U.S. patent application number 15/213308 was filed with the patent office on 2016-11-10 for scalable video signal encoding/decoding method and apparatus.
This patent application is currently assigned to KT CORPORATION. The applicant listed for this patent is KT CORPORATION. Invention is credited to Joo Young KIM, Bae Keun LEE.
Application Number | 20160330458 15/213308 |
Document ID | / |
Family ID | 52628623 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160330458 |
Kind Code |
A1 |
LEE; Bae Keun ; et
al. |
November 10, 2016 |
SCALABLE VIDEO SIGNAL ENCODING/DECODING METHOD AND APPARATUS
Abstract
A scalable video signal decoding method according to the present
invention comprises determining a corresponding picture of a
reference layer used for inter-layer prediction of a current
picture within a current layer, generating an interlayer reference
picture by up-sampling the determined corresponding picture,
generating a reference picture list including the interlayer
reference picture, and performing an inter prediction of the
current picture on the basis of the reference picture list.
Inventors: |
LEE; Bae Keun; (Seoul,
KR) ; KIM; Joo Young; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KT CORPORATION |
Gyeonggi-do |
|
KR |
|
|
Assignee: |
KT CORPORATION
Gyeonggi-do
KR
|
Family ID: |
52628623 |
Appl. No.: |
15/213308 |
Filed: |
July 18, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14916130 |
Mar 2, 2016 |
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PCT/KR2014/008101 |
Aug 29, 2014 |
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15213308 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 19/31 20141101;
H04N 19/157 20141101; H04N 19/70 20141101; H04N 19/59 20141101;
H04N 19/573 20141101; H04N 19/513 20141101; H04N 19/593 20141101;
H04N 19/187 20141101; H04N 19/105 20141101; H04N 19/176 20141101;
H04N 19/53 20141101; H04N 19/172 20141101; H04N 19/58 20141101;
H04N 19/46 20141101; H04N 19/39 20141101; H04N 19/30 20141101; H04N
19/33 20141101; H04N 19/159 20141101 |
International
Class: |
H04N 19/187 20060101
H04N019/187; H04N 19/159 20060101 H04N019/159; H04N 19/172 20060101
H04N019/172; H04N 19/513 20060101 H04N019/513; H04N 19/176 20060101
H04N019/176; H04N 19/31 20060101 H04N019/31; H04N 19/33 20060101
H04N019/33; H04N 19/573 20060101 H04N019/573; H04N 19/39 20060101
H04N019/39; H04N 19/105 20060101 H04N019/105 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 2013 |
KR |
10-2013-0105673 |
Aug 28, 2014 |
KR |
10-2014-0112865 |
Claims
1-15. (canceled)
16. A method for decoding a video signal by a decoding apparatus,
the method comprising: determining, based on inter-layer reference
information relating to a current picture of a current layer, a
corresponding picture of a reference layer to be used for
inter-layer prediction of the current picture; generating an
inter-layer reference picture by up-sampling the determined
corresponding picture; generating a reference picture list based on
the inter-layer reference picture; and performing inter prediction
for the current picture based on the reference picture list.
17. The method of claim 16, wherein the corresponding picture is
determined based on whether or not the corresponding picture
belongs to a same access unit as the current picture.
18. The method of claim 17, wherein the inter-layer reference
picture includes at least one a first inter-layer reference picture
and a second inter-layer reference picture, and wherein the first
inter-layer reference picture is representative of a reference
picture on which a filtering is performed on a integer position
thereof, and the second inter-layer reference picture is
representative of a reference picture on which the filtering is not
performed on the integer position thereof.
19. The method of claim 18, wherein when a reference picture
relating to a current block included in the current picture is
determined to be the inter-layer reference picture, a motion vector
of the current block is set equal to (0,0).
20. The method of claim 16, the method further comprising:
obtaining a reference active flag from a bitstream, the reference
active flag indicating whether a restriction that corresponding
pictures of all layers having a direct dependency with the current
layer are used for inter-layer prediction of the current picture is
applied or not; and obtaining the inter-layer reference information
based on the reference active flag.
21. The method of claim 20, wherein the inter-layer reference
information includes at least one of an inter-layer prediction
flag, number information of reference pictures, or a reference
layer identifier.
22. The method of claim 21, wherein the inter-layer prediction flag
indicates whether the inter-layer prediction is used for decoding
the current picture, the number information of the reference
pictures indicates a number of corresponding pictures to be used
for the inter-layer prediction of the current picture, and the
reference layer identifier is a layer identifier of each of layers
including the corresponding pictures to be used for the inter-layer
prediction of the current picture.
23. The method of claim 22, wherein the reference layer identifier
is obtained only when the number of the corresponding pictures to
be used for the inter-layer prediction of the current picture is
different from a number of layers having the direct dependency with
the current layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a scalable video signal
encoding/decoding method and device.
BACKGROUND ART
[0002] Recently, demand for high-resolution, high-quality video
such as HD (High Definition) video and UHD (Ultra High Definition)
video is increasing in various application fields. As video data
has high-resolution, high-quality images, the amount of data is
higher than for existing video data. Therefore, when the video data
is transmitted using media such as existing wired and wireless
broadband lines or is stored in existing storage media,
transmission costs and storage costs increase. To solve these
problems caused by the high-resolution, high-quality video data,
high-efficiency video compression techniques may be used.
[0003] As video compression techniques, there are various
techniques such as an inter-prediction technique for predicting the
values of pixels included in a current picture from pictures that
precede or follow the current picture, an intra-prediction
technique for predicting the values of pixels in the current
picture using information about the pixels included in the current
picture, an entropy coding technique, in which the shortest code is
assigned to the most frequently used value and the longest code is
assigned to the least frequently used value, and the like. Video
data may be effectively compressed using these video compression
techniques, and may then be transmitted or stored.
[0004] Meanwhile, with the increase in demand for high-resolution
video, demand for stereoscopic video content, as a new video
service, is also increasing. Discussions on video compression
techniques for effectively providing high-resolution and
super-resolution stereoscopic video content are underway.
DISCLOSURE
Technical Problem
[0005] An object of the present invention is to provide a method
and device for determining a corresponding picture of a reference
layer to be used for inter-layer prediction of a current picture,
upon encoding/decoding scalable video signals.
[0006] Another object of the present invention is to provide a
method and device for up-sampling a corresponding picture of a
reference layer, upon encoding/decoding scalable video signals.
[0007] A further object of the present invention is to provide a
method and device for constructing a reference picture list using
an inter-layer reference picture, upon encoding/decoding scalable
video signals.
[0008] Yet another object of the present invention is to provide a
method and device for effectively deriving texture information of a
current layer via inter-layer prediction, upon encoding/decoding
scalable video signals.
Technical Solution
[0009] A scalable video signal decoding method and device according
to the present invention is characterized by determining a
corresponding picture of a reference layer to be used for
inter-layer prediction of a current picture in a current layer,
generating an inter-layer reference picture by up-sampling the
determined corresponding picture, generating a reference picture
list including the inter-layer reference picture, and performing
inter-prediction of the current picture based on the reference
picture list.
[0010] The corresponding picture of the reference layer according
to the present invention may be determined based on inter-layer
reference information for the current picture.
[0011] The inter-layer reference information according to the
present invention may include at least one of an inter-layer
prediction flag, information about a number of reference pictures,
and a reference layer identifier.
[0012] The inter-layer prediction flag according to the present
invention may be acquired based on a reference active flag, and the
reference active flag may be information indicating whether
corresponding pictures of all layers having a direct dependency
with the current layer are used for inter-layer prediction of the
current picture.
[0013] The determined corresponding picture according to the
present invention may be a corresponding picture of a layer
specified by a reference layer identifier among layers having a
direct dependency with the current layer.
[0014] A scalable video signal encoding method and device according
to the present invention is characterized by determining a
corresponding picture of a reference layer to be used for
inter-layer prediction of a current picture in a current layer,
generating an inter-layer reference picture by up-sampling the
determined corresponding picture, generating a reference picture
list including the inter-layer reference picture, and performing
inter-prediction of the current picture based on the reference
picture list.
[0015] The corresponding picture of the reference layer according
to the present invention may be determined based on inter-layer
reference information for the current picture.
[0016] The inter-layer reference information according to the
present invention may include at least one of an inter-layer
prediction flag, information about a number of reference pictures,
and a reference layer identifier.
[0017] The inter-layer prediction flag according to the present
invention may be acquired based on a reference active flag, and the
reference active flag may be information indicating whether
corresponding pictures of all layers having a direct dependency
with the current layer are used for inter-layer prediction of the
current picture.
[0018] The determined corresponding picture according to the
present invention may be a corresponding picture of a layer
specified by a reference layer identifier among layers having a
direct dependency with the current layer.
Advantageous Effects
[0019] In accordance with the present invention, a corresponding
picture of a reference layer to be used for inter-layer prediction
of a current picture in a current layer may be effectively
determined.
[0020] In accordance with the present invention, a picture of a
reference layer may be effectively up-sampled.
[0021] In accordance with the present invention, a reference
picture list including an inter-layer reference picture may be
effectively constructed.
[0022] In accordance with the present invention, texture
information of a current layer may be effectively derived via
inter-layer prediction.
DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a block diagram schematically showing an encoding
device according to an embodiment of the present invention;
[0024] FIG. 2 is a block diagram schematically showing a decoding
device according to an embodiment of the present invention;
[0025] FIG. 3 is a flowchart showing a procedure for performing
inter-prediction of a current layer using the corresponding picture
of a reference layer according to an embodiment to which the
present invention is applied;
[0026] FIG. 4 illustrates a method for determining the
corresponding picture of a reference layer based on a reference
active flag according to an embodiment to which the present
invention is applied;
[0027] FIG. 5 illustrates a syntax table for a reference active
flag according to an embodiment to which the present invention is
applied;
[0028] FIG. 6 illustrates a method for acquiring inter-layer
reference information for a current picture according to an
embodiment to which the present invention is applied;
[0029] FIG. 7 illustrates a syntax table for inter-layer reference
information according to an embodiment to which the present
invention is applied;
[0030] FIG. 8 illustrates a method for determining the
corresponding picture of a reference layer based on a reference
present flag according to an embodiment to which the present
invention is applied;
[0031] FIG. 9 illustrates a syntax table for a reference present
flag according to an embodiment to which the present invention is
applied;
[0032] FIG. 10 illustrates a method for acquiring inter-layer
reference information for a current picture according to an
embodiment to which the present invention is applied;
[0033] FIG. 11 illustrates a syntax table for inter-layer reference
information according to an embodiment to which the present
invention is applied;
[0034] FIG. 12 is a flowchart showing a method for up-sampling the
corresponding picture of a reference layer according to an
embodiment to which the present invention is applied;
[0035] FIG. 13 is a diagram showing a method for specifying a
short-term reference picture stored in a decoding picture
buffer;
[0036] FIG. 14 illustrates a method for specifying a long-term
reference picture according to an embodiment to which the present
invention is applied; and
[0037] FIG. 15 illustrates a method for constructing a reference
picture list using a short-term reference picture and a long-term
reference picture according to an embodiment to which the present
invention is applied.
BEST MODE
[0038] A scalable video signal decoding method and device according
to the present invention is characterized by determining a
corresponding picture of a reference layer to be used for
inter-layer prediction of a current picture in a current layer,
generating an inter-layer reference picture by up-sampling the
determined corresponding picture, generating a reference picture
list including the inter-layer reference picture, and performing
inter-prediction of the current picture based on the reference
picture list.
[0039] The corresponding picture of the reference layer according
to the present invention may be determined based on inter-layer
reference information for the current picture.
[0040] The inter-layer reference information according to the
present invention may include at least one of an inter-layer
prediction flag, information about a number of reference pictures,
and a reference layer identifier.
[0041] The inter-layer prediction flag according to the present
invention may be acquired based on a reference active flag, and the
reference active flag may be information indicating whether
corresponding pictures of all layers having a direct dependency
with the current layer are used for inter-layer prediction of the
current picture.
[0042] The determined corresponding picture according to the
present invention may be a corresponding picture of a layer
specified by a reference layer identifier among layers having a
direct dependency with the current layer.
[0043] A scalable video signal encoding method and device according
to the present invention is characterized by determining a
corresponding picture of a reference layer to be used for
inter-layer prediction of a current picture in a current layer,
generating an inter-layer reference picture by up-sampling the
determined corresponding picture, generating a reference picture
list including the inter-layer reference picture, and performing
inter-prediction of the current picture based on the reference
picture list.
[0044] The corresponding picture of the reference layer according
to the present invention may be determined based on inter-layer
reference information for the current picture.
[0045] The inter-layer reference information according to the
present invention may include at least one of an inter-layer
prediction flag, information about a number of reference pictures,
and a reference layer identifier.
[0046] The inter-layer prediction flag according to the present
invention may be acquired based on a reference active flag, and the
reference active flag may be information indicating whether
corresponding pictures of all layers having a direct dependency
with the current layer are used for inter-layer prediction of the
current picture.
[0047] The determined corresponding picture according to the
present invention may be a corresponding picture of a layer
specified by a reference layer identifier among layers having a
direct dependency with the current layer.
MODE FOR INVENTION
[0048] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the attached
drawings. The terms or words used in the present specification and
claims should not be construed as being limited to ordinary
meanings or dictionary definitions. The present invention should be
understood to have meanings and concepts coping with the technical
spirit of the present invention based on the principle that an
inventor can appropriately define the concepts of terms in order to
best describe his or her invention. Therefore, the embodiments
described in the specification and the configurations illustrated
in the drawings are merely preferred examples and do not
exhaustively present the technical spirit of the present invention.
Accordingly, it should be appreciated that there may be various
equivalents and modifications that can replace the embodiments and
the configurations at the time at which the present application is
filed.
[0049] In this specification, when it is said that one element is
`connected` or `coupled` with another element, it may mean that the
one element may be directly connected or coupled with the other
element and a third element may be `connected` or `coupled` between
the two elements. Furthermore, in this specification, when it is
said that a specific element is `included`, it may mean that
elements other than the specific element are not excluded and that
additional elements may be included in the embodiments of the
present invention or the scope of the technical spirit of the
present invention.
[0050] Terms such as `first` and `second` may be used to describe
various elements, but the elements are not restricted by the terms.
The terms are used only to distinguish one element from the other
element. For example, a first element may be named a second element
without departing from the scope of the present invention.
Likewise, a second element may be named a first element.
[0051] Furthermore, element modules described in the embodiments of
the present invention are independently shown in order to indicate
different and characteristic functions, but this does not mean that
each of the element modules is formed of a separate piece of
hardware or software. That is, the element modules are arranged and
included for convenience of description, and at least two of the
element modules may form one element module or one element module
may be divided into a plurality of element modules to perform their
own functions. An embodiment in which the element modules are
integrated and an embodiment in which the element modules are
separated are included in the scope of the present invention,
unless it departs from the essence of the present invention.
[0052] Furthermore, in the present invention, some elements are not
essential elements for performing essential functions, but may be
optional elements for improving only performance. The present
invention may be implemented using only essential elements for
implementing the essence of the present invention other than
elements used merely to improve performance, and a structure
including only essential elements, but not optional elements used
only to improve performance, is included in the scope of the
present invention.
[0053] Video encoding and decoding that supports a multi-layer
bitstream is called scalable video coding. Because there is a
strong correlation between the multiple layers, when prediction is
performed using this correlation, duplicate elements may be removed
and video encoding performance may be improved. Predicting the
current layer using information about another layer is referred to
as inter-layer prediction.
[0054] The multi-layers may have different resolutions, and the
resolution may mean at least one of a spatial resolution, a
temporal resolution, and image quality. At the time of inter-layer
prediction, resampling such as up-sampling or down-sampling of a
layer may be performed in order to adjust a resolution.
[0055] FIG. 1 is a block diagram schematically illustrating an
encoding device according to an embodiment of the present
invention.
[0056] An encoding device 100 according to the present invention
includes an encoding unit 100a for an upper layer and an encoding
unit 100b for a lower layer.
[0057] The upper layer may be called a current layer or an
enhancement layer, and the lower layer may be called an enhancement
layer having resolution lower than that of the upper layer, a base
layer or a reference layer. At least one of the spatial resolution,
temporal resolution based on a frame rate, color format, and image
quality based on a quantization step size may differ between the
upper layer and the lower layer. When a change of resolution is
required for inter-layer prediction, up-sampling or down-sampling
of the layer may be performed.
[0058] The encoding unit 100a for the upper layer may include a
partitioning unit 110, a prediction unit 120, a transform unit 130,
a quantization unit 140, a rearrangement unit 150, an entropy
coding unit 160, an inverse quantization unit 170, an
inverse-transform unit 180, a filter unit 190, and memory 195.
[0059] The encoding unit 100b for the lower layer may include a
partitioning unit 111, a prediction unit 125, a transform unit 131,
a quantization unit 141, a rearrangement unit 151, an entropy
coding unit 161, an inverse quantization unit 171, an
inverse-transform unit 181, a filter unit 191, and memory 196.
[0060] The encoding unit may be implemented by a video encoding
method described in an embodiment of the present invention, which
will be described below, but the operations of some parts may not
be performed in order to reduce the complexity of the encoding
device or to enable fast real-time encoding. For example, rather
than a method in which all intra-prediction mode methods are used
to select the optimal intra-encoding method, a method in which one
is selected from among a limited number of intra-prediction modes
and the selected one is set as the final intra-prediction mode may
be performed for real-time encoding when the prediction unit
performs intra-prediction. In another example, a prediction block
used for intra-prediction or inter-prediction may have a limited
shape.
[0061] The unit of a block processed in the encoding device may be
a coding unit for performing coding, a prediction unit for
performing prediction, or a transform unit for performing
transformation. The coding unit, the prediction unit, and the
transform unit may be represented as CU, PU, and TU,
respectively.
[0062] Each of the partitioning units 110 and 111 may partition a
layer by partitioning a layer picture into multiple combinations of
coding blocks, prediction blocks, and transform blocks, and by
selecting one combination of coding blocks, prediction blocks, and
transform blocks based on a predetermined reference (for example, a
cost function). For example, in order to partition a layer picture
into coding units, a recursive tree structure such as a QuadTree
structure may be used. Hereinafter, in an embodiment of the present
invention, a coding block may mean not only a block for encoding
but also a block for decoding.
[0063] A prediction block may be a unit for performing prediction,
such as intra-prediction or inter-prediction. A block for
intra-prediction may be a block having the form of a square, such
as 2N.times.2N or N.times.N. As a block for inter-prediction, there
are a block in the form of a square, such as 2N.times.2N and
N.times.N, a block in the form of a rectangle, such as 2N.times.N
and N.times.2N, and a block having an asymmetric form, obtained by
a prediction block partitioning method using Asymmetric Motion
Partitioning (AMP). The transform unit 115 may use different
transform methods depending on the form of the prediction
block.
[0064] Each of the prediction units 120 and 125 of the encoding
units 100a and 100b may include an intra-prediction unit 121 or 126
for performing intra-prediction and an inter-prediction unit 122 or
127 for performing inter-prediction. The prediction unit 120 of the
encoding unit 100a for the upper layer may further include an
inter-layer prediction unit 123, which performs prediction of the
upper layer using the information relating to the lower layer.
