Patent Publication Number: US-2017359577-A1

Title: Method and device for encoding or decoding multi-layer image, using interlayer prediction

Description:
TECHNICAL FIELD 
     The inventive concept relates to methods and apparatuses for improving performance of inter-layer prediction in a process of encoding or decoding a multilayer video including a plurality of layers. 
     BACKGROUND ART 
     As hardware for reproducing and storing high resolution or high quality video content is being developed and supplied, a need for a video codec for effectively encoding or decoding the high resolution or high quality video content is increasing. According to a conventional video codec, a video is encoded according to a limited encoding method based on a coding unit of a tree structure. 
     Image data of a space domain is transformed into coefficients of a frequency domain by frequency transformation. According to a video codec, an image is split into blocks having a predetermined size, discrete cosine transformation (DCT) is performed on each block, and frequency coefficients are encoded in block units, for rapid calculation of frequency transformation. Compared with image data of a space domain, coefficients of a frequency domain are easily compressed. In particular, since an image pixel value of a space domain is represented by a prediction error through inter prediction or intra prediction of a video codec, when frequency transformation is performed on the prediction error, a large amount of data may be transformed to 0. According to a video codec, an amount of data may be reduced by replacing data that is consecutively and repeatedly generated with small-sized data. 
     A multilayer video codec encodes and decodes a first layer video and at least one second layer video. Amounts of data of the first layer video and the second layer video may be reduced by removing inter-layer redundancy and temporal/spatial redundancy of the first layer video and the second layer video. 
     In the related art, whether or how to perform residual prediction of a multilayer video is determined based on whether a disparity vector is to be derived from a neighboring block of a current coding unit. 
     However, a reference picture related to another layer is always required to perform residual prediction, but syntax of whether or how to perform residual prediction is transmitted even when a reference picture related to another layer does not exist in a reference picture list of a current coding unit. Accordingly, since an unnecessary operation is performed, processing efficiency is degraded. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     Even when a reference picture on another layer different from a layer of a current picture required in a process of performing inter-layer prediction does not exist in a reference picture list related to a current coding unit, a process of unnecessarily generating or acquiring a bitstream including syntax of whether or how to perform residual prediction needs to be skipped in a process of encoding or decoding a video. 
     Technical Solution 
     According to an embodiment, there is provided a method of decoding a video including a multilayer, the method including: setting, when a reference picture for inter-layer prediction is included in a reference picture list, first information to indicate that a disparity vector is available; and performing residual prediction based on the first information and whether a disparity vector is to be derived from a neighboring block of a current coding unit. 
     According to another embodiment, there is provided an apparatus for decoding a video including a multilayer, the apparatus including a controller configured to determine whether a reference picture for inter-layer prediction is included in a reference picture list; set, when the reference picture is included in the reference picture list, first information to indicate that a disparity vector is available; and perform residual prediction based on the first information and whether a disparity vector is to be derived from a neighboring block of a current coding unit. 
     Advantageous Effects of the Invention 
     According to an embodiment, when a reference picture on another layer different from a layer of a current picture required in a process of performing inter-layer prediction does not exist in a reference picture list related to a current coding unit, since a bitstream including syntax of whether or how to perform residual prediction is not generated or acquired, an unnecessary operation may be skipped and thus an efficient video encoding or decoding process may be performed. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a block diagram of a video decoding apparatus for decoding a video including a multilayer. 
         FIG. 1B  illustrates a block diagram of a video encoding apparatus for encoding a video including a multilayer. 
         FIG. 2  illustrates a flowchart of a process of decoding a video including a multilayer by a video decoding apparatus. 
         FIG. 3A  illustrates semantics for a process of determining whether a reference picture available in inter-layer prediction is included in a reference picture list. 
         FIG. 3B  illustrates semantics for a process of setting second information. 
         FIG. 3C  illustrates semantics for a process of using a default disparity vector when a disparity vector is not to be derived from a neighboring block of a current coding unit. 
