KR20180041577A - Method and apparatus for encoding/decoding an image - Google Patents

Abstract

The present invention relates to encoding and decoding an image. A method and an apparatus for encoding/decoding an image according to an embodiment of the present invention includes deriving an intra prediction mode of a reconstructed pixel region based on the reference pixel region of at least one pixel region that has been reconstructed, deriving the prediction mode of a current block based on the intra prediction mode of the derived reconstructed pixel region, obtaining the intra prediction block of the current block using the derived intra prediction mode, and reconstructing the current block by adding the obtained intra prediction block to the residual blocks of the block. It is possible to improve the efficiency of intra prediction.

Description

METHOD AND APPARATUS FOR ENCODING / DECODING AN IMAGE [0002]

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

In recent years, demand for multimedia data such as video has been rapidly increasing on the Internet. However, the rate at which the bandwidth of a channel develops is hard to follow the amount of multimedia data that is rapidly increasing. In order to solve these problems, VCEG (Video Coding Expert Group) of ITU-T and MPEG / Moving Picture Expert Group of ISO / IEC are continuously studying and improving video compression standards.

The video compression consists largely of intra-picture prediction, inter-picture prediction, transform, quantization, entropy coding, and an in-loop filter. Among them, intra prediction is a technique of generating a prediction block for a current block using reconstructed pixels existing around the current block.

Conventional intra-frame prediction generates pixels at a fractional position through an interpolation process using reference pixels at integer positions, and generates prediction blocks using the pixels at the generated fractional positions. In this case, depending on which integer position reference pixels are used and which interpolation method is applied, the error between the original pixel value and the predicted value is affected.

In addition, the conventional intra-picture prediction technique needs to encode a significant amount of information about the prediction mode in order to inform the video decoding apparatus which intra-picture prediction mode of the plurality of intra-picture prediction modes is used for intra-picture prediction of the input image .

An object of the present invention is to improve intra picture prediction efficiency by introducing an intra picture prediction mode of an image to be encoded or decoded using an already reconstructed pixel area in encoding / decoding an image.

According to an aspect of the present invention, there is provided an image encoding / decoding method and an image encoding method for decoding an intra prediction mode of a reconstructed pixel region based on a reference pixel region of at least one pixel region, And derives an intra prediction mode of the current block based on the derived intra prediction mode of the reconstructed pixel region, obtains an intra prediction block of the current block using the derived intra prediction mode, The current block can be restored by adding the intra-prediction block and the residual block of the current block.

According to an aspect of the present invention, there is provided a method and apparatus for decoding an image, the method comprising: obtaining information indicating a method of deriving an intra-prediction mode from an input bitstream; Accordingly, whether to perform the intra prediction mode prediction of the reconstructed pixel area can be selected.

According to an aspect of the present invention, there is provided a method and apparatus for decoding an image, the apparatus comprising: a decoding unit configured to determine a number of available intra-prediction modes or a list of available intra- An 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.

According to an aspect of the present invention, there is provided an image encoding method and apparatus for encoding an information indicating a method of deriving an intra prediction mode of a current block and encoding the information to a bitstream, The video decoding apparatus may selectively derive an intra prediction mode of the reconstructed pixel region according to information indicating a method of deriving an intra prediction mode of the current block.

According to the present invention, the efficiency of compressing an image can be improved by efficiently applying an intra prediction technique used to encode and decode 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 the intra prediction mode.
3 is a diagram for explaining the planar mode.
4 is a diagram for explaining the DC mode.
5 is a diagram for explaining an example of generating a prediction block.
6 is a block diagram of 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 view 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 the DIMD according to the present invention.
11 is a flowchart for explaining a method of decoding an intra prediction mode when an image is decoded using the 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.
FIG. 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 views for explaining a modification of the DIMD for transmitting the template index.
16 is a flowchart for explaining a method of encoding an intra prediction mode according to a DIMD in which a template index is used.
17 is a flowchart for explaining a coding method of an intra prediction mode according to a DIMD in which a template index is used.
18 is a diagram for explaining an example of setting an intra-frame prediction mode derived using a template as an MPM candidate.
19 is a view for explaining MPM candidate setting according to an embodiment of the present invention.

