Filtering-based image coding device and method

Abstract

To provide a method for increasing image / video coding efficiency.SOLUTION: According to the embodiments of the present document, etc., sub-pictures and / or virtual boundaries can be used for coding an image. For example, sub-pictures in the current picture can be used for predicting, reconstructing, and / or filtering the current picture. Virtual boundaries can be used for filtering reconstructed samples of the current picture. Through image coding based on the sub-pictures and / or virtual boundaries according to the embodiments of the present document, etc., the subjective / objective quality of an image can be improved, and the consumption of hardware resources necessary for the coding can be reduced.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This document relates to a filtering-based image coding apparatus and method. [Background technology]

[0002] In recent years, demand for high-resolution, high-quality images / videos, such as 4K or 8K or higher UHD (Ultra High Definition) images / videos, has been increasing in various fields. As the resolution and quality of image / video data increases, the amount of information or bits to be transmitted increases relatively compared to existing image / video data. Therefore, when image data is transmitted using a medium such as an existing wired or wireless broadband line, or when image / video data is stored using an existing storage medium, transmission costs and storage costs increase.

[0003] In addition, interest in and demand for immersive media such as VR (Virtual Reality), AR (Artificial Reality) content, and holograms have been increasing in recent years, and the broadcast of images / videos with different image characteristics from real images, such as game images, has been increasing.

[0004] Therefore, there is a need for highly efficient image / video compression technology to effectively compress and transmit, store, and play back high-resolution, high-quality image / video information having the above-mentioned various characteristics.

[0005] Specifically, in order to improve subjective / objective visual quality, an in-loop filtering procedure is performed, and there is discussion on a method for improving the signaling efficiency of information for performing in-loop filtering based on a virtual boundary. Also, the application of sub-pictures to improve the performance of prediction and restoration in image coding is being considered. Summary of the Invention [Means for solving the problem]

[0006] According to one embodiment of this document, a method and apparatus for improving the efficiency of image / video coding is provided.

[0007] According to one embodiment of the present document, an efficient method and apparatus for applying filtering is provided.

[0008] According to one embodiment of the present document, a method and apparatus for efficiently applying deblocking, sample adaptive loop (SAO), and adaptive loop filtering (ALF) is provided.

[0009] According to one embodiment of this document, in-loop filtering is performed based on a virtual boundary.

[0010] According to one embodiment of this document, whether or not resampling for a reference picture is available determines whether or not the SPS (sequence parameter set) includes additional virtual boundary-related information (e.g., information regarding the number and location of virtual boundaries).

[0011] According to one embodiment of this document, image coding is performed based on sub-pictures.

[0012] According to one embodiment of this document, the sub-pictures used in image coding are coded independently.

[0013] According to one embodiment of this document, a picture contains only one sub-picture, and said sub-pictures are coded independently.

[0014] According to one embodiment of this document, a picture is generated based on a sub-picture merging procedure, and the sub-pictures may be independently coded sub-pictures.

[0015] According to one embodiment of this document, each sub-picture used in image coding is treated as a picture.

[0016] According to one embodiment of the present document, an encoding device for video / image encoding is provided.

[0017] According to one embodiment of the present document, there is provided a computer-readable digital storage medium having encoded video / image information stored thereon, the encoded video / image information being generated by the video / image encoding method disclosed in at least one of the embodiments of the present document.

[0018] According to one embodiment of the present document, there is provided a computer-readable digital storage medium having stored thereon encoded information or encoded video / image information that causes a decoding device to perform the video / image decoding method disclosed in at least one of the embodiments of the present document. [Effects of the Invention]

[0019] According to one embodiment of this document, the overall image / video compression efficiency can be increased.

[0020] According to one embodiment of this document, subjective / objective visual quality can be enhanced through efficient filtering.

[0021] According to one embodiment of this document, a virtual boundary based in-loop filtering procedure can be performed efficiently and the filtering performance can be improved.

[0022] According to one embodiment of this document, information for virtual boundary based in-loop filtering can be efficiently signaled.

[0023] According to one embodiment of this document, sub-picture related information is signaled efficiently, thus improving the subjective / objective quality of the image and reducing the consumption of hardware resources required for coding. [Brief explanation of the drawings]

[0024] [Figure 1] 1 illustrates schematically an example of a video / image coding system to which embodiments of the present document can be applied. [Figure 2] 1 is a diagram illustrating the configuration of a video / image encoding device that can be applied to an embodiment of the present document. [Figure 3] 1 is a diagram illustrating the configuration of a video / image decoding device that can be applied to an embodiment of the present document. [Figure 4] 1 shows an exemplary hierarchical structure for coded images / videos. [Figure 5] 1 is a flowchart illustrating an encoding method based on filtering in an encoding device. [Figure 6] 1 is a flowchart illustrating a decoding method based on filtering in a decoding device. [Figure 7] 1 illustrates a schematic diagram of an example video / image encoding method and associated components according to an embodiment (or others) of the present document; [Figure 8] 1 illustrates a schematic diagram of an example video / image encoding method and associated components according to an embodiment (or others) of the present document; [Figure 9] 1 illustrates a schematic diagram of an example image / video decoding method and associated components according to an embodiment(s) of the present document; [Figure 10] 1 illustrates a schematic diagram of an example image / video decoding method and associated components according to an embodiment(s) of the present document; [Figure 11] 1 illustrates an example of a content streaming system to which embodiments disclosed herein may be applied. DETAILED DESCRIPTION OF THE INVENTION

[0025] This document may be modified in various ways and may have various embodiments. Specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit this document to the specific embodiment. Common terms used in this document are used merely to describe specific embodiments and are not intended to limit the technical ideas of this document. A singular expression includes a plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0026] Meanwhile, each component in the drawings described in this document is illustrated independently for the convenience of explaining the different characteristic functions, and does not mean that each component is realized by separate hardware or software. For example, two or more components may be combined to form a single component, or a single component may be divided into multiple components. Embodiments in which each component is integrated and / or separated are also included within the scope of this document as long as they do not deviate from the essence of this document.

[0027] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used to refer to the same components in the drawings, and duplicated descriptions of the same components will be omitted.

[0028] This document relates to video / image coding. For example, methods / embodiments disclosed in this document may relate to the Versatile Video Coding (VVC) standard (ITU-T Rec. H.266), next-generation video / image coding standards beyond VVC, or other video coding-related standards (e.g., the High Efficiency Video Coding (HEVC) standard (ITU-T Rec. H.265), the essential video coding (EVC) standard, the AVS2 standard, etc.).

[0029] This document presents various embodiments relating to video / image coding, which, unless otherwise stated, may also be implemented in combination with one another.

[0030] In this document, video can refer to a collection of a series of images over time. A picture generally refers to a unit that shows one image at a specific time, and a slice / tile is a unit that constitutes part of a picture in coding. A slice / tile may contain one or more coding tree units (CTUs). A picture may consist of one or more slices / tiles. A picture may consist of one or more tile groups. A tile group may contain one or more tiles.

[0031] A pixel or a pel may refer to the smallest unit constituting one picture (or image). A term corresponding to a pixel may also be used: "sample." A sample generally refers to a pixel or a pixel value, and may refer to only a pixel / pixel value of a luma component, or may refer to only a pixel / pixel value of a chroma component. Alternatively, a sample may refer to a pixel value in the spatial domain, or, when such a pixel value is transformed into the frequency domain, may refer to a transform coefficient in the frequency domain.

[0032] A unit refers to a basic unit of image processing. A unit includes at least one of a specific region of a picture and information about that region. One unit includes one luma block and two chroma (e.g., cb, cr) blocks. The term unit may be used interchangeably with terms such as block or area. In general, an MxN block includes a set (or array) of samples or transform coefficients consisting of M columns and N rows.

[0033] In this document, " / " and "," are interpreted as "and / or." For example, "A / B" is interpreted as "A and / or B," and "A, B" is interpreted as "A and / or B." Additionally, "A / B / C" means "at least one of A, B, and / or C." Also, "A, B, C" means "at least one of A, B, and / or C."

[0034] Additionally, in this document, "or" is interpreted as "and / or." For example, "A or B" can mean 1) only "A," 2) only "B," or 3) "A and B." In other words, in this document, "or" can mean "additionally or alternatively."

[0035] As used herein, "at least one of A and B" can mean "A only," "B only," or "both A and B." Furthermore, as used herein, the expressions "at least one of A or B" and "at least one of A and / or B" can be interpreted in the same way as "at least one of A and B."

[0036] Furthermore, in this specification, "at least one of A, B and C" can mean "A only," "B only," "C only," or "any combination of A, B and C." Furthermore, "at least one of A, B or C" and "at least one of A, B and / or C" can mean "at least one of A, B and C."

[0037] Furthermore, parentheses used in this specification may mean "for example." Specifically, when "prediction (intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction." In other words, "prediction" in this specification is not limited to "intra prediction," and "intra prediction" may be proposed as an example of "prediction." Furthermore, when "prediction (i.e., intra prediction)" is displayed, "intra prediction" may be proposed as an example of "prediction."

[0038] Technical features described separately in one drawing in this specification may be realized separately or simultaneously.

[0039] FIG. 1 shows a schematic diagram of an example of a video / image coding system to which this document can be applied.

[0040] As shown in Figure 1, a video / image coding system may include a source device and a receiving device. The source device may transmit encoded video / image information or data to the receiving device in file or streaming form via a digital storage medium or a network.

[0041] The source device may comprise a video source, an encoding device, and a sending unit. The receiving device may comprise a receiving unit, a decoding device, and a renderer. The encoding device may be called a video / image encoding device, and the decoding device may be called a video / image decoding device. The transmitter may be included in the encoding device. The receiver may be included in the decoding device. The renderer may comprise a display unit, which may be a separate device or an external component.

