U.S. patent number RE47,759 [Application Number 14/927,025] was granted by the patent office on 2019-12-03 for method and apparatus for encoding video, and method and apparatus for decoding video.
This patent grant is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The grantee listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Alexander Alshin, Elena Alshina, Vadim Seregin, Nikolay Shlyakhov.
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United States Patent |
RE47,759 |
Alshina , et al. |
December 3, 2019 |
Method and apparatus for encoding video, and method and apparatus
for decoding video
Abstract
Disclosed are a video encoding method and apparatus and a video
decoding method and apparatus. The method of encoding video
includes: producing a first predicted coding unit of a current
coding unit, which is to be encoded; determining whether the
current coding unit comprises a portion located outside a boundary
of a current picture; and producing a second predicted coding unit
is produced by changing a value of pixels of the first predicted
coding unit by using the pixels of the first predicted coding unit
and neighboring pixels of the pixels when the current coding unit
does not include a portion located outside a boundary of the
current picture. Accordingly, a residual block that is the
difference between the current encoding unit and the second
predicted encoding unit, can be encoded, thereby improving video
prediction efficiency.
Inventors: |
Alshina; Elena (Suwon-si,
KR), Alshin; Alexander (Suwon-si, KR),
Seregin; Vadim (Suwon-si, KR), Shlyakhov; Nikolay
(Suwon-si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Suwon-si |
N/A |
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO., LTD.
(Suwon-si, KR)
|
Family
ID: |
44081986 |
Appl.
No.: |
14/927,025 |
Filed: |
October 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14849073 |
Sep 9, 2015 |
RE47254 |
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Reissue of: |
12964688 |
Dec 9, 2010 |
8548052 |
Oct 1, 2013 |
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Reissue of: |
12964688 |
Dec 9, 2010 |
8548052 |
Oct 1, 2013 |
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Foreign Application Priority Data
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Dec 9, 2009 [KR] |
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10-2009-0121935 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N
19/134 (20141101); H04N 19/176 (20141101); H04N
19/122 (20141101); H04N 19/105 (20141101); H04N
19/119 (20141101); H04N 19/61 (20141101); H04N
19/61 (20141101); H04N 19/134 (20141101); H04N
19/11 (20141101); H04N 19/122 (20141101); H04N
19/176 (20141101); H04N 19/46 (20141101); H04N
19/85 (20141101); H04N 19/119 (20141101); H04N
19/105 (20141101); H04N 19/11 (20141101); H04N
19/85 (20141101); H04N 19/46 (20141101) |
Current International
Class: |
H04N
7/12 (20060101); H04N 19/176 (20140101); H04N
19/105 (20140101); H04N 19/46 (20140101); H04N
19/122 (20140101); H04N 19/61 (20140101); H04N
19/11 (20140101); H04N 19/85 (20140101); H04N
19/134 (20140101); H04N 19/119 (20140101) |
Field of
Search: |
;375/240.13 |
References Cited
[Referenced By]
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Foreign Patent Documents
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2001239 |
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Sep 2017 |
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EP |
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10-2008-0088042 |
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Oct 2008 |
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KR |
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1020110044486 |
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Apr 2011 |
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2008117933 |
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Oct 2008 |
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WO |
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Apr 2009 |
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WO |
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2010002214 |
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Jan 2010 |
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WO |
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Primary Examiner: Leung; Christina Y.
Attorney, Agent or Firm: Sughrue Mion, PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This .[.application.]. .Iadd.is a continuation reissue application
of U.S. application Ser. No. 14/849,073, which was filed on Sep. 9,
2015, which is a reissue application of U.S. Pat. No. 8,548,052,
which was filed as U.S. patent application Ser. No. 12/964,688 on
Dec. 9, 2010 and issued on Oct. 1, 2013, which is the subject of
four other co-pending reissue applications including U.S. Ser. No.
14/849,073 filed on Sep. 9, 2015, U.S. Ser. No. 14/926,968 filed on
Oct. 29, 2015, U.S. Ser. No. 14/926,883 filed on Oct. 29, 2015, and
U.S. Ser. No. 14/927,096 filed on Oct. 29, 2015, and which
.Iaddend.claims priority from Korean Patent Application No.
10-2009-0121935, filed on Dec. 9, 2009 in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein
.Iadd.by reference .Iaddend.in its entirety .[.by reference.]..
Claims
What is claimed is:
.[.1. A method of decoding video, the method comprising: extracting
information regarding a prediction mode for a current decoding
unit, which is to be decoded, from a received bitstream; producing
a first predicted decoding unit of the current decoding unit, based
on the extracted information; determining whether the current
decoding unit includes a portion located outside a boundary of a
current picture; and producing a second predicted decoding unit by
changing values of pixels of the first predicted decoding unit by
using pixels of the first predicted decoding unit and neighboring
pixels of the pixels when the current decoding unit does not
include the portion located outside the boundary of the current
picture, and skipping the producing the second predicted decoding
unit when the current decoding unit includes the portion located
outside the boundary of the current picture..].
.[.2. The method of claim 1, wherein the determining whether the
current decoding unit includes the portion located outside the
boundary of the current picture comprises obtaining index
information indicating whether the producing the second predicted
decoding unit is to be performed..].
.[.3. The method of claim 2, wherein: if the index information has
a first predetermined value, the index information indicates that
the producing the second predicted decoding unit is not to be
performed; and if the index information has a second predetermined
value, the index information indicates that the producing the
second predicted decoding unit is to be performed..].
.[.4. An apparatus for decoding video, the apparatus comprising: an
entropy decoder which extracts information regarding a prediction
mode for a current decoding unit, which is to be decoded, from a
received bitstream; a predictor which produces a first predicted
decoding unit of the current decoding unit, based on the extracted
information; a determiner which determines whether the current
decoding unit includes a portion located outside a boundary of a
current picture; and a post-processor which produces a second
predicted decoding unit by changing values of pixels of the first
predicted decoding unit by using the pixels of the first predicted
decoding unit and neighboring pixels of the pixels when the current
decoding unit does not include the portion located outside the
boundary of the current picture, and which skips the producing the
second predicted decoding unit when the current decoding unit
includes the portion located outside the boundary of the current
picture..].
.[.5. The apparatus of claim 4, wherein the determiner obtains
index information indicating whether a process of producing the
second predicted decoding unit is to be performed..].
.[.6. The apparatus of claim 5, wherein: if the index information
has a first predetermined value, the index information indicates
that the process of producing the second predicted decoding unit is
not to be performed; and if the index information has a second
predetermined value, the index information indicates that the
process of producing the second predicted decoding unit is to be
performed..].
.[.7. A non-transitory computer readable recording medium having
recorded thereon a program code for executing the method of claim
1..].
.Iadd.8. An apparatus configured to restoring an encoded block, the
apparatus comprising: one or more processors; and a memory storing
a program which, when executed, causes the one or more processors
to: split an image into a plurality of maximum coding units based
on information about a size of a maximum coding unit, and determine
at least one coding unit included in the maximum coding unit among
the plurality of maximum coding units by splitting the maximum
coding unit based on split information; extract information
regarding a prediction mode of a current block included in the at
least one coding unit, from a received bitstream; determine
neighboring pixels of the current block used for intra prediction
by using available neighboring pixels of the current block when the
extracted information indicates the prediction mode of the current
block is intra prediction, produce a first prediction value of the
current block including a first pixel located on a top border in
the current block and a second pixel located on a left border in
the current block and a third pixel located on a upper left corner
in the current block by calculating an average value of at least
one of the neighboring pixels adjacent to the current block, and
produce a second prediction value of the first pixel by using a
weighted average value of the first prediction value and a pixel
value of one neighboring pixel adjacent to the first pixel and
located on a same column with the first pixel, a second prediction
value of the second pixel by using a weighted average value of the
first prediction value and a pixel value of one neighboring pixel
adjacent to the second pixel and located on a same row with the
second pixel, and a second prediction value of the third pixel by
using a weighted average value of the first prediction value, a
pixel value of one neighboring pixel adjacent to the third pixel
and located on a same column with the third pixel, and a pixel
value of one neighboring pixel adjacent to the third pixel and
located on a same row with the third pixel; obtain residual of the
first pixel, residual of the second pixel and residual of the third
pixel from the received bitstream; restore the current block
including a restored pixel value of the first pixel obtained by
adding the residual of the first pixel and the second prediction
value of the first pixel, a restored pixel value of the second
pixel obtained by adding the residual of the second pixel and the
second prediction value of the second pixel, a restored pixel value
of the third pixel obtained by adding the residual of the third
pixel and the second prediction value of the third pixel; and
output a restored current block including the restored pixel value
of the first pixel, the restored pixel value of the second pixel,
and the restored pixel value of the third pixel, wherein, when the
neighboring pixels of the current block are located within a
boundary of a current picture, the neighboring pixels of the
current block located within the boundary of the current picture
are determined as available. .Iaddend.
.Iadd.9. An apparatus of encoding video, the apparatus comprising:
one or more processors; and a memory storing a program which, when
executed, causes the one or more processors to: split, by the one
or more processors, an image into a plurality of maximum coding
units based on information about a size of a maximum coding unit;
determine, by the one or more processors, at least one coding unit
included in the maximum coding unit among the plurality of maximum
coding units by splitting the maximum coding unit based on split
information; determine, by the one or more processors, neighboring
pixels of a current block used for intra prediction by using
available neighboring pixels of the current block when a prediction
mode of the current block is intra prediction; produce, by the one
or more processors, a first prediction value of the current block
including a first pixel located on a top border in the current
block and a second pixel located on a left border in the current
block and a third pixel located on a upper left corner in the
current block, by calculating an average value of at least one of
the available neighboring pixels adjacent to the current block;
produce, by the one or more processors, a second prediction value
of the first pixel by using a weighted average value of the first
prediction value and a pixel value of one neighboring pixel
adjacent to the first pixel and located on a same column with the
first pixel, a second prediction value of the second pixel by using
a weighted average value of the first prediction value and a pixel
value of one neighboring pixel adjacent to the second pixel and
located on a same row with the second pixel, and a second
prediction value of the third pixel by using a weighted average
value of the first prediction value, a pixel value of one
neighboring pixel adjacent to the third pixel and located on a same
column with the third pixel, and a pixel value of one neighboring
pixel adjacent to the third pixel and located on a same row with
the third pixel; obtain, by the one or more processors, residual of
the current block including a first residual of the first pixel
obtained by using the second prediction value of the first pixel, a
second residual of the second pixel obtained by using the second
prediction value of the second pixel and a third residual of the
third pixel obtained by using the second prediction value of the
third pixel; and output the prediction mode of the current block,
the first residual of the first pixel, the second residual of the
second pixel and the third residual of the third pixel into a
bitstream, wherein, when the neighboring pixels of the current
block are located within boundary of a current picture, the
neighboring pixels of the current block located within the boundary
of a current picture are determined as available. .Iaddend.
.Iadd.10. An apparatus comprising a non-transitory
computer-readable storage medium storing thereon instructions that,
when executed by one or more processors of the apparatus, cause the
one or more processors to execute operations to generate image data
corresponding to a video bitstream, the image data comprising: an
encoded data obtained by performing intra prediction on a current
block; and a prediction mode information of the current block,
wherein the operations, executed using the at least one processor
of the apparatus, include: splitting an image into a plurality of
maximum coding units and generating information about a size of a
maximum coding unit, determining at least one coding unit included
in the maximum coding unit among the plurality of maximum coding
units by splitting the maximum coding unit and generating split
information, when a prediction mode of the current block is intra
prediction mode, determining neighboring pixels of the current
block used for intra prediction by using available neighboring
pixels of the current block, producing a first prediction value of
the current block including a first pixel located on a top border
in the current block and a second pixel located on a left border in
the current block and a third pixel located on a upper left corner
in the current block, by calculating an average value of at least
one of the available neighboring pixels adjacent to the current
block, and producing a second prediction value of the first pixel
by using a weighted average value of the first prediction value and
a pixel value of one neighboring pixel adjacent to the first pixel
and located on a same column with the first pixel, a second
prediction value of the second pixel by using a weighted average
value of the first prediction value and a pixel value of one
neighboring pixel adjacent to the second pixel and located on a
same row with the second pixel, and a second prediction value of
the third pixel by using a weighted average value of the first
prediction value, a pixel value of one neighboring pixel adjacent
to the third pixel and located on a same column with the third
pixel, and a pixel value of one neighboring pixel adjacent to the
third pixel and located on a same row with the third pixel, wherein
the encoded data includes residual of the current block including a
first residual of the first pixel obtained by using the second
prediction value of the first pixel, a second residual of the
second pixel obtained by using the second prediction value of the
second pixel and a third residual of the third pixel obtained by
using the second prediction value of the third pixel, and wherein,
when the neighboring pixels of the current block are located within
boundary of a current picture, the neighboring pixels of the
current block located within the boundary of a current picture are
determined as available. .Iaddend.
Description
BACKGROUND
1. Field
One or more exemplary embodiments relate to a video encoding method
and apparatus and a video decoding method and apparatus that are
capable of improving video compression efficiency by performing
post-processing according to a location of predicted video
data.
2. Description of the Related Art
In an image compression method, such as Moving Picture Experts
Group (MPEG)-1, MPEG-2, MPEG-4, or H.264/MPEG-4 Advanced Video
Coding (AVC), a picture is divided into macroblocks in order to
encode an image. Each of the macroblocks is encoded in all encoding
modes that can be used in inter prediction or intra prediction, and
then is encoded in an encoding mode that is selected according to a
bitrate used to encode the macroblock and a distortion degree of a
decoded macroblock based on the original macroblock. As hardware
for reproducing and storing high resolution or high quality video
content is being developed and supplied, a need for a video codec
for effectively encoding or decoding the high resolution or high
quality video content is increasing. In a related art video codec,
a video is encoded in units of macroblocks each having a
predetermined size.
SUMMARY
One or more exemplary embodiments provide a video encoding method
and apparatus and a video decoding method and apparatus for
improving video compression efficiency by generating a new
predicted block by changing a value of each pixel in a predicted
block through post-processing according to a location of a
predicted block in a picture.
According to an aspect of an exemplary embodiment, there is
provided a method of encoding video, the method including:
producing a first predicted coding unit of a current coding unit
that is to be encoded; determining whether the current coding unit
includes a portion located outside a boundary of a current picture;
and producing a second predicted coding unit by changing a value of
pixels of the first predicted coding unit by using the pixels of
the first predicted coding unit and neighboring pixels of the
pixels when the current coding unit does not include the portion
located outside the boundary of the current picture, and skipping
the producing the second predicted coding unit when the current
coding unit includes a portion located outside a boundary of the
current picture.
According to an aspect of another exemplary embodiment, there is
provided an apparatus for encoding video, the apparatus including:
a predictor which produces a first predicted coding unit of a
current coding unit that is to be encoded; a determiner which
determines whether the current coding unit includes a portion
located outside a boundary of a current picture; and a
post-processor which produces a second predicted coding unit by
changing values of pixels of the first predicted coding unit by
using the pixels of the first predicted coding unit and neighboring
pixels of the pixels when the current coding unit does not include
the portion located outside the boundary of the current picture,
and skipping the producing the second predicted coding unit when
the current coding unit includes the portion located outside the
boundary of the current picture.
