KR20160055772A - Method for predicting quantization parameter based on intra prediction mode and apparatus using the same - Google Patents

Abstract

Disclosed are a method for predicting a quantization coefficient based on an intra prediction mode and an apparatus using the same. The method comprises: a step of selecting a reference adjacent block as a reference for predicting a quantization coefficient based on an intra prediction mode of the current block; a step of determining an estimated value of a quantization coefficient of the current block based on a quantization coefficient of the reference adjacent block; and a step of acquiring and reverse-quantizing the quantization coefficient of the current block by adding the estimated value of the quantization coefficient to a differential value of a decoded quantization coefficient of the current block. The present invention provides a method for predicting a quantization coefficient based on an intra prediction mode so as to improve image encoding / decoding efficiency.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting a quantization coefficient based on an intra-

More particularly, the present invention relates to a method and apparatus for predicting a quantization coefficient of a current block based on an intra prediction mode to quantize / dequantize the same.

Recently, the demand for high resolution and high quality images such as high definition (HD) image and ultra high definition (UHD) image is increasing in various applications. As the image data has high resolution and high quality, the amount of data increases relative to the existing image data. Therefore, when the image data is transmitted using a medium such as a wired / wireless broadband line or stored using an existing storage medium, The storage cost is increased. High-efficiency image compression techniques can be utilized to solve such problems as image data becomes high-resolution and high-quality.

An inter picture prediction technique for predicting a pixel value included in a current picture from a previous or a subsequent picture of a current picture by an image compression technique, an intra picture prediction technique for predicting a pixel value included in a current picture using pixel information in a current picture, There are various techniques such as an entropy encoding technique in which a short code is assigned to a value having a high appearance frequency and a long code is assigned to a value having a low appearance frequency. Image data can be effectively compressed and transmitted or stored using such an image compression technique.

The present invention provides a method of predicting a quantization coefficient based on an intra prediction mode for increasing a coding / decoding efficiency of an image.

The present invention provides an apparatus for performing a method of predicting a quantization coefficient based on an intra prediction mode for increasing a coding / decoding efficiency of an image.

According to one aspect of the present invention, a video decoding method is provided. The method includes the steps of: selecting a reference neighboring block to be referred to in a quantization coefficient prediction based on an intra prediction mode of a current block; determining a quantized coefficient prediction value of the current block based on a quantization coefficient of the reference neighboring block; And obtaining a quantized coefficient of the current block by adding the predicted coefficient value and the decoded quantization coefficient difference value of the current block, and dequantizing the quantized coefficient.

In the reference neighboring block selection step, if the intra prediction mode is the vertical direction prediction mode, the upper block positioned at the upper end of the current block may be selected as the reference neighboring block.

In the reference neighboring block selection step, if the intra prediction mode is the horizontal direction prediction mode, the left block located on the left side of the current block may be selected as the reference neighboring block.

If the intra prediction mode is the remaining directional prediction mode excluding the vertical direction and the horizontal direction, at least one block among the blocks located at the upper, left, upper right, and lower left end of the current block is referred to as the reference peripheral It can be selected as a block.

Prediction coefficients of the current block can be determined by applying weights to the quantization coefficients of the reference neighboring blocks based on the directionality of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in the clockwise direction with respect to the vertical direction prediction mode in the reference peripheral block selection step, the upper block positioned at the upper end of the current block and the upper right block positioned at the upper right end are referred to as the reference Prediction coefficients of the current block by applying weights to the quantization coefficients of the upper block and the upper right block based on the direction of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in a counterclockwise direction with respect to the vertical direction prediction mode in the reference peripheral block selection step, the upper block positioned at the upper end of the current block and the left block located at the left side are referred to as reference surroundings Prediction coefficients of the current block by applying weights to the quantization coefficients of the upper block and the left block based on the direction of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in the clockwise direction with respect to the horizontal direction prediction mode in the reference peripheral block selection step, the left block located at the left side of the current block and the upper block positioned at the upper side are referred to as the reference neighboring block Prediction coefficients of the current block by applying weights to the quantization coefficients of the left block and the upper block on the basis of the directionality of the intra prediction mode.

Wherein if the intra prediction mode is a prediction mode having an anticlockwise angle with respect to the horizontal direction prediction mode in the reference peripheral block selection step, the left block positioned at the left side of the current block and the lower left block located at the lower left side, And a quantization coefficient prediction value of the current block can be determined by applying a weight to the quantization coefficients of the left block and the lower left block based on the directionality of the intra prediction mode.

