CN118318447A

CN118318447A - Image encoding/decoding method and apparatus for adaptively changing resolution and method of transmitting bitstream

Info

Publication number: CN118318447A
Application number: CN202280078594.0A
Authority: CN
Inventors: 南廷学; 柳先美; 林宰显; 金昇焕
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2021-10-04
Filing date: 2022-10-04
Publication date: 2024-07-09

Abstract

Provided are an image encoding/decoding method and apparatus. According to one embodiment of the present disclosure, an image decoding method performed by an image decoding apparatus may include the steps of: deriving a reference picture for inter prediction of a current picture; deriving a resolution ratio between the reference image and the current image; and changing the resolution of the reference image based on a resolution ratio, wherein the resolution ratio is derived based on the resolution index information of the bitstream.

Description

Image encoding/decoding method and apparatus for adaptively changing resolution and method of transmitting bitstream

Technical Field

The present disclosure relates to an image encoding/decoding method and apparatus, and more particularly, to an image encoding/decoding method and apparatus that adaptively modifies resolution when resolutions of a reference picture and a current picture are different, and a method of transmitting a bitstream generated by the image encoding method/apparatus of the present disclosure.

Background

Recently, demands for high resolution and high quality images, such as High Definition (HD) images and Ultra High Definition (UHD) images, are increasing in various fields. As the resolution and quality of image data improves, the amount of information or bits transmitted increases relatively as compared to existing image data. An increase in the amount of transmission information or the amount of bits results in an increase in transmission costs and storage costs.

Therefore, an efficient image compression technique is required to efficiently transmit, store, and reproduce information about high resolution and high quality images.

Disclosure of Invention

Technical problem

It is an object of the present disclosure to provide an image encoding/decoding method and apparatus having improved encoding/decoding efficiency.

It is another object of the present disclosure to provide an image encoding/decoding method and apparatus that adaptively modifies resolution.

Another object of the present disclosure is to provide an image encoding/decoding method and apparatus that performs reference picture resampling.

It is another object of the present disclosure to provide an image encoding/decoding method and apparatus that selects one of various candidate resolutions for one image.

Another object of the present disclosure is to provide a method of transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure.

It is another object of the present disclosure to provide a recording medium storing a bitstream generated by an image encoding method or apparatus according to the present disclosure.

It is another object of the present disclosure to provide a recording medium storing a bitstream received, decoded, and used for reconstructing an image by an image decoding apparatus according to the present disclosure.

The technical problems addressed by the present disclosure are not limited to the above technical problems, and other technical problems not described herein will become apparent to those skilled in the art from the following description.

Technical proposal

According to one embodiment of the present disclosure, an image encoding method performed by an image encoding apparatus may include the steps of: the method includes determining a reference picture for inter prediction of a current picture, deriving a resolution ratio between the reference picture and the current picture, and modifying a resolution of the reference picture based on the resolution ratio. Resolution index information indicating the resolution ratio may be encoded into the bitstream.

According to one embodiment of the present disclosure, the resolution index information may indicate one of a plurality of resolution ratios.

According to one embodiment of the present disclosure, the resolution ratio may include a first resolution ratio of 2 and a second resolution ratio of 3/2.

According to one embodiment of the present disclosure, the resolution may be applied in units of group of pictures (GOP).

According to one embodiment of the disclosure, the resolution ratio may be determined based on an initial quantization parameter of a first picture in the GOP.

According to one embodiment of the disclosure, the resolution ratio may be derived by downscaling the first picture to a particular resolution.

According to one embodiment of the present disclosure, the initial quantization parameter may be compared to a particular quantization parameter value.

According to one embodiment of the disclosure, the resolution ratio may be determined further based on a peak signal-to-noise ratio (PSNR) of the first picture in the GOP.

According to one embodiment of the present disclosure, the PSNR of the first picture may be compared with a specific PSNR value.

According to an embodiment of the present disclosure, the image encoding method may further include the steps of: it is determined whether to perform reference picture resampling on the current picture.

According to one embodiment of the present disclosure, the reference picture resampling may be performed based on whether BDOF, DMVR, PROF or TMVP is applied.

According to one embodiment of the present disclosure, an image decoding method performed by an image decoding apparatus may include the steps of: deriving a reference picture for inter prediction of a current picture, deriving a resolution ratio between the reference picture and the current picture, and modifying a resolution of the reference picture based on the resolution ratio. The resolution ratio may be derived based on resolution index information of the bitstream.

According to one embodiment of the present disclosure, an image encoding apparatus may include a memory and at least one processor connected to the memory. The processor may derive a reference picture for inter prediction of a current picture, derive a resolution ratio between the reference picture and the current picture, and modify a resolution of the reference picture based on the resolution ratio. Resolution index information indicating the resolution ratio may be encoded into the bitstream.

According to one embodiment of the present disclosure, an image decoding apparatus may include a memory and at least one processor connected to the memory. The processor may derive a reference picture for inter prediction of a current picture, derive a resolution ratio between the reference picture and the current picture, and modify a resolution of the reference picture based on the resolution ratio. The resolution ratio may be derived based on resolution index information of the bitstream.

According to one embodiment of the present disclosure, a bit stream transmission apparatus may include: at least one processor configured to obtain a bitstream; and a transmitter configured to transmit the bitstream. The bitstream is generated by an image encoding method. The image encoding method may include the steps of: the method includes determining a reference picture for inter prediction of a current picture, deriving a resolution ratio between the reference picture and the current picture, and modifying a resolution of the reference picture based on the resolution ratio. Resolution index information indicating the resolution ratio may be encoded into the bitstream.

According to one embodiment of the present disclosure, a bitstream generated by an image encoding apparatus or an image encoding method may be transmitted.

According to one embodiment of the present disclosure, a method of transmitting a bitstream generated by an image encoding method may include the steps of: the method includes determining a reference picture for inter prediction of a current picture, deriving a resolution ratio between the reference picture and the current picture, and modifying a resolution of the reference picture based on the resolution ratio. Resolution index information indicating the resolution ratio may be encoded into the bitstream.

According to one embodiment of the present disclosure, a bitstream generated by an image encoding method may be stored and recorded in a computer readable medium.

According to one embodiment of the present disclosure, a bitstream generated by an image encoding method may be transmitted by a bitstream transmission device.

The features briefly summarized above with respect to the present disclosure are merely exemplary aspects of the present disclosure that are described in detail below and do not limit the scope of the present disclosure.

Advantageous effects

According to the present disclosure, an image encoding/decoding method and apparatus having improved encoding/decoding efficiency may be provided.

According to the present disclosure, an image encoding/decoding method and apparatus that adaptively modifies resolution may be provided.

According to the present disclosure, an image encoding/decoding method and apparatus performing reference picture resampling may be provided.

According to the present disclosure, an image encoding/decoding method and apparatus for determining an optimal resolution may be provided.

According to the present disclosure, an image encoding/decoding method and apparatus for selecting one of various candidate resolutions for one image may be provided.

In addition, according to the present disclosure, a method of transmitting a bitstream generated by an image encoding method or apparatus according to the present disclosure may be provided.

In addition, according to the present disclosure, a recording medium storing a bitstream generated by the image encoding method or apparatus according to the present disclosure may be provided.

In addition, according to the present disclosure, a recording medium storing a bitstream received, decoded, and used to reconstruct an image by an image decoding apparatus according to the present disclosure may be provided.

Those skilled in the art will appreciate that the effects that can be achieved by the present disclosure are not limited to what has been particularly described hereinabove, and other advantages of the present disclosure will be more clearly understood from the detailed description.

Drawings

Fig. 1 is a diagram schematically illustrating a video encoding system to which one embodiment of the present disclosure is applied.

Fig. 2 is a diagram schematically illustrating an image encoding apparatus to which one embodiment of the present disclosure is applied.

Fig. 3 is a diagram schematically illustrating an image decoding apparatus to which one embodiment of the present disclosure is applied.

Fig. 4 to 8 are diagrams illustrating a general inter prediction encoding/decoding process.

Fig. 9 to 10 are diagrams illustrating an image encoding or decoding method according to an embodiment of the present disclosure.

Fig. 11 is a diagram for explaining an image encoding or decoding apparatus according to an embodiment of the present disclosure.

Fig. 12 is a view showing a content streaming system to which the embodiment of the present disclosure is applied.

Detailed Description

Embodiments of the present disclosure will be described in detail below with reference to the drawings to facilitate implementation by those skilled in the art. However, the present disclosure may be embodied in a variety of different forms and is not limited to the embodiments described herein.

In describing the present disclosure, if it is determined that detailed descriptions of related known functions or constructions unnecessarily obscure the scope of the present disclosure, detailed descriptions thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are given to like parts.

In this disclosure, when a component is "connected," "coupled," or "linked" to another component, it can include not only direct connections, but also indirect connections in which intervening components exist. In addition, when an element is "comprising" or "having" other elements, it is intended that the other elements may be included, unless otherwise indicated, without excluding the other elements.

In this disclosure, the terms first, second, etc. are used solely for the purpose of distinguishing one component from another and not limitation of the order or importance of the components unless otherwise indicated. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

In this disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not necessarily mean that the components must be separated. That is, multiple components may be integrated in one hardware or software unit or one component may be distributed and implemented in multiple hardware or software units. Accordingly, integrated or distributed implementations of these components are included within the scope of this disclosure, even if not specifically stated.

