Image encoding / decoding method and apparatus based on whether reference between layers is determined for sublayer, and method of transmitting bitstream

Abstract

An image encoding / decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus according to the present disclosure can include the steps of determining whether direct reference is made between layers; and determining a number of sub-layers of a current layer based on whether direct reference is made between layers.

Description

Technical Field

[0001] This disclosure relates to image encoding / decoding methods and apparatus, and more specifically, to an image encoding and decoding method and apparatus for determining sublayers based on interlayer references, and a method for transmitting a bitstream generated by the image encoding method / apparatus of this disclosure. Background Technology

[0002] Recently, the demand for high-resolution and high-quality images (such as high-definition (HD) and ultra-high-definition (UHD) images) is increasing across various fields. With the improvement in image data resolution and quality, the amount of information or bits transmitted increases relatively compared to existing image data. This increase in the amount of information or bits transmitted leads to increased transmission and storage costs.

[0003] Therefore, efficient image compression technology is needed to effectively send, store, and reproduce information about high-resolution and high-quality images. Summary of the Invention

[0004] Technical issues

[0005] The purpose of this disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] Another object of this disclosure is to provide an image encoding / decoding method and apparatus that improves encoding / decoding efficiency by determining sublayers based on interlayer references.

[0007] Another object of this disclosure is to provide a method for transmitting a bitstream generated by an image encoding method or device according to this disclosure.

[0008] Another object of this disclosure is to provide a recording medium storing a bitstream generated by an image encoding method or apparatus according to this disclosure.

[0009] Another object of this disclosure is to provide a recording medium that stores a bitstream received, decoded, and used to reconstruct an image by an image decoding apparatus according to this disclosure. For example, a bitstream that enables the image decoding apparatus according to this disclosure to perform an image decoding method according to this disclosure can be stored in the recording medium.

[0010] The technical problems solved by this disclosure are not limited to those described above. Other technical problems not described herein will become clear to those skilled in the art through the following description.

[0011] Technical solution

[0012] An image decoding method performed by an image decoding device according to one aspect of this disclosure may include the following steps: determining an interlayer direct reference; and determining the number of sublayers of the current layer based on the interlayer direct reference.

[0013] Additionally, an image decoding device may include a memory and at least one processor. The at least one processor may be configured to determine inter-layer direct references and, based on these inter-layer direct references, determine the number of sub-layers of the current layer.

[0014] Alternatively, an image coding method performed by an image coding device may include: determining interlayer direct references; and determining the number of sublayers of the current layer based on the interlayer direct references.

[0015] Alternatively, according to another aspect of the transmission method of this disclosure, a bit stream generated by an image encoding device or method according to this disclosure can be transmitted.

[0016] Additionally, according to another aspect of this disclosure, a computer-readable recording medium can store a bitstream generated by an image encoding method or apparatus according to this disclosure.

[0017] Additionally, according to another aspect of this disclosure, a computer-readable recording medium can store a bitstream that enables a decoding device to perform an image decoding method according to this disclosure.

[0018] The features briefly outlined above are merely exemplary aspects of the following detailed description of this disclosure and do not limit the scope of this disclosure.

[0019] Beneficial effects

[0020] According to this disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0021] Furthermore, according to this disclosure, an image encoding / decoding method and apparatus can be provided to improve encoding / decoding efficiency by determining sublayers based on interlayer references.

[0022] Furthermore, according to this disclosure, a method for transmitting a bitstream generated by an image encoding method or device according to this disclosure can be provided.

[0023] Furthermore, according to this disclosure, a recording medium storing a bitstream generated by an image encoding method or apparatus according to this disclosure can be provided.

[0024] Furthermore, according to this disclosure, a recording medium may be provided that stores a bitstream that is received, decoded, and used to reconstruct an image by an image decoding device according to this disclosure.

[0025] Those skilled in the art will understand that the effects achievable through this disclosure are not limited to those specifically described above, and that other advantages of this disclosure will become clearer from the detailed description. Attached Figure Description

[0026] Figure 1 This is a view schematically illustrating a video encoding system to which embodiments of this disclosure are applicable.

[0027] Figure 2 This is a schematic view illustrating an image encoding device to which embodiments of the present disclosure are applicable.

[0028] Figure 3 This is a schematic view illustrating an image decoding device to which embodiments of the present disclosure are applicable.

[0029] Figure 4 and Figure 5 This is a view illustrating an example of the screen decoding and encoding process according to an implementation method.

[0030] Figure 6 This is a view showing the layer structure of the encoded image according to an embodiment.

[0031] Figures 7 to 8 This is an example of a view based on multi-layered encoding and decoding.

[0032] Figure 9 This is a view illustrating the syntax structure of a VPS according to an embodiment of this disclosure.

[0033] Figures 10 to 14 This is a view illustrating pseudocode for deriving VPS-related variables according to an embodiment of this disclosure.

[0034] Figure 15 This is a view illustrating the syntax structure of a VPS according to another embodiment of this disclosure.

[0035] Figure 16 This is a view illustrating pseudocode for deriving VPS-related variables according to another embodiment of this disclosure.

[0036] Figure 17 This is a view illustrating the syntax structure of a VPS according to another embodiment of this disclosure.

[0037] Figure 18 This is a view illustrating pseudocode for deriving VPS-related variables according to another embodiment of this disclosure.

[0038] Figure 19 This is a view illustrating an encoding and / or decoding method according to another embodiment of the present disclosure.

[0039] Figure 20 This is a view illustrating the content streaming system to which embodiments of this disclosure are applicable. Detailed Implementation

[0040] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, this disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0041] In describing this disclosure, detailed descriptions of relevant known functions or constructions will be omitted if they unnecessarily obscure the scope of this disclosure. In the accompanying drawings, portions irrelevant to the description of this disclosure are omitted, and similar reference numerals are assigned to similar portions.

[0042] In this disclosure, when a component is "connected," "linked," or "coupled" to another component, it may include not only a direct connection but also an indirect connection with intermediate components. Furthermore, when a component "comprises" or "has" other components, unless otherwise stated, it means that other components may be included, not excluded.

[0043] In this disclosure, the terms first, second, etc., may be used only for the purpose of distinguishing one component from other components and do not limit the order or importance of the components, unless otherwise stated. Accordingly, within the scope of this 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.

[0044] In this disclosure, the components are distinguished from each other to clearly describe each feature, but this does not mean that the components must be separate. That is, multiple components may be integrated and implemented in a single hardware or software unit, or a single component may be distributed and implemented in multiple hardware or software units. Therefore, unless otherwise stated, these implementations, in which components are integrated or distributed, are included within the scope of this disclosure.

[0045] In this disclosure, the components described in the various embodiments are not necessarily essential components, and some components may be optional. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included within the scope of this disclosure. In addition, embodiments that include other components besides those described in the various embodiments are also included within the scope of this disclosure.

[0046] This disclosure relates to the encoding and decoding of images. Unless redefined in this disclosure, the terms used herein may have the general meaning commonly used in the art to which this disclosure pertains.

[0047] The methods / implementations disclosed in this disclosure are applicable to the methods disclosed in the Multifunctional Video Coding (VVC) standard. Additionally, the methods / implementations disclosed in this disclosure are applicable to the methods disclosed in the Basic Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second-generation Audio Video Coding (AVS2) standard, or next-generation video / image coding standards (e.g., H.267 or H.268).

[0048] This disclosure provides various implementations of video / image encoding, and implementations not described herein may be combined and performed.

[0049] In this disclosure, "video" can mean a collection of images over time. A "picture" typically refers to a unit representing an image at a specific time, and a slice / piece is a coding unit that constitutes part of a picture in coding. A slice / piece may include one or more coding tree units (CTUs). A CTU may be divided into one or more CUs.

[0050] A frame can consist of one or more slices / tiles. A tile is a rectangular area within a specific tile row and a specific tile column in a frame, and can consist of multiple CTUs. A tile column can be defined as a rectangular area of ​​a CTU, and can have a height equal to the height of the frame and a width specified by a syntax element signaled from a bitstream portion such as a frame parameter set. A tile row can be defined as a rectangular area of ​​a CTU, and can have a width equal to the width of the frame and a height specified by a syntax element signaled from a bitstream portion such as a frame parameter set.

[0051] Tiled scanning is a specific ordering of CTUs that divide a frame. Here, CTUs are ordered consecutively in a CTU raster scan, while the tiles in a frame are ordered consecutively in a frame tile raster scan. A slice consists of an integer number of complete tiles or an integer number of consecutive complete CTU rows within a frame tile. Slices can be exclusively contained within a single NAL unit.

[0052] A frame can be divided into two or more sub-frames. A sub-frame can be a rectangular area of ​​one or more slices of the frame.

[0053] A frame can include one or more tile groups. A tile group can include one or more tiles. A tile can represent a rectangular area of ​​a CTU row within a tile in the frame. A tile can include one or more tiles. A tile can represent a rectangular area of ​​a CTU row within a tile. A tile can be divided into multiple tiles, each of which can include one or more CTU rows belonging to the tile. Tiles that are not divided into multiple tiles can also be considered as tiles.

[0054] A "pixel" or "pixel" can refer to the smallest unit that makes up a picture (or image). Additionally, "sample" can be used as the term corresponding to a pixel. A sample can generally represent a pixel or a pixel value, or it can represent only the pixel / pixel value of the luminance component or only the pixel / pixel value of the chrominance component.

[0055] In this disclosure, "unit" can refer to a basic unit of image processing. A unit may include a specific region of an image and at least one of the information associated with that region. A unit may include a luminance block and two chrominance blocks (e.g., Cb and Cr). In some cases, the term "unit" may be used interchangeably with terms such as "sample array," "block," or "region." In general, an M×N block may include a set (or array) of samples (or sample arrays) with M columns and N rows, or a set (or array) of transform coefficients.

[0056] In this disclosure, "current block" can mean one of "current coding block," "current coding unit," "coding target block," "decoding target block," or "processing target block." When performing prediction, "current block" can mean "current prediction block" or "prediction target block." When performing transform (inverse transform) / quantization (dequantization), "current block" can mean "current transform block" or "transform target block." When performing filtering, "current block" can mean "filter target block."

[0057] Additionally, in this disclosure, unless explicitly stated as a chroma block, "current block" may mean "the luminance block of the current block". "The chroma block of the current block" can be expressed by including an explicit description of a chroma block such as "chroma block" or "current chroma block".

[0058] In this disclosure, the forward slash " / " or "," should be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" can mean "A and / or B". Furthermore, "A / B / C" and "A / B / C" can mean "at least one of A, B and / or C".

[0059] In this disclosure, the term "or" should be interpreted as indicating "and / or". For example, expressing "A or B" can include 1) only "A", 2) only "B", and / or 3) both "A and B". In other words, in this disclosure, the term "or" should be interpreted as indicating "additionally or alternatively".

[0060] In this disclosure, "at least one of A and B" may mean "only A", "only B" or "both A and B". Furthermore, in this disclosure, "at least one of A or B" or "at least one of A and / or B" may be interpreted as the same as "at least one of A and B".

[0061] Furthermore, in this disclosure, "at least one of A, B, and C" may mean "only A," "only B," "only C," or "any combination of A, B, and C." Additionally, in this disclosure, "at least one of A, B, or C" or "at least one of A, B, and / or C" may be interpreted as the same as "at least one of A, B, and C."

[0062] Furthermore, the parentheses used in this disclosure may mean "for example". Specifically, when describing "prediction (intra-frame prediction)", "intra-frame prediction" may be cited as an example of "prediction". In other words, the "prediction" in this disclosure is not limited to "intra-frame prediction", and "intra-frame prediction" may be cited as an example of "prediction". In addition, even when describing "prediction (i.e., intra-frame prediction)", "intra-frame prediction" may be cited as an example of "prediction".