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

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

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

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

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

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

1, an image encoding apparatus 100 includes an image division unit 101, an intra-frame prediction unit 102, an inter-frame prediction unit 103, a subtraction unit 104, a conversion unit 105, An inverse transform unit 106, an entropy encoding unit 107, an inverse quantization unit 108, an inverse transformation unit 109, a multiplication unit 110, a filter unit 111, and a memory 112.

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

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

The image divider 100 may divide the input image into at least one block. At this time, 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 conversion unit (TU). The partitioning may be performed based on at least one of a quadtree or a binary tree. The quad tree is a method of dividing the upper block into sub-blocks whose width and height are half of the upper block. A binary tree is a method of dividing an upper block into sub-blocks, either width or height, which is half of the upper block. Through the binary tree-based partitioning described above, a block can have a square as well as a non-square shape.

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

The predicting units 102 and 103 may include an inter-picture predicting unit 103 for performing inter-prediction and an intra-picture predicting unit 102 for performing intra-prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit and to determine concrete information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. At this time, the processing unit in which the prediction is performed may be different from the processing unit in which the prediction method and the concrete contents are determined. For example, the method of prediction, the prediction mode and the like are determined as a prediction unit, and the execution of the prediction may be performed in a conversion unit.

The residual value (residual block) between the generated prediction block and the original block can be input to the conversion unit 105. In addition, the prediction mode information, motion vector information, and the like used for prediction can be encoded by the entropy encoding unit 107 and transmitted to the decoder along with the residual value. When a specific encoding mode is used, it is also possible to encode the original block as it is without generating a prediction block through the predicting units 102 and 103, and to transmit it to the decoding unit.

The intra prediction unit 102 may determine the intra prediction mode of the current block and generate one or a plurality of prediction blocks using the reference pixels according to the determined intra prediction mode. If the prediction mode of the neighboring block of the current block in which intra prediction is to be performed is inter prediction, a reference pixel included in a neighboring block to which inter prediction is applied may be replaced with a reference pixel in another neighboring block to which intra prediction is applied. That is, when the reference pixel is not available, the reference pixel information that is not available may be replaced with at least one reference pixel of the available reference pixels.

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

The intra prediction 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 the reference pixels of the current block and can 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 on the basis of the pixel value obtained by interpolating the reference pixel, the reference pixel interpolator 102 interpolates the reference pixel, Lt; / RTI > The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates the prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

A residual block including residue 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 can be generated. The generated residual block may be input to the conversion unit 130 and converted.

2 is a diagram for explaining an example of the intra prediction mode. The intra prediction mode shown in FIG. 2 has a total of 35 modes. The 0-th mode represents a planar mode, the 1-th mode represents a DC mode, and the 2-th to 34-th modes represent an angular mode.

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

4 is a diagram for explaining the DC mode. Calculates the average of the restored pixels around the current block, and uses the average value as a predicted value of all the pixels in the current block.

5 is a diagram for explaining an example of generating a prediction block using mode 10 (horizontal mode) and mode 26 (vertical mode) in FIG. In the case of using the 10th mode, each reference pixel tangent to the left side of the current block is copied in the right direction to generate a prediction block of the current block. Similarly, in the 26th mode, each reference pixel tangent to the upper side of the current block is copied downward to generate a prediction block of the current block.

Referring again to FIG. 1, the inter-picture predicting unit 103 may predict a prediction unit based on information of at least one of a previous picture or a following picture of the current picture. In some cases, The prediction unit may be predicted on the basis of information of a certain area. The inter-picture predicting unit 103 may include a reference picture interpolating unit, a motion predicting unit, and a motion compensating unit.

In the reference picture interpolating unit, reference picture information is supplied from the memory 112 and pixel information of an integer pixel or less can be generated in the reference picture. In the case of a luminance pixel, a DCT-based interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of quarter pixels. In the case of a color difference signal, a DCT-based 4-tap interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of 1/8 pixel.

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

The subtracting unit 104 subtracts the current block to be encoded from the intra prediction unit 102 or the inter prediction unit 103 to generate a residual block of the current block.