[0065] Each of the prediction units 120 and 125 may determine
whether to perform inter-prediction or intra-prediction of a
prediction block. When intra-prediction is performed, an
intra-prediction mode is determined based on a prediction block,
and a process for processing intra-prediction based on the
determined intra-prediction mode may be performed based on a
transform block. A residual (residual block) between the generated
prediction block and the original block may be input to the
transform units 130 and 131. Also, the prediction mode information
used for prediction, motion information, and the like are encoded
along with the residual by the entropy coding unit 130, and may be
transmitted to the decoding device.
[0066] When a Pulse Code Modulation (PCM) mode is used, the
original block may be encoded unchanged without performing
prediction using the prediction units 120 and 125, and may be
transmitted to a decoding unit.
[0067] Each of the intra-prediction units 121 and 126 may generate
an intra-predicted block based on reference pixels located around
the current block (the prediction target block). In the
intra-prediction method, the intra-prediction mode may have a
directional prediction mode, which uses reference pixels according
to the prediction direction, and a non-directional mode, which does
not consider a prediction direction. The mode for predicting luma
information may be different from the mode for predicting chroma
information. Intra-prediction mode, obtained by predicting luma
information, or the predicted luma information may be used to
predict chroma information. Meanwhile, if the reference pixels are
not available, a prediction block may be generated by replacing the
unavailable reference pixels with other pixels.
[0068] A prediction block may include multiple transform blocks. If
the size of a prediction block is the same as the size of a
transform block when performing intra-prediction, intra-prediction
of the prediction block may be performed based on a left pixel, an
upper-left pixel, and an upper pixel of the prediction block.
However, as the time of intra-prediction, when the sizes of the
prediction block and the transform block are different and multiple
transform blocks are included inside the prediction block,
neighboring pixels adjacent to the transform blocks are used as
reference pixels to perform the intra-prediction. Here, the
neighboring pixels adjacent to the transform block may include at
least one of neighboring pixels adjacent to the prediction block
and previously decoded pixels in the prediction blocks.
[0069] However, if the size of a prediction block is different from
that of a transform block when performing intra-prediction and thus
the prediction block includes multiple transform blocks,
intra-prediction may be performed based on reference pixels
determined based on the transform block.
[0070] The intra-prediction method may generate a prediction block
after applying a Mode-Dependent Intra Smoothing (MDIS) filter to
reference pixels according to the intra-prediction mode. The type
of MDIS filter applied to the reference pixels may vary. The MDIS
filter is an additional filter applied to an intra-predicted block
generated by performing intra-prediction, and may be used for
reducing a residual between reference pixels and the
intra-predicted block, generated after performing prediction. When
MDIS filtering is performed, different filtering may be performed
on reference pixels and on some columns included in the
intra-predicted block according to the direction of the
intra-prediction mode.
[0071] Each of the inter-prediction units 122 and 127 may perform
prediction by referring to the information about a block included
in at least one of the picture preceding and the picture following
the current picture. Each of the inter-prediction units 122 and 127
may include a reference picture interpolation unit, a motion
prediction unit, and a motion compensation unit.
[0072] The reference picture interpolation unit may receive
reference picture information from memory 195 or 196 and may
generate information about a pixel, which is smaller than an
integer pixel, from the reference picture. For a luma pixel, a
DCT-based 8-tap interpolation filter, which differently sets filter
coefficients to generate information about a pixel that is smaller
than an integer pixel in units of 1/4 pixels, may be used. For
chroma signals, a DCT-based 4-tap interpolation filter, which
differently sets filter coefficients to generate information about
a pixel that is smaller than an integer pixel in units of 1/8
pixels, may be used.
[0073] Each of the inter-prediction units 122 and 127 may perform
motion prediction based on the reference picture interpolated by
the reference picture interpolation unit. As a method for
calculating a motion vector, various methods, such as a Full
search-based Block Matching Algorithm (FBMA), a Three-Step Search
(TSS) algorithm, and a New Three-Step Search (NTS) Algorithm, may
be used. The motion vector may have a motion vector value
corresponding to 1/2 or 1/4 of the interpolated pixel. Each of the
inter-prediction units 122 and 127 may perform prediction on a
current block using any one of various inter-prediction
methods.
[0074] As the inter-prediction method, any of various methods such
as a skip method, a merge method, and a Motion Vector Prediction
(MVP) method may be used.
[0075] In inter-prediction, motion information, that is,
information about a reference index, a motion vector, and a
residual signal, is entropy-coded and then transferred to the
decoding unit. When a skip mode is applied, a residual signal is
not generated, and thus a procedure for transforming and quantizing
a residual signal may be omitted.
[0076] The inter-layer prediction unit 123 performs inter-layer
prediction for predicting an upper layer using information about
the lower layer. The inter-layer prediction unit 123 may perform
inter-layer prediction using the texture information, motion
information, etc. of the lower layer.
[0077] The inter-layer prediction may be performed by setting the
picture of the lower layer as a reference picture and performing
prediction on the current block of the upper layer using the motion
information in the picture of the lower layer (reference layer).
The picture of the reference layer, used as a reference picture in
the inter-layer prediction, may be a picture that is sampled so as
to match the resolution of the current layer. Also, the motion
information may include a motion vector and a reference index. In
this case, the motion vector value for the picture of the reference
layer may be set to (0, 0).
[0078] As an example of the inter-layer prediction, a prediction
method that uses the picture of a lower layer as a reference
picture is described, but the present invention is not limited to
this. The inter-layer prediction unit 123 may additionally perform
inter-layer texture prediction, inter-layer motion prediction,
inter-layer syntax prediction, inter-layer residual prediction, and
the like.
[0079] The inter-layer texture prediction may derive the texture of
the current layer based on the texture of the reference layer. The
texture of the reference layer may be sampled to match the
resolution of the current layer, and the inter-layer prediction
unit 123 may predict the texture of the current layer based on the
sampled texture of the reference layer.
[0080] The inter-layer motion prediction may derive the motion
vector of the current layer based on the motion vector of the
reference layer. In this case, the motion vector of the reference
layer may be scaled to match the resolution of the current layer.
The inter-layer syntax prediction may predict the syntax of the
current layer based on the syntax of the reference layer. For
example, the inter-layer prediction unit 123 may use the syntax of
the reference layer as the syntax of the current layer. Also, the
inter-layer residual prediction may reconstruct the picture of the
current layer using the residual between the restored picture of
the reference layer and the restored picture of the current
layer.
[0081] A residual block including residual information, which is
the difference between the prediction block generated by each of
the prediction units 120 and 125 and the reconstructed block of the
prediction block, is generated, and the residual block is input to
the corresponding transform unit 130 or 131.
[0082] Each of the transform units 130 and 131 may transform the
residual block using a transform method such as a Discrete Cosine
Transform (DCT) or Discrete Sine Transform (DST). Whether to apply
DCT or DST to transform the residual block may be determined based
on the intra-prediction mode information of the prediction block
used to generate the residual block and the size information of the
prediction block. That is, each of the transform units 130 and 131
may use different transform methods depending on the size of the
prediction block and the prediction method.
[0083] Each of the quantization units 140 and 141 may quantize
values transformed in the frequency domain by the corresponding
transform unit 130 or 131. The quantization coefficients may change
depending on the type of block or the importance of the pictures.
The value calculated by the quantization unit 140 or 141 may be
provided to the inverse-quantization unit 170 or 17 and the
rearrangement unit 150 or 151.
[0084] Each of the rearrangement units 150 and 151 may rearrange
coefficient values of the quantized residual value. The
rearrangement unit 150 or 151 may change a 2D block format
coefficient to a 1D vector format coefficient using a coefficient
scanning method. For example, the rearrangement unit 150 or 151 may
change the 2D block format coefficient to a 1D vector format
coefficient by scanning coefficients ranging from a DC coefficient
to a high-frequency band coefficient using a zigzag scanning
method. Depending on the size of the transform block and on the
intra-prediction mode, a vertical scanning method for scanning 2D
block format coefficients in a column direction and a horizontal
scanning method for scanning 2D block format coefficients in a row
direction, rather than the zigzag scanning method, may be used.
That is, the determination of which one of the zigzag scanning,
vertical scanning, and horizontal scanning methods is to be used
may be made depending on the size of the transform block and the
intra-prediction mode.
[0085] Each of the entropy coding units 160 and 161 may perform
entropy coding based on the values calculated by the rearrangement
unit 150 or 151. The entropy coding may be implemented using, for
example, various coding methods such as Exponential Golomb,
Context-Adaptive Variable Length Coding (CAVLC), and
Context-Adaptive Binary Arithmetic Coding (CABAC).
[0086] The entropy coding units 160 and 161 may perform entropy
coding based on a predetermined coding method by receiving various
information, such as residual coefficient information and block
type information of a coding block, prediction mode information,
partition unit information, prediction block information and
transmission unit information, motion vector information, reference
frame information, interpolation information for a block, filtering
information, and the like, from the rearrangement units 150 and 151
and the prediction units 120 and 125. Also, the entropy coding
units 160 and 161 may entropy-code the coefficient value of a
coding unit, input from the rearrangement units 150 and 151.
[0087] Each of the entropy coding units 160 and 161 may encode the
intra-prediction mode information of the current block by
binary-coding the intra-prediction mode information. The entropy
coding units 160 and 161 may include a codeword mapping unit for
the binary coding, and may perform the binary coding differently
depending on the size of the prediction block for intra-prediction.
The codeword mapping unit may adaptively generate a codeword
mapping table through a binary coding operation, or may have a
previously generated mapping table. In another embodiment, the
entropy coding units 160 and 161 may represent the intra-prediction
mode information about the current block using a code-num mapping
unit for performing code-num mapping and a codeword mapping unit
for performing codeword mapping. The code-num mapping unit and the
codeword mapping unit may generate a code-num mapping table and a
codeword mapping table, respectively, or may respectively have a
previously generated code-num mapping table and codeword mapping
table.