According to an aspect of another exemplary embodiment, there is
provided a method of decoding video, the method including:
extracting information regarding a prediction mode for a current
decoding unit, which is to be decoded, from a received bitstream;
producing a first predicted decoding unit of the current decoding
unit, based on the extracted information; determining whether the
current decoding unit includes a portion located outside a boundary
of a current picture; and producing a second predicted decoding
unit by changing values of pixels of the first predicted decoding
unit by using the pixels of the first predicted decoding unit and
neighboring pixels of the pixels when the current decoding unit
does not include the portion located outside the boundary of the
current picture, and skipping the producing the second predicted
decoding unit when the current decoding unit includes the portion
located outside the boundary of the current picture.
According to an aspect of another exemplary embodiment, there is
provided an apparatus for decoding video, the apparatus including:
an entropy decoder which extracts information regarding a
prediction mode for a current decoding unit, which is to be
decoded, from a received bitstream; a predictor which produces a
first predicted decoding unit of the current decoding unit, based
on the extracted information; a determiner which determines whether
the current decoding unit includes a portion located outside a
boundary of a current picture; and a post-processor which produces
a second predicted decoding unit by changing a value of pixels of
the first predicted decoding unit by using the pixels of the first
predicted decoding unit and neighboring pixels of the pixels when
the current decoding unit does not include the portion located
outside the boundary of the current picture, and skipping the
producing the second predicted decoding unit when the current
decoding unit includes the portion located outside the boundary of
the current picture.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features will become more apparent by
describing in detail exemplary embodiments thereof with reference
to the attached drawings in which:
FIG. 1 is a block diagram of an apparatus for encoding a video,
according to an exemplary embodiment;
FIG. 2 is a block diagram of an apparatus for decoding a video,
according to an exemplary embodiment;
FIG. 3 is a diagram for describing a concept of coding units
according to an exemplary embodiment;
FIG. 4 is a block diagram of an image encoder based on coding units
according to an exemplary embodiment;
FIG. 5 is a block diagram of an image decoder based on coding units
according to an exemplary embodiment;
FIG. 6 is a diagram illustrating deeper coding units according to
depths, and partitions according to an exemplary embodiment;
FIG. 7 is a diagram for describing a relationship between a coding
unit and transform units, according to an exemplary embodiment;
FIG. 8 is a diagram for describing encoding information of coding
units corresponding to a coded depth, according to an exemplary
embodiment;
FIG. 9 is a diagram of deeper coding units according to depths,
according to an exemplary embodiment;
FIGS. 10 through 12 are diagrams for describing a relationship
between coding units, prediction units, and transform units,
according to an exemplary embodiment;
FIG. 13 is a diagram for describing a relationship between a coding
unit, a prediction unit or a partition, and a transform unit,
according to encoding mode information of Table 1;
FIG. 14 is a block diagram of an intra prediction apparatus
according to an exemplary embodiment;
FIG. 15 is a table showing a number of intra prediction modes
according to the size of a coding unit, according to an exemplary
embodiment;
FIGS. 16A to 16C are diagrams for explaining intra prediction modes
that may be performed on a coding unit having a predetermined size,
according to exemplary embodiments;
FIG. 17 is a drawing for explaining intra prediction modes that may
be performed on a coding unit having a predetermined size,
according to other exemplary embodiments;
FIGS. 18A through 18C are reference diagrams for explaining inter
prediction modes having various directionalities according to an
exemplary embodiment;
FIG. 19 is a reference diagram for explaining a bi-linear mode
according to an exemplary embodiment;
FIG. 20 is a reference diagram for explaining post-processing of a
first predicted coding unit, according to an exemplary
embodiment;
FIG. 21 is a reference diagram for explaining an operation of a
post-processor according to an exemplary embodiment;
FIG. 22 is a reference diagram for explaining neighboring pixels to
be used by a post-processor according to an exemplary
embodiment;
FIG. 23 is a flowchart illustrating a method of encoding video
according to an exemplary embodiment;
FIG. 24 is a reference diagram for explaining an indexing process
for post-processing a coding unit according to an exemplary
embodiment;
FIG. 25 is a reference diagram for explaining an indexing process
for post-processing a coding unit according to another exemplary
embodiment; and
FIG. 26 is a flowchart illustrating a method of decoding video
according to an exemplary embodiment.
FIG. 27 is a diagram for explaining a relationship between a
current pixel and neighboring pixels located on an extended line
having a directivity of (dx, dy);
FIG. 28 is a diagram for explaining a change in a neighboring pixel
located on an extended line having a directivity of (dx, dy)
according to a location of a current pixel, according to an
exemplary embodiment; and
FIGS. 29 and 30 are diagrams for explaining a method of determining
an intra prediction mode direction, according to exemplary
embodiments.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Hereinafter, the exemplary embodiments will be described more fully
with reference to the accompanying drawings, in which exemplary
embodiments are shown. In the exemplary embodiments, unit may or
may not refer to a unit of size, depending on its context.
A video encoding method and apparatus and a video decoding method
and apparatus according to exemplary embodiments will now be
described with reference to FIGS. 1 to 13.
Hereinafter, a coding unit is an encoding data unit in which the
image data is encoded at an encoder side and an encoded data unit
in which the encoded image data is decoded at a decoder side,
according to exemplary embodiments. Also, a coded depth indicates a
depth where a coding unit is encoded. Furthermore, an image may
denote a still image for a video or a moving image, that is, the
video itself.
FIG. 1 is a block diagram of a video encoding apparatus 100,
according to an exemplary embodiment. The video encoding apparatus
100 includes a maximum coding unit splitter 110, a coding unit
determiner 120, and an output unit 130.
The maximum coding unit splitter 110 may split a current picture
based on a maximum coding unit for the current picture of an image.
If the current picture is larger than the maximum coding unit,
image data of the current picture may be split into the at least
one maximum coding unit. The maximum coding unit according to an
exemplary embodiment may be a data unit having a size of
32.times.32, 64.times.64, 128.times.128, 256.times.256, etc.,
wherein a shape of the data unit is a square having a width and
height in squares of 2. The image data may be output to the coding
unit determiner 120 according to the at least one maximum coding
unit.
A coding unit according to an exemplary embodiment may be
characterized by a maximum size and a depth. The depth denotes a
number of times the coding unit is spatially split from the maximum
coding unit, and as the depth deepens or increases, deeper encoding
units according to depths may be split from the maximum coding unit
to a minimum coding unit. A depth of the maximum coding unit is an
uppermost depth and a depth of the minimum coding unit is a
lowermost depth. Since a size of a coding unit corresponding to
each depth decreases as the depth of the maximum coding unit
deepens, a coding unit corresponding to an upper depth may include
a plurality of coding units corresponding to lower depths.
As described above, the image data of the current picture is split
into the maximum coding units according to a maximum size of the
coding unit, and each of the maximum coding units may include
deeper coding units that are split according to depths. Since the
maximum coding unit according to an exemplary embodiment is split
according to depths, the image data of a spatial domain included in
the maximum coding unit may be hierarchically classified according
to depths.
A maximum depth and a maximum size of a coding unit, which limit
the total number of times a height and a width of the maximum
coding unit are hierarchically split, may be predetermined.
The coding unit determiner 120 encodes at least one split region
obtained by splitting a region of the maximum coding unit according
to depths, and determines a depth to output a finally encoded image
data according to the at least one split region. In other words,
the coding unit determiner 120 determines a coded depth by encoding
the image data in the deeper coding units according to depths,
according to the maximum coding unit of the current picture, and
selecting a depth having the least encoding error. Thus, the
encoded image data of the coding unit corresponding to the
determined coded depth is finally output. Also, the coding units
corresponding to the coded depth may be regarded as encoded coding
units.
The determined coded depth and the encoded image data according to
the determined coded depth are output to the output unit 130.
The image data in the maximum coding unit is encoded based on the
deeper coding units corresponding to at least one depth equal to or
below the maximum depth, and results of encoding the image data are
compared based on each of the deeper coding units. A depth having
the least encoding error may be selected after comparing encoding
errors of the deeper coding units. At least one coded depth may be
selected for each maximum coding unit.
The size of the maximum coding unit is split as a coding unit is
hierarchically split according to depths, and as the number of
coding units increases. Also, even if coding units correspond to
same depth in one maximum coding unit, it is determined whether to
split each of the coding units corresponding to the same depth to a
lower depth by measuring an encoding error of the image data of the
each coding unit, separately. Accordingly, even when image data is
included in one maximum coding unit, the image data is split to
regions according to the depths and the encoding errors may differ
according to regions in the one maximum coding unit, and thus the
coded depths may differ according to regions in the image data.
Thus, one or more coded depths may be determined in one maximum
coding unit, and the image data of the maximum coding unit may be
divided according to coding units of at least one coded depth.
Accordingly, the coding unit determiner 120 may determine coding
units having a tree structure included in the maximum coding unit.
The coding units having a tree structure according to an exemplary
embodiment include coding units corresponding to a depth determined
to be the coded depth, from among all deeper coding units included
in the maximum coding unit. A coding unit of a coded depth may be
hierarchically determined according to depths in the same region of
the maximum coding unit, and may be independently determined in
different regions. Similarly, a coded depth in a current region may
be independently determined from a coded depth in another
region.
A maximum depth according to an exemplary embodiment is an index
related to the number of splitting times from a maximum coding unit
to a minimum coding unit. A first maximum depth according to an
exemplary embodiment may denote the total number of splitting times
from the maximum coding unit to the minimum coding unit. A second
maximum depth according to an exemplary embodiment may denote the
total number of depth levels from the maximum coding unit to the
minimum coding unit. For example, when a depth of the maximum
coding unit is 0, a depth of a coding unit, in which the maximum
coding unit is split once, may be set to 1, and a depth of a coding
unit, in which the maximum coding unit is split twice, may be set
to 2. Here, if the minimum coding unit is a coding unit in which
the maximum coding unit is split four times, 5 depth levels of
depths 0, 1, 2, 3 and 4 exist, and thus the first maximum depth may
be set to 4, and the second maximum depth may be set to 5.
Prediction encoding and transformation may be performed according
to the maximum coding unit. The prediction encoding and the
transformation are also performed based on the deeper coding units
according to a depth equal to or depths less than the maximum
depth, according to the maximum coding unit. Transformation may be
performed according to method of orthogonal transformation or
integer transformation.
Since the number of deeper coding units increases whenever the
maximum coding unit is split according to depths, encoding
including the prediction encoding and the transformation is
performed on all of the deeper coding units generated as the depth
deepens. For convenience of description, the prediction encoding
and the transformation will now be described based on a coding unit
of a current depth, in a maximum coding unit.
The video encoding apparatus 100 may variably select a size or
shape of a data unit for encoding the image data. In order to
encode the image data, operations, such as prediction encoding,
transformation, and entropy encoding, are performed, and at this
time, the same data unit may be used for all operations or
different data units may be used for each operation.
For example, the video encoding apparatus 100 may select not only a
coding unit for encoding the image data, but also a data unit
different from the coding unit so as to perform the prediction
encoding on the image data in the coding unit.
In order to perform prediction encoding in the maximum coding unit,
the prediction encoding may be performed based on a coding unit
corresponding to a coded depth, i.e., based on a coding unit that
is no longer split to coding units corresponding to a lower depth.
Hereinafter, the coding unit that is no longer split and becomes a
basis unit for prediction encoding will now be referred to as a
prediction unit. A partition obtained by splitting the prediction
unit may include a prediction unit or a data unit obtained by
splitting at least one of a height and a width of the prediction
unit.
For example, when a coding unit of 2N.times.2N (where N is a
positive integer) is no longer split and becomes a prediction unit
of 2N.times.2N, and a size of a partition may be 2N.times.2N,
2N.times.N, N.times.2N, or N.times.N. Examples of a partition type
include symmetrical partitions that are obtained by symmetrically
splitting a height or width of the prediction unit, partitions
obtained by asymmetrically splitting the height or width of the
prediction unit, such as 1:n or n:1, partitions that are obtained
by geometrically splitting the prediction unit, and partitions
having arbitrary shapes.
A prediction mode of the prediction unit may be at least one of an
intra mode, a inter mode, and a skip mode. For example, the intra
mode or the inter mode may be performed on the partition of
2N.times.2N, 2N.times.N, N.times.2N, or N.times.N. Also, the skip
mode may be performed only on the partition of 2N.times.2N. The
encoding is independently performed on one prediction unit in a
coding unit, thereby selecting a prediction mode having a least
encoding error.
The video encoding apparatus 100 may also perform the
transformation on the image data in a coding unit based not only on
the coding unit for encoding the image data, but also based on a
data unit that is different from the coding unit.
In order to perform the transformation in the coding unit, the
transformation may be performed based on a data unit having a size
smaller than or equal to the coding unit. For example, the data
unit for the transformation may include a data unit for an intra
mode and a data unit for an inter mode.
A data unit used as a base of the transformation will now be
referred to as a transform unit. A transformation depth indicating
the number of splitting times to reach the transform unit by
splitting the height and width of the coding unit may also be set
in the transform unit. For example, in a current coding unit of
2N.times.2N, a transformation depth may be 0 when the size of a
transform unit is also 2N.times.2N, may be 1 when each of the
height and width of the current coding unit is split into two equal
parts, totally split into 4.sup.1 transform units, and the size of
the transform unit is thus N.times.N, and may be 2 when each of the
height and width of the current coding unit is split into four
equal parts, totally split into 4.sup.2 transform units and the
size of the transform unit is thus N/2.times.N/2. For example, the
transform unit may be set according to a hierarchical tree
structure, in which a transform unit of an upper transformation
depth is split into four transform units of a lower transformation
depth according to the hierarchical characteristics of a
transformation depth.
Similarly to the coding unit, the transform unit in the coding unit
may be recursively split into smaller sized regions, so that the
transform unit may be determined independently in units of regions.
Thus, residual data in the coding unit may be divided according to
the transformation having the tree structure according to
transformation depths.
Encoding information according to coding units corresponding to a
coded depth requires not only information about the coded depth,
but also about information related to prediction encoding and
transformation. Accordingly, the coding unit determiner 120 not
only determines a coded depth having a least encoding error, but
also determines a partition type in a prediction unit, a prediction
mode according to prediction units, and a size of a transform unit
for transformation.
Coding units according to a tree structure in a maximum coding unit
and a method of determining a partition, according to exemplary
embodiments, will be described in detail later with reference to
FIGS. 3 through 12.
The coding unit determiner 120 may measure an encoding error of
deeper coding units according to depths by using Rate-Distortion
Optimization based on Lagrangian multipliers.
The output unit 130 outputs the image data of the maximum coding
unit, which is encoded based on the at least one coded depth
determined by the coding unit determiner 120, and information about
the encoding mode according to the coded depth, in bitstreams.
The encoded image data may be obtained by encoding residual data of
an image.
