KR20220016938A - Method and apparatus for encoding/decoding an image - Google Patents

Abstract

A main object of the present invention is to improve efficiency of intra prediction by inducing an intra prediction mode of an image to be encoded or decoded using a previously reconstructed pixel region. According to the present invention, a method and device for encoding/decoding image obtain reference pixel line index information from bit-stream, select a reference pixel line for a current block from a plurality of reference pixel lines based on the reference pixel line index information, induce an intra prediction mode of the current block, and reset the derived intra prediction mode. The prediction block of the current block may be generated by performing intra prediction based on the selected reference pixel line and the reset intra prediction mode.

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.

In addition, in the conventional intra prediction technique, significant information about the prediction mode must be encoded in order to inform the video decoding apparatus which intra prediction mode among a plurality of intra prediction modes is used for intra prediction of the input image. .

A main object of the present invention is to improve the efficiency of intra prediction by inducing an intra prediction mode of an image to be encoded or decoded using an already reconstructed pixel region when encoding/decoding an image.

An image encoding/decoding method and apparatus according to an embodiment of the present invention for achieving the above object induces an intra prediction mode of the reconstructed pixel region based on the already reconstructed reference pixel region of at least one pixel region and, based on the derived intra prediction mode of the reconstructed pixel region, derive an intra prediction mode of the current block, obtain an intra prediction block of the current block using the derived intra prediction mode, and The current block may be reconstructed by adding the intra prediction block and the residual block of the current block.

An image decoding method and apparatus according to an embodiment of the present invention for achieving the above object obtains information indicating a method of inducing an intra prediction mode from an input bitstream, and adds information indicating a method of inducing an intra prediction mode. Accordingly, whether to induce the intra prediction mode of the reconstructed pixel region may be selected.

An image decoding method and apparatus according to an embodiment of the present invention for achieving the above object are available for specifying the number of the plurality of available intra prediction modes or a list of the plurality of available intra prediction modes in an input bitstream. One intra prediction mode information may be obtained, and the intra prediction mode of the current block may be derived based on the available intra prediction mode information.

In an image encoding method and apparatus according to an embodiment of the present invention for achieving the above object, information indicating a method of inducing an intra prediction mode of a current block is encoded and included in a bitstream, and the bitstream is received The image decoding apparatus may selectively perform the step of inducing the intra prediction mode of the reconstructed pixel region according to information indicating a method of inducing the intra prediction mode of the current block.

According to the present invention, the compression efficiency of an image can be improved by efficiently applying an intra prediction technique used for encoding and decoding an image.

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.
7 is a view for explaining a DIMD according to the first embodiment of the present invention.
8 is a diagram for explaining a DIMD according to a third embodiment of the present invention.
9 is a flowchart for explaining a DIMD according to the present invention.
10 is a flowchart illustrating a method of encoding an intra prediction mode when an image is encoded using DIMD according to the present invention.
11 is a flowchart illustrating a method of decoding an intra prediction mode when decoding an image using DIMD according to the present invention.
12 is a view for explaining a seventh embodiment according to the present invention.
13 is a flowchart illustrating a process of encoding an intra prediction mode when the seventh embodiment of the present invention is applied.
14 is a flowchart illustrating a process of decoding an intra prediction mode when the seventh embodiment of the present invention is applied.
15A and 15B are diagrams for explaining a modified example of DIMD for transmitting a template index.
16 is a flowchart illustrating a method of encoding an intra prediction mode according to DIMD using a template index.
17 is a flowchart illustrating a method of encoding an intra prediction mode according to DIMD using a template index.
18 is a diagram for explaining an example of setting an intra prediction mode derived using a template as an MPM candidate.
19 is a diagram for explaining MPM candidate setting 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 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 determine an intra prediction mode of the current block, and generate one or a plurality of prediction blocks using reference pixels according to the determined intra prediction mode. 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 block generated by the prediction units 102 and 103 and the original block of the prediction block 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 Predictors 607 and 608 may be included.

