KR20130069452A - Method and apparatus of in-loop filtering by adaptive band offset bands, and appparatus for decoding and encoding by adaptive band offset bands - Google Patents

Abstract

PURPOSE: An in-loop filtering method and an apparatus capable of using an adaptive band offset section and an encoding/decoding apparatus capable of using the adaptive band offset section are provided to adaptively select the section standard of a central section and a side section in the band offset compensation by considering the property of the pixel value distribution of the surrounding block, thereby improving the selection probability of a suitable offset according to the pixel property. CONSTITUTION: An in-loop filtering apparatus removes the block distortion of a reconstructed picture by a deblocking filtering(S110). The apparatus applies an adaptive SAO(Sample Adaptive Offset) to the deblocking filtered image(S120). The apparatus selectively applies an adaptive ALF(Adaptive Loop Filter) to an image in which the SAO is applied to(S130). When applying the SAP, an adaptive band offset is applied to the current block in which the sample offset will be applied to. [Reference numerals] (AA) Start; (BB) Finish; (S110) Deblocking filtering; (S120) Deblocking filtered image; (S130) SAO is applied

Description

In-loop filtering method and apparatus using an adaptive band offset interval, and an encoding and decoding apparatus using an adaptive band offset interval BAND OFFSET BANDS}

The present invention relates to encoding and decoding of video data, and more particularly, to a method and apparatus for adaptively applying an offset on a pixel basis to a reconstructed image.

When an image is encoded at a low bit rate, the image is stored in a frame memory in a state where block artifacts occur in a reconstructed image, and an image including the block artifacts is included in a motion compensation process of a next picture. When encoding with reference, deterioration of image quality may be propagated. In order to solve this problem, in the H.264 / AVC standard, block distortion may be performed before storing a reconstructed image in a frame memory without knowing the original image. Use adaptive deblocking filtering to remove block artifacts.

The deblocking filtering is a passive filter for removing only block distortion in a state in which the original image is not known, and actively performs a difference value between an original image and a reconstructed image. There is a limit that cannot compensate.

[Prior Art Literature]

(Patent Document 1) Korean Unexamined Patent Publication No. 10-2011-0083369 ("Video encoding method and apparatus using deblocking filtering, and video decoding method and apparatus using deblocking filtering", Samsung Electronics Co., Ltd., July 20, 2011 open)

As a technique for compensating the offset between the original image and the reconstructed image, there is an adaptive sample offset (SAO) method. The adaptive sample offset method is a method of obtaining a difference value between an original image and a reconstructed image, and adding an offset to the reconstructed image in order to correct an error of a decimal point operation that may occur in the process of obtaining a reconstructed image.

Offsets are applied for each pixel. There are two modes of offsets, a band offset and an edge offset. The band offset is divided into 32 parts by dividing the total level of the pixel into 32 parts, and divided into two parts by 16 central bands and 16 side bands. There are four modes of edge offset: 0 degrees, 45 degrees, 90 degrees, 135 degrees depending on the direction. Offsets are obtained separately for each mode, and the least cost mode is selected on a rate-distortion basis.

In the offset mode, each frame included in the image is divided into blocks of various sizes by using a quad-tree splitting method, and a different offset mode is determined for each block. In the two modes, the band offset method is uniformly divided into a center section and a side section. The band offset section selected by the above criteria does not efficiently reflect the characteristics of the pixel and the block.

In the present invention for solving the above-described problem, in performing the adaptive sample offset (SAO) for the reconstructed image, in determining the interval of the band offset of the two methods of SAO We propose a method of adaptively distinguishing the center section from the side section in consideration of the characteristics of pixels and blocks.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide an in-loop filtering method for adaptively applying a band offset type and a band offset value of SAO according to a current mode in performing SAO processing of a band offset method. will be.

Another object of the present invention is to provide an image encoding and decoding apparatus for adaptively distinguishing a center section and a side section based on pixel value distribution of a reference range associated with a corresponding block in performing SAO processing of a band band offset scheme. .

An in-loop filtering method using an adaptive band offset interval for achieving the above object of the present invention includes a deblocking filtering step of removing block distortion of a reconstructed picture; And applying a sample adaptive offset (SAO) to the deblocking filtered image, wherein applying the sample offset comprises adaptive band according to a current block to which the sample offset is to be applied. Applying an offset.

In the present invention, the adaptive band offset is introduced as a concept for enabling the SAO procedure to be more suitable for the current block by determining the band offset interval or type according to the current block to which the SAO procedure is to be applied.

