KR102357282B1 - Method and apparatus for encoding/decoding an image - Google Patents

Abstract

An image encoding/decoding method and apparatus according to the present invention selects at least one reference pixel line from among a plurality of reference pixel lines, and based on at least one pixel value included in the selected at least one reference pixel line A prediction value of one pixel in the current block may be derived.

Description

Image encoding/decoding method and apparatus

The present invention relates to a method and apparatus for encoding/decoding a video signal, and more particularly, to a method and apparatus for encoding/decoding an image using improved intra prediction.

Recently, the demand for multimedia data such as moving pictures is rapidly increasing on the Internet. However, it is difficult to keep up with the rapidly increasing amount of multimedia data at the rate of development of the bandwidth of the channel. In order to solve this problem, VCEG (Video Coding Expert Group) of ITU-T, an international standardization organization, and MPEG (Moving Picture Expert Group) of ISO/IEC are continuously researching improved video compression standards through joint research.

Video compression is largely composed of intra prediction, inter prediction, transformation, quantization, entropy coding, and in-loop filter. Among them, intra prediction refers to a technology of generating a prediction block for the current block using reconstructed pixels existing around the current block.

In the conventional intra prediction, fractional-position pixels are generated through an interpolation process using integer-positioned reference pixels, and a prediction block is generated using the generated fractional-position pixels. In this case, the error between the original pixel value and the predicted value is affected depending on whether reference pixels at an integer position are used and whether an interpolation method is applied.

A main object of the present invention is to improve intra prediction efficiency by performing intra prediction using a plurality of reference pixel lines in encoding/decoding an image.

A main object of the present invention is to improve intra prediction efficiency by inducing an intra prediction block using an interpolation method selected from among a plurality of interpolation methods in encoding/decoding an image.

A main object of the present invention is to provide a filtering method capable of reducing discontinuity between an intra prediction block and a neighboring region when intra prediction is performed using a plurality of reference pixel lines in encoding/decoding an image.

In an image decoding method and apparatus according to the present invention, at least one reference pixel line is selected from among a plurality of reference pixel lines, and based on the value of at least one pixel included in the selected at least one reference pixel line, the current A prediction value of one pixel in a block can be derived.

An image decoding method and apparatus according to the present invention obtains reference pixel line index information from an input bitstream, and selects the at least one reference pixel line from among the plurality of reference pixel lines based on the reference pixel line index information. You can choose.

The image decoding method and apparatus according to the present invention may select at least one reference pixel line for each pixel in the current block based on the position of each pixel in the current block.

An image decoding method and apparatus according to the present invention selects one of a plurality of interpolation methods and performs interpolation using at least one pixel included in the selected at least one reference pixel line by using the selected interpolation method. can be performed to obtain the predicted value. The selected interpolation method may be selected based on index information indicating one of a plurality of interpolation methods.

The method and apparatus for decoding an image according to the present invention may derive a prediction value of all pixels of the current block to obtain a prediction block of the current block, and filter the prediction block.

The image decoding method and apparatus according to the present invention may filter a predetermined region of the current block according to the size of the current block or an intra prediction mode of the current block.

In an image encoding method and apparatus according to the present invention, at least one reference pixel line is selected from among a plurality of reference pixel lines, and based on at least one pixel value included in the selected at least one reference pixel line, the current A prediction value of one pixel in a block can be obtained.

The image encoding method and apparatus according to the present invention may encode reference pixel line index information indicating the selected at least one reference pixel line, and include the encoded reference pixel line index information in a bitstream.

The image encoding method and apparatus according to the present invention may select at least one reference pixel line for each pixel in the current block based on the position of each pixel in the current block.

The image encoding method and apparatus according to the present invention may select at least one reference pixel line for each pixel in the current block based on the intra prediction mode of the current block.

An image encoding method and apparatus according to the present invention selects one of a plurality of interpolation methods and performs interpolation using at least one pixel included in the selected at least one reference pixel line by using the selected interpolation method. can be performed to obtain the predicted value.

An image encoding method and apparatus according to the present invention, Index information indicating one of the plurality of interpolation methods may be encoded and included in the bitstream.

The method and apparatus for encoding an image according to the present invention may derive the prediction values of all pixels of the current block to obtain the prediction block of the current block, and then filter the prediction block.

An image encoding method and apparatus according to the present invention may filter a predetermined region of the current block according to the size of the current block or an intra prediction mode of the current block.

According to the present invention, by applying a more effective intra prediction technique, it is possible to improve the image compression efficiency and the image quality of the reproduced image. Also, by applying the filtering method capable of reducing the discontinuity between the intra prediction block and the surrounding area according to the present invention, the quality of the reproduced image can be improved.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
2 is a diagram for explaining an example of an intra prediction mode.
3 is a diagram for explaining a planar mode.
4 is a diagram for explaining a DC mode.
5 is a diagram for explaining an example of generating a prediction block.
6 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
7A and 7B are diagrams for explaining a method of deriving an intra prediction pixel using interpolation.
8 is a diagram for explaining an interpolation method or an implicit method of selecting interpolation coefficients.
9 is a flowchart illustrating a process of selecting an intra prediction mode by an image encoding apparatus.
10 is a flowchart illustrating a process in which one of a plurality of interpolation methods is selected by an image encoding apparatus.
11 is a flowchart illustrating a process of encoding interpolation method index information by an image encoding apparatus.
12 is a flowchart illustrating a process of decoding interpolation method index information by an image decoding apparatus.
13 is a diagram for explaining derivation of a prediction pixel in a screen using a plurality of reference pixel lines, according to an embodiment of the present invention.
14 is a flowchart for explaining a process of deriving a predicted pixel value in a screen according to an embodiment of the present invention.
15 is a flowchart illustrating a process of adaptively determining a reference pixel line to be used for intra prediction for each prediction block.
16 is a flowchart illustrating a process in which reference pixel line index information is encoded by an image encoding apparatus.
17 is a flowchart illustrating a process in which reference pixel line index information is decoded by an image decoding apparatus.
18 and 19 are diagrams for explaining a method of determining a reference pixel line without transmitting a reference pixel line index.
20 is a diagram for explaining smoothing between a prediction block and a reference pixel line.
21 shows a case in which a common reference pixel line is used for all transform blocks in the current block.
22A to 22D illustrate a case in which a reference pixel line is selected for each transform block and used for intra prediction.

