Patent Publication Number: US-2021168403-A1

Title: Encoder, decoder, encoding method, and decoding method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. continuation application of PCT International Patent Application Number PCT/JP2019/030531 filed on Aug. 2, 2019, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/714,986 filed on Aug. 6, 2018, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an encoder, a decoder, an encoding method, and a decoding method. 
     2. Description of the Related Art 
     Conventionally H.265 has been known as a standard for encoding moving pictures. H.265 is also referred to as High-Efficiency Video Coding (HEVC) (H.265 (ISO/IEC 23008-2 HEVC)/HEVC (High Efficiency Video Coding)) (Non-patent Literature (NPL) 1). 
     SUMMARY 
     It should be noted that these general or specific aspects of the present disclosure may be implemented as a system, a device, a method, an integrated circuit, a computer program, or a computer-readable non-volatile recording medium such as a CD-ROM, or may be implemented as any combination of a system, a device, a method, an integrated circuit, a computer program, and a recording medium. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  is a block diagram illustrating a functional configuration of an encoder according to an embodiment; 
         FIG. 2  is a flow chart indicating one example of an overall encoding process performed by the encoder; 
         FIG. 3  is a conceptual diagram illustrating one example of block splitting; 
         FIG. 4A  is a conceptual diagram illustrating one example of a slice configuration; 
         FIG. 4B  is a conceptual diagram illustrating one example of a tile configuration; 
         FIG. 5A  is a chart indicating transform basis functions for various transform types; 
         FIG. 5B  is a conceptual diagram illustrating example spatially varying transforms (SVT); 
         FIG. 6A  is a conceptual diagram illustrating one example of a filter shape used in an adaptive loop filter (ALF); 
         FIG. 6B  is a conceptual diagram illustrating another example of a filter shape used in an ALF; 
         FIG. 6C  is a conceptual diagram illustrating another example of a filter shape used in an ALF; 
         FIG. 7  is a block diagram indicating one example of a specific configuration of a loop filter which functions as a deblocking filter (DBF); 
         FIG. 8  is a conceptual diagram indicating an example of a deblocking filter having a symmetrical filtering characteristic with respect to a block boundary; 
         FIG. 9  is a conceptual diagram for illustrating a block boundary on which a deblocking filter process is performed; 
         FIG. 10  is a conceptual diagram indicating examples of Bs values; 
         FIG. 11  is a flow chart illustrating one example of a process performed by a prediction processor of the encoder; 
         FIG. 12  is a flow chart illustrating another example of a process performed by the prediction processor of the encoder; 
         FIG. 13  is a flow chart illustrating another example of a process performed by the prediction processor of the encoder; 
         FIG. 14  is a conceptual diagram illustrating sixty-seven intra prediction modes used in intra prediction in an embodiment; 
         FIG. 15  is a flow chart illustrating an example basic processing flow of inter prediction; 
         FIG. 16  is a flow chart illustrating one example of derivation of motion vectors; 
         FIG. 17  is a flow chart illustrating another example of derivation of motion vectors; 
         FIG. 18  is a flow chart illustrating another example of derivation of motion vectors; 
         FIG. 19  is a flow chart illustrating an example of inter prediction in normal inter mode; 
         FIG. 20  is a flow chart illustrating an example of inter prediction in merge mode; 
         FIG. 21  is a conceptual diagram for illustrating one example of a motion vector derivation process in merge mode; 
         FIG. 22  is a flow chart illustrating one example of frame rate up conversion (FRUC) process; 
         FIG. 23  is a conceptual diagram for illustrating one example of pattern matching (bilateral matching) between two blocks along a motion trajectory; 
         FIG. 24  is a conceptual diagram for illustrating one example of pattern matching (template matching) between a template in a current picture and a block in a reference picture; 
         FIG. 25A  is a conceptual diagram for illustrating one example of deriving a motion vector of each sub-block based on motion vectors of a plurality of neighboring blocks; 
         FIG. 25B  is a conceptual diagram for illustrating one example of deriving a motion vector of each sub-block in affine mode in which three control points are used; 
         FIG. 26A  is a conceptual diagram for illustrating an affine merge mode; 
         FIG. 26B  is a conceptual diagram for illustrating an affine merge mode in which two control points are used; 
         FIG. 26C  is a conceptual diagram for illustrating an affine merge mode in which three control points are used; 
         FIG. 27  is a flow chart illustrating one example of a process in affine merge mode; 
         FIG. 28A  is a conceptual diagram for illustrating an affine inter mode in which two control points are used; 
         FIG. 28B  is a conceptual diagram for illustrating an affine inter mode in which three control points are used; 
         FIG. 29  is a flow chart illustrating one example of a process in affine inter mode; 
         FIG. 30A  is a conceptual diagram for illustrating an affine inter mode in which a current block has three control points and a neighboring block has two control points; 
         FIG. 30B  is a conceptual diagram for illustrating an affine inter mode in which a current block has two control points and a neighboring block has three control points; 
         FIG. 31A  is a flow chart illustrating a merge mode process including decoder motion vector refinement (DMVR); 
         FIG. 31B  is a conceptual diagram for illustrating one example of a DMVR process; 
         FIG. 32  is a flow chart illustrating one example of generation of a prediction image; 
         FIG. 33  is a flow chart illustrating another example of generation of a prediction image; 
         FIG. 34  is a flow chart illustrating another example of generation of a prediction image; 
         FIG. 35  is a flow chart illustrating one example of a prediction image correction process performed by an overlapped block motion compensation (OBMC) process; 
         FIG. 36  is a conceptual diagram for illustrating one example of a prediction image correction process performed by an OBMC process; 
         FIG. 37  is a conceptual diagram for illustrating generation of two triangular prediction images; 
         FIG. 38  is a conceptual diagram for illustrating a model assuming uniform linear motion; 
         FIG. 39  is a conceptual diagram for illustrating one example of a prediction image generation method using a luminance correction process performed by a local illumination compensation (LIC) process; 
         FIG. 40  is a block diagram illustrating a mounting example of the encoder; 
         FIG. 41  is a block diagram illustrating a functional configuration of a decoder according to an embodiment; 
         FIG. 42  is a flow chart illustrating one example of an overall decoding process performed by the decoder; 
         FIG. 43  is a flow chart illustrating one example of a process performed by a prediction processor of the decoder; 
         FIG. 44  is a flow chart illustrating another example of a process performed by the prediction processor of the decoder; 
         FIG. 45  is a flow chart illustrating an example of inter prediction in normal inter mode in the decoder; 
         FIG. 46  is a block diagram illustrating a mounting example of the decoder; 
         FIG. 47  is a diagram illustrating an outline of a first example of a pipeline configuration for the decoder according to the embodiment; 
         FIG. 48  is a diagram illustrating processing timings in a time sequence in which stage processing is performed on each current block to be processed in the first example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 49  is a flow chart illustrating a flow of an inter prediction process in the first example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 50  is a diagram illustrating an outline of a second example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 51  is a diagram illustrating processing timings in a time sequence in which stage processing is performed on each current block to be processed in the second example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 52  is a flow chart illustrating a flow of an inter prediction process in the second example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 53  is a flow chart illustrating a flow of an inter prediction process in a third example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 54  is a diagram illustrating the details of a BIO process when a prediction image that has been corrected using an LIC process is further corrected in the third example of the pipeline configuration for the decoder according to the embodiment; 
         FIG. 55  is a flow chart illustrating an operation example of the encoder according to the embodiment; 
         FIG. 56  is a flow chart illustrating an operation example of the decoder according to the embodiment; 
         FIG. 57  is a block diagram illustrating an overall configuration of a content providing system for implementing a content distribution service; 
         FIG. 58  is a conceptual diagram illustrating one example of an encoding structure in scalable encoding; 
         FIG. 59  is a conceptual diagram illustrating one example of an encoding structure in scalable encoding; 
         FIG. 60  is a conceptual diagram illustrating an example of a display screen of a web page; 
         FIG. 61  is a conceptual diagram illustrating an example of a display screen of a web page; 
         FIG. 62  is a block diagram illustrating one example of a smartphone; and 
         FIG. 63  is a block diagram illustrating an example of a configuration of a smartphone. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     [Underlying Knowledge Forming Basis of the Present Disclosure] 
     [Underlying Knowledge Forming Basis of the Present Disclosure] 
     An encoder, for instance, may perform a process, which is referred to as “motion compensation (MC)”, of detecting an amount of motion of an object and generating an effective prediction image using the result of the detection. The motion compensation process involves three modes of a bi-directional optical flow (BIO) mode, an overlapped block motion compensation (OBMC) mode, and a local illumination compensation (LIC) mode. The BIO mode is a mode for deriving a motion vector based on a model assuming uniform linear motion. The OBMC mode is a mode for generating an inter prediction signal for each of sub-blocks in a current block by performing a weighted addition of adding: a prediction signal based on motion information obtained from motion estimation in a reference picture; and a prediction signal based on the motion information of a neighboring block in a current picture. The LIC mode is a mode for correcting luminance when a prediction image is generated. It has been a problem that when both the BIO mode and the LIC mode are applied to a current block to be processed, a long processing time is required. 
     In view of the above, an encoder according to one aspect of the present disclosure is, for example, an encoder that encodes a moving picture using an inter prediction process and includes circuitry and memory coupled to the circuitry. In the inter prediction process, when performing a correction process which is a local illumination compensation (LIC) process for a prediction image, the circuitry, in operation: performs the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process; and after the correction process, determines, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     With such an encoder, it is possible to greatly shorten a feedback process for LIC parameter derivation, which is carried out for a reconstructed image of a block neighboring a current block to be processed. Namely, the encoder is capable of shortening a processing time required for pipeline control including an LIC process, thereby reducing a waiting time of each of the processes included in the pipeline control. Accordingly, the encoder is highly capable of completing the processing of all of blocks in a picture within a processing time assigned to one picture even when the encoder has low processing performance. 
     For example, in the encoder according to one aspect of the present disclosure, the finally-derived motion vector is a motion vector corrected using a decoder motion vector refinement (DMVR) process when an inter prediction mode in the inter prediction process is a merge mode. 
     This feature enables the encoder to use, for the LIC process, a motion vector with which a cost calculated through the DMVR process is the lowest. Accordingly, the encoder is more capable of enhancing coding accuracy than a conventional encoder. 
     For example, in the encoder according to one aspect of the present disclosure, in a pipeline processing, the circuitry performs the following in a same processing stage as a processing stage of a process of adding the prediction image to a residual image to generate a reconstructed image: a process of deriving a correction parameter to be used in the LIC process, with reference to a reconstructed image of a processed block neighboring a current block to be processed; and a process of performing the correction process on the prediction image using the correction parameter. 
     This feature enables the encoder to perform the LIC parameter derivation process near the end of the inter prediction process. Accordingly, the encoder is capable of shortening the processing time required for pipeline control including an LIC process. The encoder is therefore highly capable of completing the processing of all of blocks in a picture within a processing time assigned to one picture even when the encoder has low processing performance. 
     For example, a decoder according to one aspect of the present disclosure is, for example, a decoder that decodes a moving picture using an inter prediction process and includes: circuitry and memory coupled to the circuitry. In the inter prediction process, when performing a correction process which is a local illumination compensation (LIC) process for a prediction image, the circuitry, in operation: performs the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process; and after the correction process, determines, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     With such a decoder, it is possible to greatly shorten a feedback process for LIC parameter derivation, which is carried out for a reconstructed image of a block neighboring a current block to be processed. Namely, the decoder is capable of shortening a processing time required for pipeline control including an LIC process, thereby reducing a waiting time of each of the processes included in the pipeline control. Accordingly the decoder is highly capable of completing the processing of all of blocks in a picture within a processing time assigned to one picture even when the decoder has low processing performance. 
     For example, in the encoder according to one aspect of the present disclosure, the finally-derived motion vector is a motion vector corrected using a DMVR process when an inter prediction mode in the inter prediction process is a merge mode. 
     This feature enables the decoder to use, for the LIC process, a motion vector with which a cost calculated through the DMVR process is the lowest. Accordingly, the decoder is more capable of enhancing coding accuracy than a conventional decoder. 
     For example, in the encoder according to one aspect of the present disclosure, in a pipeline processing, the circuitry performs the following in a same processing stage as a processing stage of a process of adding the prediction image to a residual image to generate a reconstructed image: a process of deriving a correction parameter to be used in the LIC process, with reference to a reconstructed image of a processed block neighboring a current block to be processed; and a process of performing the correction process on the prediction image using the correction parameter. 
     This feature enables the decoder to perform the LIC parameter derivation process near the end of the inter prediction process. Accordingly, the decoder is capable of shortening the processing time required for pipeline control including an LIC process. The decoder is therefore highly capable of completing the processing of all of blocks in a picture within a processing time assigned to one picture even when the decoder has low processing performance. 
     For example, an encoding method according to one aspect of the present disclosure is an encoding method for encoding a moving picture using an inter prediction process, and includes: when, in the inter prediction process, a correction process which is an LIC process for a prediction image is to be performed, performing the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process, and after the correction process, determining, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     With such an encoding method, the same advantageous effects as those attained with the aforementioned encoder can be produced. 
     For example, a decoding method according to one aspect of the present disclosure is a decoding method for decoding a moving picture using an inter prediction process, and includes, when, in the inter prediction process, a correction process which is an LIC process for a prediction image is to be performed, performing the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process, and after the correction process, determining, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     With such a decoding method, the same advantageous effects as those attained with the aforementioned decoder can be produced. 
     An encoder according to one aspect of the present disclosure may include, for example, a partitioner, an intra predictor, an inter predictor, a loop filter, a transformer, a quantizer, and an entropy encoder. 
     The partitioner may partition a picture into a plurality of blocks. The intra predictor may perform intra prediction on a block included in the plurality of blocks. The inter predictor may perform inter prediction on the block. The transformer may transform prediction errors between an original image and a prediction image obtained through the intra prediction or the inter prediction to generate transform coefficients. The quantizer may quantize the transform coefficients to generate quantized coefficients. The entropy encoder may encode the quantized coefficients to generate an encoded bitstream. The loop filter may apply a filter to a reconstructed image of the block. 
     Moreover, the encoder may be, for example, an encoder that encodes a video including pictures. 
     When performing a correction process which is a local illumination compensation (LIC) process for a prediction image, the inter predictor may perform the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process; and after the correction process, determine, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     A decoder according to one aspect of the present disclosure may include, for example, an entropy decoder, an inverse quantizer, an inverse transformer, an intra predictor, an inter predictor, and a loop filter. 
     The entropy decoder may decode, from an encoded bitstream, quantized coefficients of a block in a picture. The inverse quantizer may inverse quantize the quantized coefficients to obtain transform coefficients. The inverse transformer may inverse transform the transform coefficients to obtain prediction errors. The intra predictor may perform intra prediction on the block. The inter predictor may perform inter prediction on the block. The loop filter may apply a filter to a reconstructed image generated using a prediction image obtained through the intra prediction or the inter prediction and the prediction errors. 
     Moreover, the decoder may decode a video including pictures. 
     When performing a correction process which is a local illumination compensation (LIC) process for a prediction image, the inter predictor may perform the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process; and after the correction process, determine, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     General or specific aspects of the present disclosure may be implemented as a system, a device, a method, an integrated circuit, a computer program or, a non-transitory computer-readable recording medium such as a CD-ROM, or may be implemented as any given combination of a system, a device, a method, an integrated circuit, a computer program, and a recording medium. 
     Hereinafter, embodiments will be described with reference to the drawings. Note that the embodiments described below each show a general or specific example. The numerical values, shapes, materials, components, the arrangement and connection of the components, steps, the relation and order of the steps, etc., indicated in the following embodiments are mere examples, and are not intended to limit the scope of the claims. 
     Embodiments of an encoder and a decoder will be described below. The embodiments are examples of an encoder and a decoder to which the processes and/or configurations presented in the description of aspects of the present disclosure are applicable. The processes and/or configurations can also be implemented in an encoder and a decoder different from those according to the embodiments. For example, regarding the processes and/or configurations as applied to the embodiments, any of the following may be implemented. 
     (1) Any of the components of the encoder or the decoder according to the embodiments presented in the description of aspects of the present disclosure may be substituted or combined with another component presented anywhere in the description of aspects of the present disclosure. 
     (2) In the encoder or the decoder according to the embodiments, discretionary changes may be made to functions or processes performed by one or more components of the encoder or the decoder, such as addition, substitution, removal, etc., of the functions or processes. For example, any function or process may be substituted or combined with another function or process presented anywhere in the description of aspects of the present disclosure. 
     (3) In methods implemented by the encoder or the decoder according to the embodiments, discretionary changes may be made such as addition, substitution, and removal of one or more of the processes included in the method. For example, any process in the method may be substituted or combined with another process presented anywhere in the description of aspects of the present disclosure. 
     (4) One or more components included in the encoder or the decoder according to embodiments may be combined with a component presented anywhere in the description of aspects of the present disclosure, may be combined with a component including one or more functions presented anywhere in the description of aspects of the present disclosure, and may be combined with a component that implements one or more processes implemented by a component presented in the description of aspects of the present disclosure. 
     (5) A component including one or more functions of the encoder or the decoder according to the embodiments, or a component that implements one or more processes of the encoder or the decoder according to the embodiments, may be combined or substituted with a component presented anywhere in the description of aspects of the present disclosure, with a component including one or more functions presented anywhere in the description of aspects of the present disclosure, or with a component that implements one or more processes presented anywhere in the description of aspects of the present disclosure. 
     (6) In methods implemented by the encoder or the decoder according to the embodiments, any of the processes included in the method may be substituted or combined with a process presented anywhere in the description of aspects of the present disclosure or with any corresponding or equivalent process. 
     (7) One or more processes included in methods implemented by the encoder or the decoder according to the embodiments may be combined with a process presented anywhere in the description of aspects of the present disclosure. 
     (8) The implementation of the processes and/or configurations presented in the description of aspects of the present disclosure is not limited to the encoder or the decoder according to the embodiments. For example, the processes and/or configurations may be implemented in a device used for a purpose different from the moving picture encoder or the moving picture decoder disclosed in the embodiments. 
     Embodiment 1 
     [Encoder] 
     First, an encoder according to an embodiment will be described.  FIG. 1  is a block diagram illustrating a functional configuration of encoder  100  according to the embodiment. Encoder  100  is a video encoder which encodes a video in units of a block. 
     As illustrated in  FIG. 1 , encoder  100  is an apparatus which encodes an image in units of a block, and includes splitter  102 , subtractor  104 , transformer  106 , quantizer  108 , entropy encoder  110 , inverse quantizer  112 , inverse transformer  114 , adder  116 , block memory  118 , loop filter  120 , frame memory  122 , intra predictor  124 , inter predictor  126 , and prediction controller  128 . 
     Encoder  100  is implemented as, for example, a generic processor and memory. In this case, when a software program stored in the memory is executed by the processor, the processor functions as splitter  102 , subtractor  104 , transformer  106 , quantizer  108 , entropy encoder  110 , inverse quantizer  112 , inverse transformer  114 , adder  116 , loop filter  120 , intra predictor  124 , inter predictor  126 , and prediction controller  128 . Alternatively, encoder  100  may be implemented as one or more dedicated electronic circuits corresponding to splitter  102 , subtractor  104 , transformer  106 , quantizer  108 , entropy encoder  110 , inverse quantizer  112 , inverse transformer  114 , adder  116 , loop filter  120 , intra predictor  124 , inter predictor  126 , and prediction controller  128 . 
     Hereinafter, an overall flow of processes performed by encoder  100  is described, and then each of constituent elements included in encoder  100  will be described. 
     [Overall Flow of Encoding Process] 
       FIG. 2  is a flow chart indicating one example of an overall encoding process performed by encoder  100 . 
     First, splitter  102  of encoder  100  splits each of pictures included in an input image which is a video into a plurality of blocks having a fixed size (e.g., 128×128 pixels) (Step Sa_ 1 ). Splitter  102  then selects a splitting pattern for the fixed-size block (also referred to as a block shape) (Step Sa_ 2 ). In other words, splitter  102  further splits the fixed-size block into a plurality of blocks which form the selected splitting pattern. Encoder  100  performs, for each of the plurality of blocks, Steps Sa_ 3  to Sa_ 9  for the block (that is a current block to be encoded). 
     In other words, a prediction processor which includes all or part of intra predictor  124 , inter predictor  126 , and prediction controller  128  generates a prediction signal (also referred to as a prediction block) of the current block to be encoded (also referred to as a current block) (Step Sa_ 3 ). 
     Next, subtractor  104  generates a difference between the current block and a prediction block as a prediction residual (also referred to as a difference block) (Step Sa_ 4 ). 
     Next, transformer  106  transforms the difference block and quantizer  108  quantizes the result, to generate a plurality of quantized coefficients (Step Sa_ 5 ). It is to be noted that the block having the plurality of quantized coefficients is also referred to as a coefficient block. 
     Next, entropy encoder  110  encodes (specifically, entropy encodes) the coefficient block and a prediction parameter related to generation of a prediction signal to generate an encoded signal (Step Sa_ 6 ). It is to be noted that the encoded signal is also referred to as an encoded bitstream, a compressed bitstream, or a stream. 
     Next, inverse quantizer  112  performs inverse quantization of the coefficient block and inverse transformer  114  performs inverse transform of the result, to restore a plurality of prediction residuals (that is, a difference block) (Step Sa_ 7 ). 
     Next, adder  116  adds the prediction block to the restored difference block to reconstruct the current block as a reconstructed image (also referred to as a reconstructed block or a decoded image block) (Step Sa_ 8 ). In this way, the reconstructed image is generated. 
     When the reconstructed image is generated, loop filter  120  performs filtering of the reconstructed image as necessary (Step Sa_ 9 ). 
