KR20170124076A - Method and apparatus for encoding and decoding a video signal group - Google Patents

Abstract

The present invention relates to a method and a device for encoding and decoding of a video signal group, which improve compression efficiency of an image by efficiently encoding/decoding coefficients in a partial block. The method for encoding an image signal according to the present invention comprises the following steps of: encoding a partial block coefficient flag representing whether a current partial block coefficient is a non-zero coefficient; encoding a first flag representing whether an absolute value of the coefficient is greater than one; encoding a second flag representing whether the absolute value of the coefficient is greater than two; encoding the remaining unencoded coefficient based on the first and second flags in the current partial block; and encoding a code with respect to the coefficient of the current partial block.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and an apparatus for encoding and decoding a video signal group,

The present invention relates to a method and apparatus for encoding / decoding coefficients in a transform block.

In recent years, demand for multimedia data such as video has been rapidly increasing on the Internet. However, the rate at which the bandwidth of a channel develops is hard to follow the amount of multimedia data that is rapidly increasing.

The present invention has a main purpose of improving the compression efficiency of an image by efficiently encoding / decoding coefficients in a partial block.

A video signal encoding method and apparatus according to the present invention encodes a partial block coefficient flag indicating whether a coefficient of a current partial block is a non-zero coefficient and outputs a first flag indicating whether an absolute value of the coefficient is greater than 1 Encoding the second flag indicating whether the absolute value of the coefficient is greater than 2, encoding the remaining coefficients not encoded based on the first flag or the second flag in the current partial block, The sign for the coefficient of the partial block can be encoded.

The method and apparatus for encoding an image signal according to the present invention can encode a maximum value among the absolute values of the coefficients of the current partial block.

The method and apparatus for encoding an image signal according to the present invention may further include determining whether an absolute value of all coefficients in the current partial block is smaller than a current threshold value, Value flag can be encoded.

In the method and apparatus for coding an image signal according to the present invention, if the absolute value of all coefficients in the current partial block is greater than or equal to the current threshold, the first threshold flag is coded to be false, If the absolute value of all of the coefficients is less than the current threshold value, the first threshold value flag may be encoded as true.

In the video signal encoding method and apparatus according to the present invention, if the first threshold flag is encoded to be false, the current threshold value may be updated to a next threshold value.

In the video signal encoding method and apparatus according to the present invention, at least one of the first flag or the second flag may be selectively encoded according to the value of the first threshold flag.

In the video signal encoding method and apparatus according to the present invention, the current threshold value may be any one of threshold values within a predetermined threshold value range.

In the video signal encoding method and apparatus according to the present invention, the predetermined threshold may be determined based on at least one of a quantization parameter, a block size, and a pixel value range.

The method and apparatus for decoding a video signal according to the present invention decodes a partial block coefficient flag indicating whether a coefficient of a current partial block is a non-zero coefficient and outputs a first flag indicating whether the absolute value of the coefficient is larger than 1 Decodes a second flag indicating whether the absolute value of the coefficient is greater than 2, decodes a remaining coefficient not decoded on the basis of the first flag or the second flag in the current partial block, The sign for the coefficient of the partial block can be decoded.

The video signal decoding method and apparatus according to the present invention can decode a maximum value among the absolute values of the coefficients of the current partial block.

The method and apparatus for decoding a video signal according to the present invention can decode a first threshold flag for the current partial block.

In the method and apparatus for decoding a video signal according to the present invention, if the first threshold flag is false, the absolute value of all coefficients in the current partial block is greater than or equal to a current threshold value, If true, the absolute value of all coefficients in the current partial block may be less than the current threshold.

In the video signal decoding method and apparatus according to the present invention, when the first threshold flag is false, the current threshold value may be updated to a next threshold value.

In the video signal decoding method and apparatus according to the present invention, at least one of the first flag or the second flag may be selectively decoded according to the value of the first threshold flag.

In the method and apparatus for decoding a video signal according to the present invention, the current threshold value may be a threshold value within a predetermined threshold value range.

In the video signal decoding method and apparatus according to the present invention, the predetermined threshold may be determined based on at least one of a quantization parameter, a block size, and a pixel value range.

According to the present invention, the efficiency of compressing an image can be improved by efficiently encoding / decoding the coefficients of the transform block.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
FIG. 3 illustrates a method of encoding a coefficient of a transform block according to an embodiment to which the present invention is applied.
FIG. 4 illustrates a method of encoding a maximum value of a coefficient of a partial block according to an embodiment of the present invention.
FIG. 5 illustrates a method of encoding a first threshold flag for a partial block according to an embodiment of the present invention. Referring to FIG.
FIG. 6 illustrates a method of encoding a second threshold value flag for a partial block according to an embodiment of the present invention. Referring to FIG.
FIG. 7 illustrates a method of decoding a coefficient of a transform block according to an embodiment of the present invention. Referring to FIG.
FIG. 8 illustrates a method of decoding a maximum value of a coefficient of a partial block according to an embodiment of the present invention.
FIG. 9 illustrates a method of decoding a first threshold flag for a partial block according to an embodiment of the present invention.
FIG. 10 illustrates a method of decoding a second threshold value flag for a partial block according to an embodiment of the present invention.
FIG. 11 illustrates a method of deriving a first / second threshold flag for a current partial block according to an embodiment of the present invention. Referring to FIG.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the same reference numerals will be used for the same constituent elements in the drawings, and redundant explanations for the same constituent elements will be omitted.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.

1, the image encoding apparatus 100 includes a picture division unit 110, prediction units 120 and 125, a transform unit 130, a quantization unit 135, a reordering unit 160, an entropy encoding unit An inverse quantization unit 140, an inverse transform unit 145, a filter unit 150, and a memory 155. [

Each of the components shown in FIG. 1 is shown independently to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is composed of separate hardware or one software configuration unit. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of the constituent units may be combined to form one constituent unit, or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and separate embodiments of the components are also included within the scope of the present invention, unless they depart from the essence of the present invention.

In addition, some of the components are not essential components to perform essential functions in the present invention, but may be optional components only to improve performance. The present invention can be implemented only with components essential for realizing the essence of the present invention, except for the components used for the performance improvement, and can be implemented by only including the essential components except the optional components used for performance improvement Are also included in the scope of the present invention.

The picture division unit 110 may divide the inputted picture into at least one block. At this time, a block may mean a coding unit (CU), a prediction unit (PU), or a conversion unit (TU). The partitioning may be performed based on at least one of a quadtree or a binary tree. The quad tree is a method of dividing the upper block into sub-blocks whose width and height are half of the upper block. A binary tree is a method of dividing an upper block into sub-blocks, either width or height, which is half of the upper block. Through the binary tree-based partitioning described above, a block can have a square as well as a non-square shape.

Hereinafter, in the embodiment of the present invention, a coding unit may be used as a unit for performing coding, or may be used as a unit for performing decoding.

The prediction units 120 and 125 may include an inter prediction unit 120 for performing inter prediction and an intra prediction unit 125 for performing intra prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit and to determine concrete information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. At this time, the processing unit in which the prediction is performed may be different from the processing unit in which the prediction method and the concrete contents are determined. For example, the method of prediction, the prediction mode and the like are determined as a prediction unit, and the execution of the prediction may be performed in a conversion unit. The residual value (residual block) between the generated prediction block and the original block can be input to the conversion unit 130. [ In addition, the prediction mode information, motion vector information, and the like used for prediction can be encoded by the entropy encoding unit 165 together with the residual value and transmitted to the decoder. When a particular encoding mode is used, it is also possible to directly encode the original block and transmit it to the decoding unit without generating a prediction block through the prediction units 120 and 125.

