KR20210040240A - Video signal encoding method and apparatus and video decoding method and apparatus - Google Patents

Abstract

Provided are a video signal processing method using tile, brick, and slice information signaling encoding, and a device therefor. According to the present invention, video signal coding efficiency may be improved.

Description

Video signal processing method and apparatus TECHNICAL FIELD [Video signal encoding method and apparatus and video decoding method and apparatus]

The present invention relates to a video signal processing method and apparatus.

Video images are compression-encoded by removing spatio-temporal redundancy and inter-view redundancy, which can be stored in a format suitable for a storage medium or transmitted through a communication line.

The present invention is to improve the coding efficiency of a video signal.

In order to solve the above problems, the present invention provides a tile, brick, and slice information signaling encoding method and apparatus.

The video signal processing method and apparatus according to the present invention can improve video signal coding efficiency through a prediction method using tile, brick, and slice information signaling encoding.

One Basic coding block structure

A picture is divided into a plurality of basic coding units (Coding Tree Unit, hereinafter, CTU) as shown in Figure 1.

Picture 1

It is configured so that it does not overlap with other CTUs. For example, the CTU size may be set to 128x128 in the entire sequence, and any one of 128x128 to 256x256 may be selected and used in picture units.

A coding block/coding unit (CU) may be generated by hierarchically dividing the CTU. Prediction and transformation may be performed in units of coding units, and become a basic unit for determining a prediction coding mode. The prediction encoding mode refers to a plurality of methods of generating a predicted image, such as intra prediction (intra prediction, hereinafter, intra prediction), inter prediction (hereinafter, inter prediction), or combined prediction. It can be mentioned. In more detail, for example, a prediction block may be generated by using at least one of intra prediction, inter prediction, and complex prediction in a coding unit unit. In the inter prediction mode, when the reference picture indicates the current picture, a prediction block may be generated in an area within the current picture that has already been decoded. Since a prediction block is generated using a reference picture index and a motion vector, it can be included in inter prediction. Intra prediction is a method of generating a prediction block using information of the current picture, inter prediction is a method of generating a prediction block using information of another picture that has already been decoded, and composite prediction is a method of mixing inter prediction and intra prediction. This is how you use it.

The CTU can be divided (partitioned) into a quad tree, binary tree or triple tree, as shown in Figure 2. The divided block can be further divided into a quad tree, binary tree, or triple tree. The method of dividing the current block into 4 square partitions is called quad tree partitioning, the method of dividing the current block into 2 irregular partitions is called binary tree partitioning, and the method of dividing the current block into 3 irregular partitions It is defined as binary tree partitioning.

Binary partitioning in the vertical direction ( SPLIT_BT_VER in Figure 2 ) is called vertical binary tree partitioning, and binary tree partitioning in the horizontal direction ( SPLIT_BT_HOR in Figure 2 ) is defined as horizontal binary tree partitioning.

Triple-tree partitioning in the vertical direction ( SPLIT_TT_VER in Fig. 2 ) is called vertical triple-tree partitioning, and triple-tree partitioning in the horizontal direction ( SPLIT_TT_HOR in Fig. 2 ) is defined as horizontal triple-tree partitioning.

The number of additional divisions is called partitioning depth, and the maximum value of the partitioning depth may be set differently for each sequence or picture/tile set, and different partitioning depths according to the partitioning tree type (quad tree/binary tree/triple tree) It can be set to have, and a syntax indicating this can be signaled.

Picture 2

The divided coding block may be further divided by a method such as quad partitioning, binary partitioning, or multi-partitioning to configure a coding unit, or may configure a coding unit without further partitioning.

Figure 3

As shown in Figure 3 , a coding unit can be hierarchically set for one CTU, and a coding unit can be partitioned using at least one of coding units using binary tree partitioning, quad tree partitioning/triple tree partitioning. This method is defined as multi tree partitioning.

A coding unit generated by dividing an arbitrary coding unit having a partitioning depth of k is referred to as a lower coding unit, and the partitioning depth is k+1. A coding unit having a partitioning depth k including a lower coding unit having a partitioning depth k+1 is referred to as an upper coding unit.

The partitioning type of the current coding unit may be limited according to the partitioning type of the upper coding unit and/or the partitioning type of the coding units surrounding the current coding unit.

Here, the partitioning type represents an indicator indicating which partitioning of binary tree partitioning, quad tree partitioning/triple tree partitioning is used.

2 How to generate predictive image

In video encoding, a predicted image can be generated by a plurality of methods, and a method of generating a predicted image is referred to as a predictive encoding mode.

The prediction encoding mode may include an intra prediction encoding mode, an inter prediction encoding mode, a current picture reference encoding mode, or a combined prediction mode.

The inter prediction coding mode is a prediction coding mode that generates a prediction block (prediction image) of the current block using information of a previous picture, and the intra prediction coding mode is a prediction that generates a prediction block using samples adjacent to the current block. It is called an encoding mode. A prediction block may be generated using an image that has already been reconstructed of the current picture, and this is defined as a current picture reference mode or an intra block copy mode.

A prediction block may be generated by using at least two or more of an inter prediction encoding mode, an intra prediction encoding mode, or a current picture reference encoding mode, which is referred to as a combined prediction mode.

2.1 Intra prediction coding method

In intra prediction , as shown in Fig. 4 , an already coded boundary sample around the current block is used to generate intra prediction, and this is defined as an intra reference sample.

The average value of the intra reference sample is predicted by setting the value of all samples in the predicted block (DC mode), or the vertical direction predicted sample generated by weighted predicting the horizontal direction prediction sample and the vertical direction reference sample generated by performing horizontal reference weighted prediction. After generation, a prediction sample may be generated by weighted prediction of a horizontal direction prediction sample and a vertical direction prediction sample (Planar mode), or intra prediction may be performed using a directional intra prediction mode.

Figure 4

As shown in the left figure of Figure 5, intra prediction can be performed using 33 directions (total of 35 intra prediction modes), and 65 directions (total of 67 intra prediction modes) as shown in the right figure of Figure 5 May be. In the case of using directional intra prediction, an intra reference sample (reference reference sample) may be generated in consideration of the direction of the intra prediction mode, and intra prediction may be performed therefrom.

An intra reference sample on the left side of the coding unit is referred to as a left intra reference sample, and an intra reference sample on the upper side of the coding unit is referred to as an upper intra reference sample.

When directional intra prediction is performed, as shown in Table 1, an intra direction parameter (intraPredAng), which is a parameter indicating a prediction direction (or a prediction angle), may be set according to the intra prediction mode. Table 1 below is only an example based on a directional intra prediction mode having a value of 2 to 34 when 35 intra prediction modes are used. It goes without saying that the prediction directions (or prediction angles) of the directional intra prediction modes are further subdivided so that more than 33 directional intra prediction modes can be used.

Picture 5

Table 1

Figure 6

When intraPredAng is negative (for example, when the intra prediction mode index is between 11 and 25), as shown in Figure 6 , the left intra reference sample and the upper intra reference sample are configured in 1D according to the angle of the intra prediction mode. It can be reconstructed as a one-dimensional reference sample (Ref_1D).

Figure 7

When the intra prediction mode index is between 11 and 18, a one-dimensional reference sample can be generated in a counterclockwise direction from an intra reference sample located on the upper right side of the current block to an intra reference sample located on the lower left side, as shown in Figure 7.

In other modes, a one-dimensional reference sample may be generated using only an upper side intra reference sample or a left side intra reference sample.

Figure 8

When the intra prediction mode index is between 19 and 25, a one-dimensional reference sample can be generated in a clockwise direction from an intra reference sample located at the lower left side of the current block to an intra reference sample located at the right side of the current block as shown in Figure 8.

A weight-related parameter ifact applied to at least one reference sample determined based on the reference sample determination index iIdx and iIdx may be derived as in Equations (1) to (2) below. iIdx and i _fact are variably determined according to the slope of the directional intra prediction mode, and a reference sample specified by iIdx may correspond to an integer pel.

iIdx = (y+1) * P _ang /32 (One)

i _fact = [(y+1) * P _ang ] & 31 (2)

A prediction image may be derived by specifying at least one one-dimensional reference sample for each prediction sample. For example, a position of a one-dimensional reference sample that can be used to generate a prediction sample may be specified in consideration of a slope value of a directional intra prediction mode. Each prediction sample may have a different directional intra prediction mode. A plurality of intra prediction modes may be used for one prediction block. A plurality of intra prediction modes may be expressed as a combination of a plurality of non-directional intra prediction modes, a combination of one non-directional intra prediction mode and at least one directional intra prediction mode, or a plurality of directional intra prediction modes. It can also be expressed as a combination of modes. Different intra prediction modes may be applied for each predetermined sample group in one prediction block. A predetermined sample group may consist of at least one sample. The number of sample groups may be variably determined according to the size/number of samples of the current prediction block, or may be a fixed number pre-set in the encoder/decoder independently of the size/number of samples of the prediction block.

Specifically, for example, the position of the one-dimensional reference sample may be specified using the reference sample determination index iIdx.

When the slope of the intra prediction mode cannot be expressed with only one one-dimensional reference sample according to the slope of the intra prediction mode, a first prediction image may be generated by interpolating adjacent one-dimensional reference samples as shown in Equation (3). When the angular line according to the slope/angle of the intra prediction mode does not pass the reference sample located in the integer pel, a first prediction image may be generated by interpolating a reference sample adjacent to the left/right or above/below the corresponding angular line. . The filter coefficient of the interpolation filter used at this time may be determined based on _{i fact.} For example, the filter coefficient of the interpolation filter may be derived based on a distance between a fractional pel located on an angular line and a reference sample located on the integer pel.

