Method for decoding image using simplified residual data coding in image coding system and device therefor

Abstract

To provide a method for decoding an image.SOLUTION: The method for decoding an image executed by a decoder in the present document includes the steps of: acquiring image information including a residual syntax element for a current residual coefficient in a current block; deriving the current residual coefficient on the basis of the residual syntax element; and deriving a restoration sample of the current block on the basis of the current residual coefficient.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] This document relates to image coding technology, and more particularly, to an image decoding method and apparatus for coding current residual data into simplified residual data without applying level mapping when all context-coded bits in a block are currently used in an image coding system.

Background Art

[0002] Recently, the demand for high-resolution and high-quality images such as HD (High Definition) images and UHD (Ultra High Definition) images has been increasing in various fields. As the image data becomes higher in resolution and quality, the amount of information or bits to be transmitted relatively increases compared to existing image data. Therefore, when transmitting image data using a medium such as an existing wired or wireless broadband line or storing image data using an existing recording medium, the transmission cost and storage cost increase.

[0003] Accordingly, in order to effectively transmit, store, and reproduce high-resolution and high-quality image information, a high-efficiency image compression technology is required.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The technical problem of this document is to provide a method and apparatus for increasing image coding efficiency.

[0005] Another technical problem of this document is to provide a method and apparatus for increasing the efficiency of residual coding.

Means for Solving the Problems

[0006] According to one embodiment of this document, an image decoding method executed by a decoding device is provided. The method includes: obtaining image information including a residual syntax element or the like for a current residual coefficient in a current block; deriving the current residual coefficient based on the residual syntax element or the like; and deriving a restored sample of the current block based on the current residual coefficient.

[0007] According to another embodiment of this document, a decoding device that executes image decoding is provided. The decoding device includes: an entropy decoding unit that obtains image information including a residual syntax element or the like for a current residual coefficient in a current block; a residual processing unit that derives the current residual coefficient based on the residual syntax element or the like; and an addition unit that derives a restored sample of the current block based on the current residual coefficient.

[0008] According to still another embodiment of this document, a video encoding method executed by an encoding device is provided. The method includes: deriving a current residual coefficient for a current block; and encoding image information including a residual syntax element or the like for the current residual coefficient.

[0009] According to still another embodiment of this document, a video encoding device is provided. The encoding device includes: a residual processing unit that derives a current residual coefficient for a current block; and an entropy encoding unit that encodes image information including a residual syntax element or the like for the current residual coefficient.

Advantages of the Invention

[0010] According to this document, the efficiency of residual coding can be improved.

[0011] According to this document, the residual coefficients to which simplified residual data coding is applied can be derived without performing level mapping, reducing the coding complexity and improving the overall residual coding efficiency.

Brief Description of Drawings

[0012]

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Embodiments for Carrying Out the Invention

[0013] This document can be modified in various ways and can have various embodiments. Specific embodiments are illustrated in the drawings and will be described in detail. However, this is not intended to limit this document to specific embodiments. The terms commonly used in this specification are merely used to describe specific embodiments and are not used with the intention of limiting the technical idea of this document. Singular expressions include plural expressions unless the context clearly indicates otherwise. Terms such as "including" or "having" in this specification are intended to specify the existence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that the existence or possibility of addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof is not precluded in advance.

[0014] On the other hand, each configuration in the drawings described in this document is independently illustrated for the convenience of explaining different characteristic functions. It does not mean that each configuration is realized by separate hardware or separate software. For example, among the configurations, two or more configurations can be combined to form one configuration, and one configuration can also be divided into multiple configurations. Embodiments in which each configuration is integrated and / or separated are included in the scope of rights of this document as long as they do not deviate from the essence of this document.

[0015] Hereinafter, with reference to the accompanying drawings, the preferred embodiments of this document will be described in more detail. Hereinafter, for the same components on the drawings, the same reference numerals are used, and overlapping descriptions for the same components can be omitted.

[0016] FIG. 1 schematically shows an example of a video / image coding system to which the embodiments of this document can be applied.

[0017] As shown in FIG. 1, the video / image coding system can include a first device (source device) and a second device (receiver device). The source device can transmit encoded video / image information or data to the receiver device in the form of a file or a stream via a digital recording medium or a network.

[0018] The source device can include a video source, an encoding device, and a transmitting unit. The receiver device can include a receiving unit, a decoding device, and a renderer. The encoding device can be called a video / image encoding device, and the decoding device can be called a video / image decoding device. The transmitter can be included in the encoding device. The receiver can be included in the decoding device. The renderer can include a display unit, and the display unit can also be composed of a separate device or an external component.

[0019] The video source can obtain video / images through processes such as video / image capture, synthesis, or generation. The video source can include a video / image capture device and / or a video / image generation device. The video / image capture device can be equipped with, for example, one or more cameras, a video / image archive containing previously captured video / images, etc. The video / image generation device can be equipped with, for example, a computer, a tablet, and a smartphone, etc., and can (electronically) generate video / images. For example, virtual video / images can be generated via a computer, etc., in which case the video / image capture process can be replaced during the process of generating related data.

[0020] The encoding device can encode the input video / image. The encoding device can execute a series of procedures such as prediction, transformation, quantization, etc. for compression and coding efficiency. The encoded data (encoded video / image information) can be output in the form of a bitstream.

[0021] The transmitting unit can transmit the encoded video / image information or data output in the form of a bitstream to the receiving unit of the receiving device via a digital recording medium or a network in file or streaming form. The digital recording medium can include various recording media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitting unit can include elements for generating media files via a predetermined file format and can include elements for transmission via a broadcast / communication network. The receiving unit can receive / extract the bitstream and transmit it to the decoding device.

[0022] The decoding device can execute a series of procedures such as inverse quantization, inverse transformation, prediction, etc. corresponding to the operation of the encoding device to decode the video / image.

[0023] The renderer can render the decoded video / image. The rendered video / image can be displayed via the display unit.

[0024] This document relates to video / image coding. For example, the methods / embodiments disclosed in this document can be applied to the methods disclosed in the VVC (versatile video coding) standard, EVC (essential video coding) standard, AV1 (AOMedia Video 1) standard, AVS2 (2nd generation of audio video coding standard), or the next-generation video / image coding standard (e.g., H.267 or H.268, etc.).

[0025] This document presents various embodiments related to video / image coding, and unless otherwise stated, the embodiments can also be executed in combination with each other.

[0026] In this document, "video" may mean a collection of a series of "images" over time. "Picture" generally means a unit indicating one image in a specific time period, and "subpicture / slice / tile" is a unit constituting a part of a picture in coding. A subpicture / slice / tile may include one or more CTUs (Coding Tree Units). One picture may be composed of one or more subpictures / slices / tiles. One picture may be composed of a group of one or more tiles. One tile group may include one or more tiles. A brick represents a rectangular region of CTU rows within a tile in a picture. A tile may be partitioned into multiple bricks, each of which consists of one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick.A brick scan shows a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a brick, bricks within a tile are ordered consecutively in a raster scan of the bricks of the tile, and tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture. Also, a subpicture may represent a rectangular region of one or more slices within a picture. That is, a subpicture contains one or more slices that collectively cover a rectangular region of a picture. A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture.The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements in the picture parameter set. The tile row is a rectangular region of CTUs having a height specified by syntax elements in the picture parameter set and a width equal to the width of the picture. A tile scan is a specific sequential ordering of CTUs partitioning a picture in which the CTUs are ordered consecutively in CTU raster scan in a tile whereas tiles in a picture are ordered consecutively in a raster scan of the tiles of the picture.A slice includes an integer number of bricks of a picture that maybe exclusively contained in a single NAL unit. A slice may consists of either a number of complete tiles or only a consecutive sequence of complete bricks of one tile. In this document, tile group and slice may be used interchangeably. For example, in this document, tile group / tile group header may be called slice / slice header.

[0027] A pixel or pel can mean the smallest unit that makes up a picture (or image). Also, the term "sample" can be used as the term corresponding to a pixel. A sample can generally indicate a pixel or the value of a pixel, and can also indicate only the pixel / pixel value of the luma component, or only the pixel / pixel value of the chroma component.

[0028] A unit can indicate the basic unit of image processing. A unit can include at least one of a specific region of a picture and information related to the region. One unit can include one luma block and two chroma (e.g., cb, cr) blocks. A unit can, in some cases, be used interchangeably with terms such as block or area. In general, an M×N block can include a set (or array) of samples (or sample array) consisting of M columns and N rows, or a set (or array) of transform coefficients.

[0029] As used herein, "A or B" can mean "only A", "only B", or "both A and B". In other words, as used herein, "A or B" can be construed as "A and / or B". For example, as used herein, "A, B, or C" can mean "only A", "only B", "only C", or "any combination of A, B, and C".

[0030] As used herein, the slash ( / ) and comma can mean "and / or". For example, "A / B" can mean "A and / or B". Accordingly, "A / B" can mean "only A", "only B", or "both A and B". For example, "A, B, C" can mean "A, B, or C".

[0031] As used herein, "at least one of A and B" can mean "only A", "only B", or "both A and B". Also, as used herein, the expressions "at least one of A or B" and "at least one of A and / or B" can be construed in the same manner as "at least one of A and B".

[0032] Also, in this specification, "at least one of A, B, and C" may mean "only A", "only B", "only C", or "any combination of A, B, and C". Also, "at least one of A, B, or C" and "at least one of A, B, and / or C" may mean "at least one of A, B, and C".

[0033] Also, the parentheses used in this specification may mean "for example". Specifically, when it is displayed as "prediction (intra prediction)", "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". Also, when it is displayed as "prediction (i.e., intra prediction)", "intra prediction" may be proposed as an example of "prediction".

[0034] The technical features separately described within one drawing in this specification may be realized individually or simultaneously.

[0035] The following drawings are created to illustrate a specific example of this specification. Since the names of the specific devices and the names of the specific signals / messages / fields described in the drawings are presented exemplarily, the technical features of this specification are not limited to the specific names used in the following drawings.

[0036] FIG. 2 is a diagram schematically explaining the configuration of a video / image encoding device to which the embodiments of this document can be applied. Hereinafter, the video encoding device can include an image encoding device.

[0037] As shown in FIG. 2, the encoding device 200 can be configured to 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 can include an inter-prediction unit 221 and an intra-prediction unit 222. The residual processor 230 can include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 can further include a subtractor 231. The adder 250 can be called a reconstructor or a reconstructed block generator. The above-described image partitioner 210, predictor 220, residual processor 230, entropy encoder 240, adder 250, and filter 260 can be configured by one or more hardware components (e.g., an encoder chipset or a processor) according to an embodiment. Also, the memory 270 can include a DPB (decoded picture buffer) and can also be configured by a digital recording medium. The hardware component can further include the memory 270 as an internal / external component.

[0038] The image segmentation unit 210 can divide an input image (or picture, frame) input to the encoding device 200 into one or more processing units. As an example, the processing unit can be called a coding unit (CU). In this case, the coding unit can be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) by a QTBTTT (Quad-tree binary-tree ternary-tree) structure. For example, one coding unit can be divided into multiple coding units with a deeper depth based on a quad-tree structure, a binary-tree structure, and / or a ternary structure. In this case, for example, the quad-tree structure can be applied first, and the binary-tree structure and / or the ternary structure can be applied later. Or, the binary-tree structure can also be applied first. The coding procedure according to this document can be executed based on the final coding unit that cannot be further divided. In this case, based on the coding efficiency according to the image characteristics, etc., the largest coding unit can be immediately used as the final coding unit, or, if necessary, the coding unit can be recursively divided into coding units with a deeper depth, and the coding unit with the optimal size can be used as the final coding unit. Here, the coding procedure can include procedures such as prediction, transformation, and restoration described later. As another example, the processing unit can further include a prediction unit (PU: Prediction Unit) or a transform unit (TU: Transform Unit). In this case, the prediction unit and the transform unit can each be divided or partitioned from the aforementioned final coding unit.The prediction unit is a unit of sample prediction, and the conversion unit is a unit for deriving a conversion coefficient and / or a unit for deriving a residual signal from the conversion coefficient.

[0039] The unit can, in some cases, be used interchangeably with terms such as block or area. In general, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample can generally represent a pixel or a pixel value, and can represent only the pixel / pixel value of the luma component, or only the pixel / pixel value of the chroma component. A sample can be used as a term corresponding to a pixel or a pel for one picture (or image).

