Method and apparatus for signaling image information, 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 particularly to a method and apparatus for efficiently signaling video information, and a decoding method and apparatus utilizing the same. [Background technology]

[0002] Recently, the demand for high-resolution and high-quality images has been increasing in various application fields. However, as an image has higher resolution and quality, the amount of information about the image also increases.

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

[0004] In order to effectively transmit, store, or play back high-resolution, high-quality video information, highly efficient video compression techniques are available.

[0005] To improve the efficiency of video compression, inter-prediction and intra-prediction can be used. Inter-prediction predicts pixel values ​​of a current picture by referring to information from other pictures, while intra-prediction predicts pixel values ​​by using relationships between pixels within the same picture.

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

[0007] The information for creating the reference picture list is transferred from the encoding device to the decoding device, which is able to create the reference picture list based on the information received from the encoding device to effectively perform inter prediction. Summary of the Invention [Problem 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 encoding / decoding the video information.

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

[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 performing inter-prediction.

[0011] SUMMARY OF THE PRESENT EMBODIMENTS The present invention aims to provide a method and apparatus for efficiently constructing a reference picture list for inter-prediction based on received information. [Means for solving the problem]

[0012] One embodiment of the present invention is a video information notification method, comprising the steps of performing inter-prediction on a current picture and notifying information including reference picture information indicating the inter-prediction result and reference pictures available for inter-prediction, wherein 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 in POC order with POCs for pictures before the current picture at the beginning, followed by POCs for pictures after the current picture, in POC order.

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

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

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

[0016] In this case, the POC information in the reference picture information is arranged in POC order, in descending order of the POC of the reference pictures for reference pictures before the current picture, and in POC order, in ascending order of the POC of the reference pictures for reference pictures after the current picture. If the target reference picture is one of the pictures before the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, and one of the pictures after the current picture that is closest to the current picture in POC order, the base picture is the current picture. If the target reference picture is not one of the pictures before the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, and one of the pictures after the current picture that is closest to the current picture in POC order, the base picture may be a reference picture corresponding to the POC information immediately before the POC information of the target reference picture in the reference picture information.

[0017] In this case, 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 a reference picture available in the reference picture information may be information indicating, among the reference pictures indicated by the reference picture information, the magnitude of the POC difference between the target reference picture and the base picture, the number of cases in which the sign of the POC difference is negative, and the number of cases in which the sign of the POC difference is positive, and the POC information of the reference picture in the reference picture information can be aligned based on the POC of the target reference picture.

[0019] In this case, 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] In addition, at this time, the POC information in the reference picture information is arranged in POC order, in descending order of the POC of the reference pictures for reference pictures before the current picture, and in POC order, in ascending order of the POC of the reference pictures for reference pictures after the current picture. If the target reference picture is one of the pictures before the current picture and the picture after the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, the base picture is the current picture. If the target reference picture is not one of the pictures before the current picture and the picture after the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, the base 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 the steps of: entropy decoding received bitstream information to obtain reference picture information including POC information of reference pictures available for predicting a current picture; and making a prediction for a current block using a reference picture list constructed based on the POC of each reference picture derived from the reference picture information, wherein the POC information of the reference pictures in the reference picture information is arranged in POC order with the POC for pictures prior to the current picture at the beginning, followed by the POC for pictures after the current picture, in POC order.

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

[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 picture in the reference picture information can be aligned based on the POC of the target reference picture.

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

[0025] In this case, the POC information may also 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 (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 picture in the reference picture information can be aligned based on the POC of the target reference picture.

[0027] In this case, the POC information in the reference picture information is arranged in descending POC order for reference pictures before the current picture, and in ascending POC order for reference pictures after the current picture. If Pi is one of the pictures before the current picture and the picture after the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, the base picture is the current picture. If Pi is not one of the pictures before the current picture and the picture after the current picture that is closest to the current picture in POC order among the reference pictures indicated by the reference picture information, the base picture may be the reference picture corresponding to the (i-1)th POC information in the reference picture information.

[0028] In addition, the reference picture information may include information indicating a precedence / sequence relationship between the POC of each target reference picture and the POC of the current picture.

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

[0030] In this case, if k is 0, the first reference picture is the current picture, if k is not 0, the first reference picture is a reference picture corresponding to the (k-1)th POC difference information, if j is n, the second reference picture is the current picture, and if j is not n, the second reference picture is a reference picture corresponding to the (n-1)th POC difference information. Effect of the Invention

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

[0032] According to the present invention, it is possible to effectively notify information for creating a reference picture list for performing inter prediction.

[0033] According to the present invention, it is possible to reduce the transfer overhead when transferring information for creating a reference picture list.

[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 constructed with low complexity based on the received information. [Brief description of the drawings]

[0035] [Figure 1] 1 is a block diagram illustrating an outline of an encoding device (video encoding device) according to one embodiment of the present invention. [Diagram 2] 1 is a block diagram illustrating a video decoding device according to an embodiment of the present invention. [Diagram 3] 1 is a diagram for illustrating an example of a candidate block that can be used when performing inter-prediction on a current block. FIG. [Figure 4] 1 is a diagram illustrating an example of a reference picture set notified from an encoding device to a decoding device. FIG. [Diagram 5] FIG. 2 is a diagram showing an example of a reference relationship between B pictures in which bidirectional prediction is performed. [Figure 6] FIG. 2 is a diagram illustrating an example of a reference relationship between a B picture and a P picture. [Figure 7] 4 is a flowchart for explaining an encoding method performed by an encoding device according to the present invention. [Figure 8] 4 is a flowchart for explaining a decoding method performed by a decoding device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Since the present invention can be modified in various ways and can have various embodiments, a specific embodiment will be illustrated in the drawings and described in detail. However, this does not limit the present invention to a specific embodiment. The terms used in this specification are used to describe a specific embodiment and are not intended to limit the technical idea of ​​the present invention. A singular expression includes a plural expression unless the context is clear. In this specification, the terms "include" or "have" specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and it should be understood that they do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0037] Meanwhile, each component in the drawings described in the present invention is shown independently for convenience of explanation of separate characteristic functions in the video encoding / decoding device, and does not mean that each component is realized by separate hardware or software. For example, two or more components among the components may be combined to form one component, or one component may be divided into multiple components. An embodiment in which each component is integrated and / or separated is also included in the scope of the present invention as long as it does not deviate from the essence of the present invention.

