KR20210111901A - Intra prediction method and apparatus using the method - Google Patents

Abstract

An in-screen prediction method and an apparatus using the method are disclosed. The in-screen prediction method includes setting the lower right pixel as a DC prediction value, interpolating the lower right pixel and the nth upper reference pixel to calculate the predicted value of the nth column, and interpolating the lower right pixel and the nth left reference pixel to the nth row The method may include calculating a predicted value of , and calculating a predicted value of a pixel included in a prediction unit excluding the n-th row and the n-th column by performing bidirectional linear interpolation. Accordingly, by using the improved intra prediction method, when the intra prediction method is performed, a prediction block close to the value of the original block is generated, thereby increasing the encoding/decoding efficiency.

Description

INTRA PREDICTION METHOD AND APPARATUS USING THE METHOD

The present invention relates to an intra prediction method and an apparatus using the method, and more particularly, to a decoding method and apparatus.

Recently, the demand for high-resolution and high-quality images such as HD (High Definition) images and UHD (Ultra High Definition) images is increasing in various application fields. As the image data becomes higher resolution and higher quality, the amount of data relatively increases compared to the existing image data. storage costs will increase. High-efficiency image compression techniques can be used to solve these problems that occur as image data becomes high-resolution and high-quality.

Inter-screen prediction technology that predicts pixel values included in the current picture from pictures before or after the current picture with image compression technology, intra-picture prediction technology that predicts pixel values included in the current picture using pixel information in the current picture, Various techniques exist, such as entropy encoding technology in which a short code is assigned to a value with a high frequency of occurrence and a long code is assigned to a value with a low frequency of occurrence.

It is an object of the present invention to provide an intra prediction method for increasing image encoding/decoding efficiency.

Another object of the present invention is to provide an apparatus for performing an intra prediction method for increasing image encoding/decoding efficiency.

In an in-screen prediction method according to an aspect of the present invention for achieving the above object of the present invention, the lower right pixel is set as a DC predicted value, the lower right pixel and the nth upper reference pixel are interpolated to obtain the predicted value of the nth column. calculating the predicted value of the nth row by interpolating the lower right pixel and the nth left reference pixel, and performing bidirectional linear interpolation to calculate the predicted value of the pixel included in the prediction unit except for the nth row and the nth column may include steps.

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention is to use the average of the upper left reference pixel, the nth upper reference pixel, and the nth left reference pixel to calculate the lower right pixel setting, calculating the predicted value of the nth column by interpolating the lower right pixel and the nth upper reference pixel, and calculating the predicted value of the nth row by interpolating the lower right pixel and the nth left reference pixel, and performing bidirectional linear interpolation and calculating a predicted value of a pixel included in a prediction unit excluding the n-th row and the n-th column.

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention includes the steps of setting the lower right pixel as a DC prediction value, interpolating the lower right pixel and the nth upper reference pixel to the nth calculating the predicted value of the column and interpolating the lower right pixel and the nth left reference pixel to calculate the predicted value of the nth row; calculating a first predicted value of a pixel included in a prediction unit excluding the n-th row and n-th column by performing and calculating a second predicted value of the pixel by bi-directionally linearly interpolating pixels existing in the .

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention is to use the average of the upper left reference pixel, the nth upper reference pixel, and the nth left reference pixel to calculate the lower right pixel setting, interpolating the lower right pixel and the nth upper reference pixel to calculate the predicted value of the nth column, and interpolating the lower right pixel and the nth left reference pixel to calculate the predicted value of the nth row, upper reference pixel, left calculating a first predicted value of a pixel included in a prediction unit excluding the nth row and the nth column by performing diagonal interpolation based on the values of the reference pixel, the nth column, and the nth row, and the nth row and the nth row The method may include calculating a second predicted value of the pixel by bi-directionally linear interpolating pixels existing at the top, bottom, left, and right of the pixel included in the prediction unit except for column n.

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-described other object of the present invention is the average value of each upper reference pixel and the n-th left reference pixel, and the predicted value of the pixel included in the n-th row and generating a predicted value of a pixel of a prediction unit except for the n-th row by interpolating the pixel included in the n-th row and the upper reference pixel.

In addition, in the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention, the average value is calculated for each left reference pixel value and the n+1th upper reference pixel value and included in the nth column. The method may include generating a predicted value of a pixel in the n-th column and generating a predicted value of a pixel of a prediction unit excluding the n-th column by interpolating a pixel included in the n-th column and a left reference pixel.

In addition, the in-screen prediction method according to another aspect of the present invention for achieving the above-described other object of the present invention comprises the steps of calculating the predicted value of the lower right pixel, the predicted value of the lower right pixel and the nth left reference pixel. using the interpolation value as the predicted value of the pixel included in the nth row, and using the predicted value of the lower right pixel and the interpolated value of the nth upper reference pixel as the predicted value of the pixel included in the nth row and the nth row and the nth column The prediction values of the remaining pixels of the prediction unit except for the n column are the upper reference pixel included in the same column in the vertical direction of the prediction target pixel, the pixels in the nth row, and the left reference pixel included in the same row in the horizontal direction of the prediction target pixel. and bidirectionally interpolating the pixels in the nth column. The calculating of the predicted value of the lower right pixel may include calculating an average value of the nth left reference pixel and the nth upper reference pixel as the predicted value of the lower right pixel. The calculating of the predicted value of the lower right pixel may include calculating an average value of the 2n-th upper reference pixel and the 2n-th left reference pixel as the predicted value of the lower right pixel. Calculating the predicted value of the lower right pixel may include calculating an upper average pixel, which is an average value of an n-th upper reference pixel and a 2n-th upper reference pixel, and a left average pixel, which is an average value of the n-th left reference pixel and the 2n-th left reference pixel. and calculating the average value of the upper average pixel and the left average pixel as the predicted value of the lower right pixel. The calculating of the predicted value of the lower right pixel may include an average value of an upper middle pixel positioned between the nth upper reference pixel and the 2nth upper reference pixel, and an average value of a left middle pixel positioned between the nth left reference pixel and the 2nth left reference pixel. It may be a step of calculating the predicted value of the lower right pixel by using .