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 derivation of an intra prediction mode. Hereinafter, various embodiments and applications related to derivation, encoding, and decoding of an intra prediction mode according to the present invention will be described with reference to the drawings. When the intra prediction mode derivation according to the present invention is applied, the image encoding apparatus and the image decoding apparatus can induce the intra prediction mode by the same method and/or the same standard, so information for notifying the intra prediction mode itself is provided to the image. There is no need to pass it to the decryption device.

<Induction of intra prediction mode by video decoding device>

In this embodiment, induction of the intra prediction mode by the video decoding apparatus is described. The derivation of the intra prediction mode by the image decoding apparatus according to the present invention is hereinafter referred to as DIMD (Decoder-side Intra Mode Derivation) for short. However, DIMD may be equally performed by an image encoding apparatus. Therefore, despite the name DIMD, DIMD may be performed by each of the image encoding apparatus 100 and the image decoding apparatus 600 . In particular, DIMD may be equally performed by the intra prediction unit 102 of the image encoding apparatus 100 and the intra prediction unit 607 of the image decoding apparatus 600 , respectively.

Hereinafter, various embodiments of the DIMD according to the present invention will be described with reference to the drawings.

(Example 1)

7 is a view for explaining a DIMD according to the first embodiment of the present invention. According to an embodiment of the present invention, an intra prediction mode of the current block may be induced by using already reconstructed pixels located around the current block.

Referring to FIG. 7 , it is assumed that the size of the current block 2001 to be encoded or decoded is M x N, the size of the template A 2004 is P x N, and the size of the template B 2003 is M x Q. As shown in FIG. 7 , the reference pixel region 2002 is composed of a region located to the left of the template A 2004 and an region located above the template B 2003 .

Assuming that the values of R and S among the values indicating the size of the reference pixel region 2002 are each 1, the reference pixel region 2002 includes 2(Q+N) + 2(P+M) + 1 reference pixels. include

According to an embodiment of the present invention, prediction values of the template A 2004 and the template B 2003 are calculated using reference pixels in the reference pixel region 2002 according to each of the available intra prediction modes. At this time, template A (2004) and template B (2003) are treated as one area. For example, according to each of the 35 intra prediction modes as shown in FIG. 2 , the prediction values of the template A ( 2004 ) and the template B ( 2003 ) are calculated using reference pixels in the reference pixel region 2002 . . SAD (Sum of Absolute Difference) corresponding to the sum of the differences between the restored values of template A (2004) and template B (2003) and template A (2004) and template B (2003) predicted according to the prediction mode within each screen save Thereafter, an intra prediction mode having the smallest sum of absolute difference (SAD) may be selected as the intra prediction mode of the current block 2001 .

Since the intra prediction mode of the current block 2001 is induced using pixels already reconstructed by the image encoding apparatus 100 or the decoding apparatus 600, both the image encoding apparatus 100 and the image decoding apparatus 600 A prediction mode within the same screen can be induced.

Meanwhile, the intra prediction mode applied to the luminance pixels may be equally applied to the chrominance pixels. Since the encoding apparatus 100 does not transmit the intra prediction mode to the decoding apparatus 600, there is no overhead burden. Therefore, it is also possible to add an in-screen prediction mode at 1/2 position, 1/3 position, or 1/4 position between angular modes. In this case, information on the number of used intra prediction modes may be transmitted to the decoding apparatus 600 using various methods. As an example, it may be encoded through a block header or an upper header of the block, for example, a slice header, a picture header, a sequence header, etc. using an exponential power of 2 and transmitted to the decoding apparatus 600 . Alternatively, information on the number of available intra prediction modes is transmitted to the decoding apparatus 600 using a method of transmitting an index indicating one of a plurality of intra prediction mode lists composed of different numbers of intra prediction modes. may be transmitted.

In addition, in the above-described embodiment, two templates, template A 2004 and template B 2003, are used to derive the intra prediction mode of the current block 2001, but three or more templates may be used.

Also, in the above-described embodiment, the final intra prediction mode was derived by applying all of the intra prediction modes to the template A (2004) and/or the template B (2003). Among the modes, the final intra prediction mode of the current block 2001 may be derived.

