WO2024262883A1 - Image encoding/decoding method and apparatus, and recording medium for storing bitstream - Google Patents

Abstract

Provided are an image encoding/decoding method and apparatus, a recording medium for storing a bitstream, and a transmission method. The image decoding method comprises the steps of: obtaining, from a bitstream, a bin string corresponding to a syntax element, wherein the syntax element represents a combination of an intra prediction mode of the current block and a reference sample line used for intra prediction; obtaining the syntax element by inverse-binarizing the bin string; and performing intra prediction on the current block on the basis of the syntax element, wherein at least some bins of the bin string are obtained by means of bypass decoding, and bins other than bypass-coded bins of the bin string may be bins obtained by means of arithmetic decoding.

Description

Video encoding/decoding method, device and recording medium storing bitstream

The present invention relates to a video encoding/decoding method, a device, and a recording medium storing a bitstream. Specifically, the present invention relates to a video encoding/decoding method, a device, and a recording medium storing a bitstream for a syntax element used in template-based multiple reference line (TMRL) intra prediction.

Recently, the demand for high-resolution, high-quality images such as UHD (Ultra High Definition) images is increasing in various application fields. As image data becomes higher in resolution and quality, the amount of data increases relatively compared to existing image data. Therefore, when transmitting image data using media such as existing wired and wireless broadband lines or storing image data using existing storage media, the transmission and storage costs increase. In order to solve these problems that occur as image data becomes higher in resolution and quality, high-efficiency image encoding/decoding technology for images with higher resolution and quality is required.

One of the entropy coding methods, context-based adaptive binary arithmetic coding (CABAC), provides high coding performance. However, CABAC has a disadvantage of low throughput. This is due to the regular coding engine of CABAC. Specifically, the regular coding engine uses the probability state and range updated through the coding of the previous bin for coding the next bin. Therefore, each bin has high data dependency and is not processed in parallel. In addition, it may take a lot of time to read the probability interval and determine the current state.

Therefore, various tools are being discussed to improve entropy encoding efficiency.

The purpose of the present invention is to provide a video encoding/decoding method and device with improved encoding/decoding efficiency.

In addition, the present invention aims to provide a recording medium storing a bitstream generated by an image decoding method or device according to the present invention.

In addition, the present invention aims to provide a prediction method for solving the problems of the existing entropy encoding with respect to syntactic elements used in template-based multiple reference line (TMRL) intra prediction.

A video decoding method according to one embodiment of the present invention may include the steps of: obtaining an empty string corresponding to a syntax element from a bitstream, the syntax element representing a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction, obtaining the syntax element by inversely binarizing the empty string, and performing intra prediction of the current block based on the syntax element, wherein at least some bins of the empty string are obtained by bypass decoding, and bins excluding bypass-coded bins of the empty string are obtained by arithmetic decoding.

In the above image decoding method, the intra prediction of the current block may be characterized by using an intra prediction mode indicated by the syntax element and a reference sample line indicated by the syntax element among a plurality of reference sample lines adjacent to the current block.

In the above image decoding method, the syntax element may be characterized by indicating one candidate from a candidate list including candidates indicating different combinations of intra prediction modes and reference sample lines used for intra prediction.

In the above image decoding method, the intra prediction modes of the candidates may be characterized as being intra prediction modes excluding a predetermined mode.

In the above image decoding method, the candidates in the candidate list may be characterized as being a plurality of candidates selected based on a cost value of intra prediction based on a combination of an intra prediction mode and a reference sample line.

In the above image decoding method, it may be characterized in that the cost value is determined based on a comparison result between a result value of intra prediction based on a combination of an intra prediction mode and a reference sample line and a prediction value corresponding to a template including samples adjacent to the current block.

In the above image decoding method, the template may be characterized by including samples of a reference sample line most adjacent to the current block.

In the above image decoding method, the cost value may be measured using any one of a sum of absolute differences (SAD) measurement method, a sum of squared difference (SSD) measurement method, and a sum of absolute transformed differences.

In the above image decoding method, the empty string may be an empty string binarized in the form of a truncated Golomb Rice code, and the empty string may be characterized by including a prefix and a suffix.

In the above image decoding method, it may be characterized in that a bin corresponding to a prefix of the empty string is obtained by the arithmetic decoding, and a bin corresponding to a suffix of the empty string is obtained by the bypass decoding.

In the above image decoding method, it may be characterized in that at least some of the bins corresponding to the prefix of the empty string and the bins corresponding to the suffix of the empty string are obtained by the arithmetic decoding.

In the above image decoding method, the empty string may be an empty string binarized into a truncated single code form, and it may be characterized in that a number of bins less than or equal to a preset number among the empty strings are obtained by the arithmetic decoding.

A video encoding method according to one embodiment of the present invention comprises the steps of: deriving a syntax element indicating a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction; generating an empty string by binarizing the syntax element; and generating a bitstream by encoding each bin of the empty string according to an encoding method corresponding to each bin, wherein bypass coding is applied to at least some bins of the empty string, and arithmetic coding is applied to bins other than bins to which bypass coding of the empty string is applied.

A non-transitory computer-readable recording medium according to one embodiment of the present invention can store a bitstream generated by a video encoding method, including the steps of: deriving a syntax element indicating a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction; generating an empty string by binarizing the syntax element; and generating a bitstream by encoding each bin of the empty string according to an encoding method corresponding to each bin, wherein bypass coding is applied to at least some bins of the empty string, and arithmetic coding is applied to bins except for bins to which bypass coding of the empty string is applied.

A transmission method according to one embodiment of the present invention includes a step of transmitting the bitstream, and an image encoding method includes a step of deriving a syntax element indicating a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction, a step of binarizing the syntax element to generate an empty string, and a step of generating a bitstream by encoding each bin of the empty string according to an encoding method corresponding to each bin, wherein bypass coding is applied to at least some bins of the empty string, and arithmetic coding is applied to bins other than bins to which bypass coding of the empty string is applied. A bitstream generated by the image encoding method can be transmitted.

The features briefly summarized above regarding the present disclosure are merely exemplary aspects of the detailed description of the present disclosure that follows and do not limit the scope of the present disclosure.

According to the present invention, a video encoding/decoding method and device with improved encoding/decoding efficiency can be provided.

In addition, according to the present invention, an entropy encoding/decoding method for a syntactic element used in template-based multiple reference line (TMRL) intra prediction can be provided.

In addition, according to the present invention, an entropy encoding/decoding method can be provided that reduces the complexity of an encoder/decoder and improves throughput without significant loss of coding efficiency by reducing the number of context-coded bins when coding index values for TMRL intra prediction.

The effects obtainable from the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by a person skilled in the art to which the present disclosure belongs from the description below.

Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

FIG. 2 is a block diagram showing the configuration of one embodiment of a decryption device to which the present invention is applied.

FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

FIG. 4 is a diagram for explaining a CABAC encoding structure for a syntax element according to one embodiment of the present invention.

