KR20100046289A - Video encoding/decoding apparatus, adaptive deblocking filter and deblocing filtering method, and recording medium therefor - Google Patents

Abstract

PURPOSE: A video encoding/decoding apparatus, an adaptive de-blocking filter and a de-blocking filtering method, and a recording medium therefor are provided to remove block distortion efficiently by applying a de-blocking filter of pixel unit to plural directions. CONSTITUTION: A boundary strength decision unit(191) determines the strength of a boundary between current sub blocks. A direction selection unit(193) selects plural preset directions one by one. A pixel selection unit(195) selects a pixel to be filtered. According to pixel relation between selected pixels, a filtering decision unit(197) decides the filtering for the selected direction. A filtering unit(199) performs the filtering operation for the selected pixels of the selected direction.

Description

Video encoding / decoding apparatus, adaptive deblocking filtering and deblocing filtering method, and recording medium therefor}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video encoding / decoding apparatus, and more particularly, to a video encoding / decoding apparatus for effectively removing a blocking artifact occurring in an apparatus for encoding using block-based discrete cosine transform and quantization. Apparatus and method for adaptive deblocking filtering and recording medium deblocking filter and filtering method.

In general, in most commercial video compression schemes and devices (H.263, H.264, MPEG-4, H.264 / AVC), block-based discrete cosine transforms are used to reduce spatial redundancy of images. DCT) and quantization techniques. In this case, the transforms of block units that do not overlap each other are independently subjected to discrete cosine transform and quantization without any correlation between neighboring blocks or pixels, thereby causing data loss, and in particular, greatly increasing the quantization value. In low bit-rate video, the blocking phenomenon, which is a structured discontinuity of pixel values, appears clearly at the interface between blocks, which is called blocking artifact. Blocking artifacts not only significantly reduce the picture quality of the video screen, but are also stored in the frame memory with block distortion, and the image with block distortion is referenced in the motion compensation process, so that image quality deterioration is propagated, which greatly reduces the compression performance. There is a problem.

For this reason, this problem can be solved by using a low-band filter that reduces the blocking artifacts before the decoder stores the decoded image in the reference frame memory and also improves the image quality in the decoder. The technique is called deblocking filter.

However, if there is an edge present in the image or an object boundary in the screen at the block boundary surface, applying the deblocking filter to this may cause the edge portion of the original image to be damaged, thereby causing deterioration of image quality.

Therefore, the deblocking filter in the H.264 / AVC video codec adaptively performs filtering for each boundary of a block having 4x4 pixels, which is a block unit performing quantization with DCT. In more detail, if the boundary of the block is determined to be the edge of the real image or the boundary of the object, the filtering is not performed. If the boundary is determined to be distortion due to blocking artifacts, the problem is solved.

However, since the H.264 / AVC deblocking filter determines the existence of an edge only in the vertical and horizontal directions, when a boundary of an edge or an object is placed in a diagonal direction, discontinuity occurs in diagonal pixels of the boundary between blocks. There is still a problem that blocking artifacts can occur.

In order to solve the above problems, the present invention, by determining the edge direction in the pixel unit in the vertical and horizontal direction as well as a number of other directions at the boundary between blocks, and remove the blocking artifacts by performing deblocking filtering in that direction An object of the present invention is to provide a video encoding / decoding apparatus, an adaptive deblocking filtering apparatus and a filtering method, and a recording medium for improving image quality.

According to an aspect of an embodiment of the present invention to achieve the above object, a boundary strength determination unit for determining the strength of the boundary between the sub-blocks of the current block; A direction selector which sequentially selects one of a plurality of preset directions based on the boundary; A pixel selector which selects pixels to filter based on the selected direction; A filtering determiner configured to determine whether to filter the selected direction according to a relationship between pixel values between the selected pixels; An adaptive deblocking filtering device including a filtering unit which performs filtering on the selected pixels in the selected direction according to the determined filtering is provided.

According to another aspect of an embodiment of the present invention to achieve the above object, a boundary strength determination step of determining the strength of the boundary between sub-blocks of the current block; A direction selection step of sequentially selecting one of a plurality of preset directions based on the boundary; Selecting a pixel to filter based on the selected direction; A filtering determination step of determining whether to filter in the selected direction according to the relationship of pixel values between the selected pixels; An adaptive deblocking filtering method including a filtering step of performing filtering on the selected pixels in the selected direction according to the determined filtering is provided.

In the filtering determining unit or the filtering determining step, the relationship between the pixel values between the selected pixels is an absolute value of the pixel value difference between the first pixels facing the boundary, and the two sides on the basis of the boundary are determined. If the absolute value of the pixel value difference between the first pixel and the first pixel, and the absolute value of the pixel value difference between the second pixel and the first pixel on the other side based on the boundary, respectively satisfy the condition less than the preset thresholds, The selected direction may be determined as the filtering direction.

The filtering unit or the filtering step may perform filtering by selecting one or more of the plurality of filtering directions when the determined filtering directions are multiple.

The preset plurality of directions may include, for example, 45 degrees, 90 degrees, and 135 degrees, or in another example, 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees. May comprise a diagram.

