WO2020004833A1

WO2020004833A1 - Method and device for adaptively determining dc coefficient

Info

Publication number: WO2020004833A1
Application number: PCT/KR2019/007054
Authority: WO
Inventors: 남정학
Original assignee: 엘지전자 주식회사
Priority date: 2018-06-29
Filing date: 2019-06-12
Publication date: 2020-01-02

Abstract

A picture decoding method performed by a decoding device according to one embodiment of the present invention comprises the steps of: decoding a DC coefficient from a bitstream; deriving a first updated DC coefficient on the basis of a scale flag indicating whether or not to apply scaling to the decoded DC coefficient; deriving a second updated DC coefficient on the basis of an offset flag indicating whether or not to apply an offset to the first updated DC coefficient; deriving a transform coefficient on the basis of the second updated DC coefficient; deriving a residual sample on the basis of the transform coefficient; and deriving a recovery sample on the basis of the residual sample.

Description

Method and apparatus for adaptively determining DC coefficients

The present invention relates to a still image or moving picture encoding / decoding method, and more particularly, to a method and an apparatus for adaptively determining a DC coefficient.

Recently, the demand for high resolution and high quality images such as high definition (HD) images and ultra high definition (UHD) images is increasing in various fields. The higher the resolution and the higher quality of the image data, the more information or bit rate is transmitted than the existing image data. Therefore, the image data can be transmitted by using a medium such as a conventional wired / wireless broadband line or by using a conventional storage medium. In the case of storage, the transmission cost and the storage cost are increased.

Accordingly, a high efficiency image compression technique is required to effectively transmit, store, and reproduce high resolution, high quality image information.

An object of the present invention is to provide a method and apparatus for improving image coding efficiency.

Another technical problem of the present invention is to provide a method and apparatus for adaptively determining a DC coefficient.

Another technical problem of the present invention is to provide a method and apparatus for applying scaling to DC coefficients.

Another technical problem of the present invention is to provide a method and apparatus for applying an offset to a DC coefficient.

Another technical problem of the present invention is to provide a method and apparatus for applying scaling and / or offset to a DC coefficient.

Another technical problem of the present invention is to provide a method and apparatus for applying scaling and / or offset to a DC coefficient based on comparison with a threshold.

According to an embodiment of the present invention, a picture decoding method performed by a decoding apparatus is provided. The method includes: decoding a DC coefficient from a bitstream, deriving a first updated DC coefficient based on a scale flag indicating whether scaling is to be applied to the decoded DC coefficient, 1 deriving a second updated DC coefficient based on an offset flag indicating whether to apply an offset to the updated DC coefficient, deriving a transform coefficient based on the second updated DC coefficient, Deriving a residual sample based on the transform coefficients and deriving a reconstructed sample based on the residual sample.

According to another embodiment of the present invention, a decoding device for performing picture decoding is provided. The decoding apparatus may further include an entropy decoding unit configured to decode DC coefficients from a bitstream, derive a first updated DC coefficient based on a scale flag indicating whether to apply scaling to the decoded DC coefficients, A DC coefficient updater for deriving a second updated DC coefficient based on an offset flag indicating whether to apply an offset to the first updated DC coefficient, and a transform coefficient based on the second updated DC coefficient And an inverse transform unit for deriving a residual sample based on the transform coefficient, and an adder for deriving a reconstructed sample based on the residual sample.

According to the present invention, the overall video / video compression efficiency can be improved.

According to the present invention, the DC coefficient can be adaptively determined.

According to the present invention, scaling can be effectively applied to DC coefficients.

According to the present invention, the offset can be effectively applied to the DC coefficient.

According to the present invention, entropy coding for DC coefficients can be efficiently performed by applying scaling and / or offset to DC coefficients, and image coding efficiency can be increased based on the DC coefficients.

According to the present invention, scaling and / or offset can be effectively applied to a DC coefficient based on comparison with a threshold.

1 is a diagram schematically illustrating a configuration of an encoding apparatus according to an embodiment.

2 is a diagram schematically illustrating a configuration of a decoding apparatus according to an embodiment.

3 is a diagram schematically illustrating a configuration of a decoding apparatus according to another exemplary embodiment.

4 is a flowchart illustrating an example of applying a scaling and / or offset to a DC coefficient by a decoding apparatus according to an embodiment.

5 is a flowchart illustrating another example of applying a scaling and / or offset to a DC coefficient by a decoding apparatus according to an embodiment, based on a comparison with a threshold value.

6 is a flowchart illustrating an example in which a decoding apparatus adaptively applies a plurality of scaling to a DC coefficient, according to an embodiment.

7 is a flowchart illustrating an operation of a decoding apparatus according to an embodiment.

8 is a block diagram illustrating a configuration of a decoding apparatus according to an embodiment.

9 is a diagram illustrating a structure of a content streaming system according to an embodiment.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the invention to the specific embodiments. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the spirit of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. The terms "comprise" or "having" in this specification are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features It is to be understood that the numbers, steps, operations, components, parts or figures do not exclude in advance the presence or possibility of adding them.

On the other hand, each configuration in the drawings described in the present invention are shown independently for the convenience of description of the different characteristic functions, it does not mean that each configuration is implemented by separate hardware or separate software. For example, two or more of each configuration may be combined to form one configuration, or one configuration may be divided into a plurality of configurations. Embodiments in which each configuration is integrated and / or separated are also included in the scope of the present invention without departing from the spirit of the present invention.

The following description relates to video / picture coding. For example, the methods / embodiments disclosed in this document may include a versatile video coding (VVC) standard, an essential video coding (EVC) standard, an AOMedia Video 1 (AV1) standard, a second generation of audio video coding standard (AVS2), or next-generation video / It can be applied to the method disclosed in the image coding standard (ex. H.267, H.268, etc.).

