KR102450863B1 - Method and Apparatus for Encoding and Decoding Motion Vector - Google Patents

Abstract

The present invention relates to image encoding or decoding for efficiently encoding an image. According to one aspect of the present invention, there is provided a method for encoding a motion vector of a current block, the method comprising: determining a differential motion vector for the current block with a default resolution; determining one or more resolution candidates from among a plurality of motion vector resolutions according to the determined absolute value of the differential motion vector; selecting a resolution for expressing the determined differential motion vector from among one or more resolution candidates; calculating a value to be encoded as a differential motion vector of the current block by applying a function corresponding to the selected resolution to the determined differential motion vector; and encoding information on the calculated value and resolution information representing the selected resolution among the plurality of motion vector resolutions as information on the differential motion vector.

Description

Apparatus and method for encoding or decoding a motion vector {Method and Apparatus for Encoding and Decoding Motion Vector}

The present invention relates to image encoding or decoding for efficiently encoding an image.

The content described in this section merely provides background information for the present embodiment and does not constitute the prior art.

Since moving image data has a larger amount of data than audio data or still image data, it requires a lot of hardware resources, including memory, to store or transmit itself without compression processing. Therefore, in general, when storing or transmitting moving picture data, the moving picture data is compressed and stored or transmitted using an encoder, and the decoder receives the compressed moving picture data, decompresses it, and reproduces the data. As such a video compression technology, H.264/AVC and High Efficiency Video Coding (HEVC) established in early 2013, which improved encoding efficiency by about 40% of H.264/AVC, exist.

In inter prediction encoding, which is one of prediction methods for encoding or decoding, information obtained by encoding a residual block generated after predicting the current block and motion information used for predicting the current block is transmitted to a decoding apparatus. signaling. Here, the motion information includes information about a reference picture used to predict the current block and information about a motion vector. In the case of the existing HEVC standard, motion vectors are expressed in units of 1/4 pixel.

However, as the size, resolution, and frame rate of an image gradually increase, the amount of data to be encoded also increases. Therefore, a compression technique with better encoding efficiency than the conventional compression technique is required.

The present invention provides an image encoding or decoding technique for efficiently encoding an image by adjusting a resolution for expressing a differential motion vector according to the characteristics of an image and a block.

According to one aspect of the present invention, there is provided a method for encoding a motion vector of a current block, the method comprising: determining a differential motion vector for the current block with a default resolution; determining one or more resolution candidates from among a plurality of motion vector resolutions according to the determined absolute value of the differential motion vector; selecting a resolution to express the determined differential motion vector from among the one or more resolution candidates; calculating a value to be encoded as a differential motion vector of the current block by applying a function corresponding to the selected resolution to the determined differential motion vector; and encoding the calculated value as differential motion vector information, and encoding resolution information representing the selected resolution among the plurality of motion vector resolutions.

According to another aspect of the present invention, there is provided a method for decoding a motion vector of a current block, the method comprising: decoding differential motion vector information of the current block; selecting one resolution from among a plurality of motion vector resolutions by decoding resolution information indicating the resolution of the differential motion vector; restoring a differential motion vector of the current block by applying a function corresponding to the selected resolution to a value determined by the differential motion vector information; and determining a predicted motion vector of the current block, and reconstructing the motion vector of the current block using the reconstructed differential motion vector and the predicted motion vector.

According to another aspect of the present invention, in an image decoding apparatus for decoding a motion vector of a current block, a differential motion vector index is determined by decoding differential motion vector information of the current block, and a resolution of the differential motion vector is determined. a decoding unit that selects one resolution from among a plurality of motion vector resolutions by decoding the displayed resolution information, and restores the differential motion vector of the current block by applying a function corresponding to the selected resolution to the determined differential motion vector index; and an inter prediction unit that determines the predicted motion vector of the current block and reconstructs the motion vector of the current block using the reconstructed differential motion vector and the predicted motion vector.

1 is a block diagram of an image encoding apparatus according to an embodiment of the present invention.
2 is an exemplary diagram of a neighboring block of a current block.
3 is a flowchart illustrating a method of operating an image encoding apparatus according to an embodiment of the present invention.
4 is a block diagram of an image decoding apparatus according to an embodiment of the present invention.
5 is a flowchart illustrating a method of operating an image decoding apparatus according to an embodiment of the present invention.
6 is a flowchart illustrating an example of a specific operation method of an image decoding apparatus according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that in adding identification codes to the components of each drawing, the same components are given the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a block diagram of an image encoding apparatus 100 according to an embodiment of the present invention.

The image encoding apparatus 100 includes a block divider 110 , a predictor 120 , a subtractor 130 , a transform unit 140 , a quantizer 145 , an encoder 150 , an inverse quantizer 160 , It includes an inverse transform unit 165 , an adder 170 , a filter unit 180 , and a memory 190 . Each component of the encoding apparatus 100 may be implemented as a hardware chip, or may be implemented as software and a microprocessor may be implemented to execute a function of software corresponding to each component.

The block divider 110 divides each picture constituting an image into a plurality of coding tree units (CTUs) and then recursively divides the CTUs using a tree structure. A leaf node in the tree structure becomes a coding unit (CU), which is a basic unit of encoding. The tree structure is a QuadTree (QT) in which the upper node splits into four lower nodes, or a QTBT (QuadTree, QT) structure that combines the QT structure and the binary tree (BT) structure in which the upper node splits into two lower nodes. plus BinaryTree) structure can be used.

The prediction unit 120 generates a prediction block by predicting the current block. The prediction unit 120 includes an intra prediction unit 122 and an inter prediction unit 124 . Here, the current block is a basic unit of encoding corresponding to a leaf node in the tree structure, and means a CU to be currently encoded. Alternatively, the current block may be one of a plurality of subblocks divided from the CU.

The intra prediction unit 122 predicts pixels in the current block by using pixels (reference pixels) located around the current block in the current picture including the current block. A plurality of intra prediction modes exist according to a prediction direction, and neighboring pixels to be used and an operation expression are defined differently according to each prediction mode.

The inter prediction unit 124 searches for a block most similar to the current block in the reference picture encoded and decoded before the current picture, and generates a prediction block for the current block using the searched block. Then, a motion vector (MV) corresponding to displacement between the current block in the current picture and the prediction block in the reference picture is generated. Motion information including information on a reference picture and information on a motion vector used to predict the current block is encoded by the encoder 150 and transmitted to the image decoding apparatus.

Various methods may be used to minimize the amount of bits required to encode motion information.

When the reference picture and motion vector of the current block are the same as the reference picture and motion vector of the neighboring block, the motion information of the current block may be transmitted to the decoding apparatus by encoding information for identifying the neighboring block. This method is called 'merge mode'.

In the merge mode, the inter prediction unit 124 selects a predetermined number of merge candidate blocks (hereinafter, referred to as 'merge candidates') from neighboring blocks of the current block.

As the neighboring blocks for inducing the merge candidate, as shown in FIG. 2 , the left block (L), the upper block (A), the upper right block (AR), and the lower left block (BL) adjacent to the current block in the current picture. ), all or part of the upper left block AL may be used. Also, a block located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture in which the current block is located may be used as a merge candidate. For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be further used as merge candidates.

The inter prediction unit 124 constructs a merge list including a predetermined number of merge candidates by using these neighboring blocks. A merge candidate to be used as motion information of the current block is selected from among the merge candidates included in the merge list, and merge index information for identifying the selected candidate is generated. The generated merge index information is encoded by the encoder 150 and transmitted to the image decoding apparatus.

Another method of encoding motion information is to encode a motion vector difference (MVD).

In this method, the inter prediction unit 124 derives motion vector predictor (MVP) candidates for the motion vector of the current block using neighboring blocks of the current block. As the neighboring blocks used to derive the predicted motion vector candidates, the left block (L), the upper block (A), the upper right block (AR), the lower left block (L) adjacent to the current block in the current picture shown in FIG. BL), all or part of the upper left block AL may be used. In addition, a block located in a reference picture (which may be the same as or different from the reference picture used to predict the current block) other than the current picture in which the current block is located is used as a neighboring block used to derive prediction motion vector candidates. may be For example, a block co-located with the current block in the reference picture or blocks adjacent to the co-located block may be used.

The inter prediction unit 124 derives predicted motion vector candidates by using the motion vectors of the neighboring blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, a differential motion vector is calculated by subtracting the predicted motion vector from the motion vector of the current block.

The predicted motion vector may be obtained by applying a predefined function (eg, a median value, an average value operation, etc.) to the predicted motion vector candidates. In this case, the image decoding apparatus also knows the predefined function. Also, since the neighboring block used to derive the predicted motion vector candidate is a block that has already been encoded and decoded, the image decoding apparatus already knows the motion vector of the neighboring block. Therefore, the image encoding apparatus 100 does not need to encode information for identifying the predicted motion vector candidate. Accordingly, in this case, information on the differential motion vector and information on the reference picture used to predict the current block are encoded.

Meanwhile, the predicted motion vector may be determined by selecting any one of the predicted motion vector candidates. In this case, information for identifying the selected predicted motion vector candidate is additionally encoded together with information on the differential motion vector and information on the reference picture used to predict the current block.

The subtractor 130 generates a residual block by subtracting the prediction block generated by the intra prediction unit 112 or the inter prediction unit 124 from the current block.

The transform unit 140 transforms the residual signal in the residual block having pixel values in the spatial domain into transform coefficients in the frequency domain. The transform unit 140 may transform the residual signals in the residual block using the size of the current block as a transform unit, or divide the residual block into a plurality of smaller sub-blocks and convert the residual signals in the transform unit of the sub-block size. You can also convert There may be various methods for dividing the residual block into smaller subblocks. For example, it may be divided into subblocks of the same size as defined previously, or a quadtree (QT) method using the residual block as a root node may be used.