The adaptive band offset procedure of the present invention is included in the adaptive sample offset step, and the adaptive band offset procedure adaptively determines the band offset interval in consideration of the distribution of pixel values of pixels belonging to the reference range associated with the current block. Determining a sample offset type of the current block in consideration of the adaptively determined band offset period; And summing sample offsets for pixels belonging to the current block in consideration of the determined band offset period.

In the present invention, a reference range is an area specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion, or an area specified by pixels belonging to a block having similarity according to a predetermined criterion with the current block. Can be. In particular, an area specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion may include at least one area of an upper block, a left block, and an upper right block of the current block. According to a predetermined criterion, an area specified by pixels belonging to an area adjacent to the current block may be set to a set of pixels surrounding the current block with a predetermined thickness.

In the present invention, the band offset period includes a central band and a side band, and adaptively determining the band offset period is in the reference range among all bands in which a pixel value may exist. The method may include determining a band offset section according to the current block in consideration of a band to which the pixels belonging most belong.

In the present invention, the center section may determine the center section so that the band including the most pixels in the reference range is the center of the center section, or may be adaptively determined in consideration of the pixel value distribution of the pixels in the reference range. It is possible. In addition, the size of the center section may be determined such that the number of bands in which pixel values of pixels belonging to the reference range are distributed and the size of the center section have a negative correlation within a predetermined reference range.

In addition, the central bands may be determined such that the pixel values of the largest pixels of the reference range are distributed, and the center bands are 1/2 of the total number of bands. In the adaptive sample offset processing step, if the reference range does not exist, the central bands are determined so that the center of the entire interval becomes the center of the central band, but the central bands are You can decide to occupy half of the full range.

In addition, in the present invention, the band offset section is adapted to adapt the central bands, the first side bands, and the second side bands in consideration of the pixel value distribution of the pixels within the reference range. Can be determined as

According to another aspect of the present invention, there is provided a decoding apparatus using an adaptive band offset interval, including: a deblocking filter for removing block distortion of a reconstructed image; And a SAO processor configured to adaptively offset the deblocking filtered image (SAO), wherein the SAO processor is configured to band the current block based on a pixel value distribution characteristic of a reference range associated with the current block. The offset period may be determined. Here, the reference range may be a set of pixels of neighboring blocks of the current block, and the reference range may be a set of pixels of an upper block and a left block of the current block.

The reference range may be a set of pixels surrounding the current block with a predetermined thickness, and the reference range may be a set of pixels of the current block. Here, the SAO processing unit may determine a section in which the pixel values of the reference range are distributed as central bands, and the SAO processing unit is the center of the pixel value in which the largest pixel of the reference range is distributed. The central bands may be determined to be such that the central bands occupy 1/2 of the entire range. In addition, the SAO processor determines the central bands such that the center of the entire section is the center of the central band when the reference range does not exist, but the central band is the full range. It may be characterized by occupying 1/2 of.

According to another aspect of the present invention, there is provided an encoding apparatus using an adaptive band offset interval including a deblocking filter for removing block distortion of a reconstructed image; And a SAO processor configured to adaptively offset the deblocking filtered image (SAO), wherein the SAO processor is configured to band the current block based on a pixel value distribution characteristic of a reference range associated with the current block. The offset period may be determined. Here, the reference range may be a set of pixels of neighboring blocks of the current block, and the reference range may be a set of pixels of an upper block and a left block of the current block. The reference range may be a set of pixels surrounding the current block with a predetermined thickness, and the reference range may be a set of pixels of the current block.

Here, the SAO processing unit may determine a section in which the pixel values of the reference range are distributed as central bands, and the SAO processing unit is the center of the pixel value in which the largest pixel of the reference range is distributed. The central bands may be determined to be such that the central bands occupy 1/2 of the entire range. In addition, the SAO processor determines the central bands such that the center of the entire section is the center of the central band when the reference range does not exist, but the central band is the full range. It may be characterized by occupying 1/2 of.

According to the above-described in-loop filtering method and image decoding apparatus, in the band offset correction, an appropriate selection criterion between the center section and the side section is appropriately selected in consideration of the characteristics of the pixel value distribution of the neighboring block. Improves the choice of offset. Therefore, an appropriate offset is selected according to the characteristics of each pixel, and pixel values are more appropriately corrected, thereby improving video encoding efficiency and reconstructed image quality.

In addition, since two intervals are determined for each block by using the reference range associated with the current block without using additional information, the compression efficiency can be improved without additional bit rate consumption, and the image quality improvement due to the improvement of the offset efficiency is shown, thereby improving the subjective quality. You can also expect.

