U.S. patent application number 14/569752 was filed with the patent office on 2015-04-09 for method and apparatus of deriving intra prediction mode using most probable mode group.
The applicant listed for this patent is INFOBRIDGE PTE. LTD.. Invention is credited to Soo Mi OH, Moonock YANG.
Application Number | 20150098500 14/569752 |
Document ID | / |
Family ID | 48191356 |
Filed Date | 2015-04-09 |
United States Patent
Application |
20150098500 |
Kind Code |
A1 |
OH; Soo Mi ; et al. |
April 9, 2015 |
METHOD AND APPARATUS OF DERIVING INTRA PREDICTION MODE USING MOST
PROBABLE MODE GROUP
Abstract
Provided is a method that constructs an MPM group including
three intra prediction modes, determines the intra prediction mode
of the MPM group specified by the prediction mode index as the
intra prediction mode of the current prediction unit if the mode
group indicator indicates the MPM group, and derives the intra
prediction mode of the current prediction unit using the prediction
mode index and the three prediction modes of the MPM group if the
mode group indicator does not indicate the MPM group. Accordingly,
additional bits resulted from increase of a number of intra
prediction mode are effectively reduced. Also, an image compression
ratio can be improved by generating a prediction block similar to
an original block.
Inventors: |
OH; Soo Mi; (Seongnam-si,
KR) ; YANG; Moonock; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INFOBRIDGE PTE. LTD. |
Singapore |
|
SG |
|
|
Family ID: |
48191356 |
Appl. No.: |
14/569752 |
Filed: |
December 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14349985 |
Apr 4, 2014 |
8948259 |
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PCT/CN2012/083972 |
Nov 2, 2012 |
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14569752 |
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Current U.S.
Class: |
375/240.02 |
Current CPC
Class: |
H04N 19/122 20141101;
H04N 19/176 20141101; H04N 19/593 20141101; H04N 19/172 20141101;
H04N 19/129 20141101; H04N 19/86 20141101; H04N 19/46 20141101;
H04N 19/117 20141101; H04N 19/91 20141101; H04N 19/44 20141101;
H04N 19/625 20141101; H04N 19/157 20141101; H04N 19/124 20141101;
H04N 19/61 20141101; H04N 19/159 20141101; H04N 19/463 20141101;
H04N 19/103 20141101; H04N 19/11 20141101 |
Class at
Publication: |
375/240.02 |
International
Class: |
H04N 19/11 20060101
H04N019/11 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2011 |
KR |
10-2011-0114606 |
Claims
1. An apparatus for generating a prediction block, comprising: an
entropy decoding unit for entropy-decoding a mode group indicator
and a prediction mode index; an intra prediction mode decoding unit
for constructing a Most Probable Mode (MPM) group including three
intra prediction modes using a left intra prediction mode and an
above intra prediction mode of a current prediction unit, and
deriving an intra prediction mode of the current prediction unit
using the mode group indicator and the prediction mode index; a
reference pixel filtering unit for adaptively filtering reference
pixels of a current block according to a size of a transform unit
and the intra prediction mode; and a prediction block generating
unit for generating the prediction block according to the intra
prediction mode, wherein if the mode group indicator indicates the
MPM group, the intra prediction mode decoding unit determines an
intra prediction mode of the MPM group specified by the prediction
mode index as the intra prediction mode of the current prediction
unit, and if the mode group indicator does not indicate the MPM
group, the intra prediction mode decoding unit derives the intra
prediction mode of the current prediction unit by performing
ordered steps of: increasing a value of the prediction mode index
by one if the prediction mode index is equal to or greater than a
first candidate of the MPM group; increasing the value of the
prediction mode index by one if the prediction mode index is equal
to or greater than a second candidate of the MPM group; increasing
the value of the prediction index if the prediction mode index is
equal to or greater than a third candidate of the MPM group; and
determining the value of the prediction mode index as the mode
number of the intra prediction mode of the current prediction
unit.
2. The apparatus of claim 1, wherein the first candidate is an
intra prediction mode having lowest mode number, the second
candidate is an intra prediction mode having middle mode number and
the third candidate is an intra prediction mode having highest mode
number.
3. The apparatus of claim 1, wherein the three intra prediction
modes are reordered in the order of mode number to determine the
first candidate, the second candidate and the third candidate.
4. The apparatus of claim 1, wherein when the left intra prediction
mode is not equal to the above intra prediction mode and at least
one of the left intra prediction mode and the above intra
prediction mode is a non-directional intra prediction mode, the MPM
group includes both the non-directional intra prediction modes.
5. The apparatus of claim 4, wherein when the left intra prediction
mode and the above intra prediction mode are non-directional intra
prediction modes, the MPM group includes both the non-directional
intra prediction modes and a vertical mode.
6. The apparatus of claim 1, wherein a size of the current block is
equal to the size of a transform unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of the U.S. patent
application Ser. No. 14/349,985, filed on Apr. 4, 2014, which is a
371 of international Patent Application No. PCT/CN2012/083972,
filed on Nov. 2, 2012, which claims priority to Korean Patent
Application 10-2011-0114606, filed on Nov. 4, 2011, which are
incorporated by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method and an apparatus
of deriving an intra prediction mode, and more particularly, to a
method of constructing an MPM group using neighboring intra
prediction modes and deriving the intra prediction mode using the
MPM group and intra prediction information.
BACKGROUND ART
[0003] In image compression methods such as MPEG-1, MPEG-2, MPEG-4
and H.264/MPEG-4 AVC, one picture is divided into macroblocks to
encode an image. Then, the respective macroblocks are encoded using
inter prediction or intra prediction.