[0088] Each of the inverse quantization units 170 and 171 and the
inverse transform unit 180 or 181 may inverse-quantize the values
quantized by the quantization unit 140 or 141 and inverse-transform
the values transformed by the transform unit 130 or 131. The
residual value generated by the inverse quantization unit 170 or
171 and the inverse transform unit 180 or 181 may be combined with
the prediction block predicted by the motion estimation unit, the
motion compensation unit, and the intra-prediction unit, which are
included in the prediction unit 120 or 125, and thus a
reconstructed block may be generated.
[0089] Each of the filter units 190 and 191 may include at least
one of a deblocking filter and an offset correction unit.
[0090] The deblocking filter may remove block distortion, generated
due to the boundaries between blocks, in the reconstructed picture.
Whether to perform deblocking, namely, whether to apply the
deblocking filter to the current block, may be determined based on
the pixels included in some rows or columns of the block. When the
deblocking filter is applied to a block, a strong filter or a weak
filter may be applied according to the required strength of
deblocking filtering. Also, in applying the deblocking filter, when
vertical filtering and horizontal filtering are performed, the
vertical filtering and the horizontal filtering may be processed in
parallel.
[0091] The offset correction unit may correct an offset between the
picture on which deblocking is performed and the original picture
in pixel units. In order to perform the offset correction on a
specific picture, a method in which the pixels included in the
picture are divided into certain areas, the area to which an offset
is to be applied is determined, and the offset is applied to the
area may be used, or a method in which the offset is applied in
consideration of the information about the edge of each pixel may
be used.
[0092] Each of the filter units 190 and 191 may be implemented
using only a deblocking filter, or using both a deblocking filter
and offset correction, rather than using all of a deblocking filter
and offset correction.
[0093] Each of the memory 195 and 196 may store the reconstructed
block or pictures calculated by the filter unit 190 or 191, and the
reconstructed block and pictures stored in the memory may be
provided to the prediction unit 120 or 125 when intra-prediction is
performed.
[0094] Information output from the entropy coding unit 100b of the
lower layer and information output from the entropy coding unit
100a of the upper layer are multiplexed by the MUX 197, and may
then be output in the form of a bitstream.
[0095] The MUX 197 may be included in the encoding unit 100a of the
upper layer or the encoding unit 100b of the lower layer, or may be
implemented as a separate device or module, unlike the encoding
unit 100.
[0096] FIG. 2 is a block diagram schematically showing a decoding
device according to an embodiment of the present invention.
[0097] As shown in FIG. 2, a decoding device 200 includes a
decoding unit 200a of an upper layer and a decoding unit 200b of a
lower layer.
[0098] The decoding unit 200a of the upper layer may include an
entropy decoding unit 210, a rearrangement unit 220, an
inverse-quantization unit 230, an inverse-transform unit 245, a
prediction unit 250, a filter unit 260, and memory 270.
[0099] The decoding unit 200b of the lower layer may include an
entropy decoding unit 211, a rearrangement unit 221, an
inverse-quantization unit 231, an inverse-transform unit 241, a
prediction unit 251, a filter unit 261, and memory 271.
[0100] When a bitstream including multiple layers is transmitted
from the encoding device, a demultiplexer (DEMUX) 280 demultiplexes
the information corresponding to each of the layers and transmits
the result to the decoding unit 200a or 200b of each of the layers.
The input bitstream may be decoded through a process that is the
reverse of the process of the encoding device.
[0101] Each of the entropy decoding units 210 and 211 may perform
entropy-decoding through the reverse of the entropy-coding process
performed by the entropy coding unit of the encoding device. Among
the pieces of information decoded by the entropy decoding units 210
and 211, information required to generate a prediction block is
provided to the prediction units 250 and 251, and a residual,
entropy-decoded by the entropy decoding unit, may be input to the
rearrangement units 220 and 221.
[0102] Each of the entropy decoding units 210 and 211 may use at
least one of CABAC and CAVLC, like the entropy coding units 160 and
161.
[0103] Each of the entropy decoding units 210 and 211 may decode
information about intra-prediction and inter-prediction performed
by the encoding device. Each of the entropy decoding units 210 and
211 includes a codeword mapping unit that has a codeword mapping
table for generating an intra-prediction mode number from a
received codeword. The codeword mapping table may be stored in
advance, or may be generated adaptively. When a codeNum mapping
table is used, a codeNum mapping unit for performing codeNum
mapping may be additionally arranged.
[0104] Each of the rearrangement units 220 and 221 may rearrange
the bitstream, entropy-decoded by the entropy decoding unit 210 or
211, based on the arrangement method used by the encoding unit. The
coefficients, represented in one-dimensional vector form, may be
rearranged as 2-dimensional block-type coefficients by being
reconstructed. Each of the rearrangement units 220 and 221 receives
the information about the coefficient scanning method performed by
the encoding unit, and may rearrange the coefficients using a
method in which inverse scanning is performed based on the sequence
of scanning performed by the encoding unit.
[0105] Each of the inverse-quantization units 230 and 231 may
perform inverse quantization based on the quantization parameter
provided by the encoding device and the rearranged coefficients of
the block.
[0106] Each of the inverse-transform units 240 and 241 may perform
inverse DCT or inverse DST, which correspond to DCT and DST
performed by the corresponding transform unit 130 or 131, on the
result of quantization performed by the encoding device. The
inverse-transform may be performed in transmission units determined
by the encoding device. In the transform unit of the encoding
device, DCT and DST may be selectively performed according to
multiple pieces of information, such as the prediction method, the
size of the current block, the prediction direction, and the like.
The inverse-transform unit 240 or 241 of the decoding device may
perform inverse transform based on the information about the
transform performed by the transform unit of the encoding device.
Transform may be performed based on a coding block rather than a
transform block.
[0107] Each of the prediction units 250 and 251 may generate a
prediction block based on information about the generation of the
prediction block, provided by the entropy decoding units 210 and
211, and information about previously decoded blocks or pictures,
provided from the corresponding memory 270 or 271.
[0108] Each of the prediction units 250 and 251 may include a
prediction unit determination unit, an inter-prediction unit, and
an intra-prediction unit.
[0109] The prediction unit determination unit receives various
information, including prediction unit information input from the
entropy decoding unit, prediction mode information about an
intra-prediction method, motion prediction information about an
inter-prediction method, and the like, separates a prediction block
from a current coding block, and determines whether the prediction
block performs intra-prediction or inter-prediction.
[0110] The inter-prediction unit may perform inter-prediction of
the current prediction block based on information included in at
least one of the picture preceding and the picture following the
current picture, which includes the current prediction block, using
information required for inter-prediction of the current prediction
block provided by the encoding device. In order to perform
inter-prediction, it may be determined whether the method used as
the motion prediction method of the prediction block included in
the coding block based on the corresponding coding block is a skip
mode, a merge mode, or a mode (AMVP mode) using a Motion vector
Predictor (MVP).
[0111] The intra-prediction unit may generate a prediction block
based on information about reconstructed pixels in the current
picture. When the prediction block is a prediction block on which
intra-prediction is performed, intra-prediction may be performed
based on the intra-prediction mode information about the prediction
block, provided by the encoding device. The intra-prediction unit
may include an MDIS filter for performing filtering on reference
pixels of the current block, a reference pixel interpolation unit
for generating reference pixels in units smaller than a single
pixel by interpolating the reference pixels, and a DC filter for
generating a prediction block through filtering when the prediction
mode of the current block is a DC mode.
[0112] The prediction unit 250 of the decoding unit 200a of the
upper layer may further include an inter-layer prediction unit for
performing inter-layer prediction, in which the upper layer is
predicted using information about the lower layer.
[0113] The inter-layer prediction unit may perform inter-layer
prediction by using intra-prediction mode information, motion
information, etc.
[0114] The inter-layer prediction is implemented such that
prediction of a current block of the upper layer is performed by
adopting a lower layer picture as a reference picture and using
motion information relating to the picture of the lower layer
(reference layer).
[0115] In the inter-layer prediction, a picture of the reference
layer, which is used as a reference picture, may be sampled
suitably for the resolution of a current layer. In addition, the
motion information may include the motion vector and reference
index. At this point, a motion vector value for the reference layer
picture may be set to (0, 0).
[0116] As an example of the inter-layer prediction, a prediction
method for using the lower layer picture as a reference picture is
described, but is not limited thereto. The inter-layer prediction
unit 123 may additionally perform an inter-layer texture
prediction, an inter-layer motion prediction, an inter-layer syntax
prediction, and an inter-layer residual prediction, etc.
[0117] The inter-layer texture prediction may derive texture of a
current layer based on texture of the reference layer. The
reference layer texture may be sampled suitably for the resolution
of the current layer, and the inter-layer prediction unit may
predict the current layer texture based on the sampled texture. The
inter-layer motion prediction may derive a motion vector of the
current layer based on the motion vector of the reference layer.
Here, the motion vector of the reference layer may be scaled
suitably for the resolution of the current layer. In the
inter-layer syntax prediction, current layer syntax may be
predicted based on the reference layer syntax. For example, the
inter-layer prediction unit 123 may use the reference layer syntax
as current layer syntax. In addition, in the inter-layer residual
prediction, the picture of the current layer may be reconstructed
by using a difference between a reconstructed image of the
reference layer and a reconstructed image of the current layer.
[0118] The reconstructed block or picture may be provided to each
of the filter units 260 and 261. Each of the filter units 260 and
261 may include a deblocking filter and an offset correcting
unit.
[0119] Information on whether a deblocking filter is applied to a
corresponding block or picture and information on whether a strong
filter or a weak filter is applied, when the deblocking filter is
applied, may be received from the encoding device. The deblocking
filter of the decoding device may receive deblocking filter-related
information provided from the encoding device and the decoding
device may perform deblocking filtering on a corresponding
block.