[0040] The encoding device 200 can subtract a prediction signal (predicted block, predicted sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from an input image signal (original block, original sample array) to generate a residual signal (residual signal, residual block, residual sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, as shown in the figure, the unit that subtracts the prediction signal (predicted block, predicted sample array) from the input image signal (original block, original sample array) within the encoder 200 can be called the subtraction unit 231. The prediction unit can perform prediction on a block to be processed (hereinafter referred to as the current block) and generate a predicted block including predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit can generate various pieces of information related to prediction, such as prediction mode information, and transmit them to the entropy encoding unit 240 as described later in the description of each prediction mode. The information related to prediction can be encoded by the entropy encoding unit 240 and output in the form of a bit stream.

[0041] The intra prediction unit 222 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located in the neighborhood of the current block according to the prediction mode, or can also be located remotely. In intra prediction, the prediction mode can include a plurality of non - directional modes and a plurality of directional modes. The non - directional modes can include, for example, the DC mode and the Planar Mode. The directional modes can include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of fineness of the prediction direction. However, this is only an example, and more or fewer directional prediction modes can be used depending on the setting. The intra prediction unit 222 can also determine the prediction mode to be applied to the current block by using the prediction mode applied to the adjacent blocks.

[0042] The inter prediction unit 221 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between adjacent blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the adjacent blocks can include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing 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 can be called by names such as a collocated reference block and a collocated CU (colCU), and the reference picture including the temporal neighboring block can also be called a collocated picture (colPic). For example, the inter prediction unit 221 can construct a motion information candidate list based on adjacent blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction can be executed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 221 can use the motion information of adjacent blocks as the motion information of the current block. In the case of the skip mode, a residual signal may not be transmitted, which is different from the merge mode.In the case of the motion information prediction (motion vector prediction, MVP) mode, the motion vector of an adjacent 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.

[0043] The prediction unit 220 can generate a prediction signal based on various prediction methods described below. For example, for the prediction of one block, the prediction unit can apply not only intra prediction or inter prediction, but also simultaneously apply intra prediction and inter prediction. This can be called combined inter and intra prediction (CIIP). Also, the prediction unit can be based on the intra block copy (IBC) prediction mode or the palette mode for the prediction of the block. The IBC prediction mode or the palette mode can be used for content image / video coding such as games, for example, like SCC (screen content coding). IBC basically performs prediction within the current picture, but can be executed similarly to inter prediction in terms of deriving a reference block within the current picture. That is, IBC can utilize at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, the sample values within the picture can be signaled based on information regarding the palette table and the palette index.

[0044] The prediction signal generated via the prediction unit (including the inter prediction unit 221 and / or the intra prediction unit 222) can be used to generate a restored signal or can be used to generate a residual signal. The conversion unit 232 can generate transform coefficients by applying a conversion technique to the residual signal. For example, the conversion technique can include at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen - Loeve Transform), GBT (Graph - Based Transform), or CNT (Conditionally Non - linear Transform). Here, when the GBT represents the relationship information between pixels as a graph, it means the conversion obtained from this graph. The CNT means generating a prediction signal using all previously reconstructed pixels and the conversion obtained based on that. Also, the conversion process can be applied to pixel blocks having the same size of a square and can also be applied to non - square, variable - size blocks.

[0045] The quantization unit 233 quantizes the transform coefficients and transmits them to the entropy encoding unit 240. The entropy encoding unit 240 can encode the quantized signal (information regarding the quantized transform coefficients) and output it as a bitstream. The information regarding the quantized transform coefficients can be called residual information. The quantization unit 233 can reorder the quantized transform coefficients in block form into a one-dimensional vector form based on the coefficient scan order, and can also generate the information regarding the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoding unit 240 can execute various encoding methods such as, for example, exponential Golomb, CAVLC (context-adaptive variable length coding), CABAC (context-adaptive binary arithmetic coding), etc. The entropy encoding unit 240 can encode, together or separately, in addition to the quantized transform coefficients, information necessary for video / image restoration (e.g., values of syntax elements, etc.). The encoded information (e.g., encoded video / image information) can be transmitted or stored in the form of a bitstream in units of NAL (network abstraction layer) units. The video / image information can further include information regarding 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). Also, the video / image information can further include general constraint information. Information and / or syntax elements transmitted / signaled from the encoding device to the decoding device in this document can be included in the video / image information. The video / image information can be encoded through the above-described encoding procedure and included in the bitstream.The bitstream can be transmitted via a network or stored in a digital recording medium. Here, the network can include a broadcast network and / or a communication network, etc., and the digital recording medium can include various recording media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The signal output from the entropy encoding unit 240 can be configured such that a transmission unit (not shown) for transmitting and / or a storage unit (not shown) for storing are internal / external elements of the encoding device 200, or the transmission unit can also be included in the entropy encoding unit 240.

[0046] The quantized transform coefficients output from the quantization unit 233 can be used to generate a prediction signal. For example, a residual signal (residual block or residual sample) can be restored by applying inverse quantization and inverse transformation to the quantized transform coefficients via the inverse quantization unit 234 and the inverse transformation unit 235. The addition unit 250 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the restored residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222. When there is no residual for the block to be processed, as in the case where the skip mode is applied, the predicted block can be used as the reconstructed block. The addition unit 250 can be called a restoration unit or a reconstructed block generation unit. The generated reconstructed signal can be used for intra prediction of the next block to be processed within the current picture and, as will be described later, can also be used for inter prediction of the next picture after passing through filtering.

[0047] On the other hand, LMCS (luma mapping with chroma scaling) can also be applied during the picture encoding and / or restoration process.

[0048] The filtering unit 260 can apply filtering to the restored signal to improve subjective / objective image quality. For example, the filtering unit 260 can apply various filtering methods to the restored picture to generate a modified restored picture, and store the modified restored picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filtering unit 260 can generate various information related to filtering and transmit it to the entropy encoding unit 240, as will be described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoding unit 240 and output in the form of a bit stream.

[0049] The modified restored picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 221. Through this, when inter prediction is applied, the encoding device can avoid prediction mismatches between the encoding device 200 and the decoding device 300, and can also improve the encoding efficiency.

[0050] The memory 270 DPB can store the modified restored picture for use as a reference picture in the inter prediction unit 221. The memory 270 can store the motion information of the block where the motion information in the current picture was derived (or encoded) and / or the motion information of the block in the already restored picture. The stored motion information can be transmitted to the inter prediction unit 221 for utilization as the motion information of spatially adjacent blocks or temporally adjacent blocks. The memory 270 can store the restored samples of the restored blocks in the current picture and transmit them to the intra prediction unit 222.

[0051] FIG. 3 is a diagram schematically illustrating the configuration of a video / image decoding apparatus to which the embodiments of the present document can be applied.

[0052] As shown in FIG. 3, the decoding apparatus 300 can be configured to 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 can include an inter-predictor 331 and an intra-predictor 332. The residual processor 320 can include a dequantizer 321 and an inverse transformer 322. The entropy decoder 310, the residual processor 320, the predictor 330, the adder 340, and the filter 350 described above can be configured by one hardware component (e.g., a decoder chipset or a processor) according to an embodiment. Also, the memory 360 can include a DPB (decoded picture buffer) and can also be configured by a digital recording medium. The hardware component can further include the memory 360 as an internal / external component.

[0053] When a bitstream including video / image information is input, the decoding device 300 can restore an image corresponding to the process in which the video / image information was processed by the encoding device in FIG. 2. For example, the decoding device 300 can derive units / blocks based on the block division related information obtained from the bitstream. The decoding device 300 can execute decoding using the processing units applied in the encoding device. Therefore, the processing unit for decoding is, for example, a coding unit, and the coding unit can be divided according to a quad-tree structure, a binary tree structure, and / or a ternary tree structure from a coding tree unit or a maximum coding unit. One or more transform units can be derived from the coding unit. Then, the restored image signal decoded and output via the decoding device 300 can be reproduced via a reproducing device.

[0054] The decoding device 300 can receive the signal output from the encoding device of FIG. 2 in the form of a bitstream, and the received signal can be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 can parse the bitstream to derive information (e.g., video / image information) necessary for image restoration (or picture restoration). The video / image information can further include information regarding 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). Also, the video / image information can further include general constraint information. The decoding device can further decode a picture based on the information regarding the parameter set and / or the general constraint information. The signaling / received information and / or syntax elements described later in this document can be decoded via the decoding procedure and obtained from the bitstream. For example, the entropy decoding unit 310 can decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output values of syntax elements necessary for image restoration, quantized values of transform coefficients regarding residuals, etc. More specifically, the CABAC entropy decoding method receives bins corresponding to each syntax element in the bitstream, determines a context model using the syntax element information to be decoded, the decoding information of the surrounding and the block to be decoded, or the information of the symbols / bins decoded in the previous step, predicts the occurrence probability of a bin based on the determined context model, and executes arithmetic decoding of the bin to generate a symbol corresponding to the value of each syntax element. At this time, the CABAC entropy decoding method can update the context model using the information of the symbols / bins decoded for the context model of the next symbol / bin after determining the context model.Of the information decoded by the entropy decoding unit 310, the information related to prediction is provided to the prediction unit (inter prediction unit 332 and intra prediction unit 331), and the residual value for which entropy decoding is performed by the entropy decoding unit 310, that is, the quantized transform coefficient and related parameter information can be input to the residual processing unit 320. The residual processing unit 320 can derive a residual signal (residual block, residual sample, residual sample array). Also, of the information decoded by the entropy decoding unit 310, the information related to filtering can be provided to the filtering unit 350. On the other hand, a receiving unit (not shown) that receives the signal output from the encoding device can be further configured as an internal / external element of the decoding device 300, or the receiving unit is a component of the entropy decoding unit 310. On the other hand, the decoding device according to this document can be called a video / image / picture decoding device, and the decoding device can also be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder can include the entropy decoding unit 310, and the sample decoder can include at least one of the inverse quantization unit 321, inverse transform unit 322, addition unit 340, filtering unit 350, memory 360, inter prediction unit 332, and intra prediction unit 331.

[0055] In the inverse quantization unit 321, the quantized transform coefficient can be inverse quantized to output a transform coefficient. The inverse quantization unit 321 can reorder the quantized transform coefficients in a two-dimensional block form. In this case, the reordering can be performed based on the coefficient scan order executed by the encoding device. The inverse quantization unit 321 can perform inverse quantization on the quantized transform coefficient using a quantization parameter (for example, quantization step size information) to obtain a transform coefficient.

[0056] In the inverse transformation unit 322, the transformation coefficients are inversely transformed to obtain a residual signal (residual block, residual sample array).

[0057] The prediction unit can perform a prediction on the current block and generate a predicted block including predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied to the current block based on the information regarding the prediction output from the entropy decoding unit 310, and can determine a specific intra / inter prediction mode.

[0058] The prediction unit 320 can generate a prediction signal based on various prediction methods described later. For example, the prediction unit can apply not only intra prediction or inter prediction for the prediction of one block, but also can apply intra prediction and inter prediction simultaneously. This can be called combined inter and intra prediction (CIIP). Also, the prediction unit can be based on the intra block copy (IBC) prediction mode or the palette mode for the prediction of a block. The IBC prediction mode or the palette mode can be used for content image / video coding such as games, for example, like SCC (screen content coding). IBC basically performs prediction within the current picture, but can be executed similarly to inter prediction in terms of deriving a reference block within the current picture. That is, IBC can utilize at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, information regarding the palette table and the palette index can be included in and signaled in the video / image information.

[0059] The intra prediction unit 331 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located in the neighborhood of the current block or away from it depending on the prediction mode. In intra prediction, the prediction mode can include a plurality of non - directional modes and a plurality of directional modes. The intra prediction unit 331 can also determine the prediction mode to be applied to the current block using the prediction mode applied to the adjacent block.

[0060] The inter prediction unit 332 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. At this time, in order to reduce the amount of motion information transmitted from the inter prediction mode, the motion information can be predicted in units of blocks, sub - blocks, or samples based on the correlation of the motion information between the adjacent block and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the adjacent blocks can include spatial neighboring blocks existing within the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter prediction unit 332 can construct a motion information candidate list based on the adjacent blocks and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter prediction can be executed based on various prediction modes, and the information regarding the prediction can include information indicating the mode of inter prediction for the current block.