The inter-prediction unit 120 may predict a prediction unit based on information of at least one of a previous picture or a following picture of the current picture, and may predict a prediction unit based on information of a partially- Unit may be predicted. The inter prediction unit 120 may include a reference picture interpolation unit, a motion prediction unit, and a motion compensation unit.

In the reference picture interpolating section, the reference picture information is supplied from the memory 155 and pixel information of an integer pixel or less can be generated in the reference picture. In the case of a luminance pixel, a DCT-based interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of quarter pixels. In the case of a color difference signal, a DCT-based 4-tap interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of 1/8 pixel.

The motion prediction unit may perform motion prediction based on the reference picture interpolated by the reference picture interpolating unit. Various methods such as Full Search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) can be used as methods for calculating motion vectors. The motion vector may have a motion vector value of 1/2 or 1/4 pixel unit based on the interpolated pixel. The motion prediction unit can predict the current prediction unit by making the motion prediction method different. Various methods such as a skip method, a merge method, and an AMVP (Advanced Motion Vector Prediction) method can be used as the motion prediction method.

The intra prediction unit 125 can generate a prediction unit based on reference pixel information around the current block which is pixel information in the current picture. In the case where the neighboring block of the current prediction unit is the block in which the inter prediction is performed so that the reference pixel is the pixel performing the inter prediction, the reference pixel included in the block in which the inter prediction is performed is referred to as the reference pixel Information. That is, when the reference pixel is not available, the reference pixel information that is not available may be replaced by at least one reference pixel among the available reference pixels.

In intra prediction, the prediction mode may have a directional prediction mode in which reference pixel information is used according to a prediction direction, and a non-directional mode in which direction information is not used in prediction. The mode for predicting the luminance information may be different from the mode for predicting the chrominance information and the intra prediction mode information or predicted luminance signal information used for predicting the luminance information may be utilized to predict the chrominance information.

The intra prediction method can generate a prediction block after applying an AIS (Adaptive Intra Smoothing) filter to the reference pixel according to the prediction mode. The type of the AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit can be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. In the case where the prediction mode of the current prediction unit is predicted using the mode information predicted from the peripheral prediction unit, if the intra prediction mode of the current prediction unit is the same as the intra prediction mode of the current prediction unit, The prediction mode information of the current block can be encoded by performing entropy encoding if the prediction mode of the current prediction unit is different from the prediction mode of the neighbor prediction unit.

In addition, a residual block including a prediction unit that has been predicted based on the prediction unit generated by the prediction units 120 and 125 and a residual value that is a difference value from the original block of the prediction unit may be generated. The generated residual block may be input to the transform unit 130. [

The transforming unit 130 can transform the residual block including the residual data by using a conversion method such as DCT, DST, or the like. At this time, the conversion method can be determined based on the intra prediction mode of the prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted into the frequency domain by the conversion unit 130. [ The quantization factor may vary depending on the block or the importance of the image. The values calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reorder unit 160.

The reordering unit 160 can reorder the coefficient values with respect to the quantized residual values.

The reordering unit 160 may change the two-dimensional block type coefficient to a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan a DC coefficient to a coefficient in the high frequency region using a predetermined scan type, and change it into a one-dimensional vector form.

The entropy encoding unit 165 may perform entropy encoding based on the values calculated by the reordering unit 160. For entropy encoding, various encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be used.

The entropy encoding unit 165 receives the residual value count information of the encoding unit, the block type information, the prediction mode information, the division unit information, the prediction unit information and the transmission unit information, and the motion information of the motion unit from the reordering unit 160 and the prediction units 120 and 125 Vector information, reference frame information, interpolation information of a block, filtering information, and the like.

The entropy encoding unit 165 can entropy-encode the coefficient value of the encoding unit input by the reordering unit 160. [

The inverse quantization unit 140 and the inverse transformation unit 145 inverse quantize the quantized values in the quantization unit 135 and inversely transform the converted values in the conversion unit 130. [ The residual value generated by the inverse quantization unit 140 and the inverse transform unit 145 is combined with the prediction unit predicted through the motion estimation unit, the motion compensation unit and the intra prediction unit included in the prediction units 120 and 125, A block (Reconstructed Block) can be generated.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove block distortion caused by the boundary between the blocks in the reconstructed picture. It may be determined whether to apply a deblocking filter to the current block based on pixels included in a few columns or rows included in the block to determine whether to perform deblocking. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the deblocking filtering strength required. In applying the deblocking filter, horizontal filtering and vertical filtering may be performed concurrently in performing vertical filtering and horizontal filtering.

The offset correction unit may correct the offset of the deblocked image with respect to the original image in units of pixels. In order to perform offset correction for a specific picture, pixels included in an image are divided into a predetermined number of areas, and then an area to be offset is determined and an offset is applied to the area. Alternatively, Can be used.

Adaptive Loop Filtering (ALF) can be performed based on a comparison between the filtered reconstructed image and the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and different filtering may be performed for each group. The information related to whether to apply the ALF may be transmitted for each coding unit (CU), and the shape and the filter coefficient of the ALF filter to be applied may be changed according to each block. Also, an ALF filter of the same type (fixed form) may be applied irrespective of the characteristics of the application target block.

The memory 155 may store the reconstructed block or picture calculated through the filter unit 150 and the reconstructed block or picture stored therein may be provided to the predictor 120 or 125 when the inter prediction is performed.

2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.

2, the image decoder 200 includes an entropy decoding unit 210, a reordering unit 215, an inverse quantization unit 220, an inverse transform unit 225, prediction units 230 and 235, 240, and a memory 245 may be included.

When an image bitstream is input in the image encoder, the input bitstream may be decoded in a procedure opposite to that of the image encoder.

The entropy decoding unit 210 can perform entropy decoding in a procedure opposite to that in which entropy encoding is performed in the entropy encoding unit of the image encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied in accordance with the method performed by the image encoder.

The entropy decoding unit 210 may decode information related to intra prediction and inter prediction performed in the encoder.

The reordering unit 215 can perform reordering based on a method in which the entropy decoding unit 210 rearranges the entropy-decoded bitstreams in the encoding unit. The coefficients represented by the one-dimensional vector form can be rearranged by restoring the coefficients of the two-dimensional block form again. The reordering unit 215 can perform reordering by receiving information related to the coefficient scanning performed by the encoding unit and performing a reverse scanning based on the scanning order performed by the encoding unit.

The inverse quantization unit 220 can perform inverse quantization based on the quantization parameters provided by the encoder and the coefficient values of the re-arranged blocks.

The inverse transform unit 225 may inversely transform the dequantized transform coefficients using a predetermined transform method. At this time, the conversion method can be determined based on information on the prediction method (inter / intra prediction), size / type of block, intra prediction mode, and the like.

The prediction units 230 and 235 can generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit 210 and the previously decoded block or picture information provided in the memory 245. [

The prediction units 230 and 235 may include a prediction unit determination unit, an inter prediction unit, and an intra prediction unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 210, prediction mode information of the intra prediction method, motion prediction related information of the inter prediction method, and identifies prediction units in the current coding unit. It is possible to determine whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 predicts the current prediction based on the information included in at least one of the previous picture of the current picture or the following picture including the current prediction unit by using information necessary for inter prediction of the current prediction unit provided by the image encoder, Unit can be performed. Alternatively, the inter prediction may be performed on the basis of the information of the partial region previously reconstructed in the current picture including the current prediction unit.