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention includes the steps of calculating the predicted value of the lower right pixel, the value from the n+1th left reference pixel to the 2nth left reference pixel using as the predicted value of the pixel included in the nth row, and using the values from the n+1th upper reference pixel to the 2nth upper reference pixel as the predicted value of the pixel included in the nth column, the nth row and the nth column The prediction values of the remaining pixels of the prediction unit except and bidirectionally interpolating pixels in n columns.

In addition, the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention includes the steps of calculating the predicted value of the lower right pixel, the value from the n+1th left reference pixel to the 2nth left reference pixel and bidirectional interpolation of values from the n+1th upper reference pixel to the 2nth upper reference pixel and using them as prediction values of pixels included in the nth row and nth column, and the remainder of the prediction unit excluding the nth row and nth column The prediction value of the pixel is obtained by bidirectional interpolation between the upper reference pixel and the nth row pixels included in the same column in the vertical direction of the prediction target pixel, and the left reference pixel and the nth column pixels included in the same row in the horizontal direction of the prediction target pixel. may include the step of

In addition, in the intra-screen prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention, the left reference pixel value, the 2nth upper reference pixel value, and the 2nth upper reference pixel value existing in the same row in the horizontal direction, and the same column in the vertical direction Calculating the existing upper reference pixel value and the 2nth left reference pixel value, and predicting the left reference pixel value, the 2nth upper reference pixel value, the upper reference pixel value, and the 2nth left reference pixel value by bidirectional linear interpolation The method may include calculating a predicted value of a pixel included in the unit.

In addition, the intra prediction method according to another aspect of the present invention for achieving the above-mentioned other object of the present invention is horizontal interpolation using the left reference pixel value and the 2nth upper reference pixel value existing in the same row in the horizontal direction. performing vertical interpolation using the upper reference pixel value and the 2nth left reference pixel value existing in the same column in the vertical direction, and adding a value obtained by multiplying the horizontal interpolation and vertical interpolation values by a constant weight The method may include calculating a predicted value of a pixel included in the unit.

As described above, according to the intra prediction method and the apparatus using the intra prediction method according to the embodiment of the present invention, a prediction block close to the value of the original block is generated when the intra prediction method is performed by using the improved intra prediction method Thus, it is possible to increase the encoding/decoding efficiency.

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 decoder according to another embodiment of the present invention.
3 illustrates a prediction unit and a reference pixel according to an embodiment of the present invention.
4 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.
5 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.
6 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.
7 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.
8 is a conceptual diagram illustrating an improved vertical intra-screen prediction method according to an embodiment of the present invention.
9 is a conceptual diagram illustrating an improved horizontal intra-screen prediction method according to an embodiment of the present invention.
10 is a conceptual diagram illustrating a method of calculating a prediction unit through the enhanced planar mode according to an embodiment of the present invention.
11 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.
12 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.
13 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.
14 is a conceptual diagram illustrating a method of generating a lower right pixel in an enhanced planar mode according to an embodiment of the present invention.
15 is a conceptual diagram illustrating a method of generating an n-th row and an n-th column when a planar mode is performed according to an embodiment of the present invention.
16 is a conceptual diagram illustrating a method of generating an n-th row and an n-th column when an enhanced planar mode is performed according to an embodiment of the present invention.
17 is a conceptual diagram illustrating a prediction method according to an improved planar mode according to an embodiment of the present invention.
18 is a conceptual diagram illustrating a prediction method according to a planar mode according to an embodiment of the present invention.
19 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
20 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
21 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
22 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
23 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
24 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.
25 is a conceptual diagram illustrating an improved planar mode prediction method according to an embodiment of the present invention.
26 is a conceptual diagram illustrating a method of performing a planar mode when a 2n-th left reference pixel or a 2n-th upper reference pixel does not exist according to an embodiment of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

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

When a component is referred to as being “connected” or “connected” to another component, it is understood that the other component may be directly connected or connected to the other component, but other components may exist in between. it should be On the other hand, when it is mentioned that a certain element is "directly connected" or "directly connected" to another element, it should be understood that no other element is present in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

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

Referring to FIG. 1 , the image encoding apparatus 100 includes a picture division unit 105 , a prediction unit 110 , a transform unit 115 , a quantization unit 120 , a rearrangement unit 125 , and an entropy encoding unit 130 . , an inverse quantization unit 135 , an inverse transform unit 140 , a filter unit 145 , and a memory 150 .

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

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

The picture divider 105 may divide the input picture into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture splitter 105 divides one picture into a combination of a plurality of coding units, prediction units, and transformation units, and combines one coding unit, prediction unit, and transformation unit based on a predetermined criterion (eg, a cost function). can be selected to encode the picture.

For example, one picture may be divided into a plurality of coding units. In order to split a coding unit in a picture, a recursive tree structure such as a quad tree structure may be used. A coding unit that is split into other coding units using one image or the largest coding unit as a root is split coding. It can be divided with as many child nodes as the number of units. A coding unit that is no longer split according to certain restrictions becomes a leaf node. That is, when it is assumed that only square splitting is possible for one coding unit, one coding unit may be split into up to four different coding units.

Hereinafter, in an embodiment of the present invention, the meaning of a coding unit may be used not only as a unit for encoding but also as a unit for decoding.

A prediction unit has a shape such as at least one square or rectangle of the same size within one coding unit, and the shape of one prediction unit among the split prediction units within one coding unit is different from that of another prediction unit. It can be divided into shapes.

When the prediction unit for performing intra prediction based on the coding unit is not the minimum coding unit, intra prediction may be performed without dividing the prediction unit into a plurality of prediction units (NxN).

The prediction unit 110 may include an inter prediction unit performing inter prediction and an intra prediction unit performing intra prediction. Whether to use inter prediction or to perform intra prediction for a prediction unit may be determined, and specific information (eg, intra prediction mode, motion vector, reference picture, etc.) according to each prediction method may be determined. In this case, a processing unit in which prediction is performed and a processing unit in which a prediction method and specific content are determined may be different. For example, a prediction method and a prediction mode may be determined in a prediction unit, and prediction may be performed in a transformation unit. A residual value (residual block) between the generated prediction block and the original block may be input to the transform unit 115 . In addition, prediction mode information, motion vector information, etc. used for prediction may be encoded by the entropy encoder 130 together with a residual value and transmitted to a decoder. When a specific encoding mode is used, it is also possible to encode the original block as it is without generating the prediction block through the prediction unit 110 and transmit it to the decoder.