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

The quantization unit 106 may quantize the values converted into the frequency domain by the conversion unit 105. The quantization factor may vary depending on the block or the importance of the image. The values calculated by the quantization unit 106 may be provided to the inverse quantization unit 108 and the entropy coding unit 107. [

The transforming unit 105 and / or the quantizing unit 106 may be selectively included in the image encoding apparatus 100. That is, the image encoding apparatus 100 can perform at least one of conversion or quantization on the residual data of the residual block, or may skip both the conversion and the quantization, thereby encoding the residual block. A block entering the input of the entropy encoding unit 107 is generally referred to as a transform block even though either the transform or the quantization is not performed in the image coding apparatus 100 or both the transform and the quantization are not performed. The entropy coding unit 107 entropy-codes the 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 encoding unit 107 receives the residual value coefficient information of the encoding unit and the block type information, the prediction mode information, the division unit information, the prediction unit information, the transmission unit information, the motion vector information, the reference frame information , Block interpolation information, filtering information, and the like. In the entropy encoding unit 107, the coefficient of the transform block is encoded in units of partial blocks in the transform block by encoding a non-zero coefficient, a coefficient having an absolute value of 1 or larger than 2, . The coefficient that is not encoded with only the flag can be encoded through the absolute value of the difference between the coefficient encoded through the flag and the coefficient of the actual conversion block. The inverse quantization unit 108 and the inverse transformation unit 109 dequantize the quantized values in the quantization unit 106 and inversely transform the values converted in the conversion unit 105. The residual value generated in the inverse quantization unit 108 and the inverse transformation unit 109 is predicted through the motion estimation unit, the motion compensation unit and the intra prediction unit 102 included in the prediction units 102 and 103 A reconstructed block can be created by combining with prediction units. The multiplier 110 generates a reconstruction block by multiplying the prediction block generated by the prediction units 102 and 103 and the residual block generated through the inverse transform unit 109. [

The filter unit 111 may include at least one of a deblocking filter, an offset correction unit, and an Adaptive Loop Filter (ALF).

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

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

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

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

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

6, an image decoding apparatus 600 includes an entropy decoding unit 601, an inverse quantization unit 602, an inverse transformation unit 603, a multiplication unit 604, a filter unit 605, a memory 606, Prediction units 607 and 608, as shown in FIG.

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

The entropy decoding unit 601 can perform entropy decoding in a procedure opposite to that in which the entropy encoding unit 107 of the image encoding apparatus 100 performs entropy encoding. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied in accordance with the method performed by the image encoder. In the entropy decoding unit 601, the coefficient of the transform block is based on a non-zero coefficient, a coefficient whose absolute value is 1 or larger than 2, and various kinds of flags indicating the sign of a coefficient, etc., Lt; / RTI > A coefficient not represented by only the flag can be decoded through a sum of a coefficient represented by a flag and a signaled coefficient.

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

The inverse transform unit 603 performs inverse transform on the transform block to generate a residual block. At this time, the conversion method can be determined on the basis of the prediction method (inter or intra prediction), the size and / or type of the block, the intra prediction mode, and the like. And operates substantially the same as the inverse conversion unit 109 of Fig.

The multiplication unit 604 generates a reconstruction block by multiplying the prediction block generated by the intra prediction unit 607 or the inter prediction unit 608 and the residual block generated through the inverse transform unit 603. And operates substantially the same as the vaporization section 110 of FIG.

The filter unit 605 reduces various types of noise occurring in the restored blocks.

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

When information on whether or not a deblocking filter has been applied to the corresponding block or picture from the image encoding apparatus 100 and a deblocking filter are applied, information on whether a strong filter or a weak filter is applied can be provided. In the deblocking filter of the video decoding apparatus 600, the deblocking filter related information provided from the video encoding apparatus 100 is provided, and the video decoding apparatus 600 can 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 and the offset value information during encoding.

The ALF may be applied to an encoding unit based on ALF application information, ALF coefficient information, and the like provided from the image encoding apparatus 100. Such ALF information may be provided in a specific set of parameters. The filter unit 605 operates substantially the same as the filter unit 111 of Fig.