[0042] A video source can acquire video / images through a video / image capture, synthesis, or generation process. A video source can include a video / image capture device and / or a video / image generation device. A video / image capture device can include, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. A video / image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video / images. For example, a virtual video / image can be generated via a computer, etc., in which case the video / image capture process can be replaced by a process in which related data is generated.

[0043] An encoding device can encode input video / images. The encoding device can perform a series of steps such as prediction, transformation, and quantization for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0044] The transmitter may transmit the encoded video / image information or data output in the form of a bitstream to a receiver of a receiving device via a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter may include elements for generating a media file in a predetermined file format and elements for transmission via a broadcast / communication network. The receiver may receive / extract the bitstream and transmit it to a decoding device.

[0045] The decoding device can decode the video / image by performing a series of steps such as inverse quantization, inverse transform, prediction, etc., which correspond to the operations of the encoding device.

[0046] The renderer can render the decoded video / image, and the rendered video / image can be displayed via the display unit.

[0047] 2 is a diagram illustrating the configuration of a video / image encoding device to which this document can be applied. Hereinafter, the term "video encoding device" may include an image encoding device.

[0048] As shown in FIG. 2, the encoding device 200 may include an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 may include an inter predictor 221 and an intra predictor 222. The residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 may further include a subtractor 231. The adder 250 may be referred to as a reconstructor or a reconstructed block generator. The image dividing unit 210, the predicting unit 220, the residual processing unit 230, the entropy encoding unit 240, the adding unit 250, and the filtering unit 260 may be configured by one or more hardware components (e.g., an encoder chipset or a processor) depending on the embodiment. Also, the memory 270 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium. The hardware components may further include the memory 270 as an internal / external component.

[0049] The image division unit 210 may divide an input image (or picture, frame) input to the encoding device 200 into one or more processing units. For example, the processing units may be called coding units (CUs). In this case, the coding units may be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) using a quad-tree, binary-tree, ternary-tree (QTBTTT) structure. For example, one coding unit may be divided into multiple coding units of deeper depths based on a quad-tree structure, a binary tree structure, and / or a ternary structure. In this case, for example, the quad-tree structure may be applied first, and then the binary tree structure and / or ternary structure may be applied. Alternatively, the binary tree structure may be applied first. The coding procedure according to the present disclosure may be performed based on a final coding unit that is not further divided. In this case, the largest coding unit may be used as the final coding unit based on coding efficiency according to image characteristics, or the coding unit may be recursively divided into coding units of lower depths as needed, and a coding unit of an optimal size may be used as the final coding unit. Here, the coding procedure may include procedures such as prediction, transformation, and restoration, which will be described later. As another example, the processing unit may further include a prediction unit (PU) or a transform unit (TU). In this case, the prediction unit and the transform unit may each be divided or partitioned from the final coding unit.The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving transform coefficients and / or a unit for deriving a residual signal from the transform coefficients.

[0050] The term "unit" may be used interchangeably with terms such as "block" or "area." In general, an MxN block may refer to a set of samples or transform coefficients consisting of M columns and N rows. A sample generally refers to a pixel or a pixel value, and may refer to only a pixel / pixel value of a luma component, or may refer to only a pixel / pixel value of a chroma component. A sample can be used as a term corresponding to one pixel or pel of a picture (or image).

[0051] The subtraction unit 231 may subtract a prediction signal (predicted block, prediction sample, or prediction sample array) output from the prediction unit 220 from an input image signal (original block, original sample, or original sample array) to generate a residual signal (residual block, residual sample, or residual sample array), and the generated residual signal is transmitted to the conversion unit 232. The prediction unit 220 may perform prediction on a block to be processed (hereinafter, referred to as a current block) and generate a predicted block including prediction samples for the current block. The prediction unit 220 may determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit may generate various information related to prediction, such as prediction mode information, and transmit the information to the entropy encoding unit 240, as will be described later in the description of each prediction mode. The prediction information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0052] The intra prediction unit 222 may predict the current block by referring to samples in the current picture. The referenced samples may be located adjacent to or distant from the current block depending on the prediction mode. Prediction modes in intra prediction may include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes may include, for example, DC mode and planar mode. The directional modes may include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the granularity of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the settings. The intra prediction unit 222 may also determine the prediction mode to be applied to the current block using the prediction modes applied to neighboring blocks.

[0053] The inter prediction unit 221 may derive a predicted block for a current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. In this case, to reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction direction (such as L0 prediction, L1 prediction, or Bi prediction). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be called a collocated reference block, a collocated CU (col CU), etc., and the reference picture including the temporal neighboring block may be called a collocated picture (colPic). For example, the inter predictor 221 may construct a motion information candidate list based on neighboring blocks and generate information indicating which candidate is used to derive a motion vector and / or a reference picture index for the current block. Inter prediction may be performed based on various prediction modes, and for example, in the case of a skip mode or a merge mode, the inter predictor 221 may use motion information of neighboring blocks as motion information of the current block. In the case of the skip mode, unlike the merge mode, a residual signal may not be transmitted.In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block can be used as a motion vector predictor, and the motion vector of the current block can be indicated by signaling the motion vector difference.

[0054] The prediction unit 220 may generate a prediction signal based on various prediction methods, which will be described later. For example, the prediction unit may apply intra prediction or inter prediction for prediction of a block, or may simultaneously apply intra prediction and inter prediction. This may be referred to as combined inter and intra prediction (CIIP). The prediction unit may also perform intra block copy (IBC) for prediction of a block. The intra block copy may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be similar to inter prediction in that it derives a reference block within the current picture. That is, IBC may use at least one of the inter prediction techniques described herein.

[0055] The prediction signal generated by the inter prediction unit 221 and / or the intra prediction unit 222 may be used to generate a reconstructed signal or a residual signal. The transform unit 232 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include a discrete cosine transform (DCT), a discrete sine transform (DST), a graph-based transform (GBT), or a conditionally non-linear transform (CNT). Here, GBT refers to a transform obtained from a graph representing relationship information between pixels. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to pixel blocks having the same square size or non-square blocks of variable sizes.

[0056] The quantization unit 233 quantizes the transform coefficients and transmits the quantized signal to the entropy encoding unit 240. The entropy encoding unit 240 encodes the quantized signal (information about the quantized transform coefficients) and outputs it as a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantization unit 233 may rearrange the quantized transform coefficients in a block form into a one-dimensional vector form based on a coefficient scan order, and may generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoding unit 240 may perform various encoding methods, such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. In addition to the quantized transform coefficients, the entropy encoding unit 240 may also encode information required for video / image restoration (e.g., values ​​of syntax elements, etc.) together with or separately from the quantized transform coefficients. The encoded information (e.g., encoded video / image information) may be transmitted or stored in the form of a bitstream in units of network abstraction layer (NAL) units. The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. Signaling / transmitted information and / or syntax elements described later in this document may be encoded through the encoding procedure described above and included in the bitstream. The bitstream may be transmitted via a network or stored in a digital storage medium.Here, the network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as a USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for transmitting the signal output from the entropy encoding unit 240 and / or a storage unit (not shown) for storing the signal may be configured as an internal / external element of the encoding device 200, or the transmitter may be included in the entropy encoding unit 240.

[0057] The quantized transform coefficients output from the quantization unit 233 may be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) may be reconstructed by applying inverse quantization and inverse transform to the quantized transform coefficients via the inverse quantization unit 234 and the inverse transform unit 235. The adder 155 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample, or reconstructed sample array) by adding the reconstructed residual signal to the prediction signal output from the prediction unit 220. When there is no residual for the current block, such as when skip mode is applied, the predicted block may be used as the reconstructed block. The generated reconstructed signal may be used for intra prediction of the next block to be processed in the current picture, and may also be used for inter prediction of the next picture after filtering, as described below.

[0058] Meanwhile, luma mapping with chroma scaling (LMCS) can be applied during picture encoding and / or reconstruction.

[0059] The filtering unit 260 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 260 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture and store the modified reconstructed picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset (SAO), an adaptive loop filter, a bilateral filter, etc. The filtering unit 260 may generate various information related to filtering and transmit it to the entropy encoding unit 240, as will be described later in connection with each filtering method. The filtering information may be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0060] The modified reconstructed picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 221. When inter prediction is applied through this, the encoding device can avoid prediction mismatch between the encoding device 100 and the decoding device, and can also improve coding efficiency.

[0061] The DPB of the memory 270 may store a modified reconstructed picture to be used as a reference picture in the inter predictor 221. The memory 270 may store motion information of a block from which motion information in the current picture is derived (or encoded) and / or motion information of a block in an already reconstructed picture. The stored motion information may be transmitted to the inter predictor 221 to be used as motion information of a spatially neighboring block or a temporally neighboring block. The memory 270 may store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 222.

[0062] FIG. 3 is a diagram illustrating the configuration of a video / image decoding device to which this document can be applied.

[0063] As shown in FIG. 3, the decoding device 300 may include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filter 350, and a memory 360. The predictor 330 may include an inter predictor 331 and an intra predictor 332. The residual processor 320 may include a dequantizer 321 and an inverse transformer 322. The entropy decoder 310, residual processor 320, predictor 330, adder 340, and filter 350 may be configured as a single hardware component (e.g., a decoder chipset or processor) according to an embodiment. The memory 360 may include a decoded picture buffer (DPB) or may be configured as a digital storage medium. The hardware components may further include a memory 360 as an internal / external component.