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 an element is referred to as being “connected” or “connected” to another element, it is understood that it may be directly connected or connected to the other element, but other elements 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, embodiments of the present invention will be described in 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 an image division unit 101 , an intra prediction unit 102 , an inter prediction unit 103 , a subtraction unit 104 , a transform unit 105 , and a quantization unit. 106 , an entropy encoding unit 107 , an inverse quantization unit 108 , an inverse transform unit 109 , a multiplication unit 110 , a filter unit 111 , and a memory 112 .

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 of these components Integrated embodiments and separate embodiments of the components are also included in the scope of the present invention without departing from the essence of the present invention.

In addition, some of the components are not essential components for performing essential functions in the present invention, but may be optional components for merely improving performance. The present invention can be implemented by including only essential components to implement the essence of the present invention, except for components used for 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 image dividing unit 100 may divide the input image into at least one block. In this case, the input image may have various shapes and sizes, such as a picture, a slice, a tile, and a segment. A block may mean a coding unit (CU), a prediction unit (PU), or a transformation unit (TU). The division may be performed based on at least one of a quadtree and a binary tree. The quad tree divides the upper block into lower blocks whose width and height are half that of the upper block. Binary tree is a method of dividing the upper block into lower blocks whose either width or height is half that of the upper block. Through the binary tree-based partitioning described above, a block may have a non-square shape as well as a square shape.

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

The prediction units 102 and 103 may include an inter prediction unit 103 performing inter prediction and an intra prediction unit 102 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 105 . In addition, prediction mode information, motion vector information, etc. used for prediction may be encoded in the entropy encoder 107 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 predictors 102 and 103 and transmit it to the decoder.

The intra prediction unit 102 may generate a prediction block based on reference pixel information around the current block, which is pixel information in the current picture. When the prediction mode of the neighboring block of the current block to which intra prediction is to be performed is inter prediction, a reference pixel included in the neighboring block to which the inter prediction is applied may be replaced with a reference pixel in another neighboring block to which the intra prediction is applied. 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 to be used.

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 and a mode for predicting chrominance information may be different, and intra prediction mode information used for predicting luminance information or predicted luminance signal information may be utilized to predict chrominance information.

The intra prediction unit 102 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a filter that performs filtering on reference pixels of the current block, and may adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. 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.

When the intra prediction mode of the intra prediction unit 102 is a prediction unit that performs intra prediction based on a pixel value obtained by interpolating the reference pixel, the reference pixel interpolation unit of the intra prediction unit 102 interpolates the reference pixel to the reference pixel at the fractional unit position. can create 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 a prediction block through filtering when the prediction mode of the current block is the DC mode.

A residual block including residual information that is a difference value between the prediction unit generated by the prediction units 102 and 103 and the original block of the prediction unit may be generated. The generated residual block may be input to the transform unit 130 and transformed.

2 is a diagram for explaining an example of an intra prediction mode. The intra prediction mode shown in FIG. 2 has a total of 35 modes. Mode 0 indicates a planar mode, mode 1 indicates a DC mode, and modes 2 to 34 indicate an angular mode.

3 is a diagram for explaining a planar mode. In order to generate the predicted value of the first pixel P1 in the current block, the reconstructed pixel located at the same position along the Y axis and the reconstructed pixel T present at the upper right of the current block are linearly interpolated as shown. Similarly, in order to generate the predicted value of the second pixel P2, the reconstructed pixel located at the same position along the X-axis and the reconstructed pixel L existing at the lower left of the current block are linearly interpolated and generated as shown. A value obtained by averaging the two prediction pixels P1 and P2 becomes the final prediction pixel. In the planar mode, a prediction block of the current block is generated by inducing prediction pixels in the same manner as above.

4 is a diagram for explaining a DC mode. After calculating the average of the reconstructed pixels around the current block, the average value is used as a predicted value of all pixels in the current block.

FIG. 5 is a diagram for explaining an example of generating a prediction block using mode 10 (horizontal mode) and mode 26 (vertical mode) of FIG. 2 . When mode 10 is used, a prediction block of the current block is generated by copying each reference pixel adjacent to the left side of the current block in the right direction. Similarly, in mode 26, a prediction block of the current block is generated by copying each reference pixel adjacent to the upper side of the current block in a downward direction.

Referring back to FIG. 1 , the inter prediction unit 103 may predict a prediction unit based on information on at least one of a picture before or after the current picture, and in some cases, encoding in the current picture is completed. A prediction unit may be predicted based on information on a partial area. The inter prediction unit 103 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 112 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 in which filter coefficients are different to generate pixel information of integer pixels or less in units of 1/4 pixels may be used. 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.

The subtraction unit 104 generates a residual block of the current block by subtracting the block to be currently encoded and the prediction block generated by the intra prediction unit 102 or the inter prediction unit 103 .

The transform unit 105 may transform the residual block including the residual data using a transform method such as DCT, DST, or Karhunen Loeve Transform (KLT). In this case, the transform method may be determined based on the intra prediction mode of the prediction unit used to generate the residual block. For example, according to the intra prediction mode, DCT may be used in a horizontal direction and DST may be used in a vertical direction.

The quantization unit 106 may quantize the values transformed in the frequency domain by the transform unit 105 . The quantization coefficient may vary according to blocks or the importance of an image. The value calculated by the quantizer 106 may be provided to the inverse quantizer 108 and the entropy encoder 107 .

The transform unit 105 and/or the quantizer 106 may be selectively included in the image encoding apparatus 100 . That is, the image encoding apparatus 100 may encode the residual block by performing at least one of transform or quantization on the residual data of the residual block, or skipping both transform and quantization. Even if either transform or quantization is not performed in the image encoding apparatus 100 or neither transform nor quantization is performed, a block entering the input of the entropy encoder 107 is generally referred to as a transform block. The entropy encoding unit 107 entropy-encodes input data. 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 encoder 107 receives the residual value coefficient information and block type information of the coding unit, prediction mode information, partition unit information, prediction unit information and transmission unit information, motion vector information, and reference frame information from the prediction units 102 and 103 . , block interpolation information, filtering information, etc. can be encoded. In the entropy encoding unit 107, the coefficients of the transform block are encoded in units of sub-blocks within the transform block, and various kinds of flags indicating non-zero coefficients, coefficients having absolute values greater than 1 or 2, and signs of coefficients are encoded. can be Coefficients that are not encoded using only the flag may be encoded using an absolute value of a difference between a coefficient encoded through the flag and a coefficient of an actual transform block. The inverse quantizer 108 and the inverse transform unit 109 inversely quantize the values quantized by the quantizer 106 and inversely transform the values transformed by the transform unit 105 . The residual values generated by the inverse quantization unit 108 and the inverse transform unit 109 are predicted through the motion estimation unit, the motion compensator, and the intra prediction unit 102 included in the prediction units 102 and 103 . It may be combined with a prediction unit to generate a reconstructed block. The multiplier 110 multiplies the prediction block generated by the prediction units 102 and 103 and the residual block generated through the inverse transform unit 109 to generate a reconstructed block.