The memory 606 stores the reconstruction block generated by the multiplication unit 604. And operates substantially the same as the memory 112 of Fig.

The prediction units 607 and 608 may generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit 601 and the previously decoded block or picture information provided in 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 determination unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 601, prediction mode information of the intra prediction method, motion prediction related information of the inter prediction method, and identifies prediction units in the current coding unit. It is possible to determine whether the unit performs inter prediction or intra prediction. The inter picture prediction unit 608 uses the information necessary for inter prediction of the current prediction unit provided by the image coding apparatus 100 to generate information on at least one of the previous picture of the current picture including the current prediction unit or the following picture The inter prediction of the current prediction unit can be performed. Alternatively, the inter prediction may be performed on the basis of the information of the partial region previously reconstructed in the current picture including the current prediction unit.

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

Intra prediction unit 607 generates a prediction block using the pixels located near the current block to be coded and the previously reconstructed pixels.

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 the reference pixels of the current block and can adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering can be performed on the reference pixels of the current block using the prediction mode of the prediction unit and the AIS filter information provided by the image coding 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 intra-picture prediction unit 607 interpolates the reference pixels to interpolate the reference pixels in the fractional unit position when the prediction mode of the prediction unit is a prediction unit that performs intra-prediction based on the pixel value obtained by interpolating the reference pixels Can be generated. The reference pixel at the generated fractional unit position can be used as the predictive pixel of the pixel in the current block. The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates the prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

Intra prediction section 607 operates substantially the same as intraframe prediction section 102 in FIG.

The inter-picture prediction unit 608 generates an inter-prediction block using the reference picture and the motion information stored in the memory 606. The inter-picture predicting unit 608 operates substantially the same as the inter-picture predicting unit 103 of Fig.

The present invention particularly relates to the derivation of an intra prediction mode, and various embodiments and applications related to the derivation, coding and decoding of the intra prediction mode according to the present invention will be described with reference to the drawings. Since the intra-picture prediction mode can be induced by the image encoding apparatus and the image decoding apparatus according to the same method and / or the same reference by applying the intra-picture prediction mode induction method according to the present invention, It is not necessary to transfer it to the decryption apparatus.

<Induction of Intra-picture Prediction Mode by Video Decoding Apparatus>

In this embodiment, the derivation of the intra prediction mode by the video decoding apparatus is described. The in-picture prediction mode derivation by the image decoding apparatus according to the present invention is hereinafter referred to as a DIMD (Decoder-side Intra Mode Derivation). However, the DIMD can be similarly performed by the image encoding apparatus. Accordingly, the DIMD can be performed by the image encoding apparatus 100 and the image decoding apparatus 600, respectively, despite the name of DIMD. In particular, the DIMD may be performed by the intra-frame prediction unit 102 of the image coding apparatus 100 and the intra-frame 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.

(Embodiment 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 a current block can be derived using already reconstructed pixels located around the current block.

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 on the left side of the template A 2004 and an area 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 1, the reference pixel region 2002 is divided into 2 (Q + N) + 2 (P + M) + 1 reference pixels .

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

Since the intra-picture prediction mode of the current block 2001 is derived using the pixels already reconstructed by the image coding apparatus 100 or the decoding apparatus 600, both of the image coding apparatus 100 and the image decoding apparatus 600 The same intra-picture prediction mode can be derived.

On the other hand, the intra-picture prediction mode applied to the luminance pixels can be equally applied to the chrominance pixels. Since the intra-picture prediction mode is not transmitted to the decoding apparatus 600 by the coding apparatus 100, overhead is not burdened. Thus, it is also possible to add an intra prediction mode at 1/2 position, 1/3 position, or 1/4 position between angular modes. Information on the number of intra prediction modes used at this time can be transmitted to the decoding apparatus 600 using various methods. For example, an exponent of 2 may be used to encode a block header or an upper header of the block, for example, a slice header, a picture header, a sequence header, or the like, and then transmitted to the decoding apparatus 600. Or a method of transmitting an index indicating one of a plurality of intra prediction mode lists constituted by different numbers of intra prediction modes, information on the number of available intra prediction modes is transmitted to the decoding apparatus 600 .