According to another aspect of the present invention, an image decoding apparatus is provided. The image decoding apparatus includes an entropy decoding unit decoding an intra prediction mode information of a current block and a reference neighboring block to be referred to a quantization coefficient prediction based on the intra prediction mode of the decoded current block, And a dequantizer for obtaining the quantized coefficients of the current block by adding the quantized coefficient predicted values and the decoded quantized coefficient difference values of the current block based on the quantized coefficients of the current block, do.

According to another aspect of the present invention, a video encoding method is provided. The method includes the steps of: selecting a reference neighboring block to be referred to in a quantization coefficient prediction based on an intra prediction mode of a current block; determining a quantized coefficient prediction value of the current block based on a quantization coefficient of the reference neighboring block; And encoding the quantized coefficient difference value obtained by subtracting the quantized coefficient predicted value from the quantized coefficient of the block.

In the reference neighboring block selection step, if the intra prediction mode is the vertical direction prediction mode, the upper block positioned at the upper end of the current block may be selected as the reference neighboring block.

In the reference neighboring block selection step, if the intra prediction mode is the horizontal direction prediction mode, the left block located on the left side of the current block may be selected as the reference neighboring block.

If the intra prediction mode is the remaining directional prediction mode excluding the vertical direction and the horizontal direction, at least one block among the blocks located at the upper, left, upper right, and lower left end of the current block is referred to as the reference peripheral It can be selected as a block.

Prediction coefficients of the current block can be determined by applying weights to the quantization coefficients of the reference neighboring blocks based on the directionality of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in the clockwise direction with respect to the vertical direction prediction mode in the reference peripheral block selection step, the upper block positioned at the upper end of the current block and the upper right block positioned at the upper right end are referred to as the reference Prediction coefficients of the current block by applying weights to the quantization coefficients of the upper block and the upper right block based on the direction of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in a counterclockwise direction with respect to the vertical direction prediction mode in the reference peripheral block selection step, the upper block positioned at the upper end of the current block and the left block located at the left side are referred to as reference surroundings Prediction coefficients of the current block by applying weights to the quantization coefficients of the upper block and the left block based on the direction of the intra prediction mode.

If the intra prediction mode is a prediction mode having an angle in the clockwise direction with respect to the horizontal direction prediction mode in the reference peripheral block selection step, the left block located at the left side of the current block and the upper block positioned at the upper side are referred to as the reference neighboring block Prediction coefficients of the current block by applying weights to the quantization coefficients of the left block and the upper block on the basis of the directionality of the intra prediction mode.

Wherein if the intra prediction mode is a prediction mode having an anticlockwise angle with respect to the horizontal direction prediction mode in the reference peripheral block selection step, the left block positioned at the left side of the current block and the lower left block located at the lower left side, And a quantization coefficient prediction value of the current block can be determined by applying a weight to the quantization coefficients of the left block and the lower left block based on the directionality of the intra prediction mode.

According to another aspect of the present invention, an image encoding apparatus is provided. The image encoding apparatus includes a predictor for determining an intra prediction mode of a current block and a reference neighboring block to be referred to in quantization coefficient prediction based on an intra prediction mode of the current block and based on the quantization coefficient of the reference neighboring block And a quantization unit for determining a quantized coefficient predictive value of the current block and encoding a difference value obtained by subtracting the quantized coefficient predictive value from the quantized coefficient of the current block.

The reference neighboring block to be referred to in the quantization coefficient prediction is determined based on the direction of the intra prediction mode of the current block to be currently encoded / decoded. By using the quantization coefficient of the reference neighboring block having a similar probability to the quantization coefficient of the current block, Quantized / dequantized. In addition, it is possible to efficiently perform encoding / decoding by applying a weight to reference neighboring blocks according to the direction of the intra-prediction mode of the current 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.
3 is a diagram for explaining a method of predicting a quantization coefficient according to a direction of an intra prediction mode according to an embodiment of the present invention.
4 is a diagram illustrating an example of direction and mode values of an intra-prediction mode according to an embodiment of the present invention.
5 is a flowchart illustrating an image encoding method to which the present invention is applied.
6 is a flowchart illustrating a video decoding method to which the present invention is applied.

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, an image encoding apparatus 100 includes a picture dividing 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 the separate embodiments of the components are also included in the scope of the present invention unless otherwise departing from the spirit 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 input picture into at least one processing unit. At this time, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture dividing unit 110 divides a picture into a plurality of coding units, a prediction unit, and a combination of conversion units, and generates a coding unit, a prediction unit, and a conversion unit combination To encode a picture.

For example, one picture may be divided into a plurality of coding units. In order to divide an encoding unit in a picture, a recursive tree structure such as a quad tree structure can be used. An encoding unit, which is divided into other encoding units with one image or a maximum-size encoding unit as a root, Can be divided by the number of child nodes. Under certain constraints, an encoding unit that is no longer segmented becomes a leaf node. That is, when it is assumed that only one square division is possible for one coding unit, one coding unit can be divided into a maximum of four different coding units.