[0038] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, the same reference numerals are used to refer to the same components in the drawings, and duplicated descriptions of the same components will be omitted.

[0039] Fig. 1 is a block diagram showing an outline of 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 division unit 105, a prediction unit 110, a transformation unit 115, a quantization unit 120, a reordering unit 125, an entropy encoding unit 130, a dequantization unit 135, an inverse transformation unit 140, a filter unit 145, and a memory 150.

[0040] The picture division unit 105 can divide 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 transform unit (hereinafter, referred to as TU), or a coding 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 described later. The prediction unit 110 performs prediction on a processing unit of a picture in the picture division unit 105 to generate a prediction block. The processing unit of a picture in the prediction unit 110 may be a CU, a TU, or a PU. In addition, the prediction unit 110 may determine whether the prediction performed on the corresponding processing unit is inter prediction or intra prediction, and may determine specific contents of each prediction method (e.g., a prediction mode, etc.). At this time, the processing unit in which the prediction is performed may be different from the processing unit in which the prediction method and the specific contents of the prediction method are determined. For example, the prediction method and prediction mode are determined in units of PU, and the prediction may be performed in units of TU.

[0042] In the inter prediction, a prediction block can be generated by performing prediction based on information of at least one of a picture previous to and / or a picture following the current picture, whereas in the intra prediction, a prediction block can be generated by performing prediction based on pixel information within the current picture.

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

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

[0045] Information such as the index of the reference picture selected through inter prediction, the motion vector (e.g., MVP), and the residual signal are entropy coded and transmitted to the decoding device. When the skip mode is adopted, the residual can be used as a prediction block to be reconstructed, so that the residual does not need to be generated, transformed, quantized, or transmitted.

[0046] When intra prediction is performed, a prediction mode is determined on a PU basis, and prediction can be performed on a PU basis. Alternatively, a prediction mode is determined on a PU basis, and intra prediction can be performed on a TU basis.

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

[0048] In intra prediction, a predicted block may be generated after applying a filter to a reference sample, where whether or not to apply a filter to the reference sample may be determined according to an intra prediction mode and / or a size of a current block.

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

[0050] Residual values ​​(residual blocks or residual signals) between the generated prediction block and the original block are input to the conversion unit 115. In addition, prediction mode information, motion vector information, etc. used for prediction are encoded together with the residual values ​​by the entropy encoding unit 130 and transmitted to the decoding device.

[0051] The transform unit 115 performs a transform on the residual block in a transform unit to generate transform coefficients. The transform unit in the transform unit 115 may be a TU and may have a quad tree structure. In this case, the size of the transform unit may be determined within a predetermined maximum and minimum size range. The transform unit 115 may transform the residual block using a discrete cosine transform (DCT) and / or a discrete sine transform (DST).

[0052] The quantization unit 120 may generate quantized coefficients by quantizing the residual values ​​transformed by the transformation unit 115. The values ​​calculated by the quantization unit 120 are provided to the inverse quantization unit 135 and the reordering unit 125.

[0053] The rearrangement unit 125 rearranges the quantized coefficients provided from the quantization unit 120. By rearranging the quantized coefficients, the encoding efficiency in the entropy encoding unit 130 can be improved. The rearrangement unit 125 can rearrange the quantized coefficients in a two-dimensional block form into a one-dimensional vector form by a coefficient scanning method. The rearrangement unit 125 can also improve the entropy encoding efficiency in the entropy encoding unit 130 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 may perform entropy encoding on the quantized coefficients reordered by the reordering unit 125. For the entropy encoding, an encoding method such as Exponential Golomb, Context Adaptive Variable Length Coding (CAVLC), Context Adaptive Binary Arithmetic Coding (CABAC), etc. may be used. The entropy encoding unit 130 may encode various information such as CU quantization coefficient information, block type information, prediction mode information, partition unit information, PU information, transmission unit information, motion vector information, reference picture information, block interpolation information, and filter information transmitted from the reordering unit 125 and the prediction unit 110.

[0055] The entropy encoder 130 may also make certain changes to the parameter set or syntax to be transmitted, if necessary.

[0056] The inverse quantization unit 135 inverse quantizes the values ​​quantized by the quantization unit 120, and the inverse transform unit 140 inverse transforms the values ​​inverse quantized by the inverse quantization unit 135. A reconstructed block can be generated by combining the residual values ​​generated by the inverse quantization unit 135 and the inverse transform unit 140 with the prediction block predicted by the prediction unit 110.

[0057] 1 illustrates that a reconstructed block is generated by combining a residual block and a predicted block through an adder. In this case, the adder can be regarded as a separate unit (reconstructed block generator) that generates a reconstructed block.

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

[0059] The deblocking filter can remove distortion that occurs at the boundaries between blocks in the restored picture. The ALF can perform filtering based on a comparison between the restored image and the original image after blocks are removed through the deblocking filter. The ALF may only be performed when high efficiency is adopted. The SAO restores the offset difference between the original image and the pixel unit for the residual block where the deblocking filter is adopted, and is adopted in the form of band offset, edge offset, etc.

