KR101895389B1 - Method and Apparatus for image encoding - Google Patents

Abstract

The present invention relates to an image encoding method, and more particularly, to an image encoding method including: acquiring a plurality of motion vectors in an enhancement layer; Calculating a partition function based on a deviation of the motion vector; Comparing the result of the partition function with a threshold value; And determining whether to partition the predictive unit according to the comparison result. Thus, partitioning of the enhancement layer is rapidly determined, and more efficient encoding becomes possible.

Description

[0001] The present invention relates to a method and apparatus for image encoding,

The present invention relates to a video encoding method and apparatus.

H.264 / AVC is a video compression standard technology with high compression efficiency. In H.264 / AVC, the original signal can be predictively encoded through an intra prediction technique for eliminating correlation in an image and an inter prediction technique for eliminating correlation between images. The H.264 / AVC encoder performs discrete cosine transform (DCT) encoding and quantization on the difference value between the original signal and the prediction signal. The quantized signal is then entropy encoded after being aligned by a zigzag scanning method.

Recently, ITU-T VCEG (Video Coding Experts Group) and ISO / IEC MPEG (Moving Picture Experts Group) have formed Joint Collaborative Team on Video Coding (JCT-VC) And it is known that the compression efficiency is improved by about 40% or more as compared with the existing standard H.264 / AVC. H.264 / AVC and HEVC are basically block-based image coders. However, unlike H.264 / AVC, which performs MB (Macroblock) -based encoding with a fixed size of 16x16, Coding is performed in units of blocks having various sizes ranging from a maximum size of 64x64 to 8x8. In this case, the most basic coding block unit is referred to as a CU (Coding Unit).

In addition, a motion vector is predicted on a block-by-block basis. In this case, the block is referred to as a prediction unit (PU). The CU is divided into several PUs.

When an enhancement layer is generated in scalable high efficiency video coding (SHVC) such as HEVC, a base layer and a block unit may be different. Conventionally, the enhancement layer and the base layer are compared Partition the blocks of the hierarchy.

In this paper, we propose a method for partitioning a scalable video coding (SVC) based on the relationship between a layer and a base layer when creating an enhancement layer in SVC (scalable video coding).

The location of the base layer is used to access the partitions of the base layer, and the partition of the enhancement layer is copied. At this time, the default size of the partition is the smallest PU size.

The partition of the enhancement layer is filled with partitions of the base layer, and the depth of sub-partitions is determined by recursively proceeding the process.

If four sub-partitions on the same partition do not have the same prediction mode, the process is terminated. Otherwise, the intra prediction data and the motion data are compared according to a prediction mode.

If the compared data is the same as all sub-partitions, the depth is reduced and the process is done at the next small depth after the combination process.

If the prediction mode is inter, the size of the partition is determined by comparing motion variables of the lower partitions.

In the previous study 1, if the enhancement layer is partitioned, the combination process is recursively performed when it starts with the smallest PU (Prediction Unit) unit and is the same as the sub-partition.

However, since all the partitions and sub-partitions are recursively compared starting from the smallest PU unit, there is a problem that the encoding time is long.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide an image coding method and apparatus for performing partitioning more quickly at the time of coding.

According to an aspect of the present invention, there is provided an image encoding method including: acquiring a plurality of motion vectors in an enhancement layer; Calculating a partition function based on a deviation of the motion vector; Comparing the result of the partition function with a threshold value; And determining whether to partition the prediction unit according to the comparison result.

Here, the partition function is preferably based on the depth of the prediction unit.

In addition, the partition function may weight the deviation of the motion vector, or may weight the depth of the prediction unit.

Here, the partition function is preferably proportional to the deviation of the motion vector.

It is preferable that the partition function is inversely proportional to the depth of the prediction unit.

As a result of comparing the result of the partition function with a threshold value, if the result of the partition function is greater than the threshold value, the partitioning of the prediction unit is performed. If the result of the partition function is less than the threshold value , It is preferable to select a motion vector without performing partitioning of the prediction unit.

According to the present invention, partitioning of the enhancement layer can be performed more quickly by using the relationship of motion vectors in the enhancement layer, thereby improving coding efficiency.

1 schematically shows an example of the structure of an image encoding apparatus.
2 schematically shows an example of the structure of a video decoding apparatus.
3 shows an example of a picture to be coded / decoded and a reference picture.
4 shows an example of a motion vector of the enhancement layer.
FIG. 5 is a block diagram of an embodiment of the present invention,
FIG. 5 is a flowchart showing a video encoding method. FIG.