[0064] When a bitstream including video / image information is input, the decoding device 300 can reconstruct an image corresponding to the process in which the video / image information was processed by the encoding device of FIG. 3. For example, the decoding device 300 can derive units / blocks based on block division-related information obtained from the bitstream. The decoding device 300 can perform decoding using the processing unit applied by the encoding device. Therefore, the processing unit for decoding can be, for example, a coding unit, and the coding unit can be divided from a coding tree unit or a maximal coding unit according to a quad tree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units can be derived from the coding unit. The reconstructed image signal decoded and output by the decoding device 300 can be reproduced by a playback device.

[0065] The decoding device 300 may receive a signal output from the encoding device of FIG. 3 in the form of a bitstream, and the received signal may be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 may parse the bitstream to derive information (e.g., video / image information) necessary for image restoration (or picture restoration). The video / image information may further include information on various parameter sets, such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). The video / image information may also include general constraint information. The decoding device may further decode pictures based on the information on the parameter sets and / or the general constraint information. Signaling / received information and / or syntax elements, which will be described later in this document, may be decoded via the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 may decode information in a bitstream based on a coding method such as Exponential-Golomb coding, CAVLC, or CABAC, and output values ​​of syntax elements required for image restoration and quantized values ​​of transform coefficients related to residuals. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, determines a context model using information on the syntax element to be decoded and decode information on adjacent and current blocks, or information on symbols / bins decoded in previous steps, predicts the occurrence probability of the bins based on the determined context model, and performs arithmetic decoding of the bins to generate symbols corresponding to the values ​​of each syntax element. After determining the context model, the CABAC entropy decoding method may update the context model using information on the decoded symbols / bins for the context model of the next symbol / bin.Among the information decoded by the entropy decoding unit 310, information related to prediction is provided to the prediction unit 330, and residual information entropy decoded by the entropy decoding unit 310, i.e., quantized transform coefficients and related parameter information, may be input to the inverse quantization unit 321. Among the information decoded by the entropy decoding unit 310, information related to filtering may be provided to the filtering unit 350. Meanwhile, a receiving unit (not shown) that receives a signal output from the encoding device may be further configured as an internal / external element of the decoding device 300, or the receiving unit may be a component of the entropy decoding unit 310. Meanwhile, the decoding device according to this document may be referred to as a video / image / picture decoding device, and the decoding device may be divided into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include the entropy decoding unit 310, and the sample decoder may include at least one of the inverse quantization unit 321, the inverse transform unit 322, the prediction unit 330, the addition unit 340, the filtering unit 350, and the memory 360.

[0066] The inverse quantization unit 321 may inverse quantize the quantized transform coefficients and output the transform coefficients. The inverse quantization unit 321 may rearrange the quantized transform coefficients in a two-dimensional block format. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the encoding device. The inverse quantization unit 321 may inverse quantize the quantized transform coefficients using a quantization parameter (e.g., quantization step size information) to obtain transform coefficients.

[0067] The inverse transform unit 322 performs inverse transform on the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0068] The prediction unit may perform prediction on a current block and generate a predicted block including prediction samples for the current block. The prediction unit may determine whether intra prediction or inter prediction is applied to the current block based on information about the prediction output from the entropy decoding unit 310, and may determine a specific intra / inter prediction mode.

[0069] The predictor may generate a prediction signal based on various prediction methods, which will be described later. For example, the predictor may apply intra prediction or inter prediction for prediction of a block, or may simultaneously apply intra prediction and inter prediction. This may be referred to as combined inter and intra prediction (CIIP). The predictor may also perform intra block copy (IBC) for prediction of a block. The intra block copy may be used for content image / video coding, such as games, such as screen content coding (SCC). IBC basically performs prediction within a current picture, but may be performed similarly to inter prediction in deriving a reference block within the current picture. That is, IBC may utilize at least one of the inter prediction techniques described in this document. Palette mode may be considered an example of intra coding or intra prediction.

[0070] The intra prediction unit 331 can predict a current block by referring to samples in a current picture. The referenced samples can be located adjacent to or distant from the current block depending on the prediction mode. In intra prediction, prediction modes can include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 can also determine a prediction mode to be applied to the current block using prediction modes applied to neighboring blocks.

[0071] The inter prediction unit 332 may derive a predicted block for the current block based on a reference block (reference sample array) identified by a motion vector on a reference picture. To reduce the amount of motion information transmitted in inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on the inter prediction direction (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. For example, the inter prediction unit 332 may construct a motion information candidate list based on the neighboring blocks and derive a motion vector and / or a reference picture index for the current block based on received candidate selection information. Inter prediction may be performed based on various prediction modes, and the prediction information may include information indicating the inter prediction mode for the current block.

[0072] The adder 340 may generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the obtained residual signal to the predicted signal (predicted block, predicted sample array) output from the prediction unit. When there is no residual for the current block, such as when skip mode is applied, the predicted block may be used as the reconstructed block.

[0073] The adder 340 may be referred to as a reconstruction unit or a reconstruction block generator. The generated reconstruction signal may be used for intra prediction of a next block to be processed in the current picture, may be output after filtering as described below, or may be used for inter prediction of a next picture.

[0074] Meanwhile, LMCS (luma mapping with chroma scaling) can be applied during the picture decoding process.

[0075] The filtering unit 350 may apply filtering to the reconstructed signal to improve subjective / objective image quality. For example, the filtering unit 350 may apply various filtering methods to the reconstructed picture to generate a modified reconstructed picture, and may transmit the modified reconstructed picture to the memory 360, specifically, to the DPB of the memory 360. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, an adaptive loop filter, a bilateral filter, etc.

[0076] The (modified) reconstructed picture stored in the DPB of the memory 360 can be used as a reference picture in the inter predictor 332. The memory 360 can store motion information of a block from which motion information in the current picture is derived (or decoded) and / or motion information of a block in an already reconstructed picture. The stored motion information can be transmitted to the inter predictor 332 to be used as motion information of a spatially neighboring block or a temporally neighboring block. The memory 360 can store reconstructed samples of reconstructed blocks in the current picture and transmit them to the intra predictor 331.

[0077] In this specification, the embodiments described for the prediction unit 330, inverse quantization unit 321, inverse transform unit 322, and filtering unit 350 of the decoding device 300 can also be applied identically or correspondingly to the prediction unit 220, inverse quantization unit 234, inverse transform unit 235, and filtering unit 260 of the encoding device 200, respectively.

[0078] As described above, prediction is performed to improve compression efficiency when performing video coding. Through this, a predicted block including predicted samples for a current block, which is a block to be coded, can be generated. Here, the predicted block includes predicted samples in the spatial domain (or pixel domain). The predicted block is derived in the same way by an encoding device and a decoding device. The encoding device signals information (residual information) regarding the residual between the original block and the predicted block, rather than the original sample values ​​of the original block, to the decoding device, thereby improving image coding efficiency. The decoding device derives a residual block including residual samples based on the residual information, combines the residual block with the predicted block to generate a reconstructed block including reconstructed samples, and generates a reconstructed picture including the reconstructed block.

[0079] The residual information may be generated through a transform and quantization procedure. For example, an encoding device may derive a residual block between the original block and the predicted block, perform a transform procedure on residual samples (residual sample array) included in the residual block to derive transform coefficients, and perform a quantization procedure on the transform coefficients to derive quantized transform coefficients, and then signal the related residual information (via a bitstream) to a decoding device. Here, the residual information may include information such as value information, position information, transform technique, transform kernel, and quantization parameter of the quantized transform coefficients. The decoding device may derive residual samples (or residual blocks) by performing an inverse quantization / inverse transform procedure based on the residual information. The decoding device may generate a reconstructed picture based on the predicted block and the residual block. The encoding device may also derive a residual block by inverse quantizing / inverse transforming the quantized transform coefficients for reference for inter-prediction of a future picture, and generate a reconstructed picture based on the residual block.

[0080] In this document, at least one of quantization / dequantization and / or transform / inverse transform may be omitted. When the quantization / dequantization is omitted, the quantized transform coefficients may be referred to as transform coefficients. When the transform / inverse transform is omitted, the transform coefficients may also be referred to as coefficients or residual coefficients, or may still be referred to as transform coefficients for the sake of uniformity of expression.

[0081] In this document, quantized transform coefficients and transform coefficients may be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, residual information may include information about the transform coefficient(s), and the information about the transform coefficient(s) may be signaled via residual coding syntax. Transform coefficients may be derived based on the residual information (or information about the transform coefficient(s), and scaled transform coefficients may be derived through an inverse transform (scaling) of the transform coefficients. Residual samples may be derived based on an inverse transform (transform) of the scaled transform coefficients. This may be similarly applied / expressed in other parts of this document.

[0082] A prediction unit of an encoding / decoding device may perform inter prediction on a block-by-block basis to derive predicted samples. Inter prediction may refer to prediction derived in a manner dependent on data elements (e.g., sample values ​​or motion information) of pictures other than the current picture. When inter prediction is applied to a current block, a predicted block (prediction sample array) for the current block may be derived based on a reference block (reference sample array) identified by a motion vector in a reference picture indicated by a reference picture index. In this case, to reduce the amount of motion information transmitted in the inter prediction mode, motion information of the current block may be predicted in block, sub-block, or sample units based on correlation of motion information between neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include information on an inter prediction type (e.g., L0 prediction, L1 prediction, Bi prediction, etc.). When inter prediction is applied, neighboring blocks may include spatial neighboring blocks in the current picture and temporal neighboring blocks in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc., and the reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, a candidate list of motion information may be constructed based on neighboring blocks of the current block, and flag or index information indicating which candidate is selected (used) to derive a motion vector and / or a reference picture index of the current block may be signaled. Inter prediction is performed based on various prediction modes. For example, in skip mode and merge mode, the motion information of the current block may be the same as the motion information of the selected neighboring block.In the skip mode, unlike the merge mode, a residual signal may not be transmitted. In the motion vector prediction (MVP) mode, the motion vector of a selected neighboring block is used as a motion vector predictor, and a motion vector difference may be signaled. In this case, the motion vector of the current block may be derived using the sum of the motion vector predictor and the motion vector difference.

