in the P block or the Q block. The same first reference

value may be used regardless of the position of the currently

filtered pixel in the P block or the Q block.

[0254] The second reference value may be derived using at least

one of a pixel farthest from the edge (hereinafter, referred to as

a first pixel) among pixels of the filtering area belonging to the

Q block or neighboring pixels of the filtering area. The

neighboring pixel may mean at least one pixel adjacent to the right direction of the filtering area. For example, the second reference value may be derived as an average value between one first pixel and one neighboring pixel. Alternatively, the second reference value may be derived as an average value between two or more first pixels and two or more adjacent pixels adjacent to the right side of the filtering area.

[0255] For the weighted average, predetermined weights fl and f2

may be applied to the first reference value and the second

reference value, respectively. Specifically, the encoding/decoding

apparatus may define a plurality of weight sets, and may set the

weight fl by selectively using any one of the plurality of weight

sets. The selection may be performed in consideration of the length

(or number of pixels) of the filtering region belonging to the Q

block. For example, the encoding/decoding apparatus may define a

weight set as shown in Table 9 below. Each weight set may consist

of one or more weights corresponding to each location of the pixel

to be filtered. Accordingly, from among a plurality of weights

belonging to the selected weight set, a weight corresponding to

the position of the current pixel q may be selected and applied to

a current pixel q. The number of weights constituting the weight

set may be the same as the length of the filtering region belonging

to the Q block. A plurality of weights constituting one weight set

may be sampled at a predetermined interval within a range of an

integer greater than 0 and less than 64. Here, 64 is only an example, and may be larger or smaller than 64. The predetermined interval may be 9, 13, 17, 21, 25 or more. The interval may be variably determined according to the length L of the filtering region included in the Q block. Alternatively, a fixed spacing may be used regardless of L.

[0256] [Table 9]

Length of filtering area belonging to Q block (L) Weight set

L>5 {59,50,41,32,23, 14,5}

{58,45,32, 19,6}

L<5 {53,32,11}

[0257] Referring to Table 9, when the length (L) of the filtering

area belonging to the Q block is greater than 5, {59, 50, 41, 32,

23, 14, 5} may be selected among three weight sets, and when L is

, {58, 45, 32, 19, 61 may be selected, and when L is less than 5,

{53, 32, 111 may be selected. However, Table 9 is only an example

of a weight set, and the number of weight sets defined in the

encoding/decoding apparatus may be 2, 4 or more.

[0258] Also, when L is 7 and the current pixel is a first pixel

qO based on the edge, a weight 59 may be applied to the current

pixel. When the current pixel is a second pixel ql based on the

edge, a weight 50 may be applied to the current pixel, and when

the current pixel is a seventh pixel q6 based on the edge, a weight may be applied to the current pixel.

[0259] A weight f2 may be determined based on the pre-determined

weight fl. For example, the weight f2 may be determined as a value

obtained by subtracting the weight fl from a pre-defined constant.

Here, the pre-defined constant is a fixed value pre-defined in the

encoding/decoding apparatus, and may be 64. However, this is only

an example, and an integer greater than or less than 64 may be

used.

[0260] 2. In case of middle filter-based deblocking filtering

[0261] The filter length of the middle filter may be smaller than

the filter length of the long filter. The length (or number of

pixels) of the filtering region according to the middle filter may

be smaller than the length of the filtering region according to

the aforementioned long filter.

[0262] For example, the length of the filtering area according to

the middle filter may be 6, 8 or more. Here, the length of the

filtering region belonging to the P block may be the same as the

length of the filtering region belonging to the Q block. However,

the present invention is not limited thereto, and the length of

the filtering region belonging to the P block may be longer or

shorter than the length of the filtering region belonging to the

Q block.

[0263] Specifically, a filtered pixel fq may be derived using a

current pixel q and at least one neighboring pixel adjacent to the current pixel q. Here, the neighboring pixel may include at least one of one or more pixels adjacent to the left of the current pixel q (hereinafter, left peripheral pixels) or one or more pixels adjacent to the right of the current pixel q (hereinafter, right peripheral pixels).

[0264] For example, when the current pixel q is qO, two left

neighboring pixels p0 and pl and two right neighboring pixels ql

and q2 may be used. When the current pixel q is q1, two left

neighboring pixels p0 and qO and one right neighboring pixel q2

may be used. When the current pixel q is q2, three left neighboring

pixels p0, qO, and ql and one right neighboring pixel q3 may be

used.

[0265] 3. Short filter-based deblocking filtering

[0266] The filter length of the short filter may be smaller than

that of the middle filter. The length (or number of pixels) of the

filtering region according to the short filter may be smaller than

the length of the filtering region according to the above-described

middle filter. For example, the length of the filtering region

according to the short filter may be 2, 4 or more.

[0267] Specifically, a filtered pixel fq may be derived by adding

or subtracting a predetermined first offset offsett) to a current

pixel q. Here, the first offset may be determined based on a

difference value between the pixels of the P block and the pixels

of the Q block. For example, as shown in Equation 5 below, the first offset may be determined based on a difference value between the pixel p0 and the pixel qO and a difference value between the pixel pl and the pixel ql. However, filtering for the current pixel q may be performed only when the first offset is smaller than a predetermined threshold. Here, the threshold is derived based on the above-described quantization parameter (QP) and block boundary strength (BS), and a detailed description thereof will be omitted.

