Image information notification method and apparatus, and decoding method and apparatus using the same

Abstract

To provide a method for signaling image information in coding / decoding image information, and a decoding method using the method.SOLUTION: The method for signaling image information according to the present invention comprises steps of: performing inter-prediction for a current picture; and signaling information including a result of the inter-prediction and reference picture information indicating reference pictures usable in the inter prediction. The reference picture information contains POC information of the usable reference pictures. The POC information of the usable reference pictures in the reference picture information is configured such that POCs for the pictures existing before the current picture in terms of a POC sequence are located at the front, and POCs for the pictures existing after the current picture in terms of the POC sequence are located following the POCs located at the front.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to video compression technology, and more specifically, to a method and apparatus for efficiently signaling video information, and a decoding method and apparatus using the same.

Background Art

[0002] Recently, the demand for high-resolution and high-quality videos has been increasing in various application fields. However, as the video has higher resolution and better quality, the amount of information related to the corresponding video also increases accordingly.

[0003] Therefore, when transferring video information using a medium such as a conventional wired or wireless broadband line, or storing video information using an existing storage medium, the transfer cost and storage cost of the information increase.

[0004] In order to effectively transfer, store, or play back information of high-resolution and high-quality videos, high-efficiency video compression technology can be used.

[0005] To improve the efficiency of video compression, inter prediction and intra prediction can be used. In the inter prediction method, the pixel value of the current picture is predicted by referring to the information of other pictures, and in the intra prediction method, the pixel value is predicted by using the relationship between pixels within the same picture.

[0006] When adopting inter prediction, the encoding device and the decoding device perform prediction based on a reference picture list that indicates the reference pictures available for the current block (current picture).

[0007] The information for creating the reference picture list is transferred from the encoding device to the decoding device. The decoding device can create a reference picture list based on the information received from the encoding device and effectively perform inter prediction.

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a method and apparatus for effectively notifying video information in video information encoding / decoding.

[0009] An object of the present invention is to provide a method and apparatus for effectively notifying information for inter prediction in video information encoding / decoding.

[0010] An object of the present invention is to provide a method and apparatus for effectively notifying information for creating a reference picture list for inter prediction.

[0011] An object of the present invention is to provide a method and apparatus for effectively configuring a reference picture list for inter prediction based on received information.

Means for Solving the Problems

[0012] One embodiment of the present invention is a video information notification method, including a step of performing inter prediction on a current picture, and a step of notifying information including reference picture information indicating an inter prediction result and reference pictures available for inter prediction, where the reference picture information includes picture order count (POC) information of available reference pictures, and the POC information of available reference pictures in the reference picture information is arranged such that the POCs for pictures before the current picture are placed at the head part in POC order, and the POCs for pictures after the current picture are subsequently placed in POC order.

[0013] At this time, the POC information is arranged in descending order of the POC of the reference picture for reference pictures before the current picture in POC order, and in ascending order of the POC of the reference picture for reference pictures after the current picture in POC order.

[0014] The POC information may be the POC difference between the target reference picture and other pictures among the reference pictures indicated by the reference picture information, and in the reference picture information, the POC information of the reference pictures can be aligned based on the POC of each target reference picture.

[0015] The POC information of the reference pictures includes the magnitude and sign of the POC difference between the target reference picture and the reference picture among the reference pictures indicated by the reference picture information, and in the reference picture information, the POC information of the reference pictures can be aligned based on the POC of the target reference picture.

[0016] At this time, within the reference picture information, the POC information is arranged in POC order. For the reference pictures before the current picture, it is in descending order of the POC of the reference pictures, and for the reference pictures after the current picture, it is in ascending order of the POC of the reference pictures. When the target reference picture is one of the pictures closest to the current picture among the pictures before the current picture in POC order and one of the pictures closest to the current picture among the pictures after the current picture among the reference pictures indicated by the reference picture information, the reference picture is the current picture. When the target reference picture is not one of the pictures closest to the current picture among the pictures before the current picture in POC order and one of the pictures closest to the current picture among the pictures after the current picture among the reference pictures indicated by the reference picture information, the reference picture may be the reference picture corresponding to the POC information immediately before the POC information of the target reference picture in the reference picture information.

[0017] Also, at this time, the sign of the POC difference may be the sign of the difference between the POC of the target reference picture and the POC of the current picture.

[0018] The POC information of the reference pictures available in the reference picture information may be information indicating the magnitude of the POC difference and the number of cases where the sign of the POC difference is negative and the number of cases where the sign of the POC difference is positive among the reference pictures indicated by the reference picture information. The POC information of the reference pictures in the reference picture information can be aligned based on the POC of the target reference picture.

[0019] At this time, the sign of the POC difference may be the sign of the difference between the POC of the target reference picture and the POC of the current picture.

[0020] Also, at this time, within the reference picture information, the POC information is arranged in POC order. For reference pictures before the current picture, it is in descending order of the POC of the reference pictures, and for reference pictures after the current picture, it is in ascending order of the POC of the reference pictures. When the target reference picture is either one of the pictures closest to the current picture among the pictures before the current picture in POC order and the pictures closest to the current picture among the pictures after the current picture among the reference pictures indicated by the reference picture information, the reference picture is the current picture. When the target reference picture is not either one of the pictures closest to the current picture among the pictures before the current picture in POC order and the pictures closest to the current picture among the pictures after the current picture among the reference pictures indicated by the reference picture information, the reference picture may be the reference picture corresponding to the POC information immediately before the POC information of the target reference picture in the reference picture information.

[0021] Another embodiment of the present invention is a method for decoding video information, comprising: entropy-decoding information of a received bitstream to obtain reference picture information including POC information of reference pictures available for prediction of a current picture; and performing prediction on a current block by using a reference picture list configured based on the POC of each reference picture derived from the reference picture information, wherein in the reference picture information, the POC information of the reference pictures is arranged such that, in POC order, the POCs for pictures before the current picture are placed at the head portion, and in POC order, the POCs for pictures after the current picture are subsequently placed.

[0022] The POC information is arranged such that, in POC order, for reference pictures before the current picture, it is in descending order of the POC of the reference pictures, and for reference pictures after the current picture, it is in ascending order of the POC of the reference pictures.

[0023] The i-th (i is an integer) POC information POCi in the reference picture information is the POC information of the reference picture Pi, and POCi includes the magnitude of the POC difference between Pi and the reference picture in the reference picture information, and the POC information of the reference pictures in the reference picture information can be arranged based on the POC of the target reference picture.

[0024] At this time, within the reference picture information, the POC information is arranged in POC order. For reference pictures before the current picture, it is in descending order of the POC of the reference picture, and for reference pictures after the current picture, it is in ascending order of the POC of the reference picture. If Pi is one of the reference pictures indicated by the reference picture information, and among the pictures before the current picture in POC order, it is the picture closest to the current picture, and among the pictures after the current picture, it is the picture closest to the current picture, then the reference picture is the current picture. If Pi is not one of the pictures closest to the current picture among the pictures before the current picture in POC order and the pictures after the current picture indicated by the reference picture information, then the reference picture may be the reference picture corresponding to the (i - 1)-th POC information in the reference picture information.

[0025] Also, at this time, the POC information can include information indicating the sign of the difference between the POC of the target reference picture and the POC of the current picture.

[0026] The i-th (where i is an integer) POC information POCi in the reference picture information is the POC information of the reference picture Pi. POCi includes the magnitude of the POC difference between Pi and the reference picture in the reference picture information. In the reference picture information, the POC information of the reference pictures can be sorted based on the POC of the target reference picture.

[0027] At this time, within the reference picture information, the POC information is arranged in POC order. For reference pictures before the current picture, it is in descending order of the POC of the reference picture, and for reference pictures after the current picture, it is in ascending order of the POC of the reference picture. When Pi is one of the pictures closest to the current picture among the pictures before the current picture in POC order among the reference pictures indicated by the reference picture information, and one of the pictures closest to the current picture among the pictures after the current picture, the reference picture is the current picture. When Pi is not one of the pictures closest to the current picture among the pictures before the current picture in POC order among the reference pictures indicated by the reference picture information, and one of the pictures closest to the current picture among the pictures after the current picture, the reference picture may be the reference picture corresponding to the (i - 1)-th POC information in the reference picture information.