     Encoder  100  then determines whether encoding of the entire picture has been finished (Step Sa_ 10 ). When determining that the encoding has not yet been finished (No in Step Sa_ 10 ), processes from Step Sa_ 2  are executed repeatedly. 
     Although encoder  100  selects one splitting pattern for a fixed-size block, and encodes each block according to the splitting pattern in the above-described example, it is to be noted that each block may be encoded according to a corresponding one of a plurality of splitting patterns. In this case, encoder  100  may evaluate a cost for each of the plurality of splitting patterns, and, for example, may select the encoded signal obtainable by encoding according to the splitting pattern which yields the smallest cost as an encoded signal which is output. 
     As illustrated, the processes in Steps Sa_ 1  to Sa_ 10  are performed sequentially by encoder  100 . Alternatively, two or more of the processes may be performed in parallel, the processes may be reordered, etc. 
     [Splitter] 
     Splitter  102  splits each of pictures included in an input video into a plurality of blocks, and outputs each block to subtractor  104 . For example, splitter  102  first splits a picture into blocks of a fixed size (for example, 128×128). Other fixed block sizes may be employed. The fixed-size block is also referred to as a coding tree unit (CTU). Splitter  102  then splits each fixed-size block into blocks of variable sizes (for example, 64×64 or smaller), based on recursive quadtree and/or binary tree block splitting. In other words, splitter  102  selects a splitting pattern. The variable-size block is also referred to as a coding unit (CU), a prediction unit (PU), or a transform unit (TU). It is to be noted that, in various kinds of processing examples, there is no need to differentiate between CU, PU, and TU; all or some of the blocks in a picture may be processed in units of a CU, a PU, or a TU. 
       FIG. 3  is a conceptual diagram illustrating one example of block splitting according to an embodiment. In  FIG. 3 , the solid lines represent block boundaries of blocks split by quadtree block splitting, and the dashed lines represent block boundaries of blocks split by binary tree block splitting. 
     Here, block  10  is a square block having 128×128 pixels (128×128 block). This 128×128 block  10  is first split into four square 64×64 blocks (quadtree block splitting). 
     The upper-left 64×64 block is further vertically split into two rectangular 32×64 blocks, and the left 32×64 block is further vertically split into two rectangular 16×64 blocks (binary tree block splitting). As a result, the upper-left 64×64 block is split into two 16×64 blocks  11  and  12  and one 32×64 block  13 . 
     The upper-right 64×64 block is horizontally split into two rectangular 64×32 blocks  14  and  15  (binary tree block splitting). 
     The lower-left 64×64 block is first split into four square 32×32 blocks (quadtree block splitting). The upper-left block and the lower-right block among the four 32×32 blocks are further split. The upper-left 32×32 block is vertically split into two rectangle 16×32 blocks, and the right 16×32 block is further horizontally split into two 16×16 blocks (binary tree block splitting). The lower-right 32×32 block is horizontally split into two 32×16 blocks (binary tree block splitting). As a result, the lower-left 64×64 block is split into 16×32 block  16 , two 16×16 blocks  17  and  18 , two 32×32 blocks  19  and  20 , and two 32×16 blocks  21  and  22 . 
     The lower-right 64×64 block  23  is not split. 
     As described above, in  FIG. 3 , block  10  is split into thirteen variable-size blocks  11  through  23  based on recursive quadtree and binary tree block splitting. This type of splitting is also referred to as quadtree plus binary tree (QTBT) splitting. 
     It is to be noted that, in  FIG. 3 , one block is split into four or two blocks (quadtree or binary tree block splitting), but splitting is not limited to these examples. For example, one block may be split into three blocks (ternary block splitting). Splitting including such ternary block splitting is also referred to as multi-type tree (MBT) splitting. 
     [Picture Structure: Slice/Tile] 
     A picture may be configured in units of one or more slices or tiles in order to decode the picture in parallel. The picture configured in units of one or more slices or tiles may be configured by splitter  102 . 
     Slices are basic encoding units included in a picture. A picture may include, for example, one or more slices. In addition, a slice includes one or more successive coding tree units (CTU). 
       FIG. 4A  is a conceptual diagram illustrating one example of a slice configuration. For example, a picture includes 11×8 CTUs and is split into four slices (slices 1 to 4). Slice 1 includes sixteen CTUs, slice 2 includes twenty-one CTUs, slice 3 includes twenty-nine CTUs, and slice 4 includes twenty-two CTUs. Here, each CTU in the picture belongs to one of the slices. The shape of each slice is a shape obtainable by splitting the picture horizontally. A boundary of each slice does not need to be coincide with an image end, and may be coincide with any of the boundaries between CTUs in the image. The processing order of the CTUs in a slice (an encoding order or a decoding order) is, for example, a raster-scan order. A slice includes header information and encoded data. Features of the slice may be described in header information. The features include a CTU address of a top CTU in the slice, a slice type, etc. 
     A tile is a unit of a rectangular region included in a picture. Each of tiles may be assigned with a number referred to as TileId in raster-scan order. 
       FIG. 4B  is a conceptual diagram indicating an example of a tile configuration. For example, a picture includes 11×8 CTUs and is split into four tiles of rectangular regions (tiles 1 to 4). When tiles are used, the processing order of CTUs are changed from the processing order in the case where no tile is used. When no tile is used, CTUs in a picture are processed in raster-scan order. When tiles are used, at least one CTU in each of the tiles is processed in raster-scan order. For example, as illustrated in  FIG. 4B , the processing order of the CTUs included in tile 1 is the order which starts from the left-end of the first row of tile 1 toward the right-end of the first row of tile 1 and then starts from the left-end of the second row of tile 1 toward the right-end of the second row of tile 1. 
     It is to be noted that the one tile may include one or more slices, and one slice may include one or more tiles. 
     [Subtractor] 
     Subtractor  104  subtracts a prediction signal (prediction sample that is input from prediction controller  128  indicated below) from an original signal (original sample) in units of a block input from splitter  102  and split by splitter  102 . In other words, subtractor  104  calculates prediction errors (also referred to as residuals) of a block to be encoded (hereinafter also referred to as a current block). Subtractor  104  then outputs the calculated prediction errors (residuals) to transformer  106 . 
     The original signal is a signal which has been input into encoder  100  and represents an image of each picture included in a video (for example, a luma signal and two chroma signals). Hereinafter, a signal representing an image is also referred to as a sample. 
     [Transformer] 
     Transformer  106  transforms prediction errors in spatial domain into transform coefficients in frequency domain, and outputs the transform coefficients to quantizer  108 . More specifically, transformer  106  applies, for example, a defined discrete cosine transform (DCT) or discrete sine transform (DST) to prediction errors in spatial domain. The defined DCT or DST may be predefined. 
     It is to be noted that transformer  106  may adaptively select a transform type from among a plurality of transform types, and transform prediction errors into transform coefficients by using a transform basis function corresponding to the selected transform type. This sort of transform is also referred to as explicit multiple core transform (EMT) or adaptive multiple transform (AMT). 
     The transform types include, for example, DCT-II, DCT-V, DCT-VIII, DST-I, and DST-VII.  FIG. 5A  is a chart indicating transform basis functions for the example transform types. In  FIG. 5A , N indicates the number of input pixels. For example, selection of a transform type from among the plurality of transform types may depend on a prediction type (one of intra prediction and inter prediction), and may depend on an intra prediction mode. 
     Information indicating whether to apply such EMT or AMT (referred to as, for example, an EMT flag or an AMT flag) and information indicating the selected transform type is normally signaled at the CU level. It is to be noted that the signaling of such information does not necessarily need to be performed at the CU level, and may be performed at another level (for example, at the bit sequence level, picture level, slice level, tile level, or CTU level). 
     In addition, transformer  106  may re-transform the transform coefficients (transform result). Such re-transform is also referred to as adaptive secondary transform (AST) or non-separable secondary transform (NSST). For example, transformer  106  performs re-transform in units of a sub-block (for example, 4×4 sub-block) included in a transform coefficient block corresponding to an intra prediction error. Information indicating whether to apply NSST and information related to a transform matrix for use in NSST are normally signaled at the CU level. It is to be noted that the signaling of such information does not necessarily need to be performed at the CU level, and may be performed at another level (for example, at the sequence level, picture level, slice level, tile level, or CTU level). 
     Transformer  106  may employ a separable transform and a non-separable transform. A separable transform is a method in which a transform is performed a plurality of times by separately performing a transform for each of a number of directions according to the number of dimensions of inputs. A non-separable transform is a method of performing a collective transform in which two or more dimensions in multidimensional inputs are collectively regarded as a single dimension. 
     In one example of a non-separable transform, when an input is a 4×4 block, the 4×4 block is regarded as a single array including sixteen elements, and the transform applies a 16×16 transform matrix to the array. 
     In another example of a non-separable transform, a 4×4 input block is regarded as a single array including sixteen elements, and then a transform (hypercube givens transform) in which givens revolution is performed on the array a plurality of times may be performed. 
     In the transform in transformer  106 , the types of bases to be transformed into the frequency domain according to regions in a CU can be switched. Examples include spatially varying transforms (SVT). In SVT, as illustrated in  FIG. 5B , CUs are split into two equal regions horizontally or vertically, and only one of the regions is transformed into the frequency domain. A transform basis type can be set for each region. For example, DST7 and DST8 are used. In this example, only one of these two regions in the CU is transformed, and the other is not transformed. However, both of these two regions may be transformed. In addition, the splitting method is not limited to the splitting into two equal regions, and can be more flexible. For example, the CU may be split into four equal regions, or information indicating splitting may be encoded separately and be signaled in the same manner as the CU splitting. It is to be noted that SVT is also referred to as sub-block transform (SBT). 
     [Quantizer] 
     Quantizer  108  quantizes the transform coefficients output from transformer  106 . More specifically, quantizer  108  scans, in a determined scanning order, the transform coefficients of the current block, and quantizes the scanned transform coefficients based on quantization parameters (QP) corresponding to the transform coefficients. Quantizer  108  then outputs the quantized transform coefficients (hereinafter also referred to as quantized coefficients) of the current block to entropy encoder  110  and inverse quantizer  112 . The determined scanning order may be predetermined. 
     A determined scanning order is an order for quantizing/inverse quantizing transform coefficients. For example, a determined scanning order may be defined as ascending order of frequency (from low to high frequency) or descending order of frequency (from high to low frequency). 
     A quantization parameter (QP) is a parameter defining a quantization step (quantization width). For example, when the value of the quantization parameter increases, the quantization step also increases. In other words, when the value of the quantization parameter increases, the quantization error increases. 
     In addition, a quantization matrix may be used for quantization. For example, several kinds of quantization matrices may be used correspondingly to frequency transform sizes such as 4×4 and 8×8, prediction modes such as intra prediction and inter prediction, and pixel components such as luma and chroma pixel components. It is to be noted that quantization means digitalizing values sampled at determined intervals correspondingly to determined levels. In this technical field, quantization may be referred to using other expressions, such as rounding and scaling, and may employ rounding and scaling. The determined intervals and levels may be predetermined. 
     Methods using quantization matrices include a method using a quantization matrix which has been set directly at the encoder side and a method using a quantization matrix which has been set as a default (default matrix). At the encoder side, a quantization matrix suitable for features of an image can be set by directly setting a quantization matrix. This case, however, has a disadvantage of increasing a coding amount for encoding the quantization matrix. 
     There is a method for quantizing a high-frequency coefficient and a low-frequency coefficient without using a quantization matrix. It is to be noted that this method is equivalent to a method using a quantization matrix (flat matrix) whose coefficients have the same value. 
     The quantization matrix may be specified using, for example, a sequence parameter set (SPS) or a picture parameter set (PPS). The SPS includes a parameter which is used for a sequence, and the PPS includes a parameter which is used for a picture. Each of the SPS and the PPS may be simply referred to as a parameter set. 
     [Entropy Encoder] 
     Entropy encoder  110  generates an encoded signal (encoded bitstream) based on quantized coefficients which have been input from quantizer  108 . More specifically, entropy encoder  110 , for example, binarizes quantized coefficients, and arithmetically encodes the binary signal, and outputs a compressed bit stream or sequence. 
     [Inverse Quantizer] 
     Inverse quantizer  112  inverse quantizes quantized coefficients which have been input from quantizer  108 . More specifically, inverse quantizer  112  inverse quantizes, in a determined scanning order, quantized coefficients of the current block. Inverse quantizer  112  then outputs the inverse quantized transform coefficients of the current block to inverse transformer  114 . The determined scanning order may be predetermined. 
     [Inverse Transformer] 
     Inverse transformer  114  restores prediction errors (residuals) by inverse transforming transform coefficients which have been input from inverse quantizer  112 . More specifically, inverse transformer  114  restores the prediction errors of the current block by applying an inverse transform corresponding to the transform applied by transformer  106  on the transform coefficients. Inverse transformer  114  then outputs the restored prediction errors to adder  116 . 
     It is to be noted that since information is lost in quantization, the restored prediction errors do not match the prediction errors calculated by subtractor  104 . In other words, the restored prediction errors normally include quantization errors. 
     [Adder] 
     Adder  116  reconstructs the current block by adding prediction errors which have been input from inverse transformer  114  and prediction samples which have been input from prediction controller  128 . Adder  116  then outputs the reconstructed block to block memory  118  and loop filter  120 . A reconstructed block is also referred to as a local decoded block. 
     [Block Memory] 
     Block memory  118  is, for example, storage for storing blocks in a picture to be encoded (hereinafter referred to as a current picture) which is referred to in intra prediction. More specifically, block memory  118  stores reconstructed blocks output from adder  116 . 
     [Frame Memory] 
     Frame memory  122  is, for example, storage for storing reference pictures for use in inter prediction, and is also referred to as a frame buffer. More specifically, frame memory  122  stores reconstructed blocks filtered by loop filter  120 . 
     [Loop Filter] 
     Loop filter  120  applies a loop filter to blocks reconstructed by adder  116 , and outputs the filtered reconstructed blocks to frame memory  122 . A loop filter is a filter used in an encoding loop (in-loop filter), and includes, for example, a deblocking filter (DF or DBF), a sample adaptive offset (SAO), and an adaptive loop filter (ALF). 
     In an ALF, a least square error filter for removing compression artifacts is applied. For example, one filter selected from among a plurality of filters based on the direction and activity of local gradients is applied for each of 2×2 sub-blocks in the current block. 
     More specifically, first, each sub-block (for example, each 2×2 sub-block) is categorized into one out of a plurality of classes (for example, fifteen or twenty-five classes). The classification of the sub-block is based on gradient directionality and activity. For example, classification index C (for example, C=5D+A) is derived based on gradient directionality D (for example, 0 to 2 or 0 to 4) and gradient activity A (for example, 0 to 4). Then, based on classification index C, each sub-block is categorized into one out of a plurality of classes. 
     For example, gradient directionality D is calculated by comparing gradients of a plurality of directions (for example, the horizontal, vertical, and two diagonal directions). Moreover, for example, gradient activity A is calculated by adding gradients of a plurality of directions and quantizing the result of addition. 
     The filter to be used for each sub-block is determined from among the plurality of filters based on the result of such categorization. 
     The filter shape to be used in an ALF is, for example, a circular symmetric filter shape.  FIG. 6A  through  FIG. 6C  illustrate examples of filter shapes used in ALFs.  FIG. 6A  illustrates a 5×5 diamond shape filter,  FIG. 6B  illustrates a 7×7 diamond shape filter, and  FIG. 6C  illustrates a 9×9 diamond shape filter. Information indicating the filter shape is normally signaled at the picture level. It is to be noted that the signaling of such information indicating the filter shape does not necessarily need to be performed at the picture level, and may be performed at another level (for example, at the sequence level, slice level, tile level, CTU level, or CU level). 
     The ON or OFF of the ALF is determined, for example, at the picture level or CU level. For example, the decision of whether to apply the ALF to luma may be made at the CU level, and the decision of whether to apply ALF to chroma may be made at the picture level. Information indicating ON or OFF of the ALF is normally signaled at the picture level or CU level. It is to be noted that the signaling of information indicating ON or OFF of the ALF does not necessarily need to be performed at the picture level or CU level, and may be performed at another level (for example, at the sequence level, slice level, tile level, or CTU level). 
     The coefficient set for the plurality of selectable filters (for example, fifteen or up to twenty-five filters) is normally signaled at the picture level. It is to be noted that the signaling of the coefficient set does not necessarily need to be performed at the picture level, and may be performed at another level (for example, at the sequence level, slice level, tile level, CTU level, CU level, or sub-block level). 
     [Loop Filter&gt;Deblocking Filter] 
     In a deblocking filter, loop filter  120  performs a filter process on a block boundary in a reconstructed image so as to reduce distortion which occurs at the block boundary. 
       FIG. 7  is a block diagram illustrating one example of a specific configuration of loop filter  120  which functions as a deblocking filter. 
     Loop filter  120  includes: boundary determiner  1201 ; filter determiner  1203 ; filtering executor  1205 ; process determiner  1208 ; filter characteristic determiner  1207 ; and switches  1202 ,  1204 , and  1206 . 
     Boundary determiner  1201  determines whether a pixel to be deblock-filtered (that is, a current pixel) is present around a block boundary. Boundary determiner  1201  then outputs the determination result to switch  1202  and processing determiner  1208 . 
     In the case where boundary determiner  1201  has determined that a current pixel is present around a block boundary, switch  1202  outputs an unfiltered image to switch  1204 . In the opposite case where boundary determiner  1201  has determined that no current pixel is present around a block boundary, switch  1202  outputs an unfiltered image to switch  1206 . 
     Filter determiner  1203  determines whether to perform deblocking filtering of the current pixel, based on the pixel value of at least one surrounding pixel located around the current pixel. Filter determiner  1203  then outputs the determination result to switch  1204  and processing determiner  1208 . 
     In the case where filter determiner  1203  has determined to perform deblocking filtering of the current pixel, switch  1204  outputs the unfiltered image obtained through switch  1202  to filtering executor  1205 . In the opposite case were filter determiner  1203  has determined not to perform deblocking filtering of the current pixel, switch  1204  outputs the unfiltered image obtained through switch  1202  to switch  1206 . 
     When obtaining the unfiltered image through switches  1202  and  1204 , filtering executor  1205  executes, for the current pixel, deblocking filtering with the filter characteristic determined by filter characteristic determiner  1207 . Filtering executor  1205  then outputs the filtered pixel to switch  1206 . 
     Under control by processing determiner  1208 , switch  1206  selectively outputs a pixel which has not been deblock-filtered and a pixel which has been deblock-filtered by filtering executor  1205 . 
     Processing determiner  1208  controls switch  1206  based on the results of determinations made by boundary determiner  1201  and filter determiner  1203 . In other words, processing determiner  1208  causes switch  1206  to output the pixel which has been deblock-filtered when boundary determiner  1201  has determined that the current pixel is present around the block boundary and filter determiner  1203  has determined to perform deblocking filtering of the current pixel. In addition, other than the above case, processing determiner  1208  causes switch  1206  to output the pixel which has not been deblock-filtered. A filtered image is output from switch  1206  by repeating output of a pixel in this way. 
       FIG. 8  is a conceptual diagram indicating an example of a deblocking filter having a symmetrical filtering characteristic with respect to a block boundary. 
     In a deblocking filter process, one of two deblocking filters having different characteristics, that is, a strong filter and a weak filter is selected using pixel values and quantization parameters. In the case of the strong filter, pixels p0 to p2 and pixels q0 to q2 are present across a block boundary as illustrated in  FIG. 8 , the pixel values of the respective pixel q0 to q2 are changed to pixel values q′0 to q′2 by performing, for example, computations according to the expressions below. 
         q′ 0=( p 1+2× p 0+2× q 0+2× q 1+ q 2+4)/8
 
         q′ 1=( p 0+ q 0+ q 1+ q 2+2)/4 
         q′ 2=( p 0+ q 0+ q 1+3× q 2+2× q 3+4)/8
 
     It is to be noted that, in the above expressions, p0 to p2 and q0 to q2 are the pixel values of respective pixels p0 to p2 and pixels q0 to q2. In addition, q3 is the pixel value of neighboring pixel q3 located at the opposite side of pixel q2 with respect to the block boundary. In addition, in the right side of each of the expressions, coefficients which are multiplied with the respective pixel values of the pixels to be used for deblocking filtering are filter coefficients. 
     Furthermore, in the deblocking filtering, clipping may be performed so that the calculated pixel values are not set over a threshold value. In the clipping process, the pixel values calculated according to the above expressions are clipped to a value obtained according to “a computation pixel value±2×a threshold value” using the threshold value determined based on a quantization parameter. In this way, it is possible to prevent excessive smoothing. 
       FIG. 9  is a conceptual diagram for illustrating a block boundary on which a deblocking filter process is performed.  FIG. 10  is a conceptual diagram indicating examples of Bs values. 
     The block boundary on which the deblocking filter process is performed is, for example, a boundary between prediction units (PU) having 8×8 pixel blocks as illustrated in  FIG. 9  or a boundary between transform units (TU). The deblocking filter process may be performed in units of four rows or four columns. First, boundary strength (Bs) values are determined as indicated in  FIG. 10  for block P and block Q illustrated in  FIG. 9 . 
     According to the Bs values in  FIG. 10 , whether to perform deblocking filter processes of block boundaries belonging to the same image using different strengths is determined. The deblocking filter process for a chroma signal is performed when a Bs value is 2. The deblocking filter process for a luma signal is performed when a Bs value is 1 or more and a determined condition is satisfied. The determined condition may be predetermined. It is to be noted that conditions for determining Bs values are not limited to those indicated in  FIG. 10 , and a Bs value may be determined based on another parameter. 