         FIG. 3D  illustrates a process of acquiring predetermined information from a bitstream or generating a bitstream including predetermined information based on first information related to availability of a disparity vector in a current coding unit. 
         FIG. 4A  illustrates a block diagram of an inter-layer video decoding apparatus. 
         FIG. 4B  illustrates a block diagram of an inter-layer video encoding apparatus. 
         FIG. 5A  illustrates an inter-layer prediction structure, according to an embodiment. 
         FIG. 5B  is a diagram illustrating multiview video frames acquired through a multiview camera and depth map frames acquired through a depth camera. 
         FIG. 6A  is a diagram illustrating an encoding tool used in an encoding or decoding process. 
         FIG. 6B  is a diagram illustrating the contents of an encoding tool according to prediction unit size, prediction mode, and color depth information. 
         FIG. 7  illustrates a block diagram of a video encoding apparatus based on coding units of a tree structure. 
         FIG. 8  illustrates a block diagram of a video decoding apparatus based on coding units of a tree structure. 
         FIG. 9  illustrates a concept of coding units. 
         FIG. 10  illustrates a block diagram of an image encoder based on coding units. 
         FIG. 11  illustrates a block diagram of an image decoder based on coding units. 
         FIG. 12  illustrates deeper coding units according to depths, and partitions. 
         FIG. 13  illustrates a relationship between a coding unit and transformation units. 
         FIG. 14  illustrates a plurality of pieces of encoding information according to depths. 
         FIG. 15  illustrates deeper coding units according to depths. 
         FIGS. 16, 17, and 18  illustrate a relationship between coding units, prediction units, and transformation units, according to an embodiment. 
         FIG. 19  illustrates a relationship between a coding unit, a prediction unit, and a transformation unit, according to encoding mode information of Table 1. 
         FIG. 20  illustrates a physical structure of a disc in which a program is stored. 
         FIG. 21  illustrates a disc drive for recording and reading a program by using the disc. 
         FIG. 22  illustrates an overall structure of a content supply system for providing a content distribution service. 
         FIGS. 23 and 24  illustrate external and internal structures of a mobile phone to which a video encoding method and a video decoding method are applied. 
         FIG. 25  illustrates a digital broadcasting system employing a communication system. 
         FIG. 26  illustrates a network structure of a cloud computing system using the video encoding apparatus and the video decoding apparatus. 
     
    
    
     BEST MODE 
     According to an embodiment, there is provided a method of decoding a video including a multilayer, the method including: setting, when a reference picture for inter-layer prediction is included in a reference picture list, first information to indicate that a disparity vector is available; and performing residual prediction based on the first information and whether a disparity vector is to be derived from a neighboring block of a current coding unit. 
     The method may further include setting, based on the first information, second information to indicate that the reference picture is available in a residual prediction process. 
     The method may further include acquiring, based on the first information, third information from a bitstream, the third information indicating whether to perform residual prediction in a current coding unit. 
     The performing of the residual prediction may include setting a disparity vector of the current coding unit by using a default disparity vector when the first information indicates that the reference picture is included in the reference picture list and a disparity vector is not to be derived from a neighboring block of the current coding unit. 
     The default disparity vector may represent a value indicating a layer including a current picture among the multilayer, and the setting of the first information may include setting the first information to a non-zero value. 
     The acquiring of the third information from the bitstream may include acquiring the third information from the bitstream when the second information indicates that the reference picture is available in residual prediction and not acquiring the third information from the bitstream when the second information does not indicate that the reference picture is available in the residual prediction. 
     The method may further include determining not to perform residual prediction when the third information represents 0 and performing the residual prediction by using a weight determined based on the third information when the third information represents a value greater than 0. 
     The method may further include: acquiring, when the first information represents a value greater than 0, fourth information from a bitstream, the fourth information indicating whether to perform depth image-based block partitioning; and performing inter-sample prediction based on the fourth information. 