[0028] Also, at this time, the reference picture information can include information indicating the order relationship between the POC of each target reference picture and the POC of the current picture.

[0029] Also, the POC information includes POC difference information and sign information. Among the m reference pictures indicated by the reference picture information, when the number of reference pictures before the current picture in POC order is n, for the POCk which is the k-th (0 ≦ k ≦ n - 1) POC difference information among the POC difference information, the POC of the reference picture k corresponding to POCk may be the difference between the POC of the first reference picture and POCk. For the POCj which is the j-th (n ≦ j ≦ m) POC difference information among the POC difference information, the POC of the reference picture j corresponding to POCj may be the sum of the POC of the second reference picture and POCj.

[0030] At this time, when k is 0, the first reference picture is the current picture. When k is not 0, the first reference picture is the reference picture corresponding to the (k - 1)-th POC difference information. When j is n, the second reference picture is the current picture. When j is not n, the second reference picture may be the reference picture corresponding to the (n - 1)-th POC difference information.

Advantages of the Invention

[0031] According to the present invention, in the encoding / decoding of video information, video information can be effectively notified.

[0032] According to the present invention, information for creating a reference picture list for performing inter prediction can be effectively notified.

[0033] According to the present invention, the transfer overhead when transferring information for creating a reference picture list can be reduced.

[0034] According to the present invention, after receiving information for creating a reference picture list, a reference picture list for inter prediction can be effectively configured with low complexity based on the received information.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

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Figure 8

Best Mode for Carrying Out the Invention

[0036] Since the present invention can be subjected to various modifications and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this does not limit the present invention to specific embodiments. The terms used in this specification are used to describe specific embodiments and are not intended to limit the technical idea of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. Terms such as "comprising" or "having" in this specification are used to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that the presence or addition possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof is not precluded in advance.

[0037] On the other hand, each configuration in the drawings described in the present invention is shown independently for the convenience of explaining separate characteristic functions in the video encoding device / decoding device, and does not mean that each configuration is implemented by different hardware or different software. For example, among each configuration, two or more configurations 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 rights of the present invention as long as they do not depart from the essence of the present invention.

[0038] Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. Hereinafter, the same reference numerals will be used for the same components in the drawings, and redundant descriptions of the same components will be omitted.

[0039] FIG. 1 is a block diagram schematically showing an encoding device (video encoding device) according to an embodiment of the present invention. As shown in FIG. 1, the encoding device 100 includes a picture splitting unit 105, a prediction unit 110, a conversion unit 115, a quantization unit 120, a reordering unit 125, an entropy encoding unit 130, an inverse quantization unit 135, an inverse conversion unit 140, a filter unit 145, and a memory 150.

[0040] The picture splitting unit 105 can split the input picture into at least one processing unit block. At this time, the block as the processing unit may be a prediction unit (hereinafter referred to as PU), a conversion unit (hereinafter referred to as TU), or an encoding unit (hereinafter referred to as CU).

[0041] The prediction unit 110 includes an inter prediction unit that performs inter prediction and an intra prediction unit that performs intra prediction, as will be described later. The prediction unit 110 performs prediction on the processing unit of the picture by the picture splitting unit 105 to generate a prediction block. The processing unit of the picture in the prediction unit 110 may be a CU, a TU, or a PU. Further, the prediction unit 110 can determine whether the prediction performed on the corresponding processing unit is inter prediction or intra prediction, and determine the specific content of each prediction method (for example, prediction mode, etc.). At this time, the processing unit on which the prediction is performed and the processing unit on which the prediction method and the specific content of the prediction method are determined may be different. For example, the prediction method and prediction mode, etc. are determined in PU units, and the prediction can also be performed in TU units.

[0042] Depending on the inter prediction, a prediction block can be generated by performing prediction based on the information of at least one picture among the previous picture and / or the subsequent picture of the current picture. Also, depending on the intra prediction, a prediction block can be generated by performing prediction based on the pixel information within the current picture.

[0043] As methods of inter prediction, skip mode, merge mode, motion vector prediction (MVP), etc. can be used. In inter prediction, for a PU, a reference picture can be selected, and a reference block of the same size as the PU can be selected. The reference block can be selected in integer pixel units. Next, a prediction block is generated such that the residual signal with the current PU is minimized and the magnitude of the motion vector is also minimized.

[0044] The prediction block may be generated in integer sample units, or may be generated in sub-pixel units such as 1 / 2 pixel units or 1 / 4 pixel units. At this time, the motion vector can also be expressed in units less than integer pixels. For example, for luminance samples, it can be expressed in 1 / 4 pixel units, and for chrominance samples, it can be expressed in 1 / 8 pixel units.

[0045] Information such as the index of the reference picture selected through inter prediction, the motion vector (e.g., MVP), and the residual signal is entropy-coded and transmitted to the decoding device. When the skip mode is adopted, since the residual can be used as the prediction block to restore the block, it is not necessary to generate, transform, quantize, and transfer the residual.

[0046] When performing intra prediction, the prediction mode is determined in PU units, and prediction can be performed in PU units. Also, the prediction mode is determined in PU units, and intra prediction can be performed in TU units.

[0047] In intra prediction, the prediction mode can have 33 directional prediction modes and at least two or more non-directional modes. The non-directional modes can include the DC prediction mode and the planar mode.

[0048] In intra prediction, after applying a filter to the reference samples, a prediction block can be generated. At this time, whether to apply a filter to the reference samples can be determined according to the intra prediction mode and / or size of the current block.

[0049] The PU may be blocks of various sizes / forms. For example, in the case of inter prediction, the PU may be a 2N×2N block, a 2N×N block, an N×2N block, or an N×N block (N is an integer), etc. In the case of intra prediction, the PU may be a 2N×2N block or an N×N block (N is an integer), etc. At this time, the PU with an N×N block size can be set to be applied only in specific cases. For example, it can be determined to use only the PU with an NxN block size for the minimum-sized CU, or to use it only for intra prediction. In addition to the PUs of the sizes described above, PUs such as N×mN blocks, mN×N blocks, 2N×mN blocks, or mN×2N blocks (m < 1) can also be further defined and used.

[0050] The residual value (residual block or residual signal) between the generated prediction block and the original block is input to the conversion unit 115. Also, the prediction mode information, motion vector information, etc. used for prediction are encoded by the entropy encoding unit 130 together with the residual value and transmitted to the decoding device.

[0051] The conversion unit 115 performs conversion on the residual block in conversion units and generates conversion coefficients. The conversion unit in the conversion unit 115 may be a TU and can have a quadtree structure. At this time, the size of the conversion unit can be determined within a range of a predetermined maximum and minimum size. The conversion unit 115 can perform conversion on the residual block using discrete cosine transform (DCT) and / or discrete sine transform (DST).

[0052] The quantization unit 120 can quantize the residual value converted by the conversion unit 115 to generate quantization coefficients. The values calculated from the quantization unit 120 are provided to the inverse quantization unit 135 and the rearrangement unit 125.

[0053] The reordering unit 125 reorders the quantized coefficients provided by the quantization unit 120. By reordering the quantized coefficients, the encoding efficiency in the entropy encoding unit 130 can be increased. The reordering unit 125 can reorder the quantized coefficients in two-dimensional block form into a one-dimensional vector form by means of a coefficient scanning method. In the reordering unit 125, the entropy encoding efficiency in the entropy encoding unit 130 can also be increased by changing the order of coefficient scanning based on the probabilistic statistics of the coefficients transferred from the quantization unit.