The filter unit 111 may include at least one of a deblocking filter, an offset correcting unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion caused by the 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, horizontal filtering and vertical filtering may be concurrently processed when vertical filtering and horizontal filtering are performed.

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 account can be used to apply

Adaptive loop filtering (ALF) may be performed 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 ALF, the luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficients of the ALF filter to be applied may vary according to each block. In addition, the ALF filter of the same type (fixed type) may be applied regardless of the characteristics of the block to be applied.

The memory 112 may store the reconstructed block or picture calculated through the filter unit 111 , and the stored reconstructed block or picture may be provided to the predictors 102 and 103 when inter prediction is performed.

6 is a block diagram illustrating an image decoding apparatus 600 according to an embodiment of the present invention.

Referring to FIG. 6 , the image decoding apparatus 600 includes an entropy decoding unit 601 , an inverse quantization unit 602 , an inverse transform unit 603 , an increment unit 604 , a filter unit 605 , a memory 606 and It may include prediction units 607 and 608 .

When an image bitstream generated by the image encoding apparatus 100 is input to the image decoding apparatus 600 , the input bitstream may be decoded according to a process opposite to that performed by the image encoding apparatus 100 . .

The entropy decoding unit 601 may perform entropy decoding in a procedure opposite to that performed by the entropy encoding unit 107 of the image encoding apparatus 100 . For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied corresponding to the method performed by the image encoder. In the entropy decoding unit 601, the coefficients of the transform block are based on various kinds of flags indicating non-zero coefficients, coefficients with absolute values greater than 1 or 2, and signs of coefficients in units of partial blocks within the transform block. can be decrypted as Coefficients that are not expressed only by the flag may be decoded through the sum of the coefficients expressed through the flags and the signaled coefficients.

The entropy decoding unit 601 may decode information related to intra prediction and inter prediction performed by the encoder. The inverse quantization unit 602 performs inverse quantization on a quantized transform block to generate a transform block. It operates substantially the same as the inverse quantization unit 108 of FIG. 1 .

The inverse transform unit 603 generates a residual block by performing inverse transform on the transform block. In this case, the transformation method may be determined based on information about a prediction method (inter or intra prediction), a size and/or a shape of a block, an intra prediction mode, and the like. It operates substantially the same as the inverse transform unit 109 of FIG. 1 .

The incrementer 604 generates a reconstructed block by multiplying the prediction block generated by the intra prediction unit 607 or the inter prediction unit 608 and the residual block generated by the inverse transform unit 603 . It operates substantially the same as the increment 110 of FIG. 1 .

The filter unit 605 reduces various types of noise generated in the reconstructed blocks.

The filter unit 605 may include a deblocking filter, an offset correction unit, and an ALF.

Information on whether a deblocking filter is applied to a corresponding block or picture and information on whether a strong filter or a weak filter is applied when the deblocking filter is applied from the image encoding apparatus 100 may be provided. The deblocking filter of the image decoding apparatus 600 may receive the deblocking filter related information provided from the image encoding apparatus 100 , and the image decoding apparatus 600 may perform deblocking filtering on 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 during encoding and information on the offset value.

ALF may be applied to a coding unit based on information on whether ALF is applied, ALF coefficient information, etc. provided from the image encoding apparatus 100 . Such ALF information may be provided by being included in a specific parameter set. The filter unit 605 operates substantially the same as the filter unit 111 of FIG. 1 .

The memory 606 stores the restoration block generated by the incrementer 604 . It operates substantially the same as the memory 112 of FIG. 1 .

The prediction units 607 and 608 may generate a prediction block based on the prediction block generation related information provided from the entropy decoding unit 601 and previously decoded block or picture information provided from the memory 606 .

The prediction units 607 and 608 may include an intra prediction unit 607 and an inter prediction unit 608 . Although not shown separately, the prediction units 607 and 608 may further include a prediction unit determining unit. The prediction unit determining unit receives various information such as prediction unit information input from the entropy decoder 601, 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 predicts It may be determined whether the unit performs inter prediction or intra prediction. The inter prediction unit 608 uses information required for inter prediction of the current prediction unit provided from the image encoding apparatus 100 to provide information included in at least one of a picture before or after the current picture including the current prediction unit. Inter prediction may be performed on the current prediction unit based on . Alternatively, inter prediction may be performed based on information on a pre-restored partial region in the current picture including the current prediction unit.

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

The intra prediction unit 607 generates a prediction block using previously reconstructed pixels located around the block to be currently encoded.

The intra prediction unit 607 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a filter that performs filtering on reference pixels of the current block, and may adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on the reference pixel of the current block by using the prediction mode and AIS filter information of the prediction unit provided by the image encoding apparatus 100 . 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 interpolation unit of the intra prediction unit 607 interpolates the reference pixel to select the reference pixel at the fractional unit position when the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value obtained by interpolating the reference pixel. can create The generated reference pixel at the fractional unit position may be used as a prediction pixel of a pixel in the current block. 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 a prediction block through filtering when the prediction mode of the current block is the DC mode.

The intra prediction unit 607 operates substantially the same as the intra prediction unit 102 of FIG. 1 .

The inter prediction unit 608 generates an inter prediction block by using reference pictures stored in the memory 606 , and motion information. The inter prediction unit 608 operates substantially the same as the inter prediction unit 103 of FIG. 1 .

The present invention particularly relates to intra prediction. Hereinafter, various embodiments of the present invention will be described in more detail with reference to the drawings.

< Interpolation for in-screen prediction>

7A and 7B are diagrams for explaining a method of deriving an intra prediction pixel using interpolation. Assuming that the prediction angle of mode m, which is one of the intra prediction modes of FIG. 2, is the same as that of FIG. 7A, when intra prediction is performed using mode m, the reference pixel X to be used for prediction is an integer pixel position. does not exist. Therefore, the reference pixel X at the fractional pixel position is generated by performing interpolation using the reference pixels A and B that exist at the integer pixel positions to the left and right of the reference pixel X. The generated reference pixel X is used as a prediction pixel of the pixel at the P position in the current block.