[0083] The motion information may include L0 motion information and / or L1 motion information depending on the inter-prediction type (L0 prediction, L1 prediction, Bi prediction, etc.). A motion vector in the L0 direction may be referred to as an L0 motion vector or MVL0, and a motion vector in the L1 direction may be referred to as an L1 motion vector or MVL1. Prediction based on an L0 motion vector may be referred to as L0 prediction, prediction based on an L1 motion vector may be referred to as L1 prediction, and prediction based on both the L0 motion vector and the L1 motion vector may be referred to as bi-prediction (Bi) prediction. Here, an L0 motion vector may indicate a motion vector associated with a reference picture list L0 (L0), and an L1 motion vector may indicate a motion vector associated with a reference picture list L1 (L1). The reference picture list L0 may include pictures that are earlier in output order than the current picture, and the reference picture list L1 may include pictures that are later in output order than the current picture. The previous picture may be called a forward (reference) picture, and the subsequent picture may be called a backward (reference) picture. The reference picture list L0 may further include, as reference pictures, pictures that are subsequent to the current picture in output order. In this case, the previous picture may be indexed first in the reference picture list L0, and the subsequent picture may be indexed thereafter. The reference picture list L1 may further include, as reference pictures, pictures that are subsequent to the current picture in output order. In this case, the subsequent picture may be indexed first in the reference picture list L1, and the previous picture may be indexed thereafter. Here, the output order may correspond to a picture order count (POC) order.

[0084] FIG. 4 shows an exemplary hierarchical structure for coded images / videos.

[0085] As shown in Figure 4, coded images / videos are divided into a VCL (video coding layer) that handles the image / video decoding process and itself, a lower system that transmits and stores coded information, and a NAL (network abstraction layer) that exists between the VCL and the lower system and is responsible for network adaptation functions.

[0086] The VCL can generate VCL data including compressed image data (slice data), or can generate parameter sets including information such as a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), and a Video Parameter Set (VPS), or an SEI (Supplemental Enhancement Information) message that is additionally required for the image decoding process.

[0087] In NAL, NAL units can be generated by adding header information (NAL unit header) to RBSP (Raw Byte Sequence Payload) generated by VCL. In this case, RBSP refers to slice data, parameter sets, SEI messages, etc. generated by VCL. The NAL unit header can contain NAL unit type information identified by the RBSP data included in the corresponding NAL unit.

[0088] As shown in the drawing, NAL units can be classified into VCL NAL units and non-VCL NAL units according to the RBSP generated by the VCL. A VCL NAL unit can refer to a NAL unit containing information about an image (slice data), and a non-VCL NAL unit can refer to a NAL unit containing information necessary for decoding an image (parameter set or SEI message).

[0089] The VCL NAL unit and non-VCL NAL unit can be transmitted over a network with header information according to the data standard of the lower system. For example, the NAL unit can be transformed into a data format of a predetermined standard such as H.266 / VVC file format, RTP (Real-time Transport Protocol), TS (Transport Stream), etc. and transmitted over various networks.

[0090] As mentioned above, the NAL unit type of an NAL unit can be identified by the RBSP data structure included in the corresponding NAL unit, and information about such NAL unit type can be stored and signaled in the NAL unit header.

[0091] For example, NAL units can be broadly classified into VCL NAL unit types and non-VCL NAL unit types depending on whether the NAL unit contains information about an image (slice data). The VCL NAL unit types can be classified according to the nature and type of pictures included in the VCL NAL unit, and the non-VCL NAL unit types can be classified according to the type of parameter set.

[0092] The following is an example of a NAL unit type identified by the type of parameter set that the non-VCL NAL unit type includes.

[0093] -APS (Adaptation Parameter Set) NAL unit: Type for NAL units including APS

[0094] -DPS (Decoding Parameter Set) NAL unit: Type for NAL units containing DPS

[0095] -VPS (Video Parameter Set) NAL unit: Type for NAL unit containing VPS

[0096] -SPS (Sequence Parameter Set) NAL unit: Type for NAL unit including SPS

[0097] -PPS (Picture Parameter Set) NAL unit: Type for NAL unit including PPS

[0098] -PH (Picture header) NAL unit: Type for NAL unit including PH

[0099] The above-mentioned NAL unit type has syntax information for the NAL unit type, and the syntax information can be stored in a NAL unit header and signaled. For example, the syntax information can be nal_unit_type, and the NAL unit type can be specified by the nal_unit_type value.

[0100] Meanwhile, as described above, one picture may include multiple slices, and one slice may include a slice header and slice data. In this case, one picture header may be added to multiple slices (slice header and slice data set) in one picture. The picture header (picture header syntax) may include information / parameters commonly applicable to the picture. In this document, slices may be mixed with or replaced by tile groups. Also, in this document, slice headers may be mixed with or replaced by type group headers.

[0101] The slice header (slice header syntax, slice header information) can include information / parameters commonly applicable to the slices. The APS (APS syntax) or PPS (PPS syntax) can include information / parameters commonly applicable to one or more slices or pictures. The SPS (SPS syntax) can include information / parameters commonly applicable to one or more sequences. The VPS (VPS syntax) can include information / parameters commonly applicable to multiple layers. The DPS (DPS syntax) can include information / parameters commonly applicable to video in general. The DPS can include information / parameters related to concatenation of coded video sequences (CVSs). In this document, the term "High level syntax (HLS)" can include at least one of the APS syntax, PPS syntax, SPS syntax, VPS syntax, DPS syntax, picture header syntax, and slice header syntax.

[0102] In this document, image / video information encoded from an encoding device to a decoding device and signaled in the form of a bitstream may include not only intra-picture partitioning-related information, intra / inter prediction information, residual information, in-loop filtering information, etc., but also information included in the slice header, information included in the picture header, information included in the APS, information included in the PPS, information included in the SPS, information included in the VPS, and / or information included in the DPS. In addition, the image / video information may further include information of a NAL unit header.

[0103] Meanwhile, in order to compensate for differences between an original image and a reconstructed image due to errors that occur during the compression encoding process, such as quantization, an in-loop filtering procedure may be performed on the reconstructed samples or pictures, as described above. As described above, the in-loop filtering may be performed in a filter unit of an encoding device and a filter unit of a decoding device, and a deblocking filter, SAO, and / or adaptive loop filter (ALF) may be applied. For example, the ALF procedure may be performed after the deblocking filtering procedure and / or SAO procedure is completed. However, in this case, the deblocking filtering procedure and / or SAO procedure may be omitted.

[0104] A detailed description of picture reconstruction and filtering will be given below. In image / video coding, a reconstructed block may be generated based on intra prediction / inter prediction for each block, and a reconstructed picture including the reconstructed block may be generated. If a current picture / slice is an I picture / slice, blocks included in the current picture / slice may be reconstructed based only on intra prediction. On the other hand, if the current picture / slice is a P or B picture / slice, blocks included in the current picture / slice may be reconstructed based on intra prediction or inter prediction. In this case, intra prediction may be applied to some blocks in the current picture / slice, and inter prediction may be applied to the remaining blocks.

[0105] Intra prediction may refer to a prediction that generates prediction samples for a current block based on reference samples in a picture to which the current block belongs (hereinafter referred to as the current picture). When intra prediction is applied to the current block, neighboring reference samples used for intra prediction of the current block may be derived. The neighboring reference samples of the current block may include samples adjacent to the left boundary and bottom-left neighboring samples of the current block having a size of nW×nH, a total of 2×nH samples adjacent to the top boundary and top-right neighboring samples of the current block, and one sample adjacent to the top-left neighboring sample of the current block. Alternatively, the neighboring reference samples of the current block may include upper neighboring samples of multiple columns and left neighboring samples of multiple rows. In addition, the neighboring reference samples of the current block may include a total of nH samples adjacent to the right boundary of the current block having a size of nW×nH, a total of nW samples adjacent to the bottom boundary of the current block, and one sample adjacent to the bottom-right of the current block.

[0106] However, some of the neighboring reference samples of the current block may not yet be decoded or may not be available. In this case, the decoder may construct neighboring reference samples to be used for prediction by substituting unavailable samples as available samples, or may construct neighboring reference samples to be used for prediction through interpolation of available samples.