     [Prediction Processor (Intra Predictor, Inter Predictor, Prediction Controller)] 
       FIG. 11  is a flow chart illustrating one example of a process performed by the prediction processor of encoder  100 . It is to be noted that the prediction processor includes all or part of the following constituent elements: intra predictor  124 ; inter predictor  126 ; and prediction controller  128 . 
     The prediction processor generates a prediction image of a current block (Step Sb_ 1 ). This prediction image is also referred to as a prediction signal or a prediction block. It is to be noted that the prediction signal is, for example, an intra prediction signal or an inter prediction signal. Specifically, the prediction processor generates the prediction image of the current block using a reconstructed image which has been already obtained through generation of a prediction block, generation of a difference block, generation of a coefficient block, restoring of a difference block, and generation of a decoded image block. 
     The reconstructed image may be, for example, an image in a reference picture, or an image of an encoded block in a current picture which is the picture including the current block. The encoded block in the current picture is, for example, a neighboring block of the current block. 
       FIG. 12  is a flow chart illustrating another example of a process performed by the prediction processor of encoder  100 . 
     The prediction processor generates a prediction image using a first method (Step Sc_ 1   a ), generates a prediction image using a second method (Step Sc_ 1   b ), and generates a prediction image using a third method (Step Sc_ 1   c ). The first method, the second method, and the third method may be mutually different methods for generating a prediction image. Each of the first to third methods may be an inter prediction method, an intra prediction method, or another prediction method. The above-described reconstructed image may be used in these prediction methods. 
     Next, the prediction processor selects any one of a plurality of prediction methods generated in Steps Sc_ 1   a , Sc_ 1   b , and Sc_ 1   e  (Step Sc_ 2 ). The selection of the prediction image, that is selection of a method or a mode for obtaining a final prediction image may be made by calculating a cost for each of the generated prediction images and based on the cost. Alternatively, the selection of the prediction image may be made based on a parameter which is used in an encoding process. Encoder  100  may transform information for identifying a selected prediction image, a method, or a mode into an encoded signal (also referred to as an encoded bitstream). The information may be, for example, a flag or the like. In this way, the decoder is capable of generating a prediction image according to the method or the mode selected based on the information in encoder  100 . It is to be noted that, in the example illustrated in  FIG. 12 , the prediction processor selects any of the prediction images after the prediction images are generated using the respective methods. However, the prediction processor may select a method or a mode based on a parameter for use in the above-described encoding process before generating prediction images, and may generate a prediction image according to the method or mode selected. 
     For example, the first method and the second method may be intra prediction and inter prediction, respectively, and the prediction processor may select a final prediction image for a current block from prediction images generated according to the prediction methods. 
       FIG. 13  is a flow chart illustrating another example of a process performed by the prediction processor of encoder  100 . 
     First, the prediction processor generates a prediction image using intra prediction (Step Sd_ 1   a ), and generates a prediction image using inter prediction (Step Sd_ 1   b ). It is to be noted that the prediction image generated by intra prediction is also referred to as an intra prediction image, and the prediction image generated by inter prediction is also referred to as an inter prediction image. 
     Next, the prediction processor evaluates each of the intra prediction image and the inter prediction image (Step Sd_ 2 ). A cost may be used in the evaluation. In other words, the prediction processor calculates cost C for each of the intra prediction image and the inter prediction image. Cost C may be calculated according to an expression of an R-D optimization model, for example, C=D+λ×R. In this expression, D indicates a coding distortion of a prediction image, and is represented as, for example, a sum of absolute differences between the pixel value of a current block and the pixel value of a prediction image. In addition. R indicates a predicted coding amount of a prediction image, specifically, the coding amount required to encode motion information for generating a prediction image, etc. In addition, X indicates, for example, a multiplier according to the method of Lagrange multiplier. 
     The prediction processor then selects the prediction image for which the smallest cost C has been calculated among the intra prediction image and the inter prediction image, as the final prediction image for the current block (Step Sd_ 3 ). In other words, the prediction method or the mode for generating the prediction image for the current block is selected. 
     [Intra Predictor] 
     Intra predictor  124  generates a prediction signal (intra prediction signal) by performing intra prediction (also referred to as intra frame prediction) of the current block by referring to a block or blocks in the current picture and stored in block memory  118 . More specifically, intra predictor  124  generates an intra prediction signal by performing intra prediction by referring to samples (for example, luma and/or chroma values) of a block or blocks neighboring the current block, and then outputs the intra prediction signal to prediction controller  128 . 
     For example, intra predictor  124  performs intra prediction by using one mode from among a plurality of intra prediction modes which have been defined. The intra prediction modes include one or more non-directional prediction modes and a plurality of directional prediction modes. The defined modes may be predefined. 
     The one or more non-directional prediction modes include, for example, the planar prediction mode and DC prediction mode defined in the H.265/high-efficiency video coding (HEVC) standard. 
     The plurality of directional prediction modes include, for example, the thirty-three directional prediction modes defined in the H.265/HEVC standard. It is to be noted that the plurality of directional prediction modes may further include thirty-two directional prediction modes in addition to the thirty-three directional prediction modes (for a total of sixty-five directional prediction modes).  FIG. 14  is a conceptual diagram illustrating sixty-seven intra prediction modes in total that may be used in intra prediction (two non-directional prediction modes and sixty-five directional prediction modes). The solid arrows represent the thirty-three directions defined in the H.265/HEVC standard, and the dashed arrows represent the additional thirty-two directions (the two non-directional prediction modes are not illustrated in  FIG. 14 ). 
     In various kinds of processing examples, a luma block may be referred to in intra prediction of a chroma block. In other words, a chroma component of the current block may be predicted based on a luma component of the current block. Such intra prediction is also referred to as cross-component linear model (CCLM) prediction. The intra prediction mode for a chroma block in which such a luma block is referred to (also referred to as, for example, a CCLM mode) may be added as one of the intra prediction modes for chroma blocks. 
     Intra predictor  124  may correct intra-predicted pixel values based on horizontal/vertical reference pixel gradients. Intra prediction accompanied by this sort of correcting is also referred to as position dependent intra prediction combination (PDPC). Information indicating whether to apply PDPC (referred to as, for example, a PDPC flag) is normally signaled at the CU level. It is to be noted that the signaling of such information does not necessarily need to be performed at the CU level, and may be performed at another level (for example, at the sequence level, picture level, slice level, tile level, or CTU level). 
     [Inter Predictor] 
     Inter predictor  126  generates a prediction signal (inter prediction signal) by performing inter prediction (also referred to as inter frame prediction) of the current block by referring to a block or blocks in a reference picture, which is different from the current picture and is stored in frame memory  122 . Inter prediction is performed in units of a current block or a current sub-block (for example, a 4×4 block) in the current block. For example, inter predictor  126  performs motion estimation in a reference picture for the current block or the current sub-block, and finds out a reference block or a sub-block which best matches the current block or the current sub-block. Inter predictor  126  then obtains motion information (for example, a motion vector) which compensates a motion or a change from the reference block or the sub-block to the current block or the sub-block. Inter predictor  126  generates an inter prediction signal of the current block or the sub-block by performing motion compensation (or motion prediction) based on the motion information. Inter predictor  126  outputs the generated inter prediction signal to prediction controller  128 . 
     The motion information used in motion compensation may be signaled as inter prediction signals in various forms. For example, a motion vector may be signaled. As another example, the difference between a motion vector and a motion vector predictor may be signaled. 
     [Basic Flow of Inter Prediction] 
       FIG. 15  is a flow chart illustrating an example basic processing flow of inter prediction. 
     First, inter predictor  126  generates a prediction signal (Steps Se_ 1  to Se_ 3 ). Next, subtractor  104  generates the difference between a current block and a prediction image as a prediction residual (Step Se_ 4 ). 
     Here, in the generation of the prediction image, inter predictor  126  generates the prediction image through determination of a motion vector (MV) of the current block (Steps Se_ 1  and Se_ 2 ) and motion compensation (Step Se_ 3 ). Furthermore, in determination of an MV, inter predictor  126  determines the MV through selection of a motion vector candidate (MV candidate) (Step Se_ 1 ) and derivation of an MV (Step Se_ 2 ). The selection of the MV candidate is made by, for example, selecting at least one MV candidate from an MV candidate list. Alternatively, in derivation of an MV, inter predictor  126  may further select at least one MV candidate from the at least one MV candidate, and determine the selected at least one MV candidate as the MV for the current block. Alternatively, inter predictor  126  may determine the MV for the current block by performing estimation in a reference picture region specified by each of the selected at least one MV candidate. It is to be noted that the estimation in a reference picture region may be referred to as motion estimation. 
     In addition, although Steps Se_ 1  to Se_ 3  are performed by inter predictor  126  in the above-described example, a process that is for example Step Se_ 1 , Step Se_ 2 , or the like may be performed by another constituent element included in encoder  100 . 
     [Motion Vector Derivation Flow] 
       FIG. 16  is a flow chart illustrating one example of derivation of motion vectors. 
     Inter predictor  126  derives an MV of a current block in a mode for encoding motion information (for example, an MV). In this case, for example, the motion information is encoded as a prediction parameter, and is signaled. In other words, the encoded motion information is included in an encoded signal (also referred to as an encoded bitstream). 
     Alternatively, inter predictor  126  derives an MV in a mode in which motion information is not encoded. In this case, no motion information is included in an encoded signal. 
     Here, MV derivation modes may include a normal inter mode, a merge mode, a FRUC mode, an affine mode, etc. which are described later. Modes in which motion information is encoded among the modes include the normal inter mode, the merge mode, the affine mode (specifically, an affine inter mode and an affine merge mode), etc. It is to be noted that motion information may include not only an MV but also motion vector predictor selection information which is described later. Modes in which no motion information is encoded include the FRUC mode, etc. Inter predictor  126  selects a mode for deriving an MV of the current block from the modes, and derives the MV of the current block using the selected mode. 
       FIG. 17  is a flow chart illustrating another example of derivation of motion vectors. 
     Inter predictor  126  derives an MV of a current block in a mode in which an MV difference is encoded. In this case, for example, the MV difference is encoded as a prediction parameter, and is signaled. In other words, the encoded MV difference is included in an encoded signal. The MV difference is the difference between the MV of the current block and the MV predictor. 
     Alternatively, inter predictor  126  derives an MV in a mode in which no MV difference is encoded. In this case, no encoded MV difference is included in an encoded signal. 
     Here, as described above, the MV derivation modes include the normal inter mode, the merge mode, the FRUC mode, the affine mode, etc. which are described later. Modes in which an MV difference is encoded among the modes include the normal inter mode, the affine mode (specifically, the affine inter mode), etc. Modes in which no MV difference is encoded include the FRUC mode, the merge mode, the affine mode (specifically, the affine merge mode), etc. Inter predictor  126  selects a mode for deriving an MV of the current block from the plurality of modes, and derives the MV of the current block using the selected mode. 
     [Motion Vector Derivation Flow] 
       FIG. 18  is a flow chart illustrating another example of derivation of motion vectors. The MV derivation modes which are inter prediction modes include a plurality of modes and are roughly divided into modes in which an MV difference is encoded and modes in which no motion vector difference is encoded. The modes in which no MV difference is encoded include the merge mode, the FRUC mode, the affine mode (specifically, the affine merge mode), etc. These modes are described in detail later. Simply, the merge mode is a mode for deriving an MV of a current block by selecting a motion vector from an encoded surrounding block, and the FRUC mode is a mode for deriving an MV of a current block by performing estimation between encoded regions. The affine mode is a mode for deriving, as an MV of a current block, a motion vector of each of a plurality of sub-blocks included in the current block, assuming affine transform. 
     More specifically, as illustrated when the inter prediction mode information indicates 0 (0 in Sf_ 1 ), inter predictor  126  derives a motion vector using the merge mode (Sf_ 2 ). When the inter prediction mode information indicates 1 (1 in Sf_ 1 ), inter predictor  126  derives a motion vector using the FRUC mode (Sf_ 3 ). When the inter prediction mode information indicates 2 (2 in Sf_ 1 ), inter predictor  126  derives a motion vector using the affine mode (specifically, the affine merge mode) (Sf_ 4 ). When the inter prediction mode information indicates 3 (3 in Sf_ 1 ), inter predictor  126  derives a motion vector using a mode in which an MV difference is encoded (for example, a normal inter mode (Sf_ 5 ). 
     [MV Derivation&gt;Normal Inter Mode] 
     The normal inter mode is an inter prediction mode for deriving an MV of a current block based on a block similar to the image of the current block from a reference picture region specified by an MV candidate. In this normal inter mode, an MV difference is encoded. 
       FIG. 19  is a flow chart illustrating an example of inter prediction in normal inter mode. 
     First, inter predictor  126  obtains a plurality of MV candidates for a current block based on information such as MVs of a plurality of encoded blocks temporally or spatially surrounding the current block (Step Sg_ 1 ). In other words, inter predictor  126  generates an MV candidate list. 
     Next, inter predictor  126  extracts N (an integer of 2 or larger) MV candidates from the plurality of MV candidates obtained in Step Sg_ 1 , as motion vector predictor candidates (also referred to as MV predictor candidates) according to a determined priority order (Step Sg_ 2 ). It is to be noted that the priority order may be determined in advance for each of the N MV candidates. 
     Next, inter predictor  126  selects one motion vector predictor candidate from the N motion vector predictor candidates, as the motion vector predictor (also referred to as an MV predictor) of the current block (Step Sg_ 3 ). At this time, inter predictor  126  encodes, in a stream, motion vector predictor selection information for identifying the selected motion vector predictor. It is to be noted that the stream is an encoded signal or an encoded bitstream as described above. 
     Next, inter predictor  126  derives an MV of a current block by referring to an encoded reference picture (Step Sg_ 4 ). At this time, inter predictor  126  further encodes, in the stream, the difference value between the derived MV and the motion vector predictor as an MV difference. It is to be noted that the encoded reference picture is a picture including a plurality of blocks which have been reconstructed after being encoded. 
     Lastly, inter predictor  126  generates a prediction image for the current block by performing motion compensation of the current block using the derived MV and the encoded reference picture (Step Sg_ 5 ). It is to be noted that the prediction image is an inter prediction signal as described above. 
     In addition, information indicating the inter prediction mode (normal inter mode in the above example) used to generate the prediction image is, for example, encoded as a prediction parameter. 
     It is to be noted that the MV candidate list may be also used as a list for use in another mode. In addition, the processes related to the MV candidate list may be applied to processes related to the list for use in another mode. The processes related to the MV candidate list include, for example, extraction or selection of an MV candidate from the MV candidate list, reordering of MV candidates, or deletion of an MV candidate. 
     [MV Derivation&gt;Merge Mode] 
     The merge mode is an inter prediction mode for selecting an MV candidate from an MV candidate list as an MV of a current block, thereby deriving the MV. 
       FIG. 20  is a flow chart illustrating an example of inter prediction in merge mode. 
     First, inter predictor  126  obtains a plurality of MV candidates for a current block based on information such as MVs of a plurality of encoded blocks temporally or spatially surrounding the current block (Step Sh_ 1 ). In other words, inter predictor  126  generates an MV candidate list. 
     Next, inter predictor  126  selects one MV candidate from the plurality of MV candidates obtained in Step Sh_ 1 , thereby deriving an MV of the current block (Step Sh_ 2 ). At this time, inter predictor  126  encodes, in a stream, MV selection information for identifying the selected MV candidate. 
     Lastly, inter predictor  126  generates a prediction image for the current block by performing motion compensation of the current block using the derived MV and the encoded reference picture (Step Sh_ 3 ). 
     In addition, information indicating the inter prediction mode (merge mode in the above example) used to generate the prediction image and included in the encoded signal is, for example, encoded as a prediction parameter. 
       FIG. 21  is a conceptual diagram for illustrating one example of a motion vector derivation process of a current picture in merge mode. 
     First, an MV candidate list in which MV predictor candidates are registered is generated. Examples of MV predictor candidates include: spatially neighboring MV predictors which are MVs of a plurality of encoded blocks located spatially surrounding a current block; temporally neighboring MV predictors which are MVs of surrounding blocks on which the position of a current block in an encoded reference picture is projected; combined MV predictors which are MVs generated by combining the MV value of a spatially neighboring MV predictor and the MV of a temporally neighboring MV predictor; and a zero MV predictor which is an MV having a zero value. 
     Next, one MV predictor is selected from a plurality of MV predictors registered in an MV predictor list, and the selected MV predictor is determined as the MV of a current block. 
     Furthermore, the variable length encoder describes and encodes, in a stream, merge_idx which is a signal indicating which MV predictor has been selected. 
     It is to be noted that the MV predictors registered in the MV predictor list described in  FIG. 21  are examples. The number of MV predictors may be different from the number of MV predictors in the diagram, the MV predictor list may be configured in such a manner that some of the kinds of the MV predictors in the diagram may not be included, or that one or more MV predictors other than the kinds of MV predictors in the diagram are included. 
     A final MV may be determined by performing a decoder motion vector refinement (DMVR) process to be described later using the MV of the current block derived in merge mode. 
     It is to be noted that the MV predictor candidates are MV candidates described above, and the MV predictor list is the MV candidate list described above. It is to be noted that the MV candidate list may be referred to as a candidate list. In addition, merge_idx is MV selection information. 
     [MV Derivation&gt;FRUC Mode] 
     Motion information may be derived at the decoder side without being signaled from the encoder side. It is to be noted that, as described above, the merge mode defined in the H.265/HEVC standard may be used. In addition, for example, motion information may be derived by performing motion estimation at the decoder side. In an embodiment, at the decoder side, motion estimation is performed without using any pixel value in a current block. 
     Here, a mode for performing motion estimation at the decoder side is described. The mode for performing motion estimation at the decoder side may be referred to as a pattern matched motion vector derivation (PMMVD) mode, or a frame rate up-conversion (FRUC) mode. 
     One example of a FRUC process in the form of a flow chart is illustrated in  FIG. 22 . First, a list of a plurality of candidates each having a motion vector (MV) predictor (that is, an MV candidate list that may be also used as a merge list) is generated by referring to a motion vector in an encoded block which spatially or temporally neighbors a current block (Step Si_ 1 ). Next, a best MV candidate is selected from the plurality of MV candidates registered in the MV candidate list (Step Si_ 2 ). For example, the evaluation values of the respective MV candidates included in the MV candidate list are calculated, and one MV candidate is selected based on the evaluation values. Based on the selected motion vector candidates, a motion vector for the current block is then derived (Step Si_ 4 ). More specifically, for example, the selected motion vector candidate (best MV candidate) is derived directly as the motion vector for the current block. In addition, for example, the motion vector for the current block may be derived using pattern matching in a surrounding region of a position in a reference picture where the position in the reference picture corresponds to the selected motion vector candidate. In other words, estimation using the pattern matching and the evaluation values may be performed in the surrounding region of the best MV candidate, and when there is an MV that yields a better evaluation value, the best MV candidate may be updated to the MV that yields the better evaluation value, and the updated MV may be determined as the final MV for the current block. A configuration in which no such a process for updating the best MV candidate to the MV having a better evaluation value is performed is also possible. 
     Lastly, inter predictor  126  generates a prediction image for the current block by performing motion compensation of the current block using the derived MV and the encoded reference picture (Step Si_ 5 ). 
     A similar process may be performed in units of a sub-block. 
     Evaluation values may be calculated according to various kinds of methods. For example, a comparison is made between a reconstructed image in a region in a reference picture corresponding to a motion vector and a reconstructed image in a determined region (the region may be, for example, a region in another reference picture or a region in a neighboring block of a current picture, as indicated below). The determined region may be predetermined. The difference between the pixel values of the two reconstructed images may be used for an evaluation value of the motion vectors. It is to be noted that an evaluation value may be calculated using information other than the value of the difference. 
     Next, an example of pattern matching is described in detail. First, one MV candidate included in an MV candidate list (for example, a merge list) is selected as a start point of estimation by the pattern matching. For example, as the pattern matching, either a first pattern matching or a second pattern matching may be used. The first pattern matching and the second pattern matching are also referred to as bilateral matching and template matching, respectively. 
     [MV Derivation&gt;FRUC&gt;Bilateral Matching] 
     In the first pattern matching, pattern matching is performed between two blocks along a motion trajectory of a current block which are two blocks in different two reference pictures. Accordingly, in the first pattern matching, a region in another reference picture along the motion trajectory of the current block is used as a determined region for calculating the evaluation value of the above-described candidate. The determined region may be predetermined. 
       FIG. 23  is a conceptual diagram for illustrating one example of the first pattern matching (bilateral matching) between the two blocks in the two reference pictures along the motion trajectory. As illustrated in  FIG. 23 , in the first pattern matching, two motion vectors (MV0, MV1) are derived by estimating a pair which best matches among pairs in the two blocks in the two different reference pictures (Ref0, Ref1) which are the two blocks along the motion trajectory of the current block (Cur block). More specifically, a difference between the reconstructed image at a specified location in the first encoded reference picture (Ref0) specified by an MV candidate and the reconstructed image at a specified location in the second encoded reference picture (Ref1) specified by a symmetrical MV obtained by scaling the MV candidate at a display time interval is derived for the current block, and an evaluation value is calculated using the value of the obtained difference. It is possible to select, as the final MV, the MV candidate which yields the best evaluation value among the plurality of MV candidates, and which is likely to produce good results. 
     In the assumption of a continuous motion trajectory, the motion vectors (MV0, MV1) specifying the two reference blocks are proportional to temporal distances (TD0, TD1) between the current picture (Cur Pic) and the two reference pictures (Ref0, Ref1). For example, when the current picture is temporally located between the two reference pictures and the temporal distances from the current picture to the respective two reference pictures are equal to each other, mirror-symmetrical bi-directional motion vectors are derived in the first pattern matching. 