[0063] In this disclosure, the technical features described individually in a single figure can be implemented individually or simultaneously.

[0064] Overview of Video Encoding Systems

[0065] Figure 1 This is a view showing a video encoding system according to this disclosure.

[0066] The video encoding system according to the embodiment may include a source device 10 and a receiving device 20. The source device 10 may deliver encoded video and / or image information or data to the receiving device 20 in the form of a file or stream via a digital storage medium or network.

[0067] The source device 10 according to an embodiment may include a video source generator 11, an encoding device 12, and a transmitter 13. The receiving device 20 according to an embodiment may include a receiver 21, a decoding device 22, and a renderer 23. The encoding device 12 may be referred to as a video / image encoding device, and the decoding device 22 may be referred to as a video / image decoding device. The transmitter 13 may be included in the encoding device 12. The receiver 21 may be included in the decoding device 22. The renderer 23 may include a display, and the display may be configured as a separate device or an external component.

[0068] The video source generator 11 can acquire video / images through a process of capturing, compositing, or generating video / images. The video source generator 11 may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device may include, for example, a computer, tablet computer, and smartphone, and can generate video / images (electronically). For example, virtual video / images can be generated by a computer, etc. In this case, the video / image capture process can be replaced by a process of generating related data.

[0069] The encoding device 12 can encode the input video / image. For compression and encoding efficiency, the encoding device 12 can perform a series of processes such as prediction, transformation, and quantization. The encoding device 12 can output the encoded data (encoded video / image information) in the form of a bitstream.

[0070] Transmitter 13 can transmit encoded video / image information or data, output in bitstream form, to receiver 21 of receiving device 20 in the form of a file or stream via digital storage medium or network. Digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. Transmitter 13 can include elements for generating media files according to a predetermined file format and may include elements for transmission via broadcast / communication networks. Receiver 21 can extract / receive bitstreams from storage medium or network and transmit the bitstreams to decoding device 22.

[0071] The decoding device 22 can decode video / images by performing a series of processes (such as dequantization, inverse transform, and prediction) corresponding to the operation of the encoding device 12.

[0072] Renderer 23 can render decoded video / images. The rendered video / images can be displayed on a monitor.

[0073] Overview of Image Encoding Devices

[0074] Figure 2 This is a schematic view illustrating an image encoding device to which embodiments of the present disclosure are applicable.

[0075] like Figure 2As shown, the image source device 100 may include an image segmenter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame predictor 180, an intra-frame predictor 185, and an entropy encoder 190. The inter-frame predictor 180 and the intra-frame predictor 185 may be collectively referred to as "predictors". The transformer 120, quantizer 130, dequantizer 140, and inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

[0076] In some embodiments, all or at least some of the multiple components configuring the image source device 100 may be configured by a single hardware component (e.g., an encoder or a processor). Additionally, the memory 170 may include a decoded screen buffer (DPB) and may be configured by a digital storage medium.

[0077] Image segmenter 110 can segment an input image (or picture or frame) input to image source device 100 into one or more processing units. For example, a processing unit may be called a coding unit (CU). A coding unit can be obtained by recursively segmenting a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree / binary tree / tritree (QT / BT / TT) structure. For example, a coding unit can be segmented into multiple coding units of greater depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the segmentation of coding units, a quadtree structure can be applied first, and a binary tree structure and / or a ternary tree structure can be applied later. The encoding process according to this disclosure can be performed based on the final coding unit that is no longer segmented. The maximum coding unit can be used as the final coding unit, or a deeper coding unit obtained by segmenting the maximum coding unit can be used as the final coding unit. Here, the encoding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). Prediction units and transform units can be partitioned or segmented from the final coding unit. Prediction units can be sample prediction units, and transform units can be units used to derive transform coefficients and / or units used to derive residual signals from transform coefficients.

[0078] The predictor (inter-frame predictor 180 or intra-frame predictor 185) can perform prediction on the block to be processed (the current block) and generate a prediction block that includes prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction based on the current block or CU. The predictor can generate various information related to the prediction of the current block and send the generated information to the entropy encoder 190. The information about the prediction can be encoded in the entropy encoder 190 and output as a bitstream.

[0079] Intra-predictor 185 can predict the current block by referencing samples in the current frame. Depending on the intra-prediction mode and / or intra-prediction technique, the reference samples may be located among the neighbors of the current block or may be placed separately. Intra-prediction modes may include multiple non-directional modes and multiple directional modes. Non-directional modes may include, for example, DC mode and planar mode. Depending on the level of detail in the prediction direction, directional modes may include, for example, 33 or 65 directional prediction modes. However, this is merely an example, and more or fewer directional prediction modes may be used depending on the settings. Intra-predictor 185 can determine the prediction mode to be applied to the current block by using prediction modes applied to neighboring blocks.

[0080] Inter-frame predictor 180 can deduce the predicted block of the current block based on a reference block (reference sample array) specified by motion vectors on a reference frame. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. The reference frame including the reference block and the reference frame including the temporally neighboring block may be the same or different. The temporally neighboring block may be referred to as a juxtaposed reference block, a juxtaposed CU (colCU), etc. The reference frame including the temporally neighboring block may be referred to as a juxtaposed frame (colPic). For example, inter-frame predictor 180 can configure a motion information candidate list based on neighboring blocks and generate information indicating which candidate to use to deduce the motion vector and / or reference frame index of the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in skip mode and merge mode, the inter-frame predictor 180 can use motion information from neighboring blocks as motion information for the current block. In skip mode, unlike merge mode, residual signals may not be sent. In motion vector prediction (MVP) mode, motion vectors from neighboring blocks can be used as motion vector predictors, and the motion vector of the current block can be signaled by encoding motion vector differences and indicators of the motion vector predictors. The motion vector difference can refer to the difference between the motion vector of the current block and the motion vector predictor.

[0081] The predictor can generate a prediction signal based on various prediction methods and techniques described below. For example, the predictor can apply not only intra-frame prediction or inter-frame prediction, but also both intra-frame prediction and inter-frame prediction simultaneously to predict the current block. A prediction method that simultaneously applies both intra-frame prediction and inter-frame prediction to predict the current block can be called Combined Intra-Frame and Inter-Frame Prediction (CIIP). Alternatively, the predictor can perform Intra-Frame Block Copy (IBC) to predict the current block. Intra-Frame Block Copy can be used for content image / video coding in games, such as Screen Content Coding (SCC). IBC is a method of predicting the current frame using a previously reconstructed reference block in the current frame at a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current frame can be encoded as a vector (block vector) corresponding to the predetermined distance. IBC essentially performs prediction in the current frame, but can be performed similarly to inter-frame prediction because the reference block is derived within the current frame. That is, IBC can use at least one of the inter-frame prediction techniques described in this disclosure.

[0082] The predicted signal generated by the predictor can be used to generate a reconstructed signal or a residual signal. Subtractor 115 generates a residual signal (residual block or residual sample array) by subtracting the predicted signal (predicted block or predicted sample array) output from the predictor from the input image signal (original block or original sample array). The generated residual signal can be sent to transformer 120.

[0083] Transformer 120 can generate transform coefficients by applying transform techniques to the residual signal. For example, the transform techniques may include at least one of Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), Karhunen-Loève Transform (KLT), Graph-Based Transform (GBT), or Conditional Nonlinear Transform (CNT). Here, GBT refers to a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. Furthermore, the transform processing can be applied to square pixel blocks of the same size or to blocks of variable size instead of square.

[0084] Quantizer 130 can quantize the transform coefficients and send them to entropy encoder 190. Entropy encoder 190 can encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients can be referred to as residual information. Quantizer 130 can rearrange the block-type quantized transform coefficients into a one-dimensional vector form based on the coefficient scan order, and generate information about the quantized transform coefficients based on the one-dimensional vector form of the quantized transform coefficients.

[0085] The entropy encoder 190 can perform various encoding methods, such as exponential Columbus coding, context-adaptive variable-length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoder 190 can encode, together or separately, information required for video / image reconstruction other than the quantization transform coefficients (e.g., values ​​of syntax elements). The encoded information (e.g., encoded video / image information) can be transmitted or stored in bitstream form at the Network Abstraction Layer (NAL) level. The video / image information may also include information about various parameter sets, such as Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), or Video Parameter Set (VPS). Additionally, the video / image information may include general constraint information. The signaled information, transmitted information, and / or syntax elements described in this disclosure can be encoded and included in the bitstream through the above encoding process.

[0086] The bitstream can be transmitted over a network or stored in a digital storage medium. The network may include broadcast networks and / or communication networks, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for transmitting the signal output from the entropy encoder 190 and / or a storage unit (not shown) for storing the signal may be included as internal / external components of the image source device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0087] The quantization transform coefficients output from quantizer 130 can be used to generate residual signals. For example, the residual signal (residual block or residual sample) can be reconstructed by applying dequantization and inverse transform to the quantization transform coefficients through dequantizer 140 and inverse transformer 150.

[0088] Adder 155 adds the reconstructed residual signal to the prediction signal output from inter-frame predictor 180 or intra-frame predictor 185 to generate a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as in the case of applying a skip mode, the prediction block can be used as a reconstructed block. Adder 155 can be referred to as a reconstructor or reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current frame, and can be used for inter-frame prediction of the next frame by filtering as described below.

[0089] Filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, filter 160 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 170, specifically in the DPB of memory 170. Various filtering methods can include, for example, deblocking filtering, sample adaptive shifting, adaptive loop filtering, bilateral filtering, etc. Filter 160 can generate various filtering-related information and send the generated information to entropy encoder 190, as described later in the description of each filtering method. The filtering-related information can be encoded by entropy encoder 190 and output as a bitstream.

[0090] The modified reconstructed frame sent to memory 170 can be used as a reference frame in inter-frame predictor 180. When inter-frame prediction is applied through image source device 100, prediction mismatch between image source device 100 and image decoding device can be avoided and coding efficiency can be improved.

[0091] The DPB of memory 170 can store modified reconstructed frames for use as reference frames in inter-frame predictor 180. Memory 170 can store motion information of blocks used to derive (or encode) motion information in the current frame and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 180 and used as motion information for spatially or temporally neighboring blocks. Memory 170 can store reconstructed samples of reconstructed blocks in the current frame and can transmit the reconstructed samples to intra-frame predictor 185.

[0092] Overview of image decoding devices

[0093] Figure 3 This is a schematic view illustrating an image decoding device to which embodiments of the present disclosure are applicable.

[0094] like Figure 3 As shown, the image receiving device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, and an intra-frame predictor 265. The inter-frame predictor 260 and the intra-frame predictor 265 may be collectively referred to as "predictors". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0095] According to an embodiment, all or at least some of the multiple components configuring the image receiving device 200 may be configured by hardware components (e.g., a decoder or a processor). Additionally, the memory 250 may include a decoded screen buffer (DPB) or may be configured by a digital storage medium.

[0096] The image receiving device 200, which has already received a bitstream including video / image information, can perform operations related to... Figure 2 The image is reconstructed by processing corresponding to the processing performed by the image source device 100. For example, the image receiving device 200 can use a processing unit applied in an image encoding device to perform decoding. Therefore, the decoding processing unit can be, for example, an encoding unit. The encoding unit can be obtained by segmenting a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image receiving device 200 can be reproduced by a reproduction device (not shown).

