Image conversion-based image encoding / decoding method, method for transmitting bit stream, and recording medium for storing bit stream

Abstract

An image encoding / decoding method, a bit stream transmission method, and a computer-readable recording medium for storing a bit stream are provided. An image decoding method according to the present disclosure is an image decoding method performed by an image decoding device, and may comprise the steps of: reconstructing a picture from a bitstream; and transforming the reconstructed picture based on one of the at least one candidate transformation, where the at least one candidate transformation corresponds to a rotational transformation or a symmetric transformation for the picture.

Description

Technical Field

[0001] The present disclosure relates to an image encoding / decoding method, a method for transmitting a bitstream, and a recording medium storing the bitstream, and to an image encoding / decoding method, a method for transmitting a bitstream, and a recording medium storing the bitstream based on image transformation. Background Art

[0002] Recently, the demand for high-resolution and high-quality images such as high-definition (HD) images and ultra-high-definition (UHD) images is increasing in various fields. As the resolution and quality of image data are improved, the amount of information or the amount of bits transmitted is relatively increased compared to existing image data. The increase in the amount of information or the amount of bits transmitted leads to an increase in transmission cost and storage cost.

[0003] Therefore, there is a need for efficient image compression technology to effectively transmit, store, and reproduce information about high-resolution and high-quality images. Summary of the invention

[0004] Technical issues

[0005] An object of the present disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] In addition, the object of the present disclosure is to propose an image pre-processing / post-processing method.

[0007] In addition, the present disclosure aims to propose an image pre-processing / post-processing method of a coding tree unit or a coding unit.

[0008] In addition, an object of the present disclosure is to propose a method of selecting an optimal preprocessing method from various preprocessing methods.

[0009] In addition, an object of the present disclosure is to provide a non-transitory recording medium storing a bit stream generated by the image encoding method according to the present disclosure.

[0010] In addition, an object of the present disclosure is to provide a non-transitory recording medium that stores a bit stream received and decoded by the image decoding device according to the present disclosure and used to reconstruct an image.

[0011] In addition, an object of the present disclosure is to provide a method of transmitting a bit stream generated by the image encoding method according to the present disclosure.

[0012] The technical problems solved by the present disclosure are not limited to the above-mentioned technical problems, and other technical problems not described herein will become apparent to those skilled in the art from the following description.

[0013] Technical Solution

[0014] An image decoding method according to one aspect of the present disclosure is an image decoding method performed by an image decoding device. The image decoding method may include reconstructing a picture from a bitstream and transforming the reconstructed picture based on any one of at least one candidate transformation. At least one candidate transformation may be a rotation transformation or a symmetric transformation for the picture.

[0015] According to another aspect of the present disclosure, an image coding method is an image coding method performed by an image coding device. The image coding method may include transforming a picture based on any one of at least one candidate transformation, and encoding the transformed picture in a bitstream. At least one candidate transformation may be a rotation transformation or a symmetric transformation for the picture.

[0016] In addition, a computer-readable recording medium according to another aspect of the present disclosure may store a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0017] In addition, a transmission method according to another aspect of the present disclosure may transmit a bit stream generated by the image encoding method or apparatus according to the present disclosure.

[0018] The features described above in brief summary of the present disclosure are merely exemplary aspects of the following detailed description of the present disclosure and do not limit the scope of the present disclosure.

[0019] Beneficial Effects

[0020] According to the present disclosure, it is possible to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0021] In addition, according to the present disclosure, it is possible to generate an input image optimized for image encoding.

[0022] In addition, according to the present disclosure, it is possible to improve the encoding and decoding performance of prediction.

[0023] Furthermore, according to the present disclosure, it is possible to provide a non-transitory recording medium that stores a bit stream generated by the image encoding method according to the present disclosure.

[0024] Furthermore, according to the present disclosure, it is possible to provide a non-transitory recording medium that stores a bit stream that is received and decoded by the image decoding device according to the present disclosure and is used to reconstruct an image.

[0025] Furthermore, according to the present disclosure, it is possible to provide a method of transmitting a bit stream generated by the image encoding method according to the present disclosure.

[0026] Those skilled in the art will appreciate that the effects that can be achieved by the present disclosure are not limited to what has been specifically described above, and other advantages of the present disclosure will be more clearly understood from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a view schematically showing a video coding system to which an embodiment of the present disclosure is applicable.

[0028] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0029] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0030] Figure 4 is a diagram showing the raster scan order.

[0031] Figure 5 is a diagram schematically showing an example of pre-processing and post-processing of an image.

[0032] Figure 6 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure.

[0033] Figure 7 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0034] Figure 8 is a diagram showing an example of a preprocessing method.

[0035] Fig. 9 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure.

[0036] Fig.10 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure.

[0037] Fig.11 is a flowchart illustrating an image encoding method according to another embodiment of the present disclosure.

[0038] Fig.12 is a flowchart illustrating an image decoding method according to another embodiment of the present disclosure.

[0039] Fig.13 is a diagram schematically showing another example of pre-processing and post-processing of an image.

[0040] Fig.14 is a diagram showing a content streaming system to which an embodiment of the present disclosure is applicable. DETAILED DESCRIPTION

[0041] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so as to be easily implemented by those skilled in the art. However, the present disclosure can be implemented in various forms and is not limited to the embodiments described herein.

[0042] In describing the present disclosure, if it is determined that the detailed description of related known functions or configurations makes the scope of the present disclosure unnecessarily ambiguous, the detailed description thereof will be omitted. In the drawings, parts irrelevant to the description of the present disclosure are omitted, and like reference numerals are attached to like parts.

[0043] In the present disclosure, when a component is "connected", "coupled" or "linked" to another component, it may include not only a direct connection relationship but also an indirect connection relationship with intermediate components. In addition, when a component "includes" or "has" other components, unless otherwise specified, it means that other components may be further included rather than excluded.

[0044] In the present disclosure, the terms first, second, etc. are used only for the purpose of distinguishing one component from other components, and do not limit the order or importance of the components unless otherwise specified. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0045] In the present disclosure, components that are distinguished from each other are intended to clearly describe each feature and do not mean that the components must be separated. That is, multiple components can be integrated and implemented in one hardware or software unit, or one component can be distributed and implemented in multiple hardware or software units. Therefore, even if not specifically stated, embodiments in which components are integrated or components are distributed are also included in the scope of the present disclosure.