1 is a flowchart of an in-loop filtering method using an adaptive band offset interval according to an embodiment of the present invention.
FIG. 2 is a detailed flowchart of the adaptive sample offset processing step of FIG. 1.
3 is a conceptual diagram when a neighboring block is set as a reference range.
4 is a conceptual diagram when a pixel around a current block is set as a reference range.
5 is a conceptual diagram of setting pixels of a current block as a reference range.
6 is a diagram illustrating a center section and a side section according to a conventional standard.
7 illustrates an example in which the pixel value distribution range of the reference range is set to the center section.
8 illustrates an example in which a center section is set based on the largest distribution pixel value of the reference range pixel.
9 is an example of setting a center section, a first side section, and a second side section according to an embodiment of the present invention.
10 is a block diagram illustrating a configuration of an apparatus for decoding an image using an adaptive band offset interval according to an embodiment of the present invention.
11 is a block diagram illustrating a configuration of an image encoding apparatus using an adaptive band offset interval, according to an embodiment of the present invention.
12 is a block diagram illustrating a configuration of the in-loop filter of FIGS. 10 to 11.
FIG. 13 is a detailed block diagram of an adaptive sample offset processor of FIG. 12.

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.

In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. 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.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. 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.

In addition, the components shown in the embodiments of the present invention are shown independently to represent different characteristic functions, which does not mean that each component is composed of separate hardware or software constituent units. That is, each constituent unit is included in each constituent unit for convenience of explanation, and at least two constituent units of the constituent units may be combined to form one constituent unit, or one constituent unit may be divided into a plurality of constituent units to perform a function. The integrated embodiments and separate embodiments of the components are also included within the scope of the present invention, unless they depart from the essence of the present invention.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

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

In order to apply the adaptive band offset interval, the statistical characteristics of pixel values of the reference neighboring block are calculated by checking whether the neighboring block can be referred to, and the interval discrimination criterion is determined based on this. The center section and the side section are divided according to the determined section discrimination criteria, and offset correction is performed for each block mode. The present invention does not require additional information because it uses information of a block already decoded before the current block.

In-loop Filtering  Way

1 is a flowchart of an in-loop filtering method using an adaptive band offset interval according to an embodiment of the present invention. The in-loop filtering method shown in FIG. 1 includes the following steps performed in time series in the in-loop filter shown in FIG. 12.

As shown in FIG. 1, first, deblocking filtering to remove block distortion of a reconstructed image is performed (S110). When video is encoded at low bit rate, it is stored in frame memory in the state where block distortion occurs in the decoded image, and the image quality degradation is propagated because it is encoded by referring to the image including the block distortion in the motion compensation process of the next picture. To this end, adaptive deblocking filtering is used to remove block distortion before storing the reconstructed image in the frame memory.

Thereafter, the deblocking filtered image is subjected to a sample adaptive offset (SAO) process (S120). In the present embodiment, the adaptive sample offset processing step S120 is characterized in that the sample offset is adaptively applied according to the current block to which the adaptive sample offset is to be applied. The existing adaptive sample offset classifies pixel values of pixels included in the current block according to a band offset category prepared in advance, and determines band widths by determining whether the pixel values are central bands or side bands. It was a concept of adaptively determining the type of each pixel.

In the adaptive sample offset according to an embodiment of the present invention, since the center section may be defined differently according to the current block, the boundary region for determining the type of the band offset is adaptively determined according to the current block. have. When the boundary region is determined, the center section and the side section are also determined, and in the present embodiment, the boundary region for distinguishing the section may consider the pixel value distribution of pixels located in the reference range associated with the current block, and thus the band offset of the current block. There is a feature in determining the interval.

As described above, the adaptive sample offset processing step S120 is to compensate for the DC offset with respect to the pixels to which the deblocking filter is processed. Here, the DC offset refers to an average difference value between pixels processed by the deblocking filter after transform and quantization and original pixels, and may be regarded as an offset value due to transform and quantization. After the deblocking filter, the current block (coding unit) may determine whether to selectively turn on / off a sample adaptive offset (SAO) in units of partitioned blocks of the current block.

FIG. 2 is a detailed flowchart of the adaptive sample offset processing step of FIG. 1. 2, the adaptive sample offset processing step S120 will be described in more detail.

As shown in FIG. 2, the adaptive sample offset processing step (S120) may be performed by the adaptive sample offset processing unit (1120 of FIG. 12) in time series, that is, the frame division step (S210). The verification step S220, the pixel value distribution characteristic extraction step S230, the band offset section determination step S240, and the offset mode determination step S250 may be included. It does not require additional information compared to the existing method.