FIG. 5 is a diagram for explaining a CABAC decoding structure for a syntax element according to one embodiment of the present invention.

FIG. 6 is a diagram for explaining a template-based multi-reference sample line intra prediction method according to one embodiment of the present invention.

FIG. 7 is a diagram for explaining intra-template matching according to one embodiment of the present invention.

FIG. 8 is a flowchart illustrating an entropy decryption method according to an embodiment of the present invention.

FIG. 9 is a flowchart illustrating an entropy encoding method according to an embodiment of the present invention.

FIG. 10 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

The present invention may have various modifications and embodiments, and thus specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In the drawings, similar reference numerals refer to the same or similar functions throughout the various aspects. The shapes and sizes of elements in the drawings may be provided by way of example for clearer description. The detailed description of the exemplary embodiments described below refers to the accompanying drawings, which illustrate specific embodiments by way of example. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments. It should be understood that the various embodiments are different from each other, but are not necessarily mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention with respect to one embodiment. In addition, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the embodiment. Accordingly, the following detailed description is not intended to be taken in a limiting sense, and the scope of the illustrative embodiments is defined only by the appended claims, along with the full scope equivalents to which such claims are entitled, if properly described.

In the present invention, the terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are only used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and/or includes a combination of a plurality of related described items or any item among a plurality of related described items.

The components shown in the embodiments of the present invention are independently depicted to indicate different characteristic functions, and do not mean that each component is formed as a separate hardware or software configuration unit. That is, each component is listed and included as a separate component for convenience of explanation, and at least two components among each component may be combined to form a single component, or one component may be divided into multiple components to perform a function, and such integrated embodiments and separate embodiments of each component are also included in the scope of the present invention as long as they do not deviate from the essence of the present invention.

The terminology used in the present invention is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In addition, some components of the present invention are not essential components that perform essential functions in the present invention and may be optional components that merely enhance performance. The present invention may be implemented by including only essential components for implementing the essence of the present invention excluding components used only for enhancing performance, and a structure including only essential components excluding optional components used only for enhancing performance is also included in the scope of the present invention.

In an embodiment, the term "at least one" can mean one of a number greater than or equal to 1, such as 1, 2, 3, and 4. In an embodiment, the term "a plurality of" can mean one of a number greater than or equal to 2, such as 2, 3, and 4.

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In describing the embodiments of this specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of this specification, the detailed description will be omitted, and the same reference numerals will be used for the same components in the drawings, and duplicate descriptions of the same components will be omitted.

Glossary of Terms

Hereinafter, “video” may mean one picture constituting a video, and may also represent the video itself. For example, “encoding and/or decoding of a video” may mean “encoding and/or decoding of a video,” and may also mean “encoding and/or decoding of one of the videos constituting the video.”

Hereinafter, "moving image" and "video" may be used with the same meaning and may be used interchangeably. In addition, the target image may be an encoding target image that is a target of encoding and/or a decoding target image that is a target of decoding. In addition, the target image may be an input image input to an encoding device and may be an input image input to a decoding device. Here, the target image may have the same meaning as the current image.

Hereinafter, the terms encoder and image encoding device may be used interchangeably and have the same meaning.

Hereinafter, the terms decoder and image decoding device may be used interchangeably and interchangeably.

Hereinafter, “image”, “picture”, “frame” and “screen” may be used with the same meaning and may be used interchangeably.

Hereinafter, the “target block” may be an encoding target block that is a target of encoding and/or a decoding target block that is a target of decoding. In addition, the target block may be a current block that is a target of current encoding and/or decoding. For example, “target block” and “current block” may be used with the same meaning and may be used interchangeably.

Hereinafter, "block" and "unit" may be used interchangeably and may be used interchangeably. In addition, "unit" may mean including a luminance (Luma) component block and a corresponding chroma component block in order to distinguish it from a block. For example, a coding tree unit (CTU) may be composed of one luma component (Y) coding tree block (CTB) and two chroma component (Cb, Cr) coding tree blocks related to it.

Hereinafter, “sample”, “pixel” and “pixel” may be used interchangeably with each other with the same meaning. Here, a sample may represent a basic unit constituting a block.

Hereinafter, “inter” and “between screens” may be used interchangeably and have the same meaning.

Hereinafter, “intra” and “within screen” may be used interchangeably and have the same meaning.

Figure 1 is a block diagram showing the configuration according to one embodiment of an encoding device to which the present invention is applied.

The encoding device (100) may be an encoder, a video encoding device, or an image encoding device. The video may include one or more images. The encoding device (100) may sequentially encode one or more images.

Referring to FIG. 1, an encoding device (100) may include an image segmentation unit (110), an intra prediction unit (120), a motion prediction unit (121), a motion compensation unit (122), a switch (115), a subtractor (113), a transformation unit (130), a quantization unit (140), an entropy encoding unit (150), an inverse quantization unit (160), an inverse transformation unit (170), an adder (117), a filter unit (180), and a reference picture buffer (190).

In addition, the encoding device (100) can generate a bitstream including encoded information through encoding an input image, and output the generated bitstream. The generated bitstream can be stored in a computer-readable recording medium, or can be streamed through a wired/wireless transmission medium.

The video segmentation unit (110) can segment the input video into various forms to increase the efficiency of video encoding/decoding. That is, the input video is composed of multiple pictures, and one picture can be hierarchically segmented and processed for compression efficiency, parallel processing, etc. For example, one picture can be segmented into one or multiple tiles or slices, and then segmented again into multiple CTUs (Coding Tree Units). Alternatively, one picture can be segmented into multiple sub-pictures defined as groups of rectangular slices, and each sub-picture can be segmented into the tiles/slices. Here, the sub-pictures can be utilized to support the function of partially independently encoding/decoding and transmitting the picture. Since multiple sub-pictures can be individually restored, they have the advantage of being easy to edit in applications that configure multi-channel input into one picture. In addition, tiles can be segmented horizontally to generate bricks. Here, a brick can be utilized as a basic unit of intra-picture parallel processing. In addition, one CTU can be recursively split into a quad tree (QT: Quadtree), and the terminal node of the split can be defined as a CU (Coding Unit). The CU can be split into a prediction unit (PU) and a transformation unit (TU) to perform prediction and splitting. Meanwhile, the CU can be utilized as a prediction unit and/or a transformation unit itself. Here, for flexible splitting, each CTU can be recursively split into not only a quad tree (QT) but also a multi-type tree (MTT: Multi-Type Tree). Splitting of a CTU into a multi-type tree can start from the terminal node of a QT, and the MTT can be composed of a BT (Binary Tree) and a TT (Triple Tree). For example, the MTT structure can be distinguished into vertical binary split mode (SPLIT_BT_VER), horizontal binary split mode (SPLIT_BT_HOR), vertical ternary split mode (SPLIT_TT_VER), and horizontal ternary split mode (SPLIT_TT_HOR). In addition, the minimum block size (MinQTSize) of the quad tree of the luma block during splitting can be set to 16x16, the maximum block size (MaxBtSize) of the binary tree can be set to 128x128, and the maximum block size (MaxTtSize) of the triple tree can be set to 64x64. In addition, the minimum block size (MinBtSize) of the binary tree and the minimum block size (MinTtSize) of the triple tree can be set to 4x4, and the maximum depth (MaxMttDepth) of the multi-type tree can be set to 4. In addition, a dual tree that uses different CTU split structures for luma and chrominance components can be applied to improve the encoding efficiency of the I slice. On the other hand, in P and B slices, the luminance and chrominance CTBs (Coding Tree Blocks) within the CTU can be split into a single tree sharing the coding tree structure.