In the present disclosure, the components described in the respective embodiments are not necessarily indispensable components, and some components may be optional components. Thus, embodiments consisting of a subset of the components described in the embodiments are also included within the scope of the present disclosure. Further, embodiments that include other components in addition to those described in the various embodiments are included within the scope of the present disclosure.

The present disclosure relates to encoding and decoding of images, and unless redefined in the present disclosure, terms used in the present disclosure may have their ordinary meanings commonly used in the art to which the present disclosure pertains.

In this disclosure, "picture" generally means a basis representing one image in a specific period of time, and a slice/tile is an encoded basis constituting a part of a picture. A picture may be made up of one or more slices/tiles. In addition, a slice/tile may include one or more Coding Tree Units (CTUs).

In this disclosure, "pixel" or "picture element (pel)" may mean the smallest unit that constitutes a picture (or image). Further, "sample" may be used as a term corresponding to a pixel. One sample may generally represent a pixel or a value of a pixel, or may represent a pixel/pixel value of only a luminance component or a pixel/pixel value of only a chrominance component.

In the present disclosure, "unit" may represent a basic unit of image processing. The unit may include at least one of a specific region of the picture and information related to the region. One unit may include one luminance block and two chrominance (e.g., cb, cr) blocks. In some cases, a cell may be used interchangeably with terms such as "sample array," block, "or" region. In general, an mxn block may comprise M columns of N rows of samples (sample array) or a set (or array) of transform coefficients.

In the present disclosure, the "current block" may mean one of "current encoding block", "current encoding unit", "encoding target block", "decoding target block", or "processing target block". When performing prediction, the "current block" may mean a "current prediction block" or a "prediction target block". When performing transform (inverse transform)/quantization (dequantization), a "current block" may mean a "current transform block" or a "transform target block". When filtering is performed, "current block" may mean "filtering target block".

Further, in the present disclosure, unless explicitly stated as a chroma block, "current block" may mean "luma block of current block". The "chroma block of the current block" may be expressed by including an explicit description of a chroma block such as "chroma block" or "current chroma block".

In this disclosure, the terms "/" and "," should be interpreted as indicating "and/or". For example, the expressions "A/B" and "A, B" may mean "A and/or B". In addition, "a/B/C" and "A, B, C" may mean at least one of "A, B and/or C.

In this disclosure, the term "or" should be interpreted as indicating "and/or". For example, the expression "a or B" may include 1) "a only", 2) "B only" and/or 3) "both a and B". In other words, in this disclosure, the term "or" should be interpreted as indicating "additionally or alternatively".

Overview of video coding systems

Fig. 1 is a view illustrating a video encoding system according to the present disclosure.

The video encoding system according to an embodiment may include an encoding apparatus 10 and a decoding apparatus 20. Encoding device 10 may transfer the encoded video and/or image information or data in file or streaming form to decoding device 20 via a digital storage medium or network.

The encoding apparatus 10 according to the embodiment may include a video source generator 11, an encoding unit (encoder) 12, and a transmitter 13. The decoding apparatus 20 according to an embodiment may include a receiver 21, a decoding unit (decoder) 22, and a renderer 23. The encoding unit 12 may be referred to as a video/image encoding device, and the decoding unit 22 may be referred to as a video/image decoding device. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display, and the display may be configured as a separate device or an external component.

The video source generator 11 may acquire video/images through a process of capturing, synthesizing, or generating the video/images. The video source generator 11 may comprise video/image capturing means and/or video/image generating means. The video/image capturing means may comprise, for example, one or more cameras, video/image files comprising previously captured video/images, etc. Video/image generating means may comprise, for example, computers, tablets and smart phones, and may (electronically) generate video/images. For example, virtual video/images may be generated by a computer or the like. In this case, the video/image capturing process may be replaced by a process of generating related data.

The encoding unit 12 may encode the input video/image. The encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization for compression and encoding efficiency. The encoding unit 12 may output encoded data (encoded video/image information) in the form of a bitstream.

The transmitter 13 may obtain the encoded video/image information or data output in the form of a bitstream and forward it in the form of a file or stream transmission over a digital storage medium or network to the receiver 21 of the decoding apparatus 20 or another external object. The digital storage medium may include various storage media such as USB, SD, CD, DVD, blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file through a predetermined file format and may include an element for transmitting through a broadcast/communication network. The transmitter 13 may be provided as a transmission device separate from the encoding apparatus 10, and in this case, the transmission device may include at least one processor that acquires encoded video/image information or data output in the form of a bitstream, and a transmission unit for transmitting the encoded video/image information or data in the form of a file or stream transmission. The receiver 21 may extract/receive a bit stream from a storage medium or a network and transmit the bit stream to the decoding unit 22.

The decoding unit 22 may decode the video/image by performing a series of processes such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding unit 12.

The renderer 23 may render the decoded video/images. The rendered video/image may be displayed by a display.

Overview of image coding apparatus

Fig. 2 is a view schematically showing an image encoding apparatus to which the embodiments of the present disclosure are applicable.

As shown in fig. 2, the image encoding apparatus 100 may include an image divider 110, a subtractor 115, a transformer 120, a quantizer 130, an inverse quantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter prediction unit 180, an intra prediction unit 185, and an entropy encoder 190. The inter prediction unit 180 and the intra prediction unit 185 may be collectively referred to as "prediction units". The transformer 120, quantizer 130, inverse quantizer 140, and inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

In some implementations, all or at least some of the plurality of components configuring the image encoding device 100 may be configured by one hardware component (e.g., an encoder or a processor). Further, the memory 170 may include a Decoded Picture Buffer (DPB) and may be configured by a digital storage medium.

The image divider 110 may divide an input image (or picture or frame) input to the image encoding apparatus 100 into one or more processing units. For example, the processing unit may be referred to as a Coding Unit (CU). The coding units may be obtained by recursively partitioning the Coding Tree Units (CTUs) or Largest Coding Units (LCUs) according to a quadtree binary tree (QT/BT/TT) structure. For example, one coding unit may be partitioned into multiple coding units of deeper depth based on a quadtree structure, a binary tree structure, and/or a trigeminal tree structure. For the partitioning of the coding units, a quadtree structure may be applied first, and then a binary tree structure and/or a trigeminal tree structure may be applied. The encoding process according to the present disclosure may be performed based on the final encoding unit that is not subdivided. The maximum coding unit may be used as the final coding unit, or a coding unit of a deeper depth obtained by dividing the maximum coding unit may be used as the final coding unit. Here, the encoding process may include processes of prediction, transformation, and reconstruction, which will be described later. As another example, the processing unit of the encoding process may be a Prediction Unit (PU) or a Transform Unit (TU). The prediction unit and the transform unit may be divided or partitioned from the final coding unit. The prediction unit may be a sample prediction unit and the transform unit may be a unit for deriving transform coefficients and/or a unit for deriving residual signals from the transform coefficients.

The prediction unit (the inter prediction unit 180 or the intra prediction unit 185) may perform prediction on a block to be processed (a current block) and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction on the basis of the current block or CU. The prediction unit may generate various information related to prediction of the current block and transmit the generated information to the entropy encoder 190. Information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

An intra prediction unit (intra predictor) 185 may predict the current block by referring to samples in the current picture. The reference samples may be located in the neighbors of the current block or may be placed separately, depending on the intra prediction mode and/or intra prediction technique. The intra prediction modes may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, a DC mode and a planar mode. Depending on the degree of detail of the prediction direction, the directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is merely an example, and more or fewer directional prediction modes may be used depending on the setting. The intra prediction unit 185 may determine a prediction mode applied to the current block by using a prediction mode applied to neighboring blocks.

The inter prediction unit (inter predictor) 180 may derive a prediction block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring block and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring blocks may be referred to as collocated reference blocks, collocated CUs (colcus), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on neighboring blocks and generate information specifying which candidate to use to derive a motion vector and/or a reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 180 may use motion information of a neighboring block as motion information of the current block. In the case of the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of a Motion Vector Prediction (MVP) mode, a motion vector of a neighboring block may be used as a motion vector predictor, and a motion vector of a current block may be signaled by encoding a motion vector difference and an indicator of the motion vector predictor. The motion vector difference may mean a difference between a motion vector of the current block and a motion vector predictor.

The prediction unit may generate the prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may apply not only intra prediction or inter prediction but also intra prediction and inter prediction at the same time to predict the current block. A prediction method of simultaneously applying both intra prediction and inter prediction to predict a current block may be referred to as Combined Inter and Intra Prediction (CIIP). In addition, the prediction unit may perform Intra Block Copy (IBC) to predict the current block. Intra block copying may be used for content image/video encoding of games and the like, for example, screen content encoding (SCC). IBC is a method of predicting a current picture using a previously reconstructed reference block in the current picture at a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similar to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in this disclosure.

The prediction signal generated by the prediction unit may be used to generate a reconstructed signal or to generate a residual signal. The subtractor 115 may generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal may be transmitted to the transformer 120.

The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transformation techniques may include at least one of Discrete Cosine Transformation (DCT), discrete Sine Transformation (DST), karhunen-lo ve transformation (KLT), graph-based transformation (GBT), or Conditional Nonlinear Transformation (CNT). Here, GBT refers to a transformation obtained from a graph when relationship information between pixels is represented by the graph. CNT refers to a transformation obtained based on a prediction signal generated using all previously reconstructed pixels. Further, the transform process may be applied to square pixel blocks having the same size or may be applied to blocks having a variable size instead of square.

