RU2805218C2 - Image coding method based on transformation and a device - Google Patents

Abstract

FIELD: image coding.

SUBSTANCE: extracting the residual sample, wherein the step for extracting the residual sample comprises the following steps: extracting a nullable block for the current block; extracting a context model for position information of the last significant coefficient based on the width or height of the current block; extracting the position value of the last significant coefficient based on the context model; and extracting the position of the last significant coefficient based on the value of the position information of the last significant coefficient and the width or height of the nullable block.

EFFECT: increase in efficiency of image encoding.

10 cl, 13 dwg, 15 tbl

Description

State of the art

Field of technology to which the invention relates

[1] The present disclosure generally relates to image encoding technology, and more particularly to a transform-based image encoding method in an image encoding system and apparatus therefor.

Description of the Prior Art

[2] Nowadays, the demand for high-quality high-definition images/videos, for example, 4K, 8K or even higher ultra-high definition (UHD) images/videos, is growing in various fields of technology. As image/video data becomes increasingly higher resolution and higher quality, the amount of information transmitted, or bit capacity, increases compared to traditional image data. Therefore, when image data is transmitted using a medium such as a traditional wired/wireless broadband line, or image/video data is stored using an existing storage medium, transmission costs and storage costs for them increase.

[3] Additionally, nowadays, interest and demand for immersive multimedia such as virtual reality (VR), artificial reality (AR) or hologram content, etc. is growing, and broadcasting for images/videos having features images different from the features of real images, such as a game image, are increased.

[4] Accordingly, there is a need for high-performance image/video compression technology for efficiently compressing and transmitting or storing and reproducing information of high-quality, high-resolution images/videos having various features as described above.

The essence of the invention

[5] The technical aspect of the present disclosure is to provide a method and apparatus for improving the efficiency of image encoding.

[6] Another technical aspect of the present disclosure is to provide a method and apparatus for improving efficiency in residual coding.

[7] Yet another technical aspect of the present disclosure is to provide a method and apparatus for increasing efficiency in encoding the last non-zero transform coefficient.

[8] Yet another technical aspect of the present disclosure is to provide a method and apparatus for transform coefficient encoding based on high frequency nulling to improve the efficiency of residual encoding.

[9] Yet another technical aspect of the present disclosure is to provide a method and apparatus for encoding position information relative to the last significant coefficient in a current block (or current transform block) based on high frequency nulling.

[10] Yet another technical aspect of the present disclosure is to provide a method and apparatus for extracting the maximum value of suffix information relative to the position of the last significant transform coefficient based on the size of the region to which high-frequency nulling is not applied in a current block when encoding the coefficients conversions for the current block (or current transform block) based on high-frequency nulling.

[11] Yet another technical aspect of the present disclosure is to provide a method and apparatus for extracting a context model for position information of the last significant transform coefficient based on the size of the current block when encoding transform coefficients for the current block (or current transform block) on based on high frequency zeroing.

[12] According to an embodiment of the present disclosure, an image decoding method performed by decoding equipment is provided. The method includes retrieving a residual sample, and retrieving the residual sample includes: retrieving a nullable block for a current block; retrieving a context model for position information of the last significant coefficient based on the width or height of the current block; extracting the position information value of the last significant coefficient based on the context model; and retrieving the position of the last significant coefficient based on the value of the position information of the last significant coefficient and the width or height of the block to be reset.

[13] The width of the block being reset may be smaller than the width of the current block.

[14] The height of the block being reset may be less than the height of the current block.

[15] The position information of the last significant coefficient may include prefix information of the last significant coefficient and suffix information of the last significant coefficient, the prefix information of the last significant coefficient may include X-axis prefix information and Y-axis prefix information, and a context increment for the information X-axis prefix and Y-axis prefix information can be retrieved based on the width or height of the current block.

[16] The maximum value allowed for last significant coefficient prefix information may be retrieved based on the size of the nullable block.

[17] The width or height of a nullable block can be retrieved based on the width or height of the current block.

[18] When the width of the current block is 32, and the height of the current block is 32 or less, the width of the nullable block can be set to 16, and when the width of the current block is not 32, or the height of the current block is 64 or greater, the width of the nullable block can be set equal to the smaller value of the width of the current block and 32.

[19] When the height of the current block may be 32, and the width of the current block is 32 or less, the height of the nullable block is set to 16, and when the height of the current block is not 32, or the width of the current block is 64 or greater, the height of the nullable block may be be set equal to the smaller value of the height of the current block and 32.

[20] According to another embodiment of the present disclosure, an image encoding method performed by encoding equipment is provided. The method may include encoding the residual information, and the encoding includes: retrieving a nullable block for the current block; retrieving the position of the last significant coefficient based on the width or height of the block being zeroed; retrieving a context model for position information of the last significant coefficient based on the width or height of the current block; and encoding the position information of the last significant coefficient based on the context model.

[21] According to yet another embodiment of the present disclosure, a digital storage medium that stores image data including encoded image information and a bit stream generated according to an image encoding method carried out by encoding equipment may be provided.

[22] According to yet another embodiment of the present disclosure, a digital storage medium that stores image data including encoded image information and a bit stream may be provided to instruct decoding equipment to perform an image decoding method.

[23] According to the present disclosure, it is possible to improve the overall efficiency of image/video compression.

[24] According to the present disclosure, it is possible to improve efficiency in residual coding.

[25] According to the present disclosure, it is possible to improve efficiency when encoding the position of the last significant transform coefficient.

[26] According to the present disclosure, it is possible to improve the efficiency of residual coding by encoding a transform coefficient based on high-frequency nulling.

[27] According to the present disclosure, it is possible to improve the efficiency of image encoding by encoding position information relative to the last significant transform coefficient in the current block (or current transform block) based on high-frequency nulling.

[28] According to the present disclosure, it is possible to improve the efficiency of image encoding by extracting a context model for position information of the last significant transform coefficient based on a predetermined block size when encoding transform coefficients for a current block (or a current transform block) based on high-frequency nulling.

[29] The benefits that may be obtained by specific examples of the present disclosure are not limited to the benefits mentioned above. For example, there may be various technical effects that those skilled in the art may understand or learn from the present disclosure. Accordingly, the specific advantages of the present disclosure are not limited to those explicitly described in the present disclosure, and may include various advantages that may be understood or derived from the technical features of the present disclosure.

Brief description of drawings

[30] FIG. 1 schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.

[31] FIG. 2 is a diagram fundamentally illustrating a configuration of video/image encoding equipment to which the present disclosure is applicable.

[32] FIG. 3 is a diagram fundamentally illustrating a configuration of video/image decoding equipment to which the present disclosure is applicable.

[33] FIG. 4 schematically illustrates a multiple conversion technology according to an embodiment of the present disclosure.

[34] FIG. 5 illustrates 32-point nulling according to an embodiment of the present disclosure.

[35] FIG. 6 illustrates a residual block segment according to an embodiment of the present disclosure.

[36] FIG. 7 is a flowchart illustrating the operation of a video decoding apparatus according to an embodiment of the present disclosure.

[37] FIG. 8 is a block diagram illustrating a configuration of decoding equipment according to an embodiment of the present disclosure.

[38] FIG. 9 is a flowchart illustrating a residual sample extraction process according to an embodiment of the present disclosure.

[39] FIG. 10 is a flowchart illustrating the operation of a video encoding apparatus according to an embodiment of the present disclosure.

[40] FIG. 11 is a block diagram illustrating a configuration of encoding equipment according to an embodiment of the present disclosure.

[41] FIG. 12 is a flowchart illustrating a process of encoding residual information according to an embodiment of the present disclosure.

[42] FIG. 13 illustrates the structure of a content streaming system to which the present disclosure applies.

Detailed Description of Embodiments

[43] Although the present disclosure is subject to various modifications and includes various embodiments, specific embodiments thereof are shown in the drawings by way of example and are described in detail below. However, it is not intended to limit the present disclosure to the specific embodiments disclosed herein. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the technical intent of the present disclosure. Singular forms may include plural forms unless the context clearly indicates otherwise. Terms such as “include” and “have” are intended to indicate that there are features, figures, steps, operations, elements, components, or combinations thereof used in the description below, and as such should not understand that the possibility of the presence or addition of one or more other features, numbers, steps, operations, elements, components or combinations of the above is excluded in advance.

[44] Meanwhile, each component in the drawings described herein is illustrated independently for convenience of description with respect to characteristic functions different from each other, and however, it is not intended that each component is implemented by separate hardware or software. For example, any two or more of these components may be combined to form one component, and any one component may be divided into multiple components. Embodiments in which components are combined and/or separated are intended to fall within the scope of the patent rights of this disclosure, provided that they do not depart from the spirit of this disclosure.

[45] Hereinafter, preferred embodiments of the present disclosure are explained in more detail with reference to the accompanying drawings. In addition, identical reference numbers are used for identical components in the drawings, and repeated descriptions for identical components are omitted.

[46] This document relates to video/image coding. For example, the method/example disclosed in this document may relate to the VVC (Video Versatile Coding) standard (ITU-T Recommendation H.266), the next generation video/image coding standard after VVC, or other related video coding standards (for example, to the HEVC (High Efficiency Video Coding) standard (ITU-T recommendation H.265), to the EVC (fundamental video coding) standard, to the AVS2 standard, etc.).

[47] Herein, a variety of embodiments related to video/image coding may be provided, and unless otherwise noted, embodiments may be combined and executed.

[48] In this document, video can mean a collection of sequences of images over time. In general, a frame means a unit representing an image in a particular time zone, and a slice/tile is a unit constituting a part of a frame. A slice/tile may include one or more coding tree units (CTUs). One frame can consist of one or more slices/tiles. One frame can consist of one or more groups of tiles. One tile group may include one or more tiles.

[49] Pixel or pel can mean the smallest unit that makes up one frame (or image). Additionally, "sample" can be used as a term corresponding to a pixel. A sample may generally represent a pixel or a pixel value, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chroma component. Alternatively, a sample can mean a pixel value in the spatial domain, or when that pixel value is converted into a frequency domain, it can mean a conversion factor in the frequency domain.

[50] The unit may represent a basic image processing unit. The unit may include at least one of a specific area and information associated with the area. One unit may include one block of luma signals and two blocks of chrominance signals (eg, Cb, Cr). "Unit" and a term such as "block", "zone", etc. may be used instead of each other according to circumstances. In general, an MxN block may include a set (or array) of samples (or arrays of samples) or transform coefficients, consisting of M columns and N rows.

[51] In this document, the terms "/" and "," shall be interpreted to indicate "and/or". For example, the expression "A/B" could mean "A and/or B". Additionally, "A, B" may mean "A and/or B". Additionally, "A/B/C" may mean "at least one of A, B and/or C". In addition, "A/B/C" may mean "at least one of A, B and/or C".

[52] Additionally, as used herein, the term “or” should be interpreted to indicate “and/or.” For example, the expression "A or B" may include 1) A only, 2) B only, and/or 3) both A and B. In other words, the term "or" in this document should be interpreted to indicate "in addition or alternatively."

[53] In the present disclosure, “at least one of A and B” may mean “A only,” “B only,” or “both A and B.” In addition, in the disclosure, the expression “at least one of A or B” or “at least one of A and/or B” can be interpreted as “at least one of A and B”.

[54] In addition, in the present disclosure, “at least one of A, B, and C” may mean “A only,” “B only,” “C only,” or “any combination of A, B, and C.” In addition, "at least one of A, B or C" or "at least one of A, B and/or C" may mean "at least one of A, B and C".

[55] In addition, a parenthesis used in this disclosure may mean "for example." In particular, when specifying "forecasting (intra prediction)" this may mean that "intra prediction" is offered as an example of "forecasting". Thus, “prediction” in the present disclosure is not limited to “internal forecasting,” and “internal forecasting” may be offered as an example of “prediction.” In addition, when indicating "forecasting (ie, internal forecasting)", it may also mean that "internal forecasting" is proposed as an example of "forecasting".

[56] Technical features separately described in a single drawing in this disclosure may be implemented separately or may be implemented simultaneously.

[57] FIG. 1 schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.

[58] Referring to FIG. 1, the video/image encoding system may include a first device (source device) and a second device (receiver device). A source device may deliver encoded information or video/image data in file or streaming form to a receiving device via a digital storage medium or network.

[59] The source device may include a video source, encoding equipment, and a transmitter. The receiving device may include a receiver, decoding hardware, and a rendering module. The encoding apparatus may be referred to as "video/image encoding apparatus" and the decoding apparatus may be referred to as "video/image decoding apparatus." The transmitter can be included in encoding equipment. The receiver can be included in the decoding equipment. The rendering module may include a display, and the display may be configured as a separate device or an external component.

[60] A video source may obtain video/image through a video/image capture, synthesis, or shaping process. The video source may include a video/image capture device and/or a video/image generation device. The video/image capturing device may include, for example, one or more cameras, video/image archives including previously captured video/images, and the like. The video/image generating apparatus may include, for example, a computer, a tablet computer, and a smartphone, and may (electronically) generate the video/image. For example, a virtual video/image may be generated via a computer or the like. In this case, the video/image capturing process can be replaced by the associated data generation process.

