KR102439871B1 - Methods and apparatus for video transform encoding/decoding - Google Patents

Abstract

An image decoding method according to the present invention obtains context information on a decoding object block, derives an inverse transform method for the decoding object block using the context information, and performs inverse transformation on the decoding object block using the derived inverse transform method carry out According to the present invention, image compression performance can be improved while the amount of transmitted information is minimized.

Description

Video transcoding/decoding method and apparatus {METHODS AND APPARATUS FOR VIDEO TRANSFORM ENCODING/DECODING}

The present invention relates to image processing, and more particularly, to an image encoding/decoding method and apparatus.

Recently, as broadcasting services with high definition (HD) resolution are expanding not only domestically but also worldwide, many users are getting used to high-resolution and high-definition images, and accordingly, many institutions are spurring the development of next-generation imaging devices. In addition, as interest in UHD (Ultra High Definition) having a resolution four times higher than that of HDTV increases along with HDTV, a compression technology for higher resolution and high-definition images is required.

The image compression technology includes an inter prediction technology that predicts a pixel value included in the current picture from temporally previous and/or subsequent pictures, and an intra prediction technology that predicts a pixel value included in the current picture using pixel information in the current picture. (intra) prediction technology, a transformation technology that decomposes an original video signal into a signal in the frequency domain, an inverse transformation technology that restores a signal in the frequency domain to an original video signal, assigns a short code to a symbol with a high frequency of appearance and assigns a short code to the frequency of appearance There is an entropy encoding technique in which a long code is assigned to a symbol with a low . Image data can be efficiently compressed by these image compression techniques.

It is an object of the present invention to provide an image encoding method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

Another technical object of the present invention is to provide an image decoding method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

Another technical object of the present invention is to provide a conversion method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

Another technical object of the present invention is to provide an inverse transform method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

Another technical object of the present invention is to provide an entropy encoding method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

Another technical object of the present invention is to provide an entropy decoding method and apparatus capable of improving image compression performance while minimizing the amount of transmitted information.

An image decoding method is provided. The method includes at least one of a decoding object block, a block already decoded before performing the decoding of the decoding object block, and information included in pixel values of a pixel already reconstructed before the decoding of the decoding object block by using at least one of the decoding object block Obtaining context information on In the step of deriving the inverse transform method for the decoding object block using the context information, the inverse transform method is derived using at least one of a method of selecting one of a plurality of inverse transform methods and a method of updating an initial inverse transform equation and, the plurality of inverse transform methods are inverse transform methods previously determined before decoding is performed on the decoding object block, and the initial inverse transform equation is an inverse transform equation previously determined before decoding is performed on the decoding object block.

According to the image encoding method according to the present invention, the amount of transmitted information can be minimized and image compression performance can be improved.

According to the image decoding method according to the present invention, the amount of transmitted information can be minimized and image compression performance can be improved.

According to the conversion method according to the present invention, image compression performance can be improved while the amount of transmitted information is minimized.

According to the inverse transform method according to the present invention, the amount of transmitted information can be minimized and image compression performance can be improved.

According to the entropy encoding method according to the present invention, image compression performance can be improved while the amount of transmitted information is minimized.

According to the entropy decoding method according to the present invention, image compression performance can be improved while the amount of transmitted information is minimized.

1 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment.
2 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment.
3 is a flowchart schematically illustrating a conversion method according to an embodiment of the present invention.
4 is a flowchart schematically illustrating an entropy encoding method according to an embodiment of the present invention.
5 is a flowchart schematically illustrating an entropy decoding method according to an embodiment of the present invention.
6 is a flowchart schematically illustrating an inverse transform method according to an embodiment of the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely with reference to drawings. In describing the embodiments of the present specification, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

When it is said that a component is “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be In addition, the description of "including" a specific configuration in the present invention does not exclude configurations other than the corresponding configuration, and means that additional configurations may be included in the practice of the present invention or the scope of the technical spirit of the present invention.

Terms such as first, second, etc. may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

In addition, the components shown in the embodiment of the present invention are shown independently to represent different characteristic functions, and it does not mean that each component is composed of separate hardware or a single software component. That is, each component is listed as each component for convenience of description, and at least two components of each component are combined to form one component, or one component can be divided into a plurality of components to perform a function, and each Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention without departing from the essence of the present invention.

