Intra prediction method and device in image coding system

Patent metadata

Field	Value
Publication number	US-10721492-B2
Application number	US-201615762946-A
Country	US
Kind code	B2
Filing date	Sep 8, 2016
Priority date	Sep 23, 2015
Publication date	Jul 21, 2020
Grant date	Jul 21, 2020

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.

First claim

What is claimed is:

1. An intra prediction method performed in an image decoding apparatus, comprising steps of:
receiving intra prediction mode information and split flag information through a bit stream;
deriving, based on the split flag information, a plurality of non-square transform units (TUs) from a current prediction unit (PU), wherein the split flag information represents whether the current PU is vertically or horizontally split into the non-square TUs;
deriving, based on the intra prediction mode information, a first intra direction mode;
generating, based on a first prediction direction of the first intra direction mode, a prediction value of a first target sample in a current TU, among the non-square TUs;
deriving first neighbor samples of the current TU;
deriving a reference sample neighboring a second target sample within the current block TU based on the first 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
generating a prediction value of the second target sample in the current TU based on the modified prediction direction and the first neighbor samples,
wherein the modified prediction direction used for generating the prediction value of the second target sample in the current TU is different from the first prediction direction used for generating the prediction value of the first target sample in the current TU.

2. 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.

3. The intra prediction method of claim 2 , wherein the modified prediction direction is determined based on an equation below,

DirRefine
⁡

(

P
ref

⁡

(

x
,
y

)

)

=

argmin

m
-
r

≤
a
≤

m
+
r

⁢

{



PRED

P
ref

⁡

(

x
,
y

)

⁡

(
a
)

-

P
ref

⁡

(

x
,
y

)



}

wherein DirRefine(P ref (x,y)) is the modified prediction direction, PREDP ref (x,y)(a) is one of the n neighbor samples, P ref (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.

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

5. 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).

6. 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 TU and located on a right side of the target sample based on the modified prediction direction.

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

8. 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).

9. 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 TU and located at a bottom of the target sample based on the modified prediction direction.

10. The intra prediction method of claim 1 , further comprising a step of receiving an angle refine flag through the bit strea

Assignees

• Lg Electronics Inc

Inventors

• Son Eunyong
• Heo Jin
• Park Seungwook
• Yea Sehoon

Classifications

• H04N19/61 Primary

  in combination with predictive coding · CPC title

• H04N19/44

  Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder · CPC title

• H04N19/11

  among a plurality of spatial predictive coding modes · CPC title

• H04N19/105 Primary

  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 · CPC title

• H04N19/176

  the region being a block, e.g. a macroblock · CPC title