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and redundant description of the same components is omitted.

In the present specification, a video may mean a series of images over time. A picture generally refers to a unit representing one image in a specific time zone, and a slice is a unit constituting a part of a picture in coding. One picture may be composed of a plurality of slices, and if necessary, the picture and the slice may be mixed with each other.

A pixel or a pel may refer to a minimum unit constituting one picture (or image). Also, 'sample' may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may only represent pixel / pixel values of the luma component, or only pixel / pixel values of the chroma component.

A unit represents the basic unit of image processing. The unit may include at least one of a specific region of the picture and information related to the region. The unit may be used interchangeably with terms such as block or area in some cases. In a general case, an M × N block may represent a set of samples or transform coefficients composed of M columns and N rows.

1 is a diagram schematically illustrating a configuration of a video encoding apparatus to which the present invention may be applied. Hereinafter, the encoding / decoding device may include a video encoding / decoding device and / or an image encoding / decoding device, and the video encoding / decoding device is used as a concept including the image encoding / decoding device, or the image encoding / decoding device is It may be used in a concept including a video encoding / decoding device.

Referring to FIG. 1, the (video) encoding apparatus 100 may include a picture partitioning module 105, a prediction module 110, a residual processing module 120, and an entropy encoding unit ( The entropy encoding module 130 may include an adder 140, a filtering module 150, and a memory 160. The residual processor 120 may include a substractor 121, a transform module 122, a quantization module 123, a rearrangement module 124, and a dequantization module 125. ) And an inverse transform module 126.

The picture divider 105 may divide the input picture into at least one processing unit.

As an example, the processing unit may be called a coding unit (CU). In this case, the coding unit may be recursively split from the largest coding unit (LCU) according to a quad-tree binary-tree (QTBT) structure. For example, one coding unit may be divided into a plurality of coding units of a deeper depth based on a quad tree structure, a binary tree structure, and / or a ternary tree structure. In this case, for example, the quad tree structure may be applied first, and the binary tree structure and the ternary tree structure may be applied later. Alternatively, the binary tree structure / tunary tree structure may be applied first. The coding procedure according to the present invention may be performed based on the final coding unit that is no longer split. In this case, the maximum coding unit may be used as the final coding unit immediately based on coding efficiency according to the image characteristic, or if necessary, the coding unit is recursively divided into coding units of lower depths and optimized. A coding unit of size may be used as the final coding unit. Here, the coding procedure may include a procedure of prediction, transform, and reconstruction, which will be described later.

As another example, the processing unit may include a coding unit (CU) prediction unit (PU) or a transform unit (TU). The coding unit may be split from the largest coding unit (LCU) into coding units of deeper depths along the quad tree structure. In this case, the maximum coding unit may be used as the final coding unit immediately based on coding efficiency according to the image characteristic, or if necessary, the coding unit is recursively divided into coding units of lower depths and optimized. A coding unit of size may be used as the final coding unit. If a smallest coding unit (SCU) is set, the coding unit may not be split into smaller coding units than the minimum coding unit. Here, the final coding unit refers to a coding unit that is the basis of partitioning or partitioning into a prediction unit or a transform unit. The prediction unit is a unit partitioning from the coding unit and may be a unit of sample prediction. In this case, the prediction unit may be divided into sub blocks. The transform unit may be divided along the quad tree structure from the coding unit, and may be a unit for deriving a transform coefficient and / or a unit for deriving a residual signal from the transform coefficient. Hereinafter, a coding unit may be called a coding block (CB), a prediction unit is a prediction block (PB), and a transform unit may be called a transform block (TB). A prediction block or prediction unit may mean a specific area in the form of a block within a picture, and may include an array of prediction samples. In addition, a transform block or a transform unit may mean a specific area in a block form within a picture, and may include an array of transform coefficients or residual samples.

The prediction unit 110 performs prediction on a block to be processed (hereinafter, may mean a current block or a residual block), and generates a predicted block including prediction samples for the current block. can do. The unit of prediction performed by the prediction unit 110 may be a coding block, a transform block, or a prediction block.

The prediction unit 110 may determine whether intra prediction or inter prediction is applied to the current block. As an example, the prediction unit 110 may determine whether intra prediction or inter prediction is applied on a CU basis.

In the case of intra prediction, the prediction unit 110 may derive a prediction sample for the current block based on reference samples outside the current block in the picture to which the current block belongs (hereinafter, referred to as the current picture). In this case, the prediction unit 110 may (i) derive the prediction sample based on the average or interpolation of neighboring reference samples of the current block, and (ii) the neighbor reference of the current block. The prediction sample may be derived based on a reference sample present in a specific (prediction) direction with respect to the prediction sample among the samples. In case of (i), it may be called non-directional mode or non-angle mode, and in case of (ii), it may be called directional mode or angular mode. In intra prediction, the prediction mode may have, for example, 33 directional prediction modes and at least two non-directional modes. The non-directional mode may include a DC prediction mode and a planner mode (Planar mode). The prediction unit 110 may determine the prediction mode applied to the current block by using the prediction mode applied to the neighboring block.

In the case of inter prediction, the prediction unit 110 may derive the prediction sample for the current block based on the sample specified by the motion vector on the reference picture. The prediction unit 110 may apply one of a skip mode, a merge mode, and a motion vector prediction (MVP) mode to derive a prediction sample for the current block. In the skip mode and the merge mode, the prediction unit 110 may use the motion information of the neighboring block as the motion information of the current block. In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted. In the MVP mode, the motion vector of the current block may be derived using the motion vector of the neighboring block as a motion vector predictor.