[0046] In the present disclosure, the components described in the various embodiments do not necessarily mean essential components, and some components may be optional components. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included in the scope of the present disclosure. In addition, embodiments including other components in addition to the components described in the various embodiments are included in the scope of the present disclosure.

[0047] The present disclosure relates to encoding and decoding of images, and unless otherwise defined in the present disclosure, terms used in the present disclosure may have general meanings commonly used in the technical field to which the present disclosure belongs.

[0048] In the present disclosure, a "picture" generally refers to a unit representing an image at a specific time, and a slice / tile is a coding unit constituting a part of a picture, and a picture may be composed of one or more slices / tiles. In addition, a slice / tile may include one or more coding tree units (CTUs).

[0049] "Pixel" or "picture element" may mean the smallest unit constituting a picture (or image). In addition, "sample" may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may represent only a pixel / pixel value of a luminance component or only a pixel / pixel value of a chrominance component.

[0050] In the present disclosure, a "unit" may refer to a basic unit of image processing. The unit may include at least one of a specific area of ​​a picture and information related to the area. In some cases, the unit may be used interchangeably with terms such as "sample array", "block" or "area". In general, an M×N block may include M columns and N rows of samples (or sample arrays) or a set (or array) of transform coefficients.

[0051] In the present disclosure, "current block" may mean one of "current coding block", "current coding unit", "coding target block", "decoding target block" or "processing target block". When prediction is performed, "current block" may mean "current prediction block" or "prediction target block". When transform (inverse transform) / quantization (dequantization) is performed, "current block" may mean "current transform block" or "transform target block". When filtering is performed, "current block" may mean "filtering target block".

[0052] In addition, in the present disclosure, unless explicitly stated as a chroma block, "current block" may mean a block including a luma component block and a chroma component block or a "luminance block of the current block". The luma component block of the current block may be expressed by an explicit description including a luma component block such as "luminance block" or "current luma block". In addition, "chroma component block of the current block" may be expressed by an explicit description including a chroma component block such as "chroma block" or "current chroma block".

[0053] In the present disclosure, the slash " / " or "," may be interpreted as indicating "and / or". For example, the expressions "A / B" and "A, B" may mean "A and / or B". In addition, "A / B / C" and "A, B, C" may mean "at least one of A, B and / or C".

[0054] In the present disclosure, the term "or" should be interpreted to indicate "and / or". For example, the expression "A or B" may include 1) only "A", 2) only "B", or 3) both "A and B". In other words, in the present disclosure, the term "or" should be interpreted to indicate "additionally or alternatively".

[0055] Overview of the video compilation system

[0056] Figure 1 is a view schematically showing a video coding system to which an embodiment of the present disclosure is applicable.

[0057] The video coding system according to an embodiment may include an encoding device 10 and a decoding device 20. The encoding device 10 may deliver the encoded video and / or image information or data to the decoding device 20 via a digital storage medium or a network in the form of a file or streaming.

[0058] The encoding device 10 according to the embodiment may include a video source generator 11, an encoding unit (encoder) 12, and a transmitter 13. The decoding device 20 according to the embodiment may include a receiver 21, a decoding unit (decoder) 22, and a renderer 23. The encoding unit 12 may be referred to as a video / image encoding device, and the decoding unit 22 may be referred to as a video / image decoding device. The transmitter 13 may be included in the encoding unit 12. The receiver 21 may be included in the decoding unit 22. The renderer 23 may include a display and the display may be configured as a separate device or an external component.

[0059] The video source generator 11 can obtain the video / image by the process of capturing, synthesizing or generating the video / image. The video source generator 11 may include a video / image capturing device and / or a video / image generating device. The video / image capturing device may include, for example, one or more cameras, a video / image archive including previously captured videos / images, etc. The video / image generating device may include, for example, a computer, a tablet computer, and a smart phone, and may (electronically) generate the video / image. For example, a virtual video / image may be generated by a computer, etc. In this case, the video / image capturing process may be replaced by a process of generating relevant data.

[0060] The encoding unit 12 may encode the input video / image. For compression and coding efficiency, the encoding unit 12 may perform a series of processes such as prediction, transformation, and quantization. The encoding unit 12 may output the encoded data (encoded video / image information) in the form of a bitstream.

[0061] The transmitter 13 can obtain the encoded video / image information or data output in the form of a bit stream and forward it to the receiver 21 of the decoding device 20 or another external object in the form of a file or stream transmission through a digital storage medium or a network. The digital storage medium may include various storage media, such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmitter 13 may include an element for generating a media file in a predetermined file format and may include an element for transmission through a broadcast / communication network. The transmitter 13 may be provided as a transmission device separate from the encoding device 12, and in this case, the transmission device may include at least one processor, which obtains the encoded video / image information or data output in the form of a bit stream; and a transmission unit, which is used to send it in the form of a file or stream transmission. The receiver 21 may extract / receive a bit stream from a storage medium or a network and send the bit stream to the decoding unit 22.

[0062] The decoding unit 22 may decode a video / image by performing a series of processes such as dequantization, inverse transformation, and prediction corresponding to the operations of the encoding unit 12 .

[0063] The renderer 23 may render the decoded video / image. The rendered video / image may be displayed through a display.

[0064] Overview of Image Coding Device

[0065] Figure 2 is a diagram schematically showing an image encoding device to which an embodiment of the present disclosure is applicable.

[0066] like Figure 2 As shown in , the image encoding device 100 may include an image partitioner 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame prediction unit 180, an intra-frame prediction unit 185, and an entropy encoder 190. The inter-frame prediction unit 180 and the intra-frame prediction unit 185 may be collectively referred to as a "prediction unit". The transformer 120, the quantizer 130, the dequantizer 140, and the inverse transformer 150 may be included in a residual processor. The residual processor may further include a subtractor 115.

[0067] In some embodiments, all or at least some of the components configuring the image encoding apparatus 100 may be configured by one hardware component (eg, an encoder or a processor). In addition, the memory 170 may include a decoded picture buffer (DPB) and may be configured by a digital storage medium.