The encoding device (100) may perform encoding on the input image in the intra mode and/or the inter mode. Alternatively, the encoding device (100) may perform encoding on the input image in a third mode (e.g., IBC mode, Palette mode, etc.) other than the intra mode and the inter mode. However, if the third mode has functional characteristics similar to the intra mode or the inter mode, it may be classified as the intra mode or the inter mode for convenience of explanation. In the present invention, the third mode will be classified and described separately only when a specific explanation is required.

When the intra mode is used as the prediction mode, the switch (115) can be switched to intra, and when the inter mode is used as the prediction mode, the switch (115) can be switched to inter. Here, the intra mode can mean an intra-screen prediction mode, and the inter mode can mean an inter-screen prediction mode. The encoding device (100) can generate a prediction block for an input block of an input image. In addition, after the prediction block is generated, the encoding device (100) can encode a residual block using a residual of the input block and the prediction block. The input image can be referred to as a current image which is a current encoding target. The input block can be referred to as a current block which is a current encoding target or an encoding target block.

If the prediction mode is intra mode, the intra prediction unit (120) can use samples of blocks already encoded/decoded around the current block as reference samples. The intra prediction unit (120) can perform spatial prediction on the current block using the reference sample, and can generate prediction samples for the input block through spatial prediction. Here, intra prediction can mean prediction within the screen.

As an intra prediction method, non-directional prediction modes such as DC mode and Planar mode and directional prediction modes (e.g., 65 directions) can be applied. Here, the intra prediction method can be expressed as an intra prediction mode or an intra-screen prediction mode.

When the prediction mode is inter mode, the motion prediction unit (121) can search for an area that best matches the input block from the reference image during the motion prediction process, and can derive a motion vector using the searched area. At this time, the search area can be used as the area. The reference image can be stored in the reference picture buffer (190). Here, when encoding/decoding for the reference image is processed, it can be stored in the reference picture buffer (190).

The motion compensation unit (122) can generate a prediction block for the current block by performing motion compensation using a motion vector. Here, inter prediction can mean inter-screen prediction or motion compensation.

The above motion prediction unit (121) and motion compensation unit (122) can generate a prediction block by applying an interpolation filter to a portion of an area within a reference image when the value of a motion vector does not have an integer value. In order to perform inter-screen prediction or motion compensation, it is possible to determine whether the motion prediction and motion compensation method of a prediction unit included in a corresponding encoding unit is one of Skip Mode, Merge Mode, Advanced Motion Vector Prediction (AMVP) mode, and Intra Block Copy (IBC) mode based on the encoding unit, and perform inter-screen prediction or motion compensation according to each mode.

In addition, based on the above inter-screen prediction method, the AFFINE mode of sub-PU based prediction, the SbTMVP (Subblock-based Temporal Motion Vector Prediction) mode, and the MMVD (Merge with MVD) mode, the GPM (Geometric Partitioning Mode) mode of PU based prediction can be applied. In addition, in order to improve the performance of each mode, the HMVP (History based MVP), the PAMVP (Pairwise Average MVP), the CIIP (Combined Intra/Inter Prediction), the AMVR (Adaptive Motion Vector Resolution), the BDOF (Bi-Directional Optical-Flow), the BCW (Bi-predictive with CU Weights), the LIC (Local Illumination Compensation), the TM (Template Matching), the OBMC (Overlapped Block Motion Compensation), etc. can be applied.

Among these, AFFINE mode is a technology that is used in both AMVP and MERGE modes and also has high encoding efficiency. Since the conventional video coding standard performs MC (Motion Compensation) by considering only the parallel translation of the block, there was a disadvantage in that it could not properly compensate for motions that occur in reality, such as zoom in/out and rotation. To supplement this, a four-parameter affine motion model using two control point motion vectors (CPMV) and a six-parameter affine motion model using three control point motion vectors can be applied to inter prediction. Here, CPMV is a vector representing an affine motion model of one of the upper left, upper right, and lower left of the current block.

The subtractor (113) can generate a residual block using the difference between the input block and the predicted block. The residual block may also be referred to as a residual signal. The residual signal may mean the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming, quantizing, or transforming and quantizing the difference between the original signal and the predicted signal. The residual block may be a residual signal in block units.

The transform unit (130) can perform a transform on the residual block to generate a transform coefficient and output the generated transform coefficient. Here, the transform coefficient can be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit (130) can also skip the transform on the residual block.

A quantized level can be generated by applying quantization to a transform coefficient or a residual signal. In the following embodiments, a quantized level may also be referred to as a transform coefficient.

For example, a 4x4 luminance residual block generated through within-screen prediction can be transformed using a basis vector based on DST (Discrete Sine Transform), and a basis vector based on DCT (Discrete Cosine Transform) can be used to transform the remaining residual blocks. In addition, a transform block can be divided into a quad tree shape for one block using RQT (Residual Quad Tree) technology, and after performing transformation and quantization on each transform block divided through RQT, a coded block flag (cbf) can be transmitted to increase encoding efficiency when all coefficients become 0.

Alternatively, the Multiple Transform Selection (MTS) technique can be applied to perform transformation by selectively using multiple transformation bases. That is, instead of dividing the CU into TUs through the RQT, a function similar to TU division can be performed through the Sub-block Transform (SBT) technique. Specifically, the SBT is applied only to inter-screen prediction blocks, and unlike the RQT, the current block can be divided into ½ or ¼ sizes in the vertical or horizontal direction, and then the transformation can be performed on only one of the blocks. For example, if it is divided vertically, the transformation can be performed on the leftmost or rightmost block, and if it is divided horizontally, the transformation can be performed on the topmost or bottommost block.

Additionally, LFNST (Low Frequency Non-Separable Transform), a secondary transform technique that additionally transforms the residual signal converted to the frequency domain through DCT or DST, can be applied. LFNST additionally performs a transform on the low-frequency region of 4x4 or 8x8 in the upper left, so that the residual coefficients can be concentrated in the upper left.

The quantization unit (140) can generate a quantized level by quantizing a transform coefficient or a residual signal according to a quantization parameter (QP), and can output the generated quantized level. At this time, the quantization unit (140) can quantize the transform coefficient using a quantization matrix.