In the case of inter prediction, the neighboring block may include a spatial neighboring block existing in the current picture and a temporal neighboring block present in the reference picture. A reference picture including the temporal neighboring block may be called a collocated picture (colPic). The motion information may include a motion vector and a reference picture index. Information such as prediction mode information and motion information may be encoded (entropy) and output in the form of a bitstream.

When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture. Reference pictures included in a reference picture list may be sorted based on a difference in a picture order count (POC) between a current picture and a corresponding reference picture. The POC corresponds to the display order of the pictures and may be distinguished from the coding order.

The subtraction unit 121 generates a residual sample which is a difference between the original sample and the prediction sample. When the skip mode is applied, residual samples may not be generated as described above.

The transform unit 122 generates transform coefficients by transforming the residual sample in units of transform blocks. The transform unit 122 may perform the transform according to the size of the transform block and the prediction mode applied to the coding block or the prediction block that spatially overlaps the transform block. For example, if intra prediction is applied to the coding block or the prediction block that overlaps the transform block, and the transform block is a 4 × 4 residual array, the residual sample is configured to perform a discrete sine transform (DST) transform kernel. The residual sample may be transformed using a discrete cosine transform (DCT) transform kernel.

The quantization unit 123 may quantize the transform coefficients to generate quantized transform coefficients.

The reordering unit 124 rearranges the quantized transform coefficients. The reordering unit 124 may reorder the quantized transform coefficients in the form of a block into a one-dimensional vector form through a coefficient scanning method. Although the reordering unit 124 has been described in a separate configuration, the reordering unit 124 may be part of the quantization unit 123.

The entropy encoding unit 130 may perform entropy encoding on the quantized transform coefficients. Entropy encoding may include, for example, encoding methods such as exponential Golomb, context-adaptive variable length coding (CAVLC), context-adaptive binary arithmetic coding (CABAC), and the like. The entropy encoding unit 130 may encode information necessary for video reconstruction other than the quantized transform coefficients (for example, a value of a syntax element) together or separately according to entropy encoding or a predetermined method. The encoded information may be transmitted or stored in units of network abstraction layer (NAL) units in the form of bitstreams. The bitstream may be transmitted over a network or may be stored in a digital storage medium. The network may include a broadcasting network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like.

The inverse quantization unit 125 inverse quantizes the quantized values (quantized transform coefficients) in the quantization unit 123, and the inverse transformer 126 inverse transforms the inverse quantized values in the inverse quantization unit 125 to generate a residual sample. Create

The adder 140 reconstructs the picture by combining the residual sample and the predictive sample. The residual sample and the predictive sample may be added in units of blocks to generate a reconstructed block. Although the adder 140 has been described in a separate configuration, the adder 140 may be part of the predictor 110. The adder 140 may also be called a reconstruction module or a restore block generator.

The filter unit 150 may apply a deblocking filter and / or a sample adaptive offset to the reconstructed picture. Through deblocking filtering and / or sample adaptive offset, the artifacts of the block boundaries in the reconstructed picture or the distortion in the quantization process can be corrected. The sample adaptive offset may be applied on a sample basis and may be applied after the process of deblocking filtering is completed. The filter unit 150 may apply an adaptive loop filter (ALF) to the reconstructed picture. ALF may be applied to the reconstructed picture after the deblocking filter and / or sample adaptive offset is applied.

The memory 160 may store reconstructed pictures (decoded pictures) or information necessary for encoding / decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 150. The stored reconstructed picture may be used as a reference picture for (inter) prediction of another picture. For example, the memory 160 may store (reference) pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list.

FIG. 2 is a diagram schematically illustrating a configuration of a video / video decoding apparatus to which the present invention can be applied. Hereinafter, the video decoding apparatus may include an image decoding apparatus.

2, the video decoding apparatus 200 may include an entropy decoding module 210, a residual processing module 220, a prediction module 230, and an adder 240. ), A filtering module 250, and a memory 260. The residual processor 220 may include a rearrangement module 221, a dequantization module 222, and an inverse transform module 223. In addition, although not shown, the video decoding apparatus 200 may include a receiver that receives a bitstream including video information. The receiver may be configured as a separate module or may be included in the entropy decoding unit 210.

When a bitstream including video / image information is input, the video decoding apparatus 200 may reconstruct a video / image / picture in response to a process in which video / image information is processed in the video encoding apparatus.

For example, the video decoding apparatus 200 may perform video decoding using a processing unit applied in the video encoding apparatus. Thus, the processing unit block of video decoding may be, for example, a coding unit, and in another example, a coding unit, a prediction unit, or a transform unit. The coding unit may be split along the quad tree structure, binary tree structure and / or ternary tree structure from the largest coding unit.

The prediction unit and the transform unit may be further used in some cases, in which case the prediction block is a block derived or partitioned from the coding unit and may be a unit of sample prediction. At this point, the prediction unit may be divided into subblocks. The transform unit may be divided along the quad tree structure from the coding unit, and may be a unit for deriving a transform coefficient or a unit for deriving a residual signal from the transform coefficient.

The entropy decoding unit 210 may parse the bitstream and output information necessary for video reconstruction or picture reconstruction. For example, the entropy decoding unit 210 decodes information in a bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, quantized values of syntax elements necessary for video reconstruction, and residual coefficients. Can be output.

More specifically, the CABAC entropy decoding method receives a bin corresponding to each syntax element in a bitstream, and decodes syntax element information and decoding information of neighboring and decoding target blocks or information of symbols / bins decoded in a previous step. The context model is determined using the context model, the probability of occurrence of a bin is predicted according to the determined context model, and arithmetic decoding of the bin is performed to generate a symbol corresponding to the value of each syntax element. can do. In this case, the CABAC entropy decoding method may update the context model by using the information of the decoded symbol / bin for the context model of the next symbol / bin after determining the context model.