Hereinafter, in the embodiment of the present invention, the meaning of a coding unit can be used not only in the unit of coding but also in the meaning of a unit of decoding.

The prediction unit may be a prediction unit having a shape of at least one square or a rectangle having the same size in one coding unit or a shape of one prediction unit among the prediction units divided in one coding unit is different from the shape of another prediction unit It can be divided into shapes.

It is possible to perform intra-picture prediction without dividing the prediction unit performing intra-picture prediction based on the coding unit into a plurality of prediction units (N x N) when the prediction unit is not the minimum coding unit at the time of generation.

The prediction units 120 and 125 may include an inter-prediction unit 120 for performing inter-picture prediction and an intra-prediction unit 125 for performing intra-picture prediction. It is possible to determine whether to use intra-picture prediction or intra-picture prediction for a prediction unit, and to determine concrete information (for example, intra-picture 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 the prediction may 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. The inter-prediction unit 120 may include a reference picture interpolator, a motion estimator, and a motion compensator.

In the reference picture interpolating unit, 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 to calculate 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 differently performing the motion prediction method. As the motion prediction method, various methods such as a skip method, a merge method, and an AMVP (Advanced Motion Vector Prediction) method can be used.

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 blocks of the current prediction unit are the blocks in which the inter-screen prediction is performed, and the reference pixels are the pixels performing the inter-screen prediction, the intra-picture prediction is performed on the reference pixels included in the block in which the inter- Block 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 the 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 prediction information is not used. The mode for predicting the luminance information may be different from the mode for predicting the chrominance information, and intra prediction mode information or predicted luminance signal information in which luminance information is predicted can be used to predict the chrominance information.

When intra prediction is performed, when the size of the prediction unit is the same as the size of the conversion unit, on the basis of the pixel existing on the left side of the prediction unit, the pixel existing on the upper left side, I can perform my prediction. However, if the size of the prediction unit differs from the size of the conversion unit when intra prediction is performed, the intra prediction can be performed using the reference pixel based on the conversion unit. It is also possible to use intra prediction using N x N divisions for only the minimum coding unit.

In the intra prediction method, an AIS (Adaptive Intra Smoothing) filter can be applied to a reference pixel according to a prediction mode, and a prediction block can be generated. The type of the AIS filter applied to the reference pixel may be different. 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. When the prediction mode of the current prediction unit is predicted using the mode information predicted from the peripheral prediction unit and 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 transform unit 130 transforms the residual block including the residual information of the prediction unit generated through the original block and the predictors 120 and 125 into a transform such as DCT (Discrete Cosine Transform) or DST (Discrete Sine Transform) Method. ≪ / RTI > Whether to apply the DCT or the DST to transform the residual block can be determined based on the intra prediction mode information 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 rearranging unit 160 may convert the coefficients of the block into a one-dimensional vector form by using up-right scanning. A vertical scan that scans two-dimensional block type coefficients in the column direction instead of the upright scan, and a horizontal scan that scans two-dimensional block type coefficients in the row direction may be used according to the size of the conversion unit and the intra prediction mode. That is, it is possible to determine whether any scan method among the upright scan, the vertical scan and the horizontal scan is to be used according to the size of the conversion unit and the intra prediction mode.

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 coefficient information of the encoding unit, the block type information, the prediction mode information, the division unit information, the prediction unit information, the transmission unit information, the motion 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 the 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, a method of dividing a pixel included in an image into a predetermined number of regions, determining an area to be offset and applying an offset to the corresponding area, or considering an edge of each pixel, 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 a reconstructed block or a picture calculated through the filter unit 150 and the reconstructed block or the picture may be provided to the predictor 120 or 125 when the inter-picture 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 can decode information related to intra-picture prediction and inter-picture prediction performed by 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 perform inverse DCT and inverse DST on the DCT and DST performed by the transform unit on the quantization result performed by the image encoder. The inverse transform can be performed based on the transmission unit determined by the image encoder. In the transform unit of the image encoder, DCT and DST can be selectively performed according to a plurality of information such as a prediction method, a size and a prediction direction of a current block, and an inverse transform unit 225 of the image decoder performs transform The inverse transform can be performed based on the transformed information.

The prediction units 230 and 235 may 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. [

As described above, when the intra prediction is performed in the same manner as in the image encoder, when the size of the prediction unit and the size of the conversion unit are the same, pixels located on the left side of the prediction unit, pixels located on the upper left side, The intra prediction is performed on the prediction unit on the basis of the existing pixel. However, when the intra prediction is performed, when the size of the prediction unit differs from the size of the conversion unit, Prediction can be performed. It is also possible to use an intra prediction in which N x N division is used only for the minimum coding unit.