[0060] On the other hand, the filter unit 145 does not need to apply a filter to a reconstructed block used in inter prediction.

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

[0062] 2 is a block diagram illustrating a video decoding device according to an embodiment of the present invention. As illustrated in FIG. 2, the video decoding device 200 may include an entropy decoding unit 210, a reordering unit 215, a dequantization unit 220, an inverse transform 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 by which video information is processed in the video encoding device.

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

[0065] Among the information decoded in the entropy decoding unit 210, information for generating a prediction block is provided to the prediction unit 230, and the residual value entropy decoded in the entropy decoding unit 210 can be input to the reordering unit 215.

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

[0067] The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoding device and the coefficient values ​​of the reordered blocks.

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

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

[0070] If the prediction mode for the current PU is an intra prediction mode, intra prediction can be performed to generate a prediction block based on pixel information in the current picture.

[0071] When the prediction mode for the current PU is an inter prediction mode, inter prediction for the current PU may be performed based on information included in at least one of a previous picture or a subsequent picture of the current picture. In this case, motion information required for inter prediction of the current PU provided from the video encoding device, such as information regarding a motion vector and a reference picture index, may be derived from a skip flag, a merge flag, etc. received from the encoding device.

[0072] The reconstructed block may be generated using a predicted block generated by the prediction unit 230 and a residual block provided by the inverse transform unit 225. In FIG 2, it is described that the predicted block and the residual block are added together in an adder to generate a reconstructed block. In this case, the adder may be regarded as a separate unit (reconstructed block generator) that generates a reconstructed block.

[0073] If skip mode is adopted, the residual is not transferred and the prediction block can be the reconstructed block.

[0074] The reconstructed blocks and / or pictures may be provided to a filter unit 235, which may apply deblocking filtering, SAO and / or ALF, etc., to the reconstructed blocks and / or pictures.

[0075] The memory 240 can store the reconstructed pictures or blocks for use as reference pictures or blocks, and can provide the reconstructed pictures to an output.

[0076] Meanwhile, the coded or decoded picture is stored in a memory, for example, a decoded picture buffer (DPB). When coding or decoding a current picture, the previous picture stored in the DPB is referenced to perform prediction for the current picture.

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

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

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

[0080] For convenience of explanation, a neighboring block used for predicting a current block in inter prediction is called a "candidate block."

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

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

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

[0084] The prediction unit of the encoding device and the decoding device can use blocks at predetermined positions around the current block 400 as candidate blocks. For example, in the example of Fig. 3, two blocks A0 410 and A1 420 located at the lower left corner of the current block, and three blocks B0 430, B1 440, and B2 450 located at the upper right corner and upper left corner of the current block can be selected as candidate blocks. In addition to spatially adjacent blocks, the above-mentioned Col block 460 can be used as a candidate block as a temporal candidate block.

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

[0086] On the other hand, with regard to the reference picture used in inter prediction, the reference picture for the current block can be derived from the reference picture of the neighboring block or can be indicated from the decoding device. In the case of skip mode or merge mode, the prediction unit of the decoding device can use the reference picture of the neighboring block as the reference picture of the current block. In the case of using 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 that have been coded / decoded before the current picture are stored in a memory (e.g., DPB) and can be used to predict the current block (current picture). A 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, and a B slice is a slice decoded through intra prediction or inter prediction using at most two motion vectors and two reference pictures, where the reference pictures include a short term reference picture and a long term reference picture.

[0089] 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. 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 of P slices that perform unidirectional prediction, and L0 and L1 are used for inter-prediction of blocks of B slices that perform bidirectional prediction.

[0090] When decoding P slices and B slices through inter prediction, the decoding device constructs a reference picture list. Reference pictures used for inter prediction are specified through the reference picture list. A 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 make up the reference picture list via the reference picture index may be stored in a memory (eg, a DPB).

[0093] The pictures stored in the memory (pictures previously coded / decoded of the current picture) are managed by the coding device and the decoding device, which keep the pictures necessary for predicting the current block and release the pictures not used for predicting the current block from the memory.

[0094] When a sliding window method is used as a method for managing reference pictures, reference pictures can be managed in a simple manner in which they are stored in memory and then released after a certain time has passed, but there are some problems with this method. For example, even if there are reference pictures that are no longer needed, they cannot be directly released from memory, which reduces efficiency. Also, since they are released from memory after a certain time, it is difficult to manage long-term reference pictures.

[0095] Considering the problem of the sliding window method, a memory management command operation (MMCO) method may be used in which the encoding device directly notifies instructions regarding management of reference pictures. However, even if the MMCO method is used, if a picture loss occurs during the notification process and the lost picture contains an MMCO command, the lost MMCO information cannot be restored, and the memory (DPB) cannot be maintained in an accurate state in which the currently required picture is managed. Therefore, inter prediction may also be performed inaccurately.

[0096] To solve the above problem, a method can be used to transfer a list of reference pictures required in the decoding process of a slice from each slice header. A kind of abstract container containing a list of reference pictures in a slice header can be called "RefPicList". Or, as explained above, in order to distinguish between reference picture list 0 and reference picture list 1 configured in a decoding device, a 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] A reference picture set or RefPicList (hereinafter, for convenience of explanation and to distinguish from a reference picture list, referred to as a "reference picture set") includes reference pictures used for referencing a current picture / slice or a future picture / slice. For example, a reference picture set is information transferred from an encoding device to a decoding device, and pictures included in the reference picture set can be identified by a POC. The POC indicates the display order of pictures. In this case, the POC of a reference picture included in the reference picture set may be a relative POC with respect to the POC of the current picture.