According to another aspect of an embodiment of the present invention to achieve the above object, a prediction unit for predicting the current block of the image to generate a prediction block; A subtraction unit for generating a residual block by subtracting the prediction block from the current block; A transformer for converting the residual block into a frequency domain; A quantizer for quantizing the transformed residual block; An encoder which encodes the quantized residual block; An inverse quantizer for inversely quantizing the residual block; An inverse transform unit for inversely transforming the inverse quantized residual block into a residual block having a pixel signal on a time axis; An adder configured to add the prediction block to the inverse transformed residual block to restore a current block; And deblocking and filtering the reconstructed current block, selecting pixels to be filtered in a plurality of preset directions based on the boundary of the reconstructed current block, and reconstructing the corresponding block according to the relationship of pixel values between the selected pixels. A video encoding apparatus including a deblocking filter unit configured to determine whether to filter and to perform filtering on the selected pixels in the corresponding direction according to the determined filtering.

According to another aspect of an embodiment of the present invention to achieve the above object, a decoding unit for decoding the bitstream to extract the residual block; An inverse quantizer for inversely quantizing the residual block; An inverse transform unit for inversely transforming the inverse quantized residual block; A prediction unit for predicting a current block to generate a prediction block; An adder configured to add the inverse transformed residual block and the prediction block to restore the current block; And deblocking and filtering the current block restored by the adder, selecting pixels to be filtered according to a plurality of preset directions based on the boundary of the current block, and selecting corresponding pixels according to the relationship between pixel values among the selected pixels. A video decoding apparatus including a deblocking filter unit configured to determine whether to filter for and to filter the selected pixels in the corresponding direction according to the determined filtering.

The deblocking filter unit of the video encoding / decoding apparatus may have a relationship between pixel values between the selected pixels, an absolute value of pixel value differences between first pixels facing the boundary, and one side based on the boundary. The absolute value of the pixel value difference between the second pixel and the first pixel of, and the absolute value of the pixel value difference between the second pixel and the first pixel on the other side with respect to the boundary satisfy each of the preset thresholds. In this case, the corresponding direction may be determined as the filtering direction.

According to another aspect of an embodiment of the present invention to achieve the above object, a boundary strength determination function for determining the strength of the boundary between sub-blocks of the current block; A direction selection function for sequentially selecting one of a plurality of preset directions based on the boundary; A pixel selection function for selecting pixels to be filtered based on the selected direction; A filtering determination function for determining whether to filter in the selected direction according to a relationship of pixel values between the selected pixels; A computer readable recording medium having recorded thereon a program including a filtering function for performing filtering on the selected pixels in the selected direction according to the determined filtering is provided.

The filtering determination function may include a relationship between pixel values between the selected pixels, an absolute value of pixel value differences between first pixels facing the boundary, and a second pixel and a first pixel on one side based on the boundary. If the absolute value of the pixel value difference between the absolute value and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the boundary are respectively smaller than the preset thresholds, the selected direction is filtered. Can be determined.

According to an exemplary embodiment of the present invention, the block blocking phenomenon due to the discontinuity in the diagonal direction caused by the edges of the plurality of diagonal directions is applied by applying the deblocking filter in units of pixels not only in the vertical horizontal direction but also in many other directions. Effective removal occurs.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but there may be another configuration between each component. It is to be understood that the elements may be "connected", "coupled" or "connected".

Since the video screen is composed of 30 frames in one second, the difference is small between one frame and neighboring frames, and thus cannot be distinguished by the human eye. Because of this, if 30 frames are sprayed in one second, the human eye perceives the frames as continuous.

As such, when the previous frame is similar to the current frame, the pixel value of the next frame can be predicted from the known pixel values constituting the previous frame. This is called inter-prediction.

The encoding and decoding of such video data is performed based on a motion prediction technique. The motion prediction is performed by referring to past frames or referring to both past and future frames based on the time axis. The frame referred to to encode or decode the current frame is called a reference frame. In block-based video encoding, one still image (frame) constituting a video is divided into macroblocks and subblocks constituting the macroblock, and motion is predicted in units of blocks and encoding is performed.

In addition, the correlation of the pixel signal may be used to predict the next pixel and to encode the prediction error in the same frame. This is called intra-prediction.

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

The video encoding apparatus 100 according to an embodiment of the present invention includes a predictor 110, a subtractor 120, a transformer 130, a quantizer 140, an encoder 150, and an inverse quantizer 160. ), An inverse transform unit 170, an adder 180, and a deblocking filter unit 190.

The video encoding apparatus 100 may be a personal computer (PC), a notebook computer, a personal digital assistant (PDA), a portable multimedia player (PMP), or a PlayStation Portable (PSP). And a communication device such as a communication modem for communicating with various devices or a wired / wireless communication network, a memory for storing various programs and data for encoding an image, and a program. It means a variety of devices having a microprocessor, etc. for execution and operation and control.

As described above, the prediction unit 110 may use the current prediction using any one or a combination of intra prediction based on motion prediction or intra prediction that predicts the next pixel using the correlation of pixel signals within the same frame. A block (or macroblock) can be predicted.

For example, the predictor 110 may be divided into a motion estimator (not shown) and a motion compensator (not shown). The motion estimator finds the motion prediction value of the macroblock of the current frame in the reference frame and outputs the difference of the motion as a motion vector. That is, the macroblock to be searched is searched within a predetermined search area of the reference frame to find the most similar macroblock and the degree of movement thereof is output as a motion vector. The motion compensation unit obtains a prediction macro block corresponding to the obtained motion vector from the reference frame.

As another example, the predictor 110 is an intra predictor that predicts a current macroblock of a current frame using a neighboring macroblock of a current macroblock in an image, and at least one pixel value of at least one neighboring macroblock. The predicted macroblock is predicted by calculating a predicted pixel value of each pixel of the current macroblock using. Here, the peripheral macroblock may be one or more peripheral macroblocks that are compressed before the current macroblock and located around the current macroblock.