     According to another embodiment, there is provided an apparatus for decoding a video including a multilayer, the apparatus including a controller configured to determine whether a reference picture for inter-layer prediction is included in a reference picture list; set, when the reference picture is included in the reference picture list, first information to indicate that a disparity vector is available; and perform residual prediction based on the first information and whether a disparity vector is to be derived from a neighboring block of a current coding unit. 
     The controller may set, based on the first information, second information to indicate that the reference picture is available in a residual prediction process. 
     The apparatus may further include an information acquirer acquiring, based on the first information, third information from a bitstream, the third information indicating whether to perform residual prediction in a current coding unit. 
     The controller may set a disparity vector of the current coding unit by using a default disparity vector when the first information indicates that the reference picture is included in the reference picture list and a disparity vector is not to be derived from a neighboring block of the current coding unit. 
     The controller may determine not to perform residual prediction when the third information represents 0 and perform residual prediction by using a weight determined based on the third information when the third information represents a value greater than 0. 
     The information acquirer may acquire, when the first information represents a value greater than 0, fourth information from a bitstream, the fourth information indicating whether to perform depth image-based block partitioning, and the controller may perform inter-sample prediction based on the fourth information. 
     MODE OF THE INVENTION 
     Hereinafter, an inter-layer video encoding technique and an inter-layer video decoding technique of determining a disparity vector by using a reference layer depth map, according to an embodiment, will be described with reference to  FIGS. 1A to 6B . Also, a video encoding method and a video decoding method based on coding units of a tree structure, according to an embodiment, which are applicable to the above video encoding method and video decoding method, will be described with reference to  FIGS. 7 to 20 . Also, embodiments, to which the above video encoding method and video decoding method are applicable, will be described with reference to  FIGS. 21 to 26 . 
     Hereinafter, the term “image” may refer to a still image or a moving image of a video, or a video itself. 
     Hereinafter, the term “sample” may refer to data that is assigned to a sampling position of an image and is to be processed. For example, residuals of blocks or pixel values in an image of the space domain may be samples. 
     Hereinafter, the term “current block” may refer to a block of an image that is to be encoded or decoded. 
     Hereinafter, the term “neighboring block” may refer to at least one encoded or decoded block that is adjacent to a current block. For example, the neighboring block may be located at a top end of the current block, a right top end of the current block, a left side of the current block, or a left top end of the current block. Also, it may include not only a spatially adjacent block but also a temporally adjacent block. For example, a temporally adjacent neighboring block may include a co-located block co-located with a current block of a reference picture or a neighboring block of the co-located block. 
     Hereinafter, the term “layer image” may refer to images of the same type or a particular view. In a multiview video, a layer image may refer to depth images or texture images input at a particular point. For example, in a three-dimensional (3D) image, each of a left view texture image, a right view texture image, and a depth image may constitute a layer image. That is, the left view texture image, the right view texture image, and the depth image may constitute a first layer image, a second layer image, and a third layer image respectively. 
       FIG. 1A  illustrates a block diagram of a video decoding apparatus  10  for decoding a video including a multilayer, according to an embodiment. 
     Referring to  FIG. 1A , the video decoding apparatus  10  may include a controller  11  that may perform image processing for decoding a video including a multilayer and an information acquirer  12  that may acquire information necessary to decode a video from a bitstream. 
     According to an embodiment, the controller  11  may determine whether a reference picture for inter-layer prediction is included in a reference picture list. Various types of reference pictures may be included in the reference picture list. For example, pictures having temporally different reproduction orders may be included as pictures available for performance of inter prediction, and pictures having different layer identifiers for layer identification may be included as pictures available for performance of inter-layer prediction. 
       FIG. 2  illustrates a flowchart of a process of decoding a video including a multilayer by the video decoding apparatus  10 , according to an embodiment. 
     In operation S 210 , the controller  11  of the video decoding apparatus  10  may determine whether a reference picture for inter-layer prediction is included in a reference picture list. When the reference picture for inter-layer prediction is included in the reference picture list, the controller  11  of the video decoding apparatus  10  may set first information to indicate that a disparity vector is available. 