P(x,y) = ((32-i _fact )/32)* Ref_1D(x+iIdx+1) + (i _fact /32)* Ref_1D(x+iIdx+2) (3)

When the slope of the intra prediction mode can be expressed with only one one-dimensional reference sample (when the i _fact value is 0), the first prediction image can be generated as shown in Equation (4) below.

P(x,y) = Ref_1D(x+iIdx+1) (4)

2.2 Wide-angle intra prediction coding method

The prediction angle of the directional intra prediction mode may be set between 45 and -135 as shown in Figure 9.

Figure 9

When the intra prediction mode is performed in the amorphous coding unit, there may be a disadvantage of predicting a current sample from an intra reference sample far from the current sample instead of an intra reference sample close to the current sample due to a predefined prediction angle.

For example, as shown in the left figure of Fig. 10 , in a coding unit whose width is larger than the height of the coding unit (hereinafter, horizontal coding unit), intra prediction is performed at a far distance L instead of a close sample T. I can. As another example, as shown in the right figure of Figure 10, in a coding unit whose height is larger than the width of the coding unit (hereinafter, the vertical coding unit), the intra-distance sample T from the distant sample T instead of the close sample L You can make predictions.

Figure 10

In the amorphous coding unit, intra prediction may be performed at a prediction angle wider than a predefined prediction angle, and this is defined as a wide angle intra prediction mode.

내지

의 예측 각도를 가질 수 있으며, 기존 인트라 예측 모드에서 사용된 각도를 벗어나는 예측 각도를 와이드 앵글 각도라고 정의 한다. Wide angle intra prediction mode

To

It can have a prediction angle of, and a prediction angle that deviates from the angle used in the existing intra prediction mode is defined as a wide angle angle.

In the left figure of Figure 10 , sample A in the horizontal direction coding unit can be predicted from the intra reference sample T using the wide-angle intra prediction mode.

In the right figure of Figure 10 , sample A in the vertical direction coding unit can be predicted from the intra reference sample L using the wide-angle intra prediction mode.

N+M intra prediction modes may be defined by adding M wide angle angles to N existing intra prediction modes. Specifically, for example, as shown in Table 2, a total of 95 intra prediction modes may be defined by adding 28 wide angle angles to 67 intra modes.

The intra prediction mode that the current block can use may be determined according to the shape of the current block. For example, 65 directional intra prediction modes may be selected from among 95 directional intra prediction modes based on at least one of a size of a current block, an aspect ratio (eg, a ratio of width and height), and a reference line index.

Table 2

The intra prediction mode angle shown in Table 2 may be adaptively determined based on at least one of a shape of a current block and a reference line index. For example, the intraPredAngle of Mode 15 may be set to have a larger value when the current block is a square than when the current block is an amorphous. Alternatively, the intraPredAngle of Mode 75 may be set to have a larger value when a non-adjacent reference line is selected than when an adjacent reference line is selected.

When using the wide-angle intra prediction mode, the length of the upper intra reference sample can be set to 2W+1, and the length of the left intra reference sample can be set to 2H+1, as shown in Figure 11.

Figure 11

In the case of using wide-angle intra prediction, when the intra prediction mode of the wide-angle intra prediction mode is encoded, the number of intra prediction modes increases, and thus encoding efficiency may be lowered. The wide-angle intra prediction mode can be encoded by replacing the existing intra prediction mode that is not used in the wide-angle intra prediction mode, and the replaced prediction mode is called a wide-angle replacement mode. The wide angle replacement mode may be an intra prediction mode in a direction opposite to the wide angle intra prediction mode.

Specifically, for example, when 35 intra predictions are used as shown in Figure 12 , wide-angle intra prediction mode 35 can be encoded using intra prediction mode 2, which is a wide-angle replacement mode, and wide-angle intra prediction mode 36 is used for wide-angle replacement. It can be encoded in intra prediction mode 3, which is a mode.

Figure 12

The replacement mode and number may be differently set according to the shape of the coding block or the ratio of the height to the width of the coding block. Specifically, for example, Table 3 shows intra prediction modes used according to the ratio of the width and height of a coding block.

Table 3

After generating the intra prediction image, the intra prediction image may be updated for each sample based on the sample position, and this is defined as a sample position-based intra-weighted prediction method (Position dependent prediction combination, PDPC).

2.3 Multi-line intra prediction coding method

As shown in Figure 13 below, intra prediction may be performed on a plurality of intra reference lines, which is referred to as a multi-line intra prediction coding method.

Fig. 13

Intra prediction may be performed by selecting any one of a plurality of intra reference lines composed of an adjacent intra parallel line and a non-adjacent intra reference line, and this is referred to as a multi-line intra prediction method. The non-adjacent intra reference line is a first non-adjacent intra reference line (non-adjacent reference line index 1), a second non-adjacent intra reference line (non-adjacent reference line index 2), and a third non-adjacent intra reference line (non-adjacent reference line). It can be composed of index 3). Only some of the non-adjacent intra reference lines may be used. For example, only a first non-adjacent intra reference line and a second non-adjacent intra reference line may be used, or only a first non-adjacent intra reference line and a third non-adjacent intra reference line may be used.

An intra reference line index (intra_luma_ref_idx), a syntax specifying a reference line used for intra prediction, may be signaled in units of coding units.

Specifically, when using an adjacent intra reference line, a first non-adjacent intra reference line, and a third non-adjacent intra reference line, intra_luma_ref_idx may be defined as shown in Table 4 below.

Table 4

When a non-adjacent intra reference line is used, it may be set not to use a non-directional intra prediction mode. That is, when a non-adjacent intra reference line is used, it may be restricted not to use the DC mode or the planar mode.

The number of samples belonging to the non-adjacent intra reference line may be set to be larger than the number of samples of the adjacent intra parallel line. Also, the number of samples of the i+1th non-adjacent intra reference line may be set to be greater than the number of samples of the ith non-adjacent intra reference line. The difference between the number of upper samples of the i-th non-adjacent intra reference line and the number of upper samples of the i-1th non-adjacent intra reference line may be represented by the reference sample number offset offsetX[i].

offsetX[1] represents a difference between the number of upper samples of the first non-adjacent intra reference line and the number of upper samples of the adjacent intra reference line. The difference between the number of left samples of the i-th non-adjacent intra reference line and the number of left samples of the i-1th non-adjacent intra reference line may be expressed as a reference sample number offset offsetY[i]. offsetY[1] represents a difference value between the number of left samples of the first non-adjacent intra reference line and the number of left samples of the adjacent intra reference line.

A non-adjacent intra reference line with an intra reference line index of i may be composed of an upper non-adjacent reference line refW + offsetX[i], a left non-adjacent reference line refH+ offsetY[i], and an upper left sample. The number of included samples may consist of refW + refH + offsetX[i] + offsetY[i] +1.

refW =2* nTbW (5)

refH =2*　*nTbH (6)

In equations (5) to (6), nTbW represents the width of the coding unit, nTbH represents the height of the coding unit, and whRatio can be defined as in the following equation (7).

whRatio = log2(nTbW/nTbH) (7)

In the multi-line intra prediction coding method, when a non-adjacent intra reference line is used, the wide-angle intra mode may be set not to be used. Alternatively, if the MPM mode of the current coding unit is a wide-angle intra mode, the multi-line intra prediction coding method may be set not to be used.

In this case, a non-adjacent intra reference line with an intra reference line index of i may consist of an upper non-adjacent reference line W + H + offsetX[i], a left non-adjacent reference line H + W + offsetY[i], and an upper left sample. , The number of samples belonging to the non-adjacent intra reference line may be composed of 2W + 2H + offsetX[i] + offsetY[i] +1, and the values of offsetX[i] and offsetY[i] may vary depending on the whRatio value. have.

For example, if the whRatio value is greater than 1, you can set the offsetX[i] value to 1 and the offsetY[i] value to 0. If the whRatio value is less than 1, you can set the offsetX[i] value to 0, offsetY[ i] You can also set the value to 1.

2.5 Inter prediction coding and decoding method

A method of generating a prediction block (prediction image) of a block in a current picture using information of a previous picture is referred to as an inter prediction encoding mode.

A prediction block may be generated from a specific block in a previous picture of the current block.

In the encoding step, the block with the smallest reconstruction error among the blocks in the previous picture can be selected by searching around a collocated block, and the x-axis difference and y-axis difference between the upper left sample of the current block and the upper left sample of the selected block Is defined as a motion vector, and can be signaled by transmitting it to a bitstream. A block generated through interpolation from a specific block of a reference picture specified by a motion vector is called a motion compensated predictor block.

As shown in Fig. 14 , the collocated block represents the block of the picture with the same location and size of the current block and the upper left sample. The corresponding picture may be specified from the same syntax as the reference picture reference.

Fig. 14

In the inter prediction encoding mode, a prediction block may be generated in consideration of the motion of an object.

For example, if you know how and in which direction an object in the previous picture moved in the current picture, a prediction block (prediction image) can be generated by differentiating a block considering motion in the current block, and this is defined as a motion prediction block. .

A residual block may be generated by differentiating a motion prediction block or a corresponding prediction block from the current block.

When motion occurs in an object, if the motion prediction block is used rather than the corresponding prediction block, the energy of the residual block decreases, and compression performance may be improved.

This method of using a motion prediction block is called motion compensation prediction, and most inter prediction coding uses motion compensation prediction.

A value indicating in which direction and to what extent the object in the previous picture has moved in the current picture is called a motion vector. As the motion vector, motion vectors having different pixel precisions may be used in units of sequences, groups of tiles, or blocks. For example, the pixel precision of a motion vector in a specific block may be at least one of octor-pel, quarter-pel, half-pel, integer pel, and 4 integer pel.

In the inter prediction mode, an inter prediction method using translaton motion and an affine inter prediction method using affine motion may be selectively used.