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

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

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

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

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

1 schematically shows an example of the structure of an image encoding apparatus.

1, the image encoding apparatus 100 includes a motion prediction unit 111, a motion compensation unit 112, an intra prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, A quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transformation unit 170, an adder 175, a filter unit 180, and a reference image buffer 190.

The image encoding apparatus 100 performs encoding in an intra mode or an inter mode with respect to an input image and outputs a bit stream. In the embodiment of the present invention, intra prediction can be used in the same way as inter prediction, and inter prediction can be used in the same meaning as inter prediction. The intra prediction method and the inter prediction method may be selectively used for the prediction unit in order to determine an optimal prediction method for the prediction unit. The image encoding apparatus 100 generates a prediction block for the original block of the input image, and then encodes the difference between the original block and the prediction block.

In the intra prediction mode, the intra prediction unit 120 (or the intra prediction unit can also be used as a term having the same meaning) performs spatial prediction using the pixel values of the already coded blocks around the current block And generates a prediction block.

In the case of the inter-picture prediction mode, the motion prediction unit 111 finds a motion vector by searching an area of the reference picture stored in the reference picture buffer 190, which is best matched with the input block, in the motion prediction process. The motion compensation unit 112 generates a prediction block by performing motion compensation using a motion vector.

The subtracter 125 generates a residual block by a difference between the input block and the generated prediction block. The transforming unit 130 performs a transform on the residual block to output a transform coefficient. The quantization unit 140 quantizes the input transform coefficient according to the quantization parameter and outputs a quantized coefficient. The entropy encoding unit 150 entropy-codes the input quantized coefficients according to a probability distribution to output a bit stream.

Since the HEVC performs inter prediction coding, i.e., inter prediction coding, the currently encoded image needs to be decoded and stored for use as a reference image. Accordingly, the quantized coefficients are inversely quantized in the inverse quantization unit 160 and inversely transformed in the inverse transformation unit 170. The inverse quantized and inverse transformed coefficients are added to the prediction block through the adder 175 and a reconstruction block is generated.

The restoration block passes through the filter unit 180 and the filter unit 180 applies at least one of a deblocking filter, a sample adaptive offset (SAO), and an adaptive loop filter (ALF) can do. The filter unit 180 may be referred to as an adaptive in-loop filter. The deblocking filter can remove block distortion occurring at the boundary between the blocks. The SAO may add a proper offset value to the pixel value to compensate for coding errors. The ALF may perform filtering based on a comparison between the reconstructed image and the original image, and may be performed only when high efficiency is applied. The restoration block having passed through the filter unit 180 is stored in the reference image buffer 190.

2 schematically shows an example of the structure of a video decoding apparatus.

2, the image decoding apparatus 200 includes an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, a motion compensation unit 250, 260 and a reference image buffer 270.

The video decoding apparatus 200 receives the bit stream output from the encoder and decodes the video stream into an intra mode or an inter mode, and outputs a reconstructed video, i.e., a reconstructed video. In the intra mode, a prediction block is generated using an intra prediction mode, and a prediction block is generated using an inter prediction method in an inter mode. The video decoding apparatus 200 obtains a residual block from the input bitstream, generates a prediction block, and then adds the residual block and the prediction block to generate a reconstructed block, that is, a reconstruction block.

The entropy decoding unit 210 entropy-decodes the input bitstream according to a probability distribution and outputs a quantized coefficient. The quantized coefficients are inversely quantized in the inverse quantization unit 220 and inversely transformed in the inverse transformation unit 230. As a result of inverse quantization / inverse transformation of the quantized coefficients, a residual block is generated.

In the intra-picture prediction mode, the intra-prediction unit 240 (or the inter-picture prediction unit) performs spatial prediction using the pixel values of the already coded blocks around the current block to generate a prediction block.

In the inter-view prediction mode, the motion compensation unit 250 generates a prediction block by performing motion compensation using a motion vector and a reference image stored in the reference image buffer 270.

The residual block and the prediction block are added through the adder 255, and the added block is passed through the filter unit 260. [ The filter unit 260 may apply at least one of a deblocking filter, SAO, and ALF to a restoration block or a restored picture. The filter unit 260 outputs a reconstructed image, that is, a reconstructed image. The restored image is stored in the reference image buffer 270 and can be used for inter-view prediction.