     According to an embodiment, in order to determine whether a reference picture available for inter-layer prediction is included among at least one picture included in the reference picture list, the controller  11  may determine whether a view index that is layer identification information of the reference pictures included in the reference picture list is equal to a view index of a reference picture candidate group that is available in inter-layer prediction of a current picture. Herein, the current picture may correspond to a picture included in an enhancement layer on which inter-layer prediction is performed. That is, in the enhancement layer including the current picture, the controller  11  may perform inter-layer prediction with reference to lower layers lower than the enhancement layer. The controller  11  may determine index values smaller than a view index of the current picture as a view index of the reference picture candidate group. For example, the view index of the reference picture candidate group may be included in the range of 0 to a value smaller by 1 than a value of the view index of the current picture. The controller  11  may determine whether a view index of at least one picture in the reference picture list of the current picture is equal to the view index of the reference picture candidate group. When there is a reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture, the controller  11  may determine that the reference picture available in inter-layer prediction is included in the reference picture list. 
     According to an embodiment, in order to determine whether a reference picture for inter-layer prediction is included in the reference picture list, the controller  11  may determine whether there is a reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture. In addition, the controller  11  may compare an index representing the reproduction order of the current picture with an index representing the reproduction order of the reference picture having the same value as the view index of the reference picture candidate group. For example, the controller  11  may compare a picture order count (POC) of the current picture with a POC of the reference picture having the same value as the view index of the reference picture candidate group. That is, the controller  11  may determine whether a POC of the reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture is equal to a POC of the current picture and may determine that the reference picture for inter-layer prediction is included in the reference picture list, when the POCs are equal to each other. 
       FIG. 3A  illustrates semantics for a process of determining whether a reference picture available in inter-layer prediction is included in a reference picture list. DispAvailFlag  30   b  may be information indicating whether a disparity vector is available in a current coding unit. In addition, according to an embodiment, DispAvailFlag  30   b  may be information indicating whether an inter-view reference picture that is a reference picture available in inter-layer prediction is included in a reference picture list. DefaultRefViewIdx may be information representing a default value of a reference view index among a plurality of layers constituting a multilayer video. ViewIdx(RefPicListX[i]) may be information representing a view index ViewIdx of an ith picture Ref PicListX[i] in a reference picture list of a slice including a current coding unit, and candViewIdx may be information about an index for identifying a reference view index candidate group related to the current coding unit. According to an embodiment, candViewIdx may be information representing a view index of a current view, and candViewIdx may represent a value in the range of 0 to ViewIdx−1 in relation to a view index ‘ViewIdx’ related to the current view. DiffPicOrdercnt(CurrPic, Ref PicListX[i]) may include information about a POC difference between a current picture CurrPic related to a current coding unit and an ith picture Ref PicListX[i] in a reference picture list. Referring to  FIG. 3A , the controller  11  according to an embodiment may determine, based on first information, whether a disparity vector is available in a current coding unit. 
     According to an embodiment, the controller  11  may determine, based on DispAvailFlag  30   b , whether a reference picture available in inter-layer prediction exists in a reference picture list. In addition, when a reference picture available in inter-layer prediction exists in a reference picture list, a disparity vector may be determined to be available. The first information may be information indicating that a reference picture available in inter-layer prediction is included in a reference picture list related to a slice related to a current coding unit. That is, the controller  11  may set a value represented by the first information differently according to whether a reference picture of another layer (or view) is included in a reference picture list related to a slice including a current coding unit. 
     According to an embodiment, even when the first information indicates that a reference picture of another layer (or view) is included in a reference picture list related to a slice including a current coding unit, when a disparity vector fails to be derived from a neighboring block of a current coding unit, the controller  11  may set a disparity vector of a current coding unit by using a default disparity vector. 
     Also, the controller  11  according to an embodiment may determine whether there is a reference picture having the same view index as a reference picture candidate group available in inter-layer prediction among the reference pictures included in a reference picture list related to a current coding unit ( 31   b ). A view index of the reference picture candidate group may have the range of 0 to a value smaller by 1 than a view index related to a current picture. 