In addition, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for merely improving performance. The present invention can be implemented by including only essential components to implement the essence of the present invention except for components used for improving performance, and only having a structure including essential components excluding optional components used for improving performance Also included in the scope of the present invention.

1 is a block diagram illustrating a configuration of an image encoding apparatus according to an embodiment. Referring to FIG. 1 , the image encoding apparatus 100 includes a motion prediction unit 111 , a motion compensation unit 112 , an intra prediction unit 120 , a switch 115 , a subtractor 125 , and a transform unit 130 . , a quantizer 140 , an entropy encoder 150 , an inverse quantizer 160 , an inverse transform unit 170 , an adder 175 , a filter unit 180 , and a reference image buffer 190 .

The image encoding apparatus 100 may perform encoding on an input image in an intra mode or an inter mode and output a bit stream. Intra prediction refers to intra prediction, and inter prediction refers to inter prediction. In the intra mode, the switch 115 is switched to intra, and in the inter mode, the switch 115 is switched to inter. The image encoding apparatus 100 may generate a prediction block for an input block of an input image, and then encode a difference between the input block and the prediction block.

In the intra mode, the intra prediction unit 120 may generate a prediction block by performing spatial prediction using pixel values of an already encoded block around the current block.

In the inter mode, the motion predictor 111 may obtain a motion vector by finding a region that best matches the input block in the reference image stored in the reference image buffer 190 during the motion prediction process. The motion compensator 112 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 190 .

The subtractor 125 may generate a residual block by the difference between the input block and the generated prediction block. The transform unit 130 may perform transform on the residual block to output a transform coefficient. The transformation method may include a fixed transformation method, an optimal transformation method, a transformation method for each intra prediction mode (MDDT: Mode Dependent Directional Transform), and the like. Each detail will be described later.

The quantization unit 140 may quantize the input transform coefficient according to the quantization parameter to output a quantized coefficient.

The entropy encoding unit 150 may output a bit stream by performing entropy encoding based on the values calculated by the quantization unit 140 or encoding parameter values calculated during the encoding process.

When entropy encoding is applied, a small number of bits are allocated to a symbol having a high probability of occurrence and a large number of bits are allocated to a symbol having a low probability of occurrence to express the symbol, so that bits for symbols to be encoded The size of the column may be reduced. Accordingly, compression performance of image encoding may be improved through entropy encoding.

For entropy encoding, an encoding method such as exponential golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC) may be used. For example, a table for performing entropy encoding, such as a variable length coding (VLC) table, may be stored in the entropy encoder 150 , and the entropy encoder 150 may store the stored variable length encoding. Entropy encoding can be performed using a (VLC) table. Also, for another example, the entropy encoding unit 150 binarizes a symbol to convert it into a bin, predicts the probability of occurrence of a bin according to a context model, and performs arithmetic encoding of the bin. A CABAC entropy encoding method for generating a bitstream may be used. Here, bin means a value (0 or 1) of each binary number when a symbol is expressed as a column of binary numbers through binarization.

The entropy encoding unit 150 may perform entropy encoding according to an entropy encoding model. The entropy encoding model may include, for example, a frequency of occurrence of a symbol, an occurrence probability value, or a probability transition model. In another embodiment, the entropy encoding model may include information on a binary encoding method. Here, the binary encoding method may include variable length encoding, arithmetic encoding, and the like.

The quantized coefficient may be inverse quantized by the inverse quantizer 160 and inversely transformed by the inverse transform unit 170 . The inverse-quantized and inverse-transformed coefficients may be added to the prediction block through the adder 175 and a reconstructed block may be generated.

The reconstructed block passes through the filter unit 180, and the filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) to the reconstructed block or the reconstructed picture. can do. The reconstructed block passing through the filter unit 180 may be stored in the reference image buffer 190 .

2 is a block diagram illustrating a configuration of an image decoding apparatus according to an embodiment. Referring to FIG. 2 , the image decoding apparatus 200 includes an entropy decoding unit 210 , an inverse quantization unit 220 , an inverse transform unit 230 , an intra prediction unit 240 , a motion compensator 250 , and a filter unit. 260 and a reference image buffer 270 .