The information related to the prediction among the information decoded by the entropy decoding unit 210 is provided to the prediction unit 230, and the residual value on which the entropy decoding has been performed by the entropy decoding unit 210, that is, the quantized transform coefficient, is used as a reordering unit ( 221 may be input.

The reordering unit 221 may rearrange the quantized transform coefficients in a two-dimensional block form. The reordering unit 221 may perform reordering in response to coefficient scanning performed by the encoding apparatus. Here, the rearrangement unit 221 has been described in a separate configuration, but the rearrangement unit 221 may be part of the inverse quantization unit 222.

The inverse quantization unit 222 may dequantize the quantized transform coefficients based on the (inverse) quantization parameter and output the transform coefficients. In this case, information for deriving a quantization parameter may be signaled from the encoding apparatus.

The inverse transform unit 223 may inversely transform transform coefficients to derive residual samples.

The prediction unit 230 may perform prediction on the current block and generate a predicted block including prediction samples for the current block. The unit of prediction performed by the prediction unit 230 may be a coding block, a transform block, or a prediction block.

The prediction unit 230 may determine whether to apply intra prediction or inter prediction based on the information about the prediction. In this case, a unit for determining which of intra prediction and inter prediction is to be applied and a unit for generating a prediction sample may be different. In addition, the unit for generating a prediction sample in inter prediction and intra prediction may also be different. For example, whether to apply inter prediction or intra prediction may be determined in units of CUs. In addition, for example, in inter prediction, a prediction mode may be determined and a prediction sample may be generated in PU units, and in intra prediction, a prediction mode may be determined in PU units and a prediction sample may be generated in TU units.

In the case of intra prediction, the prediction unit 230 may derive the prediction sample for the current block based on the neighbor reference samples in the current picture. The prediction unit 230 may derive the prediction sample for the current block by applying the directional mode or the non-directional mode based on the neighbor reference samples of the current block. In this case, the prediction mode to be applied to the current block may be determined using the intra prediction mode of the neighboring block.

In the case of inter prediction, the prediction unit 230 may derive the prediction sample for the current block based on the sample specified on the reference picture by the motion vector on the reference picture. The prediction unit 230 may apply any one of a skip mode, a merge mode, and an MVP mode to derive a prediction sample for the current block. In this case, motion information required for inter prediction of the current block provided by the video encoding apparatus, for example, information about a motion vector, a reference picture index, and the like may be obtained or derived based on the prediction information.

In the skip mode and the merge mode, the motion information of the neighboring block may be used as the motion information of the current block. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

The prediction unit 230 may construct a merge candidate list using motion information of available neighboring blocks, and may use information indicated by the merge index on the merge candidate list as a motion vector of the current block. The merge index may be signaled from the encoding device. The motion information may include a motion vector and a reference picture. When the motion information of the temporal neighboring block is used in the skip mode and the merge mode, the highest picture on the reference picture list may be used as the reference picture.

In the skip mode, unlike the merge mode, the difference (residual) between the prediction sample and the original sample is not transmitted.

In the MVP mode, the motion vector of the current block may be derived using the motion vector of the neighboring block as a motion vector predictor. In this case, the neighboring block may include a spatial neighboring block and a temporal neighboring block.

For example, when the merge mode is applied, a merge candidate list may be generated by using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block, which is a temporal neighboring block. In the merge mode, the motion vector of the candidate block selected from the merge candidate list is used as the motion vector of the current block. The information about the prediction may include a merge index indicating a candidate block having an optimal motion vector selected from candidate blocks included in the merge candidate list. In this case, the prediction unit 230 may derive the motion vector of the current block by using the merge index.

As another example, when the Motion Vector Prediction (MVP) mode is applied, a motion vector predictor candidate list may be generated using a motion vector of a reconstructed spatial neighboring block and / or a motion vector corresponding to a Col block, which is a temporal neighboring block. Can be. That is, the motion vector of the reconstructed spatial neighboring block and / or the Col vector, which is a temporal neighboring block, may be used as a motion vector candidate. The prediction information may include a prediction motion vector index indicating an optimal motion vector selected from the motion vector candidates included in the list. In this case, the prediction unit 230 may select the predicted motion vector of the current block from the motion vector candidates included in the motion vector candidate list using the motion vector index. The prediction unit of the encoding apparatus may obtain a motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and may encode the output vector in a bitstream form. That is, MVD may be obtained by subtracting the motion vector predictor from the motion vector of the current block. In this case, the prediction unit 230 may obtain a motion vector difference included in the information about the prediction, and derive the motion vector of the current block by adding the motion vector difference and the motion vector predictor. The prediction unit may also obtain or derive a reference picture index or the like indicating a reference picture from the information about the prediction.

The adder 240 may reconstruct the current block or the current picture by adding the residual sample and the predictive sample. The adder 240 may reconstruct the current picture by adding the residual sample and the predictive sample in block units. Since the residual is not transmitted when the skip mode is applied, the prediction sample may be a reconstruction sample. Although the adder 240 has been described in a separate configuration, the adder 240 may be part of the predictor 230. The adder 240 may also be called a reconstruction module or a reconstruction block generator.

The filter unit 250 may apply the deblocking filtering sample adaptive offset, and / or ALF to the reconstructed picture. In this case, the sample adaptive offset may be applied in units of samples and may be applied after deblocking filtering. ALF may be applied after deblocking filtering and / or sample adaptive offset.

The memory 260 may store reconstructed pictures (decoded pictures) or information necessary for decoding. Here, the reconstructed picture may be a reconstructed picture after the filtering process is completed by the filter unit 250. For example, the memory 260 may store pictures used for inter prediction. In this case, pictures used for inter prediction may be designated by a reference picture set or a reference picture list. The reconstructed picture can be used as a reference picture for another picture. In addition, the memory 260 may output the reconstructed picture in an output order.