In order to perform the inter prediction, it is determined whether the motion prediction method of the prediction unit included in the encoding unit is based on a skip mode, a merge mode, or an AMVP mode It can be judged.

The intra prediction unit 235 can generate a prediction block based on the pixel information in the current picture. If the prediction unit is a prediction unit that performs intra prediction, the intra prediction can be performed based on the intra prediction mode information of the prediction unit provided by the image encoder. The intraprediction unit 235 may include an AIS (Adaptive Intra Smoothing) filter, a reference pixel interpolator, and a DC filter. The AIS filter performs filtering on the reference pixels of the current block and can determine whether to apply the filter according to the prediction mode of the current prediction unit. The AIS filtering can be performed on the reference pixel of the current block using the prediction mode of the prediction unit provided in the image encoder and the AIS filter information. When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter may not be applied.

The reference pixel interpolator may interpolate the reference pixels to generate reference pixels in units of pixels less than or equal to an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on pixel values obtained by interpolating reference pixels. The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates the prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The restored block or picture may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

When information on whether a deblocking filter is applied to a corresponding block or picture from the image encoder or a deblocking filter is applied, information on whether a strong filter or a weak filter is applied can be provided. In the deblocking filter of the video decoder, the deblocking filter related information provided by the video encoder is provided, and the video decoder can perform deblocking filtering for the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction applied to the image, offset information, and the like during encoding.

The ALF can be applied to an encoding unit on the basis of ALF application information and ALF coefficient information provided from an encoder. Such ALF information may be provided in a specific parameter set.

The memory 245 may store the reconstructed picture or block to be used as a reference picture or a reference block, and may also provide the reconstructed picture to the output unit.

FIG. 3 illustrates a method of encoding a coefficient of a transform block according to an embodiment to which the present invention is applied.

In the image encoding apparatus, the coefficients of the transform block can be encoded in a predetermined block unit (hereinafter referred to as a partial block). The transform block may be composed of one or more partial blocks. The partial block may be a NxM block. Here, N and M are natural numbers, and N and M may be the same or different from each other. That is, the partial block may be a square or a non-square block. The size / shape of the partial block may be fixed (for example, 4x4) predefined in the image encoding apparatus, or may be variably determined according to the size / type of the transform block. Alternatively, the image encoding apparatus may determine the size / shape of the optimal partial block in consideration of the coding efficiency and may encode it. Information about the size / shape of the encoded partial block may be signaled in at least one of a sequence, a picture, a slice, or a block level.

In the image encoding apparatus, the order of encoding the partial block belonging to the transform block may be determined according to a predetermined scan type (hereinafter referred to as a first scan type). The order of encoding coefficients belonging to the partial block may be determined according to a predetermined scan type (hereinafter referred to as a second scan type). The first scan type and the second scan type may be the same or different. The first / second scan type may be a diagonal scan, a vertical scan, or a horizontal scan. However, the present invention is not limited to this, and one or more scan types having a predetermined angle may be further added. The first and second scan types may include coding block related information (e.g., maximum / minimum size, division technique, etc.), size / type of conversion block, size / shape of partial block, prediction mode, Direction, angle, etc.) of the intra prediction mode, or inter prediction related information.

The image encoding apparatus can encode position information of a coefficient that is not initially 0 (hereinafter, referred to as a non-zero coefficient) in the above-described encoding sequence in the conversion block. Encoding can be performed sequentially from a partial block including the non-zero coefficient. Hereinafter, a process of coding coefficients of partial blocks will be described with reference to FIG.

The partial block flag for the current partial block can be encoded (S300). The partial block flag can be encoded in units of partial blocks. The partial block flag may indicate whether there is at least one non-zero coefficient in the current partial block. For example, if the partial block flag is a first value, the current partial block indicates that at least one non-zero coefficient is present, and if the partial block flag is a second value, all coefficients of the current partial block are 0 .

The partial block coefficient flag for the current partial block may be encoded (S310). The partial block coefficient flag may be coded on a coefficient basis. The partial block coefficient flag may indicate whether the coefficient is a non-zero coefficient. For example, if the coefficient is a non-zero coefficient, the partial block coefficient flag is encoded to a first value, and if the coefficient is zero, the partial block coefficient flag may be encoded to a second value. The partial block coefficient flag may be selectively encoded according to the partial block flag. For example, it can be encoded for each coefficient of the partial block only if there is at least one non-zero coefficient in the current partial block (i.e., the partial block flag is the first value).

A flag indicating whether the absolute value of the coefficient is greater than 1 (hereinafter referred to as a first flag) can be encoded (S320). The first flag may be selectively encoded according to the value of the partial block coefficient flag. For example, if the coefficient is a non-zero coefficient (i.e., the partial block coefficient flag is a first value), the first flag can be encoded by checking whether the absolute value of the coefficient is greater than 1 . If the absolute value of the coefficient is greater than 1, the first flag is encoded to a first value, and if the absolute value of the coefficient is not greater than 1, the first flag may be encoded to a second value.

(Hereinafter referred to as a second flag) indicating whether the absolute value of the coefficient is greater than 2 (S330). The second flag may be selectively encoded according to the value of the first flag. For example, if the coefficient is greater than 1 (i.e., the first flag is a first value), the second flag may be encoded by checking whether the absolute value of the coefficient is greater than two. If the absolute value of the coefficient is greater than 2, the second flag is encoded to a first value, and if the absolute value of the coefficient is not greater than 2, the second flag may be encoded to a second value.

The number of at least one of the first flag or the second flag may be at least one to at most (N * M). Alternatively, at least one of the first flag or the second flag may be a fixed number (e.g., one, two, or more) predefined in the image encoding apparatus. The number of the first and second flags may be determined based on the bit depth of the input image, the dynamic range of the original pixel value in an arbitrary region of the image, the block size / depth, the segmentation technique (eg, quad tree, (eg, DCT, DST), whether to skip conversion, quantization parameters, prediction mode (eg, intra / inter mode), and so on. In addition to the first / second flags, an n-th flag indicating whether the absolute value of the coefficient is greater than n may be additionally encoded. Here, n may mean a natural number greater than 2. The number of the n-th flags may be one, two, or more, and may be determined in the same / similar manner as the first / second flags described above.

The remaining coefficients that are not encoded based on the first / second flags may be encoded in the current partial block (S340). Here, the encoding may be a process of encoding the coefficient value itself. The remaining coefficients may be equal to or greater than two.

A sign for a coefficient of the partial block can be encoded (S350). The code can be encoded in the form of a flag in units of coefficients. The code can be selectively encoded according to the value of the partial block coefficient flag described above. For example, the code may be encoded only when the coefficient is a non-zero coefficient (i.e., the partial block coefficient flag is a first value).

On the other hand, coefficient coding of the above-mentioned partial block may further involve a process of specifying a range of coefficient values belonging to the partial block. Through the above process, it can also be confirmed whether or not at least one non-zero coefficient exists in the partial block. The above process can be implemented through at least one of the following (A) maximum value encoding, (B) first threshold value flag encoding, or (C) second threshold value flag encoding. The above process may be implemented in any one of steps S300 to S350 described above, or may be implemented in a form that is substituted for at least one of steps S300 to S350. Hereinafter, the process of specifying the range of the coefficient values belonging to the partial block will be described in detail with reference to FIG. 4 to FIG.