The image decoding apparatus 200 may receive a bitstream output from the encoder, perform decoding in an intra mode or an inter mode, and output a reconstructed image, that is, a reconstructed image. In the case of the intra mode, the switch may be switched to the intra mode, and in the case of the inter mode, the switch may be switched to the inter mode. The image decoding apparatus 200 may generate a reconstructed block, that is, a reconstructed block by obtaining a reconstructed residual block from the received bitstream, generating a prediction block, and adding the reconstructed residual block and the prediction block.

The entropy decoding unit 210 may entropy-decode the input bitstream according to a probability distribution to generate symbols including symbols in the form of quantized coefficients. The entropy decoding method is similar to the entropy encoding method described above.

When the entropy decoding method is applied, a small number of bits are allocated to a symbol having a high occurrence probability and a large number of bits are allocated to a symbol having a low occurrence probability to represent the symbol, so that the size of the bit stream for each symbol is can be reduced. Accordingly, the compression performance of image decoding may be improved through the entropy decoding method.

The entropy decoding unit 210, like the entropy encoding unit 150, may perform entropy decoding according to an entropy decoding model. The entropy decoding model may include, for example, a symbol's frequency of occurrence, an occurrence probability value, or a probability transition model. Also, according to another embodiment, the entropy decoding model may include information about a binary encoding method. Here, the binary encoding method may include variable length encoding, arithmetic encoding, and the like.

The quantized coefficient is inverse quantized by the inverse quantization unit 220 and inverse transformed by the inverse transformation unit 230 , and as a result of inverse quantization/inverse transformation of the quantized coefficient, a reconstructed residual block may be generated. When the inverse transform is performed, the fixed transform method, the optimal transform method, the intra prediction mode-specific transform method (MDDT: Mode Dependent Directional Transform), etc. described above in the embodiment of FIG. 1 may be applied inversely. Each detail will be described later.

In the intra mode, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of an already encoded block around the current block. In the inter mode, the motion compensator 250 may generate a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 270 .

The reconstructed residual block and the prediction block are added through the adder 255 , and the added block passes through the filter unit 260 . The filter unit 260 may apply at least one of a deblocking filter, SAO, and ALF to a reconstructed block or a reconstructed picture. The filter unit 260 outputs a reconstructed image, that is, a reconstructed image. The restored image may be stored in the reference image buffer 270 and used for inter prediction.

As described above in the embodiments of FIGS. 1 and 2 , the transformation method may include a fixed transformation method, an optimal transformation method, and a transformation method for each intra prediction mode.

The fixed transformation method is a method of performing transformation or inverse transformation using a fixed transformation expression such as DCT (Discrete Cosine Transform). The fixed transformation method cannot reflect the change in the characteristics of the encoding target signal, and thus has a limit in compression performance.

The optimal transformation method is a method in which a transformation is performed by obtaining statistics such as auto-correlation or covariance of an encoding target signal, and then determining a transformation expression according to the statistics. As an example of the optimal transform method, there may be a Karhunen-Loeve transform (KLT) or the like. The optimal transformation method may perform signal adaptive transformation. However, in the optimal transformation method, since the decoder cannot know information on statistics or transformation equations by itself, there is a disadvantage that an additional amount of encoding bits is required to transmit the information on statistics or the transformation equation itself to the decoder.

In the mode-dependent directional transform (MDDT) method for each prediction mode in the screen, an optimal transformation equation is previously determined for a plurality of training data for each prediction mode in the screen, and then the predetermined optimal transformation equation is fixedly used. How to perform the conversion. The optimal transformation equation may be a transformation equation using KLT, DCT, Discrete Sine Transform (DST), or the like.

In the transformation method for each intra prediction mode, signal characteristics according to the prediction mode may be reflected, and since additional encoding bits transmitted from the encoder to the decoder are not required, compression performance may be improved. However, when the characteristics of the encoding target signal are different from those of the training data, compression performance may be limited.

Therefore, in order to minimize the occurrence of additional encoding bits transmitted from the encoder to the decoder and to improve image compression performance, transform/decode using context information obtained from an encoding/decoding target block, an already encoded/decoded block, or an already reconstructed pixel value. A method for performing an inverse transform may be provided.

3 is a flowchart schematically illustrating a conversion method according to an embodiment of the present invention. The transformation according to the embodiment of FIG. 3 may be performed in the encoder, or in an embodiment, the transformation unit of the encoder.