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

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

[0100] The set of reference pictures is notified from the encoding device to the decoding device for each P slice and B slice.

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

[0102] When creating the reference picture list L0, the reference picture list is created by assigning reference picture indexes from pictures with a POC smaller than that of the current picture among the received set of reference pictures (pictures before the current picture in POC order or pictures whose relative POC sign has a negative value) and pictures with a POC larger than that of the current picture (pictures after the current picture in POC order or pictures whose relative POC sign has a positive value).

[0103] For example, until all reference picture indexes that make up the reference picture list have been assigned, (i) for pictures in the reference picture set for the current picture / slice that have a smaller POC than the current picture's POC, lower reference picture indexes are assigned to pictures that are closer to the current picture in POC order, and then (ii) for pictures in the reference picture set for the current picture / slice that have a larger POC than the current picture's POC, lower reference picture indexes are assigned to pictures that are closer to the current picture in POC order.

[0104] When creating the reference picture list L1, the reference picture list is created by assigning reference picture indexes from pictures with a POC greater than that of the current picture among the received set of reference pictures that have a smaller POC than that of the current picture (pictures before the current picture in POC order or pictures whose relative POC sign has a negative value) and pictures with a POC greater than that of the current picture (pictures after the current picture in POC order or pictures whose relative POC sign has a positive value).

[0105] For example, until all reference pictures that make up the reference picture list have been assigned, (i) for pictures in the reference picture set for the current picture / slice that have a POC greater than that of the current picture, lower reference picture indexes are assigned to pictures that are closer to the current picture in POC order, and then (ii) for pictures in the reference picture set for the current picture / slice that have a POC less than that of the current picture, lower reference picture indexes are assigned to pictures that are closer to the current picture in POC order.

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

[0107] Hereinafter, this specification will describe a method for creating a reference picture set of short-term reference pictures and creating a reference picture list, and hereinafter, reference pictures refer to short-term reference pictures.

[0108] In this case, in order to reduce the number of bits of the notified reference picture set and reduce the complexity of the process of creating a reference picture list in the decoder, the reference pictures (information on the reference pictures, e.g., POC values) in the reference picture set (list of reference pictures) can be aligned and transmitted.

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

[0110] For example, in a reference picture set, a reference picture (picture information) with a smaller POC than that of a current picture is placed, and then a reference picture (picture information) with a larger POC than that of the current picture is placed. In this case, the information of the reference picture to be placed may be the POC of the reference picture, the relative POC of the reference picture, or the size and sign of the relative POC of the reference picture.

[0111] If the information to be placed is the POC of a reference picture, in the reference picture set, the POCs of reference pictures with smaller POCs than the POC of the current picture are placed in order of closestness to the POC of the current picture, and then the POCs of reference pictures with larger POCs than the POC of the current picture are placed in order of closestness to the POC of the current picture.

[0112] When the information to be arranged is the relative POC of a reference picture, the relative POC for the reference picture with a smaller POC than the POC of the current picture is arranged first, followed by the relative POC for the reference picture with a larger POC than the POC of the current picture. For example, the relative POC for the reference picture with a smaller POC than the POC of the current picture in the reference picture set is arranged in the order of the POC of the reference picture (descending order), and then the relative POC for the reference picture with a larger POC than the POC of the current picture is arranged in the order of the POC of the reference picture (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 a reference picture set, a relative POC can be expressed 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 POC order. Therefore, instead of transmitting information specifically indicating the sign (+ or -) of the relative POC, the magnitude of the relative POC for the reference picture before the current picture in the POC order can be transmitted first, and then the magnitude of the relative POC for the reference picture after the current picture can be transmitted. A decoding device receiving a set of reference pictures can determine that the magnitude of the relative POC received first is for the reference picture before the current picture in the POC order, and the magnitude of the relative POC received later is for the reference picture after the current picture in the POC order. In this case, information indicating the number of reference pictures before the current picture and the number of reference pictures after the current picture in the POC order can be transmitted together.

[0115] When transmitting the relative POC size, the relative POC size for reference pictures in the reference picture set that have a smaller POC than the current picture's POC are arranged in the order of the reference pictures' POC (descending order), and then the relative POC size for reference pictures that have a larger POC than the current picture's POC are arranged in the order of the reference pictures' POC (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 use the method in Table 1 to determine the magnitude and sign of the relative POC of the reference pictures that it signals via the reference picture set.

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

[0119] abs_ref_pic[i] specifies the magnitude of relative POC for the i-th reference picture in the reference picture set. When the relative POC code of the i-th reference picture is the same as the code of the relative POC of the i-1-th reference picture, the difference value 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 relative POC of the i-th reference picture. That is, when the relative POC code of the i-th reference picture is the same as the code of the relative POC of the i-1-th reference picture, the magnitude of 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 a reference POC value that is transferred from the encoding device or is preset, and is used to calculate the first relative POC in 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 code of the relative POC of the i-1-th reference picture. In this case, the i-th reference picture is the first picture in the reference picture set, or the i-1-th reference picture is a picture before the current picture in the POC order, and the i-th reference picture is a picture after the current picture in the POC order. Therefore, if the relative POC code of the i-th reference picture is not the same as the code of the relative POC 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, the code of the i-th reference picture and the relative POC are the same again, so 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.

[0122] The encoding device may transmit the magnitude and sign of the relative POC of the reference pictures derived as described above as a set of reference pictures. In addition, when transmitting the magnitude of the relative POC of the reference pictures, the encoding device may first transmit the magnitude of the relative POC for the reference pictures before the current picture in the POC order in which the codes are transmitted, and then transmit the magnitude of the relative POC for the reference pictures after the current picture. In this case, the encoding device may transmit information indicating the number of reference pictures whose relative POC sign is '-' (pictures before the current picture in the POC order) and the number of reference pictures whose relative POC sign is '+' (pictures after the current picture in the POC order).