[61] The encoding apparatus may encode the input video/image. The encoding hardware may perform a sequence of procedures, such as prediction, transform, and quantization, for efficient compression and encoding. Encoded data (encoded video/image information) may be output in the form of a bit stream.

[62] A transmitter may transmit information or encoded video/image data output in the form of a bitstream to a receiver of a receiving device via a digital storage medium or network in the form of a file or streaming. The digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-Ray, HDD, SSD, and the like. The transmitter may include an element for generating a multimedia file through a predefined file format and may include an element for transmission through a broadcast/communication network. The receiver may receive/extract the bit stream and transmit the received/extracted bit stream to decoding equipment.

[63] The decoding apparatus may decode the video/image by performing a series of procedures such as dequantization, deconversion, prediction, and the like, corresponding to the operation of the encoding apparatus.

[64] The rendering module can render the decoded video/image. The video/image prepared by rendering can be displayed through the display.

[65] FIG. 2 is a diagram fundamentally illustrating the configuration of a video/image encoding apparatus to which the present disclosure is applicable. Hereinafter in this document, what is referred to as “video encoding apparatus” may include image encoding apparatus.

[66] Referring to FIG. 2, encoding apparatus 200 may include an image segmentation module 210, a prediction module 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The prediction module 220 may include an inter-prediction module 221 and a cross-prediction module 222. internal forecasting. Residual processor 230 may include a transformer 232, a quantizer 233, a dequantizer 234, an inverse transformer 235. The residual processor 230 may further include a subtractor 231. The adder 250 may be referred to as a “recovery module” or a “recovery block generator.” The image segmentation module 210, prediction module 220, residual processor 230, entropy encoder 240, adder 250, and filter 260, which are described above, may be composed of one or more hardware components (eg, encoder chipsets or processors) according to an embodiment. Additionally, storage device 270 may include a decoded frame buffer (DPB) and may be configured with a digital storage medium. The hardware component may further include a storage device 270 as an internal/external component.

[67] The image segmentation module 210 may segment an input image (either a frame or a video frame) input to the encoding apparatus 200 into one or more processing units. As one example, the processing unit may be referred to as a "coding unit (CU)". In this case, starting from a coding tree unit (CTU) or largest coding unit (LCU), the coding unit can be recursively segmented according to a quadtree, binary tree, and ternary tree (QTBTTT) structure. For example, one coding unit may be divided into multiple coding units of greater depth based on a quadtree structure, a binary tree structure, and/or a ternary structure. In this case, for example, a quadtree structure may be applied first, and a binary tree structure and/or a ternary structure may be subsequently applied. Alternatively, a binary tree structure may be used first. The encoding procedure according to the present disclosure may be performed based on the final encoding unit, which is not further segmented. In this case, the maximum encoding unit can be used directly as the final encoding unit based on the encoding efficiency according to the characteristic of the image. Alternatively, the coding unit can be recursively segmented into coding units of additional greater depth as needed, so that the optimally sized coding unit can be used as the final coding unit. Here, the encoding procedure may include procedures such as prediction, transformation and reconstruction, which are described below. As another example, the processing unit may further include a prediction unit (PU) or a transformation unit (TU). In this case, the prediction unit and the transformation unit may be split or segmented from the above-described final encoding unit. The prediction unit may be a sample prediction unit, and the transformation unit may be a unit for extracting a transformation coefficient and/or a unit for extracting a residual signal from the transformation coefficient.

[68] "Unit" and a term such as "block", "zone", etc. may be used instead of each other according to circumstances. In general, an MxN block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample may generally represent a pixel or a pixel value, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chrominance signal component. Sampling can be used as a term corresponding to a pixel or pel of a single frame (or image).

[69] The subtractor 223 subtracts the prediction signal (predicted block, prediction sample array) output from the inter-prediction module 221 or the intra-prediction module 222 from the input image signal (source block, source sample array) to generate a residual signal (residual block, residual sample array), and the generated residual signal is transmitted to converter 232. In this case, as shown, a module that subtracts the prediction signal (predicted block, prediction sample array) from the input image signal (source block, source sample array) at encoder 200 , may be called "subtractor 231". The prediction module may perform prediction for a target processing block (hereinafter referred to as a "current block") and may generate a prediction block including prediction samples for the current block. The prediction module may determine whether intra prediction or inter prediction is applied based on the current block or CU. As explained below in the description of each prediction mode, the prediction module may generate various prediction-related information, such as prediction mode information, and transmit the generated information to the entropy encoder 240. Information regarding the prediction may be encoded in the entropy encoder 240 and output in the form of a stream bits

[70] The intra prediction module 222 may predict the current block by reference to the samples in the current frame. Samples for the link can be located in an adjacent node or spaced from the current block according to the prediction mode. In intraprediction, prediction modes may include a plurality of non-directional modes and a plurality of directed modes. Omnidirectional modes may include, for example, DC mode and planar mode. The directional mode may include, for example, 33 directional prediction modes or 65 directional prediction modes according to the granularity of the prediction direction. However, this is merely an example, and more or less directional prediction modes may be used depending on the setting. The intra prediction module 222 may determine the prediction mode applied to the current block by using the prediction mode applied to the adjacent block.

[71] The inter-prediction unit 221 can extract a predicted block for the current block based on a reference block (an array of reference samples) indicated by a motion vector for the reference frame. At this time, in order to reduce the amount of motion information transmitted in the inter-prediction mode, motion information may be predicted on a block, sub-block, or sample basis based on the correlation of motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction direction information (L0-prediction, L1-prediction, bi-prediction, etc.). In the case of inter-prediction, the neighbor block may include a spatial neighbor block existing in the current frame and a temporal neighbor block existing in the reference frame. The reference frame including the reference block and the reference frame including the temporary adjacent block may be identical to each other or different from each other. A temporary neighbor block may be called a “co-located reference block”, a “col-located CU (colCU)”, etc., and a reference frame including a temporary neighboring block may be called a “col-located frame (colPic)”. For example, the inter-prediction module 221 may configure a list of motion information candidates based on neighboring blocks and generate information indicating which candidate is used to retrieve the motion vector and/or reference frame index of the current block. Mutual prediction can be performed based on different prediction modes. For example, in the case of the skip mode and the merge mode, the inter-prediction unit 221 may use the motion information of the adjacent block as the motion information of the current block. In the skip mode, unlike the combine mode, the residual signal may not be transmitted. In the case of a motion information prediction mode (motion vector prediction, MVP), the motion vector of an adjacent block may be used as a motion vector predictor, and the motion vector of the current block may be indicated by signaling a motion vector difference.

[72] The prediction module 220 may generate a prediction signal based on various prediction methods. For example, the prediction module may apply intra-prediction or inter-prediction to make predictions regarding one block, and may also apply intra-prediction and inter-prediction simultaneously. This may be referred to as "combined inter-intraprediction (CIIP)". Additionally, the prediction module may be based on an intra-block copy (IBC) prediction mode or a palette mode to perform prediction relative to a block. The IBC prediction mode or palette mode can be used for encoding image/video content of a game and the like, for example, screen content encoding (SCC). Although IBC essentially performs prediction in the current block, it can perform similar to inter prediction in that it retrieves the reference block in the current block. Thus, the IBC may use at least one of the inter-prediction technologies described in the present disclosure.

[73] The prediction signal generated through the inter prediction module 221 and/or the intra prediction module 222 can be used to generate a reconstructed signal or generate a residual signal. Converter 232 may generate conversion coefficients by applying conversion technology to the residual signal. For example, the transform technology may include at least one of a discrete cosine transform (DCT), a discrete sine transform (DST), a Karhunen-Loeve transform (KLT), a graph-based transform (GBT), or a conditionally nonlinear transform (CNT). ). Here, GBT means a graph-derived transformation when the relationship information between pixels is represented by the graph. CNT means the transformation obtained from the prediction signal generated using all the previously reconstructed pixels. In addition, the conversion process can be applied to square pixel blocks that are identical in size, or can be applied to blocks that are variable in size rather than square.

[74] Quantizer 233 may quantize transform coefficients and transmit them to entropy encoder 240, and entropy encoder 240 may encode the quantized signal (information regarding the quantized transform coefficients) and output the encoded signal in a bit stream. Information regarding the quantized transform coefficients may be referred to as "residual information". Quantizer 233 may re-arrange the block quantized transform coefficients into one-dimensional vector form based on the scanning order of the coefficients, and generate information regarding the quantized transform coefficients based on the quantized transform coefficients in one-dimensional vector form. The entropy encoder 240 may implement various encoding techniques, such as, for example, exponential Golomb coding, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), and the like. Entropy encoder 240 may encode information needed to reconstruct video/images other than quantized transform coefficients (eg, syntax element values, etc.), together or separately. Encoded information (eg, encoded video/image information) may be transmitted or stored based on Network Abstraction Layer (NAL) units in the form of a bit stream. The video/image information may further include information regarding various parameter sets, such as an adaptation parameter set (APS), a frame parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS), and the like. Additionally, the video/image information may further include general restriction information. In the present disclosure, information and/or syntax elements that are transmitted/signaled in overhead signals to the decoding equipment from the encoding equipment may be included in the video/image information. The video/image information may be encoded through the encoding procedure described above and included in the bit stream. The bit stream may be transmitted over a network or stored on a digital storage medium. Here, the network may include a broadcast network, a communications network, and the like, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-Ray, HDD, SSD, and etc. A transmitter (not shown) that transmits the signal output from the entropy encoder 240 and/or a storage module (not shown) that stores it may be configured as an internal/external element of the encoding hardware 200, or the transmitter may be included in the entropy encoder 240 .

[75] The quantized transform coefficients output from quantizer 233 can be used to generate a predictive signal. For example, by applying dequantization and inverse transform to the quantized transform coefficients through dequantizer 234 and inverter 235, the residual signal (residual block or residual samples) can be recovered. The adder 155 adds the reconstructed residual signal with the prediction signal output from the inter-prediction module 221 or the intra-prediction module 222, so that a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array) can be generated. When there is no remainder for the target processing block, as in the case when the skip mode is applied, the predicted block can be used as the reconstructed block. The adder 250 may be referred to as a "recovery module" or a "recovered block generator." The generated reconstructed signal can be used to internally predict the next target processing block in the current block and, as described below, can be used to inter-predict the next frame through filtering.

[76] Meanwhile, in the process of encoding and/or restoring frames, luma conversion with chrominance scaling (LMCS) may be applied.

[77] Filter 260 may enhance the subjective/objective quality of the video by applying filtering to the reconstructed signal. For example, filter 260 may generate a modified reconstructed frame by applying various filtering techniques to the reconstructed frame and may store the modified reconstructed frame in storage device 270, particularly in the DPB of storage device 270. Various filtering techniques may include, for example, deletion filtering blocking, sampled adaptive offset, adaptive contour filter, bilateral filter, etc. As explained below in the description of each filtering method, the filter 260 may generate various filtering-related information and transmit the generated information to the entropy encoder 240. The filtering information may be encoded in the entropy encoder 240 and output in the form of a bit stream.

[78] The modified reconstructed frame, which is transferred to the storage device 270, can be used as a reference frame in the inter-prediction unit 221. By doing this, the encoding equipment can prevent prediction mismatch in the encoding equipment 100 and the decoding equipment when inter-prediction is applied, and can also improve encoding efficiency.

[79] The DPB of the storage device 270 may store the modified reconstructed frame to use as a reference frame in the inter-prediction module 221. Memory 270 may store block motion information in the current frame from which motion information is extracted (or encoded), and/or block motion information in an already reconstructed frame. The stored motion information may be transmitted to the inter-prediction unit 221 for use as neighboring block motion information or temporary neighbor block motion information. Memory 270 may store reconstructed samples of reconstructed blocks in the current frame and transmit them to intra prediction module 222.

[80] FIG. 3 is a diagram fundamentally illustrating the configuration of a video/image decoding apparatus to which the present disclosure is applicable.

[81] Referring to FIG. 3, video decoding apparatus 300 may include an entropy decoder 310, a residual processor 320, a prediction module 330, an adder 340, a filter 350, and a memory 360. The prediction module 330 may include an inter-prediction module 331 and an intra-prediction module 332. Residual processor 320 may include a dequantizer 321 and an inverse converter 321. Entropy decoder 310, residual processor 320, prediction module 330, adder 340, and filter 350, which are described above, may be comprised of one or more hardware components (e.g., chipsets or decoder processors) according to an embodiment. Additionally, storage device 360 may include a decoded frame buffer (DPB) and may be configured with a digital storage medium. The hardware component may further include storage device 360 as an internal/external component.

