KR20180086135A - Image encoding method/apparatus, image decoding method/apparatus and recording medium for storing bitstream - Google Patents

Abstract

The present invention provides an image encoding method and an image decoding method. The image decoding method according to the present invention includes the steps of decoding information about a clipping range for a current block and performing sample adaptive offset (SAO) filtering based on the information about the clipping range. The information about the clipping range includes information about the maximum value and the minimum value of pixel values included in the current block. Accordingly, the present invention can improve compression efficiency.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method and apparatus, an image decoding method and apparatus, and a recording medium storing a bitstream.

The present invention relates to an image encoding / decoding method and apparatus. To an image encoding / decoding method and apparatus capable of improving compression efficiency by using a pixel range for an arbitrary image area.

In recent years, demand for multimedia data such as video has been rapidly increasing on the Internet. However, the rate at which the bandwidth of a channel develops is hard to follow the amount of multimedia data that is rapidly increasing. As part of this trend, Video Coding Expert Group (VCEG) of the International Organization for Standardization (ITU-T) and MPEG (Moving Picture Expert Group) of ISO / IEC are studying video compression standards through cooperative research.

An object of the present invention is to provide an image encoding / decoding method and apparatus capable of improving compression efficiency in image encoding / decoding.

It is another object of the present invention to provide an image encoding / decoding method and apparatus capable of improving compression efficiency by using a pixel range for an arbitrary image area in image encoding / decoding.

It is another object of the present invention to provide a computer-readable recording medium storing a bitstream generated by a video encoding method / apparatus according to the present invention.

The method of decoding an image according to the present invention includes the steps of decoding information on a clipping range for a current block and performing sample adaptive offset (SAO) filtering based on information on the clipping range And information on the clipping range may include information on a maximum value and a minimum value of pixel values included in the current block.

In the video decoding method according to the present invention, the information on the clipping range for the current block may be transmitted in units of the current block or an arbitrary region including the current block.

In the image decoding method according to the present invention, the arbitrary area unit may include at least one of a picture unit, a tile unit, and a slice unit.

In the image decoding method according to the present invention, the information on the maximum value and the minimum value may include information on one of the maximum value and the minimum value, and information on a difference between the maximum value and the minimum value.

In the image decoding method according to the present invention, when the SAO mode for the current block is a band offset (BO) mode, decoding an initial band point related to a start position of a band section to which the band offset is applied And decoding M offset information for a band interval to which the band offset is applied, wherein M may be determined based on the decoded initial band point and at least one of the minimum value and the maximum value .

The image decoding method according to the present invention may further comprise the step of classifying the interval between the maximum value and the minimum value into 32 bands when the SAO mode for the current block is a band offset mode, The initial band point for the starting position of the applicable band interval may be a point for the 32 reassociated bands.

A method of encoding an image according to the present invention includes the steps of: determining a clipping range for a current block; performing sample adaptive offset (SAO) filtering based on the clipping range; And the information on the clipping range may include information on a maximum value and a minimum value of pixel values included in the current block.

In the image encoding method according to the present invention, the information on the clipping range for the current block may be encoded in units of the current block or an arbitrary region including the current block.

In the image encoding method according to the present invention, the arbitrary area unit may include at least one of a picture unit, a tile unit, and a slice unit.

In the image encoding method according to the present invention, the information on the maximum value and the minimum value may include information on one of the maximum value and the minimum value, and information on the difference between the maximum value and the minimum value.

In the image coding method according to the present invention, when the SAO mode for the current block is a band offset (BO) mode, a step of determining an initial band point with respect to a start position of a band section to which the band offset is applied , Determining M offset information for a band interval to which the band offset is applied, and encoding the initial band point and M offset information, wherein M is a value obtained by multiplying the initial band point and the minimum value And the maximum value.

In the image encoding method according to the present invention, when the SAO mode for the current block is a band offset mode, the method further comprises re-segmenting the interval between the maximum value and the minimum value into 32 bands, The initial band point for the starting position of the applicable band interval may be a point for the 32 reassociated bands.

A video decoding apparatus according to the present invention includes: a decoding unit that decodes information on a clipping range of a current block; and a filtering unit that performs sample adaptive offset (SAO) filtering based on the information on the clipping range And the information on the clipping range may include information on the maximum value and the minimum value of the pixel values included in the current block.

An image encoding apparatus according to the present invention includes: an encoding unit that determines a clipping range for a current block and encodes information about the clipping range; and a sample adaptive offset (SAO) filtering And the information on the clipping range may include information on the maximum value and the minimum value of the pixel values included in the current block.

The computer-readable recording medium according to the present invention can store a bitstream generated by the image encoding method or the image encoding apparatus according to the present invention.

According to the present invention, an image encoding / decoding method and apparatus capable of improving compression efficiency can be provided.

Also, according to the present invention, an image encoding / decoding method and apparatus capable of improving compression efficiency by using a pixel range for an arbitrary image region can be provided.

Also, according to the present invention, there can be provided a video encoding method according to the present invention or a computer readable recording medium storing a bit stream generated by the video encoding apparatus.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.
3 is a diagram for explaining the EO (Edge Offset) mode.
4 is a diagram for explaining a BO (Band Offset) mode.
FIG. 5 is a diagram for explaining a method of encoding SAO information in the image encoding apparatus 100. FIG.
FIG. 6 is a diagram for explaining a method of decoding SAO information in the video decoding apparatus 200. FIG.
FIG. 7 is a diagram for explaining an available region clipping range and an available band of the BO mode.
FIG. 8 is a diagram showing the usable band sections of the BO mode subdivided into 32 band sections again.
FIG. 9 is a diagram for explaining a method of correcting coefficients of residual blocks using a clipping range in an arbitrary area unit. FIG.
10 is a diagram for explaining a method of coding clipping information in units of pictures.
11 is a diagram for explaining a method of decoding clipping information on a picture-by-picture basis.
12 is a diagram for explaining a method of encoding clipping information in units of blocks.
13 is a diagram for explaining a method of decoding clipping information in units of blocks.
14 is a diagram for explaining a method of encoding SAO information based on a clipping range according to an embodiment of the present invention.
15 is a diagram for explaining a method of decoding SAO information based on a clipping range according to an embodiment of the present invention.
16 is a diagram for explaining a process of performing DMVD (Decoder-Side Motion Vector Derivation) based on a clipping range according to another embodiment of the present invention.
17 is a diagram for explaining a process of performing deblocking filtering based on a clipping range according to another embodiment of the present invention.