     [MV Derivation&gt;FRUC&gt;Template Matching] 
     In the second pattern matching (template matching), pattern matching is performed between a block in a reference picture and a template in the current picture (the template is a block neighboring the current block in the current picture (the neighboring block is, for example, an upper and/or left neighboring block(s))). Accordingly, in the second pattern matching, the block neighboring the current block in the current picture is used as the determined region for calculating the evaluation value of the above-described candidate. 
       FIG. 24  is a conceptual diagram for illustrating one example of pattern matching (template matching) between a template in a current picture and a block in a reference picture. As illustrated in  FIG. 24 , in the second pattern matching, the motion vector of the current block (Cur block) is derived by estimating, in the reference picture (Ref0), the block which best matches the block neighboring the current block in the current picture (Cur Pic). More specifically, it is possible that the difference between a reconstructed image in an encoded region which neighbors both left and above or either left or above and a reconstructed image which is in a corresponding region in the encoded reference picture (Ref) and is specified by an MV candidate is derived, an evaluation value is calculated using the value of the obtained difference, and the MV candidate which yields the best evaluation value among a plurality of MV candidates is selected as the best MV candidate. 
     Such information indicating whether to apply the FRUC mode (referred to as, for example, a FRUC flag) may be signaled at the CU level. In addition, when the FRUC mode is applied (for example, when a FRUC flag is true), information indicating an applicable pattern matching method (either the first pattern matching or the second pattern matching) may be signaled at the CU level. It is to be noted that the signaling of such information does not necessarily need to be performed at the CU level, and may be performed at another level (for example, at the sequence level, picture level, slice level, tile level, CTU level, or sub-block level). 
     [MV Derivation&gt;Affine Mode] 
     Next, the affine mode for deriving a motion vector in units of a sub-block based on motion vectors of a plurality of neighboring blocks is described. This mode is also referred to as an affine motion compensation prediction mode. 
       FIG. 25A  is a conceptual diagram for illustrating one example of deriving a motion vector of each sub-block based on motion vectors of a plurality of neighboring blocks. In  FIG. 25A , the current block includes sixteen 4×4 sub-blocks. Here, motion vector v 0  at an upper-left corner control point in the current block is derived based on a motion vector of a neighboring block, and likewise, motion vector v 1  at an upper-right corner control point in the current block is derived based on a motion vector of a neighboring sub-block. Two motion vectors v 0  and v 1  may be projected according to an expression (1A) indicated below, and motion vectors (v x , v y ) for the respective sub-blocks in the current block may be derived. 
     
       
         
           
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     Here, x and y indicate the horizontal position and the vertical position of the sub-block, respectively, and w indicates a determined weighting coefficient. The determined weighting coefficient may be predetermined. 
     Such information indicating the affine mode (for example, referred to as an affine flag) may be signaled at the CU level. It is to be noted that the signaling of the information indicating the affine mode does not necessarily need to be performed at the CU level, and may be performed at another level (for example, at the sequence level, picture level, slice level, tile level, CTU level, or sub-block level). 
     In addition, the affine mode may include several modes for different methods for deriving motion vectors at the upper-left and upper-right corner control points. For example, the affine mode include two modes which are the affine inter mode (also referred to as an affine normal inter mode) and the affine merge mode. 
     [MV Derivation&gt;Affine Mode] 
       FIG. 25B  is a conceptual diagram for illustrating one example of deriving a motion vector of each sub-block in affine mode in which three control points are used. In  FIG. 25B , the current block includes sixteen 4×4 blocks. Here, motion vector v 0  at the upper-left corner control point for the current block is derived based on a motion vector of a neighboring block, and likewise, motion vector v 1  at the upper-right corner control point for the current block is derived based on a motion vector of a neighboring block, and motion vector v 2  at the lower-left corner control point for the current block is derived based on a motion vector of a neighboring block. Three motion vectors v 0 , v 1 , and v 2  may be projected according to an expression (1B) indicated below, and motion vectors (v x , v y ) for the respective sub-blocks in the current block may be derived. 
     
       
         
           
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     Here, x and y indicate the horizontal position and the vertical position of the center of the sub-block, respectively, w indicates the width of the current block, and h indicates the height of the current block. 
     Affine modes in which different numbers of control points (for example, two and three control points) are used may be switched and signaled at the CU level. It is to be noted that information indicating the number of control points in affine mode used at the CU level may be signaled at another level (for example, the sequence level, picture level, slice level, tile level. CTU level, or sub-block level). 
     In addition, such an affine mode in which three control points are used may include different methods for deriving motion vectors at the upper-left, upper-right, and lower-left corner control points. For example, the affine modes include two modes which are the affine inter mode (also referred to as the affine normal inter mode) and the affine merge mode. 
     [MV Derivation&gt;Affine Merge Mode] 
       FIG. 26A ,  FIG. 26B , and  FIG. 26C  are conceptual diagrams for illustrating the affine merge mode. 
     As illustrated in  FIG. 26A , in the affine merge mode, for example, motion vector predictors at respective control points of a current block are calculated based on a plurality of motion vectors corresponding to blocks encoded according to the affine mode among encoded block A (left), block B (upper), block C (upper-right), block D (lower-left), and block E (upper-left) which neighbor the current block. More specifically, encoded block A (left), block B (upper), block C (upper-right), block D (lower-left), and block E (upper-left) are checked in the listed order, and the first effective block encoded according to the affine mode is identified. Motion vector predictors at the control points of the current block are calculated based on a plurality of motion vectors corresponding to the identified block. 
     For example, as illustrated in  FIG. 26B , when block A which neighbors to the left of the current block has been encoded according to an affine mode in which two control points are used, motion vectors v 3  and v 4  projected at the upper-left corner position and the upper-right corner position of the encoded block including block A are derived. Motion vector predictor v 0  at the upper-left corner control point of the current block and motion vector predictor v 1  at the upper-right corner control point of the current block are then calculated from derived motion vectors v 3  and v 4 . 
     For example, as illustrated in  FIG. 26C , when block A which neighbors to the left of the current block has been encoded according to an affine mode in which three control points are used, motion vectors v 3 , v 4 , and v 5  projected at the upper-left corner position, the upper-right corner position, and the lower-left corner position of the encoded block including block A are derived. Motion vector predictor v 0  at the upper-left corner control point of the current block, motion vector predictor v 1  at the upper-right corner control point of the current block, and motion vector predictor v 2  at the lower-left corner control point of the current block are then calculated from derived motion vectors v 3 , v 4 , and v 5 . 
     It is to be noted that this method for deriving motion vector predictors may be used to derive motion vector predictors of the respective control points of the current block in Step Sj_ 1  in  FIG. 29  described later. 
       FIG. 27  is a flow chart illustrating one example of the affine merge mode. 
     In affine merge mode as illustrated, first, inter predictor  126  derives MV predictors of respective control points of a current block (Step Sk_ 1 ). The control points are an upper-left corner point of the current block and an upper-right corner point of the current block as illustrated in  FIG. 25A , or an upper-left corner point of the current block, an upper-right corner point of the current block, and a lower-left corner point of the current block as illustrated in  FIG. 25B . 
     In other words, as illustrated in  FIG. 26A , inter predictor  126  checks encoded block A (left), block B (upper), block C (upper-right), block D (lower-left), and block E (upper-left) in the listed order, and identifies the first effective block encoded according to the affine mode. 
     When block A is identified and block A has two control points, as illustrated in  FIG. 26B , inter predictor  126  calculates motion vector v 0  at the upper-left corner control point of the current block and motion vector v 1  at the upper-right corner control point of the current block from motion vectors v 3  and v 4  at the upper-left corner and the upper-right corner of the encoded block including block A. For example, inter predictor  126  calculates motion vector v 0  at the upper-left corner control point of the current block and motion vector v 1  at the upper-right corner control point of the current block by projecting motion vectors v 1  and v 4  at the upper-left corner and the upper-right corner of the encoded block onto the current block. 
     Alternatively, when block A is identified and block A has three control points, as illustrated in  FIG. 26C , inter predictor  126  calculates motion vector v 0  at the upper-left corner control point of the current block, motion vector v 1  at the upper-right corner control point of the current block, and motion vector v 2  at the lower-left corner control point of the current block from motion vectors v 3 , v 4 , and v 5  at the upper-left corner, the upper-right corner, and the lower-left corner of the encoded block including block A. For example, inter predictor  126  calculates motion vector v 0  at the upper-left corner control point of the current block, motion vector v 1  at the upper-right corner control point of the current block, and motion vector v 2  at the lower-left corner control point of the current block by projecting motion vectors v 3 , v 4 , and v 5  at the upper-left corner, the upper-right corner, and the lower-left corner of the encoded block onto the current block. 
     Next, inter predictor  126  performs motion compensation of each of a plurality of sub-blocks included in the current block. In other words, inter predictor  126  calculates, for each of the plurality of sub-blocks, a motion vector of the sub-block as an affine MV, by using either (i) two motion vector predictors v 0  and v 1  and the expression (1A) described above or (ii) three motion vector predictors v 0 , v 1 , and v 2  and the expression (1B) described above (Step Sk_ 2 ). Inter predictor  126  then performs motion compensation of the sub-blocks using these affine MVs and encoded reference pictures (Step Sk_ 3 ). As a result, motion compensation of the current block is performed to generate a prediction image of the current block. 
     [MV Derivation&gt;Affine Inter Mode] 
       FIG. 28A  is a conceptual diagram for illustrating an affine inter mode in which two control points are used. 
     In the affine inter mode, as illustrated in  FIG. 28A , a motion vector selected from motion vectors of encoded block A, block B, and block C which neighbor the current block is used as motion vector predictor v 0  at the upper-left corner control point of the current block. Likewise, a motion vector selected from motion vectors of encoded block D and block E which neighbor the current block is used as motion vector predictor v 1  at the upper-right corner control point of the current block. 
       FIG. 28B  is a conceptual diagram for illustrating an affine inter mode in which three control points are used. 
     In the affine inter mode, as illustrated in  FIG. 28B , a motion vector selected from motion vectors of encoded block A, block B, and block C which neighbor the current block is used as motion vector predictor v 0  at the upper-left corner control point of the current block. Likewise, a motion vector selected from motion vectors of encoded block D and block E which neighbor the current block is used as motion vector predictor v 1  at the upper-right corner control point of the current block. Furthermore, a motion vector selected from motion vectors of encoded block F and block G which neighbor the current block is used as motion vector predictor v 2  at the lower-left corner control point of the current block. 
       FIG. 29  is a flow chart illustrating one example of an affine inter mode. 
     In the affine inter mode as illustrated, first, inter predictor  126  derives MV predictors (v 0 , v 1 ) or (v 0 , v 1 , v 2 ) of respective two or three control points of a current block (Step Sj_ 1 ). The control points are an upper-left corner point of the current block and an upper-right corner point of the current block as illustrated in  FIG. 25A , or an upper-left corner point of the current block, an upper-right corner point of the current block, and a lower-left corner point of the current block as illustrated in  FIG. 25B . 
     In other words, inter predictor  126  derives the motion vector predictors (v 0 , v 1 ) or (v 0 , v 1 , v 2 ) of respective two or three control points of the current block by selecting motion vectors of any of the blocks among encoded blocks in the vicinity of the respective control points of the current block illustrated in either  FIG. 28A  or  FIG. 28B . At this time, inter predictor  126  encodes, in a stream, motion vector predictor selection information for identifying the selected two motion vectors. 
     For example, inter predictor  126  may determine, using a cost evaluation or the like, the block from which a motion vector as a motion vector predictor at a control point is selected from among encoded blocks neighboring the current block, and may describe, in a bitstream, a flag indicating which motion vector predictor has been selected. 
     Next, inter predictor  126  performs motion estimation (Step Sj_ 3  and Sj_ 4 ) while updating a motion vector predictor selected or derived in Step Sj_ 1  (Step Sj_ 2 ). In other words, inter predictor  126  calculates, as an affine MV, a motion vector of each of sub-blocks which corresponds to an updated motion vector predictor, using either the expression (1A) or expression (1B) described above (Step Sj_ 3 ). Inter predictor  126  then performs motion compensation of the sub-blocks using these affine MVs and encoded reference pictures (Step Sj_ 4 ). As a result, for example, inter predictor  126  determines the motion vector predictor which yields the smallest cost as the motion vector at a control point in a motion estimation loop (Step Sj_ 5 ). At this time, inter predictor  126  further encodes, in the stream, the difference value between the determined MV and the motion vector predictor as an MV difference. 
     Lastly, inter predictor  126  generates a prediction image for the current block by performing motion compensation of the current block using the determined MV and the encoded reference picture (Step Sj_ 6 ). 
     [MV Derivation&gt;Affine Inter Mode] 
     When affine modes in which different numbers of control points (for example, two and three control points) are used may be switched and signaled at the CU level, the number of control points in an encoded block and the number of control points in a current block may be different from each other.  FIG. 30A  and  FIG. 30B  are conceptual diagrams for illustrating methods for deriving motion vector predictors at control points when the number of control points in an encoded block and the number of control points in a current block are different from each other. 
     For example, as illustrated in  FIG. 30A , when a current block has three control points at the upper-left corner, the upper-right corner, and the lower-left corner, and block A which neighbors to the left of the current block has been encoded according to an affine mode in which two control points are used, motion vectors v 3  and v 4  projected at the upper-left corner position and the upper-right corner position in the encoded block including block A are derived. Motion vector predictor v 0  at the upper-left corner control point of the current block and motion vector predictor v 1  at the upper-right corner control point of the current block are then calculated from derived motion vectors v 3  and v 4 . Furthermore, motion vector predictor v 2  at the lower-left corner control point is calculated from derived motion vectors v 0  and v 1 . 
     For example, as illustrated in  FIG. 30B , when a current block has two control points at the upper-left corner and the upper-right corner, and block A which neighbors to the left of the current block has been encoded according to the affine mode in which three control points are used, motion vectors v 3 , v 4 , and v 5  projected at the upper-left corner position, the upper-right corner position, and the lower-left corner position in the encoded block including block A are derived. Motion vector predictor v 0  at the upper-left corner control point of the current block and motion vector predictor v 1  at the upper-right corner control point of the current block are then calculated from derived motion vectors v 3 , v 4 , and v 5 . 
     It is to be noted that this method for deriving motion vector predictors may be used to derive motion vector predictors of the respective control points of the current block in Step Sj_ 1  in  FIG. 29 . 
     [MV Derivation&gt;DMVR] 
       FIG. 31A  is a flow chart illustrating a relationship between the merge mode and DMVR. 
     Inter predictor  126  derives a motion vector of a current block according to the merge mode (Step Sl_ 1 ). Next, inter predictor  126  determines whether to perform estimation of a motion vector, that is, motion estimation (Step Sl_ 2 ). Here, when determining not to perform motion estimation (No in Step Sl_ 2 ), inter predictor  126  determines the motion vector derived in Step Sl_ 1  as the final motion vector for the current block (Step Sl_ 4 ). In other words, in this case, the motion vector of the current block is determined according to the merge mode. 
     When determining to perform motion estimation in Step Sl_ 1  (Yes in Step Sl_ 2 ), inter predictor  126  derives the final motion vector for the current block by estimating a surrounding region of the reference picture specified by the motion vector derived in Step Sl_ 1  (Step Sl_ 3 ). In other words, in this case, the motion vector of the current block is determined according to the DMVR. 
       FIG. 31B  is a conceptual diagram for illustrating one example of a DMVR process for determining an MV. 
     First, (for example, in merge mode) the best MVP which has been set to the current block is determined to be an MV candidate. A reference pixel is identified from a first reference picture (L0) which is an encoded picture in the L0 direction according to an MV candidate (L0). Likewise, a reference pixel is identified from a second reference picture (L1) which is an encoded picture in the L1 direction according to an MV candidate (L1). A template is generated by calculating an average of these reference pixels. 
     Next, each of the surrounding regions of MV candidates of the first reference picture (L0) and the second reference picture (L1) are estimated, and the MV which yields the smallest cost is determined to be the final MV. It is to be noted that the cost value may be calculated, for example, using a difference value between each of the pixel values in the template and a corresponding one of the pixel values in the estimation region, the values of MV candidates, etc. 
     It is to be noted that the processes, configurations, and operations described here typically are basically common between the encoder and a decoder to be described later. 
     Exactly the same example processes described here do not always need to be performed. Any process for enabling derivation of the final MV by estimation in surrounding regions of MV candidates may be used. 
     [Motion Compensation&gt;BIO/OBMC] 
     Motion compensation involves a mode for generating a prediction image, and correcting the prediction image. The mode is, for example, BIO and OBMC to be described later. 
       FIG. 32  is a flow chart illustrating one example of generation of a prediction image. 
     Inter predictor  126  generates a prediction image (Step Sm_ 1 ), and corrects the prediction image, for example, according to any of the modes described above (Step Sm_ 2 ). 
       FIG. 33  is a flow chart illustrating another example of generation of a prediction image. 
     Inter predictor  126  determines a motion vector of a current block (Step Sn_ 1 ). Next, inter predictor  126  generates a prediction image (Step Sn_ 2 ), and determines whether to perform a correction process (Step Sn_ 3 ). Here, when determining to perform a correction process (Yes in Step Sn_ 3 ), inter predictor  126  generates the final prediction image by correcting the prediction image (Step Sn_ 4 ). When determining not to perform a correction process (No in Step Sn_ 3 ), inter predictor  126  outputs the prediction image as the final prediction image without correcting the prediction image (Step Sn_ 5 ). 
     In addition, motion compensation involves a mode for correcting a luminance of a prediction image when generating the prediction image. The mode is, for example, LIC to be described later. 
       FIG. 34  is a flow chart illustrating another example of generation of a prediction image. 
     Inter predictor  126  derives a motion vector of a current block (Step So_ 1 ). Next, inter predictor  126  determines whether to perform a luminance correction process (Step So_ 2 ). Here, when determining to perform a luminance correction process (Yes in Step So_ 2 ), inter predictor  126  generates the prediction image while performing a luminance correction process (Step So_ 3 ). In other words, the prediction image is generated using LIC. When determining not to perform a luminance correction process (No in Step So_ 2 ), inter predictor  126  generates a prediction image by performing normal motion compensation without performing a luminance correction process (Step So_ 4 ). 
     [Motion Compensation&gt;OBMC] 
     It is to be noted that an inter prediction signal may be generated using motion information for a neighboring block in addition to motion information for the current block obtained from motion estimation. More specifically, the inter prediction signal may be generated in units of a sub-block in the current block by performing a weighted addition of a prediction signal based on motion information obtained from motion estimation (in the reference picture) and a prediction signal based on motion information for a neighboring block (in the current picture). Such inter prediction (motion compensation) is also referred to as overlapped block motion compensation (OBMC). 
     In OBMC mode, information indicating a sub-block size for OBMC (referred to as, for example, an OBMC block size) may be signaled at the sequence level. Moreover, information indicating whether to apply the OBMC mode (referred to as, for example, an OBMC flag) may be signaled at the CU level. It is to be noted that the signaling of such information does not necessarily need to be performed at the sequence level and CU level, and may be performed at another level (for example, at the picture level, slice level, tile level, CTU level, or sub-block level). 
     Examples of the OBMC mode will be described in further detail.  FIGS. 35 and 36  are a flow chart and a conceptual diagram for illustrating an outline of a prediction image correction process performed by an OBMC process. 
     First, as illustrated in  FIG. 36 , a prediction image (Pred) is obtained through normal motion compensation using a motion vector (MV) assigned to the processing target (current) block. In  FIG. 36 , the arrow “MV” points a reference picture, and indicates what the current block of the current picture refers to in order to obtain a prediction image. 
     Next, a prediction image (Pred_L) is obtained by applying a motion vector (MV_L) which has been already derived for the encoded block neighboring to the left of the current block to the current block (re-using the motion vector for the current block). The motion vector (MV_L) is indicated by an arrow “MV_L” indicating a reference picture from a current block. A first correction of a prediction image is performed by overlapping two prediction images Pred and Pred_L. This provides an effect of blending the boundary between neighboring blocks. 
     Likewise, a prediction image (Pred_U) is obtained by applying a motion vector (MV_U) which has been already derived for the encoded block neighboring above the current block to the current block (re-using the motion vector for the current block). The motion vector (MV_U) is indicated by an arrow “MV_U” indicating a reference picture from a current block. A second correction of a prediction image is performed by overlapping the prediction image Pred_U to the prediction images (for example. Pred and Pred_L) on which the first correction has been performed. This provides an effect of blending the boundary between neighboring blocks. The prediction image obtained by the second correction is the one in which the boundary between the neighboring blocks has been blended (smoothed), and thus is the final prediction image of the current block. 
     Although the above example is a two-path correction method using left and upper neighboring blocks, it is to be noted that the correction method may be three- or more-path correction method using also the right neighboring block and/or the lower neighboring block. 
     It is to be noted that the region in which such overlapping is performed may be only part of a region near a block boundary instead of the pixel region of the entire block. 
     It is to be noted that the prediction image correction process according to OBMC for obtaining one prediction image Pred from one reference picture by overlapping additional prediction image Pred_L and Pred_U have been described above. However, when a prediction image is corrected based on a plurality of reference images, a similar process may be applied to each of the plurality of reference pictures. In such a case, after corrected prediction images are obtained from the respective reference pictures by performing OBMC image correction based on the plurality of reference pictures, the obtained corrected prediction images are further overlapped to obtain the final prediction image. 
     It is to be noted that, in OBMC, the unit of a current block may be the unit of a prediction block or the unit of a sub-block obtained by further splitting the prediction block. 