[82] When a bitstream including video/image information is input, the decoding apparatus 300 can reconstruct an image corresponding to the process by which the video/image information is processed in the encoding apparatus of FIG. 2. For example, decoding apparatus 300 may extract units/blocks based on block segmentation information obtained from the bit stream. The decoding apparatus 300 can perform decoding by using a processing unit applied in the encoding apparatus. Therefore, a decoding processing unit, for example, may be an encoding unit, which may be segmented along a quadtree structure, a binary tree structure, and/or a ternary tree structure from an encoding tree unit or a largest encoding unit. One or more transformation units may be derived from a coding unit. Also, the reconstructed image signal decoded and output through the decoding apparatus 300 can be reproduced through the playback unit.

[83] The decoding apparatus 300 may receive a signal output from the encoding apparatus of FIG. 2 in the form of a bit stream, and the received signal can be decoded through an entropy decoder 310. For example, an entropy decoder 310 can parse the bit stream to extract information (eg, video/image information) required for image reconstruction (or frame reconstruction). The video/image information may further include information regarding various parameter sets, such as an adaptation parameter set (APS), a frame parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS), and the like. Additionally, the video/image information may further include general restriction information. The decoding apparatus may further decode the frame based on information regarding the parameter set and/or general constraint information. In the present disclosure, the signaling/receiving information and/or syntax elements that are described below can be decoded by a decoding procedure and obtained from the bit stream. For example, entropy decoder 310 may decode information in a bit stream based on an encoding method such as exponential Golomb coding, CAVLC, CABAC, and the like, and may output the value of a syntax element required for image reconstruction and quantized transform coefficient values with respect to remainder. More specifically, the entropy CABAC decoding method may take a resolution element corresponding to each syntax element in the bitstream, determine a context model using decoding the information of target syntax elements and decoding the information of adjacent and decodable target blocks or the symbol/resolution element information decoded in a previous step. , predict the probability of generating a resolution element according to a certain context model, and perform arithmetic decoding of the permission element to generate a symbol corresponding to each value of the syntactic element. Here, the entropy CABAC decoding method can update the context model using the symbol/entry element information decoded for the context model of the next symbol/entry element after determining the context model. Information regarding prediction from the information decoded in the entropy decoder 310 may be provided to the prediction module (inter prediction module 332 and intra prediction module 331), and the residual values, i.e. quantized transform coefficients for which entropy decoding is performed in entropy decoder 310 and associated parameter information may be input to residual processor 320. Residual processor 320 may extract a residual signal (residual block, residual samples, array of residual samples). Additionally, information regarding filtering from information decoded in the entropy decoder 310 may be provided to the filter 350. Meanwhile, a receiver (not shown) that receives a signal output from the encoding equipment may further constitute the decoding equipment 300 as an internal/external element. , and the receiver may be a component of the entropy decoder 310. Meanwhile, the decoding apparatus according to the present disclosure may be called “video/image/frame encoding apparatus,” and the decoding apparatus may be classified into an information decoder (video/image/frame information decoder) and selective decoder (video/image/frame sampling decoder). The information decoder may include an entropy decoder 310, and the sample decoder may include at least one of a dequantizer 321, an inverter 322, an adder 340, a filter 350, a memory 360, an inter-prediction module 332, and an intra-prediction module 331 .

[84] The dequantizer 321 may output transform coefficients by dequantizing the quantized transform coefficients. The dequantizer 321 may re-arrange the quantized transform coefficients in the form of a two-dimensional block. In this case, the re-arrangement may perform the re-arrangement based on the scanning order of the coefficients, which is performed in the encoding apparatus. The dequantizer 321 may perform dequantization on the quantized transform coefficients using a quantization parameter (eg, quantization step size information) and obtain the transform coefficients.

[85] The dequantizer 322 obtains the residual signal (residual block, array of residual samples) by inversely transforming the transform coefficients.

[86] Prediction module 230 may perform prediction for the current block and may generate a predicted block including prediction samples for the current block. The prediction module can determine whether intra prediction or inter prediction is applied to the current block based on the prediction information output from the entropy decoder 310, and in particular can determine the intra/inter prediction mode.

[87] The prediction module can generate a prediction signal based on various prediction methods. For example, the prediction module may apply intra-prediction or inter-prediction to make predictions regarding one block, and may also apply intra-prediction and inter-prediction simultaneously. This may be referred to as "combined inter-intraprediction (CIIP)". In addition, the prediction module can perform intra-block copy (IBC) to predict for a block. In-block copying can be used to encode game image/video content and the like, for example, screen content encoding (SCC). Although IBC essentially performs prediction in the current block, it can perform similar to inter prediction in that it retrieves the reference block in the current block. Thus, the IBC may use at least one of the inter-prediction technologies described in the present disclosure.

[88] The intra prediction module 331 may predict the current block by reference to the samples in the current frame. Samples for the link can be located in an adjacent node or spaced from the current block according to the prediction mode. In intraprediction, prediction modes may include a plurality of non-directional modes and a plurality of directed modes. The intra prediction unit 331 may determine the prediction mode applied to the current block by using the prediction mode applied to the adjacent block.

[89] The inter-prediction unit 332 may extract a predicted block for the current block based on a reference block (an array of reference samples) indicated by a motion vector for the reference frame. At this time, in order to reduce the amount of motion information transmitted in the inter-prediction mode, motion information may be predicted on a block, sub-block, or sample basis based on the correlation of motion information between a neighboring block and the current block. The motion information may include a motion vector and a reference frame index. The motion information may further include inter-prediction direction information (L0-prediction, L1-prediction, bi-prediction, etc.). In the case of inter-prediction, the neighbor block may include a spatial neighbor block existing in the current frame and a temporal neighbor block existing in the reference frame. For example, the inter-prediction module 332 may configure a motion information candidate list based on neighboring blocks and extract the motion vector and/or reference frame index of the current block based on the received candidate selection information. The inter-prediction may be performed based on various prediction modes, and the information regarding the prediction may include information indicating the inter-prediction mode for the current block.

[90] The adder 340 can generate a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array) by adding the resulting residual signal with a predicted signal (predicted block, predicted sample array) output from the prediction unit 330. When there is no remainder for the target processing block, as in the case when the skip mode is applied, the predicted block can be used as the reconstructed block.

[91] The adder 340 may be referred to as a “recovery module” or a “recovered block generator.” The generated reconstructed signal may be used to internally predict the next target processing block in the current block and, as described below, may be output by filtering or used to inter-predict the next frame.

[92] Meanwhile, in the process of decoding frames, luma conversion with chrominance scaling (LMCS) may be applied.

[93] Filter 350 may enhance the subjective/objective quality of the video by applying filtering to the reconstructed signal. For example, filter 350 may generate a modified reconstructed frame by applying various filtering techniques to the reconstructed frame and may transfer the modified reconstructed frame to storage device 360, particularly to a DPB of storage device 360. Various filtering techniques may include, for example, deletion filtering blocking, sampled adaptive offset, adaptive contour filter, bilateral filter, etc.

[94] The (modified) reconstructed frame, which is stored in the DPB of the storage device 360, can be used as a reference frame in the inter-prediction unit 332. Storage device 360 may store block motion information in the current frame from which motion information is extracted (or decoded), and/or block motion information in an already reconstructed frame. The stored motion information may be transmitted to the inter-prediction unit 260 for use as neighbor block motion information or temporary neighbor block motion information. Storage device 360 may store reconstructed samples of reconstructed blocks in the current frame and transmit them to intra prediction module 331.

[95] In this detailed description, the examples described in prediction module 330, dequantizer 321, inverse converter 322, and filter 350 of decoding apparatus 300 may be similarly or correspondingly applied to prediction module 220, dequantizer 234, inverse converter 235, and filter 260 of decoding apparatus 200. coding, respectively.

[96] As described above, prediction is performed in order to improve compression efficiency when performing video encoding. Due to this, a predicted block can be generated including predictive samples for the current block, which is the target encoding block. Here, the predicted block includes predictive samples in a spatial domain (or pixel domain). The predicted block can be identically retrieved in the encoding equipment and the decoding equipment, and the encoding equipment can improve the efficiency of image encoding by signaling to the decoding equipment not the original sample value of the original block itself, but information regarding the remainder (residual information) between the original block and the predicted block . The decoding apparatus may extract a residual block including residual samples based on the residual information, generate a reconstructed block including the reconstructed samples by adding the residual block with the predicted block, and generate a reconstructed frame including the reconstructed blocks.

[97] Residual information can be generated through transformation and quantization procedures. For example, the encoding apparatus may extract a residual block between an original block and a predicted block, extract transform coefficients by performing a transform procedure on the residual samples (an array of residual samples) included in the residual block, and extract quantized transform coefficients by performing a quantization procedure on the transform coefficients, such as that it can signal associated residual information to decoding equipment (via a bit stream). Here, the residual information may include value information, position information, conversion technology, conversion kernel, quantization parameter, and the like. quantized conversion coefficients. The decoding apparatus may perform a quantization/dequantization procedure and extract residual samples (or a block of residual samples) based on the residual information. The decoding apparatus may generate a reconstructed block based on the predicted block and the residual block. The encoding apparatus may extract the residual block by dequantizing/de-converting the quantized transform coefficients for the next frame inter-prediction reference, and may generate a reconstructed frame based on it.

[98] FIG. 4 schematically illustrates a multiple conversion technology according to an embodiment of the present disclosure.

[99] Referring to FIG. 4, the converter may correspond to the converter in the encoding apparatus of FIG. 2, and the inverse converter may correspond to the inverse converter in the encoding apparatus of the above FIG. 2 or the inverse converter in the decoding equipment of FIG. 3.

[100] The converter can extract (primary) transform coefficients by performing a primary transform based on the residual samples (residual sample array) in the residual block (S410). This primary transformation may be called the "base transformation". Herein, the primary transform may be based on multiple transform selection (MTS), and when the multiple transform is applied as the primary transform, it may be referred to as a "multi-core transform".

[101] The multi-core transform may represent a transform method further using discrete cosine transform (DCT) type 2 and discrete sine transform (DST) type 7, DCT type 8 and/or DST type 1. Thus, the multi-core transform may represent a transform method for converting the spatial domain residual signal (or residual block) into frequency domain transform coefficients (or primary transform coefficients) based on a plurality of transform kernels selected from DCT Type 2, DST Type 7, DCT Type 8, and DST Type 1. Herein, the primary conversion coefficients may be called "temporary conversion coefficients" from the point of view of the converter.

[102] Thus, when the traditional conversion method is applied, transform coefficients can be generated by applying a spatial domain to frequency domain transform to a residual signal (or residual block) based on DCT type 2. However, when multi-core transform is applied, the transform coefficients (or primary transform coefficients) may be generated by applying a spatial domain to frequency domain transform to a residual signal (or residual block) based on DCT type 2, DST type 7, DCT type 8 and/or DST type 1. Here, DCT type 2 , DST type 7, DCT type 8 and DST type 1 may be called "transformation types", "transform kernels" (transform kernels or transform cores). These DCT/DST types can be specified based on basis functions.

[103] If a multiple base transform is performed, a vertical transform kernel and a horizontal transform kernel for the target block may be selected from among the transform kernels, a vertical transform for the target block may be performed based on the vertical transform kernel, and a horizontal transform for the target block may be performed based on horizontal transformation kernels. Here, a horizontal transform may represent a transform for the horizontal components of the target block, and a vertical transform may represent a transform for the vertical components of the target block. The vertical transform kernel/horizontal transform kernel may be adaptively determined based on the prediction mode and/or transform index of the target block (CU or subblock) including the residual block.

[104] Additionally, according to the example, if the primary transformation is performed by applying the MTS, the transformation relationship for the transformation kernels can be specified by setting specific basis functions to predetermined values and combining the basis functions to be applied in the vertical transformation or horizontal transformation. For example, when the horizontal transformation kernel is expressed as trTypeHor and the vertical direction transformation kernel is expressed as trTypeVer, a trTypeHor or trTypeVer value of 0 may be specified for DCT2, a trTypeHor or trTypeVer value of 1 may be specified for DST7, and a trTypeHor or trTypeVer value of 2 may be specified for DCT8.

[105] In this case, the MTS index information may be encoded and signaled to decoding equipment to indicate any of a plurality of sets of transform cores. For example, an MTS index of 0 may indicate that trTypeHor and trTypeVer are equal to 0, an MTS index of 1 may indicate that trTypeHor and trTypeVer are equal to 1, an MTS index of 2 may indicate that trTypeHor is equal to 2 , and the value of trTypeVer is 1, an MTS index of 3 may indicate that the value of trTypeHor is 1 and the value of trTypeVer is 2, and an MTS index of 4 may indicate that both the values of trTypeHor and trTypeVer are 2.

[106] In one example, sets of transformation kernels according to MTS index information are illustrated in the following table.

[107] Tab. 1

[108] In another example, trTypeHor and trTypeVer according to the MTS index information (mts_idx[x][y]) and prediction mode (CuPredMode[x][y]) for the current block (eg, the current encoding block) are illustrated as follows.