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

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

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

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

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

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

1, an image encoding apparatus 100 includes an image division unit 101, an intra-frame prediction unit 102, an inter-frame prediction unit 103, a subtraction unit 104, a conversion unit 105, An entropy encoding unit 107, an inverse quantization unit 108, an inverse transformation unit 109, an addition unit 110, a filter unit 111, and a memory 112. [

Each of the components shown in FIG. 1 is shown independently to represent different characteristic functions in the image encoding apparatus, and does not mean that each component is composed of separate hardware or one software configuration unit. 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.

In addition, some of the components are not essential components to perform essential functions in the present invention, but may be optional components only to improve performance. The present invention can be implemented only with components essential for realizing the essence of the present invention, except for the components used for the performance improvement, and can be implemented by only including the essential components except the optional components used for performance improvement Are also included in the scope of the present invention.

The image divider 100 may divide the input image into at least one block. At this time, the input image may have various shapes and sizes such as a picture, a slice, a tile, and a segment. A block may mean a coding unit (CU), a prediction unit (PU), or a conversion unit (TU). The partitioning may be performed based on at least one of a quadtree or a binary tree. The quad tree is a method of dividing the upper block into sub-blocks whose width and height are half of the upper block. A binary tree is a method of dividing an upper block into sub-blocks, either width or height, which is half of the upper block. Through the binary tree-based partitioning described above, a block can have a square as well as a non-square shape.

Hereinafter, in the embodiment of the present invention, a coding unit may be used as a unit for performing coding, or may be used as a unit for performing decoding.

The predicting units 102 and 103 may include an inter-picture predicting unit 103 for performing inter-prediction and an intra-picture predicting unit 102 for performing intra-prediction. It is possible to determine whether to use inter prediction or intra prediction for a prediction unit and to determine concrete information (e.g., intra prediction mode, motion vector, reference picture, etc.) according to each prediction method. At this time, the processing unit in which the prediction is performed may be different from the processing unit in which the prediction method and the concrete contents are determined. For example, the method of prediction, the prediction mode and the like are determined as a prediction unit, and the execution of the prediction may be performed in a conversion unit.

The residual value (residual block) between the generated prediction block and the original block can be input to the conversion unit 105. In addition, the prediction mode information, motion vector information, and the like used for prediction can be encoded by the entropy encoding unit 107 and transmitted to the decoder along with the residual value. When a specific encoding mode is used, it is also possible to encode the original block as it is without generating a prediction block through the predicting units 102 and 103, and to transmit it to the decoding unit.

The intra prediction unit 102 can generate a prediction block based on reference pixel information around the current block which is pixel information in the current picture. If the prediction mode of the neighboring block of the current block in which intra prediction is to be performed is inter prediction, a reference pixel included in a neighboring block to which inter prediction is applied may be replaced with a reference pixel in another neighboring block to which intra prediction is applied. That is, when the reference pixel is not available, the reference pixel information that is not available may be replaced with at least one reference pixel of the available reference pixels.

In intra prediction, the prediction mode may have a directional prediction mode in which reference pixel information is used according to a prediction direction, and a non-directional mode in which direction information is not used in prediction. The mode for predicting the luminance information may be different from the mode for predicting the chrominance information and the intra prediction mode information or predicted luminance signal information used for predicting the luminance information may be utilized to predict the chrominance information.

The intra prediction unit 102 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a filter that performs filtering on the reference pixels of the current block and can adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter may not be applied.

When the intra prediction mode of the intra prediction unit 102 is a prediction unit that performs intra prediction on the basis of the pixel value obtained by interpolating the reference pixel, the reference pixel interpolator 102 interpolates the reference pixel, Lt; / RTI > The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates the prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

A residual block including residue information that is a difference value between the prediction unit generated by the prediction units 102 and 103 and the original block of the prediction unit can be generated. The generated residual block may be input to the conversion unit 130 and converted.

The inter-picture predicting unit 103 may predict a prediction unit based on information of at least one picture of a previous picture or a following picture of the current picture, and may predict a prediction unit based on information of a partially coded area in the current picture The prediction unit may also be predicted. The inter-picture predicting unit 103 may include a reference picture interpolating unit, a motion predicting unit, and a motion compensating unit.

In the reference picture interpolating unit, reference picture information is supplied from the memory 112 and pixel information of an integer pixel or less can be generated in the reference picture. In the case of a luminance pixel, a DCT-based interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of quarter pixels. In the case of a color difference signal, a DCT-based 4-tap interpolation filter having a different filter coefficient may be used to generate pixel information of an integer number of pixels or less in units of 1/8 pixel.

The motion prediction unit may perform motion prediction based on the reference picture interpolated by the reference picture interpolating unit. Various methods such as Full Search-based Block Matching Algorithm (FBMA), Three Step Search (TSS), and New Three-Step Search Algorithm (NTS) can be used as methods for calculating motion vectors. The motion vector may have a motion vector value of 1/2 or 1/4 pixel unit based on the interpolated pixel. The motion prediction unit can predict the current prediction unit by making the motion prediction method different. Various methods such as a skip method, a merge method, and an AMVP (Advanced Motion Vector Prediction) method can be used as the motion prediction method. The subtracting unit 104 subtracts the current block to be encoded from the intra prediction unit 102 or the inter prediction unit 103 to generate a residual block of the current block.

The transforming unit 105 can transform the residual block, which is a difference between the original block and the prediction block, to generate a transform block. The transform block may be the smallest unit in which the transform and quantization process is performed. The conversion unit 105 may convert the residual signal into the frequency domain and generate a transform block including the transform coefficient. A transform method such as DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), KLT (Karhunen Loeve Transform) and the like can be used to transform the residual block including the residual data into the frequency domain. The transform coefficients can be generated by transforming the residual signal into the frequency domain using the transform method. Matrix operations using a basis vector may be performed to facilitate the transformation. It is possible to use a variety of conversion methods in a matrix operation depending on which prediction mode the prediction block is encoded. For example, the transform method may be determined based on the intra prediction mode of the prediction unit used to generate the residual block. For example, depending on the intra prediction mode, DCT may be used in the horizontal direction, and DST may be used in the vertical direction.

The quantization unit 106 may quantize the values converted into the frequency domain by the conversion unit 105. That is, the quantization unit 106 may quantize the transform coefficients of the transform block generated from the transform unit 105 to generate a quantized transform coefficient having a quantized transform coefficient. As the quantization method, Dead Zone Uniform Threshold Quantization (DZUTQ) or a Quantization Weighted Matrix may be used. Or various quantization methods such as an improved quantization method can be used. The quantization factor may vary depending on the block or the importance of the image. The values calculated by the quantization unit 106 may be provided to the inverse quantization unit 108 and the entropy coding unit 107. [

The transforming unit 105 and / or the quantizing unit 106 may be selectively included in the image encoding apparatus 100. That is, the image encoding apparatus 100 can perform at least one of conversion or quantization on the residual data of the residual block, or may skip both the conversion and the quantization, thereby encoding the residual block. A block entering the input of the entropy encoding unit 107 is generally referred to as a transform block even though either the transform or the quantization is not performed in the image coding apparatus 100 or both the transform and the quantization are not performed.

