KR20130107611A - Methods of encoding and decoding using bottom-up prediction mode decision and apparatuses for using the same - Google Patents

Abstract

Disclosed are an image encoding and decoding method using a bottom-up prediction mode method and an apparatus using the method. The decoding method may include dividing an encoding target image into minimum coding units, determining an intra prediction mode of the minimum coding unit, and performing merging based on the intra prediction mode of the minimum coding unit. Therefore, unnecessary computational complexity may be reduced when determining an intra prediction mode of an image.

Description

Image encoding and decoding using the bottom-up prediction mode method and a device using the method {METHODS OF ENCODING AND DECODING USING BOTTOM-UP PREDICTION MODE DECISION AND APPARATUSES FOR USING THE SAME}

The present invention relates to an image encoding and decoding method, and more particularly, to an image encoding and decoding method using a bottom-up prediction mode method and an apparatus using the method.

Recently, broadcasting service having high definition (HD) resolution has been expanded not only in domestic but also in the world, so that many users are accustomed to high definition and high definition video, and accordingly, many organizations are spurring development for next generation video equipment. In addition, with the increase of interest in UHD (Ultra High Definition) having resolution more than 4 times of HDTV in addition to HDTV, a compression technique for a higher resolution and a higher image quality is required.

For image compression, an inter prediction technique for predicting pixel values included in a current picture from a previous and / or subsequent picture in time, and predicting pixel values included in a current picture using pixel information in the current picture. An intra prediction technique, an entropy encoding technique of allocating a short code to a symbol with a high frequency of appearance and a long code to a symbol with a low frequency of appearance may be used.

It is a first object of the present invention to provide a screen division method for increasing image encoding efficiency and reducing computational complexity.

It is a second object of the present invention to provide an apparatus for performing a screen division method for increasing image encoding efficiency and reducing computational complexity.

According to an aspect of the present invention, there is provided a video encoding and decoding method using a bottom-up prediction mode method, and an apparatus using the method splits an image to be encoded into a minimum coding unit and performs the minimum coding. The method may include determining an intra prediction mode of a unit and performing merging based on the intra prediction mode of the minimum coding unit.

As described above, the video encoding and decoding method using the bottom-up prediction mode method and the apparatus using the bottom-up prediction mode are iteratively calculated in determining the intra-picture prediction mode by using the bottom-up prediction mode determination method. This can reduce computational complexity.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating a configuration of an image decoding apparatus according to another embodiment of the present invention.
3 is a flowchart illustrating a bottom-up merge coding method according to an embodiment of the present invention.
4 illustrates a state in which an encoding target video unit is divided by a minimum coding unit.
5 is a conceptual diagram illustrating a method of determining an encoding mode with respect to a split minimum coding unit according to an embodiment of the present invention.
6 is a conceptual diagram illustrating a method of determining whether to merge in a bottom-up coding structure determination method according to an embodiment of the present invention.
7 is a conceptual diagram illustrating a block merging method according to an embodiment of the present invention.
8 is a conceptual diagram illustrating a block merging method according to an embodiment of the present invention.
9 is a block diagram illustrating a part of an image encoding apparatus according to an embodiment of the present invention.

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

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

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

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination 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 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.

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. In order to determine an optimal prediction method for the prediction unit, an intra prediction method and an inter prediction method may be selectively used 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-picture prediction mode, the intra-prediction unit 120 (or the intra-picture prediction unit can also be used as a term having the same meaning) performs spatial prediction using pixel values of 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.

The entropy encoding unit 150 according to an embodiment of the present invention maps an input codeword to a code number by referring to a codeword mapping table, calculates the mapped code number as a table index, and accumulates the number of occurrences of the code number and the code. The index mapping table may be updated based on at least one of a number of consecutive occurrences of the number, information about encoding and decoding of neighboring blocks, and threshold information for updating the index mapping table.