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

In the above-described embodiment, the final intra-prediction mode is derived by applying all of the intra-picture prediction modes to the template A 2004 and / or the template B 2003. However, Mode prediction mode of the current block 2001 may be derived.

(Second Embodiment)

In the first embodiment described above, two template A 2004 and template B 2003 are regarded as one area. However, in the present embodiment, the two templates A 2004 and the template B 2003 are treated as separate areas. Specifically, one of the two prediction modes derived after deriving the prediction mode of the current block using each template may be finally selected.

For example, the angle modes existing on the left side of the 18th angle mode are applied to the template A 2004 only on the basis of the 18th angle mode (the upper left 45-degree direction intra-frame prediction mode) shown in FIG. 2, . And determines the mode having the minimum value among the SAD values calculated for each mode as the intra-frame prediction mode of the template A (2004).

Next, the angle modes existing on the right side of the angle mode 18 are applied to the template B (2003), and SAD is obtained, respectively. Mode prediction mode of the template B (2003) is determined as the mode having the minimum value among the SAD values calculated for each mode. And then selects one of the intra-frame prediction mode of the determined template A 2004 and the intra-frame prediction mode of the template B 2003 as the prediction mode of the current block 2001 finally.

The SAD value corresponding to the DC mode and the SAD value corresponding to the planar mode can be obtained by applying the DC mode and the planar mode to each template. Thereafter, the SAD value corresponding to the mode selected as the in-screen prediction mode 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, I can choose my prediction mode.

(Third Embodiment)

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

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

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

In Fig. 8, the template on the upper side of the current block 2101 is not available, and only the template A on the left side 2104 is available.

If the encoding apparatus 100 and the decoding apparatus 600 use 35 intra-picture prediction modes as illustrated in FIG. 2, but any one of the two templates is unavailable, as shown in FIG. 8 35 intra-picture prediction modes can be applied to only one template 2104 by setting a range as shown in FIG. In FIG. 8, the left lower 45 degrees direction is set to the intra-picture prediction mode 2, the horizontal direction is set to the intra-picture prediction mode 34, and 33 angular modes exist between the prediction mode 2 and the prediction mode 34 Respectively.

It is possible to derive the intra prediction mode of the current block 2101 after performing the DIMD by applying the set of 33 angular modes, the DC mode and the planar mode as described above to the template A 2104 available.

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

(Fourth Embodiment)

9 is a flowchart for explaining a DIMD according to the present invention. This relates to the first to third embodiments described above. 9 can be performed by the intra-frame prediction unit 102 of the image coding apparatus 100 and the intra-frame prediction unit 607 of the image decoding apparatus 600, respectively.

Referring to FIG. 9, an intra prediction mode of the reconstructed pixel region is derived based on a reference pixel region of at least one pixel region that has been reconstructed (S2201). Here, at least one pixel region may be template A (2004, 2104) and / or template B (2003) in the above embodiments. However, it is needless to say that the present invention 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 embodiments. However, it is needless to say that the present invention is not limited to these reference pixel regions.

Next, the 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 to the residual block of the current block (S2207).

(Fifth Embodiment)

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

First, information indicating whether to perform the DIMD according to the present invention is encoded (S2501). This information informs the image decoding apparatus 600 of the method of deriving the intra prediction mode. That is, whether the intra prediction mode is derived using the DIMD according to the present invention or whether another intra prediction mode is derived is signaled.

After determining whether the DIMD according to the present invention is used (S2502), if it has been used, the process is terminated and the intra prediction mode of the current block is derived 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 can be used as a method other than the intra prediction mode derivation using the DIMD according to the present invention.

The MPM flag and the MPM index information indicating whether the intra prediction mode of the current block belongs to the MPM list (most probable mode list) are further 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. Therefore, if the intra prediction mode of the current block belongs to the MPM list (most probable mode list), it is possible to signal to the decoding apparatus 600 using a very small number of bits. The MPM index information indicates which mode among the modes belonging to the MPM list (most probable mode list) the intra prediction mode of the current block.