The inter prediction unit may predict a prediction unit based on information on at least one of a picture before or after a picture of the current picture. The inter prediction unit may include a reference picture interpolator, a motion prediction unit, and a motion compensator.

The reference picture interpolator may receive reference picture information from the memory 150 and generate pixel information of integer pixels or less in the reference picture. In the case of luminance pixels, a DCT-based 8-tap interpolation filter (DCT-based Interpolation Filter) with different filter coefficients may be used to generate pixel information of integer pixels or less in units of 1/4 pixels. In the case of the color difference signal, a DCT-based 4-tap interpolation filter in which filter coefficients are different to generate pixel information of integer pixels or less in units of 1/8 pixels may be used.

The motion prediction unit may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating the motion vector, various methods such as Full search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) may be used. 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 may predict the current prediction unit by using a different 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 may be used.

Hereinafter, in an embodiment of the present invention, a method of constructing a candidate prediction motion vector list when performing inter prediction using the AMVP method is disclosed.

The intra prediction unit may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If the neighboring block of the current prediction unit is a block on which inter prediction is performed, and thus the reference pixel is a pixel on which inter prediction is performed, the reference pixel included in the block on which the inter prediction is performed is subjected to intra prediction. It can be used by replacing the reference pixel information of the block. That is, when the reference pixel is not available, the unavailable reference pixel information may be replaced with 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 directional information is not used when prediction is performed. A mode for predicting luminance information may be different from a mode for predicting chrominance information, and to predict color difference information, information on an intra prediction mode from which the luminance information is predicted or information on a predicted luminance signal may be used.

If the size of the prediction unit and the size of the transformation unit are the same when performing in-screen prediction, the prediction unit for the prediction unit is based on the pixel on the left, the pixel on the upper left, and the pixel on the top of the prediction unit. Although prediction is performed, when the size of the prediction unit is different from the size of the transformation unit when intra prediction is performed, the intra prediction may be performed using a reference pixel based on the transformation unit. In addition, intra prediction using NxN splitting may be used only for the smallest coding unit.

The intra prediction method may generate a prediction block after applying a Mode Dependent Intra Smoothing (MDIS) filter to a reference pixel according to a prediction mode. The type of MDIS 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 may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When predicting the prediction mode of the current prediction unit using the mode information predicted from the neighboring prediction unit, when the intra-screen prediction mode of the current prediction unit and the neighboring prediction unit are the same, the current prediction unit and the current prediction unit using predetermined flag information Information that the prediction modes of the neighboring prediction units are the same may be transmitted, and if the prediction modes of the current prediction unit and the neighboring prediction units are different, entropy encoding may be performed to encode the prediction mode information of the current block.

In addition, a residual block including residual information, which is a difference value between a prediction unit and an original block of the prediction unit, in which prediction is performed based on the prediction unit generated by the prediction unit 110 may be generated. The generated residual block may be input to the transform unit 115 . The transform unit 115 converts the residual block including the original block and the residual information of the prediction unit generated by the prediction unit 110 to a transform method such as DCT (Discrete Cosine Transform) or DST (Discrete Sine Transform). can be used to convert Whether DCT or DST is applied to transform the residual block may be determined based on intra prediction mode information of a prediction unit used to generate the residual block.

The quantizer 120 may quantize the values transformed by the transform unit 115 into the frequency domain. The quantization coefficient may change according to blocks or the importance of an image. The value calculated by the quantization unit 120 may be provided to the inverse quantization unit 135 and the rearrangement unit 125 .

The rearrangement unit 125 may rearrange the coefficient values on the quantized residual values.

The reordering unit 125 may change the two-dimensional block form coefficient into a one-dimensional vector form through a coefficient scanning method. For example, the rearrangement unit 125 may scan from DC coefficients to coefficients in a high frequency region using a zig-zag scan method and may change it into a one-dimensional vector form. Depending on the size of the transform unit and the intra prediction mode, a vertical scan method that scans two-dimensional block shape coefficients in the column direction, and a horizontal scan method that scans two-dimensional block shape coefficients in the row direction, rather than the zig-zag scan method, will be used. can That is, according to the size of the transform unit and the intra prediction mode, it is possible to determine which scan method among the zigzag scan, the vertical scan, and the horizontal scan is to be used.

The entropy encoding unit 130 may perform entropy encoding based on the values calculated by the reordering unit 125 . For entropy encoding, various encoding methods such as Exponential Golomb, Variable Length Coding (VLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be used.

The entropy encoding unit 130 receives the residual value coefficient information and block type information of the coding unit, prediction mode information, division unit information, prediction unit information and transmission unit information, and motion vector information from the reordering unit 125 and the prediction unit 110 . , reference frame information, block interpolation information, filtering information, etc. can be encoded.

The entropy encoder 130 may entropy-encode the coefficient values of the coding units input from the reordering unit 125 .

The inverse quantizer 135 and the inverse transform unit 140 inversely quantize the values quantized by the quantizer 120 and inversely transform the values transformed by the transform unit 115 . The residual value generated by the inverse quantizer 135 and the inverse transform unit 140 is combined with a prediction unit predicted through the motion estimator, the motion compensator, and the intra prediction unit included in the prediction unit 110 to a reconstructed block ( Reconstructed Block) can be created.

The filter unit 145 may include at least one of a deblocking filter, an offset correcting unit, and an adaptive loop filter (ALF).

The deblocking filter 145 may remove block distortion caused by a boundary between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply the deblocking filter to the current block based on pixels included in several columns or rows included in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter can be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, when vertical filtering and horizontal filtering are performed, horizontal filtering and vertical filtering may be processed in parallel.

The offset correcting unit may correct an offset from the original image in units of pixels with respect to the image on which the deblocking has been performed. In order to perform offset correction on a specific picture, a method of dividing pixels included in an image into a certain number of regions, determining the region to be offset and applying the offset to the region, or taking edge information of each pixel into consideration can be used to apply

An adaptive loop filter (ALF) may perform filtering based on a value obtained by comparing 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 corresponding group is determined, and filtering can be performed differentially for each group. As for information related to whether to apply the ALF, the luminance signal may be transmitted for each coding unit (CU), and the size and coefficient of the ALF to be applied may vary according to each block. The ALF may have various forms, and the number of coefficients included according to the filter may also vary. Such ALF filtering-related information (filter coefficient information, ALF On/Off information, filter type information) may be transmitted while being included in a predetermined parameter set in the bitstream.

