KR20240013891A - Method and Apparatus for Encoding and Decoding Motion Vector - Google Patents

Abstract

The present invention relates to image encoding or decoding for efficiently encoding images. According to one aspect of the present invention, a method of encoding a motion vector of a current block includes: determining a differential motion vector for the current block at a default resolution; determining one or more resolution candidates among a plurality of motion vector resolutions according to the size (absolute value) of the determined differential motion vector; selecting a resolution to express 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 about the calculated value and resolution information representing the selected resolution among the plurality of motion vector resolutions as information about 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 images.

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

Since the amount of video data is larger than that of audio data or still image data, it requires a lot of hardware resources, including memory, to store or transmit it without processing for compression. Therefore, typically, when storing or transmitting video data, an encoder is used to compress the video data and store or transmit it, and a decoder receives the compressed video data, decompresses it, and plays it. These video compression technologies include H.264/AVC and HEVC (High Efficiency Video Coding), which was established in early 2013 and improved coding efficiency by about 40% of H.264/AVC.

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

However, as the size, resolution, and frame rate of images gradually increase, the amount of data that must be encoded is also increasing. Therefore, a compression technology with better encoding efficiency than existing compression technologies is required.

The present invention provides an image encoding or decoding technology for efficiently encoding images by adjusting the resolution of expressing differential motion vectors according to the characteristics of images and blocks.

According to one aspect of the present invention, a method for encoding a motion vector of a current block is provided. The method includes selecting a resolution for the differential motion vector of the current block from a plurality of motion vector resolutions, the plurality of motion vector resolutions including a default resolution and at least two alternative resolutions; encoding the differential motion vector, which is the difference between the motion vector of the current block and the predicted motion vector, according to the selected resolution; and encoding resolution information to indicate the resolution among the plurality of motion vector resolutions. In addition, encoding the resolution information may include encoding a first syntax element indicating whether the resolution for the differential motion vector is the default resolution; And when the resolution for the differential motion vector is not the default resolution, encoding a second syntax element indicating the resolution for the differential motion vector among the alternative resolutions.

According to another aspect of the present invention, a method for decoding the motion vector of the current block is provided. The method includes 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, the plurality of motion vector resolutions including a default resolution and at least two alternative resolutions; Restoring the differential motion vector of the current block using the selected resolution; and determining a predicted motion vector of the current block, and restoring the motion vector of the current block using the restored differential motion vector and the predicted motion vector. In addition, decoding the resolution information may include decoding a first syntax element indicating whether the resolution for the differential motion vector is the default resolution; And when the resolution for the differential motion vector is not the default resolution, decoding a second syntax element indicating the resolution for the differential motion vector among the alternative resolutions.

According to another aspect of the present invention, a recording medium that is readable by a decoder and stores a bitstream to be decoded by an image decoding method is provided. Decoding the bitstream includes 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, wherein the plurality of motion vector resolutions include a default resolution and at least two alternative resolutions; Restoring the differential motion vector of the current block using the selected resolution; and determining a predicted motion vector of the current block, and restoring the motion vector of the current block using the restored differential motion vector and the predicted motion vector. In addition, decoding the resolution information may include decoding a first syntax element indicating whether the resolution for the differential motion vector is the default resolution; And when the resolution for the differential motion vector is not the default resolution, decoding a second syntax element indicating the resolution for the differential motion vector among the alternative resolutions.

1 is a block diagram of a video encoding device according to an embodiment of the present invention.
Figure 2 is an example diagram of neighboring blocks of the current block.
Figure 3 is a flowchart showing a method of operating a video encoding device according to an embodiment of the present invention.
Figure 4 is a block diagram of an image decoding device according to an embodiment of the present invention.
Figure 5 is a flowchart showing a method of operating a video decoding device according to an embodiment of the present invention.
Figure 6 is a flowchart showing an example of a specific operating method of a video decoding device according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through illustrative drawings. In adding identification codes to components in each drawing, it should be noted that the same components are given the same codes as much as possible even if they are shown in different drawings. Additionally, 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 will be omitted.

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

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

The block division unit 110 divides each picture constituting the image into a plurality of CTUs (Coding Tree Units) and then recursively divides the CTUs using a tree structure. The leaf node in the tree structure becomes the CU (Coding Unit), the basic unit of encoding. The tree structure is either QuadTree (QT), where the upper node is divided into four lower nodes, or QTBT (QuadTree), which is a combination of the QT structure and BinaryTree (BT) structure, where the upper node is divided into two lower nodes. plus BinaryTree) structure can be used.

The prediction unit 120 predicts the current block and generates a prediction 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 above tree structure and means the CU to be currently encoded. Alternatively, the current block may be one subblock among a plurality of subblocks divided from the CU.

The intra prediction unit 122 predicts pixels within the current block using pixels (reference pixels) located around the current block within the current picture including the current block. There are multiple intra prediction modes depending on the prediction direction, and the surrounding pixels and calculation formulas to be used are defined differently for each prediction mode.

The inter prediction unit 124 searches for a block most similar to the current block in a reference picture that has been 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 the displacement between the current block in the current picture and the prediction block in the reference picture is generated. Motion information including information about reference pictures and motion vectors used to predict the current block is encoded by the encoder 150 and transmitted to the video decoding device.

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

If 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 can be transmitted to the decoding device by encoding information that can identify 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 shown in Figure 2, the surrounding blocks for deriving merge candidates include the left block (L), top block (A), top right block (AR), and bottom left block (BL) adjacent to the current block in the current picture. ), all or part of the upper left block (AL) can be used. Additionally, a block located within a reference picture (which may be the same or different from the reference picture used to predict the current block) other than the current picture where 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 (co-located block) or blocks adjacent to the co-located block may be additionally used as merge candidates.

The inter prediction unit 124 uses these neighboring blocks to construct a merge list including a predetermined number of merge candidates. 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 is generated to identify the selected candidate. The generated merge index information is encoded by the encoder 150 and transmitted to the video decoding device.

Another way to encode motion information is to encode a motion vector difference (MVD).