7B is a diagram for explaining the relationship between the pixels X, A, and B; Referring to FIG. 7B , the distance between the pixels X and A is S1, and the distance between the pixels B and X is S2. Depending on the ratio of the distances S1 and S2, various interpolation methods can be used to derive the pixel X. Various interpolation methods such as linear interpolation, cubic convolution interpolation, and B-spline interpolation may be applied to the interpolation method used at this time.

There are various methods for allowing the image decoding apparatus 100 to know which interpolation method is applied among a plurality of available interpolation methods or which interpolation coefficient set is used. The first method is a method in which the image encoding apparatus 100 transmits index information indicating which interpolation method among a plurality of available interpolation methods is applied to the image decoding apparatus 600 . In this case, the video encoding apparatus 100 may set index information indicating the interpolation method in units of blocks or through a higher header. Here, the setting through the upper header means that the setting is performed using a header of a larger unit than the block unit, such as a slice segment header, a picture parameter set, and a sequence parameter set. it means. Index information indicating the interpolation method included in the upper header may be encoded by the image encoding apparatus 100 and transmitted to the image decoding apparatus 600 .

As another method, the encoding apparatus 100 and the decoding apparatus 600 equally store a plurality of preset interpolation coefficient sets, and interpolation coefficient index information indicating which set is selected and used for encoding is stored in blocks or blocks. It may be notified to the decryption apparatus 600 through the upper header.

As another method, instead of the image encoding apparatus 100 transmitting the index information indicating the above-described interpolation method or interpolation coefficient index information indicating which interpolation coefficient set is used to the image decoding apparatus 600, The image encoding apparatus 100 and the image decoding apparatus 600 may equally derive the interpolation coefficients in an implicit method.

Specifically, the image encoding apparatus 100 and the image decoding apparatus 600 may derive interpolation coefficients through the same method using previously reconstructed pixels. For example, using R reference pixels (ie, pixels already reconstructed), it is enlarged or reduced by using one interpolation filter by a factor of R x K (K is an arbitrary real number). Thereafter, the original R reference pixels are reconstructed through an inverse process using the same interpolation filter. An optimal interpolation filter may be determined according to how much difference there is between the values of the restored R reference pixels and the values of the original reference pixels.

FIG. 8 is a diagram for explaining an interpolation method and/or another method of selecting interpolation coefficients by the image encoding apparatus 100 or the image decoding apparatus 600 implicitly. Referring to FIG. 8 , a 4x4 block including the pixel P corresponds to a current block to be decoded through intra prediction. A plurality of reference pixel lines including previously reconstructed pixels located around the current block are used for an interpolation method or an interpolation coefficient determination. 8 , each reference pixel line may include a predetermined number of pixels in one horizontal line and a predetermined number of pixels in one vertical line. Alternatively, the reference pixel line may be composed of a predetermined number of pixels in one horizontal line or a predetermined number of pixels in one vertical line.

Referring back to FIG. 8 , pixels in reference pixel line 0 are predicted using pixels in reference pixel line 1 . In this case, the same N directional modes as the intra prediction mode of the current block are used for prediction. For example, since the reference pixel X corresponding to the prediction pixel of the pixel R in the reference pixel line 0 is not an integer-positioned pixel, the reference pixel X is interpolated using two integer-positioned reference pixels as in FIGS. 7A and 7B . can be induced. In this case, a specific interpolation method and interpolation coefficients are used.

In this way, after generating predicted values of pixels in the reference pixel line 0, a difference value between each predicted value and each original pixel value is calculated, and then the respective difference values are summed. By repeating the above process using the interpolation methods and interpolation coefficients available in the image encoding apparatus 100 or the image decoding apparatus 600, the interpolation method and/or interpolation coefficients when the sum of the respective difference values is minimized is finally obtained to select

The aforementioned interpolation may be performed by a reference pixel interpolator included in each of the intra prediction unit 102 of the image encoding apparatus 100 and the intra prediction unit 607 of the image decoding apparatus 600 .

9 is a flowchart illustrating a process in which an optimal intra prediction mode is selected by the image encoding apparatus 100 . At this time, it is assumed that the interpolation method is set by block unit or upper header.

Referring to FIG. 9 , the variable m indicating the prediction mode number in the screen is initialized to 0, and is initialized to COST_BEST = MAX_VALUE, which is a variable to store the optimal cost value (S901). Here, MAX_VALUE is the maximum value that can be stored in the COST_BEST variable, and it is a very large value that cannot be obtained when calculating the cost. The total number of prediction modes in a preset screen is set in the variable M (S901). BEST_INTRA_MODE indicating the optimal intra prediction mode for the current block is initialized to 0 (S901).

After that, according to the intra prediction mode m, an interpolation position corresponding to each pixel position of the prediction block is found, an interpolation value is generated using a preset interpolation method or one of a plurality of interpolation methods set in the upper header, and then the prediction block is generated (S902). Then, COST_m, which is a cost value corresponding to m, is calculated using the generated prediction block (S903). Here, COST_m may be calculated using the number of bits required to encode the intra-picture mode and the difference between the prediction block and the current block. If COST_m is less than or equal to COST_BEST (S904), m is stored in BEST_INTRA_MODE, which is a variable for storing the optimal in-screen prediction mode, cost_m is stored in the COST_BEST variable, and m is incremented by 1 (S905). If COST_m is greater than COST_BEST, only m is increased by 1 (S906). Finally, if m reaches the maximum number of prediction modes in the screen, it ends. Otherwise, it returns to S902 and repeats. Here, if the interpolation method uses a predetermined method in the image encoding apparatus 100 or the image decoding apparatus 600, S1 and S2 are set using the methods of FIGS. 7 and 8, and the pixel X is set using the predetermined interpolation method. to create A prediction block is generated using the same method for all pixels in the prediction block. Alternatively, if multiple interpolation methods are used, the contents of step S902 may be changed.

In addition, multiple interpolation methods may be adaptively applied to each prediction block. At this time, the contents of step S902 among the steps shown in FIG. 9 are changed.

10 is a flowchart illustrating a process in which one of a plurality of interpolation methods is selected by the image encoding apparatus 100 .