[109] Tab. 2

[110] The converter can extract modified (secondary) conversion coefficients by performing secondary conversion based on the (primary) conversion coefficients (S420). The primary transform is a conversion from the spatial domain to the frequency domain, and the secondary transform is a conversion to a more compressive expression by exploiting the correlation existing between the (primary) transform coefficients. The secondary transformation may include an inseparable transformation. In this case, the secondary transform may be called a "non-separable secondary transform (NSST)" or a "mode-dependent non-separable secondary transform (MDNSST)". The inseparable secondary transform may be a transform that generates modified transform coefficients (or secondary transform coefficients) for the residual signal by a secondary transform, based on the inseparable transform matrix of the (primary) transform coefficients extracted through the primary transform. At this time, the vertical transform and horizontal transform may not be applied separately (or the horizontal and vertical transforms may not be applied independently) to the (primary) transform coefficients, but the transforms may be applied immediately based on the inseparable transform matrix. In other words, an inseparable secondary transform may represent a transform method in which the vertical and horizontal components of the (primary) transform coefficients are not separated, and, for example, the two-dimensional signals (transform coefficients) are recomposed into a one-dimensional signal through a particular defined direction (for example, the row-first direction or column-first direction), and then modified transform coefficients (or secondary transform coefficients) are generated based on the inseparable transform matrix. For example, according to row first order, MxN blocks are arranged in a line in the order "first row, second row, ..., and Nth row". According to column first order, MxN blocks are arranged in a line in the order "first column, second column, ..., and Nth column". An inseparable secondary transform may be applied to the upper left region of a block configured with (primary) transform coefficients (hereinafter in this document, may be referred to as a “transform coefficient block”). For example, if the width (W) and height (H) of the transform coefficient block are equal to or greater than 8, an inseparable secondary 8×8 transform may be applied to the upper left 8×8 region of the transform coefficient block. Additionally, if the width (W) and height (H) of the transform coefficient block are equal to or greater than 4, and the width (W) or height (H) of the transform coefficient block is less than 8, then an inseparable 4x4 secondary transform can be applied to the left upper region min (8, W) x min(8, H) block of transformation coefficients. However, the embodiment is not limited to this and, for example, even if only the condition that the width (W) or height (H) of the transform coefficient block is equal to or greater than 4 is satisfied, the inseparable 4x4 secondary transform can be applied to the left upper area min(8, W) x min(8, H) of the block of transformation coefficients.

[111] The converter may perform an inseparable secondary transform based on the selected transform kernels and may obtain modified (secondary) transform coefficients. As described above, the modified transform coefficients may be extracted as transform coefficients quantized through a quantizer, and may be encoded and signaled to the decoding apparatus and transmitted to a dequantizer/inverse converter in the encoding apparatus.

[112] Meanwhile, as described above, if the secondary transform is omitted, the (primary) transform coefficients that represent the output of the primary (separable) transform can be extracted as transform coefficients quantized through a quantizer as described above, and can be encoded and transmitted in service signals to the decoding equipment and transmitted to the dequantizer/inverse converter in the encoding equipment.

[113] The inverse converter may perform a sequence of procedures in the reverse order of the order in which they are performed in the above-described converter. The inverse converter can receive (dequantized) transform coefficients and extract the (primary) transform coefficients by performing a secondary (inverse) transform (S450), and can obtain a residual block (residual samples) by performing a primary (inverse) transform on the (primary) transform coefficients (S460 ). In this regard, the primary conversion coefficients may be referred to as "modified conversion coefficients" from the point of view of the inverse converter. As described above, the encoding equipment and decoding equipment can generate a reconstructed block based on the residual block and the predicted block, and can generate a reconstructed image based on the reconstructed block.

[114] The decoding apparatus may further include a secondary inverse transform application determining unit (or an element for determining whether or not a secondary inverse transform should be applied) and a secondary inverse transform determining unit (or an element for determining whether the secondary inverse transform is applied). transformation). The secondary inverse transform application determination module may determine whether or not to apply the secondary inverse transform. For example, the secondary inverse transform may be NSST or RST, and the secondary inverse transform application determination module may determine whether or not to apply the secondary inverse transform based on the secondary transform flag obtained by parsing the bitstream. In another example, the secondary inverse transform application determining unit may determine whether or not to apply the secondary inverse transform based on the transform coefficient of the residual block.

[115] The secondary inverse transform determination module may determine the secondary inverse transform. In this case, the secondary inverse transform determining unit may determine the secondary inverse transform applied to the current block based on the set for the NSST (or RST) transform specified according to the intra prediction mode. In an embodiment, the method for determining the secondary transformation may be determined depending on the method for determining the primary transformation. Various combinations of primary transformations and secondary transformations may be determined according to the internal prediction mode. Additionally, in the example, the secondary inverse transform determination module may determine the region to which the secondary inverse transform is applied based on the size of the current block.

[116] Meanwhile, as described above, if the secondary (inverse) transform is omitted, the (dequantized) transform coefficients can be received, the primary (separable) inverse transform can be performed, and the residual block (residual samples) can be obtained. As described above, the encoding equipment and decoding equipment can generate a reconstructed block based on the residual block and the predicted block, and can generate a reconstructed image based on the reconstructed block.

[117] Meanwhile, in the present disclosure, reduced secondary transform (RST), in which the size of the transformation matrix (kernel) is reduced, can be applied in the concept of NSST to reduce the amount of computation and storage required for the non-separable secondary transform.

[118] Meanwhile, the transformation kernel, the transformation matrix and the coefficient constituting the transformation kernel matrix, i.e. the kernel coefficient or matrix coefficient described in the present disclosure may be expressed in 8 bits. This may be a condition for implementation in decoding apparatus and encoding apparatus, and allows the storage space required to store the conversion kernel to be reduced, with a performance penalty that can be accommodated sufficiently compared to the existing 9 bits or 10 bits. In addition, expressing the kernel matrix in 8 bits can enable the use of a small multiplier and may be more suitable for single instruction multiple data (SIMD) instructions used for optimal software implementation.

[119] As used herein, the term "RST" may mean a transformation that is performed on the residual samples for a target block based on a transformation matrix whose size is reduced according to a reduction factor. When performing a reduced transformation, the amount of computation required for the transformation may be reduced due to the reduction in the size of the transformation matrix. Thus, RST can be used to solve the problem of computational complexity encountered in non-separable transformation or large block size transformation.

[120] RST may be referred to by various terms such as "reduced transform", "reduced secondary transform", "reduced transform", "simplified transform", "simple transform", etc., and named by which may be called RST, is not limited to the examples listed. Alternatively, since RST is primarily performed in the low frequency region including a non-zero coefficient in the transform block, it may be referred to as "low frequency non-separable transform (LFNST)".

[121] Meanwhile, when the secondary inverse transform is performed based on the RST, the inverse transformer 235 of the encoding apparatus 200 and the inverse transformer 322 of the decoding apparatus 300 may include an inverse shortened secondary transformer that extracts modified transform coefficients based on the inverse RST transform coefficients, and an inverse primary transformer that extracts residual samples for the target block based on the inverse primary transform of the modified transform coefficients. Reverse the primary transformation means the inverse transformation of the primary transformation applied to the remainder. In the present disclosure, extracting a transform coefficient based on a transform may mean extracting a transform coefficient by applying a transform.

[122] Later in this document, multiple selection (or set) for reduced adaptive (or explicit) transform (RMTS) is described.

[123] As described above, when combinations of multiple transforms (DCT2, DST7, DCT8, DST1, DCT5, etc.) in a multiple transform set (explicit multiple transform or adaptive multiple transform) are selectively used for the primary transform, the transform can be applied only to a predefined region to reduce complexity, rather than performing the transformation in all cases, thereby significantly reducing worst-case complexity.

[124] For example, when the primary transform is applied to an MxM pixel block based on the above reduced transform (RT) method, only the calculation for the RxR (M>=R) transform block may be performed instead of obtaining the MxM transform block. As a result, significant coefficients (non-zero coefficients) exist only in the RxR region, and coefficients existing in another region can be treated as zeros without calculation. The following table illustrates three examples of reduced adaptive multiple transform (RAMT) using the reduced transform coefficient (R) preset according to the block size to which the primary transform is applied.

[125] Tab. 3

Conversion size Short conversion 1 Shortcut conversion 2 Shortcut Conversion 3 8x8 4x4 6x6 6x6 16×16 8x8 12x12 8x8 32×32 16×16 16×16 16×16 64x64 32×32 16×16 16×16 128x128 32×32 16×16 16×16

[126] According to an example, when applying the shortened multiple transforms illustrated above, the shortened transform coefficient can be determined based on the primary transform. For example, when the primary transform is DCT2, the calculation is simple compared to other primary transforms, and therefore the reduced transform may not be used for a small block, or a relatively large R-value may be used for a small block, thereby minimizing the performance penalty coding. For example, different shortened transform coefficients can be used for DCT2 and other transforms as follows.

[127] Tab. 4

Conversion size Short conversion for DCT2 Reduced conversion other than DCT2 8x8 8x8 4x4 16×16 16×16 8x8 32×32 32×32 16×16 64x64 32×32 32×32 128x128 32×32 32×32

[128] As shown in Table 4, when the primary transform is DCT2, the transform size is not changed when the block size to be converted is 8×8 or 16×16, and the reduced transform size is limited to 32×32 when the block size is 32x32 or larger.

[129] Alternatively, according to the example, when the value of the flag indicating whether or not MTS is applied is 0 (ie, when DCT2 is applied to the horizontal and vertical directions), only the 32 coefficients on the left or top can be left, and the high frequency components can reset to zero, i.e. set to zero for the (horizontal and vertical) directions (zero-based embodiment 1).

[130] For example, in a transformation unit (TU) of 64×64, the transformation coefficients are left only in the upper left region of 32×32, in a TU of 64×16, the transformation coefficients are left only in the upper left region of 32×16, and in a TU of 8× 64, the transform coefficients are left only in the upper left 8x32 region. Thus, the conversion factors exist according to only up to a maximum length of 32 in width and height.

[131] This nulling method may be applied only to a residual signal to which intra prediction is applied, or may be applied only to a residual signal to which inter prediction is applied. Alternatively, the nulling method may be applied to both the residual signal to which the intra prediction is applied and the residual signal to which the inter prediction is applied.

[132] Changing the size of a transform block, which may be expressed as the above nulling or high-frequency nulling, means the process of nulling (defining as zeros) transform coefficients associated with a high frequency of a certain value or more in a (transform) block having a first width (or length ) in W1 and the first height (or length) in H1. When high-frequency nulling is applied, transform coefficient values for all transform coefficients outside the low-frequency transform coefficient region configured based on the second width in W2 and the second height in H2 from among the transform coefficients in the (transform) block may be determined (set) as zeros. The portion external to the low-frequency conversion coefficient region may be referred to as the “high-frequency transformation coefficient region.” In an example, the low frequency transform coefficient region may be a rectangular region positioned at the upper left end of the (transform) block.

[133] Thus, high-frequency zeroing can be specified as setting all transform coefficients at the position specified by an X coordinate of N or more and a Y coordinate of M or more to zero, with the horizontal value of the X coordinate of the upper left position of the current transform block ( TB) is set to 0, and the vertical Y coordinate value of it is set to 0 (with the X coordinates increasing from left to right and the Y coordinates increasing down).

[134] When used herein, a specific term or expression is used to specify specific information or concept. For example, as described above, in the present disclosure, a process of zeroing transform coefficients associated with a high frequency of a certain value or more in a (transform) block having a first width (or length) in W1 and a first height (or length) in H1 is specified as "high-frequency nulling", a region in which nulling is performed through high-frequency nulling is specified as a "high-frequency conversion coefficient region" and a region in which nulling is not performed is specified as a "low-frequency transformation coefficient region". The second width (or length) in W2 and the second height (length) in H2 are used to express the size of the low frequency transform coefficient region.

[135] However, "high-frequency zeroing" can be replaced by various terms such as high-frequency zeroing (high-frequency zeroing-out, high-frequency zeroing-out, high-frequency zero-out) and zeroing, and "high-frequency conversion coefficient region" may be replaced by various terms such as high-frequency nulling application area, high-frequency nulling region, high-frequency region, high-frequency coefficient region, high-frequency nulling region and nulling region, and "low-frequency conversion coefficient region" may be replaced by various terms, such as the area without high-frequency nulling, the low-frequency area, the low-frequency coefficient area, and the restricted area. Thus, a particular term or expression used herein to specify a particular information or concept is to be interpreted throughout the detailed description in light of the various operations, functions and benefits of the content indicated by the term, without limitation by designation.

[136] Alternatively, according to the example, the low-frequency transform coefficient region means the remaining region after high-frequency nulling is performed, or the region in which a significant transform coefficient remains, and may be called a “nulling region” or a “nulling block.”

[137] According to an example, when the value of the flag indicating whether or not MTS is applied is 1, i.e. when another transformation (DST7 or DCT8) other than DCT2 is applicable for the horizontal direction and the vertical direction, the transformation coefficients can only be left in the upper left region, and the remaining region can be reset as follows (nulling-based embodiment 2).