The quantization unit 145 quantizes the transform coefficients output from the transform unit 140 , and outputs the quantized transform coefficients to the encoder 150 .

The encoder 150 generates a bitstream by encoding the quantized transform coefficients using an encoding method such as CABAC. In addition, the encoder 150 encodes information on the size of a CTU located in the uppermost layer of the tree structure and partition information for splitting a block from the CTU into a tree structure, so that the decoding apparatus divides the block in the same way as the encoding apparatus. make it possible For example, in the case of QT division, QT division information indicating whether a block of an upper layer is divided into four blocks of a lower layer is encoded. In the case of BT division, starting from a block corresponding to a leaf node of QT, BT division information indicating whether each block is divided into two blocks and the type of division is encoded.

The encoder 150 encodes information on a prediction type indicating whether the current block is encoded by intra prediction or inter prediction, and encodes intra prediction information or inter prediction information according to the prediction type.

Meanwhile, when the current block is inter-predicted, the encoder 150 encodes syntax elements for inter prediction information. Syntax elements for inter prediction information include the following.

(a) Mode information indicating whether motion information of the current block is encoded in a merge mode or a differential motion vector encoding mode

(b) Syntax elements for motion information

When the motion information is encoded by the merge mode, the encoder 150 uses merge index information indicating which of the merge candidates is selected as a candidate for extracting the motion information of the current block as a syntax element for the motion information. encode

On the other hand, when motion information is encoded by a differential motion vector encoding mode, information on the differential motion vector and information on a reference picture are encoded as syntax elements for motion information. If the prediction motion vector is determined by selecting any one candidate from among a plurality of prediction motion vector candidates, the syntax element for the motion information further includes prediction motion vector identification information for identifying the selected candidate. include

The inverse quantization unit 160 inverse quantizes the quantized transform coefficients output from the quantization unit 145 to generate transform coefficients. The inverse transform unit 165 restores the residual block by transforming the transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain.

The adder 170 reconstructs the current block by adding the reconstructed residual block to the prediction block generated by the prediction unit 120 . Pixels in the reconstructed current block are used as reference pixels when intra-predicting the next block.

The filter unit 180 deblocks and filters the boundary between the reconstructed blocks in order to remove a blocking artifact caused by block-by-block encoding/decoding, and stores the deblocking-filtering in the memory 190 . When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of blocks in a picture to be encoded later.

For reference, the image encoding apparatus 100 may encode the current block using a skip mode. In the skip mode, only motion information of the current block is encoded, and no other information about the current block, such as information on the residual block, is encoded. The above-described merge index information may be used as motion information of the current block. When the current block is encoded in the skip mode, the image decoding apparatus 100 sets the motion information of the merge candidate indicated by the merge index information decoded from the bitstream as the motion information of the current block. Then, the prediction block predicted by the motion information of the current block is restored as the current block.

The present invention relates to a method and apparatus for encoding or decoding a motion vector, and it is possible to improve encoding efficiency by adjusting a resolution for expressing a differential motion vector according to characteristics of images and blocks.

First, motion vector resolution will be described. The motion vector resolution may be adaptively determined between integer pixel resolution and fractional pixel resolution. The motion vector resolution is the minimum unit for determining the motion vector. Also, the motion vector resolution may mean the resolution of the reference picture for motion compensation of the current block, that is, to which pixel the reference picture is interpolated. For example, if the resolution of the motion vector is 1/4 pixel, the reference picture is interpolated to the unit of 1/4 pixel, and the motion vector is measured to the unit of 1/4 pixel. Here, the minimum unit for determining the motion vector is a fractional pixel unit such as 1/2 pixel, 1/4 pixel, 1/8 pixel, etc., or an integer pixel unit such as 1 pixel, 2 pixels, 3 pixels, etc. ) can be a unit. The differential motion vector resolution as well as the motion vector resolution can be adaptively selected between the fractional pixel resolution and the integer pixel resolution.

A motion vector may be expressed in units of fractional pixels when a region in which motion is fine is predicted, and a motion vector may be expressed in units of integer pixels when a region in which a motion is large is predicted. Meanwhile, when the difference between the motion vector of the current block and the predicted motion vector is small, the differential motion vector may be expressed in units of fractional pixels, and if the difference is large, the differential motion vector may be expressed in units of integer pixels. Depending on the characteristics of the image, it may be appropriate to express motion vectors and differential motion vectors at fractional pixel resolution rather than integer pixel resolution. will do

In the existing HEVC standard, motion vectors and differential motion vectors are expressed at 1/4 pixel resolution. Table 1 shows an example of a differential motion vector (quarter-pixel mvd) expressed in 1/4 pixel resolution and a differential motion vector index (mvd index) provided thereto.

mvd index quarter-pixel mvd 0 0 One 0.25 2 0.5 3 0.75 4 One 5 1.25 6 1.5 7 1.75 8 2 ... ...

The differential motion vector determined by the inter prediction unit may have values expressed in units of 1/4 pixels as shown in Table 1. However, in order to signal values that include a fractional part in addition to the integer part, a differential motion vector index (mvd index), which is a value obtained by multiplying an actual determined absolute value of a quarter-pixel mvd by 4, and a sign of the determined differential motion vector ( sign) value is encoded as information of the differential motion vector of the current block.

Table 2 shows syntax elements expressing information on differential motion vectors in HEVC.

mvd_coding(　x0,　y0,　refList　) { Descriptor abs_ mvd _ greater0 _flag [ 0 ] ae(v) abs_ mvd _ greater0 _flag [ 1 ] ae(v) if( abs_mvd_greater0_flag[　0　] ) abs_ mvd _ greater1 _flag [ 0 ] ae(v) if( abs_mvd_greater0_flag[　1　] ) abs_ mvd _ greater1 _flag [ 1 ] ae(v) if( abs_mvd_greater0_flag[　0　] ) { if( abs_mvd_greater1_flag[　0　] ) abs_ mvd _ minus2 [ 0 ] ae(v) mvd _sign_flag [ 0 ] ae(v) } if( abs_mvd_greater0_flag[　1　] ) { if( abs_mvd_greater1_flag[　1　] ) abs_ mvd _ minus2 [ 1 ] ae(v) mvd _sign_flag [ 1 ] ae(v) } }

abs__ mvd _ greater0 _flag [ ] indicates whether the differential motion vector index is greater than 0, and abs_ mvd _ greater1 _flag [] indicates whether the differential motion vector index is greater than 1. abs_ mvd _ minus2 [ ] represents a value obtained by subtracting 2 from a differential motion vector index, and mvd_sign_flag [] represents a sign of a differential motion vector. [0] represents the horizontal axis component (ie, the x component) of the differential motion vector, and [1] represents the vertical axis component (ie, the y component) of the differential motion vector.

Table 3 shows the binarization technique of the syntax elements mentioned in Table 2.

Syntax element
Binarization Process Parameter
mvd

abs_mvd_greater0_flag[　] FL Max=1 abs_mvd_greater1_flag[　] FL Max=1 abs_ mvd _ minus2 [　] EG k-th=1 mvd _sign_flag[　] FL Max=1

FL is a fixed-length-based binarization technique, and requires a maximum value (Max) of a corresponding syntax element. EG (Exponential Golomb) is a binarization technique based on a multiplier of 2, and requires information about the order (k-th). Table 4 shows the code bins of the EG for each order.

Code
Num k=0 k=1 k=2 0 0 00 000 One 100 01 001 2 101 1000 010 3 11000 1001 011 4 11001 1010 10000 5 11010 1011 10001 6 11011 110000 10010 7 1110000 110001 10011 8 1110001 110010 10100 9 1110010 110011 10101 10 1110011 110100 10110 ... ... ... ...

Table 5 shows syntax elements and the required number of bits for representing the quarter-pixel mvd information of the current block determined according to the 1/4 pixel resolution in HEVC.

quarter-pixel mvd 0 0.25 -0.50 0.75 -1.00 2.25 13.00 -22.50 43.75 mvd index 0 One 2 3 4 9 52 90 175 abs_mvd_greater0_flag 0 One One One One One One One One abs_mvd_greater1_flag - 0 One One One One One One One abs_ mvd _ minus2 - - 2 bits (0) 2 bits (1) 4 bits (2) 6 bits (7) 10 bits (50) 12 bits (88) 14 bits (173) mvd _sign_flag - 0 One 0 One 0 0 One 0 Total bits One
bit 3 bits 5 bits 5 bits 7 bits 9 bits 13 bits 15 bits 17 bits

In Table 5, the mvd index is the index value of the actually obtained differential motion vector (quarter-pixel mvd). As shown in Table 1, the mvd index is a value obtained by multiplying the absolute value of the differential motion vector (quarter-pixel mvd) by 4. The number of bits required for abs_ mvd _ minus2 is obtained from the coding result by subtracting 2 from the mvd index based on EG with k-th equal to 1 (refer to Table 3). Hereinafter, the same applies to the description of the embodiments of the present invention. The mvd index minus 2 is shown in parentheses below the number of bits required for abs_ mvd _ minus2 .

The present invention proposes a method for efficiently encoding or decoding an image by reducing the amount of bits required to express differential motion vector information. Various embodiments of the present invention to be described below are respectively applied to both the horizontal axis component (x component) and the vertical axis component (y component) of the differential motion vector. However, for convenience of description, one component will be described as the basis. In addition, the present invention is not limited to expressing a differential motion vector, but can be used to express a motion vector itself.

Example One

In the present embodiment, in a differential motion vector expressed in fractional pixel units, such as 1/2 pixel, 1/4 pixel, 1/8 pixel, 1/16 pixel, etc., the integer part and the decimal part are separated and expressed efficiently. is about For example, when the determined differential motion vector value is "3.75", "3" belonging to the integer part and ".75" belonging to the decimal part are separately expressed.