The memory 150 may store the reconstructed block or picture calculated through the filter unit 145 , and the stored reconstructed block or picture may be provided to the prediction unit 110 when inter prediction is performed.

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

Referring to FIG. 2 , the image decoder 200 includes an entropy decoding unit 2110 , a reordering unit 215 , an inverse quantization unit 220 , an inverse transform unit 225 , a prediction unit 230 , and a filter unit 235 . , the memory 240 may be included.

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

The entropy decoding unit 210 may perform entropy decoding in a procedure opposite to that performed by the entropy encoding unit of the image encoder, and the residual value obtained by performing entropy decoding in the entropy decoding unit is input to the reordering unit 215 . can be

The entropy decoder 210 may decode information related to intra prediction and inter prediction performed by the encoder. As described above, if there are certain restrictions when performing intra prediction and inter prediction in the video encoder, entropy decoding is performed based on these restrictions to provide information related to intra prediction and inter prediction for the current block. can receive

The reordering unit 215 may perform reordering based on a method of rearranging the entropy-decoded bitstream by the entropy decoding unit 210 by the encoder. Coefficients expressed in the form of a one-dimensional vector may be restored and rearranged as coefficients in the form of a two-dimensional block. The reordering unit may receive information related to coefficient scanning performed by the encoder and perform the rearrangement by performing a reverse scanning method based on the scanning order performed by the corresponding encoder.

The inverse quantizer 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the reordered coefficient values of the 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. Inverse transform may be performed based on a transmission unit determined by the image encoder. In the transform unit of the video encoder, DCT and DST may be selectively performed according to a plurality of pieces of information, such as a prediction method, the size of the current block, and the prediction direction. Inverse transformation may be performed based on the converted transformation information.

When performing the transformation, the transformation may be performed based on the coding unit instead of the transformation unit.

The prediction unit 230 may generate a prediction block based on the prediction block generation related information provided from the entropy decoding unit 210 and previously decoded block or picture information provided from the memory 240 .

As described above, when the size of the prediction unit and the size of the transformation unit are the same when intra prediction is performed in the same manner as in the operation in the image encoder, the pixel present on the left side of the prediction unit, the pixel present on the upper left side, and the upper In-screen prediction of the prediction unit is performed based on the existing pixel, but when the size of the prediction unit and the size of the transformation unit are different when performing intra prediction, the reference pixel based on the transformation unit is used in the screen prediction can be made. In addition, intra prediction using NxN splitting may be used only for the smallest coding unit.

The prediction unit 230 may include a prediction unit determiner, an inter prediction unit, and an intra prediction unit. The prediction unit determining unit receives various information such as prediction unit information input from the entropy decoder, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and divides the prediction unit from the current coding unit, and the prediction unit It is possible to determine whether to perform inter prediction or intra prediction. The inter prediction unit uses information necessary for inter prediction of the current prediction unit provided from the image encoder to determine the current prediction unit based on information included in at least one of the pictures before or after the current picture including the current prediction unit. Inter-screen prediction can be performed for

Whether a method of predicting a motion of a prediction unit included in a corresponding coding unit based on a coding unit to perform inter prediction is a skip mode, a merge mode, or an AMVP mode can be judged

Hereinafter, in an embodiment of the present invention, a method of constructing a candidate prediction motion vector list when performing inter prediction using the AMVP method is disclosed.

The intra prediction unit may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit on which intra prediction is performed, intra prediction may be performed based on intra prediction mode information of the prediction unit provided from the image encoder. The intra prediction unit may include an MDIS filter, a reference pixel interpolator, and a DC filter. The MDIS filter is a part that performs filtering on the reference pixel of the current block, and can be applied by determining whether to apply the filter according to the prediction mode of the current prediction unit. MDIS filtering may be performed on the reference pixel of the current block by using the prediction mode and MDIS filter information of the prediction unit provided by the image encoder. When the prediction mode of the current block is a mode in which MDIS filtering is not performed, the MDIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit in which intra prediction is performed based on a pixel value obtained by interpolating the reference pixel, the reference pixel interpolator may interpolate the reference pixel to generate a reference pixel of a pixel unit having an integer value or less. When the prediction mode of the current prediction unit is a prediction mode that generates a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter may generate the prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 235 . The filter unit 235 may include a deblocking filter, an offset correcting unit, and an ALF.

Information on whether a deblocking filter is applied to the corresponding block or picture and information on whether a strong filter or a weak filter is applied when the deblocking filter is applied may be provided from the video encoder. The deblocking filter of the image decoder may receive deblocking filter-related information provided from the image encoder, and the image decoder may perform deblocking filtering on the corresponding block. As in the video encoder, vertical deblocking filtering and horizontal deblocking filtering are first performed, but at least one of vertical deblocking and horizontal deblocking may be performed on an overlapping portion. In a portion where vertical deblocking filtering and horizontal deblocking filtering overlap, vertical deblocking filtering or horizontal deblocking filtering that has not been previously performed may be performed. Parallel processing of deblocking filtering is possible through this deblocking filtering process.

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

The ALF may perform filtering based on a value obtained by comparing the reconstructed image and the original image after filtering. ALF may be applied to a coding unit based on information on whether ALF is applied or not, ALF coefficient information, etc. provided from the encoder. Such ALF information may be provided by being included in a specific parameter set.

The memory 240 may store the reconstructed picture or block to be used as a reference picture or reference block, and may also provide the reconstructed picture to an output unit.

As described above, hereinafter, in the embodiment of the present invention, a coding unit is used as a term for a coding unit for convenience of description, but it may also be a unit for performing decoding as well as coding.

Also, an image encoding method and an image decoding method, which will be described later in an embodiment of the present invention, may be performed by each component included in the image encoder and image decoder described above with reference to FIGS. 1 and 2 . The meaning of the constituent part may include not only a hardware meaning but also a software processing unit that may be performed through an algorithm.