[0054] The entropy encoding unit 130 can perform entropy encoding on the quantized coefficients reordered by the reordering unit 125. For entropy encoding, encoding methods such as, for example, Exponential Golomb, Context Adaptive Variable Length Coding (CAVLC), Context Adaptive Binary Arithmetic Coding (CABAC), etc. can be used. The entropy encoding unit 130 can encode various information such as the quantized coefficient information and block type information, prediction mode information, division unit information, PU information and transfer unit information, motion vector information, reference picture information, block interpolation information, filter information, etc. of the CU transmitted from the reordering unit 125 and the prediction unit 110.

[0055] Also, the entropy encoding unit 130 can, if necessary, make certain changes to the parameter set or syntax (syntax) to be transferred.

[0056] The inverse quantization unit 135 inverse-quantizes the value quantized by the quantization unit 120, and the inverse transform unit 140 inverse-transforms the value inverse-quantized by the inverse quantization unit 135. By combining the residual value generated by the inverse quantization unit 135 and the inverse transform unit 140 with the predicted block predicted by the prediction unit 110, a restored block can be generated.

[0057] FIG. 1 illustrates that a restoration block is generated by combining a residual block and a prediction block via an adder. At this time, the adder can also be regarded as a separate unit (restoration block generation unit) that generates the restoration block.

[0058] The filter unit 145 can apply a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) to the restored picture.

[0059] The deblocking filter can remove the distortion generated at the boundary between blocks in the restored picture. The ALF can perform filtering based on the value obtained by comparing the restored video with the original video after the block has been removed via the deblocking filter. The ALF may be performed only when high efficiency is adopted. The SAO restores the offset difference from the original video for each pixel in the residual block to which the deblocking filter is applied, and is adopted in the form of a band offset, an edge offset, etc.

[0060] On the other hand, for the restoration block used for inter prediction, the filter unit 145 may not apply a filter.

[0061] The memory 150 can store the restoration block or picture calculated via the filter unit 145. The restoration block or picture stored in the memory 150 can be provided to the prediction unit 110 that performs inter prediction.

[0062] FIG. 2 is a block diagram schematically showing a video decoding apparatus according to an embodiment of the present invention. As shown in FIG. 2, the video decoding apparatus 200 can include an entropy decoding unit 210, a reordering unit 215, an inverse quantization unit 220, an inverse transformation unit 225, a prediction unit 230, a filter unit 235, and a memory 240.

[0063] When a video bitstream is input to a video encoding device, the input bitstream can be decoded according to the procedure in which video information is processed by the video encoding device.

[0064] For example, when variable length coding (hereinafter referred to as VLC), such as CAVLC, is used to perform entropy coding in a video encoding device, the entropy decoding unit 210 can also perform entropy decoding by being implemented with the same VLC table as the VLC table used in the encoding device. Also, when CABAC is used to perform entropy coding in a video encoding device, the entropy decoding unit 210 can perform entropy decoding using CABAC correspondingly.

[0065] Among the information decoded by the entropy decoding unit 210, the information for generating a prediction block is provided to the prediction unit 230, and the residual value for which entropy decoding has been performed by the entropy decoding unit 210 can be input to the rearrangement unit 215.

[0066] The rearrangement unit 215 can rearrange the bitstream entropy decoded by the entropy decoding unit 210 based on the method of rearrangement performed in the video encoding device. The rearrangement unit 215 can rearrange the coefficients expressed in the form of a one-dimensional vector back into the form of coefficients of a two-dimensional block. The rearrangement unit 215 can receive information related to the coefficient scan performed in the encoding device and perform rearrangement by scanning in reverse based on the scan order performed in the encoding device.

[0067] The inverse quantization unit 220 can perform inverse quantization based on the quantization parameter provided from the encoding device and the coefficient values of the rearranged block.

[0068] The inverse transform unit 225 can perform inverse DCT and / or inverse DST on the quantization result performed in the video encoding device with respect to the DCT and DST performed by the transform unit of the encoding device. The inverse transform can be performed based on the transfer unit determined by the encoding device or the division unit of the video. In the transform unit of the encoding device, DCT and / or DST can be selectively performed according to a plurality of pieces of information such as a prediction method, the size of the current block, and a prediction direction, and the inverse transform unit 225 of the decoding device can perform an inverse transform based on the transform information performed in the transform unit of the encoding device.

[0069] The prediction unit 230 can generate a prediction block based on the prediction block generation related information provided from the entropy decoding unit 210 and the previously decoded block and / or picture information provided from the memory 240.

[0070] Currently, when the prediction mode for the PU is the intra prediction mode, intra prediction for generating a prediction block based on the pixel information within the current picture can be performed.

[0071] Currently, when the prediction mode for the PU is the inter prediction mode, inter prediction for the current PU can be performed based on the information included in at least one of the previous picture or the subsequent picture of the current picture. At this time, the motion information necessary for the inter prediction of the current PU provided from the video encoding device, such as motion vectors, reference picture indexes, etc., can be derived from the skip flag, merge flag, etc. received from the encoding device.

[0072] The restored block can be generated using the prediction block generated from the prediction unit 230 and the residual block provided from the inverse transform unit 225. FIG. 2 illustrates that the prediction block and the residual block are combined by an adder to generate a restored block. At this time, the adder can be regarded as a separate unit (restored block generation unit) for generating the restored block.

[0073] When skip mode is adopted, the residual is not transferred, and the prediction block can be made into a restoration block.

[0074] The restored block and / or picture can be provided to the filter unit 235. The filter unit 235 can employ block distortion removal filtering, SAO, and / or ALF, etc. for the restored block and / or picture.

[0075] The memory 240 can store the restored picture or block so that it can be used as a reference picture or reference block, and can also provide the restored picture to the output unit.

[0076] On the other hand, the encoded or decoded picture is stored in a memory, for example, a decoded picture buffer (DPB). When encoding or decoding the current picture, the previous picture stored in the DPB is referred to for predicting the current picture.

[0077] Specifically, the encoding device and the decoding device can maintain a list of previously encoded / decoded pictures in the reference picture list for use in inter prediction.

[0078] When inter prediction is adopted, the encoding device and the decoding device can perform prediction on the target block (current block) of the current picture by referring to other pictures. As shown in FIGS. 1 and 2, the inter prediction may be performed in the prediction unit in the encoding device and the decoding device.

[0079] When performing inter prediction, as described above, the current block is predicted by using the information of the available neighboring blocks adjacent to the current block. At this time, the neighboring blocks include the available blocks (hereinafter referred to as "Col blocks" for convenience of explanation) among the blocks co-located with the current block in the reference picture that the current block can refer to.

[0080] For the sake of convenience in explanation, the surrounding blocks used to perform prediction on the current block in inter prediction are referred to as "candidate blocks".

[0081] In inter prediction, prediction on the current block is performed using the information of candidate blocks. In the case of skip mode or merge mode, among the candidate blocks, the motion information (e.g., motion vector) and the reference picture for the selected block are used as the motion information and the reference picture for the current block.

[0082] When using MVP, among the candidate blocks, the motion information (e.g., motion vector) for the selected block is used as the motion vector for the current block, and the reference picture information for the current block is transferred from the encoding device to the decoding device. The difference MVD between the MVP derived from the candidate blocks and the motion vector for the current block is transferred from the encoding device to the decoding device, and the prediction unit of the decoding device can derive the motion information for the current block based on the MVP and the MVD.

[0083] FIG. 3 is a diagram schematically explaining an example of candidate blocks that can be used when performing inter prediction on the current block.

[0084] The prediction units of the encoding device and the decoding device can use the blocks at predetermined positions around the current block 400 as candidate blocks. For example, in the example of FIG. 3, two blocks A0410 and A1420 arranged at the lower left end of the current block, and three blocks B0430, B1440, and B2450 at the upper right end and the upper left end of the current block can be selected as candidate blocks. In addition to the spatially adjacent blocks, the above-mentioned Col block 460 can be used as a temporal candidate block.

[0085] When performing inter prediction, the motion information for the current block, as described above, either directly uses the motion information of the selected block among the surrounding blocks, or is derived based on the motion information of the selected block among the surrounding blocks.