2.4.1 Afine inter prediction coding and decoding method

There are many cases in which a motion of a specific object does not appear linearly in a video. For example, in an image using affine motion such as camera zoom-in, zoom-out, rotation, and affine transformation that enables transformation into arbitrary shapes, as shown in Figure 15, the object's When only the translation motion vector is used for motion, the motion of the object cannot be effectively expressed, and coding performance may be degraded.

Fig. 15

Affine motion can be expressed as the following equation (8).

(8)

(8)

Expressing affine motion using a total of six parameters is effective for images with complex motion, but encoding efficiency may be degraded due to the large number of bits used to encode affine motion parameters.

Accordingly, affine motion can be simplified and expressed with four parameters, and this is defined as a four-parameter afine motion model. Equation (9) expresses affine motion with four parameters.

(9)

(9)

The four-parameter affine motion model may include motion vectors at two control points of the current block. The control point may include an upper left corner, an upper right corner, and a lower left corner of the current block. As an example, as shown in the left figure of Figure 16 , the 4 parameter affine motion model is determined by the motion vector sv0 at the upper left sample (x0,y0) of the coding unit and the motion vector sv1 at the upper right sample (x1,y1) of the coding unit. Can be determined, and sv ₀ and sv ₁ are defined as affine seed vectors. _{Hereinafter, it is assumed that the affine seed vector sv 0} located in the upper left corner is the first affine seed vector, and the affine seed vector sv ₁ located in the upper right corner is the second affine seed vector. In the 4-parameter affine motion model, it is also possible to replace one of the 1/2 affine seed vectors with the affine seed vector located in the lower left corner.

Fig 16

The 6-parameter affine motion model is an _{affine motion model in which the motion vector sv 2} of the residual control point (e.g., sample (x2,y2) in the lower left corner) is added to the 4-parameter affine motion model as shown in the right figure of Figure 16. . Hereinafter, assuming that the affine seed vector sv ₀ located at the upper left is the first affine seed vector, the affine seed vector sv ₁ located at the upper right is the second affine seed vector, and the affine seed vector located at the lower left Assume that sv ₂ is the third affine seed vector.

Information about the number of parameters for expressing affine motion may be encoded in the bitstream. For example, a flag indicating whether 6 parameters are used and a flag indicating whether 4 parameters are used may be encoded in a tile group, a tile, a coding unit, or a CTU unit. Accordingly, a 4-parameter affine motion model to a 6-parameter affine motion model may be selectively used in units of tile groups, coding units, or CTUs.

A motion vector can be derived for each sub-block of the coding unit using the affine seed vector, as shown in Figure 17, and this is defined as an affine sub-block vector. _

Figure 17

The affine sub-block vector can also be derived as in Equation (10) below. Here, the reference sample position (x,y) of the sub-block may be a sample located at a corner of the block (eg, an upper left sample), or a sample having at least one of the x-axis or y-axis at the center (eg, a center sample) .

(10)

(10)

Motion compensation may be performed in units of coding units or in units of sub-blocks within the coding unit by using the afine sub-block vector, and this is defined as an afine inter prediction mode. In Equation (10), (x ₁ -x ₀ ) may be the same as the width of the coding unit and the width of the unit w, or may be set to w/2 or w/4.

2.5.2 Merge mode coding method

Motion information (motion vector, reference picture index, etc.) of the current coding unit is not encoded, and can be derived from motion information of neighboring blocks. Motion information of any one of the neighboring blocks can be set as motion information of the current coding unit, and this is defined as a merge mode.

Neighboring blocks used for the remaining mode may be a picture 28 remaining candidate indices from 0 to 4 and the block are adjacent to the coding unit as the (current boundary with the abutting block of the coded unit), as shown in Figure 28, the remaining candidate index from 5 to 26 of the It may be a non-adjacent block.

Fig. 28

When the distance of the merge candidate to the current block exceeds a predefined threshold, it may be set as not available.

For example, a predefined threshold may be set to the height of the CTU (ctu_height) or ctu_height+N, and this is defined as a merge candidate usable threshold. That is, the y-axis coordinate (y _{i ) of the merge candidate and the y-axis coordinate difference (y 0} ) (i.e., y _i- y ₀ ) of the upper left sample of the current coding unit (hereinafter, the reference sample of the current coding unit) are the merge candidate available threshold. If it is greater than the value, the merge candidate may be set as not available. Here, N is a predefined offset value. Specifically, for example, N may be set to 16 or ctu_height may be set.

Fig. 29

When there are many merge candidates crossing the CTU boundary, many unusable merge candidates occur, and encoding efficiency may be lowered. Merge candidates present above the coding unit (hereinafter, upper merge candidates) may be set as small as possible, and merge candidates present at the left and lower portions of the coding unit (hereinafter, lower left merge candidates) may be set as many as possible.

As shown in Figure 29, the difference between the y-axis coordinate of the current coding unit reference sample and the y-axis coordinate of the upper merge candidate may be set so as not to exceed twice the height of the coding unit.

It can be set so that the difference between the x-axis coordinates of the reference sample of the current coding unit and the x-axis coordinates of the lower left merge candidate does not exceed twice the width of the coding unit.

A merge candidate adjacent to the current coding unit is called an adjacent merge candidate, and a merge candidate that is not adjacent to the current coding unit is defined as a non-adjacent merge candidate.

A flag isAdjacentMergeflag indicating whether the merge candidate of the current coding unit is an adjacent merge candidate may be signaled.

If the isAdjacentMergeflag value is 1, it indicates that the motion information of the current coding unit can be derived from the neighboring merge candidate, and if the isAdjacentMergeflag value is 0, it indicates that the motion information of the current coding unit can be derived from the non-adjacent merge candidate.

2.4.3 Inter-decoding area merge method

Motion information (motion vector and reference picture index) of a coding unit that is already encoded by inter prediction in the current picture can be stored in a list having a predefined size, which is defined as an inter-region motion information list.

Motion information (motion vector and reference picture index) in the inter-region motion information list is called an inter-decoding region merge candidate.

The inter decoding region merge candidate can be used as a merge candidate of the current coding unit, and this method is defined as an inter decoding region merge method.

When the tile group is initialized, the inter-region motion information list is empty, and when a partial region of a picture is encoded/decoded, it can be added to the inter-region motion information list. The initial inter decoding region merge candidate of the inter region motion information list may be signaled through the tile group header.

If the coding unit is to inter-prediction encoding / decoding may update the motion information of the coding unit in the inter-domain motion information list, as shown in Figure 30. When the number of inter-decoding region merge candidates in the inter-region motion information list is the maximum value, the value with the smallest inter-region motion information list index (firstly, the inter-decoding region merge candidate in the inter-region motion information list) is removed. , A motion vector of the most recently encoded/decoded inter-region may be added as an inter-decoding region merge candidate.

Fig. 30

The motion vector mvCand of the decoded coding unit may be updated in the inter-region motion information list HmvpCandList. At this time, if the motion information of the decoded coding unit is the same as any one of the motion information in the inter-region motion information list (when both the motion vector and the reference index are the same), the inter-region motion information list is not updated, or as shown in Figure 32 . The motion vector mvCand of the coding unit decoded together may be stored at the end of the inter-region motion information list. At this time, if the index of HmvpCandList that has the same motion information as mvCand is hIdx, HMVPCandList [i] can be set to HVMPCandList[i-1] for all i larger than hIdx as shown in Figure 32. When sub-block merge candidates are used in the currently decoded coding unit, motion information of the representative sub-block in the coding unit may be stored in the inter-region motion information list.

As an example, the representative subblock in the coding unit is shown in Figure 31 . Likewise, it may be set as the upper left sub-block in the coding unit or as the middle sub-block in the coding unit.

Fig. 31

Fig. 32

A total of NumHmvp motion information (motion vector and reference picture index) can be stored in the inter-region motion information list, and NumHmvp is defined as the size of the inter-region motion information list.

The size of the inter-region motion information list may use a predefined value. The inter-region motion information list size may be signaled in the tile group header. For example, the size of the inter-region motion information list may be defined as 16, may be defined as 6, or may be defined as 5.

In a coding unit that is inter prediction and has an affine motion vector, it may be limited not to have an inter-region motion information list.

Alternatively, in the case of inter prediction and an affine motion vector, the affine subblock vector may be added to the inter-region motion information list. In this case, the position of the sub-block may be set to the upper left or upper right, or the center sub-block.

Alternatively, the average motion vector value of each control point may be added to the inter-region merge candidate list.

If the motion vector MV0 derived by encoding/decoding a specific coding unit is the same as any one of the inter-decoding region merge candidates, MV0 may not be added to the inter-region motion information list. Alternatively, an existing inter-decoding region merge candidate having the same motion vector as MV0 may be deleted, and the index allocated to MV0 may be updated by newly including MV0 in the decoding region merge candidate.

In addition to the inter-region motion information list, an inter-region motion information long term list HmvpLTList may be configured. The size of the inter-region motion information long term list may be set equal to the size of the inter-region motion information list, or may be set to a different value.

The inter-region motion information long term list may be composed of an inter-decoding region merge candidate initially added to the tile group start position. After the inter-region motion information long term list is configured with all available values, the inter-region motion information list may be configured, or motion information in the inter-region motion information list may be set as motion information of the inter-region motion information long term list.

At this time, the inter-region motion information long-term list configured once may be updated again when no update is performed, a decoded region of the tile group is more than half of the entire tile group, or may be set to be updated every m CTU lines. The inter-region motion information list may be updated whenever the inter-region is decoded, or may be set to be updated in units of CTU lines.

The motion information and partition information or type of the coding unit may be stored in the inter-region motion information list. The inter-decoding region merging method may be performed using only inter-region merge candidates having a similar partition information and shape as the current coding unit.

Alternatively, an inter-region merge candidate list may be individually configured according to the block type. In this case, one of a plurality of inter-region merge candidate lists may be selected and used according to the shape of the current block.