First, the image encoding apparatus according to the present embodiment determines a differential motion vector for a current block. In this case, the determined absolute value of the differential motion vector may be expressed in integer pixel units or fractional pixel units according to the set motion vector resolution. However, this embodiment may be applied to a case where the absolute value of the differential motion vector is expressed in fractional pixel units.

When the absolute value of the differential motion vector is determined in fractional pixel units, the image encoding apparatus separates the determined absolute value of the differential motion vector into an integer part and a fractional part. Then, information on the absolute value of the differential motion vector, that is, information indicating a value corresponding to an integer part and information indicating a value corresponding to a decimal part, is encoded. Information indicating the sign of the differential motion vector is also separately encoded.

For example, when the image encoding apparatus expresses the absolute value of a differential motion vector, an integer part (pre-point) is expressed by three syntax elements, and a decimal part (post-point) is expressed by one syntax element. can The sign of the differential motion vector is expressed as a flag. An example of syntax elements is as follows.

- abs_ mvd _zero_only_flag (pre-point) : A flag indicating whether the absolute value of the differential motion vector is only 0.

- abs_ mvd _ less1 _flag (pre-point) : A flag indicating whether the absolute value of the differential motion vector is less than 1.

- abs_ mvd _ minus1 ( pre-point) : The value obtained by subtracting 1 from the integer part of the absolute value of the differential motion vector

- abs_ mvd _post_type (post-point) : Type information indicating the fractional part of the absolute value of the differential motion vector (for example, if it is 1/4 pixel, there are 4 types 0:.00, 1:.25, 2:.50 , 3:.75)

- mvd _sign_flag : A flag indicating the sign of the differential motion vector.

The four types of information indicating the fractional part described with respect to abs_mvd_post_type are merely examples and are not necessarily limited thereto. The value and number of type information may vary according to motion vector resolution.

An example of the structure of the syntax elements of this embodiment is shown in Table 6.

mvd_coding(　x0,　y0,　refList　) { Descriptor abs_ mvd _zero_only_flag [ ] ae(v) if(!abs_mvd_zero_only_flag[　] ) abs_ mvd _ less1 _flag [ ] ae(v) if(!abs_mvd_zero_only_flag[　] ) { if(!abs_mvd_less1_flag[　] ) abs_ mvd _ minus1 [ ] ae(v) abs_ mvd _post_type [ ] ae(v) mvd _sign_flag [ ] ae(v) } }

An example of a binarization method for the syntax elements of this embodiment is shown in Table 7. Since there are 4 types for abs_mvd_post_type , the Max value for FL of the corresponding syntax is set to 3. However, the present invention is not limited thereto, and the Max value for FL may vary according to motion vector resolution.

Syntax element Binarization Process Parameter Pre-point

abs_mvd_zero_only_flag FL Max=1 abs_ mvd _ less1 _flag FL Max=1 abs_ mvd _ minus1 EG k-th=1 post-point abs_ mvd _post_type FL Max=3 Sign mvd _sign_flag FL Max1

Table 8 shows the number of bits calculated according to the present embodiment for the same differential motion vector as in Table 5 above. The number of bits required for abs_ mvd _ minus1 The number in parentheses below represents the value obtained by subtracting 1 from the integer part of the absolute value of the differential motion vector.

quarter-pixel mvd 0 0.25 -0.50 0.75 -1.00 2.25 13.00 -22.50 43.75 mvd value (pre_point) 0 0 0 0 One 2 13 22 43 abs_mvd_zero_only_flag One 0 0 0 0 0 0 0 0 abs_ mvd _ less1 _flag - One One One 0 0 0 0 0 abs_ mvd _ minus1 - - - - 2 bits (0) 2 bits (0) 6 bits (12) 8
bits (21) 10 bits (42) mvd value (post_point) .25 .50 .75 .00 .25 .00 .50 .75 abs_ mvd _post_type - 01 10 11 00 01 00 10 11 mvd _sign_flag - 0 One 0 One 0 0 One 0 Total bits 1 bit 5 bits 5 bits 5 bits 7 bits 7 bits 11 bits 13
bits 15
bits

Comparing the total number of bits calculated in Table 5 and Table 8, when the differential motion vector value of 1/4 pixel resolution is 0.25, the number of bits in this embodiment is calculated to be larger, but 2.25, 13.00, -22.50, 43.75 For the value of , the number of bits calculated in this embodiment is smaller. Although omitted in this specification, when comparing the total number of bits according to each of the HEVC method and the method of the present embodiment for quarter-pixel mvd values from 0 to 40 in addition to the values shown in Table 8, the same in all cases except for the case of 0.25 The result may be that the number of bits or less is required. That is, the differential motion vector encoding method according to the present embodiment is more efficient than HEVC.

The image decoding apparatus decodes differential motion vector information of the current block from the bitstream. Here, the differential motion vector information includes information on the absolute value of the differential motion vector (eg , abs_ mvd _zero_only_flag , abs_ mvd _ less1 _flag, abs_ mvd _ minus1 , abs_mvd_post_type ) and information on a sign ( eg, mvd ) . and information on the absolute value of the differential motion vector includes information indicating a value corresponding to an integer part and information indicating a value corresponding to a decimal part, as described above.

The image decoding apparatus restores the absolute value of the differential motion vector by using information indicating a value corresponding to an integer part of the decoded absolute value of the differential motion vector and information indicating a value corresponding to a decimal part. Then, the differential motion vector of the current block is reconstructed using the information on the sign of the decoded differential motion vector and the absolute value of the recovered differential motion vector.

The image decoding apparatus determines a predicted motion vector of the current block, and reconstructs the motion vector of the current block using the reconstructed differential motion vector and the determined predicted motion vector.

Example 2

In this embodiment, the absolute value of the differential motion vector expressed in fractional pixel units is divided into an integer part and a decimal part, but syntax elements different from those of the first embodiment are used.

The image encoding apparatus according to the present embodiment also divides the determined absolute value of the differential motion vector into an integer part and a fractional part when the absolute value of the differential motion vector is determined in fractional pixel units. Then, information about the absolute value of the differential motion vector, that is, information representing a value corresponding to an integer part and information representing a value corresponding to a decimal part, is encoded. Information indicating the sign of the differential motion vector is also separately encoded. However, as information indicating a value corresponding to the integer part, syntax elements different from those of the first embodiment may be used.

For example, in the image encoding apparatus according to the present embodiment, in expressing the absolute value of a differential motion vector, an integer part (pre-point) is expressed by four syntax elements, and a fractional part (post-point) is one It can be expressed as a syntax element. The sign of the differential motion vector is expressed as a flag. An example of syntax elements is as follows.

- abs_ mvd _zero_only_flag (pre-point) : A flag indicating whether the absolute value of the differential motion vector is only 0.

- abs_ mvd _greater_equal_1_flag (pre-point) : A flag indicating whether the absolute value of the differential motion vector is 1 or more.

- abs_ mvd _greater_equal_2_flag (pre-point) : A flag indicating whether the absolute value of the differential motion vector is 2 or more.

- abs_ mvd _ minus2 ( pre-point) : The value obtained by subtracting 2 from the integer part of the absolute value of the differential motion vector

- abs_ mvd _post_type (post-point) : Type information indicating the fractional part of the absolute value of the differential motion vector (for example, if it is 1/4 pixel, there are 4 types 0:.00, 1:.25, 2:.50 , 3:.75)

- mvd _sign_flag : A flag indicating the sign of the differential motion vector.

The four types of information indicating the fractional part described with respect to abs_mvd_post_type are merely examples and are not necessarily limited thereto. The value and number of type information may vary according to motion vector resolution.

An example of a structure for the syntax elements of this embodiment is shown in Table 9.

mvd_coding(　x0,　y0,　refList　) { Descriptor abs_ mvd _zero_only_flag [ ] ae(v) if(!abs_mvd_zero_only_flag[　] ) abs_ mvd _greater_equal_1_flag [ ] ae(v) if(!abs_mvd_zero_only_flag[　] ) if(abs_mvd_greater_equal_1_flag[　] ) abs_ mvd _greater_equal_2_flag [ ] ae(v) if(!abs_mvd_zero_only_flag[　] ) { if(abs_mvd_greater_equal_1_flag[　] ) if(abs_mvd_greater_equal_2_flag[　] ) abs_ mvd _ minus2 [ ] ae(v) abs_ mvd _post_type [ ] ae(v) mvd _sign_flag [ ] ae(v) } }

An example of a binarization method for the syntax elements of this embodiment is shown in Table 10. Since there are 4 types of abs_mvd_post_type , the Max value for FL of the corresponding syntax is set to 3. However, the present invention is not limited thereto, and the Max value for FL may vary according to motion vector resolution.

Syntax element Binarization Process Parameter Pre-point

abs_mvd_zero_only_flag FL Max=1 abs_mvd_greater_equal_1_flag FL Max=1 abs_mvd_greater_equal_2_flag FL Max=1 abs_ mvd _ minus2 EG k-th=1 post-point abs_ mvd _post_type FL Max=3 Sign mvd _sign_flag FL Max1

Table 11 shows the number of bits calculated according to the present embodiment for the same differential motion vector as in Table 5 above. The number of bits required for abs_ mvd _ minus2 The number in parentheses below represents the value obtained by subtracting 2 from the absolute value of the differential motion vector.

quarter-pixel mvd 0 0.25 -0.50 0.75 -1.00 2.25 13.00 -22.50 43.75 mvd value (pre_point) 0 0 0 0 One 2 13 22 43 abs_mvd_zero_only_flag One 0 0 0 0 0 0 0 0 abs_mvd_greater_equal_1_flag - 0 0 0 One One One One One abs_mvd_greater_equal_2_flag 0 One One One One abs_ mvd _ minus2 - - - - - 2 bits (0) 6 bits (11) 8
bits (20) 10 bits (41) mvd value (post_point) .25 .50 .75 .00 .25 .00 .50 .75 abs_ mvd _post_type - 01 10 11 00 01 00 10 11 mvd _sign_flag - 0 One 0 One 0 0 One 0 Total bits 1 bit 5 bits 5 bits 5 bits 6 bits 8 bits 12 bits 14
bits 16
bits

Comparing the total number of bits calculated in Table 5 and Table 11, when the differential motion vector value of 1/4 pixel resolution is 0.25, the number of bits in this embodiment is calculated to be larger, but -1.00, 2.25, 13.00, - At values of 22.50 and 43.75, the number of bits calculated in this embodiment is smaller. That is, the differential motion vector encoding method according to the present embodiment is more efficient than HEVC.