Methods for improving the prediction performance of the encoding / decoding apparatus include a method of increasing the accuracy of the interpolation image and a method of predicting the difference signal. Here, the difference signal is a signal indicating the difference between the original image and the predicted image.

In the present invention, the term " difference signal " may be replaced by a " difference signal ", " residual block ", or " difference block " depending on the context. Those skilled in the art may influence the idea You will be able to distinguish this within the scope of not giving.

In the embodiment of the present invention, a coding unit (CU) is used as a coding unit for convenience of explanation, but it may be a unit for performing not only coding but also decoding. Hereinafter, the image encoding method described in the embodiment of the present invention can be implemented in accordance with the functions of the respective modules described in FIGS. 1 and 2, and such an encoder and a decoder are included in the scope of the present invention. That is, the image encoding / decoding method to be described later in the embodiment of the present invention can be performed in each component included in the image encoder and the image decoder described in FIG. 1 and FIG. The meaning of the constituent part may include not only a hardware meaning but also a software processing unit which can be performed through an algorithm.

In the image encoding / decoding according to the embodiments of FIGS. 1 and 2, a CU structure in which a single-sized macro block is expanded to various sizes may be defined for efficient encoding of an image. The CU is a unit in which a video is encoded by a video encoder and can be hierarchically divided with depth information based on a quad tree structure. CUs can have various sizes such as 8 × 8, 16 × 16, 32 × 32, and 64 × 64. The largest CU is called the LCU (Largest Coding Unit), and the smallest CU is called the SCU (Smallest Coding Unit). All CUs except SCUs are assigned split_flag information and indicate whether or not the corresponding CU is divided according to the value of split_flag. The encoder may adjust the size of the LCU in the encoding process according to various video signal characteristics. The CU can be divided into PU (Prediction Unit) for use in intra or inter prediction, and can be divided into TU (Transform Unit) for conversion and quantization. Hereinafter, a block means a unit of encoding / decoding. In the encoding / decoding process, the image is divided into a predetermined size and then encoded / decoded. Thus, a block may also be referred to as CU, PU, TU, etc., and one block may be divided into sub-blocks of smaller size.

Here, PU denotes a basic unit of prediction and / or motion compensation performance. A PU can be divided into a plurality of partitions, and each partition is called a PU partition (prediction unit partition). When the PU is divided into a plurality of partitions, the PU partitions can be a basic unit of performing prediction and / or motion compensation. Hereinafter, in the embodiment of the present invention, the PU may mean a PU partition.

Meanwhile, HEVC (High Efficiency Video Coding) uses a motion vector prediction method based on Advanced Motion Vector Prediction (AMVP).

In the motion vector prediction method based on the improved motion vector prediction method, not only the motion vector (MV) of the reconstructed block located around the current block to be encoded / decoded but also the motion vector of the current block to be encoded / decoded in the reference picture A motion vector of a block existing in a position or a corresponding position can be used. At this time. A block located at the same position or a position corresponding to a spatially corresponding position in the reference picture as a block to be coded / decoded is referred to as a collocated block, a motion vector of an equal position block is referred to as a collocated motion vector or a temporal motion It is called a temporal motion vector. However, the collocated block may be a block existing in the same position as the block to be encoded / decoded, that is, a block existing at the corresponding position, have.

In the motion information merge method, motion information is inferred not only from neighboring reconstructed blocks but also from equivalent position blocks, and uses the motion information as motion information of a current block to be encoded / decoded. At this time, the motion information includes inter-prediction mode information indicating a reference picture index, a motion vector, a uni-direction or a bi-direction necessary for inter prediction, a reference picture list ), Prediction mode information about whether the image is coded in the intra-prediction mode or the inter-prediction mode, and the like.

The predicted motion vector predicted in the current block to be coded / decoded includes not only motion vectors of neighboring blocks spatially adjacent to the current block to be coded / decoded, but also motion vectors of neighboring blocks that are temporally adjacent to the current block to be coded / Lt; / RTI >

3 shows an example of a picture to be coded / decoded and a reference picture.

Referring to FIG. 3, a block X represents a current block to be encoded / decoded in a picture 310 to be encoded / decoded. Block A, block B, block C, block D and block E are located around a block to be encoded / Lt; / RTI > A block T in the reference picture 320 indicates an equivalent position block existing at a position corresponding to the block to be encoded / decoded.

