KR102548881B1 - 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 an inverse transform on the decoding object block using the derived inverse transform method. carry out According to the present invention, video compression performance can be improved while minimizing the amount of transmitted information.

Description

Video conversion encoding / 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 expanded not only domestically but also globally, many users are getting used to high-resolution and high-definition images, and many organizations are accelerating the development of next-generation video equipment. 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 a higher resolution and higher quality image is required.

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

A technical problem of the present invention is to provide a video encoding method and apparatus capable of improving video compression performance while minimizing the amount of transmitted information.

Another technical problem of the present invention is to provide a video decoding method and apparatus capable of improving video compression performance while minimizing the amount of transmitted information.

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

Another technical problem 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 problem 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 uses at least one of information included in a decoding object block, a block already decoded before decoding the decoding object block, and pixel values of pixels already reconstructed before decoding the decoding object block, to perform the decoding object block. Obtaining context information for , deriving an inverse transformation method for the decoding object block using the context information, and performing inverse transformation on the decoding object block using the derived inverse transformation method, In the step of deriving an inverse transform method for the decoding target block using the context information, the inverse transform method is derived by 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. The plurality of inverse transformation methods are inverse transformation methods previously determined before decoding the decoding object block, and the initial inverse transformation equation is an inverse transformation equation previously determined before decoding the decoding object block.

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

According to the video decoding method according to the present invention, video compression performance can be improved while minimizing the amount of transmitted information.

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

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

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

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

1 is a block diagram showing a configuration of an image encoding apparatus according to an embodiment.
2 is a block diagram showing 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.

It is understood that when a component is referred to as “connected” or “connected” to another component, it may be directly connected or connected to the other component, but other components may exist in the middle. 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 and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

In addition, components appearing in the embodiments of the present invention are shown independently to represent different characteristic functions, and do not mean that each component is made of separate hardware or a single software component unit. That is, each component is listed and included as each component for convenience of explanation, and at least two components of each component can be combined to form a single component, or one component can be divided into a plurality of components to perform a function, and each of these components can be divided into a plurality of components. Integrated embodiments and separated embodiments of components are also included in the scope of the present invention as long as they do not depart from the essence of the present invention.

In addition, some of the components may be optional components for improving performance rather than essential components that perform essential functions in the present invention. The present invention can be implemented by including only components essential to implement the essence of the present invention, excluding components used for performance improvement, and a structure including only essential components excluding optional components used for performance improvement. Also included in the scope of the present invention.

1 is a block diagram showing a configuration of an image encoding apparatus according to an embodiment. Referring to FIG. 1 , the video encoding apparatus 100 includes a motion estimation unit 111, a motion compensation unit 112, an intra prediction unit 120, a switch 115, a subtractor 125, and a transform unit 130. , a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 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 encode an input image in an intra mode or an inter mode and output a bit stream. Intra prediction means prediction within a picture, and inter prediction means prediction between pictures. In the intra mode, the switch 115 is switched to intra, and in the inter mode, the switch 115 is switched to inter. After generating a prediction block for an input block of an input image, the image encoding apparatus 100 may encode a difference between the input block and the prediction block.

In the case of the intra mode, the intra predictor 120 may generate a prediction block by performing spatial prediction using pixel values of previously encoded blocks adjacent to the current block.

In the case of the inter mode, the motion estimation unit 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 in 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 a difference between the input block and the generated prediction block. The transform unit 130 may output a transform coefficient by performing transform on the residual block. Transformation methods 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. Details of each are described later.

The quantization unit 140 may quantize the input transform coefficient according to a quantization parameter and 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 the encoding parameter values calculated in the encoding process.

When entropy encoding is applied, a small number of bits are allocated to a symbol with a high probability of occurrence and a large number of bits are allocated to a symbol with a low probability of occurrence to represent the symbol, thereby reducing the number of bits for symbols to be coded. The size of the column may be reduced. Therefore, compression performance of image encoding can be improved through entropy encoding.