[0097] Image receiving device 200 can receive images in bitstream form from Figure 2The signal output by the image encoding device. The received signal can be decoded by the entropy decoder 210. For example, the entropy decoder 210 can parse the bitstream to derive the 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 adaptive parameter sets (APS), picture parameter sets (PPS), sequence parameter sets (SPS), or video parameter sets (VPS). In addition, the video / image information may also include general constraint information. The image decoding device can also decode the picture based on the information about the parameter sets and / or general constraint information. The information and / or syntax elements notified / received by signals described in this disclosure can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on encoding methods such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residuals. More specifically, the CABAC entropy decoding method can receive bins corresponding to each syntax element in the bitstream, determine a context model using information about the target syntax element, decoding information of neighboring blocks and the target block, or information about symbols / bins decoded in the previous stage, perform arithmetic decoding on the bins based on the determined context model by predicting the occurrence probability of the bins, and generate symbols corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model after determining the context model by using the information of the decoded symbols / bins for the context model of the next symbol / bin. The prediction-related information in the information decoded by the entropy decoder 210 can be provided to the predictors (inter-frame predictor 260 and intra-frame predictor 265), and the residual values ​​(i.e., quantization transform coefficients and related parameter information) from the entropy decoding performed in the entropy decoder 210 can be input to the dequantizer 220. In addition, the filtering information in the information decoded by the entropy decoder 210 can be provided to the filter 240. Furthermore, the receiver (not shown) for receiving signals output from the image encoding device may be further configured as an internal / external element of the image receiving device 200, or the receiver may be a component of the entropy decoder 210.

[0098] Furthermore, the image decoding apparatus according to this disclosure can be referred to as a video / image / screen decoding apparatus. The image decoding apparatus can be divided into an information decoder (video / image / screen information decoder) and a sample decoder (video / image / screen sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include at least one of a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, or an intra-frame predictor 265.

[0099] Dequantizer 220 can dequantize the quantized transform coefficients and output transform coefficients. Dequantizer 220 can rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement can be performed based on the coefficient scan order performed in the image encoding device. Dequantizer 220 can obtain transform coefficients by performing dequantization on the quantized transform coefficients using quantization parameters (e.g., quantization step size information).

[0100] The inverse transformer 230 can perform inverse transformation on the transformation coefficients to obtain the residual signal (residual block, residual sample array).

[0101] The predictor can perform prediction on the current block and generate a prediction block that includes prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction to the current block based on the prediction information output from the entropy decoder 210, and can determine a specific intra-frame / inter-frame prediction mode (prediction technique).

[0102] Similar to the predictor described in the image source device 100, the predictor can generate a prediction signal based on various prediction methods (techniques) that will be described later.

[0103] Intra-predictor 265 can predict the current block by referring to samples in the current frame. The description of intra-predictor 185 also applies to intra-predictor 265.

[0104] Inter-frame predictor 260 can deduce the predicted block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference frame. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. For example, inter-frame predictor 260 can configure a motion information candidate list based on neighboring blocks and deduce the motion vector and / or reference frame index of the current block based on the received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and the information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0105] Adder 235 generates a reconstruction signal (reconstructed frame, reconstruction block, reconstruction sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (including inter-frame predictor 260 and / or intra-frame predictor 265). If the block to be processed has no residual, such as when a skip mode is applied, the prediction block can be used as a reconstruction block. The description of adder 155 also applies to adder 235. Adder 235 may be referred to as a reconstructor or reconstruction block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current frame, and can be used for inter-frame prediction of the next frame by filtering as described below.

[0106] Filter 240 can improve the quality of subjective / objective images by applying filtering to the reconstructed signal. For example, filter 240 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 250, specifically in the DPB of memory 250. Various filtering methods may include, for example, deblocking filtering, adaptive sample shifting, adaptive loop filtering, bilateral filtering, etc.

[0107] The (modified) reconstructed frame stored in the DPB of memory 250 can be used as a reference frame in inter-frame predictor 260. Memory 250 can store motion information of blocks used to derive (or decode) motion information in the current frame and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 260 to be used as motion information for spatially or temporally neighboring blocks. Memory 250 can store reconstructed samples of reconstructed blocks in the current frame and transmit the reconstructed samples to intra-frame predictor 265.

[0108] In this disclosure, the embodiments described in the filter 160, inter-frame predictor 180 and intra-frame predictor 185 of the image source device 100 can be applied equally or correspondingly to the filter 240, inter-frame predictor 260 and intra-frame predictor 265 of the image receiving device 200.

[0109] General image / video encoding process

[0110] In image / video coding, the frames of an image / video can be encoded / decoded according to the decoding order. The output order of the decoded frames can be set differently from the decoding order, and based on this, not only forward prediction but also backward prediction can be performed during inter-frame prediction.

[0111] Figure 4 An example of an illustrative screen decoding process to which embodiments of this disclosure apply is shown. Figure 4In this process, S410 can be executed in the entropy decoder 210 of the decoding device, S420 can be executed in the predictor including the intra-frame predictor 265 and the inter-frame predictor 260, S430 can be executed in the residual processor including the dequantizer 220 and the inverse transformer 230, S440 can be executed in the adder 235, and S450 can be executed in the filter 240. S410 can include the information decoding process described in this disclosure, S420 can include the inter-frame / intra-frame prediction process described in this disclosure, S430 can include the residual processing process described in this disclosure, S440 can include the block / frame reconstruction process described in this disclosure, and S450 can include the in-loop filtering process described in this disclosure.

[0112] Reference Figure 4 The image decoding process can schematically include a process of obtaining image / video information from the bitstream (through decoding) (S410), an image reconstruction process (S420 to S440), and an in-loop filtering process for the reconstructed image (S450). The image reconstruction process can be performed based on prediction samples and residual samples obtained through inter-frame / intra-frame prediction (S420) and residual processing (S430) (dequantization and inverse transform of quantization transform coefficients) described in this disclosure. A modified reconstructed image can be generated by an in-loop filtering process on the reconstructed image generated by the image reconstruction process. The modified reconstructed image can be output as a decoded image, stored in the decoded image buffer or memory 250 of the decoding device, and used as a reference image in the inter-frame prediction process when the image is later decoded. In some cases, the in-loop filtering process can be omitted. In this case, the reconstructed image can be output as a decoded image, stored in the decoded image buffer or memory 250 of the decoding device, and used as a reference image in the inter-frame prediction process when the image is later decoded. As described above, the in-loop filtering process (S450) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filter (ALF) process, and / or a bilateral filter process, some or all of which may be omitted. Furthermore, one or more of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filter (ALF) process, and / or the bilateral filter process may be applied sequentially, or all of them may be applied sequentially. For example, the SAO process may be performed after applying the deblocking filtering process to the reconstructed image. Alternatively, for example, the ALF process may be performed after applying the deblocking filtering process to the reconstructed image. This can be performed similarly even in an encoding device.

[0113] Figure 5 An example of an illustrative screen encoding process to which embodiments of this disclosure apply is shown. Figure 5 In the middle, S510 can be included in the above reference. Figure 2S520 can be executed in the predictor of the intra-frame predictor 185 or inter-frame predictor 180 of the described coding apparatus. S530 can be executed in the residual processor including the transformer 120 and / or the quantizer 130. S510 can include the inter-frame / intra-frame prediction process described in this disclosure, S520 can include the residual processing process described in this disclosure, and S530 can include the information encoding process described in this disclosure.

[0114] Reference Figure 5 The image encoding process can be schematically described as including not only the process of encoding information used for image reconstruction (e.g., prediction information, residual information, segmentation information, etc.) and outputting it in the form of a bitstream, but also the process of generating a reconstructed image of the current image and the process of applying in-loop filtering to the reconstructed image (optional), as shown in the reference. Figure 2 The encoding device can derive (modified) residual samples from the quantized transform coefficients using dequantizer 140 and inverse transformer 150, and generate a reconstructed frame based on the predicted sample as the output of S510 and the (modified) residual samples. The reconstructed frame thus generated can be equal to the reconstructed frame generated in the decoding device. Similar to the decoding device, the modified reconstructed frame can be generated through an in-loop filtering process on the reconstructed frame, can be stored in the decoded frame buffer or memory 170, and can be used as a reference frame in the inter-frame prediction process when the frame is later encoded. As mentioned above, in some cases, some or all of the in-loop filtering process can be omitted. When the in-loop filtering process is performed, the (in-loop) filtering-related information (parameters) can be encoded in the entropy encoder 190 and output as a bitstream. The decoding device can perform the in-loop filtering process based on the filtering-related information using the same method as the encoding device.

[0115] This in-loop filtering process reduces noise (e.g., block artifacts and ringing artifacts) that occurs during image / video encoding, and improves subjective / objective visual quality. Furthermore, by performing the in-loop filtering process in both the encoding and decoding devices, the encoding and decoding devices can derive the same prediction results, increasing the reliability of image encoding and reducing the amount of data that needs to be sent for image encoding.

[0116] As described above, the image reconstruction process can be performed not only in the decoding device but also in the encoding device. Reconstruction blocks can be generated on a block-by-block basis based on intra-frame prediction / inter-frame prediction, and a reconstructed image including these blocks can be generated. When the current image / slice / patch group is an I-frame / slice / patch group, the blocks included in the current image / slice / patch group can be reconstructed based solely on intra-frame prediction. Furthermore, when the current image / slice / patch group is a P-frame / slice / patch group or a B-frame / slice / patch group, the blocks included in the current image / slice / patch group can be reconstructed based on either intra-frame prediction or inter-frame prediction. In this case, inter-frame prediction can be applied to some blocks in the current image / slice / patch group, and intra-frame prediction can be applied to the remaining blocks. The color components of the image can include luma and chroma components, and unless explicitly limited in this disclosure, the methods and implementations of this disclosure are applicable to both luma and chroma components.

[0117] Examples of coding layers and structures

[0118] For example, encoded video / images according to this disclosure can be processed according to the coding layers and structures described below.

[0119] Figure 6 This is a view showing the layer structure of an encoded image. Encoded images can be classified into the Video Coding Layer (VCL) for image decoding and processing, the lower layer system for sending and storing encoded information, and the Network Abstraction Layer (NAL) that exists between the VCL and the lower layer system and is responsible for network adaptation functions.

[0120] In VCL, VCL data that includes compressed image data (slice data) can be generated, or additional enhancement information (SEI) messages required for image decoding processing can be generated, or parameter sets that include information such as picture parameter set (PPS), sequence parameter set (SPS), or video parameter set (VPS).

[0121] In NAL, header information (NAL cell header) can be added to the raw byte sequence payload (RBSP) generated in VCL to generate NAL cells. In this case, RBSP refers to the slice data, parameter set, and SEI message generated in VCL. The NAL cell header may include NAL cell type information specified according to the RBSP data included in the corresponding NAL cell.

[0122] As shown in the figure, NAL units can be classified into VCL NAL units and non-VCL NAL units based on the RBSP generated in the VCL. A VCL NAL unit can refer to a NAL unit that includes information about the image (slice data), while a non-VCL NAL unit can refer to a NAL unit that includes information required for decoding the image (parameter set or SEI message).

[0123] VCL NAL units and non-VCL NAL units can be appended with header information and sent over the network according to the data standard of the underlying system. For example, NAL units can be modified to data in a predetermined standard format (e.g., H.266 / VVC file format, RTP (Real-Time Transport Protocol), or TS (Transport Stream)) and sent over various networks.

[0124] As described above, in a NAL cell, the NAL cell type can be specified according to the RBSP data structure included in the corresponding NAL cell, and information about the NAL cell type can be stored in the NAL cell header and notified by a signal.

[0125] For example, this can be broadly categorized into VCLNAL unit types and non-VCL NAL unit types based on whether the NAL unit includes information about the image (slice data). VCL NAL unit types can be categorized based on the nature and type of the image included in the VCL NAL unit, while non-VCL NAL unit types can be categorized based on the type of parameter set.