[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, a case where the reference value (refValue) is the POC value of the current picture will be described as an example.

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

[0126] When the relative POC code of the i-th reference picture is the same as the code of the relative POC 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 is the magnitude of the relative POC of the first reference picture. That is, when the relative POC code of the i-th reference picture is the same as the code of the relative POC 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).

[0127] The relative POC code of the i-th reference picture may not be the same as the code of the relative POC of the i-1-th reference picture. In this case, the i-th reference picture is the first picture in the reference picture set, or the i-1-th reference picture is a picture before the current picture in the POC order, and the i-th reference picture is a picture after the current picture in the POC order. Therefore, if the relative POC code of the i-th reference picture is not the same as the code of the relative POC 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. Then, in the case of the i+1-th reference picture, it is again the same as the code of the relative POC of the i-th reference picture, so 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 may transmit the magnitudes and signs of the relative POC of the reference pictures derived as described above as a set of reference pictures. In addition, when transmitting the magnitudes of the relative POC of the reference pictures, the encoding device may first transmit the magnitudes of the relative POC for the reference pictures before the current picture in the POC order in which the codes are transmitted, and then transmit the magnitudes of the relative POC for the reference pictures after the current picture. In this case, the encoding device may transmit information indicating the number of reference pictures whose relative POC sign is '-' (pictures before the current picture in the POC order) and the number of reference pictures whose relative POC sign is '+' (pictures after the current picture in the POC order).

[0129] The decoder receives information about the set of reference pictures from the encoder and is able to construct or reconstruct the set of reference pictures based on this information.

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

[0131] The decoding device can reconstruct the POC available for predicting the current block (picture) by the method of 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 a reference picture set can be reconstructed 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] The decoding device can explicitly receive the code of the relative POC from the encoding device, as shown in Table 3, and restore the POC of the reference picture.

[0134] When the code of the i-th reference picture in the reference picture set is the same as the code of the i-1-th reference picture and the code of the i-th reference picture is '-', the POC of the i-th reference picture is a reference value (refValue) minus the relative POC sum from the 1st reference picture (0th reference picture) to the i-th reference picture. When the code of the i-th reference picture in the reference picture set is the same as the code of the i-1-th reference picture and the code of the i-th reference picture is '+', the POC of the i-th reference picture is a reference value (refValue) plus the relative POC from the 1st reference picture (0th reference picture) to the i-th reference picture.

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

[0136] When the code of the i-th reference picture in a reference picture set is different from the code of the i-1-th reference picture, the i-th reference picture is the first picture in the i-th reference picture set, 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 code of the i-th reference picture in the reference picture set is different from the code of the i-1-th reference picture and the code of the i-th reference picture is '-', the POC of the i-th reference picture is a reference value (refValue) minus the relative POC of the i-th reference picture. When the code of the i-th reference picture in the reference picture set is different from the code of the i-1-th reference picture and the code of the i-th reference picture is '+', the POC of the i-th reference picture is a reference value (refValue) plus the relative POC of the i-th reference picture.

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

[0139] In other words, the relative POC for the first reference picture among the reference pictures in the reference picture set is the POC difference with the reference value (refValue). The relative POC for the pictures before the current picture in the reference picture set, excluding the first reference picture, is the POC difference with the immediately preceding reference picture. The relative POC for the first picture after the current picture among the reference pictures in the reference picture set is the POC difference with 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 in the reference picture set to the last reference picture) is the POC difference with the immediately preceding reference picture. Here, before and after the current picture are determined based on the POC order. Also, the immediately preceding reference picture means the picture immediately preceding in the sorting order in the reference picture set.

[0140] Table 4 shows another example of a method for recovering the reference picture information (POC) in a decoding device receiving a set of reference pictures. [Table 4]

[0141] In order to clearly explain the features of the present invention, the method of Table 4 will be described using an example in which the number of reference pictures included in the reference picture set is two, and the reference value (refValue) for calculating the first relative POC value in Table 3 is the POC of the current picture.

[0142] The decoder can explicitly receive the code of the relative POC from the encoder and reconstruct the POC of the reference picture.

[0143] When the code of the i-th reference picture in the reference picture set is the same as the code of the i-1-th reference picture and the code of the i-th reference picture is '-', the POC of the i-th reference picture is the POC of the current picture minus the relative POC of the i-th reference picture and the relative POC of the i-1-th reference picture.When the code of the i-th reference picture in the reference picture set is the same as the code of the i-th reference picture and the code of the i-th reference picture is '+', the POC of the i-th reference picture is the POC of the current picture plus the relative POC of the i-th reference picture and the relative POC of the i-1-th reference picture.

[0144] When the code of the i-th reference picture in the reference picture set is different from the code of the i-1-th reference picture, the i-th reference picture is the first picture in the i-th reference picture set, 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 code of the i-th reference picture in the reference picture set is different from the code of the i-1-th reference picture and the code of the i-th reference picture is '-', the POC of the i-th reference picture is the POC of the current picture minus the relative POC of the i-th reference picture. When the code of the i-th reference picture in the reference picture set is different from the code of the i-1-th reference picture and the code of the i-th reference picture is '+', the POC of the i-th reference picture is the POC of the current picture plus the relative POC of the i-th reference picture.