In this method, the inter prediction unit 124 uses neighboring blocks of the current block to derive motion vector predictor (MVP) candidates for the motion vector of the current block. The surrounding blocks used to derive predicted motion vector candidates include the left block (L), top block (A), top right block (AR), and bottom left block adjacent to the current block in the current picture shown in FIG. 2. BL), or all or part of the upper left block (AL) can be used. Additionally, a block located within a reference picture (which may be the same or different from the reference picture used to predict the current block) rather than the current picture where the current block is located will be used as a neighboring block used to derive predicted motion vector candidates. It may be possible. For example, a block co-located with the current block within the reference picture or blocks adjacent to the co-located block may be used.

The inter prediction unit 124 derives predicted motion vector candidates using the motion vectors of the surrounding blocks, and determines a predicted motion vector for the motion vector of the current block using the predicted motion vector candidates. Then, the predicted motion vector is subtracted from the motion vector of the current block to calculate the differential motion vector.

The predicted motion vector can be obtained by applying a predefined function (eg, median, average value calculation, etc.) to the predicted motion vector candidates. In this case, the video decoding device also knows the predefined function. In addition, since the surrounding block used to derive the predicted motion vector candidate is a block for which encoding and decoding have already been completed, the video decoding device also already knows the motion vector of the surrounding block. Therefore, the video encoding device 100 does not need to encode information for identifying predicted motion vector candidates. Therefore, in this case, information about the differential motion vector and information about the reference picture used to predict the current block are encoded.

Meanwhile, the predicted motion vector may be determined by selecting one of the predicted motion vector candidates. In this case, information for identifying the selected predicted motion vector candidate is additionally encoded, along with information about the differential motion vector and information about 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 converter 140 converts the residual signal in the residual block with pixel values in the spatial domain into a transform coefficient in the frequency domain. The converter 140 may convert the residual signals in the residual block using the size of the current block as a conversion unit, or divide the residual block into a plurality of smaller subblocks and convert the residual signals into a conversion unit of the subblock size. You can also convert it. There may be various ways to divide the residual block into smaller subblocks. For example, it may be divided into predefined subblocks of the same size, or QT (quadtree) type division may be used with the residual block as the root node.

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 about the size of the CTU located in the highest layer of the tree structure and splitting information for splitting the block from the CTU into the tree structure, so that the decoding device splits the block in the same way as the encoding device. make it possible For example, in the case of QT division, QT division information indicating whether a block in the upper layer is divided into four blocks in the lower layer is encoded. In the case of BT splitting, starting from the block corresponding to the leaf node of the QT, BT splitting information indicating whether each block is split into two blocks and the type of splitting is encoded.

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

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

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

(b) Syntax elements for motion information

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

On the other hand, when the motion information is encoded by a mode that encodes a differential motion vector, information about the differential motion vector and information about the reference picture are encoded as syntax elements for the motion information. If the predicted motion vector is determined by selecting one candidate among a plurality of predicted motion vector candidates, the syntax element for the motion information further includes predicted motion vector identification information to identify the selected candidate. Includes.

The inverse quantization unit 160 inversely 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 converting the transform coefficients output from the inverse quantization unit 160 from the frequency domain to the spatial domain.

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

The filter unit 180 performs deblocking filtering on the boundaries between restored blocks to remove blocking artifacts caused by block-level encoding/decoding and stores them in the memory 190. When all blocks in one picture are reconstructed, the reconstructed picture is later used as a reference picture for inter prediction of blocks in the picture to be encoded.

For reference, the video encoding device 100 may encode the current block using skip mode. In skip mode, only the motion information of the current block is encoded and no other information about the current block, such as information about the residual block, is encoded. The above-described merge index information can be used as motion information of the current block. When the current block is encoded in skip mode, the video 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. And 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 device for encoding or decoding a motion vector, and can improve encoding efficiency by adjusting the resolution of expressing the differential motion vector according to the characteristics of the image and block.

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

When predicting an area with subtle movement, the motion vector may be expressed in fractional pixel units, and when predicting an area with large movement, the motion vector may be expressed in integer pixel units. Meanwhile, if 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 fractional pixel units, and conversely, if the difference is large, the differential motion vector may be expressed in integer pixel units. Depending on the characteristics of the video, there may be cases where it is appropriate to express motion vectors and differential motion vectors with fractional pixel resolution rather than integer pixel resolution. However, in this case, the fractional parts below the integer must be signaled to the video decoding device, so the amount of bits required increases. I do it.

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

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

Table 2 shows syntax elements expressing information of 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 the value obtained by subtracting 2 from the differential motion vector index, and mvd_sign_flag [] represents the sign of the differential motion vector. [0] represents the horizontal axis component (i.e., x component) of the differential motion vector, and [1] represents the vertical axis component (i.e., y component) of the differential motion vector.

Table 3 shows the binarization technique for 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 that requires the maximum value (Max) of the 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 EG by 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 number of bits required to represent differential motion vector (quarter-pixel mvd) information of the current block determined according to 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, mvd index is the index value of the actually obtained differential motion vector (quarter-pixel mvd), and is a value obtained by multiplying the absolute value of the differential motion vector (quarter-pixel mvd) by 4, as shown in Table 1. The number of bits required for abs_mvd_minus2 is obtained from the result of coding the mvd index minus 2 based on EG (see Table 3) where k-th is 1. Hereinafter, the same applies to the description of embodiments of the present invention. The value of mvd index minus 2 is displayed in parentheses below the number of bits required for abs_mvd_minus2 .

The present invention proposes a method for efficiently encoding or decoding images by reducing the amount of bits required to express differential motion vector information. Various embodiments of the present invention, which will be described below, are applied to both the horizontal axis component (x component) and the vertical axis component (y component) of the differential motion vector, respectively. However, for convenience of explanation, the explanation is based on one ingredient. Additionally, the present invention is not limited to expressing differential motion vectors, but can be used to express the motion vector itself.