For entropy encoding, encoding methods such as exponential gollomb, context-adaptive variable length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC) may be used. For example, the entropy encoding unit 150 may store a table for performing entropy encoding, such as a Variable Length Coding/Code (VLC) table, and the entropy encoding unit 150 may store the stored variable length coding. Entropy encoding can be performed using a (VLC) table. In another example, the entropy encoding unit 150 binarizes symbols, converts them into bins, predicts the probability of occurrence of bins according to a context model, and performs arithmetic encoding of the bins. A CABAC entropy encoding method for generating a bitstream may be used. Here, a bin means a value (0 or 1) of each binary number when a symbol is expressed as a sequence 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 symbol occurrence frequency, an occurrence probability value, or a probability transition model. Also, as another embodiment, the entropy encoding 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 may be inversely quantized in the inverse quantization unit 160 and inversely transformed in the inverse transformation unit 170 . The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175, and a reconstructed block may be generated.

The reconstructed block passes through a 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. A reconstructed block that has passed through the filter unit 180 may be stored in the reference image buffer 190 .

2 is a block diagram showing 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 compensation unit 250, and a filter unit. 260 and a reference image buffer 270.

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

The entropy decoding unit 210 may generate symbols including symbols in the form of quantized coefficients by entropy decoding the input bitstream according to a probability distribution. 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 with a high probability of occurrence and a large number of bits are allocated to a symbol with a low probability of occurrence to express the symbol, thereby increasing the size of the bit stream for each symbol. can be reduced Therefore, 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, an occurrence frequency of symbols, an occurrence probability value, or a probability transition model. Also, as 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 coefficients are inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230, and as a result of inverse quantization/inverse transformation of the quantized coefficients, a reconstructed residual block may be generated. When the inverse transform is performed, the fixed transform method, the optimal transform method, the transform method for each intra prediction mode (MDDT: Mode Dependent Directional Transform), and the like described above in the embodiment of FIG. 1 may be reversely applied. Details of each are described later.

In the case of the intra mode, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of previously encoded blocks adjacent to the current block. In the case of the inter mode, the motion compensation unit 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 predicted block are added through an adder 255, and the added block passes through a 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 restored image. The reconstructed 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 conversion method may include a fixed conversion method, an optimal conversion method, a conversion method for each intra-prediction mode, and the like.

The fixed transform method is a method of performing transform or inverse transform using a fixed transform equation such as DCT (Discrete Cosine Transform). The fixed conversion method cannot reflect changes in characteristics of a signal to be encoded, and thus has limitations in compression performance.

An optimal conversion method is a method of performing conversion by obtaining statistics such as auto-correlation or covariance of a signal to be encoded and then determining a conversion equation based on the statistics. As an example of an optimal transformation method, there may be a Karhunen-Loeve Transform (KLT) or the like. An optimal conversion method may perform conversion adaptively to a signal. However, in the optimal conversion method, since the decoder cannot know information about the statistics or the conversion equation itself, there is a disadvantage in that an additional amount of coded bits is required to transmit the information about the statistics or the conversion equation itself to the decoder.

The Mode Dependent Directional Transform (MDDT) method determines the optimal transformation formula for a plurality of training data for each intra-prediction mode in advance, and then uses the predetermined optimal transformation formula fixedly. How to do the conversion. The optimal conversion equation may be a conversion equation using KLT, DCT, DST (Discrete Sine Transform), and the like.

In the conversion method for each intra-prediction mode, signal characteristics according to prediction modes can be reflected, and compression performance can be improved because additional encoding bits transmitted from an encoder to a decoder are not required. However, if the characteristics of the signal to be encoded are different from those of the training data, compression performance may be limited.

Therefore, in order to minimize the generation of additional coded bits transmitted from the encoder to the decoder and improve image compression performance, transform/decode using context information obtained from a block to be coded/decoded, a block that has already been coded/decoded, or a pixel value that has already been restored. A method of performing the inverse transform may be provided.

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

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

As an embodiment, the context information may include encoding parameters of an encoding target block or encoding parameters of an already encoded block. Coding parameters may include prediction mode information, motion or movement information, quantization information, block size information, or filter information.

Prediction mode information may include, for example, information indicating inter-prediction or intra-prediction and/or information indicating which prediction direction and/or prediction method are used in detail. The motion or movement information includes, for example, information indicating whether a motion vector or motion (disparity) vector is encoded, vector size information, reference image index and/or information about the number of reference images, and the like. can 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 about the size of the block, whether the block is divided, the type of division of the block, the position of the division boundary of the block, and/or the direction of the division boundary of the block. The filter information includes information indicating whether an interpolation filter, a denoising filter, a debanding filter, a deblocking filter, etc. are applied, filter coefficient information, and/or filter strength. may include information about

Values of the above encoding parameters may be directly used as context information. In addition, after a combination or occurrence frequency of encoding parameter values is obtained, the combination or occurrence frequency information may be used as context information.