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 the residual mode group. The residual mode group may include all intra prediction modes other than the intra prediction modes belonging to the MPM list. In step S2503, encoding of MPM (Most Probable Mode) is performed by encoding the MPM flag.

Referring again to FIG. 10, after checking whether the MPM is used (S2504), if not used, the mode is re-aligned except the MPM candidate 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 has been applied is encoded (S2506) and the process ends.

(Sixth Embodiment)

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

First, information indicating whether the 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 whether another intra prediction mode is derived.

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

However, if the DIMD according to the present invention is not used, the MPM (Most Probable Mode) application is decoded (S2603). In step S2603, the MPM flag can 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 the residual mode group. The residual mode group may include all intra prediction modes other than the intra prediction modes belonging to the MPM list.

Next, after confirming whether or not the MPM is used (S2604), if the MPM is not used, the modes other than the MPM candidates are rearranged and 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 ends.

(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 using a plurality of reference pixel lines in a template. \

As shown in Fig. 12, it is assumed that two lines of reference pixel line 1 and reference pixel line 2 are used as reference pixel lines of the template. It is assumed that the lengths of the templates P and Q are 1, respectively.

The angle modes existing on the right side of the upper left 45-degree direction mode are defined as the upper-side angle mode, and the template B and upper reference pixel lines are used. Also, the left angle mode is defined as the left angle mode based on the left upper 45 degree direction mode, and the template A and the reference pixel lines on the left side 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-picture prediction mode candidate 1 is generated. Thereafter, the template is predicted using the reference pixel line 1 of the template, and an optimal intra-picture prediction mode candidate 2 is generated. If the in-picture prediction mode candidates 1 and 2 are the same, the prediction mode is selected as the in-picture prediction mode of the current block. If so, it is determined whether to perform one of the DIMD methods according to various embodiments of the present invention described above.

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

First, intraframe prediction mode candidates are derived using the reference pixel line of the template (S2801). After that, it is determined whether intra-picture prediction mode candidates are the same (S2802). If they are the same, the same mode is selected as the intra-picture prediction mode of the current block. If the in-picture prediction mode candidates are not the same, whether to perform the DIMD according to the present invention is encoded (S2803).

The subsequent steps S2804 S2808 are substantially the same as S2502 through S2506 shown in FIG. 10, and detailed description will be omitted.

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

<Variation example of DIMD: Transmission of template index>

When the DIMD according to the above-described various embodiments is used, the intra prediction mode itself is not signaled. However, in the present embodiment, the candidate intra prediction mode is derived using a plurality of templates, and index information indicating which of the modes is used is transmitted to the decoding apparatus 600 by the encoding apparatus 100. [ 15A and 15B are diagrams for explaining a modified example of a DIMD for transmitting a template index. The DIMD of the present invention is used to generate intraprediction mode candidates using two templates and designate them using an index Method. R and S representing the size of the reference pixel region of the template shown in Fig. 15A or 15B are assumed to be 1 for ease of explanation.

15A, an intra prediction mode candidate 1 is derived using the pixels in the reference pixel region 3103 of the template in the template A 3102. [ 15B, the intra prediction mode candidate 2 is derived using the pixels in the reference pixel region 3105 of the template in the template B (3104). The index indicating the in-picture prediction mode candidate derived from a certain template is transmitted to the decoding apparatus 600 by encoding an index indicating the in-picture prediction mode of the current block 3101. [

On the other hand, whether a block including the template is coded in an intra prediction mode can be used in this embodiment. For example, in Fig. 15A and Fig. 15B, when the intra-frame prediction mode of the block including the template A 3102 is the intra-frame prediction mode A, A 3102 and the intra-picture prediction modes determined by applying the intra-picture prediction modes are the same. It is also possible to allocate bits at the time of candidate placement for index setting according to the priority. Likewise, when there are a plurality of templates other than the template A 3102, it is also possible to set priorities at the time of bit allocation using the above conditions.

16 is a flowchart for explaining a method of encoding an intra prediction mode according to a DIMD in which a template index is used.