The entropy coding unit 107 entropy-codes the input data. The entropy encoding unit 107 may encode the quantized transform block and output a bit stream. That is, the entropy encoding unit 107 may encode the quantized transform coefficients of the quantized transform block output from the quantization unit 106 using various encoding techniques such as entropy encoding. Further, the entropy encoding unit 107 can encode additional information (e.g., information on a prediction mode, a quantization coefficient, and the like) necessary for decoding the corresponding block in a video decoding apparatus described later. For entropy encoding, various encoding methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be used.

The entropy encoding unit 107 receives the residual value coefficient information of the encoding unit and the block type information, the prediction mode information, the division unit information, the prediction unit information, the transmission unit information, the motion vector information, the reference frame information , Block interpolation information, filtering information, and the like. In the entropy encoding unit 107, the coefficient of the transform block is encoded in units of partial blocks in the transform block by encoding a non-zero coefficient, a coefficient having an absolute value of 1 or larger than 2, . The coefficient that is not encoded with only the flag can be encoded through the absolute value of the difference between the coefficient encoded through the flag and the coefficient of the actual conversion block. The inverse quantization unit 108 and the inverse transformation unit 109 dequantize the quantized values in the quantization unit 106 and inversely transform the values converted in the conversion unit 105. The residual value generated in the inverse quantization unit 108 and the inverse transformation unit 109 is predicted through the motion estimation unit, the motion compensation unit and the intra prediction unit 102 included in the prediction units 102 and 103 A reconstructed block can be created by combining with prediction units. The addition unit 110 adds the residual blocks generated through the inverse transform unit 109 to the prediction blocks generated by the prediction units 102 and 103 to generate reconstruction blocks.

The filter unit 111 may include at least one of a deblocking filter, an offset correction unit, and an Adaptive Loop Filter (ALF).

The deblocking filter can remove block distortion caused by the boundary between the blocks in the reconstructed picture. It may be determined whether to apply a deblocking filter to the current block based on pixels included in a few columns or rows included in the block to determine whether to perform deblocking. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied according to the deblocking filtering strength required. In applying the deblocking filter, horizontal filtering and vertical filtering may be performed concurrently in performing vertical filtering and horizontal filtering.

The offset correction unit may correct the offset of the deblocked image with respect to the original image in units of pixels. In order to perform offset correction for a specific picture, a method of dividing a pixel included in an image into a predetermined number of regions and determining an area to be offset and applying an offset to the corresponding area (band offset mode, BO mode) A method of applying an offset in consideration of edge information of a pixel (edge offset mode, EO mode) can be used.

Adaptive Loop Filtering (ALF) can be performed based on a comparison between the filtered reconstructed image and the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and different filtering may be performed for each group. The information related to whether to apply the ALF may be transmitted for each coding unit (CU), and the shape and the filter coefficient of the ALF filter to be applied may be changed according to each block. Also, an ALF filter of the same type (fixed form) may be applied irrespective of the characteristics of the application target block.

The memory 112 may store the reconstructed block or picture calculated through the filter unit 111 and the reconstructed block or picture stored therein may be provided to the predictor 102 or 103 when the inter prediction is performed.

The intra-picture prediction unit 102 and the inter-picture prediction unit 103 may collectively be referred to as a prediction unit. The prediction unit can generate a prediction block using the neighboring pixels of the current block or a reference picture that has been already decoded. The prediction block may generate one or more prediction blocks in the current block. If there is only one intra-block prediction block, the prediction block may have the same shape as the current block. When the prediction block is generated, a residual block corresponding to the difference between the current block and the prediction block can be generated. By applying various techniques such as Rate-Distortion Optimization (RDO) to the generated residual block, the optimal prediction mode can be determined. For example, the following equation 1 can be used for the calculation of RDO.

In Equation (1), D (), R () and J () denote the deterioration by quantization, the rate of the compressed stream and the RD cost, respectively. Denotes a coding mode. lambda is a Lagrangian multiplier and is used as a scale correction coefficient for matching the unit of error amount and bit amount. In order to select the optimum encoding mode in the encoding process, the J (), that is, the RD cost when the corresponding mode is applied, must be smaller than that when the other modes are applied. Bit rate and error can be considered simultaneously when calculating the RD cost.

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

2, the image decoding apparatus 200 includes an entropy decoding unit 201, an inverse quantization unit 202, an inverse transformation unit 203, an addition unit 204, a filter unit 205, a memory 206, Prediction units 207 and 208, as shown in FIG.

When an image bitstream generated by the image encoding apparatus 100 is input to the image decoding apparatus 200, the input bitstream may be decoded according to a process opposite to that performed by the image encoding apparatus 100 .

The entropy decoding unit 201 can perform entropy decoding in a procedure opposite to that in which the entropy encoding unit 107 of the image encoding apparatus 100 performs entropy encoding. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied in accordance with the method performed by the image encoder. In the entropy decoding unit 201, the coefficient of the transform block is based on a non-zero coefficient, a coefficient having an absolute value of 1 or larger than 2, and various kinds of flags indicating the sign of a coefficient, etc., Lt; / RTI > A coefficient not represented by only the flag can be decoded through a sum of a coefficient represented by a flag and a signaled coefficient.

The entropy decoding unit 201 may decode information related to the intra prediction and the inter prediction performed in the encoder.

The inverse quantization unit 202 performs inverse quantization on the quantized transform block to generate a transform block. And operates substantially the same as the inverse quantization unit 108 of FIG.

The inverse transform unit 203 performs inverse transform on the transform block to generate a residual block. At this time, the conversion method can be determined on the basis of the prediction method (inter or intra prediction), the size and / or type of the block, the intra prediction mode, and the like. And operates substantially the same as the inverse conversion unit 109 of Fig.

The adding unit 204 adds the residual block generated through the inverse transform unit 203 and the prediction block generated by the intra prediction unit 207 or the inter prediction unit 208 to generate a reconstruction block. And operates substantially the same as the adder 110 of Fig.

The filter unit 205 reduces various types of noise occurring in the reconstructed blocks.

The filter unit 205 may include a deblocking filter, an offset correction unit, and an ALF.