[0004] In intra prediction, a current block of the picture is
encoded not using a reference picture, but using values of
reconstructed pixels spatially adjacent to the current block. An
optimal prediction mode with little distortion is selected out of a
plurality of intra prediction modes by comparing a prediction block
generated using the adjacent pixel values with an original block.
Then, using the selected intra prediction mode and the adjacent
pixel values, prediction values of the current block are
calculated. Differences between the prediction values and pixels
values of the original current block are calculated and then
encoded through transform coding, quantization and entropy coding.
The intra prediction mode is also encoded.
[0005] According to H.264 standard, there are nine modes in
4.times.4 intra prediction. The nine modes are a vertical mode, a
horizontal mode, a DC mode, a diagonal down-left mode, a diagonal
down-right mode, a vertical right mode, a vertical left mode, a
horizontal-up mode and a horizontal-down mode. One mode is selected
among the nine modes to generate a prediction block of the current
block, the mode information is transmitted to the decoder.
[0006] In HEVC standard under development, the number of intra
prediction modes increases to 18 or 35, the size of coding unit
lies between 8.times.8 and 128.times.128. The coding unit has
similar purpose to the macroblock of H.264/AVC.
[0007] Accordingly, if the intra prediction mode is encoded using
the same method of H.264/AVC, the coding efficiency deteriorates
because the number of intra prediction modes is greater than that
of H.264/AVC. Also, as the size of the coding unit increases and
the number of intra prediction modes increases, quantization method
and scanning method should be modified to enhance the coding
efficiency.
DISCLOSURE
Technical Problem
[0008] The present invention is directed to a method and apparatus
of constructing an MPM group using neighboring intra prediction
modes and deriving the intra prediction mode using the MPM group
and intra prediction information.
Technical Solution
[0009] One aspect of the present invention provides a method of
deriving an intra prediction mode of a current prediction unit,
comprising: entropy-decoding a mode group indicator and a
prediction mode index, constructing an MPM group including three
intra prediction modes, determining whether the mode group
indicator indicates the MPM group or not, determining an intra
prediction mode of the MPM group specified by the prediction mode
index as the intra prediction mode of the current prediction unit
if the mode group indicator indicates the MPM group, and deriving
the intra prediction mode of the current prediction unit using the
prediction mode index and the three prediction modes of the MPM
group if the mode group indicator does not indicate the MPM
group.
Advantageous Effects
[0010] A method according to the present invention constructs an
MPM group including three intra prediction modes, determines the
intra prediction mode of the MPM group specified by the prediction
mode index as the intra prediction mode of the current prediction
unit if the mode group indicator indicates the MPM group, and
derives the intra prediction mode of the current prediction unit
using the prediction mode index and the three prediction modes of
the MPM group if the mode group indicator does not indicate the MPM
group. Therefore, coding efficiency of intra prediction mode is
improved by encoding the intra prediction mode of the current block
using a plurality of most probable candidates. Also, coding
efficiency of intra prediction mode is improved by generating the
prediction block very similar to an original block and by
minimizing the amount of bits required to encode the residual
block.
DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a block diagram of an image coding apparatus
according to the present invention.
[0012] FIG. 2 is a conceptual diagram illustrating intra prediction
modes according to the present invention.
[0013] FIG. 3 is a block diagram of an image decoding apparatus
according to the present invention.
[0014] FIG. 4 is a flow chart illustrating a method of generating a
prediction block in intra prediction according to the present
invention.
[0015] FIG. 5 is a flow chart illustrating a procedure of restoring
intra prediction mode according to the present invention.
[0016] FIG. 6 is a conceptual diagram illustrating positions of
reference pixels of a current block according to the present
invention.
[0017] FIG. 7 is a block diagram illustrating an apparatus of
generating a prediction block in intra prediction according to the
present invention.
MODE FOR INVENTION
[0018] Hereinafter, various embodiments of the present invention
will be described in detail with reference to the accompanying
drawings. However, the present invention is not limited to the
exemplary embodiments disclosed below, but can be implemented in
various types. Therefore, many other modifications and variations
of the present invention are possible, and it is to be understood
that within the scope of the disclosed concept, the present
invention may be practiced otherwise than as has been specifically
described.
[0019] FIG. 1 is a block diagram of an image coding apparatus 100
according to the present invention.
[0020] Referring to FIG. 1, the image coding apparatus 100
according to the present invention includes a picture division unit
101, a transform unit 103, a quantization unit 104, a scanning unit
105, an entropy coding unit 106, an inverse quantization unit 107,
an inverse transform unit 108, a post-processing unit 110, a
picture storing unit 111, an intra prediction unit 112, an inter
prediction unit 113, a subtracter 102 and an adder 109.
[0021] The picture division unit 101 divides a picture or a slice
into a plurality of largest coding units (LCUs), and divides each
LCU into one or more coding units. The picture division unit 101
determines prediction mode of each coding unit and a size of
prediction unit and a size of transform unit.
[0022] An LCU includes one or more coding units. The LCU has a
recursive quad tree structure to specify a division structure.
Information specifying the maximum size and the minimum size of the
coding unit is included in a sequence parameter set. The division
structure is specified by one or more split coding unit flags
(split_cu_flags). The coding unit has a size of 2N.times.2N.