[0068] The image partitioner 110 may partition an input image (or picture or frame) input to the image encoding device 100 into one or more processing units. For example, a processing unit may be referred to as a coding unit (CU). A coding unit may be obtained by recursively partitioning a coding tree unit (CTU) or a maximum coding unit (LCU) according to a quadtree binary tree ternary tree (QT / BT / TT) structure. For example, a coding unit may be partitioned into multiple coding units of a deeper depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the partitioning of the coding unit, a quadtree structure may be applied first, and a binary tree structure and / or a ternary tree structure may be applied later. The coding process according to the present disclosure may be performed based on a final coding unit that is no longer partitioned. The maximum coding unit may be used as the final coding unit, or a coding unit of a deeper depth obtained by partitioning the maximum coding unit may be used as the final coding unit. Here, the coding process may include the prediction, transformation, and reconstruction processes described later. As another example, the processing unit of the coding process may be a prediction unit (PU) or a transformation unit (TU). The prediction unit and the transform unit may be split or partitioned from the final coding unit. The prediction unit may be a unit of sample prediction, and the transform unit may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient.

[0069] The prediction unit (inter prediction unit 180 or intra prediction unit 185) may perform prediction on the block to be processed (current block) and generate a prediction block including prediction samples for the current block. The prediction unit may determine whether to apply intra prediction or inter prediction based on the current block or CU. The prediction unit may generate various information related to the prediction of the current block and send the generated information to the entropy encoder 190. Information about the prediction may be encoded in the entropy encoder 190 and output in the form of a bitstream.

[0070] The intra prediction unit 185 can predict the current block by referring to the samples in the current picture. Depending on the intra prediction mode and / or the intra prediction technology, the reference samples can be located in the neighbors of the current block or can be placed separately. The intra prediction mode may include multiple non-directional modes and multiple directional modes. The non-directional mode may include, for example, a DC mode and a plane mode. Depending on the level of detail of the prediction direction, the directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes. However, this is only an example, and more or fewer directional prediction modes may be used depending on the setting. The intra prediction unit 185 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring blocks.

[0071] The inter prediction unit 180 may derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block may be the same or different. The temporal neighboring block may be referred to as a collocated reference block, a collocated CU (colCU), etc. The reference picture including the temporal neighboring block may be referred to as a collocated picture (colPic). For example, the inter prediction unit 180 may configure a motion information candidate list based on the neighboring blocks and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction may be performed based on various prediction modes. For example, in the case of skip mode and merge mode, the inter prediction unit 180 may use the motion information of the neighboring block as the motion information of the current block. In the case of skip mode, unlike the merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the neighboring block may be used as a motion vector predictor, and the motion vector of the current block may be signaled by encoding a motion vector difference and an indicator for the motion vector predictor. The motion vector difference may mean the difference between the motion vector of the current block and the motion vector predictor.

[0072] The prediction unit may generate a prediction signal based on various prediction methods and prediction techniques described below. For example, the prediction unit may apply not only intra prediction or inter prediction, but also both intra prediction and inter prediction at the same time, so as to predict the current block. The prediction method of applying both intra prediction and inter prediction to predict the current block may be referred to as combined inter and intra prediction (CIIP). In addition, the prediction unit may perform intra-block copying (IBC) on the prediction of the current block. Intra-block copying may be used for content image / video coding of games, etc., such as screen content coding (SCC). IBC is a method of predicting the current picture using a previously reconstructed reference block in the current picture at a position separated by a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current picture may be encoded as a vector (block vector) corresponding to a predetermined distance. IBC basically performs prediction in the current picture, but may be performed similarly to inter prediction because the reference block is derived within the current picture. That is, IBC may use at least one of the inter prediction techniques described in the present disclosure.

[0073] The prediction signal generated by the prediction unit can be used to generate a reconstruction signal or to generate a residual signal. The subtractor 115 can generate a residual signal (residual block or residual sample array) by subtracting the prediction signal (prediction block or prediction sample array) output from the prediction unit from the input image signal (original block or original sample array). The generated residual signal can be sent to the transformer 120.

[0074] The transformer 120 may generate transform coefficients by applying a transform technique to the residual signal. For example, the transform technique may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a karhunen-loève transform (KLT), a graph-based transform (GBT), or a conditional nonlinear transform (CNT). Here, GBT means a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. In addition, the transform process may be applied to square pixel blocks of the same size or may be applied to blocks of variable size rather than square.

[0075] The quantizer 130 may quantize the transform coefficients and send them to the entropy encoder 190. The entropy encoder 190 may encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients may be referred to as residual information. The quantizer 130 may rearrange the quantized transform coefficients in a block type into a one-dimensional vector form based on a coefficient scanning order, and generate information about the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form.

[0076] The entropy encoder 190 may perform various encoding methods, such as, for example, exponential Golomb, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), etc. The entropy encoder 190 may encode information necessary for video / image reconstruction in addition to quantized transform coefficients (e.g., values ​​of syntax elements, etc.) together or separately. The encoded information (e.g., encoded video / image information) may be transmitted or stored in units of a network abstraction layer (NAL) in the form of a bitstream. The video / image information may further include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may further include general constraint information. The information transmitted by the signal, the transmitted information, and / or the syntax elements described in the present disclosure may be encoded and included in the bitstream through the above-mentioned encoding process.

[0077] The bit stream may be transmitted through a network or may be stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) that transmits a signal output from the entropy encoder 190 and / or a storage unit (not shown) that stores the signal may be included as an internal / external element of the image encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0078] The quantized transform coefficient output from the quantizer 130 may be used to generate a residual signal. For example, the residual signal (residual block or residual sample) may be reconstructed by applying dequantization and inverse transform to the quantized transform coefficient via the dequantizer 140 and the inverse transformer 150.

[0079] The adder 155 adds the reconstructed residual signal to the prediction signal output from the inter-frame prediction unit 180 or the intra-frame prediction unit 185 to generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array). If there is no residual of the block to be processed, such as the case where the skip mode is applied, the prediction block can be used as the reconstructed block. The adder 155 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0080] The filter 160 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 160 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 170, specifically, in the DPB of the memory 170. Various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filter 160 can generate various information related to filtering and send the generated information to the entropy encoder 190, as described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoder 190 and output in the form of a bit stream.