2.7 Symmetric MVD (Symmetric MVD) coding method

Fig. 40

As shown in Figure 40 , the symmetric MVD of the motion vector difference (MVD) of the motion vector used in L0 (the MVD with the same vector size and opposite direction) can be set as the MVD of L1, and this is called a symmetric MVD encoding method. When using symmetric MVD coding, the MV can be derived as shown in the following equations (19) to (20).

(mvx0, mvy0) (mvp_x0 + mvd_x0, mvpy0 + mvdy0) (19)

(mvx0, mvy0) (mvp_x0-mvd_x0, mvpy0-mvdy0) (20)

That is, the motion prediction information of LIST1 is mv

A flag sym_mvd_flag indicating whether symmetric MVD is used in units of coding units may be signaled through a bitstream. If the value of sym_mvd_flag is 1, it indicates that the coding unit uses the symmetric MVD coding method.

When using symmetric MVD coding, the first unidirectional reference picture has a smaller POC (Picture Order Count, picture output order) than the current picture in the first unidirectional reference picture list (RefPicList0), and the picture closest to the current picture (hereinafter, Left minimum distance picture), and the first unidirectional reference picture index (RefPicList0) can be set as the reference picture index of the left minimum distance picture. Here, the nearest picture means a reference picture having the smallest difference between the POC of the current picture and the reference picture.

Alternatively, the first unidirectional reference picture may be set to RefPicList0[0].

In the case of using symmetric MVD coding, the second unidirectional reference picture can be set as a picture having a larger POC than the current picture in the second unidirectional reference picture list (RefPicList1) and closest to the current picture (hereinafter, the minimum distance picture on the right). , The second unidirectional reference picture index RefPicList1 may be set as a reference picture index of the right minimum distance picture.

Alternatively, the second unidirectional reference picture may be set to RefPicList1[1].

When there is no picture with a smaller POC than the current picture in the first unidirectional reference picture list, a picture having a larger POC than the current picture in the first unidirectional reference picture list and the closest to the current picture may be set as the first unidirectional reference picture. /

When there is no picture with a larger POC than the current picture in the second unidirectional reference picture list, a picture with a smaller POC than the current picture in the second unidirectional reference picture list and the closest to the current picture may be set as the second unidirectional reference picture.

When the POC of the first unidirectional reference picture and the POC of the second unidirectional reference picture are smaller than the POC of the current picture, and the POC of the first unidirectional reference picture and the POC of the second unidirectional reference picture are the same, symmetric mvd encoding is not used. May be. Specifically, a syntax table as shown in Table 5 may be used.

Table 5

When the first unidirectional reference picture and the second unidirectional reference picture are both on the left side of the current picture, or both are on the right side, instead of symmetric MVD, the MVD of L1 is scaled and used as shown in the following equations (21) to (22). May be.

(mvx0, mvy0) (mvp_x0 + mvd_x0, mvpy0 + mvdy0) (21)

(mvx0, mvy0) (mvp_x0 + scale*mvd_x0, mvpy0-mvdy0) (22)

In the following equations (21) to (22), the scale value can be defined as in equations (23) to (24).

scale = abs(POC_Curr-POC_L0) / abs(POC_Curr-POC_L1) (23)

scale = abs(POC_Curr-POC_L1) / abs(POC_Curr-POC_L0) (24)

In Equations (23) to (24), POC_Curr represents the POC value of the current picture, POC_L0 represents the POC value of the first unidirectional reference picture, and POC_L1 represents the POC value of the second unidirectional reference picture.

If there is a reference picture having a greater POC value than the current picture in the second unidirectional reference picture list, and at least one picture having a smaller POC value than the current picture in the first unidirectional reference picture list exists, the symmetric MVD encoding method is not used. May not.

Alternatively, when there is no reference picture having a lower POC value than the current picture in the first unidirectional reference picture list, and at least one reference picture having a larger POC value than the current picture in the second unidirectional reference picture list exists, the symmetric MVD encoding method May not be used.

3 Transform and quantization

An image obtained by subtracting the predicted image from the original image is called a residual image.

The residual image may be decomposed into binary frequency components through a two-dimensional transform such as a discrete cosine transform (DCT). Even if high-frequency components are removed from an image, there is a characteristic that significant distortion does not occur. If the value corresponding to the high frequency is decreased or set to 0, the compression efficiency can be increased while the visual distortion is not large.

Discrete sine transform (DST) may be used according to the size of the prediction block or the prediction mode. Specifically, for example, when the prediction block/coding block is in the intra prediction mode and the size of the prediction block/coding block is smaller than NxN, the DST transform may be used, and other prediction blocks/coding blocks may be set to use the DCT.

DCT is a process that decomposes (transforms) an image into 2D frequency components using a cosine transform, and the frequency components at that time are expressed as a base image. For example, if DCT transformation is performed in an NxN block, N ² basic pattern components can be obtained. Performing DCT transformation is to obtain the size of each of the basic pattern components included in the original pixel block. The size of each basic pattern component is defined as a DCT coefficient.

In general, a discrete cosine transform (DCT) is mainly used in an image in which many non-zero components are distributed in a low frequency, and a Discrete Sine Transform (DST) may be used in an image in which a large number of high-frequency components are distributed.

DST represents a process of decomposing (converting) an image into 2D frequency components using sin transformation. A 2D image can be decomposed (transformed) into a 2D frequency component using a transformation method other than DCT or DST transformation, and this is defined as 2D image transformation.

Among the residual images, a 2D image transformation may not be performed in a specific block, and this is defined as transform skip. Quantization can be applied after the transform skip. Whether to allow the transform skip may be determined based on at least one of the size or shape of the coding unit. As an example, the transform skip may be limited to be used only in coding units of a specific size or less. For example, it is possible to set the transform skip to be used only in blocks smaller than 32x32. Alternatively, it is possible to restrict the use of transform skip to only a square block. Specifically, for example, transformation skip may be applied in units of 32x32, 16x16, 8x8, and 4x4 blocks.

Alternatively, when the sub-partition intra coding method is used, transformation skip may be selectively applied in units of sub-partitions. Specifically, as shown in Figure 41 , transform skip may be used in the upper sub-partition, DST7 in the horizontal direction and DCT8 (tu_mts_idx 3) in the vertical direction may be performed in the lower sub-partition.

Fig. 41

DCT, DST, or 2D image transformation may be applied to an arbitrary block in the 2D image, and the transformation used in this case is defined as a first transformation. After performing the first transformation, transformation may be performed again in a partial region of the transformation block, and this is defined as a second transformation.

The first transformation may use one of a plurality of transformation cores. Specifically, for example, one of DCT2, DCT8, or DST7 may be selected and used in the transform block. Alternatively, the transform cores of the horizontal direction transformation and the vertical direction transformation of the transformation block may be individually determined. Accordingly, the horizontal direction transformation and the vertical direction transformation may be the same or different. Different transform cores may be used in the horizontal direction transformation and the vertical direction transformation, and this is defined as a multiple transformation core encoding method (Multiple Transform Selection (MTS)).

Block units for performing the first transformation and the second transformation may be set differently from each other. Specifically, for example, after performing the first transform in an 8x8 block of the residual image, the second transform may be performed for each 4x4 sub-block. For another example, after performing the first transform in each 4x4 block, the second transform may be performed in each 8x8 block.

The residual image to which the first transform is applied is defined as a first transform residual image.

DCT, DST, or 2D image transformation may be applied to the first transform residual image, and the transform used in this case is defined as a second transform. The 2D image to which the second transformation is applied is defined as a second transformation residual image.

A sample value in the block after performing the first transformation and/or the second transformation or the sample value in the block after performing the transformation skip is defined as a transform coefficient. Quantization refers to the process of dividing a transform coefficient by a predefined value to reduce the energy of a block. A value defined to apply quantization to a transform coefficient is defined as a quantization parameter.

A predefined quantization parameter may be applied in units of sequences or blocks. Typically, a quantization parameter can be defined with a value between 1 and 63.

After performing transformation and quantization, inverse quantization and inverse transformation may be performed to generate a residual reconstructed image. A first reconstructed image may be generated by adding a predicted image to the residual reconstructed image.

Index information'tu_mts_idx' indicating the transformation type of the current block may be signaled through a bitstream. tu_mts_idx may refer to one of a plurality of transform type candidates representing an example of a combination of a vertical transform type and a horizontal transform transform type. On the basis of the transformation type candidate specified by tu_mts_idx, whether to skip the vertical direction transformation and the horizontal direction transformation, and the vertical direction transformation core and the horizontal direction transformation core may be determined. The conversion core may include at least one of DCT2, DCT8, and DST7. As shown in Table 5, a transform type candidate may be set for each tu_mts_idx. Specifically, as shown in Table 6, if tu_mts_idx is 0, DCT-II can be applied to both horizontal and vertical direction conversion, and if tu_mts_idx is 2, DCT-VIII is applied to horizontal direction conversion, and vertical direction conversion DST-VII can be applied to.

Table 6

In the case of using the sub-partition encoding method, a different set of transform cores may be used for each sub-partition, or the same set of transform cores may be used for each coding unit. In this case, only the first sub-partition may signal tu_mts_idx through the bitstream.

Specifically, for example, as shown in the left figure of Figure 42, DST7 may be used as the horizontal direction transform core and DCT8 may be used as the vertical direction transform core in all sub-partitions in the coding unit. As another example, as shown in the right figure of Figure 42, DCT8 may be used as the horizontal direction transform core and DST8 may be used as the vertical direction transform core in all sub-partitions in the coding unit.

Fig. 32

5 In-loop filtering

In-loop filtering is a technique that adaptively performs filtering on a decoded image in order to reduce the loss of information that occurs during quantization and encoding. A deblocking filter, a sample adaptive offset filter (SAO), and an adaptive loop filter (ALF) are examples of in-loop filtering.