[0023] A coding unit includes one or more prediction units. In
intra prediction, the size of the prediction unit is 2N.times.2N or
N.times.N. In inter prediction, the size of the prediction unit is
2N.times.2N, 2N.times.N, N.times.2N or N.times.N. When the
prediction unit is an asymmetric partition in inter prediction, the
size of the prediction unit may also be one of hN.times.2N,
(2-h)N.times.2N, 2N.times.hN and 2N.times.(2-h)N. The value of h is
1/2.
[0024] A coding unit includes one or more transform units. The
transform unit has a recursive quad tree structure to specify a
division structure. The division structure is specified by one or
more split transform unit flags (split_tu_flags). Information
specifying the maximum size and the minimum size of the transform
unit is included in a sequence parameter set.
[0025] The intra prediction unit 112 determines an intra prediction
mode of a current prediction unit and generates one or more
prediction blocks using the intra prediction mode. The prediction
block has the same size of the transform unit. The intra prediction
unit 112 generates reference pixels if there are unavailable
reference pixels of a current block, filters adaptively the
reference pixels of the current block according to the size of the
current block and the intra prediction mode, and generates a
prediction block of the current block. The current block has the
same size of the prediction block.
[0026] FIG. 2 is a conceptual diagram illustrating intra prediction
modes according to the present invention. As shown in FIG. 2, the
number of intra prediction modes is 35. The DC mode and the planar
mode are non-directional intra prediction modes and the others are
directional intra prediction modes.
[0027] The inter prediction unit 113 determines motion information
of the current prediction unit using one or more reference pictures
stored in the picture storing unit 111, and generates a prediction
block of the prediction unit. The motion information includes one
or more reference picture indexes indicating the reference pictures
and one or more motion vectors.
[0028] The transform unit 103 transforms residual signals generated
using an original block and a prediction block to generate a
transformed block. The residual signals are transformed in
transform units. A transform type is determined by the prediction
mode and the size of the transform unit. The transform type is a
DCT-based integer transform or a DST-based integer transform.
[0029] The quantization unit 104 determines a quantization
parameter for quantizing the transformed block. The quantization
parameter is a quantization step size. The quantization parameter
is determined per quantization unit having a size equal to or
larger than a reference size. A quantization unit of the reference
size is referred to as a minimum quantization unit. If the size of
the coding unit is equal to or larger than the reference size, the
coding unit becomes the quantization unit. A plurality of coding
unit may be included in the minimum quantization unit. The
reference size is one of allowable sizes of the coding unit. The
reference size is determined per a picture and included in the
picture parameter set.
[0030] The quantization unit 104 generates a quantization parameter
predictor and generates a differential quantization parameter by
subtracting the quantization parameter predictor from the
quantization parameter. The differential quantization parameter is
encoded and transmitted to the decoder. If there are no residual
signals to be transmitted in the coding unit, the differential
quantization parameter of the coding unit may not be
transmitted.
[0031] The quantization parameter predictor is generated by using
quantization parameters of neighboring coding units and/or a
quantization parameter of previous coding unit.
[0032] The quantization unit 104 sequentially retrieves a left
quantization parameter, an above quantization parameter and a
previous quantization parameter in this order. An average of the
first two available quantization parameters retrieved in that order
is set as the quantization parameter predictor when at least two
quantization parameters are available. When only one quantization
parameter is available, the available quantization parameter is set
as the quantization parameter predictor. The left quantization
parameter is a quantization parameter of the left neighboring
coding unit. The above quantization parameter is a quantization
parameter of the above neighboring coding unit. The previous
quantization parameter is a quantization parameter of a previous
coding unit in coding order.
[0033] The quantization unit 104 quantizes the transformed block
using a quantization matrix and the quantization parameter to
generate a quantized block. The quantized block is provided to the
inverse quantization unit 107 and the scanning unit 105.
[0034] The scanning unit 105 determines a scan pattern and applies
the scan pattern to the quantized block. When CABAC (Context
adaptive binary arithmetic coding) is used for entropy coding, the
scan pattern is determined as follows.
[0035] In intra prediction, the scan pattern is determined by the
intra prediction mode and the size of the transform unit. The scan
pattern is selected among a diagonal scan, a vertical scan and a
horizontal scan. The quantized transform coefficients of the
quantized block are divided into significant coefficients, sign
flags and levels. The scan pattern is applied to the significant
coefficients, sign flags and levels respectively.
[0036] When the size of the transform unit is equal to or smaller
than a first size, the horizontal scan is selected for the vertical
mode and a predetermined number of neighboring intra prediction
modes of the vertical mode, the vertical scan is selected for the
horizontal mode and the predetermined number of neighboring intra
prediction modes of the horizontal mode, and the diagonal scan is
selected for the other intra prediction modes. The first size is
8.times.8.
[0037] When the size of the transform unit is larger than the first
size, the diagonal scan is selected for all intra prediction
modes.
[0038] In inter prediction, a predetermined scan pattern is used.
The predetermined scan pattern is the diagonal scan.
[0039] When the size of the transform unit is larger than a second
size, the quantized block is divided into a plurality of subsets
and scanned. The second size is 4.times.4. The scan pattern for
scanning the subsets is the same as the scan pattern for scanning
quantized transform coefficients of each subset. The quantized
transform coefficients of each subset are scanned in the reverse
direction. The subsets are also scanned in the reverse
direction.
[0040] Last non-zero position is encoded and transmitted to the
decoder. The last non-zero position specifies position of last
non-zero quantized transform coefficient within the transform
unit.
[0041] Non-zero subset flags are determined and encoded. The
non-zero subset flag indicates whether the subset contains non-zero
coefficients or not. The non-zero subset flag is not defined for a
subset covering a DC coefficient and a subset covering last
non-zero coefficient.