[0126] Below are examples of NAL cell types specified based on the type of parameter set / information included in non-VCL NAL cell types.

[0127] - DCI (Decoding Capability Information) NAL Unit: Includes NAL unit types for DCI.

[0128] -VPS (Video Parameter Set) NAL Unit: Includes the NAL unit type of VPS.

[0129] -SPS (Sequence Parameter Set) NAL Unit: Includes NAL unit types related to SPS.

[0130] -PPS (Picture Parameter Set) NAL Unit: Includes the NAL unit type of PPS.

[0131] -APS (Adaptive Parameter Set) NAL Units: Includes NAL unit types related to APS.

[0132] -PH (Header) NAL Unit: Includes the NAL unit type PH.

[0133] The aforementioned NAL unit type can have syntax information for the NAL unit type, and this syntax information can be stored in the NAL unit header and signaled. For example, this syntax information can be nal_unit_type, and the NAL unit type can be specified as the value nal_unit_type.

[0134] Furthermore, as mentioned above, a frame can include multiple slices, and a slice can include a slice header and slice data. In this case, a frame header can be further added to the multiple slices (slice headers and slice data sets) in a frame. The frame header (frame header syntax) can include information / parameters that are common to the frame.

[0135] A slice header (slice header syntax) may include information / parameters commonly applicable to a slice. An APS (APS syntax) or PPS (PPS syntax) may include information / parameters commonly applicable to one or more slices or frames. An SPS (SPS syntax) may include information / parameters commonly applicable to one or more sequences. A VPS (VPS syntax) may be information / parameters commonly applicable to multiple layers. A DCI (DCI syntax) may include information / parameters commonly applicable to the overall video. A DCI may include information / parameters related to decoding capabilities. In this disclosure, the High-Level Syntax (HLS) may include at least one of the following: APS syntax, PPS syntax, SPS syntax, VPS syntax, DCI syntax, frame header syntax, or slice header syntax. Furthermore, in this disclosure, the Low-Level Syntax (LLS) may include, for example, slice data syntax, CTU syntax, coding unit syntax, transform unit syntax, etc.

[0136] In this disclosure, the image / video information encoded in the encoding device and signaled to the decoding device in the form of a bitstream may include not only intra-frame segmentation related information, intra / inter-frame prediction information, residual information, and intra-loop filtering information, but also information about slice headers, frame headers, APS, PPS, SPS, VPS, and / or DCI. Additionally, the image / video information may also include general constraint information and / or information about NAL unit headers.

[0137] NAL unit for video information signaling

[0138] Screen information can be signaled in units of NAL units. For example, screen information can be signaled as follows. The sublayer is the time-scalable layer of the time-scalable bitstream, composed of VCL NAL units with a specific value for the variable TemporalId and associated non-VCL NAL units. The variable TemporalId can be derived as follows:

[0139] [Formula 1]

[0140] TemporalId=nuh_temporal_id_plus1-1

[0141] The syntax element `nuh_temproal_id_plus1` used to signal the value of the variable `TemporalId` can be signaled through the NAL unit header of the NAL unit. When the value of `nal_unit_type` in the NAL unit header is in the range IDR_W_RADL to RSV_IRAP_12 (inclusive), the value of `TemporalId` should be equal to 0. When the value of `nal_unit_type` is equal to STSA_NUT and the value of `vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]` is equal to 1, the value of `TemporalId` should not be equal to 0. The value of `TemporalId` should be the same for all VCL NAL units in the AU. The value of `TemporalId` for the encoded screen, PU, ​​or AU is the value of `TemporalId` for the VCL NAL units of the encoded screen, PU, ​​or AU. The value of `TemporalId` for a sublayer representation is the maximum value of `TemporalId` for all VCL NAL units in the sublayer representation.

[0142] The TemporalId value of a non-VCL NAL cell can be constrained as follows:

[0143] - If nal_unit_type is equal to DCI_NUT, VPS_NUT, or SPS_NUT, then TemporalId should be equal to 0 and the value of TemporalId of the AU containing the NAL unit should be equal to 0.

[0144] Otherwise, if nal_unit_type is equal to PH_NUT, then the value of TemporalId should be equal to the TemporalId of the PU containing the NAL unit.

[0145] Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT, then TemporalId should be equal to 0.

[0146] Otherwise, if nal_unit_type is equal to AUD_NUT, FD_NUT, PREFIX_SEI_NUT, or SUFFIX_SEI_NUT, then TemporalId should be equal to the TemporalId of the AU containing the NAL unit.

[0147] Otherwise, when nal_unit_type is equal to PPS_NUT, PREFIX_APS_NUT or SUFFIX_APS_NUT, the value of TemporalId should be greater than or equal to the value of TemporalId of the PU containing the NAL unit.

[0148] For example, when the NAL unit is a non-VCL NAL unit, the TemporalId value can be equal to the minimum TemporalId value of all AUs to which the non-VCL NAL unit applies. When the nal_unit_type value is equal to PPS_NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT, the TemporalId value can be greater than or equal to the TemporalId value of the AU containing it, because all PPS and APS can be included at the beginning of the bitstream (e.g., when they are transmitted out of band and the receiver places them at the beginning of the bitstream). Here, the first coded frame can have a TemporalId equal to 0.

[0149] In this implementation, the encoded frame obtained from the bitstream based on NAL unit information can be signaled by the encoding device and identified by the decoding device as follows. However, this is just an example, and other methods can be used to identify the frame.

[0150] Intra-Random Access Point (IRAP) frames are encoded frames in which all VCL NAL units have the same nal_unit_type value within the range IDR_W_RADL to CRA_NUT (inclusive). In implementations, IRAP frames do not reference any frames other than themselves for inter-frame prediction during their decoding process. IRAP frames can be either CRA or IDR frames. The first frame in the bitstream in decoding order must be an IRAP or GDR frame. If the necessary parameter set is available when reference is required, the IRAP frame, along with all subsequent non-RASL frames in the CVS in decoding order, can be correctly decoded without performing decoding processing on any frames that precede the IRAP frame in decoding order.

[0151] Clean Random Access (CRA) frames are IRAP frames whose individual VCL NAL units have a nal_unit_type equal to CRA_NUT. For example, a CRA frame does not reference any frame other than itself for inter-frame prediction during its decoding process and can be the first frame in the bitstream in decoding order, or it may appear later in the bitstream. A CRA frame can have associated RADL or RASL frames. When a CRA frame has a NoIncorrectPicOutputFlag equal to 1, the decoder may not output the associated RASL frames because they may be undecodeable because they may contain references to frames not present in the bitstream. In an implementation, if a CRA frame is an incomplete frame and no incomplete frame is output during image decoding, the CRA frame may have a NoIncorrectPicOutputFlag equal to 1.

[0152] An Instantaneous Decoding Refresh (IDR) frame is an IRAP frame whose individual VCL NAL units have a nal_unit_type equal to IDR_W_RADL or IDR_N_LP. For example, an IDR frame does not reference any frame other than itself for inter-frame prediction during its decoding process. Furthermore, an IDR frame can be the first frame in the bitstream in decoding order, or it can appear later in the bitstream. Each IDR frame is the first frame in the CVS in decoding order. When each VCL NAL unit has an IDR frame with a nal_unit_type equal to IDR_W_RADL, the IDR frame can have an associated RADL frame. When each VCL NAL unit has an IDR frame with a nal_unit_type equal to IDR_N_LP, the IDR frame does not have any associated leading frame. An IDR frame does not have an associated RASL frame.

[0153] A Random Access Decodable Leading (RADL) frame is an encoded frame whose individual VCL NAL units have a nal_unit_type equal to RADL_NUT. In this implementation, all RADL frames are leading frames. RADL frames are not used as reference frames for decoding the final frame of the same associated IRAP frame. When the syntax element field_seq_flag obtained from the bitstream is equal to 0, all RADL frames (if present) precede all non-leading frames of the same associated IRAP frame in the decoding order.

[0154] Random Access Skip Leader (RASL) frames can be encoded frames where each VCL NAL unit has a nal_unit_type equal to RASL_NUT. In the implementation, all RASL frames are leader frames of associated CRA frames. When an associated CRA frame has a NoIncorrectPicOutputFlag equal to 1, the RASL frame is not output and may not be decoded correctly because the RASL frame may contain references to frames that do not exist in the bitstream. RASL frames are not used as reference frames for decoding non-RASL frames. When field_seq_flag equals 0, all RASL frames (if present) are decoded before all non-leader frames of the same associated CRA frame in the order they are decoded.

[0155] The ending screen is a non-IRAP screen that follows the associated IRAP screen in output order and is not an STSA screen. Ending screens associated with IRAP screens also follow the IRAP screens in decoding order. Screens that follow the associated IRAP screen in output order and precede the associated IRAP screen in decoding order are not allowed.

[0156] Progressive Decoding Refresh (GDR) is a display where each VCL NAL unit has a nal_unit_type equal to GDR_NUT.

[0157] A Step-by-Step Temporal Sublayer Access (STSA) frame is an encoded frame whose each VCL NAL unit has a nal_unit_type equal to the STSA_NUT. An STSA frame can be used without using a frame with the same TemporalId as the STSA frame for inter-frame prediction reference. A frame that follows the STSA frame in decoding order and has the same TemporalId as the STSA frame can be used without using a frame that precedes the STSA frame in decoding order and has the same TemporalId as the STSA frame for inter-frame prediction reference.

[0158] STSA screens allow switching from the immediately following lower sublayer to the sublayer containing the STSA screen. STSA screens must have a TemporalId greater than 0.

[0159] In implementation, for single-layer or multi-layer bitstreams, one or more of the following constraints may be applied:

[0160] - Each frame in the bitstream other than the first frame in decoding order can be considered as associated with the previous IRAP frames in decoding order.

[0161] - When the screen is a leading screen for an IRAP screen, it should be a RADL or RASL screen.

[0162] - When the screen is the last screen of an IRAP screen, it should not be a RADL or RASL screen.

[0163] - RASL frames should not exist in the bitstream associated with IDR frames.

[0164] - There should be no RADL frame in the bitstream associated with an IDR frame having a nal_unit_type equal to IDR_N_LP. (For example, if the parameter sets are available in the bitstream or by external means at reference time, random access can be performed at the location of the IRAP PU by discarding all PUs preceding the IRAP PU and correctly decoding the IRAP frame and all subsequent non-RADL frames in decoding order.)

[0165] - Any screen that precedes the IRAP screen in decoding order should precede the IRAP screen in output order, and should precede any RADL screen associated with the IRAP screen in output order.

[0166] - Any RASL screen associated with a CRA screen should precede any RADL screen associated with a CRA screen in the output order.

[0167] - Any RASL screen associated with a CRA screen should follow any IRAP screen that precedes the CRA screen in decoding order, in output order.

[0168] - If field_seq_flag equals 0 and the current frame is a leading frame associated with an IRAP frame, then it should precede all non-leading frames associated with the same IRAP frame in decoding order. Otherwise, assuming picA and picB are the first and last leading frames associated with IRAP frames in decoding order, then at most one non-leading frame should precede picA in decoding order, and no non-leading frame should exist between picA and picB in decoding order.

[0169] Multi-layer coding

[0170] Image / video coding according to this disclosure may include multi-layer-based image / video coding. Multi-layer-based image / video coding may include scalable coding. In multi-layer-based coding or scalable coding, input signals can be processed for individual layers. Depending on the layer, the input signal (input image / video) may have different values ​​in at least one aspect: resolution, frame rate, bit depth, color format aspect ratio, or view. In this case, performing inter-layer prediction by using the differences between layers (e.g., based on scalability) can reduce redundant information transmission / processing and increase compression efficiency.