A second reconstructed image may be generated by performing at least one of a deblocking filter, a sample adaptive offset (SAO), or an adaptive loop filter (ALF) on the first reconstructed image.

After applying the deblocking filter to the reconstructed image, SAO and ALF may be applied.

In the video encoding process, transformation and quantization are performed in units of blocks. A loss occurs during the quantization process, and a discontinuity occurs at the boundary of the reconstructed image. Discontinuous images appearing at the block boundary are defined as block quality deterioration (blocking artifact).

The deblocking filter is a method of mitigating block quality deterioration (blocking artifact) occurring at a block boundary of a first image and improving encoding performance.

Fig. 43

Block quality deterioration can be alleviated by performing filtering at the block boundary, and whether the block is coded in intra prediction mode as shown in Figure 43 , or whether the difference between the absolute values of the motion vectors of neighboring blocks is greater than a predefined threshold. A block filter strength (BS) value may be determined based on at least one of whether or not reference pictures of neighboring blocks are identical to each other. When the BS value is 0, filtering is not performed, and when the BS value is 1 or 2, filtering may be performed at a block boundary.

Since quantization is performed on a transform coefficient, a ringing artifact occurs at the edge of an object, or a pixel value increases or decreases by a certain value compared to the original because quantization is performed in the frequency domain. The SAO can effectively reduce the ringing phenomenon by adding or subtracting a specific offset in units of blocks in consideration of the pattern of the first reconstructed image. SAO is composed of an edge offset (hereinafter referred to as EO) and a band offset (BO) according to characteristics of a reconstructed image. Edge offset is a method of adding an offset to a current sample differently according to a sample pattern of surrounding pixels. Band offset is to reduce coding errors by adding a certain value to a set of pixels with similar pixel brightness values in a region. By dividing the pixel brightness into 32 uniform bands, pixels having similar brightness values can be made into one set. For example, four adjacent bands can be grouped into one category. One category can be set to use the same offset value.

ALF (Adaptive Loop Filter) is a method of generating a second reconstructed image using any one of predefined filters for a first reconstructed image or a reconstructed image that has subjected deblocking filtering to the first reconstructed image as shown in Equation (25). .

(25)

(25)

Fig. 44

In this case, the filter can be selected in units of pictures or units of CTU.

In the Luma component, you can select any of the 5x5, 7x7 or 9x9 diamond shapes as shown in Figure 44 below. In the chroma component, it may be limited to use only the 5x5 diamond shape.

5 Video coding structure

Fig. 45

Figure 45 is a diagram showing the video coding structure. The input video signal can be divided into a predetermined coding unit with the smallest rate distortion value. A prediction image may be generated by performing at least one of inter prediction, intra prediction, or complex prediction for each coding unit. In order to perform inter prediction in the encoding step, motion estimation may be performed. A residual image may be generated by differentiating the predicted image from the original image.

A transform coefficient may be generated by performing a first transform and/or a second transform on the residual image, or a transform skip coefficient may be generated by performing a transform skip. Quantization may be performed on a transform coefficient or a transform skip coefficient to generate a quantized transform coefficient or a quantized transform skip coefficient.

A reconstructed image may be generated by performing inverse quantization and inverse transformation on the quantized transform coefficient or the quantized transform skip coefficient. In-loop filtering may be performed on the reconstructed image to generate a filtered reconstructed image. This filtered and reconstructed image becomes the final output image in the encoding step. The filtered reconstructed image is stored as a reference picture buffer and can be used as a reference picture in another picture.

6 Video encoding method using tiles

High-resolution images are used in immersive media applications such as panoramic video, 360-degree video or 4K/8K Ultra High Definition (UHD). Parallelization is required for real-time or low-delay encoding of high-resolution images. A certain region of a picture may be encoded and/or decoded independently of each other by using a tile.

A block in a tile can be set not to encode/decode an image by referring to data in another tile or by using it as a reference sample. For example, data in another tile is not used as a reference sample in intra prediction, or data in another tile is not used as a candidate for motion vector derivation (e.g., merge candidate, AMVP candidate, or HVMP candidate), or The data in the tile can be set not to be used for calculating the context of the symbol.

A probability table of a context adaptive binary arithmetric coding (CABAC) context may be initialized for each tile unit. You can disable the loop filter at the tile boundary (the boundary between two neighboring tiles). Alternatively, information indicating whether to use a loop filter at the tile boundary may be encoded.

Fig. 50

It may be set not to be used as a candidate for motion vector derivation (eg, a merge candidate, an AMVP candidate, or an HVMP candidate) or not to use data in another tile for calculating the context of a symbol.

A probability table of a context adaptive binary arithmetric coding (CABAC) context may be initialized for each tile unit. You can disable the loop filter at the tile boundary (the boundary between two neighboring tiles). Alternatively, information indicating whether to use a loop filter at the tile boundary may be encoded.

Fig. 50

A picture may be composed of one or at least one or more slices. The slice may be a raster-scan slice or a rectangular slice. A raster scan slice is defined as a group of one or more contiguous tile(s) when following the raster scan order. The left figure in Figure 50 shows a raster scan slice. Raster scan slices can take on a non-rectangular shape. A rectangular slice is defined as a group of tiles having a rectangular shape. The figure on the right of Figure 50 shows a square-shaped slice.

The boundary of the slice may coincide with the picture boundary and/or the tile boundary. As an example, the boundary of the slice may be set so that the left boundary and the upper boundary are located at the picture boundary, or the boundary of the slice may be set to be located at the boundary of an already decoded tile.

A slice may be composed of one or a plurality of tiles.

The tile may have a rectangular shape. Alternatively, non-rectangular-shaped tiles can be allowed. Information indicating whether a non-rectangular shape tile exists may be encoded. The boundary of the tile may coincide with the picture boundary and/or the CTU boundary.

Information indicating whether a plurality of tiles exist in a picture may be signaled through a bitstream. When there are multiple tiles in a picture, as shown in Fig. 51, tiles adjacent to the left or right may have the same height (hereinafter, horizontal tile set/tile row), or the width of the tiles adjacent to the top or bottom may be It may be configured to be the same (hereinafter, a vertical tile set/tile column). Information indicating whether the previous tile has the same height as the previous tile or information indicating whether the previous tile has the same width as the previous tile may be signaled through the bitstream.

Alternatively, all tiles except for tiles adjacent to a picture boundary in a picture may be limited to have the same size. Information indicating whether the sizes of tiles are uniform through the bitstream may be signaled through the bitstream.

Fig. 51

Table 7

Information indicating the number of vertical tile sets in a picture may be signaled through a picture parameter set, a sequence parameter set, or a slice header. As an example, the information may be the syntax num_tile_columns_minus1 shown in Table 7. In the example of Figure 51, the number of tile sets in the vertical direction is 4, and a value of the syntax num_tile_columns_minus1 indicating this can be set to 3. The syntax column_width_minus1[i] indicating the width of the i-th vertical tile set may be signaled.

Information indicating the number of horizontal tile sets in a picture may be signaled through a picture parameter set, a sequence parameter set, or a slice header. As an example, the information may be the syntax num_tile_rows_minus1 shown in Table 7. In the example of Figure 51, the number of horizontal tile sets is 3, and a value of the syntax num_tile_rows_minus1 representing this may be set to 2. The syntax row_height_minus1[i] indicating the height of the i-th horizontal tile set may be signaled.

Information indicating whether tiles have the same size may be signaled through a picture parameter set, a sequence parameter set, or a slice header. As an example, the information may be the same size tile flag uniform_tile_spacing_flag shown in Table 7. If the uniform_tile_spacing_flag value is 1, this indicates that the widths of each tile in the picture are equally divided, and the heights of the tiles are equally divided.

If the uniform_tile_spacing_flag value is 1, the syntax tile_cols_width_minus1 indicating the basic width of the tile and the syntax tile_rows_height_minus1 indicating the basic height of the tile may be signaled. Tiles other than tiles adjacent to the right/bottom boundary in the current picture may have the basic width and the basic height.

For example, if uniform_tile_spacing_flag is 1, the width of tiles other than tiles adjacent to the picture boundary may be set to (tile_cols_width_minus1+1)*CtbSizeWidth, and the height may be set to (tile_rows_hieight_minus1+1)*CtbSizeHeight.

The height of the tile at the picture boundary (tile_rows_height_minus1+1)*CtbSizeHeight or less, and the width may be (tile_cols_width_minus1+1)*CtbSizeWidth or less.

When the uniform_tile_spacing_flag value is 0, information indicating a width of a tile and information indicating a height of a tile may be encoded for each tile. As an example, the syntax tile_column_width_minus1[i] indicating the width of the tile and the syntax tile_row_height_minus1[i] indicating the height of the tile may be signaled.

For example, tile_column_width_minus1[i] represents the width of the i-th tile, and tile_row_height_minus1[i] represents the height of the i-th tile.

Fig. 52

Tiles can also consist of one or more bricks. Bricks can be units of parallel processing. Bricks can be encoded/decoded independently of each other. When encoding/decoding a block within a brick, it can be set not to refer to data of other bricks. For example, when encoding/decoding a block in a brick, data in the tab is not used as a reference sample for intra prediction, or data in the tab is a candidate for motion vector derivation (e.g., merge candidate, AMVP candidate or HVMP candidate), or data in tabs can be set not to be used for calculating the context of the symbol.

Alternatively, information indicating whether parallel processing between bricks is required may be encoded. According to the information, the availability of data included in the other brick may be determined when encoding/decoding a block included in the brick.

Bricks can be created by dividing tiles horizontally. Figure 52 shows an example in which tiles located in the rightmost row are divided into a plurality of bricks. When scanning tiles according to the raster scan sequence as shown in the picture on the right of, for a tile including multiple bricks, the next tile can be scanned after all the bricks in the tile are scanned. In addition, when scanning a tile, as shown on the left of Fig. 52, after scanning the CTB in the tile according to the raster scan order, the CTB in the next tile may be scanned according to the tile scan order. The brick boundary can coincide with the CTU boundary. That is, more than one CTU row can be defined as one brick.