For example, a quantizer using QP values of 0 to 51 can be used. Or, if the image size is larger and high encoding efficiency is required, 0 to 63 QP can be used. Also, a Dependent Quantization (DQ) method that uses two quantizers instead of one can be applied. DQ performs quantization using two quantizers (e.g., Q0 and Q1), and even without signaling information about the use of a specific quantizer, the quantizer to be used for the next transform coefficient can be selected based on the current state through a state transition model.

The entropy encoding unit (150) can generate a bitstream by performing entropy encoding according to a probability distribution on values produced by the quantization unit (140) or coding parameter values produced in the encoding process, and can output the bitstream. The entropy encoding unit (150) can perform entropy encoding on information about image samples and information for decoding the image. For example, information for decoding the image can include syntax elements, etc.

When entropy encoding is applied, a small number of bits are allocated to symbols having a high occurrence probability and a large number of bits are allocated to symbols having a low occurrence probability, thereby representing symbols, whereby the size of the bit string for symbols to be encoded can be reduced. The entropy encoding unit (150) can use an encoding method such as exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) for entropy encoding. For example, the entropy encoding unit (150) can perform entropy encoding using a Variable Length Coding/Code (VLC) table. In addition, the entropy encoding unit (150) may derive a binarization method of a target symbol and a probability model of a target symbol/bin, and then perform arithmetic encoding using the derived binarization method, probability model, and context model.

In relation to this, when applying CABAC, in order to reduce the size of the probability table stored in the decryption device, the table probability update method can be changed to a table update method using a simple formula and applied. In addition, two different probability models can be used to obtain more accurate symbol probability values.

The entropy encoding unit (150) can change a two-dimensional block form coefficient into a one-dimensional vector form through a transform coefficient scanning method to encode a transform coefficient level (quantized level).

Coding parameters may include information (flags, indexes, etc.) encoded in an encoding device (100) and signaled to a decoding device (200), such as syntax elements, as well as information derived during an encoding process or a decoding process, and may mean information necessary when encoding or decoding an image.

Here, signaling a flag or index may mean that the encoder entropy encodes the flag or index and includes it in the bitstream, and that the decoder entropy decodes the flag or index from the bitstream.

The encoded current image can be used as a reference image for other images to be processed later. Therefore, the encoding device (100) can restore or decode the encoded current image again, and store the restored or decoded image as a reference image in the reference picture buffer (190).

The quantized level can be dequantized in the dequantization unit (160) and inverse transformed in the inverse transform unit (170). The dequantized and/or inverse transformed coefficients can be combined with a prediction block through an adder (117), and a reconstructed block can be generated by combining the dequantized and/or inverse transformed coefficients and the prediction block. Here, the dequantized and/or inverse transformed coefficients mean coefficients on which at least one of dequantization and inverse transformation has been performed, and may mean a reconstructed residual block. The dequantization unit (160) and the inverse transform unit (170) can be performed in the reverse process of the quantization unit (140) and the transform unit (130).

The restoration block may pass through a filter unit (180). The filter unit (180) may apply a deblocking filter, a sample adaptive offset (SAO), an adaptive loop filter (ALF), a bilateral filter (BIF), LMCS (Luma Mapping with Chroma Scaling), etc. as a filtering technique, in whole or in part, to the restoration sample, restoration block, or restoration image. The filter unit (180) may also be called an in-loop filter. In this case, the in-loop filter is also used as a name excluding LMCS.

The deblocking filter can remove block distortion that occurs at the boundary between blocks. In order to determine whether to perform the deblocking filter, it is possible to determine whether to apply the deblocking filter to the current block based on the samples contained in several columns or rows contained in the block. When applying the deblocking filter to the block, different filters can be applied depending on the required deblocking filtering strength.

A sample adaptive offset can be used to add an appropriate offset value to the sample value to compensate for the encoding error. The sample adaptive offset can correct the offset from the original image on a sample basis for the image on which deblocking has been performed. A method can be used in which the samples included in the image are divided into a certain number of regions, and then the region to be offset is determined and the offset is applied to the region, or a method can be used in which the offset is applied by considering the edge information of each sample.

Bilateral filter (BIF) can also compensate for the offset from the original image on a sample-by-sample basis for the deblocked image.

An adaptive loop filter can perform filtering based on a comparison value between a restored image and an original image. After dividing samples included in an image into a predetermined group, a filter to be applied to each group can be determined, and filtering can be performed differentially for each group. Information related to whether to apply an adaptive loop filter can be signaled for each coding unit (CU), and the shape and filter coefficients of the adaptive loop filter to be applied can vary for each block.

In LMCS (Luma Mapping with Chroma Scaling), luma mapping (LM) refers to remapping luminance values through a piece-wise linear model, and chroma scaling (CS) refers to a technique for scaling the residual values of chroma components according to the average luminance value of the prediction signal. In particular, LMCS can be utilized as an HDR correction technique that reflects the characteristics of HDR (High Dynamic Range) images.

The restored block or restored image that has passed through the filter unit (180) may be stored in the reference picture buffer (190). The restored block that has passed through the filter unit (180) may be a part of the reference image. In other words, the reference image may be a restored image composed of restored blocks that have passed through the filter unit (180). The stored reference image may be used for inter-screen prediction or motion compensation thereafter.

FIG. 2 is a block diagram showing the configuration of one embodiment of a decryption device to which the present invention is applied.

The decoding device (200) may be a decoder, a video decoding device, or an image decoding device.

Referring to FIG. 2, the decoding device (200) may include an entropy decoding unit (210), an inverse quantization unit (220), an inverse transformation unit (230), an intra prediction unit (240), a motion compensation unit (250), an adder (201), a switch (203), a filter unit (260), and a reference picture buffer (270).

The decoding device (200) can receive a bitstream output from the encoding device (100). The decoding device (200) can receive a bitstream stored in a computer-readable recording medium, or can receive a bitstream streamed through a wired/wireless transmission medium. The decoding device (200) can perform decoding on the bitstream in an intra mode or an inter mode. In addition, the decoding device (200) can generate a restored image or a decoded image through decoding, and can output the restored image or the decoded image.

If the prediction mode used for decryption is intra mode, the switch (203) can be switched to intra. If the prediction mode used for decryption is inter mode, the switch (203) can be switched to inter.

The decoding device (200) can obtain a reconstructed residual block by decoding the input bitstream and can generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding device (200) can generate a reconstructed block to be decoded by adding the reconstructed residual block and the prediction block. The decoding target block can be referred to as a current block.

The entropy decoding unit (210) can generate symbols by performing entropy decoding according to a probability distribution for the bitstream. The generated symbols can include symbols in the form of quantized levels. Here, the entropy decoding method can be the reverse process of the entropy encoding method described above.

The entropy decoding unit (210) can change a one-dimensional vector-shaped coefficient into a two-dimensional block-shaped coefficient through a transform coefficient scanning method to decode a transform coefficient level (quantized level).