The information about the encoding mode according to coded depth
may include information about the coded depth, about the partition
type in the prediction unit, the prediction mode, and the size of
the transform unit.
The information about the coded depth may be defined by using split
information according to depths, which indicates whether encoding
is performed on coding units of a lower depth instead of a current
depth. If the current depth of the current coding unit is the coded
depth, image data in the current coding unit is encoded and output,
and thus the split information may be defined not to split the
current coding unit to a lower depth. Alternatively, if the current
depth of the current coding unit is not the coded depth, the
encoding is performed on the coding unit of the lower depth, and
thus the split information may be defined to split the current
coding unit to obtain the coding units of the lower depth.
If the current depth is not the coded depth, encoding is performed
on the coding unit that is split into the coding unit of the lower
depth. Since at least one coding unit of the lower depth exists in
one coding unit of the current depth, the encoding is repeatedly
performed on each coding unit of the lower depth, and thus the
encoding may be recursively performed for the coding units having
the same depth.
Since the coding units having a tree structure are determined for
one maximum coding unit, and information about at least one
encoding mode is determined for a coding unit of a coded depth,
information about at least one encoding mode may be determined for
one maximum coding unit. Also, a coded depth of the image data of
the maximum coding unit may be different according to locations
since the image data is hierarchically split according to depths,
and thus information about the coded depth and the encoding mode
may be set for the image data.
Accordingly, the output unit 130 may assign encoding information
about a corresponding coded depth and an encoding mode to at least
one of the coding unit, the prediction unit, and a minimum unit
included in the maximum coding unit.
The minimum unit according to an exemplary embodiment is a
rectangular data unit obtained by splitting the minimum coding unit
constituting the lowermost depth by 4. Alternatively, the minimum
unit may be a maximum rectangular data unit that may be included in
all of the coding units, prediction units, partition units, and
transform units included in the maximum coding unit.
For example, the encoding information output through the output
unit 130 may be classified into encoding information according to
coding units, and encoding information according to prediction
units. The encoding information according to the coding units may
include the information about the prediction mode and about the
size of the partitions. The encoding information according to the
prediction units may include information about an estimated
direction of an inter mode, about a reference image index of the
inter mode, about a motion vector, about a chroma component of an
intra mode, and about an interpolation method of the intra mode.
Also, information about a maximum size of the coding unit defined
according to pictures, slices, or GOPs, and information about a
maximum depth may be inserted into SPS (Sequence Parameter Set) or
a header of a bitstream.
In the video encoding apparatus 100, the deeper coding unit may be
a coding unit obtained by dividing a height or width of a coding
unit of an upper depth, which is one layer above, by two. In other
words, when the size of the coding unit of the current depth is
2N.times.2N, the size of the coding unit of the lower depth is
N.times.N. Also, the coding unit of the current depth having the
size of 2N.times.2N may include a maximum of 4 coding units of the
lower depth.
Accordingly, the video encoding apparatus 100 may form the coding
units having the tree structure by determining coding units having
an optimum shape and an optimum size for each maximum coding unit,
based on the size of the maximum coding unit and the maximum depth
determined considering characteristics of the current picture.
Also, since encoding may be performed on each maximum coding unit
by using any one of various prediction modes and transformations,
an optimum encoding mode may be determined considering
characteristics of the coding unit of various image sizes.
Thus, if an image having high resolution or large data amount is
encoded in a related art macroblock, a number of macroblocks per
picture excessively increases. Accordingly, a number of pieces of
compressed information generated for each macroblock increases, and
thus it is difficult to transmit the compressed information and
data compression efficiency decreases. However, by using the video
encoding apparatus 100, image compression efficiency may be
increased since a coding unit is adjusted while considering
characteristics of an image while increasing a maximum size of a
coding unit while considering a size of the image.
FIG. 2 is a block diagram of a video decoding apparatus 200,
according to an exemplary embodiment. The video decoding apparatus
200 includes a receiver 210, an image data and encoding information
extractor 220, and an image data decoder 230. Definitions of
various terms, such as a coding unit, a depth, a prediction unit, a
transform unit, and information about various encoding modes, for
various operations of the video decoding apparatus 200 are
identical to those described with reference to FIG. 1 and the video
encoding apparatus 100.
The receiver 210 receives and parses a bitstream of an encoded
video. The image data and encoding information extractor 220
extracts encoded image data for each coding unit from the parsed
bitstream, wherein the coding units have a tree structure according
to each maximum coding unit, and outputs the extracted image data
to the image data decoder 230. The image data and encoding
information extractor 220 may extract information about a maximum
size of a coding unit of a current picture, from a header about the
current picture or SPS.
Also, the image data and encoding information extractor 220
extracts information about a coded depth and an encoding mode for
the coding units having a tree structure according to each maximum
coding unit, from the parsed bitstream. The extracted information
about the coded depth and the encoding mode is output to the image
data decoder 230. In other words, the image data in a bit stream is
split into the maximum coding unit so that the image data decoder
230 decodes the image data for each maximum coding unit.
The information about the coded depth and the encoding mode
according to the maximum coding unit may be set for information
about at least one coding unit corresponding to the coded depth,
and information about an encoding mode may include information
about a partition type of a corresponding coding unit corresponding
to the coded depth, about a prediction mode, and a size of a
transform unit. Also, splitting information according to depths may
be extracted as the information about the coded depth.
The information about the coded depth and the encoding mode
according to each maximum coding unit extracted by the image data
and encoding information extractor 220 is information about a coded
depth and an encoding mode determined to generate a minimum
encoding error when an encoder, such as the video encoding
apparatus 100, repeatedly performs encoding for each deeper coding
unit according to depths according to each maximum coding unit.
Accordingly, the video decoding apparatus 200 may restore an image
by decoding the image data according to a coded depth and an
encoding mode that generates the minimum encoding error.
Since encoding information about the coded depth and the encoding
mode may be assigned to a predetermined data unit from among a
corresponding coding unit, a prediction unit, and a minimum unit,
the image data and encoding information extractor 220 may extract
the information about the coded depth and the encoding mode
according to the predetermined data units. The predetermined data
units to which the same information about the coded depth and the
encoding mode is assigned may be inferred to be the data units
included in the same maximum coding unit.
The image data decoder 230 restores the current picture by decoding
the image data in each maximum coding unit based on the information
about the coded depth and the encoding mode according to the
maximum coding units. In other words, the image data decoder 230
may decode the encoded image data based on the extracted
information about the partition type, the prediction mode, and the
transform unit for each coding unit from among the coding units
having the tree structure included in each maximum coding unit. A
decoding process may include a prediction including intra
prediction and motion compensation, and an inverse transformation.
Inverse transformation may be performed according to method of
inverse orthogonal transformation or inverse integer
transformation.
The image data decoder 230 may perform intra prediction or motion
compensation according to a partition and a prediction mode of each
coding unit, based on the information about the partition type and
the prediction mode of the prediction unit of the coding unit
according to coded depths.
Also, the image data decoder 230 may perform inverse transformation
according to each transform unit in the coding unit, based on the
information about the size of the transform unit of the coding unit
according to coded depths, so as to perform the inverse
transformation according to maximum coding units.
The image data decoder 230 may determine at least one coded depth
of a current maximum coding unit by using split information
according to depths. If the split information indicates that image
data is no longer split in the current depth, the current depth is
a coded depth. Accordingly, the image data decoder 230 may decode
encoded data of at least one coding unit corresponding to the each
coded depth in the current maximum coding unit by using the
information about the partition type of the prediction unit, the
prediction mode, and the size of the transform unit for each coding
unit corresponding to the coded depth, and output the image data of
the current maximum coding unit.
In other words, data units containing the encoding information
including the same split information may be gathered by observing
the encoding information set assigned for the predetermined data
unit from among the coding unit, the prediction unit, and the
minimum unit, and the gathered data units may be considered to be
one data unit to be decoded by the image data decoder 230 in the
same encoding mode.
The video decoding apparatus 200 may obtain information about at
least one coding unit that generates the minimum encoding error
when encoding is recursively performed for each maximum coding
unit, and may use the information to decode the current picture. In
other words, the coding units having the tree structure determined
to be the optimum coding units in each maximum coding unit may be
decoded. Also, the maximum size of coding unit is determined
considering resolution and an amount of image data.
Accordingly, even if image data has high resolution and a large
amount of data, the image data may be efficiently decoded and
restored by using a size of a coding unit and an encoding mode,
which are adaptively determined according to characteristics of the
image data, by using information about an optimum encoding mode
received from an encoder.
A method of determining coding units having a tree structure, a
prediction unit, and a transform unit, according to an exemplary
embodiment, will now be described with reference to FIGS. 3 through
13.
FIG. 3 is a diagram for describing a concept of coding units
according to an exemplary embodiment. A size of a coding unit may
be expressed in width.times.height, and may be 64.times.64,
32.times.32, 16.times.16, and 8.times.8. A coding unit of
64.times.64 may be split into partitions of 64.times.64,
64.times.32, 32.times.64, or 32.times.32, and a coding unit of
32.times.32 may be split into partitions of 32.times.32,
32.times.16, 16.times.32, or 16.times.16, a coding unit of
16.times.16 may be split into partitions of 16.times.16,
16.times.8, 8.times.16, or 8.times.8, and a coding unit of
8.times.8 may be split into partitions of 8.times.8, 8.times.4,
4.times.8, or 4.times.4.
In video data 310, a resolution is 1920.times.1080, a maximum size
of a coding unit is 64, and a maximum depth is 2. In video data
320, a resolution is 1920.times.1080, a maximum size of a coding
unit is 64, and a maximum depth is 3. In video data 330, a
resolution is 352.times.288, a maximum size of a coding unit is 16,
and a maximum depth is 1. The maximum depth shown in FIG. 3 denotes
a total number of splits from a maximum coding unit to a minimum
decoding unit.
If a resolution is high or a data amount is large, a maximum size
of a coding unit may be large so as to not only increase encoding
efficiency but also to accurately reflect characteristics of an
image. Accordingly, the maximum size of the coding unit of the
video data 310 and 320 having the higher resolution than the video
data 330 may be 64.
Since the maximum depth of the video data 310 is 2, coding units
315 of the video data 310 may include a maximum coding unit having
a long axis size of 64, and coding units having long axis sizes of
32 and 16 since depths are deepened to two layers by splitting the
maximum coding unit twice. Meanwhile, since the maximum depth of
the video data 330 is 1, coding units 335 of the video data 330 may
include a maximum coding unit having a long axis size of 16, and
coding units having a long axis size of 8 since depths are deepened
to one layer by splitting the maximum coding unit once.
Since the maximum depth of the video data 320 is 3, coding units
325 of the video data 320 may include a maximum coding unit having
a long axis size of 64, and coding units having long axis sizes of
32, 16, and 8 since the depths are deepened to 3 layers by
splitting the maximum coding unit three times. As a depth deepens,
detailed information may be precisely expressed.
FIG. 4 is a block diagram of an image encoder 400 based on coding
units, according to an exemplary embodiment. The image encoder 400
performs operations of the coding unit determiner 120 of the video
encoding apparatus 100 to encode image data. In other words, an
intra predictor 410 performs intra prediction on coding units in an
intra mode, from among a current frame 405, and a motion estimator
420 and a motion compensator 425 performs inter estimation and
motion compensation on coding units in an inter mode from among the
current frame 405 by using the current frame 405, and a reference
frame 495.
Data output from the intra predictor 410, the motion estimator 420,
and the motion compensator 425 is output as a quantized
transformation coefficient through a transformer 430 and a
quantizer 440. The quantized transformation coefficient is restored
as data in a spatial domain through an inverse quantizer 460 and an
inverse transformer 470, and the restored data in the spatial
domain is output as the reference frame 495 after being
post-processed through a deblocking unit 480 and a loop filtering
unit 490. The quantized transformation coefficient may be output as
a bitstream 455 through an entropy encoder 450.
In order for the image encoder 400 to be applied in the video
encoding apparatus 100, all elements of the image encoder 400,
i.e., the intra predictor 410, the motion estimator 420, the motion
compensator 425, the transformer 430, the quantizer 440, the
entropy encoder 450, the inverse quantizer 460, the inverse
transformer 470, the deblocking unit 480, and the loop filtering
unit 490 perform operations based on each coding unit from among
coding units having a tree structure while considering the maximum
depth of each maximum coding unit.
Specifically, the intra predictor 410, the motion estimator 420,
and the motion compensator 425 determines partitions and a
prediction mode of each coding unit from among the coding units
having a tree structure while considering the maximum size and the
maximum depth of a current maximum coding unit, and the transformer
430 determines the size of the transform unit in each coding unit
from among the coding units having a tree structure.
FIG. 5 is a block diagram of an image decoder 500 based on coding
units, according to an exemplary embodiment. A parser 510 parses
encoded image data to be decoded and information about encoding
required for decoding from a bitstream 505. The encoded image data
is output as inverse quantized data through an entropy decoder 520
and an inverse quantizer 530, and the inverse quantized data is
restored to image data in a spatial domain through an inverse
transformer 540.
An intra predictor 550 performs intra prediction on coding units in
an intra mode with respect to the image data in the spatial domain,
and a motion compensator 560 performs motion compensation on coding
units in an inter mode by using a reference frame 585.
The image data in the spatial domain, which passed through the
intra predictor 550 and the motion compensator 560, may be output
as a restored frame 595 after being post-processed through a
deblocking unit 570 and a loop filtering unit 580. Also, the image
data that is post-processed through the deblocking unit 570 and the
loop filtering unit 580 may be output as the reference frame
585.
In order to decode the image data in the image data decoder 230 of
the video decoding apparatus 200, the image decoder 500 may perform
operations that are performed after the parser 510.
In order for the image decoder 500 to be applied in the video
decoding apparatus 200, all elements of the image decoder 500,
i.e., the parser 510, the entropy decoder 520, the inverse
quantizer 530, the inverse transformer 540, the intra predictor
550, the motion compensator 560, the deblocking unit 570, and the
loop filtering unit 580 perform operations based on coding units
having a tree structure for each maximum coding unit.
Specifically, the intra predictor 550 and the motion compensator
560 perform operations based on partitions and a prediction mode
for each of the coding units having a tree structure, and the
inverse transformer 540 perform operations based on a size of a
transform unit for each coding unit.
FIG. 6 is a diagram illustrating deeper coding units according to
depths, and partitions, according to an exemplary embodiment. The
video encoding apparatus 100 and the video decoding apparatus 200
use hierarchical coding units so as to consider characteristics of
an image. A maximum height, a maximum width, and a maximum depth of
coding units may be adaptively determined according to the
characteristics of the image, or may be differently set by a user.
Sizes of deeper coding units according to depths may be determined
according to the predetermined maximum size of the coding unit.
In a hierarchical structure 600 of coding units, according to an
exemplary embodiment, the maximum height and the maximum width of
the coding units are each 64, and the maximum depth is 4. Since a
depth deepens along a vertical axis of the hierarchical structure
600, a height and a width of the deeper coding unit are each split.
Also, a prediction unit and partitions, which are bases for
prediction encoding of each deeper coding unit, are shown along a
horizontal axis of the hierarchical structure 600.