Referring to FIG. 10 , the image encoding apparatus 100 initializes a variable i indicating an interpolation method index to 0 and COST_BEST_i = MAX_VALUE, which is a variable to store an optimal cost value. Here, MAX_VALUE is the maximum value that can be stored in the COST_BEST_i variable, and it is a very large value that cannot be obtained when calculating the cost. The total number of preset and usable interpolation methods is set in variable i. BEST_INTERPOLATION, which is a variable that stores the optimal interpolation method used in the current block, is initialized to 0 (S1001). Thereafter, an interpolation value corresponding to each pixel position of the prediction block is generated according to the interpolation method index i, and then the prediction block is generated ( S1002 ). Then, COST_i, which is a cost value corresponding to i, is calculated using the generated prediction block (S1003). Here, COST_i is calculated using the number of bits required to encode the interpolation index and the difference between the prediction block and the current block. If COST_i is less than or equal to COST_BEST_i (S1004), i is stored in BEST_INTERPOLATION, which is a variable for storing the optimal interpolation method, cost_i is stored in the COST_BEST_i variable, and i is incremented by 1 (S1005). If COST_i is greater than COST_BEST_i, only i is increased by 1 (S1006). Finally, if i reaches the maximum number of available interpolation methods, it ends. Otherwise, it returns to S1002 and repeats. When this method is used, the number of bits encoded with the interpolation method index is additionally added to the number of bits of the intra prediction mode encoded in step S903 shown in FIG. 9 to calculate COST_m.

11 is a flowchart illustrating a process of encoding interpolation method index information when a plurality of interpolation methods are adaptively applied to each prediction block by the image encoding apparatus 100 . First, whether prediction of an intra prediction mode is predicted for each prediction block is encoded (S1101). Thereafter, after determining whether prediction has been made (S1102), if prediction is made, an index indicating which candidate is selected from prediction candidates of the intra prediction mode generated from the neighboring block is encoded (S1103). Otherwise, the remaining modes are rearranged except for prediction candidates of the intra prediction mode generated in the neighboring blocks, and the currently selected intra prediction mode is binarized and then encoded ( S1104 ). Thereafter, the used interpolation method index is coded (S1105) and the process is finished.

12 is a flowchart illustrating a process of decoding interpolation method index information by the image decoding apparatus 600 . First, it is decoded whether the prediction mode in the picture is predicted for each prediction block (S1201). Thereafter, after determining whether prediction has been made ( S1202 ), if prediction is made, an index indicating which candidate is selected from prediction candidates of the intra prediction mode generated from the neighboring block is decoded ( S1203 ). Otherwise, the currently selected intra prediction mode is decoded by rearranging the remaining modes except for prediction candidates of the intra prediction mode generated from the neighboring blocks (S2104). Thereafter, the interpolation method index used in the encoder is decoded (S1205) and the process is finished.

<Induction of prediction pixels in the screen using a plurality of reference pixel lines>

Hereinafter, derivation of an intra prediction pixel using a plurality of reference pixel lines according to another embodiment of the present invention will be described.

13 is a diagram for explaining derivation of a prediction pixel in a screen using a plurality of reference pixel lines, according to an embodiment of the present invention.

In the conventional intra prediction, one reference pixel line is used. The reference pixel line 0 shown in Fig. 13 is that. The reference pixel line 0 includes a predetermined number of reference pixels in contact with the upper end of the current block and a predetermined number of reference pixels in contact with the left side of the current block. According to the present invention, the accuracy of intra prediction can be improved by deriving a prediction pixel or a prediction block using various reference pixel lines and reference pixels belonging to the reference pixel lines. The present embodiment may be equally performed by each of the intra prediction unit 102 of the image encoding apparatus 100 and the intra prediction unit 607 of the image decoding apparatus 600 .

For the following description, it is assumed that a total of three lines are used as the reference pixel line. However, any N reference pixel lines may be used. Here, the number N of reference pixel lines may be included in a block unit or an upper header to inform the decoding apparatus 600 . Alternatively, it is also possible for the encoding apparatus 100 and the decoding apparatus 600 to use preset N reference pixel lines without encoding the number N of reference pixel lines.

Referring to FIG. 13 , a 4x4 block including the pixel P corresponds to a current block to be encoded or decoded using intra prediction. Three reference pixel lines 0, 1 and 2 are located around the current block.

When the intra prediction mode of the current block is the m-th directional mode, prediction pixels that can be used as prediction pixels of the current pixel P using three reference pixel lines 0, 1, and 2 may be X, Y, and Z. In this case, an optimal reference pixel line may be determined by generating a prediction block using each of the three reference pixel lines. The encoding apparatus 100 may encode reference pixel line index information indicating the determined optimal reference pixel line. As for the reference pixel line index, for example, as shown in FIG. 13 , a low index number may be assigned to a reference pixel line close to the current block.

14 is a flowchart for explaining a process of deriving a predicted pixel value in a screen according to an embodiment of the present invention. Referring to FIG. 14 , at least one reference pixel line to be used for intra prediction of a current block is selected from among a plurality of reference pixel lines ( S1301 ). The plurality of reference pixel lines exist in the same image as the current block to be decoded using intra prediction. The selected at least one reference pixel line may be indicated by the aforementioned reference pixel line index. As another alternative, at least one reference pixel line to be used for intra prediction of the current block may be selected using a method common to the image encoding apparatus 100 and the image decoding apparatus 600 by an implicit method to be described later. .

In addition, the selected at least one reference pixel line may be selected for each prediction block. This will be described later with reference to FIG. 15 . Alternatively, it may be adaptively selected for each pixel in the prediction block. This will be described later with reference to FIGS. 18 and 19 .

The image encoding apparatus 100 or the image decoding apparatus 600 may obtain a predicted value of one pixel in the current block based on the value of at least one pixel included in the selected at least one reference pixel line ( S1303 ). The image encoding apparatus 100 or the image decoding apparatus 600 may repeat all or some of the steps S1301 or S1303 to derive the prediction block of the current block.

15 is a flowchart illustrating a process of adaptively determining a reference pixel line to be used for intra prediction for each prediction block. At this time, step S902 shown in FIG. 9 may be replaced with steps shown in FIG. 15 .