The subtractor 120 subtracts the prediction block from the current block to generate a residual block. That is, the subtractor 120 generates a residual block having a residual signal by calculating a difference value between an original pixel value of each pixel of the current block and a predicted pixel value of each pixel of the prediction block. do.

The transformer 130 transforms the residual block into the frequency domain. That is, the transformer 130 converts the residual block into a frequency domain to generate a residual block having a frequency coefficient. Here, the transform unit 130 transforms the residual block, and various transformations for transforming the image signal of the time axis to the frequency axis, such as a Hadamard transform, Discrete Cosine Transform Based Transform, etc. The residual signal can be converted into a frequency domain using a technique, and the residual signal converted into the frequency domain becomes a frequency coefficient.

The quantizer 140 quantizes the residual block transformed by the transformer 130. That is, the quantization unit 140 quantizes the frequency coefficients of the residual block to generate quantization frequency coefficients. Here, the quantization unit 140 uses Dead Zone Uniform Threshold Quantization (DZUTQ), Quantization Weighted Matrix, or the quantization method to quantize the frequency coefficient of the residual block. Etc. can be used.

The encoder 150 generates a bitstream by encoding the frequency coefficients of the residual block quantized by the quantizer 140. In addition, when the motion vector and the rotation information are transmitted from the predictor 110, the encoder 150 may output the bitstream by encoding the quantized frequency coefficients of the residual block. As the encoding technique, an entropy encoding technique may be used, but various encoding techniques may be used without being limited thereto.

The inverse quantization unit 160 inverse quantizes the residual block quantized by the quantization unit 130. That is, the inverse quantizer 160 inversely quantizes the quantized frequency coefficients of the quantized residual block to generate frequency coefficients.

The inverse transform unit 170 inverse transforms the residual block inversely quantized by the inverse quantization unit 160. That is, the inverse transform unit 170 inversely transforms the frequency coefficients of the inverse quantized residual block to restore the residual block having the pixel signal on the time axis.

The adder 180 reconstructs the current block by adding the prediction block predicted by the predictor 110 to the residual block inversely transformed by the inverse transformer 170.

The deblocking filter 190 deblocks filtering the current block reconstructed by the adder 180. Here, the deblocking filtering refers to an operation of reducing block distortion generated by encoding an image in block units, and applying a deblocking filter to a block boundary and a macroblock boundary, or applying a deblocking filter only to a macroblock boundary or a deblocking filter. You can optionally use one of the methods that does not use. As such, the current block reconstructed by the adder 180 and deblocked filtered by the deblocking filter 190 may be input to the predictor 110 and stored as a reference picture used when predicting the next picture. .

The deblocking filter unit 190 according to an embodiment of the present invention deblocks and filters the current block, in particular, selects pixels to be filtered in a plurality of preset directions based on the boundary of the current block, and selects pixels between the selected pixels. The filtering of the corresponding direction is determined according to the relationship between the values, and filtering is performed on the pixels selected in the corresponding direction according to the determined filtering. In addition, the deblocking filter unit 190 may determine that the relationship between the pixel values between the pixels selected in each direction is based on the absolute value of the pixel value difference between the first pixels facing the boundary and based on the corresponding boundary. The absolute value of the pixel value difference between the second pixel and the first pixel on the side, and the absolute value of the pixel value difference between the second pixel and the first pixel on the other side based on the corresponding boundary are smaller than the preset thresholds, respectively. If is satisfied, the direction is determined as the filtering direction. Such a deblocking filter 190 will be described in more detail with reference to FIG. 2.

FIG. 2 is a block diagram of an adaptive deblocking filtering apparatus according to an embodiment of the present invention, and corresponds to the deblocking filter unit 190 of FIG. 1.

As shown in FIG. 2, the adaptive deblocking filtering device 190 according to an embodiment of the present invention includes a boundary strength determiner 191, a direction selector 193, a pixel selector 195, and a filtering decision. The unit 197 and the filtering unit 199 are included.

The boundary strength determiner 191 determines the strength of the boundary between sub-blocks of the current block and determines the boundary strength (BS) according to the characteristics of the block to which pixels belong to the block boundary of the current position. The BS has a value between 0 and 4 and the method of determining is specified in the H.264 / AVC standardization document, for example. That is, the boundary strength determiner 191 determines the BS value of the boundary surface of each block and determines how much strength to apply filtering according to each BS value. The BS determines whether 0 and 0 depend on the distance between the reference block for motion compensation when the block to which the boundary to be filtered currently belongs uses intra prediction encoding or when using inter prediction encoding. It is determined by a value between four.

The direction selector 193 sequentially selects one of a plurality of preset directions based on the block boundary. That is, the direction selector 193 presets a direction to filter in three directions of 45 degrees, 90 degrees, and 135 degrees with respect to the block boundary surface as shown in FIG. 3, for example, one of the three directions. Selected sequentially, or as another example, in nine directions: 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees with respect to the horizontal or vertical boundary as shown in FIG. The direction to filter can be preset and one of these nine directions can be selected sequentially.