Meanwhile, as described above, prediction is performed in order to increase compression efficiency in performing video coding. Through this, a predicted block including prediction samples of the current block, which is a coding target block, may be generated. Wherein the predicted block comprises prediction samples in the spatial domain (or pixel domain). The predicted block is derived identically in the encoding apparatus and the decoding apparatus, and the encoding apparatus decodes information (residual information) about the residual between the original block and the predicted block, not the original sample value itself of the original block. Signaling to an apparatus may increase image coding efficiency. The decoding apparatus may derive a residual block including residual samples based on the residual information, generate the reconstructed block including reconstructed samples by adding the residual block and the predicted block, and generate reconstructed blocks. A reconstructed picture may be generated.

The residual information may be generated through a transform and quantization procedure. For example, the encoding apparatus derives a residual block between the original block and the predicted block, and performs transform procedure on residual samples (residual sample array) included in the residual block to derive transform coefficients. The quantized transform coefficients may be derived by performing a quantization procedure on the transform coefficients to signal related residual information to the decoding device (via a bitstream). Here, the residual information may include information such as value information of the quantized transform coefficients, position information, a transform scheme, a transform kernel, and a quantization parameter. The decoding apparatus may perform an inverse quantization / inverse transformation procedure and derive residual samples (or residual blocks) based on the residual information. The decoding apparatus may generate a reconstructed picture based on the predicted block and the residual block. The encoding apparatus may then dequantize / inverse transform the quantized transform coefficients for reference for inter prediction of the picture to derive a residual block, and generate a reconstructed picture based thereon.

3 is a schematic block diagram of a decoding apparatus in which decoding of a video signal is performed as an embodiment to which the present invention may be applied. Referring to FIG. 3, the decoding apparatus includes an entropy decoding unit, a DC coefficient updating unit, an inverse quantization unit, an inverse transform unit, a filtering unit, a decoded picture buffer unit (DPB), an inter prediction unit, and an intra prediction unit. Can be. The reconstructed video signal output through the decoder may be reproduced through the reproducing apparatus.

The decoding apparatus may receive a signal output from the encoding apparatus, and the received signal may be entropy decoded through an entropy decoding unit. The DC coefficient updating unit applies a scale to an entropy decoded DC coefficient according to a scale flag value indicating whether scaling is applied to the decoded DC coefficient, and an offset flag indicating whether to apply an offset. By applying an offset according to the offset flag), the DC coefficient can be finally updated. In this case, the scale flag and the offset flag may be decoded from the bitstream, but embodiments are not limited thereto. The inverse quantization unit may obtain a transform coefficient from the entropy decoded signal using the quantization step size information. The inverse transform unit may inverse transform the transform coefficients to obtain a residual signal. The obtained residual signal may be added to the prediction signal output from the inter predictor or the intra predictor to generate a reconstruction signal. The filtering unit may apply filtering to the reconstruction signal and output the reconstruction signal to which the filtering is applied to the reproduction apparatus or transmit the decoded picture buffer unit. The filtered signal transmitted to the decoded picture buffer unit may be used as a reference picture in the inter predictor.

First, an entropy decoding unit according to an embodiment may decode a DC coefficient (C _DC ).

Subsequently, it may be determined whether scaling is to be applied to the decoded DC coefficients based on the value of the ADCS (Adaptive DC Scaling) flag. Here, the ADCS flag represents a flag used when determining whether to apply scaling according to the present invention. If the value of the ADCS flag is 0, scaling on the DC coefficient may not be applied. When the value of the ADCS flag is 1, a sequence parameter set (SPS), a picture parameter set (PPS), a slice header (SH) may be defined in advance in an encoding device and / or a decoding device. Alternatively, scaling is applied to DC coefficients using a scale value (eg, n) received from a Network Abstract Layer (NAL) unit. By applying scaling, the value of the first updated DC coefficient C ′ _DC may be derived based on Equation 1 below.

[Equation 1]

C ' _DC = n * C _DC

In Equation 1, C ′ _DC represents the first updated DC coefficient, n represents the scale value, and C _DC represents the decoded DC coefficient. The value of n may be, for example, 2 or 4, and the example is not limited thereto.

Then, it may be determined whether to apply an offset to the first updated DC coefficient based on the value of an offset flag. Here, the offset flag may indicate whether to correct the DC coefficient through an offset value after scaling application according to an embodiment of the present invention. When the value of the offset flag is 0, the C ′ _DC value of Equation 1 may be used as the second updated DC coefficient without separately applying an offset to the DC coefficient. When the value of the offset flag is 1, an offset may be applied to the first updated DC coefficient to derive a second updated DC coefficient.

In one embodiment, the offset value O may be determined as one half of the scale value n. Alternatively, an offset in the form of an absolute value may be applied.

For example, when the scale value n has a value of 2, an offset value 1 may be used. Alternatively, when the scale value n has a value of 4, the offset value may be determined as 2, or may be selected as one of 0, 1, 2, and 3. The value of the second updated DC coefficient by the offset may be derived based on Equation 2 below.

[Equation 2]

C " _DC = C ' _DC + O

In Equation 2, C ″ _DC represents the second updated DC coefficient, 0 represents the offset value, and C ′ _DC represents the first updated DC coefficient. According to the embodiment of FIG. Scaling and offset application to DC coefficients can be extended to a specific AC coefficient or all AC coefficients.

In this specification, the "first updated DC coefficient" and the "second updated DC coefficient" are arbitrarily divided step by step the updated DC coefficients based on the scale and / or offset. It is only one example, and therefore it is easy for a person skilled in the art that the updated DC coefficients are intended to indicate that they are a predefined DC coefficient or do not have a special meaning in the ordinal representing the updated DC coefficients. Will be understood.