Example 1

This embodiment is a method of efficiently expressing a differential motion vector expressed in fractional pixel units such as 1/2 pixel, 1/4 pixel, 1/8 pixel, 1/16 pixel, etc. by separating the integer part and the decimal part. It's about. For example, if the determined differential motion vector value is “3.75”, “3” belonging to the integer part and “.75” belonging to the decimal part are expressed separately.

First, the video encoding device according to this embodiment determines the differential motion vector for the current block. At this time, the absolute value of the determined differential motion vector may be expressed in integer pixel units or in fractional pixel units depending on the set motion vector resolution. However, this embodiment can be applied when the absolute value of the differential motion vector is expressed in fractional pixel units.

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

For example, when a video encoding device expresses the absolute value of a differential motion vector, the integer part (pre-point) is expressed with three syntax elements, and the decimal part (post-point) is expressed with one syntax element. You 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) : Flag indicating whether the absolute value of the differential motion vector is only 0.

- abs_mvd_less1_flag (pre-point) : Flag indicating whether the absolute value of the differential motion vector is less than 1.

- abs_mvd_minus1(pre-point) : 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 representing the decimal part of the absolute value of the differential motion vector (for example, for 1/4 pixel, there are four types: 0:.00, 1:.25, 2:.50, 3) :.75)

- mvd_sign_flag : Flag indicating the sign of the differential motion vector

The four types of information indicating the decimal part described for abs_mvd_post_type are only examples and are not necessarily limited thereto. The value and number of type information may vary depending on the motion vector resolution.

An example of the structure of 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 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, it is not limited to this and the Max value for FL may vary depending on the 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 this embodiment for the same differential motion vector as Table 5 described above. The number in parentheses below the number of bits required for abs_mvd_minus1 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 was 0.25, the number of bits in this example was calculated to be larger, but 2.25, 13.00, -22.50, 43.75 At 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 the HEVC method and the method of this embodiment for quarter-pixel mvd values from 0 to 40 in addition to the values shown in Table 8, it is the same in all cases except for the case of 0.25. The result may be that more or less bits are required. In other words, the differential motion vector coding method according to this embodiment is more efficient than HEVC.

The video decoding device decodes the differential motion vector information of the current block from the bitstream. Here, the differential motion vector information includes information about the absolute value of the differential motion vector (e.g. , abs_mvd_zero_only_flag, abs_mvd_less1_flag, abs_mvd_minus1, abs_mvd_post_type ) and information about the sign (e.g., mvd_sign_flag ), and the absolute value of the differential motion vector. As described above, the information about includes information indicating the value corresponding to the integer part and information indicating the value corresponding to the decimal part.

The image decoding device restores the absolute value of the differential motion vector using information indicating the value corresponding to the integer part and information indicating the value corresponding to the decimal part of the decoded absolute value of the differential motion vector. Then, the differential motion vector of the current block is restored using information about the sign of the decoded differential motion vector and the absolute value of the restored differential motion vector.

The video decoding device determines the predicted motion vector of the current block and restores the motion vector of the current block using the restored 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 expressed by dividing it into an integer part and a decimal part, but different syntax elements from Example 1 are used.

The video encoding device according to this embodiment also separates the absolute value of the determined differential motion vector into an integer part and a decimal part when determining the absolute value of the differential motion vector in fractional pixel units. Then, information about the absolute value of the differential motion vector, that is, information representing the value corresponding to the integer part and information representing the value corresponding to the decimal part, are encoded. Information indicating the sign of the differential motion vector is also encoded separately. However, syntax elements different from those in Example 1 can be used as information representing the value corresponding to the integer part.

For example, when the video encoding device according to this embodiment expresses the absolute value of the differential motion vector, the integer part (pre-point) is expressed with 4 syntax elements, and the decimal part (post-point) is expressed with 1 syntax element. 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) : Flag indicating whether the absolute value of the differential motion vector is only 0.

- abs_mvd_greater_equal_1_flag(pre-point) : Flag indicating whether the absolute value of the differential motion vector is 1 or more.

- abs_mvd_greater_equal_2_flag(pre-point) : Flag indicating whether the absolute value of the differential motion vector is 2 or more.

- abs_mvd_minus2(pre-point) : 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 representing the decimal part of the absolute value of the differential motion vector (for example, for 1/4 pixel, there are four types: 0:.00, 1:.25, 2:.50, 3) :.75)

- mvd_sign_flag : Flag indicating the sign of the differential motion vector

The four types of information indicating the decimal part described for abs_mvd_post_type are only examples and are not necessarily limited thereto. The value and number of type information may vary depending on the motion vector resolution.

An example of the structure of 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 syntax elements of this embodiment is shown in Table 10. Since there are 4 types for abs_mvd_post_type , the Max value for FL of the corresponding syntax is set to 3. However, it is not limited to this and the Max value for FL may vary depending on the 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 this embodiment for the same differential motion vector as Table 5 described above. The number in parentheses below the number of bits required for abs_mvd_minus2 represents the absolute value of the differential motion vector minus 2.

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, the number of bits in this example was calculated to be larger when the differential motion vector value of 1/4 pixel resolution was 0.25, 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. In other words, the differential motion vector coding method according to this embodiment is more efficient than HEVC.

The video decoding device decodes the differential motion vector information of the current block from the bitstream. Here, the differential motion vector information decodes information about the absolute value of the differential motion vector (e.g. , abs_mvd_zero_only_flag, abs_mvd_greater_equal_1_flag, abs_mvd_greater_equal_2_flag, abs_mvd_minus2, abs_mvd_post_type ) and information about the sign (e.g., mvd_sign_flag ).

The image decoding device restores the absolute value of the differential motion vector using information indicating the value corresponding to the integer part and information indicating the value corresponding to the decimal part of the decoded absolute value of the differential motion vector. Then, the differential motion vector of the current block is restored using information about the sign of the decoded differential motion vector and the absolute value of the restored differential motion vector.

The video decoding device determines the predicted motion vector of the current block and restores the motion vector of the current block using the restored differential motion vector and the determined predicted motion vector.

