WO2025192990A1 - Method and device for image encoding/decoding and recording medium having bitstreams stored therein - Google Patents

Abstract

Provided are a method and a device for image encoding/decoding, a recording medium having bitstreams stored therein, and a transmission method. The method for image decoding may comprise the steps of: generating an occurrence frequency histogram of an intra prediction mode regarding at least one peripheral block adjacent to the current block; generating a merge candidate list including at least one merge candidate by using the occurrence frequency histogram of the intra prediction mode of the at least one peripheral block; and performing intra prediction regarding the current block on the basis of the merge candidate list. The merge candidate list may include occurrence frequency histograms of intra prediction modes for different peripheral blocks.

Description

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

The present invention relates to a video encoding/decoding method, device, and recording medium storing a bitstream. Specifically, the present invention relates to a video encoding/decoding method, device, and recording medium storing a bitstream for intra prediction based on occurrence frequency.

Recently, the demand for high-resolution, high-quality images, such as UHD (Ultra High Definition) images, is increasing across various application fields. As image data becomes higher in resolution and quality, the relative amount of data increases compared to conventional image data. Therefore, transmitting image data using existing media such as wired or wireless broadband lines or storing it using existing storage media leads to increased transmission and storage costs. To address these issues arising from the increasing resolution and quality of image data, high-efficiency image encoding/decoding technologies for higher-resolution and higher-quality images are required.

Specifically, frequency-based intra prediction can be performed in video encoding/decoding methods. Specifically, frequency-based intra prediction can be a prediction mode that generates a prediction block based on the frequency of occurrence of the intra prediction modes of neighboring blocks adjacent to the prediction target block. In this regard, a method for improving the efficiency of frequency-based intra prediction may be needed.

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 an intra prediction method using an intra merge mode based on occurrence frequency in order to improve the efficiency of intra prediction based on the occurrence frequency as described above.

A video decoding method according to one embodiment of the present invention includes the steps of generating an occurrence frequency histogram of an intra prediction mode for at least one neighboring block adjacent to a current block, generating a merge candidate list including at least one merge candidate using the occurrence frequency histogram of the intra prediction mode of the at least one neighboring block, and performing intra prediction based on the merge candidate list to generate a prediction block of the current block, wherein the merge candidate list may include occurrence frequency histograms of intra prediction modes for different neighboring blocks.

In the above image decoding method, the surrounding blocks may include blocks spatially adjacent to the current block and blocks not spatially adjacent to the current block.

In the above image decoding method, a block that is not spatially adjacent to the current block may be included in at least one of a left area of the current block, an upper area of the current block, and an upper left area of the current block.

In the above image decoding method, an occurrence frequency histogram of an intra prediction mode for the surrounding block can be generated by accumulating intra prediction modes of blocks adjacent to the surrounding block.

In the above image decoding method, the intra prediction mode of a block adjacent to the surrounding block can be accumulated in the occurrence frequency histogram based on the size of the block adjacent to the surrounding block.

In the above image decoding method, the surrounding block may be a block that is intra-predicted based on an occurrence frequency histogram of an intra-prediction mode.

In the above image decoding method, the at least one merge candidate can be derived using a predetermined number of occurrence frequency histograms among occurrence frequency histograms of intra prediction modes of the at least one surrounding block.

In the above image decoding method, the prediction block of the current block can be generated based on one merge candidate indicated by a merge candidate index among the at least one merge candidate.

In the above image decoding method, the prediction block of the current block can be generated based on at least one intra prediction mode derived from an occurrence frequency histogram of the intra prediction mode of the one merge candidate.

In the above image decoding method, the merge candidate index can be decoded based on information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram.

In the above image decoding method, information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram may include information indicating that the intra prediction mode is a prediction mode using a merge candidate list.

In the above image decoding method, information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram can be decoded based on information indicating that the intra prediction mode is a decoder-side intra mode derivation mode.

A video encoding method according to one embodiment of the present invention includes the steps of generating an occurrence frequency histogram of an intra prediction mode for at least one neighboring block adjacent to a current block, generating a merge candidate list including at least one merge candidate using the occurrence frequency histogram of the intra prediction mode of the at least one neighboring block, and performing intra prediction for the current block based on the merge candidate list, wherein the merge candidate list may include occurrence frequency histograms of intra prediction modes for different neighboring blocks.

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, the method comprising the steps of: generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to a current block; generating a merge candidate list including at least one merge candidate using the histogram of occurrence frequencies of intra prediction modes of the at least one neighboring block; and performing intra prediction for the current block based on the merge candidate list, wherein the merge candidate list includes histograms of occurrence frequencies of intra prediction modes for different neighboring blocks.

A bitstream transmission method according to one embodiment of the present invention comprises the steps of transmitting the bitstream, generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to a current block, generating a merge candidate list including at least one merge candidate using the histogram of occurrence frequencies of intra prediction modes of the at least one neighboring block, and performing intra prediction for the current block based on the merge candidate list, wherein the merge candidate list includes histograms of occurrence frequencies of intra prediction modes for different neighboring blocks. A bitstream generated by an image encoding method can be transmitted.

The features briefly summarized above of the present invention are merely exemplary aspects of the detailed description of the present invention described below and do not limit the scope of the present invention.

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 intra prediction method can be provided that improves the efficiency of intra prediction based on occurrence frequency by using a merge mode based on occurrence frequency.