[0086] On the other hand, regarding the reference picture used for inter prediction, the reference picture for the current block can be derived from the reference pictures of neighboring blocks or can be indicated by the decoding device. In the case of skip mode or merge mode, the prediction unit of the decoding device can use the reference pictures of neighboring blocks as the reference picture for the current block. When using the MVP, the prediction unit of the decoding device can receive information indicating the reference picture for the current block from the encoding device.

[0087] Pictures encoded / decoded before the current picture are stored in a memory (e.g., DPB) and can be used for prediction of the current block (current picture). The list of pictures available for inter prediction of the current block is maintained as a reference picture list.

[0088] A P slice is a slice decoded through intra prediction or inter prediction using at most one motion vector and one reference picture. A B slice is a slice decoded through intra prediction or inter prediction using at most two motion vectors and two reference pictures. At this time, the reference pictures include a short term reference picture and a long term reference picture.

[0089] The reference picture list 0 (hereinafter referred to as "L0" for convenience of explanation) is a reference picture list used for inter prediction of P slices or B slices. The reference picture list 1 (hereinafter referred to as "L1" for convenience of explanation) is used for inter prediction of B slices. Therefore, L0 is used for inter prediction of blocks in P slices that perform unidirectional prediction, and L0 and L1 are used for inter prediction of blocks in B slices that perform bidirectional prediction.

[0090] When the decoding device decodes P slices and B slices through inter prediction, it creates (constructs) a reference picture list. The reference pictures used for inter prediction are specified through the reference picture list. The reference picture index is an index that indicates a reference picture on the reference picture list.

[0091] The reference picture list can be created based on a set of reference pictures transferred from the encoding device.

[0092] The reference pictures that create the reference picture list through the reference picture index can be stored in a memory (e.g., DPB).

[0093] The pictures stored in the memory (pictures encoded / decoded before the current picture) are managed by the encoding device and the decoding device. The encoding device and the decoding device maintain the pictures necessary for predicting the current block and release the pictures not used for predicting the current block from the memory.

[0094] As a method of managing reference pictures, when using the sliding window method, the reference pictures can be managed by a simple method of being released after a certain period of time after being stored in the memory, but there are some problems. For example, even if there are reference pictures that are no longer needed, they cannot be directly released from the memory, resulting in a decrease in efficiency. Also, after a certain period of time, they are released from the memory, making it difficult to manage long-term reference pictures.

[0095] Considering the problems of the sliding window method, a Memory Management Command Operation (MMCO) method that directly notifies instructions regarding the management of reference pictures from an encoding device may be used. However, even when using the MMCO method, picture loss occurs during the notification process. If the lost picture contains an MMCO command, the lost MMCO information cannot be restored, and as a result, the memory (DPB) cannot be maintained in the exact state where the currently required pictures are managed. Therefore, inter prediction may also be inaccurately performed.

[0096] To solve the above-described problems, a method of transferring a list of reference pictures required for the decoding process of a slice from each slice header can be used. A kind of abstract container that includes a list of reference pictures in the slice header can be called "RefPicList". Or, as described above, in order to distinguish between the reference picture list 0 and the reference picture list 1 configured in the decoding device, the list of reference pictures required in the decoding process of a slice can be called a reference picture set or a set of reference pictures.

[0097] The reference picture set or RefPicList (hereinafter, for the convenience of explanation and to distinguish it from the reference picture list, it is referred to as the "reference picture set") includes reference pictures used for the reference of the current picture / slice or future picture / slice. For example, the reference picture set is information transferred from an encoding device to a decoding device, and the pictures included in the reference picture set can be specified by the POC. The POC indicates the display order of the pictures. At this time, the POC of the reference pictures included in the reference picture set may be the relative POC with respect to the POC of the current picture.

[0098] The relative POC indicates the POC difference between two pictures within a reference picture set. In POC order, for a reference picture before the current picture (a reference picture with a POC smaller than that of the current picture), the relative POC is the POC difference from the immediately previous reference picture within the reference picture set. In POC order, for a reference picture after the current picture (a reference picture with a POC larger than that of the current picture), the relative POC is also the POC difference from the immediately previous reference picture within the reference picture set. However, for (1) the first reference picture in the reference picture set and (2) a reference picture whose relative POC sign is different from that of the previous reference picture in the reference picture set, the magnitude of the relative POC is the POC difference from the current picture.

[0099] The POC difference between two pictures within a reference picture set can be expressed by an absolute value and a sign.

[0100] The reference picture set is notified from an encoding device to a decoding device for each P slice and B slice.

[0101] The reference picture lists L0 and L1 may be created based on the reference picture set received from the encoding device, or may be explicitly transferred from the encoding device.

[0102] When creating the reference picture list L0, among the received reference picture set, for a picture with a POC smaller than that of the current picture (in POC order, a picture before the current picture or a picture with a negative relative POC sign) and a picture with a POC larger than that of the current picture (in POC order, a picture after the current picture or a picture with a positive relative POC sign), a reference picture index is assigned from the picture with a POC smaller than that of the current picture, and the reference picture list is created.

[0103] For example, until all reference picture indexes for creating a reference picture list are assigned, (i) among the set of reference pictures for the current picture / slice, for pictures with a POC smaller than the POC of the current picture, in POC order, lower reference picture indexes are assigned to pictures closer to the current picture, and then (ii) among the set of reference pictures for the current picture / slice, for pictures with a POC larger than the POC of the current picture, in POC order, lower reference picture indexes are assigned to pictures closer to the current picture.

[0104] When creating the reference picture list L1, among the received set of reference pictures, from among the pictures with a POC smaller than the POC of the current picture (pictures before the current picture in POC order or pictures with a negative sign for the relative POC) and the pictures with a POC larger than the POC of the current picture (pictures after the current picture in POC order or pictures with a positive sign for the relative POC), reference picture indexes are assigned starting from the pictures with a POC larger than the POC of the current picture to create the reference picture list.

[0105] For example, until all reference pictures for creating a reference picture list are assigned, (i) among the set of reference pictures for the current picture / slice, for pictures with a POC larger than the POC of the current picture, in POC order, lower reference picture indexes are assigned to pictures closer to the current picture, and then (ii) among the set of reference pictures for the current picture / slice, for pictures with a POC smaller than the POC of the current picture, in POC order, lower reference picture indexes are assigned to pictures closer to the current picture.

[0106] Here, the case of short-term reference pictures has been described as an example. In the case of a reference picture list including long-term reference pictures, after the processes (i) and (ii) for L0 and L1, pictures transferred as long-term reference pictures can be additionally added through the set of reference pictures.

[0107] Hereinafter, this specification describes a method of creating a set of reference pictures for short-term reference pictures and creating a reference picture list. Hereinafter, the reference picture means a short-term reference picture.

[0108] At this time, in order to reduce the number of bits of the notified set of reference pictures and reduce the complexity of the process of creating a reference picture list by a decoder, the reference pictures (reference picture information, such as POC values) in the set of reference pictures (list of reference pictures) can be arranged and transferred in an orderly manner.

[0109] The reference pictures in the set of reference pictures are notified such that (1) reference pictures with POCs smaller than the POC of the current picture are arranged in descending order of POC at the beginning part of the set of reference pictures, and then (2) reference pictures with POCs larger than the POC of the current picture are arranged in ascending order of POC.

[0110] For example, in the set of reference pictures, after arranging reference pictures (picture information) with POCs smaller than the POC of the current picture, reference pictures (picture information) with POCs larger than the POC of the current picture are arranged. At this time, the information of the reference pictures to be arranged may be the POC of the reference picture, the relative POC of the reference picture, or the magnitude and sign of the relative POC of the reference picture.

[0111] When the information to be arranged is the POC of the reference picture, in the set of reference pictures, the POCs of the reference pictures with POCs smaller than the POC of the current picture are arranged in the order closer to the POC of the current picture, and then the POCs of the reference pictures with POCs larger than the POC of the current picture are arranged in the order closer to the POC of the current picture.