Table 8

At least one of information indicating whether a tile is divided into bricks, information indicating the number of bricks in a tile, information indicating whether a tile divided into multiple bricks in a picture exists, or information indicating the size of a brick may be encoded. have. For example, as shown in Table 8, a flag brick_spliitng_present_flag indicating that at least one tile can be divided into two or more bricks may be signaled through a bitstream.

If the brick_splitting_present_flag value is 1, it indicates that at least one tile is divided into two or more bricks, and if the brick_splitting_present_flag value is 0, it indicates that there is no tile divided into two or more bricks in a picture or in pictures referencing PPS.

As shown in Table 8, a flag brick_split_flag[i] indicating whether a tile with a tile ID of i can be divided into two or more bricks can be signaled through a bitstream.

If the brick_split_flag[i] value is 1, it indicates that the tile with tile ID i is divided into two or more bricks, and if the brick_split_flag[i] value is 0, it indicates that the tile with tile ID i is not divided into two or more bricks.

As shown in Table 8, if brick_split_flag[i] for a tile with tile ID i is 1 (i.e., a tile divided into two or more bricks), the syntax uniform_brick_spacing_flag indicating whether each brick in the tile is divided equally is used. You can signal. The syntax uniform_brick_spacing_flag indicates whether the heights of bricks in the tile are uniform.

If the uniform_brick_spacing_flag value is 1, it indicates that the heights of bricks in the tile are evenly divided.

If the uniform_brick_spacing_flag value is 1, the syntax brick_height_minus1 indicating the basic height of the brick may be signaled. Bricks in a tile can have a default height.

If uniform_brick_spacing_flag is 1, excluding bricks adjacent to the picture boundary, the tile may be divided into bricks having a height of (brick_height_minus1+1)*CtbSizeHeight.

If the uniform_brick_spacing_flag value is 0, the syntax num_brick_rows_minusu1[i] indicating the number of bricks in the i-th tile and the syntax brick_row_height_minus1[i][j] indicating the height of the j-th brick in the i-th tile may be signaled.

The syntax brick_row_height_minus1[i] can signal as many as the number of bricks or the number of bricks less 1. For example, the last brick in the tile may be derived by dividing a value obtained by adding all the height values of the previous bricks from the height of the tile.

Tiles and bricks can be identified by brick index. A tile that is not included as bricks is considered to be one brick and may be assigned a brick index. For example, brick indexes may be allocated to tiles and bricks according to the raster scan order.

The syntax brick_height_minus1[i]+1 or brick_row_hegiht_minus1+1 indicating the height of the brick may be set smaller than the height of the tile including the brick index i (the number of vertical CTBs in the tile, hereinafter, rowHeight).

Specifically, for example, brick_height_minus1[i] to brick_row_height_minus1 may be set to have a value between 0 and rowHeight-2.

As shown in Table 8, a flag single_brick_per_slice_flag indicating whether each slice is composed of one brick may be signaled through a bitstream.

If single_brick_per_slice_flag is 1, it indicates that each slice referring to the PPS is composed of one brick, and if single_brick_per_slice_flag is 0, it indicates that at least one of each slice referring to the PPS is composed of two or more bricks.

Information indicating the slice type may be signaled through a bitstream. The information indicates whether the slice is a raster scan type or a rectangular shape type. For example, as shown in Table 8, a syntax rect_slice_flag indicating whether a rectangular slice is used may be signaled through a bitstream.

If rect_slice_flag is 1, it indicates that rectangular slice is used, and if rect_slice_flag is 0, it indicates that raster-scan slice is used.

Fig. 53

When using a rectangular slice, a slice area can be defined using a brick index. Specifically, information for specifying the first brick in the slice and the last brick in the slice may be determined. Here, the order of the bricks is determined by the scan order. For example, when following a raster scan, the first brick in the slice represents the upper left brick, and the last brick represents the lower right brick.

As shown in Figure 53, the syntax top_left_brick_idx indicating the brick index of the upper left brick of the i-th slice can be signaled through the bitstream.

If a rectangular slice is used, the syntax bottom_right_brick_idx_delta indicating the brick index of the lower-right brick of the i-th slice can be signaled through the bitstream as shown in Figure 53. The brick index bottom_right_brick_idx(i) of the lower-right brick of the i-th slice can be derived by summing top_left_brick_idx[i] to bottom_right_brick_idx_delta[i] as shown in Equation (26).

bottom_right_brick_idx[i] = top_left_brick_idx[i] +bottom_right_brick_idx_delta[i] (26)

Alternatively, the syntax bottom_right_brick_idx indicating the brick index of the last brick may be signaled through a bitstream.

Alternatively, horizontal index difference information indicating the difference in the brick index of the rightmost brick included in the same row as the first brick and the first brick, or vertical index difference information indicating the difference in the brick index of the lowest brick included in the same column as the first brick and the first brick. At least one of them may be encoded. For example, in a slice adjacent to a right boundary or a lower boundary of a picture, a slice may be defined using the horizontal index difference information or the vertical index difference information.

loop_filter_across_bricks_enabled_flag is a flag indicating whether to disable the loop filter in the brick boundary (two neighboring tiles or the boundary of a brick).

Table 9

If the value of brick_split_flag[i] is 1, it indicates that the tile with tile ID i is divided into two or more bricks. Accordingly, if the brick_split_flag of the tile whose tile ID is i is 1, the tile may include at least two bricks.

When the uniform_brick_spacing_flag value is 0 (uniform_brick_spacing_flag is signaled when the brick_split_flag value is 1), as shown in Table 9, the syntax num_brick_row_minus2[i] indicating the number of bricks in the i-th tile may be signaled through a bitstream.

The number of bricks in the i-th tile may be set to num_brick_row_minus2[i]+2, and num_brick_row_minus2[i] may be set to 0 to rowHeight-2.

Table 10

Alternatively, as shown in Table 10, the syntax top_left_brick_idx_minus1[i] indicating the brick index of the upper left brick of the i-th slice may be signaled through the bitstream .

In the i slice (if i is not 0) The brick index of the upper left brick always has a value greater than 0. In this case, the syntax top_left_brick_idx_minus1[i] representing a value obtained by subtracting 1 from the brick index of the upper left brick of the slice may be signaled through the bitstream. In this case, the number of bits of the syntax top_left_brick_idx_minus1[i] may be set to Ceil (Log2(NumBricksInPic-1)).

NumBricksInPic represents the number of bricks in a picture, where Ceil(a) represents the smallest integer greater than or equal to a.

In the i-th slice, the upper left brick index of the slice may be set to top_left_brick_idx_minus1[i]+1.

You can set the slice ID for each brick using the following process. BricksToSliceMap[ j] represents the slice ID of brick index j.

Table 11

Since the address of a slice increases as the slice index increases, the brick index of the upper left brick of the current slice may always be larger than the brick index of the upper left brick of the previous slice. Accordingly, a value obtained by differentiating the brick index of the upper left brick of the current slice from the brick index of the upper left brick of the previous slice may always be a value greater than 0.

When using a rectangular slice, the first brick in the current slice can be specified by using the difference between the index value of the first brick of the previous slice and the first brick of the current slice. For example, as shown in Table 11, the syntax top_left_brick_idx_delta[i] for specifying the brick index of the upper left brick of the i-th slice may be signaled through the bitstream.

The brick index top_left_brick_idx(i) of the upper left brick of the i-th slice can be derived by summing TopLeftBrickIdx(i-1) of the i-1 th slice to top_left_brick_idx_delta[i] as shown in Equation (27). The maximum number of bits of the syntax top_left_brick_idx_delta[i] may be Ceil (Log2 (NumBricksInPic-TopLeftBrickIdx(i-1))). Here, Ceil(a) represents the smallest integer greater than or equal to a.

TopLeftBrickIdx(i) = TopLeftBrickIdx(i-1) +top_left_brick_idx_delta[i] (27)

The value of TopLeftBrickIdx(0) of the first slice (ie, a slice in which i is 0) may be set to 0. In the second slice (ie, a slice in which i is 1), top_left_brick_idx[i] may be encoded instead of top_left_brick_idx_delta[i].

The brick index botRightBkIdx(i) of the lower-right brick of the i-th slice can be derived by summing the brick index TopLeftBrickIdx(i) of the lower-left brick of the i-th slice to bottom_right_brick_idx_delta[i] as shown in Equation (28).

botRightBkIdx(i) = TopLeftBrickIdx(i) + bottom_right_brick_idx_delta[i] (28)

You can set the slice ID for each brick using the following process. BricksToSliceMap[ j] represents the slice ID of brick index j.

Table 12

Alternatively, in the case of using a rectangular slice, the first brick in the current slice may be specified by using a value obtained by subtracting 1 from the index value difference between the first brick of the previous slice and the first brick of the current slice. For example, as shown in Table 12, the syntax top_left_brick_idx_delta_minus1[i] for specifying the brick index of the upper left brick of the i-th slice may be signaled through a bitstream.

The brick index top_left_brick_idx(i) of the upper left brick of the i-th slice can be derived by summing TopLeftBrickIdx(i-1) of the i-1 th slice to (top_left_brick_idx_delta_minus1[i]+1) as shown in Equation (29). The maximum number of bits of the syntax top_left_brick_idx_delta_minus1[i] may be Ceil (Log2(NumBricksInPic-TopLeftBrickIdx(i-1) -1) ). Here, Ceil(a) represents the smallest integer greater than or equal to a.