In other words, a coding unit 610 is a maximum coding unit in the
hierarchical structure 600, wherein a depth is 0 and a size, i.e.,
a height by width, is 64.times.64. The depth deepens along the
vertical axis, and a coding unit 620 having a size of 32.times.32
and a depth of 1, a coding unit 630 having a size of 16.times.16
and a depth of 2, a coding unit 640 having a size of 8.times.8 and
a depth of 3, and a coding unit 650 having a size of 4.times.4 and
a depth of 4 exist. The coding unit 650 having the size of
4.times.4 and the depth of 4 is a minimum coding unit.
The prediction unit and the partitions of a coding unit are
arranged along the horizontal axis according to each depth. In
other words, if the coding unit 610 having the size of 64.times.64
and the depth of 0 is a prediction unit, the prediction unit may be
split into partitions include in the encoding unit 610, i.e. a
partition 610 having a size of 64.times.64, partitions 612 having
the size of 64.times.32, partitions 614 having the size of
32.times.64, or partitions 616 having the size of 32.times.32.
Similarly, a prediction unit of the coding unit 620 having the size
of 32.times.32 and the depth of 1 may be split into partitions
included in the coding unit 620, i.e., a partition 620 having a
size of 32.times.32, partitions 622 having a size of 32.times.16,
partitions 624 having a size of 16.times.32, and partitions 626
having a size of 16.times.16.
Similarly, a prediction unit of the coding unit 630 having the size
of 16.times.16 and the depth of 2 may be split into partitions
included in the coding unit 630, i.e. a partition having a size of
16.times.16 included in the coding unit 630, partitions 632 having
a size of 16.times.8, partitions 634 having a size of 8.times.16,
and partitions 636 having a size of 8.times.8.
Similarly, a prediction unit of the coding unit 640 having the size
of 8.times.8 and the depth of 3 may be split into partitions
included in the coding unit 640, i.e. a partition having a size of
8.times.8 included in the coding unit 640, partitions 642 having a
size of 8.times.4, partitions 644 having a size of 4.times.8, and
partitions 646 having a size of 4.times.4.
The coding unit 650 having the size of 4.times.4 and the depth of 4
is the minimum coding unit and a coding unit of the lowermost
depth. A prediction unit of the coding unit 650 is only assigned to
a partition having a size of 4.times.4.
In order to determine the at least one coded depth of the coding
units constituting the maximum coding unit 610, the coding unit
determiner 120 of the video encoding apparatus 100 performs
encoding for coding units corresponding to each depth included in
the maximum coding unit 610.
A number of deeper coding units according to depths including data
in the same range and the same size increases as the depth deepens.
For example, four coding units corresponding to a depth of 2 are
required to cover data that is included in one coding unit
corresponding to a depth of 1. Accordingly, in order to compare
encoding results of the same data according to depths, the coding
unit corresponding to the depth of 1 and four coding units
corresponding to the depth of 2 are each encoded.
In order to perform encoding for a current depth from among the
depths, a least encoding error may be selected for the current
depth by performing encoding for each prediction unit in the coding
units corresponding to the current depth, along the horizontal axis
of the hierarchical structure 600. Alternatively, the minimum
encoding error may be searched for by comparing the least encoding
errors according to depths, by performing encoding for each depth
as the depth deepens along the vertical axis of the hierarchical
structure 600. A depth and a partition having the minimum encoding
error in the coding unit 610 may be selected as the coded depth and
a partition type of the coding unit 610.
FIG. 7 is a diagram for describing a relationship between a coding
unit 710 and transform units 720, according to an exemplary
embodiment.
The video encoding apparatus 100 or 200 encodes or decodes an image
according to coding units having sizes smaller than or equal to a
maximum coding unit for each maximum coding unit. Sizes of
transform units for transformation during encoding may be selected
based on data units that are not larger than a corresponding coding
unit.
For example, in the video encoding apparatus 100 or 200, if a size
of the coding unit 710 is 64.times.64, transformation may be
performed by using the transform units 720 having a size of
32.times.32.
Also, data of the coding unit 710 having the size of 64.times.64
may be encoded by performing the transformation on each of the
transform units having the size of 32.times.32, 16.times.16,
8.times.8, and 4.times.4, which are smaller than 64.times.64, and
then a transform unit having the least coding error may be
selected.
FIG. 8 is a diagram for describing encoding information of coding
units corresponding to a coded depth, according to an exemplary
embodiment. The output unit 130 of the video encoding apparatus 100
may encode and transmit information 800 about a partition type,
information 810 about a prediction mode, and information 820 about
a size of a transform unit for each coding unit corresponding to a
coded depth, as information about an encoding mode.
The information 800 indicates information about a shape of a
partition obtained by splitting a prediction unit of a current
coding unit, wherein the partition is a data unit for prediction
encoding the current coding unit. For example, a current coding
unit CU_0 having a size of 2N.times.2N may be split into any one of
a partition 802 having a size of 2N.times.2N, a partition 804
having a size of 2N.times.N, a partition 806 having a size of
N.times.2N, and a partition 808 having a size of N.times.N. Here,
the information 800 about a partition type is set to indicate one
of the partition 804 having a size of 2N.times.N, the partition 806
having a size of N.times.2N, and the partition 808 having a size of
N.times.N
The information 810 indicates a prediction mode of each partition.
For example, the information 810 may indicate a mode of prediction
encoding performed on a partition indicated by the information 800,
i.e., an intra mode 812, an inter mode 814, or a skip mode 816.
The information 820 indicates a transform unit to be based on when
transformation is performed on a current coding unit. For example,
the transform unit may be a first intra transform unit 822, a
second intra transform unit 824, a first inter transform unit 826,
or a second intra transform unit 828.
The image data and encoding information extractor 220 of the video
decoding apparatus 200 may extract and use the information 800,
810, and 820 for decoding, according to each deeper coding
unit.
FIG. 9 is a diagram of deeper coding units according to depths,
according to an exemplary embodiment. Split information may be used
to indicate a change of a depth. The spilt information indicates
whether a coding unit of a current depth is split into coding units
of a lower depth.
A prediction unit 910 for prediction encoding a coding unit 900
having a depth of 0 and a size of 2N_0.times.2N_0 may include
partitions of a partition type 912 having a size of
2N_0.times.2N_0, a partition type 914 having a size of
2N_0.times.N_0, a partition type 916 having a size of
N_0.times.2N_0, and a partition type 918 having a size of
N_0.times.N_0. FIG. 9 only illustrates the partition types 912
through 918 which are obtained by symmetrically splitting the
prediction unit 910, but a partition type is not limited thereto,
and the partitions of the prediction unit 910 may include
asymmetrical partitions, partitions having a predetermined shape,
and partitions having a geometrical shape.
Prediction encoding is repeatedly performed on one partition having
a size of 2N_0.times.2N 0, two partitions having a size of
2N_0.times.N_0, two partitions having a size of N_0.times.2N_0, and
four partitions having a size of N_0.times.N_0, according to each
partition type. The prediction encoding in an intra mode and an
inter mode may be performed on the partitions having the sizes of
2N_0.times.2N_0, N_0.times.2N_0, 2N_0.times.N_0, and N_0.times.N_0.
The prediction encoding in a skip mode is performed only on the
partition having the size of 2N_0.times.2N_0.
Errors of encoding including the prediction encoding in the
partition types 912 through 918 are compared, and the least
encoding error is determined among the partition types. If an
encoding error is smallest in one of the partition types 912
through 916, the prediction unit 910 may not be split into a lower
depth.
If the encoding error is the smallest in the partition type 918, a
depth is changed from 0 to 1 to split the partition type 918 in
operation 920, and encoding is repeatedly performed on coding units
930 having a depth of 2 and a size of N_0.times.N_0 to search for a
minimum encoding error.
A prediction unit 940 for prediction encoding the coding unit 930
having a depth of 1 and a size of 2N_1.times.2N_1(=N_0.times.N_0)
may include partitions of a partition type 942 having a size of
2N_1.times.2N_1, a partition type 944 having a size of
2N_1.times.N_1, a partition type 946 having a size of
N_1.times.2N_1, and a partition type 948 having a size of
N_1.times.N_1.
If an encoding error is the smallest in the partition type 948, a
depth is changed from 1 to 2 to split the partition type 948 in
operation 950, and encoding is repeatedly performed on coding units
960, which have a depth of 2 and a size of N_2.times.N_2 to search
for a minimum encoding error.
When a maximum depth is d, split operation according to each depth
may be performed up to when a depth becomes d-1, and split
information may be encoded as up to when a depth is one of 0 to
d-2. In other words, when encoding is performed up to when the
depth is d-1 after a coding unit corresponding to a depth of d-2 is
split in operation 970, a prediction unit 990 for prediction
encoding a coding unit 980 having a depth of d-1 and a size of
2N_(d-1).times.2N_(d-1) may include partitions of a partition type
992 having a size of 2N_(d-1).times.2N_(d-1), a partition type 994
having a size of 2N_(d-1).times.N_(d-1), a partition type 996
having a size of N_(d-1).times.2N_(d-1), and a partition type 998
having a size of N_(d-1).times.N_(d-1).
Prediction encoding may be repeatedly performed on one partition
having a size of 2N_(d-1).times.2N_(d-1), two partitions having a
size of 2N_(d-1).times.N_(d-1), two partitions having a size of
N_(d-1).times.2N_(d-1), four partitions having a size of
N_(d-1).times.N_(d-1) from among the partition types 992 through
998 to search for a partition type having a minimum encoding
error.
Even when the partition type 998 has the minimum encoding error,
since a maximum depth is d, a coding unit CU_(d-1) having a depth
of d-1 is no longer split to a lower depth, and a coded depth for
the coding units constituting a current maximum coding unit 900 is
determined to be d-1 and a partition type of the current maximum
coding unit 900 may be determined to be N_(d-1).times.N_(d-1).
Also, since the maximum depth is d and a minimum coding unit 980
having a lowermost depth of d-1 is no longer split to a lower
depth, split information for the minimum coding unit 980 is not
set.
A data unit 999 may be a minimum unit for the current maximum
coding unit. A minimum unit according to an exemplary embodiment
may be a rectangular data unit obtained by splitting a minimum
coding unit 980 by 4. By performing the encoding repeatedly, the
video encoding apparatus 100 may select a depth having the least
encoding error by comparing encoding errors according to depths of
the coding unit 900 to determine a coded depth, and set a
corresponding partition type and a prediction mode as an encoding
mode of the coded depth.
As such, the minimum encoding errors according to depths are
compared in all of the depths of 1 through d, and a depth having
the least encoding error may be determined as a coded depth. The
coded depth, the partition type of the prediction unit, and the
prediction mode may be encoded and transmitted as information about
an encoding mode. Also, since a coding unit is split from a depth
of 0 to a coded depth, only split information of the coded depth is
set to 0, and split information of depths excluding the coded depth
is set to 1.
The image data and encoding information extractor 220 of the video
decoding apparatus 200 may extract and use the information about
the coded depth and the prediction unit of the coding unit 900 to
decode the partition 912. The video decoding apparatus 200 may
determine a depth, in which split information is 0, as a coded
depth by using split information according to depths, and use
information about an encoding mode of the corresponding depth for
decoding.
FIGS. 10 through 12 are diagrams for describing a relationship
between coding units 1010, prediction units 1060, and transform
units 1070, according to an exemplary embodiment. The coding units
1010 are coding units having a tree structure, corresponding to
coded depths determined by the video encoding apparatus 100, in a
maximum coding unit. The prediction units 1060 are partitions of
prediction units of each of the coding units 1010, and the
transform units 1070 are transform units of each of the coding
units 1010.
When a depth of a maximum coding unit is 0 in the coding units
1010, depths of coding units 1012 and 1054 are 1, depths of coding
units 1014, 1016, 1018, 1028, 1050, and 1052 are 2, depths of
coding units 1020, 1022, 1024, 1026, 1030, 1032, and 1048 are 3,
and depths of coding units 1040, 1042, 1044, and 1046 are 4.
In the prediction units 1060, some encoding units 1014, 1016, 1022,
1032, 1048, 1050, 1052, and 1054 are obtained by splitting the
coding units in the encoding units 1010. In other words, partition
types in the coding units 1014, 1022, 1050, and 1054 have a size of
2N.times.N, partition types in the coding units 1016, 1048, and
1052 have a size of N.times.2N, and a partition type of the coding
unit 1032 has a size of N.times.N. Prediction units and partitions
of the coding units 1010 are smaller than or equal to each coding
unit.
Transformation or inverse transformation is performed on image data
of the coding unit 1052 in the transform units 1070 in a data unit
that is smaller than the coding unit 1052. Also, the coding units
1014, 1016, 1022, 1032, 1048, 1050, and 1052 in the transform units
1070 are different from those in the prediction units 1060 in terms
of sizes and shapes. In other words, the video encoding and
decoding apparatuses 100 and 200 may perform intra prediction,
motion estimation, motion compensation, transformation, and inverse
transformation individually on a data unit in the same coding
unit.
Accordingly, encoding is recursively performed on each of coding
units having a hierarchical structure in each region of a maximum
coding unit to determine an optimum coding unit, and thus coding
units having a recursive tree structure may be obtained. Encoding
information may include split information about a coding unit,
information about a partition type, information about a prediction
mode, and information about a size of a transform unit. Table 1
shows the encoding information that may be set by the video
encoding and decoding apparatuses 100 and 200.
TABLE-US-00001 TABLE 1 Split Information 0 (Encoding on Coding Unit
having Size of 2N .times. 2N and Current Depth of d) Split
Information 1 Prediction Mode Partition Type Size of Transform Unit
Repeatedly Intra Symmetrical Asymmetrical Split Information 0 Split
Information 1 Encode Inter Partition Partition of Transformation of
Transformation Coding Skip (Only Type Type Unit Unit Units 2N
.times. 2N) 2N .times. 2N 2N .times. nU 2N .times. 2N N .times. N
having 2N .times. N 2N .times. nD (Symmetrical Lower N .times. 2N
nL .times. 2N Type) Depth of N .times. N nR .times. 2N N/2 .times.
N/2 d + 1 (Asymmetrical Type)
The output unit 130 of the video encoding apparatus 100 may output
the encoding information about the coding units having a tree
structure, and the image data and encoding information extractor
220 of the video decoding apparatus 200 may extract the encoding
information about the coding units having a tree structure from a
received bitstream.
Split information indicates whether a current coding unit is split
into coding units of a lower depth. If split information of a
current depth d is 0, a depth, in which a current coding unit is no
longer split into a lower depth, is a coded depth, and thus
information about a partition type, prediction mode, and a size of
a transform unit may be defined for the coded depth. If the current
coding unit is further split according to the split information,
encoding is independently performed on four split coding units of a
lower depth.
A prediction mode may be one of an intra mode, an inter mode, and a
skip mode. The intra mode and the inter mode may be defined in all
partition types, and the skip mode is defined only in a partition
type having a size of 2N.times.2N.