[0171] Figure 7 This is a schematic block diagram of a multilayer encoding device 700 for performing multilayer video / image signal encoding, to which embodiments of this disclosure are applicable.

[0172] Figure 7 The multi-layer coding device 700 may include Figure 2 Encoding devices. With Figure 2 In comparison, Figure 7 The image segmenter 110 and adder 155 are not shown in the multi-layer coding device 700, but the multi-layer coding device 700 may include the image segmenter 110 and adder 155. In an embodiment, the image segmenter 110 and adder 155 may be included on a layer-by-layer basis. Hereinafter, Figure 7 The description will focus on multi-layer-based prediction. For example, in addition to the following description, the multi-layer coding device 700 may include the above-mentioned references. Figure 2 The technical concept of the described encoding device.

[0173] For ease of description, Figure 7The diagram illustrates a multi-layer structure consisting of two layers. However, embodiments of this disclosure are not limited to two layers, and multi-layer structures applying embodiments of this disclosure may include two or more layers.

[0174] Reference Figure 7 The encoding device 700 includes an encoder 700-1 for layer 1 and an encoder 700-0 for layer 0. Layer 0 can be a base layer, a reference layer, or a lower layer, and layer 1 can be an enhancement layer, a current layer, or a higher layer.

[0175] The encoder 700-1 of layer 1 may include a predictor 720-1, a residual processor 730-1, a filter 760-1, a memory 770-1, an entropy encoder 740-1, and a multiplexer (MUX) 770. In some embodiments, the MUX may be included as an external component.

[0176] The encoder 700-0 of layer 0 may include a predictor 720-0, a residual processor 730-0, a filter 760-0, a memory 770-0, and an entropy encoder 740-0.

[0177] Predictors 720-0 and 720-1 can perform predictions on the input image based on various prediction schemes as described above. For example, predictors 720-0 and 720-1 can perform inter-frame prediction and intra-frame prediction. Predictors 720-0 and 720-1 can perform predictions in a predetermined processing unit. The prediction unit can be a coding unit (CU) or a transform unit (TU). Prediction blocks (including prediction samples) can be generated based on the prediction results, and based on this, a residual processor can derive residual blocks (including residual samples).

[0178] Inter-frame prediction can generate prediction blocks based on information about at least one of the previous and / or next frames. Intra-frame prediction can generate prediction blocks based on neighboring samples in the current frame.

[0179] As inter-frame prediction modes or methods, the various prediction modes or methods described above can be used. In inter-frame prediction, a reference frame can be selected for the current block to be predicted, and a reference block corresponding to the current block can be selected from the reference frame. Predictors 720-0 and 720-1 can generate prediction blocks based on the reference blocks.

[0180] Additionally, predictor 720-1 can use information about layer 0 to perform predictions for layer 1. In this disclosure, for ease of description, the method of using information about another layer to predict information about the current layer is referred to as inter-layer prediction.

[0181] Information about the current layer that is predicted using information about another layer (e.g., predicted via inter-layer prediction) can be at least one of texture, motion information, unit information, or predetermined parameters (e.g., filtering parameters, etc.).

[0182] Additionally, the information about another layer used for prediction of the current layer (e.g., for inter-layer prediction) can be at least one of texture, motion information, unit information, or predetermined parameters (e.g., filtering parameters, etc.).

[0183] Inter-layer prediction: The current block can be a block in the current frame of the current layer (e.g., layer 1) or the block to be encoded. The reference block is a block in the frame (reference frame) of the same access unit (AU) as the frame (current frame) to which the prediction of the current block belongs, on the layer (reference layer, e.g., layer 0) to which the prediction of the current block belongs, and can be a block corresponding to the current block.

[0184] As an example of inter-layer prediction, there exists inter-layer motion prediction that uses motion information from a reference layer to predict the motion information of the current layer. Based on inter-layer motion prediction, the motion information of the current block can be predicted using the motion information of the reference block. That is, when deriving motion information according to the inter-frame prediction mode described below, motion information candidates can be derived based on the motion information of the inter-layer reference block rather than temporally neighboring blocks.

[0185] When applying interlayer motion prediction, predictor 720-1 can scale and use motion information from the reference block of the reference layer (i.e., the interlayer reference block).

[0186] As another example of inter-layer prediction, inter-layer texture prediction can use the texture of a reconstructed reference block as the predicted value for the current block. In this case, predictor 720-1 can scale the texture of the reference block by up-scaling. Inter-layer texture prediction can be referred to as inter-layer (reconstructed) sample prediction or simply inter-layer prediction.

[0187] In inter-layer parameter prediction, which is another example of inter-layer prediction, the derivation parameters of the reference layer can be reused in the current layer, or the parameters of the current layer can be derived based on the parameters used in the reference layer.

[0188] In interlayer residual prediction, which is another example of interlayer prediction, residual information from another layer can be used to predict the residual information of the current layer, and based on this, prediction of the current block can be performed.

[0189] In inter-layer difference prediction, which is another example of inter-layer prediction, the prediction of the current block can be performed using the difference between the images obtained by upsampling or downsampling the reconstructed image of the current layer and the reconstructed image of the reference layer.

[0190] In inter-layer syntax prediction, another example of inter-layer prediction, the syntax information of a reference layer can be used to predict or generate the texture of the current block. In this case, the syntax information of the reference layer can include information about the intra-frame prediction mode and motion information.

[0191] The various prediction methods described above can be used when predicting specific blocks.

[0192] Here, as examples of interlayer prediction, although interlayer texture prediction, interlayer motion prediction, interlayer unit information prediction, interlayer parameter prediction, interlayer residual prediction, interlayer difference prediction, interlayer syntax prediction, etc. are described, the interlayer prediction applicable in this disclosure is not limited to these.

[0193] For example, inter-layer prediction can be applied as an extension of inter-frame prediction for the current layer. That is, inter-frame prediction can be performed for the current block by including the reference frame derived from the reference layer in the reference frames that the inter-frame prediction of the current block can refer to.

[0194] In this case, inter-layer reference frames can be included in the reference frame list for the current block. Predictor 720-1 can use inter-layer reference frames to perform inter-frame prediction for the current block.

[0195] Here, the inter-layer reference frame can be a reference frame constructed by sampling the reconstructed frame of a reference layer to correspond with the current layer. Therefore, when the reconstructed frame of the reference layer corresponds to the frame of the current layer, the reconstructed frame of the reference layer can be used as the inter-layer reference frame without sampling. For example, when the width and height of the samples in the reconstructed frames of the reference layer and the current layer are the same, and the offset between the top left, top right, bottom left, and bottom right edges of the reference layer and the top left, top right, bottom left, and bottom right edges of the current layer is 0, the reconstructed frame of the reference layer can be used as the inter-layer reference frame of the current layer without resampling.

[0196] Furthermore, the reconstructed frame of the reference layer of the interlayer reference frame can be a frame belonging to the same AU as the current frame to be encoded.

[0197] When performing inter-frame prediction for the current block by including inter-layer reference frames in the reference frame list, the positions of the inter-layer reference frames in the reference frame list can differ between reference frame lists L0 and L1. For example, in reference frame list L0, the inter-layer reference frame can be located after a short reference frame preceding the current frame, while in reference frame list L1, the inter-layer reference frame can be located at the end of the reference frame list.

[0198] Here, reference frame list L0 is a list of reference frames used for inter-frame prediction of P-slices or a list of reference frames used as the first reference frame list in inter-frame prediction of B-slices. Reference frame list L1 can be a second reference frame list used for inter-frame prediction of B-slices.

[0199] Therefore, the reference frame list L0 can be composed, in sequence, of short-term reference frames preceding the current frame, inter-layer reference frames, short-term reference frames following the current frame, and long-term reference frames. The reference frame list L1 can be composed, in sequence, of short-term reference frames following the current frame, short-term reference frames preceding the current frame, long-term reference frames, and inter-layer reference frames.

[0200] In this context, a prediction (P) slice is a slice in which intra-frame prediction is performed or inter-frame prediction is performed using at most one motion vector per prediction block and a reference frame index. A double prediction (B) slice is a slice in which intra-frame prediction is performed or prediction is performed using at most two motion vectors per prediction block and a reference frame index. In this respect, an intra-frame (I) slice is a slice in which intra-frame prediction is applied only.

[0201] Additionally, when performing inter-frame prediction for the current block based on a list of reference frames including inter-layer reference frames, the list of reference frames may include multiple inter-layer reference frames derived from multiple layers.

[0202] When multiple inter-layer reference frames are included, they can be arranged alternately in reference frame lists L0 and L1. For example, suppose two inter-layer reference frames, such as inter-layer reference frames ILRPi and ILRPiJ, are included in the reference frame list for inter-frame prediction of the current block. In this case, in reference frame list L0, ILRPi can be located after a short reference frame preceding the current frame, and ILRPi can be located at the end of the list. Similarly, in reference frame list L1, ILRPi can be located at the end of the list, and ILRPi can be located after a short reference frame following the current frame.

[0203] In this case, the reference frame list L0 can be composed, in sequence, of short-term reference frames preceding the current frame, interlayer reference frames (ILRPi), short-term reference frames following the current frame, long-term reference frames, and interlayer reference frames (ILRPj). The reference frame list L1 can be composed, in sequence, of short-term reference frames following the current frame, interlayer reference frames (ILRPj), short-term reference frames preceding the current frame, long-term reference frames, and interlayer reference frames (ILRPi).

[0204] Additionally, one of the two inter-layer reference frames can be an inter-layer reference frame derived from a scalable layer used for resolution, and the other can be an inter-layer reference frame derived from a layer used to provide another view. In this case, for example, if ILRPi is an inter-layer reference frame derived from a layer used to provide a different resolution and ILRPj is an inter-layer reference frame derived from a layer used to provide a different view, then in the case of scalability-only scalable video coding without view scalability support, the reference frame list L0 can be composed in sequence of short-term reference frames before the current frame, inter-layer reference frame ILRPi, short-term reference frames after the current frame, and long-term reference frames, and the reference frame list L1 can be composed in sequence of short-term reference frames after the current frame, short-term reference frames before the current frame, long-term reference frames, and inter-layer reference frame ILRPi.

[0205] Furthermore, in inter-layer prediction, information about the inter-layer reference frame can be obtained using only sample values, only motion information (motion vectors), or both. When the reference frame index indicates an inter-layer reference frame, based on information received from the encoding device, the predictor 720-1 can use only sample values ​​of the inter-layer reference frame, only motion information (motion vectors) of the inter-layer reference frame, or both.

[0206] When using only sample values ​​from the inter-frame reference frame, predictor 720-1 can deduce samples of the block specified by the motion vector from the inter-frame reference frame as the prediction samples for the current block. Without considering scalable video coding of the view, the motion vectors in inter-frame prediction (inter-frame prediction) using the inter-frame reference frame can be set to a fixed value (e.g., 0).

[0207] When using only motion information from inter-layer reference frames, predictor 720-1 can use the motion vector specified by the inter-layer reference frames as a motion vector predictor for deriving the motion vector of the current block. Alternatively, predictor 720-1 can use the motion vector specified by the inter-layer reference frames as the motion vector of the current block.

[0208] When using both sample values ​​and motion information from the inter-layer reference frame, the predictor 720-1 can use samples from the region in the inter-layer reference frame corresponding to the current block and the motion information (motion vector) specified in the inter-layer reference frame to predict the current block.

[0209] When applying interlayer prediction, the encoding device can send a reference index of the interlayer reference frame in the reference frame list to the decoding device, and can also send information to the decoding device to specify which information (sample information, motion information, or both) to be used from the interlayer reference frame, that is, information to specify the dependency type of the interlayer prediction dependency between the two layers.