TopLeftBrickIdx(i) = TopLeftBrickIdx(i-1) +top_left_brick_idx_delta_minus1[i]+1 (29)

The value of TopLeftBrickIdx(0) of the first slice (ie, a slice in which i is 0) may be set to 0. In the second slice (ie, a slice in which i is 1), top_left_brick_idx_minus1[i] may be encoded instead of top_left_brick_idx_delta_minus1[i].

You can set the slice ID for each brick using the following process. BricksToSliceMap[ j] represents the slice ID of brick index j.

Fig. 54

As shown in Figure 54, tile partitioning of different sizes can be created according to the viewport, and this is called a viewport adaptive partitioning structure.

For example, the viewport adaptive partitioning structure in Figure 54 may be divided into slices, tiles, and bricks as shown in Figure 55 below.

Fig. 55

As shown in Figure 55, when rendering, encoding, or decoding a 360 video, a partitioning structure that uses bricks only in a specific vertical tile set among vertical tile columns can be widely used. Accordingly, bits of the picture parameter set can be reduced by using information indicating whether to use a brick in units of a tile column in the vertical direction.

Table 13

For example, as shown in Table 13, the information may be a flag brick_column_split_present_flag[j] indicating whether at least one tile belonging to a j-th vertical tile column is composed of a plurality of bricks. j may have a value less than or equal to information num_tile_columns_minus1 indicating the number of vertical tiles.

If brick_column_split_present_flag[j] is 0, it indicates that no tile is composed of a plurality of bricks in the j-th vertical tile set, and if brick_column_split_present_flag[j] is 1, at least one tile in the j-th vertical tile set This indicates that it is composed of a plurality of bricks.

Specifically, as shown in Figure 56, when bricks are used only in the 3rd tile column, brick_column_split_present_flag[3] can be set to 1.

Fig. 56

Regardless of whether tiles are equally divided, information indicating whether to use a brick in units of a vertical tile set may be encoded. Alternatively, only when it is determined that tiles are not divided equally, information indicating whether to use a brick in units of a vertical tile set may be encoded.

Alternatively, information indicating whether to use a brick in units of a vertical tile set may be encoded only for a tile set having the smallest width among the vertical tile sets.

Alternatively, information indicating whether to use a brick in units of a vertical tile set may be encoded only for a tile set whose width or height is less than or equal to a preset value among the vertical tile sets.

Alternatively, information indicating whether to use a brick in units of a vertical tile set may be encoded for only a tile set at a specific position among the vertical tile set. For example, the feature position may be adjacent to a right boundary of the picture.

When a common rule is applied to the division of tiles included in the vertical tile set, information for determining the common rule may be encoded. A common rule can indicate the number of bricks or the height of the bricks. For example, when the information indicates that the vertical direction tile sets are divided into two bricks, all tiles included in the vertical direction tile set may be divided into two bricks. Alternatively, when the information indicates that the height of the brick is brick_height, all tiles included in the vertical tile set may be divided into bricks having a height of brick_height. At this time, a tile whose height is equal to or smaller than brick_row_height may not be divided any more.

Instead of information indicating whether to use a brick in units of a vertical tile set, information indicating whether to use a brick in units of a horizontal tile set may be encoded.

As an example, a flag brick_row_split_present_flag[j] indicating whether at least one of tiles belonging to a j-th horizontal tile row is composed of a plurality of bricks may be encoded. j may have a value smaller than information num_tile_rows_minus1 indicating the number of horizontal tiles.

Table 14

In the last vertical tile set, if the values of brick_column_split_present_flag of the previous vertical tile set are all 0, the value of brick_cloumn_split_presnt_flag[num_tile_columns_minus1+1] of the last vertical tile set is not signaled and is not signaled by the encoder and decoder, as shown in Table 14. You can derive that value to 1.

Table 15

If the single_brick_per_slice_flag value is 1, it indicates that each slice referring to the PPS is composed of one brick. That is, if the value of single_brick_per_slice_flag is 1, it indicates that a plurality of bricks are not formed.

Accordingly, as shown in Table 15, if the single_brick_per_slice_flag value is 1, the flag brick_splitting_present_flag indicating whether to have a plurality of bricks may not be signaled through the bitstream. At this time, the brick_splitting_present_flag value may be set to 0.

Table 16

A syntax one_slice_in_pic_flag indicating whether the number of slices in a picture is 1 may be signaled. If the one_slice_in_pic_flag value is 1, it indicates that the number of slices in the picture is 1, and if the one_slice_in_pic_flag value is 0, it indicates that the number of slices in the picture is 2 or more. If the value of one_slice_in_pic_flag is 0, information indicating the number of slices in the picture may be additionally signaled.

As shown in Table 16, if the value of one_slice_in_pic_flag is 1, the syntax top_left_brick_idx and/or bottom_right_brick_idx_delta indicating the upper left and lower right brick IDs of the slice may not be signaled.

Table 17

Alternatively, as shown in Table 17, whether to signal single_brick_per_slice_flag or rect_slice_flag may be determined according to the value of one_slice_in_pic_flag. For example, when the value of one_slice_in_pic_flag is 1, single_brick_per_slice_flag and rect_slice_flag may not be signaled.

num_slices_in_pic_minus2 represents the number of slices in a picture. The number of slices in a picture may be determined by adding 2 to the value indicated by num_slices_in_pic_minus2.

Alternatively, information indicating a difference value between the total number of bricks and the number of slices in the picture may be encoded. The total number of bricks in a picture may be derived based on the number of tile rows, the number of tile columns, and the number of brick rows for each tile. For example, the total number of bricks may be derived as (number of tile rows * number of tile columns) + (sum of num_brick_rows_minus1 of all tiles). Since a slice includes at least one brick, the number of slices is equal to or less than the number of bricks. Accordingly, a value obtained by differentiating the number of slices from the total number of bricks may be signaled through the bitstream.

Table 18

Alternatively, as shown in Table 18, one_slice_in_pic_flag may be signaled only when the single_brick_per_slice_flag value is 0. Whether to signal rect_slice_flag may be determined according to the value of one_slice_in_pic_flag. For example, when the value of one_slice_in_pic_flag is 1, rect_slice_flag may not be signaled.

When the value of one_slice_in_pic_flag is 1 and the value of single_brick_per_slice_flag is 1, bottom_right_brick_idx_delta[i] may be signaled.

Table 19

As shown in Table 19, the syntax bottom_right_brick_idx indicating the index of the lower right brick may be signaled through the bitstream without signaling the index top_left_brick_idx of the upper left brick of the slice.

The variable TopLeftBrickIdx[sliceIdx] indicating the index of the upper left brick can also be derived as follows.

Table 20

As shown in Table 20 below, the syntax top_left_brick_idx_minus1 indicating the index of the upper left brick may be signaled through a bitstream without signaling the index bottom_right_brick_idx_delta of the lower right brick of the slice.

You can also derive the variable BottomRightBrickIdx[sliceIdx] indicating the index of the lower right brick as the following process.

Table 21

As shown in Table 21 below, the syntax top_left_brick_idx_delta indicating the index of the upper left brick may be signaled through a bitstream without signaling the index bottom_right_brick_idx_delta or the bottom_right_brick_idx of the brick at the bottom right of the slice.

In Table 21, top_left_brick_idx_delta[i] is the difference between the first brick of the previous slice (slice index i-1, hereinafter (i-1) th slice) and the first brick of the current slice (slice index i, hereinafter i th slice). Represents.

The brick index top_left_brick_idx(i) of the upper left brick of the i-th slice can be derived by summing TopLeftBrickIdx(i-1) of the i-1 th slice to top_left_brick_idx_delta[i] as shown in the equation. The maximum number of bits of the syntax top_left_brick_idx_delta[i] may be Ceil (Log2( NumBricksInPic-TopLeftBrickIdx( i -1) -1) ). Here, Ceil(a) represents the smallest integer greater than or equal to a.

TopLeftBrickIdx(i) = TopLeftBrickIdx(i-1) +top_left_brick_idx_delta[i] (30)

The value of TopLeftBrickIdx(0) of the first slice (ie, a slice in which i is 0) may be set to 0. In the second slice (ie, a slice in which i is 0), top_left_brick_idx[i] may be encoded instead of top_left_brick_idx_delta[i].

You can set the slice ID for each brick using the following process. BricksToSliceMap[j] represents the slice ID of the brick index j, and BottomRightBrickIdx[i] represents the index of the lower right brick of the i-th slice.

Table 22

As shown in Table 22 below, the syntax top_left_brick_idx_delta_minus1 indicating the index of the upper left brick can be signaled through a bitstream without signaling the index bottom_right_brick_idx_delta or bottom_right_brick_idx of the brick at the bottom right of the slice.

In Table 22, top_left_brick_idx_delta_minus1[i] is the difference between the index value of the first brick of the previous slice (slice index i-1, hereinafter (i-1) th slice) and the first brick of the current slice (slice index i, hereinafter i th slice) Represents the value minus 1.

The brick index top_left_brick_idx(i) of the upper left brick of the i-th slice can be derived by summing TopLeftBrickIdx(i-1) of the i-1 th slice to top_left_brick_idx_delta_minus1[i] as shown in Equation (31). The maximum number of bits of the syntax top_left_brick_idx_delta_minus1[i] may be Ceil (Log2( NumBricksInPic-TopLeftBrickIdx( i -1)) ). Here, Ceil(a) represents the smallest integer greater than or equal to a.

TopLeftBrickIdx(i) = TopLeftBrickIdx(i-1) +top_left_brick_idx_delta_minus1[i]+1 (31)

The value of TopLeftBrickIdx(0) of the first slice (ie, a slice in which i is 0) may be set to 0.

You can set the slice ID for each brick using the following process. BricksToSliceMap[j] represents the slice ID of the brick index j, and BottomRightBrickIdx[i] represents the index of the lower right brick of the i-th slice.

Table 23

As shown in Table 23 below, the syntax bottom_right_brick_idx_diff[i] indicating the difference between the lower right brick index of the i-th slice and the lower right brick index of the i-1th slice may be signaled through a bitstream.