When information on whether or not a deblocking filter has been applied to the corresponding block or picture from the image encoding apparatus 100 and a deblocking filter are applied, information on whether a strong filter or a weak filter is applied can be provided. In the deblocking filter of the image decoding apparatus 200, deblocking filter related information provided by the image encoding apparatus 100 may be provided, and the image decoding apparatus 200 may perform deblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction applied to the image and the offset value information during encoding.

The ALF may be applied to an encoding unit based on ALF application information, ALF coefficient information, and the like provided from the image encoding apparatus 100. Such ALF information may be provided in a specific set of parameters. The filter unit 205 operates substantially the same as the filter unit 111 of FIG.

The memory 206 stores the restoration block generated by the adder 204. [ And operates substantially the same as the memory 112 of Fig.

The prediction units 207 and 208 may generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit 201 and the previously decoded block or picture information provided in the memory 206. [

The prediction units 207 and 208 may include an intra prediction unit 207 and an inter prediction unit 208. [ Although not shown separately, the prediction units 207 and 208 may further include a prediction unit determination unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 201, prediction mode information of the intra prediction method, motion prediction related information of the inter prediction method, and identifies prediction units in the current coding unit, It is possible to determine whether the unit performs inter prediction or intra prediction. The inter picture prediction unit 208 uses the information necessary for inter prediction of the current prediction unit provided by the image encoding apparatus 100 to generate information about the current picture including the current prediction unit or information included in at least one of the following pictures The inter prediction of the current prediction unit can be performed. Alternatively, the inter prediction may be performed on the basis of the information of the partial region previously reconstructed in the current picture including the current prediction unit.

In order to perform the inter-picture prediction, whether the motion prediction method of the prediction unit included in the coding unit based on the coding unit is a skip mode, a merge mode, or an AMVP mode Can be determined.

Intra prediction unit 207 generates a prediction block using pixels that are located around the block to be currently coded and which are previously reconstructed.

The intra prediction unit 207 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a filter that performs filtering on the reference pixels of the current block and can adaptively determine whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering can be performed on the reference pixels of the current block using the prediction mode of the prediction unit and the AIS filter information provided by the image coding apparatus 100. [ When the prediction mode of the current block is a mode in which AIS filtering is not performed, the AIS filter may not be applied.

The intra-picture prediction unit 207 interpolates the reference pixels to interpolate the reference pixels in the unit of the fractional unit when the prediction mode of the prediction unit 207 is a prediction unit performing intra-prediction based on the pixel value obtained by interpolating the reference pixels Can be generated. The reference pixel at the generated fractional unit position can be used as the predictive pixel of the pixel in the current block. The reference pixel may not be interpolated in the prediction mode in which the prediction mode of the current prediction unit generates the prediction block without interpolating the reference pixel. The DC filter can generate a prediction block through filtering when the prediction mode of the current block is the DC mode.

The intra prediction unit 207 operates substantially the same as the intra prediction unit 102 of FIG.

The inter-picture prediction unit 208 generates inter-prediction blocks using the reference pictures and the motion information stored in the memory 206. [ The inter-picture predicting unit 208 operates substantially the same as the inter-picture predicting unit 103 of Fig.

Referring to Figures 3 and 4, sample adaptive offset (SAO) compensation filtering is described.

3 is a diagram for explaining the EO mode.

As shown in the upper box 301 of FIG. 3, the boundary direction between adjacent pixels around the current pixel can be classified into one of four directions information of 0, 45, 90, and 135 degrees. Also, based on the difference in pixel values between the current pixel and the adjacent pixels, it can be classified into one of four categories (categories) as shown in the lower box 302 in Fig. The pixel index x-1 in each category of the lower box 302 in Fig. 3 means the surrounding pixel 1 in each direction of the upper box 301. [ Similarly, the pixel index x means the current pixel, and the pixel index x + 1 means the surrounding pixel 2. The sign of the offset to be applied to the current pixel in each category is predetermined. For example, the sign of the offsets of category 1 and category 2 is plus (+), and the sign of the offsets of category 3 and category 4 is minus (-).

Filtering can be performed by finding the shape of the optimum direction among the four direction information for each pixel and the shape depending on the difference of the pixel value with neighboring pixels among the four categories and adding the offset value within the corresponding category. If the shape according to the difference of the pixel value between the current pixel and the surrounding pixels does not fall within the four categories shown in FIG. 3, filtering may not be performed on the current pixel.

4 is a diagram for explaining the BO mode.

In the BO mode, a range of pixels (for example, a pixel range of 0 to 255 in the case of an 8-bit image) is divided into 32 bands according to the bit depth of the input image, and four consecutive bands do. If the current pixel value belongs to four consecutive bands, the filtering can be performed by adding the offset value for the band to the current pixel value.

In the example shown in FIG. 4, the pixel range according to the bit depth of the input image is divided into 32 bands, and the bands 10 through 13 are determined as the band offset target. If the pixel value of the current pixel belongs to one of the bands 10 to 13, the filtering can be performed by adding the offset value for the band to the pixel value of the current pixel.

FIG. 5 is a diagram for explaining a method of encoding SAO information in the image encoding apparatus 100. FIG.

In step S501, information (SAO merge information) about whether to use the SAO information of the left coded block and / or the upper coded block is used as a reference based on a coding block (current block) on which SAO is performed. First, the SAO Merge_ left information is encoded. If the information is true, the SAO Merge top information is not encoded, and the process moves to step S502. If the SAO Merge_type left information is false, the SAO Merge_type top information is encoded and the process moves to step S502.

In step S502, it is determined whether the SAO Merge_left information and the SAO Merge_top information are both false or not. If both pieces of information are both false, the process proceeds to step S503. If any of the two pieces of information is true, the process ends.

In step S503, the information CIdx is set to an initial value of zero. If CIdx is 0, it means a luminance (Luma) component. If CIdx is 1, it means a chroma Cb component and when CIdx is 2, it means a chrominance chromium component. In step S503, it is determined whether CIdx is 0 or not. If the CIdx is 0, the process proceeds to step S504. Otherwise, the process proceeds to step S505.

In step S504, the SAO mode information of the luma component is encoded. The SAO mode information may be information on which mode of the EO mode, the BO mode, and the SAO non-operation mode is to be performed for the current block.

In step S505, it is determined whether the CIdx is 1 or not. If the CIdx is 1, the process proceeds to step S506. Otherwise, the process is terminated.

In step S506, the SAO mode information of the chroma component is encoded. The SAO mode information may be information on which mode of the EO mode, the BO mode, and the SAO non-operation mode is to be performed for the current block. Here, both the Cb and Cr components of the chroma component can share the same SAO mode information.

In step S507, if the SAO mode for the current block is the SAO non-operation mode, the process moves to step S516. If the SAO mode for the current block is the BO mode or the EO mode, the process moves to step S508.

In step S508, four pieces of offset absolute value information are encoded. In the case of the EO mode, the four offsets represent the offsets for each category, and in the case of the BO mode, the four offsets represent the offsets of four consecutive bands.

In step S509, it is determined whether the SAO mode for the current block is the BO mode. If the SA mode is not the BO mode, the process proceeds to step S512.

In step S510, the sign (sign) information of the four offsets of the BO mode is encoded.

In step S511, an initial band point indicating which band section the four consecutive band sections of the BO mode starts is encoded.

In step S512, it is determined whether CIdx is 0 or not. If it is 0, the process proceeds to step S513. Otherwise, the process proceeds to step S514.

In step S513, direction information of the EO mode of the luma component is encoded.

In step S514, it is determined whether the CIdx is 1 or not. If the CIdx is not 1, the procedure is terminated. If the CIdx is 1, the process proceeds to step S515.

In step S515, direction information of the EO mode of the chroma component is encoded. Here, both the Cb and Cr components of the chroma component share the same directional information.

In step S516, the current CIdx value is incremented by one, and the process proceeds to step S503, and the above-described process is repeated.

FIG. 6 is a diagram for explaining a method of decoding SAO information in the video decoding apparatus 200. FIG.

In step S601, the SAO Merge information encoded in step S501 of FIG. 5 is decoded.

In step S602, it is determined whether the SAO Merge_top and the SAO Merge_left information are both false or not. If both pieces of information are both false, the process goes to step S603, and if any one of them is true, the process ends.

In step S603, the CIdx value is initialized to 0, and it is determined whether the corresponding CIdx value is 0 or not. If the CIdx value is 0, the process proceeds to step S604. If the CIdx value is not 0, the process proceeds to step S605.

In step S604, the SAO mode information of the luma component encoded in step S504 of FIG. 5 is decoded.

In step S605, it is determined whether the CIdx is 1 or not. If the CIdx is 1, the process proceeds to step S606. Otherwise, the process is terminated.

In step S606, the SAO mode information of the chroma component encoded in step S506 of FIG. 5 is decoded. Here, both the Cb and Cr components of the chroma component can share the same SAO mode information.

In step S607, if the SAO mode for the current block is the SAO non-operation mode, the process moves to step S616. If the SAO mode for the current block is the BO mode or the EO mode, the process moves to step S608.

In step S608, the four offset absolute value information encoded in step S508 of FIG. 5 is decoded.

In step S609, it is determined whether the SAO mode for the current block is the BO mode. If the SAO mode for the current block is the BO mode, the process proceeds to step S610. Otherwise, the process proceeds to step S612.

In step S610, the sign (sign) information of the four offsets of the BO mode encoded in step S510 of FIG. 5 is decoded.

In step S611, an initial band point indicating which band section the consecutive four band sections of the BO mode encoded in step S511 of FIG. 5 starts is decoded.

In step S612, it is determined whether CIdx is 0 or not. If CIdx is 0, the process proceeds to step S613. Otherwise, the process proceeds to step S614.

In step S613, the direction information of the EO mode of the luma component encoded in step S513 of FIG. 5 is decoded.

In step S614, it is determined whether the CIdx is 1 or not. If the CIdx is not 1, the procedure is terminated. If the CIdx is 1, the process proceeds to step S615.

In step S615, the direction information of the EO mode of the chroma component encoded in step S515 of FIG. 5 is decoded. Here, both Cb and Cr components of the chroma component can share the same directional information.

In step S616, the current CIdx value is incremented by one, and the process moves to step S603, and the above-described process is repeated.

In the following description, it is assumed that the bit depth of the input image is 8 bits.

FIG. 7 is a diagram for explaining an available region clipping range and an available band of the BO mode.

The clipping range can be determined by searching the maximum value and the minimum value of the original pixels in an arbitrary area unit such as a picture, a tile, a slice, or a block unit. The clipping range can be applied to the band section of the BO mode of SAO.

7, the minimum pixel value point is 0 and the maximum pixel value point is 255 for an input image having an 8-bit depth. It is possible to scan the original pixel values in the corresponding area and then determine the maximum value and the minimum value of the pixel values included in the corresponding area. As shown in Fig. 7 (a), the maximum value of the pixel value within an arbitrary region becomes the clipping maximum value, and the minimum value becomes the clipping minimum value.

The clipping process may be performed after passing through the predicting units 102 and 103 in the image encoding apparatus 100 and then through the adder 110 and / or the filter unit 111. [ In the video decoding apparatus 200, the clipping process may be performed after passing through the prediction units 207 and 208, after the addition unit 204, and / or after passing through the filter unit 205. [

In the above-described SAO BO mode, the entire pixel period (0 to 255) is divided into 32 bands, and offset information of four consecutive bands to be filtered is used. At this time, if the clipping range is smaller than the entire pixel range, filtering can be performed considering only the bands within the clipping range.

FIG. 7 (b) shows the entire pixel period divided into 32 bands, and bands subjected to light and dark processing correspond to the clipping range of the current region, and represent the band periods in which the BO mode can be applied.

In FIG. 7B, since there are no pixels in the current area belonging to the bands 1 to 8 and 27 to 32, the bands may not be considered as bands in the SAO BO mode. Also, when the maximum value and the minimum value within the clipping range are the same, the image may be restored to the same value without going through all the processes described with reference to FIG. 1 and FIG. If the difference between the maximum value and the minimum value within the clipping range is less than N (N is an integer equal to or greater than 0), any information such as the clipping maximum value and the average value of the minimum value, To restore the image. Here, the corresponding N value can be transmitted in the header of the upper level of the current area. If the available band interval of the SAO BO mode is less than four, the number of transmitted offset values may be less than four.

FIG. 8 is a diagram showing the usable band sections of the BO mode subdivided into 32 band sections again.

As shown in Fig. 8 (a), when the band of the BO mode corresponding to the clipping range in an arbitrary region is band 9 to band 26, as shown in Fig. 8 (b) The band 9 to the band 26) can be further divided into 32 band sections.

As shown in FIG. 8B, when encoding / decoding is performed by dividing an available band section into 32 band sections, the SAO information encoding and decoding algorithm described with reference to FIGS. 5 and 6 can be used equally . In this case, since the range of one band can be further subdivided, more precise band offset filtering can be realized.

FIG. 9 is a diagram for explaining a method of correcting coefficients of residual blocks using a clipping range in an arbitrary area unit. FIG. The correction of the coefficients of the residual block described with reference to FIG. 9 may be performed on an arbitrary area basis or may not be performed.

9, the numbers displayed in the inner grid of the original block 901, the prediction block 902, the residual block 903, and the final residual block 904 indicate pixel values of the corresponding pixels. A residual block 903 is generated by subtracting the pixel value of the prediction block 902 from the pixel value of the original block 910. [ The residual block 904 is generated by correcting the residual block 903.

Assuming that the minimum value of the pixel values in an arbitrary area including the original block 901 or the original block 901 is 50 and the maximum value is 100, the clipping range of the original block 901 is 50 to 100. A pixel subjected to light-dark processing in the original block 901 means a pixel having a maximum value or a minimum value of the current clipping range.

The residual coefficient correction for the residual block 903 may be performed on the lightened pixels of the residual block 903 corresponding to the positions of the lightened pixels of the original block 901. [ Specifically, an average value (-2 in Fig. 9) of the pixel values of the residual pixels which have not undergone the light and dark processing of the residual block 903 is calculated. Thereafter, the pixels subjected to light and dark processing in the residual block 903 are replaced with the calculated average value. Through this process, a final residual block 904 can be generated. Other statistical values such as maximum value, minimum value, intermediate value, mode value, and weighted average value may be used instead of the average value used for residual coefficient correction.

10 is a diagram for explaining a method of coding clipping information in units of pictures.

In step S1001, the maximum value and the minimum value of the in-picture pixel values are searched for each local picture unit. In step S1002, the maximum value and the minimum value are encoded. The maximum and minimum values can be directly encoded. Alternatively, after encoding the minimum value, the difference value between the maximum value and the minimum value may be encoded. Alternatively, after coding the maximum value, the difference value between the maximum value and the minimum value may be encoded. At this time, the encoding information for the maximum value and the minimum value may be transmitted in the picture layer, the slice layer, or the like. The picture unit may be changed in an arbitrary area unit. The arbitrary area may be a slice, a tile, a CTU, a CU, or the like.

11 is a diagram for explaining a method of decoding clipping information on a picture-by-picture basis. In step S1101, information on the maximum and minimum values of the current picture can be decoded. Information on the maximum value and the minimum value may be included in the transmission unit transmitted from the image encoding apparatus 100. The transmission unit may be a picture layer or a slice layer. Information on the maximum value and the minimum value may be encoded and transmitted as described with reference to FIG. The picture unit may be changed in an arbitrary area unit. The arbitrary area may be a slice, a tile, a CTU, a CU, or the like.

12 is a diagram for explaining a method of encoding clipping information in units of blocks. In step S1201, the intra-block maximum value and the minimum pixel value are searched for each current block unit. In step S1202, the maximum value and the minimum value are encoded. The maximum and minimum values can be directly encoded. Alternatively, after encoding the minimum value, the difference value between the maximum value and the minimum value may be encoded. Alternatively, after coding the maximum value, the difference value between the maximum value and the minimum value may be encoded. At this time, the encoding information for the maximum value and the minimum value can be transmitted in block units. The block unit may be, for example, any encoding block unit or a prediction block unit.

13 is a diagram for explaining a method of decoding clipping information in units of blocks. In step S1301, information on the maximum value and the minimum value of the current block can be decoded. Information on the maximum value and the minimum value may be included in the transmission unit transmitted from the image encoding apparatus 100. The transmission unit may be an arbitrary encoding block unit or a prediction block unit. Information on the maximum value and the minimum value may be encoded and transmitted as described with reference to FIG.

14 is a diagram for explaining a method of encoding SAO information based on a clipping range according to an embodiment of the present invention.

The description of steps S1401 to S1406 is the same as the description of steps S501 to S506 of Fig.

In step S1407, if the SAO mode for the current block is the SAO non-operation mode, the process moves to step S1417. If the SA mode is one of the BO mode and the EO mode for the current block, the process moves to step S1408.

 In step S1408, it is determined whether or not the SAO mode for the current block is the BO mode. If the SA mode is the BO mode, the process proceeds to step S1409. Otherwise, the process proceeds to step S1412.

In step S1409, an initial band point indicating which band section the consecutive band section of the BO mode starts is encoded.

In step S1410, M offset absolute value information for the BO mode is encoded. As described above, the available band interval of the BO mode can also be changed according to the clipping range. Accordingly, the number of offsets to be transmitted may vary depending on the initial band point. Alternatively, the number of offsets to be transmitted may vary depending on the number of available bands. The M means the number of offsets to be transmitted, which may vary depending on the clipping range. For example, in the example shown in FIG. 7, if the initial band point is the 25th band, since the available bands are the 25th band and the 26th band, only the offset value can be transmitted.

In step S1411, the sign information of the offsets is encoded by the number M of offsets transmitted in step S1410.

In step S1412, it is determined whether CIdx is 0 or not. If it is 0, the process proceeds to step S1413. Otherwise, the process proceeds to step S1415.

In step S1413, four pieces of offset absolute value information used in the EO mode are encoded.

In step S1414, direction information of the EO mode of the luma component is encoded.

In step S1415, it is determined whether the CIdx is 1 or not. If the CIdx is not 1, the procedure is terminated. If the CIdx is 1, the process proceeds to step S1416.

In step S1416, direction information of the EO mode of the chroma component is encoded. Here, both Cb and Cr components of the chroma component can share the same directional information.

In step S1417, the value of CIdx is incremented by one, and the process moves to step S1403 to repeat the above-described process.

15 is a diagram for explaining a method of decoding SAO information based on a clipping range according to an embodiment of the present invention.

The description of steps S1501 to S1506 is the same as the description of steps S601 to S606 in Fig.

In step S1507, if the SAO mode for the current block is the SAO non-operation mode, the process moves to step S1517. If the SAO mode for the current block is the BO mode or the EO mode, the process moves to step S1508.

In step S1508, it is determined whether or not the SAO mode for the current block is the BO mode. If the SA mode is the BO mode, the process proceeds to step S1509. Otherwise, the process proceeds to step S1512.

In step S1509, the initial band point of the BO mode encoded in step S1409 of FIG. 14 is decoded.

In step S1510, M offset absolute value information for the BO mode encoded in step S1410 of FIG. 14 is decoded.

In step 1511, M pieces of offset code information encoded in step S1411 of FIG. 14 are decoded.

In step S1512, it is determined whether CIdx is 0 or not. If it is 0, the process proceeds to step S1513. Otherwise, the process proceeds to step S1515.

In step S1513, the four offset absolute value information used in the EO mode encoded in step S1413 of FIG. 14 is decoded.

In step S1514, the direction information of the EO mode of the luma component encoded in step S1414 of FIG. 14 is decoded.

In step S1515, it is determined whether the CIdx is 1 or not. If the CIdx is not 1, the procedure is terminated. If the CIdx is 1, the process proceeds to step S1516.

In step S1516, direction information of the EO mode of the chroma component is decoded. Here, both Cb and Cr components of the chroma component can share the same directional information.

In step S1517, the value of CIdx is incremented by one, and the process moves to step S1503, and the above-described process is repeated.

16 is a diagram for explaining a process of performing DMVD (Decoder-Side Motion Vector Derivation) based on a clipping range according to another embodiment of the present invention.

Generally, an image encoding apparatus encodes information on a motion vector, and encodes the information into a bit stream and transmits the encoded image to a video decoding apparatus. The video decoding apparatus can recover a motion vector by decoding a bitstream. In the case of DMVD, instead of explicitly encoding the information on the motion vector in the bitstream, the image decoding apparatus can derive information on the motion vector using a predetermined algorithm. For example, the predetermined algorithm may be a template matching algorithm.

According to the present invention, the image decoding apparatus can perform DMVD based on clipping characteristics. For example, DMVD can be efficiently performed by identifying the reference picture area having the same or similar clipping characteristics as the current block or the area to which the current block belongs. The clipping property may mean, but is not limited to, a clipping range and may include various information regarding clipping derived from the clipping range.

More specifically, in order to perform the DMVD, it is necessary to determine an initial motion vector, and clipping characteristics can be considered in initial motion vector determination. In the example shown in FIG. 16, when the clipping property of the current block is B, regions of the reference picture in which the clipping property is B are identified, and an initial motion vector (first or second initial motion Vector) can be determined.

Since similar blocks have similar clipping characteristics, according to the present invention, an optimal initial motion vector can be determined with a very high probability. Therefore, according to the present invention, the complexity of motion estimation of the image decoding apparatus performing DMVD can be remarkably reduced.

According to another embodiment of the present invention, the entropy encoding efficiency of the syntax element can be improved by using the clipping characteristic for entropy encoding and / or decoding. Specifically, the initial probability of a predetermined syntax element can be adaptively selected in consideration of clipping characteristics of an arbitrary video region.

For example, when the clipping range of the encoded block is wide, that is, when the difference between the maximum value and the minimum value is large, the prediction accuracy of the encoded block is relatively low. If the prediction accuracy is relatively low, the probability that the residual block includes a non-zero transform coefficient increases, and therefore, the probability of CBF_Flag of the corresponding encoded block being "1" is relatively higher than the probability of being "0".

On the contrary, when the clipping range of the encoding block is narrow, that is, when the difference between the maximum value and the minimum value is small, the prediction accuracy of the encoding block is relatively high. If the prediction accuracy is relatively high, the probability that the residual block includes a non-zero transform coefficient is low, so that the probability of CBF_Flag of the corresponding encoding block being "0" is relatively higher than the probability of being "1".

In consideration of such statistical characteristics, initial probability information having a relatively high probability that CBF_Flag is " 1 " can be used for an encoding block having a wide clipping range. Conversely, for an encoding block with a narrow clipping range, initial probability information having a relatively high probability that CBF_Flag is " 0 " can be used.

The CBF_Flag may be a flag indicating whether a non-zero conversion coefficient is included in the corresponding block. When CBF_Flag is 1, the corresponding block includes at least one non-zero transform coefficient. If CBF_Flag is 0, it means that the block does not contain non-zero transform coefficients.

As another example, when the clipping range of a coded block is wide, inter prediction between the coded blocks has a relatively high prediction accuracy. Therefore, the PredModeFlag of the coded block is relatively higher than the probability that it is " 1 "

On the contrary, when the clipping range of the encoded block is narrow, the intra prediction has a relatively high prediction accuracy for the encoded block. Therefore, the PredModeFlag of the coded block is relatively higher than the probability that it is " 0 "

In consideration of such statistical characteristics, initial probability information having a relatively high probability that PredModeFlag is " 1 " can be used for an encoding block having a wide clipping range. Conversely, for an encoding block with a narrow clipping range, initial probability information having a relatively high probability that PredModeFlag is " 0 " can be used.

The PredModeFlag may be a flag indicating a prediction method applied to the block. If PredModeFlag is 1, it means that inter-picture prediction is applied to the corresponding block. If PredModeFlag is 0, it means that intra prediction is applied to the block.

As described above, the context of a predetermined syntax element can be optimized in consideration of the characteristics related to the clipping range. The predetermined syntax element is not limited to CBF_Flag and PredModeFlag, and an adaptive context probability can be applied to other syntax elements according to the clipping range.

17 is a diagram for explaining a process of performing deblocking filtering based on a clipping range according to another embodiment of the present invention.

As shown in Fig. 17, the A block and the B block are adjacent to each other with a boundary therebetween. The clipping range of the A block is 50 to 160 and the clipping range of the B block is 90 to 200. [ In the example shown in Fig. 17, the clipping range of the A block and the clipping range of the B block are overlapped in the range of 90 to 160.

According to the present invention, deblocking filtering is adaptively performed considering characteristics of the clipping range of the A block and the clipping range of the B block. More specifically, the deblocking filtering is performed based on the overlap information of the clipping range of the A block and the clipping range of the B block.

For example, when the clipping range of the A block and the clipping range of the B block do not overlap, it is not preferable to filter the boundary between the two blocks because the two blocks are included in different areas. Therefore, in such a case, filtering may not be performed on the boundary between the A block and the B block. Alternatively, even if the filtering is performed, the filtering coefficient for pixels belonging to the same block as the pixel to be filtered can be set to be high (or extremely high), and the influence of the pixels in the adjacent block can be reduced.

When the clipping range of the A block and the clipping range of the B block partially overlap, the filtering coefficient for the pixel belonging to the same block as the pixel to be filtered can be set high. Whether or not the filtering coefficient is set to be high can be determined adaptively according to the overlap degree of the clipping range. For example, as the overlapping degree of the clipping range is lower, the filtering coefficient for pixels belonging to the same block as the pixel to be filtered can be set higher.

According to another embodiment of the present invention, the prediction mode can be limitedly used in consideration of clipping characteristics.

For example, when the clipping range of the encoding block is wide, it can be determined that all predictions of intra-picture prediction and inter-picture prediction are possible for the coded block.

On the other hand, when the clipping range of the coded block is narrow, it can be determined that only DC mode or Planar mode is applicable to the coded block in the case of intra-picture prediction and / or only merge mode is applicable in case of inter-picture prediction .

In the intra-picture prediction mode, intra-picture prediction referring to the pixels of the uppermost adjacent block can be performed if the clipping characteristics of the upper adjacent block and the clipping characteristics of the current block are similar. Conversely, if the clipping characteristics of the left adjacent block are similar to the clipping characteristics of the current block, intra prediction can be performed referring to the pixels of the left adjacent block.

In the above-described embodiment, determination of whether the clipping range is wide or narrow (determination of the wide-angle) can be performed by comparing the clipping range with a predetermined threshold value. The predetermined threshold value may be signaled through a bitstream, or a predetermined threshold value may be used in the image encoding apparatus and the image decoding apparatus. The predetermined threshold value may include a first threshold value for determining whether the clipping range is wide or a second threshold value for determining whether the clipping range is narrow. When the clipping range is located between the first threshold and the second threshold, the embodiments according to the present invention may not be applied.

In the above embodiment, determination of the degree of overlapping of the clipping range can be performed by comparison with a predetermined threshold value. The predetermined threshold value may be signaled through a bitstream, or a predetermined threshold value may be used in the image encoding apparatus and the image decoding apparatus. The degree of overlapping of the clipping range can be determined adaptively according to whether the clipping range of each block is wide or narrow. For example, when the clipping range of each of the A block and / or the B block is narrow, even if the clipping range of the two blocks is relatively narrow, it can be determined that they overlap a lot. Conversely, when the clipping range of each of the A block and / or the B block is wide, even if the clipping range of the two blocks is relatively wide, it can be determined that the overlap is small.

In the above-described embodiment, the determination as to whether or not the clipping range is similar may be determined by at least one of the degree of clipping of the clipping range and the degree of overlap of the clipping range.

In the above-described embodiment, the clipping range can be derived by decoding information on the clipping range transmitted in arbitrary area units. However, substantially similar effects can be expected by modifying the various embodiments of the present disclosure utilizing the clipping range, even though information about the clipping extent is not transmitted. For example, in the above-described embodiment, the clipping range of the area can be determined by searching the maximum value and / or the minimum value of the pixels included in the area to which the clipping range is to be induced. More specifically, in the embodiment described with reference to Fig. 17, the clipping range of the A block and / or the B block can be determined by searching the maximum value and / or the minimum value of the restored pixel of the A block and / or the B block . The clipping range determined as described above may be used in the same manner as the clipping range derived by decoding information on the clipping range.

Although the exemplary methods of this disclosure are represented by a series of acts for clarity of explanation, they are not intended to limit the order in which the steps are performed, and if necessary, each step may be performed simultaneously or in a different order. In order to implement the method according to the present disclosure, the illustrative steps may additionally include other steps, include the remaining steps except for some steps, or may include additional steps other than some steps.

The various embodiments of the disclosure are not intended to be all-inclusive and are intended to be illustrative of the typical aspects of the disclosure, and the features described in the various embodiments may be applied independently or in a combination of two or more.

In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays A general processor, a controller, a microcontroller, a microprocessor, and the like.

The scope of the present disclosure is to be accorded the broadest interpretation as understanding of the principles of the invention, as well as software or machine-executable instructions (e.g., operating system, applications, firmware, Instructions, and the like are stored and are non-transitory computer-readable medium executable on the device or computer.

Claims (15)

Decoding information about a clipping range for a current block; And
Performing sample adaptive offset (SAO) filtering based on information about the clipping range,
Wherein the information on the clipping range includes information on a maximum value and a minimum value of pixel values included in a current block. The method according to claim 1,
Wherein the information on the clipping range for the current block includes:
And the current block or the current block. 3. The method of claim 2,
Wherein the arbitrary region unit is a region-
A picture unit, a tile unit, and a slice unit. The method according to claim 1,
The information on the maximum value and the minimum value may be,
And information on one of the maximum value and the minimum value and information on a difference between the maximum value and the minimum value. The method according to claim 1,
When the SAO mode for the current block is a band offset (BO) mode,
Decoding an initial band point related to a start position of a band interval to which the band offset is applied; And
Further comprising decoding M offset information for a band interval to which the band offset is applied,
Wherein M is determined based on the decoded initial band point and at least one of the minimum value and the maximum value. The method according to claim 1,
When the SAO mode for the current block is a band offset mode,
Further comprising the step of classifying an interval between the maximum value and the minimum value into 32 bands,
Wherein the initial band point with respect to the starting position of the band interval to which the band offset is applied is a point for the 32 re-sorted bands. Determining a clipping range for the current block;
Performing sample adaptive offset (SAO) filtering based on the clipping range; And
Encoding the information about the clipping range,
Wherein the clipping range information includes information on a maximum value and a minimum value of pixel values included in a current block. 8. The method of claim 7,
Wherein the information on the clipping range for the current block includes:
Wherein the current block or the current block is encoded in units of an arbitrary region including the current block or the current block. 9. The method of claim 8,
Wherein the arbitrary region unit is a region-
A picture unit, a tile unit, and a slice unit. 8. The method of claim 7,
The information on the maximum value and the minimum value may be,
And information on one of the maximum value and the minimum value and information on a difference between the maximum value and the minimum value. 8. The method of claim 7,
When the SAO mode for the current block is a band offset (BO) mode,
Determining an initial band point for a start position of a band section to which the band offset is applied;
Determining M offset information for a band interval to which the band offset is applied; And
Further comprising the step of encoding the initial band point and the M offset information,
Wherein M is determined based on the initial band point and at least one of the minimum value and the maximum value. 8. The method of claim 7,
When the SAO mode for the current block is a band offset mode,
Further comprising the step of classifying an interval between the maximum value and the minimum value into 32 bands,
Wherein an initial band point for a starting position of a band interval to which a band offset is applied is a point for the 32 re-sorted bands. A decoding unit for decoding information on a clipping range of a current block; And
And a filtering unit that performs sample adaptive offset (SAO) filtering based on information about the clipping range,
Wherein the clipping range information includes information on a maximum value and a minimum value of pixel values included in a current block. An encoding unit for determining a clipping range for a current block and encoding information about the clipping range; And
And a filtering unit for performing a sample adaptive offset (SAO) filtering based on the clipping range,
Wherein the clipping range information includes information on a maximum value and a minimum value of pixel values included in a current block. A computer-readable recording medium storing a bit stream generated by a video encoding method,
The image encoding method includes:
Determining a clipping range for the current block;
Performing sample adaptive offset (SAO) filtering based on the clipping range; And
Encoding the information about the clipping range,
Wherein the information on the clipping range includes information on a maximum value and a minimum value of pixel values included in a current block.

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