Referring to FIG. 3 , the encoder acquires context information to be used for deriving a transformation method of an encoding object block ( S310 ). There may be various types of context information to be used for deriving the conversion method.

In an embodiment, the context information may include an encoding parameter of an encoding object block or an encoding parameter of an already encoded block. The encoding parameter may include prediction mode information, motion or motion information, quantization information, block size information, or filter information.

The prediction mode information may include, for example, information indicating whether inter prediction or intra prediction and/or information indicating which prediction direction and/or prediction method is used in detail. The motion or motion information includes, for example, information indicating whether a motion vector or motion (disparity) vector is encoded, vector size information, index of a reference image, and/or information about the number of reference images. may include The quantization information may include information about a quantization parameter, a size of a quantization step, a type of a quantization weight matrix, and/or a value of a quantization weight matrix. The block size information may include information on the size of a block, whether the block is divided, the type of block division, the position of the division boundary of the block, and/or the direction of the division boundary of the block, and the like. The filter information includes information indicating whether to apply an interpolation filter, a denoising filter, a debanding filter, a deblocking filter, etc., filter coefficient information and/or filter strength may include information about

The values of the encoding parameters as described above may be directly utilized as context information. Also, after a combination or occurrence frequency of encoding parameter values is obtained, the combination or occurrence frequency information may be utilized as context information.

In another embodiment, the context information may include transform coefficient information of an already coded block.

For example, the transform coefficient information may include information indicating whether a transform coefficient exists. The information indicating the existence of the transform coefficient may include a coded block pattern, a coded block flag, a split flag, and the like. Also, for example, the transform coefficient information may include information about a distribution of transform coefficients and/or a distribution type of transform coefficients. Information on the distribution of transform coefficients and/or the distribution type of transform coefficients includes information indicating that the transform coefficients are mainly distributed in the low-frequency region, information indicating that the transform coefficients are mainly present in a specific direction, and that the transform coefficients are evenly distributed There may be information indicating The transform coefficient information may also include information about a scan method and/or a scan order for the transform coefficients.

In another embodiment, the context information may include already reconstructed pixel values. A region in which the pixel values are obtained may be determined in various ways. For example, the pixel values may be pixel values of already reconstructed pixels among pixels spatially close to the encoding target block. As another example, the pixel values may be pixel values of already reconstructed pixels among pixels used to predict the pixel value of the encoding target block.

The encoder may use all or part of the pixel values to derive a feature value that can represent the pixel values, and then use the feature value as context information. The feature value may be, for example, a statistical value such as an average variance (variance) value and correlation (correlation). Also, the feature value may be, for example, a value representing a feature of an image, such as a gradient and an edgeness calculated from pixel values. Here, the energy may be a result obtained by applying a Sobel operator or a Laplacian operator.

The encoder is used for deriving a transformation method of the encoding object block by using at least one of the above-described encoding parameters of the encoding object block, encoding parameters of an already encoded block, transformation coefficient information of an already encoded block, and previously reconstructed pixel value information. Context information can be obtained.

Referring back to FIG. 3 , the encoder derives a transformation method applied to an encoding object block by using the obtained context information ( S320 ).

When determining a transformation method using context information, the encoder may use various methods or means. For example, a means for determining whether the context information itself is included in a specific range may be used. As another example, a means for determining whether the context information itself satisfies a specific condition may be used. As another example, a means for determining whether a difference between contextual information of the same type is included in a specific range may be used.

The encoder may derive a transformation method by using the determined result as it is. In addition, the encoder may obtain a frequency value by measuring the frequency of occurrence of context information included in a specific range and/or context information satisfying a specific condition by applying the determination means several times. In this case, the encoder may derive a transformation method using the frequency value.

In deriving the transformation method, the encoder may select one of a plurality of predetermined transformation methods.

In this case, the encoder may select one of a plurality of transformation methods having different methods. The plurality of transform methods may include KLT, DCT, DST, Hadamard transform, wavelet transform, directional transform, and the like.

The encoder may select one of a plurality of transformation equations within the same transformation method. For example, the plurality of transformation equations may be a plurality of transformation equations optimized for different training data in the KLT transformation method.

In deriving the transformation method, the encoder may update a predetermined initial transformation equation according to context information. Here, the predetermined initial transformation equation means an initial transformation equation for a transformation method such as KLT or DCT.