     One example of a method for determining whether to apply an OBMC process is a method for using an obmc_flag which is a signal indicating whether to apply an OBMC process. As one specific example, an encoder determines whether the current block belongs to a region having complicated motion. The encoder sets the obmc_flag to a value of “1” when the block belongs to a region having complicated motion and applies an OBMC process when encoding, and sets the obmc_flag to a value of “0” when the block does not belong to a region having complicated motion and encodes the block without applying an OBMC process. The decoder switches between application and non-application of an OBMC process by decoding the obmc_flag written in the stream (for example, a compressed sequence) and decoding the block by switching between the application and non-application of the OBMC process in accordance with the flag value. 
     Inter predictor  126  generates one rectangular prediction image for a rectangular current block in the above example. However, inter predictor  126  may generate a plurality of prediction images each having a shape different from a rectangle for the rectangular current block, and may combine the plurality of prediction images to generate the final rectangular prediction image. The shape different from a rectangle may be, for example, a triangle. 
       FIG. 37  is a conceptual diagram for illustrating generation of two triangular prediction images. 
     Inter predictor  126  generates a triangular prediction image by performing motion compensation of a first partition having a triangular shape in a current block by using a first MV of the first partition, to generate a triangular prediction image. Likewise, inter predictor  126  generates a triangular prediction image by performing motion compensation of a second partition having a triangular shape in a current block by using a second MV of the second partition, to generate a triangular prediction image. Inter predictor  126  then generates a prediction image having the same rectangular shape as the rectangular shape of the current block by combining these prediction images. 
     It is to be noted that, although the first partition and the second partition are triangles in the example illustrated in  FIG. 37 , the first partition and the second partition may be trapezoids, or other shapes different from each other. Furthermore, although the current block includes two partitions in the example illustrated in  FIG. 37 , the current block may include three or more partitions. 
     In addition, the first partition and the second partition may overlap with each other. In other words, the first partition and the second partition may include the same pixel region. In this case, a prediction image for a current block may be generated using a prediction image in the first partition and a prediction image in the second partition. 
     In addition, although an example in which a prediction image is generated for each of two partitions using inter prediction, a prediction image may be generated for at least one partition using intra prediction. 
     [Motion Compensation&gt;BIO] 
     Next, a method for deriving a motion vector is described. First, a mode for deriving a motion vector based on a model assuming uniform linear motion will be described. This mode is also referred to as a bi-directional optical flow (BIO) mode. 
       FIG. 38  is a conceptual diagram for illustrating a model assuming uniform linear motion. In  FIG. 38 , (vx, vy) indicates a velocity vector, and τ0 and τ1 indicate temporal distances between a current picture (Cur Pic) and two reference pictures (Ref0, Ref1). (MVx0, MVy0) indicate motion vectors corresponding to reference picture Ref0, and (MVx1, MVy1) indicate motion vectors corresponding to reference picture Ref1. 
     Here, under the assumption of uniform linear motion exhibited by velocity vectors (v x , v y ), (MVx 0 , MVy 0 ) and (MVx 1 , MVy 1 ) are represented as (v x τ 0 , v y τ 0 ) and (−v x τ 1 , −v y τ 1 ), respectively, and the following optical flow equation (2) may be employed. 
       [MATH. 3] 
       ∂ I   (k)   /∂t+v   x   ∂I   (k)   /∂x+v   y   ∂I   (k)   /∂y= 0.  (2)
 
     Here, I (k)  indicates a motion-compensated luma value of reference picture k (k=0, 1). This optical flow equation shows that the sum of (i) the time derivative of the luma value, (ii) the product of the horizontal velocity and the horizontal component of the spatial gradient of a reference image, and (iii) the product of the vertical velocity and the vertical component of the spatial gradient of a reference image is equal to zero. A motion vector of each block obtained from, for example, a merge list may be corrected in units of a pixel, based on a combination of the optical flow equation and Hermite interpolation. 
     It is to be noted that a motion vector may be derived on the decoder side using a method other than deriving a motion vector based on a model assuming uniform linear motion. For example, a motion vector may be derived in units of a sub-block based on motion vectors of neighboring blocks. 
     [Motion Compensation&gt;LIC] 
     Next, an example of a mode in which a prediction image (prediction) is generated by using a local illumination compensation (LIC) process will be described. 
       FIG. 39  is a conceptual diagram for illustrating one example of a prediction image generation method using a luminance correction process performed by a LIC process. 
     First, an MV is derived from an encoded reference picture, and a reference image corresponding to the current block is obtained. 
     Next, information indicating how the luma value changed between the reference picture and the current picture is extracted for the current block. This extraction is performed based on the luma pixel values for the encoded left neighboring reference region (surrounding reference region) and the encoded upper neighboring reference region (surrounding reference region), and the luma pixel value at the corresponding position in the reference picture specified by the derived MV. A luminance correction parameter is calculated by using the information indicating how the luma value changed. 
     The prediction image for the current block is generated by performing a luminance correction process in which the luminance correction parameter is applied to the reference image in the reference picture specified by the MV. 
     It is to be noted that the shape of the surrounding reference region illustrated in  FIG. 39  is just one example; the surrounding reference region may have a different shape. 
     Moreover, although the process in which a prediction image is generated from a single reference picture has been described here, cases in which a prediction image is generated from a plurality of reference pictures can be described in the same manner. The prediction image may be generated after performing a luminance correction process of the reference images obtained from the reference pictures in the same manner as described above. 
     One example of a method for determining whether to apply a LIC process is a method for using a lic_flag which is a signal indicating whether to apply the LIC process. As one specific example, the encoder determines whether the current block belongs to a region having a luminance change. The encoder sets the lic_flag to a value of “1” when the block belongs to a region having a luminance change and applies a LIC process when encoding, and sets the lic_flag to a value of “0” when the block does not belong to a region having a luminance change and encodes the current block without applying a LIC process. The decoder may decode the lic_flag written in the stream and decode the current block by switching between application and non-application of a LIC process in accordance with the flag value. 
     One example of a different method of determining whether to apply a LIC process is a determining method in accordance with whether a LIC process was applied to a surrounding block. In one specific example, when the merge mode is used on the current block, whether a LIC process was applied in the encoding of the surrounding encoded block selected upon deriving the MV in the merge mode process is determined. According to the result, encoding is performed by switching between application and non-application of a LIC process. It is to be noted that, also in this example, the same processes are applied in processes at the decoder side. 
     An embodiment of the luminance correction (LIC) process described with reference to  FIG. 39  is described in detail below. 
     First, inter predictor  126  derives a motion vector for obtaining a reference image corresponding to a current block to be encoded from a reference picture which is an encoded picture. 
     Next, inter predictor  126  extracts information indicating how the luma value of the reference picture has been changed to the luma value of the current picture, using the luma pixel value of an encoded surrounding reference region which neighbors to the left of or above the current block and the luma value in the corresponding position in the reference picture specified by a motion vector, and calculates a luminance correction parameter. For example, it is assumed that the luma pixel value of a given pixel in the surrounding reference region in the current picture is p0, and that the luma pixel value of the pixel corresponding to the given pixel in the surrounding reference region in the reference picture is p1. Inter predictor  126  calculates coefficients A and B for optimizing A×p1+B=p0 as the luminance correction parameter for a plurality of pixels in the surrounding reference region. 
     Next, inter predictor  126  performs a luminance correction process using the luminance correction parameter for the reference image in the reference picture specified by the motion vector, to generate a prediction image for the current block. For example, it is assumed that the luma pixel value in the reference image is p2, and that the luminance-corrected luma pixel value of the prediction image is p3. Inter predictor  126  generates the prediction image after being subjected to the luminance correction process by calculating A×p2+B=p3 for each of the pixels in the reference image. 
     It is to be noted that the shape of the surrounding reference region illustrated in  FIG. 39  is one example; a different shape other than the shape of the surrounding reference region may be used. In addition, part of the surrounding reference region illustrated in  FIG. 39  may be used. For example, a region having a determined number of pixels extracted from each of an upper neighboring pixel and a left neighboring pixel may be used as a surrounding reference region. The determined number of pixels may be predetermined. In addition, the surrounding reference region is not limited to a region which neighbors the current block, and may be a region which does not neighbor the current block. In the example illustrated in  FIG. 39 , the surrounding reference region in the reference picture is a region specified by a motion vector in a current picture, from a surrounding reference region in the current picture. However, a region specified by another motion vector is also possible. For example, the other motion vector may be a motion vector in a surrounding reference region in the current picture. 
     Although operations performed by encoder  100  have been described here, it is to be noted that decoder  200  typically performs similar operations. 
     It is to be noted that the LIC process may be applied not only to the luma but also to chroma. At this time, a correction parameter may be derived individually for each of Y, Cb, and Cr, or a common correction parameter may be used for any of Y, Cb, and Cr. 
     In addition, the LIC process may be applied in units of a sub-block. For example, a correction parameter may be derived using a surrounding reference region in a current sub-block and a surrounding reference region in a reference sub-block in a reference picture specified by an MV of the current sub-block. 
     [Prediction Controller] 
     Inter predictor  128  selects one of an intra prediction signal (a signal output from intra predictor  124 ) and an inter prediction signal (a signal output from inter predictor  126 ), and outputs the selected signal to subtractor  104  and adder  116  as a prediction signal. 
     As illustrated in  FIG. 1 , in various kinds of encoder examples, prediction controller  128  may output a prediction parameter which is input to entropy encoder  110 . Entropy encoder  110  may generate an encoded bitstream (or a sequence), based on the prediction parameter which is input from prediction controller  128  and quantized coefficients which are input from quantizer  108 . The prediction parameter may be used in a decoder. The decoder may receive and decode the encoded bitstream, and perform the same processes as the prediction processes performed by intra predictor  124 , inter predictor  126 , and prediction controller  128 . The prediction parameter may include (i) a selection prediction signal (for example, a motion vector, a prediction type, or a prediction mode used by intra predictor  124  or inter predictor  126 ), or (ii) an optional index, a flag, or a value which is based on a prediction process performed in each of intra predictor  124 , inter predictor  126 , and prediction controller  128 , or which indicates the prediction process. 
     [Mounting Example of Encoder] 
       FIG. 40  is a block diagram illustrating a mounting example of encoder  100 . Encoder  100  includes processor a1 and memory a2. For example, the plurality of constituent elements of encoder  100  illustrated in  FIG. 1  are mounted on processor a1 and memory a2 illustrated in  FIG. 40 . 
     Processor a1 is circuitry which performs information processing and is accessible to memory a2. For example, processor a1 is dedicated or general electronic circuitry which encodes a video. Processor a1 may be a processor such as a CPU. In addition, processor a1 may be an aggregate of a plurality of electronic circuits. In addition, for example, processor a1 may take the roles of two or more constituent elements out of the plurality of constituent elements of encoder  100  illustrated in  FIG. 1 , etc. 
     Memory a2 is dedicated or general memory for storing information that is used by processor a1 to encode a video. Memory a2 may be electronic circuitry, and may be connected to processor a1. In addition, memory a2 may be included in processor at. In addition, memory a2 may be an aggregate of a plurality of electronic circuits. In addition, memory a2 may be a magnetic disc, an optical disc, or the like, or may be represented as a storage, a recording medium, or the like. In addition, memory a2 may be non-volatile memory, or volatile memory. 
     For example, memory a2 may store a video to be encoded or a bitstream corresponding to an encoded video. In addition, memory a2 may store a program for causing processor a1 to encode a video. 
     In addition, for example, memory a2 may take the roles of two or more constituent elements for storing information out of the plurality of constituent elements of encoder  100  illustrated in  FIG. 1 , etc. For example, memory a2 may take the roles of block memory  118  and frame memory  122  illustrated in  FIG. 1 . More specifically, memory a2 may store a reconstructed block, a reconstructed picture, etc. 
     It is to be noted that, in encoder  100 , all of the plurality of constituent elements indicated in  FIG. 1 , etc. may not be implemented, and all the processes described above may not be performed. Part of the constituent elements indicated in  FIG. 1 , etc. may be included in another device, or part of the processes described above may be performed by another device. 
     [Decoder] 
     Next, a decoder capable of decoding an encoded signal (encoded bitstream) output, for example, from encoder  100  described above will be described.  FIG. 41  is a block diagram illustrating a functional configuration of decoder  200  according to an embodiment. Decoder  200  is a video decoder which decodes a video in units of a block. 
     As illustrated in  FIG. 41 , decoder  200  includes entropy decoder  202 , inverse quantizer  204 , inverse transformer  206 , adder  208 , block memory  210 , loop filter  212 , frame memory  214 , intra predictor  216 , inter predictor  218 , and prediction controller  220 . 
     Decoder  200  is implemented as, for example, a generic processor and memory. In this case, when a software program stored in the memory is executed by the processor, the processor functions as entropy decoder  202 , inverse quantizer  204 , inverse transformer  206 , adder  208 , loop filter  212 , intra predictor  216 , inter predictor  218 , and prediction controller  220 . Alternatively, decoder  200  may be implemented as one or more dedicated electronic circuits corresponding to entropy decoder  202 , inverse quantizer  204 , inverse transformer  206 , adder  208 , loop filter  212 , intra predictor  216 , inter predictor  218 , and prediction controller  220 . 
     Hereinafter, an overall flow of processes performed by decoder  200  is described, and then each of constituent elements included in decoder  200  will be described. 
     [Overall Flow of Decoding Process] 
       FIG. 42  is a flow chart illustrating one example of an overall decoding process performed by decoder  200 . 
     First, entropy decoder  202  of decoder  200  identifies a splitting pattern of a block having a fixed size (for example, 128×128 pixels) (Step Sp_). This splitting pattern is a splitting pattern selected by encoder  100 . Decoder  200  then performs processes of Step Sp_ 2  to Sp_ 6  for each of a plurality of blocks of the splitting pattern. 
     In other words, entropy decoder  202  decodes (specifically, entropy-decodes) encoded quantized coefficients and a prediction parameter of a current block to be decoded (also referred to as a current block) (Step Sp_ 2 ). 
     Next, inverse quantizer  204  performs inverse quantization of the plurality of quantized coefficients and inverse transformer  206  performs inverse transform of the result, to restore a plurality of prediction residuals (that is, a difference block) (Step Sp_ 3 ). 
     Next, the prediction processor including all or part of intra predictor  216 , inter predictor  218 , and prediction controller  220  generates a prediction signal (also referred to as a prediction block) of the current block (Step Sp_ 4 ). 
     Next, adder  208  adds the prediction block to the difference block to generate a reconstructed image (also referred to as a decoded image block) of the current block (Step Sp_ 5 ). 
     When the reconstructed image is generated, loop filter  212  performs filtering of the reconstructed image (Step Sp_ 6 ). 
     Decoder  200  then determines whether decoding of the entire picture has been finished (Step Sp_ 7 ). When determining that the decoding has not yet been finished (No in Step Sp_ 7 ), decoder  200  repeatedly executes the processes starting with Step Sp_ 1 . 
     As illustrated, the processes of Steps Sp_ 1  to Sp_ 7  are performed sequentially by decoder  200 . Alternatively, two or more of the processes may be performed in parallel, the processing order of the two or more of the processes may be modified, etc. 
     [Entropy Decoder] 
     Entropy decoder  202  entropy decodes an encoded bitstream. More specifically, for example, entropy decoder  202  arithmetic decodes an encoded bitstream into a binary signal. Entropy decoder  202  then debinarizes the binary signal. With this, entropy decoder  202  outputs quantized coefficients of each block to inverse quantizer  204 . Entropy decoder  202  may output a prediction parameter included in an encoded bitstream (see  FIG. 1 ) to intra predictor  216 , inter predictor  218 , and prediction controller  220 . Intra predictor  216 , inter predictor  218 , and prediction controller  220  in an embodiment are capable of executing the same prediction processes as those performed by intra predictor  124 , inter predictor  126 , and prediction controller  128  at the encoder side. 
     [Inverse Quantizer] 
     Inverse quantizer  204  inverse quantizes quantized coefficients of a block to be decoded (hereinafter referred to as a current block) which are inputs from entropy decoder  202 . More specifically, inverse quantizer  204  inverse quantizes quantized coefficients of the current block, based on quantization parameters corresponding to the quantized coefficients. Inverse quantizer  204  then outputs the inverse quantized transform coefficients of the current block to inverse transformer  206 . 
     [Inverse Transformer] 
     Inverse transformer  206  restores prediction errors by inverse transforming the transform coefficients which are inputs from inverse quantizer  204 . 
     For example, when information parsed from an encoded bitstream indicates that EMT or AMT is to be applied (for example, when an AMT flag is true), inverse transformer  206  inverse transforms the transform coefficients of the current block based on information indicating the parsed transform type. 
     Moreover, for example, when information parsed from an encoded bitstream indicates that NSST is to be applied, inverse transformer  206  applies a secondary inverse transform to the transform coefficients. 
     [Adder] 
     Adder  208  reconstructs the current block by adding prediction errors which are inputs from inverse transformer  206  and prediction samples which are inputs from prediction controller  220 . Adder  208  then outputs the reconstructed block to block memory  210  and loop filter  212 . 
     [Block Memory] 
     Block memory  210  is storage for storing blocks in a picture to be decoded (hereinafter referred to as a current picture) and to be referred to in intra prediction. More specifically, block memory  210  stores reconstructed blocks output from adder  208 . 
     [Loop Filter] 
     Loop filter  212  applies a loop filter to blocks reconstructed by adder  208 , and outputs the filtered reconstructed blocks to frame memory  214 , display device, etc. 
     When information indicating ON or OFF of an ALF parsed from an encoded bitstream indicates that an ALF is ON, one filter from among a plurality of filters is selected based on direction and activity of local gradients, and the selected filter is applied to the reconstructed block. 
     [Frame Memory] 
     Frame memory  214  is, for example, storage for storing reference pictures for use in inter prediction, and is also referred to as a frame buffer. More specifically, frame memory  214  stores a reconstructed block filtered by loop filter  212 . 
     [Prediction Processor (Intra Predictor, Inter Predictor, Prediction Controller)] 
       FIG. 43  is a flow chart illustrating one example of a process performed by a prediction processor of decoder  200 . It is to be noted that the prediction processor includes all or part of the following constituent elements: intra predictor  216 ; inter predictor  218 : and prediction controller  220 . 
     The prediction processor generates a prediction image of a current block (Step Sq_ 1 ). This prediction image is also referred to as a prediction signal or a prediction block. It is to be noted that the prediction signal is, for example, an intra prediction signal or an inter prediction signal. Specifically, the prediction processor generates the prediction image of the current block using a reconstructed image which has been already obtained through generation of a prediction block, generation of a difference block, generation of a coefficient block, restoring of a difference block, and generation of a decoded image block. 
     The reconstructed image may be, for example, an image in a reference picture, or an image of a decoded block in a current picture which is the picture including the current block. The decoded block in the current picture is, for example, a neighboring block of the current block. 
       FIG. 44  is a flow chart illustrating another example of a process performed by the prediction processor of decoder  200 . 
     The prediction processor determines either a method or a mode for generating a prediction image (Step Sr_ 1 ). For example, the method or mode may be determined based on, for example, a prediction parameter, etc. 
     When determining a first method as a mode for generating a prediction image, the prediction processor generates a prediction image according to the first method (Step Sr_ 2   a ). When determining a second method as a mode for generating a prediction image, the prediction processor generates a prediction image according to the second method (Step Sr_ 2   b ). When determining a third method as a mode for generating a prediction image, the prediction processor generates a prediction image according to the third method (Step Sr_ 2   c ). 
     The first method, the second method, and the third method may be mutually different methods for generating a prediction image. Each of the first to third methods may be an inter prediction method, an intra prediction method, or another prediction method. The above-described reconstructed image may be used in these prediction methods. 
     [Intra Predictor] 
     Intra predictor  216  generates a prediction signal (intra prediction signal) by performing intra prediction by referring to a block or blocks in the current picture stored in block memory  210 , based on the intra prediction mode parsed from the encoded bitstream. More specifically, intra predictor  216  generates an intra prediction signal by performing intra prediction by referring to samples (for example, luma and/or chroma values) of a block or blocks neighboring the current block, and then outputs the intra prediction signal to prediction controller  220 . 
     It is to be noted that when an intra prediction mode in which a luma block is referred to in intra prediction of a chroma block is selected, intra predictor  216  may predict the chroma component of the current block based on the luma component of the current block. 
     Moreover, when information parsed from an encoded bitstream indicates that PDPC is to be applied, intra predictor  216  corrects intra-predicted pixel values based on horizontal/vertical reference pixel gradients. 
     [Inter Predictor] 
     Inter predictor  218  predicts the current block by referring to a reference picture stored in frame memory  214 . Inter prediction is performed in units of a current block or a sub-block (for example, a 4×4 block) in the current block. For example, inter predictor  218  generates an inter prediction signal of the current block or the sub-block by performing motion compensation by using motion information (for example, a motion vector) parsed from an encoded bitstream (for example, a prediction parameter output from entropy decoder  202 ), and outputs the inter prediction signal to prediction controller  220 . 
     It is to be noted that when the information parsed from the encoded bitstream indicates that the OBMC mode is to be applied, inter predictor  218  generates the inter prediction signal using motion information of a neighboring block in addition to motion information of the current block obtained from motion estimation. 
     Moreover, when the information parsed from the encoded bitstream indicates that the FRUC mode is to be applied, inter predictor  218  derives motion information by performing motion estimation in accordance with the pattern matching method (bilateral matching or template matching) parsed from the encoded bitstream. Inter predictor  218  then performs motion compensation (prediction) using the derived motion information. 
     Moreover, when the BIO mode is to be applied, inter predictor  218  derives a motion vector based on a model assuming uniform linear motion. Moreover, when the information parsed from the encoded bitstream indicates that the affine motion compensation prediction mode is to be applied, inter predictor  218  derives a motion vector of each sub-block based on motion vectors of neighboring blocks. 