(Second embodiment)

In the above-described first embodiment, two templates A (2004) and template B (2003) have been described as one area. However, in this embodiment, the two templates A (2004) and B (2003) are treated as separate areas. Specifically, after each of the prediction modes of the current block is derived using each template, one mode may be finally selected from among the two derived prediction modes.

For example, based on the 18th angle mode shown in FIG. 2 (prediction mode in the upper left 45 degree screen), the angular modes existing on the left of the 18th angle mode are applied only to template A (2004) and then SAD save A mode having a minimum value among the SAD values calculated for each mode is determined as an intra prediction mode of the template A (2004).

Next, each of the angular modes on the right of the 18th angular mode is applied only to template B (2003), and then the SAD is obtained. The mode having the minimum value among the SAD values calculated for each mode is determined as the intra prediction mode of the template B (2003). Thereafter, one of the determined intra prediction mode of the template A 2004 and the intra prediction mode of the template B 2003 is finally selected as the prediction mode of the current block 2001 .

By applying the DC mode and the planar mode to each template, respectively, the SAD value corresponding to the DC mode and the SAD value corresponding to the planar mode can be obtained. Thereafter, the SAD value corresponding to the mode selected as the prediction mode in the screen of the corresponding template among the above-described angle modes, the SAD value corresponding to the DC mode, and the SAD value corresponding to the planar mode are compared with each other to obtain a final screen of each template. You can choose my prediction mode.

(Example 3)

Hereinafter, a third embodiment of the DIMD according to the present invention will be described.

A second embodiment according to the present invention relates to a method of executing DIMD using the remaining available templates when some of the templates of the current block are not available.

8 is a diagram for explaining a DIMD according to a third embodiment of the present invention.

In FIG. 8 , the template above the current block 2101 is not available, but only the template A 2104 on the left is available.

If the encoding apparatus 100 and the decoding apparatus 600 decide to use 35 intra prediction modes as illustrated in FIG. 2 , but any one of the two templates is unavailable, as shown in FIG. It is possible to apply 35 intra prediction modes to only one template 2104 by defining a range. In FIG. 8 , the lower left 45 degree direction is set as intra-screen prediction mode No. 2, the horizontal direction is set as intra-screen prediction mode No. 34, and 33 angular modes exist between prediction mode No. 2 and prediction mode No. 34 set to do so.

After performing DIMD by applying the 33 angular modes, DC mode, and planar mode set as described above to the available template A 2104 , the intra prediction mode of the current block 2101 may be derived.

If the current block 2101 corresponds to the upper boundary of the input image, so that the reference pixels 2105 on the left of the template A 2104 are available but the reference pixels on the upper side of the template A 2104 do not exist, the appropriate surrounding The upper reference pixels 2102 may be generated through padding using the pixels. The surrounding pixels used for padding may be pixels above the current block 2101 and/or template A 2104 , or reference pixels 2105 to the left of template A 2104 .

(Example 4)

9 is a flowchart for explaining a DIMD according to the present invention. It relates to the first to third embodiments described above. The method shown in FIG. 9 may be equally performed by the intra prediction unit 102 of the image encoding apparatus 100 and the intra prediction unit 607 of the image decoding apparatus 600 , respectively.

Referring to FIG. 9 , first, an intra prediction mode of the reconstructed pixel area is induced based on the already reconstructed reference pixel area of at least one pixel area ( S2201 ). Here, at least one pixel area may be template A (2004, 2104) and/or template B (2003) in the above-described embodiments. However, of course, it is not limited to these templates. The reference pixel region may correspond to the reference pixel regions 2002, 2102, and 2105 described in the above-described embodiments. However, it goes without saying that it is not limited to these reference pixel regions.

Next, an intra prediction mode of the current block is derived based on the intra prediction mode of the reconstructed pixel region derived in step S2201 ( S2203 ). After obtaining the intra prediction block of the current block using the derived intra prediction mode (S2205), the current block is reconstructed by adding the obtained intra prediction block and the residual block of the current block (S2207).

(Example 5)

10 is a flowchart illustrating a method of encoding an intra prediction mode when an image is encoded using DIMD according to the present invention.