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

For example, the transform coefficient information may include information indicating whether a transform coefficient exists. Information representing whether a transform coefficient exists may include a coded block pattern, coded block flags, split flags, 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 the transform coefficients are evenly distributed. There may be information indicating the . The transform coefficient information may also include information about a scan method and/or a scan order for transform coefficients.

As another embodiment, the context information may include already restored 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 previously reconstructed pixels among pixels located spatially close to the encoding target block. As another example, the pixel values may be pixel values of previously reconstructed pixels among pixels used to predict pixel values of the encoding target block.

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

The encoder is used to derive a transformation method of the encoding object block by using at least one of the above-described encoding parameter of the encoding object block, encoding parameter of the already encoded block, transform coefficient information of the already encoded block, and previously reconstructed pixel value information. Contextual information can be obtained.

Referring back to FIG. 3 , the encoder derives a transform method applied to the encoding target block using the acquired context information (S320).

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

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

When deriving a transform method, the encoder may select one of a plurality of predetermined transform methods.

At this time, the encoder may select one of a plurality of conversion methods differing in the method itself. A 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 a conversion method, the encoder may update a predetermined initial conversion equation according to contextual information. Here, the predetermined initial conversion equation means an initial conversion equation for conversion methods such as KLT and DCT, for example.

The initial conversion equation may be determined in advance at various stages. For example, an initial conversion formula may be determined in advance in a sequence step or in a group of picture (GOP) step. GOP means a picture group, that is, a group of pictures. Also, as another example, an initial transform equation may be determined in advance in stages such as a picture, a slice, a coding unit, or a transformation unit.

The process of determining whether to update the initial transformation equation and/or actually updating the initial transformation equation may be performed prior to transformation of the encoding target 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 target block.

In deriving a transformation method using the obtained context information, the encoder uses at least one of the methods for selecting one of the plurality of predetermined transformation methods described above and the methods for 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 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 in units of blocks using contextual information about a block to be encoded. In addition, the encoder may perform transformation in a context-adaptable or signal-adaptive manner by performing transformation using the transformation method and/or transformation equation. Therefore, the encoder can perform transformation adaptively as much as possible according to the change in the characteristics of the signal to be encoded.

Also, in the embodiment of FIG. 3 , information used to derive a conversion method and/or a conversion equation or to obtain context information is information that a decoder can obtain without additional information transmitted from the encoder. Therefore, in the conversion 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.

Transformation coefficients generated as a result of transformation may be quantized according to a quantization parameter and provided to an 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. When the conversion method is context-adaptively derived as in the embodiment of FIG. 3 , the probability or frequency of symbol occurrence or the binary encoding method may vary according to context information during entropy encoding. Accordingly, in an embodiment, when a transform method is context adaptively derived, an entropy encoding model may also be context adaptively derived.

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

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

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

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

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

The derived entropy encoding model may include, for example, a symbol occurrence frequency, an occurrence probability value, or a probability transition model. As another example, the entropy encoding model may include information about 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 , information used to derive an entropy coding model is information that a 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 can perform entropy encoding using the acquired context information, so that the encoding can be performed adaptively as much as possible according to the change in the characteristics of the encoding target signal.

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

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

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

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

As an embodiment, the context information may include encoding parameters of a decoding object block and/or encoding parameters of an already decoded block. Coding parameters may include prediction mode information, motion or movement information, quantization information, block size information, or filter information.

Prediction mode information may include, for example, information indicating inter-prediction or intra-prediction and/or information indicating which prediction direction and/or prediction method are used in detail. The motion or movement information includes, for example, information indicating whether a motion vector or motion (disparity) vector is encoded, vector size information, reference image index and/or information about the number of reference images, and the like. can 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 about the size of the block, whether the block is divided, the type of division of the block, the position of the division boundary of the block, and/or the direction of the division boundary of the block. The filter information includes information indicating whether an interpolation filter, a denoising filter, a debanding filter, a deblocking filter, etc. are applied, filter coefficient information, and/or filter strength. may include information about

Values of the above encoding parameters may be directly used as context information. In addition, after a combination or occurrence frequency of encoding parameter values is obtained, the combination or occurrence frequency information may be used as context information.