The initial conversion equation may be predetermined in various steps. For example, the initial transformation equation may be predetermined in a sequence step, or may be predetermined in a group of picture (GOP) step. GOP means a picture group, that is, a group of pictures. Also, as another example, the initial transformation equation may be predetermined in a step such as a picture, a slice, a coding unit, or a transformation unit.

Determination of whether to update the initial transformation equation and/or the actual update process of the initial transformation equation may be performed before transformation of the encoding object block. In addition, the process of determining whether to update the initial transformation equation and/or actually updating the initial transformation equation may be performed after transformation of the encoding object block.

In deriving a transformation method using the obtained context information, the encoder may use at least one of the above-described methods of selecting one of a plurality of predetermined transformation methods and methods of updating a predetermined initial transformation equation according to the context information. can

Referring back to FIG. 3 , the encoder performs transformation on the encoding target block of the input image by using the derived transformation method ( S330 ). Transformation may be performed in units of transform blocks.

The encoder may derive an optimal transformation method and/or transformation equation for each block by using context information on the encoding object block. In addition, the encoder may perform transformation by using the transformation method and/or transformation equation, thereby performing transformation in a context-adaptvie or signal-adaptive manner. Accordingly, the encoder can perform transformation as much as possible adaptively according to changes in the characteristics of the encoding target signal.

Also, in the embodiment of FIG. 3 , information used for deriving a transformation method and/or transformation equation or acquiring context information is information that a decoder can obtain without additional additional information transmitted from an encoder. Accordingly, in the transformation method according to the embodiment of the present invention, the amount of additional bits transmitted from the encoder to the decoder may be minimized or may not be generated.

The transform coefficients generated as a result of the transform may be quantized according to a quantization parameter and provided to the entropy encoder. As described above in the embodiment of FIG. 1 , the entropy encoding unit may perform entropy encoding according to an entropy encoding model. As in the embodiment of FIG. 3 , when the transformation method is derived adaptively in context, the probability or frequency of symbol occurrence or the binary encoding method may vary according to context information during entropy encoding. Therefore, according to an embodiment, when the transformation method is derived adaptively in context, the entropy encoding model may also be derived adaptively in context.

4 is a flowchart schematically illustrating an entropy encoding method according to an embodiment of the present invention. The entropy encoding according to the embodiment of FIG. 4 may be performed in the encoder, or in an embodiment, the entropy encoding unit of the encoder.

Referring to FIG. 4 , the encoder obtains context information used for deriving an entropy encoding model ( S410 ).

The context information may not be separately obtained context information in the entropy encoding process, and the context information obtained in the transformation process may be used as it is in the entropy encoding process.

The encoder derives an entropy encoding model using the obtained context information (S420).

As described above in the embodiment of FIG. 3 , in deriving the transformation method, the encoder may select one of a plurality of predetermined transformation methods. In this case, the encoder may transmit or signal an indicator indicating which method is selected among a plurality of predetermined transformation methods. The encoder may use the obtained context information to derive the entropy encoding model of the indicator. As an embodiment, the encoder may update the entropy encoding model for a plurality of predetermined transformation methods according to intra prediction mode values of neighboring block(s) of the encoding object block. The method of deriving the entropy encoding model is not limited to the above embodiment, and may be determined differently depending on the type of the obtained context information, the method of deriving the transformation method, and the like.

The derived entropy encoding model may include, for example, a symbol's frequency of occurrence, an occurrence probability value, or a probability transition model. As another example, the entropy encoding model may include information on a binary encoding method. Here, the binary encoding method may include variable length encoding, arithmetic encoding, and the like.

Referring back to FIG. 4 , the encoder performs entropy encoding using the derived entropy encoding model ( S430 ).

In the embodiment of FIG. 4 , the information used to derive the entropy encoding model is information that the decoder can obtain without additional information transmitted from the encoder. Therefore, when the entropy encoding method according to the embodiment of the present invention is used, the amount of additional bits transmitted from the encoder to the decoder can be minimized. In addition, the encoder performs entropy encoding using the obtained context information, so that encoding can be performed as adaptively as possible according to a change in the characteristics of a signal to be encoded.