The quantized level can be dequantized in the dequantization unit (220) and detransformed in the inverse transform unit (230). The quantized level can be generated as a restored residual block as a result of the dequantization and/or detransformation. At this time, the dequantization unit (220) can apply a quantization matrix to the quantized level. The dequantization unit (220) and the detransform unit (230) applied to the decoding device can apply the same technology as the dequantization unit (160) and the detransform unit (170) applied to the encoding device described above.

When the intra mode is used, the intra prediction unit (240) can generate a prediction block by performing spatial prediction on the current block using sample values of already decoded blocks surrounding the block to be decoded. The intra prediction unit (240) applied to the decoding device can apply the same technology as the intra prediction unit (120) applied to the encoding device described above.

When the inter mode is used, the motion compensation unit (250) can perform motion compensation using a motion vector and a reference image stored in the reference picture buffer (270) for the current block to generate a prediction block. The motion compensation unit (250) can apply an interpolation filter to a part of the reference image to generate a prediction block when the value of the motion vector does not have an integer value. In order to perform motion compensation, it is possible to determine whether the motion compensation method of the prediction unit included in the corresponding encoding unit is a skip mode, a merge mode, an AMVP mode, or a current picture reference mode based on the encoding unit, and to perform motion compensation according to each mode. The motion compensation unit (250) applied to the decoding device can apply the same technology as the motion compensation unit (122) applied to the encoding device described above.

The adder (201) can add the restored residual block and the prediction block to generate a restored block. The filter unit (260) can apply at least one of an Inverse-LMCS, a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the restored block or the restored image. The filter unit (260) applied to the decoding device can apply the same filtering technology as that applied to the filter unit (180) applied to the encoding device described above.

The filter unit (260) can output a restored image. The restored block or restored image can be stored in the reference picture buffer (270) and used for inter prediction. The restored block that has passed through the filter unit (260) can be a part of the reference image. In other words, the reference image can be a restored image composed of restored blocks that have passed through the filter unit (260). The stored reference image can be used for inter-screen prediction or motion compensation thereafter.

FIG. 3 is a diagram schematically showing a video coding system to which the present invention can be applied.

A video coding system according to one embodiment may include an encoding device (10) and a decoding device (20). The encoding device (10) may transmit encoded video and/or image information or data to the decoding device (20) in the form of a file or streaming through a digital storage medium or a network.

An encoding device (10) according to one embodiment may include a video source generating unit (11), an encoding unit (12), and a transmitting unit (13). A decoding device (20) according to one embodiment may include a receiving unit (21), a decoding unit (22), and a rendering unit (23). The encoding unit (12) may be called a video/image encoding unit, and the decoding unit (22) may be called a video/image decoding unit. The transmitting unit (13) may be included in the encoding unit (12). The receiving unit (21) may be included in the decoding unit (22). The rendering unit (23) may include a display unit, and the display unit may be configured as a separate device or an external component.

The video source generation unit (11) can obtain a video/image through a process of capturing, synthesizing, or generating a video/image. The video source generation unit (11) can include a video/image capture device and/or a video/image generation device. The video/image capture device can include, for example, one or more cameras, a video/image archive including previously captured video/image, etc. The video/image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate a video/image. For example, a virtual video/image can be generated through a computer, etc., and in this case, the video/image capture process can be replaced with a process of generating related data.

The encoding unit (12) can encode the input video/image. The encoding unit (12) can perform a series of procedures such as prediction, transformation, and quantization for compression and encoding efficiency. The encoding unit (12) can output encoded data (encoded video/image information) in the form of a bitstream. The detailed configuration of the encoding unit (12) can also be configured in the same manner as the encoding device (100) of FIG. 1 described above.

The transmission unit (13) can transmit encoded video/image information or data output in the form of a bitstream to the reception unit (21) of the decoding device (20) through a digital storage medium or a network in the form of a file or streaming. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit (13) can include an element for generating a media file through a predetermined file format and can include an element for transmission through a broadcasting/communication network. The reception unit (21) can extract/receive the bitstream from the storage medium or network and transmit it to the decoding unit (22).

The decoding unit (22) can decode video/image by performing a series of procedures such as inverse quantization, inverse transformation, and prediction corresponding to the operation of the encoding unit (12). The detailed configuration of the decoding unit (22) can also be configured in the same manner as the decoding device (200) of FIG. 2 described above.

The rendering unit (23) can render the decrypted video/image. The rendered video/image can be displayed through the display unit.

That is, the encoder can generate and transmit a bitstream by performing entropy encoding on information for decoding an image, including syntactic elements, etc. The encoder can use an encoding method such as CABAC for entropy encoding.

And, the decoder can obtain a bitstream and decode the obtained bitstream using a decoding method such as CABAC. And, the decoder can obtain information for decoding a block to be decoded based on the decoding result of the bitstream, and generate a prediction block of the block to be decoded.

The CABAC encoding structure of the encoding device and the CABAC decoding structure of the decoding device are each described below.

FIG. 4 is a diagram for explaining a CABAC encoding structure for a syntax element according to one embodiment of the present invention.

Referring to FIG. 4, the CABAC encoding structure includes a binarization structure that binarizes a syntactic element to generate an empty or blank string, and a binary arithmetic coder structure that encodes the empty or blank string. In addition, the binary arithmetic coder may include a regular coding engine and a bypass coding engine based on a context model of a context modeler. Here, the regular coding engine may be an arithmetic coding structure.

If the syntax element is already a binary value, the CABAC encoding structure can use the value of the syntax element as it is without additionally performing binarization on the syntax element. On the other hand, if the syntax element is not a binary value, the CABAC encoding structure can convert the value of the syntax element that is not a binary value into a binary value by binarizing it. Each binary digit 0 or 1 that constitutes the binary value is defined as a bin. And, a structure that lists multiple bins is defined as a bin string. For example, if the bin string after binarization is 110, 1, 1, and 0 are each called a bin.

Thereafter, the bins or empty strings of the binarized syntax elements can be regular coded or bypass coded according to an encoding method corresponding to each bin. Here, the regular coding can be context-model-based binary arithmetic coding (CABAC). In the regular coding process, a context model reflecting a probability value for a bin can be assigned. And, the bin can be encoded based on the assigned context model. In the regular coding process, encoding is performed for the bin, and the context model for the bin can be updated. A bin that is regular coded as described above by the regular coding engine is referred to as a context-coded bin.

On the other hand, unlike the regular coding process, the bypass coding process can be a coding process that omits the process of estimating the probability for the input bin and the process of updating the context model applied to the bin. Instead of assigning a context model to the bin, the bypass coding process can encode the bin by applying a uniform (or fixed) probability distribution. Since the bypass coding process applies a uniform (or fixed) probability distribution, it can encode a number of bins in one coding cycle, thereby improving the speed of entropy coding. The bins that are bypass-coded by the bypass coding engine as described above are referred to as bypass-coded bins.

FIG. 5 is a diagram for explaining a CABAC decoding structure for a syntax element according to one embodiment of the present invention.