The adaptive sample offset processing unit 1120 performs block division on a frame or block to be subjected to adaptive sample offset processing in the deblocking filtered image. In this step S210, the signal input to the frame divider is a decoded frame signal. For example, the adaptive sample offset processor may divide the entire frame into quad-trees, and may split the granularity up to four levels in detail. The size of the divided block and the offset mode per block are determined. The size of the block and the offset mode per block are determined according to the rate-distortion cost. The rate-distortion cost is computed for all partitioning steps to get the proper partitioning method, resulting in the lowest cost partitioning form.

The adaptive sample offset processor 1120 searches for reference ranges among neighboring blocks. Since the size of the current block may vary, the size of the neighboring block may also vary, and the pixels within a predetermined range may be used instead of the shape of the block. If there is no reference block of the current block, the process may move to the band offset section determination step S250 without performing the pixel value distribution characteristic extraction step S230.

The adaptive sample offset processor 1120 extracts the pixel value distribution characteristic (S230). In this step, the adaptive sample offset processor determines a criterion for distinguishing the center section and the side section from the band offset by using the pixel value distribution of the reference range. The discrimination criterion may be a pixel value average of the reference range or a section on the band category to which the pixel value average belongs. When the pixels of the reference range are displayed on the quantized band category, the section on the band category having the highest frequency is used as the distinguishing criteria. You can decide. In addition, the length of the distribution range is calculated through a pixel value distribution histogram, and when the length of the distribution range is short, the size (number of bands) of the band offset section is adjusted to refer to a high possibility of the presence of pixels in the distribution. Narrow band offset interval can be set.

In the band offset section determination step (S240), the entire band for the pixel value is divided into two sections. In the band offset, a center section and a side section are defined, and a method of determining the center section may be determined based on a section in which pixel values of a reference range associated with the current block are distributed. The side section is determined as the remaining portion except the determined center section. If there is no pixel value distribution characteristic information because it cannot refer to the neighboring block, the half of the center of the entire possible pixel values is determined as the center section, and the rest of the rest can be determined as the side sections. have.

In the offset mode determination step (S250), based on the above-described center section and side section, which section is more efficient for the current block is determined through a rate-distortion technique. In the offset mode determination step (S250), the evaluation may be performed not only the band offset mode using the center section and the side section, but also the edge offset method, which is a conventional method, and is optimally evaluated by a rate-distortion technique for various block sizes. Determine the mode and size of the.

The information generated as a result of the offset mode determination step S250 includes, for example, offset information, frame division information, and mode information. The information is included in a slide header to be used in the decoder. The adaptive band offset interval generated by the present invention is determined using the peripheral information without adding additional information to the bit string, so that there is no bit rate loss.

In the adaptive sample offset processing step (S120), a reference range may be set in various ways to adaptively determine a band offset interval. The embodiment to be described below assumes an RGB image, which is a general format of an image capturing apparatus, as an input signal, and is described based on an HEVC image compression standard including an adaptive sample offset (SAO) technology. It is not limited to description of this embodiment.

In the band offset performed by the conventional adaptive sample offset (SAO), the entire band is divided into a fixed center section and a side section. This conventional method is not efficient because it does not consider the adaptability to the pixel. However, in the present invention, since the center section of the band offset is determined through the reference range pixel value distribution characteristic associated with the current block, the offset can be more efficiently corrected in the corresponding block.

In order to determine the adaptive band interval, the pixel value distribution characteristic of the reference range associated with the current block should be obtained. Before explaining an embodiment of a method of setting the reference range, the concept will be described in more detail.

In the present embodiment, the reference range is a region of the region specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion, or of a region specified by pixels belonging to a block having similarity according to a predetermined criterion with the current block. Used in the sense. Here, the region adjacent to the current block may include at least one of a left block (or an area), an upper block, and an upper right block of the current block. A block having similarity according to a predetermined criterion is a block having a similar pixel value distribution as the current block. It may mean a block determined to be.

The size of the current block for SAO processing varies from 8 * 8 to 64 * 64. If the size of the current block is small, the distribution of pixel values may be biased. To determine the sample offset mode or offset value for the current block more appropriately, consider the pixel values of the pixels in the reference range associated with the current block. It is desirable to. It is a feature of the present invention to determine an adjacent region having similarity with the current block as a reference region in advance, and determine an offset band interval of the current block in consideration of the pixel value distribution of the reference region.