     [MV Derivation&gt;Normal Inter Mode] 
     When information parsed from an encoded bitstream indicates that the normal inter mode is to be applied, inter predictor  218  derives an MV based on the information parsed from the encoded bitstream and performs motion compensation (prediction) using the MV. 
       FIG. 45  is a flow chart illustrating an example of inter prediction in normal inter mode in decoder  200 . 
     Inter predictor  218  of decoder  200  performs motion compensation for each block. Inter predictor  218  obtains a plurality of MV candidates for a current block based on information such as MVs of a plurality of decoded blocks temporally or spatially surrounding the current block (Step Ss_ 1 ). In other words, inter predictor  218  generates an MV candidate list. 
     Next, inter predictor  218  extracts N (an integer of 2 or larger) MV candidates from the plurality of MV candidates obtained in Step Ss_ 1 , as motion vector predictor candidates (also referred to as MV predictor candidates) according to a determined priority order (Step Ss_ 2 ). It is to be noted that the priority order may be determined in advance for each of the N MV predictor candidates. 
     Next, inter predictor  218  decodes motion vector predictor selection information from an input stream (that is, an encoded bitstream), and selects, one MV predictor candidate from the N MV predictor candidates using the decoded motion vector predictor selection information, as a motion vector (also referred to as an MV predictor) of the current block (Step Ss_ 3 ). 
     Next, inter predictor  218  decodes an MV difference from the input stream, and derives an MV for a current block by adding a difference value which is the decoded MV difference and a selected motion vector predictor (Step Ss_ 4 ). 
     Lastly, inter predictor  218  generates a prediction image for the current block by performing motion compensation of the current block using the derived MV and the decoded reference picture (Step Ss_ 5 ). 
     [Prediction Controller] 
     Prediction controller  220  selects either the intra prediction signal or the inter prediction signal, and outputs the selected prediction signal to adder  208 . As a whole, the configurations, functions, and processes of prediction controller  220 , intra predictor  216 , and inter predictor  218  at the decoder side may correspond to the configurations, functions, and processes of prediction controller  128 , intra predictor  124 , and inter predictor  126  at the encoder side. 
     [Mounting Example of Decoder] 
       FIG. 46  is a block diagram illustrating a mounting example of decoder  200 . Decoder  200  includes processor b1 and memory b2. For example, the plurality of constituent elements of decoder  200  illustrated in  FIG. 41  are mounted on processor b1 and memory b2 illustrated in  FIG. 46 . 
     Processor b1 is circuitry which performs information processing and is accessible to memory b2. For example, processor b1 is dedicated or general electronic circuitry which decodes a video (that is, an encoded bitstream). Processor b1 may be a processor such as a CPU. In addition, processor b1 may be an aggregate of a plurality of electronic circuits. In addition, for example, processor b1 may take the roles of two or more constituent elements out of the plurality of constituent elements of decoder  200  illustrated in  FIG. 41 , etc. 
     Memory b2 is dedicated or general memory for storing information that is used by processor b1 to decode an encoded bitstream. Memory b2 may be electronic circuitry, and may be connected to processor b1. In addition, memory b2 may be included in processor b1. In addition, memory b2 may be an aggregate of a plurality of electronic circuits. In addition, memory b2 may be a magnetic disc, an optical disc, or the like, or may be represented as a storage, a recording medium, or the like. In addition, memory b2 may be a non-volatile memory, or a volatile memory. 
     For example, memory b2 may store a video or a bitstream. In addition, memory b2 may store a program for causing processor b1 to decode an encoded bitstream. 
     In addition, for example, memory b2 may take the roles of two or more constituent elements for storing information out of the plurality of constituent elements of decoder  200  illustrated in  FIG. 41 , etc. Specifically, memory b2 may take the roles of block memory  210  and frame memory  214  illustrated in  FIG. 41 . More specifically, memory b2 may store a reconstructed block, a reconstructed picture, etc. 
     It is to be noted that, in decoder  200 , all of the plurality of constituent elements illustrated in  FIG. 41 , etc. may not be implemented, and all the processes described above may not be performed. Part of the constituent elements indicated in  FIG. 41 , etc. may be included in another device, or part of the processes described above may be performed by another device. 
     Definitions of Terms 
     The respective terms may be defined as indicated below as examples. 
     A picture is an array of luma samples in monochrome format or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 color format. A picture may be either a frame or a field. 
     A frame is the composition of a top field and a bottom field, where sample rows 0, 2, 4, . . . originate from the top field and sample rows 1, 3, 5, . . . originate from the bottom field. 
     A slice is an integer number of coding tree units contained in one independent slice segment and all subsequent dependent slice segments (if any) that precede the next independent slice segment (if any) within the same access unit. 
     A tile is a rectangular region of coding tree blocks within a particular tile column and a particular tile row in a picture. A tile may be a rectangular region of the frame that is intended to be able to be decoded and encoded independently, although loop-filtering across tile edges may still be applied. 
     A block is an M×N (M-column by N-row) array of samples, or an M×N array of transform coefficients. A block may be a square or rectangular region of pixels including one Luma and two Chroma matrices. 
     A coding tree unit (CTU) may be a coding tree block of luma samples of a picture that has three sample arrays, or two corresponding coding tree blocks of chroma samples. Alternatively a CTU may be a coding tree block of samples of one of a monochrome picture and a picture that is coded using three separate color planes and syntax structures used to code the samples. 
     A super block may be a square block of 64×64 pixels that consists of either 1 or 2 mode info blocks or is recursively partitioned into four 32×32 blocks, which themselves can be further partitioned. 
     [First Example of Inter Prediction Process] 
       FIG. 47  is a diagram illustrating an outline of a first example of a pipeline configuration for the decoder according to the embodiment. In Stage 1 which is one of stages in pipeline control illustrated in  FIG. 47 , decoder  200  performs entropy decoding on an input stream to be decoded, to obtain information necessary for a decoding process. Subsequently in Stages 2 and 3, decoder  200  performs an inverse quantization process and an inverse transform process using the information obtained in Stage 1, to decode a residual image. Subsequently, decoder  200  performs an intra prediction process or an inter prediction process to decode a prediction image. Decoder  200  then adds the residual image to the prediction image to generate a reconstructed image. In Stage 4, decoder  200  performs a loop filtering process on the reconstructed image to generate a decoded image. 
     In the inter prediction process, decoder  200  firstly determines a motion vector (MV) and then performs a motion compensation (MC) process on a current block to be processed, using the determined motion vector, to generate a first prediction image. 
     In the case of using an LIC process, decoder  200  derives an LIC parameter using the first prediction image. Decoder  200  then performs image correction using the LIC process with the use of the derived LIC parameter. Next, when an inter prediction mode is a merge mode, decoder  200  performs a DMVR (MV correction) process using the prediction image corrected using the LIC process. Decoder  200  then performs again the motion compensation (MC) process using the motion vector corrected in the DMVR process, to generate a second prediction image. 
     In the case of using a BIO process, decoder  200  derives a BIO parameter using the second prediction image. Decoder  200  then performs a BIO correction process on the image of the current block, using the derived BIO parameter. Subsequently, decoder  200  applies an OBMC process to the image corrected using the BIO process, to obtain a final prediction image. 
     The final prediction image generated by decoder  200  in Stage 3 is used for reference as a neighboring reconstructed image in the decoding process of a block following the current block in a processing order. Therefore, the final prediction image is fed back as an input for an intra prediction process or an LIC parameter derivation process. In the intra prediction process or the LIC parameter derivation process, it is necessary to place a process related to the feedback in one stage in order to refer to a neighboring reconstructed image that belongs to a block immediately before the current block in the processing order. As a result, Stage 3 includes many processes to form a stage requiring a long processing time, as illustrated in  FIG. 47 . 
     The outline of the pipeline configuration illustrated in  FIG. 47  is one example, and one or more of the processes illustrated therein may be removed or a process not illustrated therein may be added or a method of sectioning stages in pipeline control may be changed. 
       FIG. 48  is a diagram illustrating processing timings in a time sequence in which stage processing is performed on each current block to be processed in the first example of the pipeline configuration for the decoder according to the embodiment. 
       FIG. 48  illustrates the timings of processing stages in pipeline control with respect to five current blocks to be processed, that is, CU0 through CU4 illustrated in  FIG. 48 . Since CU0, CU1, and CU4 are blocks each having a size that is several times as large as the size of CU2 or CU3, the processing time of each of the stages in the processing of CU0, CU1, or CU4 is also several times as long as that in the processing of CU2 or CU3. Moreover, since the processing time of Stage 3 in the processing in the pipeline control is long, as illustrated in  FIG. 47 , it is assumed that Stage 3 requires a processing time twice as long as the processing time of other stage in the processing in the pipeline control in  FIG. 48 . 
     Each stage of the processing in the pipeline control is started after the same stage of a current block, which is processed immediately before a current block to be processed in a processing order, is waited to end. For example, the processing of Stage 3 for CU1 is started from time t8 when the processing of Stage 3 for CU0 is ended. Since the processing time of Stage 3 is twice as long as that of other stage in the processing of CU0, a waiting time equivalent to a time period from t0 to t2 is generated, in the processing of CU1, from the time when the processing of Stage 2 is completed until the time when the processing of Stage 3 is started. 
     Thus, in each processing performed on current blocks CU1 through CU4, a waiting time is generated after the processing of Stage 2 is completed until the processing of Stage 3 is started. The waiting time accumulates each time the processing proceeds from current block CU1 to current block CU2, from current block CU2 to current block CU3, and from current block CU3 to current block CU4. This therefore results in a waiting time equivalent to a time period from t0 to t6 from the time when the processing of Stage 2 is completed until the time when the processing of Stage 3 is started in the processing of CU4. 
     As a result, at a time point when the decoding process of one picture is completed, a processing time that is required for all the processing for one picture and includes waiting times reaches approximately twice as long as a processing time that is required for all the processing for one picture and excludes waiting times. For this reason, it might be difficult for decoder  200  to complete the processing of all of blocks in one picture within a processing time assigned to one picture. 
       FIG. 49  is a flow chart illustrating a flow of an inter prediction process in the first example of the pipeline configuration for the decoder according to the embodiment. 
     First, decoder  200  starts a loop performed per prediction block unit (step S 100 ). 
     Next, decoder  200  selects an inter prediction mode from among a plurality of modes (e.g., a normal inter mode, a merge mode, etc.) (step S 101 ). 
     When selecting a normal inter mode as the inter prediction mode (normal inter mode at step S 101 ), decoder  200  derives a motion vector for normal inter mode (step S 102 ). In step S 102 , decoder  200  refers to a motion vector of a processed block neighboring a current block to be processed, obtains a prediction motion vector, and creates a prediction motion vector list for normal inter mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list and adds a motion vector difference (MVD) to the specified prediction motion vector, to determine a motion vector, thereby deriving the motion vector. 
     Next, decoder  200  performs a motion compensation (MC) process on the current block (step S 103 ). Here, decoder  200  generates a prediction image. 
     Subsequently, decoder  200  determines whether to apply an LIC process to the current block (step S 104 ). The determination may be performed based on information related to whether the LIC process has been applied to a processed block neighboring the current block or based on a signal that is explicitly written into a bitstream and indicates whether the LIC process is to be applied. Alternatively, the determination may be performed by explicitly writing, into a bitstream, a signal indicating whether the LIC process is to be applied. 
     When applying the LIC process to the current block (Yes in step S 104 ), decoder  200  derives an LIC parameter using the prediction image generated in step S 103  (step S 105 ). In the derivation of the LIC parameter, since decoder  200  uses a reconstructed image of a block neighboring the current block, the feedback process described with reference to  FIG. 47  is necessary. 
     Decoder  200  then corrects the prediction image using the LIC process (step S 106 ). After step S 106 , decoder  200  performs the process in step S 114 . 
     When not applying the LIC process (No in step S 104 ), decoder  200  skips the processes in steps S 105  and S 106 . Namely, decoder  200  performs the process in step S 114  after step S 104  in this case. 
     When selecting a merge mode as the inter prediction mode (merge mode in step S 101 ), decoder  200  derives a motion vector for merge mode (step S 107 ). In step S 107 , decoder  200  refers to a motion vector of a processed block neighboring the current block, obtains a prediction motion vector, and creates a prediction motion vector list for merge mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list and determines the specified prediction motion vector as a motion vector, thereby deriving the motion vector. 
     Next, decoder  200  performs a motion compensation (MC) process on the current block (step S 108 ). Here, decoder  200  generates a prediction image. 
     Subsequently, decoder  200  determines whether to apply an LIC process to the current block (step S 109 ). The determination may be performed based on information related to whether the LIC process has been applied to a processed block neighboring the current block or based on a signal that is explicitly written into a bitstream and indicates whether the LIC process is to be applied. Alternatively, the determination may be performed by explicitly writing, into a bitstream, a signal indicating whether the LIC process is to be applied. 
     When applying the LIC process to the current block (Yes in step S 109 ), decoder  200  derives an LIC parameter using the prediction image generated in step S 108  (step S 110 ). In the derivation of the LIC parameter, since decoder  200  uses a reconstructed image of a block neighboring the current block, the feedback process described with reference to  FIG. 47  is necessary. 
     Decoder  200  then corrects the prediction image using the LIC process (step S 111 ). Next, decoder  200  proceeds to step S 112 . 
     When not applying the LIC process to the current block (No in step S 109 ), decoder  200  skips the processes in steps S 110  and S 111 . Namely, decoder  200  performs the process in step S 112  after step S 109  in this case. 
     Decoder  200  performs a DMVR process on the current block and corrects the motion vector (step S 112 ). 
     Subsequently, decoder  200  performs again the motion compensation (MC) process on the current block using the motion vector corrected in step S 112  (step S 113 ). Here, decoder  200  generates again a prediction image. 
     Next, decoder  200  determines whether the LIC process has been applied to the current block (step S 114 ). 
     When determining that the LIC process has not been applied to the current block (No in step S 114 ), decoder  200  determines whether to apply a BIO process to the current block (step S 115 ). The determination of whether to apply the BIO process to the current block may be performed in accordance with a condition such as a prediction mode, a prediction direction, or a block size, or based on a signal that is explicitly written into a bitstream and indicates whether the BIO process is to be applied to the current block. Alternatively the determination may be performed by explicitly writing, into a bitstream, a signal indicating whether the BIO process is to be applied. 
     When determining that the LIC process has been applied to the current block (Yes in step S 114 ), decoder  200  proceeds to step S 118 . 
     When determining that the BIO process is to be applied to the current block (Yes in step S 115 ), decoder  200  derives a BIO parameter (step S 116 ). 
     Subsequently, decoder  200  corrects, for the current block, the prediction image using the BIO process (step S 11   7 ). 
     When determining that the BIO process is not to be applied to the current block (No in step S 115 ), decoder  200  proceeds to step S 118 . 
     Next, decoder  200  determines whether to apply an OBMC process to the current block (step S 118 ). The determination may be performed based on information related to whether the OBMC process has been applied to a processed block neighboring the current block or based on a signal that is explicitly written into a bitstream and indicates whether the OBMC process is to be applied. Alternatively, the determination may be performed by explicitly writing, into a bitstream, a signal indicating whether the OBMC process is to be applied. 
     When determining that the OBMC process is to be applied to the current block (Yes in step S 118 ), decoder  200  performs a correction process using the OBMC process on a final prediction image generated before step S 118  (step S 119 ). Decoder  200  determines the prediction image generated in step S 119  as a final prediction image. 
     When determining that the OBMC process is not to be applied to the current block (No in step S 118 ), decoder  200  proceeds to step S 120 . 
     Decoder  200  then ends the loop performed per prediction block unit (step S 120 ). 
     Note that the flow of the processes described with reference to  FIG. 49  is one example, and one or more of the processes illustrated therein may be removed, or a process or a condition-based determination not illustrated therein may be added. 
     Although the operation performed by decoder  200  has been described with reference to  FIG. 49 , “decoder  200 ” may read “encoder  100 ”. In such a case, “decoding, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. Alternatively, “parsing, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. 
     [Second Example of Inter Prediction Process] 
       FIG. 50  is a diagram illustrating an outline of a second example of the pipeline configuration for the decoder according to the embodiment. Decoder  200  operates, as will be described below, differently from the first example described with reference to  FIG. 47 . In Stage 1 which is one of stages in pipeline control illustrated in  FIG. 50 , decoder  200  performs entropy decoding on an input stream to be decoded, to obtain information necessary for a decoding process. Next, decoder  200  determines a motion vector (MV) in Stage 2 in an inter prediction process. In Stage 2, in the case of performing a DMVR process, decoder  200  subsequently performs a provisional motion compensation (MC) process for DMVR process using the determined motion vector, to generate a first prediction image. Decoder  200  then performs the DMVR (MV correction) process using the first prediction image in Stage 3. In the case of having performed the DMVR process, decoder  200  performs a motion compensation (MC) process using the motion vector (MV) corrected in the DMVR process in Stage 3, to generate a second prediction image. In the case of not having performed the DMVR process, decoder  200  performs the motion compensation (MC) process using the motion vector (MV) that has not been corrected in the DMVR process in Stage 3, to generate a second prediction image. 
     Next, in Stage 4, in the case of using an LIC process, decoder  200  derives an LIC parameter using the second prediction image and performs an LIC correction process on the second prediction image using the derived LIC parameter. In the case of using a BIO process, decoder  200  derives a BIO parameter using the second prediction image and performs a BIO correction process on the second prediction image using the derived BIO parameter. In Stage 4, decoder  200  adds the corrected prediction image to a residual image to generate a reconstructed image. 
     Stage 3, in the first example, which includes many processes and requires a long processing time can be divided into Stage 3 and Stage 4 each including processes whose number is approximately the same as the number of processes included in other stage. Stage 3 and Stage 4 in the second example each have a shorter processing time than Stage 3 in the first example. 
     Since a reconstructed image generated in Stage 4 is used for reference as a neighboring reconstructed image in the decoding process of a block following the current block in a processing order, the reconstructed image is fed back as an input for an intra prediction process or an LIC parameter derivation process. In the second example, since the LIC parameter derivation process is performed nearer to the end of the inter prediction process than the first example, it is possible to reduce the number of processes related to the feedback more than the first example. 
     The outline of the pipeline configuration illustrated in  FIG. 50  is one example, and one or more of the processes illustrated therein may be removed or a process not illustrated therein may be added or a method of sectioning stages in pipeline control may be changed. 
       FIG. 51  is a diagram illustrating processing timings in a time sequence in which stage processing is performed on each current block to be processed in the second example of the pipeline configuration for the decoder according to the embodiment.  FIG. 51 , like  FIG. 48 , illustrates the timings of processing stages in pipeline control with respect to five current blocks to be processed, that is, CU0 through CU4 illustrated in  FIG. 51 . S 1  through S 5  in  FIG. 51  represent Stage 1 through Stage 5. In the second example illustrated in  FIG. 51 , Stage 3 which is a processing stage in the pipeline control illustrated in the first example is divided into two stages of Stage 3 and Stage 4, which is different from the first example. As a result, Stage 3 and Stage 4 in the second example each requires a processing time that is approximately the same as that required for other stage. 
     Each stage of the processing in the pipeline control is started after the same stage of a current block, which is processed immediately before a current block to be processed in a processing order, is waited to end. For example, the processing of Stage 3 for CU1 is started from time t6 when the processing of Stage 3 for CU0 is ended. Since the processing time of Stage 3 is as long as that of other stage in the processing of CU0, decoder  200  is capable of starting the processing of Stage 3 without any waiting time after the processing of Stage 2 is ended in the processing of CU1. 
     In the processing of CU2, on the other hand, since the block size of CU2 is smaller than that of CU1 that is a block immediately before CU2 in the processing order, a waiting time is generated between Stage 2 and Stage 3. The waiting time generated between Stage 2 and Stage 3, however, is not carried over to the processing of the next block following CU2 in the processing order. In other words, the waiting time generated between Stage 2 and Stage 3 does not accumulate and disappears at the time point when the processing of CU4 is performed. 
     As a result, a processing time that is required for all the processing for one picture and includes waiting times is approximately the same as a processing time that is required for all the processing for one picture and excludes waiting times. Decoder  200  is therefore highly capable of completing the processing of all of blocks in one picture within a processing time assigned to one picture. 
       FIG. 52  is a flow chart illustrating a flow of an inter prediction process in the second example of the pipeline configuration for the decoder according to the embodiment. The following description provides only differences between the first and second examples and similarities therebetween will be omitted. 
     First, decoder  200  starts a loop performed per prediction block unit (step S 200 ). 
     Next, decoder  200  selects an inter prediction mode from among a plurality of modes (e.g., a normal inter mode, a merge mode, etc.) (step S 201 ). 
     When selecting a normal inter mode as the inter prediction mode (normal inter mode at step S 201 ), decoder  200  derives a motion vector for normal inter mode (step S 202 ). In step S 202 , decoder  200  refers to a motion vector of a processed block neighboring a current block to be processed, obtains a prediction motion vector, and creates a prediction motion vector list for normal inter mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list and adds a motion vector difference (MVD) to the specified prediction motion vector, to determine a motion vector, thereby deriving the motion vector. Decoder  200  subsequently performs the process in S 206 . 
     When selecting a merge mode as the inter prediction mode (merge mode in step S 201 ), decoder  200  derives a motion vector for merge mode (step S 203 ). In step S 203 , decoder  200  refers to a motion vector of a processed block neighboring the current block, obtains a prediction motion vector, and creates a prediction motion vector list for merge mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list and determines the specified prediction motion vector as a motion vector, thereby deriving the motion vector. 
     Next, decoder  200  performs a provisional motion compensation (MC) process for DMVR process on the current block (step S 204 ). Here, decoder  200  generates a provisional prediction image. 