[0061] The adder 340 can generate a restored signal (restored picture, restored block, restored sample array) by adding the obtained residual signal to the predicted signal (predicted block, predicted sample array) output from the prediction unit (including the inter prediction unit 332 and / or the intra prediction unit 331). When there is no residual for the block to be processed, such as when the skip mode is applied, the predicted block can be used as the restored block.

[0062] The adder 340 can be referred to as a restoration unit or a restored block generation unit. The generated restored signal can be used for intra prediction of the next block to be processed in the current picture, can be output after filtering as described later, or can also be used for inter prediction of the next picture.

[0063] On the other hand, LMCS (luma mapping with chroma scaling) can also be applied in the picture decoding process.

[0064] The filtering unit 350 can apply filtering to the restored signal to improve the subjective / objective image quality. For example, the filtering unit 350 can apply various filtering methods to the restored picture to generate a modified restored picture, and can transmit the modified restored picture to the memory 360, specifically, the DPB of the memory 360. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0065] The (corrected) restored picture stored in the DPB of the memory 360 can be used as a reference picture in the inter prediction unit 332. The memory 360 can store the motion information of the block from which the motion information in the current picture was derived (or decoded) and / or the motion information of the block in the already restored picture. The stored motion information can be transmitted to the inter prediction unit 260 for utilization as the motion information of spatially adjacent blocks or temporally adjacent blocks. The memory 360 can store the restored samples of the restored blocks in the current picture and can transmit them to the intra prediction unit 331.

[0066] In this specification, the embodiments described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding device 200 can also be applied to the filtering unit 350, the inter prediction unit 332, and the intra prediction unit 331 of the decoding device 300 so as to be identical or corresponding.

[0067] In this document, at least one of quantization / inverse quantization and / or transform / inverse transform can be omitted. When the quantization / inverse quantization is omitted, the quantized transform coefficient can be called a transform coefficient. When the transform / inverse transform is omitted, the transform coefficient can be called a coefficient or a residual coefficient, or can still be called a transform coefficient for the sake of uniformity of expression.

[0068] In this document, the quantized transform coefficients and the transform coefficients can each be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, the residual information can include information regarding the transform coefficients (etc.), and the information regarding the transform coefficients (etc.) can be signaled via a residual coding syntax. The transform coefficients can be derived based on the residual information (or the information regarding the transform coefficients (etc.)), and the scaled transform coefficients can be derived via an inverse transform (scaling) with respect to the transform coefficients. Residual samples can be derived based on an inverse transform (transformation) with respect to the scaled transform coefficients. This can be applied / expressed in the same way in other parts of this document.

[0069] As described above, the encoding device can execute various encoding methods such as, for example, exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), etc. Also, the decoding device can decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output values of syntax elements necessary for image restoration, quantized values of transform coefficients regarding the residual, etc.

[0070] For example, the coding methods etc. described above can be performed as described later.

[0071] FIG. 4 exemplarily shows context - adaptive binary arithmetic coding (CABAC) for encoding a syntax element. For example, in the encoding process of CABAC, when the input signal is a syntax element that is not a binary value, the encoding device can binarize the value of the input signal to convert the input signal into a binary value. Also, when the input signal is already a binary value (i.e., when the value of the input signal is a binary value), binarization is not performed and it can be bypassed. Here, each binary number 0 or 1 that constitutes a binary value can be called a bin. For example, when the binary string after binarization is 110, each of 1, 1, and 0 is called one bin. The bin (etc.) for one syntax element can represent the value of the syntax element.

[0072] Thereafter, the binarized bins etc. of the syntax element can be input as a regular encoding engine or a bypass encoding engine. The regular encoding engine of the encoding device can assign a context model that reflects a probability value to the bin, and can encode the bin based on the assigned context model. The regular encoding engine of the encoding device can update the context model for the bin after encoding each bin. The bins encoded as described above can be represented as context - coded bins.

[0073] On the other hand, when the binary bins of the syntax element are input to the bypass encoding engine, they can be coded as follows. For example, the bypass encoding engine of the encoding device omits the procedure of estimating the probability for the input bin and the procedure of updating the probability model applied to the bin after encoding. When bypass encoding is applied, the encoding device can apply a uniform probability distribution instead of allocating a context model to encode the input bin, thereby improving the encoding speed. The bin encoded as described above can be represented as a bypass bin.

[0074] Entropy decoding can be represented as a process of performing the same process as the above-described entropy encoding in reverse order.

[0075] For example, when the syntax element is decoded based on the context model, the decoding device can receive the bin corresponding to the syntax element through the bitstream, and use the decoding information of the decoding target block or the peripheral block or the information of the symbol / bin decoded in the previous step and the syntax element to determine the context model, predict the occurrence probability of the received bin according to the determined context model, and perform arithmetic decoding of the bin to derive the value of the syntax element. Thereafter, the context model of the bin to be decoded next can be updated in the determined context model.

[0076] Also, for example, when a syntax element is bypass decoded, the decoding device can receive a bin corresponding to the syntax element via a bit stream and apply a uniform probability distribution to decode the input bin. In this case, the procedure for deriving the context model of the syntax element and the procedure for updating the context model applied to the bin after decoding can be omitted.

[0077] As described above, residual samples and the like can be derived into quantized transform coefficients and the like through the conversion and quantization processes. The quantized transform coefficients and the like can also be called transform coefficients and the like. In this case, the transform coefficients and the like within the block can be signaled in the form of residual information. The residual information can include a residual coding syntax. That is, the encoding device can construct a residual coding syntax as residual information, encode this, and output it in the form of a bit stream. The decoding device can decode the residual coding syntax from the bit stream to derive residual (quantized) transform coefficients and the like. The residual coding syntax can include syntax elements such as whether a transform has been applied to the block, where the position of the last valid transform coefficient within the block is, whether there are valid transform coefficients within a sub-block, and what the magnitude / symbol of the valid transform coefficient is, as will be described later.

[0078] For example, the (quantized) transform coefficients (i.e., the residual information) can be encoded and / or decoded based on syntax elements such as transform_skip_flag, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag, sig_coeff_flag, par_level_flag, abs_level_gt1_flag, abs_level_gt3_flag, abs_remainder, coeff_sign_flag, dec_abs_level, mts_idx, etc. Syntax elements related to residual data encoding / decoding can be represented as shown in the following tables.

[0079]

Table 1-1

[0080]

Table 1-2

[0081]

Table 1-3

[0082]

Table 1-4

[0083] The transform_skip_flag indicates whether the transformation is skipped for an associated block. The transform_skip_flag can be a syntax element of the transform skip flag. The associated block can be a CB (Coding Block) or a TB (Transform Block). For the transformation (and quantization) and residual coding procedures, the CB and the TB can be used interchangeably. For example, as described above, residual samples and the like are derived for a CB, and (quantized) transform coefficients and the like can be derived through the transformation and quantization of the residual samples and the like. Information (such as syntax elements) that efficiently represents the position, magnitude, sign, etc. of the (quantized) transform coefficients and the like can be generated and signaled through the residual coding procedure. The quantized transform coefficients and the like can be simply referred to as transform coefficients and the like. Generally, when the CB is not larger than the maximum TB, the size of the CB can be the same as the size of the TB. In this case, the target block to be transformed (and quantized) and residually coded can be referred to as a CB or a TB. On the other hand, when the CB is larger than the maximum TB, the target block to be transformed (and quantized) and residually coded can be referred to as a TB. Hereinafter, it will be described that syntax elements and the like related to residual coding are signaled in units of the transform block TB. This is an example, and as described above, the TB can be used interchangeably with the coding block CB.

[0084] On the other hand, the syntax elements and the like signaled after the transform skip flag is signaled can be the same as the syntax elements and the like disclosed in Table 2 described below. The specific description of the syntax elements and the like will be as described below.

[0085]

Table 2-1

[0086]

Table 2-2

[0087]

Table 2-3

[0088]

Table 3-1

[0089]

Table 3-2

[0090]

Table 3-3

[0091]

Table 3-4

[0092]

Table 3-5

[0093]

Table 3-6

[0094]

Table 4-1

[0095]

Table 4-2

[0096]

Table 4-3

[0097] According to this embodiment, as shown in Table 2, residual coding can be branched according to the value of the syntax element transform_skip_flag of the conversion skip flag. That is, different syntax elements can be used for residual coding based on the value of the conversion skip flag (based on whether conversion can be skipped). The residual coding used when conversion skip is not applied (i.e., when conversion is applied) can be called regular residual coding (RRC), and the residual coding when conversion skip is applied (i.e., when conversion is not applied) can be called transform skip residual coding (TSRC). Also, the regular residual coding can also be called general residual coding. Also, the regular residual coding can be called the regular residual coding syntax structure, and the transform skip residual coding can be called the transform skip residual coding syntax structure. Table 3 can represent the syntax elements of residual coding when the value of transform_skip_flag is 0, i.e., when conversion is applied, and Table 4 can represent the syntax elements of residual coding when the value of transform_skip_flag is 1, i.e., when conversion is not applied.

[0098] Specifically, for example, a conversion skip flag that indicates whether conversion of a conversion block can be skipped can be parsed, and it can be determined whether the conversion skip flag is 1. When the value of the conversion skip flag is 0, as shown in Table 3, syntax elements such as last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, sb_coded_flag, sig_coeff_flag, abs_level_gtx_flag, par_level_flag, abs_remainder, coeff_sign_flag, and / or dec_abs_level for the residual coefficients of the conversion block can be parsed, and the residual coefficients can be derived based on the syntax elements. In this case, the syntax elements can also be parsed sequentially, and the parsing procedure can also be changed. Also, the abs_level_gtx_flag can indicate abs_level_gt1_flag and / or abs_level_gt3_flag. For example, abs_level_gtx_flag[n][0] can be an example indication of the first conversion coefficient level flag (abs_level_gt1_flag), and the abs_level_gtx_flag[n][1] can be an example indication of the second conversion coefficient level flag (abs_level_gt3_flag).

[0099] Referring to Table 3 above, last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, sb_coded_flag, sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag, abs_remainder, coeff_sign_flag, and / or dec_abs_level can be encoded / decoded. On the other hand, the sb_coded_flag can also be denoted as coded_sub_block_flag.

[0100] In one embodiment, the encoding device can encode the (x, y) position information of the last non-zero transform coefficient in the transform block based on the syntax elements last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix. More specifically, the last_sig_coeff_x_prefix represents the prefix of the column position of the last significant coefficient in the scanning order within the transform block, the last_sig_coeff_y_prefix represents the prefix of the row position of the last significant coefficient in the scanning order within the transform block, the last_sig_coeff_x_suffix represents the suffix of the column position of the last significant coefficient in the scanning order within the transform block, and the last_sig_coeff_y_suffix represents the suffix of the row position of the last significant coefficient in the scanning order within the transform block. Here, the significant coefficient can represent the non-zero coefficient. Also, the scanning order can be the upper-right diagonal scanning order. Alternatively, the scanning order can be the horizontal scanning order or the vertical scanning order. The scanning order can be determined based on whether intra / inter prediction is applied to the target block (CB or CB including TB) and / or the specific intra / inter prediction mode.

[0101] Next, after the encoding device divides the conversion block into 4×4 sub-blocks or the like, for each 4×4 sub-block, it can use a 1-bit syntax element coded_sub_block_flag to indicate whether there are non-zero coefficients in the current sub-block.

[0102] If the value of coded_sub_block_flag is 0, since there is no more information to be transmitted, the encoding device can terminate the encoding process for the current sub-block. Conversely, if the value of coded_sub_block_flag is 1, the encoding device can continue the encoding process for sig_coeff_flag. The sub-block containing the last non-zero coefficient does not require encoding of coded_sub_block_flag, and the sub-block containing the DC information of the conversion block is likely to contain non-zero coefficients, so coded_sub_block_flag can be assumed to have a value of 1 without being encoded.