[0268] [Equation 5]

[0269] offset1=(9*(q0- p0)-3*(ql-pl)+8) » 4

[0270] Alternatively, the filtered pixel fq may be derived by

adding a predetermined second offset (offset2) to the current pixel

q. Here, the second offset may be determined in consideration of

at least one of a difference (or change amount) between the current

pixel q and the neighboring pixels or the first offset. Here, the

neighboring pixels may include at least one of a left pixel or a

right pixel of the current pixel q. For example, the second offset

may be determined as in Equation 6 below.

[0271] [Equation 6]

[0272] offset2=(((q2+qO+1) » 1)-ql-offsetl) » 1

[0273] The above-described filtering method is not limited to

being applied only to the deblocking filter, and may be applied

similarly or similarly to an adaptive sample offset (SAO), an

adaptive loop filter (ALF), etc., which are examples of an in-loop filter.

[0274]

[0275] Exemplary methods of the present disclosure are expressed

as a series of operations for clarity of explanation, but this is

not intended to limit the order in which steps are performed, and

each step may be performed simultaneously or in a different order

if necessary. In order to implement the method according to the

present disclosure, the exemplary steps may include additional

steps, other steps may be included excluding some steps, or may

include additional other steps excluding some steps.

[0276] Various embodiments of the present disclosure are not

intended to list all possible combinations, but to describe

representative aspects of the present disclosure, and matters

described in the various embodiments may be applied independently

or may be applied in combination of two or more.

[0277] In addition, various embodiments of the present disclosure

may be implemented by hardware, firmware, software, or a

combination thereof. For implementation by hardware, one or more

ASICs (Application Specific Integrated Circuits), DSPs (Digital

Signal Processors), DSPDs (Digital Signal Processing Devices),

PLDs (Programmable Logic Devices), FPGAs (Field Programmable Gate

Arrays), general purpose It may be implemented by a processor

(general processor), a controller, a microcontroller, a

microprocessor, etc.

[0278] The scope of the present disclosure includes software or

machine-executable instructions (e.g., operating systems,

applications, firmware, programs, etc.) that cause an operation

according to the method of various embodiments to be executed on

a device or computer, and or a non-transitory computer-readable

medium (non-transitory computer-readable medium) which stores such

software or instructions etc., and is executable on a device or a

computer.

Industrial Applicability

[0279] The present invention may be used to encode/decode a video

signal.

Claims

1. A method of decoding an image, comprising:

dividing one picture into a plurality of division units;

determining whether to perform filtering on a boundary of a

current division unit based on a predetermined flag; and

performing filtering on the boundary of the current division

unit in response to the determination,

wherein the division unit includes at least one of a sub

picture, a slice, or a tile,

wherein the flag includes at least one of a first flag

indicating whether filtering is performed on a boundary of a

division unit within the one picture or a second flag indicating

whether filtering is performed on the boundary of the current

division unit in the one picture.

2. The method of claim 1, wherein when the first flag is a

first value, it is restricted so that filtering is not performed

on the boundary of the division unit within the one picture, and

when the first flag is a second value, the restriction on the

boundary of the division unit within the picture is not imposed,

wherein when the second flag is the first value, it is

restricted so that filtering is not performed on the boundary of

the current division unit, and when the second flag is the second

value, filtering is allowed to be performed on the boundary of the current division unit.

3. The method of claim 2, wherein the second flag is decoded

only when it is not restricted so that filtering is not performed

on the boundary of the division unit within the one picture

according to the first flag.

4. The method of claim 1, wherein whether to perform

filtering on the boundary of the current division unit is

determined by further considering a third flag indicating whether

filtering is performed on a boundary of a neighboring division

unit adjacent to the current block unit.

5. The method of claim 4, wherein a position of the

neighboring division unit is determined based on whether the

boundary of the current division unit is a vertical boundary or a

horizontal boundary.

6. The method of claim 1, wherein performing the filtering

comprises:

specifying a block boundary for deblocking filtering;

deriving a decision value for the block boundary;

determining a filter type for the deblocking filtering based

on the decision value; and performing the filtering on the block boundary based on the filter type.

7. A method of encoding an image, comprising:

dividing one picture into a plurality of division units;

determining whether to perform filtering on a boundary of a

current division unit; and

performing filtering on the boundary of the current division

unit in response to the determination,

wherein the division unit includes at least one of a sub

picture, a slice, or a tile,

wherein determining whether to perform filtering on the

boundary of the current division unit comprises,

encoding at least one of a first flag indicating whether

filtering is performed on a boundary of a division unit within the

one picture or a second flag indicating whether filtering is

performed on the boundary of the current division unit in the one

picture.

8. The method of claim 7, wherein when it is determined that

filtering is restricted not to be performed on the boundary of the

division unit within the one picture, the first flag is encoded as

a first value, and when it is determined that the restriction is

not imposed on the boundary of the division unit within the picture, the first flag is encoded as a second value, wherein when it is determined that filtering is restricted not to be performed on the boundary of the current division unit, the second flag is encoded as the first value, and when it is determined that filtering is allowed to be performed on the boundary of the current division unit, the second flag is encoded as the second value.

9. The method of claim 8, wherein the second flag is encoded

only when it is not restricted so that filtering is not performed

on the boundary of the division unit within the one picture.

10. The method of claim 7, wherein whether to perform

filtering on the boundary of the current division unit is

determined by further considering a third flag indicating whether

filtering is performed on a boundary of a neighboring division

unit adjacent to the current block unit.

11. The method of claim 10, wherein a position of the

neighboring division unit is determined based on whether the

boundary of the current division unit is a vertical boundary or a

horizontal boundary.

12. The method of claim 7, wherein performing the filtering comprises: specifying a block boundary for deblocking filtering; deriving a decision value for the block boundary; determining a filter type for the deblocking filtering based on the decision value; and performing the filtering on the block boundary based on the filter type.