The prediction units 230 and 235 may include a prediction unit determination unit, an inter picture 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 picture prediction method, and identifies prediction units in the current coding unit , It is possible to determine whether the prediction unit performs inter-picture prediction or intra-picture prediction. The inter prediction unit 230 predicts an inter prediction based on information included in at least one of a previous picture or a following picture of a current picture including a current prediction unit using information necessary for inter- It is possible to perform inter-picture prediction on a prediction unit.

In order to perform the inter-picture prediction, whether the motion prediction method of the prediction unit included in the coding unit is based on a skip mode, a merge mode, or an AMVP mode Can be determined.

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 an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra-frame prediction on the basis of the pixel value obtained by interpolating the 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.

Information on whether or not a deblocking filter is applied to the corresponding block or picture from the image encoder and information on whether a strong filter or a weak filter is applied can be provided when the deblocking filter is applied. 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 and the offset value information 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 provide the reconstructed picture to the output unit.

As described above, in the embodiment of the present invention, a coding unit (coding unit) is used as a coding unit for convenience of explanation, but it may be a unit for performing not only coding but also decoding.

Hereinafter, a method of predicting a quantization coefficient according to the direction of an intra prediction mode using the image encoding apparatus and the decoding apparatus and quantizing / dequantizing the quantization coefficient will be described.

If the current prediction unit is the intra prediction mode, the current block is likely to have a similar quantization coefficient to the neighboring blocks according to the directionality of the intra prediction mode. For example, if the intra prediction mode has a prediction mode value close to the vertical direction, it is highly likely that the intra prediction mode has a similar quantization coefficient value to that of the neighboring block located at the upper side of the neighboring block located at the left side of the current block, It is highly likely to have a similar quantization coefficient value to the neighboring block located on the left side of the neighboring block located at the upper end of the current block. Accordingly, the present invention provides a method of predicting a quantization coefficient of a current block using a quantization coefficient of a neighboring block based on a direction of an intra prediction mode.

3 is a diagram for explaining a method of predicting a quantization coefficient according to a direction of an intra prediction mode according to an embodiment of the present invention. 3 (a) shows an intra-prediction mode in which each intra-prediction mode has a different directionality, and each intra-prediction mode is assigned a different mode value. 3 (b) is a diagram showing reference neighboring blocks to be referred to in quantization coefficient prediction of a current block according to an embodiment of the present invention.

Referring to FIGS. 3A and 3B, in order to predict a quantization coefficient of a current block according to an embodiment of the present invention, a reference neighboring block to be referred to in quantization coefficient prediction is determined based on an intra- And determines the predicted value of the quantization coefficient of the current block based on the quantization coefficient of the selected reference neighboring block.

If the intra prediction mode of the current block 300 is the vertical direction prediction mode, the upper block 310 positioned at the upper end of the current block 300 is selected as the reference neighbor block, and the intra prediction mode of the current block 300 is the horizontal direction prediction Mode, the left block 320 located on the left side of the current block is selected as the reference neighboring block.

For example, if the intra prediction mode of the current block 300 is a prediction mode in which the vertical direction prediction mode (e.g., mode value 0) and the vertical direction prediction mode (e.g., mode values 20, 11, 21, 22, 12, and 23, the upper block 310 positioned at the upper end of the current block 300 may be selected as a reference neighbor block. (For example, mode values 28, 15, 29, 30, and 16) in which the intraprediction mode of the current block 300 is located in a horizontally predicted mode (e.g., mode value 1) , 31), the left block 320 located on the left side of the current block 300 can be selected as the reference neighboring block.

The quantized coefficient prediction value of the current block can be determined using the quantization coefficients of the selected reference neighboring blocks as shown in the following Equations (1) and (2).

Equation (1) is an example of expressing the quantized coefficient predicted value (QP _predict ) of the current block using the quantization coefficient value (QP (Above_block)) of the upper block when the prediction mode of the current block is the vertical direction prediction mode.

Equation (2) is an example showing the quantized coefficient prediction value (QP _predict ) of the current block using the quantization coefficient value (QP (Left_block)) of the left block when the prediction mode of the current block is the horizontal direction prediction mode.

As described above, in the case where the intra prediction mode has a clear directionality such as a vertical or horizontal direction, a method of predicting a quantization coefficient of a current block by referring to an upper block or a left block is effective. However, In the case of the directional prediction mode, it is not effective to determine the predicted value of the quantization coefficient of the current block by applying the same quantization coefficients of the upper block or the left block.