Embodiments of the present invention, which will be described below, efficiently encode images by adaptively selecting the resolution of the differential motion vector from a plurality of motion vector resolutions according to the characteristics of the image and block and expressing the differential motion vector at the selected resolution. . For example, if the size (absolute value) of the differential motion vector is small, the differential motion vector is expressed in fractional pixel units (e.g., 1/4 pixel), and conversely, if the size (absolute value) is large, the differential motion vector is expressed in integer pixel units (e.g., 1/4 pixel). Express the differential motion vector (e.g. 1 pixel, 4 pixels).

The video encoding device can activate/deactivate the adaptive resolution selection function by inserting a flag ( adaptive_MV_resolution_enbaled_flag ) indicating whether to adaptively select one resolution among a plurality of motion vector resolutions into header information. For example, when a video encoding device adaptively selects one resolution among a plurality of motion vector resolutions, adaptive_MV_resolution_enbaled_flag is encoded as on, and when it does not adaptively select a resolution, adaptive_MV_resolution_enbaled_flag is encoded as off ( can be encoded as off).

adaptive_MV_resolution_enbaled_flag can be inserted into one or more of the Sequence Parameter Set (SPS), Picture Parameter Set (PPS), and Slice (or Coding Tree Unit (CTU)) headers. For example, if whether to adaptively select motion vector resolution is determined on a per-image sequence basis, a flag is inserted in SPS; if it is decided on a per-picture basis, a flag is inserted in PPS; and on a slice (or CTU) basis. If each decision is made, 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 encoded as on.

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

The video encoding device encodes resolution information to indicate a resolution selected from a plurality of motion vector resolutions in units of encoding target blocks. A plurality of motion vector resolutions may be predefined, and a default resolution and other resolutions to replace the default resolution (i.e., alternative resolutions) may be included. Here, the default resolution and alternative resolutions may be a predetermined specific motion vector resolution shared by the video encoding device and the video decoding device, or the video encoding device may use a higher-level video area (e.g., video sequence, picture, slice, CTU, etc.) It may be a value determined in and signaled to the video decoding device.

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 video encoding device determines whether the motion vector resolution is 1/4 pixel resolution as the selected resolution information. Information indicating whether it is a pixel resolution and, if it is an integer pixel resolution, information indicating whether it is a 1-pixel resolution or a 4-pixel resolution are encoded. Hereinafter, the syntax element encoded as information indicating whether the motion vector resolution is 1/4 pixel resolution or integer pixel resolution is referred to as first_bin , and the syntax element encoded as information indicating whether the motion vector resolution is 1 pixel resolution or 4 pixel resolution is referred to as second_bin . It is called.

In this case, if the value of first_bin is encoded as "0", the differential motion vector is expressed at 1/4 pixel resolution, and if the value of first_bin is encoded as "1", second_bin is additionally encoded. If the value of second_bin is coded as "0", the differential motion vector is expressed with 1 pixel resolution, and if it is coded as "1", the differential motion vector is expressed with 4 pixel resolution.

As another example, the video decoding device can 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 at 1/4 pixel resolution, and the value of mvd_resolution_flag is set to "10". When decoded, the differential motion vector can be 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.

Resolution information may be signaled to the video decoding device for each of the x and y components of the differential motion vector, or may be signaled to the video decoding device by determining the resolution of the same differential motion vector for the x and y components.

Example 3

This embodiment relates to a method of adaptively selecting one resolution from a plurality of motion vector resolutions. For example, the default resolution is defined as 1/4 pixel resolution, and alternative 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 at any one of 1/4 pixel resolution, 1 pixel resolution, or 4 pixel resolution. Indicates syntax elements for representing and the number of bits required.

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}, 1 pixel resolution was applied to {-15.75, 19.50}, and {-22.50, 34.25 , -43.75}, 4 pixel resolution was applied. 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 this embodiment, the value to be encoded corresponding to the differential motion vector is calculated using the same method for all plural resolutions. The formula for calculating the differential motion vector index ( mvd_index ), which is the value to be encoded corresponding to the differential motion vector, is as shown in Equation 1.

In Equation 1, mvd_resolution represents the selected resolution, mvd represents the differential motion vector expressed at the selected resolution, and mvd_index represents the 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, and when 1 pixel resolution is applied, the absolute value of the differential motion vector is rounded down, rounded, or rounded. Apply this to obtain a differential motion vector (e.g. multiple of 1) expressed at 1 pixel resolution, then divide it by 1 (pixel) to obtain the mvd index. When 4-pixel resolution is applied, apply any of rounding, rounding, or rounding to the absolute value of the differential motion vector to obtain a differential motion vector expressed at 4-pixel resolution (e.g., a multiple of 4), and then divide it into 4 (pixels). ) to obtain the mvd index. Among the mvd index values, the number shown in parentheses represents the differential motion vector value expressed by the absolute value of the differential motion vector at each selected resolution. The number in parentheses below the number of bits required for abs_mvd_minus2 represents the value obtained by subtracting 2 from the mvd index.

Example 4

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

Figure 3 is a flowchart showing a method of operating a video encoding device according to an embodiment of the present invention.

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

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

The video encoding device may determine one or more resolution candidates among a plurality of motion vector resolutions according to the size (absolute value) of the determined differential motion vector and a predetermined offset value. For example, if the size (absolute value) of the determined differential motion vector is between “α” and “β” or below, 1/4 pixel resolution is determined as a resolution candidate, and if it is over “β” but below “γ”, 1/4 pixel resolution is selected. and 1 pixel resolution are determined as resolution candidates, and if it exceeds “γ”, 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution can be determined as resolution codes.

The video encoding device selects a resolution to express the determined differential motion vector from among one or more resolution candidates (S330). At this time, the video encoding device selects a resolution for expressing the differential motion vector determined based on RDO (Rate Distortion Optimization). 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 video encoding device calculates a value to be encoded as the differential motion vector of the current block by applying a function corresponding to the selected resolution to the determined differential motion vector (S340). The video encoding apparatus encodes the value calculated in step S340 as differential motion vector information and encodes resolution information to indicate a resolution selected from among a plurality of motion vector resolutions (S350).