As 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. Information representing whether a transform coefficient exists may include a coded block pattern, coded block flags, split flags, 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. The 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 the transform coefficients are evenly distributed. There may be information indicating the . The transform coefficient information may also include information about a scan method and/or a scan order for transform coefficients.

As another embodiment, the context information may include already restored 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 located spatially close to the decoding target block. As another example, the pixel values may be pixel values of previously reconstructed pixels among pixels used to predict pixel values of the decoding target block.

The decoder may use all or part of the pixel values to derive a feature value representing the pixel values, and then use the feature value as context information. The feature value may be, for example, a statistical value such as a variance or deviation value or a correlation value. Also, the feature value may be a value indicating a feature of the image, such as a gradient and edgeness calculated from pixel values, for example.

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

The decoder derives an entropy decoding model using the acquired 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 when deriving an inverse transform method. At this time, the decoder parses the bitstream to obtain an indicator for selecting a transformation method, and then selects one of a plurality of predetermined inverse transformation methods according to the indicator value. The decoder may use previously obtained context information to derive an entropy decoding model necessary for parsing the indicator. As an embodiment, the decoder may update an entropy decoding model for a plurality of predetermined inverse transform methods according to intra-prediction mode values of neighboring block(s) of the decoding object block. A method of deriving an entropy decoding model is not limited to the above embodiment, and may be determined differently depending on the type of acquired context information, an inverse transformation method derivation method, and the like.

The derived entropy decoding model may include, for example, an occurrence frequency of a symbol, an occurrence probability value, or a probability transition model. As another example, 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.

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

In the embodiment of FIG. 5 , information used to derive an entropy decoding model is information that a decoder can obtain without additional information transmitted from the encoder. Therefore, 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 can perform entropy decoding using the acquired context information, thereby performing decoding adaptively as much as possible according to changes in the characteristics of the 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 a decoder, and in one embodiment, may be performed in an inverse transform unit of the decoder.

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

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

Referring back to FIG. 6 , the decoder derives an inverse transform method applied to the decoding target block using the acquired context information (S620).

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

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

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

At this time, the decoder may select one of a plurality of inverse transform methods differing in the method itself. A 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 transformation equations may be a plurality of inverse transformation equations optimized for different training data in the KLT transformation method.

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

The initial inverse transform equation may be determined in advance at various stages. For example, an initial inverse transformation equation may be determined in advance in a sequence step or in a group of picture (GOP) step. Also, as another example, an initial inverse transformation equation may be determined in advance in stages such as a picture, a slice, a coding unit, or a transformation unit.

A process of determining whether to update the initial inverse transformation equation and/or actually updating the initial inverse transformation equation may be performed prior to inverse transformation of the decoding target block. In addition, the process of determining whether to update the initial inverse transformation equation and/or actually updating the initial inverse transformation equation may be performed after inverse transformation of the decoding target block.

In deriving an inverse transformation method using the obtained context information, the decoder selects at least one of the methods for selecting one of the plurality of predetermined inverse transformation methods and the methods for updating the initial predetermined inverse transformation equation according to the context information. available.

Referring back to FIG. 6 , the decoder performs inverse transformation on the decoding target block using the derived inverse transformation 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 optimal inverse transform equation on a block-by-block basis using context information on a decoding target block. In addition, the decoder may perform inverse transformation in a context-adaptive or signal-adaptive manner by performing inverse transformation using the inverse transformation method and/or the inverse transformation formula. Therefore, the decoder can perform inverse transform adaptively as much as possible according to changes 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 obtain context information is information that a decoder can obtain without additional information transmitted from the encoder. Therefore, in the inverse transform method according to an 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 transformation and/or entropy decoding can be performed as adaptively as possible according to changes in characteristics of a signal to be decoded without generating additional coded bits transmitted from an encoder to a decoder. there is. Accordingly, compression performance of image encoding and decoding is improved.

