EP-4738817-A1 - INTRA PREDICTION DEVICE, ENCODING DEVICE, DECODING DEVICE, AND PROGRAM

EP4738817A1EP 4738817 A1EP4738817 A1EP 4738817A1EP-4738817-A1

Abstract

An intra prediction apparatus that performs intra prediction in units of blocks obtained by dividing an image includes: an area specification means configured to specify a decoded area around a target block for intra prediction as a prediction trial area, and specify a decoded area adjacent to the prediction trial area as a reference area; a cost calculation means configured to calculate a cost using a cost function by performing, for each intra prediction mode, a prediction trial of predicting the prediction trial area from the reference area; and a prediction mode determination means configured to determine at least one intra prediction mode to be used for the intra prediction according to the cost. The prediction trial area includes a plurality of sub-areas classified according to a relative positional relationship with the target block. The cost calculation means performs weighting for each of the sub-areas when calculating the cost of each intra prediction mode.

Inventors

NEMOTO, Shimpei
IWAMURA, Shunsuke
ICHIGAYA, ATSURO

Assignees

Nippon Hoso Kyokai

Dates

Publication Date: 20260506
Application Date: 20240628

Claims (9)

An intra prediction apparatus that performs intra prediction in units of blocks obtained by dividing an image, comprising: an area specification means configured to specify a decoded area around a target block for the intra prediction as a prediction trial area, and specify a decoded area adjacent to the prediction trial area as a reference area; a cost calculation means configured to calculate a cost using a cost function by performing, for each intra prediction mode, a prediction trial of predicting the prediction trial area from the reference area; and a prediction mode determination means configured to determine at least one intra prediction mode to be used for the intra prediction according to the cost, wherein the prediction trial area includes a plurality of sub-areas classified according to a relative positional relationship with the target block, and the cost calculation means performs weighting for each of the sub-areas when calculating the cost of each intra prediction mode.
The intra prediction apparatus according to claim 1, wherein the cost calculation means sets a weight for each of the plurality of sub-areas according to a reference area position, which is a position of the reference area referred to in the intra prediction mode used for the prediction trial, and respective positions of the plurality of sub-areas.
The intra prediction apparatus according to claim 2, wherein the cost calculation means sets a weight for a second sub-area whose distance from the reference area position is a second distance longer than a first distance to be larger than a weight for a first sub-area whose distance from the reference area position is the first distance.
The intra prediction apparatus according to any one of claims 1 to 3, wherein the cost calculation means includes, for each intra prediction mode used for the prediction trial: a weight setting means configured to set a weight for each of the sub-areas according to the intra prediction mode; a prediction trial means configured to perform a prediction trial for each of the sub-areas by the intra prediction mode; and a weighted calculation means configured to calculate the cost for each of the sub-areas and apply the weight according to a result of the prediction trial to derive a weighted cost of the intra prediction mode, and the prediction mode determination means determines at least one intra prediction mode to be used for the intra prediction according to the weighted cost of each intra prediction mode.
The intra prediction apparatus according to any one of claims 1 to 3, wherein the plurality of sub-areas includes a left sub-area which is a decoded area on the left side of the target block, and an upper sub-area which is a decoded area on the upper side of the target block.
The intra prediction apparatus according to claim 1, wherein the cost calculation means calculates the cost only for a sub-area different from a part of the sub-areas by setting zero as a weight for the part of the sub-areas among the plurality of sub-areas.
An encoding apparatus comprising the intra prediction apparatus according to claim 1.
A decoding apparatus comprising the intra prediction apparatus according to claim 1.
A program for causing a computer to function as the intra prediction apparatus according to claim 1.

Description

TECHNICAL FIELD The present disclosure relates to an intra prediction apparatus, an encoding apparatus, a decoding apparatus, and a program. BACKGROUND ART In video coding schemes such as HEVC (High Efficiency Video Coding) and VVC (Versatile Video Coding), an encoding apparatus generates a prediction block, which is a prediction image for a coding block (CU: Coding Unit) obtained by dividing an original image into block units, and transforms, quantizes, and entropy-encodes a difference between the coding block of the original image and the prediction block to transmit the difference. As methods for generating a prediction image, inter prediction using correlation between frames and intra prediction using correlation within a frame are available. As intra prediction methods, in addition to Planar prediction and DC prediction, directional prediction which is linear prediction can be selected from 33 directions in HEVC and 65 directions in VVC. In intra prediction, a technique is being studied in which a peripheral area of a target block to be encoded is used as a prediction trial area (also referred to as a "template") and using reference pixels for the prediction trial area to perform a prediction trial, thereby deriving an intra prediction mode and using this intra prediction mode for prediction (see, for example, Non-Patent Literature 1). This technique utilizes the fact that cost calculations for intra prediction in the prediction trial area match in both the encoding apparatus and the decoding apparatus. According to such a technique, for example, it is possible to reduce the overhead of signaling the intra prediction mode and to derive an additional directional prediction that subdivides intervals between conventional prediction directions to form a new prediction direction. CITATION LIST NON-PATENT LITERATURE Non-Patent Literature 1 JVET-C0061 "Decoder-side intra mode derivation" SUMMARY OF INVENTION An intra prediction apparatus according to a first aspect is an intra prediction apparatus that performs intra prediction in units of blocks obtained by dividing an image, comprising: an area specification means configured to specify a decoded area around a target block for the intra prediction as a prediction trial area, and specify a decoded area adjacent to the prediction trial area as a reference area; a cost calculation means configured to calculate a cost using a cost function by performing, for each intra prediction mode, a prediction trial of predicting the prediction trial area from the reference area; and a prediction mode determination means configured to determine at least one intra prediction mode to be used for the intra prediction according to the cost. The prediction trial area includes a plurality of sub-areas classified according to a relative positional relationship with the target block. The cost calculation means performs weighting for each of the sub-areas when calculating the cost. An encoding apparatus according to a second aspect comprises the intra prediction apparatus according to the first aspect. A decoding apparatus according to a third aspect comprises the intra prediction apparatus according to the first aspect. A program according to a fourth aspect causes a computer to function as the intra prediction apparatus according to the first aspect. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a configuration of an encoding apparatus according to an embodiment.FIG. 2 is a diagram for explaining intra prediction modes according to the embodiment.FIG. 3 is a diagram for explaining TIMD according to the embodiment.FIG. 4 is a diagram showing a configuration of an intra predictor according to the embodiment.FIG. 5 is a diagram for explaining an operation of the intra predictor according to the embodiment.FIG. 6 is a diagram showing a configuration of a decoding apparatus according to the embodiment.FIG. 7 is a diagram showing a configuration of an intra predictor according to the embodiment.FIG. 8 is a diagram showing an example of an operation of the intra predictor according to the embodiment.FIG. 9 is a diagram for explaining a modification of TIMD according to the embodiment. DESCRIPTION OF EMBODIMENTS In a derivation technique of an intra prediction mode using a template, a prediction mode having the best result of cost calculation of intra prediction in a prediction trial area on an encoding apparatus side and a decoding apparatus side, or a prediction mode for which a result of cost calculation exceeds a threshold even during derivation, is selected. However, there is room for improvement in such a technique from the viewpoint of improving prediction accuracy in intra prediction. Therefore, the present disclosure provides an intra prediction apparatus, an encoding apparatus, a decoding apparatus, and a program capable of improving prediction accuracy in intra prediction. An encoding apparatus and a decoding apparatus including an intra prediction apparatus accordi