First, information indicating whether DIMD is performed according to the present invention is encoded (S2501). This information is information informing the video decoding apparatus 600 of a method of inducing an intra prediction mode. That is, it signals whether the intra prediction mode is derived using the DIMD according to the present invention or whether the intra prediction mode is derived using another method.

After determining whether or not the DIMD according to the present invention is used (S2502), if used, the process is terminated, and the intra prediction mode of the current block is induced by the DIMD.

However, if the DIMD according to the present invention is not used, whether or not MPM (Most Probable Mode) is applied is encoded (S2503). MPM may be used as a method other than inducing an intra prediction mode using DIMD according to the present invention.

An MPM flag indicating whether the intra prediction mode of the current block belongs to a most probable mode list and MPM index information are additionally transmitted to the decoding apparatus 600 . The number of intra prediction modes included in the MPM list is very small compared to the total number of intra prediction modes. Accordingly, if the intra prediction mode of the current block belongs to an MPM list (most probable mode list), it is possible to signal to the decoding apparatus 600 using very few bits. The MPM index information indicates whether the intra prediction mode of the current block corresponds to which mode among modes belonging to the MPM list (most probable mode list).

If the MPM flag is 1, the intra prediction mode of the current block belongs to the MPM list, and if the flag is 0, the intra prediction mode of the current block belongs to a residual mode group. The residual mode group may include all intra prediction modes other than intra prediction modes belonging to the MPM list. In step S2503, the encoding of whether MPM (Most Probable Mode) is applied is performed by encoding the MPM flag.

Referring back to FIG. 10, after checking whether the MPM is used (S2504), if not used, the remaining modes except for the MPM candidates are rearranged and the intra prediction mode of the current block is encoded (S2505). If the MPM is used, the MPM index indicating which intra prediction mode candidate is applied (S2506) is encoded and then ended.

(Example 6)

11 is a flowchart illustrating a method of decoding an intra prediction mode when an image is decoded using a DIMD according to the present invention.

First, information indicating whether DIMD is performed according to the present invention is decoded (S2601). This information indicates whether the intra prediction mode is derived using the DIMD according to the present invention or the intra prediction mode is derived using another method.

After determining whether the DIMD according to the present invention is used (S2602), if the DIMD is used, the process ends, and the intra prediction mode of the current block is induced by the DIMD.

However, if the DIMD according to the present invention is not used, whether or not MPM (Most Probable Mode) is applied is decoded (S2603). In step S2603, the MPM flag may be decoded.

If the MPM flag is 1, the intra prediction mode of the current block belongs to the MPM list, and if the flag is 0, the intra prediction mode of the current block belongs to a residual mode group. The residual mode group may include all intra prediction modes other than intra prediction modes belonging to the MPM list.

Next, after checking whether the MPM is used (S2604), if not used, the remaining modes except for the MPM candidates are rearranged and then the intra prediction mode of the current block is decoded (S2505). If the MPM is used, the MPM index indicating which intra prediction mode candidate is applied is decoded (S2506) and then the process is finished.

(Seventh embodiment)

12 is a view for explaining a seventh embodiment according to the present invention. A seventh embodiment of the present invention relates to a method of deriving an intra prediction mode by using a plurality of reference pixel lines in a template.

As shown in Fig. 12, it is assumed that two lines, a reference pixel line 1 and a reference pixel line 2, are used as reference pixel lines of the template. The length of the template, P and Q, is assumed to be 1, respectively.

Angle modes existing on the right side of the upper left 45 degree direction mode are defined as upper angle modes, and template B and reference pixel lines above it are used. Also, angle modes existing on the left side of the upper left 45 degree direction mode are defined as left angle modes, and template A and reference pixel lines on the left are used. Thereafter, prediction is performed for each reference pixel line as shown in FIG. 12 according to the intra prediction mode. For example, the reference pixel line 1 of the template is predicted using the reference pixel line 2 of the template, and an optimal intra prediction mode candidate 1 is generated. Then, the template is predicted by using the reference pixel line 1 of the template, and an optimal intra prediction mode candidate 2 is generated. If the intra prediction mode candidates 1 and 2 are identical, the prediction mode is selected as the intra prediction mode of the current block. If different, it is determined whether to perform one of the above-described DIMD methods according to various embodiments of the present invention.