Referring to FIG. 5, the CABAC decoding structure includes a binary arithmetic decoder structure that decodes a bitstream to obtain a bin or an empty string corresponding to a syntax element, and a debinarization structure that debinarizes the bin or the empty string to output the syntax element. In addition, the binary arithmetic decoder may include a regular coding engine and a bypass coding engine based on a context model. Here, the regular coding engine may be a context model-based binary arithmetic coding structure.

Entropy decoding may be a process of performing the entropy encoding process described above in reverse order. For example, if a syntax element is encoded based on a context model, a decoder may obtain a bin or an empty string corresponding to the syntax element from a received bitstream. The decoder may determine a context model of the bin or the empty string using at least one of information from the syntax element, the decoding target block, the decoding information of the surrounding blocks, or the information of the syntax element/bin decoded in the previous step. Then, the decoder may predict the occurrence probability of the obtained bin according to the context model, and perform arithmetic decoding to derive the value of the bin or the empty string corresponding to the syntax element. Thereafter, the context model of the decoded bin may be updated based on the context model determined through the above process.

If the syntax element is bypass decoded, the decoder can obtain a bin or a bin string corresponding to the syntax element through the bitstream, and decode it by applying a uniform (or fixed) probability distribution to the obtained bin. In this case, the procedure for deriving a context model of the syntax element and the procedure for updating the context model applied to the bin after decoding can be omitted.

If the decoded syntax element is an empty string, the decoder can debinarize the empty string to obtain the syntax element. On the other hand, if the decoded syntax element is a single blank, the decoder can skip the debinarization process and use the blank value as the value of the syntax element.

Here, the syntax element may include a syntax element regarding intra prediction, a syntax element regarding inter prediction, etc. And, according to one embodiment of the present invention, the syntax element regarding intra prediction may be a syntax element regarding template-based multiple reference line (TMRL) intra prediction.

Template-based multiple reference sample line intra prediction may be an intra prediction based on a method of signaling by combining an intra prediction mode of a block and reference sample lines used for intra prediction of the block. One embodiment of a template-based multiple reference sample line intra prediction method may be as described below.

FIG. 6 is a diagram for explaining a template-based multi-reference sample line intra prediction method according to one embodiment of the present invention.

Referring to FIG. 6, TMRL intra prediction can be performed using an intra prediction mode for a current block (610) and N multiple reference samples. The number of intra prediction mode candidates used in TMRL intra prediction can be M. In this case, M is a positive integer greater than or equal to 1. Among the intra prediction modes, an arbitrary mode preset in a decoder/encoder may not be used for TMRL intra prediction. According to one embodiment, the arbitrary mode preset may be a planar mode or an undirected prediction mode.

And, referring to FIG. 6, multiple sample lines (620, 631, 632, 633) used for TMRL intra prediction are illustrated. Here, the neighboring sample line (reference line 0, 620) closest to the current block (610) is used as a template, and the next adjacent N reference sample lines (631, 632, 633) can be used as multiple reference sample lines. At this time, N is a positive integer greater than or equal to 2.

There are a total of N x M combinations of N reference sample lines (631, 632, 633) and M intra-screen prediction modes. And, for TMRL intra prediction, a candidate list including candidates indicating different combinations of intra prediction modes and reference sample lines used for intra prediction can be generated.

In one embodiment, the candidate list for TMRL intra prediction may use all N x M combinations. On the other hand, in another embodiment, the candidate list for TMRL intra prediction may include only K candidates determined based on a cost value of an intra prediction value based on a combination of an intra prediction mode and a reference sample line. Here, the cost value may be a result value of a cost function based on a comparison result of a prediction value using a template induced by template matching and an intra prediction value using a combination of an intra prediction mode and a reference sample line.

Here, the K candidates can be K candidates selected in order of having small cost values among N x M combinations. And, the K candidates can be sorted in a set order (e.g. sorted in ascending order by cost value, etc.) to form a candidate list. Here, K can be an integer greater than or equal to 1 and less than or equal to N x M.

Here, the cost function can use at least one of the following methods: sum of absolute differences (SAD), sum of squared differences (SSD), and sum of absolute transformed differences (SATD).

Here, template matching to derive cost values can be as described below.

FIG. 7 is a diagram for explaining intra-template matching according to one embodiment of the present invention.

Referring to FIG. 7, intra template matching prediction can determine an optimal prediction block for a current block in a reconstructed area (730) within a current picture (700) based on a current block (710). Specifically, in intra template matching prediction, a set of adjacent reference samples surrounding a current block (710) can be defined as a current template (720). Then, a template matching-based search can be performed within a reconstructed area (730) based on the current template (720) to find a reference template (740) that is a template with the highest similarity to the current template (720), and a matching block (750) can be determined. Here, the matching block (750) can be used as a prediction block for the current block (710).

Meanwhile, template matching-based search can be performed in pre-defined regions (R1, R2, R3, R4) among the pre-restored regions (730), and the search order can be R1, R2, R3, R4.

That is, the reference template (740) having the highest similarity to the current L-shaped template (720) surrounding the current block is searched in the search area, and the block adjacent to the reference template (740) is determined as a matching block. However, the shape of the template may be a shape other than the L-shape. For example, the template having a shape other than the L-shape may be a left template including a left-side surrounding sample of the block, and an upper template including a top-side surrounding sample of the block.

Alternatively, when performing template matching, the template may be a template of a shape implicitly determined from among various forms of templates using samples around blocks predefined in the encoder and decoder, such as an L-shaped template, a left template, an upper template, or the like based on information such as the size and position of the current block.

In TMRL intra prediction, an index value of a candidate representing a combination of a reference line and an intra prediction mode used for intra prediction of a current block among a constructed candidate list may be signaled. The index of a candidate representing a combination of a reference line and an intra prediction mode used for intra prediction of a current block may be referred to as a TMRL index. The value of the TMRL index may be entropy encoded through CABAC (context-based adaptive binary arithmetic coding).

The value of the TMRL index may not be a binary value. Therefore, the TMRL index may be binarized before being entropy encoded. For example, the TMRL index may be binarized by the truncated Golomb-Rice code method. The indices of the candidates included in the candidate list used for TMRL intra prediction may be expressed as codewords binarized by the truncated Golomb-Rice code method as follows.

However, the embodiment of Table 1 is only an example of expressing the indices of candidates included in the candidate list used for TMRL intra prediction in the form of codewords. The indices of candidates included in the candidate list used for TMRL intra prediction can be binarized using various binarization methods (e.g., truncated unary code, etc.).

However, when CABAC encoding is applied to the TMRL index, the encoding process may be delayed due to the context model update (or probability update) process of regular coding. For example, if two bins that are regular coded use the same context model, the value of the first bin may affect the probability model. Therefore, before coding the second bin, the context (or probability) value that has changed due to the value of the first bin must be updated. The context (or probability) update process may cause a delay in the coding cycle. That is, the process of repeatedly calling the same context and waiting for the context (or probability) model update after coding each bin causes a bottleneck in the encoder/decoder and reduces the throughput of encoding/decoding. In addition, even if bins showing low correlation are regular coded, the performance gain may be small or almost nonexistent compared to regular coding for bins with higher correlation.