In the embodiment of the present invention, if the intra prediction mode of the current block 300 is the remaining directional prediction mode excluding the vertical direction and the horizontal direction, the upper block 310 located in the periphery of the current block according to the magnitudes of the vertical direction component and the horizontal direction component , The left block 320, the upper right block 330, and the lower left block 340 are selected as reference peripheral blocks.

For example, if the intra prediction mode of the current block 300 is a prediction mode having the same directionality as the mode values 3, 18, 10, 19, 4, 26, 14, 27 and 7, The upper block 310 located on the left side and the left block 320 located on the left side can be selected as reference neighboring blocks. Since the mode values 3, 18, 10, 19, and 4 of the intraprediction mode include more vertical direction components than the horizontal direction components, it is possible to have a quantization coefficient similar to that of the upper block 310, Is high. On the other hand, since the mode values 26, 14, 27, and 7 of the intraprediction mode include more horizontal direction components than the vertical direction components, there is a high possibility that the mode values 26, 14, 27 and 7 of the intra prediction mode have quantization coefficients similar to those of the left block 320 .

Therefore, in the embodiment of the present invention, the quantization coefficient prediction value of the current block is determined by applying a weight to the quantization coefficient of the reference neighboring block based on each mode value, i.e., the direction of the intra prediction mode.

For example, if the intra prediction mode is a prediction mode (for example, mode values 3, 18, 10, 19, 4) having anticlockwise angles with respect to the vertical direction prediction mode, The predicted value of the quantized coefficient of the current block 300 may be determined by applying a higher weight to the quantized coefficient of the current block 300. [ If the intra prediction mode is a prediction mode (for example, mode values 26, 14, 27, 7) having an angle in the clockwise direction with respect to the horizontal direction prediction mode, the intra prediction mode is set to the quantization coefficient of the left block 320 rather than the upper block 310 The predicted value of the quantization coefficient of the current block 300 can be determined by applying a higher weight.

In Equation (3), if the intra-prediction mode of the current block is a prediction mode having an angle in the counterclockwise direction with respect to the vertical direction prediction mode, a weight is applied to the quantization coefficients of the left block and the upper block according to the degree of the directionality of the prediction mode (QP _predict ) of the current block.

In Equation (4), when the intra-prediction mode of the current block is a prediction mode having an angle in the clockwise direction with respect to the horizontal direction prediction mode, a weight is applied to the quantization coefficients of the left block and the upper block according to the degree of directionality of the prediction mode (QP _predict ) of the current block.

In Equations (3) and (4), QP _predict (Current_block) is the quantization coefficient predictive value of the current block, QP (Left_block) is the quantization coefficient of the left block, and QP (Above_block) is the quantization coefficient of the upper block.

The weights applied to the left block and the upper block in Equations (3) and (4) are only examples, and the present invention is not limited thereto. In addition, different weights may be applied to the left block and the upper block according to each mode value.

As another example, when the intra prediction mode of the current block 300 is a prediction mode (for example, mode values 5, 24, 13, 25, 6) having an angle in the clockwise direction on the basis of the vertical direction prediction mode, The upper block 310 and the upper right block 330 may be selected as reference neighboring blocks considering the directionality of the intra prediction mode. At this time, the predicted value of the quantization coefficient of the current block 300 can be determined by applying a weight to the upper block 310 and the upper right block 330 according to the degree of directionality of the intra prediction mode.

Equation (5) applies a weight to the quantization coefficients of the upper block and the upper right block according to the degree of the directionality of the prediction mode when the intra-prediction mode of the current block is a prediction mode having an angle in the clockwise direction with respect to the vertical direction prediction mode (QP _predict ) of the current block.

Here, QP _predict (Current_block) is the quantized coefficient prediction value of the current block, QP (Above_block) is the quantized coefficient at the top of the block, QP (AboveRight_block) is the quantized coefficient at the top right of the block.

In Equation (5), the weights applied to the upper block and the upper right block are examples, and the present invention is not limited thereto. In addition, different weights may be applied to the upper block and the upper right block, depending on the mode value.

As another example, when the intra prediction mode of the current block 300 is a prediction mode (e.g., mode values 8, 32, 17, 33, 9) having an anticlockwise angle with respect to the horizontal direction prediction mode, The left block 320 and the lower left block 340 may be selected as reference neighboring blocks in consideration of the direction of the intra prediction mode with reference to the block located on the left side of the block 300. [ In this case, the predicted values of the quantization coefficients of the current block 300 can be determined by applying weights to the left block 320 and the lower left block 340 according to the degree of directionality of the intra prediction mode (see Equation 6).

In Equation (6), when the intra-prediction mode of the current block is a prediction mode having a counterclockwise angle with respect to the horizontal direction prediction mode, a weight is assigned to the quantization coefficients of the left block and the lower- And the quantized coefficient predicted value (QP _predict ) of the current block is applied.