Hereinafter, the intra prediction method according to an embodiment of the present invention may be used instead of the existing intra prediction method or may be selectively used with the existing intra prediction mode based on flag information. Hereinafter, the intra prediction mode according to the embodiment of the present invention may be referred to as an advanced intra prediction mode (AIP). Advanced_intra_pred_flag information, which is information on whether to predict using a general prediction method other than the prediction mode (AIP), can be transmitted by being included in a sequence parameter set (SPS) or picture parameter set (PPS) or a constant higher syntax structure such as a slice header. have. The AIP mode may be transmitted for a luminance signal or a chrominance signal, respectively, for a luminance signal, through advanced_intra_pred_flag, and for a chrominance signal, through advanced_intra_pred_chroma_flag.

3 illustrates a prediction unit and a reference pixel according to an embodiment of the present invention.

Referring to FIG. 3 , hereinafter, in an embodiment of the present invention, a reference pixel may be classified into an upper reference pixel 300 , an upper left reference pixel 310 , and a left reference pixel 320 .

If the size of the block is nxn and the number of upper reference pixels is n, the first reference pixel among the upper reference pixels is the first upper reference pixel, the rightmost pixel is the nth upper reference pixel, and among the left reference pixels The uppermost pixel may be referred to as a first left reference pixel, and the lowermost pixel may be referred to as an nth left reference pixel. In this way, the n+1-th pixel sequentially located immediately to the right of the n-th upper reference pixel is referred to as an n+1-th upper reference pixel 330 , and the 2n-th pixel is referred to as a 2n-th upper reference pixel 340 . Similarly, an n+1-th pixel located immediately below the n-th left reference pixel is referred to as an n+1-th left reference pixel 350 , and a pixel located 2n-th is referred to as a 2n-th lower reference pixel 360 .

The prediction unit may be expressed as a first row to an n-th row and a first column to an n-th column for each column and row based on the row and column including the pixel.

4 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.

Referring to FIG. 4 , in order to perform intra prediction using the DC mode, the lower right pixel 410 is set as a DC prediction value ( 400 ).

A DC prediction value may be calculated using the average value of the upper reference pixel, the left reference pixel, and the upper left pixel of the prediction unit, and this value may be used as the predicted value of the lower right pixel 410 .

The predicted value of the nth column is calculated using the lower right pixel 410 and the nth upper reference pixel 423 , and the predicted value of the nth row is calculated using the lower right pixel 410 and the nth left reference pixel 426 . may (420).

Bidirectional linear prediction is performed to calculate prediction values of pixels included in the remaining prediction units except for the n-th row and the n-th column ( 440 ).

That is, pixels included in the remaining prediction units except for the nth row and the nth column are the upper reference pixel 445 positioned above the vertical direction and the pixel 450 from the nth row positioned below the horizontal direction to the left in the horizontal direction. A prediction value of the pixel may be generated by performing linear prediction on the reference pixel 455 and the pixel 460 in the n-th column to the right in the horizontal direction.

5 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.

Referring to FIG. 5 , a lower right pixel 520 is generated using the average of the upper left reference pixel 505 , the nth upper reference pixel 510 , and the nth left reference pixel 515 ( 500 ).

The generated lower right pixel 520 and the nth upper reference pixel 525 are interpolated to generate a predicted value of the pixel 530 included in the nth column, and the generated lower right pixel 520 and the nth left reference pixel 535 are generated. ) to generate a predicted value of the pixel 537 included in the n-th row ( 540 ).

By performing linear interpolation, a predicted value of the pixel included in the n-th column can be generated by giving a constant weight to the lower-right pixel 520 and the n-th upper-right reference pixel 525 according to the distance, and similarly to the lower-right pixel 520 . and the nth lower left reference pixel 535 may be interpolated to generate a predicted value of the pixel included in the nth row.

Based on the predicted values of the upper reference pixel 545 and the left reference pixel 550 located in the vertical upper direction, the predicted value of the pixel 555 included in the generated n-th row, and the predicted value of the pixel 557 included in the n-th column, bidirectional linear Prediction is performed to predict prediction values of pixels included in the remaining prediction units except for the n-th row and the n-th column ( 560 ).

6 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.

Referring to FIG. 6 , the lower right pixel is set as a DC prediction value ( 600 ).

The lower right pixel 610 may generate a DC prediction value by calculating an average value of the upper reference pixel, the left reference pixel, and the upper left pixel.

The nth upper reference pixel 615 and the lower right pixel 610 are interpolated to generate a predicted value of the pixel included in the nth column, and the nth left reference pixel 617 and the lower right reference pixel 610 are interpolated to generate the nth A prediction value of a pixel included in a row may be generated ( 620 ).

Predicted values of pixels included in the remaining prediction units except for the nth row and nth column are generated based on the reference pixel values existing in the diagonal direction and the predicted pixel values of the nth row and nth column ( 640 ).

Linear interpolation is performed using the existing reference pixel value and the predicted pixel values of the n-th row and the n-th column by performing linear interpolation using one pixel at the upper right and one pixel at the lower left in the oblique direction. A first prediction value of the remaining pixels included in the prediction unit except for the n-th column may be generated.

The second prediction value ( 670) is created (660).

A pixel 675 that is one pixel above the current prediction pixel in the vertical direction, a pixel 680 that is one pixel below the vertical direction of the current prediction pixel, and one pixel to the left horizontally to the left of the current prediction pixel. A second prediction value 670 may be generated by interpolating the pixel 685 and the pixel 690 existing one pixel to the right in the horizontal direction of the current prediction pixel.

7 is a conceptual diagram illustrating an intra prediction method using an improved DC mode according to an embodiment of the present invention.

Referring to FIG. 7 , a lower right pixel 710 is generated by using the average of the upper left reference pixel 703 , the nth upper reference pixel 706 , and the nth left reference pixel 709 ( S700 ).

The n-th upper reference pixel 706 and the lower right pixel 710 are interpolated to generate a predicted value 713 of the pixel included in the n-th column, and the n-th left reference pixel 709 and the lower right reference pixel 710 are interpolated. Thus, a predicted value of the pixel 715 included in the n-th row may be generated ( 720 ).

Prediction values of pixels included in the remaining prediction units excluding the nth row and nth column are generated based on the reference pixel values existing in the oblique direction and the predicted pixel values of the nth row and nth column ( S740 ).

Among the reference pixel values and the predicted pixel values of the n-th row and the n-th column, one pixel present in the upper right and one pixel present in the lower left in a diagonal direction (eg, 45 degrees) are used. Interpolation may be performed to generate a first prediction value of a pixel included in the remaining prediction units except for the n-th row and the n-th column.