[0107] When neighboring reference samples are derived, (i) a predicted sample may be derived based on an average or interpolation of neighboring reference samples of the current block, or (ii) the predicted sample may be derived based on a reference sample of the neighboring reference samples of the current block that exists in a specific (prediction) direction relative to the predicted sample. (i) This may be referred to as a non-directional mode or a non-angular mode, and (ii) this may be referred to as a directional mode or an angular mode. Furthermore, the predicted sample may be generated by interpolating the first and second neighboring samples, which are located in the opposite direction to the prediction direction of the intra-prediction mode of the current block, based on the predicted sample of the current block among the neighboring reference samples. This may be referred to as linear interpolation intra-prediction (LIP). Alternatively, a chroma predicted sample may be generated based on a luma sample using a linear model. This may be referred to as LM mode. In addition, a temporary predicted sample of the current block may be derived based on filtered neighboring reference samples, and a predicted sample of the current block may be derived by weighting the temporary predicted sample and at least one reference sample derived according to the intra prediction mode from the existing neighboring reference samples, i.e., non-filtered neighboring reference samples. The above-mentioned case may be referred to as Position Dependent Intra Prediction (PDPC). In addition, intra prediction coding may be performed by selecting a reference sample line with the highest prediction accuracy from multiple neighboring reference sample lines of the current block, deriving a predicted sample using a reference sample located in the prediction direction of the corresponding line, and signaling the reference sample line used to a decoding device.The above-described case may be referred to as multi-reference line (MRL) intra prediction or MRL-based intra prediction. Furthermore, the current block may be divided into vertical or horizontal sub-partitions, and intra prediction may be performed based on the same intra prediction mode. Neighboring reference samples may be derived and used for each sub-partition. That is, in this case, the intra prediction mode for the current block is equally applied to the sub-partitions, and neighboring reference samples may be derived and used for each sub-partition, thereby improving intra prediction performance in some cases. This prediction method may be referred to as intra sub-partitions (ISP) or ISP-based intra prediction. The above-described intra prediction method may be referred to as an intra prediction type, distinguished from the intra prediction modes in Tables 1 and 2. The intra prediction type may be referred to by various terms, such as an intra prediction technique or an additional intra prediction mode. For example, the intra prediction type (or additional intra prediction mode, etc.) may include at least one of the LIP, PDPC, MRL, and ISP. A general intra prediction method excluding specific intra prediction types such as LIP, PDPC, MRL, and ISP may be referred to as a normal intra prediction type. The normal intra prediction type may be generally applied when the specific intra prediction types are not applied, and prediction may be performed based on the intra prediction mode. Meanwhile, post-processing filtering may be performed on the derived prediction samples as needed.

[0108] Specifically, the intra prediction procedure may include an intra prediction mode / type determination step, a neighboring reference sample derivation step, and an intra prediction mode / type-based prediction sample derivation step. If necessary, a post-processing filtering step may be performed on the derived prediction samples.

[0109] A modified reconstructed picture is generated by the in-loop filtering procedure, and the modified reconstructed picture is output from the decoding device as a decoded picture. The modified reconstructed picture can also be stored in a decoded picture buffer or memory of the encoding / decoding device and used as a reference picture in subsequent inter-prediction procedures when encoding / decoding pictures. The in-loop filtering procedure may include a deblocking filtering procedure, a sample adaptive offset (SAO) procedure, and / or an adaptive loop filter (ALF) procedure, as described above. In this case, one or some of the deblocking filtering procedure, the sample adaptive offset (SAO), the adaptive loop filter (ALF), and the bilateral filter procedure may be applied sequentially, or all of them may be applied sequentially. For example, the deblocking filtering procedure may be applied to the reconstructed picture before the SAO procedure. Alternatively, the deblocking filtering procedure may be applied to the reconstructed picture before the ALF procedure. This is also performed in the encoding device.

[0110] Deblocking filtering is a filtering technique that removes distortions that occur at boundaries between blocks in a reconstructed picture. The deblocking filtering procedure may, for example, derive a target boundary in a reconstructed picture, determine a boundary strength (bS) for the target boundary, and perform deblocking filtering on the target boundary based on the bS. The bS may be determined based on the prediction modes of two blocks adjacent to the target boundary, the motion vector difference, whether the reference pictures are the same, whether there are significant non-zero coefficients, etc.

[0111] SAO is a method for compensating for an offset difference between a reconstructed picture and an original picture on a sample-by-sample basis, and may be applied based on a type such as a band offset or an edge offset. According to SAO, samples are classified into different categories according to each SAO type, and an offset value may be added to each sample based on the category. Filtering information for SAO may include information on whether SAO is applicable, SAO type information, SAO offset value information, etc. SAO may also be applied to a reconstructed picture after the deblocking filtering is applied.

[0112] An adaptive loop filter (ALF) is a technique for filtering a reconstructed picture on a sample-by-sample basis based on filter coefficients according to a filter shape. An encoding apparatus can determine whether to apply an ALF, the ALF shape, and / or ALF filtering coefficients by comparing a reconstructed picture with an original picture, and signal the determination to a decoding apparatus. That is, filtering information for the ALF can include information on whether to apply an ALF, ALF filter shape information, ALF filtering coefficient information, etc. The ALF can also be applied to a reconstructed picture after the deblocking filtering has been applied.

[0113] 5 is a flowchart illustrating an encoding method based on filtering in an encoding device, which may include steps S500 to S530.

[0114] In step S500, the encoding apparatus generates a reconstructed picture, which can be performed based on the above-described reconstructed picture (or reconstructed sample) generation procedure.

[0115] In step S510, the encoding device may determine whether in-loop filtering is applied (across the virtual boundary) based on the in-loop filtering-related information, where the in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, or ALF.

[0116] In step S520, the encoding apparatus may generate a modified reconstructed picture (modified reconstructed sample) based on the determination in step S510, where the modified reconstructed picture (modified reconstructed sample) may be a filtered reconstructed picture (filtered reconstructed sample).

[0117] In step S530, the encoding device may encode the image / video information including the in-loop filtering related information based on the in-loop filtering procedure.

[0118] 6 is a flowchart illustrating a filtering-based decoding method in a decoding device, which may include steps S600 to S630.

[0119] In step S600, the decoding device can obtain image / video information including in-loop filtering related information from a bitstream, where the bitstream can be based on encoded image / video information transmitted from an encoding device.

[0120] In step S610, the decoding apparatus can generate a reconstructed picture, which can be performed based on the above-described reconstructed picture (or reconstructed sample) generation procedure.

[0121] In step S620, the decoding device may determine whether in-loop filtering is applied (across the virtual boundary) based on the in-loop filtering-related information, where the in-loop filtering may include at least one of the above-mentioned deblocking filtering, SAO, or ALF.

[0122] In step S630, the decoding apparatus may generate a modified reconstructed picture (modified reconstructed sample) based on the determination in step S620, where the modified reconstructed picture (modified reconstructed sample) may be a filtered reconstructed picture (filtered reconstructed sample).

[0123] As described above, an in-loop filtering procedure can be applied to the reconstructed picture. In this case, to further improve the subjective / objective visual quality of the reconstructed picture, a virtual boundary can be defined and the in-loop filtering procedure can be applied across the virtual boundary. The virtual boundary includes, for example, a discontinuous edge of a 360-degree image, a VR image, or a picture-in-picture (PIP). For example, the virtual boundary exists at a predetermined predetermined position, and its presence and / or position can be signaled. For example, the virtual boundary is located at the fourth sample line from the top of a CTU row (specifically, for example, above the fourth sample line from the top of the CTU row). As another example, information regarding the presence and / or position of the virtual boundary can be signaled via an HLS. The HLS includes an SPS, a PPS, a picture header, a slice header, etc., as described above.

[0124] The following describes high-level syntax signaling and semantics for embodiments of this document.

[0125] One embodiment of this document includes a method for controlling a loop filter. This method for controlling a loop filter can be applied to a reconstructed picture. An in-loop filter (loop filter) can be used for decoding an encoded bitstream. The loop filter includes the above-mentioned deblocking, SAO, and ALF. An SPS includes flags related to each of the deblocking, SAO, and ALF. The flags indicate whether each tool is available for coding a coded layer video sequence (CLVS) or coded video sequence (CVS) that references the SPS.

[0126] In one example, if a loop filter is available for coding a picture in a CVS, application of the loop filter is controlled to avoid crossing certain boundaries. For example, the loop filter can be controlled to avoid crossing subpicture boundaries, the loop filter can be controlled to avoid crossing tile boundaries, the loop filter can be controlled to avoid crossing slice boundaries, and / or the loop filter can be controlled to avoid crossing virtual boundaries.

[0127] The in-loop filtering-related information includes information, syntax, syntax elements, and / or semantics described in this document (or embodiments included therein). The in-loop filtering-related information includes information regarding whether an in-loop filtering procedure (in whole or in part) is applicable across a specific boundary (e.g., a virtual boundary, a sub-picture boundary, a slice boundary, and / or a tile boundary). Image information included in a bitstream includes a high level syntax (HLS), which includes the in-loop filtering-related information. Based on a determination of whether the in-loop filtering procedure is applicable across a specific boundary, modified (or filtered) reconstructed samples (reconstructed pictures) are generated. In one example, when the in-loop filtering procedure is disabled for all blocks / boundaries, the modified reconstructed samples may be identical to the reconstructed samples. In another example, the modified reconstructed samples include modified reconstructed samples derived based on in-loop filtering. However, in this case, based on the determination, some of the reconstructed samples (e.g., reconstructed samples across a virtual boundary) may not be in-loop filtered. For example, reconstructed samples that cross certain boundaries (including at least one of virtual boundaries, sub-picture boundaries, slice boundaries, and / or tile boundaries for which in-loop filtering execution is enabled) may be in-loop filtered, while reconstructed samples that cross other boundaries (including at least one of virtual boundaries, sub-picture boundaries, and / or tile boundaries for which in-loop filtering execution is disabled) may not be in-loop filtered.

[0128] In one example, in-loop filtering related information, related to whether an in-loop filtering procedure is performed across a virtual boundary, includes an SPS virtual boundary presence flag, a picture header virtual boundary presence flag, information about the number of virtual boundaries, information about the location of the virtual boundaries, etc.

[0129] In the embodiments described herein, the information about the position of the virtual border includes information about the x-coordinate of the vertical virtual border and / or information about the y-coordinate of the horizontal virtual border. Specifically, the information about the position of the virtual border includes information about the x-coordinate of the vertical virtual border and / or information about the y-coordinate of the horizontal virtual border in luma sample units. The information about the position of the virtual border also includes information about the number of pieces of information (syntax elements) about the x-coordinate of the vertical virtual border present in the SPS. The information about the position of the virtual border also includes information about the number of pieces of information (syntax elements) about the y-coordinate of the horizontal virtual border present in the SPS. Alternatively, the information about the position of the virtual border includes information about the number of pieces of information (syntax elements) about the x-coordinate of the vertical virtual border present in the picture header. The information about the position of the virtual border also includes information about the number of pieces of information (syntax elements) about the y-coordinate of the horizontal virtual border present in the picture header.

