# US 2018/0295384 A1 · Intra prediction method and device in image coding system

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- Number: US 2018/0295384 A1
- Document ID: US20180295384A1
- Status: Published application
- Kind: A1
- Application number: 15/762,946
- Filed: 2016-09-08
- Published: 2018-10-11
- Earliest claimed: 2015-09-23
- Assignees: LG Electronics Inc.
- Applicants: LG Electronics Inc.
- Inventors: Eunyong SON; Jin HEO; Seungwook PARK; Sehoon YEA
- Web page: https://patentgrep.com/patent/US20180295384A1

## CPC

- H04N 19/61: in combination with predictive coding
- H04N 19/105: Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
- H04N 19/11: among a plurality of spatial predictive coding modes
- H04N 19/176: the region being a block, e.g. a macroblock
- H04N 19/182: the unit being a pixel
- H04N 19/196: being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters (processing of motion vectors H04N19/513)
- H04N 19/44: Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
- H04N 19/96: Tree coding, e.g. quad-tree coding
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

An intra prediction method includes: receiving intra prediction mode information through a bitstream; deriving an intra prediction mode of a current block as a first intra directional mode on the basis of the intra prediction mode information; deriving first neighboring samples of the current block; deriving a reference sample adjacent to a target sample in the current block on the basis of a prediction direction of the first intra directional mode; deriving second neighboring samples of a neighboring block to which the reference sample belongs; determining a modified prediction direction on the basis of a comparison between the reference sample and at least one of the second neighboring samples; and deriving a prediction value for the target sample on the basis of the modified prediction direction and the first neighboring samples.

## Claims

### Claim 1

An intra prediction method performed in an image decoding apparatus, comprising steps of:
receiving intra prediction mode information through a bit stream;
deriving an intra prediction mode of a current block as a first intra direction mode based on the intra prediction mode information;
deriving first neighbor samples of the current block;
deriving a reference sample neighboring a target sample within the current block based on a prediction direction of the first intra direction mode;
deriving second neighbor samples of a neighbor block to which the reference sample belongs;
determining a modified prediction direction based on a comparison between the reference sample and at least one of the second neighbor samples; and
deriving a prediction value of the target sample based on the modified prediction direction and the first neighbor samples.

### Claim 2 (depends on 1)

The intra prediction method of claim 1, further comprising steps of:
deriving a neighbor sample 1 located in a prediction direction of a second intra direction mode of the neighbor block based on the reference sample from the second neighbor samples;
deriving n neighbor samples from the second neighbor samples based on neighbor samples located within a specific distance from the neighbor sample 1,
wherein a direction indicative of a sample belonging to the n neighbor samples and having a smallest difference with the reference sample is determined to be the modified prediction direction based on a comparison between the n neighbor samples and the reference sample.

### Claim 3 (depends on 2)

The intra prediction method of claim 2, wherein the modified prediction direction is determined based on an equation below,
DirRefine
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(
P
ref
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x
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y
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)
=
argmin
m
-
r
≤
a
≤
m
+
r

{

PRED
P
ref
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(
x
,
y
)

(
a
)
-
P
ref

(
x
,
y
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}
wherein DirRefine(Pref(x,y)) is the modified prediction direction, PREDPref(x,y)(a) is one of the n neighbor samples, Pref(x,y) is the reference sample, m is the prediction direction of the second intra direction mode, r is a positive integer, and the n is 2r−1.

### Claim 4 (depends on 1)

The intra prediction method of claim 1, wherein if the first intra direction mode is one of Nos. 2 to 17 intra prediction modes, the neighbor block is a left block of the current block and the target sample neighbors a left boundary of the current block.

### Claim 5 (depends on 4)

The intra prediction method of claim 4, wherein:
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 2 to 6 intra prediction modes, a sample position of the reference sample is (x−1,y+1),
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 7 to 13 intra prediction modes, a sample position of the reference sample is P(x−1,y), and
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 14 to 17 intra prediction modes, a sample position of the reference sample is (x−1,y−1).

### Claim 6 (depends on 5)

The intra prediction method of claim 5, further comprising a step of deriving a prediction value of a sample belongs to samples of the current block and located on a right side of the target sample based on the modified prediction direction.

### Claim 7 (depends on 1)

The intra prediction method of claim 1, wherein if the first intra direction mode is one of Nos. 18 to 34 intra prediction modes, the neighbor block is a top block of the current block and the target sample neighbors a top boundary of the current block.

### Claim 8 (depends on 7)

The intra prediction method of claim 7, wherein:
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 18 to 22 intra prediction modes, a sample position of the reference sample is (x−1,y−1),
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 23 to 29 intra prediction modes, a sample position of the reference sample is (x,y−1), and
when a sample position of the target sample is (x,y) and the first intra direction mode is one of the Nos. 30 to 34 intra prediction modes, a sample position of the reference sample is (x+1,y−1).

### Claim 9 (depends on 8)

The intra prediction method of claim 8, further comprising a step of deriving a prediction value of a sample belonging to samples of the current block and located at a bottom of the target sample based on the modified prediction direction.

### Claim 10 (depends on 1)

The intra prediction method of claim 1, further comprising a step of deriving a plurality of non-square transform units (TU) overlapping a current prediction unit (PU),
wherein the current block is one of the non-square TUs.

### Claim 11 (depends on 10)

The intra prediction method of claim 10, wherein:
when a size of the current PU is N×N and the first intra direction mode is one of Nos. 2 to 17 intra prediction modes, the current PU is split into the non-square TUs of a w×N(1≤w<N) size, and
when a size of the current PU is N×N and the first intra direction mode is one of Nos. 18 to 34 intra prediction modes, the current PU is split into the non-square TUs of an N×h(1≤h<N) size.

### Claim 12 (depends on 10)

The intra prediction method of claim 10, further comprising a step of receiving a vertical split flag through the bit stream,
wherein when a value of the vertical split flag is 1, the current PU is split into the non-square TUs of a w×N(1≤w<N) size, and
when a value of the vertical split flag is 0, the current PU is split into the non-square TUs of an N×h(1≤h<N) size.

### Claim 13 (depends on 1)

The intra prediction method of claim 1, further comprising a step of receiving an angle refine flag through the bit stream,
wherein when a value of the angle refine flag is 1, the prediction value of the target sample is derived based on the modified prediction direction.

### Claim 14 (depends on 13)

The intra prediction method of claim 13, wherein the angle refine flag is received when an intra prediction mode index of the first intra direction mode is greater than 1.

### Claim 15

An intra prediction method performed in an image encoding apparatus, comprising steps of:
deriving a first intra direction mode and first neighbor samples of a current block;
determining a reference sample neighboring a target sample within the current block based on a prediction direction of the first intra direction mode;
deriving second neighbor samples of a neighbor block to which the reference sample belongs;
determining a modified prediction direction based on a comparison between the reference sample and at least one of the second neighbor samples;
deriving a prediction value of the target sample based on the modified prediction direction and the first neighbor samples; and
encoding and outputting intra prediction mode information indicative of the first intra direction mode.