Referring to FIG. 15 , a variable n indicating a reference pixel line index is initialized to 0, and COST_BEST_n = MAX_VALUE, which is a variable to store an optimal cost value. Here, MAX_VALUE is the maximum value that can be stored in the COST_BEST_n variable, and it is a very large value that cannot be obtained when calculating the cost. The total number of preset reference pixel lines is set in the variable N. BEST_n indicating the optimal reference pixel line index in the current block is initialized to 0 (S1401). Thereafter, an interpolation position corresponding to each pixel position of the prediction block is found according to the reference pixel line index n, and the prediction block is generated ( S1402 ). Then, COST_n, which is a cost value corresponding to n, is calculated using the generated prediction block (S1403). Here, COST_n is calculated using the number of bits required to encode the reference pixel line n and the difference between the prediction block and the current block. If COST_n is less than or equal to COST_BEST_n (S1404), n is stored in BEST_n, which is a variable for storing the optimal reference pixel line, cost_n is stored in the COST_BEST_n variable, and n is incremented by 1 (S1405). If COST_n is greater than COST_BEST_n, only n is increased by 1 (S1406). Finally, if n has reached the maximum number of reference pixel lines, it ends, otherwise it returns to S1402 and repeats.

16 is a flowchart illustrating a process of encoding, by the encoding apparatus 100, reference pixel line index information indicating the selected reference pixel line when a reference pixel line is adaptively selected for each prediction block. First, whether prediction of an intra prediction mode is predicted for each prediction block is encoded (S1501). Thereafter, after determining whether prediction has been made ( S1502 ), if prediction has been made, an index indicating which candidate is selected from prediction candidates of the intra prediction mode generated from the neighboring block is encoded ( S1503 ). Otherwise, the remaining modes are rearranged except for prediction candidates of the intra prediction mode generated from the neighboring blocks, and the currently selected intra prediction mode is binarized and then encoded (S1504). Thereafter, the used reference pixel line index is encoded (S1505) and the process is finished.

17 is a flowchart illustrating a process in which reference pixel line index information indicating the selected reference pixel line is decoded by the decoding apparatus 600 when a reference pixel line is adaptively selected for each prediction block. First, it is decoded whether the prediction mode in the picture is predicted for each prediction block (S1601). Thereafter, after determining whether prediction has been made (S1602), if prediction is made, an index indicating which candidate is selected from the prediction candidates of the intra prediction mode generated from the neighboring block is decoded (S1603). Otherwise, the currently selected intra prediction mode is decoded by rearranging the remaining modes except for prediction candidates of the intra prediction mode generated from the neighboring blocks (S1604). After that, the used reference pixel line index is decoded (S1605) and the process is finished.

Next, a method of adaptively determining a reference pixel line for each pixel position of a prediction block without transmitting a reference pixel line index will be described with reference to FIGS. 18 and 19 .

For each pixel in the prediction block, the precision of the position of the prediction pixel obtained through interpolation within each reference pixel line may be different. Accordingly, among the prediction pixels obtained through interpolation in each reference pixel line, the prediction pixel closest to the integer pixel position may be selected as the prediction pixel of the current pixel P. In this case, the above process may be applied to predetermined N reference pixel lines.

If there are a plurality of prediction pixels at integer pixel positions, a prediction pixel close to the current block may be selected as the final prediction pixel.

19 is a reference diagram for explaining a method of adaptively selecting a reference pixel line without transmitting a reference pixel line index. As shown in FIG. 19 , a line having many lines in which a prediction pixel exists at an integer position is given priority, and a prediction pixel line can be adaptively selected for each prediction block. If it is assumed that the precision and frequency of interpolated pixels used to generate a prediction block using each reference pixel line are the same as in FIG. 19 , the line may be selected by weighting it according to the precision of each pixel position.

Referring back to FIG. 19 , when a prediction block is generated using line 1, integer position prediction pixels are 5, 1/2 position prediction pixels are 3, 1/4 position prediction pixels are 4, and 1/ Two 8 position prediction pixels, one 1/16 position prediction pixel, and one 1/32 position prediction pixel were selected. Accordingly, the total number of pixels in the prediction block is 16. The case of the reference pixel line 2 and the reference pixel line 3 can be described in the same way.

If priority is given only to integer pixel positions, line 1 having the most integer positions may be selected as the reference pixel line. Alternatively, it is also possible to assign a weight to each position to calculate the sum of the weight and the frequency, and then to select a line having the largest calculated value as the reference pixel line. Alternatively, it is also possible to assign a weight to each line to calculate the sum of the weight and the frequency, and then select the line having the largest calculated value as the reference pixel line. Alternatively, it is also possible to calculate the sum of weights and frequencies by giving weights to both lines and positions, and then select a line having the largest calculated value as a reference pixel line.

As another embodiment, it is also possible to generate a prediction block using weighted pixels by weighting each line. For example, when pixel values at positions X, Y, and Z of FIG. 13 exist, it is also possible to select the weighted value as the prediction pixel at the P position by adding more weight as it approaches the block. Alternatively, it is also possible to select the weighted value as the prediction pixel at the P position by adding more weight as it approaches the integer pixel position. Alternatively, in addition to a method of deriving a prediction pixel using a weighted sum, that is, a weighted average, a value of a prediction pixel may be derived using an arithmetic mean or a median value.

Alternatively, it may be coded using a reference pixel line index, and may be used to exclude one of N lines. For example, when the reference pixel line index is set to 1, N-1 lines excluding line 1 are used. In this case, when interpolating the predicted value using the m-th mode, a higher priority may be given as it approaches the integer pixel position, or a different priority may be given according to the precision of the interpolated position. Prediction values may be generated in lines other than line 1 on a pixel-by-pixel basis without dividing lines according to such predetermined priorities.

Alternatively, it is also possible for the encoding apparatus 100 to encode whether a method of directly encoding a reference pixel line index or a method for not encoding the reference pixel line index is used in block units or in a higher header, and then transmit it to the decoding apparatus 600 . .

<Smoothing between prediction block and reference pixel line>

Hereinafter, smoothing between a prediction block and a reference pixel line will be described as another embodiment of the present invention.

When a prediction block is derived using predetermined pixel(s) in a reference pixel line, discontinuity may exist between a reference pixel line and a prediction block not used for derivation of the prediction block, or between a region adjacent to the prediction block and the prediction block. . Smoothing may be used to reduce these discontinuities. Smoothing may correspond to a kind of low-pass filter.

Smoothing according to an embodiment of the present invention may be performed by each of the intra prediction unit 102 of the image encoding apparatus 100 and the intra prediction unit 607 of the image decoding apparatus 600 .