The quantizer 130 may quantize the transform coefficients and send them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients of the block type into a one-dimensional vector form based on the coefficient scan order and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

The entropy encoder 190 may perform various encoding methods, such as exponential golomb, context Adaptive Variable Length Coding (CAVLC), context Adaptive Binary Arithmetic Coding (CABAC), and the like. The entropy encoder 190 may encode information (e.g., values of syntax elements, etc.) required for video/image reconstruction other than quantized transform coefficients together or separately. The encoded information (e.g., encoded video/image information) may be transmitted or stored in units of Network Abstraction Layers (NAL) in the form of a bitstream. The video/image information may also include information about various parameter sets, such as an Adaptive Parameter Set (APS), a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), or a Video Parameter Set (VPS). In addition, the video/image information may also include general constraint information. The signaled information, transmitted information, and/or syntax elements described in this disclosure may be encoded and included in the bitstream through the encoding process described above.

The bit stream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcast network and/or a communication network, and the digital storage medium may include USB, SD, CD, DVD, blu-ray, HDD, SSD, etc. various storage media. A transmitter (not shown) transmitting a signal output from the entropy encoder 190 and/or a storage unit (not shown) storing the signal may be included as an internal/external element of the image encoding apparatus 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

The quantized transform coefficients output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transform to the quantized transform coefficients by the dequantizer 140 and the inverse transformer 150.

The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter prediction unit 180 or the intra prediction unit 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If the block to be processed has no residual, for example, in case of applying a skip mode, the prediction block may be used as a reconstructed block. Adder 155 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and may be used for inter prediction of the next picture by filtering as described below.

The filter 160 may improve subjective/objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed slice and store the modified reconstructed slice in the memory 170, specifically, the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive shifting, adaptive loop filtering, bilateral filtering, and the like. The filter 160 may generate various information related to filtering and transmit the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering may be encoded by the entropy encoder 190 and output in the form of a bitstream.

The modified reconstructed picture sent to the memory 170 may be used as a reference picture in the inter prediction unit 180. When the inter prediction is applied by the image encoding apparatus 100, prediction mismatch between the image encoding apparatus 100 and the image decoding apparatus can be avoided and encoding efficiency can be improved.

The DPB of the memory 170 may store the modified reconstructed picture to be used as a reference picture in the inter prediction unit 180. The memory 170 may store motion information of a block from which motion information in a current picture is derived (or encoded) and/or motion information of a block in a picture that has been reconstructed. The stored motion information may be transmitted to the inter prediction unit 180 and used as motion information of a spatial neighboring block or motion information of a temporal neighboring block. The memory 170 may store reconstructed samples of the reconstructed block in the current picture and may transfer the reconstructed samples to the intra prediction unit 185.

Overview of image decoding apparatus

Fig. 3 is a view schematically showing an image decoding apparatus to which the embodiments of the present disclosure are applicable.

As shown in fig. 3, the image decoding apparatus 200 may include an entropy decoder 210, an inverse quantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter predictor 260, and an intra prediction unit 265. The inter predictor (inter prediction unit) 260 and the intra predictor (intra prediction unit) 265 may be collectively referred to as "prediction unit (predictor)". The inverse quantizer 220 and the inverse transformer 230 may be included in a residual processor.

According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (e.g., a decoder or a processor). Further, the memory 170 may include a Decoded Picture Buffer (DPB) or may be configured by a digital storage medium.

The image decoding apparatus 200, which has received the bitstream including the video/image information, may reconstruct an image by performing a process corresponding to the process performed by the image encoding apparatus 100 of fig. 2. For example, the image decoding apparatus 200 may perform decoding using a processing unit applied in the image encoding apparatus. Thus, the decoded processing unit may be, for example, an encoding unit. The coding unit may be obtained by dividing a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image decoding apparatus 200 may be reproduced by a reproducing apparatus (not shown).

The image decoding apparatus 200 may receive a signal output in the form of a bit stream from the image encoding apparatus of fig. 2. The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video/image information) required for image reconstruction (or picture reconstruction). The video/image information may also include information about various parameter sets, such as an Adaptive Parameter Set (APS), a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), or a Video Parameter Set (VPS). In addition, the video/image information may also include general constraint information. The image decoding apparatus may further decode the picture based on the information on the parameter set and/or the general constraint information. The signaled/received information and/or syntax elements described in this disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes information in a bitstream based on an encoding method such as exponential golomb coding, CAVLC, or CABAC, and outputs values of syntax elements required for image reconstruction and quantized values of transform coefficients of a residual. More specifically, the CABAC entropy decoding method may receive a bin corresponding to each syntax element in a bitstream, determine a context model using decoding target syntax element information, decoding information of neighboring blocks and decoding target blocks, or information of previously decoded symbols/bins, perform arithmetic decoding on the bin by predicting occurrence probability of the bin according to the determined context model, and generate a symbol corresponding to a value of each syntax element. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol/bin for the context model of the next symbol/bin after determining the context model. The prediction-related information among the information decoded by the entropy decoder 210 may be provided to the prediction units (the inter predictor 260 and the intra prediction unit 265), and the residual value on which the entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and the related parameter information may be input to the inverse quantizer 220. In addition, information about filtering among the information decoded by the entropy decoder 210 may be provided to the filter 240. In addition, a receiver (not shown) for receiving a signal output from the image encoding apparatus may be further configured as an internal/external element of the image decoding apparatus 200, or the receiver may be a component of the entropy decoder 210.

Further, the image decoding apparatus according to the present disclosure may be referred to as a video/image/picture decoding apparatus. The image decoding apparatus can be classified into an information decoder (video/image/picture information decoder) and a sample decoder (video/image/picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include at least one of an inverse quantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter prediction unit 260, or an intra prediction unit 265.

The inverse quantizer 220 may dequantize the quantized transform coefficients and output the transform coefficients. The inverse quantizer 220 may rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement may be performed based on the coefficient scan order performed in the image encoding apparatus. The inverse quantizer 220 may perform dequantization on quantized transform coefficients by using quantization parameters (e.g., quantization step size information) and obtain transform coefficients.

The inverse transformer 230 may inverse transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples of the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on information about prediction output from the entropy decoder 210, and may determine a specific intra/inter prediction mode (prediction technique).

As described in the prediction unit of the image encoding apparatus 100, the prediction unit may generate a prediction signal based on various prediction methods (techniques) described later.

The intra predictor 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 applies equally to the intra prediction unit 265.

The inter predictor 260 may derive a prediction block of the current block based on a reference block (reference sample array) specified by the motion vector on the reference picture. In this case, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring block and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction direction (L0 prediction, L1 prediction, bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. For example, the inter predictor 260 may configure a motion information candidate list based on neighboring blocks and derive a motion vector and/or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and the information on prediction may include information specifying an inter prediction mode of the current block.

The adder 235 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to a prediction signal (prediction block, prediction sample array) output from a prediction unit (including the inter predictor 260 and/or the intra prediction unit 265). If the block to be processed has no residual (e.g., when the skip mode is applied), the prediction block may be used as a reconstructed block. The description of adder 155 applies equally to adder 235. Adder 235 may be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and may be used for inter prediction of the next picture by filtering as described below.

The filter 240 may improve subjective/objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 may generate a modified reconstructed picture by applying various filtering methods to the reconstructed slice and store the modified reconstructed slice in the memory 250, specifically, in the DPB of the memory 250. Various filtering methods may include, for example, deblocking filtering, sample adaptive shifting, adaptive loop filtering, bilateral filtering, and the like.

The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter predictor 260. The memory 250 may store motion information of a block from which motion information in a current picture is derived (or decoded) and/or motion information of a block in a picture that has been reconstructed. The stored motion information may be transmitted to the inter predictor 260 to be used as motion information of a spatially neighboring block or motion information of a temporally neighboring block. The memory 250 may store reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra prediction unit 265.

In the present disclosure, the embodiments described in the filter 160, the inter prediction unit 180, and the intra prediction unit 185 of the image encoding apparatus 100 may be equally or correspondingly applied to the filter 240, the inter predictor 260, and the intra predictor 265 of the image decoding apparatus 200.

Overview of CTU segmentation

As described above, the coding units may be acquired by recursively partitioning Coding Tree Units (CTUs) or Largest Coding Units (LCUs) according to a quadtree/binary tree/trigeminal tree (QT/BT/TT) structure. For example, CTUs may be first partitioned into quadtree structures. Thereafter, the leaf nodes of the quadtree structure may be further segmented by the multi-type tree structure.

The partitioning according to the quadtree means that the current CU (or CTU) is equally partitioned into four. By partitioning according to a quadtree, the current CU may be partitioned into four CUs having the same width and the same height. When the current CU is no longer partitioned into a quadtree structure, the current CU corresponds to a leaf node of the quadtree structure. The CUs corresponding to the leaf nodes of the quadtree structure may no longer be partitioned and may be used as the final encoding unit described above. Alternatively, the CUs corresponding to the leaf nodes of the quadtree structure may be further partitioned by the multi-type tree structure.

Overview of inter prediction

Hereinafter, inter prediction according to the present disclosure will be described.