[0042] The inverse quantization unit 107 inversely quantizes the
quantized transform coefficients of the quantized block.
[0043] The inverse transform unit 108 inversely transforms the
inverse quantized block to generate residual signals of the spatial
domain.
[0044] The adder 109 generates a reconstructed block by adding the
residual block and the prediction block.
[0045] The post-processing unit 110 performs a deblocking filtering
process for removing blocking artifact generated in a reconstructed
picture.
[0046] The picture storing unit 111 receives post-processed image
from the post-processing unit 110, and stores the image in picture
units. A picture may be a frame or a field.
[0047] The entropy coding unit 106 entropy-codes the
one-dimensional coefficient information received from the scanning
unit 105, intra prediction information received from the intra
prediction unit 112, motion information received from the inter
prediction unit 113, and so on.
[0048] FIG. 3 is a block diagram of an image decoding apparatus 200
according to the present invention.
[0049] The image decoding apparatus 200 according to the present
invention includes an entropy decoding unit 201, an inverse
scanning unit 202, an inverse quantization unit 203, an inverse
transform unit 204, an adder 205, a post processing unit 206, a
picture storing unit 207, an intra prediction unit 208 and an inter
prediction unit 209.
[0050] The entropy decoding unit 201 extracts the intra prediction
information, the inter prediction information and the
one-dimensional coefficient information from a received bit stream.
The entropy decoding unit 201 transmits the inter prediction
information to the inter prediction unit 209, the intra prediction
information to the intra prediction unit 208 and the coefficient
information to the inverse scanning unit 202.
[0051] The inverse scanning unit 202 uses an inverse scan pattern
to generate two dimensional quantized block. It is supposed that
CABAC is used as entropy coding method. The inverse scan pattern is
one of the diagonal scan, the vertical scan and the horizontal
scan.
[0052] In intra prediction, the inverse scan pattern is determined
by the intra prediction mode and the size of the transform unit.
The inverse scan pattern is selected among the diagonal scan, the
vertical scan and the horizontal scan. The selected inverse scan
pattern is applied to the significant coefficients, the sign flags
and the levels respectively generate the quantized block.
[0053] When the size of the transform unit is equal to or smaller
than the first size, the horizontal scan is selected for the
vertical mode and a predetermined number of neighboring intra
prediction modes of the vertical mode, the vertical scan is
selected for the horizontal mode and the predetermined number of
neighboring intra prediction modes of the horizontal mode, and the
diagonal scan is selected for the other intra prediction modes. The
first size is 8.times.8.
[0054] When the size of the transform unit is larger than the first
size, the diagonal scan is selected for all intra prediction
modes.
[0055] In inter prediction, the diagonal scan is used.
[0056] When the size of the transform unit is larger than the
second size, the significant coefficients, the sign flags and the
levels are inversely scanned in the unit of the subset to generate
subsets. And the subsets are inversely scanned to generate the
quantized block. The second size is 4.times.4.
[0057] The inverse scan pattern used for generating each subset is
the same as the inverse scan pattern used for generating the
quantized block. The significant coefficients, the sign flags and
the levels are scanned in the reverse direction. The subsets are
also scanned in the reverse direction.
[0058] The last non-zero position and the non-zero subset flags are
received from the encoder. The last non-zero position is used to
determine the number of subsets to be generated. The non-zero
subset flags are used to determine the subsets to be generated by
applying the inverse scan pattern. The subset covering the DC
coefficient and the subset covering the last non-zero coefficient
are generated using the inverse scan pattern because the non-zero
subset flags for a subset covering a DC coefficient and a subset
covering last non-zero coefficient are not transmitted.
[0059] The inverse quantization unit 203 receives the differential
quantization parameter from the entropy decoding unit 201 and
generates the quantization parameter predictor. The quantization
parameter predictor is generated through the same operation of the
quantization unit 104 of FIG. 1. Then, the inverse quantization
unit 203 adds the differential quantization parameter and the
quantization parameter predictor to generate the quantization
parameter of the current coding unit. If the current coding unit is
equal to or larger than the minimum quantization unit and the
differential quantization parameter for the current coding unit is
not received from the encoder, the differential quantization
parameter is set to 0.
[0060] The inverse quantization unit 203 inversely quantizes the
quantized block.
[0061] The inverse transform unit 204 inversely transforms the
inversely quantized block to restore a residual block. The inverse
transform type is adaptively determined according to the prediction
mode and the size of the transform unit. The inverse transform type
is the DCT-based integer transform or the DST-based integer
transform.
[0062] The intra prediction unit 208 restores the intra prediction
mode of the current prediction unit using the received intra
prediction information, and generates a prediction block according
to the restored intra prediction mode. The prediction block has the
same size of the transform unit. The intra prediction unit 250
generates reference pixels if there are unavailable reference
pixels of the current block, and filters adaptively the reference
pixels of the current block according to the size of the current
block and the intra prediction mode. The current block has the same
size of the transform unit.
[0063] The inter prediction unit 209 restores the motion
information of the current prediction unit using the received inter
prediction information, and generates a prediction block using the
motion information.
[0064] The post-processing unit 206 operates the same as the
post-processing unit 110 of FIG. 1.
[0065] The picture storing unit 207 receives post-processed image
from the post-processing unit 206, and stores the image in picture
units. A picture may be a frame or a field.
[0066] The adder 205 adds the restored residual block and a
prediction block to generate a reconstructed block.