In addition, according to the present invention, intra prediction efficiency can be improved.

The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present invention 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.

Figure 2 is a block diagram showing the configuration according to 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 drawing for explaining a surrounding block of a current block according to one embodiment of the present invention.

FIG. 5 is a drawing for explaining a surrounding block of a current block according to one embodiment of the present invention.

FIG. 6 is a drawing for explaining a surrounding block of a current block according to one embodiment of the present invention.

FIG. 7 is a drawing for explaining a surrounding block of a current block according to one embodiment of the present invention.

Figure 8 is a flowchart illustrating an image decoding method according to an embodiment of the present invention.

FIG. 9 is a drawing exemplarily showing a content streaming system to which an embodiment according to the present invention can be applied.

The present invention is susceptible to various modifications and embodiments. Therefore, 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 rather to encompass all modifications, equivalents, and substitutes falling within the spirit and scope of the present invention. In the drawings, similar reference numerals designate the same or similar functions throughout. The shape and size of elements in the drawings may be provided by way of example only for clarity. The detailed description of the exemplary embodiments described below refers to the accompanying drawings, which illustrate specific embodiments. 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, while different, 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. Furthermore, it should be understood that the location or arrangement of individual components within each disclosed embodiment may be modified without departing from the spirit and scope of the embodiment. Accordingly, the detailed description set forth below is not intended to be taken in a limiting sense, and the scope of the exemplary embodiments, if properly described, is defined only by the appended claims, along with the full scope equivalents to which such claims are entitled.

In the present invention, terms such as first, second, etc. may be used to describe various components, but the components should not be limited by these terms. These terms are used solely to distinguish 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 multiple related described items or any of multiple related described items.

The components shown in the embodiments of the present invention are independently depicted to represent different characteristic functions, and do not mean that each component is composed of separate hardware or a single software component. 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 a single component may be divided into multiple components to perform a function, and such integrated 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 herein is merely 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 merely for performance enhancement. The present invention may be implemented by including only components essential to realizing the essence of the present invention, excluding components used only for performance enhancement, and a structure including only essential components, excluding optional components used only for performance enhancement, is also within the scope of the present invention.

In an embodiment, the term "at least one" may 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" may 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 described in detail 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. The same reference numerals will be used for identical components in the drawings, and duplicate descriptions of identical components will be omitted.

Glossary of Terms

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

Hereinafter, the terms "video" and "movie" may be used interchangeably and have the same meaning. Furthermore, the target image may be an encoding target image, which is the target of encoding, and/or a decoding target image, which is the target of decoding. Furthermore, the target image may be an input image input to an encoding device, or 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 have the same meaning.

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

Hereinafter, the term "target block" may refer to an encoding target block, which is the target of encoding, and/or a decoding target block, which is the target of decoding. Furthermore, the target block may refer to a current block, which is the target of current encoding and/or decoding. For example, the terms "target block" and "current block" may be used interchangeably and have the same meaning.

Hereinafter, "block" and "unit" may be used with the same meaning and may be used interchangeably. In addition, "unit" may mean including a luminance component block and a corresponding chroma component block 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 associated with it.

Hereinafter, the terms “sample,” “pixel,” and “pixel” may be used interchangeably and have the same meaning. Here, a sample may represent a basic unit that constitutes 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. A video may include one or more images. The encoding device (100) may sequentially encode one or more images.

Referring to FIG. 1, the 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).

Additionally, 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 via 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 more tiles or slices, which can then be segmented into multiple Coding Tree Units (CTUs). Alternatively, one picture can first be segmented into multiple sub-pictures defined as groups of rectangular slices, and each sub-picture can then 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 each be individually restored, there is an advantage of easy editing in applications that configure multi-channel input into a single picture. In addition, tiles can be segmented horizontally to generate bricks. Here, a brick can be utilized as the basic unit of intra-picture parallel processing. In addition, one CTU can be recursively split into a quadtree (QT), and the terminal node of the split can be defined as a coding unit (CU). The CU can be split into a prediction unit (PU) and a transformation unit (TU), and prediction and splitting can be performed. 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 a multi-type tree (MTT) as well as a quadtree (QT). 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 binary tree (BT) and a triple tree (TT). For example, the MTT structure can be divided 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, in order to increase the encoding efficiency of the I slice, a dual tree that uses different CTU split structures for luma and chrominance components can be applied. 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 that shares the coding tree structure.

The encoding device (100) may perform encoding on the input image in intra mode and/or 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 inter mode. However, if the third mode has functional characteristics similar to the intra mode or inter mode, it may be classified as intra mode or inter mode for convenience of explanation. In the present invention, the third mode will be classified and described separately only when a specific description 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 that is currently a target of encoding. The input block can be referred to as a current block that is currently a target of encoding or an encoding target block.

When 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 samples, 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, as well as 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 derive a motion vector using the searched area. At this time, the area can be used as a search 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 may 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 the reference image when the value of the 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 the prediction unit included in the 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 and 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), and the OBMC (Overlapped Block Motion Compensation) 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. In the existing video coding standard, since MC (Motion Compensation) is performed 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 4-parameter affine motion model using two control point motion vectors (CPMV) and a 6-parameter affine motion model using three control point motion vectors can be applied to inter prediction. Here, CPMV is a vector representing the 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 refer to 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 may be a coefficient value generated by performing a transform on the residual block. When the transform skip mode is applied, the transform unit (130) may also skip the transform on the residual block.