The following inter prediction may be represented by the inter prediction unit in the above-described inter prediction-based video/image decoding method and decoding apparatus on the decoder side. In addition, in the case of an encoder, it can be represented by the above-described inter prediction-based video/image encoding method and inter prediction unit in the encoding apparatus. In addition, the encoded data may be stored in the form of a bitstream.

The prediction unit of the encoding apparatus/decoding apparatus may derive the prediction samples by performing inter prediction on a per block basis. Inter-prediction may be prediction derived in a manner according to data elements (e.g., sample values or motion information) of pictures other than the current picture. When inter prediction is applied to a current block, a prediction block (prediction sample array) of the current block may be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture indicated by a reference picture index. Here, in order to reduce the amount of motion information transmitted in the inter prediction mode, motion information of a current block may be predicted on a per block, sub-block, or sample basis based on a motion information correlation between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may also include inter prediction type (L0 prediction, L1 prediction, bi prediction, etc.) information. When inter prediction is applied, the neighboring blocks may include a spatial neighboring block present in the current picture and a temporal neighboring block present in the reference picture. The reference picture comprising the reference block may be the same or different from the reference picture comprising the temporal neighboring block. The temporal neighboring blocks may be referred to as collocated reference blocks or collocated CUs (colcus). The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the motion information candidate list may be constructed based on neighboring blocks of the current block. Flag or index information indicating which candidate to select (use) to derive a motion vector and/or a reference picture index of the current block may be signaled. Inter prediction may be performed based on various prediction modes. For example, in case of the skip mode and the merge mode, the motion information of the current block may be identical to the motion information of the selected neighboring block. In the case of the skip mode, unlike the merge mode, the residual signal may not be transmitted. In the case of a motion information prediction (motion vector prediction (MVP)) mode, the motion vector of the selected neighboring block may be used as a motion vector predictor and a motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

The motion information may include L0 motion information and/or L1 motion information according to inter prediction types (L0 prediction, L1 prediction, bi prediction, etc.). The motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and the motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on an L0 motion vector may be referred to as L0 prediction. Prediction based on an L1 motion vector may be referred to as L1 prediction. Prediction based on both L0 and L1 motion vectors may be referred to as bi-prediction. Here, the L0 motion vector may refer to a motion vector associated with the reference picture list L0 (L0), and the L1 motion vector may refer to a motion vector associated with the reference picture list L1 (L1). The reference picture list L0 may include a picture preceding the current picture in terms of output order as a reference picture. The reference picture list L1 may include pictures subsequent to the current picture in terms of output order. The previous picture may be referred to as a forward (reference) picture, and the following picture may be referred to as a backward (reference) picture. The reference picture list L0 may further include a picture subsequent to the current picture in terms of output order as a reference picture. In this case, within the reference picture list L0, the previous picture may be first indexed, and the subsequent picture may be indexed. The reference picture list L1 may further include a picture preceding the current picture in terms of output order as a reference picture. In this case, within the reference picture list 1, the following picture may be first indexed, and the preceding picture may be next indexed. Here, the output order may correspond to a Picture Order Count (POC) order.

For example, fig. 4 to 6 schematically show a video/image encoding process based on inter prediction and inter prediction units in an encoding apparatus.

Fig. 4 is a diagram illustrating a video/image encoding method based on inter prediction, and fig. 5 is a diagram illustrating an inter prediction unit in an encoding apparatus.

The encoding apparatus may perform inter prediction on the current block (S1000). The encoding apparatus may derive inter prediction modes and motion information of the current block and may generate prediction samples of the current block. In this context, the processes of determining the intra prediction mode, deriving the motion information, and generating the prediction samples may be performed simultaneously, or any one process may be performed before the other processes. For example, the inter prediction unit 180 of the encoding apparatus may include a prediction mode determination unit 181, a motion information derivation unit 182, and a prediction sample derivation unit 183. The prediction mode determination unit 181 may determine a prediction mode for the current block. The motion information deriving unit 182 may derive motion information of the current block. The prediction sample derivation unit 183 may derive prediction samples of the current block. For example, the inter prediction unit 180 of the encoding apparatus may search a predetermined region (search region) of the reference picture for a block similar to the current block through motion estimation, and may derive a reference block having a minimum difference from the current block or less than or equal to a predetermined standard. Based on this, a reference picture index indicating a reference picture in which a reference block is located may be derived, and a motion vector may be derived based on a position difference between the reference block and the current block. The encoding apparatus may determine a mode applied to the current block among various prediction modes. The encoding apparatus may compare RD costs of various prediction modes and may determine the best prediction mode of the current block.

For example, when the skip mode or the merge mode is applied to the current block, the encoding apparatus may construct a merge candidate list described later, and may derive a reference block having the smallest difference from the current block or less than or equal to a predetermined standard among reference blocks indicated by the merge candidates included in the merge candidate list. In this case, a merge candidate associated with the derived reference block may be selected, and merge index information indicating the selected merge candidate may be generated and signaled to the decoding device. Motion information of the current block may be derived using motion information of the selected merge candidate.

As another example, when (a) MVP mode is applied to the current block, the encoding apparatus may construct (a) MVP candidate list described later, and may use a motion vector of an MVP candidate selected among MVP candidates included in the (a) MVP candidate list as a Motion Vector Predictor (MVP) of the current block. In this case, for example, a motion vector indicating a reference block derived by the above-described motion estimation may be used as the motion vector of the current block. Among mvp candidates, the mvp candidate having the motion vector having the smallest difference from the motion vector of the current block may be the selected mvp candidate. A Motion Vector Difference (MVD) which is a difference value obtained by subtracting mvp from a motion vector of a current block may be derived. In this case, information about the MVD may be signaled to the decoding device. In addition, when the (a) MVP mode is applied, the value of the reference picture index may be constructed as reference picture index information and may be separately signaled to the decoding apparatus.

The encoding apparatus may derive residual samples based on the prediction samples (S1010). The encoding device may compare the prediction samples of the current block with the original samples to derive residual samples.

The encoding apparatus encodes image information including prediction information and residual information (S1020). The encoding apparatus may output the encoded image information in the form of a bitstream. The prediction information is an information item related to the prediction process, and may include prediction mode information (e.g., a skip flag, a merge flag, or a mode index) and information about motion information. The information on the motion information may include candidate selection information (e.g., a merge index, mvp flag, or mvp index) as information to derive the motion vector. In addition, the information on the motion information may include the above-described information on MVD and/or reference picture index information. In addition, the information on the motion information may include information indicating whether to apply L0 prediction, L1 prediction, or bi-prediction. The residual information is information about residual samples. The residual information may include information about quantized transform coefficients of the residual samples.

The output bitstream may be stored in a (digital) storage medium and transmitted to the decoding device or may be transmitted to the decoding device through a network.

Further, as described above, the encoding apparatus may generate a reconstructed picture (including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is to derive the same prediction result as that performed in the decoding apparatus by the encoding apparatus, and accordingly, the encoding efficiency can be improved. Thus, the encoding device may store the reconstructed slice (or reconstructed sample, reconstructed block) in memory and may use it as a reference picture for inter prediction. As described above, the loop filtering process may also be applied to the reconstructed slice.

For example, fig. 7 to 8 schematically show a video/image decoding process based on inter prediction and inter prediction units in a decoding apparatus.

Fig. 7 is a diagram illustrating a video/image decoding method based on inter prediction, and fig. 8 is a diagram illustrating an inter prediction unit in a decoding apparatus.

The decoding apparatus may perform operations corresponding to the operations performed by the encoding apparatus. The decoding apparatus may perform prediction on the current block based on the received prediction information, and may derive prediction samples.

Specifically, the decoding apparatus may determine a prediction mode for the current block based on the received prediction information (S1100). The decoding apparatus may determine which inter prediction mode to apply to the current block based on prediction mode information in the prediction information.

For example, based on the merge flag, it may be determined whether to apply a merge mode or to determine (a) an MVP mode to the current block. Alternatively, one of various inter prediction mode candidates may be selected based on the mode index. The inter prediction mode candidates may include a skip mode, a merge mode, and/or (a) an MVP mode, or may include various inter prediction modes described later.

The decoding apparatus may derive motion information of the current block based on the determined inter prediction mode (S1110). For example, when the skip mode or the merge mode is applied to the current block, the decoding apparatus may construct a merge candidate list described later, and may select one merge candidate from among the merge candidates included in the merge candidate list. The selection may be performed based on the above-described selection information (merge index). Motion information of the current block may be derived using motion information of the selected merge candidate. The motion information of the selected merge candidate may be used as the motion information of the current block.

As another example, when (a) MVP mode is applied to the current block, the decoding apparatus may construct (a) MVP candidate list described later, and may use a motion vector of an MVP candidate selected among MVP candidates included in the (a) MVP candidate list as a Motion Vector Predictor (MVP) of the current block. The selection may be performed based on the above-described selection information (mvp flag or mvp index). In this case, the MVD of the current block may be derived based on the information on the MVD, and the motion vector of the current block may be derived based on mvp and MVD of the current block. In addition, a reference picture index of the current block may be derived based on the reference picture index information. The picture indicated by the reference picture index in the reference picture list related to the current block may be derived as a reference picture referred to by inter prediction of the current block.