     Subsequently, decoder  200  performs a DMVR process on the current block and corrects the motion vector (step S 205 ). 
     Decoder  200  then performs a motion compensation (MC) process on the current block using the motion vector derived in step S 202  or the motion vector corrected in step S 205  (step S 206 ). Here, decoder  200  generates a prediction image. 
     Subsequently, decoder  200  determines whether to apply an LIC process to the current block (step S 207 ). 
     When determining that the LIC process is to be applied to the current block (Yes in step S 207 ), decoder  200  derives an LIC parameter using the prediction image generated in step S 206  (step S 211 ). 
     Next, decoder  200  corrects the prediction image using the LIC process (step S 212 ). 
     When determining that the LIC process is not to be applied to the current block (No in step S 207 ), decoder  200  determines whether to apply a BIO process to the current block (step S 208 ). 
     When determining that the BIO process is to be applied to the current block (Yes in step S 208 ), decoder  200  derives a BIO parameter using the prediction image generated in step S 206  (step S 209 ). 
     Subsequently, decoder  200  corrects the prediction image using the BIO process (step S 210 ), and determines the corrected prediction image as a final prediction image. 
     When determining that the BIO process is not to be applied to the current block (No in step S 208 ), decoder  200  skips steps S 209  and S 210 . 
     Decoder  200  then ends the loop performed per prediction block unit (step S 213 ). 
     In the first example described with reference to  FIG. 49 , an OBMC process is additionally performed, but in the second example described with reference to  FIG. 52 , the OBMC process is not performed. This is to reduce the number of processes related to a feedback for a reconstructed image of a block neighboring the current block which are performed for LIC parameter derivation. 
     Note that, in the second example, a DMVR process is applied in the case where decoder  200  has selected a merge mode in step S 201 . However, applying and not applying a DMVR process may be switched according to a condition such as a prediction mode, a prediction direction, or a block size. 
     In the second example, although other process is not performed after a prediction image correction process using a BIO process or an LIC process, an OBMC process may be additionally applied when decoder  200  determines not to apply the LIC process to the current block, as illustrated in the first example. Alternatively another process other than the OBMC process may be applied when decoder  200  determines not to apply the LIC process to the current block. Here, another process other than the OBMC process may be a BIO process. 
     The flow of the processes described with reference to  FIG. 52  is one example, and one or more of the processes illustrated therein may be removed, or a process or a condition-based determination not illustrated therein may be added. 
     Although the operation performed by decoder  200  is described with reference to  FIG. 52 , “decoding” may read “encoding”. In such a case, “decoding, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. Alternatively, “parsing, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. 
     [Advantageous Effects of Second Example of Inter Prediction Process] 
     With the configuration illustrated in the second example described with reference to  FIG. 50  through  FIG. 52 , the number of processes related to a feedback for a reconstructed image of a block neighboring a current block to be processed, which are performed for LIC parameter derivation, will be greatly reduced compared to the first example. Accordingly, decoder  200  is capable of reducing a processing time required for stages including an LIC process in pipeline control. In the second example, a waiting time until stage processing starts in pipeline control, which is generated with the configuration according to the first example, is reduced. Accordingly, decoder  200  is highly capable of completing the processing of all of blocks in a picture within a processing time assigned to one picture. 
     [Third Example of Inter Prediction Process] 
       FIG. 53  is a flow chart illustrating a flow of an inter prediction process in the third example of the pipeline configuration for the decoder according to the embodiment. The following description provides only a difference between the second and third examples and similarities therebetween will be omitted. 
     The difference between the third example and the second example is as follows. In the second example, decoder  200  applies either an LIC process or a BIO process to a current block to be processed after motion compensation is performed in step S 206 , whereas the third example shows a case where decoder  200  applies both the LIC process and the BIO process to the current block. 
     First, decoder  200  starts a loop performed per prediction block unit (step S 300 ). 
     Next, decoder  200  selects an inter prediction mode from among a plurality of modes (e.g., a normal inter mode, a merge mode, etc.) (step S 301 ). 
     When selecting a normal inter mode as the inter prediction mode (normal inter mode at step S 301 ), decoder  200  derives a motion vector for normal inter mode (step S 302 ). In step S 302 , decoder  200  refers to a motion vector of a processed block neighboring a current block to be processed, obtains a prediction motion vector, and creates a prediction motion vector list for normal inter mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list and adds a motion vector difference (MVD) to the specified prediction motion vector, to determine a motion vector, thereby deriving the motion vector. Decoder  200  subsequently performs the process in S 306 . 
     When selecting a merge mode as the inter prediction mode (merge mode in step S 301 ), decoder  200  derives a motion vector for merge mode (step S 303 ). In step S 303 , decoder  200  refers to a motion vector of a processed block neighboring the current block, obtains a prediction motion vector, and creates a prediction motion vector list for merge mode. Decoder  200  then specifies one prediction motion vector from the created prediction motion vector list, and determines the specified prediction motion vector as a motion vector, thereby deriving the motion vector. 
     Next, decoder  200  performs a provisional motion compensation (MC) process for DMVR process on the current block (step S 304 ). Here, decoder  200  generates a provisional prediction image. 
     Subsequently, decoder  200  performs a DMVR process on the current block and corrects the motion vector (step S 305 ). 
     Decoder  200  then performs a motion compensation (MC) process on the current block using the motion vector derived in step S 302  or the motion vector corrected in step S 305  (step S 306 ). Here, decoder  200  generates a prediction image. 
     Next, decoder  200  determines whether to apply a BIO process to the current block (step S 307 ). 
     When determining that the BIO process is to be applied to the current block (Yes in step S 307 ), decoder  200  derives a BIO parameter using the prediction image generated in step S 306  (step S 308 ). 
     When determining that the BIO process is not to be applied to the current block (No in step S 307 ), decoder  200  sets a default value for a BIO parameter. The default value set here is a value such that a result obtained in the case of performing correction using the BIO process with the use of the default value on the current block is same as a result obtained in the case of not performing the correction using the BIO process on the current block. 
     Decoder  200  also determines whether to apply an LIC process to the current block (step S 309 ). Decoder  200  may perform the process in step S 309  and the process in step S 307  in parallel. 
     When determining that the LIC process is to be applied to the current block (Yes in step S 309 ), decoder  200  derives an LIC parameter using the prediction image generated in step S 306  (step S 310 ). 
     Subsequently, decoder  200  corrects the prediction image using the LIC process (step S 311 ). 
     Next, decoder  200  corrects the prediction image using the BIO process with the use of the BIO parameter derived in step S 308  (step S 312 ). In the case where decoder  200  has performed the LIC process, the prediction image corrected using the LIC process is a prediction image to be input. In the case otherwise, the prediction image generated in step S 306  is the prediction image to be input. 
     Decoder  200  then corrects the prediction image using the BIO process. When determining that the BIO process is not to be applied to the current block in step S 307 , decoder  200  does not need to correct the prediction image using the BIO process. 
     In other words, combinations each being a pair of application/non-application of a BIO process and application/non-application of an LIC process are as follows: 
     (1) not applying a BIO process and not applying an LIC process: a prediction image is not corrected; 
     (2) applying a BIO process and not applying an LIC process: a prediction image is corrected using the BIO process only; 
     (3) not applying a BIO process and applying an LIC process: a prediction image using the LIC process only; and 
     (4) applying a BIO process and applying an LIC process: a prediction image is corrected using the LIC process and is further corrected using the BIO process. 
     Subsequently, decoder  200  ends the loop performed per prediction block unit (step S 313 ). 
     Decoder  200  ends the operation here. 
     Note that the flow of the processes described with reference to  FIG. 53  is one example, and one or more of the processes illustrated therein may be removed, or a process or a condition-based determination not illustrated therein may be added. 
     Although the operation performed by decoder  200  is described with reference to  FIG. 53 , “decoding” may read “encoding”. In such a case, “decoding, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. Alternatively, “parsing, from a bitstream, a signal required for processing performed by decoder  200 ” should read “encoding, into a bitstream, a signal required for processing performed by encoder  100 ”. 
       FIG. 54  is a diagram illustrating the details of a BIO process when a prediction image that has been corrected using an LIC process is further corrected in the third example of the pipeline configuration for the decoder according to the embodiment. 
     First, decoder  200  derives a gradient value (G x , G y ) and a prediction image difference value (ΔI) using Equation 1. I 0  denotes a prediction image of Ref0 and I 1  denotes a prediction image of Ref1. I x   0  denotes a gradient image in direction x generated from the prediction image of Ref0 and I x   1  denotes a gradient image in direction x generated from the prediction image of Ref1. I y   0  denotes a gradient image in direction y generated from the prediction image of Ref0 and I y   1  denotes a gradient image in direction y generated from the prediction image of Ref1. 
     Subsequently, decoder  200  derives, for each sub-block using Equation 2, a median value using the gradient value and the prediction image difference value that are derived using Equation 1. A median value is derived for each sub-block by using weight w, and the gradient values and prediction image difference values of pixels corresponding to a pixel area in a range specified by Decoder  200  then derives a local motion estimation value (u, v), for each sub-block using Equation 3, with the use of the median values derived using the process presented by Equation 2. Furthermore, decoder  200  derives a correction value (b) per pixel using Equation 4. 
     Lastly, decoder  200  generates a corrected prediction image (prediction sample) from the prediction images (I 0  and I 1 ) and the correction value (b), using Equation 5. 
     Some of the processes presented by Equation 1 through Equation 5 correspond to a BIO parameter derivation process shown in  FIG. 53 , and the other/others of the processes corresponds/correspond to the prediction image correction process using a BIO process, which is shown in  FIG. 53 . It may be defined, for example, that the processes presented by Equation 1 through Equation 3 correspond to the BIO parameter derivation process while the processes presented by Equations 4 and 5 correspond to the prediction image correction process using a BIO process. In this case, a BIO parameter is a local motion estimation value (u, v). When decoder  200  applies an LIC process to the current block in the process shown in  FIG. 53 , gradient images (I x   0 , I x   1 , I y   0 , I y   1 ) in Equation 4 and prediction images (I 0  and I 1 ) in Equation 5 are derived from prediction images corrected using the LIC process. 
     Alternatively, it may be defined that the processes presented by Equation 1 through Equation 4 correspond to the BIO parameter derivation process while the process presented by Equation 5 corresponds to the prediction image correction process using a BIO process. In this case, a BIO parameter is a correction value b). When decoder  200  applies an LIC process to the current block in the process shown in  FIG. 53 , only prediction images (I 0  and I 1 ) in Equation 5 are prediction images corrected using the LIC process. 
     Note that decoder  200  may be configured to perform the processes presented by Equation 4 and Equation 5 and at the same time perform correction using an LIC process, instead of performing, in advance, the correction using an LIC process on prediction images to be used in Equation 4 and Equation 5. 
     Note that the above-described arithmetic equations are examples, and one or more of the arithmetic equations may be omitted or simplified, or some of the arithmetic equations may be expressed as one arithmetic equation or replaced by a different arithmetic equation, or a different arithmetic equation may be added, as long as the same advantageous effects can be attained. 
     Note that encoder  100  may be replaced with decoder  200  in the description provided with reference to  FIG. 54 . 
     [Advantageous Effects of Third Example of Inter Prediction Process] 
     The configuration described with reference to  FIG. 53  and  FIG. 54  enables decoder  200  to further apply an LIC process to a prediction image while maintaining the pipeline configuration described in the second example even when a BIO process is applied to the prediction image. Accordingly, decoder  200  is highly capable of further enhancing decoding efficiency without affecting the processing performance of decoder  200 . In other words, decoder  200  is capable of enhancing decoding efficiency without increasing the processing performance of decoder  200 . Namely with the configuration described in the third example, there is no need for decoder  200  to increase the processing performance thereof to enhance decoding efficiency. 
     Note that “decoding” may read “encoding” in the description provided with reference to  FIG. 47  through  FIG. 54 . 
     [Implementations] 
       FIG. 55  is a flow chart illustrating an operation example of the encoder according to the embodiment. Specifically, encoder  100  includes circuitry and memory, and the circuitry in encoder  100  performs the operation shown in  FIG. 55 , using the memory in encoder  100 . The circuitry and memory included in encoder  100  correspond to processor a1 and memory a2 illustrated in  FIG. 40 , respectively. 
     When performing, in an inter prediction process, a correction process which is an LIC process for a prediction image, encoder  100  firstly performs the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process (step S 400 ). 
     Next, encoder  100  determines the prediction image subjected to the correction process in step S 400  as a final prediction image (step S 401 ). Encoder  100  does not apply another correction process other than the correction process performed in step S 400 , to the prediction image on which the correction process is performed in step S 400 . 
     Moreover, in encoder  100 , the motion vector finally derived in the stage before the correction process performed in step S 400  may be a motion vector corrected using a DMVR process when an inter prediction mode in the inter prediction process is a merge mode. 
     In a pipeline processing, the circuitry may perform in parallel (i) a process of deriving a correction parameter used in an LIC process with reference to a reconstructed image of a processed block neighboring a current block to be processed and a process of correcting a prediction image using the correction parameter, and (ii) a process of generating a reconstructed image by adding the prediction image to a residual image. 
       FIG. 56  is a flow chart illustrating an operation example of the decoder according to the embodiment. Specifically, decoder  200  includes circuitry and memory and the circuitry in decoder  200  performs the operation shown in  FIG. 56 , using the memory in decoder  200 . The circuitry and memory included in decoder  200  correspond to processor b1 and memory b2, respectively illustrated in  FIG. 46 . 
     When performing, in an inter prediction process, a correction process which is an LIC process for a prediction image, decoder  200  firstly performs the correction process on a prediction image generated using a motion vector finally derived in a stage before the correction process (step S 500 ). 
     Next, decoder  200  determines the prediction image subjected to the correction process in step S 500  as a final prediction image (step S 501 ). Decoder  200  does not apply another correction process other than the correction process performed in step S 500 , to the prediction image on which the correction process is performed in step S 500 . 
     Moreover, in decoder  200 , the motion vector finally derived in the stage before the correction process performed in step S 500  may be a motion vector corrected using a DMVR process when an inter prediction mode in the inter prediction process is a merge mode. 
     In a pipeline processing, the circuitry may perform in parallel (i) a process of deriving a correction parameter to be used in an LIC process with reference to a reconstructed image of a processed block neighboring a current block to be processed and a process of correcting a prediction image using the correction parameter, and (ii) a process of generating a reconstructed image by adding the prediction image to a residual image. 
     [Supplementary Information] 
     Encoder  100  and decoder  200  according to the present embodiment may be used as an image encoder and an image decoder, respectively, or may be used as a video encoder and a video decoder, respectively. 
     In each of the aforementioned embodiments, each of the elements may be configured of dedicated hardware or may be implemented by executing a software program suitable for the element. Each of the elements may be implemented by a program executor such as a CPU or a processor reading and executing a software program recorded on a recording medium such as a hard disc or a semiconductor memory. 
     Specifically, encoder  100  and decoder  200  may each include processing circuitry, and storage electrically coupled to the processing circuitry and accessible from the processing circuitry. For example, the processing circuitry corresponds to processor a1 or b1 and the storage corresponds to memory a2 or b2. 
     The processing circuitry includes at least one of the dedicated hardware and the program executor, and performs processing using the storage. If the processing circuitry includes a program executor, the storage stores a software program to be executed by the program executor. 
     The software which implements encoder  100  or decoder  200  according to each of the aforementioned embodiments, for instance, is a program as follows. 
     Namely, the program may cause a computer to execute an encoding method for encoding a moving picture using an inter prediction process that includes: when, in the inter prediction process, a correction process which is an LIC process for a prediction image is to be performed, performing the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process, and after the correction process, determining, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     Alternatively, the program may cause a computer to execute a decoding method for decoding a moving picture using an inter prediction process that includes: when, in the inter prediction process, a correction process which is an LIC process for a prediction image is to be performed, performing the correction process on a prediction image generated using a finally-derived motion vector that is finally derived in a stage before the correction process, and after the correction process, determining, as a final prediction image, the prediction image subjected to the correction process, without applying other correction process on the prediction image. 
     The elements may be circuits as described above. These circuits may constitute one circuitry as a whole, or may be separate circuits. Each element may be implemented by a general-purpose processor or by a dedicated processor. 
     Processing performed by a specific element may be performed by a different element. The order of performing processes may be changed or the processes may be performed in parallel. An encoder/decoder may include encoder  100  and decoder  200 . 
     The ordinal numbers such as the first and the second used in the description may be switched where necessary. A new ordinal number may be provided for or any of the existing ordinal numbers may be removed from the elements. 
     The above has given a description of aspects of encoder  100  and decoder  200  based on the embodiments, yet the aspects of encoder  100  and decoder  200  are not limited to the embodiments. The aspects of encoder  100  and decoder  200  may also encompass various modifications that may be conceived by those skilled in the art to the embodiments, and embodiments achieved by combining elements in different embodiments, without departing from the scope of the present disclosure. 
     This aspect may be implemented in combination with at least one or more of the other aspects according to the present disclosure. In addition, one or more of the processes in the flow charts, one or more of the constituent elements of the apparatuses, and part of the syntax described in this aspect may be implemented in combination with other aspects. 
     Embodiment 2 
     [Implementations and Applications] 
     As described in each of the above embodiments, each functional or operational block may typically be realized as an MPU (micro processing unit) and memory, for example. Moreover, processes performed by each of the functional blocks may be realized as a program execution unit, such as a processor which reads and executes software (a program) recorded on a recording medium such as ROM. The software may be distributed. The software may be recorded on a variety of recording media such as semiconductor memory. Note that each functional block can also be realized as hardware (dedicated circuit). Various combinations of hardware and software may be employed. 
     The processing described in each of the embodiments may be realized via integrated processing using a single apparatus (system), and, alternatively, may be realized via decentralized processing using a plurality of apparatuses. Moreover, the processor that executes the above-described program may be a single processor or a plurality of processors. In other words, integrated processing may be performed, and, alternatively, decentralized processing may be performed. 
     Embodiments of the present disclosure are not limited to the above exemplary embodiments; various modifications may be made to the exemplary embodiments, the results of which are also included within the scope of the embodiments of the present disclosure. 
     Next, application examples of the moving picture encoding method (image encoding method) and the moving picture decoding method (image decoding method) described in each of the above embodiments will be described, as well as various systems that implement the application examples. Such a system may be characterized as including an image encoder that employs the image encoding method, an image decoder that employs the image decoding method, or an image encoder-decoder that includes both the image encoder and the image decoder. Other configurations of such a system may be modified on a case-by-case basis. 
     [Usage Examples] 
       FIG. 56  illustrates an overall configuration of content providing system ex 100  suitable for implementing a content distribution service. The area in which the communication service is provided is divided into cells of desired sizes, and base stations ex 106 , ex 107 , ex 108 , ex 109 , and ex 110 , which are fixed wireless stations in the illustrated example, are located in respective cells. 
     In content providing system ex 100 , devices including computer ex 111 , gaming device ex 112 , camera ex 113 , home appliance ex 114 , and smartphone ex 115  are connected to internet ex 101  via internet service provider ex 102  or communications network ex 104  and base stations ex 106  through ex 110 . Content providing system ex 100  may combine and connect any combination of the above devices. In various implementations, the devices may be directly or indirectly connected together via a telephone network or near field communication, rather than via base stations ex 106  through ex 110 . Further, streaming server ex 103  may be connected to devices including computer ex 111 , gaming device ex 112 , camera ex 113 , home appliance ex 114 , and smartphone ex 115  via, for example, internet ex 101 . Streaming server ex 103  may also be connected to, for example, a terminal in a hotspot in airplane ex 117  via satellite ex 116 . 
     Note that instead of base stations ex 106  through ex 110 , wireless access points or hotspots may be used. Streaming server ex 103  may be connected to communications network ex 104  directly instead of via internet ex 101  or internet service provider ex 102 , and may be connected to airplane ex 117  directly instead of via satellite ex 116 . 
     Camera ex 113  is a device capable of capturing still images and video, such as a digital camera. Smartphone ex 115  is a smartphone device, cellular phone, or personal handy-phone system (PHS) phone that can operate under the mobile communications system standards of the 2G, 3G, 3.9G, and 4G systems, as well as the next-generation  50  system. 
     Home appliance ex 114  is, for example, a refrigerator or a device included in a home fuel cell cogeneration system. 
     In content providing system ex 100 , a terminal including an image and/or video capturing function is capable of, for example, live streaming by connecting to streaming server ex 103  via, for example, base station ex 106 . When live streaming, a terminal (e.g., computer ex 111 , gaming device ex 112 , camera ex 113 , home appliance ex 114 , smartphone ex 115 , or a terminal in airplane ex 117 ) may perform the encoding processing described in the above embodiments on still-image or video content captured by a user via the terminal, may multiplex video data obtained via the encoding and audio data obtained by encoding audio corresponding to the video, and may transmit the obtained data to streaming server ex 103 . In other words, the terminal functions as the image encoder according to one aspect of the present disclosure. 
     Streaming server ex 103  streams transmitted content data to clients that request the stream. Client examples include computer ex 111 , gaming device ex 112 , camera ex 113 , home appliance ex 114 , smartphone ex 115 , and terminals inside airplane ex 117 , which are capable of decoding the above-described encoded data. Devices that receive the streamed data may decode and reproduce the received data. In other words, the devices may each function as the image decoder, according to one aspect of the present disclosure. 