[138] - When the width (w) is equal to or greater than 2 ⁿ , only the transform coefficients corresponding to the length in w/2 ^p on the left can be retained, and the remaining transform coefficients can be set fixed to zero (zeroed).

[139] - When the height (h) is equal to or greater than 2 ^m , only the transformation coefficients corresponding to the length in h/2 ^q above and remaining transformation coefficients can be set fixed to zero (zeroed).

[140] Here, m, n, p and q may be integers equal to or greater than 0, and specifically may be the following:

[141] 1) (m, n, p, q)=(5, 5, 1, 1)

[142] 2) (m, n, p, q)=(4, 4, 1, 1)

[143] In configuration 1), the transform coefficients remain only in the left upper region 16×16 in the TU 32×16, and the transform coefficients remain only in the left upper region 8×16 in the TU 8×32.

[144] This nulling method may be applied only to a residual signal to which intra prediction is applied, or may be applied only to a residual signal to which inter prediction is applied. Alternatively, the nulling method may be applied to both the residual signal to which the intra prediction is applied and the residual signal to which the inter prediction is applied.

[145] Alternatively, according to another example, when the value of the flag indicating whether or not MTS is applied is 1, i.e. when another transformation (DST7 or DCT8) other than DCT2 is applicable for the horizontal direction and the vertical direction, the transformation coefficients can only be left in the upper left region, and the remaining region can be reset as follows (nulling-based embodiment 3).

[146] - When height (h) is equal to or greater than width (w) and equal to or greater than 2 ⁿ , only the transform coefficients in the upper left region wx(h/2 ^p ) may be retained, and the remaining transform coefficients may be set fixed to zero ( reset to zero).

[147] - When the width (w) exceeds the height (h) and is equal to or greater than 2 ^m , only the transform coefficients in the upper left region (w/2 ^q )xh, and the remaining transform coefficients can be set fixed to zero (zeroed).

[148] Under the above conditions, when the height (h) and width (w) are identical, the vertical length decreases (h/2 ^p ), but the horizontal length can decrease (w/2 ^q ).

[149] Here, m, n, p and q may be integers equal to or greater than 0, and specifically may be the following:

[150] 1) (m, n, p, q)=(4, 4, 1, 1)

[151] 2) (m, n, p, q)=(5, 5, 1, 1)

[152] In configuration 1), the transform coefficients remain only in the left upper region 16×16 in the TU 32×16, and the transform coefficients remain only in the left upper region 8×8 in the TU 8×16.

[153] This nulling method may be applied only to a residual signal to which intra prediction is applied, or may be applied only to a residual signal to which inter prediction is applied. Alternatively, the nulling method may be applied to both the residual signal to which the intra prediction is applied and the residual signal to which the inter prediction is applied.

[154] In the above embodiments, the range of conversion coefficients is limited depending on where the value of the flag indicating whether or not MTS is applied is 0, or where the value of the flag indicating whether or not MTS is applied is 1. According to one example, combinations of these embodiments are possible.

[155] 1) Null-based embodiment 1 + Null-based embodiment 2

[156] 2) Null-based embodiment 1 + Null-based embodiment 3

[157] As mentioned in nulling-based Embodiment 2 and nulling-based Embodiment 3, nulling may be applied only to a residual signal to which intra prediction is applied, or may be applied only to a residual signal to which inter prediction is applied. Alternatively, the nulling method may be applied to both the residual signal to which the intra prediction is applied and the residual signal to which the inter prediction is applied. Accordingly, when the MTS flag is 1, the following table can be configured (when the MTS flag is 0, the nulling-based embodiment 1 can be applied).

[158] Tab. 5

Configuration Index Residual internal prediction signals Residual mutual prediction signals 1 Zeroing does not apply Zeroing does not apply 2 Zeroing does not apply Embodiment 2 based on zeroing 3 Zeroing does not apply Embodiment 3 based on zeroing 4 Embodiment 2 based on zeroing Zeroing does not apply 5 Embodiment 2 based on zeroing Embodiment 2 based on zeroing 6 Embodiment 2 based on zeroing Embodiment 3 based on zeroing 7 Embodiment 3 based on zeroing Zeroing does not apply 3 Embodiment 3 based on zeroing Embodiment 2 based on zeroing 9 Embodiment 3 based on zeroing Embodiment 3 based on zeroing

[159] In the nulling-based Embodiment 1, the nulling-based Embodiment 2, and the nulling-based Embodiment 3, a region necessarily including a value of 0 in the TU is clearly defined. Thus, the region other than the upper left region in which the transform coefficient is allowed to exist is set to zero. Accordingly, according to an embodiment, it can be configured to bypass a region in which the transform coefficient is definitely set to 0 by entropy encoding the residual signal, instead of performing residual encoding. For example, the following configuration is possible.

[160] 1) In HEVC or VVC, a flag indicating whether or not a non-zero transform coefficient exists in one coefficient group (CG, which may be 4x4 or 2x2 depending on the shapes of the subblock and TU block and component luminance signal/chrominance signal component), encoded (subblock_flag). Only when subblock_flag is 1 is the interior of the CG scanned and the coefficient level values are encoded. Accordingly, for CGs belonging to the region in which nulling is performed, subblock_flag may be set to a default value of 0 instead of encoding.

[161] 2) In HEVC or VVC, the position of the last coefficient (last_coefficient_position_x in the X-axis direction and last_coefficient_position_y in the Y-axis direction) in forward scanning order is encoded first. Typically, last_coefficient_position_x and last_coefficient_position_y can have a maximum value (TU-1 width) and a maximum value (TU-1 height), respectively. However, when the region in which a non-zero coefficient can exist is limited due to nulling, the maximum values of last_coefficient_position_x and last_coefficient_position_y are also limited. Accordingly, the maximum values of last_coefficient_position_x and last_coefficient_position_y can be limited to zero and can then be encoded. For example, when the binarization method applied to last_coefficient_position_x and last_coefficient_position_y is a truncated unary binarization, the maximum length of the truncated unary code (the codeword length that last_coefficient_position_x and last_coefficient_position_y can have) may be reduced based on the adjusted maximum values.

[162] As described above, nulling can be applied, in particular, in the case where the left upper region 32×32 is a region of low frequency transform coefficients (hereinafter referred to as “32-point reduced MTS” or “RMTS32”), in case the MTS scheme is used, and in any case if the 32-point DST7 or 32-point DCT8 is used.

[163] FIG. 5 illustrates 32-point nulling according to an example of the present disclosure.

[164] As shown in FIG. 5, when a block is divided and a transform is applied to area A, DST7 or DCT8 may be applied to each side, and the pair of transforms applied in the horizontal and vertical directions is not limited to the example illustrated in FIG. 5. In FIG. 5, the width and height of the entire block are denoted by w and h, respectively, and the width and height of the block to which the separable transformation is actually applied are expressed as a pair (width, height), which is (w1, h) or (w, h1) ; w1 can be equal to 1/2 or 1/4 of w, and h1 can also be equal to 1/2 or 1/4 of h.

[165] The block to which the transformation is applied may be positioned on the left or right, or at the top or bottom of the entire block, as shown in FIG. 5. Additionally, the block of FIG. 5 may be a residual signal generated by inter-prediction. A flag indicating whether or not the transform should be applied to only one sub-block of the residual signal segmented as shown in FIG. 5 may be signaled, and when the flag is 1, a flag indicating whether or not it is a 16×32 block as shown in FIG. 5 may also be specified by signaling.

[166] A flag indicating whether or not block A to which the transformation is actually applied is positioned to the left or right in the entire block, or a flag indicating whether block A is positioned above or below may also be signaled.

[167] As illustrated in FIG. 5, when horizontal transform and vertical transform are determined for a particular block, instead of designating horizontal transform and vertical transform by MTS signaling, if the horizontal side and vertical side have a length of 32, RMTS32 proposed above can be applied in each direction. For example, when a block is vertically segmented in FIG. 5, if the height of block A is 32, zeroing can be applied in the vertical direction. In particular, when block A is 16x32, the top left 16x16 block may be set to zero, and therefore a significant coefficient can only exist in the corresponding size region. In RMTS32, residual coding may be omitted for the region that is being nulled, or only the region that is not nulling may be scanned and may be subject to residual coding.

[168] FIG. 6 illustrates a residual block segment according to an embodiment of the present disclosure.

[169] The residual block may be segmented as shown in FIG. 6, and the width and height of the block A to which the transformation is actually applied may be w/4 and h/4, respectively, due to the width (w) and height (h) of the original transformation block.

[170] In general, RMTS32 can be applied to any block to which the transform is applied if DST7 or DCT8 having a length of 32 is applicable in each of the horizontal direction and the vertical direction. Whether DST7 or DCT8 having a length of 32 is applied may be determined by predetermined signaling or may be determined without signaling according to a predetermined encoding condition.

[171] Specification text describing nulling according to the embodiments of FIG. 5 and fig. 6 is illustrated in the following table. In the following table, the transform may be applied to the residual signal generated through inter-prediction, and may be called "sub-block transform (SBT)". The residual signal block is segmented into two segment blocks by SBT, and a separate transformation can be applied to only one of the segmented blocks.

[172] Tab. 6

7.3.4.6. Coding Unit Syntax

[173] Table 6 shows the syntax of the CU to which inter-prediction is applied, and the segment shape to which SBT is applied can be determined by the four syntax elements in Table 6.

[174] - cu_sbt_flag indicates whether or not SBT is applied to a CU, and cu_sbt_quad_flag is flag information indicating whether or not the block to which the transformation is applied constitutes 1/4 of the entire block when one CU is segmented into two segment blocks . When cu_sbt_quad_flag is 0, the segment block is 1/2 the size of the entire block. When cu_sbt_quad_flag is 1, the segment block is 1/4 the size of the CU width or height. When the width of the CU is w and its height is h, the height of the segment block may be h1=(1/4) x h, or the width of the segment block may be w1=(1/4) x w.

[175] - cu_sbt_horizontal_flag equal to 1 indicates that the CU is horizontally segmented, and cu_sbt_horizontal_flag equal to 0 indicates that the CU is vertically segmented.

[176] With respect to cu_sbt_pos_flag, a flag value of 0 indicates that the transformation is applied to the top or left block of segments in a horizontal or vertical segment, and a flag value of 1 indicates that the transformation is applied to the bottom or right block of segments.

[177] The following table illustrates trTypeHor and trTypeVer according to cu_sbt_horizontal_flag and cu_sbt_pos_flag.

[178] Tab. 7

[179] As described above, when the horizontal transform kernel is designated by trTypeHor and the vertical transform kernel is designated by trTypeVer, a trTypeHor or trTypeVer value of 0 may be set to DCT2, a trTypeHor or trTypeVer value to 1 may be set to DST7, and a trTypeHor or trTypeVer value may be set to 1. 2 can be set for DCT8. Accordingly, when the length of at least one side of the block of segments to which the transformation is applied is 64 or greater, DCT2 may be applied in both the horizontal direction and the vertical direction, and otherwise, DST7 or DCT8 may be applied.

[180] Tab. 8

7.3.4.11. Conversion unit syntax

[181] Tab. 9

7.3.4.12. Residual encoding syntax

[182] Table 8 shows part of the TU syntax according to the example, and Table 9 shows part of the residual encoding syntax.

[183] In Table 8, tu_mts_idx[x0][y0] denotes the MTS index applied to the transform block, and trTypeHor and trTypeVer may be determined according to the MTS index, as shown in Table 1.

[184] The syntax elements last_sig_coeff_x_prefix, last_sig_coeff_y_prefix, last_sig_coeff_x_suffix and last_sig_coeff_y_suffix in Table 9 denote position information (x, y) relative to the last non-zero transform coefficient in the transform block. Specifically, last_sig_coeff_x_prefix denotes the column position prefix of the last significant coefficient in scan order in the transform block, last_sig_coeff_y_prefix denotes the row position prefix of the last significant coefficient in scan order in the transform block, last_sig_coeff_x_suffix denotes the column position suffix of the last significant coefficient in scan order in the transform block, and last_sig_coeff_y_suffix denotes the row position suffix of the last significant coefficient in scan order in the transform block. Here, a significant coefficient may mean a non-zero coefficient. The scanning order may be a right-up diagonal scanning order. Alternatively, the scanning order may be a horizontal scanning order or a vertical scanning order. The scanning order may be determined based on whether or not intra/inter prediction is applied to the target block (CB or CB including TB), and/or a particular intra/inter prediction mode.

[185] The nulling region may be specified in table 9 residual encoding based on tu_mts_idx[x0][y0] in table 8.