Further, as will be described later, the motion information of the current block may be derived without constructing a candidate list. In this case, the motion information of the current block may be derived according to a procedure described in a prediction mode described later. In this case, the candidate list configuration as described above may be omitted.

The decoding apparatus may generate a prediction sample of the current block based on the motion information of the current block (S1120). In this case, a reference picture may be derived based on a reference picture index of the current block, and a prediction sample of the current block may be derived using a sample of the reference block indicated on the reference picture by a motion vector of the current block. In this case, as described later, in some cases, a prediction sample filtering process may be further performed on all or some of the prediction samples of the current block.

For example, the inter prediction unit 260 of the decoding apparatus may include a prediction mode determination unit 261, a motion information derivation unit 262, and a prediction sample derivation unit 263. The prediction mode determination unit 181 may determine the prediction mode of the current block based on the received prediction mode information. The motion information deriving unit 182 may derive motion information (motion vector and/or reference picture index) of the current block based on the received information on the motion information. The prediction sample derivation unit 183 may derive prediction samples of the current block.

The decoding apparatus may generate residual samples of the current block based on the received residual information (S1130). The decoding apparatus may generate a reconstructed sample of the current block based on the prediction sample and the residual sample, and may generate a reconstructed picture based thereon (S1140). Thereafter, as described above, a loop filtering process may be further applied to the reconstructed picture.

As described above, the inter prediction process may include the steps of determining an inter prediction mode, deriving motion information from the determined prediction mode, and performing prediction (generating a prediction sample) based on the derived motion information. The inter prediction process may be performed in the encoding device and the decoding device as described above.

Fig. 8 is a diagram illustrating an inter prediction process.

Various inter prediction modes may be used to predict a current block in a picture. For example, various modes such as a merge mode, a skip mode, a Motion Vector Prediction (MVP) mode, an affine mode, a sub-block merge mode, and a merge (MMVD) mode with MVD, etc., may be used. Decoder-side motion vector refinement (DMVR) mode, adaptive Motion Vector Resolution (AMVR) mode, bi-prediction with CU-level weights (BCW), bi-directional optical flow (BDOF), etc. may also be used as additional modes in addition or instead. Affine mode may be referred to as affine motion prediction mode. The MVP mode may be referred to as an Advanced Motion Vector Prediction (AMVP) mode. In this document, some modes and/or motion information candidates derived from some modes may be included as one of the motion information candidates of other modes. For example, HMVP candidates may be added as merge candidates in merge/skip mode, or may be added as MVP candidates in MVP mode.

Prediction mode information indicating an inter prediction mode of the current block may be signaled from the encoding device to the decoding device. The prediction mode information may be included in the bitstream and received by the decoding device. The prediction mode information may include index information indicating one of a plurality of candidate modes. Alternatively, the inter prediction mode may be indicated through hierarchical signaling of flag information. In this case, the prediction mode information may include one or more flags. For example, a skip flag may be signaled to indicate whether a skip mode is applied, and if a skip mode is not applied, a merge flag may be signaled to indicate whether a merge mode is applied, and if a merge mode is not applied, an MVP mode is indicated or a flag for an additional category may be further signaled. Affine mode may be signaled in an independent mode or may be signaled in a mode according to a merge mode or MVP mode. For example, affine patterns may include affine merge patterns and affine MVP patterns.

Further, information indicating whether the above list0 (L0) prediction, list0 (L1) prediction, or bi-prediction is used in the current block (current coding unit) may be signaled in the current block. This information may be referred to as motion prediction direction information, inter prediction direction information, or inter prediction indication information, and may be configured/encoded/signaled, for example, in the form of an inter predidc syntax element. That is, the inter_pred_idc syntax element may indicate whether the aforementioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used for the current block (current coding unit). In this document, for convenience of description, an inter prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by an inter_pred_idc syntax element may be indicated as a motion prediction direction. The L0 prediction may be denoted as pred_l0, the L1 prediction may be denoted as pred_l1, and the BI-prediction may be denoted as pred_bi. For example, the following prediction type may be indicated according to a value of the inter_pred_idc syntax element.

TABLE 1

As described above, a picture may include one or more slices. The slice may have one of slice types including an intra (I) slice, a predictive (P) slice, and a bi-predictive (B) slice. The slice type may be indicated based on slice type information. For blocks in an I slice, inter prediction may not be used for prediction, and only intra prediction may be used. Of course, even in this case, the original sample values may be encoded and signaled without prediction. Intra prediction or inter prediction may be used for blocks in P slices, and only unidirectional prediction may be used when inter prediction is used. Furthermore, intra prediction or inter prediction may be used for blocks in B slices, and at most bi-prediction may be used when inter prediction is used.

L0 and L1 may include reference pictures previously encoded/decoded before the current picture. For example, L0 may include reference pictures before and/or after the current picture in POC order, and L1 may include reference pictures after and/or before the current picture in POC order. In this case, L0 may be assigned a reference picture index lower than the current reference picture with respect to the previous reference picture in POC order, and L1 may be assigned a reference picture index lower than the current picture with respect to the previous reference picture in POC order. In the case of B slices, bi-directional prediction may be applied, and in this case, uni-directional bi-directional prediction may be applied or bi-directional prediction may be applied. Bi-directional prediction may be referred to as true bi-directional prediction.

Specifically, for example, information on an inter prediction mode of a current block may be encoded at a level such as a CU (CU syntax) and signaled or implicitly determined according to a condition. In this case, in some modes, information may be explicitly signaled, and in other modes, the information may be implicitly derived.

For example, the CU syntax may carry information about the (inter) prediction mode as follows.

TABLE 2

Here, the cu_skip_flag may indicate whether a skip mode is applied to a current block (CU).

The pred_mode_flag being equal to 0 specifies that the current coding unit is coded in inter prediction mode. The pred_mode_flag being equal to 1 specifies that the current coding unit is coded in intra prediction mode.

Pred_mode_ IBC _flag equal to 1 specifies that the current coding unit is coded in IBC prediction mode. pred_mode_ IBC _flag equal to 0 specifies that the current coding unit is not coded in IBC prediction mode.

The pcm_flag [ x0] [ y0] being equal to 1 specifies that there is a pcm_sample () syntax structure and that the transform_tree () syntax structure is not present in the coding unit that contains the luma coding block at position (x 0, y 0). The absence of the pcm_sample () syntax structure is specified by pcm_flag [ x0] [ y0] being equal to 0. That is, the pcm_flag may specify whether a Pulse Code Modulation (PCM) mode is applied to the current block. When the PCM mode is applied to the current block, prediction/transform/quantization or the like is not applied, and the value of the original sample within the current block may be encoded and signaled.

Intra_mip_flag [ x0] [ y0] equals 1 the intra prediction type specified for luma samples is matrix-based intra prediction (MIP). intra_mip_flag [ x0] [ y0] equals 0 specifying that the intra prediction type for luma samples is not MIP. That is, intra_mipflag may specify whether MIP prediction mode (type) is applied to (luma samples of) the current block.

Intra_chroma_pred_mode [ x0] [ y0] specifies the intra prediction mode for chroma samples in the current block.

General_merge_flag [ x0] [ y0] specifies whether to infer (derive) inter prediction parameters for the current coding unit from neighboring inter prediction partitions. That is, the general_merge_flag may indicate that general merging is available, and when the value of the general_merge_flag is 1, the normal merge mode, mmvd mode, and merge sub-block mode (sub-block merge mode) may be available. For example, when the value of general_merge_flag is 1, the merge data syntax may be parsed from the encoded video/image information (or bitstream), and the merge data syntax may be configured/encoded to include the following information.

TABLE 3

Here, the regular_merge_flag [ x0] [ y0] equal to 1 designates that the inter prediction parameter of the current coding unit is generated using the conventional merge mode. That is, the regular_merge_flag indicates whether a merge mode (normal merge mode) is applied to the current block.

Mmvd _merge_flag [ x0] [ y0] equals 1 specifies that a merge mode with a motion vector difference (MMVD) is used to generate the inter prediction parameters for the current coding unit. That is, mmvd _merge_flag indicates whether MMVD is applied to the current block.

Mmvd _cand_flag [ x0] [ y0] specifies whether the first (0) candidate or the second (1) candidate in the merge candidate list is used with motion vector differences derived from mmvd _distance_idx [ x0] [ y0] and mmvd _direction_idx [ x0] [ y0 ].

Mmvd _distance_idx [ x0] [ y0] specifies the index used to derive MMVDDISTANCE [ x0] [ y0 ].

Mmvd _direction_idx [ x0] [ y0] specifies the index used to derive MmvdSign [ x0] [ y0 ].

Merge_ subblock _flag [ x0] [ y0] specifies whether merge mode is used to generate sub-block based inter prediction parameters for the current coding unit. That is, the merge_ subblock _flag may specify whether the sub-block merge mode (or affine merge mode) is applied to the current block.

Merge_ subblock _idx [ x0] [ y0] specifies a merge candidate list of the sub-block-based merge candidate list.

Ciip _flag [ x0] [ y0] specifies whether the combined inter-picture merging and intra-picture prediction is applied to the current coding unit.

Merge_trie_idx0 [ x0] [ y0] specifies the first merge candidate index of the triangle shape based motion compensation candidate list.

Merge_trie_idx1 [ x0] [ y0] specifies the second merge candidate index of the triangle shape based motion compensation candidate list.

Merge_idx [ x0] [ y0] specifies the merge candidate index of the merge candidate list.