The pixel selector 195 selects pixels to filter based on the direction selected by the direction selector 193. That is, the pixel selector 195 is, for example, as shown in FIG. 4 with respect to one direction selected from three directions of 45 degrees, 90 degrees, and 135 degrees by the direction selector 193 as shown in FIG. 3. Likewise, the pixels to be filtered are selected, or as another example, the nine directions of 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees as shown in FIG. The pixels to be filtered are selected as shown in Figs. 6 to 14 for one of the selected directions.

The filtering determiner 197 determines whether to filter the corresponding direction selected by the direction selector 193 according to the relationship between the pixel values between the pixels selected by the pixel selector 195. In other words, the filtering determiner 197 determines that the relationship between the pixel values between the pixels selected by the pixel selector 195 is the absolute value of the pixel value difference between the first pixels facing the boundary, based on the boundary. The absolute value of the pixel value difference between the second pixel and the first pixel on one side, and the absolute value of the pixel value difference between the second pixel and the first pixel on the other side based on the corresponding boundary are smaller than the preset thresholds, respectively. If the condition is satisfied, the direction selected by the direction selector 193 is determined as the filtering direction. A detailed example of the filtering determination process in the filtering determination unit 197 will be described later.

The filtering unit 199 performs deblocking filtering on the pixels in the corresponding direction according to the filtering determined by the filtering determining unit 197, but when the filtering direction determined by the filtering determining unit 197 is multiple, One or more filtering directions may be selected to perform filtering.

FIG. 15 is a flowchart of an adaptive deblocking filtering method according to an embodiment of the present invention, which is applied to the apparatus of FIG. 2 and described with the operation of the apparatus.

In order to explain an embodiment of the present invention, first, deblocking of H.264 (“Advanced video coding for generic audiovisual services”, Draft, ITU-T Recommendation H.264, Mar, 2005, p. 182 to p.194) Briefly explain the filtering method.

In the deblocking filtering method of H.264, filtering is performed in the vertical direction as shown in FIG. 16 based on the boundary surface of the discrete cosine transform (DCT) and the quantization unit of the 4x4 block of the residual signal. Filter in the horizontal direction as follows.

First, before applying the deblocking filter, when there are blocks composed of p0 to p3 and blocks composed of q0 to q3 as shown in FIG. 18, a block boundary strength (BS) value is determined for the boundary of each block. The strength of the filter boundary is determined based on the block boundary strength value of the filter. The filtering strength is 0 depending on whether the block to which the boundary to be filtered currently belongs uses intra prediction encoding or when distance between the reference blocks for motion compensation is used when inter prediction encoding is used. It is determined by a value between and 4.

If the block boundary strength value is determined, it is determined whether the filtering should be performed by determining whether the pixels of the boundary surface of each block are the boundary surface distorted by the blocking artifact or the edge present in the actual image. In case H.264 does not satisfy the following [Equation 1], it is determined that the edge exists in the real image and filtering is not performed. If the condition is satisfied, H.264 judges that the boundary is distorted by blocking artifacts. Blocking filter will be performed.

[Equation 1]

①

;

;

②

;

;

,

는 양자화 파라미터(Quantization Parameter)에 따라 적응적으로 그 값이 결정되는 값으로써, 현재 경계 면이 블록킹 아티팩트로 발생한 화소 값의 차이인지, 실제 에지에 의한 것인지를 판별할 수 있는 문턱치(Threshold) 값을 의미한다. 양자화 정도가 큰 경우에는 블록킹 아티팩트의 정도가 더욱 크게 발생하므로 문턱치의 값이 크게 설정되는 구조로 되어 있다.here

,

Is a value that is adaptively determined according to a quantization parameter, and is a threshold value for determining whether a current boundary is a difference between pixel values caused by blocking artifacts or an actual edge. it means. If the degree of quantization is large, the degree of blocking artifacts is greater, and thus the threshold value is set large.

When it is determined whether filtering is performed or not, the low band filtering is used according to the block boundary strength value to smooth the pixels on both sides of the boundary surface. The calculation method for filtering can be used, for example, using the method specified in H.264 (“Advanced video coding for generic audiovisual services”, Draft, ITU-T Recommendation H.264, Mar, 2005, p. 182 to p.194). Can be.

As described above, the deblocking filter of H.264 determines the filter strength according to the encoding property of the block, and determines whether or not the edge exists by using [Equation 1] on the block boundary surface, while preserving the edge components as much as possible, each boundary surface By adaptively performing deblocking filtering on, we reduce blocking artifacts. However, when the deblocking filtering is performed only in the horizontal and vertical directions as described above, the distortion due to blocking artifacts caused by the discontinuity in the diagonal direction cannot be corrected.

In more detail, when the deblocking filter is performed only in the existing horizontal and vertical directions, as shown in FIG. 19 (a), when there are diagonal edge components on the block boundary surface, p0 to p3 pixels and q0 to When [Equation 1] is applied to the boundary surface composed of q3 pixels, the condition is not satisfied and the edge is not determined and the deblocking filtering is not performed. However, if the block boundary strength values of the A blocks and the B blocks are equal to or greater than 1, it can be observed that discontinuities of pixel values occur due to blocking artifacts even though p0 and dq0 have the same value. Therefore, in order to solve the blocking artifacts caused by the discontinuity between the pixels occurring in the diagonal direction, it is necessary to adaptively perform the deblocking filtering in the diagonal direction as well as the vertical and horizontal directions. More specifically, if low-band filtering is performed on the boundary surface in the diagonal direction as shown in (b) of FIG. 19, the pixel values of p0 and q0 are changed and smoothed to solve the distortion caused by the discontinuity of pixel values at the block boundary surface. Could be.