The image decoding apparatus decodes differential motion vector information of the current block from the bitstream. Here, the differential motion vector information includes information on absolute values of differential motion vectors (eg, abs_ mvd _zero_only_flag , abs_ mvd _greater_equal_1_flag, abs_mvd_greater_equal_2_flag, abs_ mvd _equal_2_flag , _flabs_ mvd _minus2 sign , abs_ sign (eg: d sign _post_type ) ) is decoded.

The image decoding apparatus restores the absolute value of the differential motion vector by using information indicating a value corresponding to an integer part of the decoded absolute value of the differential motion vector and information indicating a value corresponding to a decimal part. Then, the differential motion vector of the current block is reconstructed using the information on the sign of the decoded differential motion vector and the absolute value of the recovered differential motion vector.

The image decoding apparatus determines a predicted motion vector of the current block, and reconstructs the motion vector of the current block using the reconstructed differential motion vector and the determined predicted motion vector.

The embodiments of the present invention, which will be described below, efficiently encode an image by adaptively selecting a resolution of a differential motion vector from among a plurality of motion vector resolutions according to the characteristics of an image and a block and expressing the differential motion vector at the selected resolution. . For example, when the magnitude of the differential motion vector (absolute value) is small, the differential motion vector is expressed in fractional pixel units (eg 1/4 pixel), and conversely, when the absolute value is large, the differential motion vector is expressed in integer pixel units ( For example: 1 pixel, 4 pixels) to express a differential motion vector.

The video encoding apparatus may activate/deactivate the adaptive resolution selection function by inserting a flag ( adaptive_MV_resolution_enbaled_flag ) indicating whether to adaptively select one resolution from among a plurality of motion vector resolutions in header information. For example, when the video encoding apparatus adaptively selects one resolution from among a plurality of motion vector resolutions, adaptive_MV_resolution_enbaled_flag is turned on, and when the resolution is not adaptively selected, adaptive_MV_resolution_enbaled_flag is set. It can be coded as off.

The adaptive_MV_resolution_enbaled_flag may be inserted into one or more of a sequence parameter set ( SPS ), a picture parameter set ( PPS ), and a slice (or Coding Tree Unit: CTU) header. For example, when whether or not to adaptively select the motion vector resolution is determined for each image sequence unit, a flag is inserted into the SPS, and when it is determined for each picture unit, the flag is inserted into the PPS, slice (or CTU) unit If each is determined, it is inserted into the slice (or CTU) header.

Embodiments to be described below assume that a flag indicating whether to adaptively select one resolution from among a plurality of motion vector resolutions is coded on.

The image encoding apparatus adaptively selects a resolution for displaying a differential motion vector in units of a coding object block (CU: Coding Unit or CTB: Coding Tree Block). That is, the image encoding apparatus selects one resolution from among a plurality of predefined motion vector resolutions as a resolution for displaying the differential motion vector.

The image encoding apparatus encodes resolution information for indicating a resolution selected from among a plurality of motion vector resolutions in units of encoding object blocks. A plurality of motion vector resolutions may be predefined, and a default resolution and other resolutions to replace the default resolution (ie, alternative resolutions) may be included. Here, the default resolution and the alternative resolutions may be a predetermined specific motion vector resolution shared between the image encoding apparatus and the image decoding apparatus, or the image encoding apparatus uses a higher-level image region (eg, image sequence, picture, slice, CTU, etc.) It may be a value determined by and signaled to the image decoding apparatus.

For example, if the default resolution is defined as 1/4 pixel resolution and the alternative resolutions are defined as 1 pixel resolution and 4 pixel resolution, the image encoding apparatus determines whether the motion vector resolution is 1/4 pixel resolution as selected resolution information as an integer. Information indicating whether the resolution is pixel resolution and information indicating whether the resolution is 1 pixel or 4 pixels in the case of integer pixel resolution are encoded. Hereinafter, first_bin is a syntax element encoded as information indicating whether the motion vector resolution is 1/4 pixel resolution or integer pixel resolution, and second_bin is a syntax element encoded as information indicating whether the motion vector resolution is 1 pixel resolution or 4 pixel resolution is called

In this case, when the value of first_bin is encoded as “0”, a differential motion vector is expressed at 1/4 pixel resolution, and when the value of first_bin is encoded as “1”, second_bin is additionally encoded. When the value of second_bin is encoded as “0”, a differential motion vector is expressed with a resolution of 1 pixel, and when the value of second_bin is encoded with a resolution of “1”, a differential motion vector is expressed with a resolution of 4 pixels.

As another example, the image decoding apparatus may decode mvd_resolution_flag as information indicating the resolution of the differential motion vector. When mvd _resolution_flag is binarized in the TU (Truncated Unary) method (Max=2), when the value of mvd _resolution_flag is decoded to “0”, the differential motion vector is expressed with 1/4 pixel resolution, and the value of mvd_resolution_flag is “10”. ", the differential motion vector is expressed with 1-pixel resolution, and when the value of mvd _resolution_flag is decoded with "11", the differential motion vector can be expressed with 4-pixel resolution.

The resolution information may be signaled to the image decoding apparatus for each of the x and y components of the differential motion vector, or may be signaled to the image decoding apparatus by determining the resolution of the same differential motion vector with respect to the x and y components.

Example 3

This embodiment relates to a method of adaptively selecting one resolution from among a plurality of motion vector resolutions. For example, a default resolution is defined as quarter pixel resolution, and alternate resolutions are defined as 1 pixel resolution and 4 pixel resolution.

Table 12 shows the differential motion vector (quarter-pixel mvd) value of the current block determined according to the 1/4 pixel resolution to any one of 1/4 pixel resolution, 1 pixel resolution, or 4 pixel resolution. It indicates syntax elements and the required number of bits to represent .

quarter-pixel mvd 0 0.75 -2.25 10.00 -15.75 19.50 -22.50 34.25 -43.75 mvd index 0 3 9 40 16 20 6
(16) 9 (20) 11
(44) abs_mvd_greater0_flag 0 One One One One One One One One abs_mvd_greater1_flag - One One One One One One One One abs_ mvd _ minus2 - 2 bits
(One) 6 bits
(7) 10 bits (38) 8
bits (14) 8 bits (18) 4
bits (4) 6 bits (7) 6
bits (9) mvd _sign_flag - 0 One 0 One 0 One 0 One 1 ^st bin
(quarter or integer) - 0 0 0 One One One One One 2nd ^bin ( 1 or 4) - - - - 0 0 One One One Total bits 1 bit 6 bits 10
bits 14 bits 13 bits 13 bits 9
bits 11 bits 11 bits

Among the quarter-pixel mvd values in Table 12, 1/4 pixel resolution was applied to {0, 0.75, -2.25, 10.00}, and 1 pixel resolution was applied to {-15.75, 19.50}, and {-22.50, 34.25 , -43.75}, a resolution of 4 pixels was applied. The mvd index is a value calculated to express the absolute value of quarter-pixel mvd. That is, the differential motion vector index (mvd index) is a value to be encoded corresponding to the differential motion vector.

In the present embodiment, a value to be encoded corresponding to a differential motion vector is calculated in the same single method for all the plurality of resolutions. A formula for obtaining a differential motion vector index ( mvd_index ), which is a value to be encoded corresponding to a differential motion vector , is as shown in Equation (1).

In Equation 1, mvd _resolution is the selected resolution, mvd is a differential motion vector expressed at the selected resolution, and mvd_index represents a value to be encoded.

For example, when 1/4 pixel resolution is applied, the mvd index is calculated by multiplying the absolute value of the differential motion vector by 4; Apply to obtain a differential motion vector (eg, a multiple of 1) expressed at 1 pixel resolution, and then divide it by 1 (pixel) to obtain the mvd index. When 4-pixel resolution is applied, a differential motion vector expressed in 4-pixel resolution (eg, a multiple of 4) is obtained by applying any one of rounding, rounding, or rounding up to the absolute value of the differential motion vector, and then ) to get the mvd index. Among the values of the mvd index, the number indicated in parentheses represents the differential motion vector value expressed by the absolute differential motion vector at each selected resolution. The number of bits required for abs_ mvd _ minus2 The number in parentheses below represents the mvd index minus 2.

Example 4

In this embodiment, the same method of encoding a differential motion vector as described in Embodiment 3 can be applied. However, in the present embodiment, when the image encoding apparatus uses any one of a plurality of predefined motion vector resolutions as the resolution for displaying the differential motion vector, the method for displaying the differential motion vector more efficiently based on a predetermined offset suggest a way Hereinafter, it will be described in detail with reference to FIG. 3 .

3 is a flowchart illustrating a method of operating an image encoding apparatus according to an embodiment of the present invention.

The image encoding apparatus first determines a differential motion vector for the current block with a default resolution (S310). The image encoding apparatus determines one or more resolution candidates from among a plurality of motion vector resolutions according to the determined absolute value of the differential motion vector (S320). For example, the plurality of motion vector resolutions may include 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution, and the default resolution may be 1/4 pixel resolution.

The image encoding apparatus may set an offset corresponding to each of a plurality of motion vector resolutions. Here, the offset may be a predetermined default value shared between the image encoding apparatus and the image decoding apparatus, or may be a value determined by the image encoding apparatus and signaled to the image decoding apparatus as header information such as SPS, PPS, and slice header. For example, when using 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution as a plurality of motion vector resolutions, "α" is an offset for 1/4 pixel resolution, and "β" is an offset for 1 pixel resolution. ” and “γ” as the offset for 4 pixel resolution.