[0112] When the information to be configured is the relative POC of the reference picture, the relative POC for the reference picture with a POC smaller than the POC of the current picture is first configured, and then the relative POC for the reference picture with a POC larger than the POC of the current picture is configured. For example, the relative POCs for the reference pictures with POCs smaller than the POC of the current picture within the set of reference pictures are arranged in the order of POCs of the reference pictures (descending order), and then the relative POCs for the reference pictures with POCs larger than the POC of the current picture are arranged in the order of POCs of the reference pictures (ascending order). Here, the relative POC for a reference picture is the difference value between the POC of the current picture and the POC of the reference picture.

[0113] Within the set of reference pictures, the relative POC can be represented by the magnitude (absolute value) of the relative POC and the sign of the relative POC.

[0114] The sign of the relative POC of a reference picture indicates whether the reference picture is before or after the current picture in the order of POCs. Therefore, instead of transferring information specifically indicating the sign of the relative POC (+ or -), the magnitude of the relative POC for the reference pictures before the current picture in the order of POCs can be transferred first, and then the magnitude of the relative POC for the reference pictures after the current picture can be transferred. The decoding device that receives the set of reference pictures can first determine that the magnitude of the received relative POC is for the reference pictures before the current picture in the order of POCs, and the magnitude of the relatively POC received later is for the reference pictures after the current picture in the order of POCs. At this time, information representing both the number of reference pictures before the current picture and the number of reference pictures after the current picture in the order of POCs can be transferred together.

[0115] Even when transferring the magnitude of the relative POC, the magnitudes of the relative POCs for the reference pictures with POCs smaller than the POC of the current picture within the set of reference pictures are arranged in the order of POCs of the reference pictures (descending order), and then the magnitudes of the relative POCs for the reference pictures with POCs larger than the POC of the current picture are arranged in the order of POCs of the reference pictures (ascending order).

[0116] Table 1 shows an example of a method for determining the magnitude and sign of the relative POC in an encoding device. [Table 1]

[0117] The encoding device can determine the magnitude and sign of the relative POC of the reference picture to be notified via the reference picture set using the method in Table 1.

[0118] sign_ref_pic[i] specifies the sign of the relative POC for the i-th reference picture in the reference picture set. When the POC (ref_pic[i]) of the i-th reference picture is greater than the POC (currentPOC) of the current picture, the value of the sign sign_ref_pic[i] of the relative POC for the i-th reference picture indicates '+'. When the POC (ref_pic[i]) of the i-th reference picture is not greater than the POC (currentPOC) of the current picture, the value of the sign sign_ref_pic[i] of the relative POC for the i-th reference picture indicates '-'.

[0119] abs_ref_pic[i] specifies the magnitude of the relative POC for the i-th reference picture in the reference picture set. When the relative POC sign of the i-th reference picture is the same as the relative POC sign of the (i - 1)-th reference picture, the difference between the difference between the POC of the i-th reference picture and the reference value (refValue) and the difference between the POC of the (i - 1)-th reference picture and the reference value (refValue) is the magnitude of the relative POC of the i-th reference picture. That is, when the relative POC sign of the i-th reference picture is the same as the relative POC sign of the (i - 1)-th reference picture, the magnitude of the relative POC of the i-th reference picture is the POC difference between adjacent reference pictures in the reference picture set (the difference between the POC of the i-th reference picture and the POC of the (i - 1)-th reference picture).

[0120] The reference value (refValue) is either transferred from an encoding device or a preset reference POC value, and becomes the reference POC value for calculating the first relative POC within the reference picture set. For example, the reference value (refValue) may be the POC value of the current picture.

[0121] The relative POC code of the i-th reference picture may not be the same as the relative POC code of the (i - 1)-th reference picture. In this case, it is the case where the i-th reference picture in the reference picture set is the first picture, or the (i - 1)-th reference picture in the reference picture set is a picture before the current picture in POC order, and the i-th reference picture is a picture after the current picture in POC order. Therefore, when the relative POC code of the i-th reference picture is not the same as the relative POC code of the (i - 1)-th reference picture, the magnitude of the relative POC of the i-th reference picture is the difference between the POC of the i-th reference picture and the reference value (refValue). Next, in the case of the (i + 1)-th reference picture, since the relative POC code is the same as that of the i-th reference picture again, the magnitude of the relative POC of the (i + 1)-th reference picture is the difference between the POC of the (i + 1)-th reference picture and the POC of the i-th reference picture again.

[0122] The encoding device can transfer the magnitude and code of the relative POC of the reference pictures derived as described above as the reference picture set. Also, when transferring the magnitude of the relative POC of the reference pictures, the encoding device can first transfer the magnitude of the relative POC for the reference pictures before the current picture in the POC order in which the code is transferred, and then transfer the magnitude of the relative POC for the reference pictures after the current picture. In this case, the encoding device can transfer information indicating the number of reference pictures (pictures before the current picture in POC order) with the relative POC code being '-' and the number of reference pictures (pictures after the current picture in POC order) with the relative POC code being '+'.

[0123] Table 2 shows another example of a method for determining the magnitude and sign of the relative POC in an encoding device. [Table 2]

[0124] In Table 2, the case where the reference value (refValue) is the POC value of the current picture will be described as an example.

[0125] Similar to Table 1, in Table 2, when the POC (ref_pic[i]) of the i-th reference picture is greater than the POC (currentPOC) of the current picture, the value of the sign sign_ref_pic[i] of the relative POC for the i-th reference picture indicates '+'. When the POC (ref_pic[i]) of the i-th reference picture is not greater than the POC (currentPOC) of the current picture, the value of the sign sign_ref_pic[i] of the relative POC for the i-th reference picture indicates '-'.

[0126] When the relative POC sign of the i-th reference picture is the same as the relative POC sign of the (i - 1)-th reference picture, the difference between the difference between the POC of the i-th reference picture and the POC of the current picture and the difference between the POC of the (i - 1)-th reference picture and the POC of the current picture becomes the magnitude of the relative POC of the first reference picture. That is, when the relative POC sign of the i-th reference picture is the same as the relative POC sign of the (i - 1)-th reference picture, the magnitude of the relative POC of the i-th reference picture is the POC difference between adjacent reference pictures within the reference picture set (the difference between the POC of the i-th reference picture and the POC of the (i - 1)-th reference picture).

[0127] The relative POC code of the i-th reference picture may not be the same as the relative POC code of the (i - 1)-th reference picture. In this case, either the i-th reference picture in the reference picture set is the first picture, or the (i - 1)-th reference picture in the reference picture set is a picture before the current picture in POC order, and the i-th reference picture is a picture after the current picture in POC order. Therefore, when the relative POC code of the i-th reference picture is not the same as the relative POC code of the (i - 1)-th reference picture, the magnitude of the relative POC of the i-th reference picture is the difference between the POC of the i-th reference picture and the POC of the current picture. Next, in the case of the (i + 1)-th reference picture, since it becomes the same as the relative POC code of the i-th reference picture again, the magnitude of the relative POC of the (i + 1)-th reference picture is again the difference between the POC of the (i + 1)-th reference picture and the POC of the i-th reference picture.

[0128] The encoding device can transfer the magnitude and code of the relative POC of the reference pictures derived as described above as the reference picture set. Also, when transferring the magnitude of the relative POC of the reference pictures, the encoding device can first transfer the magnitude of the relative POC for the reference pictures before the current picture in the POC order in which the code is transferred, and then transfer the magnitude of the relative POC for the reference pictures after the current picture. In this case, the encoding device can transfer information indicating the number of reference pictures (pictures before the current picture in POC order) with a relative POC code of '-' and the number of reference pictures (pictures after the current picture in POC order) with a relative POC code of '+'.

[0129] The decoding device can receive information regarding the reference picture set from the encoding device and configure or restore the reference picture set based on this information.