Step S340 will be described in detail as follows. The video encoding device 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 in the selected resolution and the offset corresponding to the selected resolution as a differential motion vector of the current block. Calculate the value to be encoded.

In this embodiment, the value to be encoded corresponding to the differential motion vector is calculated using the same method for all plural resolutions. The value to be encoded corresponding to the differential motion vector means the differential motion vector index ( mvd_index ), and the formula for calculating the differential motion vector index ( mvd_index ) is as shown in Equation 2 and Equation 3.

In Equation 2 and Equation 3, mvd_resolution represents the selected resolution, mvd_resolution_offset represents the offset corresponding to the selected resolution, mvd represents the differential motion vector expressed by the selected resolution, and mvd_index represents the value to be encoded.

The video encoding device may calculate a value to be encoded as the differential motion vector of the current block by subtracting the offset corresponding to the selected resolution from the differential motion vector expressed at the selected resolution and dividing the value from which the offset was subtracted by the selected resolution. For example, the default resolution is set to 1/4 pixel resolution, the alternative resolutions are set to 1 pixel resolution and 4 pixel resolution, and the offset values are set to α=0, β=1, and γ=4, and the determined differential motion vector is 8.75. Let's assume it was. If the 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 at 1 pixel resolution, the differential motion vector of the current block is The value to be encoded as a vector is (9-1)/(1) = 8, and when displayed at 4 pixel resolution, the value to be encoded as the differential motion vector of the current block is (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 of rounding, rounding, and rounding to the absolute value of the differential motion vector mentioned in Example 3 to be a multiple of the resolution. . Another example of this is described below with reference to Table 13.

Table 13 shows an example of the number of bits calculated according to this embodiment for the same quarter-pixel mvd as Table 12 described above. In Table 13, 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=10, and γ=20. Among the quarter-pixel mvd values, 1/4 pixel resolution was applied to {0, 0.75, -2.25, 10.00}, 1 pixel resolution was applied to {-15.75, 19.50}, and {-22.50, 34.25, -43.75 }, a resolution of 4 pixels was applied. However, 1/4 pixel resolution can 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}. To determine this, the video encoding device selects a resolution to express the differential motion vector determined based on 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)x4 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

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

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

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

Comparing Table 13 with Table 12 in Example 3, 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. You can check it.

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

Example 5

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

Some steps described with reference to FIG. 3 are equally applied to the video encoding device according to the embodiment. However, there is a difference in 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 an image encoding device to select one or more resolution candidates from a plurality of motion vector resolutions according to the size (absolute value) of the differential motion vector determined as the default resolution will be described. If the value of the differential motion vector for the current block determined at the default resolution is a multiple of the alternative resolution, it may be advantageous in terms of bit quantity to express the differential motion vector at the alternative resolution rather than the default resolution. In this embodiment, if the determined differential motion vector size (absolute value) is a multiple of the first alternative resolution, the first alternative resolution is determined as a resolution candidate, and if it is a multiple of the second alternative resolution, the second alternative resolution is determined as the resolution candidate. And, if it is not a multiple of the first and second alternative resolutions, 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 example above. In a general case, the first alternative resolution may mean the resolution of the largest value among a plurality of alternative resolutions. That is, the first alternative resolution, the second alternative resolution, the third alternative resolution, etc. may be designated in order of the size of the alternative resolution.

For example, the plurality of motion vector resolutions include 1/4 pixel resolution, 1 pixel resolution and 4 pixel resolution, the default resolution is 1/4 pixel resolution, the first alternate resolution is 4 pixel resolution and the second alternate resolution is. may be 1 pixel resolution. The size (absolute value) of the differential motion vector determined as the default resolution is a multiple of the first alternative resolution: 4, 8, 12,... In this case, a 4-pixel resolution is determined as a resolution candidate, and the size (absolute value) of the differential motion vector determined as the default resolution is 1, 2, 3, 5, 6,... which are multiples of the second alternative resolution. In this case, 1 pixel resolution is determined as a resolution candidate, and for other differential motion vector sizes (absolute values), the default resolution, first alternative resolution, and second alternative resolution are determined as resolution candidates. in other words. If the size of the determined differential motion vector is a multiple of 4, it is better to express it at the first alternative resolution of 4 pixels rather than at the default resolution of 1/4 pixel, using the fewest bits without losing the size of the determined differential motion vector. It becomes a way to express it.

The video encoding device utilizes the characteristics of the above-mentioned examples to the fullest to generate differential motion vectors for a plurality of motion vector resolutions based on the motion vector resolution optimal for specific differential motion vector sizes (absolute values) among the plurality of predefined motion vector resolutions. Efficiently maps the index (mvd index). Specifically, specific differential motion vector sizes (absolute values) are restricted so that each can be expressed only at the optimal motion vector resolution, and an index corresponding to a plurality of motion vector resolutions is set.

The video encoding device assigns an index that increases by 1 in ascending order to the magnitudes of differential motion vectors expressed at the selected resolution. As in the above-mentioned 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, the differential motion vector sizes (absolute values) and indices are shown in the table Same as 14.

mvd
index (Q) Quarter-pixels
mvd mvd
index (O) One-pixel
mvd mvd
index (F) Four-pixels
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 ... ...

The differential motion vector sizes belonging to 1/4 pixel resolution are given an index (Q), the differential motion vector sizes belonging to 1 pixel resolution are given an index (O), and the differential motion vector sizes belonging to 4 pixel resolution are given an index (Q). is given an index (F). Index (Q) starts from 0, and index (O) and index (F) start from 1. According to the index assignment method in Table 1 described above, an index of "5" is assigned to the size of the differential motion vector determined at the default resolution with a value of "1.25", but according to the present embodiment, an index of "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 video encoding device calculates a value to be encoded as the 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 video encoding device expresses the differential motion vector size (absolute value) at the selected resolution and determines an index to be assigned to the differential motion vector size expressed at the selected resolution. The determined index becomes the value to be encoded as the differential motion vector of the current block.