[0103] If it is determined that the value of coded_sub_block_flag is 1 and there are non-zero coefficients in the current sub-block, the encoding device can encode sig_coeff_flag having binary values according to the reverse-scanned order. The encoding device can encode 1-bit syntax element sig_coeff_flag for each transform coefficient according to the scan order. If the value of the transform coefficient at the current scan position is not 0, the value of sig_coeff_flag can be 1. Here, in the case of a sub-block including the last non-zero coefficient, since sig_coeff_flag does not need to be encoded for the last non-zero coefficient, the encoding process for the sub-block can be omitted. Level information encoding can be performed only when sig_coeff_flag is 1, and four syntax elements or the like can be used in the level information encoding process. More specifically, each sig_coeff_flag[xC][yC] can represent whether the level (value) of the transform coefficient at each transform coefficient position (xC, yC) in the current TB is non-zero. In one embodiment, the sig_coeff_flag can correspond to an example of a syntax element of a valid coefficient flag indicating whether the quantized transform coefficient is a non-zero valid coefficient.

[0104] The remaining level values after encoding for sig_coeff_flag can be derived as follows. That is, the syntax element remAbsLevel representing the level value to be encoded can be derived as follows.

[0105]

Equation

[0106] Here, coeff means the actual transform coefficient value.

[0107] Also, abs_level_gt1_flag can indicate whether the remAbsLevel at the scanning position (n) is greater than 1. For example, when the value of abs_level_gt1_flag is 0, the absolute value of the conversion coefficient at that position can be 1. Also, when the value of the abs_level_gt1_flag is 1, the remAbsLevel representing the level value to be encoded later can be updated as follows in the following formula.

[0108]

Number

[0109] Also, the least significant coefficient (LSB) value of remAbsLevel described in the above formula 2 can be encoded as follows in formula 3 below via par_level_flag.

[0110]

Number

[0111] Here, par_level_flag[n] can represent the parity of the conversion coefficient level (value) at the scanning position n.

[0112] After the par_leve_flag encoding, the conversion coefficient level value remAbsLevel to be encoded can be updated as follows in the following formula.

[0113]

Number

[0114] The abs_level_gt3_flag can indicate whether the remAbsLevel at the scanning position (n) is greater than 3. Encoding for the abs_remainder can be performed only when the abs_level_gt3_flag is 1. The relationship between the actual conversion coefficient value, coeff, and each syntax element can be as follows in the following formula.

[0115]

Number

[0116] Also, the following table represents an example and the like related to the above-mentioned formula 5.

[0117]

Table 5

[0118] Here, |coeff| represents the conversion coefficient level (value), and can also be displayed as AbsLevel for the conversion coefficient. Also, the sign of each coefficient can be encoded using the coeff_sign_flag, which is a 1-bit symbol.

[0119] Also, for example, when the value of the conversion skip flag is 1, as shown in Table 4, syntax elements such as sb_coded_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gtx_flag, par_level_flag, and / or abs_remainder for the residual coefficients of the conversion block can be parsed, and the residual coefficients can be derived based on the syntax elements. In this case, the syntax elements can be parsed sequentially, and the parsing procedure can also be changed. Also, the abs_level_gtx_flag can indicate abs_level_gt1_flag, abs_level_gt3_flag, abs_level_gt5_flag, abs_level_gt7_flag, and / or abs_level_gt9_flag. For example, abs_level_gtx_flag[n][j] can be a flag indicating whether the absolute value or level (value) of the conversion coefficient at the scanning position n is greater than (j << 1)+1. The (j << 1)+1 can be replaced by a predetermined critical value such as a first critical value, a second critical value, etc. in some cases.

[0120] On the one hand, CABAC provides high performance, but has the drawback that its throughput performance is not good. This is due to the normalization encoding engine of CABAC. Normalization encoding (i.e., encoding through the normalization encoding engine of CABAC) shows high data dependence because it uses the probability state and range updated through the encoding of previous bins, and it takes a lot of time to read the probability interval and determine the current state. The throughput problem of CABAC can be solved by restricting the number of context-coded bins. For example, as in Table 1 or Table 3 described above, the sum of the bins used to represent sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag can be restricted to the number according to the size of the block. Also, for example, as in Table 4 described above, the sum of the bins used to represent sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag, abs_level_gt5_flag, abs_level_gt7_flag, and abs_level_gt9_flag can be restricted to the number according to the size of the block.As an example, when the block is a 4×4 size block, the sum of bins etc. for the sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag or sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag, abs_level_gt5_flag, abs_level_gt7_flag, abs_level_gt9_flag can be limited to 32 (or, for example, 28), and when the block is a 2×2 size block, the sum of bins etc. for the sig_coeff_flag, abs_level_gt1_flag, par_level_flag, abs_level_gt3_flag can be limited to 8 (or, for example, 7). The limited number of the bins etc. can be indicated by remBinsPass1 or RemCcbs. Or, as an example, for a higher CABAC throughput, the number of context coded bins can be limited for a block (CB or TB) including the coding target CG. In other words, the number of context coded bins can be limited in block (CB or TB) units. For example, when the size of the current block is 16×16, regardless of the current CG, the number of context coded bins for the current block can be limited to 1.75 times the number of pixels of the current block, that is, 448.

[0121] In this case, if the encoding device uses all the context coding bins with a limited number for encoding context elements, the remaining coefficients can be binarized through the binarization method for the coefficients described later without using context coding, and bypass coding can be executed. In other words, for example, when the number of context coded bins coded for 4×4 CG is 32 (or, for example, 28), or when the number of context coded bins coded for 2×2 CG is 8 (or, for example, 7), sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag that are to be coded in more context coding bins may not be coded and can be immediately coded in dec_abs_level. Or, for example, when the number of context coded bins coded for a 4×4 block is limited to 1.75 times the number of pixels in the entire block, that is, 28, sig_coeff_flag, abs_level_gt1_flag, par_level_flag, and abs_level_gt3_flag that are to be coded in more context coding bins may not be coded and, as shown in Table 6 described later, can be immediately coded in dec_abs_level.

[0122]

Table 6

[0123] The |coeff| value can be derived based on dec_abs_level. In this case, the conversion coefficient value |coeff| can be derived as follows in the following mathematical formula.

[0124]

Equation

[0125] Also, the coeff_sign_flag can represent the sign of the conversion coefficient level at the scanning position (n). That is, the coeff_sign_flag can represent the sign of the conversion coefficient at the scanning position (n).

[0126] FIG. 5 is a diagram illustrating an example of conversion coefficients and the like within a 4×4 block.

[0127] The 4×4 block in FIG. 5 shows an example of quantized coefficients and the like. The block shown in FIG. 5 can be a 4×4 conversion block or a 4×4 sub-block of an 8×8, 16×16, 32×32, or 64×64 conversion block. The 4×4 block in FIG. 5 can represent a luma block or a chroma block.

[0128] On the other hand, as described above, when the input signal is a syntax element that is not binary, the encoding device can binarize the value of the input signal to convert the input signal into a binary value. Also, the decoding device can decode the syntax element to derive the binarized value of the syntax element (i.e., the binarized bin), and can inverse-binarize the binarized value to derive the value of the syntax element. The binarization process can be performed by a Truncated Rice (TR) binarization process, a k-th order Exp-Golomb (EGk) binarization process, a Limited k-th order Exp-Golomb (Limited EGk), or a Fixed-length (FL) binarization process, etc., which will be described later. Also, the inverse-binarization process can be performed based on the TR binarization process, the EGk binarization process, or the FL binarization process to represent the process of deriving the value of the syntax element.

[0129] For example, the TR binary evolution process can be performed as follows.

[0130] The input of the TR binary evolution process can be the requirements for TR binary evolution and cMax and cRiceParam for the syntax element. Also, the output of the TR binary evolution process can be the TR binary evolution for the value symbolVal corresponding to the bin string.

[0131] Specifically, as an example, when there is a suffix bin string for the syntax element, the TR bin string for the syntax element can be the concatenation of the prefix bin string and the suffix bin string, and when the suffix bin string does not exist, the TR bin string for the syntax element can be the prefix bin string. For example, the prefix bin string can be derived as described later.

[0132] The prefix value of the symbolVal for the syntax element can be derived as in the following formula.

[0133]

Equation

[0134] Here, prefixVal can represent the prefix value of the symbolVal. The prefix of the TR bin string of the syntax element (i.e., the prefix bin string) can be derived as described later.

[0135] For example, when the prefixVal is smaller than cMax >> cRiceParam, the prefix bin string can be a bit string of length prefixVal + 1 indexed by binIdx. That is, when the prefixVal is smaller than cMax >> cRiceParam, the prefix bin string can be a bit string of prefixVal + 1 bits pointed to by binIdx. The bins for binIdx smaller than prefixVal can be the same as 1. Also, the bin for binIdx the same as prefixVal can be the same as 0.

[0136] For example, the bin string derived by the unary binarization for the prefixVal can be as shown in the following table.

[0137]

Table 7

[0138] On the other hand, when the prefixVal is not smaller than cMax >> cRiceParam, the prefix bin string can be a bit string with a length of cMax >> cRiceParam and all bins being 1.

[0139] Also, when cMax is larger than symbolVal and cRiceParam is larger than 0, a suffix bin string of the TR bin string may exist. For example, the suffix bin string can be derived as described later.

[0140] The suffix value of the symbolVal for the syntax element can be derived as in the following formula.

[0141]

Equation

[0142] Here, suffixVal can represent the suffix value of the symbolVal.

[0143] The suffix of the TR bin string (i.e., the suffix bin string) can be derived based on the FL binary evolution process for suffixVal where the cMax value is (1 << cRiceParam) - 1.

[0144] On the other hand, if the value of the input parameter cRiceParam is 0, the TR binary evolution can be exactly truncated unary binarization, and the same cMax value as the possible maximum value of the syntax element to be decoded can always be used.

[0145] Also, for example, the EGk binary evolution process can be performed as follows. The syntax element coded by ue(v) can be an Exp - Golomb coded syntax element.

[0146] As an example, the 0 - th order Exp - Golomb (EG0) binary evolution process can be performed as follows.

[0147] The parsing process for the syntax element can start from the current position of the bit stream, read the bits including the first non - zero bit, and begin by counting the number of leading bits such as 0. The process can be represented as shown in the following table.

[0148]

Table 8

[0149] Also, the variable codeNum can be derived as in the following formula.

[0150]

Number

[0151] Here, the value returned by read_bits(leadingZeroBits), that is, the value represented by read_bits(leadingZeroBits), can be interpreted as the binary representation of an unsigned integer for the most significant bit recorded first.

[0152] The structure of the Exp-Golomb code that separates the bit string into "prefix" bits and "suffix" bits can be represented as in the following table.

[0153]

Table 9

[0154] The "prefix" bits can be the bits parsed as described above for the leadingZeroBits calculation and can be represented as 0 or 1 of the bit string in Table 9. That is, the bit string disclosed as 0 or 1 in Table 9 above can represent the prefix bit string. The "suffix" bits can be the bits parsed in the calculation of codeNum and can be represented as xi in Table 9 above. That is, the bit string disclosed as xi in Table 9 above can represent the suffix bit string. Here, i can be a value in the range from 0 to LeadingZeroBits - 1. Also, each xi can be the same as 0 or 1.

[0155] The bit string assigned to the [[ID=]],

[0156] [Table 10]

[0157] When the descriptor of the syntax element is ue(v), that is, when the syntax element is coded with ue(v), the value of the syntax element can be the same as codeNum.

[0158] Also, for example, the EGk binary evolution process can be performed as follows.

[0159] The input of the EGk binary evolution process can be a request for EGk binary evolution. Also, the output of the EGk binary evolution process can be the EGk binary evolution for the value symbolVal corresponding to the bit string.

[0160] The bit string of the EGk binary evolution process for symbolVal can be derived as follows.

[0161] [Table 11]

[0162] Referring to Table 11 described above, the binary value X can be added to the end of the bit string via each call of put(x). Here, x can be 0 or 1.

[0163] Also, for example, the Limited EGk binary evolution process can be performed as follows.

[0164] The input of the Limited EGk binary evolution process can be the requirements for Limited EGk binary evolution, the rice parameter riceParam, the variable log2TransformRange representing the binary logarithm of the maximum value, and the variable maxPreExtLen representing the maximum prefix extension length. Also, the output of the Limited EGk binary evolution process can be the Limited EGk binary evolution for the value symbolVal corresponding to the bit string.