[186] When cu_sbt_flag is 1, the height of the block to which the transform is applied is 32 or less (log2TbHeight<6), and its width is 32 (log2TbWidth<6 andand log2TbWidth>4), the width of the transform block is set to 16 (log2TbWidth= 4). In other cases in which cu_sbt_flag is not equal to 1, the height of the transform block is greater than 32, or the width of the transform block is not 32, the width of the transform block may be set to the lesser of the transform block width and 32. Thus, the maximum width of the transform block may be limited 32 by resetting.

[187] Similarly, when cu_sbt_flag is 1, the width of the block to which the transform is applied is 32 or less (log2TbWidth<6) and its height is 32 (log2TbHeight<6 andand log2TbHeight>4), the height of the transform block is set to 16 ( log2TbHeight=4). In other cases in which cu_sbt_flag is not equal to 1, the transform block width is greater than 32, or the transform block height is not 32, the transform block height may be set to the lesser of the transform block height and 32. Thus, the maximum transform block height may be limited 32 by resetting.

[188] According to Table 7, when the length of at least one side of the segment block is 64 or more, DCT2 can be applied in both the horizontal direction and the vertical direction, and otherwise, DST7 or DCT8 can be applied. Accordingly, when SBT is applied, nulling can be performed by applying RMTS32 only when all two sides of the block of segments to which the transformation is applied have a length of 32 or less. Thus, when the block length in each direction is 32, only 16 transform coefficients can be left by using DST7 or DCT8 having a length of 32.

[189] As shown in Table 9, when using RMTS32, encoding can be performed by considering the width and height of the remaining region (low frequency transform coefficient region) that is not zeroed as the actual width and height of the TU, instead of using the width and height of the original transform unit for encoding (log2TbWidth=Min(log2TbWidth, 5) or log2TbHeight=Min(log2TbHeight, 5)).

[190] For example, when the height x width of the original TU is 32×16, if RMTS32 is applied, a non-zero coefficient exists only in the upper left region of 16×16 by zeroing. Accordingly, the width and height of the TU may be set to 16 and 16, respectively, and then the syntax elements (eg, last_sig_coeff_x_prefix and last_sig_coeff_y_prefix) may be encoded.

[191] In general, according to the residual encoding of Table 9, the actual width and height of the TU are changed by changing the values of log2TbWidth and log2TbHeight before encoding last_sig_coeff_x_prefix, and the syntax elements are then encoded according to the changed values.

[192] When the TU size is reduced to the region of low-frequency transform coefficients due to zeroing of the high-frequency transform coefficient, the semantics of the syntax elements of Table 9 are illustrated in Table 10.

[193] Tab. 10

- last_sig_coeff_x_prefix specifies the column position prefix of the last significant coefficient in scan order in the transform block. Last_sig_coeff_x_prefix values must be in the range 0 to (log2TbWidth<<1)-1, inclusive.
When last_sig_coeff_x_prefix is not present, it is logically output to 0.
- last_sig_coeff_y_prefix specifies the line position prefix of the last significant coefficient in scan order in the transform block. Last_sig_coeff_y_prefix values must be in the range 0 to (log2TbHeight<<1)-1, inclusive.
When last_sig_coeff_y_prefix is not present, it is logically output to 0.

[194] Referring to Table 10, last_sig_coeff_x_prefix and last_sig_coeff_y_prefix are limited to values ranging from 0 to (log2TbWidth<<1)-1 or (log2TbHeight<<1)-1, where log2TbWidth or log2TbHeight may be the width or height of the reduced transform block size as shown in Table 9.

[195] When the size of the transform block is changed, the size of the transform block used to select the last_sig_coeff_x_prefix and last_sig_coeff_y_prefix contexts may also change. Table 11 illustrates the context increment (ctxInc) extraction process to extract last_sig_coeff_x_prefix and last_sig_coeff_y_prefix, and Table 12 illustrates the binarization of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix given the shortened TU. Since the context can be selected and divided by context increment, the context model can be retrieved based on the context increment.

[196] Tab. eleven

9.5.4.2.4. ctxInc extraction process for last_sig_coeff_x_prefix and last_sig_coeff_y_prefix syntax elements
The inputs to this process are the variable binIdx, the color component index cIdx, the binary logarithm of the transform block width log2TbWidth, and the transform block height log2TbHeight.
The output of this process is the variable ctxInc.
The log2TbSize variable is retrieved as follows:
- If the syntax element to be parsed is last_sig_coeff_x_prefix, log2TbSize is set to log2TbWidth.
- Otherwise (the syntax element to be parsed is last_sig_coeff_y_prefix), log2TbSize is set to log2TbHeight.
The ctxOffset and ctxShift variables are retrieved as follows:
- If cIdx is 0, ctxOffset is set to 3*(log2TbSize-2)+((log2TbSize-1)>>2), and ctxShift is set to (log2ThSize+1)>>2.
- Otherwise (cIdx greater than 0), ctxOffset is set to 21, and ctxShift is set to Clip3 (0, 2, 2 ^log2TbSize >>3).
The ctxInc variable is retrieved as follows:
- ctxInc=(binIdx>>ctxShift)+ctxOffset (9-31)

[197] Tab. 12

[198] As shown in Table 11, the log2TbSize variable is set to log2TbWidth when last_sig_coeff_x_prefix is parsed and to log2TbHeight when last_sig_coeff_y_prefix is parsed, where log2TbWidth and log2TbHeight denote the width and height of a shortened TU, such as the low frequency transform coefficient region.

[199] Additionally, the maximum values (cMax) of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix in Table 12 are also set based on the width and height of the shortened TU, such as the low-frequency transform coefficient region (cMax=(log2TbWidth<<1)-1, cMax=(log2TbHeight<< 1)-1). When truncated unary to binary is used to binarize last_sig_coeff_x_prefix and last_sig_coeff_y_prefix, the maximum values (cMax) of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix can be set to be identical to the maximum values of the codewords used to binarize last_sig_coeff_x_prefix and last_s ig_coeff_y_prefix. Therefore, the maximum length of the prefix codeword indicating the prefix information of the last significant coefficient can be extracted based on the size of the nullable block.

[200] An embodiment of the present disclosure proposes using the size of the original TU rather than the reduced TU region of low-frequency transform coefficients for the CABAC context for two syntax elements, i.e. last_sig_coeff_x_prefix and last_sig_coeff_y_prefix.

[201] Table 13 shows the residual encoding syntactic elements and the semantics corresponding to them, according to an embodiment.

[202] Tab. 13

- last_sig_coeff_x_prefix specifies the column position prefix of the last significant coefficient in scan order in the transform block. Last_sig_coeff_x_prefix values must be in the range 0 to (log2ZoTbWidth<<1)-1, inclusive. When last_sig_coeff_x_prefix is not present, it is logically output to 0.
- last_sig_coeff_y_prefix specifies the line position prefix of the last significant coefficient in scan order in the transform block. Last_sig_coeff_y_prefix values must be in the range 0 to (log2ZoTbHeight<<1)-1, inclusive. When last_sig_coeff_y_prefix is not present, it is logically output to 0.

[203] According to Table 13, two new variables (log2ZoTbWidth and log2ZoTbHeight) may be proposed indicating the shortened width and shortened height. The TU size may finally be updated to log2ZoTbWidth and log2ZoTbHeight after parsing the position syntax of the last significant coefficient (log2TbWidth = log2ZoTbWidth, log2TbHeight = log2ZoTbHeight).

[204] Thus, according to the present embodiment, residual samples can be retrieved based on position information relative to the last significant coefficient, in which the context model can be retrieved based on the size of the original transform block, the size of which is constant, and the position of the last significant coefficient can be retrieved by based on the size of the block being reset. Here, the size, specifically the width or height, of the nullable block is less than the size, width or height, of the original transform block.

[205] When the context model is extracted based on the size of the original transform block, the size of which is constant, log2TbWidth and log2TbHeight used to extract the context increment (ctxInc) in Table 11 can be interpreted as the width and height of the original transform block.

[206] According to Table 13, Table 12, in which the position of the last significant coefficient is retrieved based on the size (log2ZoTbWidth and log2ZoTbHeight) of the block being nulled, can be changed to Table 14.

[207] Tab. 14

[208] According to Table 14, the maximum values (cMax) of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix are set based on log2ZoTbWidth and log2ZoTbHeight corresponding to the width and height of the shortened TU, such as the low-frequency transform coefficient region (cMax=(log2ZoTbWidth<<1)-1, cMax=( log2ZoTbHeight<<1)-1). When truncated unary to binary is used to binarize last_sig_coeff_x_prefix and last_sig_coeff_y_prefix, the maximum values (cMax) of last_sig_coeff_x_prefix and last_sig_coeff_y_prefix can be set to be identical to the maximum values of the codewords used to binarize last_sig_coeff_x_prefix and last_s ig_coeff_y_prefix. Therefore, the maximum length of the prefix codeword indicating the prefix information of the last significant coefficient can be extracted based on the size of the nullable block.

[209] Table 15 shows the test result for performing context selection by applying the size of the reduced TU based on a test in which context selection is performed based on the size of the original TU.

[210] Tab. 15

Main profile 10, completely internal Compared to VTM-4.0 Y U V EncT DecT Class A1 0.24% 0.19% 0.15% 101% 103% Class A2 0.12% 0.20% 0.06% 101% 103% Class B 0.10% 0.13% 0.11% 100% 100% Class C 0.03% -0.03% 0.02% 101% 105% Class E 0.03% 0.07% -0.05% 103% 107% Generally 0.10% 0.11% 0.06% 101% 103% Class D 0.02% -0.15% -0.14% 102% 108% Class F 0.01% 0.04% 0.04% 103% 105% SCC class 0.02% 0.00% -0.01% 103% 102%

[211] As shown in Table 15, when context selection is performed by applying the reduced TU size, a reduction in the BD coefficient of approximately 0.10% is observed compared to a test in which context selection is performed based on the size of the original TU. Thus, to improve efficiency in residual coding, it is proposed to perform context selection based on the original TU rather than the shortened TU, i.e. areas of low-frequency conversion coefficients.

[212] The following drawings are provided to describe specific examples of the present disclosure. While specific device designations or designations of particular signals/messages/fields illustrated in the drawings are provided for illustrative purposes, the technical features of the present disclosure are not limited to the specific designations used in the drawings below.

[213] FIG. 7 is a flowchart illustrating the operation of a video decoding apparatus according to an embodiment of the present disclosure.

[214] FIG. 7 is a flowchart illustrating operation of the decoding apparatus according to the embodiment, and FIG. 8 is a block diagram illustrating the configuration of decoding equipment according to the embodiment.

[215] Each operation illustrated in FIG. 7 may be performed by the decoding apparatus 300 illustrated in FIG. 3. In particular, S700 and S710 may be performed by the entropy decoder 310 illustrated in FIG. 3, S720 may be performed by the dequantizer 321 illustrated in FIG. 3, S730 may be performed by the inverse converter 322 illustrated in FIG. 3, and S740 may be performed by the adder 340 illustrated in FIG. 3. The operations of S700 to S740 are based on some of the above details explained with reference to FIGS. 4-6. Therefore, a description of specific details overlapping with the details explained above with reference to FIG. 4-6, omitted or given briefly.

[216] As shown in FIG. 8, the decoding apparatus of an embodiment may include an entropy decoder 310, a dequantizer 321, an inverter 322, and an adder 340. However, in some cases, all of the components shown in FIG. 8 may not represent essential components of the decoding hardware, and the decoding hardware may be configured with more or fewer components than those shown in FIG. 8.

[217] In the decoding apparatus according to an embodiment, the entropy decoder 310, dequantizer 321, inverter 322, and adder 340 may be configured as separate chips, or at least two components may be configured as a single chip.

[218] The decoding apparatus according to the embodiment may receive a bit stream including residual information (S700). In particular, the entropy decoder 310 of the decoding apparatus may receive a bit stream including residual information.

[219] The decoding apparatus according to the embodiment can extract quantized transform coefficients for the current block based on residual information included in the bitstream (S710). In particular, the entropy decoder 310 of the decoding apparatus can quantize transform coefficients for the current block based on the residual information included in the bit stream.

[220] The decoding apparatus according to an embodiment can convert coefficients from quantized transform coefficients based on a dequantization process. In particular, the dequantizer 321 of the decoding apparatus can extract transform coefficients from the quantized transform coefficients based on a dequantization process.

[221] The decoding apparatus according to the embodiment can extract residual samples for the current block by applying an inverse transform to the extracted transform coefficients (S720). In particular, the inverse transform 322 of the decoding apparatus may extract residual samples for the current block by applying an inverse transform to the extracted transform coefficients.

[222] The decoding apparatus according to the embodiment can generate a reconstructed frame based on the residual samples for the current block (S740). In particular, the decoding apparatus adder 340 may generate a reconstructed frame based on the residual samples for the current block.

[223] In an embodiment, the unit of the current block may be a transform block (TB).

[224] In an embodiment, each of the transform coefficients for the current block may be associated with a high frequency transform coefficient region including a transform coefficient of 0, or a low frequency transform coefficient region including at least one significant transform coefficient .