The information about the partition type may indicate symmetrical
partition types having sizes of 2N.times.2N, 2N.times.N,
N.times.2N, and N.times.N, which are obtained by symmetrically
splitting a height or a width of a prediction unit, and
asymmetrical partition types having sizes of 2N.times.nU,
2N.times.nD, nL.times.2N, and nR.times.2N, which are obtained by
asymmetrically splitting the height or width of the prediction
unit. The asymmetrical partition types having the sizes of
2N.times.nU and 2N.times.nD may be respectively obtained by
splitting the height of the prediction unit in 1:3 and 3:1, and the
asymmetrical partition types having the sizes of nL.times.2N and
nR.times.2N may be respectively obtained by splitting the width of
the prediction unit in 1:3 and 3:1
The size of the transform unit may be set to be two types in the
intra mode and two types in the inter mode. In other words, if
split information of the transform unit is 0, the size of the
transform unit may be 2N.times.2N, which is the size of the current
coding unit. If split information of the transform unit is 1, the
transform units may be obtained by splitting the current coding
unit. Also, if a partition type of the current coding unit having
the size of 2N.times.2N is a symmetrical partition type, a size of
a transform unit may be N.times.N, and if the partition type of the
current coding unit is an asymmetrical partition type, the size of
the transform unit may be N/2.times.N/2.
The encoding information about coding units having a tree structure
may include at least one of a coding unit corresponding to a coded
depth, a prediction unit, and a minimum unit. The coding unit
corresponding to the coded depth may include at least one of a
prediction unit and a minimum unit containing the same encoding
information.
Accordingly, it is determined whether adjacent data units are
included in the same coding unit corresponding to the coded depth
by comparing encoding information of the adjacent data units. Also,
a corresponding coding unit corresponding to a coded depth is
determined by using encoding information of a data unit, and thus a
distribution of coded depths in a maximum coding unit may be
determined.
Accordingly, if a current coding unit is predicted based on
encoding information of adjacent data units, encoding information
of data units in deeper coding units adjacent to the current coding
unit may be directly referred to and used.
Alternatively, if a current coding unit is predicted based on
encoding information of adjacent data units, data units adjacent to
the current coding unit are searched using encoding information of
the data units, and the searched adjacent coding units may be
referred for predicting the current coding unit.
FIG. 13 is a diagram for describing a relationship between a coding
unit, a prediction unit or a partition, and a transform unit,
according to encoding mode information of Table 1. A maximum coding
unit 1300 includes coding units 1302, 1304, 1306, 1312, 1314, 1316,
and 1318 of coded depths. Here, since the coding unit 1318 is a
coding unit of a coded depth, split information may be set to 0.
Information about a partition type of the coding unit 1318 having a
size of 2N.times.2N may be set to be one of a partition type 1322
having a size of 2N.times.2N, a partition type 1324 having a size
of 2N.times.N, a partition type 1326 having a size of N.times.2N, a
partition type 1328 having a size of N.times.N, a partition type
1332 having a size of 2N.times.nU, a partition type 1334 having a
size of 2N.times.nD, a partition type 1336 having a size of
nL.times.2N, and a partition type 1338 having a size of
nR.times.2N.
When the partition type is set to be symmetrical, i.e. the
partition type 1322, 1324, 1326, or 1328, a transform unit 1342
having a size of 2N.times.2N is set if split information (TU size
flag) of a transform unit is 0, and a transform unit 1344 having a
size of N.times.N is set if a TU size flag is 1.
When the partition type is set to be asymmetrical, i.e., the
partition type 1332, 1334, 1336, or 1338, a transform unit 1352
having a size of 2N.times.2N is set if a TU size flag is 0, and a
transform unit 1354 having a size of N/2.times.N/2 is set if a TU
size flag is 1.
Referring to FIG. 13, the TU size flag is a flag having a value or
0 or 1, but the TU size flag is not limited to 1 bit, and a
transform unit may be hierarchically split having a tree structure
while the TU size flag increases from 0.
In this case, the size of a transform unit that has been actually
used may be expressed by using a TU size flag of a transform unit,
according to an exemplary embodiment, together with a maximum size
and minimum size of the transform unit. According to an exemplary
embodiment, the video encoding apparatus 100 is capable of encoding
maximum transform unit size information, minimum transform unit
size information, and a maximum TU size flag. The result of
encoding the maximum transform unit size information, the minimum
transform unit size information, and the maximum TU size flag may
be inserted into an SPS. According to an exemplary embodiment, the
video decoding apparatus 200 may decode video by using the maximum
transform unit size information, the minimum transform unit size
information, and the maximum TU size flag.
For example, if the size of a current coding unit is 64.times.64
and a maximum transform unit size is 32.times.32, then the size of
a transform unit may be 32.times.32 when a TU size flag is 0, may
be 16.times.16 when the TU size flag is 1, and may be 8.times.8
when the TU size flag is 2.
As another example, if the size of the current coding unit is
32.times.32 and a minimum transform unit size is 32.times.32, then
the size of the transform unit may be 32.times.32 when the TU size
flag is 0. Here, the TU size flag cannot be set to a value other
than 0, since the size of the transform unit cannot be less than
32.times.32.
As another example, if the size of the current coding unit is
64.times.64 and a maximum TU size flag is 1, then the TU size flag
may be 0 or 1. Here, the TU size flag cannot be set to a value
other than 0 or 1.
Thus, if it is defined that the maximum TU size flag is
MaxTransformSizeIndex, a minimum transform unit size is
MinTransformSize, and a transform unit size is RootTuSize when the
TU size flag is 0, then a current minimum transform unit size
CurrMinTuSize that can be determined in a current coding unit, may
be defined by Equation (1):
CurrMinTuSize=max(MinTransformSize,RootTuSize/(2{circumflex over (
)}MaxTransformSizeIndex)) (1)
Compared to the current minimum transform unit size CurrMinTuSize
that can be determined in the current coding unit, a transform unit
size RootTuSize when the TU size flag is 0 may denote a maximum
transform unit size that can be selected in the system. In Equation
(1), RootTuSize/(2{circumflex over ( )}MaxTransformSizeIndex)
denotes a transform unit size when the transform unit size
RootTuSize, when the TU size flag is 0, is split a number of times
corresponding to the maximum TU size flag, and MinTransformSize
denotes a minimum transformation size. Thus, a smaller value from
among RootTuSize/(2{circumflex over ( )}MaxTransformSizeIndex) and
MinTransformSize may be the current minimum transform unit size
CurrMinTuSize that can be determined in the current coding
unit.
According to an exemplary embodiment, the maximum transform unit
size RootTuSize may vary according to the type of a prediction
mode.
For example, if a current prediction mode is an inter mode, then
RootTuSize may be determined by using Equation (2) below. In
Equation (2), MaxTransformSize denotes a maximum transform unit
size, and PUSize denotes a current prediction unit size.
RootTuSize=min(MaxTransformSize,PUSize) (2)
That is, if the current prediction mode is the inter mode, the
transform unit size RootTuSize when the TU size flag is 0, may be a
smaller value from among the maximum transform unit size and the
current prediction unit size.
If a prediction mode of a current partition unit is an intra mode,
RootTuSize may be determined by using Equation (3) below. In
Equation (3), PartitionSize denotes the size of the current
partition unit. RootTuSize=min(MaxTransformSize,PartitionSize)
(3)
That is, if the current prediction mode is the intra mode, the
transform unit size RootTuSize when the TU size flag is 0 may be a
smaller value from among the maximum transform unit size and the
size of the current partition unit.
However, the current maximum transform unit size RootTuSize that
varies according to the type of a prediction mode in a partition
unit is just an example and is not limited thereto.
Intra prediction performed by the intra predictor 410 of the image
encoder 400 illustrated in FIG. 4 and the intra predictor 550 of
the image decoder 500 illustrated in FIG. 5 according to one or
more exemplary embodiments, will now be described in detail. In the
following description, an encoding unit denotes a current encoded
block in an encoding process of an image, and a decoding unit
denotes a current decoded block in a decoding process of an image.
The encoding unit and the decoding unit are different in that the
encoding unit is used in the encoding process and the decoding unit
is used in the decoding. For the consistency of terms, except for a
particular case, the encoding unit and the decoding unit may be
referred to as a coding unit in both the encoding and decoding
processes. Also, one of ordinary skill in the art would understand
by the present specification that an intra prediction method and
apparatus according to an exemplary embodiment may also be applied
to perform intra prediction in a general video codec.
FIG. 14 is a block diagram of an intra prediction apparatus 1400
according to an exemplary embodiment. Referring to FIG. 14, the
intra prediction apparatus 1400 includes a predictor 1410, a
determiner 1415, and a post-processor 1420. The predictor 1410
intra predicts a current coding unit by using intra prediction
modes determined according to the size of the current coding unit,
and outputs a first predicted coding unit. The determiner 1415
determines whether the current coding unit has a portion located
outside a boundary of a current picture, and produces an index
MPI_PredMode according to the determination result.
The index MPI_PredMode indicates whether what kind of
Multi-Parameter Intra-prediction (MPI), which will be described in
detail later, is to be performed. Referring to Table 2, if the
index MPI_PredMode is 0, it indicates that the MPI is not performed
to produce a second predicted coding unit, and if the index
MPI_PredMode is greater than 0, it indicates that the MPI is to be
performed so as to produce the second predicted coding unit.
TABLE-US-00002 TABLE 2 MPI_PredMode MPI Mode Name Meaning 0
MPI_Mode0 Do not perform MPI 1 MPI_Mode1 Perform MPI . . . . . . .
. . MPI_PredModelMAX MPI_ModelMAX Perform MPI
According to Table 2, the index MPI_PredMode is 0 or 1 depending on
whether the MPI is to be performed. However, in a case where N
modes are present as MPI modes, the MPI_PredMode may have integral
value ranging from 0 to N so as to express the case where the MPI
will not be performed and the N modes.
If the determiner 1415 determines that the current coding unit does
not include any portion located outside a boundary of the picture,
that is, when the index MPI_PredMode is not 0, then the
post-processor 1420 produces the second predicted coding unit by
perform the MPI by using neighboring pixels of pixels that
constitute the first predicted coding unit so as to change the
pixel values of the pixels of the first predicted coding unit.
FIG. 15 is a table showing a number of intra prediction modes
according to the size of a coding unit, according to an exemplary
embodiment. According to an exemplary embodiment, a number of intra
prediction modes may be determined according to the size of a
coding unit (a decoding unit in the case of a decoding process).
Referring to FIG. 15, if the size of a coding unit that is to be
intra predicted is, for example, N.times.N, then numbers of intra
prediction modes that are to be actually performed on prediction
units having sizes of NMin.times.NMin, . . . , NMax.times.NMax
(NMin can be 2 and NMax can be 128) may be depend on prediction
unit size. In Example 2 prediction unit sizes are 4.times.4,
8.times.8, 16.times.16, 32.times.32, 64.times.64 and 128.times.128.
The number of intra prediction modes in this example are 5, 9, 9,
17, 33, 5, and 5, respectively. For another example, when a size of
a coding unit to be intra-predicted is N.times.N, numbers of intra
prediction modes to be actually performed on coding units having
sizes of 2.times.2, 4.times.4, 8.times.8, 16.times.16, 32.times.32,
64.times.64, and 128.times.128 may be set to be 3, 17, 34, 34, 34,
5, and 5. A reason why a number of intra prediction modes that are
to be actually performed is determined according to the size of a
coding unit, is because overhead for encoding prediction mode
information varies according to the size of the coding unit. In
other words, although a small-sized coding unit occupies a small
area in an entire image, overhead for transmitting additional
information, e.g., a prediction mode, regarding the small-sized
coding unit may be large. Thus, when a small-sized coding unit is
encoded using too many prediction modes, a number of bits may
increase, thus degrading compression efficiency. A large-sized
coding unit, e.g., a coding unit having a size of 64.times.64 or
more, is highly likely to be selected as a coding unit for a flat
region of an image. Compression efficiency may also be degraded
when a large-sized coding unit selected to encode such a flat
region is encoded using too many prediction modes.
Thus, according to an exemplary embodiment, coding unit size may be
largely classified into at least three sizes: N1.times.N1
(2.ltoreq.N1.ltoreq.4, N1 denotes an integer), N2.times.N2
(8.ltoreq.N2.ltoreq.32, N2 denotes an integer), and N3.times.N3
(64.ltoreq.N3, N3 denotes an integer). If a number of intra
prediction modes that are to be performed on each coding unit
having a size of N1.times.N1 is A1 (A1 denotes a positive integer),
a number of intra prediction modes that are to be performed on each
coding unit having a size of N2.times.N2 is A2 (A2 denotes a
positive integer), and a number of intra prediction modes that are
to be performed on each coding unit having a size of N3.times.N3 is
A3 (A3 denotes a positive integer), then a number of intra
prediction modes that are to be performed according to the size of
a coding unit, may be determined to satisfy A3.ltoreq.A1.ltoreq.A2.
That is, if a current picture is divided into a small-sized coding
unit, a medium-sized coding unit, and a large-sized coding unit,
then a number of prediction modes that are to be performed on the
medium-sized coding unit may be greater than those of prediction
modes to be performed on the small-sized coding unit and the
large-sized coding unit. However, another exemplary embodiment is
not limited thereto and a large number of prediction modes may also
be set to be performed on the small-sized and medium-sized coding
units. The numbers of prediction modes according to the size of
each coding unit illustrated in FIG. 15 are just an example and may
thus be variable.
FIGS. 16A to 16C are drawings for explaining intra prediction modes
that may be performed on a coding unit having a predetermined size,
according to exemplary embodiments. FIG. 16A is a table showing
intra prediction modes that may be performed on a coding unit
having a predetermined size, according to an exemplary embodiment.
Referring to FIGS. 15 and 16A, for example, if a coding unit having
a size of 4.times.4 is intra predicted, a vertical mode (mode 0), a
horizontal mode (mode 1), a direct-current (DC) mode (mode 2), a
diagonal down-left mode (mode 3), a diagonal down-right mode (mode
4), a vertical-right mode (mode 5), a horizontal-down mode (mode
6), a vertical-left mode (mode 7), or a horizontal-up mode (mode 8)
may be performed.
FIG. 16B illustrate directions of the intra prediction modes
illustrated in FIG. 16A, according to an exemplary embodiment. In
FIG. 16B, values assigned to arrows denote mode values when
prediction is performed in directions indicated with the arrows,
respectively. Here, mode 2 is a DC prediction mode having no
direction and is thus not illustrated in FIG. 16B.
FIG. 16C illustrate intra prediction methods that may be performed
on the coding unit illustrated in FIG. 16A, according to an
exemplary embodiment. Referring to FIG. 16C, a predicted coding
unit is produced using neighboring pixels A to M of a current
coding unit according to an available intra prediction mode
determined according to the size of the current coding unit. For
example, a method of prediction encoding a current coding unit
having a size of 4.times.4 according to the vertical mode (mode 0)
of FIG. 16A, will be described. First, pixel values of the pixels A
to D adjacent to the top of the 4.times.4 coding unit are predicted
as pixel values of the 4.times.4 coding unit. Specifically, the
pixel values of the pixel A are predicted as four pixel values of
pixels at a first column of the 4.times.4 coding unit, the pixel
values of the pixel B are predicted as four pixel values of pixels
at a second column of the 4.thrfore.4 coding unit, the pixel values
of the pixel C are predicted as four pixel values of pixels at a
third column of the 4.times.4 coding unit, and the pixel values of
the pixel D are predicted as four pixel values of pixels at a
fourth column of the 4.times.4 current coding unit. Then, error
values between actual pixel values of pixels included in a
predicted 4.times.4 coding unit predicted using the pixels A to D
and the original 4.times.4 coding unit are calculated and
encoded.