     In addition, according to an embodiment, the controller  11  may determine whether a POC of a current picture is equal to a POC of a reference picture having the same view index as a reference picture candidate group among the reference pictures included in a reference picture list ( 31   c ). 
     When the conditions  31   a ,  31   b , and  31   c  are all determined to be satisfied, the controller  11  may set a default reference view index  30   a  by using a candidate reference view index related to a current coding unit and may also set the first information to a non-zero value. That is, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  11  may set a default reference view index  30   a  by using a candidate reference view index related to a current coding unit and may set the first information of DispAvailFlag  30   b  to indicate that a disparity vector is available. Referring to  FIG. 3A , according to an embodiment, when DispAvailFlag  30   b  represents 0, it may be determined that a value of DispAvailFlag  30   b  that is information about the availability of a disparity vector for a current coding unit has not yet been set ( 31   a ). When all of the other conditions ( 31   b  and  31   c ) are satisfied in addition to the determination ( 31   a ) about DispAvailFlag  30   b , the controller  11  may set a default reference view index  30   a  by using a candidate reference view index related to a current coding unit and may set DispAvailFlag  30   b  to have a value of 1. 
     According to an embodiment, even when a disparity vector is not to be derived from a neighboring block of a current coding unit, a disparity vector of a current coding unit may be set by using a default disparity vector and a default reference view index  30   a  of a current coding unit. In addition, since a reference picture available in inter-layer prediction is included in a reference picture list, efficient decoding may be performed by acquiring syntax necessary for residual prediction in inter-layer prediction. 
     According to an embodiment, when a reference picture exists in a reference picture list, the controller  11  of the video decoding apparatus  10  may set the first information to indicate that a disparity vector is available. 
     According to an embodiment, when it is determined in operation S 210  that a reference picture for inter-layer prediction is included in a reference picture list, the controller  11  may set the first information to indicate that a disparity vector is available. Herein, whether a disparity vector is available may be determined based on a predetermined data unit, for example, a current coding unit. According to an embodiment, by acquiring information about a disparity vector from a neighboring block of a current coding unit, the controller  11  may determine whether the disparity vector is available in the current coding unit. 
     According to another embodiment, even when information about a disparity vector fails to be acquired from a neighboring block of a current coding unit, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  11  may determine a disparity vector of the current coding unit as a default disparity vector. In this way, even when a disparity vector of a current coding unit is determined based on a default disparity vector, the controller  11  may set the first information to indicate that a disparity vector is available. According to an embodiment, a default disparity vector may represent a value indicating a layer including a current picture. For example, the default disparity vector may have a value of (0,0). 
       FIG. 3C  illustrates semantics for a process of using a default disparity vector when a disparity vector is not to be derived from a neighboring block of a current coding unit by the controller  11  of the video decoding apparatus  10 , according to an embodiment. 
     According to an embodiment, the controller  11  of the video decoding apparatus  10  may determine whether a disparity vector is to be derived from a neighboring block of a current coding unit. When it is determined that a disparity vector is to be derived from a neighboring block, the controller  11  may set the first information to indicate that a disparity vector is available and may set a disparity vector for a current coding unit as a disparity vector of neighboring blocks. In addition, when it is determined that a disparity vector is to be derived from a neighboring block, the controller  11  may set a reference picture available for inter-layer prediction in a current coding unit as a reference picture available for inter-layer prediction in a neighboring block. 