[0130] The following table shows an example syntax and semantics of a sequence parameter set (SPS) according to this embodiment.

[0131] [Table 1]

[0132] [Table 2]

[0133] The following table shows an example syntax and semantics of a picture parameter set (PPS) according to this embodiment.

[0134] [Table 3]

[0135] [Table 4]

[0136] The following table shows an exemplary syntax and semantics of a picture header according to this embodiment.

[0137] [Table 5-1]

[0138] [Table 5-2]

[0139] [Table 6-1]

[0140] [Table 6-2]

[0141] The following table shows an example syntax and semantics of a slice header according to this embodiment.

[0142] [Table 7]

[0143] [Table 8]

[0144] The following describes information related to sub-pictures and information about virtual boundaries that can be used in in-loop filtering, and their signaling.

[0145] If a picture contains multiple sub-pictures but none of the sub-pictures have boundaries that are treated like picture boundaries, the benefits of using sub-pictures cannot be realized. In one embodiment of this document, the picture / video information for picture coding includes information for treating sub-pictures like pictures, which is called a picture treatment flag (e.g., subpic_treated_as_pic_flag[i]).

[0146] To signal the layout of subpictures, a flag (e.g., subpic_present_flag) related to whether subpictures are present is signaled. This may be called a subpicture present flag. If the value of subpic_present_flag is 1, information about the number of subpictures into which the picture is divided (e.g., sps_num_subpics_minus1) is signaled. In one example, the number of subpictures into which the picture is divided may be equal to sps_num_subpics_minus1+1 (sps_num_subpics_minus1 plus 1). Possible values ​​of sps_num_subpics_minus1 include 0, which means that there is only one subpicture in the picture. If a picture contains only one subpicture, signaling of subpicture-related information is considered a redundant procedure because the subpicture itself is a picture.

[0147] In existing embodiments, when a picture contains only one subpicture and subpicture signaling is present, the value of a picture handling flag (e.g., subpic_treated_as_pic_flag[i]) and / or the value of a flag related to whether loop filtering is performed across subpictures (e.g., loop_filter_across_enabled_flag) can be 0 or 1. Here, when the value of subpic_treated_as_pic_flag[i] is 0, a problem occurs that is inconsistent with the case where a subpicture boundary is a picture boundary. This requires an additional overlapping procedure to make the decoder confirm that a picture boundary is a subpicture boundary.

[0148] When a picture is generated based on a merging procedure of two or more subpictures, all subpictures used in the merging procedure must be independently coded subpictures (subpictures whose picture handling flag (subpic_treated_as_pic_flag[i]) has a value of 1). This is because, when a subpicture that is not an independently coded subpicture (referred to as the "first subpicture" in this paragraph) is merged, a problem may occur after merging because a block in the first subpicture is coded with reference to a reference block that exists outside the first subpicture.

[0149] Also, when a picture is partitioned into sub-pictures, sub-picture ID signaling may or may not be present. If sub-picture ID signaling is present, it is present (contained) in the SPS, PPS, and / or picture header (PH). Cases where sub-picture ID signaling is not present in the SPS include cases where a bitstream is generated as a result of a sub-picture merging procedure. Therefore, when sub-picture ID signaling is not included in the SPS, it is preferable that all sub-pictures are coded independently.

[0150] In an image coding procedure using virtual boundaries, information about the location of the virtual boundaries can be signaled in the SPS or picture header. Signaling information about the location of the virtual boundaries in the SPS means that the location remains unchanged within the CLVS. However, if reference picture resampling (RPR) is enabled for the CLVS, pictures within the CLVS have different sizes. Here, reference picture resampling (also called adaptive resolution change (ARC)) is performed for normal coding of pictures with different resolutions (spatial resolutions). For example, reference picture resampling includes upsampling and downsampling. Reference picture resampling achieves high coding efficiency for adapting bit rate and spatial resolution. Considering reference picture resampling, it is necessary to ensure that the locations of the virtual boundaries are all within one picture.

[0151] In the existing ALF procedure, k-th order Exponential-Golomb coding, where k=3, is used to signal the absolute values ​​of the luma and chroma ALF coefficients. However, k-th order Exponential-Golomb coding is problematic because it incurs significant computational overhead and complexity.

[0152] The embodiments described in the following paragraphs propose solutions to solve the aforementioned problems, and the embodiments may be applied independently, or at least two or more embodiments may be applied in combination.

[0153] In one embodiment of this document, if subpicture signaling is present and a picture has only one subpicture, the only subpicture is an independently coded subpicture. For example, if a picture has only one subpicture, the only subpicture is an independently coded subpicture, and the value of the picture treated flag (e.g., subpic_treated_as_pic_flag[i]) for the only subpicture is 1. This allows duplication procedures related to subpictures to be omitted.

[0154] In one embodiment of this document, when subpicture signaling is present, the number of subpictures may be more than 1. In one example, when subpicture signaling is present (e.g., the value of subpics_present_flag is 1), the information about the number of subpictures (e.g., sps_num_subpics_minus1) is greater than 0, and the number of subpictures may be sps_num_subpics_minus1+1 (sps_num_subpics_minus1 plus 1). In another example, the information about the number of subpictures is sps_num_subpics_minus2, and the number of subpictures may be sps_num_subpics_minus2+2 (sps_num_subpics_minus2 plus 2). In yet another example, the subpicture present flag subpics_present_flag can be replaced with information about the number of subpictures sps_num_subpics_minus1, and thus subpicture signaling can be present if sps_num_subpics_minus1 is greater than 0.

[0155] In one embodiment of this document, when a picture is divided into sub-pictures, at least one of the sub-pictures may be an independently coded sub-picture, where the picture treatment flag (e.g., subpic_treated_as_pic_flag[i]) for the independently coded sub-picture has a value of 1.

[0156] In one embodiment of this document, the sub-pictures of a picture based on a merging procedure of two or more sub-pictures may be independently coded sub-pictures.

[0157] In one embodiment of this document, if subpicture ID (identification) signaling is present in a location other than the SPS (other syntax, other high-level syntax information), all subpictures are independently coded subpictures, and the value of the picture handling flag (e.g., subpic_treated_as_pic_flag) for all subpictures may be 1. In one example, subpicture ID signaling is present in the PPS, in which case all subpictures may be independently coded subpictures. In another example, subpicture ID signaling is present in the picture header, in which case all subpictures may be independently coded subpictures.

[0158] In one embodiment of this document, if virtual boundary signaling is present in the SPS for CLVS and reference picture resampling is enabled, all horizontal virtual boundary positions may be within the minimum picture height of the picture referencing the SPS, and all vertical virtual boundary positions may be within the minimum picture width of the picture referencing the SPS.

[0159] In one embodiment of this document, when reference picture resampling (RPR) is enabled, the virtual boundary signaling is included in the picture header, i.e., when reference picture resampling is enabled, the virtual boundary signaling may not be included in the SPS.

[0160] In one embodiment of this document, fixed length coding (FLC) accompanied by the number of bits (or bit length) is used to signal the ALF data. In one example, the information about the ALF data includes information about the bit length of the ALF luma coefficient absolute values ​​(e.g., alf_luma_coeff_abs_len_minus1) and / or information about the bit length of the ALF chroma coefficient absolute values ​​(e.g., alf_chroma_coeff_abs_len_minus1). For example, the information about the bit length of the ALF luma coefficient absolute values ​​and / or the information about the bit length of the ALF chroma coefficient absolute values ​​can be ue(v) coded.

[0161] The following table shows an example syntax of an SPS according to this embodiment.

[0162] [Table 9]

[0163] The following table shows exemplary semantics for syntax elements included in the syntax.

[0164] [Table 10]

[0165] The following table shows an example syntax of an SPS according to this embodiment.

[0166] [Table 11]

[0167] The following table shows exemplary semantics for syntax elements included in the syntax.

[0168] [Table 12]

[0169] The following table shows an exemplary syntax for ALF data according to this embodiment.

[0170] [Table 13]

[0171] The following table shows exemplary semantics for syntax elements included in the syntax.

[0172] [Table 14]

[0173] According to the embodiments of this document described in conjunction with the table above, image coding based on sub-pictures and / or virtual boundaries improves the subjective / objective quality of the image and reduces the consumption of hardware resources required for coding.

[0174] 7 and 8 show a schematic diagram of an example video / image encoding method and associated components according to an embodiment (or others) of this document.

[0175] The method disclosed in FIG. 7 may be performed by the encoding device disclosed in FIG. 2 or 8. Specifically, for example, S700 and S730 of FIG. 7 may be performed by the prediction unit 220 of the encoding device of FIG. 8, S710 and S720 of FIG. 7 may be performed by the residual processing unit 230 of the encoding device of FIG. 8, S740 of FIG. 7 may be performed by the filtering unit 260 of the encoding device of FIG. 8, and S750 of FIG. 7 may be performed by the entropy encoding unit 240 of the encoding device of FIG. 8. Also, although not shown in FIG. 7, prediction samples or prediction-related information may be derived by the prediction unit 220 of the encoding device in FIG. 7, and a bitstream may be generated from the residual information or prediction-related information by the entropy encoding unit 240 of the encoding device. The method disclosed in FIG. 7 may include the embodiments described above in this document.