[0146] Also, as described in Table 3, information explicitly indicating the code for the relative POC of the reference picture may not be transferred. In this case, the decoding device can determine that the code of the relative POC arranged at the beginning of the reference picture set is '-' (minus), and that the code of the relative POC arranged at the end of the reference picture set is '+' (plus). At this time, the encoding device can also transfer information indicating the number of relative POCs whose code is '-' and the number of relative POCs whose code is '+'. From the beginning of the reference picture set, the decoding device determines that the relative POCs whose code is '-' indicated by the encoding device have the code '-', and determines that the remaining relative POCs have the code '+', and can restore the POC (ref_pic[i]) of the i-th reference signal as described above.

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

[0148] Hereinafter, a specific example in which the present invention is adopted will be described, in which the reference value (refValue) is the POC of the current picture.

[0149] Fig. 4 is a diagram for explaining an example of a reference picture set notified from an encoding device to a decoding device. The example in Fig. 4 shows a case where nine P slices (P pictures) P0 to P9 performing unidirectional prediction refer to each other.

[0150] Table 5 shows an example where the signaled reference picture set for the example of FIG. 4 is composed of the POCs of the reference pictures.

[0151] [Table 5]

[0152] As shown in Figure 4 and Table 5, the reference picture set for the current picture includes the POCs of the reference pictures that the current picture can refer to. In the reference picture set, the reference pictures are ordered in POC order, with lower indexes being assigned to reference pictures closer to the current picture.

[0153] For example, in the example of Figure 4 and Table 5, if the current picture is P6 (POC=26), the reference pictures that the current picture can refer to are P5, P4, and P0. Therefore, the reference picture set for the current picture P6, which has a POC of 26, is composed of the POCs of P5, P4, and P0, and a lower index is assigned to a reference picture closer to the current picture in POC order.

[0154] In the example of FIG. 4 and Table 5, in the case of reference pictures before the current picture in POC order, they are sorted in descending order within the reference picture set, but the reference picture set still reports the POC of the reference pictures.

[0155] Alternatively, as explained above, a reference picture collection can signal the relative POC of the reference pictures.

[0156] Table 6 shows an example of a reference picture set notified in the case of FIG. 4, and is intended to explain an example in which the reference picture set is configured from the relative POC of the reference pictures. [Table 6]

[0157] In Table 6, the reference picture set of the current picture for FIG. 4 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] Table 5 describes the case where the POC of a reference picture in a reference picture set is transferred as is, but the example of Table 6 describes the case where the relative POC of a reference picture in a reference picture set is transferred.

[0159] The relative POC of a reference picture before the current picture in POC order (a reference picture with a smaller POC than the current picture) is the POC difference with the previous reference picture in the reference picture set. The relative POC code transmitted in the reference picture set indicates whether the reference picture is before the current picture or after the current picture in POC order.

[0160] For example, in the example of FIG. 4 and Table 6, if the current picture is P5, the pictures that the current picture can refer to are P4, P3, and P0, with POCs of 24, 23, and 20, respectively.

[0161] When the reference picture set for P5 transmits the relative POC, the reference picture set arranges the magnitude and sign of the relative POC of the reference picture for P5 in a predetermined order and transmits it. As described above, in the example of FIG. 4 showing the reference relationship between P slices, the reference picture is a picture before the current picture in the POC order, and the reference pictures in the reference picture set are arranged in descending order.

[0162] Therefore, in the reference picture set for P5, the relative POC magnitudes are sorted in the order of P4, P3, and P0. As shown in Table 6, the relative POC magnitude of P4 transferred to the reference picture set for P5 is 1 with a sign '-', the relative POC magnitude of P3 is 1 with a sign '-', and the relative POC magnitude of P0 is 3 with a sign '-'.

[0163] In this case, it is also possible to transmit a reference picture set in which reference pictures before the current picture (the size of the relative POC of the reference picture) are aligned in the front part of the reference picture set and reference pictures after the current picture (the size of the relative POC of the reference picture) are aligned in the back part of the reference picture set in POC order without a relative POC code. In this case, information indicating the number of reference pictures before the current picture in POC order (reference pictures with a '-' relative POC code) and the number of reference pictures after the current picture in POC order (reference pictures with a '+' relative POC code) can be transmitted together.

[0164] Unlike Fig. 4 which shows the reference relationships between P pictures which perform unidirectional prediction, Fig. 5 is a diagram showing an example of the reference relationships between B pictures which perform bidirectional prediction. Fig. 5 shows a schematic diagram of the reference relationships between nine B pictures B0 to B8.

[0165] Table 7 shows an example of a reference picture set notified in the case of FIG. 5, and is intended to explain an example in which the reference picture set is configured from the relative POC of the reference pictures. [Table 7]

[0166] Also in the example of Table 7 and FIG. 5, the reference picture collection can transmit the relative POC of the reference pictures instead of transmitting the POC of the reference pictures as is.

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

[0168] Referring to Table 7, taking the current picture B5 as an example, the reference picture set is composed of B4, B2, B6, and B8. When the reference picture set is composed of relative POCs, the magnitude of the relative POC to which the lowest index is assigned in the reference picture set is for B4, and is 1, which is the difference 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, and is 2, which is the difference 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 sign of the relative POC for B6 is different from that of the relative POC for B2, which is the previous reference picture, the magnitude of the relative POC for B6 is 1, which is the POC difference with the current picture, and the sign is '+'. The magnitude of the relative POC to which the last index is assigned is for B8, and is 2, which is the difference between the POC of B6 and B8, and the sign is '+'.