[0210] Figure 8 This is a schematic block diagram of a decoding apparatus to which embodiments of the present disclosure are applicable for performing decoding of multi-layer video / image signals. Figure 8 The decoding device may include Figure 3 Decoding devices. Figure 8 The realigner shown can be omitted or included in the dequantizer. This diagram focuses on multi-level prediction. Alternatively, it may include... Figure 3 Description of the decoding device.

[0211] exist Figure 8 In the examples provided, for ease of description, a multi-layer structure consisting of two layers will be described. However, it should be noted that the embodiments of this disclosure are not limited thereto, and the multi-layer structure to which the embodiments of this disclosure are applied may include two or more layers.

[0212] Reference Figure 8 The decoding device 800 may include a layer 1 decoder 800-1 and a layer 1 decoder 800-0. The layer 1 decoder 800-1 may include an entropy decoder 810-1, a residual processor 820-1, a predictor 830-1, an adder 840-1, a filter 850-1, and a memory 860-1. The layer 0 decoder 800-2 may include an entropy decoder 810-0, a residual processor 820-0, a predictor 830-0, an adder 840-0, a filter 850-0, and a memory 860-0.

[0213] When a bitstream containing image information is received from an encoding device, the demultiplexer (DEMUX) 805 can demultiplex the information from each layer and send the information to the decoding devices of each layer.

[0214] Entropy decoders 810-1 and 810-0 can perform decoding corresponding to the encoding method used in the encoding device. For example, when the encoding device uses CABAC, entropy decoders 810-1 and 810-0 can perform entropy decoding using CABAC.

[0215] When the prediction mode of the current block is intra-prediction mode, predictors 830-1 and 830-0 can perform intra-prediction of the current block based on neighboring reconstructed samples in the current frame.

[0216] When the prediction mode for the current block is inter-frame prediction mode, predictors 830-1 and 830-0 can perform inter-frame prediction for the current block based on information included in at least one frame before or after the current frame. Some or all of the motion information required for inter-frame prediction can be derived by examining information received from the encoding device.

[0217] When the skip mode is applied as the inter-frame prediction mode, no residual is sent from the encoding device, and the prediction block can be a reconstruction block.

[0218] Furthermore, the predictor 830-1 of layer 1 can perform inter-frame prediction or intra-frame prediction using only information about layer 1 and perform inter-layer prediction using information about another layer (layer 0).

[0219] As information about the current layer that is predicted using information about another layer (e.g., predicted via inter-layer prediction), it may include at least one of texture, motion information, unit information, and predetermined parameters (e.g., filtering parameters, etc.).

[0220] As information about another layer used for prediction of the current layer (e.g., for inter-layer prediction), at least one of texture, motion information, unit information, and predetermined parameters (e.g., filtering parameters, etc.) may exist.

[0221] In inter-layer prediction, the current block can be a block in the current frame of the current layer (e.g., layer 1), and can be the block to be decoded. The reference block can be a block in the frame (reference frame) of the same access unit (AU) as the frame (current frame) to which the prediction of the current block belongs, on the layer (reference layer, e.g., layer 0) to which the prediction of the current block belongs, and can be the block corresponding to the current block.

[0222] The multilayer decoding device 800 can perform interlayer prediction as described in the multilayer coding device 700. For example, the multilayer decoding device 800 can perform interlayer texture prediction, interlayer motion prediction, interlayer unit information prediction, interlayer parameter prediction, interlayer residual prediction, interlayer difference prediction, interlayer syntax prediction, etc. The multilayer decoding device 800 can perform interlayer prediction as described, but the interlayer prediction applicable in this disclosure is not limited to this.

[0223] When a reference frame index is received from the encoding device or when a reference frame index derived from a neighboring block indicates an interlayer reference frame in the reference frame list, the predictor 830-1 can use the interlayer reference frame to perform interlayer prediction. For example, when the reference frame index indicates an interlayer reference frame, the predictor 830-1 can deduce the sample values ​​of the region specified by the motion vector in the interlayer reference frame as the prediction block for the current block.

[0224] In this case, inter-layer reference frames can be included in the reference frame list for the current block. Predictor 830-1 can use inter-layer reference frames to perform inter-frame prediction for the current block.

[0225] As described above in the multi-layer encoding device 700, in the operation of the multi-layer decoding device 800, the inter-layer reference frame can be a reference frame constructed by sampling the reconstructed frame of the reference layer to correspond with the current layer. The processing for the case where the reconstructed frame of the reference layer corresponds to the frame of the current layer can be performed in the same manner as the encoding processing.

[0226] Furthermore, as described above in the multilayer encoding device 700, in the operation of the multilayer decoding device 800, the reconstructed frame of the reference layer from which the interlayer reference frame is derived can be a frame belonging to the same AU as the current frame to be encoded.

[0227] Furthermore, as described above in the multilayer coding device 700, in the operation of the multilayer decoding device 800, when inter-frame prediction of the current block is performed by including interlayer reference frames in the reference frame list, the positions of the interlayer reference frames in the reference frame list L0 and L1 may be different.

[0228] Furthermore, as described above in the multilayer coding device 700, in the operation of the multilayer decoding device 800, when inter-frame prediction of the current block is performed based on a reference frame list including inter-layer reference frames, the reference frame list may include multiple inter-layer reference frames derived from multiple layers, and the arrangement of the inter-layer reference frames may be performed to correspond to the encoding process described.

[0229] Furthermore, as described above in the multilayer encoding device 700, in the operation of the multilayer decoding device 800, information about the interlayer reference frame can be obtained using only sample values, only motion information (motion vectors), or both sample values ​​and motion information.

[0230] The multilayer decoding device 800 can receive reference indices of interlayer reference frames in the reference frame list from the multilayer encoding device 700 and perform interlayer prediction based on these indices. Additionally, the multilayer decoding device 800 can receive information from the multilayer encoding device 700 specifying which information (sample information, motion information, or both) is used from the interlayer reference frames; that is, information specifying the dependency type of the interlayer prediction dependency between two layers.

[0231] High-Level Syntax (HLS) Signaling and Semantics

[0232] As described above, the HLS can be encoded and / or signaled for use in video and / or image encoding. As described above, the video / image information of this disclosure can be included in the HLS. Furthermore, image / video encoding methods can be performed based on this image / video information.

[0233] Video Parameter Set Signaling

[0234] A Video Parameter Set (VPS) is a set of parameters used to carry layer information. For example, layer information may include information about the Output Layer Set (OLS), information about the profile layer level, information about the relationship between the OLS and the hypothetical reference decoder, and information about the relationship between the OLS and the Decoded Picture Buffer (DPB). A VPS may not be necessary for decoding the bitstream. The VPS Raw Byte Sequence Payload (RBSP) should be available for decoding processing before being referenced, either in at least one Access Unit (AU) with TemporalId equal to 0, or provided by external means. All VPS NAL units in the Encoded Video Sequence (CVS) with a specific vps_video_parameter_set_id value should have the same content.

[0235] Figure 9 This is a view illustrating the syntax structure of a VPS according to an embodiment of this disclosure. The following will describe... Figure 9 Syntax elements.

[0236] `vps_video_parameter_set_id` provides an identifier for the VPS. Other syntax elements can use `vps_video_parameter_set_id` to reference the VPS. The value of `vps_video_parameter_set_id` should be greater than 0.

[0237] `vps_max_layers_minus1` can specify the maximum number of layers allowed in each CVS of the reference VPS. For example, adding 1 to `vps_max_layers_minus1` specifies the maximum number of layers allowed in each CVS of the reference VPS.

[0238] Increasing `vps_max_sublayers_minus1` by 1 specifies the maximum number of time-limited sublayers that can exist in the layers of each CVS of the reference VPS.

[0239] A `vps_all_layers_same_num_sublayers_flag` value of 1 specifies that the number of time sublayers is the same for all layers across all CVSs of the reference VPS. A `vps_all_layers_same_num_sublayers_flag` value of 0 specifies that the number of time sublayers can be the same or different for layers across all CVSs of the reference VPS. When the value of `vps_all_layers_same_num_sublayers_flag` is not provided in the bitstream, its value can be inferred to be 1.

[0240] A `vps_all_independent_layers_flag` value of 1 specifies that all layers in CVS are encoded independently without using inter-layer prediction. A `vps_all_independent_layers_flag` value of 0 specifies that one or more layers in CVS can be encoded using inter-layer prediction.

[0241] `vps_layer_id[i]` can specify the `nuh_layer_id` value of the `i`-th layer. For any two non-negative integer values ​​`m` and `n`, when `m` is less than `n`, the value of `vps_layer_id[m]` should be less than `vps_layer_id[n]`. Here, `nuh_layer_id` is a syntax element in the NAL cell header that is signaled and can specify the identifier of the NAL cell.

[0242] A value of 1 for `vps_independent_layer_flag[i]` specifies that layer i does not use inter-layer prediction. A value of 0 for `vps_independent_layer_flag[i]` specifies that layer i can use inter-layer prediction, and the syntax element `vps_direct_ref_layer_flag[i][j]` can be obtained from the VPS. Here, `j` can be in the range of 0 to i-1 (inclusive). When a value for `vps_independent_layer_flag[i]` does not exist in the bitstream, the value of `vps_independent_layer_flag[i]` can be inferred to be equal to 1.

[0243] A value of 0 for `vps_direct_ref_layer_flag[i][j]` specifies that the layer at index `j` is not a direct reference layer to the layer at index `i`. A value of 1 for `vps_direct_ref_layer_flag[i][j]` specifies that the layer at index `j` is a direct reference layer to the layer at index `i`. When `vps_direct_ref_layer_flag[i][j]` is not obtained from the bitstream for `i` and `j` in the range 0 to `vps_max_layers_minus1` (inclusive), its value can be inferred to be 0. When `vps_independent_layer_flag[i]` is 0, there should exist at least one `j` value in the range 0 to `i-1` (inclusive) such that `vps_direct_ref_layer_flag[i][j]` is equal to 1.

[0244] In the implementation method, use Figure 10 The pseudocode is used to derive the variables NumDirectRefLayers[i], DirectRefLayerIdx[i][d], NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j].

[0245] The variable GeneralLayerIdx[i], which specifies the layer index of the layer whose nuh_layer_id is equal to vps_layer_id[i], can be derived as shown in the following formula.

[0246] [Equation 2]

[0247] for(i=0;i<=vps_max_layers_minus1;i++)

[0248] GeneralLayerIdx[vps_layer_id[i]]=i

[0249] A value of 1 for `max_tid_ref_present_flag[i]` specifies that the syntax element `max_tid_il_ref_pics_plus1[i]` is provided from the bitstream. A value of 0 for `max_tid_ref_present_flag[i]` specifies that the syntax element `max_tid_il_ref_pics_plus1[i]` is not provided from the bitstream.

[0250] A value of 0 for `max_tid_il_ref_pics_plus1[i]` specifies that non-IRAP frames of layer i should not use inter-layer prediction. A value greater than 0 for `max_tid_il_ref_pics_plus1[i]` specifies that for decoding frames of layer i, no frames with a TemporalId greater than `max_tid_il_ref_pics_plus1[i] - 1` are used as ILRP (Inter-Layer Reference Frames). When the value of `max_tid_il_ref_pics_plus1[i]` is not obtained from the bitstream, its value can be inferred to be 7.