[0176] As shown in FIG. 7, an encoding apparatus may derive at least one reference picture (S700). The encoding apparatus may perform a prediction procedure based on the at least one reference picture. Specifically, the encoding apparatus may generate a prediction sample for the current block based on a prediction mode. In this case, various prediction methods disclosed herein, such as inter prediction or intra prediction, may be applied. The encoding apparatus may generate a prediction sample for the current block in the current picture based on the prediction procedure. For example, the encoding apparatus may perform an inter prediction procedure based on the at least one reference picture and generate a prediction sample based on the inter prediction procedure.

[0177] The encoding device may generate / derive residual samples (S710). The encoding device may derive residual samples for a current block, which may be derived based on original samples of the current block and the predicted samples. In one example, the encoding device may generate residual samples based on the at least one reference picture in step S700. For example, the encoding device may generate predicted samples for the current block based on the at least one reference picture, and then generate residual samples based on the predicted samples.

[0178] The encoding device may derive transform coefficients based on a transform procedure for the residual samples, for example, the transform procedure may include at least one of DCT, DST, GBT, or CNT.

[0179] The encoding device may derive quantized transform coefficients based on a quantization procedure for the transform coefficients, and the quantized transform coefficients may have a one-dimensional vector form based on a coefficient scanning order.

[0180] The encoding apparatus may generate residual information (S720). The encoding apparatus may generate the residual information based on the residual samples for the current block. The encoding apparatus may generate residual information representing the quantized transform coefficients. The residual information may be generated through various encoding methods such as Exponential-Golomb, CAVLC, CABAC, etc.

[0181] The encoding device may generate reconstructed samples based on the residual information. The reconstructed samples may be generated by adding residual samples based on the residual information to predicted samples. Specifically, the encoding device may perform prediction (intra- or inter-prediction) on the current block and generate reconstructed samples based on original samples and predicted samples generated from the prediction.

[0182] The reconstructed samples may include reconstructed luma samples and reconstructed chroma samples. Specifically, the residual samples may include residual luma samples and residual chroma samples. The residual luma samples may be generated based on the original luma samples and the predicted luma samples. The residual chroma samples may be generated based on the original chroma samples and the predicted chroma samples. The encoding device may derive transform coefficients for the residual luma samples (luma transform coefficients) and / or transform coefficients for the residual chroma samples (chroma transform coefficients). The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0183] The encoding device may generate reference picture-related information (S730). The encoding device may generate the reference picture-related information based on the at least one reference picture. The reference picture-related information may be used for inter prediction by a decoding device.

[0184] The encoding apparatus may generate in-loop filtering-related information for reconstructed samples of the current picture (S740). The encoding apparatus may perform an in-loop filtering procedure on the reconstructed samples and generate in-loop filtering-related information based on the in-loop filtering procedure. For example, the in-loop filtering-related information may include information about the virtual boundaries described above in this document (e.g., an SPS virtual boundary available flag, a picture header virtual boundary available flag, an SPS virtual boundary present flag, a picture header virtual boundary present flag, information about the location of the virtual boundary, etc.).

[0185] The encoding device may encode video / image information (S750). The image information may include residual information, prediction-related information, reference picture-related information, virtual boundary-related information (and / or additional virtual boundary-related information), and / or in-loop filtering-related information. The encoded video / image information may be output in the form of a bitstream. The bitstream may be transmitted to a decoding device via a network or a storage medium.

[0186] The image / video information may include various information according to embodiments of this document, for example, the image / video information may include information disclosed in at least one of Tables 1 to 14 above.

[0187] In one embodiment, the image information may include a sequence parameter set (SPS). For example, whether the SPS includes additional virtual boundary-related information may be determined based on whether resampling for the at least one reference picture is available. Here, resampling for the at least one reference picture may be performed by the above-mentioned reference picture resampling (RPR). The additional virtual boundary-related information may also be simply referred to as virtual boundary-related information. The term "additional" is used to distinguish it from virtual boundary-related information such as an SPS virtual boundary presence flag and / or a PH virtual boundary presence flag.

[0188] In one embodiment, the additional virtual boundary related information may include the number of virtual boundaries and the locations of the virtual boundaries.

[0189] In one embodiment, the additional virtual boundary related information may include information regarding the number of vertical virtual boundaries, information regarding the positions of the vertical virtual boundaries, information regarding the number of horizontal virtual boundaries, and information regarding the positions of the horizontal virtual boundaries.

[0190] In one embodiment, the image information may include a reference picture resampling availability flag, for example, based on the reference picture resampling availability flag, it may be determined whether resampling is available for the at least one reference picture.

[0191] In one embodiment, the SPS may include an SPS virtual boundary present flag associated with whether the SPS includes the additional virtual boundary-related information. Based on whether resampling for the at least one reference picture is available, the value of the SPS virtual boundary present flag may be determined to be 0.

[0192] In one embodiment, the additional virtual boundary-related information may not be included in the SPS based on the availability of resampling for the at least one reference picture, and the image information may include picture header information, and the picture header information may include the additional virtual boundary-related information.

[0193] In one embodiment, the current picture may include a sub-picture as a single sub-picture, and the sub-picture may be independently coded. The reconstructed sample may be generated based on the sub-picture, sub-picture-related information may be generated based on the sub-picture, and the image information may include the sub-picture-related information.

[0194] In one embodiment, the subpicture treated as picture flag may not be present in the image information. Therefore, the value of the subpicture treated as picture flag may be set by the decoding device through inference (guessing or prediction). In one example, the value of the subpicture treated as picture flag may be set to 1.

[0195] In one embodiment, the current picture may include a subpicture. In one example, the subpicture may be derived based on a merging procedure of two or more independently coded subpictures. The reconstructed sample may be generated based on the subpicture, subpicture-related information may be generated based on the subpicture, and the image information may include the subpicture-related information.

[0196] 9 and 10 show a schematic diagram of an example video / image decoding method and associated components according to an embodiment (or others) of this document.

[0197] The method disclosed in Fig. 9 may be performed by the decoding device disclosed in Fig. 3 or 10. Specifically, for example, S900 of Fig. 9 may be performed by the entropy decoding unit 310 of the decoding device, S910 of Fig. 9 may be performed by the prediction unit 310 of the decoding device, S920 may be performed by the residual processing unit 320 and / or the addition unit 340 of the decoding device, and S930 may be performed by the filtering unit 350 of the decoding device. The method disclosed in Fig. 9 may include the embodiments described above in this document.

[0198] 9, a decoding device may receive / acquire video / image information (S900). The video / image information may include residual information, prediction-related information, reference picture-related information, virtual boundary-related information (and / or additional virtual boundary-related information), and / or in-loop filtering-related information. The decoding device may receive / acquire the image / video information via a bitstream.

[0199] The image / video information may include various information according to embodiments of this document, for example, the image / video information may include information disclosed in at least one of Tables 1 to 14 above.

[0200] The decoding device may derive quantized transform coefficients. The decoding device may derive quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector form based on a coefficient scan order. The quantized transform coefficients may include quantized luma transform coefficients and / or quantized chroma transform coefficients.

[0201] The decoding device may derive transform coefficients. The decoding device may derive transform coefficients based on an inverse quantization procedure for the quantized transform coefficients. The decoding device may derive luma transform coefficients through inverse quantization based on quantized luma transform coefficients. The decoding device may derive chroma transform coefficients through inverse quantization based on quantized chroma transform coefficients.

[0202] The decoding device may generate / derive residual samples. The decoding device may derive residual samples based on an inverse transform procedure for the transform coefficients. The decoding device may derive residual luma samples through an inverse transform procedure based on luma transform coefficients. The decoding device may derive residual chroma samples through an inverse transform procedure based on chroma transform coefficients.

[0203] The decoding device may derive at least one reference picture based on reference picture-related information (S910). The decoding device may perform a prediction procedure based on the at least one reference picture. Specifically, the decoding device may generate a prediction sample for the current block based on a prediction mode. In this case, various prediction methods disclosed herein, such as inter prediction or intra prediction, may be applied. The decoding device may generate a prediction sample for the current block in the current picture based on the prediction procedure. For example, the decoding device may perform an inter prediction procedure based on the at least one reference picture and generate a prediction sample based on the inter prediction procedure.

[0204] The decoding device may generate / derive reconstructed samples (S920). The decoding device may generate reconstructed samples based on a predicted sample and a residual sample. The decoding device may generate reconstructed samples based on a summation between a predicted sample and an original sample. For example, the decoding device may generate / derive reconstructed luma samples and / or reconstructed chroma samples. The decoding device may generate reconstructed luma samples and / or reconstructed chroma samples based on the residual information. The decoding device may generate reconstructed samples based on the residual information. The reconstructed samples may include reconstructed luma samples and / or reconstructed chroma samples. The luma components of the reconstructed samples may correspond to the reconstructed luma samples, and the chroma components of the reconstructed samples may correspond to the reconstructed chroma samples. The decoding device may generate predicted luma samples and / or predicted chroma samples through a prediction procedure. The decoding device may generate reconstructed luma samples based on a predicted luma sample and a residual luma sample. The decoding device may generate reconstructed chroma samples based on a predicted chroma sample and a residual chroma sample.

[0205] The decoding device may generate modified (filtered) reconstruction samples (S930). The decoding device may generate the modified reconstruction samples based on an in-loop filtering procedure on the reconstruction samples. The decoding device may generate the modified reconstruction samples based on in-loop filtering-related information. The decoding device may use a deblocking procedure, an SAO procedure, and / or an ALF procedure to generate the modified reconstruction samples.