FIG. 4 illustrates a method of encoding a maximum value of a coefficient of a partial block according to an embodiment of the present invention.

Referring to FIG. 4, the maximum value among the absolute values of the coefficients of the current partial block can be encoded (S400). Through the maximum value, the range of the coefficient value belonging to the current partial block can be inferred. For example, when the maximum value is m, the coefficient of the current partial block may fall within the range of 0 to m. The maximum value may be selectively encoded according to the value of the partial block flag described above. For example, it can only be coded if the current partial block contains at least one non-zero coefficient (i.e., the partial block flag is the first value). If the coefficients of the current partial block are all 0 (i.e., the partial block flag is the second value), the maximum value may be derived to be zero.

Further, through the maximum value, it may be determined whether or not at least one non-zero coefficient is included in the current partial block. For example, if the maximum value is greater than 0, the current partial block includes at least one non-zero coefficient, and if the maximum value is zero, all coefficients of the current partial block may be zero. Therefore, the maximum value encoding may be performed in place of the encoding of the partial block flag of S300.

FIG. 5 illustrates a method of encoding a first threshold flag for a partial block according to an embodiment of the present invention. Referring to FIG.

The first threshold flag of the present invention may indicate whether or not all the coefficients of the partial block are smaller than a predetermined threshold value. The number of thresholds may be N (N > = 1), where the range of thresholds is {T ₀ , T ₁ , T ₂ , ... , T _N-1 }. Here, the 0th threshold value of T ₀ is a minimum value, (N-1) th threshold value of T _N-1 refers to the maximum value, respectively, and, {T _0, T _1, T _2, ... , T _N-1 } may be those in which the threshold values are arranged in ascending order. The number of the thresholds may be set in the image coding apparatus. The image encoding apparatus can determine the optimal number of thresholds in consideration of the coding efficiency and encode the number.

The threshold value may be obtained by setting the minimum value to 1 and increasing the minimum value by n (n > = 1). The threshold value may be set in the image encoding apparatus. The image encoding apparatus can determine the optimum threshold value in consideration of the encoding efficiency and encode the optimal threshold value.

The range of the threshold value may be determined differently according to the quantization parameter (QP). The QP may be set at a level of at least one of a sequence, a picture, a slice, and a transform block.

For example, if the QP is greater than a predetermined QP threshold, it can be expected that the distribution of the zero coefficients in the transform block will increase. In this case, the threshold value range may be determined as {3}, the first / second threshold value flag encoding process may be omitted, and the coefficients of the partial block may be encoded through the above-described steps S300 to S350.

On the other hand, when the QP is smaller than the predetermined QP threshold, it can be predicted that the distribution of the non-zero coefficients in the transform block becomes large. In this case, the range of the threshold can be determined as {3, 5} or {5, 3}.

That is, the threshold value range when the QP is small can have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the QP is large. The number of the QP thresholds may be one, two, or more. The QP threshold may be set in the image encoding apparatus. For example, the QP threshold may correspond to a median of a range of QPs available in the image encoding apparatus. Alternatively, the image encoding apparatus may determine an optimum QP threshold considering encoding efficiency, and encode the optimal QP threshold.

Alternatively, the range of the threshold value may be determined differently depending on the size / shape of the block. Here, a block may mean a coding block, a prediction block, a transform block, or a partial block. The size may be expressed by at least one of the width, height, sum of width and height, or number of coefficients.

For example, when the size of the block is smaller than the predetermined threshold size, the range of the threshold value is determined as {3}, the first / second threshold value flag encoding process is omitted, and the above-described steps S300 to S350 are repeated The coefficients of the partial block can be encoded. On the other hand, when the size of the block is larger than the predetermined threshold size, the range of the threshold can be determined to be {3, 5} or {5, 3}.

That is, the threshold value range when the block size is small may have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the block size is large. The number of critical dimensions may be one, two, or more. The threshold size may be set in the image encoding apparatus. For example, the critical dimension is represented by axb, where a and b are 2, 4, 8, 16, 32, 64 or more, and a and b may be the same or different. Alternatively, the image encoding apparatus may determine the optimal threshold size in consideration of the encoding efficiency and encode the optimal threshold size.

Alternatively, the range of the threshold value may be determined differently depending on the pixel value range. The pixel value range may be expressed by a maximum value and / or a minimum value of pixels belonging to a predetermined area. At this time, the predetermined area may mean at least one of a sequence, a picture, a slice, or a block.

For example, when the difference between the maximum value and the minimum value of the pixel value range is smaller than the predetermined threshold difference value, the range of the threshold value is determined as {3}, or the first / second threshold value flag encoding process is omitted And the coefficient of the partial block can be encoded through steps S300 to S350 described above. On the other hand, when the difference is larger than the predetermined threshold difference value, the range of the threshold value can be determined to be {3, 5} or {5, 3}.

That is, the threshold value range when the difference is small may have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the difference is large. The number of threshold difference values may be one, two, or more. The threshold difference value may be set in the image encoding apparatus. Alternatively, the image encoding apparatus may determine the optimal threshold difference value in consideration of the encoding efficiency and encode the optimal threshold difference value.

Referring to FIG. 5, it may be determined whether the absolute value of all coefficients in the current partial block is smaller than the current threshold (S500).

If the absolute value of all coefficients is not smaller than the current threshold value, the first threshold value flag may be encoded as "false" (S510). In this case, the current threshold value (i-th threshold value) is updated to the next threshold value ((i + 1) -th threshold value) (S520), and the above-described step S500 is performed based on the updated current threshold value . Alternatively, if the absolute value of all the coefficients is not smaller than the current threshold value, the first threshold value flag encoding process of step S510 may be omitted, and the current threshold value may be updated to the next threshold value.

When the current threshold value reaches the maximum value of the threshold value or when the number of the threshold values is 1, the current threshold value may be updated by adding a predetermined constant to the current threshold value. The predetermined constant may be an integer greater than or equal to one. At this time, the update may be repeatedly performed until the first threshold value flag is encoded as "true ". Based on the updated current threshold value, step S500 may be performed. Alternatively, if the current threshold has reached the maximum value of the threshold, or if the number of thresholds is one, the updating process may end.

If the absolute value of all coefficients is smaller than the current threshold value, the first threshold value flag may be encoded as "true" (S530).

As described above, when the first threshold flag for the i-th threshold is "true", this may indicate that the absolute value of all coefficients in the partial block is smaller than the i-th threshold. On the other hand, if the first threshold flag for the i-th threshold is "false", this may indicate that the absolute value of all coefficients in the partial block is greater than or equal to the i-th threshold. Based on the first threshold flag that is "true ", a range of the coefficient value belonging to the partial block can be specified. That is, when the first threshold value flag for the i-th threshold value is "true ", the coefficient belonging to the partial block may fall within the range of 0 to (i-th threshold value -1).

According to the encoded first threshold value flag, at least one of steps S300 to S350 described above may be omitted.

For example, when the range of the threshold is {3, 5}, at least one of the first threshold flag for the threshold value "3 " or the first threshold flag for the threshold value" 5 & . When the first threshold value flag for the threshold value "3 " is" true ", the absolute value of all the coefficients in the partial block may fall within the range of 0 to 2. In this case, the coefficient of the partial block is encoded by performing the remaining steps except at least one of the steps of S330 or S340 described above, or the coefficients of the partial block are encoded by performing the remaining steps except S300, S330, or S340 It is possible.