Here, QP _predict (Current_block) is the quantized coefficient prediction value of the current block, QP (Left_block) is the quantized coefficients in the left block, QP (LeftBelow_block) is the quantized coefficients in the lower left block.

The weights applied to the left block and the lower left block in Equation (6) are only examples, and the present invention is not limited thereto. In addition, different weights may be applied to the left block and the lower left block according to each mode value.

The mode value assigned to the intra prediction mode shown in FIG. 3A is one example, and the intra prediction mode to which the mode value is allocated, as shown in FIG. 4, The method of predicting the quantization coefficient of the quantized coefficient can be similarly applied. 4, description of a method of predicting a quantization coefficient of a current block according to an embodiment of the present invention will be omitted.

As described above, the quantization coefficient of the current block can be signaled by predicting the quantization coefficient of the current block according to the embodiment of the present invention. Hereinafter, a quantization coefficient difference value DeltaQP is encoded and transmitted using a method of predicting a quantization coefficient of a current block according to an embodiment of the present invention, and the transmitted quantization coefficient difference value DeltaQP is decoded, A method of acquiring the quantization coefficient value of the bitstream is described.

FIG. 5 is a flowchart illustrating an image encoding method to which the present invention is applied. Each step of FIG. 5 may be performed in a configuration corresponding to the image encoding apparatus described with reference to FIG.

Referring to FIG. 5, a new coding unit (CU) of the current picture is input (S500). The encoding unit input step (S500) divides the current picture into basic units for intraprediction / inter prediction.

The encoding apparatus generates reference pixels (S510). The reference pixel generation step (S510) generates reference pixels required for intra prediction based on the pixels adjacent to the current block performing the current prediction.

The encoding apparatus determines an intra prediction mode for the current block (S520). The intra prediction mode determination step S520 determines an optimal prediction mode based on the prediction unit and encodes the prediction mode of the current block.

The encoding apparatus obtains a residual signal by subtracting the pixel value of the current block and the pixel value of the prediction block in pixel units (S530), and converts the obtained residual signal (S540). The residual signal conversion step (S540) converts the residual signal to generate a transform coefficient.

The encoding apparatus quantizes the transform coefficients (S550). The transform coefficient quantization step (S550) quantizes the transform coefficient using the quantization coefficient of the current block, and encodes the quantization coefficient difference value of the current block.

The encoding apparatus scans the transform coefficients (S560), entropy-encodes the scanned transform coefficients and the intra-prediction mode (S570).

Hereinafter, the image coding method will be described in detail.

The coding unit input step (S500) divides the current picture into coding units which are basic units of region division used for intra prediction / inter prediction. The encoding unit is always square and the size of the encoding unit can be recursively divided into four blocks having the same size using the quad tree structure as described above with reference to FIG. A Prediction Unit (PU) is a block smaller than an encoding unit, and can be divided into at least one square or rectangular shape having the same size in one encoding unit. Intra prediction of the prediction unit is basically performed in 2N * 2N or N * N block units.

The reference pixel generation step S510 generates reference pixels required for intra prediction using pixels on the rightmost vertical line of the left block adjacent to the current block and pixels on the lowermost horizontal line of the upper block adjacent to the current block. If the size of the current block is N, 2N pixels can be used as reference pixels in both the upper block and the left block.

At this time, the reference pixel may use the pixels on the rightmost vertical line of the left block adjacent to the current block and the pixels on the lowermost horizontal line of the upper block adjacent to the current block, or may use the pixels of the adjacent block by smoothing. In the case of smoothing, information on the smoothing is signaled to the decoding device. For example, when smoothing is performed, an Adaptive Intra Smoothing (AIS) filter can be applied, and the filter coefficient can be set to [1, 2, 1] and [1, 1, 4, 1, 1] Can be used. The latter of the two filter coefficients provides a sharper interface. As described above, the decoding apparatus signals information on whether a filter is used, information on which filter is used when a filter is used, information on a filter coefficient, and the like.

The intra prediction mode determination step S520 is performed for each prediction unit, and the optimal intra prediction mode is determined in consideration of the relationship between the required bit rate and the distortion amount. For example, the prediction mode decision method may be changed depending on whether the RDO (Rate Distortion Optimization) is ON or OFF state. If RDO is ON, you can choose a mode that minimizes the cost J = R + rD (where R is the amount of bits, D is the amount of distortion, and r is the Lagrangian variable). However, since the local decoding must be completed, the complexity may increase in this case. When the RDO is OFF, the prediction error can be Hadamard transformed to select the prediction mode in which the mean absolute difference (MAD) is minimized.