The formula for calculating each differential motion vector index is as shown in Equation 4 to Equation 6.

Here, int_value means the integer part of the value of the determined differential motion vector, and point_value means the decimal part. and represents the floor function, and % represents the modulus operator.

“Quarter-pixel mvd”, “One-pixel mvd”, and “Four-pixel mvd” listed 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). These are the 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 mvds. Table 16 shows the number of bits calculated according to this embodiment by selecting the same resolution for the same quarter-pixel mvd as 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 mvds larger than 40", 4 pixel resolution was arbitrarily applied, and for other quarter-pixel mvds, 1/4 pixel resolution was applied. Comparing Table 16 and Table 15, it can be seen that some of the number of bits required to encode the differential motion vector index (mvd index) value assigned according to the index assigning method according to the present embodiment has been reduced compared to Embodiment 3. there is. Table 17 shows the results of a brief comparison of the mvd index of Examples 3 and 5 and the total number of bits for expressing the mvd index for the same quarter-pixel mvd.

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

Looking at Table 17, it can be seen that 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, the number of bits for expressing the mvd index decreases. .

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

The image decoding device 400 includes a decoding unit 410, an inverse quantization unit 420, an inverse transform unit 430, a prediction unit 440, an adder 450, a filter unit 460, and a memory 470. . The components shown in FIG. 4 may be implemented as hardware chips, or may be implemented as software and have a microprocessor execute the functions of the software corresponding to each component.

The decoder 410 decodes the bitstream received from the video encoding device, extracts information related to block division, determines the current block to be decoded, and provides prediction information and residual signal information necessary to restore the current block. Extract .

The decoder 410 extracts information about the CTU size from the SPS (Sequence Parameter Set) or PPS (Picture Parameter Set), determines the size of the CTU, and divides the picture into CTUs of the determined size. Then, the CTU is determined as the highest layer of the tree structure, that is, the root node, and the CTU is divided using the tree structure by extracting the division information about the CTU. For example, when dividing a CTU using the QTBT structure, first extract the first flag (QT_split_flag) related to the division of the QT and split each node into four nodes of the lower layer. And, for the node corresponding to the leaf node of the QT, the second flag (BT_split_flag) and split type information related to the split of the BT are extracted and the leaf node is split into a BT structure.

When the decoding unit 410 determines the current block to be decoded by dividing the tree structure, it extracts information about the prediction type indicating whether the current block is intra-predicted or inter-predicted.

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

On the other hand, when the mode information indicates the differential motion vector encoding mode, the decoder 410 extracts information about the differential motion vector and information about the reference picture referenced by the motion vector of the current block as syntax elements for the motion vector. do. The decoder 410 according to an embodiment of the present invention determines a value (hereinafter referred to as 'differential motion vector index') determined by decoding the differential motion vector information of the current block, and provides resolution information indicating the resolution of the differential motion vector. By decoding , the resolution of the differential motion vector is selected from among the 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). Meanwhile, when the video encoding device uses one candidate among a plurality of prediction motion vector candidates as the prediction motion vector of the current block, prediction motion vector identification information is included in the bitstream. Therefore, in this case, not only information about the differential motion vector and information about the reference picture, but also prediction motion vector identification information is extracted as a syntax element for the motion vector.

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

The inverse quantization unit 420 inversely quantizes the quantized transform coefficients, and the inverse transformation unit 430 inversely transforms the inverse quantized transform coefficients from the frequency domain to the spatial domain to restore the residual signals, thereby generating 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 among a plurality of intra prediction modes from the syntax elements for the intra prediction mode extracted from the decoder 410, and determines the intra prediction mode of the current block according to the intra prediction mode. Use these to predict the current block.

The inter prediction unit 444 determines motion information of the current block using syntax elements 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 the mode information in the 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 device. Then, one merge candidate is selected from among the merge candidates in the merge list using the merge index information transmitted from the decoder 410. Then, the motion information of the selected merge candidate, that is, the motion vector and reference picture of the merge candidate, are 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 the motion vectors of neighboring blocks of the current block, and uses the predicted motion vector candidates to predict the current block. Determine the predicted motion vector for the motion vector of . The method by which the inter prediction unit 444 derives the predicted motion vector candidates is the same as the method by which the inter prediction unit 424 of the video encoding device derives the predicted motion vector candidates. If the video encoding device uses one candidate among a plurality of predicted motion vector candidates as the predicted motion vector of the current block, the syntax element for the motion information includes predicted motion vector identification information. Therefore, in this case, the inter prediction unit 444 may select the candidate indicated by the prediction motion vector identification information among the prediction motion vector candidates as the prediction motion vector. However, if the video encoding device determines the predicted motion vector using a predefined function for a 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 video encoding device. there is. When the predicted motion vector of the current block is determined, the inter prediction unit 444 adds the predicted motion vector and the differential motion vector delivered from the decoder 410 to determine the motion vector of the current block. Then, the reference picture referenced by the motion vector of the current block is determined using information about the reference picture transmitted from the decoder 410.

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

The adder 450 restores 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 intra prediction unit 442. Pixels in the restored current block are used as reference pixels when intra-predicting a block to be decoded later.

The filter unit 460 deblocks and filters the boundaries between restored blocks to remove blocking artifacts that occur due to block-level decoding and stores them in the memory 470. When all blocks in one picture are reconstructed, the reconstructed picture is later used as a reference picture for inter prediction of blocks in the picture to be decoded.

Hereinafter, the video decoding apparatus according to embodiments 4 and 5 of the present invention will be described in detail with reference to FIG. 5. Figure 5 is a flowchart showing a method of operating a video decoding device according to an embodiment of the present invention.

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

The video decoding device selects one resolution from a plurality of motion vector resolutions by decoding 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 (i.e., alternative resolutions) may be included. Here, the default resolution and alternative resolutions may be a predetermined specific motion vector resolution shared by the video encoding device and the video decoding device, or the video encoding device may use a high-level video area (e.g., video sequence, picture, slice, CTU, etc.) It may be a value determined in and signaled to the video decoding device.