5 is a flowchart illustrating another example of applying a scaling and / or offset to a DC coefficient by a decoding apparatus according to an embodiment, based on a comparison with a threshold (or threshold) value.

First, the entropy decoding unit according to an embodiment may decode (decode) a DC coefficient (C _DC ). The decoded DC coefficient may be concentrated in a specific range according to the value of the quantization parameter QP. In this case, it may be effective to apply an adaptive scale and offset to the DC coefficient only when the decoded (decoded) DC coefficient is larger than a specific threshold (or threshold) value. For example, when the threshold value Th is 1, when the decoded DC coefficient is 1, scaling and / or offset for the DC coefficient may not be applied. In addition, when the threshold value Th is 2, when the decoded DC coefficient is 1 or 2, scaling and / or offset with respect to the DC coefficient may not be applied. The threshold value may be predefined according to the QP value or may use a value received from a sequence parameter set, a picture parameter set, a slice header, or a network abstraction layer unit.

Subsequently, it may be determined whether scaling is to be applied to the decoded DC coefficients based on the value of the ADCS (Adaptive DC Scaling) flag. If the value of the ADCS flag is 0, scaling on the DC coefficient may not be applied. When the value of the ADCS flag is 1, a sequence parameter set (SPS), a picture parameter set (PPS), and a slice header (SH) are defined in advance in the encoding device and / or the decoding device. Alternatively, scaling may be applied to DC coefficients using a scale value (eg, n) received from a Network Abstract Layer (NAL) unit. By applying scaling, the value of the first updated DC coefficient C ′ _DC may be derived based on Equation 1 above. The scale value may be, for example, 2 or 4, and the example is not limited thereto.

For example, when the scale value n has a value of 2, an offset value 1 may be used. Alternatively, when the scale value n has a value of 4, the offset value may be determined as 2, or may be selected as one of 0, 1, 2, and 3. The value of the second updated DC coefficient by the offset may be derived based on Equation 2 above.

The scaling and offset application for the DC coefficients according to the embodiment of FIG. 5 may be extended to a specific AC coefficient or all AC coefficients.

The decoded DC coefficient may be concentrated in a specific range according to the value of the quantization parameter QP. In this case, it may be effective to apply an adaptive scale and / or offset to the DC coefficient only when the decoded (decoded) DC coefficient is larger than a specific threshold (or threshold) value. For example, when the threshold value Th is 1, when the decoded DC coefficient is 1, scaling and / or offset for the DC coefficient may not be applied. In addition, when the threshold value Th is 2, when the decoded DC coefficient is 1 or 2, scaling and / or offset with respect to the DC coefficient may not be applied. The threshold value may be predefined according to the QP value or may use a value received from a sequence parameter set, a picture parameter set, a slice header, or a network abstraction layer unit. However, the operation of determining whether to apply the adaptive scaling and / or offset to the DC coefficient based on the threshold value is not a mandatory operation, and even referring to the flowchart of FIG. 6, the adaptive scaling of the DC coefficient based on the threshold value is not required. And / or the operation of determining whether to apply the offset is omitted.

Subsequently, it may be determined whether scaling is to be applied to the decoded DC coefficients based on the value of the ADCS (Adaptive DC Scaling) flag. Here, the ADCS flag represents a flag used when determining whether to apply scaling according to the present invention. If the value of the ADCS flag is 0, scaling on the DC coefficient may not be applied. When the value of the ADCS flag is 1, a sequence parameter set (SPS), a picture parameter set (PPS), a slice header (SH) may be defined in advance in an encoding device and / or a decoding device. Alternatively, scaling may be applied to DC coefficients using a scale value (eg, n) received from a Network Abstract Layer (NAL) unit.

The decoding apparatus according to an embodiment may select one of the plurality of scale values and apply scaling to the DC coefficients based on the selected scale value. For example, the decoding apparatus may apply scaling to the DC coefficient by selecting one of the scale values n or 2n. When n is selected as the scale value, Equation 3 is shown below, and when 2n is selected as the scale value, it is shown in Equation 4 below.

[Equation 3]

C ' _DC = n * C _DC

[Equation 4]

C ' _DC = 2n * C _DC

In one embodiment, the offset value O may be determined as one of the scale values n or 2n. Alternatively, an offset in the form of an absolute value may be applied.

The offset value when the scale value is 2n may be equal to or double the offset value when the scale value is n. For example, if the offset value is 1 when the scale value n is 2, the offset value may be 1 or 2 when the scale value 2n is 4. The scaling and offset application of the DC coefficients according to the embodiment of FIG. 6 may be extended to a specific AC coefficient or all AC coefficients.

7 is a flowchart illustrating an operation of a decoding apparatus according to an embodiment, and FIG. 8 is a block diagram illustrating a configuration of a decoding apparatus according to an embodiment.

The encoding apparatus according to FIG. 1 may perform operations corresponding to the decoding apparatus according to FIGS. 7 and 8. Therefore, the contents described below with reference to FIGS. 7 and 8 may be similarly applied to the encoding apparatus according to FIG. 1.

Each step disclosed in FIG. 7 may be performed by the decoding apparatus 200 disclosed in FIG. 2 or the decoding apparatus disclosed in FIG. 3. More specifically, S700 may be performed by the entropy decoding unit 210 disclosed in FIG. 2, S710 to S720 may be performed by the DC coefficient updating unit disclosed in FIG. 3, and S730 may be inverse quantization disclosed in FIG. 2. It may be performed by the unit 222, S740 may be performed by the inverse transform unit 223 shown in FIG. 2, S750 may be performed by the adder 240 shown in FIG. In addition, operations according to S700 to S750 are based on some of the contents described above with reference to FIGS. 3 to 6. Accordingly, detailed descriptions overlapping with the foregoing descriptions in FIGS. 2 to 6 will be omitted or simply described.