FIG. 17 is drawings for explaining intra prediction modes that may
be performed on a coding unit having a predetermined size,
according to other exemplary embodiments. Referring to FIGS. 15 and
17, for example, if a coding unit having a size of 2.times.2 is
intra predicted, a total of five modes, e.g., a vertical mode, a
horizontal mode, a DC mode, a plane mode, and a diagonal down-right
mode, may be performed.
As illustrated in FIG. 15, if a coding unit having a size of
32.times.32 has 33 intra prediction modes, then directions of the
33 intra prediction modes should be set. According to an exemplary
embodiment, a prediction direction for selecting neighboring pixels
to be used as reference pixels based on pixels included in a coding
unit, is set by using a dx parameter and a dy parameter so as to
set intra prediction modes having various directionalities in
addition to the intra prediction modes described above with
reference to FIGS. 16 and 17. For example, when each of the 33
prediction modes is defined as mode N_(N is an integer from 0 to
32), mode 0, mode 1, mode 2, and mode 3 are set as a vertical mode,
a horizontal mode, a DC mode, and a plane mode, respectively, and
each of mode 4 to mode 31 may be set as a prediction mode having a
directionality of tan.sup.-1(dy/dx) by using a (dx, dy) parameter
expressed with one from among (1,-1), (1,1), (1,2), (2,1), (1,-2),
(2,1), (1,-2), (2,-1), (2,-11), (5,-7), (10,-7), (11,3), (4,3),
(1,11), (1,-1), (12,-3), (1,-11), (1,-7), (3,-10), (5,-6), (7,-6),
(7,-4), (11,1), (6,1), (8,3), (5,3), (5,7), (2,7), (5,-7), and
(4,-3) shown in Table 3.
TABLE-US-00003 TABLE 3 mode # dx dy mode 4 1 -1 mode 5 1 1 mode 6 1
2 mode 7 2 1 mode 8 1 -2 mode 9 2 -1 mode 10 2 -11 mode 11 5 -7
mode 12 10 -7 mode 13 11 3 mode 14 4 3 mode 15 1 11 mode 16 1 -1
mode 17 12 -3 mode 18 1 -11 mode 19 1 -7 mode 20 3 -10 mode 21 5 -6
mode 22 7 -6 mode 23 7 -4 mode 24 11 1 mode 25 6 1 mode 26 8 3 mode
27 5 3 mode 28 5 7 mode 29 2 7 mode 30 5 -7 mode 31 4 -3 Mode 0,
mode 1, mode 2, mode 3, and mode 32 denote a vertical mode, a
horizontal mode, a DC mode, a plane mode, and a Bi-linear mode,
respectively.
Mode 32 may be set as a bi-linear mode that uses bi-linear
interpolation as will be described later with reference to FIG.
19.
FIGS. 18A through 18C are reference diagrams for explaining intra
prediction modes having various directionalities according to
exemplary embodiments. As described above with reference to Table
3, each of intra prediction modes according to exemplary
embodiments may have directionality of tan.sup.-1(dy/dx) by using a
plurality of (dx, dy) parameters.
Referring to FIG. 18A, neighboring pixels A and B on a line 180
that extends from a current pixel P in a current coding unit, which
is to be predicted, at an angle of tan.sup.-1(dy/dx) determined by
a value of a (dx, dy) parameter according to a mode, shown in Table
3, may be used as predictors of the current pixel P. In this case,
the neighboring pixels A and B may be pixels that have been encoded
and restored, and belong to previous coding units located above and
to the left side of the current coding unit. Also, when the line
180 does not pass along neighboring pixels on locations each having
an integral value but passes between these neighboring pixels,
neighboring pixels closer to the line 180 may be used as predictors
of the current pixel P. If two pixels that meet the line 180, e.g.,
the neighboring pixel A located above the current pixel P and the
neighboring pixel B located to the left side of the current pixel
P, are present, an average of pixel values of the neighboring
pixels A and B may be used as a predictor of the current pixel P.
Otherwise, if a product of values of the dx and dy parameters is a
positive value, the neighboring pixel A may be used, and if the
product of the values of the dx and dy parameters is a negative
value, the neighboring pixel B may be used.
FIGS. 18B and 18C are reference diagrams for explaining a process
of generating a predictor when the extended line 180 of FIG. 18A
passes between, not through, neighboring pixels of integer
locations.
Referring to FIG. 18B, if the extended line 180 having an angle of
tan-1(dy/dx) that is determined according to (dx, dy) of each mode
passes between a neighboring pixel A 181 and a neighboring pixel B
182 of integer locations, a weighted average value considering a
distance between an intersection of the extended line 180 and the
neighboring pixels A 181 and B 182 close to the extended line 180
may be used as a predictor as described above. For example, if a
distance between the neighboring pixel A 181 and the intersection
of the extended line 180 having the angle of tan-1(dy/dx) is f, and
a distance between the neighboring pixel B 182 and the intersection
of the extended line 180 is g, a predictor for the current pixel P
may be obtained as (A*g+B*f)/(f+g). Here, f and g may be each a
normalized distance using an integer. If software or hardware is
used, the predictor for the current pixel P may be obtained by
shift operation as (g*A+f*B+2)>>2. As shown in FIG. 18B, if
the extended line 180 passes through a first quarter close to the
neighboring pixel A 181 from among four parts obtained by
quartering a distance between the neighboring pixel A 181 and the
neighboring pixel B 182 of the integer locations, the predictor for
the current pixel P may be acquired as (3*A+B)/4. Such operation
may be performed by shift operation considering rounding-off to a
nearest integer like (3*A+B+2)>>2.
Meanwhile, if the extended line 180 having the angle of
tan-1(dy/dx) that is determined according to (dx, dy) of each mode
passes between the neighboring pixel A 181 and the neighboring
pixel B 182 of the integer locations, a section between the
neighboring pixel A 181 and the neighboring pixel B 182 may be
divided into a predetermined number of areas, and a weighted
average value considering a distance between an intersection and
the neighboring pixel A 181 and the neighboring pixel B 182 in each
divided area may be used as a prediction value. For example,
referring to FIG. 18C, a section between the neighboring pixel A
181 and the neighboring pixel B 182 may be divided into five
sections P1 through P5 as shown in FIG. 18C, a representative
weighted average value considering a distance between an
intersection and the neighboring pixel A 181 and the neighboring
pixel B 182 in each section may be determined, and the
representative weighted average value may be used as a predictor
for the current pixel P. In detail, if the extended line 180 passes
through the section P1, a value of the neighboring pixel A may be
determined as a predictor for the current pixel P. If the extended
line 180 passes through the section P2, a weighted average value
(3*A+1*B+2)>>2 considering a distance between the neighboring
pixels A and B and a middle point of the section P2 may be
determined as a predictor for the current pixel P. If the extended
line 180 passes through the section P3, a weighted average value
(2*A+2*B+2)>>2 considering a distance between the neighboring
pixels A and B and a middle point of the section P3 may be
determined as a predictor for the current pixel P. If the extended
line 180 passes through the section P4, a weighted average value
(1*A+3*B+2)>>2 considering a distance between the neighboring
pixels A and B and a middle point of the section P4 may be
determined as a predictor for the current pixel P. If the extended
line 180 passes through the section P5, a value of the neighboring
pixel B may be determined as a predictor for the current pixel
P.
Also, if two neighboring pixels, that is, the neighboring pixel A
on the up side and the neighboring pixel B on the left side meet
the extended line 180 as shown in FIG. 18A, an average value of the
neighboring pixel A and the neighboring pixel B may be used as a
predictor for the current pixel P, or if (dx*dy) is a positive
value, the neighboring pixel A on the up side may be used, and if
(dx*dy) is a negative value, the neighboring pixel B on the left
side may be used.
The intra prediction modes having various directionalities shown in
Table 3 may be predetermined by an encoding side and a decoding
side, and only an index of an intra prediction mode of each coding
unit may be transmitted.
FIG. 19 is a reference diagram for explaining a bi-linear mode
according to an exemplary embodiment. Referring to FIG. 19, in the
bi-linear mode, a geometric average is calculated by considering a
value of a current pixel P 190 in a current coding unit, which is
to be predicted, values of pixels on upper, lower, left, and right
boundaries of the current coding unit, and the distances between
the current pixel P 190 and the upper, lower, left, and right
boundaries of the current coding unit, and is then used as a
predictor of the current pixel P 190. For example, in the bi-linear
mode, a geometric average calculated using a virtual pixel A 191, a
virtual pixel B 192, a pixel D 196, and a pixel E 197 located to
the upper, lower, left, and right sides of the current pixel P 190,
and the distances between the current pixel P 190 and the upper,
lower, left, and right boundaries of the current coding unit, is
used as a predictor of the current pixel P 190. Since the bi-linear
mode is one of intra prediction modes, neighboring pixels that have
been encoded and restored and belong to previous coding units are
used as reference pixels for prediction. Thus, pixel values in the
current coding unit are not used but virtual pixel values
calculated using neighboring pixels located to the upper and left
sides of the current coding unit are used as the pixel A 191 and
the pixel B 192.
Specifically, first, a value of a virtual pixel C 193 on a lower
rightmost point of the current coding unit is calculated by
calculating an average of values of a neighboring pixel (right-up
pixel) 194 on an upper rightmost point of the current coding unit
and a neighboring pixel (left-down pixel) 195 on a lower leftmost
point of the current coding unit, as expressed in the following
equation: C=0.5(LeftDownPixel+RightUpPixel) (4)
The virtual pixel C 193 may be obtained by shifting operation as
The Equation 4 may be the predictor for the current pixel P may be
obtained by shift operation as
C=0.5(LeftDownPixel+RightUpPixel+1)>>1.
Next, a value of the virtual pixel A 191 located on a lowermost
boundary of the current coding unit when the current pixel P 190 is
extended downward by considering the distance W1 between the
current pixel P 190 and the left boundary of the current coding
unit and the distance W2 between the current pixel P 190 and the
right boundary of the current coding unit, is calculated by using
the following equation: A=(C*W1+LeftDownPixel*W2)/(W1+W2)
A=(C*W1+LeftDownPixel*W2+((W1+W2)/2))/(W1+W2) (5)
When a value of W1+W2 in Equation 5 is a power of 2, like
2{circumflex over ( )}n,
A=(C*W1+LeftDownPixel*W2+((W1+W2)/2))/(W1+W2) may be calculated by
shift operation as A=(C*W1+LeftDownPixel*W2+2{circumflex over (
)}(n-1))>>n without division.
Similarly, a value of the virtual pixel B 192 located on a
rightmost boundary of the current coding unit when the current
pixel P 190 is extended in the right direction by considering the
distance h1 between the current pixel P 190 and the upper boundary
of the current coding unit and the distance h2 between the current
pixel P 190 and the lower boundary of the current coding unit, is
calculated by using the following equation:
B=(C*h1+RightUpPixel*h2)/(h1+h2)
B=(C*h1+RightUpPixel*h2+((h1+h2)/2))/(h1+h2) (6)
When a value of h1+h2 in Equation 6 is a power of 2, like
2{circumflex over ( )}m,
B=(C*h1+RightUpPixel*h2+((h1+h2)/2))/(h1+h2) may be calculated by
shift operation as B=(C*h1+RightUpPixel*h2+2{circumflex over (
)}(m-1))>>m without division.
Once the values of the virtual pixel B 192 on the right border and
the virtual pixel A 191 on the down border of the current pixel P
190 are determined by using Equations (4) through (6), a predictor
for the current pixel P 190 may be determined by using an average
value of A+B+D+E. In detail, a weighted average value considering a
distance between the current pixel P 190 and the virtual pixel A
191, the virtual pixel B 192, the pixel D 196, and the pixel E 197
or an average value of A+B+D+E may be used as a predictor for the
current pixel P 190. For example, if a weighted average value is
used and the size of block is 16.times.16, a predictor for the
current pixel P may be obtained as
(h1*A+h2*D+W1*B+W2*E+16)>>5. Such bilinear prediction is
applied to all pixels in the current coding unit, and a prediction
coding unit of the current coding unit in a bilinear prediction
mode is generated.
According to an exemplary embodiment, prediction encoding is
performed according to various intra prediction modes determined
according to the size of a coding unit, thereby allowing efficient
video compression based on characteristics of an image.
Meanwhile, as described with reference to FIGS. 18A through 18C, if
a predictor for the current pixel P is generated by using
neighboring pixels on or close to the extended line 180, the
extended line 180 has actually a directivity of tan-1 (dy/dx). In
order to calculate the directivity, since division (dy/dx) is
necessary, calculation is made down to decimal places when hardware
or software is used, thereby increasing the amount of calculation.
Accordingly, a process of setting dx and dy is used in order to
reduce the amount of calculation when a prediction direction for
selecting neighboring pixels to be used as reference pixels about a
pixel in a coding unit is set by using dx, and dy parameters in a
similar manner to that described with reference to Table 3.
FIG. 27 is a diagram for explaining a relationship between a
current pixel and neighboring pixels located on an extended line
having a directivity of (dy/dx), according to an exemplary
embodiment.
Referring to FIG. 27, it is assumed that a location of the current
pixel P is P(j,i), and an up neighboring pixel and a left
neighboring pixel B located on an extended line 2710 having a
directivity, that is, a gradient, of tan-1(dy/dx) and passing
through the current pixel P are respectively A and B. When it is
assumed that locations of up neighboring pixels correspond to an
X-axis on a coordinate plane, and locations of left neighboring
pixels correspond to a y-axis on the coordinate plate, the up
neighboring pixel A is located at (j+i*dx/dy,0), and the left
neighboring pixel B is located at (0,i+j*dy/dx). Accordingly, in
order to determine any one of the up neighboring pixel A and the
left neighboring pixel B for predicting the current pixel P,
division, such as dx/dy or dy/dx, is required. Such division is
very complex as described above, thereby reducing a calculation
speed of software or hardware.
Accordingly, a value of any one of dx and dy representing a
directivity of a prediction mode for determining neighboring pixels
may be determined to be a power of 2. That is, when n and m are
integers, dx and dy may be 2{circumflex over ( )}n and 2{circumflex
over ( )}m, respectively.
Referring to FIG. 27, if the left neighboring pixel B is used as a
predictor for the current pixel P and dx has a value of
2{circumflex over ( )}n, j*dy/dx necessary to determine
(0,i+j*dy/dx) that is a location of the left neighboring pixel B
becomes (j*dy/(2{circumflex over ( )}n)), and division using such a
power of 2 is easily obtained through shift operation as
(j*dy)>>n, thereby reducing the amount of calculation.