Accordingly, embodiments of the present invention allow the deblocking filter to be performed not only in the vertical and horizontal directions but also in other directions.

In Embodiment 1 of the present invention, each pixel of each boundary plane is inspected for three directions, respectively, whether the boundary plane is the boundary plane due to the actual edge or the blocking artifact, and the filtering is performed for all the directions considered to be blocking artifacts.

Example 1

Steps 1 to 5 below are performed on the pixels existing on all boundary surfaces in the vertical and horizontal directions of FIGS. 16 and 17.

Step 1: Determining boundary strength In step S1510, the boundary strength determining unit 191 determines a block boundary strength BS with respect to a boundary of a 4 × 4 block. If the BS is 0, the deblocking filtering is not performed. If the BS is 1 to 4, the BS determines whether the deblocking filtering should be performed by checking the conditional expression.

Step 2: In the direction selecting step S1530, the direction selecting unit 193 sequentially selects one of three directions of 45 degrees, 90 degrees, and 135 degrees for all the pixels on the boundary surface as shown in FIG. 3.

Step 3: In the pixel selection step S1550, the pixel selector 195 selects pixels to be filtered according to the direction selected by the direction selector 193 as shown in FIG. 4.

Step 4 and Step 5: Filtering Determination In operation S1570, the filtering determination unit 197 may determine the direction selected by the direction selection unit 193 according to the relationship of the pixel values between the pixels selected by the pixel selection unit 195. In operation S1590, the filtering unit 199 performs a deblocking filtering operation on the pixels in the direction determined by the filtering determination unit 197 according to the BS value. That is, the filtering determiner 197 determines whether the relationship between the pixel values between the pixels selected by the pixel selector 195 satisfies a preset condition, and determines to perform filtering on the direction satisfying the condition. The filtering unit 199 performs a deblocking filtering operation on the pixels in the direction determined by the filtering determination unit 197 according to the BS value. Specifically, as shown in FIG. 4, the following [Conditions 1], [Conditions 2], and [Conditions 3] are examined in the 45 °, 90 °, and 135 ° directions, respectively. The deblocking filter operation is performed by using the located pixels.

[Condition 1]

;

;

;

;

,

는 상수로 문턱치 값을 조절하여, 대각선 방향에서의 디블록킹 필터링의 수행 정도를 결정하는 것이 가능하다. In the case of 45 degree direction, if [Condition 1] is satisfied, filtering operation is performed according to BS value. In this case, the pixels used for the deblocking filter operation use p0, dp1, dp2, dp3, dq0, dq1, dq2, and dq3 as pixels positioned in the 45 degree direction. At this time,

,

It is possible to determine the degree of performance of deblocking filtering in the diagonal direction by adjusting the threshold value with a constant.

[Condition Formula 2]

;

;

;

;

In the 90 degree direction, if [Condition 2] is satisfied, the filtering operation is performed according to the BS value. At this time, the pixels used for the deblocking filter operation are p0, p1, p2, p3, q0, q1, q2, q3.

[Condition 3]

;

;

;

;

In the 135 degree direction, if the condition 3 is satisfied, the filtering operation is performed according to the BS value. In this case, the pixels used for the deblocking filter operation use p0, ap1, ap2, ap3, aq0, aq1, aq2, and aq3 as pixels located in the 135 degree direction.

In Embodiment 2 of the present invention, each pixel of each boundary plane is inspected for each of nine directions to determine whether the boundary plane is a real edge or a blocking artifact, and the filtering is performed by selecting the most suitable direction. . In Example 2 described later, one direction is selected from nine directions, but this is only an example, and even if a plurality of suitable directions are selected from other directions, they will fall within the scope of the present invention.

Example 2

Steps 1 to 5 below are performed on the pixels existing on all boundary surfaces in the vertical and horizontal directions of FIGS. 16 and 17.

Step 1: Determining boundary strength In step S1510, the boundary strength determining unit 191 determines a block boundary strength BS with respect to a boundary of a 4 × 4 block. If the BS is 0, deblocking filtering is not performed. If the BS is 1 to 4, the BS determines whether deblocking filtering should be performed by checking a conditional expression.

Step 2: In the direction selection step S1530, the direction selector 193 is 45 degrees, 56.25 degrees, and 67.5 degrees for all the pixels on the horizontal and vertical boundary planes as shown in FIGS. 5A and 5B. , One of nine directions, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees.

Step 3: In the pixel selection step S1550, the pixel selector 195 selects pixels to be filtered according to the direction selected by the direction selector 193 as illustrated in FIGS. 6 to 14.

Step 4 and Step 5: Filtering Determination In operation S1570, the filtering determination unit 197 may determine the direction selected by the direction selection unit 193 according to the relationship of the pixel values between the pixels selected by the pixel selection unit 195. In operation S1590, the filtering unit 199 performs a deblocking filtering operation on the pixels in the direction determined by the filtering determination unit 197 according to the BS value. That is, the filtering determiner 197 determines whether the relationship between the pixel values between the pixels selected by the pixel selector 195 satisfies a preset condition, and determines to perform filtering on the direction satisfying the condition. The filtering unit 199 performs a deblocking filtering operation on the pixels in the direction determined by the filtering determination unit 197 according to the BS value. Specifically, as shown in FIGS. 6 to 14, the following nine conditions of 90 degrees, 78.75 degrees, 67.5 degrees, 56.25 degrees, 45 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees are given below. [Condition 5], [Condition 6], [Condition 7], [Condition 8], [Condition 9], [Condition 10], [Condition 11], and [Condition 11], respectively. A deblocking filter operation is performed using pixels positioned in the direction.