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 video decoding device uses information indicating the resolution of the differential motion vector, and the motion vector resolution is 1. /Decodes information indicating whether it is 4 pixel resolution or integer pixel resolution, and if it is integer pixel resolution, information indicating whether it is 1 pixel resolution or 4 pixel resolution. Hereinafter, the syntax element decoded as information indicating whether the motion vector resolution is 1/4 pixel resolution or integer pixel resolution is referred to as first_bin , and the syntax element decoded as information indicating whether the motion vector resolution is 1 pixel resolution or 4 pixel resolution is referred to as second_bin . It is called.

In this case, if the value of first_bin is decoded to "0", the differential motion vector is expressed at 1/4 pixel resolution, and if the value of first_bin is decoded to "1", second_bin is additionally decoded. If the value of second_bin is decoded as "0", the differential motion vector is expressed with 1 pixel resolution, and if it is decoded as "1", the differential motion vector is expressed with 4 pixel resolution.

As another example, the video decoding device can 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 at 1/4 pixel resolution, and the value of mvd_resolution_flag is set to "10". When decoded, the differential motion vector can be 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.

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

The video decoding device 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 (i.e., differential motion vector index) (S530).

The differential motion vector decoding method (S530) of the video decoding device according to Example 3 is as follows. The video decoding device 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 restoring the differential motion vector of the current block is shown in Equation 7. Equation 7 is a function that can be applied when 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

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

The differential motion vector decoding method (S530) of the video decoding device according to Example 4 is as follows. The video decoding device first multiplies the differential motion vector index by the selected resolution. Then, the offset corresponding to the selected resolution is added to the value multiplied by the selected resolution to restore the differential motion vector of the current block. Here, the offset may be a predetermined default value shared by the video encoding device and the video decoding device, or it may be a value determined by the video encoding device and signaled to the video decoding device as header information such as SPS, PPS, slice header, etc.

For example, when using 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution as multiple 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 restoring the differential motion vector of the current block is as shown in Equation 8. Equation 8 is a function that applies when 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

In Equation 8, mvd represents the differential motion vector of the restored current block, mvd_index represents the decoded differential motion vector index, mvd_resolution represents resolution information, and mvd_resolution_offset represents the offset corresponding to the resolution. Here, if the resolution is 1/4 pixel, the offset may be “α”, if the resolution is 1 pixel, the offset may be “β”, and if the resolution is 4 pixels, the offset may be “γ”.

As another example, the video decoding device 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 added value of the offset by the selected resolution. An example of a function for restoring the differential motion vector of the current block for this case is as shown in Equation 9. Equation 9 is a function that applies when 1/4 pixel resolution, 1 pixel resolution, and 4 pixel resolution are selected.

The differential motion vector decoding method (S530) of the video decoding device according to Example 5 is as follows. The video decoding device 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, among the indices assigned to the differential motion vector sizes (absolute values) belonging to the selected resolution as shown in Table 15, the size (absolute value) of the differential motion vector corresponding to the decoded differential motion vector index of the current block is It can be determined by the differential motion vector. As described above, the differential motion vector sizes (absolute values) belonging to each selected resolution are given an index that increases by 1 in ascending order.

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

This will be explained in detail using the above-mentioned Table 14 as an example. When the video decoding device selects 1/4 pixel resolution and decodes the differential motion vector index (mvd_index) with a value of "1", the differential motion vector size "0.25" corresponding to the index of "1" is added to the current block. Restore to the differential motion vector of . As another example, if the video decoding device selects 1 pixel resolution and decodes the differential motion vector index (mvd_index) with a value of “1”, the differential motion vector size “1” corresponding to the index of the “1” value is currently It is restored as the differential motion vector of the block. As another example, if the video decoding device selects 4 pixel resolution and decodes the differential motion vector index (mvd_index) with a value of "1", the differential motion vector size "4" corresponding to the index of the value of "1" is set to "4". Restore the differential motion vector of the current block.

The function for restoring the differential motion vector of the current block using the indices given 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 that assign a differential motion vector index to the size (absolute value) of the differential motion vector.

In Equations 10 to 12, mvd represents the restored differential motion vector of the current block, and mvd_index represents the decoded differential motion vector index. and represents the floor function, and % represents the modulus operator.

Detailed operations of the video decoding apparatus according to Examples 3 to 5 will be described with reference to FIG. 6 . Figure 6 is a flowchart showing an example of a specific operating method of a video decoding device according to an embodiment of the present invention.

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

If the determined differential motion vector index value is not “0”, the video decoding device decodes the first resolution information (e.g., first bin ) indicating the resolution of the differential motion vector (S616), and the decoded first resolution information is 1/ Determine whether 4 pixel resolution or integer pixel resolution is indicated (S618). For example, when the first resolution information is decoded as "0" and indicates 1/4 pixel resolution, and when decoded as "1", it indicates integer pixel resolution, the image decoding device may decode the first resolution information as "0". When decoded, 1/4 pixel resolution is selected as the resolution of the differential motion vector (S620). Then, the video decoding device restores the differential motion vector of the current block by applying a function corresponding to 1/4 pixel resolution to the differential motion vector index (S622). The function corresponding to 1/4 pixel resolution is, for example, Equation 8 to Equation 10.

If the first resolution information is decoded as “1” instead of “0” in step S618, the video decoding device decodes the second resolution information (e.g., second bin ) indicating the resolution of the differential motion vector (S624), and 2 Determine whether the resolution information indicates 1 pixel resolution or 4 pixel resolution (S626). For example, when the second resolution information is decoded as “0” and indicates a 1-pixel resolution, and when it is decoded as “1”, it indicates a 4-pixel resolution, the video decoding device decodes the second resolution information as “0”. Then, 1 pixel resolution is selected as the resolution of the differential motion vector (S628). Then, the video decoding device restores the differential motion vector of the current block by applying a function corresponding to 1 pixel resolution to the differential motion vector index (S630). The functions corresponding to 1 pixel resolution are, for example, Equation 8, Equation 9, and Equation 11.