Likewise, if the up neighboring pixel A is used as a predictor for
the current pixel P and dy has a value of 2{circumflex over ( )}m,
i*dx/dy necessary to determine (j+i*dx/dy,0) that is a location of
the up neighboring pixel A becomes (i*dx)/(2{circumflex over (
)}m), and division using such a power of 2 is easily obtained
through shift operation as (i*dx)>>m.
FIG. 28 is a diagram for explaining a change in a neighboring pixel
located on an extended line having a directivity of (dx,dy)
according to a location of a current pixel, according to an
exemplary embodiment.
As a neighboring pixel necessary for prediction according to a
location of a current pixel, any one of an up neighboring pixel and
a left neighboring pixel is selected.
Referring to FIG. 28, when a current pixel 2810 is P(j,i) and is
predicted by using a neighboring pixel located in a prediction
direction, an up pixel A is used to predict the current pixel P
2810. When the current pixel 2810 is Q(b,a), a left pixel B is used
to predict the current pixel Q 2820.
If only a dy component of a y-axis direction from among (dx, dy)
representing a prediction direction has a power of 2 like
2{circumflex over ( )}m, while the up pixel A in FIG. 24 may be
determined through shift operation without division such as
(j+(i*dx)>>m, 0), the left pixel B requires division such as
(0, a+b*2{circumflex over ( )}m/dx). Accordingly, in order to
exclude division when a predictor is generated for all pixels of a
current block, all of dx and dy may have a type of power of 2.
FIGS. 29 and 30 are diagrams for explaining a method of determining
an intra prediction mode direction, according to exemplary
embodiments.
In general, there are many cases where linear patterns shown in an
image or a video signal are vertical or horizontal. Accordingly,
when intra prediction modes having various directivities are
defined by using parameters dx and dy, image coding efficiency may
be improved by defining values dx and dy as follows.
In detail, if dy has a fixed value of 2{circumflex over ( )}m, an
absolute value of dx may be set so that a distance between
prediction directions close to a vertical direction is narrow, and
a distance between prediction modes closer to a horizontal
direction is wider. For example, referring to FIG. 29, if dy has a
value of 2{circumflex over ( )}4, that is, 16, a value of dx may be
set to be 1,2,3,4,6,9,12, 16,0,-1,-2,-3,-4,-6,-9,-12, and -16 so
that a distance between prediction directions close to a vertical
direction is narrow and a distance between prediction modes closer
to a horizontal direction is wider.
Likewise, if dx has a fixed value of 2{circumflex over ( )}n, an
absolute value of dy may be set so that a distance between
prediction directions close to a horizontal direction is narrow and
a distance between prediction modes closer to a vertical direction
is wider. For example, referring to FIG. 30, if dx has a value of
2{circumflex over ( )}4, that is, 16, a value of dy may be set to
be 1,2,3,4,6,9,12, 16,0,-1,-2,-3,-4,-6,-9,-12, and -16 so that a
distance between prediction directions close to a horizontal
direction is narrow and a distance between prediction modes closer
to a vertical direction is wider.
Also, when one of values of dx and dy is fixed, the remaining value
may be set to be increased according to a prediction mode. For
example, if dy is fixed, a distance between dx may be set to be
increased by a predetermined value. Also, an angle of a horizontal
direction and a vertical direction may be divided in predetermined
units, and such an increased amount may be set in each of the
divided angles. For example, if dy is fixed, a value of dx may be
set to have an increased amount of a in a section less than 15
degrees, an increased amount of b in a section between 15 degrees
and 30 degrees, and an increased width of c in a section greater
than 30 degrees. In this case, in order to have such a shape as
shown in FIG. 27, the value of dx may be set to satisfy a
relationship of a<b<c.
For example, prediction modes described with reference to FIGS. 27
through 30 may be defined as a prediction mode having a directivity
of tan-1(dy/dx) by using (dx, dy) as shown in Tables 4 through
6.
TABLE-US-00004 TABLE 4 dx Dy dx dy dx dy -32 32 21 32 32 13 -26 32
26 32 32 17 -21 32 32 32 32 21 -17 32 32 -26 32 26 -13 32 32 -21 32
32 -9 32 32 -17 -5 32 32 -13 -2 32 32 -9 0 32 32 -5 2 32 32 -2 5 32
32 0 9 32 32 2 13 32 32 5 17 32 32 9
TABLE-US-00005 TABLE 5 dx Dy dx dy dx Dy -32 32 19 32 32 10 -25 32
25 32 32 14 9 32 32 32 32 19 -14 32 32 -25 32 25 -10 32 32 -19 32
32 -6 32 32 -14 -3 32 32 -10 -1 32 32 -6 0 32 32 -3 1 32 32 -1 3 32
32 0 6 32 32 1 10 32 32 3 14 32 32 6
TABLE-US-00006 TABLE 6 dx Dy dx dy dx dy -32 32 23 32 32 15 -27 32
27 32 32 19 -23 32 32 32 32 23 -19 32 32 -27 32 27 -15 32 32 -23 32
32 -11 32 32 -19 -7 32 32 -15 -3 32 32 -11 0 32 32 -7 3 32 32 -3 7
32 32 0 11 32 32 3 15 32 32 7 19 32 32 11
As described above, a predicted coding unit produced using an intra
prediction mode determined according to the size of a current
coding unit by the predictor 1410 of the intra prediction apparatus
1400 of FIG. 14, has a directionality according to the intra
prediction mode. The directionality in the predicted coding unit
may lead to an improvement in prediction efficiency when pixels of
the current coding unit that is to be predicted have a
predetermined directionality but may lead to a degradation in
prediction efficiency when these pixels do not have a predetermined
directionality. Thus, the post-processor 1420 may improve
prediction efficiency by producing a new predicted coding unit by
changing values of pixels in the predicted coding unit by using the
pixels in the predicted coding unit and at least one neighboring
pixel, as post-processing for the predicted coding unit produced
through intra prediction. In this case, the post-processor 1420
does not perform post-processing on all predicted coding units but
may perform post-processing only when the determiner 1415
determines that a current predicted coding unit does not include a
portion located outside a boundary of a picture, that is, when an
index MPI_PredMode is not 0.
FIG. 24 is a reference diagram for explaining an indexing process
for post-processing a coding unit according to an exemplary
embodiment. Referring to FIG. 24, if a current picture 2410 is
divided and encoded into coding units each having a predetermined
size, and a width Frame_width of the current picture 2410 is not a
multiple of a horizontal length of each of the coding units or a
height Frame_height of the current picture 2410 is not a multiple
of a vertical length of each of the coding units, then some portion
of the coding units (which are indicated with slant lines) extend
over right and lower boundaries of the current picture 2410 as
illustrated in FIG. 24. The determiner 1415 of FIG. 14 may set a
predetermined index MPI_PredMode for the coding units extending
over a boundary of the current picture to be 0, so that the
post-processor 1420 of FIG. 14 may skip post-processing of these
coding units.
A reason why post-processing is not performed when a current
predicted coding unit has a portion located outside a boundary of a
current coding unit, is because neighboring pixels of each pixel
are used for post-processing and pixels in the current predicted
coding unit lack neighboring pixels. Even if post-processing is
performed by producing neighboring pixels through padding or
extrapolation, prediction efficiency is not high because the
produced neighboring pixels are originally non-existent pixels.
FIG. 25 is a reference diagram for explaining an indexing process
for post-processing a coding unit according to another exemplary
embodiment. Referring to FIG. 24, if the determiner 1415 of FIG. 14
determines that a coding unit 2520 extends over a boundary 2510 of
a picture, then the coding unit 2520 may be split into deeper
coding units of a depth that is deeper than that of the coding unit
2520, and whether each of the deeper coding units has a portion
located outside a boundary of the picture may be determined, rather
than not post-processing the entire coding unit 2520. Such a
splitting process may be repeatedly performed until coding units,
e.g., coding units 2524 and 2528, which extend over the boundary
2510 of the picture are minimum coding units and cannot thus be
split any further, that is, until a current depth is a maximum
depth. Referring to FIG. 25, an index MPI_PredMode for the minimum
coding units 2524 and 2528 located outside the boundary 2510 is set
to 0 so that the minimum coding units 2524 and 2528 may not be
post-processed, and an index MPI_PredMode for minimum coding units
2522 and 2526 located within the boundary 2510 is set to be 1 so
that the minimum coding units 2522 and 2526 may be
post-processed.
A method of post-processing a predicted coding unit by the
post-processor 1420 of FIG. 14 according to an exemplary
embodiment, will now be described.
If the determiner 1415 of FIG. 14 determines that a current coding
unit does not include a portion located outside a boundary of a
picture, then the post-processor 1420 produces a second predicted
coding unit by changing values of pixels constituting a first
predicted coding unit produced by the predictor 140 of FIG. 14 by
performing post-processing using the pixels of the first predicted
coding unit and at least one neighboring pixel. The predictor 1410
produces the first predicted coding unit by using an intra
prediction mode determined according to a size of the current
coding unit, as described above.
FIG. 20 is a reference diagram for explaining post-processing of a
first predicted coding unit, according to an exemplary embodiment.
In FIG. 20, reference numerals 2010 to 2060 illustrate a process of
changing values of pixels in the first predicted coding unit by the
post-processor 1420 in chronological order.
Referring to FIG. 20, the post-processor 1420 of FIG. 14 changes
values of pixels in the first predicted coding unit 2010 by
calculating a weighted average of values of a pixel in the first
predicted coding unit 2010, which is to be changed, and neighboring
pixels of the pixel. For example, referring to FIG. 20, if a value
of a pixel 2021 of the first predicted coding unit 2010, which is
to be changed, is f[1][1], a value of a pixel 2022 located above
the pixel 2021 is f[0][1], a pixel 2023 located to the left side of
the pixel 2021 is f[1][0], and a result of changing the value
f[1][1] of the pixel 2021 is f[1][1], then f[1][1] may be
calculated using the following equation:
.function..function..function..function..function..function..function..fu-
nction..times..times.<<.times.>>.times..times..times.'.functio-
n..function..times..times..function..function..function..function..functio-
n..function. ##EQU00001##
As illustrated in FIG. 20, the post-processor 1420 changes values
of pixels included in the first predicted coding unit 2010 by
calculating a weighted average of the values of each pixel of the
first predicted coding unit and pixels located above and to the
left side of the pixel in a direction from an upper leftmost point
of the first predicted coding unit to a lower rightmost point of
the first predicted coding unit. However, such a post-processing
operation according to another exemplary embodiment is not limited
thereto, and may be sequentially performed on the pixels of the
first predicted coding unit in a direction from a upper rightmost
point of the first predicted coding unit to a lower leftmost point
of the first predicted coding unit or a direction from the lower
rightmost point of the first predicted coding unit to the upper
leftmost point of the first predicted coding unit. For example, if
the post-processor 1420 changes the values of the pixels of the
first predicted coding unit in the direction from the upper
rightmost point to the lower leftmost point unlike as illustrated
in FIG. 20, then the values of the pixels of the first predicted
coding unit are changed by calculating a weighted average of the
values of each of the pixels of the first predicted coding unit and
pixels located below and to the right side of the first predicted
coding unit.
FIG. 21 is a reference diagram for explaining an operation of the
post-processor 1420 of FIG. 14 according to an exemplary
embodiment. FIG. 22 is a reference diagram for explaining
neighboring pixels to be used by a post-processor according to an
exemplary embodiment. In FIG. 21, reference numeral 2110 denotes a
first pixel of a first predicted coding unit 2100, which is to be
changed, and reference numerals 2111 to 2118 denote neighboring
pixels of the first pixel 2110.
In the current exemplary embodiment (first exemplary embodiment),
neighboring pixels of the first pixel 2110 are not limited to those
located above and to the left side of the first predicted coding
unit, unlike as illustrated in FIG. 20. Referring to FIG. 21, the
post-processor 1420 may post-process the first pixel 2110 by using
a predetermined number of neighboring pixels selected from among
the neighboring pixels 2111 to 2118. That is, referring to FIG. 22,
a predetermined number of pixels are selected from among
neighboring pixels P1 to P8 of a first pixel c of a current coding
unit, and a value of the first pixel c is changed by performing a
predetermined operation on the selected neighboring pixels and the
first pixel c. For example, if the size of the first predicted
coding unit 2100 is m.times.n, a value of the first pixel 2110,
which is to be changed and is located at an i.sup.th column and a
i.sup.th row of the first predicted coding unit 2100, is f[i][j],
values of n pixels selected from among the neighboring pixels 2111
to 2118 of the first pixel 2110 so as to post-process the first
pixel 2110 are f1 to fn, respectively, then the post-processor 1420
changes the value of the first pixel 2110 from f[i][j] to f[i][j]
by using the following equation. Here, m denotes a positive
integer, n is 2 or 3, i denotes an integer from 0 to m-1, and j
denotes an integer from 0 to n-1.
'.times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times.'.times..times..times..times..times..times..time-
s..times..times..times..times..times. ##EQU00002##
The post-processor 1420 produces a second predicted coding unit by
changing values of all pixels included in the first predicted
coding unit 2100 by using Equation (8). In Equation (8), three
neighboring pixels are used, but another exemplary embodiment is
not limited thereto and the post-processor 1420 may perform
post-processing by using four or more neighboring pixels.
According to a second exemplary embodiment, the post-processor 1420
produces a second predicted coding unit by changing the value of
each pixel of the first predicted coding unit 2100 by using a
weighted harmonic average of the values of a pixel of the first
predicted coding unit 2100, which is to be changed, and neighboring
pixels of the pixel.
For example, the post-processor 1420 changes the value of a pixel
at the i.sup.th column and the j.sup.th row of the first predicted
coding unit 2100 from f[i][j] to f[i][j] by using neighboring
pixels located above and to the left side of the pixel, as shown in
the following equation:
'.times..alpha..beta..gamma..alpha..function..function..beta..function..f-
unction..gamma. ##EQU00003## wherein .alpha., .beta., and .gamma.
denote positive integers, and for example, .alpha.=2, .beta.=2, and
.gamma.=1.
According to a third exemplary embodiment, the post-processor 1420
produces a second predicted coding unit by changing the value of
each pixel of the first predicted coding unit 2100 by using a
weighted geometric average of values of a pixel of the first
predicted coding unit 2100, which is to be changed, and neighboring
pixels of the pixel.
For example, the post-processor 1420 changes the value of a pixel
at the i.sup.th column and the j.sup.th row of the first predicted
coding unit 2100 from f[i][j] to f[i][j] by using neighboring
pixels located above and to the left side of the pixel, as shown in
the following equation:
'.times..function..function..alpha..function..function..beta..gamma..alph-
a..beta..gamma. ##EQU00004## wherein .alpha., .beta., and .gamma.
denote positive integers, and for example, a=1, .beta.=1, and
.gamma.=2. In Equation (8) to (10), a relative large weight is
assigned to the value f[i][j] of the pixel that is to be
changed.