[0120] The offset correction unit may perform offset correction on
a reconstructed image based on the type of the offset correction
and offset value information applied to an image at the time of
coding.
[0121] Each of the memories 270 and 271 may store the reconstructed
picture or block to allow them to be used as the reference picture
or the reference block and may also output the reconstructed
picture.
[0122] The encoding device and decoding device may perform encoding
on three layers or more, not on two layers, and in this case, the
coding unit and the decoding unit for the upper layer may be
provided in plural numbers in correspondence to the number of upper
layers.
[0123] In scalable video coding (SVC) for supporting a multi-layer
structure, there is association between layers. When prediction is
performed by using this association, data duplication elements may
be removed and image coding performance may be improved.
[0124] Accordingly, when a picture (i.e. an image) of a current
layer (i.e. an enhancement layer) to be encoded/decoded is
predicted, inter-layer prediction by using information of another
layer may be performed as well as inter prediction or
intra-prediction using information of the current layer.
[0125] When the inter layer prediction is performed, prediction
samples for the current layer may be generated by using a decoded
picture of a reference layer, which is used for inter-layer
prediction, as a reference picture.
[0126] In this case, since at least one of the spatial resolution,
temporal resolution, and image quality may differ between the
current layer and the reference layer (due to the difference in
scalability between the layers), the decoded picture of the
reference layer is resampled to be adapted to the scalability of
the current layer, and may then be used as the reference picture
for the inter-layer prediction of the current layer. "Resampling"
means up-sampling or down-sampling the samples of the reference
layer picture to match the picture size of the current layer
picture.
[0127] In this specification, the current layer is the layer on
which encoding or decoding is performed, and may be an enhancement
layer or an upper layer. The reference layer is the layer that is
referred to for inter-layer prediction of the current layer, and
may be a base layer or a lower layer. The picture of the reference
layer (that is, the reference picture) used for inter-layer
prediction of the current layer may be called an inter-layer
reference picture or a reference picture between layers.
[0128] FIG. 3 is a flowchart showing a procedure for performing
inter-prediction of a current layer using the corresponding picture
of a reference layer according to an embodiment to which the
present invention is applied.
[0129] Referring to FIG. 3, a corresponding picture of a reference
layer, which is to be used for inter-layer prediction of a current
picture in a current layer, may be determined (S300).
[0130] The reference layer may mean another enhancement layer
having the resolution lower than that of the base layer or the
current layer. The corresponding picture may mean a picture located
in the same time slot as the current picture of the current
layer.
[0131] For example, the corresponding picture may be a picture
having the same Picture Order Count (POC) information as the
current picture of the current layer. The corresponding picture may
belong to the same Access Unit (AU) as the current picture of the
current layer. The corresponding picture may have the same temporal
level identifier (TemporallD) as the current picture of the current
layer. Here, the temporal level identifier may mean an identifier
for specifying each of multiple layers that are scalably coded
according to the temporal resolution.
[0132] The current block may be allowed to use the corresponding
picture(s) of one or more reference layers so as to perform
inter-layer prediction. A method for specifying such a
corresponding picture will be described later with reference to
FIGS. 4 to 11.
[0133] An inter-layer reference picture may be generated by
up-sampling the corresponding picture determined at step S300
(S310).
[0134] Here, the inter-layer reference picture may be used as a
reference picture for inter-layer prediction of the current
picture.
[0135] More specifically, the inter-layer reference picture may
include at least one of a first inter-layer reference picture and a
second inter-layer reference picture. The first inter-layer
reference picture may mean a reference picture, on which filtering
is performed on the integer position thereof, and the second
inter-layer reference picture may mean a reference picture, on
which filtering is not performed on the integer position
thereof.
[0136] Here, the integer position may mean an integer pixel of the
up-sampled corresponding picture. Alternatively, the integer
position may mean the position having a phase of 0 (i.e. the
position of an integer pixel corresponding to a multiple of n after
interpolation) when, in an up-sampling procedure, interpolation is
performed in units of a pixel less than or equal to an integer
pixel, that is, in units of l/n pixel, and then n phases are
generated. Filtering on the integer position may be performed using
neighboring integer positions. The neighboring integer positions
may be located in the same row or column as the currently filtered
integer position. The neighboring integer positions may include
multiple integer positions belonging to the same row or column.
Here, the multiple integer positions may be sequentially arranged
in the same column or row. A detailed up-sampling method will be
described later with reference to FIG. 12.
[0137] A reference picture list including the inter-layer reference
picture generated at step S310 and a temporal reference picture may
be generated (S320).
[0138] First, the reference picture list may include reference
pictures belonging to the same layer as the current picture
(hereinafter referred to as `temporal reference pictures`). The
temporal reference pictures may mean pictures having a display
order (e.g. picture order count: POC) that is different from that
of the current picture. The method for generating a reference
picture list composed of temporal reference pictures will be
described later with reference to FIGS. 13 to 15.
[0139] Meanwhile, when inter-layer prediction of the current
picture is performed, the reference picture list may further
include an inter-layer reference picture. That is, in a multi-layer
structure (e.g. in scalable video coding or multiview video
coding), not only the reference layer of the same layer, but also
the reference picture of another layer, may be used as the
reference picture of the enhancement layer.
[0140] More specifically, a picture belonging to the reference
layer may be used as a reference picture. Here, the reference layer
may be identified by a reference layer identifier (RefPiclayerId).
The reference layer identifier may be derived based on the syntax
inter_layer_pred_layer_idc (hereinafter referred to as an
`inter-layer indicator`) of a slice header. The inter-layer
indicator may mean the layer of the picture used by the current
picture so as to perform inter-layer prediction. In this way, the
reference picture list including the inter-layer reference picture
of the reference layer, specified by the reference layer
identifier, may be generated.
[0141] Meanwhile, as described at step S310, the inter-layer
reference picture may include at least one of a first inter-layer
reference picture and a second inter-layer reference picture.
Therefore, a reference picture list including any one of the first
inter-layer reference picture and the second inter-layer reference
picture, or a reference picture list both of the first inter-layer
reference picture and the second inter-layer reference picture may
be generated.
[0142] To selectively use the first inter-layer reference picture
and the second inter-layer reference picture, whether to use, on a
picture basis, both or either of the first and second inter-layer
reference pictures may be selected. Furthermore, when either of the
first and second inter-layer reference pictures is selected and
used, which one of the two pictures is to be used may be selected.
For this, the encoding device may signal information about which
one of the two pictures is to be used.
[0143] Alternatively, for the selective use of the pictures, a
reference index may be used. More specifically, using a reference
index on a prediction block basis, only the first inter-layer
reference picture or only the second inter-layer reference picture
may be selected, or both of the first and second inter-layer
reference pictures may be selected.
[0144] When an inter-layer reference picture is added to the
reference picture list, there is a need to change the range of the
number of reference pictures arranged in the reference picture list
or the number of reference indices allocated to each reference
picture.
[0145] Here, it is assumed that the range of
num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1,
which are syntax elements of the slice header that indicates the
maximum value of reference indices of the reference picture list
for the base layer, has values from 0 to 14.
[0146] When one of the first inter-layer reference picture and the
second inter-layer reference picture is used, the range of
num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1,
which are syntax elements indicating the maximum value of the
reference indices of the reference picture list for the current
layer, may be defined as the range of values from 0 to 15.
Alternatively, even if both of the first and second inter-layer
reference pictures are used, when the two inter-layer reference
pictures are added to different reference picture lists, the range
of num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1
may be defined as the range of values from 0 to 15.
[0147] For example, when the number of temporal reference pictures
in reference picture list L0 is 15, if the first or second
inter-layer reference picture is added to the reference picture
list, a total of 16 reference pictures are present, and the value
of num_ref_idx_10_active_minus1 is 15.
[0148] Alternatively, when both of the first and second inter-layer
reference pictures are used, or when two inter-layer reference
pictures are added to the same reference picture list, the range of
num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1,
which are syntax elements indicating the maximum value of the
reference indices of the reference picture list for the current
layer, may be defined as the range of values from 0 to 16.
[0149] For example, when the number of temporal reference pictures
in the reference picture list L0 is 15, and a first inter-layer
reference picture and a second inter-layer reference picture are
added to the reference picture list L0, a total of 17 reference
pictures are present, and the value of num_ref_idx_10_active_minus1
is 16.
[0150] Inter-prediction of the current layer may be performed based
on the reference picture list, generated at step S320 (S330).
[0151] More specifically, a reference picture corresponding to the
reference index of the current block is selected from the reference
picture list. The selected reference picture may be a temporal
reference picture present in the same layer as the current block or
an inter-layer reference picture up-sampled from the corresponding
picture of the reference layer.
[0152] A reference block in the reference picture is specified
based on the motion vector of the current block, and a sample value
or texture information of the current block may be predicted using
a reconstructed sample value or texture information of the
specified reference block. In this case, when the reference picture
corresponding to the reference index of the current block is an
inter-layer reference picture, the reference block may be a block
located at the same position as the current block. For this, when
the reference picture of the current block is an inter-layer
reference picture, the motion vector of the current block may be
set to (0,0).
[0153] FIG. 4 illustrates a method for determining a corresponding
picture of a reference layer based on a reference active flag
according to an embodiment to which the present invention is
applied, and FIG. 5 illustrates a syntax table for a reference
active flag according to an embodiment to which the present
invention is applied.
[0154] Referring to FIG. 4, a reference active flag may be acquired
from a bitstream (S400).
[0155] A reference active flag (all_ref_layers_active_flag) may
indicate whether the restriction that corresponding pictures of all
layers having a direct dependency with the current layer are used
for inter-layer prediction of the current picture is applied.