[0067] FIG. 4 is a flow chart illustrating a method of generating a
prediction block in intra prediction according to the present
invention.
[0068] Intra prediction information of the current prediction unit
is entropy-decoded (S110).
[0069] The intra prediction information includes a mode group
indicator and a prediction mode index. The mode group indicator is
a flag indicating whether the intra prediction mode of the current
prediction unit belongs to a most probable mode group (MPM group).
If the flag is 1, the intra prediction unit of the current
prediction unit belongs to the MPM group. If the flag is 0, the
intra prediction unit of the current prediction unit belongs to a
residual mode group. The residual mode group includes all intra
prediction modes other than the intra prediction modes belonging to
the MPM group. The prediction mode index specifies the intra
prediction mode of the current prediction unit within the group
specified by the mode group indicator.
[0070] The intra prediction mode of the current prediction unit is
derived using the intra prediction information (S120).
[0071] FIG. 5 is a flow chart illustrating a procedure of deriving
intra prediction mode according to the present invention. The intra
prediction mode of the current prediction unit is derived using the
following ordered steps.
[0072] The MPM group is constructed using intra prediction modes of
the neighboring prediction units (S121). The intra prediction modes
of the MPM group are adaptively determined by a left intra
prediction mode and an above intra prediction mode. The left intra
prediction mode is the intra prediction mode of the left
neighboring prediction unit, and the above intra prediction mode is
the intra prediction mode of the above neighboring prediction unit.
The MPM group is comprised of three intra prediction modes.
[0073] If the left or above neighboring prediction unit does not
exist, the intra prediction mode of the left or above neighboring
unit is set as unavailable. For example, if the current prediction
unit is located at the left or upper boundary of a picture, the
left or above neighboring prediction unit does not exist. If the
left or above neighboring unit is located within other slice or
other tile, the intra prediction mode of the left or above
neighboring unit is set as unavailable. If the left or above
neighboring unit is inter-coded, the intra prediction mode of the
left or above neighboring unit is set as unavailable. If the above
neighboring unit is located within other LCU, the intra prediction
mode of the left or above neighboring unit may be set as
unavailable.
[0074] When both of the left intra prediction mode and the above
intra prediction mode are available and are different each other,
the left intra prediction mode and the above intra prediction mode
are included in the MPM group and one additional intra prediction
mode is added to the MPM group. Index 0 is assigned to one intra
prediction mode of small mode number and index 1 is assigned to the
other. Alternatively, index 0 may be assigned to the left intra
prediction mode and index 1 may be assigned to the above intra
prediction mode. The additional intra prediction mode is determined
by the left and above intra prediction modes as follows.
[0075] If one of the left and above intra prediction modes is a
non-directional mode and the other is a directional mode, the other
non-directional mode is added to the MPM group. For example, if the
one of the left and above intra prediction modes is the DC mode,
the planar mode is added to the MPM group. If the one of the left
and above intra prediction modes is the planar mode, the DC mode is
added to the MPM group. If both of the left and above intra
prediction modes are non-directional modes, the vertical mode is
added to the MPM group. If both of the left and above intra
prediction modes are directional modes, the DC mode or the planar
mode is added to the MPM group.
[0076] When only one of the left intra prediction mode and the
above intra prediction mode is available, the available intra
prediction mode is included in the MPM group and two additional
intra prediction modes are added to the MPM group. The added two
intra prediction modes are determined by the available intra
prediction modes as follows.
[0077] If the available intra prediction mode is a non-directional
mode, the other non-directional mode and the vertical mode are
added to the MPM group. For example, if the available intra
prediction mode is the DC mode, the planar mode and the vertical
mode are added to the MPM group. If the available intra prediction
mode is the planar mode, the DC mode and the vertical mode are
added to the MPM group. If the available intra prediction mode is a
directional mode, two non-directional modes (DC mode and planar
mode) are added to the MPM group.
[0078] When both of the left intra prediction mode and the above
intra prediction mode are available and are same each other, the
available intra prediction mode is included in the MPM group and
two additional intra prediction modes are added to the MPM group.
The added two intra prediction modes are determined by the
available intra prediction modes as follows.
[0079] If the available intra prediction mode is a directional
mode, two neighboring directional modes are added to the MPM group.
For example, if the available intra prediction mode is the mode 23,
the left neighboring mode (mode 1) and the right neighboring mode
(mode 13) are added to the MPM group. If the available intra
prediction mode is the mode 30, the two neighboring modes (mode 2
and mode 16) are added to the MPM group. If the available intra
prediction mode is a non-directional mode, the other
non-directional mode and the vertical mode are added to the MPM
group. For example, if the available intra prediction mode is the
DC mode, the planar mode and the vertical mode are added to the MPM
group.
[0080] When both of the left intra prediction mode and the above
intra prediction mode are unavailable, three additional intra
prediction modes are added to the MPM group. The three intra
prediction modes are the DC mode, the planar mode and the vertical
mode. Indexes 0, 1 and 2 are assigned to the three intra prediction
modes in the order of the DC mode, the planar mode and the vertical
mode or in the order of the planar mode, the DC mode and the
vertical mode.
[0081] It is determined whether the mode group indicator indicates
the MPM group (S122).
[0082] If the mode group indicator indicates the MPM group, the
intra prediction of the MPM group specified by the prediction mode
index is determined as the intra prediction mode of the current
prediction unit (S123).