[0165] The bit string of the Limited EGk binary evolution process for symbolVal can be derived as follows.

[0166] [Table 12]

[0167] Also, for example, the FL binary evolution process can be performed as follows.

[0168] The input of the FL binary evolution process can be the requirements for FL binary evolution and cMax for the syntax element. Also, the output of the FL binary evolution process can be the FL binary evolution for the value symbolVal corresponding to the bit string.

[0169] FL binary evolution can be configured using a bit string having a number of bits equal to the fixed length of the symbol value symbolVal. Here, the fixed-length bits can be an unsigned integer bitstring. That is, a bit string for the symbol value symbolVal can be derived by FL binary evolution, and the bit length (i.e., the number of bits) of the bit string can be of a fixed length.

[0170] For example, the fixed length can be derived as in the following mathematical formula.

[0171]

Number

[0172] Indexing of bins and the like for binary evolution can be in a manner that uses values increasing in order from the most significant bit to the least significant bit. For example, the bin index associated with the most significant bit can be binIdx = 0.

[0173] On the other hand, for example, among the residual information, the binary evolution process for the syntax element abs_remainder can be performed as follows.

[0174] The input to the binary evolution process for the abs_remainder can be the request for the binary evolution of the syntax element abs_remainder[n], the hue component cIdx, and the luma position (x0, y0). The luma position (x0, y0) can refer to the upper left sample of the current luma transform block based on the upper left luma sample of the picture.

[0175] The output of the binary evolution process for the abs_remainder can be the binary evolution of the abs_remainder (i.e., the binary string of the abs_remainder). Available bin strings and the like for the abs_remainder can be derived by the binary evolution process.

[0176] The Rice parameter cRiceParam for the abs_remainder[n] can be derived through a Rice parameter derivation process that takes as input the hue component cIdx, the luma position (x0, y0), the current coefficient scan position (xC, yC), the binary logarithm of the width of the transform block log2TbWidth, and the binary logarithm of the height of the transform block log2TbHeight. A specific description of the Rice parameter derivation process will be given later.

[0177] Also, for example, cMax for the currently coded abs_remainder[n] can be derived based on the Rice parameter cRiceParam. The cMax can be derived as follows in the following formula.

[0178]

Equation

[0179] On the other hand, the binary conversion of the abs_remainder, that is, the bin string for the abs_remainder, can be the concatenation of a prefix bin string and a suffix bin string if the suffix bin string exists. Also, if the suffix bin string does not exist, the bin string for the abs_remainder can be the prefix bin string.

[0180] For example, the prefix bin string can be derived as described later.

[0181] The prefix value prefixVal of the abs_remainder[n] can be derived as follows in the following formula.

[0182]

Equation

[0183] The prefix of the bin string of the abs_remainder[n] (i.e., the prefix bin string) can be derived by the TR binary process for the prefixVal that uses the cMax and the cRiceParam as inputs.

[0184] If the prefix bin string is the same as the bit string in which all bits are 1 and the bit length is 6, the suffix bin string of the bin string of the abs_remainder[n] may exist and can be derived as described later.

[0185] The process for deriving the Rice parameter for the abs_remainder[n] may be as follows.

[0186] The inputs of the process for deriving the Rice parameter may be the colour component index cIdx, the luma position (x0, y0), the current coefficient scan position (xC, yC), the binary logarithm log2TbWidth of the width of the transform block, and the binary logarithm log2TbHeight of the height of the transform block. The luma position (x0, y0) can refer to the upper left sample of the current luma transform block with reference to the upper left luma sample of the picture. Also, the output of the process for deriving the Rice parameter may be the Rice parameter cRiceParam.

[0187] For example, based on a given component index cIdx and the array AbsLevel[x][y] for the transform block having the upper left luma position (x0, y0), the variable locSumAbs can be derived as in the pseudo code disclosed in the following table.

[0188] [Table 13]

[0189] After that, based on the given variable locSumAbs, the Rice parameter cRiceParam can be derived as shown in the following table.

[0190] [Table 14]

[0191] Also, for example, in the process of deriving the Rice parameter for abs_remainder[n], baseLevel can be set to 4.

[0192] Or, for example, the Rice parameter cRiceParam can be determined based on whether the transformation of the current block can be skipped. That is, when the transformation is not applied to the current TB including the current CG, in other words, when the transform skip is applied to the current TB including the current CG, the Rice parameter cRiceParam can be derived as 1.

[0193]

[0194]

Number

[0195] The suffix string of the bin string of the abs_remainder can be derived by the Limited EGk binary evolution process for the suffixVal where k is set to cRiceParam + 1, riceParam is set to cRiceParam, log2TransformRange is set to 15, and maxPreExtLen is set to 11.

[0196] ​On one hand, for example, among the residual information, the binary process for the syntax element dec_abs_level can be performed as follows.

[0197] The input to the binary process for the dec_abs_level can be the requirement for the binary of the syntax element dec_abs_level[n], the hue component cIdx, the luma position (x0, y0), the current coefficient scan position (xC, yC), the binary logarithm log2TbWidth of the width of the transform block, and the binary logarithm log2TbHeight of the height of the transform block. The luma position (x0, y0) can refer to the upper left sample of the current luma transform block based on the upper left luma sample of the picture.

[0198] The output of the binary process for the dec_abs_level can be the binary of the dec_abs_level (i.e., the binary bit string of the dec_abs_level). Available bit strings, etc. for the dec_abs_level can be derived by the binary process.

[0199] The Rice parameter cRiceParam for the dec_abs_level[n] can be derived through a Rice parameter derivation process that takes the hue component cIdx, the luma position (x0, y0), the current coefficient scan position (xC, yC), the binary logarithm log2TbWidth of the width of the transform block, and the binary logarithm log2TbHeight of the height of the transform block as inputs. A specific description of the Rice parameter derivation process will be given later.

[0200] Also, for example, cMax for the dec_abs_level[n] can be derived based on the Rice parameter cRiceParam. cMax can be derived as follows in the following formula.

[0201]

Number

[0202] On the one hand, the binary evolution for the dec_abs_level[n], that is, the bin string for the dec_abs_level[n], can be the concatenation of a prefix bin string and a suffix bin string if the suffix bin string exists. Also, if the suffix bin string does not exist, the bin string for the dec_abs_level[n] can be the prefix bin string.

[0203] For example, the prefix bin string can be derived as described later.

[0204] The prefix value prefixVal of the dec_abs_level[n] can be derived as in the following formula.

[0205]

Number

[0206] The prefix of the bin string of the dec_abs_level[n] (that is, the prefix bin string) can be derived by the TR binary evolution process for the prefixVal using the cMax and the cRiceParam as inputs.

[0207] If the prefix bin string is the same as a bit string with all bits being 1 and a bit length of 6, the suffix bin string of the bin string of the dec_abs_level[n] may exist and can be derived as described later.

[0208] The process of deriving the Rice parameter for the dec_abs_level[n] can be as follows.

[0209] The input of the process of deriving the Rice parameter can be the hue component index (colour component index) cIdx, the luma position (x0, y0), the current coefficient scan position (xC, yC), the binary logarithm (log2TbWidth) of the width of the transform block, and the binary logarithm (log2TbHeight) of the height of the transform block. The luma position (x0, y0) can refer to the top-left sample of the current luma transform block with reference to the top-left luma sample of the picture. Also, the output of the process of deriving the Rice parameter can be the Rice parameter cRiceParam.

[0210] For example, based on a given component index cIdx and the array AbsLevel[x][y] for a transform block having the top-left luma position (x0, y0), the variable locSumAbs can be derived as in the pseudo code disclosed in the following table.

[0211] [Table 15]

[0212] Thereafter, based on the given variable locSumAbs, the Rice parameter cRiceParam can be derived as in the following table.

[0213] [Table 16]

[0214] Also, for example, in the process of deriving the Rice parameter for dec_abs_level[n], baseLevel can be set to 0, and the ZeroPos[n] can be derived as in the following mathematical formula.

[0215]

Number

[0216] Also, the suffix value suffixVal of the dec_abs_level[n] can be derived as in the following mathematical formula.

[0217]

Number

[0218] The suffix bit string of the bin string of the dec_abs_level[n] can be derived through the Limited EGk binary evolution process for the suffixVal where k is set to cRiceParam + 1, truncSuffixLen is set to 15, and maxPreExtLen is set to 11.

[0219] On the other hand, the aforementioned RRC and TSRC may have the following differences.

[0220] - For example, the Rice parameter for the syntax element abs_remainder[] in TSRC can be derived to be 1. The Rice parameter cRiceParam of the syntax element abs_remainder[] in RRC can be derived based on the lastAbsRemainder and the lastRiceParam as described above, but the Rice parameter cRiceParam of the syntax element abs_remainder[] in TSRC can be derived to be 1. That is, for example, when transform skip is applied to the current block (e.g., the current TB), the Rice parameter cRiceParam for abs_remainder[] of TSRC for the current block can be derived to be 1.

[0221] - Also, for example, referring to Table 3 and Table 4, in RRC, abs_level_gtx_flag[n][0] and / or abs_level_gtx_flag[n][1] can be signaled, while in TSRC, abs_level_gtx_flag[n][0], abs_level_gtx_flag[n][1], abs_level_gtx_flag[n][2], abs_level_gtx_flag[n][3], and abs_level_gtx_flag[n][4] can be signaled. Here, the abs_level_gtx_flag[n][0] can be denoted as abs_level_gt1_flag or the first coefficient level flag, the abs_level_gtx_flag[n][1] can be denoted as abs_level_gt3_flag or the second coefficient level flag, the abs_level_gtx_flag[n][2] can be denoted as abs_level_gt5_flag or the third coefficient level flag, the abs_level_gtx_flag[n][3] can be denoted as abs_level_gt7_flag or the fourth coefficient level flag, and the abs_level_gtx_flag[n][4] can be denoted as abs_level_gt9_flag or the fifth coefficient level flag. Specifically, the first coefficient level flag can be a flag indicating whether the coefficient level is greater than a first critical value (e.g., 1), the second coefficient level flag can be a flag indicating whether the coefficient level is greater than a second critical value (e.g., 3), the third coefficient level flag can be a flag indicating whether the coefficient level is greater than a third critical value (e.g., 5), the fourth coefficient level flag can be a flag indicating whether the coefficient level is greater than a fourth critical value (e.g., 7), and the fifth coefficient level flag can be a flag indicating whether the coefficient level is greater than a fifth critical value (e.g., 9).As described above, in addition to abs_level_gtx_flag[n][0] and abs_level_gtx_flag[n][1], TSRC can further include abs_level_gtx_flag[n][2], abs_level_gtx_flag[n][3], and abs_level_gtx_flag[n][4] compared to RRC.

[0222] - Also, for example, in RRC, the syntax element coeff_sign_flag can be bypass-coded, while in TSRC, the syntax element coeff_sign_flag can be bypass-coded or context-coded.

[0223] On the one hand, this document proposes a method of applying a level mapping technique to a simplified residual data coding structure for conversion skip blocks. Here, a conversion skip block can represent a block to which conversion is not applied. Also, the level mapping technique means a technique in which, when BDPCM (block based quantized residual domain differential pulse-code modulation) is not applied to the current block (e.g., CU), the absolute coefficient level, i.e., absCoeffLevel, is mapped to a modified level coded by a method based on the (quantized) left residual sample and the upper residual sample of the current residual sample (i.e., the current residual coefficient). Under certain conditions such as lossless coding or near-lossless coding, a simplified residual data coding structure can be used for an entire coding block or conversion block, or for some subblocks / coefficient groups (CG). Or, in the proposed method, the number of context coded bins, etc., used for residual (data) coding within one TU (Transform Unit, TU) can be limited to a specific threshold, and when all the context coded bins used for the residual coding of the TU are exhausted (i.e., when the number of context coded bins for the residual coding of the TU becomes the same as the specific threshold), the simplified residual data coding structure can be used.

[0224] FIG. 6 shows an example of simplified residual data coding for one CG, transform block, or coding block. Syntax elements such as sig_coeff_flag, coeff_sign_flag, and abs_remainder can be coded in the simplified residual coding. Syntax elements for the residual coefficients within the CG, the transform block, or the coding block can be coded in the order from top to bottom as shown in FIG. 6. That is, syntax elements for the residual coefficients within the CG, the transform block, or the coding block can be coded in the order of sig_coeff_flag, coeff_sign_flag, and abs_remainder.