A second prediction value is obtained by performing bi-directional linear prediction using two horizontal pixels and two vertical pixels existing around the first prediction value of pixels included in the remaining prediction units except for the nth row and the nth column. create (760).

Pixels 745 one pixel above the current prediction pixel in the vertical direction, pixels 745 below the current prediction pixel vertically down, and one pixel to the left horizontally of the current prediction pixel. A second prediction value 770 may be generated by interpolating the pixel 755 and a pixel 757 that is one pixel to the right of the current prediction pixel in the horizontal direction.

8 is a conceptual diagram illustrating an improved vertical intra-screen prediction method according to an embodiment of the present invention.

Referring to FIG. 8 , a value obtained by averaging the n-th left reference pixel 810 and each upper reference pixel value is inserted into the n-th row ( 800 ).

Each pixel included in the n-th row may be an average value of the pixel included in the same column among the upper reference pixels and the n-th lower left reference pixel.

A pixel included in the n-th row and the upper reference pixel value are interpolated to generate predicted values of pixels included in the remaining rows except for the n-th row ( 850 ).

By using this method, it is possible to express pixel value information that is linearly changed in units of rows.

9 is a conceptual diagram illustrating an improved horizontal intra-screen prediction method according to an embodiment of the present invention.

Referring to FIG. 9 , a pixel value obtained by averaging the n+1th upper reference pixel and each left reference pixel value is inserted into the nth column ( 900 ).

Each pixel included in the n-th column may be an average value of a pixel included in the same row among left reference pixels and an n+1-th upper right reference pixel.

As another method, a pixel value obtained by averaging the n-th upper reference pixel and each left reference pixel value may be inserted into the n-th column ( 925 ).

That is, each pixel included in the n-th column may be the average value of the pixel included in the same row among the left reference pixels and the n-th upper right reference pixel.

Predicted values of pixels included in the remaining rows except for the n-th column are generated by interpolating the pixel included in the n-th column and the upper reference pixel value ( S950 ).

By using this method, it is possible to express pixel value information that changes in units of rows.

10 is a conceptual diagram illustrating a method of calculating a prediction unit through the enhanced planar mode according to an embodiment of the present invention.

Referring to FIG. 10 , in order to perform intra-screen prediction using the planar mode, the predicted value of the lower right pixel 1000 is obtained. The calculated predicted value of the lower right pixel 1000 and the interpolated value obtained by interpolating the n-th left reference pixel 1010 are used as the predicted value of the pixel included in the n-th row, and the calculated predicted value of the lower-right pixel 1000 and the second An interpolated value of the n upper reference pixel 1020 may be used as a predicted value of a pixel included in the nth column.

Bi-directional interpolation is performed based on the upper reference pixel, the left reference pixel, the upper left reference pixel, and the pixel prediction values of the n-th column and the n-th row generated in the above-mentioned step to obtain the remaining prediction units except for the n-th row and the n-th column. A predicted value of the included pixel may be calculated.

In this case, the lower right pixel may be calculated in various ways. 11 to 14 show a method of calculating a lower right pixel value according to an embodiment of the present invention.

11 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.

Referring to FIG. 11 , the lower right pixel may be calculated as an average value of the n-th left reference pixel 1100 and the n-th upper reference pixel 1110 .

That is, the calculation complexity can be reduced by using a method of calculating the lower right pixel value using only two pixel values.

12 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.

Referring to FIG. 12 , the lower right pixel may be calculated as an average value of the 2n-th upper reference pixel 1200 and the 2n-th left reference pixel 1210 .

That is, unlike the conventional method, the lower right pixel value can be calculated using only two pixel values.

When the prediction unit is located at the edge and the 2n-th upper reference pixel 1200 and the 2n-th left reference pixel 1210 do not exist, as shown in FIG. 11 , refer to the n-th lower-left reference pixel and the n-th upper-right reference pixel You can use the pixel value to generate the bottom right pixel, or you can use another method to generate the bottom right pixel.

13 is a conceptual diagram illustrating a method of calculating a lower right pixel in an improved planar mode intra-screen prediction method according to an embodiment of the present invention.

Referring to FIG. 13 , the lower right pixel includes an upper average pixel 1320 and an n-th left reference pixel 1330 generated based on the average value of the n-th upper reference pixel 1300 and the 2n-th upper reference pixel 1310 , and An average value of the 2n-th left reference pixel 1340 may be calculated using the calculated left average pixel 1350 .

That is, the lower right pixel may be calculated based on the average value of the upper average pixel 1320 and the left average pixel 1350 .

When the prediction unit is located at the edge and the corresponding pixel does not exist, as shown in FIG. 11 , the lower right pixel is generated using the nth lower left reference pixel and the nth upper right reference pixel, or the lower right pixel is generated using another method. You can create the right pixel.

14 is a conceptual diagram illustrating a method of generating a lower right pixel in an enhanced planar mode according to an embodiment of the present invention.

Referring to FIG. 14 , an upper middle pixel 1420 , an n-th left reference pixel 1430 , and a 2n-th left reference pixel 1440 located between the n-th upper reference pixel 1400 and the 2n-th upper reference pixel 1410 . ), the lower right pixel 1460 may be generated using the average value of the left middle pixel 1450 located in the middle. The middle pixel is the n+n/2-th or (n+n/2)+1-th position n+n/2 top or left reference pixel, or (n+n/2)+1 top or left reference pixel It can be a pixel.

When the prediction unit is located in the edge portion and the corresponding pixel does not exist, the lower right pixel is generated using the nth lower left reference pixel and the nth upper right reference pixel value, or the reference pixel is generated using another lower right pixel generation method. can be predicted.

15 to 16 are conceptual diagrams illustrating a method of generating by interpolating an n-th row and an n-th column included in a prediction unit in performing the enhanced planar prediction mode.

15 is a conceptual diagram illustrating a method of generating an n-th row and an n-th column when a planar mode is performed according to an embodiment of the present invention.

Referring to FIG. 15 , pixels included in the nth column except for the lower right pixel may generate a predicted value by copying pixels from the n+1th upper reference pixel to the 2n−1th upper reference pixel.

In addition, pixels included in the nth row except for the lower right pixel may generate a predicted value by copying pixels from the n+1th left reference pixel to the 2n−1th left reference pixel. The lower right pixel is the upper 2nth pixel. A predicted value may be generated by generating an average value of the pixel and the left 2n-th pixel.