3 is a conceptual diagram when a neighboring block is set as a reference range. As shown in FIG. 3, there is a method of analyzing the distribution of pixel values of the corresponding block 310 by referring to neighboring left and upper blocks. This method takes into account the order of encoding and can be used if it has not been decoded to the bottom and right of the current block. That is, the reference range 320 may be a set of pixels of the upper block and the left block of the current block 310.

Meanwhile, the neighboring blocks to be referred to are not limited to the left block and the upper block. In some cases, it may refer to all blocks adjacent to the current block, and may refer to a left block, an upper left block, an upper block, an upper right block, and a lower left block. That is, the reference range may be a set of pixels of neighboring blocks of the current block.

4 is a conceptual diagram when a pixel around a current block is set as a reference range.

As shown in FIG. 4, pixel value distribution characteristics may be obtained using pixels 420 within a constant thickness surrounding the current block 410. If the step of applying the adaptive sample offset is performed after the frames are all decoded, there is a method using all of them because there are pixel values in all parts surrounding the block. That is, the reference range 420 may be a set of pixels surrounding the current block with a preset thickness.

5 is a conceptual diagram of setting pixels of a current block as a reference range.

As shown in FIG. 5, the pixel value distribution may be obtained based on the pixel value information of the current block 510. Since the pixel value of the current block has already been decoded, the pixel value can also be used to obtain a distribution. That is, the reference range 520 may be a set of pixels of the current block.

When the distribution of pixel values of pixels belonging to the reference range is obtained, the band offset section determiner 1122 of the adaptive sample offset processing unit determines the center section.

6 is a diagram illustrating a center section and a side section according to a conventional standard. As shown in FIG. 6, in the conventional reference, a portion corresponding to half of the center of the entire interval where pixel values are uniformly determined without referring to the reference range associated with the current block is determined as the center interval 610. Both remaining portions may be determined as the side section 620. Embodiments proposed to determine the center section according to an embodiment of the present invention are as shown in FIGS. 7 to 9.

7 is a diagram when the pixel value distribution range of the reference range is set to the center section. As illustrated in FIG. 7, the band offset section determiner 1122 may determine a section in which pixel values of the reference range are distributed as central bands. When the center section is determined, both end regions of the center section serve as boundaries for distinguishing the center section and the side section.

According to another exemplary embodiment related to this, when the section in which the pixel value is distributed is distributed only in a section less than 1/2 of the entire range of the pixel value, the band offset section determiner 1122 may include a section in which the pixel value of the reference range is distributed. May be determined as the center section. In addition, the band offset section determiner 1122 may determine a region where the pixel value of the reference range is distributed over a predetermined reference value, that is, a main distribution region of the pixel value as the center section. The predetermined reference value may be, for example, a ratio of the number of pixels existing in the corresponding region to the total number of pixels belonging to the reference range.

FIG. 8 is a diagram of a case where a center section is set based on the largest distribution pixel value of a reference range pixel. As illustrated in FIG. 8, the band offset section determiner 1122 may determine central bands so that the pixel value of the largest pixel of the reference range is the center. In particular, the band offset section determiner may select a band having the largest number of pixels based on the band category as the center of the center section and determine bands located at a predetermined distance from the center as the center section.

The band offset section determiner may determine that the central bands occupy 1/2 of the entire range. If the interval in which the pixel values of the reference range are distributed is greater than half of the full range that the pixel value can have, then the range that is half of the full range may be determined based on the pixel value with the largest number present. have.

Here, when the reference range does not exist, the band offset section determiner determines the central bands so that the center of the entire section becomes the center of the central band, but the central bands are You can decide to occupy half of the full range.

9 illustrates an example in which the number of band offset sections is adjusted when the distribution range of reference range pixels is very short and the existence probability value is large in a narrow band section. As illustrated in FIG. 9, the band offset section may include a center section BO_0, a first side section BO_1, and a second side section BO_2.

In particular, the band offset section determiner may adjust the number of band offset sections to set a narrow band offset section on the basis of the highest probability of existence in the distribution. The band offset section determiner determines the central bands so that the pixel values of the largest pixels of the reference range are centered, but increases the number of band offset sections since a large probability value is distributed in a narrow range around the center section. Narrow band offset interval can be set. Here, the number of band offset sections is inversely proportional to the distribution range of the reference range pixel, and the width of the band offset sections is inversely proportional to the magnitude of the probability value of the corresponding range. In this case, unlike the conventional method of FIG. 6, three band sections are generated.