[0081] The modified reconstructed picture transmitted to the memory 170 may be used as a reference picture in the inter prediction unit 180. When inter prediction is applied by the image encoding device 100, prediction mismatch between the image encoding device 100 and the image decoding device may be avoided and encoding efficiency may be improved.

[0082] The DPB of the memory 170 may store the modified reconstructed picture for use as a reference picture in the inter-frame prediction unit 180. The memory 170 may store the motion information of the block from which the motion information in the current picture is derived (or encoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be sent to the inter-frame prediction unit 180 and used as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 170 may store the reconstructed samples of the reconstructed block in the current picture and may transmit the reconstructed samples to the intra-frame prediction unit 185.

[0083] Overview of Image Decoding Device

[0084] Figure 3 is a diagram schematically showing an image decoding device to which an embodiment of the present disclosure is applicable.

[0085] like Figure 3 As shown in , the image decoding device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame prediction unit 260, and an intra-frame prediction unit 265. The inter-frame prediction unit 260 and the intra-frame prediction unit 265 may be collectively referred to as a "prediction unit". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0086] According to an embodiment, all or at least some of the plurality of components configuring the image decoding apparatus 200 may be configured by hardware components (eg, a decoder or a processor). In addition, the memory 250 may include a decoded picture buffer (DPB) or may be configured by a digital storage medium.

[0087] The image decoding apparatus 200 having received a bit stream including video / image information may perform the same operation as that performed by Figure 2 The image may be reconstructed by a process corresponding to the process performed by the image encoding device 100. For example, the image decoding device 200 may perform decoding using a processing unit applied in the image encoding device. Therefore, the processing unit of decoding may be, for example, a coding unit. The coding unit may be obtained by partitioning the coding tree unit or the maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 may be reproduced by a reproduction device (not shown).

[0088] The image decoding apparatus 200 may receive the image in the form of a bit stream from Figure 2The received signal may be decoded by the entropy decoder 210. For example, the entropy decoder 210 may parse the bitstream to derive information (e.g., video / image information) necessary for image reconstruction (or picture reconstruction). The video / image information may further include information about various parameter sets, such as an adaptive parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). In addition, the video / image information may further include general constraint information. The image decoding device may further decode the picture based on the information about the parameter set and / or the general constraint information. The information and / or syntax elements sent / received by the signal described in the present disclosure may be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values ​​of the syntax elements necessary for image reconstruction and the quantized values ​​of the transform coefficients for the residual. More specifically, the CABAC entropy decoding method may receive a bin corresponding to each syntax element in a bitstream, determine a context model using information of a decoding target syntax element, information of a neighboring block and a decoding target block, or information of a symbol / bin decoded in a previous stage, and perform arithmetic decoding on the bin by predicting the probability of occurrence of the bin according to the determined context model, and generate a symbol corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model. Information related to prediction among the information decoded by the entropy decoder 210 may be provided to the prediction unit (inter-frame prediction unit 260 and intra-frame prediction unit 265), and the residual value for which entropy decoding is performed in the entropy decoder 210, that is, the quantized transform coefficient and related parameter information may be input to the dequantizer 220. In addition, information about filtering among the information decoded by the entropy decoder 210 may be provided to the filter 240. Meanwhile, a receiver (not shown) for receiving a signal output from the image encoding device may be further configured as an internal / external element of the image decoding device 200 , or the receiver may be a component of the entropy decoder 210 .

[0089] Meanwhile, the image decoding device according to the present disclosure may be referred to as a video / image / picture decoding device. The image decoding device may be classified into an information decoder (video / image / picture information decoder) and a sample decoder (video / image / picture sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, at least one of an inter-frame prediction unit 160 or an intra-frame prediction unit 265.

[0090] The dequantizer 220 may dequantize the quantized transform coefficient and output the transform coefficient. The dequantizer 220 may rearrange the quantized transform coefficient in the form of a two-dimensional block. In this case, the rearrangement may be performed based on the coefficient scanning order performed in the image encoding device. The dequantizer 220 may perform dequantization on the quantized transform coefficient by using a quantization parameter (e.g., quantization step size information) and obtain the transform coefficient.

[0091] The inverse transformer 230 may inversely transform the transform coefficients to obtain a residual signal (residual block, residual sample array).

[0092] The prediction unit may perform prediction on the current block and generate a prediction block including prediction samples for the current block. The prediction unit may determine whether to apply intra prediction or inter prediction to the current block based on the information about the prediction output from the entropy decoder 210, and may determine a specific intra / inter prediction mode (prediction technique).

[0093] The same as described in the prediction unit of the image encoding device 100 is that the prediction unit can generate a prediction signal based on various prediction methods (techniques) described later.

[0094] The intra prediction unit 265 may predict the current block by referring to samples in the current picture. The description of the intra prediction unit 185 is also applied to the intra prediction unit 265.

[0095] The inter prediction unit 260 may derive a prediction block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. In this case, in order to reduce the amount of motion information sent in the inter prediction mode, the motion information may be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information may include a motion vector and a reference picture index. The motion information may further include inter prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter prediction, the neighboring blocks may include spatial neighboring blocks present in the current picture and temporal neighboring blocks present in the reference picture. For example, the inter prediction unit 260 may configure a motion information candidate list based on neighboring blocks, and derive a motion vector and / or a reference picture index of the current block based on the received candidate selection information. Inter prediction may be performed based on various prediction modes, and information about the prediction may include information indicating an inter prediction mode for the current block.

[0096] The adder 235 can generate a reconstructed block by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the prediction unit (including the inter-frame prediction unit 260 and / or the intra-prediction unit 265). If there is no residual for the block to be processed, such as when the skip mode is applied, the prediction block can be used as the reconstructed block. The description of the adder 155 is also applicable to the adder 235. The adder 235 can be referred to as a reconstructor or a reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current picture, and can be used for inter-frame prediction of the next picture by filtering as described below.