First, information indicating whether or not the DIMD in which the template index is used is encoded (S3301). After determining whether the DIMD in which the template index is used has been performed (S3302), if the DIMD has been performed, the template index is encoded and terminated (S3307). If the DIMD in which the template index is used has not been performed, MPM (Most Probable Mode) is applied or not (S3303). After the MPM is applied (S3304), if the MPM is not applied, the mode is rearranged after re-sorting the remaining modes except for the MPM candidate (S3305). If MPM is applied, the MPM index is encoded to indicate which candidate is applied S3306).

17 is a flowchart for explaining a coding method of an intra prediction mode according to a DIMD in which a template index is used. 17 is substantially the same as each step shown in FIG. 16 except that it is performed by the image decoding apparatus 600, detailed description will be omitted.

15A and 15B illustrate two neighboring templates, but it is also possible to use three or more templates.

<Application example of DIMD: MPM list generation>

When the DIMD according to the present invention is used, the intra prediction mode itself is not signaled to the decoding apparatus 600, or the intra prediction mode candidate derived using any one of the plurality of templates is the intra prediction mode Is transmitted to the decoding apparatus 600 by the encoding apparatus 100. [0216]

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

It is also possible to arrange the MPM candidates in the order similar to the intra prediction mode derived by using the template after generating the MPM candidates for prediction of the intra prediction mode.

(Embodiment 1)

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

It is assumed that a block A 3503 and a block B 3505 reconstructed around the current block 3501 exist and that an intra prediction is used for the block A 3503 and an inter prediction is used for the block B 3505 . Since intra-picture prediction is not used in the block B 3505 and the intra-picture prediction mode does not exist, in this embodiment, the intra-picture prediction mode of the block B 3505 is generated using the template. The derivation of the in-picture prediction mode of the block B 3505 using the template will be described with reference to FIGS. 15B and 15B. On the other hand, when the intra-picture prediction mode of the template B 3104 is derived using the template B 3104 of FIG. 15B, the method of coding the intra-picture prediction mode, the number of intra- 100) or the image decoding apparatus 600, as shown in FIG.

(Second Embodiment)

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

19 is a view for explaining MPM candidate setting according to an embodiment of the present invention. 19, it is assumed that the intra-picture prediction mode of the left block 3703 of the current block 3701 is the 10th mode, and the template A 3705 corresponding to a portion of the left block 3703 is referred to as a reference pixel (Not shown) is assumed to be the 12th mode. The intra prediction mode of the upper block 3707 of the current block 3701 is assumed to be 28 and the reference pixels (not shown) of the template are used in the template B 3709 which is a part of the upper block 3707 And the intra-picture prediction mode derived from the intra-picture prediction mode is 28 times. In the case of the left block 3703, considering the entirety of the left block 3703, the 10th mode is advantageous for coding. However, since the 12th mode is set in the template A 3705 adjacent to the current block 3701, It can be assumed that the 12th mode is more appropriate than the 10th mode. In this case, the MPM candidate can be generated using the intra-picture prediction mode derived from the template A 3705 rather than the intra-picture prediction mode of the left block 3703 when the MPM candidate is set.

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

As another alternative, the in-picture prediction mode of the left block 3703, the intra-frame prediction mode derived from the template A 3705, the intra-frame prediction mode of the upper block 3707, It is also possible to set the MPM candidates using the four modes. In this case, since the intra-picture prediction mode derived by using the template is closer to the current block, it is also possible to allocate a lesser number of bits by imposing a higher priority in the intra-picture prediction mode derived by using the template in the MPM candidate setting Do.