[0130] Table 3 shows an example of a method for recovering (recover) the information (POC) of the reference pictures in a decoding device that receives the reference picture set.

Table 3

[0131] The decoding device can restore the POC that can be used for predicting the current block (picture) by the method in Table 3 based on the reference picture information (the magnitude of the relative POC or the magnitude and sign of the relative POC) received from the encoding device.

[0132] The POC (ref_pic[i]) of the i-th reference picture in the reference picture set can be restored based on the magnitude (abs_ref_pic[i]) and sign (sign_ref_pic[i]) of the relative POC of the i-th reference picture.

[0133] As shown in Table 3, the decoding device can receive the sign of the relative POC explicitly from the encoding device and restore the POC of the reference picture.

[0134] When the sign of the i-th reference picture in the reference picture set is the same as the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '-', the POC of the i-th reference picture is the value obtained by subtracting the sum of the relative POCs from the first reference picture (the 0-th reference picture) to the i-th reference picture from the reference value (refValue). When the sign of the i-th reference picture in the reference picture set is the same as the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '+', the POC of the i-th reference picture is the value obtained by adding the relative POC from the first reference picture (the 0-th reference picture) to the i-th reference picture to the reference value (refValue).

[0135] At this time, the reference value (refValue) is transferred from the encoding device or is a preset reference POC value, which is the reference POC value for calculating the first relative POC in the reference picture set. For example, the reference value (refValue) may be the POC value of the current picture.

[0136] When the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture, whether the i-th reference picture in the i-th reference picture set is the first picture, or the (i - 1)-th reference picture in the reference picture set is a picture before the current picture in POC order, and the i-th reference picture is a picture after the current picture in POC order.

[0137] When the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture, and the sign of the i-th reference picture is '-', the POC of the i-th reference picture is the value obtained by subtracting the relative POC of the i-th reference picture from the reference value (refValue). When the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture, and the sign of the i-th reference picture is '+', the POC of the i-th reference picture is the value obtained by adding the relative POC of the i-th reference picture to the reference value (refValue).

[0138] Also, different from the example in Table 2, the information indicating the sign for the relative POC of the reference picture may not be transferred. In this case, the decoding device can determine that the sign of the relative POC arranged at the head in the reference picture set is '-', and the sign of the relative POC arranged at the rear in the reference picture set is '+'. At this time, the encoding device can also transfer the information indicating the number of relative POCs with the sign '-' and the number of relative POCs with the sign '+'. The decoding device determines that the relative POCs for the number of relative POCs with the sign '-' indicated by the encoding device from the head of the reference picture set have the sign '-', and the remaining relative POCs have the sign '+', and can restore the POC (ref_pic[i]) of the i-th reference signal as described above.

[0139] In other words, among the reference pictures in the reference picture set, the relative POC for the first reference picture is the POC difference from the reference value (refValue). Among the reference pictures in the reference picture set, the relative POC for the pictures before the current picture excluding the first reference picture is the POC difference from the previous reference picture. Among the reference pictures in the reference picture set, the relative POC for the first picture after the current picture is the POC difference from the reference value. The relative POC for the remaining reference pictures in the reference picture set (from the second reference picture after the current picture to the last reference picture in the reference picture set) is the POC difference from the previous reference picture. Here, before and after the current picture are determined in the order of POC. Also, the previous reference picture means the picture immediately preceding in the sorted order within the reference picture set.

[0140] Table 4 shows another example of a method for restoring the information (POC) of a reference picture in a decoding apparatus that receives a reference picture set.

Table 4

[0141] The method in Table 4 will be described by taking as an example the case where the number of reference pictures included in the reference picture set is 2 and the reference value (refValue) for calculating the first relative POC value in Table 3 is the POC of the current picture in order to clearly explain the features of the present invention.

[0142] The decoding apparatus can receive the code of the relative POC explicitly from the encoding apparatus and restore the POC of the reference picture.

[0143] When the sign of the i-th reference picture in the reference picture set is the same as the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '-', the POC of the i-th reference picture is the value obtained by subtracting the relative POC of the i-th reference picture from the POC of the current picture and the relative POC of the (i - 1)-th reference picture. When the sign of the i-th reference picture in the reference picture set is the same as the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '+', the POC of the i-th reference picture is the value obtained by adding the relative POC of the i-th reference picture and the relative POC of the (i - 1)-th reference picture to the POC of the current picture.

[0144] When the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture, in the case where the i-th reference picture in the i-th reference picture set is the first picture, or the (i - 1)-th reference picture in the reference picture set is a picture before the current picture in POC order and the i-th reference picture is a picture after the current picture in POC order. In this case, the relative POC of the i-th reference picture is derived based on the POC of the current picture as can be seen from Table 2.

[0145] Therefore, when the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '-', the POC of the i-th reference picture is the value obtained by subtracting the relative POC of the i-th reference picture from the POC of the current picture. When the sign of the i-th reference picture in the reference picture set is different from the sign of the (i - 1)-th reference picture and the sign of the i-th reference picture is '+', the POC of the i-th reference picture is the value obtained by adding the relative POC of the i-th reference picture to the POC of the current picture.

[0146] Also, as described in Table 3, information explicitly indicating the sign for the relative POC of the reference picture may not be transferred. In this case, the decoding apparatus may determine that the sign of the relative POC arranged at the head in the reference picture set is ‘-’ (minus), and the sign of the relative POC arranged at the rear in the reference picture set is ‘+’. At this time, it is also possible to transfer information indicating the number of relative POCs with the sign ‘-’ and the number of relative POCs with the sign ‘+’ from the encoding apparatus. The decoding apparatus determines that the signs of the relative POCs for the number of relative POCs with the sign ‘-’ indicated by the encoding apparatus from the head of the reference picture set are ‘-’, and determines that the signs of the remaining relative POCs are ‘+’, and as described above, can restore the POC (ref_pic[i]) of the i-th reference signal.

[0147] In other words, among the reference pictures in the reference picture set, the relative POC with respect to the first reference picture is the POC difference from the current picture. Among the reference pictures in the reference picture set, the relative POC with respect to the pictures before the current picture excluding the first reference picture is the POC difference from the immediately preceding reference picture. Among the reference pictures in the reference picture set, the relative POC with respect to the first picture after the current picture is the POC difference from the current picture. The relative POCs for the remaining reference pictures in the reference picture set (from the second reference picture after the current picture to the last reference picture in the reference picture set) are the POC differences from the immediately preceding reference picture. Here, before and after the current picture are determined in the order of POC. Here, the immediately preceding reference picture means the picture immediately preceding in the arranged order in the reference picture set.

[0148] Hereinafter, an example adopted by the present invention will be specifically described when the reference value (refValue) is the POC of the current picture.

[0149] FIG. 4 is a diagram schematically explaining an example of a set of reference pictures notified from an encoding device to a decoding device. The example of FIG. 4 shows a case where nine P slices (P pictures) P0 to P9 that perform unidirectional prediction mutually reference each other.

[0150] Table 5 shows an example in which the set of reference pictures notified for the example of FIG. 4 is composed of the POCs of the reference pictures.

[0151]

Table 5

[0152] As shown in FIGS. 4 and 5, the set of reference pictures for the current picture includes the POCs of the reference pictures that the current picture can reference. In the set of reference pictures, the reference pictures are assigned lower indices to the reference pictures closer to the current picture in POC order.

[0153] For example, in the examples of FIGS. 4 and 5, when the current picture is P6 (POC = 26), the reference pictures that the current picture can reference are P5, P4, and P0. Therefore, the set of reference pictures for the current picture P6 with a POC of 26 is composed of the POCs of P5, P4, and P0, and lower indices are assigned to the reference pictures closer to the current picture in POC order.

[0154] In the examples of FIGS. 4 and 5, in the case of reference pictures before the current picture in POC order, they are sorted in descending order within the set of reference pictures, but the set of reference pictures notifies the POCs of the reference pictures as they are.

[0155] In contrast, as described above, the set of reference pictures can notify the relative POCs of the reference pictures.