Further, referring back to the CU syntax, mvp_l0_flag [ x0] [ y0] specifies the motion vector predictor index for List 0. That is, when the MVP mode is applied, mvp_l0_flag may indicate candidates of MVP selected to drive the current block in MVP candidate list 0.

Mvp_l1_flag [ x0] [ y0] has the same semantics as mvp_l0_flag, where l0 and list 0 are replaced by l1 and list 1, respectively.

Inter _ pred _ idc x0 y0 specifies whether list0, list1, or bi-prediction is to be used for the current coding unit.

Sym_mvd_flag [ x0] [ y0] equals 1 specifies that there are no mvd_coding (x 0, y0, refList, cpIdx) syntax structures and syntax elements ref_idx_l0[ x0] [ y0] and ref_idx_l1[ x0] [ y0] for refList equal to 1. That is, sym_mvd_flag indicates whether symmetrical MVD is used in MVD encoding.

Ref_idx_l0[ x0] [ y0] specifies the list 0 reference picture index for the current coding unit.

Ref_idx_l1[ x0] [ y0] has the same semantics as ref_idx_l0, where L0, L0 and list 0 are replaced by L1, L1 and list 1, respectively.

Inter_affine_flag [ x0] [ y0] equals 1 specifies that for the current coding unit, affine model-based motion compensation is used to generate prediction samples for the current coding unit when decoding P-slices or B-slices.

The cu_affine_type_flag [ x0] [ y0] equal to 1 specifies that for the current coding unit, motion compensation based on a 6-parameter affine model is used to generate prediction samples of the current coding unit when decoding P-slices or B-slices. The cu_affine_type_flag [ x0] [ y0] equal to 0 specifies that motion compensation based on a 4-parameter affine model is used to generate prediction samples for the current coding unit.

Amvr _flag [ x0] [ y0] specifies the resolution of the motion vector difference. The array indices x0, y0 specify the position (x 0, y 0) of the top-left luma sample of the coding block under consideration relative to the top-left luma sample of the picture. amvr _flag [ x0] [ y0] equals 0 specifying that the resolution of the motion vector difference is 1/4 of the luma samples. The resolution of amvr _flag [ x0] [ y0] equal to 1 to specify the motion vector difference is further specified by amvr _precision_idx [ x0] [ y0 ].

Amvr _precision_flag [ x0] [ y0] equals 0 specifying that when inter_affine_flag [ x0] [ y0] is 0, the resolution of the motion vector difference is one integer luma sample and otherwise, the resolution of the motion vector difference is 1/16 of the luma sample. amvr _precision_flag [ x0] [ y0] equals 1 specifying that when inter_affine_flag [ x0] [ y0] is 0, the resolution of the motion vector difference is four luma samples, and otherwise, the resolution of the motion vector difference is one integer luma sample. The array indices x0 and y0 specify the position (x 0, y 0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.

Bcw _idx [ x0] [ y0] specifies the weight index of bi-prediction with CU weights.

Derivation of motion information

Inter prediction may be performed using motion information of the current block. The encoding device may derive the best motion information for the current block through a motion estimation process. For example, the encoding apparatus may search for a similar reference block having high correlation in units of fractional pixels within a predetermined search range in a reference picture using an original block in an original picture for a current block, thereby deriving motion information. The similarity of the blocks may be deduced from differences in phase-based sample values. For example, the similarity of a block may be calculated based on the SAD between the current block (or a template of the current block) and the reference block (or a template of the reference block). In this case, the motion information may be derived based on the reference block having the smallest SAD in the search region. The derived motion information may be signaled to the decoding device according to various methods based on inter prediction modes.

Generation of prediction samples

The prediction block of the current block may be derived based on motion information derived from the prediction mode. The prediction block may include prediction samples (prediction sample array) of the current block. When the motion vector of the current block indicates a fractional sample unit, an interpolation process may be performed by which a prediction sample of the current block may be derived based on reference samples in the fractional sample unit within the reference picture. When affine inter prediction is applied to the current block, a prediction sample may be generated based on the sample/sub-block unit MV. When bi-prediction is applied, a prediction sample derived by weighting or weighted averaging (according to phase) a prediction sample derived based on L0 prediction (that is, prediction using MVL0 in reference picture and reference picture list L0) and a prediction sample derived based on L1 prediction (that is, prediction using MVL1 in reference picture and reference picture list L1) may be used as a prediction sample of the current block. When bi-prediction is applied, if a reference picture for L0 prediction and a reference picture for L1 prediction are located in different temporal directions (i.e., bi-prediction and bi-prediction) with respect to a current picture, it may be referred to as true bi-prediction.

As described above, a reconstructed sample and a reconstructed picture may be generated based on the derived prediction sample, and thereafter, a process such as in-loop filtering may be performed.

As described above, inter prediction may be performed based on reference pictures, and the resolution of each picture may vary in units such as a group of pictures (GOP). That is, a case may occur in which the resolutions of the current picture and the reference picture are different.

Further, even if the resolutions of the two pictures are different, if the reference picture and the current picture belong to the same CLVS (coding layer video sequence) or the like, prediction of the current picture can be performed by a Reference Picture Resampling (RPR) technique that performs additional processing for the different resolutions. According to the reference picture resampling technique, the resolution of the reference picture may be modified.

That is, the resolution can be adjusted in the picture in one layer. If the resolutions of the current picture and the reference picture are different, a resolution ratio between the reference picture and the current picture is calculated, and the reference picture can be referenced by modifying the resolution to the same size as the current picture through sampling. Further, the resolution may be determined based on a periodic time (0.5 seconds, 1 second, etc.), a predetermined number of frames (8, 16, 32, 64, 128, etc.), a plurality of GOPs (group of pictures), a plurality of RAPs (random access points), etc. When determining the resolution in this way, there is a problem that the optimal resolution cannot be determined since the resolution is mechanically determined without considering the characteristics of each picture.

To improve this, the present disclosure proposes a configuration of modifying resolution by adaptively selecting a plurality of resolution ratios. According to the present disclosure, encoding and decoding efficiency can be greatly improved by determining a resolution ratio between a current picture and a reference picture, that is, determining an optimal resolution, and resampling a reference sample by determining a resolution ratio between a reference picture and a current picture.

In addition, according to the present disclosure, as an encoder technique and a decoder technique related to an adaptive resolution modification technique, when resolutions of a reference picture and a current picture are different, a method of transmitting related information and a control method for the encoder technique and the decoder technique are provided. Thus, a solution to the above-described problems can be provided.

In addition, according to one embodiment of the present disclosure, the resolution may be determined by considering quantization parameters and/or complexity (e.g., PSNR, bit rate, etc.) of the picture, and at this time, one resolution may be selected from among various resolutions.

More specifically, according to one embodiment of the present disclosure, for an adaptive resolution modification technique and/or a Reference Picture Resampling (RPR) technique, the best resolution (i.e., the best resolution ratio) may be determined by considering quantization parameters and/or complexity of the picture.

Further, before determining the optimal resolution ratio and applying the resolution modification technique and/or the reference picture resampling technique, it may be determined whether the resolution modification technique is applied to the current picture, whether the reference picture resampling is performed, and so on. In an image encoding device, this may be encoded as specific information and included in the bitstream, but it may also be implicitly derived from other information.

Hereinafter, an embodiment of determining the optimal resolution ratio according to the present disclosure will be described.

As an example, the image encoding and/or decoding device may select one of a plurality of resolution ratios. For each group of pictures (GOP), the image encoding device may select one of a plurality of candidate resolutions based on a peak signal-to-noise ratio (PSNR) threshold that varies according to an initial quantization parameter. To determine the resolution, PSNR between a picture obtained by downsampling (downsizing) or upsampling (upsizing) (e.g., a picture obtained by downsampling or upsampling the first picture of each GOP) and an original picture (e.g., a source picture, the first picture of each GOP) may be derived for the first picture of each GOP. The PSNR of the current picture may be derived based on the PSNR of the first picture in the same GOP. Further, the resolution may be determined in units of GOP, and the GOP may include one or more pictures (pictures). That is, PSNR can be calculated between an original image and an up-sampled or down-sampled image. Here, the first picture may be downsampled (downscaled) to a resolution (half resolution) corresponding to half the original resolution, and then resampled back to the original resolution.

As an example, when using an adaptive resolution modification technique or a reference picture resampling technique, one of various candidate resolutions may be selected for one picture. For example, the candidate resolution may include 1/2, 2/3, or 1. Here, 1 may represent an original resolution, and may be up-sampled or down-sampled to each resolution. Further, the candidate resolution may be expressed as 2, 3/2, or 1. That is, the reference picture may have a resolution smaller or larger than the current picture by 2, may have a resolution smaller or larger than the current picture by 3/2, or may have the same resolution as the current picture. If they have the same resolution, the resolution ratio adjustment may not be performed.

Further, the resolution ratio may be derived from index information indicating the resolution ratio, and the index information may be included in the bitstream as VPS, SPS, PPS, a picture header, a slice header, or the like. In addition, the index information may be flag information. One of a plurality of resolution ratios may be selected using the corresponding index information. As another example, information about the resolution ratio may also be derived based on other information.

As an example, one of the resolutions may be selected according to a PSNR threshold that adaptively varies based on the quantization parameter. As one example, when Reference Picture Resampling (RPR) is performed on a picture included in any i-th GOP, a resolution ratio (scaling factor) (rpr_r) may be derived as follows.