The image encoding apparatus may determine one or more resolution candidates from among a plurality of motion vector resolutions according to the determined absolute value of the differential motion vector and a predetermined offset value. For example, when the absolute value of the determined differential motion vector is "α" or more and "β" or less, 1/4 pixel resolution is determined as a resolution candidate, and when "β" exceeds "γ", 1/4 pixel resolution is determined. and 1 pixel resolution is determined as a resolution candidate, and when "γ" is more than 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution can be determined as resolution codes.

The image encoding apparatus selects a resolution to express the determined differential motion vector from among one or more resolution candidates (S330). In this case, the image encoding apparatus selects a resolution for expressing the differential motion vector determined based on Rate Distortion Optimization (RDO). For example, if the resolution candidates are 1/4 pixel resolution, first pixel resolution, and 4 pixel resolution, one final resolution for the differential motion vector is selected by evaluation based on RDO for the three resolution candidates. .

The image encoding apparatus calculates a value to be encoded as a differential motion vector of the current block by applying a function corresponding to the selected resolution to the determined differential motion vector (S340). The image encoding apparatus encodes the value calculated in step S340 as differential motion vector information, and encodes resolution information for indicating a resolution selected from among a plurality of motion vector resolutions (S350).

Step S340 will be described in detail as follows. The image encoding apparatus expresses the differential motion vector determined in step S310 as a differential motion vector of the resolution selected in step S330, and uses the differential motion vector expressed at the selected resolution and an offset corresponding to the selected resolution as a differential motion vector of the current block. Calculates the value to be encoded.

In the present embodiment, a value to be encoded corresponding to a differential motion vector is calculated in the same single method for all the plurality of resolutions. A value to be encoded corresponding to the differential motion vector means a differential motion vector index ( mvd_index ), and the formulas for calculating the differential motion vector index ( mvd_index ) are the same as in Equations 2 and 3.

In Equations 2 and 3, mvd_resolution is the selected resolution, mvd_resolution_offset is an offset corresponding to the selected resolution, and mvd is a differential motion vector expressed at the selected resolution, and mvd_index represents a value to be encoded.

The image encoding apparatus may calculate a value to be encoded as a differential motion vector of the current block by subtracting an offset corresponding to the selected resolution from the differential motion vector expressed at the selected resolution, and dividing the subtracted value by the selected resolution. For example, the default resolution is set to 1/4 pixel resolution, the alternative resolution is set to 1 pixel resolution and 4 pixel resolution, and the offset values are set to α=0, β=1, γ=4, and the determined differential motion vector is 8.75. Suppose it was If the corresponding differential motion vector is displayed at 1/4 pixel resolution, the value to be encoded as the differential motion vector of the current block is (8.75-0)/(1/4) = 35, and if displayed with 1 pixel resolution, the differential motion of the current block A value to be encoded as a vector is (9-1)/(1) = 8, and when displayed at a resolution of 4 pixels, a value to be encoded as a differential motion vector of the current block becomes (8-4)/(4) = 1. Here, 8.75, 9, and 8 are differential motion vectors expressed at the selected resolution, and are values obtained by applying any one of rounding, rounding, and rounding up to the absolute value of the differential motion vector mentioned in Example 3 so as to be a multiple of the resolution. . Another example of this will be described later with reference to Table 13.

Table 13 shows an example of the number of bits calculated according to the present embodiment for the same quarter-pixel mvd as in Table 12 above. In Table 13, the default resolution was set to 1/4 pixel resolution, the alternative resolution was set to 1 pixel resolution and 4 pixel resolution, and the offset values were set to α=0, β=10, and γ=20. Among the quarter-pixel mvd values, 1/4 pixel resolution was applied to {0, 0.75, -2.25, 10.00}, and 1 pixel resolution was applied to {-15.75, 19.50}, and {-22.50, 34.25, -43.75 }, 4 pixel resolution is applied. However, 1/4 pixel resolution can also be applied to {-15.75, 19.50}, and 1/4 pixel resolution and 1 pixel resolution can also be applied to {-22.50, 34.25, -43.75}. For this determination, the image encoding apparatus selects a resolution for expressing the differential motion vector determined based on the RDO.

quarter-pixel mvd 0 0.75 -2.25 10.00 -15.75 19.50 -22.50 34.25 -43.75 mvd index 0
(0-0)x 4 3
(0.75-0)x4 9
(2.25-0)x4 40
(10.00-0)x4 6
(16-
10)/1 10
(20-
10)/1 One
(24-20)/4 4
(36-
20
)/4 6
(44-20
)/4 abs_mvd_greater0_flag 0 One One One One One One One One abs_mvd_greater1_flag - One One One One One 0 One One abs_ mvd _ minus2 - 2 bits (1) 6 bits (7) 10 bits (38) 4
bits
(4) 6 bits
(8) - 4 bits (2) 4
bits (4) mvd _sign_flag - 0 One 0 One 0 One 0 One 1 ^st bin
(quarter or integer) - 0 0 0 One One One One One 2nd ^bin ( 1 or 4) - - - - 0 0 One One One Total bits 1 bit 6 bits 10
bits 14 bits 9
bits 11 bits 5
bits 9 bits 9
bits

In Table 13, quarter-pixel mvd indicates a differential motion vector for the current block determined with the default resolution, and mvd index indicates a differential motion vector index, which is a value to be encoded as differential motion vector information of the current block. The mvd index may be calculated using a selected resolution, a differential motion vector expressed at the selected resolution, and an offset corresponding to the selected resolution.

First, a method of expressing the differential motion vector (hereinafter, quarter-pixel mvd) determined at the default resolution with the selected resolution is as follows. When quarter-pixel resolution is selected, the absolute value of quarter-pixel mvd is maintained as it is, and when 1-pixel resolution is selected, any one of rounding, rounding, or rounding is applied to the absolute value of quarter-pixel mvd and is a multiple of 1. The differential motion vector is expressed as the result value obtained so that . On the other hand, when 4 pixel resolution is selected, a differential motion vector is expressed as a result obtained to be a multiple of 4 by applying any one of rounding, rounding, and rounding to the absolute value of quarter-pixel mvd.

The mvd index may be calculated by subtracting the offset corresponding to the selected resolution from the differential motion vector expressed at the selected resolution as shown in Equation 2 and dividing the value from which the offset is subtracted by the selected resolution. For example, if quarter-pixel mvd "-22.50" is expressed with 4 pixel resolution, the offset corresponding to 4 pixel resolution from the absolute value "24" of the differential motion vector (four-pixel mvd) expressed with 4 pixel resolution (γ) By subtracting “20”, an offset-subtracted value “4” is obtained, and dividing this by 4, which is the selected resolution, an mvd index having a value of “1” is calculated. The calculation process of mvd index for the remaining cases is described in parentheses under the mvd index value of Table 13.

Comparing Table 13 with Table 12 in Example 3, it is found that the number of bits calculated for all differential motion vector values to which 1 pixel resolution and 4 pixel resolution are applied is reduced compared to the number of bits calculated according to Example 3 can be checked

As another example of the mvd index calculation method, as shown in Equation 3, the image encoding apparatus first divides the differential motion vector expressed at the selected resolution by the selected resolution, and subtracts the offset corresponding to the selected resolution from the value divided by the selected resolution. The mvd index may be calculated as a value to be encoded as a differential motion vector of a block.

Example 5

In this embodiment, the same method of encoding a differential motion vector as described in Embodiment 3 can be applied. In this embodiment, the image encoding apparatus efficiently maps the differential motion vector index (mvd index) to the absolute values for each of a plurality of predefined motion vector resolutions, and sets the mapped index (mvd index) to the current value. We propose a method of encoding a block as a differential motion vector.

Some of the steps described with reference to FIG. 3 are equally applied to the image encoding apparatus according to the embodiment. However, there is a difference between the method of determining the resolution candidate in step S320 and the method of calculating the value to be encoded as the differential motion vector of the current block in step S340.

First, a method for the image encoding apparatus to select one or more resolution candidates from among a plurality of motion vector resolutions according to an absolute value of a differential motion vector determined as a default resolution will be described. When the value of the differential motion vector for the current block determined with the default resolution is a multiple of the alternative resolution, it may be advantageous in terms of bit amount to express the differential motion vector with the alternative resolution rather than the default resolution. In the present embodiment, when the determined absolute value is a multiple of the first alternative resolution, the first alternative resolution is determined as a resolution candidate, and when the determined absolute value is a multiple of the second alternative resolution, the second alternative resolution is determined as the resolution candidate. and, if the first and second alternative resolutions are not multiples, the first alternative resolution, the second alternative resolution, and the default resolution may be determined as resolution candidates. Here, the number of alternative resolutions is not limited to three as in the above example. In general, the first alternative resolution may mean a resolution having the highest numerical value among the plurality of alternative resolutions. That is, the first alternative resolution, the second alternative resolution, the third alternative resolution, and the like may be designated in the order of increasing the size of the alternative resolution.

For example, the plurality of motion vector resolutions include ¼ pixel resolution, 1 pixel resolution and 4 pixel resolution, the default resolution is ¼ pixel resolution, and the first alternate resolution is 4 pixel resolution and the second alternate resolution may be 1 pixel resolution. 4, 8, 12, . In this case, 4 pixel resolution is determined as a resolution candidate, and the magnitude (absolute value) of the differential motion vector determined as the default resolution is 1, 2, 3, 5, 6, ... which is a multiple of the second alternative resolution. In the case of , a resolution of 1 pixel is determined as a resolution candidate, and a default resolution, a first alternative resolution, and a second alternative resolution are determined as resolution candidates for the absolute values of other differential motion vectors. In other words. When the size of the determined differential motion vector is a multiple of 4, it is better to express the determined differential motion vector with the smallest bits without loss of the size of the determined differential motion vector by using 4 pixels, which is the first alternative resolution, rather than the 1/4 pixel resolution, which is the default resolution. a way to express it.