와

는 상수로 문턱치 값을 조절하여, 각각의 방향에서 디블록킹 필터링의 수행 정도를 결정하는 것이 가능하다. The conditional expression for each direction is specifically as follows. At this time,

Wow

It is possible to determine the degree of performance of deblocking filtering in each direction by adjusting the threshold value with a constant.

The conditional expression for the 90 degree direction of FIG. 6 is as follows [Condition 4].

[Condition 4]

;

;

;

;

The conditional expression for the 78.75 degree direction of FIG. 7 is as follows [Condition 5].

[Condition 5]

;

;

;

;

The conditional expression for the direction of 67.5 degrees of FIG. 8 is as follows [Condition 6].

[Condition 6]

;

;

;

;

The conditional expression for the 56.25 degree direction of FIG. 9 is as follows [Condition 7].

[Condition 7]

;

;

;

;

The conditional expression for the 45 degree direction of FIG. 10 is as follows [conditional formula 8].

[Condition 8]

;

;

;

;

The conditional expression for the direction of 101.25 degree of FIG. 11 is as follows [Condition 9].

[Condition 9]

;

;

;

;

The conditional expression for the direction of 112.5 degrees in FIG. 12 is as follows [conditional expression 10].

[Condition 10]

;

;

;

;

The conditional expression for the direction of 123.75 degree of FIG. 13 is as follows [Condition 11].

[Condition 11]

;

;

;

;

Conditional formulas for the 135-degree direction of FIG. 14 are as follows.

[Condition 12]

;

;

;

;

If a plurality of directions satisfying the conditional expression are selected among all the directions shown in FIGS. 6 to 14, the filtering unit 199 calculates the amount of change between pixels on the boundary surface for each of the selected directions, and the one with the smallest amount of change. Alternatively, deblocking filtering may be performed by selecting a plurality of values in a small order of change.

는 경계 면의 화소(pixel)에서의 방향 세트에서 화소 간의 변화량을 나타낸다.

와

은 가중치(weight)를 나타내는 상수로써, 블록 간의 경계 근처 화소 간의 변화량이 경계에서 멀리 떨어져 있는 화소간의 변화량보다 전체 변화량에 더 큰 비중을 갖도록

,

을 만족하는 값으로 설정된다.The equation for calculating the amount of change between pixels in each direction at the interface is as follows.

Denotes the amount of change between pixels in the set of directions in pixels of the interface.

Wow

Is a constant that represents the weight, so that the amount of change between pixels near the boundary between blocks has a greater proportion to the total amount of change than the amount of change between pixels far away from the boundary.

,

It is set to a value satisfying.

The equation for calculating the change amount in each direction is as follows.

The changes in the nine directions of 90 degrees, 78.75 degrees, 67.5 degrees, 56.25 degrees, 45 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees and 135 degrees shown in FIGS. 6 to 14 are shown in [Equation 2] to [ Equation 10] respectively.

[Equation 2]

[Equation 3]

[Equation 4]

[Equation 5]

[Equation 6]

[Equation 7]

[Equation 8]

[Equation 9]

[Equation 10]

The pixels used when the deblocking filtering is applied to each of the nine directions, that is, the pixels selected by the pixel selector 195 are pixels marked with bold borders for each direction as shown in FIGS. 6 to 14. Use For example, the pixels used in the 67.5 degree direction of FIG. 8 are p04, p14, p25, p35, q03, q13, q22, and q32.

20 is a block diagram of a video decoding apparatus according to an embodiment of the present invention.

The video decoding apparatus 2000 according to an embodiment of the present invention includes a decoder 2010, an inverse quantizer 2020, an inverse transform unit 2030, a predictor 2040, an adder 2050, and a deblocking filter unit. 2060 may be configured to be included.

The video decoding apparatus 2000 may be a personal computer (PC), a notebook computer, a personal digital assistant (PDA), a portable multimedia player (PMP), or a PlayStation Portable (PSP). ), A communication device such as a communication modem for communicating with various devices or a wired / wireless communication network, a memory for storing various programs and data for decoding an image, and executing a program. Means a variety of devices including a microprocessor for operation and control.

The decoder 2010 extracts a residual block by decoding the bitstream. That is, the decoder 2010 decodes the bitstream, which is the image encoded by the image encoding apparatus 100, to extract the residual block, the motion vector, and the rotation information including the pixel information of the current block of the image.

The inverse quantizer 2020 inversely quantizes the residual block extracted by the decoder 2010, and the inverse transformer 2030 inversely transforms the inverse quantized residual block. Here, the inverse quantization and the inverse transform may be inversely transformed with the inverse quantization in the same manner as the inverse quantization and inverse transformation described above with reference to FIG. 1.

The prediction unit 2040 generates a prediction block by predicting the current block by compensating for the motion including the rotation movement of the current block of the image by using the motion vector and the rotation information extracted by the decoder 2010.

The adder 2050 adds the prediction block predicted by the predictor 2040 to the residual block inversely transformed by the inverse transform unit 2030 to restore the current block.