Referring to FIG. 5, the reference active flag may be acquired from
a video parameter set.
[0156] Here, whether a certain layer is a layer having a direct
dependency with the current layer may be determined based on a
direct dependency flag (direct_dependency_flag[i][j]). The
direct_dependency_flag[i][j] may indicate whether the j-th layer is
used for inter-layer prediction of the i-th layer, that is, the
current layer.
[0157] For example, when the value of the direct_dependency_flag is
1, the j-th layer may be used for inter-layer prediction of the
i-th current layer, whereas when the value of the direct dependency
flag is 0, the j-th layer may not be used for inter-layer
prediction of the i-th current layer.
[0158] Whether the value of the reference active flag is 1 may be
checked (S410).
[0159] When the value of the reference active flag is 1, the
restriction that corresponding pictures of all layers having a
direct dependency with the current layer are used for inter-layer
prediction of the current picture is applied. In this case, the
corresponding pictures of all layers having a direct dependency
with the current layer may be included in a reference picture list
for the current picture. Therefore, the corresponding pictures of
all layers having a direct dependency with the current layer may be
determined to be the corresponding pictures that are used for
inter-layer prediction of the current picture (S420).
[0160] In contrast, when the value of the reference active flag is
0, the restriction that the corresponding pictures of all layers
having a direct dependency with the current layer are used for
inter-layer prediction of the current picture is not applied. That
is, the current picture in the current layer may perform
inter-layer prediction either using the corresponding pictures of
all layers having a direct dependency with the current layer, or
selectively using only the corresponding pictures of some of all
layers having a direct dependency with the current layer. That is,
when the value of the reference active flag is 0, the corresponding
pictures of all layers having a direct dependency with the current
layer may be included in the reference picture list for the current
picture, or, alternatively, only the corresponding pictures of some
of the layers may be selectively included in the reference picture
list. Therefore, there is a need to specify corresponding pictures
to be used for inter-layer prediction of the current picture, among
the corresponding pictures of the layers having a direct dependency
with the current layer. For this, inter-layer reference information
for the current picture may be acquired (S430).
[0161] Here, the inter-layer reference information may include at
least one of an inter-layer prediction flag, information about the
number of reference pictures, and a reference layer identifier.
[0162] More specifically, the inter-layer prediction flag may
indicate whether inter-layer prediction is used during the
procedure for decoding the current picture. The information about
the number of reference pictures may indicate the number of
corresponding pictures to be used for inter-layer prediction of the
current picture. For coding efficiency, the information about the
number of reference pictures may be encoded into a value, obtained
by subtracting 1 from the number of corresponding pictures to be
used for inter-layer prediction of the current picture, and may
then be signaled. The reference layer identifier may be the layer
identifier (layerId) of each of the layers including corresponding
pictures to be used for inter-layer prediction of the current
picture.
[0163] The method for acquiring the inter-layer reference
information will be described in detail later with reference to
FIGS. 6 and 7.
[0164] The corresponding pictures to be used for inter-layer
prediction may be determined based on the inter-layer reference
information acquired at step S430 (S440).
[0165] For example, the case where the value of the inter-layer
prediction flag of the current picture is 1 means that the current
picture is used to perform inter-layer prediction. In this case, a
corresponding picture of the layer specified by the reference layer
identifier, among the layers having a direct dependency with the
current layer, may be determined to be the corresponding picture to
be used for inter-layer prediction of the current picture.
[0166] In contrast, the case where the value of the inter-layer
prediction flag of the current picture is 0 means that the current
picture is not used to perform inter-layer prediction, and thus
none of the corresponding pictures of all layers having a direct
dependency with the current layer may be used for inter-layer
prediction of the current picture.
[0167] FIG. 6 illustrates a method for acquiring inter-layer
reference information for the current picture according to an
embodiment to which the present invention is applied, and FIG. 7
illustrates a syntax table for inter-layer reference information
according to an embodiment to which the present invention is
applied.
[0168] Referring to FIG. 6, an inter-layer prediction flag may be
acquired based on a reference active flag (S600).
[0169] Referring to FIG. 7, the inter-layer prediction flag
(inter_layer_pred_enabled_flag) may be acquired only when the value
of the reference active flag (all_ref_layers_active_flag) is 0
(S700).
[0170] The case where the value of the reference active flag is 1
may mean that corresponding pictures of all layers having a direct
dependency with the current layer are used for inter-layer
prediction of the current picture. Therefore, in this case, there
is no need to signal an inter-layer prediction flag in the header
information of the current picture (e.g. slice segment header).
[0171] Further, referring to FIG. 7, when the layer identifier
(nuh_layer_id) of the current layer including the current picture
is greater than 0, the inter-layer prediction flag may be acquired.
The reason for this is that, when the layer identifier of the
current layer is 0, the current layer corresponds to a base layer
in which inter-layer prediction is not performed, among multiple
layers.
[0172] Furthermore, referring to FIG. 7, the inter-layer prediction
flag may be acquired when the number of layers (NumDirectRefLayers)
having a direct dependency with the current layer is at least one.
The reason for this is that, when there is no layer having a direct
dependency with the current layer, none of the pictures in the
current layer are used to perform inter-layer prediction.
[0173] Referring back to FIG. 6, it may be checked whether the
value of the inter-layer prediction flag, acquired at step S600, is
1 (S610).
[0174] If the value of the inter-layer prediction flag is found to
be 1 as a result of checking at step S610, information about the
number of reference pictures may be acquired (S620).
[0175] As described above with reference to FIG. 4, the information
about the number of reference pictures may indicate the number of
corresponding pictures to be used for inter-layer prediction of the
current picture among the corresponding pictures of layers having a
direct dependency with the current layer.
[0176] Therefore, referring to FIG. 7, when the number of layers
(NumDirectRefLayers) having a direct dependency with the current
layer is 1, the number of corresponding pictures to be used for
inter-layer prediction of the current picture cannot exceed 1, and
thus there is no need to signal the information about the number of
reference pictures (num_inter_layer_ref_pics_minus1). In this case,
the information about the number of reference pictures may not be
acquired, and the number of corresponding pictures to be used for
inter-layer prediction of the current picture may be derived as
1.
[0177] Meanwhile, the information about the number of reference
pictures may be restrictively acquired based on the maximum active
reference flag.
[0178] Here, the maximum active reference flag may indicate
whether, for inter-layer prediction of the current picture, only a
maximum of one corresponding picture is used. For example, when the
value of the maximum active reference flag is 1, the current
picture is used to perform inter-layer prediction using only a
maximum of one corresponding picture, whereas when the value of the
maximum active reference flag is 0, the current picture may perform
inter-layer prediction using one or more corresponding
pictures.
[0179] Referring to FIG. 7, the information about the number of
reference pictures may be acquired only when the value of the
maximum active reference flag (max_one_active_ref_layer_flag) is 0.
That is, when the value of the maximum active reference flag is 1,
the number of corresponding pictures to be used for inter-layer
prediction of the current picture is limited to 1, and thus there
is no need to signal the information about the number of reference
pictures.
[0180] Referring back to FIG. 6, a reference layer identifier may
be acquired based on the information about the number of reference
pictures, acquired at step S620 (S630).
[0181] More specifically, referring to FIG. 7, the reference layer
identifier may be acquired when the number of corresponding
pictures (NumActiveRefLayerPics) to be used for inter-layer
prediction of the current picture, among the corresponding pictures
of layers having a direct dependency with the current layer, is
different from the number of layers (NumDirectRefLayers) having a
direct dependency with the current layer. Here, the variable
NumActiveRefLayerPics is a variable derived from the information
about the number of reference pictures. For example, when the
information about the number of reference pictures is encoded into
a value, obtained by subtracting 1 from the number of corresponding
pictures to be used for inter-layer prediction of the current
picture, the variable NumActiveRefLayerPics may be derived as a
value obtained by adding 1 to the number of reference pictures
acquired at step S620.
[0182] If the variable NumActiveRefLayerPics is identical to the
variable NumDirectRefLayers, it means that the corresponding
pictures of layers having a direct dependency with the current
layer are the corresponding pictures to be used for inter-layer
prediction of the current picture. Therefore, there is no need to
signal the reference layer identifier.
[0183] FIG. 8 illustrates a method for determining the
corresponding picture of a reference layer based on a reference
present flag according to an embodiment to which the present
invention is applied, and FIG. 9 illustrates a syntax table for a
reference present flag according to an embodiment to which the
present invention is applied.
[0184] Referring to FIG. 8, a reference present flag may be
acquired from a bitstream (S800).
[0185] The reference present flag (inter_layer_pred_present_flag)
may indicate whether inter-layer reference information is signaled.
Here, since the inter-layer reference information has been
described above with reference to FIG. 4, a detailed description
thereof will be omitted. Further, referring to FIG. 9, the
reference present flag may be acquired from a video parameter set.
However, the acquisition of the reference present flag is not
limited thereto, and the reference present flag may also be
acquired from at least one of a sequence parameter set, a picture
parameter set, and a slice header.
[0186] It may be checked whether the value of the reference present
flag is 1 (S810).
[0187] When the value of the reference present flag is 0,
corresponding pictures of all layers having a direct dependency
with the current layer may be determined to be corresponding
pictures to be used for inter-layer prediction of the current
picture (S820).
[0188] Whether a certain layer has a direct dependency with the
current layer may be determined based on a direct dependency flag,
as described above with reference to FIG. 4.
[0189] In contrast, when the value of the reference present flag is
1, inter-layer reference information for the current picture may be
acquired (S830).
[0190] Here, the inter-layer reference information may include at
least one of an inter-layer prediction flag, information about the
number of reference pictures, and a reference layer identifier.