Quantized levels can be generated by applying quantization to transform coefficients or residual signals. In the following embodiments, quantized levels may also be referred to as transform coefficients.

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 the remaining residual blocks can be transformed using a basis vector based on DCT (Discrete Cosine Transform). In addition, through RQT (Residual Quad Tree) technology, the transform block is divided into a quad tree shape for one block, 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.

Another alternative is to apply Multiple Transform Selection (MTS) technology, which selectively performs transformation using multiple transformation bases. That is, instead of dividing CUs into TUs via RQT, a Sub-block Transform (SBT) technology can perform a function similar to TU division. Specifically, SBT is applied only to inter-screen prediction blocks, and unlike RQT, it can divide the current block into ½ or ¼ blocks vertically or horizontally, and then perform transformation on only one of the blocks. For example, in a vertically divided block, the transformation can be performed on the leftmost or rightmost block, and in a horizontally divided block, the transformation can be performed on the topmost or bottommost block.

Additionally, LFNST (Low Frequency Non-Separable Transform), a secondary transform technique that further 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, which allows the residual coefficients to be concentrated in the upper left.

The quantization unit (140) can generate a quantized level by quantizing a transform coefficient or 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 with QP values of 0 to 51 can be used. Alternatively, if the image size is larger and high encoding efficiency is required, a QP of 0 to 63 can be used. In addition, a Dependent Quantization (DQ) method that uses two quantizers instead of a single quantizer can be applied. DQ performs quantization using two quantizers (e.g., Q0 and Q1), but 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 during 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, the information for decoding the image can include syntax elements, etc.

When entropy encoding is applied, a small number of bits are allocated to symbols with a high occurrence probability, and a large number of bits are allocated to symbols with a low occurrence probability, thereby representing the symbols, whereby the size of the bit string for the 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 perform arithmetic encoding using the binarization method, probability model, and context model derived from the binarization method of the target symbol and the probability model of the target symbol/bin.

In this regard, when applying CABAC, the table probability update method can be changed to a simple formula-based table update method to reduce the size of the probability table stored in the decryption device. Furthermore, 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 not only information (flags, indexes, etc.) encoded in an encoding device (100) and signaled to a decoding device (200), such as syntax elements, but also 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. Accordingly, the encoding device (100) can reconstruct or decode the encoded current image again and store the reconstructed 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 inversely transformed in the inverse transformation unit (170). The dequantized and/or inversely 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 inversely transformed coefficients and the prediction block. Here, the dequantized and/or inversely transformed coefficients refer to coefficients on which at least one of dequantization and inverse transformation has been performed, and may refer to a reconstructed residual block. The dequantization unit (160) and the inverse transformation unit (170) can be performed in the reverse process of the quantization unit (140) and the transformation 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), a Luma Mapping with Chroma Scaling (LMCS), 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 referred to as an in-loop filter. In this case, the in-loop filter is also used as a name excluding LMCS.

A deblocking filter can remove block distortion that occurs at the boundaries between blocks. Whether to apply a deblocking filter to the current block can be determined based on the samples contained in several columns or rows within the block. When applying a deblocking filter to a block, different filters can be applied depending on the required deblocking filtering strength.

Sample adaptive offset can be used to compensate for encoding errors by adding an appropriate offset value to sample values. Sample adaptive offset can compensate for the offset from the original image on a sample-by-sample basis for deblocked images. This can be done by dividing the samples contained in the image into a fixed number of regions, determining the regions to be offset, and applying the offset to those regions. Alternatively, the offset can be 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 between a reconstructed image and the original image. By dividing the samples contained in the image into predetermined groups and determining the filter to be applied to each group, filtering can be performed differentially for each group. Information regarding 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 applied to each block can vary.

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 that scales the residual values of chrominance 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.

Figure 2 is a block diagram showing the configuration according to 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 a bitstream streamed through a wired/wireless transmission medium. The decoding device (200) can perform decoding on the bitstream in intra mode or 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 decode the input bitstream to obtain a reconstructed residual block and generate a prediction block. Once 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 block to be decoded may 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 may include symbols in the form of quantized levels. Here, the entropy decoding method may 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 inversely quantized in the inverse quantization unit (220) and inversely transformed in the inverse transformation unit (230). The quantized level can be generated as a restored residual block as a result of performing inverse quantization and/or inverse transformation. At this time, the inverse quantization unit (220) can apply a quantization matrix to the quantized level. The inverse quantization unit (220) and inverse transformation unit (230) applied to the decoding device can apply the same technology as the inverse quantization unit (160) and inverse transformation unit (170) applied to the encoding device described above.

When intra mode is used, the intra prediction unit (240) can generate a predicted 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 generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference picture buffer (270) on the current block. The motion compensation unit (250) can generate a prediction block by applying an interpolation filter to a portion of the reference image 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 skip mode, merge mode, AMVP mode, or current picture reference mode based on the encoding unit, and motion compensation can be performed 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 predicted 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 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 generation unit (11), an encoding unit (12), and a transmission unit (13). A decoding device (20) according to one embodiment may include a reception unit (21), a decoding unit (22), and a rendering unit (23). The encoding unit (12) may be referred to as a video/image encoding unit, and the decoding unit (22) may be referred to as a video/image decoding unit. The transmission unit (13) may be included in the encoding unit (12). The reception 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 video/images through a process of capturing, synthesizing, or generating video/images. 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/images, etc. The video/image generation device can include, for example, a computer, a tablet, a smartphone, etc., and can (electronically) generate video/images. For example, a virtual video/image can be generated through a computer, etc., in which 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) via 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 via 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.