[0097] The filter 240 can improve the subjective / objective image quality by applying filtering to the reconstructed signal. For example, the filter 240 can generate a modified reconstructed picture by applying various filtering methods to the reconstructed picture, and store the modified reconstructed picture in the memory 250, specifically, in the DPB of the memory 250. The various filtering methods may include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0098] The (modified) reconstructed picture stored in the DPB of the memory 250 may be used as a reference picture in the inter-frame prediction unit 260. The memory 250 may store the motion information of the block from which the motion information in the current picture is derived (or decoded) and / or the motion information of the reconstructed block in the picture. The stored motion information may be sent to the inter-frame prediction unit 260 so as to be utilized as the motion information of the spatial neighboring block or the motion information of the temporal neighboring block. The memory 250 may store the reconstructed samples of the reconstructed block in the current picture and transmit the reconstructed samples to the intra-frame prediction unit 265.

[0099] In the present disclosure, the embodiments described in the filter 160, the inter-frame prediction unit 180 and the intra-frame prediction unit 185 of the image encoding device 100 can be equally or correspondingly applied to the filter 240, the inter-frame prediction unit 260 and the intra-frame prediction unit 265 of the image decoding device 200.

[0100] Example

[0101] Figure 4 is a diagram showing the raster scan order. Figure 4 As shown in , in the existing video codec, encoding and decoding of an image are performed block by block in a raster scan order starting from the upper left corner to the lower right corner of the image.

[0102] Therefore, when encoding is performed using only intra-frame information, such as intra-frame prediction, only pixel information of the top and left portions of the block to be encoded may be used, which may cause a reduction in compression efficiency. In particular, when the bottom or right portion of the image or block is complex, that is, when various objects exist at the bottom or right portion of the image or block, or when there are many high-frequency components in the portion, it is difficult to predict this using the components of the top or left portion of the image, so the efficiency of intra-frame prediction may be further reduced.

[0103] The present disclosure proposes embodiments for generating and processing input images optimized for image encoding and decoding by pre-processing and post-processing of images or blocks. The embodiments described below can be performed in a combination of two or more. In addition, "pre-processing" can be referred to as "transformation", and "post-processing" can be referred to as "transformation" or "inverse transformation".

[0104] Example 1

[0105] Embodiment 1 relates to a method for improving image compression efficiency by preprocessing an input image.

[0106] The pre-processing and post-processing methods proposed in Example 1 can be performed in units of images, slices, tiles, sub-images, or sequences. In addition, the proposed pre-processing and post-processing methods can also be performed in units of CTUs or CUs. The "image" mentioned below may correspond to any one of an image, a slice, a tile, a sub-image, a sequence, a CTU, or a CU. In other words, the pre-processing and post-processing methods can be performed in units of images, slices, tiles, sub-images, sequences, CTUs, or CUs. The transformation information can be sent as additional information using a signal.

[0107] Figure 5 Schematic diagram showing an example of pre-processing and post-processing of an image.

[0108] refer to Figure 5 , preprocessing is performed on an input image (original input image) to generate a preprocessed image (after preprocessing), and preprocessing information may be encoded. The preprocessing information is decoded, and a reconstructed image may be generated based thereon, and post-processing is performed on the reconstructed image to generate a post-processed image (after post-processing).

[0109] Figure 6 is a flowchart illustrating an image encoding method according to an embodiment of the present disclosure, and Figure 7 is a flowchart illustrating an image decoding method according to an embodiment of the present disclosure.

[0110] refer to Figure 6, the image encoding device 100 may obtain a picture (input image) (S610) and perform a picture transformation (preprocessing) on ​​the picture (S620). The transformation may be performed based on any one of at least one candidate transformation. The candidate transformation may include at least one of a rotation transformation, a symmetric transformation, or a rotation and symmetric transformation for the picture. The image encoding device 100 may encode the transformed picture (S630). In this process, information about the preprocessing, i.e., transformation information, may also be encoded.

[0111] refer to Figure 7 , the image decoding apparatus 200 may perform a decoding process on a bitstream to obtain information for picture reconstruction ( S710 ), and reconstruct a picture based on the obtained information ( S720 ).

[0112] The image decoding device 200 may transform the picture based on any one of the at least one candidate transformation (S730). The process S730 may be a post-processing process. The candidate transformation may include at least one of a rotation transformation, a symmetric transformation, or a rotation and symmetric transformation for the picture. The transformation process (S730) may be performed based on transformation information obtained from the bitstream. In addition, the image decoding device 200 may obtain a final reconstructed picture through the transformation (S740).

[0113] Various transformation methods (candidate transformations) such as Equations 1 to 6 may be used for pre-processing and post-processing.

[0114] [Equation 1]

[0115]

[0116] [Equation 2]

[0117]

[0118] [Equation 3]

[0119]

[0120] [Equation 4]

[0121]

[0122] [Equation 5]

[0123]

[0124] [Equation 6]

[0125]

[0126] In Equations 1 to 6, (x, y) may represent a pixel position, W may represent a width of an image, and H may represent a height of an image. org may represent an original image, and input may represent a "pre-processed image" to which image encoding will be applied. R may represent a matrix that performs a rotation transformation, and θ may represent a rotation angle.

[0127] Equation 1 represents a left / right symmetric transformation (mirror), and Equation 2 represents an up / down symmetric transformation (flip). Equation 4 may represent a 90-degree rotation transformation (θ=90), a 180-degree rotation transformation (θ=180), and a 270-degree rotation transformation (θ=270). Equation 5 may represent a left / right symmetric transformation and a 90-degree rotation transformation (θ=90), a left / right symmetric transformation and a -90-degree rotation transformation (θ=-90). Equation 6 may represent an up / down symmetric transformation and a 90-degree rotation transformation (θ=90), an up / down symmetric transformation and a -90-degree rotation transformation (θ=-90).

[0128] For example, when the left / right symmetric transformation and the 90-degree rotation transformation are applied in units of CTU, the upper part of the original CTU moves to the left and the left part moves to the top. Therefore, all reference sample information of the original CTU can be used.

[0129] The image encoding device 100 may select an optimal transform method through RDO (Rate-Distortion Optimization) or appropriate image analysis. Figure 8 As shown in , when encoding is performed after applying flip image preprocessing to traffic flow images, compression efficiency improvements of Y-5.45%, Cb-6.16%, and Cr-7.43% can be achieved.

