Search

EP-4742660-A1 - PREDICTION DEVICE, ENCODING DEVICE, DECODING DEVICE, AND PROGRAM

EP4742660A1EP 4742660 A1EP4742660 A1EP 4742660A1EP-4742660-A1

Abstract

A prediction device that performs prediction in units of blocks obtained by dividing an image comprises: a generator configured to select a prediction process to be applied from among a plurality of prediction processes by threshold determination for each area to be predicted in the block to generate a prediction area; a determiner configured to estimate or identify a specific area to which a prediction process different from a prediction process applied to surrounding prediction areas is applied, among the prediction areas generated in the block by the generator; and a corrector configured to perform a correction process using another area on the specific area estimated or identified by the determiner.

Inventors

  • IWAMURA, Shunsuke
  • NEMOTO, Shimpei
  • KONDO, YUICHI
  • ARAI, Daichi

Assignees

  • Nippon Hoso Kyokai

Dates

Publication Date
20260513
Application Date
20240702

Claims (9)

  1. A prediction device that performs prediction in units of blocks obtained by dividing an image, comprising: a generator configured to select a prediction process to be applied from among a plurality of prediction processes by threshold determination for each area to be predicted in the block to generate a prediction area; a determiner configured to estimate or identify a specific area to which a prediction process different from a prediction process applied to surrounding prediction areas is applied, among the prediction areas generated in the block by the generator; and a corrector configured to perform a correction process using another area on the specific area estimated or identified by the determiner.
  2. The prediction device according to claim 1, wherein the block is a chroma block, each of the plurality of prediction processes is a process of predicting pixels in the chroma block by a prediction model generated using chroma reference areas around the chroma block and luma reference areas around a predetermined luma block at a position corresponding to the chroma block, and the plurality of prediction processes differ in the prediction model.
  3. The prediction device according to claim 2, wherein the generator includes: a threshold decider configured to decide one or a plurality of thresholds used for selection of the prediction model from the luma reference areas; a prediction model generator configured to generate the prediction model for each cluster determined by the one or plurality of thresholds; a prediction model selector configured to select the prediction model used for prediction of a chroma area by comparing a pixel value of a corresponding luma area in the predetermined luma block with the one or plurality of thresholds for each chroma area in the chroma block; and a cross-component predictor configured to generate a prediction pixel of the chroma area by cross-component prediction using the selected prediction model.
  4. The prediction device according to any one of claims 1 to 3, wherein the generator selects a prediction process to be applied to an area by comparing a corresponding pixel value with a threshold for each area to be predicted, and the determiner estimates an area whose corresponding pixel value is near the threshold among the areas to be predicted as the specific area.
  5. The prediction device according to any one of claims 1 to 3, wherein the determiner: stores the applied prediction process according to a result of the threshold determination for each area to be predicted; and identifies, as the specific area, an area to which a first prediction process is applied among the areas to be predicted, and for which a second prediction process different from the first prediction process is applied to at least a predetermined number of surrounding areas.
  6. The prediction device according to any one of claims 1 to 3, wherein the corrector performs a filtering process using prediction areas around the specific area on the specific area as the correction process.
  7. An encoding device comprising the prediction device according to claim 1.
  8. A decoding device comprising the prediction device according to claim 1.
  9. A program for causing a computer to function as the prediction device according to claim 1.

Description

TECHNICAL FIELD The present disclosure relates to a prediction device, an encoding device, a decoding device, and a program. BACKGROUND ART In video coding schemes such as HEVC (High Efficiency Video Coding) and VVC (Versatile Video Coding), an encoding device generates a prediction block by predicting a coding block (CU: Coding Unit) obtained by dividing an original image into block units, and performs transformation, quantization, and entropy encoding on a prediction residual, which is a difference between the coding block of the original image and the prediction block, to transmit the prediction residual. The Joint Video Experts Team (JVET) (ISO/IEC JTC1 SC29 WG5), an international standardization working group for video coding, is studying ECM (Enhanced Compression Model), which is a next-generation video coding technology. As a mode of intra prediction, which is prediction considering correlation within a frame, a prediction mode for a chroma signal called MMLM (Multi Model Linear Model) is introduced in ECM. MMLM is an extension technology of CCLM (Cross Component Linear Model) adopted in VVC. CCLM is a mode for predicting a corresponding chroma block using a decoded block of luma, and predicts prediction pixels of a target chroma block from a decoded block of luma at a corresponding position using a linear model. Herein, a reduced block obtained by downsampling the decoded block of luma according to a chroma format is used. The linear model is calculated by the least mean squares using decoded pixels adjacent to the target chroma block (chroma reference pixels) and decoded pixels adjacent to the decoded block of luma at the corresponding position (luma reference pixels). In VVC, luma and chroma reference pixels used for linear model calculation are limited to only some pixel positions to realize lightweight processing. Since CCLM is premised on the fact that distribution of luma and chroma signals in a block has a certain tendency, there is a problem that approximation accuracy significantly decreases when distribution of luma and chroma signals includes a plurality of tendencies, such as when an object boundary exists in the block. Therefore, in MMLM, a plurality of distributions are assumed, and distribution of luma and chroma signals is clustered using, for example, an average value of luma reference pixels as a threshold, and a linear model is calculated for each cluster, thereby preventing a decrease in approximation accuracy. Note that the linear model is an example of a prediction model. Specifically, in MMLM, after two linear models are calculated using luma reference pixels and chroma reference pixels, a linear model used for prediction of a chroma block is selected according to whether a pixel value of a decoded block of luma at a position corresponding to a target chroma block is larger than a threshold. Each prediction pixel of the chroma block is generated while switching the linear model for each pixel of the decoded block of luma at the position corresponding to the target chroma block. PRIOR ART DOCUMENTS NON-PATENT DOCUMENTS Non-Patent Document 1 JVET-D0110 "Enhanced Cross-component Linear Model Intra-prediction" SUMMARY OF INVENTION A prediction device according to a first aspect is a prediction device configured to perform prediction in units of blocks obtained by dividing an image, comprising: a generator configured to select a prediction process to be applied from among a plurality of prediction processes by threshold determination for each area to be predicted in the block to generate a prediction area; a determiner configured to estimate or identify a specific area to which a prediction process different from a prediction process applied to surrounding prediction areas is applied, among the prediction areas generated in the block by the generator; and a corrector configured to perform a correction process using another area on the specific area estimated or identified by the determiner. An encoding device according to a second aspect comprises the prediction device according to the first aspect. A decoding device according to a third aspect comprises the prediction device according to the first aspect. A program according to a fourth aspect causes a computer to function as the prediction device according to the first aspect. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a diagram showing a configuration of an encoding device according to an embodiment.Fig. 2 is a diagram for explaining an example of an intra prediction mode according to the embodiment.Fig. 3 is a diagram for explaining an overview of MMLM according to the embodiment.Fig. 4 is a diagram for explaining an overview of MMLM according to the embodiment.Fig. 5 is a diagram for explaining an overview of MMLM according to the embodiment.Fig. 6 is a diagram for explaining an overview of MMLM according to the embodiment.Fig. 7 is a diagram showing a configuration of an intra predictor on an encoding side according to the embod