[0083] If the mode group indicator does not indicate the MPM group,
the intra prediction of the residual mode group specified by the
prediction mode index is determined as the intra prediction mode of
the current prediction unit (S124). The intra prediction mode of
the current unit is derived using the prediction mode index and the
intra prediction modes of the MPM group as the following ordered
steps.
[0084] 1) The three intra prediction modes of the MPM group are
reordered in the mode number order. The intra prediction mode with
lowest mode number is set to a first candidate. The intra
prediction mode with middle mode number is set to a second
candidate. The intra prediction mode with highest mode number is
set to a third candidate.
[0085] 2) The prediction mode index is compared with the first
candidate. If the prediction mode index is equal to or greater than
the first candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0086] 3) The prediction mode index is compared with the second
candidate. If the prediction mode index is equal to or greater than
the second candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0087] 4) The prediction mode index is compared with the third
candidate. If the prediction mode index is equal to or greater than
the third candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0088] 5) The value of the final prediction mode index is set as
the mode number of the intra prediction mode of the current
prediction unit.
[0089] A size of the prediction block is determined based on the
transform size information specifying the size of the transform
unit (S130). The transform size infomation may be one or more
split_transform_flags specifying the size of the transform
unit.
[0090] If the size of the transform unit is equal to the size of
the current prediction unit, the size of the prediction block is
equal to the size of the current prediction unit.
[0091] If the size of the transform unit is smaller than the size
of the current prediction unit, the size of the prediction block is
equal to the size of the transform unit. In this case, a process of
generating a reconstructed block is performed on each sub-block of
the current prediction unit. That is, a prediction block and a
residual block of a current sub-block are generated and a
reconstructed block of each sub-block is generated by adding the
prediction block and the residual block. Then, a prediction block,
a residual block and a reconstructed block of the next sub-block in
decoding order are generated. The restored intra prediction mode is
used to generate all prediction blocks of all sub-block. Some
pixels of the reconstructed block of the current sub-block are used
as reference pixels of the next sub-block. Therefore, it is
possible to generate a prediction block which is more similar to
the original sub-block.
[0092] Next, it is determined whether all reference pixels of the
current block are available, and reference pixels are generated if
one or more reference pixels are unavailable (S140). The current
block is the current prediction unit or the current sub-block. The
size of the current block is the size of the transform unit.
[0093] FIG. 6 is a conceptual diagram illustrating the positions of
reference pixels of the current block according to the present
invention. As shown in FIG. 6, the reference pixels of the current
block are comprised of above reference pixels located at (x=0, . .
. , 2N-1, y=-1), left reference pixels located at (x=1-, y=0, . . .
, 2M-1) and a corner pixel located at (x=-1, y=-1). N is the width
of the current block and M is the height of the current block.
[0094] If reconstructed pixels do not exist at corresponding
positions or reconstructed pixels are located within another slice,
the reference pixels are set as unavailable. In constrained intra
prediction mode (CIP mode), the reconstructed pixels of inter mode
are also set as unavailable.
[0095] If one or more reference pixels are unavailable, one or more
reference pixels are generated for the one or more unavailable
reference pixels as follows.
[0096] If all reference pixels are unavailable, the value of
2.sup.L-1 is substituted for the values of all the reference
pixels. The value of L is the number of bits used to represent
luminance pixel value.
[0097] If available reference pixels are located at only one side
of the unavailable reference pixel, the value of the reference
pixel nearest to the unavailable pixel is substituted for the
unavailable reference pixel.
[0098] If available reference pixels are located at both sides of
the unavailable reference pixel, the average value of the reference
pixels nearest to the unavailable pixel in each side or the value
of the reference pixel nearest to the unavailable pixel in a
predetermined direction is substituted for each unavailable
reference pixel.
[0099] Next, the reference pixels are adaptively filtered based on
the intra prediction mode and the size of the current block (S150).
The size of the current block is the size of the transform
unit.
[0100] In the DC mode, the reference pixels are not filtered. In
the vertical mode and the horizontal mode, the reference pixels are
not filtered. In the directional modes other than the vertical and
horizontal modes, the reference pixels are adaptively according to
the size of the current block.
[0101] If the size of the current is 4.times.4, the reference
pixels are not filtered in all intra prediction modes. For the size
8.times.8, 16.times.16 and 32.times.32, the number of intra
prediction mode where the reference pixels are filtered increases
as the size of the current block becomes larger. For example, the
reference pixels are not filtered in the vertical mode and a
predetermined number of neighboring intra prediction mode of the
vertical mode. The reference pixels are also not filtered in the
horizontal mode and the predetermined number of neighboring intra
prediction mode of the horizontal mode. The predetermined number
lies between 0 to 7 and decreases as the size of the current block
is larger.
[0102] Next, a prediction block of the current block is generated
using the reference pixels according to the restored intra
prediction mode (S160).
[0103] In the DC mode, the prediction pixels of the prediction
block are generated by averaging the N reference pixels located at
(x=0, . . . N-1, y=-1) and the M reference pixels located at (x=-1,
y=0, . . . M-1). Then, the prediction pixel adjacent to the
reference pixel is filtered using one or two adjacent reference
pixels.
[0104] In the vertical mode, the prediction pixels of the
prediction block are generated by copying the value of the
corresponding vertical reference pixel. Then, the prediction pixels
which are adjacent to the left reference pixel are filtered by the
left neighboring reference pixel and the corner pixel.
[0105] In the horizontal mode, the prediction pixels of the
prediction block are generated by copying the value of the
corresponding horizontal reference pixel. Then, the prediction
pixels which are adjacent to the above reference pixel are filtered
by the above neighboring reference pixel and the corner pixel.