[0156] Table 6 shows an example of the set of reference pictures notified in the case of FIG. 4, and is for explaining an example in which the set of reference pictures is composed of the relative POCs of the reference pictures.

Table 6

[0157] In Table 6, for Figure 4, the reference picture set of the current picture is represented by the POC of the reference picture, the magnitude of the relative POC of the reference picture, and the relative POC code of the reference picture.

[0158] In Table 5, the case of directly transferring the POC of the reference picture in the reference picture set was described. In the example of Table 6, the case of transferring the relative POC of the reference picture in the reference picture set will be described.

[0159] In the order of POC, the relative POC of the reference picture before the current picture (the reference picture with a POC smaller than that of the current picture) is the POC difference from the immediately previous reference picture in the reference picture set. Also, the relative POC code included in the reference picture set and transferred indicates whether the corresponding reference picture is a picture before or after the current picture in the order of POC.

[0160] For example, in the example of Figure 4 and Table 6, considering the case where the current picture is P5, the pictures that can be referenced by the current picture are P4, P3, and P0, and their POCs are 24, 23, and 20 respectively.

[0161] When the reference picture set for P5 transfers the relative POC, the reference picture set arranges and transfers the magnitude and code of the relative POC of the reference picture for P5 in a predetermined order. As described above, in the example of Figure 4 representing the reference relationship between P slices, the reference pictures are pictures before the current picture in the order of POC, and in the reference picture set, the reference pictures are arranged in descending order.

[0162] Therefore, in the set of reference pictures for P5, the relative POCs are arranged in the order of P4, P3, and P0. As shown in Table 6, the relative POC of P4 transferred to the set of reference pictures for P5 has a magnitude of 1 and a sign of ‘-’, the relative POC of P3 has a magnitude of 1 and a sign of ‘-’, and the relative POC of P0 has a magnitude of 3 and a sign of ‘-’.

[0163] At this time, without the sign of the relative POC, in the order of POC, the reference pictures before the current picture (the magnitudes of the relative POCs of the reference pictures) are arranged in the front part of the set of reference pictures, and the reference pictures after the current picture (the magnitudes of the relative POCs of the reference pictures) are arranged in the rear part of the set of reference pictures, and the set of reference pictures can also be transferred. In this case, information indicating the number of reference pictures before the current picture (reference pictures with a relative POC sign of ‘-’) in the order of POC and the number of reference pictures after the current picture (reference pictures with a relative POC sign of ‘+’) in the order of POC can also be transferred together.

[0164] Figure 5 is a diagram showing an example of the reference relationship between B pictures that perform bidirectional prediction, different from Figure 4 that shows the reference relationship between P pictures that perform unidirectional prediction. In Figure 5, the reference relationships of nine B pictures B0 to B8 are schematically shown.

[0165] Table 7 shows an example of the set of reference pictures notified in the case of Figure 5, and is for explaining an example in which the set of reference pictures is composed of the relative POCs of the reference pictures.

Table 7

[0166] Also in the examples of Table 7 and Figure 5, instead of transferring the POCs of the reference pictures as they are, the relative POCs of the reference pictures can be transferred for the set of reference pictures.

[0167] In the order of POC, the relative POC of a reference picture before the current picture (a reference picture with a POC smaller than the POC of the current picture) is the POC difference from the immediately previous reference picture within the set of reference pictures. In the order of POC, the relative POC of a reference picture after the current picture (a reference picture with a POC larger than the POC of the current picture) is also the POC difference from the immediately previous reference picture within the set of reference pictures. However, in the case of (1) the first reference picture in the set of reference pictures and (2) a reference picture whose relative POC sign is different from that of the previous reference picture in the set of reference pictures, the magnitude of the relative POC is the POC difference from the current picture. In other words, in the order of POC within the set of reference pictures, among the reference pictures before the current picture, the relative POC of the reference picture closest to the current picture and among the reference pictures after the current picture, the reference picture closest to the current picture is the POC difference from the current picture.

[0168] Referring to Table 7, taking the case where the current picture is B5 as an example, the set of reference pictures consists of B4, B2, B6, and B8. When the set of reference pictures is composed of relative POCs, the magnitude of the relative POC to which the lowest index is assigned in the set of reference pictures is for B4, which is the difference value of 1 between the POC of the current picture and the POC of B4, and the sign is '-'. Next, the magnitude of the relative POC to which the second index is assigned is for B2, which is the difference value of 2 between the POC of B4 and the POC of B2, and the sign is '-'. The magnitude of the relative POC to which the third index is assigned is for B6. Since the relative POC for B6 has a different sign from the relative POC for the previous reference picture B2, the magnitude of the relative POC for B6 is the POC difference from the current picture, which is 1, and the sign is '+'. The magnitude of the relative POC to which the last index is assigned is for B8, which is the difference value of 2 between the POC of B6 and B8, and the sign is '+'.

[0169] As described above, when the reference picture set transfers only the magnitude of the relative POC of the reference pictures with respect to the current picture instead of transferring all the magnitudes and signs of the relative POCs of the reference pictures with respect to the current picture, the sign of the corresponding relative POC can be derived without explicitly transferring the sign by transferring the magnitude of the relative POC with a '-' sign before the magnitude of the relative POC with a '+' sign. In this case, information indicating both the number of relative POCs with a '-' sign and the number of relative POCs with a '+' sign can be transferred together.

[0170] For example, considering again the case where the current picture is B5 in Table 7, the encoding device can construct and transfer the reference picture set for B5 from only the relative PC magnitudes of the reference pictures, such as (1 2 1 2). As shown in Table 7, the magnitudes of the relative POCs with a '-' sign are arranged in the front part of the reference picture set. The sorting order is in descending order for the relative POCs with a '-' sign (the relative POCs with respect to the reference pictures before the current picture in POC order), as described above, and also maintains ascending order for the relative POCs with a '+' sign (the relative POCs with respect to the reference pictures after the current picture in POC order), as described above. At this time, information indicating the number of relative POCs with a '-' sign and the number of relative POCs with a '+' sign can be transferred together with the reference picture set. For example, when receiving an indication that the number of reference pictures (relative POCs) with a '-' sign in the reference picture set for B5 is 2 and the number of reference pictures (relative POCs) with a '+' sign is 2, the decoding device can determine that for the first 2 relative POCs in the reference picture set, the sign is '-', and for the last 2 relative POCs, the sign is '+'. Therefore, for the first 2 relative POCs in the reference picture set, the magnitudes are the relative POC magnitudes with respect to the reference pictures with a POC smaller than the current picture, and for the last 2 relative POCs in the reference picture set, the magnitudes are the relative POC magnitudes with respect to the reference pictures with a POC larger than the current picture.

[0171] FIG. 6 is a diagram schematically showing an example of the reference relationship between B pictures and P pictures.

[0172] In FIG. 6, the reference relationship between seven P pictures P0 to P6 that perform unidirectional prediction and two B pictures B0 and B1 that perform bidirectional prediction is shown.

[0173] Table 8 shows an example of the set of reference pictures notified in the case of FIG. 6, and is for explaining an example in which the set of reference pictures is composed of the relative POCs of the reference pictures.

[0174]

Table 8

[0175] The example of Table 8 and FIG. 6 is for the case where P pictures and B pictures are mixed, but the method of deriving the magnitude and sign of the relative POC, the method of aligning the relative POCs within the set of reference pictures, etc. are as described above.

[0176] For example, when the current picture is B1, the set of reference pictures for B1 can be composed of the relative POCs of P3, P0, and P6. The set of reference pictures is composed of the magnitudes (2 4 2) of the relative POCs for P3, P0, and P6 and their respective signs, and can be transferred to the decoding device.

[0177] Also in this case, without transferring the information indicating the sign of the relative POC, the information indicating the number of relative POCs having a '-' sign and the number of relative POCs having a '+' sign based on the alignment order can be transferred together with the set of reference pictures including the magnitude of the relative POC. For example, when the current picture is B1, the set of reference pictures (2 4 2) including the magnitude of the relative POC and the information indicating that the number of relative POCs having a '-' sign is 2 and the number of relative POCs having a '+' sign is 1 can be transferred.