The deblocking filter unit 2060 deblocks and filters the current block restored by the adder 2050, selects pixels to be filtered in a plurality of preset directions based on the boundary of the current block, and selects pixels between the selected pixels. The filtering of the corresponding direction is determined according to the relationship between the values, and filtering is performed on the pixels selected in the corresponding direction according to the determined filtering. The deblocking filter unit 2060 has an absolute value of a difference in pixel values between the first pixels facing each other based on a corresponding boundary, and a second pixel and a first pixel on one side based on the corresponding boundary. If the absolute value of the pixel value difference between the first pixel and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the corresponding boundary satisfy each of the conditions smaller than the preset thresholds, the corresponding direction is filtered. Decide on direction. When there are a plurality of determined filtering directions, the deblocking filter unit 2060 may perform filtering by selecting one or more of the plurality of filtering directions according to the amount of change in pixel values between the selected pixels. The deblocking filter 2060 is configured in the same way as the deblocking filtering device 190 of FIG. 2, for example.

The current block reconstructed by the adder 2050 is combined in picture units and output as a reconstructed image, and the current block deblocked and filtered by the deblocking filter 2060 when the predictor 2040 predicts the next picture. It may be stored as a reference picture used.

The adaptive deblocking filtering method according to an embodiment of the present invention can be implemented as computer readable codes on a computer readable recording medium. Computer-readable recording media include all kinds of recording devices that store data that can be read by a computer system. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like, which are also implemented in the form of carrier waves (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

In the above description, all elements constituting the embodiments of the present invention are described as being operated in combination, and the present invention is necessarily limited to these embodiments. In other words, within the scope of the present invention, all of the components may be selectively operated in combination with one or more. In addition, although all of the components may be implemented in one independent hardware, each or all of the components may be selectively combined to perform some or all functions combined in one or a plurality of hardware. It may be implemented as a computer program having a. Codes and code segments constituting the computer program may be easily inferred by those skilled in the art. Such a computer program may be stored in a computer readable storage medium and read and executed by a computer, thereby implementing embodiments of the present invention. The storage medium of the computer program may include a magnetic recording medium, an optical recording medium, a carrier wave medium, and the like.

In addition, the terms "comprise", "comprise" or "having" described above mean that the corresponding component may be included, unless otherwise stated, and thus excludes other components. It should be construed that it may further include other components instead. All terms, including technical and scientific terms, have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. Terms commonly used, such as terms defined in a dictionary, should be interpreted to coincide with the contextual meaning of the related art, and shall not be construed in an ideal or excessively formal sense unless explicitly defined in the present invention.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

As described above, the present invention is applied to a video encoding and decoding technique, and provides a method for applying a deblocking filter on a pixel-by-pixel basis for not only a vertical horizontal direction but also a plurality of other directions, thereby providing a plurality of diagonal directions. It is a very useful invention that effectively removes the block distortion caused by the discontinuity in the diagonal direction caused by the edges to improve the image quality.

1 is a block diagram of a video encoding apparatus according to an embodiment of the present invention;

2 is a block diagram of an adaptive deblocking filtering device according to an embodiment of the present invention;

3 is a view for explaining an example of a filtering direction according to an embodiment of the present invention;

4 is a view for explaining an example of a pixel selected according to the filtering direction of FIG. 3;

5 is a view for explaining another example of a filtering direction according to an embodiment of the present invention;

6 to 14 illustrate examples of pixels selected according to the filtering direction of FIG. 5;

15 is a flowchart of an adaptive deblocking filtering method according to an embodiment of the present invention;

16 and 17 are views showing the boundaries of the macro block in the vertical and horizontal directions,

18 illustrates an example of pixels to be horizontally and vertically filtered in the case of vertical and horizontal block boundaries;

19 is a diagram illustrating an example of filtering in a vertical direction when an edge in a diagonal direction exists, and (b) illustrates an example of filtering in a diagonal direction;

20 is a block diagram of a video decoding apparatus according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

100: encoding device (or coder)

110: prediction unit 120: subtraction unit

130: transform unit 140: quantization unit

150: encoding unit 160: inverse quantization unit

170: inverse transform unit 180: adder

190: deblocking filter unit, adaptive deblocking filtering device

191: boundary strength determination unit 193: direction selection unit

195: pixel selection unit 197: filtering determination unit

199: filtering unit

2000: decoding device (or decoder)

2010: decryption unit 2020: inverse quantization unit

2030: inverse transform unit 2040: prediction unit

2050: adder 2060: deblocking filter part

Claims (20)