If the second resolution information is decoded as “1” instead of “0” in step 626, the video decoding device selects 4 pixel resolution as the resolution of the differential motion vector (S632), and adds 4 pixel resolution to the differential motion vector index. The differential motion vector of the current block is restored by applying the corresponding function (S634). The functions corresponding to 4 pixel resolution are, for example, Equation 8, Equation 9, and Equation 12.

When the differential motion vector of the current block is restored, the video decoding device determines the predicted motion vector of the current block and restores the motion vector of the current block using the restored differential motion vector and the determined predicted motion vector (S636).

In Figures 3, 5, and 6, each process is described as being executed sequentially, but the process is not necessarily limited to this. In other words, the processes described in FIGS. 3, 5, and 6 may be applied by modifying them or executing one or more processes in parallel, so FIGS. 3, 5, and 6 are not limited to the time series order. .

The image encoding or decoding method according to this embodiment shown in FIGS. 3, 5, and 6 may be implemented as a computer program and recorded on a computer-readable recording medium. A computer-readable recording medium on which a computer program for implementing the image encoding or decoding method according to this embodiment is recorded includes all types of recording devices that store data that can be read by a computing system.

The above description is merely an illustrative explanation of the technical idea of the present embodiment, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but rather to explain it, and the scope of the technical idea of the present embodiment is not limited by these examples. The scope of protection of this embodiment should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of this embodiment.

Claims (11)

In the method of encoding the motion vector of the current block,
selecting a resolution for the differential motion vector of the current block from a plurality of motion vector resolutions, the plurality of motion vector resolutions including a default resolution and at least two alternative resolutions;
The differential motion vector, which is the difference between the motion vector of the current block and the predicted motion vector, is defined by a variable value corresponding to the selected resolution among a plurality of predefined variable values differently assigned to each of the plurality of motion vector resolutions. A step of modifying using a function;
Encoding information representing the modified differential motion vector; and
Comprising: encoding resolution information to represent the selected resolution among the plurality of motion vector resolutions,
The information representing the modified differential motion vector is,
One or more syntax elements for representing the absolute value of the modified differential motion vector, and
A motion vector encoding method comprising a syntax element for representing a sign of the modified differential motion vector. According to paragraph 1,
The motion vector encoding method of claim 1, wherein the alternative resolutions include 1 pixel resolution and 4 pixel resolution, and the default resolution is 1/4 pixel resolution. According to paragraph 1,
The step of encoding the resolution information is,
encoding a first syntax element indicating whether the resolution for the differential motion vector is the default resolution; and
If the resolution for the differential motion vector is not the default resolution, encoding a second syntax element indicating the resolution for the differential motion vector among the alternative resolutions.
A motion vector encoding method including. According to paragraph 1,
The value of the differential motion vector encoded at the selected resolution is,
Subtracting a variable value corresponding to the selected resolution from the differential motion vector,
A motion vector encoding method characterized in that the variable value is generated by dividing the subtracted value by the selected resolution. According to paragraph 1,
The value of the differential motion vector encoded at the selected resolution is,
Divide the differential motion vector by the selected resolution,
A motion vector encoding method characterized in that it is generated by subtracting a variable value corresponding to the selected resolution from a value divided by the selected resolution. In a method for decoding the motion vector of the current block,
Decoding differential motion vector information of the current block to determine a differential motion vector;
selecting a resolution of the differential motion vector from a plurality of motion vector resolutions by decoding resolution information indicating the resolution of the differential motion vector, the plurality of motion vector resolutions including a default resolution and at least two alternative resolutions;
modifying the differential motion vector using a function defined by a variable value corresponding to the selected resolution among a plurality of predefined variable values differently assigned to the plurality of motion vector resolutions; and
Determining a predicted motion vector of the current block, and restoring the motion vector of the current block using the modified differential motion vector and the predicted motion vector,
The differential motion vector information is,
One or more syntax elements for indicating the absolute value of the differential motion vector, and
A motion vector decoding method comprising a syntax element for representing a sign of the differential motion vector. According to clause 6,
The alternative resolutions include 1 pixel resolution and 4 pixel resolution, and the default resolution is 1/4 pixel resolution. According to clause 6,
Decoding the resolution information involves:
Decoding a first syntax element indicating whether the resolution for the differential motion vector is the default resolution; and
When the resolution for the differential motion vector is not the default resolution, decoding a second syntax element indicating the resolution for the differential motion vector among the alternative resolutions.
A motion vector decoding method including. According to clause 6,
The step of restoring the differential motion vector of the current block is,
multiplying the value determined by the differential motion vector information by the selected resolution; and
A motion vector decoding method comprising restoring the differential motion vector of the current block by adding a variable value corresponding to the selected resolution to a value multiplied by the selected resolution. According to clause 6,
The step of restoring the differential motion vector of the current block is,
adding a variable value corresponding to the selected resolution to a value determined by the differential motion vector information; and
A motion vector decoding method comprising multiplying a value obtained by adding the variable value by the selected resolution. A recording medium readable by a decoder, storing a bitstream to be decoded by a video decoding method,
The decoding method is,
Decoding the differential motion vector information of the current block to determine the differential motion vector;
Selecting a resolution of the differential motion vector from a plurality of motion vector resolutions by decoding resolution information indicating the resolution of the differential motion vector, wherein the plurality of motion vector resolutions include a default resolution and at least two alternative resolutions. ;
modifying the differential motion vector using a function defined by a variable value corresponding to the selected resolution among a plurality of predefined variable values differently assigned to the plurality of motion vector resolutions; and
Determining a predicted motion vector of the current block, and restoring the motion vector of the current block using the modified differential motion vector and the predicted motion vector,
The differential motion vector information is,
One or more syntax elements for indicating the absolute value of the differential motion vector, and
A recording medium comprising a syntax element for representing a sign of the differential motion vector.

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