[0169] As described above, when transmitting only the magnitudes of the relative POCs of the reference pictures for the current picture instead of transmitting all the magnitudes and signs of the relative POCs of the reference pictures for the current picture, the magnitudes of the relative POCs having a '-' sign may be transmitted before the magnitudes of the relative POCs having a '+' sign, so that the sign of the corresponding relative POC may be derived without explicitly transmitting the sign. In this case, information indicating the number of relative POCs having a '-' sign and the number of relative POCs having a '+' sign may be transmitted together.

[0170] For example, considering again the case where the current picture is B5 in Table 7, the encoding device can transmit a reference picture set for B5 consisting of only the relative PC sizes of the reference pictures, such as (1 2 1 2). As shown in Table 7, the size of the relative POC with a '-' sign is placed at the front of the reference picture set. The sorting order is descending as described above for relative POC with a '-' sign (relative POC for a reference picture before the current picture in POC order), and also maintains ascending order as described above for relative POC with a '+' sign (relative POC for a reference picture after the current picture in POC order). In this case, information indicating the number of relative POC with a '-' sign and the number of relative POC with a '+' sign can be transmitted together with the reference picture set. For example, when receiving an instruction that the number of reference pictures (relative POC) with a '-' sign in the reference picture set for B5 is 2 and the number of reference pictures (relative POC) with a '+' sign is 2, the decoding device can determine that since the code for the first two relative POCs in the reference picture set is '-' and the code for the last two relative POCs is '+', the magnitudes of the first two relative POCs in the reference picture set are the magnitudes of relative POCs for reference pictures with smaller POCs than the current picture, and the magnitudes of the last two relative POCs in the reference picture set are the magnitudes of relative POCs for reference pictures with larger POCs than the current picture.

[0171] FIG. 6 is a diagram illustrating an example of a reference relationship between a B picture and a P picture.

[0172] FIG. 6 shows 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.

[0173] Table 8 shows an example of a reference picture set notified in the case of FIG. 6, and is intended to explain an example in which the reference picture set is configured from the relative POC of the reference pictures.

[0174] [Table 8]

[0175] The examples in Table 8 and Figure 6 are for a case where P pictures and B pictures are mixed, but the method of deriving the size and sign of the relative POC, the method of arranging the relative POC within the reference picture set, etc. are as described above.

[0176] For example, if the current picture is B1, the reference picture set for B1 may consist of the relative POCs of P3, P0, and P6. The reference picture set may be transferred to the decoding device by including the magnitude (2 4 2) of the relative POCs for P3, P0, and P6 and their respective codes.

[0177] In this case, instead of transmitting information indicating the sign of the relative POC, information indicating the number of relative POCs having a '-' sign and the number of relative POCs having a '+' sign based on the sorting order can be transmitted together with the reference picture set including the size of the relative POC. For example, when the current picture is B1, a reference picture set (2 4 2) including the size of the relative POC and 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 transmitted.

[0178] 7 is a flow chart for explaining an outline of the encoding method performed by an encoding device according to the present invention. The encoding device for performing the encoding method of FIG. 7 corresponds to the encoding device described in FIG.

[0179] As shown in Fig. 7, the encoding apparatus performs prediction for a current block (S710). The encoding apparatus may perform inter prediction or intra prediction for the current block. When performing inter prediction, the encoding apparatus may select / specify a reference picture for the current block using the reference picture list configured as described above.

[0180] The encoding device transforms / quantizes the prediction result for the current block (S720). The encoding device may transform / quantize a residual block corresponding to the difference between the prediction result and the original block. In addition, if intra prediction is used, the encoding device may transform / quantize information related to the used intra prediction mode, and if inter prediction is used, the encoding device may transform / quantize motion information (information related to a motion vector / reference picture).

[0181] The encoding device entropy-encodes the transformed / quantized information (S730). CABAC may be used as the entropy encoding method.

[0182] The encoding device reports the entropy-encoded information (S740). At this time, the reported information includes a reference picture set for creating a reference picture list for the current picture (current block). The reference picture set may be configured for each slice and may be transmitted in the header of the slice.

[0183] The reference picture set can be constructed from the POCs of the reference pictures for the current block, or the reference picture set can be constructed from the relative POCs of the reference pictures to reduce transmission overhead.

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

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

[0186] FIG. 8 is a flow chart for explaining in outline 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 set of reference pictures. The set of reference pictures can be received in a slide header.

[0188] The set of reference pictures may consist of the POC of the reference pictures for the current block, or may consist of the relative POC of the reference pictures.

[0189] The decoding device may receive information indicating pictures that can be used as reference pictures for the current picture through the reference picture set. For example, the decoding device may receive POCs of pictures that can be used as reference pictures for the current picture through the reference picture set. If the reference picture set includes (1) the magnitude and sign of the relative POC for the reference picture or (2) the magnitude of the relative POC for the reference picture and the number of relative POCs having '-' and '+' signs, the decoding device may derive the POC of the corresponding reference picture based on the received information using the method of Table 4, etc.

[0190] When receiving relative POCs via a reference picture set, the relative POCs with a '-' sign are received first, and the relative POCs with a '+' sign are received next. The relative POCs with a '-' sign may be sorted in descending order according to the POCs of the reference pictures, and the relative POCs with a '+' sign may be sorted in ascending order according to the POCs of the reference pictures.

[0191] The decoding device performs 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. If the prediction method for the current block is inter-prediction, the decoding device can perform prediction using a reference picture list constructed based on the received reference picture set.

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

[0193] The decoding device reconstructs an image (S930). The current block is reconstructed based on a prediction for the current block, and the image can be reconstructed through the reconstructed block. When a skip mode is employed, the residual is not transmitted, so the predicted block can be used as the reconstructed block. When a merge mode is applied or MVP is used, the current block can be reconstructed by combining the predicted block and the residual block.