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

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 image decoding apparatus 200 obtains a residual block from the input bitstream, generates a prediction block, adds the residual block and the prediction block, and generates 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.

The entropy decoding unit 210 according to an embodiment of the present invention maps an input codeword to a code number by referring to an inverse codeword mapping table, calculates the mapped code number as a table index, and accumulates the number of occurrences of the code number, The inverse index mapping table may be updated based on at least one of the number of consecutive occurrences of the code number, information about the decoding and decoding of neighboring blocks, and threshold information for updating the inverse index mapping table.

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 reconstructed picture may be stored in the reference picture buffer 270 to be used for inter 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.

As described above, in the embodiment of the present invention, a coding unit is used as a coding unit for convenience of description, but may also be a unit for performing decoding as well as encoding. Hereinafter, an encoding / decoding method of an intra prediction mode using two candidate intra prediction modes described with reference to FIGS. 3 to 10 according to an embodiment of the present invention is implemented according to the functions of the respective modules described above with reference to FIGS. 1 and 2. These encoders and decoders are included in the scope of the present invention. That is, in the embodiment of the present invention, the image encoding method and the image decoding method to be described later may be performed by each component included in the image encoder and the image decoder described above with reference to FIGS. 1 and 2. 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.

3 is a flowchart illustrating a bottom-up merge coding method according to an embodiment of the present invention.

Referring to FIG. 3, an image is divided into minimum coding units (S300).

The bottom-up coding structure determination method divides the encoding target image into coding units having the smallest size, merges coding units having the same intra prediction mode, and encodes the same image into one mode. The complexity is improved to enable high efficiency coding. In the method of determining a top-down coding structure, after dividing one image into a maximum coding unit, a result of encoding the maximum coding unit and an additional split of the maximum coding unit into arbitrary units may be compared to determine whether to split. Therefore, in the top-down encoding structure determination process, the computational complexity increases due to the computational complexity generated in the recursive partitioning process, and the encoding time is long.

The bottom-up coding structure determination method according to an embodiment of the present invention to be described later can increase the efficiency of the encoder by removing the recursive calculation process in the bottom-down coding structure determination method.

4 illustrates a state in which an encoding target video unit is divided by a minimum coding unit.

Referring to FIG. 4, it is assumed that the encoding target video unit is 64x64 and the minimum coding unit is 4x4. The encoding target video unit and the minimum coding unit may have arbitrarily different values, and such embodiments are also included in the scope of the present invention. According to an embodiment of the present invention, a method of determining a bottom-up coding structure may divide an encoding target image unit into minimum coding units, and then determine an intra prediction mode of each minimum coding unit based on a rate distortion.

Referring to FIG. 3 again, an encoding mode of a split encoding minimum unit is determined (step S310).

An optimal intra prediction mode of a block may be determined using a rate-distortion calculation method such as a method of calculating an RD-cost for a minimum coding unit.

5 is a conceptual diagram illustrating a method of determining an encoding mode with respect to a split minimum coding unit according to an embodiment of the present invention.

Referring to FIG. 5, an encoding mode may be determined in a z scan direction with respect to a coding unit having a size twice a width and a length of a minimum coding unit. For example, when the size of the minimum coding unit is 4x4, the intra prediction mode for each coding unit may be determined in four scan coding units included in the 16x16 size, which is a double coding unit, in the z scan direction. A structure having four minimum coding units in the z scan direction may be expressed as a first merging unit in an embodiment of the present invention.

In this case, the third minimum coding unit 500 that is the left minimum coding unit for the fourth minimum coding unit that finally calculates the intra prediction mode in the z-scan direction in order to use the intra prediction method using the most probable mode (MPM) Intra-prediction using the MPM may be performed based on the intra-prediction mode of the second minimum coding unit 520 in the upper minimum coding unit. For example, when the intra prediction mode of the third minimum coding unit is the DC mode, the intra prediction mode of the second minimum coding unit is the vertical mode, and the intra prediction mode of the fourth minimum coding unit is the DC mode, The intra prediction mode of the minimum coding unit may be expressed using the MPM. In the case of the first to third minimum coding units, the intra-prediction mode information of the corresponding block may be expressed using the MPM based on the intra-prediction mode information of the coding unit existing on the left side of the block and the coding unit existing on the upper side of the block. Can be.