In this specification, we describe an occurrence-based intra coding (OBIC) method for deriving intra prediction modes. Here, the term "OBIC method" may be used interchangeably with "OBIC mode" and may be used interchangeably.

The On-By-Channel Inverse Coding (OBIC) method may refer to a method for deriving the intra prediction mode of a current block based on the occurrence frequency of the intra prediction modes of surrounding blocks. Specifically, according to the OBIC method, a histogram of occurrence frequencies (HoC) for each of the surrounding blocks of the current block can be derived. Furthermore, the intra prediction mode of the current block can be derived using the histogram of occurrence frequencies for each of the surrounding blocks.

The surrounding blocks used for the OBIC method may include adjacent surrounding blocks, which are blocks adjacent to the current block, and non-adjacent surrounding blocks, which are blocks not adjacent to the current block. The surrounding blocks used for the OBIC method may be as described below.

FIG. 4 is a diagram illustrating neighboring blocks of a current block according to one embodiment of the present invention. Specifically, FIG. 4 is a diagram illustrating adjacent neighboring blocks among neighboring blocks of the current block.

Referring to FIG. 4, adjacent neighboring blocks (403), which are blocks spatially adjacent to a current block (401) in a current picture (400), can be defined. For example, the adjacent neighboring blocks can be composed of at least one of an upper adjacent neighboring block (AD), an upper right adjacent neighboring block (E-H), a left adjacent neighboring block (I-L), a left below adjacent neighboring block (M-P), and an upper left adjacent neighboring block (Q).

Additionally, the intra-prediction mode of the current block can be derived based on adjacent neighboring blocks. For example, the intra-prediction modes of adjacent neighboring blocks can be accumulated to generate an occurrence frequency histogram. Then, the intra-prediction mode of the current block can be derived based on this occurrence frequency histogram.

Meanwhile, the location of the adjacent neighboring block in FIG. 4 is an example, and the location of the adjacent neighboring block may be any location adjacent to the current block. The location of the adjacent neighboring block may be predefined by the encoder/decoder. Alternatively, information regarding the location of the adjacent neighboring block may be determined by the encoder and transmitted to the decoder. Alternatively, the location of the adjacent neighboring block may be indicated by information regarding the current block.

FIG. 5 is a diagram illustrating neighboring blocks of a current block according to one embodiment of the present invention. Specifically, FIG. 5 is a diagram illustrating non-adjacent neighboring blocks among the neighboring blocks of the current block.

Referring to Fig. 5, a predetermined area around a current block (501) in a current picture (500) can be defined as a neighboring area (502). In addition, a block that is not spatially adjacent to the current block but is included in the neighboring area can be defined as a non-adjacent neighboring block (503).

In addition, the intra prediction mode can be derived based on non-adjacent neighboring blocks (503). For example, the intra prediction modes of non-adjacent neighboring blocks (503) can be accumulated to generate an occurrence frequency histogram. In addition, the intra prediction mode of the current block can be derived based on the occurrence frequency histogram.

Meanwhile, in FIG. 5, the surrounding area including the non-adjacent surrounding block (503) is the left area, the upper left area, and the upper area of the current block, but this is just one example, and the non-adjacent surrounding block (503) may be included in a preset area. In this case, the preset area may be any one of the current tile, the current slice, and the current picture including the current block.

Meanwhile, the locations of non-adjacent neighboring blocks in FIG. 5 are merely examples, and can be any location within the surrounding area. The locations of non-adjacent neighboring blocks can be determined by an agreement between the encoder and decoder. Furthermore, information regarding the locations of non-adjacent neighboring blocks can be determined by the encoder and transmitted to the decoder. Furthermore, the locations of non-adjacent neighboring blocks can be indicated by information regarding the current block.

Additionally, the occurrence frequency histogram may be generated based on the intra prediction modes of the surrounding blocks of the current block. Specifically, the occurrence frequency histogram may be generated by accumulating the intra prediction modes of the surrounding blocks. Here, the surrounding blocks may include at least one of adjacent surrounding blocks and non-adjacent surrounding blocks.

At this time, the intra prediction modes of the surrounding blocks can be accumulated as is to generate an occurrence frequency histogram.

Alternatively, to generate an occurrence frequency histogram, intra prediction modes of surrounding blocks can be accumulated based on the size of the surrounding blocks.

For example, the intra prediction mode of a neighboring block can be accumulated in proportion to the size of the neighboring block. That is, the value obtained by multiplying the size of the neighboring block by an arbitrary real number can be accumulated in the occurrence frequency histogram. Here, the arbitrary real number can be determined by the encoder/decoder's agreement.

For example, the size of a corresponding neighboring block may refer to a value obtained by multiplying the width and height of the corresponding neighboring block. The size of the corresponding neighboring block may be determined by the number of pixels contained in the corresponding neighboring block. For example, the intra prediction mode of the neighboring block may be accumulated in proportion to the number of pixels contained in the corresponding neighboring block. Specifically, a value obtained by multiplying the number of pixels contained in the corresponding neighboring block by a predetermined real number may be accumulated in the occurrence frequency histogram. Here, the predetermined real number may be defined by a convention of the encoder/decoder.