13 is a flowchart illustrating an intra prediction mode encoding process when the seventh embodiment of the present invention is applied.

First, intra prediction mode candidates are derived using the reference pixel line of the template (S2801). Thereafter, after determining whether the intra prediction mode candidates are the same (S2802), if they are the same, the same mode is selected as the intra prediction mode of the current block, so the flowchart ends. If the prediction mode candidates in the picture are not the same, whether or not to perform DIMD according to the present invention is encoded (S2803).

Subsequent steps S2804 and S2808 are substantially the same as S2502 to S2506 illustrated in FIG. 10 , and thus detailed description thereof will be omitted.

14 is a flowchart illustrating a process of decoding an intra prediction mode when the seventh embodiment of the present invention is applied. Each process shown in FIG. 14 is substantially the same as each process shown in FIG. 13 except that it is performed by the image decoding apparatus 600 , and thus a detailed description thereof will be omitted.

<DIMD variant: transfer of template index>

When DIMD according to the above-described various embodiments is used, the intra prediction mode itself is not signaled. However, in the present embodiment, after each candidate intra prediction mode is derived using a plurality of templates, index information indicating which mode is used is transmitted by the encoding apparatus 100 to the decoding apparatus 600 . 15A and 15B are diagrams for explaining a modified example of DIMD for transmitting a template index. Using the DIMD of the present invention, each intra prediction mode candidate is generated using two templates and then designated using the index. This is an example of the method. For convenience of explanation, it is assumed that R and S indicating the size of the reference pixel region of the template shown in FIG. 15A or 15B are 1 for convenience of description.

In FIG. 15A , the intra prediction mode candidate 1 is derived by using the pixels in the reference pixel region 3103 of the template in the template A 3102 . In FIG. 15B , the intra prediction mode candidate 2 is derived by using the pixels in the reference pixel region 3105 of the template for the template B 3104 . Next, an index indicating whether an intra prediction mode candidate derived from a certain template is an intra prediction mode of the current block 3101 is encoded and transmitted to the decoding apparatus 600 .

Meanwhile, whether a block including a template is coded in which intra prediction mode may be used in this embodiment. For example, in FIGS. 15A and 15B , when the intra prediction mode of the block including the template A 3102 is referred to as the intra prediction mode A, a template using the intra prediction mode A and reference pixels of the template If the intra prediction mode determined by applying to A 3102 is the same, a higher or lower priority may be given. It is also possible to allocate bits when arranging candidates for index setting according to the priority. Similarly, when a plurality of templates exist in addition to the template A 3102, it is also possible to set the priority when allocating bits using the above condition.

16 is a flowchart illustrating a method of encoding an intra prediction mode according to DIMD using a template index.

First, information indicating whether DIMD using a template index is performed is encoded (S3301). After determining whether DIMD using the template index has been performed (S3302), if it has been performed, the template index is encoded and terminated (S3307). If DIMD using the template index is not performed, whether or not MPM (Most Probable Mode) is applied is encoded (S3303). After checking whether or not MPM is applied (S3304), if not applied, the mode except for the MPM candidate is rearranged and then encoding is performed (S3305). If the MPM is applied, the MPM index indicating which candidate is applied is encoded ( S3306) ends.

17 is a flowchart illustrating a method of encoding an intra prediction mode according to DIMD using a template index. Each process shown in FIG. 17 is substantially the same as each process shown in FIG. 16 except that it is performed by the image decoding apparatus 600 , and thus a detailed description thereof will be omitted.

Meanwhile, although FIGS. 15A and 15B exemplify the surrounding two templates, it is also possible to use three or more templates.

<Application example of DIMD: MPM list creation>

Previously, when DIMD according to the present invention is used, the intra prediction mode itself is not signaled to the decoding apparatus 600 or an intra prediction mode candidate derived using a template among a plurality of templates is the intra prediction mode of the current block. Template index information indicating whether or not is selected is transmitted by the encoding apparatus 100 to the decoding apparatus 600 .

Hereinafter, an embodiment in which MPM (Most Probable Mode) candidates are rearranged or an MPM list is generated using the intra prediction mode derived according to DIMD will be described.