[0106] FIG. 7 is a block diagram illustrating an apparatus 300 of
generating a prediction block in intra prediction according to the
present invention.
[0107] The apparatus 300 according to the present invention
includes a parsing unit 310, a prediction mode decoding unit 320, a
prediction size determining unit 330, a reference availability
checking unit 340, a reference pixel generating unit 350, a
reference pixel filtering unit 360 and a prediction block
generating unit 370.
[0108] The parsing unit 310 restores the intra prediction
information of the current prediction unit from the bit stream.
[0109] The intra prediction information includes a mode group
indicator and a prediction mode index. The mode group indicator is
a flag indicating whether the intra prediction mode of the current
prediction unit belongs to a most probable mode group (MPM group).
If the flag is 1, the intra prediction unit of the current
prediction unit belongs to the MPM group. If the flag is 0, the
intra prediction unit of the current prediction unit belongs to a
residual mode group. The residual mode group includes all intra
prediction modes other than the intra prediction modes belonging to
the MPM group. The prediction mode index specifies the intra
prediction mode of the current prediction unit within the group
specified by the mode group indicator.
[0110] The prediction mode decoding unit 320 includes a MPM group
constructing unit 321 and a prediction mode restoring unit 322.
[0111] The MPM group constructing unit 321 constructs the MPM group
of the current prediction unit. The MPM group is constructed using
intra prediction modes of the neighboring prediction units. The
intra prediction modes of the MPM group are adaptively determined
by a left intra prediction mode and an above intra prediction mode.
The left intra prediction mode is the intra prediction mode of the
left neighboring prediction unit, and the above intra prediction
mode is the intra prediction mode of the above neighboring
prediction unit. The MPM group is comprised of three intra
prediction modes.
[0112] The MPM group constructing unit 321 checks the availability
of the left intra prediction mode and the above intra prediction
mode. If the left or above neighboring prediction unit does not
exist, the intra prediction mode of the left or above neighboring
unit is set as unavailable. For example, if the current prediction
unit is located at the left or upper boundary of a picture, the
left or above neighboring prediction unit does not exist. If the
left or above neighboring unit is located within other slice or
other tile, the intra prediction mode of the left or above
neighboring unit is set as unavailable. If the left or above
neighboring unit is inter-coded, the intra prediction mode of the
left or above neighboring unit is set as unavailable. If the above
neighboring unit is located within other LCU, the intra prediction
mode of the left or above neighboring unit is set as
unavailable.
[0113] The MPM group constructing unit 321 constructs the MPM group
as follows.
[0114] When both of the left intra prediction mode and the above
intra prediction mode are available and are different each other,
the left intra prediction mode and the above intra prediction mode
are included in the MPM group and one additional intra prediction
mode is added to the MPM group. Index 0 is assigned to one intra
prediction mode of small mode number and index 1 is assigned to the
other. Or index 0 is assigned to the left intra prediction mode and
index 1 is assigned to the above intra prediction mode. The added
intra prediction mode is determined by the left and above intra
prediction modes as follows.
[0115] If one of the left and above intra prediction modes is a
non-directional mode and the other is a directional mode, the other
non-directional mode is added to the MPM group. For example, if the
one of the left and above intra prediction modes is the DC mode,
the planar mode is added to the MPM group. If the one of the left
and above intra prediction modes is the planar mode, the DC mode is
added to the MPM group. If both of the left and above intra
prediction modes are non-directional modes, the vertical mode is
added to the MPM group. If both of the left and above intra
prediction modes are directional modes, the DC mode or the planar
mode is added to the MPM group.
[0116] When only one of the left intra prediction mode and the
above intra prediction mode is available, the available intra
prediction mode is included in the MPM group and two additional
intra prediction modes are added to the MPM group. The added two
intra prediction modes are determined by the available intra
prediction modes as follows.
[0117] If the available intra prediction mode is a non-directional
mode, the other non-directional mode and the vertical mode are
added to the MPM group. For example, if the available intra
prediction mode is the DC mode, the planar mode and the vertical
mode are added to the MPM group. If the available intra prediction
mode is the planar mode, the DC mode and the vertical mode are
added to the MPM group. If the available intra prediction mode is a
directional mode, two non-directional modes (DC mode and planar
mode) are added to the MPM group.
[0118] When both of the left intra prediction mode and the above
intra prediction mode are available and are same each other, the
available intra prediction mode is included in the MPM group and
two additional intra prediction modes are added to the MPM group.
The added two intra prediction modes are determined by the
available intra prediction modes as follows.
[0119] If the available intra prediction mode is a directional
mode, two neighboring directional modes are added to the MPM group.
For example, if the available intra prediction mode is the mode 23,
the left neighboring mode (mode 1) and the right neighboring mode
(mode 13) are added to the MPM group. If the available intra
prediction mode is the mode 30, the two neighboring modes (mode 2
and mode 16) are added to the MPM group. If the available intra
prediction mode is a non-directional mode, the other
non-directional mode and the vertical mode are added to the MPM
group. For example, if the available intra prediction mode is the
DC mode, the planar mode and the vertical mode are added to the MPM
group.
[0120] When both of the left intra prediction mode and the above
intra prediction mode are unavailable, three additional intra
prediction modes are added to the MPM group. The three intra
prediction modes are the DC mode, the planar mode and the vertical
mode. Indexes 0, 1 and 2 are assigned to the three intra prediction
modes in the order of the DC mode, the planar mode and the vertical
mode or in the order of the planar mode, the DC mode and the
vertical mode.