[0130] According to an embodiment, when the width and height of an image are changed due to preprocessing, the changed width and height may be used for encoding and decoding. For example, when an input image of 3840x2160 is rotated 90 degrees, the width and height of the rotated image become 2160 and 3840. In this case, the changed width and height (3840x2160->2160x3840) may be used for encoding and decoding. However, when preprocessing is performed in a CU unit, if a non-square block (e.g., 4x16) is rotated 90 degrees, its width and height change, and thus application may not be possible. Therefore, when preprocessing is performed in a CU unit, a method using a changed width and height may not be applied.

[0131] Transformation information indicating a transform applied in preprocessing among candidate transforms may be binarized as shown in Tables 1 to 5.

[0132] [Table 1]

[0133]

[0134] [Table 2] Symmetry

[0135]

[0136] [Table 3]

[0137]

[0138] [Table 4]

[0139]

[0140] [Table 5]

[0141]

[0142] The transform information may be a single syntax element that indicates whether to apply a transform and to apply a candidate transform to the image.

[0143] Fig. 9 is a flowchart illustrating a method for encoding an image using a single syntax element, and Fig.10 is a flowchart illustrating an image decoding method using a single syntax element.

[0144] refer to Fig. 9 , the image encoding device 100 may determine whether to perform a picture transform, and if the picture transform is performed, determine a transform method (candidate transform to be applied) (S910). If the picture transform is applied (S920), the image encoding device 100 may encode the transform information as a second value (S930), and if the picture transform is not applied (S920), the transform information may be encoded as a first value. Here, the first value of the transform information indicates that the transform is not applied, and the second value of the transform information may indicate a candidate transform of the transform applied to the image among the candidate transforms.

[0145] refer to Fig.10 , the image decoding device 200 may obtain transformation information from the bitstream (S1010) and determine a value of the transformation information (S1020). If the value of the transformation information is a first value, the image decoding device 200 may not perform the transformation (S1030), and if the value of the transformation information is a second value, the transformation may be performed based on the candidate transformation indicated by the second value (S1040).

[0146] According to an embodiment, the transformation information may include first information indicating whether to apply the transformation and second information indicating a candidate transformation to be applied. A first value of the first information may indicate that the transformation is applied, and a second value of the first information may indicate that the transformation is not applied.

[0147] Fig.11 is a flowchart illustrating an image encoding method using first information and second information, and Fig.12 is a flowchart illustrating an image decoding method using first information and second information.

[0148] refer to Fig.11 , the image encoding device 100 may determine whether to perform a picture transform, and if a picture transform is performed, determine a transform method (a candidate transform to be applied) (S1110). If a picture transform is applied (S1120), the image encoding device 100 may encode the first information as a first value and encode the second information (S1130). In contrast, if the picture transform is not applied (S1120), the image encoding device 100 may encode the first information as a second value (S1140), in which case the second information may not be encoded.

[0149] refer to Fig.12 , the image decoding device 200 may obtain the first information from the bitstream (S1210) and determine the value of the first information (S1220). If the value of the first information is the second value, the image decoding device 200 may not perform the transformation and may not decode the second information. In contrast, if the value of the first information is the first value, the image decoding device 200 may obtain the second information from the bitstream (S1230) and transform the image based on the candidate transformation indicated by the second information (S1240).

[0150] Meanwhile, the transformation information may be signaled via HLS (High Level Syntax). Examples of transformation information signaled via the SPS level are shown in Tables 6 to 8.

[0151] [Table 6]

[0152]

[0153] [Table 7]

[0154]

[0155] [Table 8]

[0156]

[0157] sps_seq_pre_processing_flag in Table 6 indicates transform information when one preprocessing method is used, and sps_seq_pre_processing_id in Table 7 indicates transform information when a plurality of preprocessing methods are used. sps_seq_pre_processing_flag in Table 8 indicates first information, and sps_seq_pre_processing_id in Table 8 indicates second information.

[0158] When binarizing using the preprocessing method of Tables 1 to 3, the syntax structure of Table 7 or Table 8 may be used. x of u(x) may be variably determined depending on the amount of preprocessed information, and for example, when binarizing using the preprocessing method of Table 1, x may be determined to be 3.

[0159] Examples of conversion information signaled via PPS level are shown in Tables 9 to 11.

[0160] [Table 9]

[0161]

[0162] [Table 10]

[0163]

[0164] [Table 11]

[0165]

[0166] pps_seq_pre_processing_flag in Table 9 indicates transformation information when one preprocessing method is used, and pps_seq_pre_processing_id in Table 10 indicates transformation information when a plurality of preprocessing methods are used. pps_seq_pre_processing_flag in Table 11 indicates first information, and pps_seq_pre_processing_id in Table 11 indicates second information.

[0167] When binarization is performed using the preprocessing method of Table 4 to Table 5, the syntax structure of Table 9 may be used. When binarization is performed using the preprocessing method of Table 1 to Table 3, the syntax structure of Table 10 or Table 11 may be used. x of u(x) may be variably determined according to the amount of information of preprocessing, and for example, when binarization is performed using the preprocessing method of Table 1, x may be determined to be 3.

[0168] Examples of conversion information signaled via PH levels are shown in Tables 12 to 14.

[0169] [Table 12]

[0170]

[0171] [Table 13]

[0172]

[0173] [Table 14]

[0174]

[0175] ph_seq_pre_processing_flag in Table 12 indicates conversion information when one preprocessing method is used, and ph_seq_pre_processing_id in Table 13 indicates conversion information when a plurality of preprocessing methods are used. ph_seq_pre_processing_flag in Table 14 indicates first information, and ph_seq_pre_processing_id in Table 14 indicates second information.

[0176] When binarization is performed using the preprocessing methods of Tables 4 to 5, the syntax structure of Table 12 may be used. When binarization is performed using the preprocessing methods of Tables 1 to 3, the syntax structure of Table 13 or Table 14 may be used. x of u(x) may be variably determined according to the amount of information of preprocessing, and for example, when binarization is performed using the preprocessing method of Table 1, x may be determined to be 3.