The image encoding apparatus utilizes the characteristics of the above-described example to the maximum, and a differential motion vector for a plurality of motion vector resolutions based on a motion vector resolution optimal for specific absolute values among a plurality of predefined motion vector resolutions. Efficiently map the index (mvd index). Specifically, by limiting specific absolute values to be expressed only at the optimal motion vector resolution, an index corresponding to a plurality of motion vector resolutions is set.

The image encoding apparatus assigns an index increasing by 1 in an ascending order to the magnitudes of the differential motion vectors expressed at the selected resolution. As in the above example, when the plurality of motion vector resolutions are 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution, and the default resolution is 1/4 pixel resolution, absolute values and indices are shown in the table. Same as 14.

mvd
index (Q) quarter-pixel
mvd mvd
index (O) One-pixel
mvd mvd
index (F) four-pixel
mvd 0 0.00 One 0.25 2 0.50 3 0.75 - - One One 4 1.25 5 1.50 6 1.75 - - 2 2 7 2.25 8 2.50 9 2.75 - - 3 3 10 3.25 11 3.50 12 3.75 - - - - One 4 13 4.25 14 4.50 15 4.75 - - 4 5 ... ... - - 2 8 ... ...

An index (Q) is assigned to differential motion vector sizes belonging to 1/4 pixel resolution, an index (O) is assigned to differential motion vector sizes belonging to 1 pixel resolution, and differential motion vector sizes belonging to 4 pixel resolution is given an index (F). The index (Q) starts from 0, and the index (O) and index (F) start from 1. According to the index assignment method in Table 1 described above, the index “5” is assigned to the magnitude of the differential motion vector determined with the default resolution having a value of “1.25”, but according to the present embodiment, the index “4” is assigned. Here, the differential motion vector index is a value to be encoded corresponding to the determined differential motion vector. In other words, the differential motion vector index is a value encoded as differential motion vector information.

The image encoding apparatus calculates a value to be encoded as a differential motion vector of the current block by applying a function corresponding to the selected resolution to the differential motion vector determined as the default resolution. Specifically, the image encoding apparatus expresses an absolute value at the selected resolution and determines an index to be assigned to the size of the differential motion vector expressed at the selected resolution. The determined index becomes a value to be encoded as a differential motion vector of the current block.

Formulas for obtaining each differential motion vector index are the same as in Equations 4 to 6.

는 바닥 함수(floor function)를 나타내고, %는 나머지 연산자(modulus operator)를 나타낸다.Here, int_value denotes an integer part of the determined differential motion vector value, and point_value denotes a fractional part. and

denotes a floor function, and % denotes a modulus operator.

"Quarter-pixel mvd", "One-pixel mvd", and "Four-pixel mvd" in Table 14 indicate the selected resolution, and the differential motion vector sizes listed in the corresponding column are all default resolutions (1/4 pixel resolution). values expressed as

Table 15 shows the number of bits calculated according to Example 3 by selecting a specific resolution from among a plurality of resolutions for various quarter-pixel mvd. Table 16 shows the number of bits calculated according to this embodiment by selecting the same resolution for the same quarter-pixel mvd as in Table 15.

quarter-pixel mvd 0 0.75 -2.25 10.00 -15.75 19.50 -22.50 34.25 -43.75 mvd index 0 3 9 10
(10) 63 78 23
(23) 34
(34) 11
(44) abs_mvd_greater0_flag 0 One One One One One One One One abs_mvd_greater1_flag - One One One One One One One One abs_ mvd _ minus2 - 2 bits (1) 6 bits (7) 6 bits (8) 10 bits
(61) 12 bits
(76) 8
bits
(21) 10 bits (32) 6
bits (9) mvd _sign_flag - 0 One 0 One 0 One 0 One 1 ^st bin
(quarter or integer) - 0 0 One 0 0 One One One 2nd ^bin ( 1 or 4) - - - 0 - - 0 0 One Total bits 1 bit 6 bits 10
bits 11 bits 14 bits 16 bits 13 bits 15 bits 11 bits

quarter-pixel mvd 0 0.75 -2.25 10.00 -15.75 19.50 -22.50 34.25 -43.75 mvd index 0 3 7 8
(10) 48 59 18
(23) 26
(34) 11 (44) abs_mvd_greater0_flag 0 One One One One One One One One abs_mvd_greater1_flag - One One One One One One One One abs_ mvd _ minus2 - 2 bits (1) 4 bits (5) 6
bits (6) 10 bits
(46) 10 bits
(57) 8
bits
(16) 8 bits (24) 6
bits (9) mvd _sign_flag - 0 One 0 One 0 One 0 One 1 ^st bin (quarter or integer) - 0 0 One 0 0 One One One 2nd ^bin ( 1 or 4) - - - 0 - - 0 0 One Total bits 1 bit 6 bits 8 bits 11 bits 14 bits 14 bits 13 bits 13 bits 11 bits

In Tables 15 and 16, 1 pixel resolution was applied to quarter-pixel mvd {10.00}, which is a multiple of 1, and 1 pixel resolution was arbitrarily applied to quarter-pixel mvd {-22.50, 34.25}, and the absolute value was " For quarter-pixel mvd over 40", 4 pixel resolution was arbitrarily applied, and for other quarter-pixel mvd, 1/4 pixel resolution was applied. Comparing Table 16 and Table 15, it can be seen that a part of the number of bits required to encode a differential motion vector index (mvd index) value assigned according to the index assignment method according to the present embodiment is reduced compared to Example 3 have. Table 17 shows the results of briefly comparing the mvd index of Examples 3 and 5 with respect to the same quarter-pixel mvd and the total number of bits for expressing the corresponding mvd index.

quarter-pixel
mvd Example 3 Example 5 Difference mvd index Total bits mvd index Total bits 0.00 0 One 0 One 0 0.25 One 4 One 4 0 0.50 2 6 2 6 0 0.75 3 6 3 6 0 1.00 One 5 0 4 -One 1.25 5 8 4 8 0 1.50 6 8 5 8 0 1.75 7 8 6 8 0 2.00 2 7 One 5 -2 2.25 9 10 7 8 -2 2.50 10 10 8 10 0 2.75 11 10 9 10 0 3.00 3 7 2 7 0 3.25 13 10 10 10 0 3.50 14 10 11 10 0 3.75 15 10 12 10 0 4.00 One 5 0 4 -One 4.25 17 12 13 10 -2 4.50 18 12 14 10 -2 4.75 19 12 15 10 -2 5.00 5 9 3 7 -2 5.25 21 12 16 12 0 5.50 22 12 17 12 0 5.75 23 12 18 12 0 6.00 6 9 4 9 0

Referring to Table 17, as the value of quarter-pixel mvd increases, the mvd index value of this embodiment becomes smaller than the mvd index value of Example 3, and accordingly, it can be seen that the number of bits for expressing the corresponding mvd index decreases. .

Hereinafter, an image decoding apparatus according to the above-described embodiments will be described with reference to FIGS. 4 to 6 . 4 is a block diagram of an image decoding apparatus according to an embodiment of the present invention.

The image decoding apparatus 400 includes a decoder 410 , an inverse quantizer 420 , an inverse transform unit 430 , a predictor 440 , an adder 450 , a filter unit 460 , and a memory 470 . . The components shown in FIG. 4 may be implemented as a hardware chip, or may be implemented as software and a microprocessor may be implemented to execute a function of software corresponding to each component.

The decoding unit 410 decodes the bitstream received from the image encoding apparatus, extracts information related to block division, determines a current block to be decoded, and predicts information necessary for reconstructing the current block and information on the residual signal, etc. to extract

The decoder 410 extracts information about the CTU size from a sequence parameter set (SPS) or a picture parameter set (PPS), determines the size of the CTU, and divides the picture into CTUs of the determined size. Then, the CTU is determined as the top layer of the tree structure, that is, the root node, and the CTU is divided using the tree structure by extracting the division information on the CTU. For example, when a CTU is split using the QTBT structure, a first flag (QT_split_flag) related to QT splitting is first extracted and each node is split into four nodes of a lower layer. In addition, with respect to a node corresponding to a leaf node of QT, a second flag (BT_split_flag) and split type information related to BT splitting are extracted and the corresponding leaf node is split into a BT structure.

When the decoding unit 410 determines a current block (current block) to be decoded through division of the tree structure, information on a prediction type indicating whether the current block is intra-predicted or inter-predicted is extracted.

When the prediction type information indicates inter prediction, the decoder 410 extracts a syntax element for the inter prediction information. First, mode information indicating whether the motion information of the current block is encoded by which mode among a plurality of encoding modes is extracted. Here, the plurality of encoding modes include a merge mode and a differential motion vector encoding mode. When the mode information indicates the merge mode, the decoder 410 extracts merge index information indicating whether to derive the motion vector of the current block from any of the merge candidates as a syntax element for the motion information.

On the other hand, when the mode information indicates a differential motion vector encoding mode, the decoder 410 extracts information on the differential motion vector and information on the reference picture referenced by the motion vector of the current block as syntax elements for the motion vector. do. The decoding unit 410 according to an embodiment of the present invention determines a value determined by decoding differential motion vector information of the current block (hereinafter, referred to as a 'differential motion vector index'), and resolution information indicating the resolution of the differential motion vector. By decoding , a resolution of a differential motion vector is selected from among a plurality of motion vector resolutions. Then, the decoder 410 restores the differential motion vector of the current block by applying a function corresponding to the selected resolution to the differential motion vector index mvd_index. On the other hand, when the video encoding apparatus uses any one of the plurality of prediction motion vector candidates as the prediction motion vector of the current block, the prediction motion vector identification information is included in the bitstream. Accordingly, in this case, information on the differential motion vector and information on the reference picture as well as the prediction motion vector identification information are extracted as syntax elements for the motion vector.