[0194] It should be noted that, in this specification, the expressions "picture included in a reference picture set" and "x-th picture of a reference picture set" are used for convenience of explanation. A picture included in a reference picture set means a picture whose POC information corresponding to the reference picture set is included, and the x-th picture of a reference picture set means a picture whose corresponding POC information is aligned to the xth position in the reference picture set.

[0195] Meanwhile, the reference relationships between pictures shown in Figures 4 to 6 are described using an example in which the temporal level is not adopted, but this is for the sake of understanding the invention, and the present invention is not limited thereto. The present invention can also be applied to a case in which the temporal level is taken into consideration and only pictures of a lower level are referred to, and in this case, the reference relationships in Tables 5 to 8 can be changed to reflect this.

[0196] In the above exemplary system, the method of the present invention is described based on a flowchart with a series of steps or blocks, but the present invention is not limited to the order of steps, and some steps can occur in a different order or simultaneously with other steps than those described above. Also, the above-mentioned embodiments include examples of various aspects. Therefore, it should be understood that the present invention includes all other alternatives, modifications and alterations that fall within the scope of the following claims.

[0197] In the above description of the present invention, when a component is said to be "coupled" or "connected" to another component, it should be understood that the other component may be directly coupled or connected to the other component, but there may be other components between the two components. In contrast, when a component is said to be "directly coupled" or "directly connected" to another component, it should be understood that there is no other component between the two components.

Claims

1. An inter prediction method performed by a decoding device, comprising: receiving picture order count (POC) information; deriving a Picture Order Count (POC) value for a reference picture based on the POC information; constructing a reference picture list based on the POC values ​​of the reference pictures; performing inter prediction on the current block based on the reference picture list to derive predicted samples of the current block; a POC value of the i-th reference picture is derived based on a POC difference derived from the POC information; the reference pictures include the reference picture before the current picture in POC order and the reference picture following the current picture in POC order; The reference picture list is constructed based on a set of reference pictures; the 0th reference picture is the first reference picture in the set of reference pictures; for the reference picture located before the current picture in the POC order, the POC difference is a difference between a POC value of the current picture and a POC value of the i-th reference picture when the i-th reference picture is a first reference picture in the set of reference pictures; the POC difference is a difference between a POC value of the i-th reference picture and a POC value of a (i-1)-th reference picture when the i-th reference picture is a second reference picture following a first reference picture to a last reference picture of the reference picture set; An inter prediction method, wherein for the reference picture list, indexes are assigned based on descending order of POC values ​​up to the reference picture before the current picture in the POC order, and indexes are assigned based on ascending order of POC values ​​up to the reference picture before the current picture in the POC order.

2. deriving, based on the POC information, a POC difference for the reference picture located before the current picture in POC order in descending POC order; The method of claim 1 , further comprising: deriving a POC difference for the reference picture that follows the current picture in POC order in ascending POC order based on the POC information.

3. 2. The method of claim 1, wherein the POC information includes first number information for identifying a number of the reference pictures located before the current picture in the POC order, and second number information for identifying a number of the reference pictures following the current picture in the POC order.

4. The method of claim 1 , wherein the POC information is signaled at a slice header level.

5. The method of claim 4 , wherein the slice header is for a P slice or a B slice.

6. A video encoding method executed by an encoding device, comprising: performing inter prediction on a current block based on a reference picture list included in a reference picture; deriving a Picture Order Count (POC) value for the reference picture; deriving POC information for the reference picture based on the derived POC value of the reference picture, the POC information indicating a POC difference with respect to the reference picture; and encoding the video information including the POC information; the reference pictures include the reference picture before the current picture in POC order and the reference picture following the current picture in POC order; The reference picture list is constructed based on a set of reference pictures; the 0th reference picture is the first reference picture in the set of reference pictures; for the reference picture located before the current picture in the POC order, the POC difference is a difference between a POC value of the current picture and a POC value of the i-th reference picture when the i-th reference picture is a first reference picture in the set of reference pictures; the POC difference is a difference between a POC value of the i-th reference picture and a POC value of a (i-1)-th reference picture when the i-th reference picture is a second reference picture following a first reference picture to a last reference picture of the reference picture set; A video encoding method, wherein for the reference picture list, indexes are assigned based on descending order of POC values ​​up to the reference picture preceding the current picture in the POC order, and indexes are assigned based on ascending order of POC values ​​up to the reference picture preceding the current picture in the POC order.

7. A method for transmitting data for an image, comprising the steps of: Obtaining a bitstream for the image, comprising: the bitstream is generated by performing inter prediction on a current block based on a reference picture list included in a reference picture, deriving a Picture Order Count (POC) value for the reference picture, deriving POC information of the reference picture based on the derived POC value of the reference picture, the POC information indicating a POC difference with respect to the reference picture, and encoding video information including the POC information to output the bitstream; transmitting the data including the bitstream; the reference pictures include the reference picture before the current picture in POC order and the reference picture following the current picture in POC order; The reference picture list is constructed based on a set of reference pictures; the 0th reference picture is the first reference picture in the set of reference pictures; for the reference picture located before the current picture in the POC order, the POC difference is a difference between a POC value of the current picture and a POC value of the i-th reference picture when the i-th reference picture is a first reference picture in the set of reference pictures; the POC difference is a difference between a POC value of the i-th reference picture and a POC value of a (i-1)-th reference picture when the i-th reference picture is a second reference picture following a first reference picture to a last reference picture of the reference picture set; A method of transmitting data, wherein for the reference picture list, indexes are assigned based on descending order of POC values ​​up to the reference picture preceding the current picture in the POC order, and indexes are assigned based on ascending order of POC values ​​up to the reference picture preceding the current picture in the POC order.

Images