Here, the band offset section determination unit determines the central bands so that the center of the entire section is the center of the central bands when the reference range does not exist, but the central bands are You can decide to occupy half of the full range.

Referring back to FIG. 1, an adaptive loop filter (ALF) may be selectively applied after the adaptive sample offset (SAO) processing step S120 (S130). Step S130 is a step that can be selected as needed. In this step, the adaptive loop filter (ALF) can compensate for errors in encoding more precisely than the deblocking filter by using a Wiener filter. Specifically, the adaptive loop filter (ALF) uses a Wiener filter that minimizes the sum of the square error of the difference between the original pixels and the decoded pixels, so that the deblocking filter and the adaptive offset ( The error can be compensated by encoding the recovered signal more precisely after SAO). The adaptive loop filter (ALF) information may be included in a slice header and transmitted to a decoder. The adaptive loop filter (ALF) information may include Wiener filter coefficients, adaptive loop filter (ALF) on / off information, and filter shape information. On / off information of the adaptive loop filter (ALF) may be included in a slice header in units of coding units and transmitted to the decoder. The filter shape may be designed to have a symmetrical shape to reduce encoder and decoder complexity.

Decryption device

10 is a block diagram illustrating a configuration of an apparatus for decoding an image using an adaptive band offset interval according to an embodiment of the present invention.

Referring to FIG. 10, a decoding apparatus according to an embodiment of the present invention includes an entropy decoder 731, an inverse quantizer 733, an inverse transformer 735, a motion compensator 737, and an intra predictor 739. And a frame buffer 741, an adder 743, and an in-loop filter 745.

The entropy decoder 731 receives the compressed bit stream and performs entropy decoding to generate quantized coefficients. The inverse quantization unit 733 and the inverse transform unit 735 restore the residual value by performing inverse quantization and inverse transformation on the quantized coefficients.

The motion compensator 737 performs motion compensation using the information decoded from the bit stream by the entropy decoder 731 to generate a predicted prediction unit.

The intra predictor 739 performs intra prediction based on an intra mode from a pixel value of a pixel already encoded around the current prediction unit in the current picture.

The adder 743 reconstructs an image by adding the residual value provided by the inverse transformer 735 and the predicted prediction unit provided by the motion compensator 737 to provide the in-loop filter 745.

FIG. 12 is a block diagram illustrating the configuration of the in-loop filter 745 of FIG. 10.

As illustrated in FIG. 12, the in-loop filter 745 may include a deblocking filter 1110 that removes block distortion of a reconstructed image, and an adaptive sample offset of the deblocking filtered image. , SAO processing unit 1120 for processing. The in-loop filter 745 is deblocking filtering to remove block distortion of the reconstructed image provided by the adder 743 and an adaptive sample offset of the deblocking filtered image. , SAO) and finally provides a reconstructed reconstructed image to the frame buffer 741.

The frame buffer 741 stores the reconstructed image. That is, the decoder performs a decoding operation by adding the compressed prediction error (residual value provided by the inverse transform unit) to the prediction unit.

As shown in FIG. 13, the SAO processor 1120 of the present exemplary embodiment includes a band offset section determiner 1122, a sample offset type determiner 1124, and a sample offset adder 1126. The SAO processor may determine a band offset period of the current block based on the pixel value distribution characteristic of the reference range associated with the current block.

The band offset section determiner may determine the reference range as a set of pixels of the neighboring block of the current block, and in particular, may determine the set of pixels of the upper block and the left block of the current block as the reference range. In addition, the set of pixels surrounding the current block with a predetermined thickness may be determined as a reference range, and may be determined to include the set of pixels of the current block.

The band offset section determiner may determine a section in which the pixel values of the reference range are distributed as the central bands, and determine the center bands so that the pixel value in which the largest pixel of the reference range is distributed is the center. However, the central bands may determine interval boundaries so that they occupy 1/2 of the entire range. In addition, when the reference range does not exist, the central bands are determined so that the center of the entire section becomes the center of the central band, but the central bands are 1/2 of the full range. Can be determined to occupy.

The sample offset type determiner 1124 determines whether the band offset type of the current block is a center section offset or a side section band offset.

The sample offset adder 1126 adds the offset values calculated for each band for pixels belonging to a section determined by the type, according to the determined sample offset type.

A detailed operation aspect of the in-loop filter 745 included in the decoding apparatus depends on the in-loop filtering method using the adaptive band offset interval according to the embodiment of the present invention described above.

Encoding device

11 is a block diagram illustrating a configuration of an image encoding apparatus using an adaptive band offset interval, according to an embodiment of the present invention.