For example, if the intra prediction mode of a specific surrounding block is mode 10 and the size of the surrounding block is 16×8, the histogram of occurrence frequencies can accumulate frequencies as many times as 128 (= 16×8) as the real number for intra prediction mode 10, that is, as many times as the real number of samples in the surrounding block. That is, the histogram of occurrence frequencies can be generated according to the following mathematical expression 1.

Here, Width may indicate the horizontal length of a specific neighboring block, and Height may indicate the vertical length of each specific neighboring block. In addition, C may be any real number. When generating a histogram of occurrence frequencies, if only the number of samples in the neighboring blocks is considered, C may be 1. Alternatively, the value of C may be determined by considering the characteristics of different neighboring blocks. For example, the value of C may be determined depending on whether a specific neighboring block is adjacent to the current block or is a non-adjacent block. Using this method, the final histogram of occurrence frequencies may be generated based on the occurrence frequencies of the intra prediction modes calculated by considering the intra prediction modes, sizes, positions, etc. of all neighboring blocks.

Alternatively, the size of the surrounding block may be determined by at least one of the width and height of the surrounding block. As another example, the intra prediction mode of the surrounding block may be accumulated in the occurrence frequency histogram based on at least one of the width and height of the surrounding block.

Meanwhile, the number of pixels contained in a given neighboring block and the number of samples in that neighboring block may have the same meaning. For example, the intra prediction mode of a neighboring block may be accumulated in proportion to the number of samples in that neighboring block.

Meanwhile, if the intra prediction mode of the pixel included in the surrounding block is a mode that uses multiple intra prediction modes, such as SGPM, TIMD, and DIMD modes, the occurrence histogram can be generated by considering multiple intra prediction modes.

Therefore, when an occurrence frequency histogram is generated, one or more intra prediction modes can be derived based on the generated occurrence frequency histogram, and intra prediction can be performed based on the derived intra prediction modes.

Specifically, according to the OBIC method, N intra prediction modes can be selected in order of occurrence frequency from a histogram of occurrence frequencies, and N prediction blocks can be generated using the selected intra prediction modes. Then, the N prediction blocks can be weighted to generate a final intra prediction block of the current block. Alternatively, the final intra prediction block can be generated by weighting a prediction block generated using the N prediction blocks and an arbitrary intra prediction mode. Here, the arbitrary intra prediction mode can be a non-directional mode such as a DC mode or a planar mode, or a predetermined directional mode. And, N is an arbitrary positive integer.

In addition, if M intra prediction modes, which are less than N, are derived from a histogram of occurrence frequencies derived from neighboring blocks of the current block, M prediction blocks can be generated using the M intra prediction modes. Then, the final intra prediction block of the current block can be generated by weighting and adding the generated M prediction blocks. Alternatively, the final intra prediction block can be generated by weighting and adding a prediction block generated using the M prediction blocks and an arbitrary intra prediction mode. Here, the arbitrary intra prediction mode can be a non-directional mode such as a DC mode or a planar mode, or a predetermined directional mode. And, M is an arbitrary positive integer.

A final intra prediction block can be generated by applying weights to prediction blocks generated using intra prediction modes selected in descending order of occurrence frequency from a histogram of occurrence frequencies. Here, the values of the weights applied to the prediction blocks generated using the selected intra prediction modes can be derived based on the occurrence frequency of each intra prediction mode from the final histogram of occurrence frequencies.

According to an embodiment of the present disclosure, when performing intra prediction, a merge candidate list including information on occurrence frequency histograms of surrounding blocks can be generated, and intra prediction can be performed using the merge candidate list. This can be referred to as an OBIC Merge (Merge of Occurrence Based Intra Coding, OBIC Merge) method. Here, the “OBIC Merge method” can be used with the same meaning as the “OBIC Merge Mode”, and the two can be used interchangeably.

Specifically, according to the OBIC merge method, a histogram of occurrence frequencies (HoC) of each of the neighboring blocks of the current block can be derived. Then, a merge candidate list including one or more merge candidates can be derived based on the histogram of occurrence frequencies of each of the neighboring blocks. A predicted block of the current block can be generated using one of the merge candidates included in the merge candidate list.

The surrounding blocks used for the OBIC merge method may include adjacent surrounding blocks, which are blocks adjacent to the current block, and non-adjacent surrounding blocks, which are blocks not adjacent to the current block. The surrounding blocks used for the OBIC merge method may be as described below.

FIG. 6 is a diagram illustrating neighboring blocks of a current block according to one embodiment of the present invention. Specifically, FIG. 6 is a diagram illustrating adjacent neighboring blocks among neighboring blocks of a current block.

Referring to Fig. 6, adjacent neighboring blocks, which are blocks spatially adjacent to the current block (601) in the current picture (600), can be defined. For example, the adjacent neighboring blocks can be composed of at least one of a left adjacent neighboring block (L), a lower left adjacent neighboring block (BL), an upper left adjacent neighboring block (AL), an upper adjacent neighboring block (A), and an upper right adjacent neighboring block (AR).