[0191] More specifically, the inter-layer prediction flag may
indicate whether inter-layer prediction is used during the
procedure for decoding the current picture. The information about
the number of reference pictures may indicate the number of
corresponding pictures to be used for inter-layer prediction of the
current picture. For coding efficiency, the information about the
number of reference pictures may be encoded into a value, obtained
by subtracting 1 from the number of corresponding pictures to be
used for inter-layer prediction of the current picture, and may
then be signaled. The reference layer identifier may mean the layer
identifier (layerId) of each of layers including corresponding
pictures to be used for inter-layer prediction of the current
picture.
[0192] The method for acquiring the inter-layer reference
information will be described in detail later with reference to
FIGS. 10 and 11.
[0193] The corresponding pictures to be used for inter-layer
prediction of the current picture may be determined based on the
inter-layer reference information acquired at step S830 (S840).
[0194] For example, the case where the value of the inter-layer
prediction flag of the current picture is 1 means that the current
picture is used to perform inter-layer prediction. In this case, a
corresponding picture of the layer specified by the reference layer
identifier, among the layers having a direct dependency with the
current layer, may be determined to be the corresponding picture to
be used for inter-layer prediction of the current picture.
[0195] In contrast, the case where the value of the inter-layer
prediction flag of the current picture is 0 means that the current
picture is not used to perform inter-layer prediction, and thus
none of the corresponding pictures of all layers having a direct
dependency with the current layer may be used for inter-layer
prediction of the current picture.
[0196] FIG. 10 illustrates a method for acquiring inter-layer
reference information for the current picture according to an
embodiment to which the present invention is applied, and FIG. 11
illustrates a syntax table for inter-layer reference information
according to an embodiment to which the present invention is
applied.
[0197] Referring to FIG. 10, an inter-layer prediction flag may be
acquired based on a reference present flag (S1000).
[0198] Referring to FIG. 11, the inter-layer prediction flag
(inter_layer_pred_enabled_flag) may be acquired only when the value
of the reference present flag (inter_layer_present_flag) is 1
(S1100). When the value of the reference present flag is 0, it may
mean that corresponding pictures of all layers having a direct
dependency with the current layer are used for inter-layer
prediction of the current picture. Therefore, in this case, there
is no need to signal an inter-layer prediction flag in the header
information of the current picture (e.g. slice segment header).
[0199] Further, referring to FIG. 11, when the layer identifier
(nuh_layer_id) of the current layer including the current picture
is greater than 0, the inter-layer prediction flag may be acquired.
The reason for this is that, when the layer identifier of the
current layer is 0, the current layer corresponds to a base layer
in which inter-layer prediction is not performed, among multiple
layers.
[0200] Furthermore, referring to FIG. 11, the inter-layer
prediction flag may be acquired when the number of layers
(NumDirectRefLayers) having a direct dependency with the current
layer is at least one. The reason for this is that, when there is
no layer having a direct dependency with the current layer, none of
the pictures in the current layer perform inter-layer
prediction.
[0201] Referring back to FIG. 10, it may be checked whether the
value of the inter-layer prediction flag, acquired at step S1000,
is 1 (S1010).
[0202] If the value of the inter-layer prediction flag is found to
be 1 as a result of checking at step S1010, information about the
number of reference pictures may be acquired (S1020).
[0203] As described above with reference to FIG. 8, the information
about the number of reference pictures may indicate the number of
corresponding pictures to be used for inter-layer prediction of the
current picture among the corresponding pictures of layers having a
direct dependency with the current layer.
[0204] Therefore, referring to FIG. 11, when the number of layers
(NumDirectRefLayers) having a direct dependency with the current
layer is 1, the number of corresponding pictures to be used for
inter-layer prediction of the current picture cannot exceed 1, and
thus there is no need to signal the information about the number of
reference pictures (num_inter_layer_ref_pics_minus1). In this case,
the information about the number of reference pictures may not be
acquired, and the number of corresponding pictures to be used for
inter-layer prediction of the current picture may be derived as
1.
[0205] Meanwhile, the information about the number of reference
pictures may be restrictively acquired based on the maximum active
reference flag.
[0206] Here, the maximum active reference flag may indicate
whether, for inter-layer prediction of the current picture, only a
maximum of one corresponding picture is used. For example, when the
value of the maximum active reference flag is 1, the current
picture is used to perform inter-layer prediction using only a
maximum of one corresponding picture, whereas when the value of the
maximum active reference flag is 0, the current picture may perform
inter-layer prediction using one or more corresponding
pictures.
[0207] Referring to FIG. 11, the information about the number of
reference pictures may be acquired only when the value of the
maximum active reference flag (max_one_active_ref_layer_flag) is 0.
That is, when the value of the maximum active reference flag is 1,
the number of corresponding pictures to be used for inter-layer
prediction of the current picture is limited to 1, and thus there
is no need to signal the information about the number of reference
pictures.
[0208] Referring back to FIG. 10, a reference layer identifier may
be acquired based on the information about the number of reference
pictures, acquired at step S1020 (S1030).
[0209] More specifically, referring to FIG. 11, the reference layer
identifier may be acquired when the number of corresponding
pictures (NumActiveRefLayerPics) to be used for inter-layer
prediction of the current picture, among the corresponding pictures
of layers having a direct dependency with the current layer, is
different from the number of layers (NumDirectRefLayers) having a
direct dependency with the current layer. Here, the variable
NumActiveRefLayerPics is a variable derived from the information
about the number of reference pictures. For example, when the
information about the number of reference pictures is encoded into
a value, obtained by subtracting 1 from the number of corresponding
pictures to be used for inter-layer prediction of the current
picture, the variable NumActiveRefLayerPics may be derived as a
value obtained by adding 1 to the number of reference pictures
acquired at step S1020.
[0210] If the variable NumActiveRefLayerPics is identical to the
variable NumDirectRefLayers, it means that the corresponding
pictures of layers having a direct dependency with the current
layer are the corresponding pictures to be used for inter-layer
prediction of the current picture. Therefore, there is no need to
signal the reference layer identifier.
[0211] FIG. 12 is a flowchart showing a method for up-sampling a
corresponding picture of a reference layer according to an
embodiment to which the present invention is applied.
[0212] Referring to FIG. 12, a reference sample position of a
reference layer, which corresponds to the current sample position
of a current layer, may be derived (S1200).
[0213] Since the current layer and the reference layer may be
different from each other in resolution, the reference sample
position corresponding to the current sample position may be
derived in consideration of the difference in resolution between
the layers. That is, the aspect ratios between the picture of the
current layer and the picture of the reference layer may be taken
into consideration. Further, since the size of the up-sampled
picture of the reference layer may not match the size of the
picture of the current layer, an offset required to correct such a
difference may be required.
[0214] For example, the reference sample position may be derived in
consideration of a scale factor and the offset of the up-sampled
reference layer.
[0215] Here, the scale factor may be calculated based on the
width-length ratio between the current picture of the current layer
and the corresponding picture of the reference layer.
[0216] The up-sampled reference layer offset may mean information
about a difference between the positions of any one sample located
at the edge of the current picture and any one sample located at
the edge of the inter-layer reference picture. For example, the
up-sampled reference layer offset may include information about the
difference between the horizontal/vertical positions of a top-left
sample of the current picture and a top-left sample of the
inter-layer reference picture and the difference between the
horizontal/vertical positions of a bottom-right sample of the
current picture and a bottom-right sample of the inter-layer
reference picture.
[0217] The up-sampled reference layer offset may be acquired from a
bitstream. For example, the up-sampled reference layer offset may
be acquired from at least one of a video parameter set, a sequence
parameter set, a picture parameter set, and a slice header.
[0218] Filter coefficients of an up-sampling filter may be
determined in consideration of a phase at the reference sample
position derived at step S1200 (S1210).
[0219] Here, as the up-sampling filter, either a fixed up-sampling
filter or an adaptive up-sampling filter may be used.
[0220] 1. Fixed Up-Sampling Filter
[0221] The fixed up-sampling filter may have preset filter
coefficients without considering features of video. A tap filter
may be used as the fixed up-sampling filter, which may be defined
with respect to each of a luminance (luma) component and a
chrominance (chroma) component. An up-sampling filter having a
precision of a 1/16 of a sample unit will be described with
reference to Tables 1 and 2.
TABLE-US-00001 TABLE 1 Coefficients of interpolation filter Phase f
f f f p [p, 0] [p, 1] [p, 2] [p, 3] f [p, 4] f [p, 5] f [p, 6] f
[p, 7] 0 0 0 0 64 0 0 0 0 1 0 1 -3 63 4 -2 1 0 2 -1 2 -5 62 8 -3 1
0 3 -1 3 -8 60 13 -4 1 0 4 -1 4 -10 58 17 -5 1 0 5 -1 4 -11 52 26
-8 3 -1 6 -1 3 -3 47 31 -10 4 -1 7 -1 4 -11 45 34 -10 4 -1 8 -1 4
-11 40 40 -11 4 -1 9 -1 4 -10 34 45 -11 4 -1 10 -1 4 -10 31 47 -9 3
-1 11 -1 3 -8 26 52 -11 4 -1 12 0 1 -5 17 58 -10 4 -1 13 0 1 -4 13
60 -8 3 -1 14 0 1 -3 8 62 -5 2 -1 15 0 1 -2 4 63 -3 1 0
[0222] Table 1 defines filter coefficients of the fixed up-sampling
filter for the luma component.
[0223] As shown in Table 1, in the case of up-sampling the luma
component, an 8-tap filter is applied. In other words,
interpolation may be performed by using a reference sample of the
reference layer, which corresponds to the current sample of the
current layer, and neighboring samples adjacent to the reference
sample. Here, the neighboring samples may be specified according to
a direction of the interpolation. For example, when the
interpolation is performed in the horizontal direction, the
neighboring samples may include 3 consecutive samples in the left
and 4 consecutive samples in the right with respect to the
reference sample. Alternatively, when the interpolation is
performed in the vertical direction, the neighboring samples may
include 3 consecutive samples toward the top end and 4 consecutive
samples toward the bottom end with respect to the reference
sample.