According to the embodiment of the present invention described above with reference to FIGS. 3 and 4, transformation and/or entropy encoding can be performed as adaptively as possible according to a change in the characteristics of a signal to be encoded without generating additional encoding bits transmitted from the encoder to the decoder. have. Accordingly, the compression performance of video encoding is improved.

Similar to the above-described transform encoding method, in the decoder, the inverse transform method may be adaptively derived according to context information. When the context adaptive inverse transform method is used in the decoder, information about the probability of occurrence of symbols used in entropy decoding may vary according to context information. Accordingly, in entropy decoding, an entropy decoding model adaptively derived according to context information may be used.

5 is a flowchart schematically illustrating an entropy decoding method according to an embodiment of the present invention. The entropy decoding according to the embodiment of FIG. 5 may be performed in the decoder, or in an embodiment, the entropy decoding unit of the decoder.

Referring to FIG. 5 , the decoder acquires context information used for deriving an entropy decoding model ( S510 ). There may be various types of context information used for deriving an entropy decoding model.

In an embodiment, the context information may include an encoding parameter of a decoding object block and/or an encoding parameter of an already decoded block. The encoding parameter may include prediction mode information, motion or motion information, quantization information, block size information, or filter information.

The prediction mode information may include, for example, information indicating whether inter prediction or intra prediction and/or information indicating which prediction direction and/or prediction method is used in detail. The motion or motion information includes, for example, information indicating whether a motion vector or motion (disparity) vector is encoded, vector size information, index of a reference image, and/or information about the number of reference images. may include The quantization information may include information about a quantization parameter, a size of a quantization step, a type of a quantization weight matrix, and/or a value of a quantization weight matrix. The block size information may include information on the size of a block, whether the block is divided, the type of block division, the position of the division boundary of the block, and/or the direction of the division boundary of the block, and the like. The filter information includes information indicating whether to apply an interpolation filter, a denoising filter, a debanding filter, a deblocking filter, etc., filter coefficient information and/or filter strength may include information about

The values of the encoding parameters as described above may be directly utilized as context information. Also, after a combination or occurrence frequency of encoding parameter values is obtained, the combination or occurrence frequency information may be utilized as context information.

In another embodiment, the context information may include transform coefficient information of an already decoded block.

For example, the transform coefficient information may include information indicating whether a transform coefficient exists. The information indicating whether the transform coefficient is present may include a coded block pattern, a coded block flag, and a split flag. Also, for example, the transform coefficient information may include information about a distribution of transform coefficients and/or a distribution type of transform coefficients. Information on the distribution of transform coefficients and/or the distribution type of transform coefficients includes information indicating that the transform coefficients are mainly distributed in the low-frequency region, information indicating that the transform coefficients are mainly present in a specific direction, and that the transform coefficients are evenly distributed There may be information indicating The transform coefficient information may also include information about a scan method and/or a scan order for the transform coefficients.

In another embodiment, the context information may include already reconstructed pixel values. A region in which the pixel values are obtained may be determined in various ways. For example, the pixel values may be pixel values of already reconstructed pixels among pixels spatially close to the decoding object block. As another example, the pixel values may be pixel values of already reconstructed pixels among pixels used to predict the pixel value of the decoding object block.

The decoder may derive a feature value representative of the pixel values by using all or part of the pixel values, and then use the feature value as context information. The feature value may be, for example, a statistical value such as an average variance (variance) value and correlation (correlation). Also, the feature value may be, for example, a value representing a feature of an image, such as a gradient and an edgeness calculated from pixel values.

The decoder uses at least one of the above-described encoding parameter of the decoding object block, the encoding parameter of the previously decoded block, transform coefficient information of the already decoded block, and the already reconstructed pixel value information to obtain context information to be used for deriving the entropy decoding model. can be obtained

The decoder derives an entropy decoding model by using the obtained context information (S520).

As will be described later in the embodiment of FIG. 6 , the decoder according to the embodiment of the present invention may select one of a plurality of predetermined inverse transform methods in deriving the inverse transform method. In this case, the decoder may parse a bitstream to obtain an indicator for selecting a transformation method, and then select one of a plurality of predetermined inverse transformation methods according to the indicator value. The decoder may use the previously obtained context information to derive an entropy decoding model necessary for parsing the indicator. As an embodiment, the decoder may update the entropy decoding model for a plurality of predetermined inverse transform methods according to the intra prediction mode value of the block(s) adjacent to the decoding object block. The method for deriving the entropy decoding model is not limited to the above embodiment, and may be determined differently depending on the type of the obtained context information, the method of deriving the inverse transformation method, and the like.