     Referring to  FIG. 3C , according to an embodiment, by acquiring information about a disparity vector from a neighboring block of a current coding unit, the controller  11  may determine whether a disparity vector of the current coding unit is to be derived. For example, as for a partial process ( 34   a ) of setting a disparity vector with reference to a neighboring block by the controller  11 , when tPredNbDvAvailFlagN is 1, since a disparity vector of a current coding unit may be derived by using a disparity vector of neighboring blocks of a current coding unit, a value of dvAvailflag that is information about the availability of a disparity vector of a current coding unit may be set to ‘1’ to indicate that a disparity vector is available, dispVec that is a disparity vector of a current coding unit may be set as tPredNbDispVecN that is a disparity vector of a neighboring block, and refViewIdx that is a reference view index indicating a layer referenced in inter-layer prediction in a current coding unit may be set as tPredNbRefViewIdxN that is a reference view index of a neighboring block. That is, when a disparity vector may be derived with reference to a neighboring block of a current coding unit, dvAvailflag that is information representing the availability of a disparity vector of a current coding unit may be set to ‘1’. 
     According to an embodiment, when a disparity vector of a current coding unit may not be derived by using a disparity vector of a neighboring block and dvAvailflag that is information about the availability of a disparity vector of a current coding unit represents ‘0’, the controller  11  of the video decoding apparatus  10  may perform a process ( 34   b ) of setting refViewIdx that is a reference view index indicating a layer referenced in inter-layer prediction in a current coding unit as DefaultRefViewIdx that is a default view index and setting a disparity vector of a current coding unit as (0, 0) that is a default disparity vector. That a disparity vector used in inter-layer prediction represents (0, 0) may mean that a layer of a reference picture referenced in inter-layer prediction is equal to a layer of a current picture. 
     According to an embodiment, since the controller  11  of the video decoding apparatus  10  may perform inter-layer prediction in a current coding unit of a current picture, a disparity vector may be used in an inter-layer prediction process in this process. For example, referring to  FIG. 3C , the controller  11  may set ( 35 ) a value of DispVec[x][y] that is a disparity vector available in inter-layer prediction of a current coding unit as a value of dispVec that is set through a predetermined process ( 38   a  or  38   b ). That is, dispVec that is a disparity vector of a current coding unit may be a value derived by using a disparity vector value of a neighboring block, and it may be a value set as a default disparity vector value when it may not be derived by using a disparity vector of a neighboring block. 
     According to an embodiment, based on whether a reference picture for inter-layer prediction is included in a reference picture list and whether information about a disparity vector may be acquired from a neighboring block of a current coding unit, the controller  11  may determine a disparity vector of a current coding unit by using a default disparity vector. For example, when a disparity vector of a current coding unit may not be determined by using a disparity vector of samples around a current coding unit and a reference picture for inter-layer prediction is included in a reference picture list, the controller  11  may determine a disparity vector of a current coding unit by using a default disparity vector. That is, even when a disparity vector fails to be derived from a neighboring block of a current coding unit, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  11  may set the first information to indicate that a disparity vector is available. 
     According to an embodiment, in principle, when a disparity vector may not be derived from a neighboring block, the first information related to a current coding unit may have different values according to the case where a disparity vector fails to be derived from a neighboring block and thus a disparity vector of a current coding unit is set as a default disparity vector value and the case where a reference picture available for inter-layer prediction is included in a reference picture list. 
     However, in the related art, the syntax for inter-layer prediction may be acquired only when the first information indicates that a disparity vector may be derived from a neighboring block. However, even when a disparity vector may not be derived from a neighboring block, when a disparity vector of a current coding unit is set as a default disparity vector value, since inter-layer prediction may be performed, it may be efficient to acquire the syntax for inter-layer prediction. 
     Thus, according to an embodiment, not only in the case where a disparity vector may not be derived from a neighboring block but also in the case where a disparity vector fails to be derived from a neighboring block and thus a disparity vector of a current coding unit is set as a default disparity vector value, the controller  11  may set the first information to indicate that a disparity vector is available and may determine whether a reference picture for residual prediction in inter-layer prediction is available, based on the set first information. This will be described below in more detail with reference to various embodiments. 
     According to an embodiment, the controller  11  of the video decoding apparatus  10  may set, based on the set first information, second information to indicate that a reference picture is available in a residual prediction process. 