If the first threshold flag for the threshold "3" is "false ", the first threshold flag for the threshold" 5 " If the first threshold flag for the threshold "5" is "false ", then at least one of the absolute values of the coefficients in the partial block may be greater than or equal to five. In this case, the coefficients of the partial block may be encoded by performing the above-described steps S300 to S350 in the same manner, or the coefficients of the partial block may be encoded by performing the remaining steps except step S300.

On the other hand, when the first threshold value flag for the threshold value "5 " is" true ", the absolute value of all coefficients in the partial block may fall within the range of 0 to 4. In this case, the coefficients of the partial block may be encoded by performing the above-described steps S300 to S350 in the same manner, or the coefficients of the partial block may be encoded by performing the remaining steps except step S300.

On the other hand, the first threshold flag of the current partial block may be derived based on the first threshold flag of another partial block. In this case, the first threshold value flag encoding process can be omitted, and this will be described with reference to FIG.

FIG. 6 illustrates a method of encoding a second threshold value flag for a partial block according to an embodiment of the present invention. Referring to FIG.

The second threshold flag of the present invention may indicate whether or not all the coefficients of the partial block are smaller than a predetermined threshold value. The number of thresholds may be N (N > = 1), where the range of thresholds is {T ₀ , T ₁ , T ₂ , ... , T _N-1 }. Here, T _{0, which} is the 0th threshold value, is the maximum value, and T _{N-1, which} is the (N-1) th threshold value, is the minimum value, and {T ₀ , T ₁ , T ₂ , ... , T _N-1 } may be those in which the threshold values are arranged in descending order. The number of the thresholds may be set in the image coding apparatus. The image encoding apparatus can determine the optimal number of thresholds in consideration of the coding efficiency and encode the number.

The threshold value may be obtained by setting the maximum value to m and decreasing the minimum value by n (n > = 1). The m may be one set in the image encoding apparatus. Alternatively, the image encoding apparatus can determine the optimal maximum value m in consideration of the coding efficiency and encode it. The threshold value may be set in the image encoding apparatus. The image encoding apparatus can determine the optimum threshold value in consideration of the encoding efficiency and encode the optimal threshold value.

The range of the threshold value may be determined differently based on at least one of a quantization parameter, a size / shape of a block, or a range of a pixel value, as shown in the embodiment of FIG.

Referring to FIG. 6, it can be determined whether the absolute value of all coefficients in the current partial block is smaller than the current threshold value (S600).

If the absolute value of all the coefficients is smaller than the current threshold value, the second threshold value flag may be encoded as "true" (S610). In this case, the current threshold value (i-th threshold value) is updated to the next threshold value ((i + 1) -th threshold value) (S620) and the above-described step S600 is performed based on the updated current threshold value . Alternatively, if the absolute value of all the coefficients is smaller than the current threshold value, the second threshold value flag encoding process in step S610 may be omitted, and the current threshold value may be updated to the next threshold value.

When the current threshold value reaches the minimum value of the threshold value or when the number of the threshold values is 1, the current threshold value may be updated by subtracting a predetermined constant from the current threshold value. The predetermined constant may be an integer greater than or equal to one. At this time, the update may be repeatedly performed until the second threshold flag is encoded as "false ". Similarly, based on the updated current threshold, step S600 described above may be performed. Alternatively, if the current threshold value has reached the minimum value of the threshold value or if the number of threshold values is one, the updating process may be terminated.

If the absolute value of all the coefficients is not smaller than the current threshold value, the second threshold value flag may be encoded as "false " (S630).

As described above, when the second threshold value flag for the i-th threshold value is "true ", this may indicate that the absolute value of all coefficients in the partial block is smaller than the i-th threshold value. On the other hand, if the second threshold flag for the i-th threshold is "false", this may indicate that at least one of the absolute values of all coefficients in the partial block is greater than or equal to the i-th threshold.

According to the encoded second threshold value flag, at least one of the above-described steps S300 to S350 may be omitted.

For example, when the range of the threshold is {5, 3}, at least one of the second threshold flag for the threshold value "5 " or the second threshold flag for the threshold value" 3 & . If the second threshold flag for the threshold "5" is "false ", at least one of the absolute values of all coefficients in the partial block may be greater than or equal to five. In this case, the coefficient of the partial block may be encoded by performing the above-described steps S310 to S350 in the same manner, or the coefficients of the partial block may be encoded by performing the remaining steps except step S300.

If the second threshold flag for the threshold "5 " is" True ", a second threshold flag for the threshold "3 " When the second threshold value flag for the threshold value "3 " is" true ", the absolute value of the intra-block coefficient may fall within the range of 0 to 2. In this case, the coefficient of the partial block is encoded by performing the remaining steps except at least one of the steps of S330 or S340 described above, or the coefficients of the partial block are encoded by performing the remaining steps except S300, S330, or S340 It is possible.

On the other hand, if the second threshold flag for the threshold "3 " is" false ", at least one of the absolute values of all coefficients in the partial block may be greater than or equal to three. In this case, the coefficients of the partial block may be encoded by performing the above-described steps S300 to S350 in the same manner, or the coefficients of the partial block may be encoded by performing the remaining steps except step S300.

On the other hand, the second threshold flag of the current partial block may be derived based on the second threshold flag of another partial block. In this case, the second threshold value flag encoding process can be omitted, and this will be described with reference to FIG.

FIG. 7 illustrates a method of decoding a coefficient of a transform block according to an embodiment of the present invention. Referring to FIG.

In the video decoding apparatus, the coefficient of the transform block can be decoded into a predetermined block unit (hereinafter referred to as a partial block). The transform block may be composed of one or more partial blocks. The partial block may be a NxM block. Here, N and M are natural numbers, and N and M may be the same or different from each other. That is, the partial block may be a square or a non-square block. The size / shape of the partial block may be fixed (e.g., 4x4) predefined in the image decoding apparatus, may be variably determined according to the size / type of the transform block, and the size / May be variably determined based on information about the type. Information about the size / shape of the partial block may be signaled in at least one of a sequence, a picture, a slice, or a block level.

In the video decoding apparatus, the order of decoding the partial blocks belonging to the conversion block may be determined according to a predetermined scan type (hereinafter referred to as a first scan type). In addition, the order of decoding coefficients belonging to the partial block may be determined according to a predetermined scan type (hereinafter referred to as a second scan type). The first scan type and the second scan type may be the same or different. The first / second scan type may be a diagonal scan, a vertical scan, or a horizontal scan. However, the present invention is not limited to this, and one or more scan types having a predetermined angle may be further added. The first and second scan types may include coding block related information (e.g., maximum / minimum size, division technique, etc.), size / type of conversion block, size / shape of partial block, prediction mode, Direction, angle, etc.) of the intra prediction mode, or inter prediction related information.

The video decoding apparatus can decode position information of a partial block including a coefficient that is not initially 0 in the decoding order (hereinafter, referred to as a non-zero coefficient) in the conversion block. It is possible to sequentially decode the partial blocks according to the position information. Hereinafter, a process of decoding the coefficients of the partial blocks will be described with reference to FIG.

The partial block flag for the current partial block can be decoded (S700). The partial block flag may be decoded in units of partial blocks. The partial block flag may indicate whether there is at least one non-zero coefficient in the current partial block. For example, if the partial block flag is a first value, the current partial block indicates that at least one non-zero coefficient is present, and if the partial block flag is a second value, all coefficients of the current partial block are 0 .