[225] In an embodiment, the residual information may include last significant coefficient prefix information and last significant coefficient suffix information regarding the position of the last significant transform coefficient among the transform coefficients for the current block.

[226] In one example, the last significant coefficient prefix information may determine a maximum value based on the size of the block being reset.

[227] In an embodiment, the position of the last significant transform coefficient may be determined based on a prefix codeword indicating the last significant coefficient prefix information and the last significant coefficient suffix information.

[228] In an embodiment, the maximum length of the prefix codeword may be determined based on the region of low frequency transform coefficients, i.e. the size of the block being reset.

[229] In an embodiment, the size of a nullable block may be determined based on the width and height of the current block.

[230] In an embodiment, the last significant coefficient prefix information may include X-axis prefix information and Y-axis prefix information, and the prefix codeword may be a codeword for X-axis prefix information and a codeword for X-axis prefix information. Y axis

[231] In one example, the X-axis prefix information may be expressed as last_sig_coeff_x_prefix, the Y-axis prefix information may be expressed as last_sig_coeff_y_prefix, and the position of the last significant conversion coefficient may be expressed as (LastSignificantCoeffX, LastSignificantCoeffY).

[232] In an embodiment, the residual information may include information regarding the size of the block being reset.

[233] FIG. 9 is a flowchart illustrating a residual sample extraction process according to an embodiment of the present disclosure.

[234] Each operation illustrated in FIG. 9 may be performed by the decoding apparatus 300 illustrated in FIG. 3. In particular, S900 and S940 may be performed by the entropy decoder 310 illustrated in FIG. 3.

[235] First, as shown, a nullable block for the current block may be retrieved (S900). As described above, a nullable block means a region of low frequency transform coefficients including a non-zero significant transform coefficient, and the width or height of the nullable block can be derived based on the width or height of the current block.

[236] Alternatively, the width or height of the nullable block may be retrieved based on flag information indicating whether the current block is segmented into subblocks and then converted or not. For example, when the value of the flag indicating whether the current block is segmented into subblocks and then converted or not is 1, the width of the segmented subblocks is 32, and the height of the subblocks is less than 64, the width of the subblocks may be set to 16. Alternatively, when the value of the flag indicating that , whether the current block is segmented into subblocks and then converted or not is 1, the height of the segmented subblocks is 32, and the width of the subblocks is less than 64, the height of the subblocks can be set to 16.

[237] Alternatively, the width or height of the nullable block may be retrieved based on the MTS index of the current block or information indicating whether or not the MTS is applied to the transformation of the current block.

[238] The size of the block being reset may be smaller than the size of the current block. In particular, the width of the nullable block may be less than the width of the current block, and the height of the nullable block may be less than the height of the current block.

[239] Specifically, when the width of the current block is 32, and the height of the current block is 32 or less, the width of the nullable block may be set to 16. Alternatively, in one example, the width of the nullable block may be limited to the case in which DST7 or DCT8 and DCT2 is not used as the conversion kernel used for the inverse primary conversion.

[240] When the above condition is not satisfied, i.e. When the width of the current block is not 32, or the height of the current block is 64 or greater, the width of the nullable block can be set to the lesser of the current block width and 32.

[241] Additionally, in particular, when the height of the current block is 32, and the width of the current block is 32 or less, the height of the nullable block may be set to 16. Alternatively, in one example, the height of the nullable block may be limited to the case in which DST7 or DCT8 , rather than DCT2, is used as the transformation kernel used for the inverse primary transformation.

[242] When the above condition is not satisfied, i.e. When the current block's height is not 32, or the current block's width is 64 or greater, the height of the nullable block can be set to the lesser of the current block's height and 32.

[243] In an embodiment, the size of the nullable block may be one of 32×16, 16×32, 16×16, or 32×32.

[244] In an embodiment, the size of the current block may be 64×64, and the size of the reset block may be 32×32.

[245] The decoding apparatus may extract a context model for position information of the last significant coefficient based on the width or height of the current block (S910).

[246] According to an embodiment, the context model may be retrieved based on the size of the original transform block rather than the size of the nullable block. Specifically, the context increment for the X-axis prefix information and the Y-axis prefix information corresponding to the last significant coefficient prefix information can be extracted based on the size of the original transform block.

[247] The decoding apparatus may extract the position value of the last significant coefficient based on the extracted context model (S920).

[248] As described above, the last significant coefficient position information may include last significant coefficient prefix information and last significant coefficient suffix information, and the last significant coefficient position value may be retrieved based on the context model.

[249] The decoding apparatus may extract the position of the last significant coefficient based on the extracted value of the position information of the last significant coefficient and the width or height of the block being reset (S930).

[250] In one example, the decoding apparatus may retrieve the position of the last significant coefficient within a nullable block size range smaller than the current block size range, rather than the original current block. Thus, the transform factor to which the transform is applied can be retrieved within the size range of the block being zeroed rather than the current block.

[251] In one example, the last significant coefficient prefix information may determine a maximum value based on the size of the block being reset.

[252] In one example, the position of the last significant coefficient may be retrieved based on a prefix codeword indicating the last significant coefficient prefix information and the last significant coefficient suffix information, and the maximum length of the prefix codeword may be determined based on the size of the nullable block.

[253] The decoding apparatus may extract residual samples based on the position of the last significant coefficient extracted based on the width or height of the nullable block (S940).

[254] The following drawings are provided to describe specific examples of the present disclosure. While specific device designations or designations of particular signals/messages/fields illustrated in the drawings are provided for illustrative purposes, the technical features of the present disclosure are not limited to the specific designations used in the drawings below.

[255] FIG. 10 is a flowchart illustrating operation of a video encoding apparatus according to an embodiment of the present disclosure, and FIG. 11 is a block diagram illustrating the configuration of encoding equipment according to the embodiment.

[256] The encoding apparatus of FIG. 10 and fig. 11 can perform operations corresponding to the operations of the decoding apparatus according to FIG. 7 and fig. 8. Therefore, the operations of the decoding apparatus illustrated in FIG. 7 and fig. 8 can be equally applied to the encoding apparatus of FIG. 10 and fig. eleven.

[257] Each operation illustrated in FIG. 10 may be performed by the encoding apparatus 200 illustrated in FIG. 2. In particular, S1000 may be performed by the subtractor 231 illustrated in FIG. 2, S1010 may be performed by the converter 232 illustrated in FIG. 2, and S1020 may be performed by the quantizer 233, and S1030 may be performed by the entropy encoder 240 illustrated in FIG. 2. Operations according to S1000-S1030 are based on a portion of the content described in FIG. 4-6. Therefore, a description of specific details overlapping with the details explained above with reference to FIG. 4-6, omitted or given briefly.

[258] As shown in FIG. 11, the encoding apparatus according to an embodiment may include a subtractor 231, a converter 232, a quantizer 233, and an entropy encoder 240. However, in some cases, all of the components shown in FIG. 11 may not represent essential components of the encoding hardware, and the encoding hardware may be configured with more or fewer components than those shown in FIG. eleven.

[259] In the encoding apparatus according to an embodiment, the subtractor 231, converter 232, quantizer 233, and entropy encoder 240 may be configured as separate chips, or at least two components may be configured as a single chip.

[260] The encoding apparatus according to the embodiment may extract residual samples for the current block (S1000). In particular, the encoder subtractor 231 may extract residual samples for the current block.

[261] The encoding apparatus according to the embodiment can transform the residual samples for the current block, thereby extracting transform coefficients for the current block (S1010). In particular, the encoder transformer 232 may transform the residual samples for the current block, thereby extracting transform coefficients for the current block.

[262] The encoding apparatus according to the embodiment can extract quantized transform coefficients from the transform coefficients based on quantization (S1020). In particular, the encoding apparatus quantizer 233 can extract quantized transform coefficients from the transform coefficients based on quantization.

[263] The encoding apparatus according to the embodiment can encode residual information including information regarding quantized transform coefficients (S1030). In particular, the entropy encoder 240 of the encoding apparatus may encode residual information including information regarding quantized transform coefficients.

[264] In an embodiment, each of the transform coefficients for the current block may be associated with a high frequency transform coefficient region including a transform coefficient of 0, or with a low frequency transform coefficient region including at least one significant transform coefficient , i.e. resettable block.

[265] In an embodiment, the residual information may include last significant coefficient prefix information and last significant coefficient suffix information regarding the position of the last significant transform coefficient among the transform coefficients for the current block.

[266] In an embodiment, the position of the last significant transform coefficient may be determined based on a prefix codeword indicating the last significant coefficient prefix information and the last significant coefficient suffix information.

[267] In one example, the last significant coefficient prefix information may determine a maximum value based on the size of the block being reset.

[268] In an embodiment, the maximum length of a prefix codeword may be determined based on the size of the nullable block.

[269] In an embodiment, the size of a nullable block may be determined based on the width and height of the current block.

[270] In an embodiment, the last significant coefficient prefix information may include X-axis prefix information and Y-axis prefix information, and the prefix codeword may be a codeword for X-axis prefix information and a codeword for X-axis prefix information. Y axis

[271] In one example, the X-axis prefix information may be expressed as last_sig_coeff_x_prefix, the Y-axis prefix information may be expressed as last_sig_coeff_y_prefix, and the position of the last significant conversion coefficient may be expressed as (LastSignificantCoeffX, LastSignificantCoeffY).

[272] In an embodiment, the residual information may include information regarding the size of the block being reset.

[273] FIG. 12 is a flowchart illustrating a process of encoding residual information according to an embodiment of the present disclosure.

[274] Each operation illustrated in FIG. 12 may be performed by the encoding apparatus 200 illustrated in FIG. 2. In particular, S1200 and S1230 may be performed by the entropy encoder 240 illustrated in FIG. 2.

[275] First, as shown, a nullable block for the current block can be retrieved (S1200). As described above, a nullable block means a region of low frequency transform coefficients including a non-zero significant transform coefficient, and the width or height of the nullable block can be derived based on the width or height of the current block.

[276] Alternatively, the width or height of the nullable block may be retrieved based on flag information indicating whether the current block is segmented into subblocks and then converted or not. For example, when the value of the flag indicating whether the current block is segmented into subblocks and then converted or not is 1, the width of the segmented subblocks is 32, and the height of the subblocks is less than 64, the width of the subblocks may be set to 16. Alternatively, when the value of the flag indicating that , whether the current block is segmented into subblocks and then converted or not is 1, the height of the segmented subblocks is 32, and the width of the subblocks is less than 64, the height of the subblocks can be set to 16.

[277] Alternatively, the width or height of the nullable block may be retrieved based on the MTS index of the current block or information indicating whether or not the MTS is applied to the transformation of the current block.

[278] The size of the block being reset may be smaller than the size of the current block. In particular, the width of the nullable block may be less than the width of the current block, and the height of the nullable block may be less than the height of the current block.

[279] Specifically, when the width of the current block is 32, and the height of the current block is 32 or less, the width of the nullable block may be set to 16. Alternatively, in one example, the width of the nullable block may be limited to the case in which DST7 or DCT8 and DCT2 is not used as the conversion kernel used for primary conversion.

[280] When the above condition is not satisfied, i.e. When the width of the current block is not 32, or the height of the current block is 64 or greater, the width of the nullable block can be set to the lesser of the current block width and 32.

[281] Additionally, in particular, when the height of the current block is 32, and the width of the current block is 32 or less, the height of the nullable block may be set to 16. Alternatively, in one example, the height of the nullable block may be limited to the case in which DST7 or DCT8 , rather than DCT2, is used as the transformation kernel used for the primary transformation.

[282] When the above condition is not satisfied, i.e. When the current block's height is not 32, or the current block's width is 64 or greater, the height of the nullable block can be set to the lesser of the current block's height and 32.

[283] In an embodiment, the size of the nullable block may be one of 32×16, 16×32, 16×16, or 32×32.

[284] In an embodiment, the size of the current block may be 64×64, and the size of the reset block may be 32×32.

[285] The encoding apparatus may extract the position of the last significant coefficient based on the extracted width or height of the nullable block (S1210).

[286] In one example, the encoding apparatus may extract the position of the last significant coefficient within a nullable block size range less than or equal to the current block size range, rather than the original current block. Thus, the transform factor to which the transform is applied can be retrieved within the size range of the block being zeroed rather than the current block.

[287] In one example, the position of the last significant coefficient may be retrieved based on a prefix codeword indicating the last significant coefficient prefix information and the last significant coefficient suffix information, and the maximum length of the prefix codeword may be determined based on the size of the nullable block.

[288] The encoding apparatus may extract a context model for the position information of the last significant coefficient based on the width or height of the current block (S1220).

[289] According to an embodiment, the context model may be retrieved based on the size of the original transform block rather than the size of the nullable block. Specifically, the context increment for the X-axis prefix information and the Y-axis prefix information corresponding to the last significant coefficient prefix information can be extracted based on the size of the original transform block.

[290] The encoding apparatus may encode the position information relative to the position value of the last significant coefficient based on the extracted context model (S1230).