[0251] The syntax element `each_layer_is_an_ols_flag` equal to 1 specifies that each OLS contains only one layer, and each layer in the referenced VPS's CVS is itself an OLS, with the individual included layer being an output layer only. `each_layer_is_an_ols_flag` equal to 0 specifies that an OLS can contain more than one layer. In implementation, if `vps_max_layers_minus1` equals 0, the value of `each_layer_is_an_ols_flag` can be inferred to be equal to 1. Otherwise, when `vps_all_independent_layers_flag` equals 0, the value of `each_layer_is_an_ols_flag` can be inferred to be equal to 0.

[0252] Setting ols_mode_idc to 0 allows you to specify that the total number of OLSs specified by the VPS is equal to vps_max_layers_minus1+1. The i-th OLS can include layers with layer indices from 0 to i (inclusive), and for each OLS, only the highest layer in the OLS can be output.

[0253] Setting ols_mode_idc to 1 specifies that the total number of OLSs specified by the VPS is equal to vps_max_layers_minus1+1. The i-th OLS can include layers with layer indices from 0 to i (inclusive), and for each OLS, all layers in the OLS can be output.

[0254] The value of ols_mode_idc equal to 2 can specify the total number of OLSs specified by the VPS, and for each OLS, the output layer is explicitly signaled and other layers are the layers that are the direct or indirect reference layers of the output layer of the OLS.

[0255] The value of ols_mode_idc should be in the range of 0 to 2 (inclusive). An ols_mode_idc value of 3 is reserved for future use. When vps_all_independent_layers_flag equals 1 and each_layer_is_an_ols_flag equals 0, the value of ols_mode_idc can be inferred to be equal to 2.

[0256] Increasing 1 to num_output_layer_sets_minus1 specifies the total number of OLS specified by the VPS when ols_mode_idc equals a predetermined value (e.g., 2).

[0257] The variable TotalNumOls specifies the total number of OLS values ​​assigned to the VPS, such as... Figure 11 The derivation is shown below.

[0258] Setting `ols_output_layer_flag[i][j]` to 1 specifies that when `ols_mode_idc` equals 2, the layer whose `nuh_layer_id` equals `vps_layer_id[j]` is the output layer of the i-th OLS. Setting `ols_output_layer_flag[i][j]` to 0 specifies that when `ols_mode_idc` equals 2, the layer whose `nuh_layer_id` equals `vps_layer_id[j]` is not the output layer of the i-th OLS.

[0259] The variables NumOutputLayersInOls[i] specifying the number of output layers in the i-th OLS, NumSubLayersInLayerInOLS[i][j] specifying the number of sublayers in the j-th layer of the i-th OLS, OutputLayerIdInOls[i][j] specifying the nuh_layer_id value of the j-th output layer in the i-th OLS, and LayerUsedAsOutputLayerFlag[k] specifying whether the k-th layer is used as an output layer in at least one OLS can be similar to Figure 12 The pseudocode derivation.

[0260] For each value of i in the range of 0 to vps_max_layers_minus1 (inclusive), the values ​​of LayerUsedAsRefLayerFlag[i] and LayerUsedAsOutputLayerFlag[i] should not be equal to 0. In other words, there should be no layer that is neither the output layer of at least one OLS nor a direct reference layer of any other layer.

[0261] For each OLS, there should be at least one layer that serves as the output layer. In other words, for any value of i in the range of 0 to TotalNumOlss-1 (inclusive), the value of NumOutputLayersInOls[i] should be greater than or equal to 1.

[0262] The variable NumLayersInOls[i], which specifies the layer number in the i-th OLS, and the variable LayerIdInOls[i][j], which specifies the nuh_layer_id value of the j-th layer in the i-th OLS, can be used as follows: Figure 13 The derivation is shown below.

[0263] In the implementation, the 0OLS only contains the lowest layer. The lowest layer can refer to the layer whose nuh_layer_id is equal to vps_layer_id[0]. In addition, for the 0OLS, the only included layer can be output.

[0264] The variable OlsLayerIdx[i][j], which specifies the OLS layer index of the layer whose nuh_layer_id is equal to LayerIdInOls[i][j], can be used as follows: Figure 14 The derivation is shown below.

[0265] The lowest layer in each OLS should be an independent layer. For example, for each i in the range of 0 to TotalNumOlss-1 (inclusive), the value of vps_independent_layer_flag[GeneralLayerIdx[LayerIdInOls[i][0]]] should be equal to 1.

[0266] Each tier should be included in at least one OLS specified by the VPS.

[0267] The signaling limit of max_tid_il_ref_pics_plus1[i]

[0268] The signaling associated with the syntax element max_tid_il_ref_pics_plus1[i] has problems in both its semantics and functionality.

[0269] For example, the semantic representation of max_tid_il_ref_pics_plus1[i] when its value is greater than 0 means that the picture in the i-th layer only uses at most max_tid_il_ref_ref_pics_plus1[i]-1 sub-layers in the reference picture for its inter-layer prediction.

[0270] This means that the image in layer i only uses at most max_tid_il_ref_ref_pics_plus1[i]-1 sub-layers in the reference image for its inter-layer prediction.

[0271] The syntax elements are designed to allow the derivation of a variable NumSubLayersInLayerInOLS[i][j] that can specify the number of sublayers in the j-th layer of the i-th OLS. Here, OLS is an abbreviation for Output Layer Set and can refer to the set of at least one layer specified by the output layer.

[0272] The variable NumSubLayersInLayerInOLS[i][j] can be used for bitstream extraction processing to remove images from sublayers within layers that are not part of the extracted output layer set.

[0273] This mechanism is not optimal when a layer uses more than one reference layer for inter-layer prediction and the number of sub-layers used from each reference layer is not the same.

[0274] For example, suppose Layer 2 references Layer 0 and Layer 1 for inter-layer prediction. For inter-layer prediction from Layer 0, only 2 sub-layers are used, while from Layer 1, 3 sub-layers are used. In this example, according to the signaling mechanism described above, Layer 2 uses 3 sub-layers for inter-layer prediction, and in this approach, it is impossible to remove sub-layers 3 or higher from Layer 0.

[0275] improve

[0276] The following implementation methods provide solutions to the above problems. These implementation methods may be applied individually or in combination.

[0277] Improvement 1. Instead of signaling a single value for all reference layers for the maximum number of sublayers used for interlayer prediction of a layer, for each reference layer of a layer, the maximum number of sublayers used from that reference layer can be signaled.

[0278] Improvement 2. The maximum number of sub-layers used from the reference layer j of layer i is only allowed if layer j is a direct reference layer of layer i.

[0279] Improvement 3: The flag indicating whether the signaling for specifying the maximum number of sub-layers for inter-layer prediction of a layer exists can be signaled as one for all layers existing in the VPS.

[0280] a) The syntax element max_tid_ref_present_flag[i] can be changed to max_tid_ref_present_flag.

[0281] b) When all layers are independent, max_tid_ref_present_flag may not exist, and when max_tid_ref_present_flag does not exist, max_tid_ref_present_flag can be inferred to be equal to 0.

[0282] Improvement 4. The derivation of NumSubLayersInLayerInOLS for direct and indirect reference layers can be solved as follows.

[0283] a) If each_layer_is_an_ols_flag[i] is equal to 1 (e.g., true), then NumSubLayersInLayerInOLS[i][0] is set to be equal to vps_max_sub_layers_minus1+1.

[0284] b) If each_layer_is_an_ols_flag is 0 (e.g., false), then for each OLS, and vps_direct_ref_layer_flag[l][k] is true, then NumSubLayersInLayerInOLS[i][GeneralLayerIdx[vps_layer_id[k]]] can be derived as max_tid_il_ref_pics_plus1[l][k].

[0285] c) When ols_mode_idc equals 2, improvement 4 can be applied.

[0286] Implementation Method 1

[0287] In the implementation method, improvements 1 and 2 can be based on... Figure 15 The changes shown are implemented using the modified VPS syntax. The following will describe the changes from the above VPS syntax. Figure 15 Syntax elements.

[0288] A value of 1 for `vps_independent_layer_flag[i]` specifies that layer i at index i does not use inter-layer prediction. A value of 0 for `vps_independent_layer_flag[i]` specifies that layer i at index i can use inter-layer prediction, and the VPS contains the syntax element `vps_direct_ref_layer_flag[i][j]`, where j is in the range of 0 to i-1 (inclusive). When the value of `vps_independent_layer_flag[i]` is not obtained from the bitstream, its value can be inferred to be 1.

[0289] A value of 1 for `max_tid_ref_present_flag[i]` indicates that the syntax element `max_tid_il_ref_pics_plus1[i][j]` exists in the bitstream. A value of 0 for `max_tid_ref_present_flag[i]` indicates that the syntax element `max_tid_il_ref_pics_plus1[i][j]` does not exist in the bitstream.

[0290] A value of 0 for `max_tid_il_ref_pics_plus1[i][j]` specifies that non-IRAP frames from layer i do not use layer j as the reference layer for inter-layer prediction. A value greater than 0 for `max_tid_il_ref_pics_plus1[i][j]` specifies that for decoding frames from layer i, no frames with a TemporalId greater than `max_tid_il_ref_pics_plus1[i][j]-1 from layer j are used for ILRP. When the value of `max_tid_il_ref_pics_plus1[i][j]` is not obtained from the bitstream, its value can be inferred to be 7.

[0291] Additionally, using the syntax elements and variables modified according to the above description, the variables NumOutputLayersInOls[i], NumSubLayersInLayerInOLS[i][j], OutputLayerIdInOls[i][j], and LayerUsedAsOutputLayerFlag[k] can be similar to Figure 16 The pseudocode has been determined.

[0292] Similar to the method described above, for each reference layer of a layer, the maximum number of sublayers used by the reference layer can be signaled, and the maximum number of sublayers used by the reference layer j of layer i can only be provided if layer j is a direct reference layer of layer i.

[0293] Implementation Method 2

[0294] In the implementation method, improvement 3 can be based on... Figure 17 The changes shown are implemented using the modified VPS syntax. For example, similar to... Figure 17 The `max_tid_ref_present_flag` flag, which specifies the presence of a signaling flag for the maximum number of sub-layers used for inter-layer prediction, can be signaled as one for all layers.

[0295] For example, changes from the syntax of the VPS mentioned above. Figure 17The syntax element max_tid_ref_present_flag being equal to 1 specifies that the syntax element max_tid_il_ref_pics_plus1[i] exists in the bitstream. The syntax element max_tid_ref_present_flag being equal to 0 specifies that the syntax element max_tid_il_ref_pics_plus1[i] does not exist in the bitstream.

[0296] Implementation Method 3

[0297] The derivation of NumOutputLayersInOls based on the above improvements 1, 2, and 4 can be used as follows: Figure 18 The pseudocode is used to execute. Figure 18 This is a view of the pseudocode that indicates the method for deriving the NumOutputLayersInOls for direct and indirect reference layers.

[0298] like Figure 18 As shown, when the value of ols_mode_idc is equal to 2, if the value of each_layer_is_an_ols_flag[i] is true, then NumSubLayersInLayerInOLS[i][0] can be set to vps_max_sub_layers_minus1+1. And if the value of each_layer_is_an_ols_flag[i] is false, and for each OLS, the value of vps_direct_ref_layer_flag[l][k] is true, then NumSubLayersInLayerInOLS[i][GeneralLayerIdx[vps_layer_id[k]]] can be derived as max_tid_il_ref_pics_plus1[l][k].

[0299] Encoding and Decoding Methods

[0300] The image encoding and decoding method performed by the image encoding and decoding apparatus according to the embodiments will be described below. Figure 19 This is a view illustrating a method for determining the number of sub-layers of the current layer so as to encode an image by an image encoding device and / or decode an image by an image decoding device according to an embodiment.