As shown in FIG. 8, a decoding apparatus according to an embodiment may include an entropy decoding unit, a DC coefficient updater, an inverse quantizer, an inverse transformer, and an adder. However, in some cases, all of the components shown in FIG. 8 may not be essential components of the decoding apparatus, and the decoding apparatus may be implemented by more or fewer components than those illustrated in FIG. 8.

In the decoding apparatus according to an embodiment, the entropy decoding unit, the DC coefficient updater, the inverse quantizer, the inverse transformer, and the adder may be implemented as separate chips, or at least two or more components may be implemented through one chip. It may be.

The decoding apparatus according to an embodiment may decode a DC coefficient from the bitstream (S700). More specifically, the entropy decoding unit of the decoding apparatus may decode the DC coefficient from the bitstream.

The decoding apparatus according to an embodiment may derive a first updated DC coefficient based on a scale flag indicating whether scaling is to be applied to the decoded DC coefficient (S710). More specifically, the DC coefficient updater of the decoding apparatus may derive the first updated DC coefficient based on the scale flag indicating whether to apply scaling to the decoded DC coefficient.

The decoding apparatus according to an embodiment may derive a second updated DC coefficient based on an offset flag indicating whether to apply an offset to the first updated DC coefficient (S720). More specifically, the DC coefficient updater of the decoding apparatus may derive the second updated DC coefficient based on an offset flag indicating whether to apply an offset to the first updated DC coefficient.

The decoding apparatus according to an embodiment may derive a transform coefficient based on the second updated DC coefficient (S730). More specifically, the dequantization unit of the decoding apparatus may derive a transform coefficient based on the second updated DC coefficient.

The decoding apparatus according to an embodiment may derive a residual sample based on the transform coefficients (S740). More specifically, the inverse transform unit of the decoding apparatus may derive the residual sample based on the transform coefficients.

The decoding apparatus according to an embodiment may derive a reconstructed sample based on the residual sample (S750). More specifically, the adder of the decoding apparatus may derive a reconstructed sample based on the residual sample.

In one embodiment, if the value of the scale flag is 1, the first updated DC coefficient is derived by multiplying the decoded DC coefficient by a scale value, and if the value of the scale flag is 0, the first updated DC The coefficient may be the same as the decoded DC coefficient.

In one embodiment, the scale value is predefined in the decoding device, or is a sequence parameter set (SPS), picture parameter set (PPS), slice header (SH) or network abstraction. It may be received from a network abstract layer (NAL) unit.

In one embodiment, if the value of the offset flag is 1, the second updated DC coefficient is derived by adding an offset value to the first updated DC coefficient, and if the value of the offset flag is 0, the second update The updated DC coefficient may be the same as the first updated DC coefficient.

In one embodiment, the offset value is predefined in the decoding device, or is a sequence parameter set (SPS), picture parameter set (PPS), slice header (SH) or network abstraction. It may be received from a network abstract layer (NAL) unit.

In one embodiment, the offset value may be half of the scale value.

In one embodiment, deriving the first updated DC coefficient based on the scale flag and deriving the second updated DC coefficient based on the offset flag, wherein the decoded DC coefficient is a threshold value. may be performed when the value is greater than the threshold value.

In one embodiment, the first updated DC coefficient may be derived based on Equation 5 below.

[Equation 5]

C ' _DC = n * C _DC

In Equation 5, C ′ _DC may represent the first updated DC coefficient, n may represent the scale value, and C _DC may represent the decoded DC coefficient.

In one embodiment, the second updated DC coefficient may be derived based on Equation 6 below.

[Equation 6]

C " _DC = C ' _DC + O

In Equation 6, C ″ _DC may represent the second updated DC coefficient, 0 may represent the offset value, and C ′ _DC may represent the first updated DC coefficient.

According to the method of operating the decoding apparatus and the decoding apparatus of FIGS. 7 and 8, the decoding apparatus decodes a DC coefficient from the bitstream (S700), and indicates whether to apply scaling to the decoded DC coefficient. A first updated DC coefficient is derived based on the scale flag (S710), and the second updated DC coefficient is based on an offset flag indicating whether to apply an offset to the first updated DC coefficient. a second updated DC coefficient (S720), a transform coefficient based on the second updated DC coefficient (S730), and a residual sample based on the transform coefficient (S740). In step S750, a reconstructed sample may be derived based on the residual sample. That is, according to FIGS. 7 and 8, entropy coding may be efficiently performed on DC coefficients by applying scaling and / or offset to DC coefficients, and image coding efficiency may be increased based on the DC coefficients.

Embodiments described in the present invention may be implemented and performed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in each drawing may be implemented and performed on a computer, processor, microprocessor, controller, or chip.

In addition, the decoder and encoder to which the embodiments of the present invention are applied include a multimedia broadcasting transmitting and receiving device, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video chat device, and a real time communication device such as video communication. Streaming devices, storage media, camcorders, video on demand (VoD) service providers, over the top video (OTT) devices, internet streaming service providers, three-dimensional (3D) video devices, video telephony video devices, and medical video devices Etc., and may be used to process video signals or data signals. For example, the OTT video device may include a game console, a Blu-ray player, an internet access TV, a home theater system, a smartphone, a tablet PC, a digital video recorder (DVR), and the like.