[291] As described above, the last significant coefficient position information may include last significant coefficient prefix information and last significant coefficient suffix information, and the last significant coefficient position value may be encoded based on the context model.

[292] In the present disclosure, at least one of quantization/dequantization and/or transform/de-transform may be omitted. When quantization/dequantization is omitted, the quantized conversion factor may be referred to as a "transformation factor". When the transform/inverse transform is omitted, the conversion factor may be called the "coefficient" or "residual coefficient" or may still be called the "transform factor" for consistency of expression.

[293] Additionally, in the present disclosure, the quantized transform coefficient and the transform coefficient may be referred to as the “transform coefficient” and the “scaled transform coefficient,” respectively. In this case, the residual information may include information regarding the transform coefficient(s), and the information regarding the transform coefficient(s) may be signaled through a residual encoding syntax. Transform coefficients can be extracted based on residual information (or information regarding the transform coefficient(s)), and scaled transform coefficients can be extracted through inverse transform (scaling) of the transform coefficients. Residual samples can be extracted based on the inverse transform (transform) of the scaled transform coefficients. These details may also be applied/expressed in other parts of this disclosure.

[294] In the above-described embodiments, the methods are explained on the basis of flowcharts of the method through a sequence of steps or blocks, but the present disclosure is not limited to the order of the steps, and a certain step may be performed in an order or step different from the order or step described higher, or simultaneously with another stage. Additionally, those skilled in the art will appreciate that the steps shown in the flowchart are not the only ones possible, and that another step may be included or one or more steps of the flowchart may be deleted without affecting scope of this disclosure.

[295] The above-described methods according to the present disclosure may be implemented in software form, and the encoding equipment and/or decoding equipment according to the disclosure may be included in an image processing device, for example, a television, a computer, a smartphone, a set-top box, a display device and so on.

[296] When the embodiments in the present disclosure are implemented by software, the above-described methods may be implemented as modules (processes, functions, etc.) to perform the above-described functions. The modules may be stored in a memory device and may be executed by a processor. The storage device may be located inside or outside the processor and may be coupled to the processor in a variety of known ways. The processor may include an application specific integrated circuit (ASIC), another chipset, logic circuit, and/or data processing device. The storage device may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and/or other data storage device. Thus, the embodiments described in the present disclosure may be implemented and executed in a processor, microprocessor, controller, or chip. For example, the functional modules shown in each drawing may be implemented and executed on a computer, processor, microprocessor, controller, or chip.

[297] Additionally, the decoding apparatus and encoding apparatus to which the present disclosure applies may be included in a multimedia broadcasting device, a mobile communication terminal, a home theater system video device, a digital cinema system video device, a surveillance camera, a video chat device, a real-time communications such as video communications, mobile streaming device, storage medium, video recording camera, video-on-demand (VoD) service delivery device, over-the-top (OTT) video device, over-the-top streaming service device Internet, a three-dimensional video device, a video telephony system video device and a medical video device, and can be used for processing a video signal or a data signal. For example, an over-the-top (OTT) video device may include a game console, Blu-ray player, Internet-enabled television, home theater system, smartphone, tablet PC, digital video recorder (DVR), etc.

[298] In addition, the processing method to which the present disclosure applies may be formed in the form of a program executed by a computer and stored on a computer-readable recording medium. Multimedia data having a data structure according to the present disclosure may also be stored on a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices and distributed storage devices on which computer-readable data is stored. The computer-readable recording medium may include, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical device. data storage. Additionally, the computer-readable recording medium includes media implemented in the form of a carrier wave (eg, Internet transmissions). In addition, the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network. Additionally, embodiments of the present disclosure may be implemented as a computer program product through program codes, and the program codes may be executed on a computer by embodiments of the present disclosure. The program codes may be stored on a computer-readable medium.

[299] FIG. 13 illustrates the structure of a content streaming system to which the present disclosure applies.

[300] Additionally, the content streaming system to which the present disclosure applies may mainly include an encoding server, a streaming server, a web server, a media storage, a user equipment, and a media input device.

[301] The encoding server functions to digitally compress content input from media input devices such as a smartphone, camera, video recorder, etc. to form a bit stream and transmit it to the streaming server. As another example, in case a media input device such as a smartphone, camera, video recorder, etc. directly generates a bit stream, the encoding server may be omitted. The bitstream may be generated by an encoding method or a bitstream generation method to which the present disclosure applies. In addition, the streaming server may store the bitstream temporarily during a process to transmit or receive the bitstream.

[302] The streaming server transmits multimedia data to the user equipment based on a user's request through a web server, which functions as a tool that informs the user as to what service is provided. When a user requests a service that the user wants, the web server passes the request to the streaming server and the streaming server streams the media data to the user. In this regard, the content streaming system may include a separate control server, in which case, the control server functions to manage commands/responses between associated equipment in the content streaming system.

[303] The streaming server may receive content from a media storage and/or encoding server. For example, in case the content is received from an encoding server, the content may be received in real time. In this case, the streaming server can store the bit stream for a predetermined period of time to smoothly provide the streaming service.

[304] For example, subscriber equipment may include a mobile phone, smartphone, laptop computer, digital broadcast terminal, personal digital assistant (PDA), portable media player (PMP), navigation device, tablet PC, tablet PC, ultrabook, wearable device (for example, a watch terminal (smart watch), a glasses terminal (smart glasses), a head-mounted display (HMD)), a digital TV, a desktop computer, a digital signage system, etc. Each of the servers in the content streaming system may operate as a distributed server, in which case, data received through each server may be processed in a distributed manner.

[305] The claims disclosed herein may be combined in various ways. For example, the technical features of the method claims of the present disclosure may be combined with the ability to be implemented or performed in hardware, and the technical features of the hardware claims may be combined with the ability to be implemented or performed in the method. Additionally, the technical features of the method claims and the hardware claims can be combined with the ability to be implemented or performed in the hardware, and the technical features of the method claims and the hardware claims can be combined with the ability to be implemented or performed in the method.

1. A method for decoding images, carried out by means of decoding equipment, the method comprising the steps of:

- receive a bit stream containing residual information;

- extracting conversion coefficients for the current block based on the residual information;

- extract residual samples for the current block based on the transform coefficients; And

- form a reconstructed frame based on residual samples,

wherein the residual information contains information about the position of the last significant coefficient, and

in this case, the extraction of residual samples contains stages in which:

- retrieve a nullable block for the current block;

- extracting a context model for the position information of the last significant coefficient based on the width or height of the current block;

- extract the position information value of the last significant coefficient based on the context model; And

- extracting the position of the last significant coefficient based on the value of the position information of the last significant coefficient and the width or height of the block being reset.

2. The method of decoding images according to claim 1, in which the width of the block being reset is less than the width of the current block.

3. The method of decoding images according to claim 1, in which the height of the block being reset is less than the height of the current block.

4. The image decoding method according to claim 1, wherein the last significant coefficient position information contains last significant coefficient prefix information and last significant coefficient suffix information,

wherein the last significant coefficient prefix information comprises X-axis prefix information and Y-axis prefix information, and

wherein the context increment for the X-axis prefix information and the Y-axis prefix information is retrieved based on the width or height of the current block.

5. The image decoding method of claim 4, wherein the maximum value allowed for the last significant coefficient prefix information is extracted based on the size of the nullable block.

6. The image decoding method of claim 1, wherein the width or height of a block to be reset is retrieved based on the width or height of the current block.

7. The image decoding method as set forth in claim 6, wherein, based on a current block width of 32 and a current block height of 32 or less, a nullable block width is set to 16, and

wherein, based on the width of the current block not being 32 or the height of the current block being 64 or greater, the width of the nullable block is set to the lesser of the current block width and 32.

8. The image decoding method as set forth in claim 6, wherein based on the height of the current block being 32 and the width of the current block being 32 or less, the height of the nullable block is set to 16, and

wherein, based on the height of the current block not being 32 or the width of the current block being 64 or greater, the height of the nullable block is set to the lesser of the height of the current block and 32.

9. A method for encoding images, carried out by means of image encoding equipment, the method comprising the steps of:

- extract residual samples for the current block;

- extract quantized transform coefficients based on residual samples for the current block; And

- encode residual information containing information regarding the quantized transformation coefficients,

wherein the residual information contains information about the position of the last significant coefficient, and

in this case, coding of residual information contains stages in which:

- retrieve a nullable block for the current block;

- extracting the position of the last significant coefficient based on the width or height of the block being reset;

- extracting a context model for the position information of the last significant coefficient based on the width or height of the current block; And

- encoding information about the position of the last significant coefficient based on the context model.

10. The image encoding method according to claim 9, in which the width of the block being reset is less than the width of the current block.

11. The image encoding method according to claim 9, in which the height of the block being reset is less than the height of the current block.

12. The image encoding method according to claim 9, wherein the last significant coefficient position information contains last significant coefficient prefix information and last significant coefficient suffix information,

wherein the last significant coefficient prefix information comprises X-axis prefix information and Y-axis prefix information, and

wherein the context increment for the X-axis prefix information and the Y-axis prefix information is retrieved based on the width or height of the current block.

13. The image encoding method of claim 12, wherein the maximum value allowed for the last significant coefficient prefix information is extracted based on the size of the nullable block.

14. The image encoding method of claim 9, wherein the width or height of a block to be nulled is retrieved based on the width or height of the current block.

15. A computer-readable digital storage medium that stores indicator information to instruct execution of an image decoding method, wherein the image decoding method comprises:

- receiving a bit stream containing residual information;

- extracting quantized transformation coefficients for the current block based on residual information;

- extracting residual samples for the current block based on quantized transform coefficients; And

- formation of a reconstructed frame based on residual samples,

wherein the residual information contains information about the position of the last significant coefficient, and

whereby the residual sample extraction contains:

- retrieving a reset block for the current block;

- extracting a context model for position information of the last significant coefficient based on the width or height of the current block;

- extracting the position information value of the last significant coefficient based on the context model; And

- extracting the position of the last significant coefficient based on the value of the position information of the last significant coefficient and the width or height of the block being reset.

Claims (37)

1. A method for decoding images, carried out by means of decoding equipment, the method comprising the steps of: - receive a bit stream containing residual information; - extracting transform coefficients for the current block by performing residual encoding based on the residual information; - extracting residual samples through a transformation process for transformation coefficients; in this case, the implementation of residual encoding contains stages in which: - extracting a nullable block for the current block based on flag information associated with whether a subblock transformation is used for the current block, a value associated with the transformation multiple selection, and the width and height of the current block; - decode position information of the last significant coefficient for the current block; And - decode the transformation coefficients for the current block; wherein decoding the position information of the last significant coefficient contains the steps of: - extracting a context model for information about the position of the last significant coefficient; And - extract the position information value of the last significant coefficient based on the context model; wherein the context model is retrieved based on the width and height of the current block, and wherein the position information value of the last significant coefficient is retrieved based on the width and height of the block being reset. 2. The method of decoding images according to claim 1, in which the width of the block being reset is less than the width of the current block. 3. The method of decoding images according to claim 1, in which the height of the block being reset is less than the height of the current block. 4. The image decoding method according to claim 1, wherein the last significant coefficient position information contains last significant coefficient prefix information and last significant coefficient suffix information, wherein the last significant coefficient prefix information comprises X-axis prefix information and Y-axis prefix information, and wherein the context increment for the X-axis prefix information and the Y-axis prefix information is retrieved based on the width or height of the current block. 5. The image decoding method of claim 4, wherein the maximum value allowed for the last significant coefficient prefix information is extracted based on the size of the nullable block. 6. A method for encoding images, carried out by means of image encoding equipment, the method comprising the steps of: - extract residual samples for the current block; - extracting transformation coefficients through a transformation process for the residual samples; And - encoding image information containing information on transform coefficients by performing residual encoding, in this case, the implementation of residual encoding contains stages in which: - extracting a nullable block for the current block based on whether a subblock transformation is used for the current block, the value associated with the transformation multiple selection, and the width and height of the current block; - extracting the position information value of the last significant coefficient for the current block; - extracting a context model for information about the position of the last significant coefficient; - encoding information about the position of the last significant coefficient based on the context model; And - encode the transformation coefficients for the current block, wherein the context model is retrieved based on the width and height of the current block, and wherein the position information value of the last significant coefficient is retrieved based on the width and height of the block being reset. 7. The image encoding method according to claim 6, in which the width of the block being reset is less than the width of the current block. 8. The image encoding method according to claim 6, in which the height of the block being reset is less than the height of the current block. 9. The image encoding method according to claim 6, wherein the last significant coefficient position information contains last significant coefficient prefix information and last significant coefficient suffix information, wherein the last significant coefficient prefix information comprises X-axis prefix information and Y-axis prefix information, and wherein the context increment for the X-axis prefix information and the Y-axis prefix information is retrieved based on the width or height of the current block. 10. The image encoding method of claim 9, wherein the maximum value allowed for the last significant coefficient prefix information is extracted based on the size of the nullable block.