[0178] FIG. 7 is a flowchart schematically explaining an encoding method performed by an encoding apparatus according to the present invention. The encoding apparatus that performs the encoding method of FIG. 7 corresponds to the encoding apparatus described in FIG. 1.

[0179] As shown in FIG. 7, the encoding apparatus performs prediction on the current block (S710). The encoding apparatus can perform inter prediction or intra prediction on the current block. When performing inter prediction, a reference picture for the current block can be selected / specified using the reference picture list configured as described above.

[0180] The encoding apparatus converts / quantizes the prediction result for the current block (S720). The encoding apparatus can convert / quantize the residual block corresponding to the difference between the prediction result and the original block. Further, when intra prediction is adopted, information regarding the adopted intra prediction mode can be converted / quantized, and when inter prediction is adopted, motion information (motion vector / information regarding the reference picture) can be converted / quantized.

[0181] The encoding apparatus entropy-encodes the converted / quantized information (S730). CABAC can be used as the method of entropy encoding.

[0182] The encoding apparatus notifies the entropy-encoded information (S740). At this time, the information to be notified includes a reference picture set for creating a reference picture list for the current picture (current block). The reference picture set can be configured for each slice and included in the slice header for transfer.

[0183] The reference picture set can be configured from the POC of the reference picture for the current block. Further, the reference picture set can also be configured from the relative POC of the reference picture to reduce the transfer overhead.

[0184] When the reference picture set is composed of relative POCs of reference pictures, the size and sign of the relative POC for pictures that can be used as reference pictures of the current picture via the reference picture set may be transferred, or the size of the relative POC and the number of relative POCs having a '-' sign and the number of relative POCs having a '+' sign may be transferred. When the relative POC is transferred, the relative POC having a '-' sign is transferred first, and the relative POC having a '+' sign is transferred next. The relative POCs having a '-' sign can be sorted in descending order according to the POC of the reference picture, and the relative POCs having a '+' sign can be sorted in ascending order according to the POC of the reference picture.

[0185] In FIG. 7, considering the content related to the reference picture set, the operation of the encoding device is schematically described so that the invention can be easily understood. However, this is for convenience of explanation, and in the present invention, the operation of the encoding device includes the various operations described in FIG. 1.

[0186] FIG. 8 is a flowchart schematically explaining the decoding method performed by the decoding device according to the present invention.

[0187] As shown in FIG. 8, the decoding device receives a bitstream from the encoding device and performs entropy decoding (S810). The bitstream received from the encoding device includes a reference picture set. The reference picture set can be received included in the slice header.

[0188] The reference picture set may be composed of the POCs of the reference pictures for the current block, or may be composed of the relative POCs of the reference pictures.

[0189] The decoding device can receive information indicating a picture that can be used as a reference picture for the current picture via a reference picture set. For example, it can receive the POC of a picture that can be used as a reference picture for the current picture via the reference picture set. When the reference picture set includes (1) the magnitude and sign of the relative POC with respect to the reference picture or (2) the magnitude of the relative POC with respect to the reference picture and the number of relative POCs having '-' and '+' signs, the POC of the corresponding reference picture can be derived using a method such as that in Table 4 based on the received information.

[0190] When receiving relative POCs via the reference picture set, the relative POCs having '-' signs are received first, and the relative POCs having '+' signs are received next. The relative POCs having '-' signs can be sorted in descending order according to the POC of the reference picture, and the relative POCs having '+' signs can be sorted in ascending order according to the POC of the reference picture.

[0191] The decoding device makes a prediction for the current block based on the entropy-decoded information (S920). The prediction method for the current block can be transferred from the encoding device. When the prediction method for the current block is inter prediction, the decoding device can make a prediction using a reference picture list configured based on the received reference picture set.

[0192] The method of creating a reference picture list from the reference picture set is as described above. The configured reference picture list can be stored in the memory of the decoding device.

[0193] The decoding device restores the video (S930). The current block is restored based on the prediction for the current block, and the video can be restored via the restored blocks. When the skip mode is adopted, since the residual is not transferred, the predicted block can be used as the restored block. When the merge mode is applied or when using the MVP, the current block can be restored by combining the predicted block and the residual block.

[0194] In this specification, expressions such as "the pictures included in the reference picture set" and "the x-th picture of the reference picture set" are used for convenience of explanation. It should be noted that the pictures included in the reference picture set mean the pictures containing the POC information corresponding to the reference picture set, and the x-th picture of the reference picture set means the picture in which the corresponding POC information is ranked x-th within the reference picture set.

[0195] On the other hand, the reference relationships between the pictures shown in FIGS. 4 to 6 are described by taking the case where the temporal level is not adopted as an example. This is for the understanding of the invention, and the present invention is not limited thereto. The present invention can be similarly applied to the case where the temporal level is considered and only the pictures at a lower level than itself are referenced. In this case, the reference relationships in Tables 5 to 8 can be changed to reflect this.

[0196] In the exemplary system described above, the method of the present invention is described based on a flowchart in a series of steps or blocks. However, the present invention is not limited to the order of the steps, and a certain step can occur in a different order from the steps described above or simultaneously with different steps. Also, the above-described embodiments include examples in various forms. Therefore, the present invention should be understood to include all other alternatives, modifications, and changes within the scope of the following claims.

[0197] In the above description of the present invention, when it is mentioned that one component is "connected to" or "connected" to another component, it should be understood that one component may be directly connected to or connected to another component, but there may be other components between the two components. On the contrary, when it is mentioned that one component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components between the two components.

Claims

1. An inter prediction method performed by a decoding device, comprising: receiving picture order count (POC) information, the POC information specifying a POC difference for a number of reference pictures; deriving POC values ​​for the plurality of reference pictures based on the POC differences; constructing a reference picture list based on the POC values ​​of the plurality of reference pictures; performing inter prediction on the current block based on the reference picture list to derive predicted samples for the current block; a POC value for the i-th reference picture is derived based on a POC difference derived from the POC information; for the plurality of reference pictures preceding the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; If i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture; for the reference pictures after the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; A method according to claim 1, wherein if i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture.

2. A video encoding method executed by an encoding device, comprising: deriving picture order count (POC) values ​​for a number of reference pictures used in inter prediction of a current picture, the number of reference pictures being before the current picture in decoding order; constructing a reference picture list based on the POC values ​​of the plurality of reference pictures; deriving POC information for the plurality of reference pictures, the POC information specifying a POC difference for the plurality of reference pictures based on the derived POC values; encoding the video information including the POC information; a POC value for the i-th reference picture is derived based on a POC difference derived from the POC information; for the plurality of reference pictures preceding the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; If i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture; for the reference pictures after the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; A method according to claim 1, wherein if i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture.

3. A method for transmitting data for video, comprising: Obtaining a bitstream of video information including picture order count (POC) information, the bitstream comprising: deriving POC values ​​for a plurality of reference pictures, the plurality of reference pictures being used for inter prediction of a current picture, the plurality of reference pictures being prior to the current picture in decoding order; constructing a reference picture list based on the POC values ​​of the plurality of reference pictures; deriving POC information for the plurality of reference pictures, the POC information specifying a POC difference for the plurality of reference pictures based on the derived POC values; encoding video information including the POC information to generate the bitstream; transmitting the data including the bitstream of the video information including the POC information; a POC value for the i-th reference picture is derived based on a POC difference derived from the POC information; for the plurality of reference pictures preceding the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; If i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture; for the reference pictures after the current picture in POC order, if i is equal to 0, the POC difference is the difference between the POC value of the current picture and the POC value of the i-th reference picture; A method according to claim 1, wherein if i is greater than 0, the POC difference is the difference between the POC value of the i-th reference picture and the POC value of the (i-1)-th reference picture.

Images