In Table 23, bottom_right_brick_idx_diff[i] is the index of the lower right brick of the previous slice (slice index i-1, hereinafter (i-1) th slice) and the lower right brick of the current slice (slice index i, hereinafter i th slice). Represents the difference value of the index.

The brick index bottomRightIdx[i] of the lower-right brick of the i-th slice can be derived by summing the BottomRightIdx(i-1) of the i-1 th slice to bottom_right_brick_idx_diff[i] as shown in Equation (32). The maximum number of bits of the syntax bottom_right_brick_idx_diff[i] may be Ceil (Log2( NumBricksInPic-BottomRightIdx( i -1)) ). Here, Ceil(a) represents the smallest integer greater than or equal to a.

BottomRightIdx[i] = BottomRightIdx[i-1] + bottom_right_brick_idx_diff[i] (32)

The BottomRightIdx[0] value of the first slice (that is, a slice in which i is 0) may be set as a bottom_right_brick_idx_diff[0] value.

You can set the slice ID for each brick using the following process. BricksToSliceMap[j] represents the slice ID of the brick index j, and BottomRightBrickIdx[i] represents the index of the lower right brick of the i-th slice.

Table 24

The sign_bottom_right_brick_idx_diff[i] in Table 24 is a syntax indicating the sign value of the difference between the lower right brick index of the i-th slice and the lower right brick index of the i-1th slice.

if i is 0, sign_bottom_right_brick_idx_diff [i] without ring signal values, bottom_right_brick_idx_diff [0] value represents the lower right-brick index of 0 ^th slice.

When i is not 0, the lower right brick index BottomRightIdx[i] of the I slice can be derived as shown in the following equation (33).

BottomRightIdx[i-1]+ sign[i] bottom_right_brick_idx_diff[i] (33)

If the value of sign_bottom_right_brick_idx_diff[i] is 1, sign[i] can be set to 1, and if the value of sign_bottom_right_brick_idx_diff[i] is 0, sign[i] can be set to -1.

Here, bottom_right_brick_idx_length_minus1 represents the bit length of bottom_right_brick_idx_diff[i].

Table 25

As shown in Table 25, bottom_right_brick_idx_length_minus1[i] can be signaled for each slice.

bottom_right_brick_idx_length_minus1[i] is a syntax indicating the bit length of bottom_right_brick_idx_diff [i].

The bit length of bottom_right_brick)idx_diff[i] can be defined as (NumBricksInPic-BottomRightBrickIdx[i-1]).

NumBricksInPic represents the total number of bricks in the picture, and BottomRightBrickIdx[i] represents the bottom right brick index of the i-th slice.

Table 26

As shown in Table 26, the lower right brick index (bottomRightBrickIdx[i]) of any i-th rectangular slice in the picture is greater than the lower right brick index (bottomRightBrickIdx[i-1]) of (i-1)-th rectangular slice A flag indicating whether to have a bottom_right_increasing_order_flag may be signaled.

If the bottom_right_increasing_order_flag value is 1, the lower right brick index (bottomRightBrickIdx[i]) of any i-th rectangular slice is greater than the lower right brick index (bottomRightBrickIdx[i-1]) of (i-1)-th rectangular slice It indicates to have.

If the value of bottom_right_increasing_order_flag is 0, it indicates that the lower right brick index of at least one rectangular slice (eg, j-th rectangular slice) has a smaller value than the lower right brick index of (j-1)-th rectangular slice.

The bit length of bottom_right_brick_idx_diff[　i　] can be defined as (NumBricksInPic　- BottomRightBrickIdx[i-1]).

Table 27

As shown in Table 27, a flag rem_tile_col_equal_flag[i] indicating whether the widths of the i-th tile column through the 0-th tile column or the i-th tile column through the (N-1)-th tile column are the same can be signaled. Here, N may be set to a value of num_tile_columns_minus1+1.

If the rem_tile_col_equal_flag[i] value is 0, the syntax tile_column_width_minus1[i] indicating the width of the i-th tile column may be expressed.

It can be defined as PrevTileColWidth, a variable representing the width of the previous tile column. If the PrevTileColWidth value is greater than tile_colum_width_minus1[i] + 1, tile_colum_width_minus1[i] + 1 can be set as the width of the tile column. If the PrevTileColWidth value is equal to or less than tile_colum_width_minus1[i] + 1, tile_column_width_minus1[i]+2 can be set as the width of the tile column.

As shown in Table 27, a flag rem_tile_row_equal_flag[i] indicating whether the widths of the 0-th tile row from the i-th tile row or the (M-1)-th tile column from the i-th tile row are the same can be signaled. Here, M may be set to a value of num_tile_rows_minus1+1.

If the rem_tile_row_equal_flag[i] value is 0, the syntax tile_column_height_minus1[i] indicating the height of the i-th tile row may be expressed.

It can be defined as a variable PrevTileRowHeight representing the height of the previous tile row. If the PrevTileRowHeight value is greater than tile_colum_height_minus1[i] + 1, tile_colum_height_minus1[i] + 1 can be set as the height of the tile row. If the PrevTileRowHeight value is equal to or less than tile_colum_height_minus1[i] + 1, tile_colum_height_minus1[i] +2 can be set as the height of the tile row.

As shown in Table 27, a flag rem_brick_equal_flag[ i ][ j] indicating whether the heights of the 0-th brick from the j-th brick or the (N-1)-th brick from the j-th tile are the same can be signaled. Here, N represents the number of bricks in the i-th tile.

When the value of rem_brick_equal_flag[ i ][ j] is 0, the syntax brick_row_height_minus1[ i ][ j] indicating the number of j-th bricks can be signaled.

It can be defined as a variable PrevBrickHeight representing the height of the previous brick.

If the PrevBrickHeight value is greater than brick_row_height_minus1[ i ][ j ]+ 1, you can set brick_row_height_minus1[ i ][ j ]+ 1 as the height of the brick. If the PrevBrickHeight value is less than or equal to brick_row_height_minus1[ i ][ j ]+ 1, you can set brick_row_height_minus1[ i ][ j ]+2 as the height of the brick.

Table 27

If the RowHeight value is an odd number and the number of bricks in a picture (NumBrickInPic) is an even number, at least one brick may have a different height. Therefore, the height of the first brick and the height of at least one of the other bricks are set differently. For example, if the height of RowHeight is odd (e.g., height is 5) and the number of bricks is even (e.g., the number of bricks is 2), the height of at least one of the first brick and the remaining bricks is It can be set differently.

Fig. 46

If the RowHeight is odd and the number of bricks in the picture (NumBrickInPic) is even, the value can be set to 0 without signaling rem_brick_equal_flag[i][j] in the first brick. That is, if the RowHeight is odd and the number of bricks in the picture (NumBrickInPic) is even, rem_brick_equal_flag[i][0] may be set to 0 without signaling.

Table 28

In the case of a rectangular slice, a syntax num_slices_in_pic_minus1 indicating the number of slices in a picture may be signaled.

A slice may be composed of one brick or may be composed of a plurality of bricks.

Fig. 47

A slice may be composed of a plurality of tiles. In this case, as shown in Table 28, the syntax slice_height_in_tiles_minus1[i] indicating the height of the i-th slice and the syntax slice_width_in_tiles_minus1[i] indicating the width of the i-th slice may be signaled.

slice_height_in_tiles_minus1[ i ]+1 represents the height of the i-th slice (SliceHeight[i]), and the basic unit representing the height of the slice is tile row.

For example, the height of slice 4 (4th slice) in Figure 47 is 2, and slice_height_in_tiles_minus1[ 4] can be set to 1.

slice_width_in_tiles_minus1[ i ]+1 represents the width of the i-th slice, and the basic unit representing the width of the slice is the tile column.

If the value of slice_width_in_tiles_minus1[ i] is 0, it indicates that the tile is one slice or a plurality of slices.

When the value of slice_width_in_tiles_minus1[i] is 0, the syntax num_slices_in_tile_minus1[i] indicating the number of slices in the tile may be signaled.

In the case of having a plurality of slices in a tile, the syntax slice_height_in_ctu_minus1[i][j] indicating the height of the slice may be signaled. slice_height_in_ctu_minus1[i][j]+1 represents the height of the j-th slice in the i-th tile, and the basic unit representing the slice height can be set as a CTU row.

The syntax tile_idx_delta[i] indicating a difference between the tile index (top left tile index) of the i+1th slice and the tile index (top left tile index) of the i-th slice (hereinafter, slice difference) may be signaled.

The syntax tile_idx_delta_sign[i] indicating whether the slice difference (i.e., the difference between the tile index of the (i+1)-th slice and the tile index of the i-th slice) is positive or negative can be signaled through the bitstream. The slice may not signal tile_idx_delta_sign[i].

Table 29

As shown in Table 29, tile_idx_delta_sign[i] may be selectively signaled to the bitstream based on the slice difference value. For example, if the syntax tile_idx_delta[i] value representing the slice difference is greater than 0, tile_idx_delta_sign[i] can be signaled, and if the tile_idx_delta[i] value is 0, tile_idx_delta_sign[i] will not be signaled. I can.

Table 30

As shown in Table 30, the value of tile_idx_delta[i] may be signaled only when a slice is composed of a plurality of tiles.

Table 31

A slice may be composed of a plurality of bricks.

As shown in Table 31, the syntax num_bricks_in_slice_minus1 indicating the number of bricks in a slice may be signaled in a slice header or a picture parameter header.

num_bricks_in_slice_minus1+1 is a syntax indicating the number of bricks in a slice.

When the height of the slice is 2 or more, the syntax brick_height_minus1[i] indicating the height of the brick can be signaled.

Claims (1)

Predictive encoding and decoding method using tile, brick, and slice information signaling encoding