Furthermore, the merge candidate list can be derived based on adjacent neighboring blocks. For example, an occurrence frequency histogram of the intra prediction mode of each adjacent neighboring block can be generated. At least some of the occurrence frequency histograms of the adjacent neighboring blocks can be selected, and an occurrence frequency histogram including the selected occurrence frequency histogram can be generated.

Meanwhile, the location of the adjacent neighboring block in FIG. 6 is an example, and the location of the adjacent neighboring block may be any location adjacent to the current block. The location of the adjacent neighboring block may be predefined by the encoder/decoder. Alternatively, information regarding the location of the adjacent neighboring block may be determined by the encoder and transmitted to the decoder. Alternatively, the location of the adjacent neighboring block may be indicated by information regarding the current block.

FIG. 7 is a diagram illustrating neighboring blocks of a current block according to one embodiment of the present invention. Specifically, FIG. 7 is a diagram illustrating non-adjacent neighboring blocks among the neighboring blocks of the current block.

Referring to Fig. 7, a predetermined area around a current block (701) in a current picture (700) can be defined as a neighboring area (702). In addition, a block that is not spatially adjacent to the current block but is included in the neighboring area can be defined as a non-adjacent neighboring block (703).

In addition, the merge candidate list can be derived based on non-adjacent neighboring blocks (703). For example, an occurrence frequency histogram of the intra prediction mode of each non-adjacent neighboring block can be generated. At least some of the occurrence frequency histograms of the non-adjacent neighboring blocks can be selected, and an occurrence frequency histogram including the selected occurrence frequency histogram can be generated.

Meanwhile, in Fig. 7, the surrounding area including the non-adjacent surrounding block (703) is the left area, the upper left area, and the upper area of the current block, but this is just one example, and the non-adjacent surrounding block (703) may be included in a preset area. In this case, the preset area may be any one of the current tile, the current slice, and the current picture including the current block.

Meanwhile, the locations of non-adjacent neighboring blocks in FIG. 7 are merely examples, and can be any location within the surrounding area. The locations of non-adjacent neighboring blocks can be determined by an agreement between the encoder and decoder. Furthermore, information regarding the locations of non-adjacent neighboring blocks can be determined by the encoder and transmitted to the decoder. Furthermore, the locations of non-adjacent neighboring blocks can be indicated by information regarding the current block.

A merge candidate list for the OBIC merge method can be generated using an intra prediction mode occurrence frequency histogram of neighboring blocks of the current block. The neighboring blocks may include at least one of the neighboring blocks illustrated in FIG. 6, which are adjacent neighboring blocks, and the non-adjacent neighboring blocks illustrated in FIG. 7, which are neighboring blocks. Alternatively, the neighboring blocks may include at least one of the neighboring blocks illustrated in FIG. 4, which are adjacent neighboring blocks, and the non-adjacent neighboring blocks illustrated in FIG. 7, which are neighboring blocks. Here, the positions and number of neighboring blocks used to generate the merge candidate list can be arbitrarily determined.

Each of the merge candidates in the merge candidate list may include histogram information of the occurrence frequency of the intra prediction mode of the surrounding blocks. Here, the merge candidate may be derived based on L occurrence frequency histograms having the highest occurrence frequency among the occurrence frequency histograms of the intra prediction modes of the surrounding blocks, taking memory usage into consideration. That is, the merge candidate list may include L occurrence frequency histogram information having the highest occurrence frequency among the occurrence frequency histograms of the intra prediction modes of the surrounding blocks. Here, L may be any positive integer.

Here, a check for overlap between the histogram information of the occurrence frequency of the surrounding blocks and the histogram information of the occurrence frequency already included in the merge candidate list can be performed. That is, if the histogram information of the occurrence frequency of the surrounding blocks is identical to the histogram information of the occurrence frequency already included in the merge candidate list, the histogram information of the occurrence frequency of the surrounding blocks may not be stored in the merge candidate list.

Here, the surrounding blocks for deriving merge candidates may be blocks predicted using the OBIC method or the OBIC merge method. If, among the surrounding blocks of the current block, there is no block predicted using the OBIC method or the OBIC merge method, the OBIC merge method cannot be applied to the current block.

According to the OBIC merge method, among the merge candidates in the constructed merge candidate list, a histogram of the occurrence frequency of a specific merge candidate indicated by a decrypted merge index can be determined. Furthermore, intra prediction for the current block can be performed using the determined occurrence frequency histogram. Here, the number of merge candidates in the merge candidate list can be configured as K, where K is any positive integer.

Specifically, according to the OBIC method, among the merge candidates in the merge candidate list, N intra prediction modes can be selected in descending order of occurrence frequency from a histogram of occurrence frequencies of specific merge candidates indicated by a merge index. N prediction blocks can be generated using the selected intra prediction modes. Then, the final intra prediction block of the current block can be generated by weighting the N prediction blocks. Alternatively, the final intra prediction block can be generated by weighting the prediction block generated using the N prediction blocks and an arbitrary intra prediction mode. Here, the arbitrary intra prediction mode can be a non-directional mode such as a DC mode or a planar mode, or a predetermined directional mode. And, N is an arbitrary positive integer.