Therefore, to efficiently entropy encode the TMRL index, one of the following methods can be used.

According to one embodiment of the present invention, the amount of time and computational resources saved by regular coding only some bins of the bin string corresponding to the TMRL index may be more important than the coding performance that can be obtained by regular coding all bins of the bin string corresponding to the TMRL index. Therefore, the encoder can encode the bin string corresponding to the TMRL index by combining regular coding and bypass coding. To this end, the encoder can encode one or more bins of the bin string corresponding to the TMRL index as context coding bins (i.e., regular coding) and encode the remaining bins of the bin string corresponding to the TMRL index as bypass coding bins (i.e., bypass coding).

Accordingly, the decoder can decode one or more context-coded bins among the bin strings corresponding to the TMRL index using the regular coding engine. And, the decoder can decode the remaining bins among the bin strings corresponding to the TMRL index that are not context-coded using the bypass coding engine.

Specifically, according to one embodiment of the present invention, when a TMRL index is binarized into a codeword form by dividing it into a prefix and a suffix as in Table 1, regular coding may be applied to bins corresponding to the prefix of the codeword, and bypass coding may be applied to bins corresponding to the suffix of the codeword. In other words, bins corresponding to the prefix of the codeword may be context coding bins, and bins corresponding to the suffix of the codeword may be bypass coding bins.

According to another embodiment of the present invention, bins corresponding to suffixes of TMRL indexes can be divided into two or more groups. [Table 2] is an example in which an index of a candidate list consisting of 20 candidates is binarized into a codeword form using a truncated Golomb-Rice code method, and bins corresponding to suffixes of the codewords are divided into two groups.

And, among the bins corresponding to the suffix of the codeword, bypass coding may be applied to the bins of some group(s), and context coding may be applied to the remaining bins.

According to one embodiment of the present invention, the encoder may apply bypass coding only to bins corresponding to suffix 1 of the codeword in Table 2, and apply context coding to bins corresponding to prefix and suffix 0. Alternatively, the encoder may apply bypass coding only to suffix 0, and apply context coding to bins corresponding to prefix and suffix 1.

That is, the bins corresponding to some groups of prefixes and suffixes of the codeword may be context coding bins, and the bins corresponding to some remaining groups of suffixes of the codeword may be bypass coding bins.

According to another embodiment of the present invention, a TMRL index can be binarized into a codeword form having no prefix and suffix using a binary code (e.g., a truncated single code, etc.) method. When the TMRL index is binarized into a codeword form having no prefix and suffix, the maximum number of context coding bins for TMRL index coding can be determined in advance. The encoder can apply context coding to a predetermined number of bins among the codewords of the TMRL index. On the other hand, the encoder can apply context coding to bins exceeding a predetermined number among the codewords of the TMRL index. That is, the predetermined number of bins among the codewords can be context coding bins, and the bins exceeding a predetermined number among the codewords can be bypass coding bins.

According to another embodiment of the present invention, the correlation of the bins of the empty string corresponding to the TMRL index may not be high. In this case, the difference in coding performance between regular coding and bypass coding for the bins of the empty string corresponding to the TMRL index may not be significant. In other words, regular coding of the bins of the empty string corresponding to the TMRL index may only cause a bottleneck and may not have much significance in terms of coding performance.

Alternatively, for some applications, the amount of time and computational resources saved by bypass-coding all bins in an empty string may be more important than the coding performance gained by regular-coding all bins in an empty string when entropy-coding the bins in an empty string corresponding to a TMRL index.

Therefore, the encoder can bypass code all bins of the empty string corresponding to the TMRL index. In this case, various types of codes can be used, such as a truncated single code in addition to a binarized code consisting of a prefix and a suffix.

FIG. 8 is a flowchart illustrating an entropy decryption method according to an embodiment of the present invention.

The video decoding device can obtain an empty string corresponding to a syntax element from a bitstream (S810). Here, at least some of the bins of the empty string are obtained by bypass decoding, and the bins except for the bypass-coded bins of the empty string can be obtained by arithmetic decoding. In addition, the syntax element can indicate a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction.

The image decoding device can obtain syntactic elements by de-binarizing an empty string (S820).

The image decoding device can perform intra prediction of the current block based on the syntax elements (S830).

Here, intra prediction of the current block can be performed using an intra prediction mode indicated by the syntax element and a reference sample line indicated by the syntax element among a plurality of reference sample lines adjacent to the current block.

Here, the syntax element can indicate one candidate from a candidate list including candidates indicating different combinations of intra prediction modes and reference sample lines used for intra prediction.

Here, the intra prediction modes of the candidates can be intra prediction modes other than a predetermined mode.

Here, the candidates in the candidate list may be multiple candidates selected based on the cost value of intra prediction based on a combination of intra prediction mode and reference sample line.

Here, the cost value can be determined based on the result of comparing the result value of intra prediction based on the combination of the intra prediction mode and the reference sample line with the prediction value corresponding to the template including samples adjacent to the current block.

Here, the template may include samples of the reference sample line closest to the current block.

Here, the cost value can be measured by any one of the sum of absolute differences (SAD) measurement method, the sum of squared difference (SSD) measurement method, and the sum of absolute transformed differences.

Here, the empty string is a binarized empty string in the form of a truncated Golomb Rice code, and the empty string may include a prefix and a suffix.

Here, the bin corresponding to the prefix of the empty string can be obtained by arithmetic decoding, and the bin corresponding to the suffix of the empty string can be obtained by bypass decoding.

Here, at least some of the bins corresponding to the prefix of the empty string and the bins corresponding to the suffix of the empty string can be obtained by arithmetic decoding.

Here, the empty string is an empty string binarized into a truncated single code form, and among the empty strings, bins less than or equal to a preset number can be obtained by the above arithmetic decoding.

FIG. 9 is a flowchart illustrating an entropy encoding method according to an embodiment of the present invention.

The video encoding device can derive a syntax element indicating a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction (S910).

The image encoding device can generate an empty string including at least one bin by binarizing a syntax element (S920). Here, bypass coding may be applied to at least some bins of the empty string, and arithmetic coding may be applied to bins other than bins to which bypass coding of the empty string has been applied.

A bitstream can be generated by encoding each bin of an empty string according to an encoding method corresponding to each bin (S930).

A bitstream can be generated by a video encoding method including the steps described in FIG. 9. The bitstream can be stored in a non-transitory computer-readable recording medium, and can also be transmitted (or streamed).

FIG. 10 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

As illustrated in FIG. 10, a content streaming system to which an embodiment of the present invention is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

The encoding server compresses content input from multimedia input devices such as smartphones, cameras, CCTVs, etc. into digital data to generate a bitstream and transmits it to the streaming server. As another example, if multimedia input devices such as smartphones, cameras, CCTVs, etc. directly generate a bitstream, the encoding server may be omitted.