Referring to FIG. 11, the image encoding apparatus includes an encoder 630, and the encoder 630 includes an inter prediction unit 632, an intra prediction unit 635, a subtractor 637, a transformer 639, and quantization. The unit 641 may include an entropy encoder 643, an inverse quantizer 645, an inverse transformer 647, an adder 649, a frame buffer 651, and an in-loop filter 653. The inter prediction predictor 632 includes a motion predictor 631 and a motion compensator 633.

The input image is divided into a recursive coding unit (CU), and the coding unit performs inter prediction in the inter prediction unit 632 or intra prediction in the intra prediction unit 635. The risk is divided into prediction units (PUs). Coding units (CUs) are partitioned in a hierarchy. The smallest CU (SCU) may have a minimum size of 8x8 pixels, and the large CU (LCU) may have a size of 64x64 pixels. Information related to the SCU and the LCU may be signaled to the decoder by a sequence parameter set (SPS).

The inter prediction unit 632 generates a motion vector by estimating the motion of the provided prediction unit to be currently encoded.

The motion predictor 631 searches for a region similar to the current block in a previous N-1 th reference picture and / or a later N + 1 th reference picture of the N th picture to which the current prediction unit is currently encoded, and then motion vector on a block basis. Create

The motion compensator 633 generates a prediction block (or predicted prediction unit) obtained by performing motion compensation using the motion vector generated from the motion predictor 631 and the reference picture.

The intra prediction unit 635 performs intra prediction on the current prediction unit according to the intra mode from already encoded pixel values around the current prediction unit in the current picture.

The subtractor 637 generates a residual value by subtracting the prediction block (or predicted prediction unit) and the current block (or current prediction unit) provided by the motion compensator 633, and the transformer 639 and the quantizer 641. ) Transforms and quantizes the residual cosine transform (DCT).

The entropy encoder 643 entropy encodes information such as quantized DCT coefficients, motion parameters, information related to the SCU and LCU, and generates a bit stream.

The inverse quantizer 645 and the inverse transformer 647 inverse quantizes and inverse transforms the quantized data through the quantizer 641. The adder 649 adds the inverse transformed data and the predictive prediction unit provided by the motion compensator 633 to reconstruct an image and provide the image to the in-loop filter 653.

FIG. 12 is a block diagram illustrating a configuration of the in-loop filter 653 of FIG. 11.

As shown in FIG. 12, the in-loop filter 653 includes a deblocking filter 1110 for removing block distortion of a reconstructed image and a sample adaptive offset for the deblocking filtered image. , SAO processing unit 1120 for processing. The in-loop filter 653 is deblocking filtering to remove block distortion of the reconstructed image provided by the adder 649, and an adaptive sample offset is applied to the deblocking filtered image. SAO) and finally provides a reconstructed reconstructed image to the frame buffer 651.

The frame buffer 651 stores the restored image.

Here, the SAO processor 1120 may determine a band offset section of the current block based on the pixel value distribution characteristic of the reference range associated with the current block.

The band offset section determiner 1122 may adaptively determine the boundary between the center section and the side section by considering the band offset section according to the current block or in consideration of the pixel value distribution of the reference range associated with the current block. Since the method of determining the band offset section has been described above, common descriptions are omitted. The description common to the sample offset type determining unit and the sample offset adding unit is omitted. Since a specific operating aspect of the in-loop filter 653 included in the encoding apparatus follows the in-loop filtering method using the adaptive band offset section according to the embodiment of the present invention, a description thereof will be omitted.

Claims (24)