In addition, if M intra prediction modes, which are less than N, are derived from a histogram of the occurrence frequency of a specific merge candidate indicated by a merge index, M prediction blocks can be generated using the M intra prediction modes. Then, the final intra prediction block of the current block can be generated by weighting and adding the generated M prediction blocks. Alternatively, the final intra prediction block can be generated by weighting and adding the prediction block generated using the M prediction blocks and an arbitrary intra prediction mode. Here, the arbitrary intra prediction mode can be a non-directional mode such as a DC mode or a planar mode, or a predetermined directional mode. And, M is an arbitrary positive integer.

A final intra prediction block can be generated by applying weights to prediction blocks generated using intra prediction modes selected in descending order of occurrence frequency from a histogram of occurrence frequencies. Here, the values of the weights applied to the prediction blocks generated using the selected intra prediction modes can be derived based on the occurrence frequency of each intra prediction mode from the final histogram of occurrence frequencies.

Meanwhile, the Occurrence-Based Intra Coding (OBIC) method can be an intra prediction mode that uses a method similar to the Decoder-side Intra Mode Derivation (DIMD) method. Therefore, a method is needed to efficiently parse information related to the DIMD method and the OBIC method.

For example, the DIMD method related information may include a DIMD mode flag, which is information indicating that the intra prediction mode is the DIMD mode. In addition, the OBIC method related information may include an OBIC mode flag, which is information indicating that the intra prediction mode is the OBIC mode, an OBIC merge mode flag, which is information indicating that the intra prediction mode is the OBIC merge mode, and a merge candidate index.

According to one embodiment of the present disclosure, an OBIC method may be defined as a sub-mode of the DIMD method. In addition, an OBIC merge mode may be defined as a sub-mode of the OBIC method.

Therefore, information related to the OBIC method can be parsed as sub-information of information related to the DIMD method. Furthermore, information related to the OBIC merge mode can be parsed as sub-information of information related to the OBIC method. Information related to the intra prediction mode can be parsed as described in Table 1 below.

That is, if the current block is intra-predicted based on DIMD mode, the value of the DIMD mode flag (dimd_flag) can be 1. And, if the value of the DIMD mode flag is 1, the OBIC mode flag (obic_flag) can be parsed.

If the current block is intra predicted based on OBIC mode, the value of the OBIC mode flag (obic_flag) can be 1. And, if the value of the OBIC mode flag is 1, the OBIC merge mode flag (obic_merge_flag) can be parsed. Here, the OBIC merge mode flag can be parsed only if there is a block among the surrounding blocks of the current block that is coded by frequency-based intra coding or frequency-based intra coding merge. Meanwhile, if the value of the OBIC mode flag is 0, information related to the DIMD mode can be parsed.

And, if the current block is intra predicted based on OBIC merge mode, the value of the OBIC merge mode flag (obic_merge_flag) may be 1. And, if the value of the OBIC merge mode flag is 1, the merge index (merge_idx) may be parsed. Meanwhile, if the value of the OBIC merge mode flag is 0, OBIC mode related information may be parsed. That is, the OBIC merge mode related information may include an OBIC merge flag indicating whether the OBIC merge mode is applied and a merge candidate index indicating a merge candidate in the merge candidate list. The OBIC merge flag and the merge candidate index may be context coded, and new context models may be added to apply context coding to the OBIC merge flag and the merge candidate index.

An image decoding method that performs intra prediction using a merge candidate list that includes information on occurrence frequency histograms of surrounding blocks may be as described below.

Figure 8 is a flowchart illustrating an image decoding method according to an embodiment of the present invention. The image decoding method of Figure 8 can be performed by an image decoding device.

Referring to FIG. 8, the image decoding device can generate an occurrence frequency histogram of an intra prediction mode for at least one surrounding block adjacent to the current block (S810).

Here, the surrounding blocks may include blocks that are spatially adjacent to the current block and blocks that are not spatially adjacent to the current block.

Here, a block that is not spatially adjacent to the current block may be included in at least one of the left area of the current block, the top area of the current block, and the upper left area of the current block.

In addition, an occurrence frequency histogram of an intra prediction mode for a neighboring block can be generated by accumulating intra prediction modes of blocks adjacent to the neighboring block. Here, the intra prediction modes of blocks adjacent to the neighboring block can be accumulated in the occurrence frequency histogram based on the size of the blocks adjacent to the neighboring block.

Here, the surrounding block may be a block that is intra-predicted based on an occurrence frequency histogram of the intra-prediction mode.

The video decoding device may generate a merge candidate list including at least one merge candidate using an occurrence frequency histogram of an intra prediction mode of at least one neighboring block (S820). Here, the merge candidate list may include occurrence frequency histograms of intra prediction modes for different neighboring blocks. In addition, at least one merge candidate of the merge candidate list may be derived using a predetermined number of occurrence frequency histograms among the occurrence frequency histograms of the intra prediction mode of at least one neighboring block.

The video decoding device can perform intra prediction based on a merge candidate list to generate a prediction block of the current block (S830). Here, the prediction block of the current block can be generated based on one merge candidate indicated by a merge candidate index among at least one merge candidate.

Here, the prediction block of the current block can be generated based on at least one intra prediction mode derived from an occurrence frequency histogram of the intra prediction mode of one merge candidate.

Meanwhile, the merge candidate index can be decoded based on information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram. Here, the information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram may include information indicating that the prediction mode utilizes a merge candidate list.

Here, information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram can be decoded based on information indicating that the intra prediction mode is a decoder-side intra mode derivation mode.