The derived entropy decoding model may include, for example, the frequency of occurrence of symbols, an occurrence probability value, or a probability transition model. As another example, the entropy decoding model may include information on a binary encoding method. Here, the binary encoding method may include variable length encoding, arithmetic encoding, and the like.

Referring back to FIG. 5 , the decoder performs entropy decoding using the derived entropy decoding model ( S530 ).

In the embodiment of FIG. 5 , the information used to derive the entropy decoding model is information that the decoder can obtain without additional information transmitted from the encoder. Accordingly, when the entropy decoding method according to the embodiment of the present invention is used, the amount of additional bits transmitted from the encoder to the decoder can be minimized. In addition, the decoder may perform entropy decoding using the obtained context information, so that decoding may be performed adaptively as much as possible according to a change in characteristics of a signal to be decoded.

Values generated as a result of entropy decoding may be provided to a quantization unit of the decoder, and the quantization unit may perform inverse quantization according to a quantization parameter. Transform coefficients generated as a result of inverse quantization may be provided to an inverse transform unit of the decoder.

6 is a flowchart schematically illustrating an inverse transform method according to an embodiment of the present invention. The inverse transform according to the embodiment of FIG. 6 may be performed in the decoder, and as an embodiment, may be performed in the inverse transform unit of the decoder.

Referring to FIG. 6 , the decoder acquires context information to be used for deriving an inverse transform method of a decoding object block ( S610 ).

The context information may not be separately obtained context information in the inverse transformation process, and the context information obtained in the entropy decoding process may be used as it is in the inverse transformation process. When the context information is not used in the entropy decoding process, the decoder may separately acquire the context information in the inverse transform process. In this case, there may be various types of context information to be used for deriving the inverse transform method, for example, the context information may be the types of information described above in the embodiment of FIG. 5 .

Referring back to FIG. 6 , the decoder derives an inverse transform method applied to a decoding object block by using the obtained context information ( S620 ).

When determining an inverse transform method using context information, the decoder may use various methods or means. For example, a means for determining whether the context information itself is included in a specific range may be used. As another example, a means for determining whether the context information itself satisfies a specific condition may be used. As another example, a means for determining whether a difference between contextual information of the same type is included in a specific range may be used.

The decoder may derive an inverse transform method by using the determined result as it is. Also, the decoder may obtain a frequency value by measuring the frequency of occurrence of context information included in a specific range and/or context information satisfying a specific condition by applying the determination means several times. In this case, the decoder may derive an inverse transform method using the frequency value.

In deriving the inverse transform method, the decoder may select one of a plurality of predetermined inverse transform methods.

In this case, the decoder may select one of a plurality of inverse transform methods having different methods. The plurality of inverse transform methods may include KLT, DCT, DST, Hadamard transform, wavelet transform, directional transform, and the like.

The decoder may select one of a plurality of inverse transform equations within the same inverse transform method. For example, the plurality of inverse transform equations may be a plurality of inverse transform equations optimized for different training data in the KLT transform method.

In deriving the inverse transform method, the decoder may update a predetermined initial inverse transform equation according to context information. Here, the predetermined initial inverse transform equation means an initial inverse transform equation for an inverse transform method such as KLT or DCT.

The initial inverse transform equation may be predetermined in various steps. For example, the initial inverse transform equation may be predetermined in a sequence step or may be predetermined in a group of picture (GOP) step. Also, as another example, the initial inverse transform equation may be predetermined in a step such as a picture, a slice, a coding unit, or a transform unit.

Determination of whether to update the initial inverse transform equation and/or the actual update process of the initial inverse transform equation may be performed before the inverse transform of the decoding object block. Also, the determination of whether to update the initial inverse transform equation and/or the actual update process of the initial inverse transform equation may be performed after the inverse transform of the decoding object block.

In deriving an inverse transform method using the obtained context information, the decoder selects at least one of the above-described methods for selecting one of a plurality of predetermined inverse transform methods and methods for updating a predetermined initial inverse transform expression according to the context information. Available.