     [Decentralized Processing] 
     Streaming server ex 103  may be realized as a plurality of servers or computers between which tasks such as the processing, recording, and streaming of data are divided. For example, streaming server ex 103  may be realized as a content delivery network (CDN) that streams content via a network connecting multiple edge servers located throughout the world. In a CDN, an edge server physically near the client may be dynamically assigned to the client. Content is cached and streamed to the edge server to reduce load times. In the event of, for example, some type of error or change in connectivity due, for example, to a spike in traffic, it is possible to stream data stably at high speeds, since it is possible to avoid affected parts of the network by, for example, dividing the processing between a plurality of edge servers, or switching the streaming duties to a different edge server and continuing streaming. 
     Decentralization is not limited to just the division of processing for streaming; the encoding of the captured data may be divided between and performed by the terminals, on the server side, or both. In one example, in typical encoding, the processing is performed in two loops. The first loop is for detecting how complicated the image is on a frame-by-frame or scene-by-scene basis, or detecting the encoding load. The second loop is for processing that maintains image quality and improves encoding efficiency. For example, it is possible to reduce the processing load of the terminals and improve the quality and encoding efficiency of the content by having the terminals perform the first loop of the encoding and having the server side that received the content perform the second loop of the encoding. In such a case, upon receipt of a decoding request, it is possible for the encoded data resulting from the first loop performed by one terminal to be received and reproduced on another terminal in approximately real time. This makes it possible to realize smooth, real-time streaming. 
     In another example, camera ex 113  or the like extracts a feature amount (an amount of features or characteristics) from an image, compresses data related to the feature amount as metadata, and transmits the compressed metadata to a server. For example, the server determines the significance of an object based on the feature amount and changes the quantization accuracy accordingly to perform compression suitable for the meaning (or content significance) of the image. Feature amount data is particularly effective in improving the precision and efficiency of motion vector prediction during the second compression pass performed by the server. Moreover, encoding that has a relatively low processing load, such as variable length coding (VLC), may be handled by the terminal, and encoding that has a relatively high processing load, such as context-adaptive binary arithmetic coding (CABAC), may be handled by the server. 
     In yet another example, there are instances in which a plurality of videos of approximately the same scene are captured by a plurality of terminals in, for example, a stadium, shopping mall, or factory. In such a case, for example, the encoding may be decentralized by dividing processing tasks between the plurality of terminals that captured the videos and, if necessary, other terminals that did not capture the videos, and the server, on a per-unit basis. The units may be, for example, groups of pictures (GOP), pictures, or tiles resulting from dividing a picture. This makes it possible to reduce load times and achieve streaming that is closer to real time. 
     Since the videos are of approximately the same scene, management and/or instructions may be carried out by the server so that the videos captured by the terminals can be cross-referenced. Moreover, the server may receive encoded data from the terminals, change the reference relationship between items of data, or correct or replace pictures themselves, and then perform the encoding. This makes it possible to generate a stream with increased quality and efficiency for the individual items of data. 
     Furthermore, the server may stream video data after performing transcoding to convert the encoding format of the video data. For example, the server may convert the encoding format from MPEG to VP (e.g., VP9), may convert H.264 to H.265, etc. 
     In this way, encoding can be performed by a terminal or one or more servers. Accordingly, although the device that performs the encoding is referred to as a “server” or “terminal” in the following description, some or all of the processes performed by the server may be performed by the terminal, and likewise some or all of the processes performed by the terminal may be performed by the server. This also applies to decoding processes. 
     [3D, Multi-Angle] 
     There has been an increase in usage of images or videos combined from images or videos of different scenes concurrently captured, or of the same scene captured from different angles, by a plurality of terminals such as camera ex 113  and/or smartphone ex 115 . Videos captured by the terminals may be combined based on, for example, the separately obtained relative positional relationship between the terminals, or regions in a video having matching feature points. 
     In addition to the encoding of two-dimensional moving pictures, the server may encode a still image based on scene analysis of a moving picture, either automatically or at a point in time specified by the user, and transmit the encoded still image to a reception terminal. Furthermore, when the server can obtain the relative positional relationship between the video capturing terminals, in addition to two-dimensional moving pictures, the server can generate three-dimensional geometry of a scene based on video of the same scene captured from different angles. The server may separately encode three-dimensional data generated from, for example, a point cloud and, based on a result of recognizing or tracking a person or object using three-dimensional data, may select or reconstruct and generate a video to be transmitted to a reception terminal, from videos captured by a plurality of terminals. 
     This allows the user to enjoy a scene by freely selecting videos corresponding to the video capturing terminals, and allows the user to enjoy the content obtained by extracting a video at a selected viewpoint from three-dimensional data reconstructed from a plurality of images or videos. Furthermore, as with video, sound may be recorded from relatively different angles, and the server may multiplex audio from a specific angle or space with the corresponding video, and transmit the multiplexed video and audio. 
     In recent years, content that is a composite of the real world and a virtual world, such as virtual reality (VR) and augmented reality (AR) content, has also become popular. In the case of VR images, the server may create images from the viewpoints of both the left and right eyes, and perform encoding that tolerates reference between the two viewpoint images, such as multi-view coding (MC), and, alternatively, may encode the images as separate streams without referencing. When the images are decoded as separate streams, the streams may be synchronized when reproduced, so as to recreate a virtual three-dimensional space in accordance with the viewpoint of the user. 
     In the case of AR images, the server may superimpose virtual object information existing in a virtual space onto camera information representing a real-world space, based on a three-dimensional position or movement from the perspective of the user. The decoder may obtain or store virtual object information and three-dimensional data, generate two-dimensional images based on movement from the perspective of the user, and then generate superimposed data by seamlessly connecting the images. Alternatively, the decoder may transmit, to the server, motion from the perspective of the user in addition to a request for virtual object information. The server may generate superimposed data based on three-dimensional data stored in the server in accordance with the received motion, and encode and stream the generated superimposed data to the decoder. Note that superimposed data typically includes, in addition to RGB values, an a value indicating transparency, and the server sets the a value for sections other than the object generated from three-dimensional data to, for example, 0, and may perform the encoding while those sections are transparent. Alternatively, the server may set the background to a determined RGB value, such as a chroma key, and generate data in which areas other than the object are set as the background. The determined RGB value may be predetermined. 
     Decoding of similarly streamed data may be performed by the client (e.g., the terminals), on the server side, or divided therebetween. In one example, one terminal may transmit a reception request to a server, the requested content may be received and decoded by another terminal, and a decoded signal may be transmitted to a device having a display. It is possible to reproduce high image quality data by decentralizing processing and appropriately selecting content regardless of the processing ability of the communications terminal itself. In yet another example, while a TV, for example, is receiving image data that is large in size, a region of a picture, such as a tile obtained by dividing the picture, may be decoded and displayed on a personal terminal or terminals of a viewer or viewers of the TV. This makes it possible for the viewers to share a big-picture view as well as for each viewer to check his or her assigned area, or inspect a region in further detail up close. 
     In situations in which a plurality of wireless connections are possible over near, mid, and far distances, indoors or outdoors, it may be possible to seamlessly receive content using a streaming system standard such as MPEG-DASH. The user may switch between data in real time while freely selecting a decoder or display apparatus including the user&#39;s terminal, displays arranged indoors or outdoors, etc. Moreover, using, for example, information on the position of the user, decoding can be performed while switching which terminal handles decoding and which terminal handles the displaying of content. This makes it possible to map and display information, while the user is on the move in route to a destination, on the wall of a nearby building in which a device capable of displaying content is embedded, or on part of the ground. Moreover, it is also possible to switch the bit rate of the received data based on the accessibility to the encoded data on a network, such as when encoded data is cached on a server quickly accessible from the reception terminal, or when encoded data is copied to an edge server in a content delivery service. 
     [Scalable Encoding] 
     The switching of content will be described with reference to a scalable stream, illustrated in  FIG. 57 , which is compression coded via implementation of the moving picture encoding method described in the above embodiments. The server may have a configuration in which content is switched while making use of the temporal and/or spatial scalability of a stream, which is achieved by division into and encoding of layers, as illustrated in  FIG. 57 . Note that there may be a plurality of individual streams that are of the same content but different quality. In other words, by determining which layer to decode based on internal factors, such as the processing ability on the decoder side, and external factors, such as communication bandwidth, the decoder side can freely switch between low resolution content and high resolution content while decoding. For example, in a case in which the user wants to continue watching, for example at home on a device such as a TV connected to the internet, a video that the user had been previously watching on smartphone ex 115  while on the move, the device can simply decode the same stream up to a different layer, which reduces the server side load. 
     Furthermore, in addition to the configuration described above, in which scalability is achieved as a result of the pictures being encoded per layer, with the enhancement layer being above the base layer, the enhancement layer may include metadata based on, for example, statistical information on the image. The decoder side may generate high image quality content by performing super-resolution imaging on a picture in the base layer based on the metadata. Super-resolution imaging may improve the SN ratio while maintaining resolution and/or increasing resolution. Metadata includes information for identifying a linear or a non-linear filter coefficient, as used in super-resolution processing, or information identifying a parameter value in filter processing, machine learning, or a least squares method used in super-resolution processing. 
     Alternatively, a configuration may be provided in which a picture is divided into, for example, tiles in accordance with, for example, the meaning of an object in the image. On the decoder side, only a partial region is decoded by selecting a tile to decode. Further, by storing an attribute of the object (person, car, ball, etc.) and a position of the object in the video (coordinates in identical images) as metadata, the decoder side can identify the position of a desired object based on the metadata and determine which tile or tiles include that object. For example, as illustrated in  FIG. 58 , metadata may be stored using a data storage structure different from pixel data, such as an SEI (supplemental enhancement information) message in HEVC. This metadata indicates, for example, the position, size, or color of the main object. 
     Metadata may be stored in units of a plurality of pictures, such as stream, sequence, or random access units. The decoder side can obtain, for example, the time at which a specific person appears in the video, and by fitting the time information with picture unit information, can identify a picture in which the object is present, and can determine the position of the object in the picture. 
     [Web Page Optimization] 
       FIG. 59  illustrates an example of a display screen of a web page on computer ex 111 , for example.  FIG. 60  illustrates an example of a display screen of a web page on smartphone ex 115 , for example. As illustrated in  FIG. 59  and  FIG. 60 , a web page may include a plurality of image links that are links to image content, and the appearance of the web page may differ depending on the device used to view the web page. When a plurality of image links are viewable on the screen, until the user explicitly selects an image link, or until the image link is in the approximate center of the screen or the entire image link fits in the screen, the display apparatus (decoder) may display, as the image links, still images included in the content or I pictures; may display video such as an animated gif using a plurality of still images or I pictures; or may receive only the base layer, and decode and display the video. 
     When an image link is selected by the user, the display apparatus performs decoding while, for example, giving the highest priority to the base layer. Note that if there is information in the HTML code of the web page indicating that the content is scalable, the display apparatus may decode up to the enhancement layer. Further, in order to guarantee real-time reproduction, before a selection is made or when the bandwidth is severely limited, the display apparatus can reduce delay between the point in time at which the leading picture is decoded and the point in time at which the decoded picture is displayed (that is, the delay between the start of the decoding of the content to the displaying of the content) by decoding and displaying only forward reference pictures (I picture, P picture, forward reference B picture). Still further, the display apparatus may purposely ignore the reference relationship between pictures, and coarsely decode all B and P pictures as forward reference pictures, and then perform normal decoding as the number of pictures received over time increases. 
     [Autonomous Driving] 
     When transmitting and receiving still image or video data such as two- or three-dimensional map information for autonomous driving or assisted driving of an automobile, the reception terminal may receive, in addition to image data belonging to one or more layers, information on, for example, the weather or road construction as metadata, and associate the metadata with the image data upon decoding. Note that metadata may be assigned per layer and, alternatively, may simply be multiplexed with the image data. 
     In such a case, since the automobile, drone, airplane, etc., containing the reception terminal is mobile, the reception terminal may seamlessly receive and perform decoding while switching between base stations among base stations ex 106  through ex 110  by transmitting information indicating the position of the reception terminal. Moreover, in accordance with the selection made by the user, the situation of the user, and/or the bandwidth of the connection, the reception terminal may dynamically select to what extent the metadata is received, or to what extent the map information, for example, is updated. 
     In content providing system ex 100 , the client may receive, decode, and reproduce, in real time, encoded information transmitted by the user. 
     [Streaming of Individual Content] 
     In content providing system ex 100 , in addition to high image quality, long content distributed by a video distribution entity, unicast or multicast streaming of low image quality, and short content from an individual are also possible. Such content from individuals is likely to further increase in popularity. The server may first perform editing processing on the content before the encoding processing, in order to refine the individual content. This may be achieved using the following configuration, for example. 
     In real time while capturing video or image content, or after the content has been captured and accumulated, the server performs recognition processing based on the raw data or encoded data, such as capture error processing, scene search processing, meaning analysis, and/or object detection processing. Then, based on the result of the recognition processing, the server—either when prompted or automatically—edits the content, examples of which include: correction such as focus and/or motion blur correction; removing low-priority scenes such as scenes that are low in brightness compared to other pictures, or out of focus; object edge adjustment; and color tone adjustment. The server encodes the edited data based on the result of the editing. It is known that excessively long videos tend to receive fewer views. Accordingly, in order to keep the content within a specific length that scales with the length of the original video, the server may, in addition to the low-priority scenes described above, automatically clip out scenes with low movement, based on an image processing result. Alternatively, the server may generate and encode a video digest based on a result of an analysis of the meaning of a scene. 
     There may be instances in which individual content may include content that infringes a copyright, moral right, portrait rights, etc. Such instance may lead to an unfavorable situation for the creator, such as when content is shared beyond the scope intended by the creator. Accordingly, before encoding, the server may, for example, edit images so as to blur faces of people in the periphery of the screen or blur the inside of a house, for example. Further, the server may be configured to recognize the faces of people other than a registered person in images to be encoded, and when such faces appear in an image, may apply a mosaic filter, for example, to the face of the person. Alternatively, as pre- or post-processing for encoding, the user may specify, for copyright reasons, a region of an image including a person or a region of the background to be processed. The server may process the specified region by, for example, replacing the region with a different image, or blurring the region. If the region includes a person, the person may be tracked in the moving picture, and the person&#39;s head region may be replaced with another image as the person moves. 
     Since there is a demand for real-time viewing of content produced by individuals, which tends to be small in data size, the decoder may first receive the base layer as the highest priority, and perform decoding and reproduction, although this may differ depending on bandwidth. When the content is reproduced two or more times, such as when the decoder receives the enhancement layer during decoding and reproduction of the base layer, and loops the reproduction, the decoder may reproduce a high image quality video including the enhancement layer. If the stream is encoded using such scalable encoding, the video may be low quality when in an unselected state or at the start of the video, but it can offer an experience in which the image quality of the stream progressively increases in an intelligent manner. This is not limited to just scalable encoding; the same experience can be offered by configuring a single stream from a low quality stream reproduced for the first time and a second stream encoded using the first stream as a reference. 
     [Other Implementation and Application Examples] 
     The encoding and decoding may be performed by LSI (large scale integration circuitry) ex 500  (see  FIG. 56 ), which is typically included in each terminal. LSI ex 500  may be configured of a single chip or a plurality of chips. Software for encoding and decoding moving pictures may be integrated into some type of a recording medium (such as a CD-ROM, a flexible disk, or a hard disk) that is readable by, for example, computer ex 111 , and the encoding and decoding may be performed using the software. Furthermore, when smartphone ex 115  is equipped with a camera, the video data obtained by the camera may be transmitted. In this case, the video data may be coded by LSI ex 600  included in smartphone ex 115 . 
     Note that LSI ex 500  may be configured to download and activate an application. In such a case, the terminal first determines whether it is compatible with the scheme used to encode the content, or whether it is capable of executing a specific service. When the terminal is not compatible with the encoding scheme of the content, or when the terminal is not capable of executing a specific service, the terminal may first download a codec or application software and then obtain and reproduce the content. 
     Aside from the example of content providing system ex 100  that uses internet ex 101 , at least the moving picture encoder (image encoder) or the moving picture decoder (image decoder) described in the above embodiments may be implemented in a digital broadcasting system. The same encoding processing and decoding processing may be applied to transmit and receive broadcast radio waves superimposed with multiplexed audio and video data using, for example, a satellite, even though this is geared toward multicast, whereas unicast is easier with content providing system ex 100 . 
     [Hardware Configuration] 
       FIG. 61  illustrates further details of smartphone ex 115  shown in  FIG. 56 .  FIG. 62  illustrates a configuration example of smartphone ex 115 . Smartphone ex 115  includes antenna ex 450  for transmitting and receiving radio waves to and from base station ex 110 , camera ex 465  capable of capturing video and still images, and display ex 458  that displays decoded data, such as video captured by camera ex 465  and video received by antenna ex 450 . Smartphone ex 115  further includes user interface ex 466  such as a touch panel, audio output unit ex 457  such as a speaker for outputting speech or other audio, audio input unit ex 456  such as a microphone for audio input, memory ex 467  capable of storing decoded data such as captured video or still images, recorded audio, received video or still images, and mail, as well as decoded data, and slot ex 464  which is an interface for SIM ex 468  for authorizing access to a network and various data. Note that external memory may be used instead of memory ex 467 . 
     Main controller ex 460 , which may comprehensively control display ex 458  and user interface ex 466 , power supply circuit ex 461 , user interface input controller ex 462 , video signal processor ex 455 , camera interface ex 463 , display controller ex 459 , modulator/demodulator ex 452 , multiplexer/demultiplexer ex 453 , audio signal processor ex 454 , slot ex 464 , and memory ex 467  are connected via bus ex 470 . 
     When the user turns on the power button of power supply circuit ex 461 , smartphone ex 115  is powered on into an operable state, and each component is supplied with power from a battery pack. 
     Smartphone ex 115  performs processing for, for example, calling and data transmission, based on control performed by main controller ex 460 , which includes a CPU, ROM, and RAM. When making calls, an audio signal recorded by audio input unit ex 456  is converted into a digital audio signal by audio signal processor ex 454 , to which spread spectrum processing is applied by modulator/demodulator ex 452  and digital-analog conversion, and frequency conversion processing is applied by transmitter/receiver ex 451 , and the resulting signal is transmitted via antenna ex 450 . The received data is amplified, frequency converted, and analog-digital converted, inverse spread spectrum processed by modulator/demodulator ex 452 , converted into an analog audio signal by audio signal processor ex 454 , and then output from audio output unit ex 457 . In data transmission mode, text, still-image, or video data may be transmitted under control of main controller ex 460  via user interface input controller ex 462  based on operation of user interface ex 466  of the main body, for example. Similar transmission and reception processing is performed. In data transmission mode, when sending a video, still image, or video and audio, video signal processor ex 455  compression encodes, via the moving picture encoding method described in the above embodiments, a video signal stored in memory ex 467  or a video signal input from camera ex 465 , and transmits the encoded video data to multiplexer/demultiplexer ex 453 . Audio signal processor ex 454  encodes an audio signal recorded by audio input unit ex 456  while camera ex 465  is capturing a video or still image, and transmits the encoded audio data to multiplexer/demultiplexer ex 453 . Multiplexer/demultiplexer ex 453  multiplexes the encoded video data and encoded audio data using a determined scheme, modulates and converts the data using modulator/demodulator (modulator/demodulator circuit) ex 452  and transmitter/receiver ex 451 , and transmits the result via antenna ex 450 . The determined scheme may be predetermined. 
     When video appended in an email or a chat, or a video linked from a web page, is received, for example, in order to decode the multiplexed data received via antenna ex 450 , multiplexer/demultiplexer ex 453  demultiplexes the multiplexed data to divide the multiplexed data into a bitstream of video data and a bitstream of audio data, supplies the encoded video data to video signal processor ex 455  via synchronous bus ex 470 , and supplies the encoded audio data to audio signal processor ex 454  via synchronous bus ex 470 . Video signal processor ex 455  decodes the video signal using a moving picture decoding method corresponding to the moving picture encoding method described in the above embodiments, and video or a still image included in the linked moving picture file is displayed on display ex 458  via display controller ex 459 . Audio signal processor ex 454  decodes the audio signal and outputs audio from audio output unit ex 457 . Since real-time streaming is becoming increasingly popular, there may be instances in which reproduction of the audio may be socially inappropriate, depending on the user&#39;s environment. Accordingly, as an initial value, a configuration in which only video data is reproduced, i.e., the audio signal is not reproduced, may be preferable; audio may be synchronized and reproduced only when an input, such as when the user clicks video data, is received. 
     Although smartphone ex 115  was used in the above example, other implementations are conceivable: a transceiver terminal including both an encoder and a decoder; a transmitter terminal including only an encoder; and a receiver terminal including only a decoder. In the description of the digital broadcasting system, an example is given in which multiplexed data obtained as a result of video data being multiplexed with audio data is received or transmitted. The multiplexed data, however, may be video data multiplexed with data other than audio data, such as text data related to the video. Further, the video data itself rather than multiplexed data may be received or transmitted. 
     Although main controller ex 460  including a CPU is described as controlling the encoding or decoding processes, various terminals often include GPUs. Accordingly, a configuration is acceptable in which a large area is processed at once by making use of the performance ability of the GPU via memory shared by the CPU and GPU, or memory including an address that is managed so as to allow common usage by the CPU and GPU. This makes it possible to shorten encoding time, maintain the real-time nature of the stream, and reduce delay. In particular, processing relating to motion estimation, deblocking filtering, sample adaptive offset (SAO), and transformation/quantization can be effectively carried out by the GPU instead of the CPU in units of pictures, for example, all at once. 
     This aspect may be implemented in combination with at least one or more of the other aspects according to the present disclosure. In addition, one or more of the processes in the flow charts, one or more of the constituent elements of the apparatuses, and part of the syntax described in this aspect may be implemented in combination with other aspects. 
     Although only some exemplary embodiments of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to, for example, television receivers, digital video recorders, car navigation systems, mobile phones, digital cameras, digital video cameras, video conference systems, and electron mirrors.