Referring back to FIG. 3, merging is performed based on the intra prediction mode of the minimum coding unit (S320).

Block merging may be performed using an intra prediction mode determined based on a minimum coding unit. In the method of determining a bottom-up block structure according to an embodiment of the present invention, various conditions for performing block merging may be used. For example, if it is assumed that a 64x64 sized block is an encoding target image unit and a 4x4 sized block is a minimum coding unit, it may be determined whether or not the minimum coding unit is merged in the first merged unit 16x16. As a condition for determining the merge, for example, when the intra prediction modes of two coding units among the minimum coding units included in the first merge unit are the same, the merge is determined to be performed, or the minimum coding unit included in the first merge unit. When the directionality of the intra prediction mode is less than a predetermined threshold and thus has a similar intra prediction mode, merging may be performed on the minimum coding units.

6 is a conceptual diagram illustrating a method of determining whether to merge in a bottom-up coding structure determination method according to an embodiment of the present invention.

Referring to FIG. 6, for example, when the intra prediction modes of the minimum coding units included in the encoding target video unit are all 1, the minimum coding units may be merged into a first merge unit to perform encoding. Conditions for performing such merging may vary as described above. After merging in a first merged unit, an intra prediction mode may be compared with another first merged unit, and further merged into a second merged unit in which a plurality of first merged units are collected. It can be performed repeatedly according to.

In further merging the first merging unit, various methods may be used.

For example, it may be determined whether the first merging unit is further merged based on an arbitrary scan direction.

7 is a conceptual diagram illustrating a block merging method according to an embodiment of the present invention.

Referring to FIG. 7, the method determines whether all of the encoding target image units are merged in a first merge unit, and in the case of merging in a first merge unit, whether the merge may be additionally merged in a second merge unit. Target image units may be merged. For example, as a condition for generating the second merging unit, when two or more intra-prediction modes of the first merge unit are the same, a method of merging in the second merging unit may be used.

8 is a conceptual diagram illustrating a block merging method according to an embodiment of the present invention.

Referring to FIG. 8, merging may be performed in a mask by applying a mask having an arbitrary size. For example, when the size of the mask is 16 × 16, it may be determined whether it can be further merged with respect to the first merge unit existing in the mask.

The coding unit structure information is updated (step S330).

When merging is performed in operation S320, the structure information of the coding units may be encoded for the encoding target image unit, and the intra prediction mode information of the coding unit may be encoded based on the structure information of the coding unit. MPM information may be used to encode intra prediction mode information of a coding unit.

In the image decoding step, decoding may be performed based on the coding unit structure information encoded in the image encoding step and the intra prediction mode information on the coding unit.

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

Referring to FIG. 9, the image encoding apparatus may include an image splitter 900, an image merger 920, and an encoding information generator 940.

The image splitter 900 may split the encoding target image unit into the minimum coding units. The image splitter may further include an intra prediction mode determiner to determine an intra prediction mode that is most suitable for the largest coding unit among the intra prediction modes. The intra prediction mode determiner may be implemented in a structure independent of the image divider.

The image merger 920 may generate a first merge unit based on intra prediction mode information of the minimum coding unit, and determine whether to merge in an additional merge unit based on the first merge unit.

The encoding information generator 940 may generate encoding information based on intra prediction mode information of the merged image.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (1)

Dividing an encoding target image into minimum coding units and determining an intra prediction mode of the minimum coding unit; And
And performing merging based on the intra prediction mode of the minimum coding unit.

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