In addition, the processing method to which the embodiments of the present invention are applied may be produced in the form of a program executed by a computer, and may be stored in a computer-readable recording medium. Multimedia data having a data structure according to the present invention can also be stored in a computer-readable recording medium. The computer readable recording medium includes all kinds of storage devices and distributed storage devices in which computer readable data is stored. The computer-readable recording medium may be, for example, a Blu-ray disc (BD), a universal serial bus (USB), a ROM, a PROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical disc. It may include a data storage device. The computer-readable recording medium also includes media embodied in the form of a carrier wave (for example, transmission over the Internet). In addition, the bitstream generated by the encoding method may be stored in a computer-readable recording medium or transmitted through a wired or wireless communication network.

In addition, embodiments of the present invention may be implemented as a computer program product by program code, which may be performed on a computer by embodiments of the present invention. The program code may be stored on a carrier readable by a computer.

The content streaming system to which the present invention is applied may largely include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

The encoding server compresses content input from multimedia input devices such as a smart phone, a camera, a camcorder, etc. into digital data to generate a bitstream and transmit the bitstream to the streaming server. As another example, when multimedia input devices such as smart phones, cameras, camcorders, etc. directly generate a bitstream, the encoding server may be omitted.

The bitstream may be generated by an encoding method or a bitstream generation method to which the present invention is applied, and the streaming server may temporarily store the bitstream in the process of transmitting or receiving the bitstream.

The streaming server transmits the multimedia data to the user device based on the user's request through the web server, and the web server serves as a medium for informing the user of what service. When a user requests a desired service from the web server, the web server delivers it to a streaming server, and the streaming server transmits multimedia data to the user. In this case, the content streaming system may include a separate control server. In this case, the control server plays a role of controlling a command / response between devices in the content streaming system.

The streaming server may receive content from a media store and / or an encoding server. For example, when the content is received from the encoding server, the content may be received in real time. In this case, in order to provide a smooth streaming service, the streaming server may store the bitstream for a predetermined time.

Examples of the user device include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), navigation, a slate PC, Tablet PCs, ultrabooks, wearable devices, such as smartwatches, glass glasses, head mounted displays, digital TVs, desktops Computer, digital signage, and the like.

Each server in the content streaming system may be operated as a distributed server, in which case data received from each server may be distributed.

The above-described method according to the present invention may be implemented in software, and the encoding device and / or the decoding device according to the present invention may perform image processing of, for example, a TV, a computer, a smartphone, a set-top box, a display device, and the like. It can be included in the device.

Each part, module, or unit described above may be a processor or hardware part that executes successive procedures stored in a memory (or storage unit). Each of the steps described in the above embodiments may be performed by a processor or hardware parts. Each module / block / unit described in the above embodiments can operate as a hardware / processor. In addition, the methods proposed by the present invention can be executed as code. This code can be written to a processor readable storage medium and thus read by a processor provided by an apparatus.

In the above-described embodiment, the methods are described based on a flowchart as a series of steps or blocks, but the present invention is not limited to the order of steps, and any steps may occur in a different order or simultaneously from other steps as described above. have. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

When embodiments of the present invention are implemented in software, the above-described method may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means. The processor may include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device.

Claims

In the picture decoding method by the decoding device,

Decoding a DC coefficient from the bitstream;

Deriving a first updated DC coefficient based on a scale flag indicating whether scaling is to be applied to the decoded DC coefficients;

Deriving a second updated DC coefficient based on an offset flag indicating whether to apply an offset to the first updated DC coefficient;

Deriving a transform coefficient based on the second updated DC coefficient;

Deriving a residual sample based on the transform coefficients; And

Deriving a reconstructed sample based on the residual sample.
The method of claim 1,

If the value of the scale flag is 1, the first updated DC coefficient is derived by multiplying the decoded DC coefficient by a scale value,

If the value of the scale flag is zero, the first updated DC coefficient is equal to the decoded DC coefficient.
The method of claim 2,

The scale value may be predefined in the decoding apparatus, or may be a sequence parameter set (SPS), a picture parameter set (PSP), a slice header (SH), or a network abstract layer (Network Abstract Layer). , NAL), picture decoding method.
The method of claim 2,

If the value of the offset flag is 1, the second updated DC coefficient is derived by adding an offset value to the first updated DC coefficient,

And if the value of the offset flag is zero, the second updated DC coefficient is equal to the first updated DC coefficient.
The method of claim 4, wherein

The offset value may be predefined in the decoding device, or may be a sequence parameter set (SPS), a picture parameter set (PSP), a slice header (SH), or a network abstract layer (Network Abstract Layer). , NAL), picture decoding method.
The method of claim 4, wherein

And the offset value is half of the scale value.
The method of claim 1,

Deriving the first updated DC coefficient based on the scale flag and deriving the second updated DC coefficient based on the offset flag, wherein the decoded DC coefficient is less than a threshold value. Characterized in that it is performed when large.
The method of claim 1,

The first updated DC coefficient is derived based on the formula below,

C ' DC = n * C DC

In the equation of claim 7, wherein C ' DC represents the first updated DC coefficients, n represents the scale value, and C DC represents the decoded DC coefficients.
The method of claim 1,

The second updated DC coefficient is derived based on the formula below,

C " DC = C ' DC + O

In the equation of claim 8, C ″ DC represents the second updated DC coefficient, 0 represents the offset value, and C ′ DC represents the first updated DC coefficient. Way.
In the decoding apparatus for performing picture decoding,

An entropy decoding unit for decoding a DC coefficient from the bitstream;

Derive a first updated DC coefficient based on a scale flag indicating whether to apply scaling to the decoded DC coefficients, and generate a first updated DC coefficient based on an offset flag indicating whether to apply an offset to the first updated DC coefficient. A DC coefficient updater for deriving an updated DC coefficient;

An inverse quantizer for deriving a transform coefficient based on the second updated DC coefficient;

An inverse transform unit for deriving a residual sample based on the transform coefficients; And

And an adder for deriving a reconstructed sample based on the residual sample.