[0177] Examples of conversion information transmitted via SH level signaling are shown in Tables 15 to 17.

[0178] [Table 15]

[0179]

[0180] [Table 16]

[0181]

[0182] [Table 17]

[0183]

[0184] sh_seq_pre_processing_flag in Table 15 indicates conversion information when one preprocessing method is used, and sh_seq_pre_processing_id in Table 16 indicates conversion information when a plurality of preprocessing methods are used. sh_seq_pre_processing_flag in Table 17 indicates first information, and sh_seq_pre_processing_id in Table 17 indicates second information.

[0185] When binarization is performed using the preprocessing method of Tables 4 to 5, the syntax structure of Table 15 may be used. When binarization is performed using the preprocessing method of Tables 1 to 3, the syntax structure of Table 16 or Table 17 may be used. x of u(x) may be variably determined according to the amount of information of preprocessing, and for example, when binarization is performed using the preprocessing method of Table 1, x may be determined to be 3.

[0186] Also, because the encoded or decoded image is stored in the picture buffer for inter-frame prediction, it may be necessary Fig.13 The post-processing method shown in performs the inter-frame prediction process in the same way as before. Fig.13 ,The reconstructed image can be stored in an image buffer after post-processing.

[0187] In the present disclosure, when the pre-processing method is performed in units of slices, tiles, and sub-pictures, the following method may be applied to store an image to which the pre-processing has been applied in a picture buffer.

[0188] - After performing the transformation by post-processing of the reconstructed image, it is stored in the picture buffer. In this case, the P / B type slice / tile / sub-image processing can be the same as the existing method. That is, the method proposed in this embodiment can only be applied to the I type slice / tile / sub-image processing.

[0189] - The reconstructed image is stored in the image buffer with the pre-processing applied. In this case, post-processing, i.e., image reconstruction work, can be added when processing P / B type slices / tiles / sub-images.

[0190] Example 2

[0191] Embodiment 2 relates to a method of signaling, through different levels, first information indicating whether to apply a transformation and second information indicating a candidate transformation to be applied.

[0192] The first level, which is a level for signaling the first information, may be a higher level than the second level, which is a level for signaling the second information.

[0193] In case of using one preprocessing method, first information (sps_seq_pre_processing_flag) may be signaled through an SPS level, and second information (ph_seq_pre_processing_flag) may be signaled through a PH level as shown in Table 18. When the first information indicates application of transformation, the second information may be signaled.

[0194] [Table 18]

[0195]

[0196] When a plurality of preprocessing methods are used, first information (sps_seq_pre_processing_flag) may be signaled through an SPS level, and second information (ph_seq_pre_processing_id) may be signaled through a PH level as shown in Table 19. When the first information indicates that a transformation is applied, the second information may be signaled.

[0197] [Table 19]

[0198]

[0199] When one preprocessing method is used, first information (sps_seq_pre_processing_flag) may be signaled through an SPS level, and second information (sh_seq_pre_processing_flag) may be signaled through an SH level as shown in Table 20. When the first information indicates that a transformation is applied, the second information may be signaled.

[0200] [Table 20]

[0201]

[0202] When a plurality of preprocessing methods are used, first information (sps_seq_pre_processing_flag) may be signaled through an SPS level, and second information (sh_seq_pre_processing_id) may be signaled through an SH level as shown in Table 21. When the first information indicates that a transformation is applied, the second information may be signaled.

[0203] [Table 21]

[0204]

[0205] Example 3

[0206] Embodiment 3 relates to a method of selecting the best candidate transform from among a plurality of candidate transforms (preprocessing method).

[0207] By identifying the edge distribution of an image or block, a candidate transform that can transform the image in a direction where vertical diagonal edges (the direction before the horizontal mode in intra prediction and the direction after the vertical mode) are likely to be reduced can be selected. For example, if there are multiple edges in the vertical diagonal direction, an up / down symmetric transform or a left / right symmetric transform can be selected. Analysis of edge distribution can be performed by applying various edge detection filters (e.g., Roberts, Sobel, Prewitt, Kirsch, Robinson, Marr-Hildreth, LoG, Canny) and algorithms to the original image or original block.

[0208] For example, when the Robinson edge feature extraction method is used, the distribution of eight edges in the first slice of the image may be as shown in Table 22.

[0209] [Table 22]

[0210]

[0211] In Table 22, E, NE, N, NW, W, SW, S, SE represent 8 edge directions, and non-edge is a flat area without an edge, and when the 8 directional feature values ​​in each pixel do not exceed a specific threshold, the non-edge is selected. The number represents the distribution of each edge feature in the entire image, and the unit is %. More precisely, in order to extract the edge features of the image, noise removal can be performed by performing smoothing filtering using a Gaussian filter or the like on the original image.

[0212] From the results in Table 22, it can be seen that if the sum of NE and SW is less than the sum of NW and SE, performing up / down symmetric (flip) preprocessing and then encoding can achieve a performance improvement of Y-0.17%.

[0213] Other methods for selecting the best candidate transform may be as follows.

[0214] -Select a candidate transform that transforms the image in a direction where complexity is likely to increase in the upper left corner of the image (or block). For example, if the right side of the image is more complex than the left side, a left / right symmetric transform may be selected. The complexity of an image can be calculated by algorithms such as comparing high frequency components by image (or block) region, object detection, etc.

[0215] -The best transform method can be selected by simple RDO for an image (or block). For simple RDO, methods such as reducing the image size by downsampling the original image, performing simple RDO (e.g., the first step RDO for selecting intra prediction mode candidates), turning off complex coding tools, or limiting the CTU block depth can be used.

[0216] - The best candidate transform for the current block can be selected through the transform information of the left block and the top block of the current block. For example, the transform information applied to the left block and the top block of the current block can be applied to the current block in the same way.

[0217] Example 4

[0218] Embodiment 4 relates to a method (preprocessing method) of selecting the best candidate transformation from among a plurality of candidate transformations.