As described above, in the first to third exemplary embodiments,
the post-processor 1420 may perform post-processing by using not
only neighboring pixels located above and to the left side of a
pixel that is to be changed, but also a predetermined number of
neighboring pixels selected from among the neighboring pixels 2111
to 2118 as illustrated in FIG. 21.
According to a fourth exemplary embodiment, the post-processor 1420
produces a second predicted coding unit by changing the value of
each pixel in the first predicted coding unit by using an average
of the values of a pixel in the first predicted coding unit, which
is to be changed, and one selected from among neighboring pixels of
the pixel.
For example, the post-processor 1420 changes the value of a pixel
at the i.sup.th column and the j.sup.th row of the first predicted
coding unit 2100 from f[i][j] to f[i][j] by using neighboring
pixels located above the pixel, as shown in the following equation:
f[i][j]=(f[i-1][j]+f[i][j-1]+1)>>1 (11)
Similarly, according to a fifth exemplary embodiment, the
post-processor 1420 produces a second predicted coding unit by
changing the value of each pixel in the first predicted coding unit
by using an average of the values of a pixel in the first predicted
coding unit, which is to be changed, and neighboring pixels located
to the left side of the pixel.
In other words, the post-processor 1420 changes the value of a
pixel at the i.sup.th column and the j.sup.th row of the first
predicted coding unit 2100 from f[i][j] to f[i][j], as shown in the
following equation: f[i][j]=(f[i-1][j]+f[i][j]+1)>>1 (12)
According to a sixth exemplary embodiment, the post-processor 1420
produces a second predicted coding unit by changing the value of
each pixel in the first predicted coding unit by using a median
between the values of a pixel of the first predicted coding unit,
which is to be changed, and neighboring pixels of the pixel.
Referring back to FIG. 21, for example, it is assumed that the
value f[i][j] of the first pixel 2110 at the i.sup.th column and
the i.sup.th row of the first predicted coding unit 2100, the value
f[i][j-1] of the second pixel 2112, and the value f[i-1][j] of the
third pixel 2111 have a relation of
f[i][j-1]>f[i-1][j]>f[i][j], in terms of block size. In this
case, the post-processor 1420 changes the value f[i][j] of the
first pixel 2110 to the median f[i-1][j] among the first to third
pixels 2110 to 2112.
In seventh to ninth exemplary embodiments, the post-processor 1420
produces a second predicted coding unit by using previous coding
units adjacent to a current coding unit, which have been encoded
and restored, rather than by using neighboring pixels of a pixel
that is to be changed.
Referring back to FIG. 21, in the seventh exemplary embodiment, the
post-processor 1420 changes the value of the first pixel 2110 to
f[i][j] by calculating an average of the value of the first pixel
2110 at the i.sup.th column and the j.sup.th row of the first
predicted coding unit 2100 and the value of the pixel 2121 that is
located at the same column as the first pixel 2110 and included in
a coding unit adjacent to the top of the current coding unit, as
shown in the following equation:
f[i][j]=(f[i][j]+f[-1][j]+1)>>1 (13), wherein f[-1][j]
denotes the value of the pixel 2121.
Similarly, in the eighth exemplary embodiment, the post-processor
1420 changes the value of the first pixel 2110 to f[i][j] by
calculating an average of the value of the first pixel 2110 at the
i.sup.th column and the j.sup.th row of the first predicted coding
unit 2100 and the value of the pixel 2122 that is located at the
same row as the first pixel 2110 and included in a coding unit
adjacent to the left side of the current coding unit, as shown in
the following equation: f[i][j]=(f[i][j]+f[j][-1]+1)>>1 (14),
wherein f[i][-1] denotes the value of the pixel 2122.
In the ninth exemplary embodiment, the post-processor 1420 changes
the value of the first pixel 2110 to f[i][j] by calculating a
weighted average of the values of the first pixel 2110 at the
i.sup.th column and the j.sup.th row of the first predicted coding
unit 2100, the pixel 2121 located at the same column as the first
pixel 2110 and included in a coding unit adjacent to the top of the
current coding unit, and the pixel 2122 located at the same row as
the first pixel 2110 and included in a coding unit adjacent to the
left side of the current coding unit, as shown in the following
equation:
f'[i][j]=((f[i][j]<<1)+f[j][-1]+f[i][j-1]+2)>>2
(15)
In a tenth exemplary embodiment, the post-processor 1420 changes
the value of the first pixel 2110 of the first predicted coding
unit 2100, which is to be changed, from f[i][j] to f[i][j] by using
one of the following equations. f'[i][j]=min(f[i][j]+i,255) (16)
f'[i][j]min(f[i][j]+j,255) (17) f'[i][j]=max(f[i][j]-i,0) (18)
f'[i][j]max(f[i][j]-j,0) (19)
In Equation (16), the pixel values of the first predicted coding
unit 2100 are changed to gradually increase from top to bottom, in
column units of the first predicted coding unit 2100. In Equation
(17), the pixel values of the first predicted coding unit 2100 are
changed to gradually increase in a right direction, in row units of
the first predicted coding unit 2100. In Equation (18), the pixel
values of the first predicted coding unit 2100 are changed to
gradually decrease from top to bottom, in column units of the first
predicted coding unit 2100. In Equation (19), the pixel values of
the first predicted coding unit 2100 are changed to gradually
decrease in the right direction, in row units of the first
predicted coding unit 2100.
In an eleventh exemplary embodiment, if the value of the first
pixel 2110, which is located at the i.sup.th column and the
j.sup.th row of the first predicted coding unit 2100 and is to be
changed, is f[i][j], the value of a pixel located at an upper
leftmost point of the first predicted coding unit 2100 is f[0][0],
the value of a pixel located at the j.sup.th column as the first
pixel 2110 and at the uppermost point of the first predicted coding
unit 2100 is f[0][j], the value of a pixel located at the i.sup.th
row as the first pixel 2110 and at the leftmost point of the first
predicted coding unit is f[i][0], and
G[i][j]=f[i][0]+f[0][j]-f[0][0], then the post-processor 1420
changes the value of the first pixel 2110 to f[i][j], as shown in
the following equation: f'[i][j]=(f[i][j]+G[i][j])/2 (20)
Equation (20) is based on a wave equation, in which the value of
each pixel in the first predicted coding unit 2100 is changed by
calculating the value G[i][j] by setting the values of a pixel on
the uppermost point of and a pixel on the leftmost point of the
first predicted coding unit 2100 to be boundary conditions so as to
smooth the value of each pixel in the first predicted coding unit
2100, and then calculating an average of the values G[i][j] and
f[i][j].
Also, if a value of a first pixel at an x.sup.th column and an
y.sup.th row of the first predicted coding unit, which is to be
changed, is f[x][y] and values of neighboring pixels located above,
below, and to the left and right sides of the first pixel are
f[x-1][y], f[x+1][y], f[x][y-1], and f[x][y+1], respectively, then
the post-processor 1420 may change the value of the first pixel to
f[x][y] by using one of the following shifting operations:
f[x,y]=(f[x,y]+f[x-1,y]+f[x,y-1]+f[x,y+1]+2)>>2
f[x,y]=(f[x,y]+f[x-1,y]+f[x,y-1]+f[x-1,y-1]+2)>>2
f[x,y]=(2*f[x,y]+f[x+1,y]+f[x,y-1]+2)>>2
f[x,y]=(2*f[x,y]+f[x-1,y]+f[x,y-1]+2)>>2
f[x,y]=(f[x,y]+f[x+1,y]+f[x,y+1]+f[x,y-1]+2)>>2
f[x,y]=(f[x,y]+f[x-1,y]+f[x,y+1]+f[x,y-1]+2)>>2
Also, the post-processor 1420 may produce a median by using the
first pixel and neighboring pixels of the first pixel, and change
the value of the first pixel by using the median. For example, the
value of the first pixel may be changed by setting a median t[x,y]
by using an equation: t
[x,y]=(2*f[x,y]+f[x-1,y]+f[x,y-1]+2)>>2, f[x,y]=t[x,y].
Similarly, the median t[x,y] between the first pixel and the
neighboring pixels may be calculated using an equation:
t[x,y]=median (f[x,y],f[x-1, y],f[x,y-1]), and may be determined as
a changed value of the first pixel.
Also, the post-processor 1420 may change the value of the first
pixel by using the following operation:
TABLE-US-00007 { t[x,y] = f[x,y] for (Int iter=0; iter<iterMax;
iter++) { laplacian[x,y] = (t[x,y]<<2) - t[x-1,y]- t[x+1,y]-
t[x,y-1]- t[x,y+1] t [x,y] =(.alpha.* t [x,y] + laplacian[x,y] )/
.alpha. } f[x,y] = t[x,y] }
Here, iterMax may be 5, and a may be 16.
Costs of bitstreams containing results of encoding second predicted
coding units produced using various post-processing modes according
to the above first through eleventh embodiments, respectively, are
compared to one another, and then, the post-processing mode having
the minimum cost is added to a header of a bitstream from among the
various post-processing modes. When the post-processing mode is
added to the bistream, it is possible to represent different
post-processing modes to be differentiated from one another by
using variable-length coding, in which a small number of bits are
assigned to a post-processing mode that is most frequently used,
based on a distribution of the post-processing mode determined
after encoding of a predetermined number of coding units is
completed. For example, if a post-processing mode according to the
first exemplary embodiment is an optimum operation leading to the
minimum cost of most coding units, a minimum number of bits are
assigned to an index indicating this post-processing mode so that
this post-processing mode may be differentiated from the other
post-processing modes.
When a coding unit is split to sub coding units and prediction is
performed in the sub coding units, a second predicted coding unit
may be produced by applying different post-processing modes to the
sub coding units, respectively, or by applying the same
post-processing mode to sub coding units belonging to the same
coding unit so as to simplify calculation and decrease an overhead
rate.
A rate-distortion optimization method may be used as a cost for
determining an optimum post-processing mode. Since a video encoding
method according to an exemplary embodiment is performed on an
intra predicted coding unit used as reference data for another
coding unit, a cost may be calculated by allocating a high weight
to a distortion, compared to the rate-distortion optimization
method. That is, in the rate-distortion optimization method, a cost
is calculated, based on a distortion that is the difference between
an encoded image and the original image and a bitrate generated, as
shown in the following equation: Cost=distortion+bit-rate (21)
In contrast, in a video encoding method according to an exemplary
embodiment, an optimum post-processing mode is determined by
allocating a high weight to a distortion, compared to the
rate-distortion optimization method, as shown in the following
equation: Cost=.alpha.*distortion+bit-rate (.alpha. denotes a real
number equal to or greater than 2) (22)
FIG. 23 is a flowchart illustrating a method of encoding video
according to an exemplary embodiment. Referring to FIG. 23, in
operation 2310, a first predicted coding unit of a current coding
unit that is to be encoded, is produced. The first predicted coding
unit is an intra predicted block produced by performing a general
intra prediction method, and one of various intra prediction modes
having various directionalities, which is determined by the size of
a coding unit.
In operation 2320, it is determined whether the current coding unit
has a portion located outside a boundary of a current picture. A
predetermined index MPI_PredMode may be produced according to the
determination result, in such a manner that post-processing for
producing a second predicted coding unit will not be performed when
the predetermined index MPI_PredMode is 0 and will be performed
when the predetermined index MPI_PredMode is 1.
If it is determined in operation 2320 that the current coding unit
does not have a portion located outside a boundary of the current
picture, then a second predicted coding unit is produced by
changing a value of each pixel of the first predicted coding unit
by using each pixel of the first predicted coding unit and at least
one neighboring pixel, in operation 2330. As described above in the
first through eleventh exemplary embodiments regarding an operation
of the post-processor 1420, a second predicted coding unit may be
produced by changing the value of each pixel in the first predicted
coding unit by performing one of various post-processing modes on a
pixel of the first predicted coding unit, which is to be changed,
and neighboring pixels thereof. Then, a residual block that is the
difference between the second predicted coding unit and the current
coding unit, is transformed, quantized, and entropy encoded so as
to generate a bitstream. Information regarding the post-processing
mode used to produce the second predicted coding unit may be added
to a predetermined region of the bitstream, so that a decoding
apparatus may reproduce the second predicted coding unit of the
current coding unit.
If it is determined in operation 2320 that the current coding unit
has a portion located outside a boundary of the current picture,
then, a second predicted coding unit is not produced, and the first
predicted coding unit is directly output as prediction information
regarding the current coding unit, in operation 2340. Then, a
residual block that is the difference between the first predicted
coding unit and the current coding unit, is transformed, quantized,
and entropy encoded so as to generate a bitstream.
FIG. 26 is a flowchart illustrating a method of decoding video
according to an exemplary embodiment. Referring to FIG. 26, in
operation 2610, information regarding a prediction mode related to
a current decoding unit that is to be decoded, is extracted from a
received bitstream.
In operation 2620, a first predicted decoding unit of the current
decoding unit is produced according to the extracted
information.
In operation 2630, it is determined whether the current decoding
unit has a portion located outside a boundary of a current picture.
A predetermined index MPI_PredMode may be produced according to the
determination result, in such a manner that post-processing for
producing a second predicted decoding unit will not be performed
when the predetermined index MPI_PredMode is 0 and will be
performed when the predetermined index MPI_PredMode is 1.
If it is determined in operation 2630 that the current decoding
unit does not have a portion located outside a boundary of the
current picture, a second predicted decoding unit is produced by
changing a value of each pixel of the first predicted decoding unit
by using each pixel of the first predicted decoding unit and
neighboring pixels of each pixel, in operation 2640. As described
above in the first through eleventh exemplary embodiments regarding
an operation of the post-processor 1420, a second predicted coding
unit may be produced by changing the value of each pixel of the
first predicted coding unit by using performing one of various
post-processing modes on a pixel of the first predicted coding
unit, which is to be changed, and neighboring pixels thereof.
If it is determined in operation 2630 that that the current
decoding unit has a portion located outside a boundary of the
current picture, post-processing for producing a second predicted
decoding unit is not performed and the first predicted decoding
unit is directly output as prediction information regarding the
current decoding unit, in operation 2650. The first predicted
decoding unit is combined with a residual block of the current
decoding unit, which is extracted from the bitstream, so as to
reproduce the current decoding unit.
An exemplary embodiment can also be embodied as computer readable
code on a computer readable recording medium. The computer readable
recording medium is any data storage device that can store data
which can be thereafter read by a computer system. Examples of the
computer readable recording medium include read-only memory (ROM),
random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks,
and optical data storage devices. The computer readable recording
medium can also be distributed over network coupled computer
systems so that the computer readable code is stored and executed
in a distributed fashion.
Exemplary embodiments can also be implemented as computer
processors and hardware devices.
While exemplary embodiments have been particularly shown and
described above, it will be understood by one of ordinary skill in
the art that various changes in form and details may be made
therein without departing from the spirit and scope of the
inventive concept as defined by the following claims. The exemplary
embodiments should be considered in a descriptive sense only and
not for purposes of limitation. Therefore, the scope of the
inventive concept is defined not by the detailed description of
exemplary embodiments but by the following claims, and all
differences within the scope will be construed as being included in
the present inventive concept.
* * * * *