Meanwhile, the steps described in FIG. 8 can be performed in the same manner in an image encoding method. Furthermore, a bitstream can be generated by an image encoding method including the steps described in FIG. 8. The bitstream can be stored on a non-transitory computer-readable recording medium and can also be transmitted (or streamed).

FIG. 9 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. 9, 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, and CCTVs into digital data, generates a bitstream, and transmits it to the streaming server. Alternatively, if multimedia input devices such as smartphones, cameras, and CCTVs directly generate bitstreams, 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 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 to inform the user of available services. When a user requests a desired service from the web server, the web server transmits the request to the streaming server, 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 control commands/responses between each device within the content streaming system.

The streaming server can receive content from a media repository and/or encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a 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 processed in a distributed manner.

The above embodiments can be performed in the same or corresponding manner in an encoding device and a 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. Alternatively, the above embodiments can be performed identically for the luminance and chrominance signals.

In the above embodiments, the methods are described based on a flowchart as a series of steps or units. However, 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. Furthermore, those skilled in the art will understand that the steps depicted in the flowchart are not exclusive, and that 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 by 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., either singly or in combination. The program commands recorded on the computer-readable recording medium may be those specifically designed and constructed for the present invention, or may be known and usable by those skilled in the art of computer software.

The bitstream generated by the 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 the 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 and DVDs, magneto-optical media such as floptical disks, and hardware devices specifically configured to store and execute program instructions such as ROMs, RAMs, and flash memories. Examples of program instructions include not only machine language codes such as those 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 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 are 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 ordinary knowledge in the technical field to which the present invention pertains 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 all things that are modified equally or equivalently to the following claims as well as the claims are considered to fall within 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 the video decryption method, A step of generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to the current block; A step of generating a merge candidate list including at least one merge candidate by using an occurrence frequency histogram of an intra prediction mode of at least one surrounding block; and A step of generating a prediction block of the current block by performing intra prediction based on the merge candidate list, A method for decoding an image, characterized in that the above merge candidate list includes occurrence frequency histograms of intra prediction modes for different surrounding blocks. In the first paragraph, An image decoding method, characterized in that the surrounding blocks include blocks spatially adjacent to the current block and blocks not spatially adjacent to the current block. In the second paragraph, An image decoding method, characterized in that a block that is not spatially adjacent to the current block is included in at least one of a left area of the current block, an upper area of the current block, and an upper left area of the current block. In the first paragraph, An image decoding method, characterized in that the occurrence frequency histogram of the intra prediction mode for the above-mentioned surrounding block is generated by accumulating the intra prediction modes of blocks adjacent to the above-mentioned surrounding block. In the fourth paragraph, An image decoding method, characterized in that the intra prediction mode of a block adjacent to the above-mentioned surrounding block is accumulated in the occurrence frequency histogram based on the size of the block adjacent to the above-mentioned surrounding block. In the first paragraph, An image decoding method, characterized in that the above-mentioned surrounding block is a block that is intra-predicted based on an occurrence frequency histogram of an intra-prediction mode. In the first paragraph, An image decoding method, characterized in that the at least one merge candidate is derived using a predetermined number of occurrence frequency histograms among occurrence frequency histograms of intra prediction modes of the at least one surrounding block. In paragraph 7, An image decoding method, characterized in that the prediction block of the current block is generated based on one merge candidate indicated by a merge candidate index among the at least one merge candidate. In paragraph 8, An image decoding method, characterized in that the prediction block of the current block is generated based on at least one intra prediction mode derived from an occurrence frequency histogram of the intra prediction mode of the one merge candidate. In paragraph 8, The above merge candidate index is, A method for decoding an image, characterized in that the image is decoded based on information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram. In the first paragraph, A video decoding method, characterized in that the information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram includes information indicating that the prediction mode uses a merge candidate list. In Article 11, A video decoding method, characterized in that information indicating that the intra prediction mode is a prediction mode based on an occurrence frequency histogram is decoded based on information indicating that the intra prediction mode is a decoder-side intra mode derivation mode. In the image encoding method, A step of generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to the current block; A step of generating a merge candidate list including at least one merge candidate by using an occurrence frequency histogram of an intra prediction mode of at least one surrounding block; and A step of performing intra prediction for the current block based on the merge candidate list is included. A video encoding method, characterized in that the above merge candidate list includes occurrence frequency histograms of intra prediction modes for different surrounding blocks. In 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 generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to the current block; A step of generating a merge candidate list including at least one merge candidate by using an occurrence frequency histogram of an intra prediction mode of at least one surrounding block; and A step of performing intra prediction for the current block based on the merge candidate list is included. A non-transitory computer-readable recording medium, characterized in that the merge candidate list includes occurrence frequency histograms of intra prediction modes for different surrounding blocks. In a method for transmitting a bitstream generated by a video encoding method, The above transmission method includes a step of transmitting the bitstream, The above image encoding method is, A step of generating a histogram of occurrence frequencies of intra prediction modes for at least one neighboring block adjacent to the current block; A step of generating a merge candidate list including at least one merge candidate by using an occurrence frequency histogram of an intra prediction mode of at least one surrounding block; and A step of performing intra prediction for the current block based on the merge candidate list is included. A transmission method, characterized in that the above merge candidate list includes occurrence frequency histograms of intra prediction modes for different surrounding blocks.