After generating the MPM candidates for prediction of the intra prediction mode, it is also possible to arrange the MPM candidates on the top in an order similar to the intra prediction mode derived using the template.

(Example 1)

18 is a diagram for explaining an example of setting an intra prediction mode derived using a template as an MPM candidate.

It is assumed that reconstructed blocks A 3503 and B 3505 exist around the current block 3501 , it is assumed that block A 3503 uses intra prediction and block B 3505 uses inter prediction. . In the block B 3505 , inter prediction is used and there is no intra prediction mode, so in the present embodiment, the intra prediction mode of the block B 3505 is generated using a template. For deriving the intra prediction mode of block B 3505 using the template, refer to the preceding descriptions related to FIGS. 15B and 15B . Meanwhile, when the intra prediction mode of the template B 3104 is derived using the template B 3104 of FIG. 15B , the method of encoding the intra prediction mode, the number of intra prediction modes and the prediction angles are determined by the video encoding apparatus ( 100) or the ones preset by the image decoding apparatus 600 should be the same.

(Second embodiment)

In this embodiment, the MPM candidate is set using which intra prediction mode the block including the template is encoded.

19 is a diagram for explaining MPM candidate setting according to an embodiment of the present invention. Referring to FIG. 19 , it is assumed that the intra prediction mode of the left block 3703 of the current block 3701 is the 10th mode, and the template reference pixel is located in the template A 3705 corresponding to a part of the left block 3703 . It is assumed that the intra prediction mode induced using the ? (not shown) is mode 12. Similarly, it is assumed that the intra prediction mode of the upper block 3707 of the current block 3701 is No. 28, and reference pixels (not shown) of the template are used for the template B 3709 which is a part of the upper block 3707 . It is assumed that the in-screen prediction mode induced by this is number 28. In the case of the left block 3703, considering the entire left block 3703, mode 10 is advantageous for encoding, but since mode 12 is set in template A 3705 adjacent to the current block 3701, the prediction mode of the current block is It can be assumed that mode 12 is more appropriate than mode 10. In this case, when setting the MPM candidate, the MPM candidate may be generated using the intra prediction mode derived from the template A 3705 rather than the intra prediction mode of the left block 3703 .

In the case of the upper block 3707 , since the intra prediction mode of the upper block 3707 and the intra prediction mode derived through the template B 3709 are the same, the same mode is used as an MPM candidate.

As another alternative, the intra prediction mode of the left block 3703, the intra prediction mode derived from the template A 3705, the intra prediction mode of the upper block 3707, and the intra prediction induced from the template B 3709 It is also possible to set a candidate for the MPM by using the four modes. In this case, since the intra prediction mode induced using the template is closer to the current block, it is also possible to assign a small number of bits by assigning a high priority to the intra prediction mode induced using the template when setting the MPM candidate. do.

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 (3)

In the video decoding method,
obtaining reference pixel line index information from the bitstream;
selecting a reference pixel line for a current block from a plurality of reference pixel lines based on the reference pixel line index information;
deriving an intra prediction mode of the current block;
resetting the derived intra prediction mode; and
generating a prediction block of the current block by performing intra prediction based on the selected reference pixel line and the reset intra prediction mode
video decoding method. In the video encoding method,
selecting a reference pixel line for a current block from a plurality of reference pixel lines;
deriving an intra prediction mode of the current block;
resetting the derived intra prediction mode; and
generating a prediction block of the current block by performing intra prediction based on the selected reference pixel line and the reset intra prediction mode;
Reference pixel line index information indicating the selected reference pixel line is encoded in the bitstream.
video encoding method. A computer-readable recording medium storing a bitstream generated by an image encoding method, the image encoding method comprising:
selecting a reference pixel line for a current block from a plurality of reference pixel lines;
deriving an intra prediction mode of the current block;
resetting the derived intra prediction mode; and
generating a prediction block of the current block by performing intra prediction based on the selected reference pixel line and the reset intra prediction mode; and
generating a bitstream by encoding the current block based on the prediction block;
Reference pixel line index information indicating the selected reference pixel line is encoded in the bitstream.
A computer-readable recording medium.

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