In-loop filtering method,
A deblocking filtering step of removing block distortion of the reconstructed picture; And applying a sample adaptive offset (SAO) to the deblocking filtered image,
And applying the adaptive sample offset comprises applying an adaptive band offset to a current block to which the sample offset is to be applied. The method of claim 1, wherein applying the adaptive band offset comprises:
And adaptively determining a band offset section in consideration of a pixel value distribution of pixels belonging to a current block to which the sample offset is applied or a reference range associated with the current block. . The method of claim 2, further comprising adaptively determining the band offset interval,
Determining a sample offset type of the current block in consideration of the adaptively determined band offset period; And summing sample offsets for pixels belonging to the current block in consideration of the determined band offset period. The method of claim 1, wherein the reference range is
An area specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion, or
And an area specified by pixels belonging to a block having similarity according to a predetermined criterion with the current block. The method of claim 4, wherein an area specified by pixels belonging to an area adjacent to the current block is determined according to a predetermined criterion.
And at least one region of an upper block, a left block, and an upper right block of the current block. The method of claim 4, wherein an area specified by pixels belonging to an area adjacent to the current block is determined according to a predetermined criterion.
And a set of pixels surrounding the current block with a preset thickness. The method of claim 2, wherein the band offset section includes a central band and a side band,
Adaptively determining the band offset interval
The in-loop filtering method according to claim 1, wherein the band offset section according to the current block is determined in consideration of the band to which the pixels belonging to the reference range are the most among the bands in which the pixel value may exist. 8. The method of claim 7,
Determining a band offset interval according to the current block in consideration of the band to which the pixels belonging to the reference range belongs most,
And determining a center section such that a band including the most pixels in the reference range is the center of the center section. The method of claim 2, wherein the band offset period includes a central band and a side band,
The size or boundary of the center section is adaptively determined in consideration of the distribution of pixel values of the pixels belonging to the reference range. The method of claim 2,
The band offset section includes a central band and side bands,
The size or boundary of the center section is determined in consideration of the degree of dispersion of the pixel value of the pixels belonging to the reference range. The method of claim 10, wherein the determining of the size of the center section in consideration of the degree of dispersion of pixel values of pixels belonging to the reference range is performed by:
In-loop filtering is characterized in that the size of the center section is determined such that the number of bands in which pixel values of pixels belonging to the reference range are distributed and the size of the center section have a negative correlation within a predetermined reference range. Way. The method of claim 2,
The band offset period includes a central band, a first side band, and a second side band, and adaptively determining the band offset period may include:
An in-loop filtering method comprising determining a boundary of the center section and a boundary of the first side section in consideration of the distribution of pixel values of pixels belonging to the reference range among all bands in which a pixel value may exist. . In the image decoding apparatus,
A deblocking filter for removing block distortion of the reconstructed image; And
Including a SAO processing unit for applying a sample offset (SAO) to the deblocking filtered image,
And the SAO processor applies an adaptive band offset according to a current block to which the sample offset is to be applied. The method of claim 13, wherein the SAO processing unit,
And a band offset section determiner for adaptively determining a band offset section in consideration of a pixel value distribution of pixels belonging to the current block to which the sample offset is applied or the reference range associated with the current block. Device. The method of claim 14, wherein the SAO processing unit,
A sample offset type determiner that determines a sample offset type of the current block in consideration of the adaptively determined band offset period;
And a sample offset adder configured to add sample offsets to pixels belonging to the current block in consideration of the determined band offset period. The method of claim 13, wherein the reference range is
An image specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion or an area specified by pixels belonging to a block having similarity according to a predetermined criterion with the current block Decryption device. The method of claim 16, wherein the area specified by pixels belonging to an area adjacent to the current block according to a predetermined criterion is:
And at least one region of an upper block, a left block, and an upper right block of the current block, or a set of pixels surrounding the current block with a predetermined thickness. The method of claim 14, wherein the band offset section includes a center section and a side section,
And the band offset section determiner determines a center section such that a band including the most pixels of the reference range is the center of the center section among all bands in which a pixel value may exist. The method of claim 14, wherein the band offset section includes a center section and a side section,
The band offset section determiner determines the size or boundary of the center section in consideration of the degree of dispersion of pixel values of pixels belonging to the reference range. 20. The method of claim 19,
The band offset section determiner,
And determining the size of the center section such that the number of bands in which pixel values of pixels belonging to the reference range are distributed and the size of the center section have a negative correlation within a predetermined reference range. The method of claim 14,
The band offset section includes a central band, first side bands, and second side bands, and the band offset section determiner includes:
The boundary of the center section and the boundary of the first side section are determined in consideration of the distribution of pixel values of pixels belonging to the reference range among all bands in which the pixel value may exist. A video encoding apparatus comprising:
A deblocking filter for removing block distortion of the reconstructed image; And
Including a SAO processing unit for processing the sample of the deblocking filtered Adaptive Sample Offset (SAO),
And the SAO processor applies an adaptive band offset according to a current block to which the sample offset is to be applied. The method of claim 22, wherein the SAO processing unit,
And a band offset section determiner configured to adaptively determine a band offset section in consideration of a pixel value distribution of pixels belonging to the current block to which the sample offset is applied or the reference range associated with the current block. Device. In an in-loop filter,
A deblocking filter for removing block distortion of the reconstructed image; And
Including a SAO processing unit for applying a sample offset (SAO) to the deblocking filtered image,
And the SAO processor applies an adaptive band offset according to a current block to which the sample offset is to be applied.

Images