[ 1]

As one example, the resolution ratio may be selected based on the scaled PSNR value (SCALEDPSNR). The variable SCALEDPSNR _i value may mean the above-described upsampled PSNR of the first picture in any i-th GOP. In addition, variables BasePSNR and BaseQP may represent specific PSNR and Quantization Parameters (QP), respectively, and each value may be predefined. The variable OffsetPSNR may represent the PSNR gap between images with two different resolutions. For example, variable OffsetPSNR may represent the PSNR gap between images having 1/2 and 2/3 resolution or 2 and 3/2 resolution as compared to the original image. The variable Decay may refer to a rate of decrease of the threshold PSNR value according to the quantization parameter, and may be maintained at a constant value or changed. Further, QP _i may refer to the initial quantization parameter for the first picture in any iGOP. The quantization parameter values and/or PSNR values may be used when determining the resolution ratio with the reference picture. In addition, the quantization parameter value may be an initial quantization parameter value, and the quantization parameter value may be compared with a specific quantization parameter value. That is, the resolution ratio may be determined based on an operation (e.g., subtraction, etc.) that compares the quantization parameter value with a particular quantization parameter value. In addition, the PSNR value may be compared with a specific PSNR value. That is, the resolution ratio may be determined based on an operation (e.g., subtraction, etc.) that compares the PSNR value with a particular PSNR value. That is, the resolution ratio between the reference picture and the current picture may be determined in units of group of pictures (GOP), and thus the same resolution ratio may be shared between pictures included in the same GOP.

According to [ formula 1] above, in one embodiment, the QP range is set to 27 to 47, and pictures for both half (1/2) (ScalingRatioHor =2.0 and ScalingRatioVer =2.0) and 2/3 (ScalingRatioHor =1.5 and ScalingRatioVer =1.5) resolutions are adjusted to the original resolution (UpscaledOutput =2), respectively, and BaseQP, offsetPSNR and Decay may be set to 37, 3, and 0.5. Here BasePSNR for RA and AI may be set to 45 and 41, respectively. Here, when an image is encoded at half (1/2) or 2/3 resolution of the original image, the QP value may be adjusted based on the offset. Furthermore, the QP value may be adjusted based on an offset defined as-6 for an image having a 1/2 resolution ratio and an offset defined as-4 for an image having a 2/3 resolution ratio. The performance test according to this can be deduced as follows. Table 4 may show the performance of the proposed embodiment in RA.

TABLE 4

	Y	U	V	EncT	DecT
						Class A1	-7.22％	3.40％	3.85％	76％	43％
Class A2	-4.17％	19.43％	16.12％	79％	57％
						Class B	-0.43％	3.75％	3.11％	95％	84％
Class C	0.00％	0.00％	0.00％	100％	101％
						Class E
Overall (L)	-2.42％	5.82％	5.03％	89％	71％
						Class D	0.00％	0.00％	0.00％	100％	100％
Class F	0.00％	0.00％	0.00％	101％	102％

In table 4, the encoding time (EncT) and decoding time (DecT) may be ignored. In addition, since the coding gain is obtained in the class A1 and the class A2, the LD test can be omitted.

In addition, the above equation 1 for deriving the resolution ratio (scaling factor) (rpr_sf) may be modified as follows.

[ 2]

As an example, as described above, variable DnUpPSNR may represent the downsampled or upsampled PSNR of the first picture in any i-th GOP. Other variables BasePSNR, baseQP, offsetPSNR and the like may have the same meaning as described in formula 1 above. QP _i may also refer to the initial quantization parameter for the first picture in the i-th GOP. Further, unlike [ formula 1], the threshold value multiplied by the quantization parameter value (or a comparison value between the quantization parameter and the initial quantization parameter value) may be specified as a specific value. That is, it may be a variable (e.g., decay) value in [ formula 1], but may be a specific value (e.g., 0.5) in [ formula 2 ].

As one embodiment according to [ formula 2], the QP range is set to 22 to 42, and pictures for half (1/2) (ScalingRatioHor =2.0 and ScalingRatioVer =2.0) and 2/3 (ScalingRatioHor =1.5 and ScalingRatioVer =1.5) resolution are adjusted to original resolution (UpscaledOutput =2), respectively, and BaseQP and OffsetPSNR may be set to 37 and 3. Here BasePSNR for RA and AI may be set to 45 and 42, respectively. Here, when an image is encoded at half (1/2) or 2/3 resolution of the original image, the QP value may be adjusted based on the offset. Furthermore, the QP value may be adjusted based on an offset defined as-6 for an image having a 1/2 resolution ratio and an offset defined as-4 for an image having a 2/3 resolution ratio. The performance test according to this can be deduced as follows. Table 5 may show the performance of the proposed implementation in AI and table 6 may show the performance of the proposed implementation in RA.

TABLE 5

	Y	U	V	EncT	DecT
						Class A1	-1.55％	2.38％	2.60％	108％	65％
Class A2	-2.81％	12.66％	9.69％	94％	74％
						Class B	0.52％	2.13％	2.27％	96％	87％
Class C	0.00％	0.00％	0.00％	98％	95％
						Class E	0.09％	0.25％	0.27％	96％	94％
Overall (L)	-0.57％	3.14％	2.73％	98％	83％
						Class D	0.02％	0.06％	0.05％	97％	99％
Class F	0.00％	0.00％	0.00％	95％	98％

TABLE 6

	Y	U	V	EncT	DecT
						Class A1	-3.48％	2.23％	3.71％	78％	54％
Class A2	-1.55％	7.82％	6.70％	86％	73％
						Class B	0.08％	1.83％	1.27％	97％	89％
Class C	0.00％	0.00％	0.00％	100％	99％
						Class E
Overall (L)	-0.98％	2.62％	2.50％	92％	80％
						Class D	0.00％	0.00％	0.00％	100％	101％
Class F	0.00％	0.00％	0.00％	101％	100％

In addition, the performance calculated for the embodiments with QP ranges from 27 to 47 may be as shown in tables 7 to 8 below. Also, [ table 7] can show the performance of the proposed implementation in AI, and [ table 8] can show the performance of the proposed implementation in RA.

TABLE 7

	Y	U	V	EncT	DecT
						Class A1	-4.87％	5.83％	4.06％	114％	51％
Class A2	-5.66％	25.61％	18.95％	101％	60％
						Class B	0.00％	3.39％	3.66％	102％	78％
Class C	0.00％	-0.05％	-0.03％	98％	93％
						Class E	0.50％	0.05％	0.18％	98％	80％
Overall (L)	-1.67％	6.18％	4.87％	102％	73％
						Class D	0.02％	0.07％	0.05％	97％	95％
Class F	0.01％	-0.01％	0.01％	96％	95％

TABLE 8

	Y	U	V	EncT	DecT
						Class A1	-7.22％	3.40％	3.85％	76％	43％
Class A2	-4.17％	19.43％	16.12％	79％	57％
						Class B	-0.43％	3.75％	3.11％	95％	82％
Class C	0.00％	0.00％	0.00％	100％	100％
						Class E
Overall (L)	-2.42％	5.82％	5.03％	89％	71％
						Class D	0.00％	0.00％	0.00％	100％	101％
Class F	0.00％	0.00％	0.00％	102％	99％

According to the above-described embodiments of the present disclosure, one resolution ratio may be selected from one or more resolution ratio candidates, so that encoding/decoding encoding efficiency may be significantly improved.

Hereinafter, embodiments of the present disclosure for adaptively modifying resolution will be described in more detail with reference to the accompanying drawings.

Fig. 9 is a diagram illustrating an image encoding method according to an embodiment of the present disclosure.

As an example, the image encoding method of fig. 9 may be performed by an image encoding apparatus. Examples of the image encoding apparatus are the same as those described with reference to the other drawings.

First, an image encoding method performed by an image encoding apparatus may determine a reference picture for inter prediction of a current picture (S1901). As an example, the resolutions of the current picture and the reference picture may be different from each other and may belong to different GOPs. That is, the resolution may be applied in units of group of pictures (GOP). The process of determining whether to perform inter prediction of a current picture or a reference picture for inter prediction of the current picture may be derived as described above with reference to other figures.

In addition, a resolution ratio between the derived reference picture and the current picture may be derived (S1902). As an example, step S1902 may be performed after determining that the resolutions of the reference picture and the current picture are different. Here, the resolution ratio may be derived as one of a plurality of resolution ratios, and the plurality of resolution ratios may be predefined. For example, the plurality of resolution ratios may include at least one of 2, 3/2, or 1, and may be represented as 1/2, 2/3, or 1. The quantization parameter or PSNR described above may be used when one resolution ratio is selected from a plurality of resolution ratios. The resolution ratio may be determined based on an initial quantization parameter of a first picture in the same GOP as the current picture. Additionally, the initial quantization parameter may be compared to a particular quantization parameter value. Furthermore, the resolution ratio may be determined further based on the PSNR of the first picture within the GOP. Here, when calculating the PSNR, the first picture may be reduced in size (downsampled) or enlarged in size (upsampled) to a specific resolution. The PSNR of the first picture may be compared with a specific PSNR value.

The resolution of the reference picture may be modified based on the resolution ratio (S1903). As an example, resolution index information indicating a resolution ratio may be encoded into a bitstream. The reference picture of modified resolution may be used as a reference picture for inter prediction of the current picture.