Meanwhile, the decoder 410 extracts information on the quantized transform coefficients of the current block as information on the residual signal.

The inverse quantization unit 420 inverse quantizes the quantized transform coefficients, and the inverse transform unit 430 inverse transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore residual signals to generate a residual block for the current block. .

The prediction unit 440 includes an intra prediction unit 442 and an inter prediction unit 444 . The intra prediction unit 442 is activated when the prediction type of the current block is intra prediction, and the inter prediction unit 444 is activated when the prediction type of the current block is intra prediction.

The intra prediction unit 442 determines the intra prediction mode of the current block from among the plurality of intra prediction modes from the syntax element for the intra prediction mode extracted from the decoder 410, and a reference pixel around the current block according to the intra prediction mode. Predict the current block using

The inter prediction unit 444 determines motion information of the current block by using the syntax element for the inter prediction mode extracted from the decoder 410 , and predicts the current block using the determined motion information.

First, the inter prediction unit 444 checks mode information in inter prediction extracted from the decoder 410 . When the mode information indicates a merge mode, the inter prediction unit 444 constructs a merge list including a predetermined number of merge candidates using neighboring blocks of the current block. The method of the inter prediction unit 444 constructing the merge list is the same as that of the inter prediction unit 424 of the video encoding apparatus. Then, one merge candidate is selected from among the merge candidates in the merge list by using the merge index information transmitted from the decoder 410 . Then, motion information of the selected merge candidate, that is, the motion vector and reference picture of the merge candidate, is set as the motion vector and reference picture of the current block.

On the other hand, when the mode information indicates the differential motion vector encoding mode, the inter prediction unit 444 derives predicted motion vector candidates using motion vectors of neighboring blocks of the current block, and uses the predicted motion vector candidates to obtain the current block. Determine the predicted motion vector for the motion vector of . A method in which the inter prediction unit 444 derives the predicted motion vector candidates is the same as the method in which the inter prediction unit 424 of the image encoding apparatus derives the predicted motion vector candidates. If the image encoding apparatus uses any one of the plurality of predicted motion vector candidates as the predicted motion vector of the current block, the syntax element for the motion information includes the predicted motion vector identification information. Accordingly, in this case, the inter prediction unit 444 may select a candidate indicated by the predicted motion vector identification information from among the predicted motion vector candidates as the predicted motion vector. However, when the image encoding apparatus determines the predicted motion vector by using a predefined function for the plurality of predicted motion vector candidates, the inter prediction unit 444 may determine the predicted motion vector by applying the same function as that of the image encoding apparatus. have. When the predicted motion vector of the current block is determined, the inter prediction unit 444 determines the motion vector of the current block by adding the predicted motion vector and the differential motion vector transmitted from the decoder 410 . Then, the reference picture referred to by the motion vector of the current block is determined by using the information on the reference picture transmitted from the decoder 410 .

When the motion vector and the reference picture of the current block are determined in the merge mode or the differential motion vector encoding mode, the inter prediction unit 442 generates a prediction block of the current block by using the block at the position indicated by the motion vector in the reference picture. do.

The adder 450 reconstructs the current block by adding the residual block output from the inverse transform unit 430 and the prediction block output from the inter prediction unit 444 or the intra prediction unit 442 . Pixels in the reconstructed current block are used as reference pixels when intra-predicting a block to be decoded later.

The filter unit 460 deblocks and filters the boundary between the reconstructed blocks in order to remove a blocking artifact caused by block-by-block decoding, and stores the deblocking filter in the memory 470 . When all blocks in one picture are reconstructed, the reconstructed picture is used as a reference picture for inter prediction of blocks in a picture to be decoded later.

Hereinafter, an image decoding apparatus according to Embodiments 4 and 5 of the present invention will be described in detail with reference to FIG. 5 . 5 is a flowchart illustrating a method of operating an image decoding apparatus according to an embodiment of the present invention.

Referring to FIG. 5 , the image decoding apparatus decodes differential motion vector information of a current block from a bitstream ( S510 ). The differential motion vector information indicates a differential motion vector index (mvd_index) value.

The image decoding apparatus selects one resolution from among a plurality of motion vector resolutions by decoding the resolution information indicating the resolution of the differential motion vector (S520). A plurality of motion vector resolutions may be predefined, and a default resolution and other resolutions to replace the default resolution (ie, alternative resolutions) may be included. Here, the default resolution and the alternative resolutions may be a predetermined specific motion vector resolution shared between the image encoding apparatus and the image decoding apparatus, or the image encoding apparatus uses a higher-level image region (eg, image sequence, picture, slice, CTU, etc.) It may be a value determined by and signaled to the image decoding apparatus.

For example, if the default resolution is defined as 1/4 pixel resolution and the alternative resolutions are defined as 1 pixel resolution and 4 pixel resolution, the image decoding apparatus is information indicating the resolution of the differential motion vector, and the motion vector resolution is 1 Information indicating whether the resolution is /4 pixel resolution or integer pixel resolution and information indicating whether the resolution is 1 pixel or 4 pixels in the case of integer pixel resolution are decoded. Hereinafter, first_bin is a syntax element to be decoded as information indicating whether the motion vector resolution is 1/4 pixel resolution or integer pixel resolution, and second_bin is a syntax element to be decoded as information indicating whether the motion vector resolution is 1 pixel resolution or 4 pixel resolution. is called

In this case, when the value of first_bin is decoded to “0”, a differential motion vector is expressed at 1/4 pixel resolution, and when decoded to “1”, second_bin is additionally decoded. When the value of second_bin is decoded to "0", a differential motion vector is expressed with a resolution of 1 pixel, and when decoded to a value of "1", a differential motion vector is expressed with a resolution of 4 pixels.

As another example, the image decoding apparatus may decode mvd_resolution_flag as information indicating the resolution of the differential motion vector. When mvd _resolution_flag is binarized in the TU (Truncated Unary) method (Max=2), when the value of mvd _resolution_flag is decoded to “0”, the differential motion vector is expressed with 1/4 pixel resolution, and the value of mvd_resolution_flag is “10”. ", the differential motion vector is expressed with 1-pixel resolution, and when the value of mvd _resolution_flag is decoded with "11", the differential motion vector can be expressed with 4-pixel resolution.

The resolution information may be decoded for each of the x component and the y component of the differential motion vector, or the same resolution of the differential motion vector may be decoded with respect to the x component and the y component.

The image decoding apparatus restores the differential motion vector of the current block by applying a function corresponding to the selected resolution to the value determined by the differential motion vector information (ie, the differential motion vector index) ( S530 ).

The differential motion vector decoding method ( S530 ) of the image decoding apparatus according to the third embodiment is as follows. The image decoding apparatus restores the differential motion vector of the current block by multiplying the differential motion vector index by the selected resolution.

An example of a function for reconstructing the differential motion vector of the current block is shown in Equation (7). Equation 7 is a function applicable to all cases where 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

In Equation 7, mvd denotes a differential motion vector of the reconstructed current block, mvd_index denotes a decoded differential motion vector index, and mvd_resolution_ denotes resolution information.

The differential motion vector decoding method ( S530 ) of the image decoding apparatus according to the fourth embodiment is as follows. The image decoding apparatus first multiplies the differential motion vector index by the selected resolution. The differential motion vector of the current block is restored by adding an offset corresponding to the selected resolution to the value multiplied by the selected resolution. Here, the offset may be a predetermined default value shared between the image encoding apparatus and the image decoding apparatus, or may be a value determined by the image encoding apparatus and signaled to the image decoding apparatus as header information such as SPS, PPS, and slice header.

For example, when 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are used as a plurality of motion vector resolutions, offsets “α”, “β” and “γ” corresponding to each resolution (provided that α < β < γ) can be set.

An example of a function for reconstructing the differential motion vector of the current block is shown in Equation (8). Equation 8 is a function applied to all cases where 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

In Equation 8, mvd denotes a differential motion vector of the reconstructed current block, mvd_index denotes a decoded differential motion vector index, mvd_resolution denotes resolution information, and mvd_resolution_offset denotes an offset corresponding to the resolution. Here, when the resolution is 1/4 pixel, the offset may be “α”, in the case of 1 pixel, the offset may be “β”, and in the case of 4 pixels, the offset may be “γ”.

As another example, the image decoding apparatus may restore the differential motion vector of the current block by adding an offset corresponding to the selected resolution to the differential motion vector index, and multiplying the value to which the offset is added by the selected resolution. An example of a function for reconstructing the differential motion vector of the current block in this case is shown in Equation (9). Equation (9) is a function applied to all cases where 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

The differential motion vector decoding method ( S530 ) of the image decoding apparatus according to the fifth embodiment is as follows. The image decoding apparatus restores the differential motion vector of the current block by applying a function corresponding to the selected resolution to the decoded differential motion vector index mvd_index. For example, as shown in Table 15, among the indices assigned to the absolute values belonging to the selected resolution, the absolute value of the differential motion vector corresponding to the decoded differential motion vector index is set to the value of the current block. It can be determined as a differential motion vector. As described above, an index increasing by 1 in an ascending order is assigned to absolute values belonging to each of the selected resolutions.

An index (Q) is assigned to differential motion vector sizes belonging to 1/4 pixel resolution, an index (O) is assigned to differential motion vector sizes belonging to 1 pixel resolution, and differential motion vector sizes belonging to 4 pixel resolution is given an index (F). The index (Q) starts from 0, and the index (O) and index (F) start from 1 and are given indices that increase by 1 in the order of the magnitude of the differential motion vector.