[0206] In one embodiment, the image information may include an SPS. For example, whether the SPS includes additional virtual boundary-related information may be determined based on whether resampling for the at least one reference picture is available. Here, the resampling for the at least one reference picture may be performed by the RPR described above. The additional virtual boundary-related information may also be simply referred to as virtual boundary-related information. The term "additional" is used to distinguish it from virtual boundary-related information such as an SPS virtual boundary presence flag and / or a PH virtual boundary presence flag.

[0207] In one embodiment, the additional virtual boundary related information may include the number of virtual boundaries and the locations of the virtual boundaries.

[0208] In one embodiment, the additional virtual boundary related information may include information regarding the number of vertical virtual boundaries, information regarding the positions of the vertical virtual boundaries, information regarding the number of horizontal virtual boundaries, and information regarding the positions of the horizontal virtual boundaries.

[0209] In one embodiment, the image information may include a reference picture resampling availability flag, for example, based on the reference picture resampling availability flag, it may be determined whether resampling is available for the at least one reference picture.

[0210] In one embodiment, the SPS may include an SPS virtual boundary present flag associated with whether the SPS includes the additional virtual boundary-related information. Based on whether resampling for the at least one reference picture is available, the value of the SPS virtual boundary present flag may be determined to be 0.

[0211] In one embodiment, the additional virtual boundary-related information may not be included in the SPS based on the availability of resampling for the at least one reference picture, and the image information may include picture header information, and the picture header information may include the additional virtual boundary-related information.

[0212] In one embodiment, the current picture may include a sub-picture as a single sub-picture, the sub-picture may be independently coded, the reconstructed sample may be generated based on the sub-picture, sub-picture-related information may be generated based on the sub-picture, and the image information may include the sub-picture-related information.

[0213] In one embodiment, the image information may not include a subpicture treated as picture flag. Therefore, the value of the subpicture treated as picture flag may be set by the decoding device through inference (guessing or prediction). In one example, the value of the subpicture treated as picture flag may be set to 1.

[0214] In one embodiment, the current picture includes a sub-picture. In one example, the sub-picture is derived based on a merging procedure of two or more independently coded sub-pictures. The reconstructed samples are generated based on the sub-pictures, sub-picture-related information is generated based on the sub-pictures, and the image information includes the sub-picture-related information.

[0215] If residual samples for the current block exist, the decoding device may receive information about the residuals for the current block. The information about the residuals may include transform coefficients related to the residual samples. The decoding device may derive residual samples (or residual sample arrays) for the current block based on the residual information. Specifically, the decoding device may derive quantized transform coefficients based on the residual information. The quantized transform coefficients may have a one-dimensional vector form based on a coefficient scanning order. The decoding device may derive transform coefficients based on a dequantization procedure for the quantized transform coefficients. The decoding device may derive residual samples based on the transform coefficients.

[0216] The decoding device may generate reconstructed samples based on (intra) predicted samples and residual samples, and derive reconstructed blocks or pictures based on the reconstructed samples. Specifically, the decoding device may generate reconstructed samples based on the sum of the (intra) predicted samples and the residual samples. As described above, the decoding device may then apply an in-loop filtering procedure, such as deblocking filtering and / or an SAO procedure, to the reconstructed pictures as needed to improve subjective / objective image quality.

[0217] For example, a decoding device can decode a bitstream or encoded information to obtain image information including all or part of the above-described information (or syntax elements). The bitstream or encoded information can be stored in a computer-readable storage medium and can be used to cause the above-described decoding method to be performed.

[0218] In the above-described embodiments, the method is described based on a flowchart as a series of steps or blocks, but the embodiment is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps than those described above. Also, those skilled in the art will understand that the steps shown in the flowchart are not exclusive, and different steps may be included, or one or more steps of the flowchart may be deleted without affecting the scope of the embodiments herein.

[0219] The methods according to the embodiments of the present document described above can be implemented in the form of software, and the encoding device and / or decoding device according to the present document can be included in devices that perform image processing, such as TVs, computers, smartphones, set-top boxes, display devices, etc.

[0220] When an embodiment of this document is implemented in software, the method described above may be implemented with modules (processes, functions, etc.) that perform the functions described above. The modules may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor in various well-known ways. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, a memory card, a storage medium, and / or other storage devices. That is, the embodiments described herein may be implemented and performed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each figure may be implemented and performed on a computer, processor, microprocessor, controller, or chip. In this case, information (e.g., information on instructions) or algorithms for implementation may be stored on a digital storage medium.

[0221] In addition, the decoding device and encoding device to which the embodiments of this document are applied may be included in a multimedia broadcast transmitting / receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video interaction device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camcorder, a customized video (VoD) service providing device, an over-the-top (OTT) video (over-the-top) device, an internet streaming service providing device, a three-dimensional (3D) video device, a virtual reality (VR) device, an augmented reality (AR) device, an image telephone video device, a transportation terminal (e.g., a vehicle terminal (including an autonomous vehicle), an airplane terminal, a ship terminal, etc.), a medical video device, etc., and may be used to process video signals or data signals. For example, over-the-top (OTT) video (over-the-top) devices may include a game console, a Blu-ray player, an internet access TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), etc.

[0222] In addition, a processing method to which an embodiment of this document is applied may be produced in the form of a computer-executable program and stored on a computer-readable recording medium. Multimedia data having a data structure according to an embodiment of this document may also be stored on a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices and distributed storage devices on which computer-readable data is stored. The computer-readable recording medium may include, for example, a Blu-ray Disc (BD), a Universal Serial Bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage device. The computer-readable recording medium may also include media implemented in the form of a carrier wave (e.g., transmission via the Internet). The bitstream generated by the encoding method may be stored on a computer-readable recording medium or transmitted via a wired or wireless communication network.

[0223] Furthermore, the embodiments of the present document may be implemented in a computer program product by program code, which may be executed by a computer in accordance with the embodiments of the present document. The program code may be stored on a computer-readable carrier.

[0224] FIG. 11 illustrates an example of a content streaming system in which the embodiments disclosed herein can be applied.

[0225] Referring to FIG. 11, a content streaming system to which the embodiments of this document are applied can broadly include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0226] The encoding server compresses content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, if a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server may be omitted.

[0227] The bitstream can be generated by an encoding method or a bitstream generation method to which an embodiment of this document is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

[0228] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server acts as an intermediary to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, which then transmits the multimedia data to the user. In this case, the content streaming system may include a separate control server, which controls commands and responses between devices in the content streaming system.

[0229] The streaming server can receive content from a media repository and / or an encoding server. For example, if content is received from the encoding server, the content can be received in real time. In this case, the streaming server can store the bitstream for a certain period of time to provide a smooth streaming service.

[0230] Examples of the user device include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a PDA (personal digital assistant), a PMP (portable multimedia player), a navigation system, a slate PC, a tablet PC, an ultrabook, a wearable device (e.g., a smartwatch, a smart glass, a head mounted display (HMD)), a digital TV, a desktop computer, a digital signage, etc.

[0231] Each server in the content streaming system can be operated as a distributed server, in which case data received by each server can be processed in a distributed manner.

[0232] The claims described in this specification may be combined in various ways. For example, the technical features of the method claims herein may be combined to be realized as an apparatus, and the technical features of the apparatus claims herein may be combined to be realized as a method. Furthermore, the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined to be realized as an apparatus, and the technical features of the method claims herein and the technical features of the apparatus claims herein may be combined to be realized as a method.

Claims

1. An image decoding method performed by a decoding device, obtaining image information including residual information and reference picture related information via a bitstream; deriving at least one reference picture based on the reference picture-related information; generating a reconstructed sample of a current picture based on the residual information and the at least one reference picture; generating modified reconstruction samples based on an in-loop filtering procedure on the reconstruction samples; the reference picture-related information is index information for the at least one reference picture; The image information includes a sequence parameter set (SPS), determining whether the SPS includes additional virtual boundary-related information based on whether resampling for the at least one reference picture is possible; the SPS includes an SPS virtual boundary present flag associated with whether the SPS includes the additional virtual boundary-related information; The method of claim 1, wherein a value of the SPS virtual boundary present flag is determined to be 0 based on the resampling being possible for the at least one reference picture.

2. An image encoding method performed by an encoding device, generating a residual sample for the current block; generating residual information based on the residual samples for the current block; deriving at least one reference picture for reconstructed samples of the current picture; generating reference picture-related information based on the at least one reference picture; generating in-loop filtering related information for reconstructed samples of the current picture; encoding image information including the residual information, the reference picture related information, and the in-loop filtering related information; the reference picture-related information is index information for the at least one reference picture; The image information includes a sequence parameter set (SPS), determining whether the SPS includes additional virtual boundary-related information based on whether resampling for the at least one reference picture is possible; the SPS includes an SPS virtual boundary present flag associated with whether the SPS includes the additional virtual boundary-related information; The method of claim 1, wherein a value of the SPS virtual boundary present flag is determined to be 0 based on the resampling being possible for the at least one reference picture.

3. In a method for transmitting data for an image, obtaining a bitstream for the image, the bitstream comprising: generating a residual sample for the current block; generating residual information based on the residual samples for the current block; deriving at least one reference picture for reconstructed samples of the current picture; generating reference picture-related information based on the at least one reference picture; generating in-loop filtering related information for reconstructed samples of the current picture; encoding image information including the residual information, the reference picture-related information, and the in-loop filtering-related information; transmitting the data including the bitstream; the reference picture-related information is index information for the at least one reference picture; The image information includes a sequence parameter set (SPS), determining whether the SPS includes additional virtual boundary-related information based on whether resampling for the at least one reference picture is possible; the SPS includes an SPS virtual boundary present flag associated with whether the SPS includes the additional virtual boundary-related information; The method of claim 1, wherein a value of the SPS virtual boundary present flag is determined to be 0 based on the resampling being possible for the at least one reference picture.

Images