The intra prediction mode for the current block may be determined from among a plurality of intra prediction modes (see a in FIG. 3) to which different mode values are assigned. The number of intra prediction modes for the luma component according to the size of the prediction unit may be as shown in Table 1 as an example.

Block size Number of prediction modes 4 * 4 17 8 * 8 34 16 * 16 34 32 * 32 34 64 * 64 3

For example, referring to the intra-prediction mode shown in FIG. 3 (a), if the size of the prediction unit is 4 * 4, 17 prediction modes in which the mode value of the intra-prediction mode is 0 to 16 can be used. Quot; 8 * 8 ", it is possible to use 34 prediction modes in which the mode value of the intra prediction mode is 0 to 33. [

3, if the mode value of the intra-prediction mode is 0, the prediction is performed in the vertical direction using the pixel values of the adjacent block. When the mode value of the intra-prediction mode is 1, Prediction can be performed. When the mode value of the intra prediction mode is 2, it is also referred to as a DC mode, and a prediction block can be generated by an average of pixel values in the current block. In the remaining modes, prediction can be performed using pixel values of adjacent blocks according to the angle.

The encoding apparatus can determine not only the prediction mode for the luma component of the current block but also the prediction mode of the chroma component.

The encoding device encodes a prediction mode for a luma component and a chroma component for the determined current block. The prediction mode of the current block is highly correlated with the prediction mode of the adjacent block adjacent to the current block so that the amount of bits transmitted to the decoding apparatus can be reduced by encoding the prediction mode of the current block using the prediction mode of the adjacent block. For example, the MPM (Most Probable Mode) of the current block can be determined, and the prediction mode of the current block can be encoded using the MPM.

In the residual signal acquisition step S530, the residual signal is obtained by dividing the pixel value of the prediction block generated in the intra-prediction mode determination step S520 and the pixel value of the current block in pixel units.

The residual signal conversion step S540 may transform the residual signal by applying a transform kernel and the size of the transform encoding kernel may be 2 * 2, 4 * 4, 8 * 8, 16 * 16, 32 * 64 * 64. Conversion coefficients are generated by the conversion, and the conversion coefficients are in the form of a two-dimensional block. For example, the transform coefficient C for an n * n block can be calculated as shown in Equation (7).

(N, n) is a transformed kernel matrix of n * n size, and B (n, n) is a matrix of n * n size transform coefficients. Is a matrix for the residual block.

The transform coefficient quantization step (S550) quantizes the transform coefficient using the quantization coefficient of the current block, and encodes the quantization coefficient difference value of the current block.

The quantization coefficient difference value of the current block is determined by determining the quantization coefficient prediction value of the current block on the basis of the intra prediction mode of the current block, and obtaining the predicted quantization coefficient value and the quantization coefficient value of the current block by a difference. The method of determining the predicted value of the quantization coefficient of the current block is performed in the same manner as in FIG. 3, and the description thereof has been given above with reference to FIG. 3, so that a detailed description thereof will be omitted.

The RDO can determine which of the residual signal and the transform coefficient to transfer. If the prediction is good, the residual signal can be transmitted as is without transcoding. It is possible to compare the cost function before and after the transcoding and to select the method in which the cost is minimized. At this time, a signal type (a residual signal or a transform coefficient) to be transmitted to the current block may be signaled, and the signal may be transmitted to the decoding apparatus.

The transform coefficient scan step S560 scans the transform coefficients of the quantized two-dimensional block form and converts the transform coefficients into one-dimensional vector form transform coefficients. For example, a scan method such as up-scan, vertical scan, and horizontal scan may be used according to the size of the conversion unit and the intra-prediction mode.

The entropy coding step (S570) entropy-codes the scanned transform coefficients and the intra prediction mode. The encoded information may be transmitted or stored via a Network Abstraction Layer (NAL) forming a compressed bitstream.

FIG. 6 is a flowchart illustrating a video decoding method to which the present invention is applied. Each step of FIG. 6 may be performed in a configuration corresponding to the video decoding apparatus described with reference to FIG.

Referring to FIG. 6, the decoding apparatus entropy decodes the received bitstream (S600). The entropy decoding step S600 obtains a residual signal or a transform coefficient for the current block from the received bitstream.

The decoding apparatus inversely scans the entropy-decoded residual signal or the transform coefficient (S610), and dequantizes the transform coefficient when the transform coefficient is generated (S620). In the dequantization step S620, a quantization coefficient value of the current block is obtained, and the dequantization coefficient is dequantized using the quantization coefficient value.

The decoding apparatus inversely transforms the dequantized transform coefficient (S630). A residual block is generated by an inverse transformation step (S630).