Table 14 described above will be described in detail with reference to an example. When the image decoding apparatus selects 1/4 pixel resolution and decodes the differential motion vector index (mvd_index) having a value of “1”, the differential motion vector size “0.25” corresponding to the index of “1” is set to the current block. It is restored as a differential motion vector of . As another example, if the image decoding apparatus selects a resolution of 1 pixel and decodes a differential motion vector index (mvd_index) having a value of “1”, the differential motion vector size “1” corresponding to the index of “1” is currently It is restored as a differential motion vector of the block. As another example, if the image decoding apparatus selects 4 pixel resolution and decodes the differential motion vector index (mvd_index) having a value of “1”, the size of the differential motion vector corresponding to the index of “1” is “4”. It is restored to the differential motion vector of the current block.

A function for reconstructing the differential motion vector of the current block using the indexes given as shown in Table 14 for each selected resolution is as shown in Equations 10 to 12. Equation 10 is a function applied when 1/4 pixel resolution is selected, Equation 11 is a function applied when 1 pixel resolution is selected, and Equation 12 is a function applied when 4 pixel resolution is selected. However, Equations 10 to 12 are merely examples, and may vary according to various embodiments of the present invention in which a differential motion vector index is assigned to an absolute value of a differential motion vector.

는 바닥 함수(floor function)를 나타내고, %는 나머지 연산자(modulus operator)를 나타낸다.In Equations 10 to 12, mvd denotes a differential motion vector of the reconstructed current block , and mvd_index denotes a decoded differential motion vector index. and

denotes a floor function, and % denotes a modulus operator.

A detailed operation of the image decoding apparatus according to the third to fifth embodiments will be described with reference to FIG. 6 . 6 is a flowchart illustrating an example of a specific operation method of an image decoding apparatus according to an embodiment of the present invention.

The image decoding apparatus decodes differential motion vector information of the current block to determine a differential motion vector index ( S610 ). The image decoding apparatus determines whether the determined differential motion vector index value is not “0” (S612), and if it is “0”, restores the differential motion vector of the current block to “0” (S614).

If the determined differential motion vector index value is not “0”, the image decoding apparatus decodes first resolution information (eg, first bin ) indicating the resolution of the differential motion vector ( S616 ), and the decoded first resolution information is 1/ It is determined whether 4-pixel resolution or integer pixel resolution is indicated (S618). For example, when the first resolution information is decoded to "0" indicates 1/4 pixel resolution and decoded to "1" indicates integer pixel resolution, the image decoding apparatus determines that the first resolution information is "0" When decoded as , 1/4 pixel resolution is selected as the resolution of the differential motion vector (S620). Then, the image decoding apparatus restores the differential motion vector of the current block by applying a function corresponding to the 1/4 pixel resolution to the differential motion vector index (S622). A function corresponding to the 1/4 pixel resolution is, for example, Equations (8) to (10).

When the first resolution information is decoded to "1" instead of "0" in step S618, the image decoding apparatus decodes second resolution information (eg, second bin ) indicating the resolution of the differential motion vector (S624), and It is determined whether the 2 resolution information indicates 1 pixel resolution or 4 pixel resolution (S626). For example, when the second resolution information is decoded to "0" indicates 1 pixel resolution and decoded to "1" indicates 4 pixel resolution, the image decoding apparatus decodes the second resolution information into "0" Then, 1 pixel resolution is selected as the resolution of the differential motion vector (S628). Then, the image decoding apparatus restores the differential motion vector of the current block by applying a function corresponding to one pixel resolution to the differential motion vector index (S630). A function corresponding to one pixel resolution is, for example, Equation 8, Equation 9, and Equation 11.

When the second resolution information is decoded as "1" instead of "0" in step 626, the image decoding apparatus selects 4 pixel resolution as the resolution of the differential motion vector (S632), and 4 pixel resolution in the differential motion vector index The differential motion vector of the current block is restored by applying the corresponding function (S634). A function corresponding to 4 pixel resolution is, for example, Equation 8, Equation 9, and Equation 12.

When the differential motion vector of the current block is reconstructed, the image decoding apparatus determines a predicted motion vector of the current block, and reconstructs the motion vector of the current block using the reconstructed differential motion vector and the determined predicted motion vector (S636).

Although it is described that each process is sequentially executed in FIGS. 3, 5 and 6 , the present invention is not limited thereto. In other words, since the process described in FIGS. 3, 5, and 6 may be changed and applied or one or more processes may be executed in parallel, FIGS. 3, 5 and 6 are not limited to a time-series order .

The image encoding or decoding method according to the present embodiment described in FIGS. 3, 5 and 6 may be implemented as a computer program and recorded in a computer-readable recording medium. The computer program for implementing the image encoding or decoding method according to the present embodiment is recorded and the computer readable recording medium includes all kinds of recording devices in which data readable by the computing system is stored.

The above description is merely illustrative of the technical idea of this embodiment, and various modifications and variations will be possible without departing from the essential characteristics of the present embodiment by those of ordinary skill in the art to which this embodiment belongs. Accordingly, the present embodiments are intended to explain rather than limit the technical spirit of the present embodiment, and the scope of the technical spirit of the present embodiment is not limited by these embodiments. The protection scope of this embodiment should be interpreted by the claims below, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present embodiment.

Claims (13)

A method of encoding a motion vector of a current block, the method comprising:
determining a differential motion vector for the current block;
selecting a resolution to be applied to the determined differential motion vector from among a plurality of motion vector resolutions;
selecting an offset corresponding to the selected resolution from among a plurality of predefined offsets allocated differently to the plurality of motion vector resolutions;
calculating a value to be encoded as a differential motion vector of the current block by applying a function to the determined differential motion vector, wherein the function is defined by the selected resolution and the offset; and
encoding the calculated value as differential motion vector information, and encoding resolution information representing the selected resolution among the plurality of motion vector resolutions;
A motion vector encoding method comprising a. According to claim 1,
The plurality of motion vector resolutions include 1/4 pixel resolution, 1 pixel resolution and 4 pixel resolution, and the default resolution is 1/4 pixel resolution. delete According to claim 1,
Calculating a value to be encoded as a differential motion vector of the current block comprises:
subtracting an offset corresponding to the selected resolution from the determined differential motion vector; and
and calculating a value to be encoded as a differential motion vector of the current block by dividing the value obtained by subtracting the offset by the selected resolution. According to claim 1,
Calculating a value to be encoded as a differential motion vector of the current block comprises:
dividing the determined differential motion vector by the selected resolution; and
and calculating a value to be encoded as a differential motion vector of the current block by subtracting an offset corresponding to the selected resolution from the value divided by the selected resolution. A method of encoding a motion vector of a current block, the method comprising:
determining a differential motion vector for the current block;
selecting a differential motion vector resolution to be applied to the determined differential motion vector from among a plurality of motion vector resolutions, wherein the plurality of motion vector resolutions include a default resolution indicating subsample unit precision and one or more replacements having integer sample unit precision. including resolution;
calculating a value to be encoded as a differential motion vector of the current block by applying a function corresponding to the resolution of the differential motion vector to the determined differential motion vector; and
encoding the calculated value as differential motion vector information and encoding resolution information for representing the selected resolution among the plurality of motion vector resolutions;
The step of selecting the differential motion vector resolution comprises:
determining the alternative resolution as the differential motion vector resolution when the determined absolute value of the differential motion vector is a multiple of the alternative resolution; and
and determining the differential motion vector resolution from among resolution candidates including the alternative resolution and the default resolution when the determined absolute value of the differential motion vector is not a multiple of the alternative resolution. Way. 7. The method of claim 6,
Calculating a value to be encoded as a differential motion vector of the current block comprises:
expressing the determined differential motion vector with the differential motion vector resolution and determining an index to be assigned to the differential motion vector expressed with the differential motion vector resolution; and
and determining the determined index as a value to be encoded as a differential motion vector of the current block. 8. The method of claim 7,
The index is given to increase by 1 in an ascending order with respect to differential motion vector sizes expressible by the differential motion vector resolution. A method for decoding a motion vector of a current block, the method comprising:
decoding differential motion vector information of the current block;
selecting a resolution of the differential motion vector from among a plurality of motion vector resolutions by decoding resolution information indicating the resolution of the differential motion vector;
restoring a differential motion vector of the current block by applying a function corresponding to the selected resolution to a value determined by the differential motion vector information; and
determining a predicted motion vector of the current block, and reconstructing the motion vector of the current block using the reconstructed differential motion vector and the predicted motion vector;
Restoring the differential motion vector of the current block comprises:
selecting an offset corresponding to the selected resolution from among a plurality of different predefined offsets assigned to each of the plurality of motion vector resolutions; and
restoring a differential motion vector of the current block by applying the function to a value determined by the differential motion vector information, wherein the function is defined by the selected resolution and the offset
A motion vector decoding method comprising: 10. The method of claim 9,
The plurality of motion vector resolutions include 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution. 10. The method of claim 9,
Restoring the differential motion vector of the current block comprises:
multiplying a value determined by the differential motion vector information by the selected resolution; and
and restoring a differential motion vector of the current block by adding an offset corresponding to the selected resolution to a value multiplied by the selected resolution. 10. The method of claim 9,
Restoring the differential motion vector of the current block comprises:
adding an offset corresponding to the selected resolution to a value determined by the differential motion vector information; and
and multiplying the value to which the offset is added by the selected resolution. An image decoding apparatus for decoding a motion vector of a current block, comprising:
A variable corresponding to a selected resolution from among a plurality of predefined variable values assigned differently to a plurality of motion vector resolutions by decoding the differential motion vector information of the current block and decoding the resolution information indicating the resolution of the differential motion vector a decoding unit that selects a value and restores a differential motion vector of the current block by applying a function defined by a variable value corresponding to the selected resolution to a value determined by the differential motion vector information; and
An inter prediction unit that determines a predicted motion vector of the current block, and reconstructs a motion vector of the current block using the reconstructed differential motion vector and the predicted motion vector
A video decoding device comprising a.

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