4 shows an example of a motion vector of the enhancement layer.

Referring to FIG. 4, the motion vector of the enhancement layer has a maximum value of four (mv0, mv1, mv2, mv3). This should be used to determine the optimal motion vector mv * of the enhancement layer LCU.

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

Referring to FIG. 5, an image encoding method according to an exemplary embodiment of the present invention calculates a partition function in an enhancement layer, compares a result of the partition function with a threshold value, Or not.

First, a motion vector of the enhancement layer is acquired (S110). The motion vector may have a maximum of four different values as shown in FIG.

Then, an average value of each motion vector is calculated, and a deviation, which is a difference between the average value and each motion vector, is calculated (S120).

Next, the result of the following partition function J is calculated using the deviation of each motion vector and the enhancement layer depth value (S130).

In more detail, the average value of the four motion vectors (mv0, mv1, mv2, mv3) is calculated, and the average of the distances between the motion vectors is calculated. This can be expressed by the following equation (1).

If the depth of the partition of the enhancement layer is large, the size of the partition becomes small. If the depth of the partition is small, the size of the partition becomes large.

Accordingly, when the partition of the enhancement layer is determined, the limit value varies depending on the depth of the partition. That is, the equation (2) for setting the weights of the variables (v) and the depths (d) of the partition calculated in Equation (1) as variables is as follows.

(Where d is the depth of the coding unit)

Thus, the partition function J is based on the deviation of the motion vector and the depth of the prediction unit. In addition, the partition function may further include weights w ₁ and w ₂ ).

Thereafter, the calculation result of the partition function is compared with a threshold value (S140).

If the result of the partition function is larger than the threshold value, the prediction unit is partitioned (S150).

If it is determined that the result of the partition function is less than the threshold value, the motion vector is selected without partitioning the prediction unit (S160).

The following is an embodiment in which the image encoding method of the present invention is programmed. The program below can be used to determine the child partition of the enhancement layer.

if (J> T)

  split;

  copy MVs;

else

  not_split;

  MV selection stage;

end

In partitioning an enhancement layer, the present invention determines a sub-partition by comparing a threshold value with a function calculated using a motion vector and depth information. It is determined whether or not to partition based on the calculated function value and the threshold value, thereby enabling faster coding.

100: image encoding device 111: motion prediction unit
112: motion compensation unit 120: intra prediction unit
125: subtracter 130:
140: quantization unit 150: entropy coding unit

Claims (16)

A video encoding method supporting a plurality of layers,
Acquiring a plurality of motion vectors in the enhancement layer;
Calculating a partition function based on a deviation of the motion vector and a depth of the enhancement layer;
Comparing the result of the partition function with a threshold value; And
(i) performing partitioning of a prediction unit in the enhancement layer if the result of the comparison is greater than the threshold, and (ii) if the result of the comparison indicates that the partition function result value is greater than the threshold Selecting a motion vector without partitioning the prediction unit in the enhancement layer and determining whether to partition the prediction unit in the enhancement layer. The method according to claim 1,
Wherein the partition function is based on a depth of the prediction unit. The method according to claim 1,
Wherein the partition function weights the deviation of the motion vector. The method of claim 2,
Wherein the partition function weights the depth of the prediction unit. The method according to claim 1,
Wherein the partition function is proportional to a deviation of the motion vector. The method according to claim 1,
Wherein the partition function is inversely proportional to a depth of the prediction unit. delete delete A processor; And
And a memory coupled to the processor and storing information for driving the processor,
The processor obtains a plurality of motion vectors from the enhancement layer, calculates a partition function based on the deviation of the motion vector and a depth of the enhancement layer, compares the result of the partition function with a threshold value, i) partitioning the prediction unit in the enhancement layer if the result of the comparison is greater than the threshold, and ii) if the result of the comparison indicates that the partition function result value is greater than the threshold value Wherein the prediction unit is configured to select a motion vector without partitioning the prediction unit in the enhancement layer to determine whether to partition the prediction unit in the enhancement layer. The method of claim 9,
Wherein the partition function is based on a depth of the prediction unit. The method of claim 9,
Wherein the partition function weights the deviation of the motion vector. The method of claim 10,
Wherein the partition function weights the depth of the prediction unit. The method of claim 9,
Wherein the partition function is proportional to a deviation of the motion vector. The method of claim 10,
Wherein the partition function is inversely proportional to a depth of the prediction unit. delete delete

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