20 is a diagram for explaining smoothing between a prediction block and a reference pixel line.

The intra prediction mode used below will be described by taking as an example a mode in which intra prediction is performed in a 45 degree up-right direction. It is also assumed that reference pixel line 1 is selected for intra prediction. Also, although smoothing using pixels A to E is described as a pixel to which smoothing is applied, the same can be applied to other pixels.

In the example of FIG. 20 , since intra prediction was performed in a 45 degree up-right direction, smoothing may be performed in a 45 degree down-left direction that is opposite to the intra prediction direction. In this case, the region of the prediction block to which smoothing is applied may be determined according to the size or shape of the prediction block of the current block. In FIG. 20, pixels belonging to a half area of the prediction block are smoothed. That is, smoothing can be applied only to pixels in the left half that are darkly displayed. Alternatively, a preset area or ratio may be used according to the size of the prediction block and/or the intra prediction mode. For example, smoothing may be applied to only 1/4 of the prediction block, and other ratios are also possible.

In FIG. 20 , since the reference pixel line 1 is determined as the reference pixel line for intra prediction, the prediction pixel A may be smoothed using the pixel D existing in the reference pixel line 1 using Equation 1 below.

In Equation 1 above, A', A, and D are the values of the prediction pixel A after smoothing, the value of the prediction pixel A before smoothing, and the value of the reference pixel D, respectively, and w1 and w2 are respectively applied to the prediction pixel A Weights and weights applied to the reference pixel D.

Also, the prediction pixel B may be smoothed using an equation similar to Equation 1 above using the pixel D existing in the reference pixel line 1.

In this case, the intensity of the smoothing may be adjusted according to the distance. Since the prediction pixel A is farther away from the pixel D in terms of distance than the prediction pixel B, smoothing is stronger when the prediction pixels A and D are smoothed than when the prediction pixels B and D are smoothed. Here, strong smoothing can be performed by smoothing the prediction pixel by giving more weight to the pixel D side.

Alternatively, the reference pixel line used for smoothing may be set to be a line close to the prediction block separately from the reference pixel line selected for intra prediction. Referring to FIG. 20 , although reference pixel line 1 is selected for intra prediction, it is also possible to set pixels used for smoothing of prediction pixels A and B to C instead of D. In this case as well, the intensity of the smoothing can be selected according to the distance. For example, when the prediction pixel B is smoothed using the reference pixel C, the same weight is applied to each, and when the prediction pixel A is smoothed using the reference pixel C, more weight is applied to the pixel C to perform smoothing. may be

When performing smoothing, it is also possible to use both directions. For example, it is assumed that smoothing is performed using the reference pixel line 0, and when the prediction pixel A is smoothed, the reference pixels F and C may be respectively weighted to perform smoothing with the prediction pixel A. When smoothing the prediction pixel B, it is also possible to smooth the prediction pixel B by giving weights to the pixels F and C, respectively. In this case, since line 1 is selected as a reference pixel line for intra prediction, it is possible to use the pixel G in the up-right direction and the pixel C in the down-left direction.

According to an embodiment of the present invention, it is also possible to vary the weight according to the distance between the reference pixel and the prediction pixel. For example, when the prediction pixel A is smoothed using the reference pixels F and C, since the distance between the pixels C and A is greater than the distance between the pixels F and A, the smoothing may be performed with a greater weight on the pixel C. Alternatively, it is also possible to perform smoothing using an arbitrary line using a preset method. It is also possible to encode whether this smoothing method is applied in block units, and it is also possible to encode through a higher header. Alternatively, it is also possible for the encoder and the decoder to perform the same according to a preset condition without encoding whether or not smoothing is applied. For example, whether to perform smoothing may be determined according to which angle of the intra prediction mode is performed. In the present embodiment, for convenience of explanation, smoothing is stronger as the distance increases, but the opposite case is also possible depending on the characteristics of the image.

Next, a unit of a block from which a reference pixel line for intra prediction is selected according to an embodiment of the present invention will be described with reference to FIGS. 21 and 22A to 22D .

Hereinafter, for convenience of description, a case in which the current block has a size of 16x16 and the current block is divided into four 8x8 transform blocks and the transformation is performed in units of 8x8 transform blocks will be described as an example. The current block may be divided into a plurality of transform blocks smaller than the size of the current block for transformation. Accordingly, when the intra prediction mode is determined in units of the current block, actual prediction may be performed in units of transform blocks by applying the determined intra prediction mode in units of transform blocks. An advantage of this method is that it can compensate for the fact that the correlation between pixels may decrease as the reference pixel moves away from the current block. Referring to FIG. 21 , when intra prediction is applied on a block-by-block basis, the pixels of the transform block A have a closer distance to the referenced pixels than the pixels of the transform block D. Accordingly, the pixels in the transform block D may have a greater distance from the reference pixels, so that prediction efficiency may be lowered.

In order to compensate for the aforementioned disadvantages, only the intra prediction mode may be determined in units of blocks, and intra prediction may be performed in units of transform blocks.

21 illustrates a case in which at least one reference pixel line selected for intra prediction of the current block is commonly used for all transform blocks in the current block when intra prediction is performed in units of transform blocks.

22A to 22D illustrate a case in which at least one reference pixel line is selected for each transform block and used for intra prediction.

Referring to FIG. 22A , when four transform blocks having a size of 8x8 are used and prediction is performed in units of transform blocks, the same reference pixel lines as those shown in FIG. 21 are used for intra prediction of transform block A. Referring to FIG.

Referring to FIG. 22B , the transform block B may use reference pixel lines as illustrated by using the pixels of the reconstructed transform block A for intra prediction. Similarly, in FIG. 22C , reference pixel lines as illustrated by using the pixels of the reconstructed transform blocks A and B may be used for intra prediction. Referring to FIG. 22D, reference pixel lines as shown using the pixels of the reconstructed transform blocks A, B, and C may be used for intra prediction.

As described above, when a plurality of reference pixel lines are used, as shown in FIG. 21 , the pixel lines determined in units of blocks may be directly applied to the case of performing prediction in units of transform blocks of FIGS. 22A to 22D . Alternatively, it is also possible to newly obtain an optimal reference pixel line in units of transform blocks. Alternatively, whether to use the optimal reference pixel line obtained in block units for the entire transformation block or to derive and use the reference pixel line for each transformation block unit is encoded through a block unit or an upper header and notified to the decoding device 600 It is possible.