The decoding apparatus generates reference pixels necessary for intra prediction (S640). The reference pixel generation step S640 generates reference pixels required for intra prediction based on the pixels adjacent to the current block performing the current decoding.

The decoding apparatus generates a prediction block based on the intra prediction mode (S650). In the prediction block generation step S650, prediction is performed based on the intra-prediction mode of the reference pixel and the current block to generate a prediction block.

The decoding apparatus adds the pixel value of the prediction block and the pixel value of the residual block to generate a reconstruction block (S660).

Hereinafter, the image decoding method will be described in detail.

The entropy decoding step S600 obtains the block type from the variable length coding (VLC) table and acquires the intra prediction mode of the current block to be currently decoded. Information on whether the signal transmitted to the current block is a residual signal or a transform coefficient can be obtained and a residual signal or a one-dimensional vector form conversion coefficient for the current block can be obtained. When side information necessary for decoding is included in the received bitstream, they may be entropy-decoded together.

In the inverse scan step S610, a residual block is generated by performing a reverse scan in the case of a residual signal, and a transform coefficient of a two-dimensional block form is generated in the case of the transform coefficient.

The inverse quantization step (S620) is performed when a two-dimensional block-type transform coefficient is generated by performing inverse scan, and obtains a quantization coefficient of the current block and dequantizes the transform coefficient. At this time, the decoding apparatus extracts and decodes the quantization coefficient difference value for the current block from the received bitstream, and obtains the quantization coefficient of the current block by adding the quantization coefficient prediction value of the current block to the decoded quantization coefficient difference value. The quantization coefficient prediction value is determined based on the intra prediction mode of the current block and is performed in the same manner as in FIG. 3 described above. The description thereof has been given above with reference to FIG. 3, so a detailed description thereof will be omitted.

In the inverse transformation step S630, the inversely quantized transform coefficient is inversely transformed to generate a residual block. The inverse transformation process can be represented by the following equation (8).

or,

In the reference pixel generation step S640, as in the encoding step, the pixels on the rightmost vertical line of the left block, which is already decoded and restored to the current block to be decoded, and the pixels on the lowermost horizontal line of the upper block adjacent to the current block to be decoded Pixels are used to generate reference pixels. At this time, when the reference pixel is generated in the encoding apparatus, signaled information, for example, information on whether or not a smoothing filter is used, information on what type of filter is used when a filter is used, Can be generated.

In the reference pixel generation step (S640), when Adaptive Intra Smoothing (AIS) filtering is applied in the encoding apparatus according to the reference pixel generation method used in the encoding apparatus, AIS filtering is also performed in the decoding apparatus. Also, filter coefficients of [1, 2, 1] and [1, 1, 4, 1, 1] can be selected using the filter type information.

The prediction block generation step S650 generates a prediction block using the intra-prediction mode and the reference pixel of the entropy-decoded current block, and the generation process of the prediction block is the same as the process used for determining the prediction mode of the encoding device.

In the reconstruction block generation step S660, the reconstructed block, i.e., the reconstruction block, is generated by adding the pixel value of the prediction block and the pixel value of the residual block in pixel units.

In the above-described embodiments, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . It will also be understood by those skilled in the art that the steps depicted in the flowchart illustrations are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention You will understand.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the claims, and all technical ideas within the scope of the claims should be construed as being included in the scope of the present invention.

Claims (6)

Determining a scan type of the current block;
Obtaining a transform coefficient for the current block based on the determined scan type;
Deriving a quantized coefficient prediction value of the current block using a first quantization coefficient of a left neighboring block adjacent to the current block and a second quantization coefficient of an upper neighboring block;
Deriving a quantization coefficient of the current block based on the quantization coefficient prediction value and the quantization coefficient difference value;
Dequantizing the transform coefficients of the current block using the derived quantization coefficients;
Transforming the dequantized transform coefficients to obtain residual samples of the current block;
Generating a reconstruction sample of the current block using the residual samples of the current block and the prediction samples of the current block; And
And applying a deblocking filter to the reconstructed sample. The method according to claim 1,
Wherein the quantized coefficient prediction value is derived as an average value of the first quantization coefficient and the second quantization coefficient. The method according to claim 1,
Wherein the quantized coefficient prediction value is derived by applying a weight to the first quantization coefficient and the second quantization coefficient. The method of claim 3,
The weighting value is any one of (1, 0), (3/4, 1/4), (1/2, 1/2), (1/4, 3/4) And the video signal is decoded. 5. The method of claim 4,
Wherein the weight is determined in consideration of a directionality of an intra prediction mode with respect to the current block. The method according to claim 1,
Wherein the scan type is determined based on at least one of a size of the current block and an intra prediction mode of the current block.

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