A boundary strength determiner for determining the strength of the boundary between sub-blocks of the current block; A direction selector which sequentially selects one of a plurality of preset directions based on the boundary; A pixel selector which selects pixels to filter based on the selected direction; A filtering determiner configured to determine whether to filter the selected direction according to a relationship between pixel values between the selected pixels; A filtering unit that performs filtering on the selected pixels in the selected direction according to the determined filtering Adaptive deblocking filtering device comprising a. The method of claim 1, The filtering determiner may include an absolute value of a difference between pixel values between first pixels facing the boundary, and a second pixel and a first pixel on one side of the boundary based on the boundary. If the absolute value of the pixel value difference between the absolute value and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the boundary are respectively smaller than the preset thresholds, the selected direction is filtered. Adaptive deblocking filtering device, characterized in that determined by. The method of claim 2, And the filtering unit performs filtering by selecting one or more of a plurality of filtering directions according to the amount of change in pixel values between the selected pixels when the determined filtering directions are plural. The method of claim 1, The predetermined plurality of directions include 45 degrees, 90 degrees, and 135 degrees. The method of claim 1, The predetermined plurality of directions include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees and 135 degrees. A boundary strength determining step of determining the strength of a boundary between sub-blocks of the current block; A direction selection step of sequentially selecting one of a plurality of preset directions based on the boundary; Selecting a pixel to filter based on the selected direction; A filtering determination step of determining whether to filter in the selected direction according to the relationship of pixel values between the selected pixels; A filtering step of performing filtering on the selected pixels in the selected direction according to the determined filtering Adaptive deblocking filtering method comprising a. The method of claim 6, In the filtering determining step, the relationship between the pixel values between the selected pixels may include an absolute value of a difference between pixel values between the first pixels facing the boundary, and a second pixel and a first pixel on the one side of the boundary based on the boundary. Filtering the selected direction when the absolute value of the pixel value difference between the pixels and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the boundary are smaller than preset thresholds, respectively Adaptive deblocking filtering method, characterized in that determined in the direction. The method of claim 7, wherein The filtering step, if the determined filtering direction is a plurality, adaptive deblocking filtering method characterized in that to perform filtering by selecting one or more of the plurality of filtering directions according to the amount of change in the pixel value between the selected pixels. The method of claim 6, The predetermined plurality of directions include 45 degrees, 90 degrees, and 135 degrees. The method of claim 6, The predetermined plurality of directions include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees and 135 degrees. A prediction unit for predicting a current block of an image and generating a prediction block; A subtraction unit for generating a residual block by subtracting the prediction block from the current block; A transformer for converting the residual block into a frequency domain; A quantizer for quantizing the transformed residual block; An encoder which encodes the quantized residual block; An inverse quantizer for inversely quantizing the residual block; An inverse transform unit for inversely transforming the inverse quantized residual block into a residual block having a pixel signal on a time axis; An adder configured to add the prediction block to the inverse transformed residual block to restore a current block; Deblocking and filtering the reconstructed current block, selecting pixels to be filtered for a plurality of preset directions based on the boundary of the reconstructed current block, and filtering for the corresponding direction according to the relationship of pixel values between the selected pixels. A deblocking filter unit configured to determine whether or not to filter the selected pixels in the corresponding direction according to the determined filtering Video encoding apparatus comprising a. The method of claim 11, The deblocking filter may include an absolute value of a pixel value difference between first pixels facing the boundary with respect to the pixel value between the selected pixels, and a second pixel and a first pixel on one side based on the boundary. Filtering the corresponding direction when the absolute value of the pixel value difference between the pixels and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the boundary are smaller than preset thresholds, respectively. Video encoding apparatus, characterized in that determined in the direction. The method of claim 12, The deblocking filter is configured to perform filtering by selecting one or more of a plurality of filtering directions according to a change amount of pixel values between the selected pixels when the determined filtering directions are multiple. A decoder which extracts a residual block by decoding the bitstream; An inverse quantizer for inversely quantizing the residual block; An inverse transform unit for inversely transforming the inverse quantized residual block; A prediction unit for predicting a current block to generate a prediction block; An adder configured to add the inverse transformed residual block and the prediction block to restore the current block; And Deblocking and filtering the current block reconstructed by the adder, selecting pixels to be filtered in a plurality of preset directions based on the boundary of the current block, and selecting the pixels to be filtered in the corresponding direction according to the relationship of pixel values between the selected pixels. A deblocking filter unit configured to determine whether to perform filtering on the selected pixels and to perform filtering on the selected pixels in the corresponding direction according to the determined filtering. Video decoding apparatus comprising a. The method of claim 14, The deblocking filter unit may have a relationship between pixel values between the selected pixels, an absolute value of pixel value differences between first pixels facing the boundary, and a second pixel and a first pixel on one side based on the boundary. If the absolute value of the pixel value difference between the absolute value and the absolute value of the pixel value difference between the second pixel and the first pixel on the basis of the boundary are respectively smaller than preset thresholds, the corresponding direction is filtered. And a video decoding apparatus. The method of claim 15, The deblocking filter module, when the determined filtering directions are plural, selects one or more of the plurality of filtering directions according to the amount of change in the pixel value between the selected pixels to perform filtering. A boundary strength determination function for determining the strength of a boundary between sub-blocks of the current block; A direction selection function for sequentially selecting one of a plurality of preset directions based on the boundary; A pixel selection function for selecting pixels to be filtered based on the selected direction; A filtering determination function for determining whether to filter in the selected direction according to a relationship of pixel values between the selected pixels; A filtering function for performing filtering on the selected pixels in the selected direction according to the determined filtering And a computer readable recording medium having recorded thereon a program. The method of claim 17, The filtering determination function may include an absolute value of a difference of pixel values between first pixels facing the boundary, and a second pixel and a first pixel on one side of the boundary based on the boundary. If the absolute value of the pixel value difference between the pixels and the absolute value of the pixel value difference between the second pixel and the first pixel on the other side with respect to the boundary are respectively smaller than the preset thresholds, the selected direction is required. A computer-readable recording medium having a program recorded thereon, wherein the recording medium is determined in a turning direction. The method of claim 18, The filtering function may be configured to perform filtering by selecting one or more of the plurality of filtering directions according to the amount of change in pixel values between the selected pixels when the determined filtering directions are plural. Recording media. The method of claim 17, The preset plurality of directions include 45 degrees, 56.25 degrees, 67.5 degrees, 78.75 degrees, 90 degrees, 101.25 degrees, 112.5 degrees, 123.75 degrees, and 135 degrees. .

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