16 is a conceptual diagram illustrating a method of generating an n-th row and an n-th column when an enhanced planar mode is performed according to an embodiment of the present invention.

Referring to FIG. 16 , in the nth column, a pixel from an n+1th upper reference pixel to a 2n-1th upper reference pixel and a pixel from an n+1th left reference pixel to a 2n−1th left reference pixel are defined as distances. Accordingly, pixels generated with linearly predicted values can be used as predicted values. For example, the second pixel 1600 in the n-th column may generate a predicted value of the corresponding pixel by performing linear interpolation of the n+2th upper reference pixel and the n+2th left reference pixel.

Similarly, in the nth row, the pixel from the n+1th upper reference pixel to the 2n-1th upper reference pixel and the pixel from the n+1th left reference pixel to the 2n-1th left reference pixel are linearly predicted according to the distance. You can use the pixels generated by the values as predictions. For example, the second pixel in the n-th row may generate a predicted value of the corresponding pixel by performing linear interpolation of the n+2th upper reference pixel and the n+2th left reference pixel.

By using the above-described method, prediction according to the planar mode may be performed after generating predicted pixel values in the n-th row and n-th column to be more influenced by pixel values that are closer in distance.

17 is a conceptual diagram illustrating a prediction method according to an improved planar mode according to an embodiment of the present invention.

Referring to FIG. 17 , four pixels may be used to generate a prediction value of a pixel included in a prediction unit.

The first pixel 1700 may be one of the n-th upper reference pixels in the first upper reference pixel positioned above the prediction target pixel in the vertical direction. The second pixel 1720 is a pixel located vertically below the prediction target pixel and may be a value obtained by copying the 2n-th lower left reference pixel 1725 .

The third pixel 1740 may be one of the n-th left reference pixels in the first left reference pixel positioned to the left of the prediction target pixel in the horizontal direction. The fourth pixel 1760 is a pixel located to the right in the horizontal direction of the prediction target pixel and may be a value obtained by copying the 2n-th upper right reference pixel 1765 .

The planar prediction method according to an embodiment of the present invention may generate a prediction value of a pixel included in a prediction unit by using a method of bidirectional linear interpolation of the first to fourth pixels.

18 is a conceptual diagram illustrating a prediction method according to a planar mode according to an embodiment of the present invention.

Referring to FIG. 18 , when prediction according to the planar mode is performed, a predicted value of a prediction unit may be generated by giving a weight of a predetermined ratio to a horizontal direction predicted value and a vertical direction predicted value.

The horizontally predicted value may be a value obtained by interpolating a value located in the same row as the prediction target pixel among the left reference pixels and the nth upper reference pixel ( 1800 ).

The vertical direction predicted value may be a value obtained by interpolating a value located in the same column as the prediction target pixel among the upper reference pixels and the nth left reference pixel ( 1850 ).

A predicted value may be generated by multiplying the horizontal direction predicted value and the vertical direction predicted value by respective weights.

Equation 1 below generates a predicted value based on a weight value.

Referring to Equation 1, a predicted value may be generated by giving a larger weight to the closer direction according to which direction is relatively close to the horizontal direction or the vertical direction.

19 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to FIG. 19 , when enhanced DC mode prediction is performed, upper reference pixels and left reference pixels are used to minimize discontinuity with neighboring prediction units. can be copied and used. The pixel value located in the first row and column 1 may be a value calculated using the first pixel value of the upper reference pixel, the first pixel value of the left reference pixel, or the first pixel value of the upper reference pixel and the first pixel value of the left reference pixel . Prediction values of pixel values remaining except for the first row and the first column may be generated by performing intra prediction using the DC mode using the values of the first row and the first column of the prediction unit.

20 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to the left side of FIG. 20 , in performing the enhanced DC mode prediction, a first upper reference pixel that is a first pixel among upper reference pixels, an n-th upper reference pixel that is an n-th pixel, and a first left one that is a first pixel among left reference pixels A prediction pixel may be generated by calculating an average value of the reference pixel and the n-th left reference pixel, which is the n-th pixel. That is, calculation complexity can be reduced when performing intra prediction through a method of calculating the predicted value of the pixel included in the prediction unit using only some pixels among the reference pixels.

Referring to the right side of FIG. 20 , in performing DC mode prediction, the average value of the n-th upper reference pixel that is the n-th pixel among the upper reference pixels, the n-th left reference pixel that is the n-th pixel among the left reference pixels, and the average value of the upper left reference pixel can be calculated to generate a prediction pixel. That is, as on the left side of FIG. 20 , calculation complexity can be reduced by using only some of the reference pixels.

21 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to FIG. 21 , the improved DC mode prediction method fills the first column and the first row with DC prediction values calculated using reference pixels ( 2100 ).

The DC predicted value included in the first row and the first column may be an average value of the upper reference pixel, the upper left reference pixel, and the left reference pixel.

Filtering is performed using the upper reference pixel, the left reference pixel, and the upper left reference pixel ( 2120 ).

Filtering may be performed on the pixels included in the first column and the first row except for the pixel positioned in the first row included in the prediction unit by using the reference pixel and the 2-tap filter. Pixels located in the first row and first column in the prediction unit may be filtered based on the first upper reference pixel and the first left reference pixel using a 3-tap filter.

DC mode prediction is performed based on the filtered pixels included in the first column and the first row to generate a predicted value of the pixel included in the prediction unit ( 2140 ). Prediction using the DC mode may be performed using the filtered average value of pixels located in the first column and the first row.

22 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to FIG. 22 , pixel values included in the first row and first column of the prediction unit may be predicted by performing intra prediction using the DC mode based on the reference pixel ( 2200 ).

The predicted value in the DC mode screen may be an average value of the upper reference pixel, the upper left reference pixel, and the left reference pixel as shown in FIG. 21 .

Filtering is performed using the upper reference pixel, the left reference pixel, the upper left reference pixel, the generated first row, and the pixel included in the first column ( 2220 ).

The predicted first column and the first row may be filtered with a reference filter value using a 2-tap filter. Pixels located in the first row and first column may be filtered based on the first upper reference pixel and the first left reference pixel using a 3-tap filter.

For the pixel values included in the remaining prediction units except for the first row and the first column, a prediction value may be generated by calculating an average value of pixel values located at the upper end of the pixel and at the left side of the pixel ( 2240 ).