Further, since fig. 9 corresponds to one embodiment of the present disclosure, some steps may be modified, deleted, or added. For example, it may further include a step of determining whether reference picture resampling is applied to the current picture or a step of encoding index information indicating a resolution ratio into the bitstream. In this case, the reference picture resampling may be determined based on whether an encoding tool (e.g., BDOF, DMVR, PROF or TMVP) is applied. In addition, the order of some steps may be changed.

Fig. 10 is a diagram illustrating an image decoding method according to an embodiment of the present disclosure.

As an example, the image decoding method of fig. 10 may be performed by an image decoding apparatus. Examples of the image decoding apparatus are the same as those described with reference to the other drawings.

In addition, each step (S1901, S1902, S1903) of the image encoding method described in fig. 9 may correspond to each step (S2001, S2002, S2003) in fig. 10. In other words, it also corresponds to each step in fig. 10 as long as it does not collide with the decoding method, and the content of the corresponding description can be applied.

First, an image decoding method performed by an image decoding apparatus may derive a reference picture for inter prediction of a current picture (S2001). As described above, whether to perform inter prediction of the current picture and the reference picture may be determined by the encoding apparatus, and resolutions of the current picture and the reference picture may be different. That is, the GOP to which the current picture belongs and the GOP to which the reference picture belongs may be identical to each other.

In addition, a resolution ratio between the derived reference picture and the current picture may be derived (S2002). Here, the resolution ratio may be derived as one of a plurality of resolution ratios, and the plurality of resolution ratios may be predefined. For example, the plurality of resolution ratios may include at least one of 2, 3/2, or 1, and may be represented as 1/2, 2/3, or 1. One of the plurality of resolution ratios may be selected by information (e.g., index information) indicating the resolution ratio decoded from the bitstream. Furthermore, the quantization parameter or PSNR described above may be used to derive the selected resolution ratio. This is the same as described above.

Thereafter, the resolution of the reference picture may be modified based on the resolution ratio (S2003). As described above, when the resolution of a reference picture is modified, inter prediction according to resampling of the reference picture may be performed. That is, the reference picture of which resolution has been modified may be used as a reference picture for inter prediction of the current picture.

Further, since fig. 10 corresponds to one embodiment of the present disclosure, some steps may be modified, deleted, or added. For example, it may further include a step of determining whether reference picture resampling is applied to the current picture or a step of decoding index information indicating a resolution ratio from a bitstream. In this case, whether to apply reference picture resampling may be determined by decoding the related information from the bitstream, or may be implicitly derived and determined from other information. In addition, reference picture resampling may be performed based on whether an encoding tool (e.g., BDOF, DMVR, PROF or TMVP) is applied. In addition, the order of some steps may be changed.

Fig. 11 is a diagram illustrating an image encoding or decoding apparatus according to an embodiment of the present disclosure.

As an example, the image encoding or decoding device 2100 may include a memory 2101 and one or more processors 2102, and the image encoding or decoding device may perform the above-described image encoding or decoding methods, respectively.

In addition, although not shown in the figures, user interfaces, I/O tools, displays, etc. may also be included.

As an example, one or more processors perform the above-described embodiments and image encoding/decoding methods, but some steps may be performed in parallel, or the order of some steps may be changed or some steps may be omitted, if possible.

According to the present disclosure described above, since the optimal resolution ratio is determined more adaptively, more detailed and more efficient reference picture resampling can be performed.

Various embodiments according to the present disclosure may be used alone or in combination with other embodiments.

While, for purposes of clarity of description, the above-described exemplary methods of the present disclosure are presented as a series of operations, it is not intended to limit the order in which the steps are performed, and the steps may be performed simultaneously or in a different order, if desired. To implement the method according to the invention, the described steps may further comprise other steps, may comprise other steps than some steps, or may comprise other additional steps than some steps.

In the present disclosure, an image encoding apparatus or an image decoding apparatus that performs a predetermined operation (step) may perform an operation (step) of confirming an execution condition or situation of the corresponding operation (step). For example, if it is described that the predetermined operation is performed when the predetermined condition is satisfied, the image encoding apparatus or the image decoding apparatus may perform the predetermined operation after determining whether the predetermined condition is satisfied.

The various embodiments of the present disclosure are not a list of all possible combinations and are intended to describe representative aspects of the present disclosure, and the items described in the various embodiments may be applied independently or in combinations of two or more.

Various embodiments of the present disclosure may be implemented in hardware, firmware, software, or a combination thereof. Where the present disclosure is implemented in hardware, the present disclosure may be implemented by an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Digital Signal Processing Device (DSPD), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a general purpose processor, a controller, a microcontroller, a microprocessor, or the like.

Further, the image decoding apparatus and the image encoding apparatus to which the embodiments of the present disclosure are applied may be included in multimedia broadcast transmitting and decoding apparatuses, mobile communication terminals, home theater video devices, digital cinema video devices, monitoring cameras, video chat devices, real-time communication devices such as video communication, mobile streaming devices, storage media, cameras, video on demand (VoD) service providing devices, OTT video (over the top video) devices, internet streaming service providing devices, three-dimensional (3D) video devices, video telephony video devices, medical video devices, and the like, and may be used to process video signals or data signals. For example, OTT video devices may include gaming machines, blu-ray players, internet access televisions, home theater systems, smart phones, tablet PCs, digital Video Recorders (DVRs), and the like.

Fig. 12 is a view showing a content streaming system to which an embodiment of the present disclosure is applicable.

As shown in fig. 12, a content streaming system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming server, a web server, a media storage device, a user device, and a multimedia input device.

The encoding server compresses content input from a multimedia input device such as a smart phone, a camera, a video camera, etc. into digital data to generate a bit stream and transmits the bit stream to the streaming server. As another example, the encoding server may be omitted when the multimedia input device of a smart phone, a camera, a video camera, etc. directly generates the bitstream.

The bitstream may be generated by an image encoding method or an image encoding apparatus to which the embodiments of the present disclosure are applied, and the streaming server may temporarily store the bitstream in transmitting or receiving the bitstream.

The streaming server transmits multimedia data to the user device based on a request of the user through the web server, and the web server serves as a medium informing the user of the service. When a user requests a desired service from a network server, the network server may deliver it to a streaming server, and the streaming server may send multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server is used to control commands/responses between devices in the content streaming system.

The streaming server may receive content from the media storage device and/or the encoding server. For example, the content may be received in real-time as the content is received from the encoding server. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

Examples of user devices may include mobile phones, smart phones, laptops, digital broadcast terminals, personal Digital Assistants (PDAs), portable Multimedia Players (PMPs), navigation devices, slate PCs, tablet PCs, superbooks, wearable devices (e.g., smart watches, smart glasses, head mounted displays), digital televisions, desktop computers, digital signage, and the like.

The respective servers in the content streaming system may operate as distributed servers, in which case the data received from the respective servers may be distributed.

The scope of the present disclosure includes software or machine-executable commands (e.g., operating system, applications, firmware, programs, etc.) for enabling the operation of the methods according to various embodiments to be performed on a device or computer, non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

Industrial applicability

Embodiments of the present disclosure may be used to encode or decode images.

Claims

1. An image encoding method performed by an image encoding apparatus, the image encoding method comprising the steps of:

determining a reference picture for inter prediction of a current picture;

deriving a resolution ratio between the reference picture and the current picture; and

The resolution of the reference picture is modified based on the resolution ratio,

Wherein resolution index information indicating the resolution ratio is encoded into the bitstream.

2. The image encoding method of claim 1, wherein the resolution index information indicates one of a plurality of resolution ratios.

3. The image encoding method of claim 1, wherein the resolution ratio comprises a first resolution ratio of 2 and a second resolution ratio of 3/2.

4. The image encoding method of claim 1, wherein the resolution is applied in units of group of pictures GOP.

5. The image encoding method of claim 4, wherein the resolution ratio is determined based on an initial quantization parameter of a first picture in the GOP.

6. The image encoding method of claim 5, wherein the initial quantization parameter is compared with a specific quantization parameter value.

7. The image encoding method of claim 4, wherein the resolution ratio is derived by downscaling the first picture to a particular resolution.

8. The image encoding method of claim 4 wherein the resolution ratio is determined based on a peak signal-to-noise ratio PSNR of a first picture in the GOP.

9. The image encoding method of claim 8, wherein the PSNR of the first picture is compared with a specific PSNR value.

10. The image encoding method according to claim 1, wherein the image encoding method further comprises the steps of: it is determined whether to perform reference picture resampling on the current picture.

11. The image encoding method of claim 10, wherein the reference picture resampling is performed based on whether BDOF, DMVR, PROF or TMVP is applied.

12. An image decoding method performed by an image decoding apparatus, the image decoding method comprising the steps of:

deriving a reference picture for inter prediction of a current picture;

Wherein the resolution ratio is derived based on resolution index information of the bitstream.

13. The image decoding method of claim 12, wherein said resolution ratio comprises a first resolution ratio of 2 and a second resolution ratio of 3/2.

14. A non-transitory computer readable medium storing a bitstream generated by the image encoding method according to claim 1.

15. A method of transmitting a bitstream generated by an image encoding method, the image encoding method comprising the steps of:

determining a reference picture for inter prediction of a current picture;