[0224] In addition, since the interpolation is performed with the
accuracy of the 1/16 sample unit, a total of 16 phases exist. This
is for supporting resolutions of various magnifications of 2 and
1.5 times.
[0225] In addition, the fixed up-sampling filter may use a filter
having different coefficients for each phase p. Except for the case
where the phase p is 0, the magnitude of each filter coefficient
may be defined to be in a range of 0 to 63. This means that
filtering is performed with 6-bit precision. Here, the phase p of 0
means an integer sample position of n-multiple, when the
interpolation is performed in a 1/n sample unit.
TABLE-US-00002 TABLE 2 Coefficients of interpolation filter Phase p
f[p, 0] f[p, 1] f[p, 2] f[p, 3] 0 0 64 0 0 1 -2 62 4 0 2 -2 58 10
-2 3 -4 56 14 -2 4 -4 54 16 -2 5 -6 52 20 -2 6 -6 46 28 -4 7 -4 42
30 -4 8 -4 36 36 -4 9 -4 30 42 -4 10 -4 28 46 -6 11 -2 20 52 -6 12
-2 16 54 -4 13 -2 14 56 -4 14 -2 10 58 -2 15 0 4 62 -2
[0226] Table 2 defines filter coefficients of the fixed up-sampling
filter for the chroma component.
[0227] As shown in Table 2, in a case of up-sampling the chroma
component, unlike the case of the luma component, a 4-tap filter
may be applied. In other words, interpolation may be performed by
using a reference sample of the reference layer, which corresponds
to a current sample, and neighboring samples adjacent to the
reference sample. Here, the neighboring samples may be specified
according to a direction of the interpolation. For example, when
the interpolation is performed in the horizontal direction, the
neighboring samples may include 1 sample in the left and 2
consecutive samples in the right with respect to the reference
sample. Alternatively, when the interpolation is performed in the
vertical direction, the neighboring samples may include 1 sample
toward the top end and 2 consecutive samples toward the bottom end
with respect to the reference sample.
[0228] Furthermore, similarly to the case of the luma component,
since the interpolation is performed with the accuracy of 1/16
sample unit, a total of 16 phases exist and different coefficients
may be used for each phase p. Except for a case where the phase p
is 0, the magnitude of each filter coefficient may be defined to be
in a range of 0 to 62. This means that the filtering is also
performed with 6-bit precision.
[0229] In the foregoing, the cases where the 8-tap filter is
applied for the luma component and the 4-tap filter is applied for
the chroma component are exemplified, but the present invention is
not limited thereto and the order of a tap filter may be variably
determined in consideration of a coding efficiency.
[0230] 2. Adaptive Up-Sampling Filter
[0231] In an encoder, optimal filter coefficients are determined by
considering features of an image without using the fixed filter
coefficients, and are signaled to be transmitted to a decoder. Like
this, an adaptive up-sampling filter uses filter coefficients that
are adaptively determined. Since the features of an image vary in a
picture unit, coding efficiency may be improved when an adaptive
up-sampling filter capable of desirably representing the features
of the image is used, rather than the fixed up-sampling filter for
all cases.
[0232] An inter-layer reference picture may be generated by
applying the filter coefficients determined at step S1210 to the
corresponding picture of the reference layer (S1220).
[0233] In detail, interpolation may be performed by applying the
determined filter coefficients of the up-sampling filter to samples
of the corresponding picture. Here, the interpolation is primarily
performed in the horizontal direction, and then secondarily
performed in the vertical direction on the samples generated after
the horizontal interpolation.
[0234] FIG. 13 is a diagram showing a method for specifying a
short-term reference picture stored in a decoding picture
buffer.
[0235] Temporal reference pictures may be stored in the decoding
picture buffer (DPB) and may be used as reference pictures when
they are required for inter-prediction of a current picture. The
temporal reference pictures stored in the decoding picture buffer
may include short-term reference pictures. Such a short-term
reference picture denotes a picture, the POC value of which does
not have a large difference from that of the current picture.
[0236] Information for specifying a short-term reference picture to
be stored in the decoding picture buffer in a current view is
composed of the output order (POC) of reference pictures and a flag
indicating whether the corresponding picture is directly referred
to by the current picture (e.g. used_by_curr_pic_s0_flag,
used_by_curr_pic_s1_flag), which are collectively called a
reference picture set. In detail, when the value of
used_by_curr_pic_s0_flag[i] is 0, if an i-th short-term reference
picture in the short-term reference picture set has a output order
(POC) value less than that of the current picture, it means that
the i-th short-term reference picture is not used as the reference
picture of the current picture. Further, when the value of
used_by_curr_pic_s1_flag[i] is 0, if an i-th short-term reference
picture in the short-term reference picture set has a output order
(POC) value greater than that of the current picture, it means that
the i-th short-term reference picture is not used as the reference
picture of the current picture.
[0237] Referring to FIG. 13, in the case of a picture having a POC
value of 26, a total of three pictures (i.e. pictures having POC
values of 25, 24, and 20) may be used as short-term reference
pictures for inter-prediction. However, since the value of
used_by_curr_pic_s0_flag of the picture having a POC of 25 is 0,
the picture having a POC value of 25 is not directly used for
inter-prediction of the picture having a POC value of 26.
[0238] In this way, short-term reference pictures may be specified
based on both the output order (POC) of the reference pictures and
the flag indicating whether the corresponding picture is used as a
reference picture by the current picture.
[0239] Meanwhile, pictures, which do not appear in the reference
picture set for the current picture, may be marked with an
indicator indicating that the pictures are not used as reference
pictures (e.g. `unused for reference`), and may then be removed
from the decoding picture buffer.
[0240] FIG. 14 illustrates a method for specifying a long-term
reference picture according to an embodiment to which the present
invention is applied.
[0241] Since a long-term reference picture has a large difference
in POC from a current picture, it may be represented using the
Least significant bit (LSB) and Most Significant Bit (MSB) of a POC
value.
[0242] Therefore, the POC value of the long-term reference picture
may be derived using the LSB of the POC value of a reference
picture, the POC value of the current picture, and a difference
between the MSB of the POC value of the current picture and the MSB
of the POC value of the reference picture.
[0243] For example, it is assumed that the POC of the current
picture is 331 and a maximum value that can be represented by LSB
is 32, and that a picture having a POC value of 308 is used as a
long-term reference picture.
[0244] In this case, the POC value of the current picture, that is,
331, may be represented by 32*10+11, wherein 10 is the MSB value,
and 11 is the LSB value. The POC value of the long-term reference
picture, that is, 308, may be represented by 32*9+20, wherein 9 is
the MSB value and 20 is the LSB value. Here, the POC value of the
long-term reference picture may be derived using an equation shown
in FIG. 14.
[0245] FIG. 15 illustrates a method for constructing a reference
picture list using a short-term reference picture and a long-term
reference picture according to an embodiment to which the present
invention is applied.
[0246] Referring to FIG. 15, a reference picture list including
temporal reference pictures may be generated in consideration of
information about whether temporal reference pictures are
short-term reference pictures and the POC values of short-term
reference pictures. Here, the reference picture list may include at
least one of reference picture list 0 for L0 prediction and
reference picture list 1 for L1 prediction.
[0247] More specifically, the reference picture list 0 may be
arranged in the sequence of a short-term reference picture
(RefPicSetCurr0) having a POC value less than that of the current
picture, a short-term reference picture (RefPicSetCurr1) having a
POC value greater than that of the current picture, and a long-term
reference picture (RefPicSetLtCurr).
[0248] Meanwhile, the reference picture list 1 may be arranged in
the sequence of a short-term reference picture (RefPicSetCurr1)
having a POC value greater than that of the current picture, a
short-term reference picture (RefPicSetCurr0) having a POC value
less than that of the current picture, and a long-term reference
picture (RefPicSetLtCurr).
[0249] Further, in order to improve encoding efficiency for
reference indices of temporal reference pictures, multiple temporal
reference pictures included in the reference picture list may be
rearranged (modified). This may be adaptively performed based on a
list modification flag (list_modification_present_flag). Here, the
list modification flag denotes information for specifying whether
to modify reference pictures in the reference picture list. The
list modification flag may be individually signaled for the
reference picture list 0 and for the reference picture list 1.
[0250] For example, reference pictures in the reference picture
list are not modified when the value of the list modification flag
(list_modification_present_flag) is 0, and the reference pictures
in the reference picture list may be modified only when the value
of the list modification flag (list_modification_present_flag) is
1.
[0251] When the value of the list modification flag
(list_modification_present_flag) is 1, the reference pictures in
the reference picture list may be modified using list entry
information (list_entry[i]). Here, `list entry information
(list_entry[i])` may specify the reference index of a reference
picture located at the current position (i.e. i-th entry) in the
reference picture list.
[0252] More specifically, a reference picture corresponding to the
list entry information (list_entry[i]) in the generated reference
picture list is specified, and the specified reference picture may
be rearranged in the i-th entry in the reference picture list.
[0253] As many pieces of list entry information as the number of
reference pictures included in the reference picture list or as the
maximum value of the reference index of the reference picture list
may be acquired. Also, the list entry information may be acquired
in consideration of the slice type of the current picture. That is,
when the slice type of the current picture is P slice, list entry
information(list_entry_l0[i]) for reference picture list 0 may be
acquired, whereas when the slice type of the current picture is B
slice, list entry information (list_entry_l1[i]) for reference
picture list 1 may be additionally acquired.
INDUSTRIAL APPLICABILITY
[0254] The present invention may be used to code video signals
having a multi-layer structure.
* * * * *