Referring back to FIG. 6 , the decoder performs inverse transform on the decoding object block by using the derived inverse transform method ( S630 ). Inverse transform may be performed on transform coefficients in units of transform blocks.

In the embodiment of FIG. 6 , the decoder may derive an optimal inverse transform method and/or an inverse transform equation for each block by using context information on the decoding object block. In addition, the decoder may perform the inverse transform by performing the inverse transform using the inverse transform method and/or the inverse transform equation, thereby performing the inverse transform adaptively in context or signal. Accordingly, the decoder can perform the inverse transformation as adaptively as possible according to a change in the characteristics of the signal to be decoded.

Also, in the embodiment of FIG. 6 , information used to derive an inverse transform method and/or an inverse transform equation or to acquire context information is information that a decoder can obtain without additional additional information transmitted from an encoder. Accordingly, in the inverse transform method according to the embodiment of the present invention, the amount of additional bits transmitted from the encoder to the decoder may be minimized or not generated.

According to the embodiment of the present invention described above with reference to FIGS. 5 and 6 , inverse transform and/or entropy decoding can be performed as adaptively as possible according to a change in the characteristics of a signal to be decoded without generating additional coding bits transmitted from the encoder to the decoder. have. Accordingly, the compression performance of image encoding and decoding is improved.

In the above embodiment, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in a different order or concurrently with other steps as described above. have. In addition, those of ordinary skill in the art will recognize that the steps shown in the flowchart are not exclusive, other steps may be included, or that one or more steps of the flowchart may be deleted without affecting the scope of the present invention. You will understand.

The above-described embodiments include examples of various aspects. It is not possible to describe every possible combination for representing the various aspects, but one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the present invention cover all other substitutions, modifications and variations falling within the scope of the following claims.

Claims (8)

receiving a bitstream related to image information;
parsing the bitstream to derive information for determining a quantization parameter for a current block;
determining a transform method for the current block from among a plurality of transform methods using information for determining a quantization parameter for the current block;
deriving a residual signal by performing transform on the current block according to the transform method; and
generating a reconstructed block for the current block using the residual signal;
The plurality of transform methods include a Hadamard transform, a discrete cosine transform, and a discrete sine transform,
Determining a transformation method for the current block includes:
Determining one of a plurality of transform methods including the Hadamard transform, the discrete cosine transform, and the discrete sine transform as the transform method for the current block using information for determining a quantization parameter for the current block including,
Inducing the residual signal comprises:
when the Hadamard transform is determined as the transform method for the current block, performing transform on the current block according to the Hadamard transform to derive the residual signal;
when the discrete cosine transform is determined as the transform method for the current block, performing transform on the current block according to the discrete cosine transform to derive the residual signal;
When the discrete sine transform is determined as the transform method for the current block, performing transform on the current block according to the discrete sine transform to derive the residual signal
video decoding method. According to claim 1,
The transformation method for the current block is determined using both information for determining a quantization parameter for the current block and information about the size of the current block.
video decoding method. 3. The method of claim 2,
The transformation method for the current block is determined by further using information indicating whether the current block is an inter prediction block or an intra prediction block.
video decoding method. delete delete delete an entropy decoding unit that receives a bitstream related to image information, parses the bitstream, and derives a quantization parameter for a current block;
determining a transform method for the current block from among a plurality of transform methods using information for determining a quantization parameter for the current block, and performing transform on the current block according to the transform method to derive a residual signal inverse transform unit; and
an adder for generating a reconstructed block for the current block by using the residual signal,
The plurality of transform methods include a Hadamard transform, a discrete cosine transform, and a discrete sine transform,
The inverse transform unit converts one of a plurality of transform methods including the Hadamard transform, the discrete cosine transform, and the discrete sine transform to the current block by using the information for determining the quantization parameter for the current block. and, when the Hadamard transform is determined as the transform method for the current block, transform the current block according to the Hadamard transform to derive the residual signal, and use the transform method for the current block. When the discrete cosine transform is determined, the residual signal is derived by performing the transform on the current block according to the discrete cosine transform, and when the discrete sine transform is determined as the transform method for the current block, in the discrete sine transform Therefore, transforming the current block to derive the residual signal
video decoding device. 8. The method of claim 7,
The inverse transform unit determines a transform method for the current block using both information for determining a quantization parameter for the current block and information on the size of the current block.
video decoding device.

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