The partial block coefficient flag for the current partial block may be decoded (S710). The partial block coefficient flag may be decoded in units of coefficients. The partial block coefficient flag may indicate whether the coefficient is a non-zero coefficient. For example, when the partial block coefficient flag is a first value, it indicates that the coefficient is a non-zero coefficient, and when the partial block coefficient flag is a second value, it may indicate that the coefficient is zero. The partial block coefficient flag may be selectively decoded according to the partial block flag. For example, only if there is at least one non-zero coefficient in the current partial block (i.e., the partial block flag is the first value), it can be decoded by the coefficient of the partial block.

A flag indicating whether the absolute value of the coefficient is greater than 1 (hereinafter referred to as a first flag) may be decoded (S720). The first flag may be selectively decoded according to the value of the partial block coefficient flag. For example, if the coefficient is a non-zero coefficient (i.e., the partial block coefficient flag is a first value), the first flag may be decoded to check whether the absolute value of the coefficient is greater than one. The absolute value of the coefficient may be 1 when the first flag is a first value and when the absolute value of the coefficient is greater than 1 and the first flag is a second value.

A flag indicating whether the absolute value of the coefficient is greater than 2 (hereinafter referred to as a second flag) can be decoded (S730). The second flag may be selectively decoded according to the value of the first flag. For example, if the coefficient is greater than 1 (i.e., the first flag is a first value), the second flag may be decoded to determine whether the absolute value of the coefficient is greater than two. The absolute value of the coefficient may be 2 when the second flag is a first value and when the absolute value of the coefficient is greater than 2 and the second flag is a second value.

The number of at least one of the first flag or the second flag may be at least one to at most (N * M). Alternatively, at least one of the first flag or the second flag may be a fixed number (e.g., one, two, or more) predefined in the image decoding apparatus. The number of the first and second flags may be determined based on the bit depth of the input image, the dynamic range of the original pixel value in an arbitrary region of the image, the block size / depth, the segmentation technique (eg, quad tree, (eg, DCT, DST), whether to skip conversion, quantization parameters, prediction mode (eg, intra / inter mode), and so on. In addition to the first / second flags, an n-th flag indicating whether the absolute value of the coefficient is greater than n may be additionally decoded. Here, n may mean a natural number greater than 2. The number of the n-th flags may be one, two, or more, and may be determined in the same / similar manner as the first / second flags described above.

The remaining coefficients that have not been decoded based on the first / second flags may be decoded in the current partial block (S740). Here, the decoding may be a process of decoding the coefficient value itself. The remaining coefficients may be equal to or greater than two.

A sign for a coefficient of the partial block can be decoded (S750). The code can be decoded in the form of a flag in units of coefficients. The code can be selectively decoded according to the value of the partial block coefficient flag described above. For example, the code may be decoded only when the coefficient is a non-zero coefficient (i.e., the partial block coefficient flag is a first value).

On the other hand, the coefficient decoding of the partial block described above may further involve a process of specifying a range of the coefficient values belonging to the partial block. Through the above process, it can also be confirmed whether or not at least one non-zero coefficient exists in the partial block. The above process can be performed through at least one of (A) decoding of a maximum value, (B) decoding of a first threshold value flag, or (C) decoding of a second threshold value flag described later. The above process may be performed in any one of steps S700 to S750 described above, or may be performed in the form of replacing at least one of steps S700 to S370. Hereinafter, the process of specifying the range of the coefficient values belonging to the partial block will be described in detail with reference to FIGS. 8 to 10. FIG.

FIG. 8 illustrates a method of decoding a maximum value of a coefficient of a partial block according to an embodiment of the present invention.

Referring to FIG. 8, information indicating the maximum absolute value of the coefficients of the current partial block can be decoded (S800). The range of the coefficient value belonging to the current partial block can be inferred through the maximum value according to the information. For example, when the maximum value is m, the coefficient of the current partial block may fall within the range of 0 to m. The information indicating the maximum value may be selectively decoded according to the value of the partial block flag described above. For example, it can only be decoded if the current partial block contains at least one non-zero coefficient (i.e., the partial block flag is the first value). If the coefficients of the current partial block are all 0 (i.e., the partial block flag is the second value), the information indicating the maximum value may be derived as zero.

Further, through the maximum value according to the information, it may be determined whether or not at least one non-zero coefficient is included in the current partial block. For example, if the maximum value is greater than 0, the current partial block includes at least one non-zero coefficient, and if the maximum value is zero, all coefficients of the current partial block may be zero. Therefore, the maximum value decoding may be performed in place of the decoding of the partial block flag of S700.

FIG. 9 illustrates a method of decoding a first threshold flag for a partial block according to an embodiment of the present invention.

The first threshold flag of the present invention may indicate whether or not all the coefficients of the partial block are smaller than a predetermined threshold value. The number of thresholds may be N (N > = 1), where the range of thresholds is {T ₀ , T ₁ , T ₂ , ... , T _N-1 }. Here, the 0th threshold value of T ₀ is a minimum value, (N-1) th threshold value of T _N-1 refers to the maximum value, respectively, and, {T _0, T _1, T _2, ... , T _N-1 } may be those in which the threshold values are arranged in ascending order. The number of the thresholds may be set in the image decoding apparatus or may be determined based on information on the number of signaling thresholds.

The threshold value may be obtained by setting the minimum value to 1 and increasing the minimum value by n (n > = 1). The threshold value may be set in the image decoding apparatus or may be determined based on information on a signaled threshold value.

The range of the threshold value may be determined differently according to the quantization parameter (QP). The QP may be set at a level of at least one of a sequence, a picture, a slice, and a transform block.

For example, if the QP is larger than the predetermined QP threshold, the threshold value range is determined as {3}, or the first / second threshold value flag decoding process is skipped and the steps S700 through S750 The coefficients of the partial block can be decoded.

On the other hand, when the QP is smaller than the predetermined QP threshold, the range of the threshold can be determined as {3, 5} or {5, 3}.

That is, the threshold value range when the QP is small can have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the QP is large. The number of the QP thresholds may be one, two, or more. The QP threshold may be set in the video decoding apparatus. For example, the QP threshold may correspond to a median of a range of QP available in the video decoding apparatus. Alternatively, the QP threshold may be determined based on information about the QP threshold signaled by the image encoding apparatus.

Alternatively, the range of the threshold value may be determined differently depending on the size / shape of the block. Here, a block may mean a coding block, a prediction block, a transform block, or a partial block. The size may be expressed by at least one of the width, height, sum of width and height, or number of coefficients.

For example, when the size of the block is smaller than the predetermined threshold size, the threshold value range is determined as {3}, the first / second threshold value flag decoding process is omitted, and the steps S700 to S750 The coefficients of the partial block can be decoded. On the other hand, when the size of the block is larger than the predetermined threshold size, the range of the threshold can be determined to be {3, 5} or {5, 3}.

That is, the threshold value range when the block size is small may have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the block size is large. The number of critical dimensions may be one, two, or more. The threshold size may be set in the image decoding apparatus. For example, the critical dimension is represented by axb, where a and b are 2, 4, 8, 16, 32, 64 or more, and a and b may be the same or different. Alternatively, the threshold size may be determined based on information about a critical size signaled by the image encoding apparatus.