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

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

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

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

Claims (15)

Deriving an intra prediction mode of a current block from a plurality of available intra prediction modes;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Deriving an intra prediction mode of the reconstructed pixel region based on the already reconstructed reference pixel region of at least one pixel region; And
And deriving an intra prediction mode of the current block based on the derived intra prediction mode of the reconstructed pixel region. The method according to claim 1,
Wherein the current block, the reconstructed pixel region, and the reference pixel region of the reconstructed pixel region are all located in the same image. 2. The method of claim 1,
Obtaining information indicating a method of deriving an intra prediction mode in an input bitstream,
Wherein the step of deriving the intra prediction mode of the reconstructed pixel region is performed according to information indicating a method of deriving the intra prediction mode. 2. The method of claim 1, wherein deriving an intra prediction mode of a current block from among the plurality of intra prediction modes available comprises:
Obtaining available intraprediction mode information specifying a number of the available intra prediction modes or a list of the available intra prediction modes in an input bitstream; And
And deriving an intra prediction mode of the current block based on the available intra prediction mode information. Deriving an intra prediction mode of a current block from a plurality of available intra prediction modes;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
And derives an intra prediction mode of the current block on the basis of the already restored pixel region, the already-reconstructed pixel region first reference pixel line, and the already reconstructed pixel region second reference pixel line A method of decoding an image. 6. The method of claim 5,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Deriving an intra prediction mode of the first reference pixel line using the second reference pixel line;
Deriving an intra prediction mode of the already reconstructed pixel region using the first reference pixel line;
And selecting the same prediction mode as the intra prediction mode of the current block if the intra prediction mode of the derived first reference pixel line is the same as the intra prediction mode of the derived already reconstructed pixel region To be decoded. Deriving an intra prediction mode of a current block;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Selecting an area used for deriving an intra prediction mode of the current block from a plurality of reconstructed pixel areas;
Deriving an intra prediction mode of the reconstructed pixel region based on the selected reference pixel region of the reconstructed pixel region; And
And deriving an intra prediction mode of the current block based on the derived intra prediction mode of the reconstructed pixel region. [8] The method of claim 7,
Obtaining index information indicating which of the plurality of reconstructed pixel regions in the input bitstream to derive an intra prediction mode of the current block;
And selecting the region to be used for deriving an intra prediction mode of the current block from among the plurality of reconstructed pixel regions based on the index information. Deriving an intra prediction mode of a current block from a plurality of available intra prediction modes;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Deriving an intra prediction mode of the reconstructed pixel region based on the already reconstructed reference pixel region of at least one pixel region; And
And deriving an intra prediction mode of the current block based on the derived intra prediction mode of the reconstructed pixel region. 10. The method of claim 9,
Wherein the current block, the reconstructed pixel region, and the reference pixel region of the reconstructed pixel region are all located in the same image. 10. The method of claim 9,
Encoding the information indicating the method of deriving the intra-prediction mode of the current block, and encoding the encoded information into a bitstream,
Wherein the video decoding apparatus having received the bitstream selectively performs a step of deriving an intra prediction mode of the reconstructed pixel region according to information indicating a method of deriving an intra prediction mode of the current block / RTI &gt; Deriving an intra prediction mode of a current block from a plurality of available intra prediction modes;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
And derives an intra prediction mode of the current block on the basis of the already restored pixel region, the already-reconstructed pixel region first reference pixel line, and the already reconstructed pixel region second reference pixel line A method of encoding an image. 13. The method of claim 12,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Deriving an intra prediction mode of the first reference pixel line using the second reference pixel line;
Deriving an intra prediction mode of the already reconstructed pixel region using the first reference pixel line;
And selecting the same prediction mode as the intra prediction mode of the current block if the intra prediction mode of the derived first reference pixel line is the same as the intra prediction mode of the derived already reconstructed pixel region To be encoded. Deriving an intra prediction mode of a current block;
Obtaining an intra prediction block of the current block using the derived intra prediction mode; And
And restoring the current block by adding the intra prediction block and the residual block of the current block,
Wherein the step of deriving the intra prediction mode of the current block comprises:
Selecting an area used for deriving an intra prediction mode of the current block from a plurality of reconstructed pixel areas;
Deriving an intra prediction mode of the reconstructed pixel region based on the selected reference pixel region of the reconstructed pixel region; And
And deriving an intra prediction mode of the current block based on the derived intra prediction mode of the reconstructed pixel region. 15. The method of claim 14,
And encoding index information indicating which region of the plurality of reconstructed pixel regions to derive an intra prediction mode of the current block, and then encoding the index information into a bitstream.

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