[0225] The sig_coeff_flag can represent a syntax element for the valid coefficient flag. The sig_coeff_flag can indicate whether the residual coefficient of the current block (CG, transform block, or coding block) is a non-zero residual coefficient. For example, the sig_coeff_flag can have a value of 0 when the value of the residual coefficient at that position is 0, and a value of 1 when it is not 0. Also, the coeff_sign_flag can represent a syntax element for the sign flag of the residual coefficient. The sig_coeff_flag can indicate the sign of the residual coefficient. For example, the coeff_sign_flag can mean the sign value of the residual coefficient at that position. There can be various ways to apply the coeff_sign_flag. For example, when the residual coefficient at that position is 0, i.e., when the value of the sig_coeff_flag for the residual coefficient is 0, the coeff_sign_flag may not be coded. For a non-zero residual coefficient, when the residual coefficient is negative, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is positive, the coeff_sign_flag can have a value of 0 (or 1). Or, regardless of the value of the sig_coeff_flag of the residual coefficient, when the residual coefficient is negative, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is positive or 0, the coeff_sign_flag can have a value of 0 (or 1). Or, when the residual coefficient is positive, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is negative or 0, the coeff_sign_flag can have a value of 0 (or 1). Also, the abs_remainder can represent a syntax element for the residual level value information or coefficient value related information.For example, the abs_remainder can mean the residual level value. For example, when the value of sig_coeff_flag for the residual coefficient is 0, the abs_remainder for the residual coefficient may not be coded, and when the value of sig_coeff_flag for the residual coefficient is 1, the abs_remainder can have a value obtained by subtracting 1 from the absolute value of the residual coefficient (absolute value - 1).

[0226] On the other hand, when regular residual coding is executed and specific conditions are satisfied, it can be converted to the simplified residual data coding shown in FIG. 6. For example, the specific conditions can be used when the residual information of the coding block is lossless or near-lossless coded, and / or when all the context coding bins that can be used when the TU-level context coding bin constraint algorithm is applied are exhausted, etc.

[0227] FIG. 7 shows another example of simplified residual data coding for one CG, transform block or coding block. Syntax elements such as dec_abs_level and coeff_sign_flag can be coded with the simplified residual coding. The syntax elements for the residual coefficients within the CG, the transform block or the coding block can be coded in the order from top to bottom as shown in FIG. 7. That is, the syntax elements for the residual coefficients within the CG, the transform block or the coding block can be coded in the order of dec_abs_level and coeff_sign_flag.

[0228] As shown in FIG. 7, the dec_abs_level can represent a syntax element for coefficient value related information, and the coeff_sign_flag can represent a syntax element for the sign flag of the residual coefficient. For example, according to the structure shown in FIG. 7, when the residual coefficient is 0, the value of dec_abs_level can be 0, and when the residual coefficient is not 0, the value of dec_abs_level can be the absolute value of the residual coefficient. Also, for example, the coeff_sign_flag can mean the sign value of the residual coefficient at that position. There can be various ways to apply the coeff_sign_flag. For example, when the residual coefficient at that position is 0, the coeff_sign_flag may not be coded. For a non-zero residual coefficient, when the residual coefficient is negative, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is positive, the coeff_sign_flag can have a value of 0 (or 1). Or, regardless of the dec_abs_level of the residual coefficient, it can always be coded. When the residual coefficient is negative, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is positive or 0, the coeff_sign_flag can have a value of 0 (or 1). Or, when the residual coefficient is positive, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is negative or 0, the coeff_sign_flag can have a value of 0 (or 1).

[0229] On the other hand, when specific conditions are met even when regular residual coding is performed, it can be converted to the simplified residual data coding shown in FIG. 7. For example, the specific conditions can be when the residual information of the coding block is lossless or near-lossless coded, and / or when all the context coding bins used when the TU-level context coding bin constraint algorithm is applied are exhausted.

[0230] FIG. 8 shows another example of simplified residual data coding for one CG, transform block, or coding block. Syntax elements such as coeff_sign_flag and dec_abs_level can be coded with the simplified residual coding. The syntax elements for the residual coefficients within the CG, the transform block, or the coding block can be coded in order from top to bottom as shown in FIG. 8. That is, the syntax elements for the residual coefficients within the CG, the transform block, or the coding block can be coded in the order of coeff_sign_flag, dec_abs_level.

[0231] As shown in FIG. 8, the coeff_sign_flag can represent a syntax element for the sign flag of the residual coefficient, and the dec_abs_level can represent a syntax element for coefficient value-related information. For example, when the residual coefficient at the position to be coded is negative, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is positive or 0, the coeff_sign_flag can have a value of 0 (or 1). Or, for example, when the residual coefficient is positive, the coeff_sign_flag can have a value of 1 (or 0), and when the residual coefficient is negative or 0, the coeff_sign_flag can have a value of 0 (or 1).

[0232] On the other hand, when regular residual coding is executed and certain conditions are met, it can be converted to the simplified residual data coding shown in FIG. 8. For example, the certain conditions can be used when the residual information of the coding block is lossless or near-lossless coded, and / or when all the context coding bins that can be used when the TU-level context coding bin constraint algorithm is applied are exhausted, etc.

[0233] On the one hand, as described above, a level mapping technique for the conversion skip mode can be used. For example, in the level mapping technique, the value of abs_level_gtx_flag[0] can be used as a value indicating whether level mapping is possible. That is, whether level mapping is possible can be determined based on the value of abs_level_gtx_flag[0]. Therefore, in a simplified residual data coding structure in which abs_level_gtx_flag[0] is not coded, decoding for the residual coefficients to which level mapping is applied cannot be accurately performed. Therefore, this document proposes a solution that does not use level mapping for coding blocks, conversion blocks, coefficient groups, and / or residual coefficients to which simplified residual data coding is applied so that the simplified residual data coding structure of FIG. 6, FIG. 7, or FIG. 8 and level mapping can be used together. According to an embodiment of this document, the simplified residual data coding structure and level mapping can be combined without problems in the residual coding for the conversion skip block.

[0234] For example, within one coding block, the residual data coding method for the conversion skip block shown in Table 4 and the simplified residual data coding method described above can be mixed. When the residual data coding for the conversion skip block is applied, the level mapping technique shown in Table 4 above can be applied as it is. When the simplified residual data coding is applied, the level mapping technique can be applied.

[0235] Tables 17 and 18 described later exemplarily show the syntax to which the embodiment proposed in this document is applied.

[0236]

Table 17

[0237]

Table 18

[0238] The above Table 17 can represent a syntax structure that prevents level mapping from being executed when all the context coding bins (where MaxCcbs represents the number of context coding bins that can be used) that can be used when the context coding bin constraint algorithm is applied are exhausted and converted into a simplified residual data coding structure. Also, the above Table 18 can represent a syntax structure to which the method proposed in this document is applied when a simplified residual data coding structure is used for the lossless coding block. Here, for example, the transquant_bypass_flag shown in Table 18 can be a syntax element indicating whether lossless coding is possible. The transquant_bypass_flag can be signaled at the CU or TU or picture level.

[0239] On the one hand, the aforementioned Tables 17 and 18 are merely examples to which the embodiments proposed in this document are applied and are not limited thereto. In this document, as an embodiment, when a simplified residual data coding structure is executed, a part for correcting the encoded / decoded levels is not executed in order to encode / decode the level-mapped residual coefficients. That is, for example, when all the context coding bins for the current block are used, the residual coefficients of the current block are not derived through level mapping, and a scheme for deriving them with a simplified residual data coding structure can be proposed. The simplified residual data coding structure can be as described above. For example, when all the context coding bins for the current block are used, the residual coefficients can be derived based on the value of the information representing the absolute value and the sign information. Also, for example, the aforementioned Table 4 can represent an example to which the embodiments proposed in this document are applied.

[0240] FIG. 9 schematically shows an image encoding method by an encoding apparatus according to this document. The method disclosed in FIG. 9 can be executed by the encoding apparatus disclosed in FIG. 2. Specifically, for example, S900 in FIG. 9 can be executed by the residual processing unit of the encoding apparatus, and S910 can be executed by the entropy encoding unit of the encoding apparatus. Also, although not shown, the process of deriving a prediction sample can be executed by the prediction unit of the encoding apparatus, the process of deriving a residual sample for the current block based on the original sample and the prediction sample for the current block can be executed by the subtraction unit of the encoding apparatus, and the process of generating a restored sample and a restored picture for the current block based on the residual sample and the prediction sample for the current block can be executed by the addition unit of the encoding apparatus.

[0241] The encoding apparatus derives a current residual coefficient for the current block (S900).

[0242] Specifically, for example, the encoding device can determine whether to perform inter prediction or intra prediction on the current block, and can determine a specific inter prediction mode or a specific intra prediction mode based on the RD cost. According to the determined mode, the encoding device can derive a prediction sample for the current block, and can derive the residual sample through subtraction of the original sample for the current block and the prediction sample.

[0243] Thereafter, for example, the encoding device can derive the current residual coefficient of the current block based on the residual sample. For example, the encoding device can determine whether transformation is to be applied to the current block. That is, the encoding device can determine whether transformation is to be applied to the residual sample of the current block. The encoding device can determine whether to apply transformation to the current block in consideration of the coding efficiency. For example, the encoding device can determine that transformation is not to be applied to the current block. A block to which the transformation is not applied can be indicated as a transformation skip block. That is, for example, the current block can be a transformation skip block.

[0244] If no transformation is applied to the current block, i.e., if no transformation is applied to the residual samples, the encoding device can derive the derived residual samples as the current residual coefficients. Also, if a transformation is applied to the current block, i.e., if a transformation is applied to the residual samples, the encoding device can execute the transformation on the residual samples to derive the current residual coefficients. The current residual coefficients can be included in the current sub-block of the current block. The current sub-block can be referred to as the current CG (coefficient group). Also, the size of the current sub-block of the current block can be 4×4 size or 2×2 size. That is, the current sub-block of the current block can include up to 16 non-zero residual coefficients or up to 4 non-zero residual coefficients.

[0245] Here, the current block can be a coding block (CB) or a transform block (TB). Also, the residual coefficient can be denoted as the transform coefficient.

[0246] On the one hand, for example, the current residual coefficient can be derived without performing level mapping. For example, among the residual coefficients of the current block, the number of context-coded residual syntax elements, etc. for the residual coefficients prior to the current residual coefficient can be the same as the number of context-coded bins (context coded bins) of the current block, and the residual syntax element for the current residual coefficient can include absolute level information for the current residual coefficient and the sign flag of the residual coefficient. The current residual coefficient can be derived without performing level mapping. Here, deriving the current residual coefficient only based on the absolute level information and the sign flag can be referred to as simplified residual data coding. That is, the residual coefficient can be derived based on simplified residual data coding. Also, for example, the context-coded bins for the current block can be entirely used as bins such as context-coded residual syntax elements for the residual coefficients prior to the current residual coefficient among the residual coefficients of the current block. The residual syntax element for the current residual coefficient can include coefficient level information for the current residual coefficient and the sign flag of the residual coefficient, and the current residual coefficient can be derived without performing level mapping.For example, when all of the context coded bins for the current block with respect to the residual syntax elements such as the previous residual coefficient of the current residual coefficient in the scanning order are used, the residual syntax elements for the current residual coefficient can include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient, and the current residual coefficient can be derived without performing level mapping.

[0247] On the other hand, for example, the level mapping can indicate a scheme shown in Table 19 described later.

[0248]

Table 19

[0249] Here, X0 can represent the left absolute coefficient level of the current residual coefficient (i.e., the coefficient level of the left residual sample (left residual coefficient)), and X1 can represent the upper absolute coefficient level (i.e., the coefficient level of the upper residual sample (upper residual coefficient)). Also, absCoeff can represent the absolute level coefficient of the current residual coefficient, and absCoeffMod can represent the level mapped through the aforementioned process.

[0250] For example, the level mapping can mean a process of deriving the maximum value among the absolute level of the left residual coefficient of the residual coefficient and the absolute level of the upper residual coefficient of the residual coefficient, comparing the maximum value with the absolute level of the residual coefficient, and correcting the absolute level of the residual coefficient based on the maximum value.