Alternatively, the range of the threshold value may be determined differently depending on the pixel value range. The pixel value range may be expressed by a maximum value and / or a minimum value of pixels belonging to a predetermined area. At this time, the predetermined area may mean at least one of a sequence, a picture, a slice, or a block.

For example, when the difference between the maximum value and the minimum value of the pixel value range is smaller than the predetermined threshold difference value, the threshold value range is determined as {3}, or the first / second threshold value flag decoding process is omitted , And decodes the coefficients of the partial block through steps S700 to S750 described above. On the other hand, when the difference is larger than the predetermined threshold difference value, the range of the threshold value can be determined to be {3, 5} or {5, 3}.

That is, the threshold value range when the difference is small may have the number and / or size (for example, maximum value) of the threshold values different from the threshold value range when the difference is large. The number of threshold difference values may be one, two, or more. The threshold difference value may be set in the image decoding apparatus or may be determined based on information about a threshold difference value signaled by the image encoding apparatus.

Referring to FIG. 9, the first threshold flag associated with the current threshold value may be decoded (S900).

The first threshold flag may indicate whether the absolute value of all the coefficients of the partial block is smaller than the current threshold value. For example, if the first threshold flag is "false ", then the absolute value of all coefficients of the partial block may be greater than or equal to the current threshold. On the other hand, when the first threshold value flag is "true ", the absolute value of all the coefficients of the partial block may be smaller than the current threshold value.

If the first threshold flag is "False ", the current threshold value (i-th threshold value) is updated to the next threshold value (i + 1) th threshold value (S910) The above-described step S900 may be performed.

When the current threshold value reaches the maximum value of the threshold value or when the number of the threshold values is 1, the current threshold value may be updated by adding a predetermined constant to the current threshold value. The predetermined constant may be an integer greater than or equal to one. At this time, the update may be repeatedly performed until the first threshold flag "true" is decoded. Alternatively, if the current threshold has reached the maximum value of the threshold, or if the number of thresholds is one, the updating process may end.

As shown in Fig. 9, when the first threshold flag is "True ", decoding of the first threshold flag may not be performed any more.

As described above, when the first threshold flag for the i-th threshold is "true", this may indicate that the absolute value of all coefficients in the partial block is smaller than the i-th threshold. On the other hand, if the first threshold flag for the i-th threshold is "false", this may indicate that the absolute value of all coefficients in the partial block is greater than or equal to the i-th threshold. Based on the first threshold flag that is "true ", a range of the coefficient value belonging to the partial block can be specified. That is, when the first threshold value flag for the i-th threshold value is "true ", the coefficient belonging to the partial block may fall within the range of 0 to (i-th threshold value -1).

According to the decoded first threshold value flag, at least one of steps S700 to S750 described above may be omitted.

For example, if the range of the threshold is {3, 5}, at least one of the first threshold flag for the threshold value "3 " or the first threshold flag for the threshold value" 5 & . When the first threshold value flag for the threshold value "3 " is" true ", the absolute value of all the coefficients in the partial block may fall within the range of 0 to 2. In this case, the coefficients of the partial block are decoded by performing the remaining steps except for at least one of the steps S730 and S740 described above, or the remaining steps excluding S700, S730 or S740 are performed to decode the coefficients of the partial block It is possible.

If the first threshold flag for the threshold "3" is "false ", the first threshold flag for the threshold" 5 " If the first threshold flag for the threshold "5" is "false ", then at least one of the absolute values of the coefficients in the partial block may be greater than or equal to five. In this case, the coefficients of the partial block may be decoded by performing the same steps S700 to S750 as described above, or the coefficients of the partial block may be decoded by performing the remaining steps except step S700.

On the other hand, when the first threshold value flag for the threshold value "5 " is" true ", the absolute value of all coefficients in the partial block may fall within the range of 0 to 4. In this case, the coefficients of the partial block may be decoded by performing the same steps S700 to S750 as described above, or the coefficients of the partial block may be decoded by performing the remaining steps except step S700.

On the other hand, the first threshold flag of the current partial block may be derived based on the first threshold flag of another partial block. In this case, the first threshold flag decoding process may be omitted, and this will be described with reference to FIG.

FIG. 10 illustrates a method of decoding a second threshold value flag for a partial block according to an embodiment of the present invention.

The second threshold flag of the present invention may indicate whether or not all the coefficients of the partial block are smaller than a predetermined threshold value. The number of thresholds may be N (N > = 1), where the range of thresholds is {T ₀ , T ₁ , T ₂ , ... , T _N-1 }. Here, T _{0, which} is the 0th threshold value, is the maximum value, and T _{N-1, which} is the (N-1) th threshold value, is the minimum value, and {T ₀ , T ₁ , T ₂ , ... , T _N-1 } may be those in which the threshold values are arranged in descending order. The number of thresholds may be set in the image decoding apparatus or may be determined based on information on the number of threshold values signaled in the image buffering apparatus.

The threshold value may be obtained by setting the maximum value to m and decreasing the minimum value by n (n > = 1). The m may be set in the image decoding apparatus or may be determined based on information about a maximum value m to be signaled by the image encoding apparatus. The threshold value may be set in the image decoding apparatus or may be determined based on information about a threshold value signaled by the image encoding apparatus.

The range of the threshold value may be determined differently based on at least one of a quantization parameter, a size / shape of a block, or a range of a pixel value, as described in the embodiment of FIG.

Referring to FIG. 10, a second threshold flag related to a current threshold value may be decoded (S1000).

The second threshold value flag may indicate whether the absolute value of all the coefficients of the partial block is smaller than the current threshold value. For example, if the second threshold flag is "false ", it may be that the absolute value of all the coefficients of the partial block is greater than or equal to the current threshold. On the other hand, when the second threshold flag is "true ", the absolute value of all the coefficients of the partial block may be smaller than the current threshold value.

If the second threshold flag is "True ", the current threshold value (i-th threshold value) is updated to the next threshold value (i + 1) th threshold value (S1010) The above step S1000 may be performed.

On the other hand, if the second threshold flag is "False ", decoding of the second threshold flag may not be performed any more.

When the current threshold value reaches the minimum value of the threshold value or when the number of the threshold values is 1, the current threshold value may be updated by subtracting a predetermined constant from the current threshold value. The predetermined constant may be an integer greater than or equal to one. At this time, the update may be repeatedly performed until a second threshold value flag of "false " is decoded. Alternatively, if the current threshold value has reached the minimum value of the threshold value or if the number of threshold values is one, the updating process may be terminated.

As described above, when the second threshold value flag for the i-th threshold value is "true ", this may indicate that the absolute value of all coefficients in the partial block is smaller than the i-th threshold value. On the other hand, if the second threshold flag for the i-th threshold is "false", this may indicate that at least one of the absolute values of all coefficients in the partial block is greater than or equal to the i-th threshold.

According to the decoded second threshold value flag, at least one of steps S700 to S750 described above may be omitted.

For example, when the range of the threshold is {5, 3}, at least one of the second threshold flag for the threshold value "5 " or the second threshold flag for the threshold value" 3 & . If the second threshold flag for the threshold "5" is "false ", at least one of the absolute values of all coefficients in the partial block may be greater than or equal to five. In this case, the coefficients of the partial block may be decoded by performing the above-described steps S710 to S750 in the same manner, or the coefficients of the partial block may be decoded by performing the remaining steps except step S700.