[0301] The image decoding device according to the embodiment includes a memory and a processor, and the decoding device can perform decoding by operating the processor according to the following embodiment. The image encoding device according to the embodiment includes a memory and a processor, and the encoding device can perform encoding in a manner corresponding to the decoding of the decoding device according to the following embodiment by operating the processor. Hereinafter, for ease of description, the operation of the decoding device will be described, but the following description applies to the encoding device.

[0302] In one implementation, the number of sub-layers of the current layer can be used to refer to the number of sub-layers belonging to the current layer. However, in another implementation, the number of sub-layers of the current layer can be used to refer to the number of sub-layers required by the current layer.

[0303] The decoding device according to the implementation can determine inter-layer direct references (S1910). Inter-layer direct references can be determined by direct reference layer information obtained from the bitstream. In addition, the direct reference layer information can indicate inter-layer direct references. For example, the direct reference layer information can be the above-mentioned syntax element vps_direct_ref_layer_flag[i][j].

[0304] Direct reference layer information can be obtained from the bitstream for the layer being encoded based on inter-layer prediction. Here, it can be determined whether to perform encoding based on inter-layer prediction based on independent layer information obtained from the bitstream. For example, independent layer information can be the syntax element vps_independent_layer_flag[i] mentioned above.

[0305] Next, the decoding device can determine the number of sub-layers of the current layer based on inter-layer direct reference (S1920).

[0306] Here, the number of sub-layers of the current layer can be determined based on whether the current layer is an output layer. In the implementation, as shown... Figure 18 As shown in the pseudocode, whether the current layer is an output layer can be determined by "if(each_layer_is_an_ols_flag)" or "if(ols_output_layer_flag[i][k])".

[0307] In the implementation, the number of sub-layers of the current layer can be determined as the maximum number of available sub-layers based on whether the current layer is an output layer. For example... Figure 18 As shown in the pseudocode, this can be achieved by “NumSubLayersInLayerInOLS[i][j]=vps_max_sub_layers_minus1+1”.

[0308] In the implementation, the number of sub-layers of the current layer can be determined as a predetermined value based on whether the current layer is not an output layer.

[0309] Here, the predetermined value can be determined based on the maximum identifier information of the frame that can be referenced for inter-layer prediction. The maximum identifier information can be information indicating that the frame with a time identifier greater than the value identified by the maximum identifier information among the multiple frames of the first layer is not used as an inter-layer reference frame for decoding the current frame of the second layer. For example, the maximum identifier information can be the above syntax element max_tid_il_ref_pics_plus1[i][j].

[0310] In the implementation, the first layer can be the current layer, and the second layer can be a layer that can use the current layer as a direct reference layer.

[0311] For example, the maximum identifier information could be Figure 18 The example shown is `max_tid_il_ref_pics_plus1[l][k]`. Furthermore, the relationship between the current layer's sub-layers and layers that can directly reference them can be determined by... Figure 18 The "if(vps_direct_ref_layer_flag[l][k])" flag.

[0312] Whether the current layer is an output layer can be determined based on the output layer set mode information obtained from the bitstream, and the output layer set mode information can be the above syntax element ols_mode_idc.

[0313] In addition, whether the current layer is an output layer can be determined based on the output layer set mode information and output layer flag obtained from the bitstream, and the output layer flag can be the above syntax element ols_output_layer_flag[i][j].

[0314] Based on this determined number of sub-layers, the decoding device can decode the current layer by performing inter-layer prediction of the current layer, and the encoding device can encode the current layer by performing inter-layer prediction of the current layer.

[0315] For example, in an implementation, the image decoding method may include the following steps: obtaining the maximum allowed number of layers (e.g., vps_max_layers_minus1) from the bitstream; identifying the current layer with a first index (e.g., i) based on the maximum allowed number of layers; obtaining an independent layer flag (e.g., vps_independent_layer_flag[i]) from the bitstream indicating whether the current layer is based on inter-layer predictive coding; obtaining a maximum time identifier signaling flag (e.g., vps_max_tid_ref_present_flag[i]) from the bitstream based on the independent layer flag; and determining a second index less than the first index (e.g., vps_max_tid_ref_present_flag[i]). ,j); obtain a direct reference layer flag (e.g., vps_direct_ref_layer_flag[i][j]) from the bitstream based on the independent layer flag, the first index, and the second index, indicating whether the reference layer with the second index is the direct reference layer of the current layer; obtain maximum time identifier information (e.g., vps_max_tid_il_ref_pics_plus1[i][j]) from the bitstream based on the maximum time identifier signaling flag and the direct reference layer flag; and determine the number of sublayers of the reference layer based on the maximum time identifier information (e.g., NumSubLayersInLayerInOLS[i][k]).

[0316] Here, the sublayer can be referenced by the current layer, and the maximum time identifier signaling flag can indicate whether the maximum time identifier information is obtained from the bitstream. Furthermore, frames in the reference layer whose time identifier values ​​are greater than the value indicated by the maximum time identifier information can be excluded from use as inter-layer reference frames for decoding the current frame of the current layer.

[0317] Here, the bitstream includes an independent layer flag (e.g., vps_independent_layer_flag[i]) indicating whether the current layer is based on inter-layer predictive coding. Additionally, a maximum time identifier signaling flag (e.g., vps_max_tid_ref_present_flag[i]) may be included in the bitstream based on whether the current layer is based on inter-layer predictive coding. Furthermore, a direct reference layer flag (e.g., vps_direct_ref_layer_flag[i][j]) indicating whether the reference layer is the direct reference layer of the current layer may be included in the bitstream.

[0318] Furthermore, based on the maximum time identifier signaling flag and the direct reference flag, the maximum time identifier information (e.g., vps_max_tid_il_ref_pics_plus1[i][j]) can be included in the bitstream. Additionally, the number of sub-layers of the reference layer that the current layer can reference (e.g., NumSubLayersInLayerInOLS[i][k]) can be encoded based on the maximum time identifier information.

[0319] In addition, in an implementation, the image encoding method may include the following steps: encoding a reference image in a reference layer; encoding a current image in the current layer based on the reference image; and generating a bitstream that includes the encoding information of the current image.

[0320] Application and Implementation Methods

[0321] Although the exemplary methods of this disclosure described above are represented as a series of operations for clarity of description, they are not intended to limit the order in which the steps are performed, and these steps may be performed simultaneously or in different orders if necessary. To implement the methods according to this disclosure, the described steps may further include other steps, including steps in addition to some steps, or may include additional steps in addition to some steps.

[0322] In this disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) can perform an operation (step) that confirms the execution conditions or circumstances of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when predetermined conditions are met, the image encoding device or the image decoding device can perform the predetermined operation after determining whether the predetermined conditions are met.

[0323] The various embodiments of this disclosure are not a list of all possible combinations and are intended to describe representative aspects of this disclosure; the matters described in the various embodiments may be applied independently or in combination of two or more.

[0324] Various embodiments of this disclosure can be implemented in hardware, firmware, software, or a combination thereof. When this disclosure is implemented in hardware, it can be implemented using application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), general-purpose processors, controllers, microcontrollers, microprocessors, etc.

[0325] Furthermore, the image decoding and image encoding devices applying the embodiments of this disclosure can be included in multimedia broadcasting transmitting and receiving devices, mobile communication terminals, home theater video devices, digital cinema video devices, surveillance cameras, video chat devices, real-time communication devices such as video communication, mobile streaming devices, storage media, cameras, video-on-demand (VoD) service providers, OTT (over-the-top video) devices, internet streaming service providers, three-dimensional (3D) video devices, video telephony devices, medical video devices, etc., and can be used to process video signals or data signals. For example, OTT video devices can include game consoles, Blu-ray players, internet access televisions, home theater systems, smartphones, tablet PCs, digital video recorders (DVRs), etc.

[0326] Figure 20 This is a view illustrating a content streaming system to which embodiments of the present disclosure can be applied.

[0327] like Figure 20 As shown, the content streaming system using the embodiments of this disclosure may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0328] An encoding server compresses content input from multimedia input devices such as smartphones, cameras, and camcorders into digital data to generate a bitstream, which is then sent to a streaming server. As another example, when multimedia input devices such as smartphones, cameras, and camcorders directly generate bitstreams, the encoding server can be omitted.

[0329] The bitstream can be generated by an image encoding method or image encoding device applying the embodiments of this disclosure, and the stream server can temporarily store the bitstream during the sending or receiving of the bitstream.

[0330] A streaming server sends multimedia data to a user's device based on a request from a web server, and the web server acts as a medium for informing the user of the service. When a user requests a service from the web server, the web server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this scenario, the content streaming system may include a separate control server. In this case, the control server is used to control the commands / responses between devices in the content streaming system.

[0331] A streaming server can receive content from media storage devices and / or encoding servers. For example, when receiving content from an encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined period of time.

[0332] Examples of user devices may include mobile phones, smartphones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0333] In a content streaming system, each server can operate as a distributed server, in which case the data received from each server can be distributed.

[0334] The scope of this disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling the operation of methods according to various embodiments to be executed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0335] Industrial applicability

[0336] The embodiments disclosed herein can be used to encode or decode images.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Determine direct interlayer references; as well as The number of sub-layers of the current layer is determined based on the inter-layer direct reference. The number of sub-layers of the current layer is determined based on the maximum identifier information, which is not the output layer. The maximum identifier information is obtained based on the inter-layer direct reference. The maximum identifier information indicates that a frame with a time identifier greater than the value identified by the maximum identifier information among multiple frames of the first layer is not used as an inter-layer reference frame for decoding the target frame of the second layer.

2. The image decoding method according to claim 1, in, The interlayer direct reference is determined by direct reference layer information obtained from the bitstream, and The direct reference layer information indicates direct references between layers.

3. The image decoding method according to claim 2, wherein, The direct reference layer information is obtained from the bitstream for layers encoded based on inter-layer prediction.

4. The image decoding method according to claim 3, wherein, Whether a layer is encoded based on inter-layer prediction is determined based on independent layer information obtained from the bitstream.

5. The image decoding method according to claim 1, wherein, The number of sub-layers of the current layer is determined based on whether the current layer is an output layer.

6. The image decoding method according to claim 5, wherein, Based on whether the current layer is an output layer, the number of sub-layers of the current layer is determined as the maximum number of available sub-layers.

7. The image decoding method according to claim 1, wherein, The first layer is the current layer, and the second layer is a layer that can use the current layer as a direct reference layer.

8. The image decoding method according to claim 1, wherein, Whether the current layer is an output layer is determined based on the output layer set mode information obtained from the bit stream.

9. The image decoding method according to claim 1, wherein, Whether the current layer is an output layer is determined based on the output layer set mode information and output layer flag obtained from the bit stream.

10. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: Determine direct interlayer references; as well as The number of sub-layers of the current layer is determined based on the inter-layer direct reference. The number of sub-layers of the current layer is determined based on the maximum identifier information, which is not the output layer. The maximum identifier information is obtained based on the inter-layer direct reference. The maximum identifier information indicates that a frame with a time identifier greater than the value identified by the maximum identifier information among multiple frames of the first layer is not used as an inter-layer reference frame for decoding the target frame of the second layer.

11. A method for transmitting a bit stream, the method comprising the steps of: The bitstream is generated based on an image encoding method; as well as Send the generated bit stream. The image encoding method includes the following steps: Determine direct interlayer references; and The number of sub-layers of the current layer is determined based on the inter-layer direct reference. The number of sub-layers of the current layer is determined based on the maximum identifier information, which is not the output layer. The maximum identifier information is obtained based on the inter-layer direct reference. The maximum identifier information indicates that a frame with a time identifier greater than the value identified by the maximum identifier information among multiple frames of the first layer is not used as an inter-layer reference frame for decoding the target frame of the second layer.

Images