[0219] By identifying the edge distribution of an image or a block, a candidate transform that can transform the image in a direction where vertical diagonal edges (a direction before a horizontal mode in intra prediction and a direction after a vertical mode) can be reduced can be selected. For example, if there are many edges in the vertical diagonal direction, an up / down symmetric transform or a left / right symmetric transform can be selected. Analysis of edge distribution can be performed by applying various edge detection filters (e.g., Roberts, Sobel, Prewitt, Kirsch, Robinson, Marr-Hildreth, LoG, Canny) and algorithms to the original image or original block.

[0220] In addition, for complex analysis of the original image, the accuracy of edge detection can be improved by applying a smoothing filter such as an LPF (low pass filter) to the original image to reduce noise and then using an edge detection filter.

[0221] For example, when the Robinson edge feature extraction method in Table 23 is used, the distribution of eight edges in the first slice of the image may be as shown in Table 24.

[0222] [Table 23]

[0223]

[0224] [Table 24]

[0225]

[0226] When using the Robinson edge feature extraction method, the eight directional 3x3 filters in Table 23 are applied to each pixel of the original image. Then, the direction of the filter with the maximum value of the eight filtering results can be called the edge direction of each pixel. For example, if the W filter value is the largest when the eight filters are applied to the pixel, it can be said that the pixel has a west edge direction. In addition, if the values ​​obtained by applying the eight filters are similar or all small, the pixel can be said to have a non-edge direction. Here, a specific value (threshold) for determining a non-edge can be experimentally determined. For example, if the values ​​of the results of applying the eight filters to the pixel are all less than a specific value (threshold) determined in advance, the pixel can be said to have a non-edge.

[0227] In Table 24, E, NE, N, NW, W, SW, S and SE represent 8 edge directions, and non-edge is a flat area without edge, and is selected when the 8 directional feature values ​​in each pixel do not exceed a specific threshold. The numbers represent the distribution of each edge feature in the entire image, and the unit is %.

[0228] Through the results in Table 24, if the sum of NE and SW is less than the sum of NW and SE, and encoding is performed after performing up-down symmetry (flipping) preprocessing, the results in Table 25 can be obtained.

[0229] [Table 25]

[0230]

[0231] The results in Table 25 use the Robinson edge feature extraction method, and after applying the 3x3 8 filter, a specific value (threshold) of 10 is used. That is, after applying the 8 filters to a pixel, if all values ​​are less than 10, the pixel is determined to be a non-edge pixel.

[0232] Other methods for selecting the best candidate transform can be as follows:

[0233] -Select candidate transforms that transform the image in a direction where complexity is likely to increase towards the top left corner of the image (or block). For example, if the right side of the image is more complex than the left side, a left / right symmetric transform may be selected. The complexity of an image may be calculated by algorithms such as comparing high frequency components by image (or block) region, object detection, etc.

[0234] - The best transform method can be selected by simple RDO of the image (or block). For simple RDO, methods such as reducing the image size by downsampling the original image, performing simple RDO (e.g., the first step RDO for selecting intra prediction mode candidates), turning off complex coding tools, or limiting the CTU block depth can be used.

[0235] - The best candidate transform for the current block can be selected by the transform information of the left block and the top block of the current block. For example, the transform information applied to the left block and the top block of the current block can be applied to the current block in the same way.

[0236] Fig.14 is a diagram showing a content streaming system to which an embodiment of the present disclosure is applicable.

[0237] like Fig.14 As shown in , a content streaming transmission system to which an embodiment of the present disclosure is applied may mainly include an encoding server, a streaming transmission server, a network server, a media storage, a user device, and a multimedia input device.

[0238] The encoding server compresses the content input from the multimedia input device such as a smartphone, camera, camcorder, etc. into digital data to generate a bitstream and transmits the bitstream to the streaming server. As another example, when the multimedia input device such as a smartphone, camera, camcorder, etc. directly generates the bitstream, the encoding server can be omitted.

[0239] A bitstream may be generated by applying the image encoding method or the image encoding device according to the embodiment of the present disclosure, and a streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0240] The streaming server sends multimedia data to the user device based on the user's request through the network server, and the network server serves as a medium for notifying the user of the service. When the user requests the required service from the network server, the network server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server serves as a command / response between devices in the content streaming system.

[0241] The streaming server may receive content from a media storage and / or encoding server. For example, when content is received from an encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

[0242] Examples of user devices may include mobile phones, smart phones, laptop computers, digital broadcast terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, tablet PCs, tablet computers, ultrabooks, wearable devices (e.g., smart watches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0243] Each server in the content streaming system may operate as a distributed server, in which case data received from each server may be distributed.

[0244] The scope of the present disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling operations of methods according to various embodiments to be performed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0245] Industrial Applicability

[0246] The embodiments of the present disclosure may be used to encode or decode an image.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising: Reconstructing pictures from bitstreams; as well as transforming the reconstructed picture based on any one of at least one candidate transformation, The at least one candidate transformation is a rotation transformation or a symmetric transformation for the picture.

2. The image decoding method according to claim 1, wherein: The transform is performed based on transform information obtained from the bitstream.

3. The image decoding method according to claim 2, wherein: The first value of the transform information indicates that the transform is not applied, and the second value of the transform information indicates any one of the at least one candidate transform.

4. The image decoding method according to claim 2, in, The transformation information includes first information indicating whether to apply the transformation and second information indicating any one of the at least one candidate transformation, and Wherein, based on the first information indicating application of the transformation, the second information is included in the transformation information.

5. The image decoding method according to claim 4, in, obtaining said first information from a first level of said bitstream, wherein the second information is obtained from a second level of the bitstream, and The first level is higher than the second level.

6. The image decoding method according to claim 1, wherein: The transform is applied to any one of a sub-picture, a slice, a tile, a coding tree unit or a coding unit of the picture.

7. An image encoding method performed by an image encoding device, the image encoding method comprising: Transforming the image based on any one of at least one candidate transformation; as well as Encode the transformed picture in the bitstream, The at least one candidate transformation is a rotation transformation or a symmetric transformation for the picture.

8. A method for transmitting a bit stream generated by an image encoding method, the image encoding method comprising: Transforming the image based on any one of at least one candidate transformation; as well as Encode the transformed picture in the bitstream, The at least one candidate transformation is a rotation transformation or a symmetric transformation for the picture.

Images