If the second threshold flag for the threshold "5" is "True ", the second threshold flag for the threshold" 3 " When the second threshold value flag for the threshold value "3 " is" true ", the absolute value of the intra-block coefficient may fall within the range of 0 to 2. In this case, the coefficients of the partial block are decoded by performing the remaining steps except for at least one of the steps S730 and S740 described above, or the remaining steps excluding S700, S730 or S740 are performed to decode the coefficients of the partial block It is possible.

On the other hand, if the second threshold flag for the threshold "3 " is" false ", at least one of the absolute values of all coefficients in the partial block may be greater than or equal to three. In this case, the coefficients of the partial block may be decoded by performing the above-described steps S700 to S750 in the same manner, or the coefficients of the partial block may be encoded by performing the remaining steps except step S700.

On the other hand, the second threshold flag of the current partial block may be derived based on the second threshold flag of another partial block. In this case, the second threshold flag decoding process may be omitted, and this will be described with reference to FIG.

FIG. 11 illustrates a method of deriving a first / second threshold flag for a current partial block according to an embodiment of the present invention. Referring to FIG.

In this embodiment, the transform block 1100 is 8x8, the partial block is 4x4, the block including the initial non-zero coefficient is 1120, and the partial block of the transform block is 1140, 1120, 1130, 1110 Are encoded / decoded in this order.

In the current partial block, the first threshold flag for a certain threshold value may be derived based on the first threshold flag of the previous partial block. For example, based on a first threshold flag that is "false" in the previous partial block, the first threshold flag of the current partial block may be derived "false ". Here, it is assumed that {3, 5, 7} is used as the range of the threshold value.

Specifically, the first threshold flag may not be coded / decoded because the coding / decoding order is earlier than the position of the partial block 1120 to which the first non-zero coefficient belongs. Only the first threshold flag for the threshold value "3 " can be encoded / decoded because the first threshold value flag for the threshold value" 3 " is "True" in the second partial block 1120 of the encoding / . In the third partial block 1130 of the encoding / decoding order, since the first threshold flag related to the threshold value "3" is "false" and the first threshold value flag relating to the threshold value "5" is "true" And a first threshold value flag for the values "3" and "5 " can be respectively encoded / decoded. In the last partial block 1110 in the encoding / decoding order, the first threshold flag related to the threshold value "3" is "false" and the first threshold value flag relating to the threshold value "5" is "false". At this time, since the first threshold flag related to the threshold value "3 " in the previous partial block 1130 is" false ", the current partial block 1110 predicts that at least one absolute value of the coefficient, Quot; false "for the first threshold value flag.

In the current partial block, the first threshold flag for a certain threshold value may be derived based on the first threshold flag of the previous partial block. For example, based on a first threshold flag that is "false" in the previous partial block, the first threshold flag of the current partial block may be derived "false ".

In this embodiment, for convenience of explanation, the conversion block 1100 is 8x8, the partial block is 4x4, the threshold range is {3, 5, 7}, the block including the initial non-zero coefficient is 1120 , It is assumed that the partial blocks of the transform block are coded / decoded in order of 1140, 1120, 1130, and 1110 according to the scan type.

Likewise, in the current partial block, a second threshold flag for a certain threshold value may be derived based on a second threshold flag of the previous partial block. For example, based on a first threshold flag that is "false" in the previous partial block, the first threshold flag of the current partial block may be derived "false ". Here, it is assumed that {7, 5, 3} is used as the range of the threshold value.

Specifically, since the encoding / decoding order is earlier than the position of the partial block 1120 to which the first non-zero coefficient belongs, the second threshold flag may not be encoded / decoded. Quot ;, the second threshold flag related to the threshold "7" is " true ", the second threshold flag related to the threshold "5" 7 ", " 5 ", and "3 " can be respectively encoded / decoded because the second threshold value flag for " 3" The second threshold flag related to the threshold value " 7 " and the second threshold value flag relating to the threshold value " 5 " are respectively " true " and " The second threshold value flag is " false ". In the last partial block 1110 in the encoding / decoding order, the second threshold flag for the threshold "3" is "false ". At this time, by using the fact that the second threshold flag related to the threshold value "3" is "false " in the previous partial block 1130, the second threshold flag related to the threshold " 3 " is not encoded / , &Quot; false ".

Although the exemplary methods of this disclosure are represented by a series of acts for clarity of explanation, they are not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In order to implement the method according to the present disclosure, the illustrative steps may additionally include other steps, include the remaining steps except for some steps, or may include additional steps other than some steps.

The various embodiments of the disclosure are not intended to be all-inclusive and are intended to illustrate representative aspects of the disclosure, and the features described in the various embodiments may be applied independently or in a combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays A general processor, a controller, a microcontroller, a microprocessor, and the like.

The scope of the present disclosure is to be accorded the broadest interpretation as understanding of the principles of the invention, as well as software or machine-executable instructions (e.g., operating system, applications, firmware, Instructions, and the like are stored and are non-transitory computer-readable medium executable on the device or computer.

Claims (12)

Encoding a partial block coefficient flag indicating whether the coefficient of the current partial block is a non-zero coefficient;
Encoding a first flag indicating whether the absolute value of the coefficient is greater than one;
Encoding a second flag indicating whether the absolute value of the coefficient is greater than 2;
Encoding residual coefficients that are not encoded based on the first flag or the second flag in the current partial block; And
And encoding a sign of a coefficient of the current partial block. The method according to claim 1,
And encoding a maximum value among the absolute values of the coefficients of the current partial block. The method according to claim 1,
Determining whether an absolute value of all coefficients in the current partial block is less than a current threshold value; And
Encoding the first threshold flag for the current partial block based on the determination result,
If the absolute value of all coefficients in the current partial block is greater than or equal to the current threshold value, the first threshold value flag is encoded to be false,
Wherein if the absolute value of all coefficients in the current partial block is smaller than the current threshold, the first threshold flag is encoded as true. The method of claim 3,
And if the first threshold flag is encoded to be false, the current threshold value is updated to a next threshold value. The method of claim 3,
Wherein at least one of the first flag and the second flag is selectively encoded according to the value of the first threshold flag. The method of claim 3,
Wherein the current threshold value is one of threshold values belonging to a range of a predetermined threshold value,
Wherein the predetermined threshold value is determined based on at least one of a quantization parameter, a block size, and a pixel value range. Decoding a partial block coefficient flag indicating whether the coefficient of the current partial block is a non-zero coefficient;
Decoding a first flag indicating whether the absolute value of the coefficient is greater than 1;
Decoding a second flag indicating whether the absolute value of the coefficient is greater than 2;
Decoding the remaining decoded coefficients based on the first flag or the second flag in the current partial block; And
And decoding a sign for a coefficient of the current partial block. 8. The method of claim 7,
And decoding the maximum value among the absolute values of the coefficients of the current partial block. 8. The method of claim 7,
Further comprising decoding a first threshold flag for the current partial block,
If the absolute value of all the coefficients in the current partial block is greater than or equal to the current threshold value,
Wherein if the first threshold flag is true, the absolute value of all coefficients in the current partial block is less than the current threshold. 10. The method of claim 9,
And if the first threshold flag is false, the current threshold value is updated to a next threshold value. 10. The method of claim 9,
Wherein at least one of the first flag and the second flag is selectively decoded according to the value of the first threshold flag. 10. The method of claim 9,
Wherein the current threshold value is one of threshold values belonging to a range of a predetermined threshold value,
Wherein the predetermined threshold value is determined based on at least one of a quantization parameter, a block size, and a pixel value range.

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