23 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to FIG. 23 , the upper reference pixel and the left reference pixel are used as prediction pixels of the prediction unit ( 2300 ). The upper reference pixel and the left reference pixel may be used as prediction values of pixels included in the first column and first row of the prediction unit.

The pixel value of the first row and first column may be a predicted value calculated based on at least one of the first left reference pixel value and the first upper reference pixel value.

The values of the remaining prediction units except for the pixel values included in the first row and the first column may be subjected to DC mode prediction based on the pixel values of the first row and first column to calculate a first predicted value ( 2320 ).

The prediction values of the remaining prediction units except for the pixel values included in the first row and the first column are average values of the pixel values located on the left and upper sides of the prediction pixel to generate a second prediction value again ( 2340 ).

24 is a conceptual diagram illustrating an improved DC mode prediction method according to an embodiment of the present invention.

Referring to FIG. 24 , a DC mode prediction value is calculated using a reference pixel.

A DC prediction value may be calculated by calculating an average of the values of the upper reference pixel, the upper left reference pixel, and the left reference pixel.

Equation 2 below shows a method of calculating a predicted value using the DC mode.

For each reference pixel, a deviation value between the predicted value using the DC mode and the reference pixel value may be calculated. Equation 3 below shows a reference pixel value and a predicted value using the DC mode.

The predicted value of the pixel included in the prediction unit may be calculated by using the DC prediction value calculated in Equation 2 and the average value of each of the x-direction deviations and the y-direction deviations obtained in Equation 3 .

By performing the prediction in this way, it is possible to reflect the characteristics of the column and row by adding or subtracting deviation values from the corresponding column and the corresponding row to the DC predicted value.

25 is a conceptual diagram illustrating an improved planar mode prediction method according to an embodiment of the present invention.

Referring to FIG. 25 , in performing the planar prediction mode, a pixel 2500 included in an upper reference pixel existing in a vertical direction included in the same column as the current prediction pixel and a 2n-th left reference pixel that is a 2n-th reference pixel in the left reference pixel Vertical interpolation may be performed using the reference pixel 2510 . In addition, horizontally using the left reference pixel value 2520 included in the same row as the current prediction pixel existing on the left side of the current prediction pixel in the horizontal direction and the 2n-th upper reference pixel 2530 that is the 2n-th reference pixel in the upper reference pixel Interpolation can be performed.

If the 2n-th left reference pixel 2510 or the 2n-th upper reference pixel 2530 does not exist, horizontal interpolation or vertical interpolation may be performed using the n-th left reference pixel or the n-th upper reference pixel.

26 is a conceptual diagram illustrating a method of performing a planar mode when a 2n-th left reference pixel or a 2n-th upper reference pixel does not exist according to an embodiment of the present invention.

The left side of FIG. 26 shows a case in which at least one of the 2n-th left reference pixel and the 2n-th upper reference pixel does not exist.

When the 2n-th left reference pixel does not exist, interpolation may be performed using the n-th left reference pixel instead of the 2n-th left reference pixel. When the 2n-th upper reference pixel does not exist, interpolation may be performed using the n-th upper reference pixel instead of the 2n-th upper reference pixel.

The right side of FIG. 26 shows a case in which the 2n-th left reference pixel and the 2n-th upper reference pixel do not exist. When the 2n-th left reference pixel and the 2n-th upper reference pixel do not exist, the planar mode may be performed using the n-th left pixel and the n-th right reference pixel.

The image encoding and image decoding methods described above may be implemented in each component of each of the image encoder and image decoder apparatuses described above with reference to FIGS. 1 and 2 .

Although it has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. will be able

Claims (7)

In the video encoding method,
determining an intra prediction mode of the current block as a planar mode;
generating prediction mode information for the intra prediction mode;
deriving four peripheral reference samples for the current block in the planar mode;
deriving a prediction sample in the current block using the four neighboring reference samples;
deriving residual information based on the prediction sample; and
Encoding video information including the prediction mode information and the residual information,
The four peripheral reference samples are
a first sample at the same position as the x-coordinate of the prediction sample and a second sample at an x-coordinate position greater than the largest x-coordinate within the current block, among samples around the upper side of the current block; and
Among the samples around the left of the current block, a third sample at the same position as the y-coordinate of the prediction sample and a fourth sample at a y-coordinate position greater than the largest y-coordinate in the current block are included. video encoding method. According to claim 1,
The current block is a block of size n Х n (n is an integer),
The second sample is any one of the n+1th sample to the 2nth sample in the x-axis direction among upper neighboring samples of the current block;
The fourth sample is any one of an n+1th sample to a 2nth sample in a y-axis direction among left neighboring samples of the current block. 3. The method of claim 2,
The second sample is a 2nth sample among the upper peripheral samples,
and the fourth sample is a 2nth sample among the left neighboring samples. According to claim 1,
The prediction sample is an image encoding method, characterized in that the prediction sample is derived by bi-directional interpolation according to a distance based on the first to fourth samples from the position of the prediction sample. 5. The method of claim 4,
An image characterized in that a weight is added to the values of the samples used for the bidirectional interpolation according to the distances, and a greater weight is applied to a sample closer to the location of the prediction sample among the first to fourth samples encoding method. A video encoding apparatus comprising:
Determine the intra prediction mode of the current block as the planar mode, generate prediction mode information for the intra prediction mode, derive 4 surrounding reference samples for the current block that is the planar mode, and the 4 surrounding reference a prediction unit for deriving a prediction sample in the current block by using the samples;
a subtraction unit for deriving a residual sample based on the prediction sample;
a transform unit for deriving transform coefficients based on the residual sample;
a quantization unit for deriving a quantized transform coefficient based on the transform coefficient; and
An entropy encoding unit for encoding image information including residual information on the prediction mode information and the quantized transform coefficients,
The four peripheral reference samples are
a first sample at the same position as the x-coordinate of the prediction sample and a second sample at an x-coordinate position greater than the largest x-coordinate within the current block, among samples around the upper side of the current block; and
Among the samples around the left of the current block, a third sample at the same position as the y-coordinate of the prediction sample and a fourth sample at a y-coordinate position greater than the largest y-coordinate in the current block are included. video encoding device. A computer-readable digital storage medium storing encoded image information generated by the image encoding method of claim 1 .

Images