The above bitstream can be generated by an image encoding method and/or an image encoding device to which an embodiment of the present invention is applied, and the streaming server can temporarily store the bitstream during the process of transmitting or receiving the bitstream.

The above streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server can act as an intermediary that informs the user of any available services. When a user requests a desired service from the web server, the web server transmits it to the streaming server, and the streaming server can transmit multimedia data to the user. At this time, the content streaming system may include a separate control server, and in this case, the control server may perform a role of controlling commands/responses between each device within the content streaming system.

The above streaming server can receive content from a media storage and/or an encoding server. For example, when 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.

Examples of the user devices may include mobile phones, smart phones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, HMDs), digital TVs, desktop computers, digital signage, etc.

Each server within the above content streaming system can be operated as a distributed server, in which case data received from each server can be distributedly processed.

The above embodiments can be performed in the same or corresponding manner in the encoding device and the decoding device. In addition, an image can be encoded/decoded using at least one or a combination of at least one of the above embodiments.

The order in which the above embodiments are applied may be different in the encoding device and the decoding device. Alternatively, the order in which the above embodiments are applied may be the same in the encoding device and the decoding device.

The above embodiments can be performed for each of the luminance and chrominance signals, or the above embodiments can be performed identically for the luminance and chrominance signals.

In the above embodiments, the methods are described based on the flowchart as a series of steps or units, but the present invention is not limited to the order of the steps, and some steps may occur in a different order or simultaneously with other steps described above. In addition, those skilled in the art will understand that the steps shown in the flowchart are not exclusive, and other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

The above embodiments may be implemented in the form of program commands that can be executed through various computer components and recorded on a computer-readable recording medium. The computer-readable recording medium may include program commands, data files, data structures, etc., alone or in combination. The program commands recorded on the computer-readable recording medium may be those specifically designed and configured for the present invention or may be those known to and available to those skilled in the art of computer software.

A bitstream generated by an encoding method according to the above embodiment can be stored in a non-transitory computer-readable recording medium. In addition, the bitstream stored in the non-transitory computer-readable recording medium can be decoded by a decoding method according to the above embodiment.

Here, examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical recording media such as CD-ROMs, DVDs, magneto-optical media such as floptical disks, and hardware devices specifically configured to store and execute program instructions such as ROMs, RAMs, flash memories, and the like. Examples of program instructions include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices may be configured to operate as one or more software modules to perform the processing according to the present invention, and vice versa.

Although the present invention has been described above with specific details such as specific components and limited examples and drawings, these have been provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those with common knowledge in the technical field to which the present invention belongs can make various modifications and variations from this description.

Therefore, the idea of the present invention should not be limited to the embodiments described above, and not only the claims described below but also all modifications equivalent to or equivalent to the claims are included in the scope of the idea of the present invention.

The present invention can be used in a device for encoding/decoding an image and a recording medium storing a bitstream.

Claims (15)

In a video decryption method, A step of obtaining an empty string corresponding to a syntax element from a bitstream, wherein the syntax element represents a combination of an intra prediction mode of a current block and a reference sample line used for intra prediction; A step of obtaining the syntactic elements by de-binarizing the above empty string; and Comprising a step of performing intra prediction of the current block based on the above syntactic elements, An image decoding method, characterized in that at least some of the bins of the above empty string are obtained by bypass decoding, and the bins of the above empty string except for the bypass-coded bins are obtained by arithmetic decoding. In the first paragraph, An image decoding method, characterized in that the intra prediction of the current block uses an intra prediction mode indicated by the syntax element and a reference sample line indicated by the syntax element among a plurality of reference sample lines adjacent to the current block. In the first paragraph, The above syntactic elements are: A method for decoding an image, characterized by indicating one candidate from a candidate list including candidates indicating different combinations of intra prediction modes and reference sample lines used for intra prediction. In the third paragraph, The intra prediction modes of the above candidates are: A video decoding method characterized by being an intra prediction mode excluding a predetermined predetermined mode. In the third paragraph, The above candidates in the above candidate list are, A method for decoding an image, characterized in that a plurality of candidates are selected based on a cost value of intra prediction based on a combination of an intra prediction mode and a reference sample line. In clause 5, The above cost values are, An image decoding method, characterized in that the result of intra prediction based on a combination of an intra prediction mode and a reference sample line is determined based on a comparison result between a prediction value corresponding to a template including samples adjacent to the current block. In Article 6, The above template is, An image decoding method, characterized in that it includes samples of a reference sample line closest to the current block. In clause 5, An image decoding method, characterized in that the above cost value is measured using any one of a sum of absolute differences (SAD) measurement method, a sum of squared difference (SSD) measurement method, and a sum of absolute transformed differences. In the first paragraph, The above empty string is an empty string binarized in the form of a truncated Golomb Rice code, An image decoding method, characterized in that the above empty string includes a prefix and a suffix. In Article 9, The bin corresponding to the prefix of the above empty string is obtained by the above arithmetic decoding, An image decoding method, characterized in that a bin corresponding to a suffix of the above empty string is obtained by the above bypass decoding. In Article 9, An image decoding method, characterized in that at least some of the bins corresponding to the prefix of the empty string and the bins corresponding to the suffix of the empty string are obtained by the arithmetic decoding. In the first paragraph, The above empty string is an empty string binarized into a truncated single code form, An image decoding method, characterized in that among the above empty strings, bins less than or equal to a preset number are obtained by the arithmetic decoding. In a video encoding method, A step of deriving a syntax element that indicates a combination of an intra prediction mode of the current block and a reference sample line used for intra prediction; A step of generating an empty string by binarizing the above syntax elements; and A step of generating a bitstream by encoding each bin of the above empty string according to an encoding method corresponding to each bin, An image decoding method, characterized in that bypass coding is applied to at least some of the bins of the above empty string, and arithmetic coding is applied to bins of the above empty string except for the bins to which bypass coding is applied. A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method, The above image encoding method is, A step of deriving a syntax element that indicates a combination of an intra prediction mode of the current block and a reference sample line used for intra prediction; A step of generating an empty string by binarizing the above syntax elements; and A step of generating a bitstream by encoding each bin of the above empty string according to an encoding method corresponding to each bin, A non-transitory computer-readable recording medium, characterized in that bypass coding is applied to at least some of the bins of the above empty string, and arithmetic coding is applied to bins of the above empty string except for the bins to which bypass coding is applied. A method for transmitting a bitstream generated by a video encoding method, The above transmission method comprises a step of transmitting the bitstream, The above image encoding method is, A step of deriving a syntax element that indicates a combination of an intra prediction mode of the current block and a reference sample line used for intra prediction; A step of generating an empty string by binarizing the above syntax elements; and A step of generating a bitstream by encoding each bin of the above empty string according to an encoding method corresponding to each bin, A transmission method, characterized in that bypass coding is applied to at least some of the bins of the above empty string, and arithmetic coding is applied to bins of the above empty string except for the bins to which bypass coding is applied.

Images