[0251] The encoding device encodes image information including a residual syntax element or the like for the current residual coefficient (S910). The encoding device can encode image information including a residual syntax element or the like for the current residual coefficient of the current block. The encoding device can encode residual information including a residual syntax element or the like for the current residual coefficient of the current block. The image information can include the residual information. For example, the encoding device can encode the image information including the residual information and output it in the form of a bitstream. The bitstream can be transmitted to the decoding device via a network or a recording medium.

[0252] Also, for example, among the residual coefficients or the like of the current block, the number of context-coded residual syntax elements or the like for the residual coefficients or the like before the current residual coefficient can be the same as the number of context coded bins or the like of the current block. That is, for example, the context coded bins or the like for the current block can be all used as the bins or the like of the context-coded residual syntax elements or the like for the residual coefficients or the like before the current residual coefficient among the residual coefficients or the like of the current block. In other words, for example, the number of context coded bins or the like for the current block can be all used for the residual syntax elements or the like for the residual coefficients or the like before the current residual coefficient in the scanning order. On the other hand, for example, the number of context coded bins or the like of the current block can be derived based on the width and height of the current block.

[0253] For example, among the residual coefficients of the current block, etc., the number of context-coded residual syntax elements, etc. for the residual coefficients, etc. before the current residual coefficient may be the same as the number of context coded bins of the current block, and the residual syntax elements, etc. for the current residual coefficient may include absolute level information for the current residual coefficient and a sign flag of the residual coefficient. For example, all of the context coded bins for the current block may be used as bins, etc. of the context-coded residual syntax elements, etc. for the residual coefficients, etc. before the current residual coefficient among the residual coefficients, etc. of the current block, and the residual syntax elements, etc. for the current residual coefficient may include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient. For example, when the number of context coded bins for the current block is all used for the residual syntax elements, etc. for the residual coefficients, etc. before the current residual coefficient in the scanning order, the residual syntax elements, etc. for the current residual coefficient may include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient. The residual syntax elements, etc. for the current residual coefficient can be encoded based on bypass. That is, the residual syntax elements, etc. for the current residual coefficient can be encoded based on a uniform probability distribution. For example, the coefficient level information can represent the absolute value of the coefficient level of the current residual coefficient. Also, the sign flag can represent the sign of the current residual coefficient.For example, when the value of the sign flag is 0, the sign flag can indicate that the coefficient level of the current residual coefficient is a positive value. When the value of the sign flag is 1, the sign flag can indicate that the coefficient level of the current residual coefficient is a negative value. The coefficient level information can be the aforementioned abs_remainder, and the sign flag can be the aforementioned coeff_sign_flag.

[0254] Also, for example, the residual information can include a transform skip flag for the current block with respect to the current block. The transform skip flag can indicate whether transformation can be applied to the current block. That is, the transform skip flag can indicate whether transformation has been applied to the residual coefficients of the current block. The syntax element representing the transform skip flag can be the aforementioned transform_skip_flag. For example, when the value of the transform skip flag is 0, the transform skip flag can indicate that transformation is not applied to the current block. When the value of the transform skip flag is 1, the transform skip flag can indicate that transformation has been applied to the current block. For example, when the current block is a transform skip block, the value of the transform skip flag for the current block can be 1.

[0255] Also, for example, the encoding device can generate residual information of the current block based on the residual sample of the current block or the like. For example, the image information can include residual information for the current block. For example, the residual information can include a residual syntax element or the like for a residual coefficient before the current residual coefficient in the scanning order. For example, the residual syntax element or the like can include syntax elements such as coded_sub_block_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder, and / or coeff_sign_flag.

[0256] For example, the context-coded residual syntax element etc. can include a valid coefficient flag indicating whether the residual coefficient is a non-zero residual coefficient, a parity level flag for the parity of the coefficient level for the residual coefficient, a sign flag representing the sign for the residual coefficient, a first coefficient level flag indicating whether the coefficient level is greater than a first critical value, and / or a second coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a second critical value. Also, for example, the context-coded residual syntax element etc. can include a third coefficient level flag indicating whether the coefficient level is greater than a third critical value, a fourth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fourth critical value, and / or a fifth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fifth critical value. Here, the valid coefficient flag can be sig_coeff_flag, the parity level flag can be par_level_flag, the sign flag can be ceff_sign_flag, the first coefficient level flag can be abs_level_gt1_flag, and the second coefficient level flag can be abs_level_gt3_flag or abs_level_gtx_flag. Also, the third coefficient level flag can be abs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient level flag can be abs_level_gt7_flag or abs_level_gtx_flag, and the fifth coefficient level flag can be abs_level_gt9_flag or abs_level_gtx_flag.

[0257] Also, for example, the residual information can include syntax elements coded on a bypass basis for the residual coefficient of the current block. The syntax element coded by bypass coding can include coefficient level information for the value of the current residual coefficient. The coefficient level information can be abs_remainder and / or dec_abs_level. Also, the syntax element coded by bypass coding can include the sign flag.

[0258] Also, for example, the encoding device can generate prediction information for the current block with respect to the current block. The image information can include prediction information for the current block. The prediction information can include information for an inter prediction mode or an intra prediction mode executed on the current block. The decoding device can execute an inter prediction or an intra prediction for the current block based on the prediction information received via the bitstream, and can derive prediction samples and the like of the current block.

[0259] On the other hand, the bitstream can be transmitted to the decoding device via a network or a (digital) recording medium. Here, the network can include a broadcast network and / or a communication network, etc., and the digital recording medium can include various recording media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc.

[0260] FIG. 10 schematically shows an encoding apparatus that executes the image encoding method according to this document. The method disclosed in FIG. 9 can be executed by the encoding apparatus disclosed in FIG. 10. Specifically, for example, the residual processing unit of the encoding apparatus in FIG. 10 can execute S900 in FIG. 9, and the entropy encoding unit of the encoding apparatus in FIG. 10 can execute S910 in FIG. 9. Also, although not shown, the process of deriving a prediction sample can be executed by the prediction unit of the encoding apparatus, and the process of deriving a residual sample for the current block based on the original sample and the prediction sample for the current block can be executed by the subtraction unit of the encoding apparatus, and the process of generating a restored sample and a restored picture for the current block based on the residual sample and the prediction sample for the current block can be executed by the addition unit of the encoding apparatus.

[0261] FIG. 11 schematically shows an image decoding method by the decoding apparatus according to this document. The method disclosed in FIG. 11 can be executed by the decoding apparatus disclosed in FIG. 3. Specifically, for example, S1100 in FIG. 11 can be executed by the entropy decoding unit of the decoding apparatus, S1110 in FIG. 11 can be executed by the residual processing unit of the decoding apparatus, and S1120 can be executed by the addition unit of the decoding apparatus. Also, although not shown, the process of receiving prediction information for the current block can be executed by the entropy decoding unit of the decoding apparatus, and the process of deriving a prediction sample for the current block can be executed by the prediction unit of the decoding apparatus.

[0262] The decoding device acquires image information including a residual syntax element or the like for a current residual coefficient within a current block (S1100). The decoding device can acquire image information including residual information for the current block via a bitstream. For example, the decoding device can acquire image information including a residual syntax element or the like for a current residual coefficient within a current block. Also, for example, the decoding device can acquire image information including a residual syntax element or the like for residual coefficients or the like within a current block. The residual information can include a residual syntax element or the like for the residual coefficients or the like. Here, the current block can be a coding block (CB) or a transform block (TB). Also, a residual coefficient can also be referred to as a transform coefficient.

[0263] Also, for example, the current block can be a transform skip block.

[0264] Also, for example, among the residual coefficients of the current block, the number of context-coded residual syntax elements, etc. for the residual coefficients before the current residual coefficient may be the same as the number of context coded bins, etc. of the current block, and the residual syntax elements, etc. for the current residual coefficient may include absolute level information for the current residual coefficient and a sign flag of the residual coefficient. The number of context coded bins, etc. of the current block can be derived based on the width and height of the current block. For example, the context coded bins, etc. for the current block can be all used as bins, etc. of the context-coded residual syntax elements, etc. for the residual coefficients before the current residual coefficient among the residual coefficients of the current block, and the residual syntax elements, etc. for the current residual coefficient may include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient. For example, when the number of context coded bins, etc. of the current block is all used for the residual syntax elements, etc. for the residual coefficients before the current residual coefficient in the scanning order, the residual syntax elements, etc. for the current residual coefficient may include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient. The residual syntax elements, etc. for the current residual coefficient can be decoded based on bypass. That is, the residual syntax elements, etc. for the current residual coefficient can be decoded based on a uniform probability distribution. For example, the coefficient level information can represent the absolute value of the coefficient level of the current residual coefficient. Also, the sign flag can represent the sign of the current residual coefficient.For example, when the value of the sign flag is 0, the sign flag can indicate that the coefficient level of the current residual coefficient is a positive value, and when the value of the sign flag is 1, the sign flag can indicate that the coefficient level of the current residual coefficient is a negative value. The coefficient level information can be the aforementioned abs_remainder, and the sign flag can be the aforementioned coeff_sign_flag.

[0265] Also, for example, the residual information can include a transform skip flag for the current block with respect to the current block. The transform skip flag can indicate whether transformation can be applied to the current block. That is, the transform skip flag can indicate whether transformation has been applied to the residual coefficients, etc. of the current block. The syntax element representing the transform skip flag can be the aforementioned transform_skip_flag. For example, when the value of the transform skip flag is 0, the transform skip flag can indicate that transformation is not applied to the current block, and when the value of the transform skip flag is 1, the transform skip flag can indicate that transformation has been applied to the current block. For example, when the current block is a transform skip block, the value of the transform skip flag for the current block can be 1.

[0266] Further, for example, the image information can include residual information for the current block. For example, the residual information can include residual syntax elements, etc. for residual coefficients before the current residual coefficient in the scanning order. For example, the residual syntax elements, etc. can include syntax elements such as coded_sub_block_flag, sig_coeff_flag, coeff_sign_flag, abs_level_gt1_flag, par_level_flag, abs_level_gtX_flag, abs_remainder and / or coeff_sign_flag.

[0267] For example, the context-coded residual syntax element or the like can include a valid coefficient flag indicating whether the residual coefficient is a non-zero residual coefficient, a parity level flag for the parity of the coefficient level with respect to the residual coefficient, a sign flag representing the sign of the residual coefficient, a first coefficient level flag indicating whether the coefficient level is greater than a first critical value, and / or a second coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a second critical value. Also, for example, the context-coded residual syntax element or the like can include a third coefficient level flag indicating whether the coefficient level is greater than a third critical value, a fourth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fourth critical value, and / or a fifth coefficient level flag indicating whether the coefficient level of the residual coefficient is greater than a fifth critical value. Here, the valid coefficient flag can be sig_coeff_flag, the parity level flag can be par_level_flag, the sign flag can be ceff_sign_flag, the first coefficient level flag can be abs_level_gt1_flag, and the second coefficient level flag can be abs_level_gt3_flag or abs_level_gtx_flag. Also, the third coefficient level flag can be abs_level_gt5_flag or abs_level_gtx_flag, the fourth coefficient level flag can be abs_level_gt7_flag or abs_level_gtx_flag, and the fifth coefficient level flag can be abs_level_gt9_flag or abs_level_gtx_flag.

[0268] Also, for example, the residual information can include syntax elements coded on a bypass basis for the residual coefficient of the current block. The syntax element coded by bypass coding can include coefficient level information for the value of the current residual coefficient. The coefficient level information can be abs_remainder and / or dec_abs_level. Also, the syntax element coded by bypass coding can include the sign flag.

[0269] On the other hand, the image information can include prediction information for the current block. The prediction information can include information for an inter prediction mode or an intra prediction mode executed on the current block. The decoding device can execute inter prediction or intra prediction for the current block based on the prediction information received via the bitstream, and can derive prediction samples of the current block and the like.

[0270] The decoding device derives the current residual coefficient based on the residual syntax element or the like (S1110). The decoding device can derive the current residual coefficient based on the residual syntax element or the like.

[0271] For example, the absolute level of the current residual coefficient can be derived as the value represented by the coefficient level information for the current residual coefficient, and the sign of the current residual coefficient can be derived as the sign represented by the sign flag.