[0121] The prediction mode restoring unit 322 derives the intra
prediction mode of the current prediction unit using the mode group
indicator and the prediction mode index as follows.
[0122] The prediction mode restoring unit 322 determines whether
the mode group indicator indicates the MPM group.
[0123] If the mode group indicator indicates the MPM group, the
prediction mode restoring unit 322 determines the intra prediction
of the MPM group specified by the prediction mode index as the
intra prediction mode of the current prediction unit.
[0124] If the mode group indicator does not indicate the MPM group,
the prediction mode restoring unit 322 determines the intra
prediction of the residual mode group specified by the prediction
mode index as the intra prediction mode of the current prediction
unit. The intra prediction mode of the current unit is derived
using the prediction mode index and the intra prediction modes of
the MPM group as the following ordered steps.
[0125] 1) The three intra prediction modes of the MPM group are
reordered in the mode number order. The intra prediction mode with
lowest mode number is set to a first candidate. The intra
prediction mode with middle mode number is set to a second
candidate. The intra prediction mode with highest mode number is
set to a third candidate.
[0126] 2) The prediction mode index is compared with the first
candidate. If the prediction mode index is equal to or greater than
the first candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0127] 3) The prediction mode index is compared with the second
candidate. If the prediction mode index is equal to or greater than
the second candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0128] 4) The prediction mode index is compared with the third
candidate. If the prediction mode index is equal to or greater than
the third candidate of the MPM group, the value of the prediction
mode index is increased by one. Otherwise, the value of the
prediction mode index is maintained.
[0129] 5) The value of the final prediction mode index is set as
the mode number of the intra prediction mode of the current
prediction unit.
[0130] The prediction size determining unit 330 determines the size
of the prediction block based on the transform size information
specifying the size of the transform unit. The transform size
information may be one or more split_transform_flags specifying the
size of the transform unit.
[0131] If the size of the transform unit is equal to the size of
the current prediction unit, the size of the prediction block is
equal to the size of the current prediction unit.
[0132] If the size of the transform unit is smaller than the size
of the current prediction unit, the size of the prediction block is
equal to the size of the transform unit. In this case, a process of
generating a reconstructed block is performed on each sub-block of
the current prediction unit. That is, a prediction block and a
residual block of a current sub-block are generated and a
reconstructed block of each sub-block is generated by adding the
prediction block and the residual block. Then, a prediction block,
a residual block and a reconstructed block of the next sub-block in
decoding order are generated. The restored intra prediction mode is
used to generate all prediction blocks of all sub-block. Some
pixels of the reconstructed block of the current sub-block are used
as reference pixels of the next sub-block. Therefore, it is
possible to generate a prediction block which is more similar to
the original sub-block.
[0133] The reference pixel availability checking unit 340
determines whether all reference pixels of the current block are
available. The current block is the current prediction unit or the
current sub-block. The size of the current block is the size of the
transform unit.
[0134] The reference pixel generating unit 350 generates reference
pixels if one or more reference pixels of the current block are
unavailable.
[0135] If all reference pixels are unavailable, the value of
2.sup.L-1 is substituted for the values of all the reference
pixels. The value of L is the number of bits used to represent
luminance pixel value.
[0136] If available reference pixels are located at only one side
of the unavailable reference pixel, the value of the reference
pixel nearest to the unavailable pixel is substituted for the
unavailable reference pixel.
[0137] If available reference pixels are located at both sides of
the unavailable reference pixel, the average value of the reference
pixels nearest to the unavailable pixel in each side or the value
of the reference pixel nearest to the unavailable pixel in a
predetermined direction is substituted for each unavailable
reference pixel.
[0138] The reference pixel filtering unit 360 adaptively filters
the reference pixels based on the intra prediction mode and the
size of the current block.
[0139] In the DC mode, the reference pixels are not filtered. In
the vertical mode and the horizontal mode, the reference pixels are
not filtered. In the directional modes other than the vertical and
horizontal modes, the reference pixels are adaptively according to
the size of the current block.
[0140] If the size of the current is 4.times.4, the reference
pixels are not filtered in all intra prediction modes. For the size
8.times.8, 16.times.16 and 32.times.32, the number of intra
prediction mode where the reference pixels are filtered increases
as the size of the current block becomes larger. For example, the
reference pixels are not filtered in the vertical mode and a
predetermined number of neighboring intra prediction mode of the
vertical mode. The reference pixels are also not filtered in the
horizontal mode and the predetermined number of neighboring intra
prediction mode of the horizontal mode. The predetermined number
lies between 0 to 7 and decreases as the size of the current block
is larger.
[0141] The prediction block generating unit 370 generates a
prediction block of the current block using the reference pixels
according to the restored intra prediction mode.
[0142] In the DC mode, the prediction pixel of the prediction block
which is not adjacent to the reference pixel is generated by
averaging the N reference pixels located at (x=0, . . . N-1, y=-1)
and the M reference pixels located at (x=-1, y=0, . . . M-1). The
prediction pixel adjacent to the reference pixel is generated using
the average value and one or two adjacent reference pixels.
[0143] In the vertical mode, the prediction pixels which are not
adjacent to the left reference pixel are generated by copying the
value of the vertical reference pixel. The prediction pixels which
are adjacent to the left reference pixel are generated by the
vertical reference pixel and variance between the corner pixel and
the left neighboring pixel.
[0144] In the horizontal mode, the prediction pixels are generated
using the same method.
[0145] While the invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *