KR20170124079A - Method and apparatus for encoding/decoding a video signal - Google Patents

Abstract

A method of decoding a video signal according to the present invention may include a step of determining whether there is a brightness change between a current image including a current block and the reference image of the current image, a step of determining a weight prediction parameter candidate for a current block if it is determined that there is the brightness change between the current image and the reference image, a step of determining a weight prediction parameter for the current block based on index information specifying any one of the weight prediction parameter candidates, and a step of performing prediction on the current block based on the weight prediction parameter. It is possible to improve inter picture prediction efficiency.

Description

TECHNICAL FIELD [0001] The present invention relates to a video signal encoding / decoding method and apparatus,

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

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. Accordingly, Video Coding Expert Group (VCEG) of ITU-T and Moving Picture Expert Group (ISO / IEC) of Moving Picture Expert Group (MPEG) of International Standardization Organization have agreed to implement High Efficiency Video Coding (HEVC) Respectively.

HEVC defines techniques such as intra prediction, inter prediction, transform, quantization, entropy coding, and in-loop filters. Among them, inter-picture prediction is performed by using motion information such as a motion vector, a reference picture index, an inter prediction indicator, and the like, it means.

The higher the correlation between images, the higher the prediction efficiency can be obtained. However, if there is a change in brightness between images such as a fade-in or a fade-out, the inter-picture prediction result may be inaccurate if the correlation between the images is lowered. In order to solve such a problem, the present invention proposes weight prediction. Here, the weight prediction may mean that, when there is a change in brightness between images, the weight is estimated by the degree of brightness change, and the estimated weight is applied to the inter-view prediction.

The main object of the present invention is to improve inter picture prediction efficiency by performing inter picture prediction using a weight in coding / decoding an image.

The present invention relates to an apparatus and a method capable of effectively performing inter-picture prediction even when a plurality of light sources exist in an image or a brightness change exists only in a local region by selectively using a weight in coding / decoding an image The main purpose is to provide.

A method and an apparatus for decoding a video signal according to the present invention determine whether there is a brightness change between a current image including a current block and a reference image of the current image and if there is a brightness change between the current image and the reference image Determines a weight prediction parameter for the current block and determines a weight prediction parameter for the current block based on index information for specifying any one of the weight prediction parameter candidates, The prediction of the current block may be performed.

In the video signal decoding method and apparatus according to the present invention, the weight prediction parameter candidate may include a first weight prediction parameter for the reference image.

In the method and apparatus for decoding a video signal according to the present invention, when the current image includes at least one region capable of deriving a second weight prediction parameter, the weight prediction parameter candidate includes at least one second weight value And may further include a prediction parameter.

In the video signal decoding method and apparatus according to the present invention, the first weight prediction parameter may be derived based on a predicted value for the first weight prediction parameter and a residual value for the first weight prediction parameter.

In the video signal decoding method and apparatus according to the present invention, the predicted value for the first weight prediction parameter may be determined according to the accuracy of the current block.

In the video signal decoding method and apparatus according to the present invention, the maximum number of weight prediction parameter candidates may be adaptively determined according to the size of the current block.

In the video signal decoding method and apparatus according to the present invention, the weight prediction parameter candidate may include an initial weight prediction parameter having a predetermined weight value.

The method and apparatus for encoding an image signal according to the present invention determine whether there is a change in brightness between a current image including a current block and a reference image of the current image and if there is a change in brightness between the current image and the reference image Determining a weight prediction parameter candidate for the current block, determining a weight prediction parameter for the current block from among the weight prediction parameter candidates, encoding the index information for specifying the determined weight prediction parameter, Based on the weight prediction parameter, prediction of the current block can be performed.

In the video signal encoding method and apparatus according to the present invention, the weight prediction parameter candidate may include a first weight prediction parameter for the reference image.

In the method and apparatus for encoding an image signal according to the present invention, when the current image includes at least one region capable of deriving a second weight prediction parameter, the weight prediction parameter candidate includes at least one second weight And may further include a prediction parameter.

The method and apparatus for encoding an image signal according to the present invention can encode a difference value indicating a difference between the predicted values for the first weighted prediction parameter and the first weighted prediction parameter.

In the video signal encoding method and apparatus according to the present invention, the predicted value for the first weight prediction parameter may be determined according to the accuracy of the current block.

In the video signal encoding method and apparatus according to the present invention, the maximum number of weight prediction parameter candidates may be adaptively determined according to the size of the current block.

In the video signal encoding method and apparatus according to the present invention, the weight prediction parameter candidate may include an initial weight prediction parameter having a preset weight value.

In the present invention, inter picture prediction is performed using a weight in encoding / decoding an image, thereby improving inter picture prediction efficiency.

The present invention can effectively perform inter-picture prediction even when a plurality of light sources exist in an image or a brightness change exists only in a local region by selectively using a weight in encoding / decoding an image.

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 block diagram schematically illustrating a motion estimation method according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating locations of neighboring blocks for obtaining motion information to be applied to a current block to be coded according to an embodiment of the present invention.
5 is a diagram illustrating a brightness change pattern between a current image including a current block and a reference image.
6 is a flowchart illustrating a method of estimating a weight prediction parameter in the image encoding apparatus.
7 is a diagram illustrating an example of performing Rate Distortion Optimization (RDO) on a prediction block using a weight parameter.
8 is a flowchart illustrating a method of encoding information related to a weight prediction parameter for a current block.
9 is a diagram showing an example of decoding a weight prediction parameter in the decoding apparatus.

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

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

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

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

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

1 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 divider 110, prediction units 120 and 125, a transform unit 130, a quantization unit 135, a reorder unit 160, an entropy encoding unit An inverse quantization unit 140, an inverse transform unit 145, a filter unit 150, and a memory 155. [

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 110 may divide the input image into at least one block. At this time, 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 quadtree or 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 prediction units 120 and 125 may include an inter-picture prediction unit 120 for performing inter-picture prediction and an intra-picture prediction unit 125 for performing intra-picture prediction. It is possible to determine whether to use intra-picture prediction or intra-picture prediction for a prediction unit, and to determine concrete information (for example, intra-picture 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 130. [ In addition, the prediction mode information, motion vector information, and the like used for the prediction may be encoded by the entropy encoding unit 165 together with the residual value and transmitted to the decoder. When a particular encoding mode is used, it is also possible to directly encode the original block and transmit it to the decoding unit without generating a prediction block through the prediction units 120 and 125.

The inter-picture predicting unit 120 may predict a prediction unit based on information of at least one of a previous image or a following image of the current image, and may predict a prediction unit based on information of a partially- The prediction unit may also be predicted. The inter-frame prediction unit 120 may include a reference image interpolator, a motion information generator, and a motion compensator.

The reference image interpolator receives the reference image information from the memory 155 and generates pixel information of an integer number or less from the reference image. 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 information generating unit may generate motion information based on the reference image interpolated by the reference image interpolating unit. Here, the motion information refers to a motion vector, a reference image index, a prediction direction, and the like. As a method for estimating a motion vector, 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. Further, the motion vector may have a motion vector value of 1/2 or 1/4 pixel unit based on the interpolated pixel. In the inter-picture prediction, the current prediction unit can be predicted by differently generating the motion information. As the motion information generation method, various methods such as a merge method using a motion vector of a neighboring block and a motion estimation method (e.g., AMVP (Adaptive Motion Vector Prediction)) can be used.

For example, FIG. 3 shows an example of generating motion information through motion estimation. The motion estimation is to determine a motion vector of a current block, a reference image index, and an inter-picture prediction direction according to the determination, when a reference block identical or similar to a prediction block in a reference image that has already been encoded and decoded is determined.

When the AMVP method is used, the encoding device generates a predicted motion vector (MVP) by predicting a motion vector estimated in the current block, calculates a difference value (MVD) between the motion vector and the generated predicted motion vector, Motion Vector Difference) can be encoded.

A method of using a motion vector of a neighboring block is to apply motion information of a neighboring block neighboring the current block to the current block. In this case, the neighboring block may include a spatial neighboring block adjacent to the current block and a temporal neighboring block existing at the same position as the current block included in the reference image. For example, FIG. 4 illustrates neighboring blocks of the current block. The encoding apparatus may determine motion information of a current block by applying motion information of neighboring blocks (spatial neighboring blocks: A to E, temporal neighboring block: Col) of the current block shown in FIG. 4 to the current block. Here, Col denotes a block having the same or similar position as the current block existing in the reference image.

The intra prediction unit 125 can generate a prediction unit based on the reference pixel information around the current block which is pixel information in the current image. In the case where the neighboring block of the current prediction unit is a block in which inter-view prediction is performed and the reference pixel is a reconstructed pixel by performing inter-picture prediction, a reference pixel included in the inter- Can be replaced with the reference pixel information of the performed block. That is, when the reference pixel is not available, the usable reference pixel information can be replaced by at least one of the available reference pixels.

In the 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 .

In the intra prediction method, an AIS (Adaptive Intra Smoothing) filter can be applied to a reference pixel according to a prediction mode, and a prediction block can be generated. The type of the AIS filter applied to the reference pixel may be different. To perform the intra prediction method, the intra prediction mode of the current prediction unit can be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When the intra prediction mode of the current prediction unit is predicted using the intra prediction mode information predicted from the peripheral prediction unit and the intra prediction mode of the current prediction unit is the same as the intra prediction mode of the current prediction unit, Information indicating that the prediction mode of the prediction unit is the same as the prediction mode of the surrounding prediction unit can be transmitted. If the prediction mode of the current prediction unit is different from the prediction mode of the surrounding prediction unit, the prediction mode information of the current block can be encoded by performing entropy coding.

In addition, a residual block including a prediction unit that has been predicted based on the prediction unit generated by the prediction units 120 and 125 and a residual value that is a difference value from the original block of the prediction unit may be generated. The generated residual block may be input to the transform unit 130. [

The transforming unit 130 may transform the residual block including residual data using a transform method such as DCT, DST, Karhunen Loeve Transform (KLT), or the like. In this case, the conversion method can be determined based on the intra prediction mode of the prediction unit used to generate the residual block. For example, DCT may be used in the horizontal direction, and DST may be used in the vertical direction, depending on the intra prediction mode.

The quantization unit 135 may quantize the values converted into the frequency domain by the conversion unit 130. [ The quantization factor may vary depending on the block or the importance of the image. The values calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reorder unit 160.

The transforming unit 130 and / or the quantizing unit 135 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 165 is generally referred to as a transform block even though either transformation or quantization is not performed in the image coding apparatus 100 or both transformation and quantization are not performed.

The reordering unit 160 can reorder the coefficient values with respect to the quantized residual values.

The reordering unit 160 may change the two-dimensional block type coefficient to a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan a DC coefficient to a coefficient in the high frequency region using a predetermined scan type, and change it into a one-dimensional vector form.

The entropy encoding unit 165 may perform entropy encoding based on the values calculated by the reordering unit 160. 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 165 receives the residual coefficient information of the encoding unit, the block type information, the prediction mode information, the division unit information, the prediction unit information, the transmission unit information, the motion Vector information, reference image information, interpolation information of a block, filtering information, and the like. In the entropy coding unit 165, the coefficients of the transform block include a flag indicating whether the absolute value of the coefficient is greater than 1, whether or not the absolute value of the coefficient is greater than 2 And the like may be coded. The entropy encoding unit 165 encodes the sign of the coefficient only for non-zero coefficients. A coefficient having an absolute value of the coefficient larger than 2 is encoded by subtracting 2 from the absolute value.

The entropy encoding unit 165 can entropy-encode the coefficient value of the encoding unit input by the reordering unit 160. [

The inverse quantization unit 140 and the inverse transformation unit 145 inverse quantize the quantized values in the quantization unit 135 and inversely transform the converted values in the conversion unit 130. [ The residual value generated by the inverse quantization unit 140 and the inverse transform unit 145 may be combined with a prediction block generated for each prediction unit through the prediction units 120 and 125 to generate a reconstructed block.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove the block distortion caused by the boundary between the blocks in the reconstructed image. It may be determined whether to apply the 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 the deblocking filter. 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 on a pixel-by-pixel basis. In order to perform offset correction for a specific image, a method of dividing a pixel included in an image into an arbitrary area and then determining an area to perform an offset and applying an offset to the corresponding area, or a method of calculating an offset by considering edge information of each pixel You can use the method to apply.

Adaptive Loop Filtering (ALF) can be performed based on a value obtained by comparing the filtered restored 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. Information related to whether to apply the ALF may be transmitted for each coding unit (CU) in the case of a luminance signal, and the shape and the filter coefficient of the ALF filter to be applied may vary depending on 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 155 may store the restored block or image calculated through the filter unit 150 and the stored restored block or image may be provided to the predicting units 120 and 125 when the inter-view prediction is performed.

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

2, the image decoder 200 includes an entropy decoding unit 210, a reordering unit 215, an inverse quantization unit 220, an inverse transform unit 225, prediction units 230 and 235, 240, and a memory 245 may be included.

When an image bitstream is input in the image encoder, the input bitstream may be decoded in a procedure opposite to that of the image encoder.

The entropy decoding unit 210 can perform entropy decoding in a procedure opposite to that in which entropy encoding is performed in the entropy encoding unit of the image encoder. 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 210, the coefficients of the transform block include a flag indicating whether the absolute value of the coefficient is greater than 1 or not, a flag indicating whether the absolute value of the coefficient is greater than 1, And the like can be decoded. Then, the entropy decoding unit 210 decodes the coefficient code for non-zero coefficients. A coefficient whose absolute value is larger than 2 can be decoded by subtracting 2.

The entropy decoding unit 210 can decode information related to intra-picture prediction and inter-picture prediction performed by the encoder.

The reordering unit 215 can perform reordering based on a method in which the entropy decoding unit 210 rearranges the entropy-decoded bitstreams in the encoding unit. The coefficients represented by the one-dimensional vector form can be rearranged by restoring the coefficients of the two-dimensional block form again. The reordering unit 215 can perform reordering by receiving information related to the coefficient scanning performed by the encoding unit and performing a reverse scanning based on the scanning order performed by the encoding unit.

The inverse quantization unit 220 can perform inverse quantization based on the quantization parameters provided by the encoder and the coefficient values of the re-arranged blocks.

The inverse transform unit 225 may inversely transform the dequantized transform coefficients using a predetermined transform method. At this time, the conversion method can be determined based on prediction method (inter-screen / intra-picture prediction), size / type of block, intra-picture prediction mode,

The prediction units 230 and 235 may generate a prediction block based on the prediction block generation related information provided by the entropy decoding unit 210 and the previously decoded block or image information provided in the memory 245. [

The prediction units 230 and 235 may include a prediction unit determination unit, an inter picture prediction unit, and an intra prediction unit. The prediction unit determination unit receives various information such as prediction unit information input from the entropy decoding unit 210, prediction mode information of the intra prediction method, motion prediction related information of the inter picture prediction method, and identifies prediction units in the current coding unit , It is possible to determine whether the prediction unit performs inter-picture prediction or intra-picture prediction. The inter-picture predicting unit 230 may use the information necessary for the inter-picture prediction of the current prediction unit provided by the image encoder, based on the information included in at least one of the previous image or the following image of the current image including the current prediction unit The inter prediction can be performed on the current prediction unit. Alternatively, inter-picture prediction may be performed on the basis of the information of the partial-region reconstructed in the current image including the current prediction unit.

In order to perform inter-picture prediction, it is possible to determine whether a motion information generation method of a prediction unit included in the coding unit is generated based on a coding unit, such as a merge method or a motion estimation method.

The intra prediction unit 235 can generate a prediction block based on the pixel information in the current image. If the prediction unit is a prediction unit that performs intra prediction, the intra prediction can be performed based on the intra prediction mode information of the prediction unit provided by the image encoder. The intra prediction unit 235 may include an Adaptive Intra Smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter performs filtering on the reference pixels of the current block and can determine whether to apply the filter according to the prediction mode of the current prediction unit. The AIS filtering can be performed on the reference pixel of the current block using the prediction mode of the prediction unit provided in the image encoder and the AIS filter information. 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 reference pixel interpolator may interpolate the reference pixels to generate reference pixels in units of pixels less than an integer value when the prediction mode of the prediction unit is a prediction unit that performs intra-frame prediction on the basis of the pixel value obtained by interpolating the reference pixels . 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 restored block or image may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

When information on whether a deblocking filter is applied to a corresponding block or an image from the image encoder or a deblocking filter is applied, information on whether a strong filter or a weak filter is applied can be provided. In the deblocking filter of the video decoder, the deblocking filter related information provided by the video encoder is provided, and the video decoder can perform deblocking filtering for 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, offset information, and the like during encoding.

The ALF can be applied to an encoding unit on the basis of ALF application information and ALF coefficient information provided from an encoder. Such ALF information may be provided in a specific set of parameters.

The memory 245 may store the reconstructed image or block to be used as a reference image or a reference block, and may provide the reconstructed image to the output unit.

5 is a diagram illustrating a brightness change pattern between a current image including a current block and a reference image.

In the case of inter-picture prediction for the current block, the greater the change in brightness between the current image and the reference image, the greater the change in brightness between the current block and the prediction block to be selected in the reference image. Therefore, it can be expected that as the error due to the inter-picture prediction of the current block increases, the energy for the residual signal of the current block also increases. And, as the energy for the residual signal increases, it can be expected that the error due to the quantization also increases. As a result, when there is a brightness change between the current image and the reference image, the error for the residual block will increase as compared to the case where there is no brightness change.

Accordingly, the present invention proposes a method of generating a weight prediction parameter by estimating a brightness change between images and performing an inter-screen prediction using the weight prediction parameter. By using the weight prediction parameter in the inter-picture prediction, it is possible to prevent the energy of the residual block from increasing sharply and to improve the prediction efficiency.

The weight prediction parameter may be generated in consideration of a change in the brightness of the current image and the reference image, such as a fade-in or a fade-out. However, when the weight prediction parameter is determined by considering only the above factors, it is difficult to cope with the case where the brightness of the current image and the reference image are changed by a plurality of light sources or the brightness of only the local area in the current image changes. Accordingly, in the present invention, a method of estimating a weight prediction parameter is also considered in consideration of the case where the brightness varies by a plurality of light sources or the case where the brightness of only the local area changes.

Hereinafter, inter picture prediction using the weight prediction parameter will be described in detail with reference to the drawings.

6 is a flowchart illustrating a method of estimating a weight prediction parameter in the image encoding apparatus.

The weight prediction parameter may be generated based on the brightness change between the current image and the reference image. For convenience of explanation, in the following embodiments, a weight prediction parameter generated based on a change in brightness between a current image and a reference image is referred to as a 'first weight prediction parameter', and a part of the current image and a reference image The weight prediction parameter generated based on the brightness change between some of the regions is referred to as a " second weight prediction parameter ".Quot;, " first ", and " second ", etc. are merely imposed for convenience in description, and it is limited that the first weight prediction parameter and the second weight prediction parameter should be of different properties It is not.

The encoding apparatus can estimate the first weight prediction parameter for the reference image using the current image and the reference image before encoding the image (S601). For example, the encoding apparatus may assign a first weight prediction parameter to each of a plurality of reference images included in the reference image list.

The first weight prediction parameter is a value generated based on a brightness variation between the reference image and the current image.

 When the first weight prediction parameter is used in the inter-picture prediction of the current block, the prediction block may be generated based on the first weight parameter for the reference block indicated by the motion vector and the reference picture including the reference block.

The first weight prediction parameter may include at least one of a multiplication parameter multiplied by the prediction pixel or an addition parameter added to the prediction pixel. At this time, the multiplication parameter and the addition parameter can be derived based on a regression analysis. For example, the following equation (1) shows an example of a regression analysis model.

In Equation (1), Y represents data of a current image, X represents data of a reference image, w represents a slope of a regression line, o represents a slice value of a regression line, and e represents a regression line prediction error. In this case, Y is a pixel value of the current image, and a whole or a part of the current image may be a range, and X may be a pixel value of the reference image and a whole or a part of the reference image may be a range.

The first weighted prediction parameter may be obtained by partially differentiating Equation (1) into w and o, respectively. For example, when the equation (1) is partially differentiated into w and o, w and o that minimize the square of the error (e) can be set as the multiplication parameter and the addition parameter, respectively.

The first weighted prediction parameter value calculated based on Equation (1) may have a real value. The first weight prediction parameter may be set to a real value calculated based on Equation (1) or an integer value obtained by integerizing a real value calculated based on Equation (1). In one example, the first weighted prediction parameter may be derived as an integer value that is derived by multiplying a real number value calculated based on Equation (1) by ^2N . The variable N used for integerizing the first weight prediction parameter may be encoded on a block-by-block, area-by-area, or upper header.

When the first weight parameter is determined, the encoding apparatus can calculate the cost according to whether the first weight parameter is applied (S602). For example, the encoder applies the first weight parameter to the reference image as a whole, calculates a sum of absolute difference (SAD) between the current image and the reference image, and a SAD between the reference image and the current image to which the first weighting parameter is not applied . If the SAD of the reference image to which the first weight parameter is applied is smaller than the SAD of the reference image to which the first weight parameter is not applied, it can be determined that a brightness change exists between the current image and the reference image. On the contrary, if the SAD of the reference image to which the first weight parameter is applied is larger than the SAD of the reference image to which the wp1 weight parameter is not applied, it can be determined that there is no brightness change (S603).

In addition to the above-described SAD, cost calculation may be performed using a sum of squared difference (SSD) or a sum of absolute transformed difference (SATD).

If it is determined that there is no brightness change between the current image and the reference image (S603), it can be determined that the weight prediction parameter is not used in the inter-scene prediction for the current image. Accordingly, the inter picture prediction can be used for the current block included in the current image without using the weight parameter.

On the other hand, if it is determined that there is a brightness change between the current image and the reference image (S603), a process of deriving the second weight parameter for each predetermined region of the current image may be performed. For example, the second weight parameter for a predetermined area in the current image may be obtained by comparing pixel values of blocks included in the predetermined area with pixel values of blocks included in the same area in the reference image, .

In order to calculate the second weight prediction parameter for a predetermined region in the current image, the current image and the reference image may be divided into a plurality of regions (S604). The current image and the reference image can be divided into a plurality of blocks having the same size. The current image and the reference image can be divided in the same manner, whereby the number of blocks in the current image and the reference image and the position of the block can be set to be the same.

In step S605, the encoding apparatus may determine whether at least one region in which a local brightness change occurs in the current image is included in the current image using the pixel values of the current image and the reference blocks.

In step S605, at least one area may be composed of a set of blocks having the same or similar pixel value ratios. For example, if the average pixel value of the first divided block in the current image is 100 and the average pixel value of the first divided block in the reference image is 80, then the first block in the current image and the first block in the reference image are 1.25 There is a difference in brightness. The encoding apparatus can group a block having a brightness difference of 1.25 times with a reference block or a block having a brightness difference similar to 1.25 times with the first block. As such, by grouping blocks having the same or similar brightness difference, regions in which a local brightness change exists can be identified.

That is, the encoding device can compare the pixel value of the block included in the current image with the pixel value included in the reference image, and treat the same or similar blocks as a single area by grouping the same or similar blocks.

The encoding apparatus can generate a second weight prediction parameter for at least one region included in the current image (S606). When there are a plurality of regions generated as a set of blocks having similar pixel value ratios to the current image, a plurality of second weight prediction parameters can be generated.

The second weighted prediction parameter for each region may be obtained using Equation (1). In this case, Y is data in a predetermined area in the current image for which a second parameter on the second weight is to be estimated, and X may be data in the same position area as the predetermined area in the reference image. For example, Y may be a pixel value in a predetermined area, and all or some of the areas may be in a range, and X may be a pixel value in the same area, and all or some of the areas may be in a range. The second weighted prediction parameter value calculated based on Equation (1) may have a real value. The second weight prediction parameter may be set to a real value calculated based on Equation (1) or to a value obtained by integerizing a real value calculated based on Equation (1). In one example, the second weighted prediction parameter may be derived as an integer value that is derived by multiplying the real number value calculated based on Equation (1) by ^2N . The variable N used for integerizing the second weight prediction parameter may be encoded on a block-by-block, area-by-area basis, or upper header. It is also possible to have the same value as N used to integerize the first weighted prediction parameter and to use different N's.

7 is a diagram illustrating an example of performing Rate Distortion Optimization (RDO) on a prediction block using a weight parameter.

6, when the brightness change between the current image and the reference image exists, the encoding device obtains the first weighted prediction parameter, and if there is a region in which the local brightness change occurs in the current image, The second weight prediction parameter may be obtained (S701). That is, the encoding device obtains a weighted prediction parameter candidate that can be applied to the current block, such as a first weighted prediction parameter or a second weighted prediction parameter, depending on whether there is a brightness change between the current image and the reference image or a local brightness change .

If there is a brightness change between the current block and the reference image, the weight prediction parameter candidate for the current block may include the first weight prediction parameter. In addition, when there is a region in which a local brightness change is present in the current image, the weight prediction parameter candidate for the current block may further include a second weight prediction parameter. If a plurality of second weight prediction parameters exist for the current image, the weight prediction parameter candidates may include a plurality of second weight prediction parameters.

The encoding apparatus can calculate the optimal weighting prediction parameter for the current block based on the calculation result after applying the weighting parameters set as the weighting prediction parameter candidates to the current block and calculating the respective costs (S702) (S703) .

Determining the weight prediction parameter for the current block corresponds to selecting one of the plurality of weight prediction parameter candidates that represents the best inter picture prediction performance for the current block. For example, if a first weighted prediction parameter is derived for a reference image and a second weighted prediction parameter is derived for a predetermined region in the current image, then the optimal weighted prediction parameter for the current block among the first weighted prediction parameter and the second weighted prediction parameter The weight prediction parameter can be selected.

For this purpose, the encoding apparatus can compare the inter-screen prediction execution results of each of the weight prediction parameter candidates, and select an optimum weight prediction parameter. For example, the encoding apparatus can determine the optimum weight prediction parameter of the current block according to the result of the inter-picture prediction of each of the first weight prediction parameter and the plurality of second weight prediction parameters for the current block.

It is also possible to compare the result of performing the inter-view prediction using the weight prediction parameter candidate with the result of performing the inter-view prediction without using the weight prediction parameter candidate, and determine whether to perform the inter- You can also decide if you want to.

In the above-described example, it is described that the weight prediction parameter includes the first weight prediction parameter and, in some cases, may further include the second weight prediction parameter. Contrary to the example described above, the first weight prediction parameter may be used as the weight prediction parameter candidate only when the second weight prediction parameter is not available or when the number of the second weight prediction parameters is a predetermined number or less.

The weight prediction parameter candidates may have a fixed number or may have a variable number. When the number of weight prediction parameter candidates is variable, the encoding apparatus can encode information indicating the number of usable weight prediction parameter candidates for the current block through a bit stream (e.g., an upper header). At this time, the number of candidates of the weight prediction parameter may be variably set according to the size or depth of the current block. Accordingly, the encoding apparatus can encode information on the number of weighted prediction parameter candidates that can be used according to the size or depth information of the block through a bitstream (e.g., an upper header).

As another example, the encoding apparatus and the decoding apparatus may be defined to use the same number of weighted prediction parameter candidates under predetermined conditions. For example, the number of weight prediction parameter candidates may be adaptively determined according to the size, type, or intra prediction mode of the current block. Assuming that the number of usable weight prediction parameters is 5, if the current block size is 8x8 or less, five weight prediction parameter candidates are used. If the current block size is 16x16, four weight prediction parameter candidates are used When the current block size is 32x32, three weight prediction parameter candidates are used. When the current block size is 64x64, two weight prediction parameter may be used.

If the second weight prediction parameter is not obtained for the current image, the current block may be encoded using the first weight prediction parameter. If there is no brightness change between the current image and the reference image, the current block may be encoded without using the weight prediction parameter, or may be encoded using the initial weight prediction parameter.

The initial weight prediction parameter means that the multiplication parameter and the addition parameter are set to initial values. Here, the initial values of the multiplication parameter and the addition parameter may be 1 and 0, respectively. As another example, the initial value of the multiplication parameter may be set to 1 " N, and the initial value of the addition parameter may be set to zero.

In the example described above, when there is no change in brightness between the current image and the reference image, the initial weight prediction parameter is illustrated as being used. It is also possible to encode the current block using the initial weight prediction parameter even when there is a brightness change between the current image and the reference image. In this case, in order to select the initial weight prediction parameter, the initial weight prediction parameter may be added as the weight prediction parameter candidate. By adding the initial weight prediction parameter as the weight prediction parameter candidate, a new index can be assigned to the initial weight prediction parameter. In this case, the index assigned to the initial weight prediction parameter may be encoded through a bitstream or may have a predetermined value.

In addition, by performing RDO using the weighted prediction parameter candidates including the first weighted prediction parameter, the second weighted prediction parameter, and the initial weighted prediction parameter, the first weighted prediction parameter, the second weighted prediction parameter, It is possible to specify an appropriate weight prediction parameter for the block.

Next, a method of encoding information related to the weight prediction parameter will be described.

8 is a flowchart illustrating a method of encoding information related to a weight prediction parameter for a current block.

Referring to FIG. 8, in step S801, the encoding apparatus encodes information on whether a brightness change exists for each reference image of the current image. Whether to use the weight prediction parameter or not is determined according to whether there is a brightness change. Therefore, the information may be used for indicating whether or not a weight prediction parameter exists in the bitstream. At this time, the information on whether there is a brightness change may be a flag of 1 bit, but is not limited thereto. In addition, information on whether there is a brightness change may be encoded in units of a prediction block or may be encoded in a higher header than a prediction block. As an example, the information may be encoded in sequence, picture, slice, or tile units. The decoding apparatus can determine whether there is a brightness change between the current image and the reference image based on the information decoded from the bitstream.

When there is no brightness change between the current image and the reference image, the encoding apparatus does not perform encoding of information related to the weight prediction parameter for the current block.

On the other hand, when there is a change in brightness between the current image and the reference image (S802), the encoding apparatus calculates information on whether the first weight prediction parameter and the current image include an area to which at least one second weight prediction parameter is assigned (S803, S804). If the current image includes the area to which the second weight prediction parameter is assigned, information on the second weight prediction parameter is additionally encoded, so that the additional weight prediction parameter other than the first weight prediction parameter Or may be used for the purpose of indicating whether or not it is. Here, the information on whether the current image includes at least one region for deriving the second weight prediction parameter may be a flag of 1 bit, but is not limited thereto. Further, information on whether or not a brightness change exists can be encoded through a higher header than a prediction block. As an example, the information may be encoded in sequence, picture, slice, or tile units.

If it is determined that the current image includes at least one region to which at least one second weight prediction parameter is assigned (S805), the encoding apparatus can encode the second weight prediction parameter for each of the M regions included in the current image ( S806).

The information on the first weight prediction parameter and the second weight prediction parameter may be coded on a prediction block basis or may be coded on a higher header than a prediction block. For example, the information on the first weight prediction parameter and the second weight prediction parameter may be encoded in units of a sequence, a picture, a slice, or a tile.

It is also possible to encode the first weight prediction parameter and the second weight prediction parameter in different layers. For example, the first weight prediction parameter may be coded on a video basis, and the second weight prediction parameter may be coded on a slice basis.

The first weight prediction parameter and the second weight prediction parameter may include a multiplication parameter and an addition parameter. At this time, the multiplication parameter can be divided into a prediction value determined based on the precision N for the multiplication parameter, and a difference value between the multiplication parameter and the prediction value. For example, 1 << N may be set as the predicted value of the multiplication parameter, and the difference between the multiplication parameter and the predicted value (1 << N) may be set as the difference value. The encoding apparatus can encode information on the multiplication parameter by encoding the difference value. The precision N of the current block can be coded on a block-by-block, slice-by-block, or picture-by-block basis, and can be transmitted to the decoding device through the bitstream.

Alternatively, it is also possible to determine the precision N of the current block in the same way in the encoding apparatus and the decoding apparatus. For example, the precision N of the current block may be determined adaptively according to the size, type, etc. of the current block.

If it is determined that the current image does not include the region to which at least one second weight prediction parameter is assigned, encoding for the second weight prediction parameter may be omitted.

Information on the number of regions included in the current block (i.e., the number of second weight prediction parameters or the number of regions capable of deriving the second weight prediction parameter) 'M' is encoded on a block-by-block basis or an upper header . Alternatively, the encoding apparatus and the decoding apparatus can determine the number of regions included in the current block in the same manner based on predetermined conditions.

If it is determined that the current image includes at least one area for deriving the second weight prediction parameter, the index information indicating the weight prediction parameter of the current block among the plurality of weight prediction parameter candidates may be encoded (S807). At this time, the index information can be encoded in units of prediction blocks.

As another example, the encoding apparatus may encode information that identifies a region in which the weight parameter and the weight prediction parameter are derived. For example, the encoding apparatus may encode the position, size, or index assigned to the region in which the second weight prediction parameter and the second weight parameter are derived.

Assuming that the index of the weight prediction parameter candidates starts from the index 0, the index information will indicate any one of '0' to '1' as the number of weight prediction parameter candidates. Here, the number of weight prediction parameter candidates may have a fixed value or may have a variable value as in the example described above.

The plurality of weight prediction parameter candidates may include at least one of a first weight prediction parameter, a second weight prediction parameter, or an initial weight prediction parameter.

Next, an example of decoding the information about the weight prediction parameter in the decoding apparatus will be described in detail.

9 is a diagram showing an example of decoding a weight prediction parameter in the decoding apparatus. Referring to FIG. 9, the decoding apparatus can decode information indicating whether the brightness of each reference image has changed from the bitstream, with respect to the current image (S901).

Based on the information, the decoding apparatus can determine whether the first weight prediction parameter exists for the current block (S902). For example, when it is determined that there is no brightness change between the current image and the reference image based on the information, the decoding apparatus may not decode information related to the weight prediction parameter.

On the other hand, if it is determined that there is a brightness change between the current image and the reference image (S902), the decoding apparatus includes at least one area for deriving the first weighted prediction parameter and the second weighted prediction parameter in the current image (S903, S904).

If at least one region capable of deriving the second weight prediction parameter is included in the current image, the decoding apparatus can decode the information related to the second weight prediction parameter from the bit stream (S905). Based on the information, the decoding apparatus can determine whether or not the second weight prediction parameter exists for the current block.

If there are a plurality of M regions in which the second weighting prediction parameter can be derived from the current image, the decoding apparatus can decode information on the M second weighting prediction parameters (S906).

At this time, information on the first weight prediction parameter and the second weight prediction parameter may be decoded in units of a prediction block or decoded in a higher header than a prediction block. For example, the information on the first weight prediction parameter and the second weight prediction parameter may be decoded in a sequence, picture, slice, or tile unit.

The first weighted prediction parameter and the second weighted prediction parameter may be decoded in different layers. For example, the first weight prediction parameter may be decoded on a video basis, while the second weight prediction parameter may be decoded on a slice basis.

The first weight prediction parameter and the second weight prediction parameter may include a multiplication parameter and an addition parameter. At this time, the decoding apparatus can decode the information indicating the difference value between the multiplication parameter and the predicted value of the multiplication parameter, according to the precision N with respect to the multiplication parameter. If the precision for the multiplication parameter is N, 1 < N can be set to a predicted value of the multiplication parameter.

Thereafter, the decoding apparatus can decode the index information specifying the weight prediction parameter of the current block among the plurality of weight prediction parameter candidates (S907). When the weight prediction parameter for the current block is specified by the index information, inter-picture prediction of the current block can be performed based on the specified weight prediction parameter.

Specifically, the decoding apparatus can acquire the first predictive pixel by performing inter-picture prediction on the current block, and apply the weight predictive parameter to the obtained first predictive pixel, thereby obtaining the second predictive pixel. In one example, the second prediction pixel can be obtained by adding the multiplication parameter to the first prediction pixel, and then adding the addition parameter.

As another example, the decoding apparatus may decode the information that identifies the region from which the weight prediction parameter and the weight prediction parameter are derived. For example, the decoding apparatus may decode the position and size of an area to which the second weighting prediction parameter and the second weighting parameter are allocated, an index allocated to the corresponding area, and the like. In this case, the decoding apparatus can adaptively select the weight prediction parameter according to whether or not the current block is included in the area to which the second weight prediction parameter is allocated. For example, when the current block is included in an area to which the second weight prediction parameter is not allocated, the decoding apparatus can select the weight prediction parameter for the current block using the first weight prediction parameter. On the other hand, when the current block is included in the area to which the second weight prediction parameter is allocated, the decoding apparatus performs inter-picture prediction on the current block using the second weight prediction parameter allocated to the area including the current block can do.

In the embodiment described above, it is determined whether or not the first weighted prediction parameter can be used as the weighted prediction parameter candidate, based on the information indicating whether a brightness change exists between the current image and the reference image, It has been described that it is determined whether or not the second weighted prediction parameter can be used as the weighted prediction parameter candidate, depending on whether or not an area capable of deriving the predicted parameter is included. That is, whether to add the second weight prediction parameter to the weight prediction candidate is determined according to whether or not the current image includes an area for deriving the weight prediction parameter.

In contrast to the example described above, when there is a brightness change between the current image and the reference image, the encoding apparatus calculates the number of usable weight prediction parameter candidates, instead of the information indicating whether the current image includes the second weight prediction parameter Or may be encoded.

In this case, the decoding apparatus can decode at least one or more weight prediction parameter candidates based on the received number information. For example, when the number of usable weight prediction parameters is N, the weight prediction parameter candidates can be configured using one first weight prediction parameter and N-1 second weight prediction parameters.

In the above-described embodiment, the weight prediction parameter is determined based on the first weight prediction parameter generated by the brightness difference between the current image and the reference image, and the first weight prediction parameter generated by the brightness difference between the partial region in the current image and the partial region in the reference image. 2 weighted prediction parameter. However, the first weight prediction parameter and the second weight prediction parameter described above are only illustrative of an embodiment in which the weight prediction parameter is generated, and the present invention is not limited thereto.

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 illustrate representative 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 (14)

Determining whether there is a brightness change between a current image including a current block and a reference image of the current image;
Determining a weight prediction parameter candidate for a current block if a change in brightness exists between the current image and the reference image;
Determining a weight prediction parameter for the current block based on index information that specifies any one of the weight prediction parameter candidates; And
And predicting the current block based on the weight prediction parameter. The method according to claim 1,
Wherein the weight prediction parameter candidate includes a first weight prediction parameter for the reference image. 3. The method of claim 2,
Wherein the weight prediction parameter candidate further includes at least one second weight prediction parameter when the current image includes at least one region capable of deriving a second weight prediction parameter. Way. 3. The method of claim 2,
The first weight prediction parameter may be a weighting factor,
A predicted value for the first weighted prediction parameter, and a residual value for the first weighted prediction parameter. 5. The method of claim 4,
Wherein the predicted value for the first weighted prediction parameter is determined according to the accuracy of the current block. The method according to claim 1,
Wherein the maximum number of the weight prediction parameter candidates is adaptively determined according to the size of the current block. The method according to claim 1,
Wherein the weight prediction parameter candidate includes an initial weight prediction parameter having a predetermined weight value. Determining whether there is a brightness change between a current image including a current block and a reference image of the current image;
Determining a weight prediction parameter candidate for a current block if a change in brightness exists between the current image and the reference image;
Determining a weight prediction parameter for the current block from among the weight prediction parameter candidates and encoding index information for specifying the determined weight prediction parameter; And
And predicting the current block based on the weight prediction parameter. 9. The method of claim 8,
Wherein the weight prediction parameter candidate includes a first weight prediction parameter for the reference image. 10. The method of claim 9,
Wherein the weight prediction parameter candidate further includes at least one second weight prediction parameter when the current image includes at least one region capable of deriving a second weight prediction parameter. Way. 10. The method of claim 9,
And a difference value indicating a difference between the first weight prediction parameter and the predicted value for the first weight prediction parameter. 12. The method of claim 11,
Wherein the predicted value for the first weighted prediction parameter is determined according to the accuracy of the current block. 9. The method of claim 8,
Wherein the maximum number of weight prediction parameter candidates is adaptively determined according to the size of the current block. 9. The method of claim 8,
Wherein the weight prediction parameter candidate includes an initial weight prediction parameter having a predetermined weight value.

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