[0272] On the one hand, for example, the current residual coefficient can be derived without performing level mapping. For example, among the residual coefficients of the current block, etc., the number of context-coded residual syntax elements, etc. for the residual coefficients before the current residual coefficient can be the same as the number of context coded bins of the current block, etc., and the residual syntax elements, etc. for the current residual coefficient can include absolute level information for the current residual coefficient and the sign flag of the residual coefficient, and the current residual coefficient can be derived without performing level mapping. Here, deriving the current residual coefficient only from the absolute level information and the sign flag can be referred to as simplified residual data coding. That is, the residual coefficient can be derived based on simplified residual data coding. Also, for example, all of the context coded bins, etc. for the current block can be used as bins, etc. of the context-coded residual syntax elements, etc. for the residual coefficients before the current residual coefficient among the residual coefficients of the current block, and the residual syntax elements, etc. for the current residual coefficient can include coefficient level information for the current residual coefficient and the sign flag of the residual coefficient, and the current residual coefficient can be derived without performing level mapping.For example, when all the numbers of context coded bins for the current block, etc. with respect to the residual syntax element of the current residual coefficient with respect to the previous residual coefficient in the scanning order are used, the residual syntax element, etc. for the current residual coefficient can include coefficient level information for the current residual coefficient and a sign flag of the residual coefficient, and the current residual coefficient can be derived without performing level mapping. Also, for example, the residual coefficient, etc. before the current residual coefficient can be derived by performing the level mapping.

[0273] On the other hand, for example, the level mapping can show the scheme shown in Table 19 above. For example, the level mapping can mean a process of deriving the maximum value among the absolute level of the left residual coefficient of the residual coefficient and the absolute level of the upper residual coefficient of the residual coefficient, comparing the maximum value with the absolute level of the residual coefficient, and correcting the absolute level of the residual coefficient based on the maximum value.

[0274] The decoding device derives the restored samples of the current block based on the current residual coefficient (S1120).

[0275] The decoding device can derive the residual samples of the current block based on the current residual coefficients. That is, the decoding device can derive the residual samples of the current block based on the current residual coefficients. As an example, when it is derived that no transformation is applied to the current block based on the transform skip flag, that is, when the value of the transform skip flag is 1, the decoding device can derive the current residual coefficients as the residual samples of the current block. Or, for example, when it is derived that no transformation is applied to the current block based on the transform skip flag, that is, when the value of the transform skip flag is 1, the decoding device can inverse-quantize the current residual coefficients to derive the residual samples of the current block. Or, for example, when it is derived that a transformation is applied to the current block based on the transform skip flag, that is, when the value of the transform skip flag is 0, the decoding device can inverse-transform the current residual coefficients to derive the residual samples of the current block. Or, for example, when it is derived that a transformation is applied to the current block based on the transform skip flag, that is, when the value of the transform skip flag is 0, the decoding device can inverse-quantize the current residual coefficients and inverse-transform the inverse-quantized coefficients to derive the residual samples of the current block.

[0276] Also, for example, the decoding device can derive the restored samples of the current block based on the residual samples. For example, the decoding device can execute an inter prediction mode or an intra prediction mode for the current block based on the prediction information received via the bitstream to derive prediction samples, and can generate the restored samples through the addition of the prediction samples and the residual samples. Also, for example, the prediction information can include information representing the intra prediction mode of the current block. The decoding device can derive the intra prediction mode of the current block based on the information representing the intra prediction mode of the current block, and can derive the prediction samples of the current block based on the reference samples, etc. of the current block and the intra prediction mode. The reference samples, etc. can include the upper reference samples, etc. and the left reference samples, etc. of the current block. For example, when the size of the current block is N×N and the x component of the top-left sample position of the current block is 0 and the y component is 0, the left reference samples, etc. can be p[-1][0] to p[-1][2N-1], and the upper reference samples, etc. can be p[0][-1] to p[2N-1][-1].

[0277] Thereafter, if necessary, in order to improve the subjective / objective image quality, loop filtering procedures such as deblocking filtering, SAO, and / or ALF procedures can be applied to the restored picture as described above.

[0278] FIG. 12 schematically shows a decoding apparatus that executes the image decoding method according to this document. The method disclosed in FIG. 11 can be executed by the decoding apparatus disclosed in FIG. 12. Specifically, for example, the entropy decoding unit of the decoding apparatus in FIG. 12 can execute S1100 in FIG. 11, the residual processing unit of the decoding apparatus in FIG. 12 can execute S1110 in FIG. 11, and the addition unit of the decoding apparatus in FIG. 12 can execute S1120 in FIG. 11. Although not shown, the process of deriving the prediction sample can be executed by the prediction unit of the decoding apparatus in FIG. 12.

[0279] As described above regarding this document, the efficiency of residual coding can be improved.

[0280] Also, according to this document, the residual coefficient to which the simplified residual data coding is applied can be derived without performing level mapping, reducing the coding complexity and improving the overall residual coding efficiency.

[0281] Also, according to this document, the residual coefficient to which the simplified residual data coding is applied may have a low correlation with the surrounding residual coefficients. Therefore, the efficiency of the level mapping executed based on the surrounding residual coefficients is low, and the level mapping is not executed for the residual coefficient to which the simplified residual data coding is applied, thereby reducing the coding complexity and improving the overall residual coding efficiency.

[0282] In the foregoing embodiments, the method is described based on a flowchart in a series of steps or blocks, but this document is not limited to the order of the steps, and certain steps can occur in a different order or simultaneously with steps different from those described above. Also, those skilled in the art can understand that the steps shown in the flowchart are not exclusive, other steps can be included, or one or more steps of the flowchart can be deleted without affecting the scope of this document.

[0283] The embodiments described in this document can be implemented and executed on a processor, microprocessor, controller, or chip. For example, the functional units illustrated in each drawing can be implemented and executed on a computer, processor, microprocessor, controller, or chip. In this case, information for implementation (e.g., information on instructions) or algorithms can be stored on a digital recording medium.

[0284] Also, the decoding device and encoding device to which the embodiments of this document are applied can be included in multimedia broadcast transmission / reception devices, mobile communication terminals, home cinema video devices, digital cinema video devices, surveillance cameras, video conferencing devices, real-time communication devices such as video communication, mobile streaming devices, recording media, camcorders, video-on-demand (VoD) service providing devices, over-the-top (OTT) video devices, Internet streaming service providing devices, three-dimensional (3D) video devices, picture phone video devices, transportation means terminals (e.g., vehicle terminals, airplane terminals, ship terminals, etc.), and medical video devices, etc., and can be used to process video signals or data signals. For example, as an over-the-top (OTT) video device, it can be equipped with a game console, Blu-ray player, Internet-connected TV, home theater system, smartphone, tablet PC, digital video recorder (DVR), etc.

[0285] In addition, the processing method to which the embodiments of this document are applied can be produced in the form of a program executed by a computer and can be stored in a computer-readable recording medium. Multimedia data having the data structure according to this document can also be stored in a computer-readable recording medium. The computer-readable recording medium includes all types of storage devices and distributed storage devices in which data that can be read by a computer is stored. The computer-readable recording medium can include, for example, Blu-ray Disc (BD), Universal Serial Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy (registered trademark) disk, and optical data storage devices. In addition, the computer-readable recording medium includes a medium realized in the form of a carrier wave (for example, transmission via the Internet). Also, a bitstream generated by an encoding method can be stored in a computer-readable recording medium or transmitted via a wired or wireless communication network.

[0286] In addition, the embodiments of this document can be realized by a computer program product with program code, and the program code can be executed by a computer according to the embodiments of this document. The program code can be stored on a carrier readable by a computer.

[0287] FIG. 13 exemplarily shows a structural diagram of a content streaming system to which the embodiments of this document are applied.

[0288] The content streaming system to which the embodiments of this document are applied can generally include an encoding server, a streaming server, a web server, a media repository, a user device, and a multimedia input device.

[0289] The encoding server compresses the content input from a multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream, and serves to transmit this to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, camcorder, etc. directly generates a bitstream, the encoding server can be omitted.

[0290] The bitstream can be generated by an encoding method or a bitstream generation method to which the embodiments of this document are applied, and the streaming server can temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0291] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server serves as a medium to inform the user of what services are available. When the user requests a desired service from the web server, the web server transmits this to the streaming server, and the streaming server transmits multimedia data to the user. At this time, the content streaming system can include another control server, and in this case, the control server serves to control commands / responses between each device within the content streaming system.

[0292] The streaming server can receive content from a media repository and / or an encoding server. For example, when it comes to receiving content from the encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0293] Examples of the user device include a mobile phone, smartphone, laptop computer, digital broadcast terminal, PDA (personal digital assistants), PMP (portable multimedia player), navigation device, slate PC, tablet PC, ultrabook, wearable device (e.g., smartwatch, smart glass, head mounted display (HMD)), digital TV, desktop computer, digital signage, etc. Each server in the content streaming system can be operated as a distributed server, and in this case, the data received by each server can be processed distributively.

[0294] The claims described in this specification can be combined in various ways. For example, the technical features of the method claims in this specification can be combined and implemented as a device, and the technical features of the device claims in this specification can be combined and implemented as a method. Also, the technical features of the method claims in this specification and the technical features of the device claims can be combined and implemented as a device, and the technical features of the method claims in this specification and the technical features of the device claims can be combined and implemented as a method.

Claims

1. In an image decoding method executed by a decoding device, a step of obtaining image information including a residual syntax element for a current residual coefficient in a current block; a step of deriving the current residual coefficient based on the residual syntax element; a step of deriving a restored sample of the current block based on the current residual coefficient, wherein, among the residual coefficients of the current block, the number of context-coded residual syntax elements for residual coefficients before the current residual coefficient is equal to the maximum number of context coding bins of the current block; the residual syntax element for the current residual coefficient includes coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient; the absolute level of the current residual coefficient is derived as a value indicated by the coefficient level information for the current residual coefficient; the sign of the current residual coefficient is derived as a sign indicated by the sign flag; at least one of the residual coefficients before the current residual coefficient is derived based on level mapping, but the current residual coefficient is derived without performing the level mapping; The level mapping for a target residual coefficient is performed based on the absolute level of the left residual coefficient of the target residual coefficient and the absolute level of the upper residual coefficient of the target residual coefficient. An image decoding method.

2. The image decoding method according to claim 1, wherein all of the context coding bins for the current block are used as bins of the context-coded residual syntax elements for the residual coefficients before the current residual coefficient.

3. In an image encoding method executed by an encoding device, a step of deriving a current residual coefficient for a current block; a step of encoding image information including a residual syntax element for the current residual coefficient. Among the residual coefficients of the current block, the number of context-coded residual syntax elements for the residual coefficients before the current residual coefficient is equal to the maximum number of context coding bins of the current block. The residual syntax element for the current residual coefficient includes coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient. The coefficient level information represents the absolute level of the current residual coefficient. The sign flag of the current residual coefficient represents the sign of the current residual coefficient. At least one of the residual coefficients before the current residual coefficient is encoded based on level mapping, while the current residual coefficient is encoded without performing the level mapping. The level mapping for a target residual coefficient is performed based on the absolute level of the left residual coefficient of the target residual coefficient and the absolute level of the upper residual coefficient of the target residual coefficient. An image encoding method.

4. All of the context coding bins for the current block are used as bins for the context-coded residual syntax elements for the residual coefficients before the current residual coefficient. The image encoding method according to claim 3.

5. A method for transmitting data for an image, Deriving a current residual coefficient for a current block; Encoding image information including a residual syntax element for the current residual coefficient to generate a bitstream; Transmitting the data including the bitstream. The method includes: Among the residual coefficients of the current block, the number of context-coded residual syntax elements for the residual coefficients before the current residual coefficient is equal to the maximum number of context coding bins of the current block. The residual syntax element for the current residual coefficient includes coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient. The coefficient level information represents the absolute level of the current residual coefficient. The sign flag of the current residual coefficient represents the sign of the current residual coefficient, At least one of the residual coefficients before the current residual coefficient is encoded based on a level mapping, while the current residual coefficient is encoded without performing the level mapping, The level mapping for a target residual coefficient is performed based on the absolute level of the left residual coefficient of the target residual coefficient and the absolute level of the upper residual coefficient of the target residual coefficient, a transmission method.

Images