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

The foregoing embodiment includes examples of various aspects. It is not possible to describe all possible combinations to represent the various aspects, but those skilled 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 (16)

delete determining a transform method for the current block from among a plurality of transform methods based on information on the current block;
deriving a residual signal by performing transformation on the current block according to the transformation method; and
Generating a reconstructed block for the current block using a prediction block for the current block and the residual signal;
In the step of determining the conversion method, the conversion method is determined based on information about division of the current block,
In the step of determining the transform method, the transform method is determined based on whether the division of the current block is performed. determining a transform method for the current block from among a plurality of transform methods based on information on the current block;
deriving a residual signal by performing transformation on the current block according to the transformation method; and
Generating a reconstructed block for the current block using a prediction block for the current block and the residual signal;
In the step of determining the conversion method, the conversion method is determined based on information about division of the current block,
In the step of determining the conversion method, the conversion method is determined based on the direction of the division. determining a transform method for the current block from among a plurality of transform methods based on information on the current block;
deriving a residual signal by performing transformation on the current block according to the transformation method; and
Generating a reconstructed block for the current block using a prediction block for the current block and the residual signal;
In the step of determining the conversion method, the conversion method is determined based on information about division of the current block,
In the step of determining the conversion method, the conversion method is determined based on the type of division. determining a transform method for the current block from among a plurality of transform methods based on information on the current block;
deriving a residual signal by performing transformation on the current block according to the transformation method; and
Generating a reconstructed block for the current block using a prediction block for the current block and the residual signal;
In the step of determining the conversion method, the conversion method is determined based on information about division of the current block,
In the step of determining the conversion method, the conversion method is determined based on the location of the boundary of the division. delete generating a prediction block for the current block;
generating a residual block for the current block based on the prediction block; and
Generating information of an encoded current block based on the transformation of the residual block
including,
A transform method for the current block is determined from among a plurality of transform methods based on the information on the current block, and the transform for the current block is performed according to the transform method;
The conversion method is determined based on information about division of the current block,
The conversion method is an image encoding method that is determined based on whether the division of the current block is performed. generating a prediction block for the current block;
generating a residual block for the current block based on the prediction block; and
Generating information of an encoded current block based on the transformation of the residual block
including,
A transform method for the current block is determined from among a plurality of transform methods based on the information on the current block, and the transform for the current block is performed according to the transform method;
The conversion method is determined based on information about division of the current block,
The video encoding method in which the conversion method is determined based on the direction of the division. generating a prediction block for the current block;
generating a residual block for the current block based on the prediction block; and
Generating information of an encoded current block based on the transformation of the residual block
including,
A transform method for the current block is determined from among a plurality of transform methods based on the information on the current block, and the transform for the current block is performed according to the transform method;
The conversion method is determined based on information about division of the current block,
The conversion method is an image encoding method determined based on the type of division. generating a prediction block for the current block;
generating a residual block for the current block based on the prediction block; and
Generating information of an encoded current block based on the transformation of the residual block
including,
A transform method for the current block is determined from among a plurality of transform methods based on the information on the current block, and the transform for the current block is performed according to the transform method;
The conversion method is determined based on information about division of the current block,
The conversion method is an image encoding method that is determined based on the position of the boundary of the segmentation. A computer-readable recording medium on which a bitstream generated by the video encoding method according to claim 7 is recorded. delete A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Contains coded information about the current block;
A transform method for the current block is determined from among a plurality of transform methods based on the encoded information on the current block, and a residual signal is derived by performing transform on the current block according to the transform method. A reconstructed block for the current block is generated using a prediction block for the current block and the residual signal;
The conversion method is determined based on information about division of the current block,
The conversion method is determined based on whether the division of the current block is performed. A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Contains coded information about the current block;
A transform method for the current block is determined from among a plurality of transform methods based on the encoded information on the current block, and a residual signal is derived by performing transform on the current block according to the transform method. A reconstructed block for the current block is generated using a prediction block for the current block and the residual signal;
The conversion method is determined based on information about division of the current block,
The conversion method is determined based on the direction of the division. A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Contains coded information about the current block;
A transform method for the current block is determined from among a plurality of transform methods based on the encoded information on the current block, and a residual signal is derived by performing transform on the current block according to the transform method. A reconstructed block for the current block is generated using a prediction block for the current block and the residual signal;
The conversion method is determined based on information about division of the current block,
The conversion method is determined based on the type of division. A computer-readable recording medium storing a bitstream for decoding an image, wherein the bitstream comprises:
Contains coded information about the current block;
A transform method for the current block is determined from among a plurality of transform methods based on the encoded information on the current block, and a residual signal is derived by performing transform on the current block according to the transform method. A reconstructed block for the current block is generated using a prediction block for the current block and the residual signal;
The conversion method is determined based on information about division of the current block,
The conversion method is determined based on the position of the boundary of the division.

Images