Example methods of the present disclosure are expressed as a series of operations for clarity of description, but this is not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In order to implement the method according to the present disclosure, other steps may be included in addition to the illustrated steps, steps may be excluded from some steps, and/or other steps may be included except for some steps.

Various embodiments of the present disclosure do not list all possible combinations but are intended to describe representative aspects of the present disclosure, and matters described in various embodiments may be applied independently or in combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. For implementation by hardware, one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general purpose It may be implemented by a processor (general processor), a controller, a microcontroller, a microprocessor, and the like.

The scope of the present disclosure includes software or machine-executable instructions (eg, operating system, application, firmware, program, etc.) that cause an operation according to the method of various embodiments to be executed on a device or computer, and such software or and non-transitory computer-readable media in which instructions and the like are stored and executable on a device or computer.

Claims (28)

In the video decoding method,
selecting at least one reference pixel line from among a plurality of reference pixel lines, wherein the plurality of reference pixel lines are located in the same image as a current block to be decoded using intra prediction; and
deriving a predicted value of at least one pixel in the current block based on at least one pixel value included in the selected at least one reference pixel line;
The deriving of the prediction value is performed in units of sub-blocks within the current block. The method of claim 1 , wherein the video decoding method comprises:
further comprising obtaining reference pixel line index information from the input bitstream;
The decoding method of an image, wherein the at least one reference pixel line is selected from among the plurality of reference pixel lines based on the reference pixel line index information. According to claim 1,
The method for decoding an image, wherein the plurality of reference pixel lines are reference pixel lines at preset positions. The method of claim 1,
The image decoding method, characterized in that the number of the plurality of reference pixel lines is three. 3. The method of claim 2,
and a larger value is assigned to the reference pixel line index information of each of the plurality of reference pixel lines as the distance between each of the reference pixel lines and the current block increases. The method of claim 1 , wherein the video decoding method comprises:
obtaining a prediction block of the current block by deriving prediction values of pixels of the current block; and
The video decoding method further comprising the step of filtering the prediction block. The method of claim 6, wherein the filtering comprises:
When the intra prediction mode of the current block is a predetermined angular mode, the first reference pixel used for prediction of the first pixel in the prediction block belongs to the same reference pixel line as the reference pixel line to which the first reference pixel belongs. The method of decoding an image, characterized in that the first pixel in the prediction block is filtered by using a second reference pixel. 8. The method of claim 7,
The second reference pixel is a reference pixel existing in a direction opposite to a prediction direction associated with the predetermined angular mode. 8. The method of claim 7,
The image decoding method, characterized in that the predetermined angular mode is an angular mode in a 45 degree up-right direction. The method of claim 7, wherein the filtering comprises:
filtering the first pixel based on a first weight according to a distance between the first pixel and the first reference pixel in the prediction block and a second weight according to a distance between the first pixel and the second reference pixel Video decoding method, characterized in that. 11. The method of claim 10,
When the distance between the first pixel and the first reference pixel is shorter than the distance between the first pixel and the second reference pixel, the value of the first weight is greater than the value of the second weight. Decryption method. 10. The method of claim 9,
and the reference pixel line to which the first reference pixel and the second reference pixel belong is a reference pixel line adjacent to the prediction block. The method of claim 6, wherein the filtering comprises:
The method of decoding an image, wherein the pixel to be filtered is determined according to the size or shape of the prediction block. In the video encoding method,
selecting at least one reference pixel line from among a plurality of reference pixel lines, wherein the plurality of reference pixel lines are located in the same image as a current block to be encoded using intra prediction; and
deriving a predicted value of at least one pixel in the current block based on at least one pixel value included in the selected at least one reference pixel line;
The deriving of the prediction value is performed in units of sub-blocks within the current block. The method of claim 14, wherein the encoding method of the image comprises:
encoding reference pixel line index information indicating the selected at least one reference pixel line; and
and including the encoded reference pixel line index information in a bitstream. 15. The method of claim 14,
The method of encoding an image, wherein the plurality of reference pixel lines are reference pixel lines at preset positions. 15. The method of claim 14,
The video encoding method, characterized in that the number of the plurality of reference pixel lines is three. 16. The method of claim 15,
The method of encoding an image, wherein a larger value is assigned to the reference pixel line index information of each of the plurality of reference pixel lines as the distance between each of the reference pixel lines and the current block increases. The method of claim 14, wherein the encoding method of the image comprises:
obtaining a prediction block of the current block by deriving prediction values of pixels of the current block; and
The video encoding method further comprising the step of filtering the prediction block. The method of claim 19, wherein the filtering comprises:
When the intra prediction mode of the current block is a predetermined angular mode, the first reference pixel used for prediction of the first pixel in the prediction block belongs to the same reference pixel line as the reference pixel line to which the first reference pixel belongs. The method of encoding an image, characterized in that the first pixel in the prediction block is filtered by using a second reference pixel. 21. The method of claim 20,
The second reference pixel is a reference pixel existing in a direction opposite to a prediction direction associated with the predetermined angular mode. 21. The method of claim 20,
The video encoding method, characterized in that the predetermined angular mode is an angular mode in a 45 degree up-right direction. The method of claim 20, wherein the filtering comprises:
filtering the first pixel based on a first weight according to a distance between the first pixel and the first reference pixel in the prediction block and a second weight according to a distance between the first pixel and the second reference pixel Video encoding method, characterized in that. 24. The method of claim 23,
When the distance between the first pixel and the first reference pixel is shorter than the distance between the first pixel and the second reference pixel, the value of the first weight is greater than the value of the second weight. encoding method. 23. The method of claim 22,
and the reference pixel line to which the first reference pixel and the second reference pixel belong is a reference pixel line adjacent to the prediction block. The method of claim 19, wherein the filtering comprises:
An image encoding method, characterized in that the pixel to be filtered is determined according to the size or shape of the prediction block. A computer-readable non-transitory storage medium comprising a bitstream decoded by an image decoding method,
The bitstream includes current reference pixel line index information,
The reference pixel line index information is used to select at least one reference pixel line among a plurality of reference pixel lines,
The plurality of reference pixel lines are located in the same image as a current block encoded using intra prediction,
The intra prediction is performed in units of sub-blocks in the current block,
and the selected at least one reference pixel line is used to derive a predicted value of at least one pixel in the current block. delete

Images