     According to an embodiment, when a reference picture for inter-layer prediction is included in a reference picture list related to a current picture and thus the first information indicates that a disparity vector is available, the video decoding apparatus  10  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. That is, when the first information does not indicate that a disparity vector is available in a slice including a current coding unit, the controller  11  may set the second information to indicate that a reference picture in a reference picture list is not available in a residual prediction process. 
     In addition, when the first information indicates that a disparity vector is available in a current coding unit and other predetermined conditions are satisfied, the controller  11  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. According to an embodiment, the controller  11  may check not only the first information but also a predetermined condition in the process of setting the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process, and the predetermined condition may include whether a temporal reference picture available in an inter prediction process exists in a reference picture list. 
     In more detail, when the current coding unit is included in a P or B slice, one or two reference picture lists may be provided. 
     The controller  11  may determine whether at least one temporal reference picture available in inter prediction exists in at least one reference picture list available in a current coding unit for inter prediction. When at least one temporal reference picture available in inter prediction exists in a reference picture list and the first information indicates that a disparity vector is available in a current coding unit, the controller  11  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. 
       FIG. 3B  illustrates semantics for a process of setting second information, according to an embodiment. 
     Referring to  FIG. 3B , according to an embodiment, the controller  11  of the video decoding apparatus  10  may set a value of RpRefPicAvailFlag  32  as the second information. RpRefPicAvailFlag  32  may be determined based on whether a temporal reference picture exists in a reference picture list. When a slice related to a current coding unit is a P slice, one reference picture list may be provided, and when the slice is a B slice, two reference picture lists may be provided. 
     The controller  11  may determine ( 33   a ) whether a temporal reference picture exists in at least one reference picture list related to a current coding unit, and may also determine whether the first information (e.g., DispAvailFlag  30   b ) indicates that a disparity vector is available. According to an embodiment, when a disparity vector related to a current coding unit may be derived from a neighboring block or may be set as a default disparity vector, the first information may have a value greater than 0. 
     Thus, when a temporal reference picture exists in at least one reference picture list related to a current coding unit and the first information indicates that a disparity vector is available, the controller  11  may set the second information of RpRefPicAvailFlag  32  as a value greater than 0. The second information may be used to determine whether to perform residual prediction. This will be described below in more detail with reference to various embodiments. 
     According to an embodiment, based on the set first information, the video decoding apparatus  10  may acquire third information indicating whether to perform residual prediction in a current coding unit from a bitstream. 
     According to an embodiment, when the first information indicates that a disparity vector is available, the controller  11  of the video decoding apparatus  10  may control the information acquirer  12  to acquire the third information indicating whether to perform residual prediction in a current coding unit from a bitstream. That is, when a disparity vector is available and a reference picture available in residual prediction is included in a reference picture list, the video decoding apparatus  10  may acquire the third information from a bitstream to perform residual prediction in inter-layer prediction in a current coding unit. Based on the acquired third information, the controller  11  may determine whether to perform residual prediction. 
     According to an embodiment, the video decoding apparatus  10  may set the second information based on the first information and may acquire the third information indicating whether to perform residual prediction in a current coding unit from a bitstream, based on the set second information. In more detail, when the first information indicates that a disparity vector is available and the second information indicates that a reference picture is available in a residual prediction process, the controller  11  of the video decoding apparatus  10  may control the information acquirer  12  to acquire the third information indicating whether to perform residual prediction in a current coding unit from a bitstream. That is, when a disparity vector is available and a reference picture available in residual prediction is included in a reference picture list, the video decoding apparatus  10  may acquire the third information from a bitstream to perform residual prediction in inter-layer prediction in a current coding unit. Based on the acquired third information, the controller  11  may determine whether to perform residual prediction. 
       FIG. 3D  illustrates a process of acquiring predetermined information from a bitstream based on first information related to the availability of a disparity vector in a current coding unit by the video decoding apparatus  10 , according to an embodiment. In  FIG. 3D , the first information may correspond to DispAvailFlag  30   b , the second information may correspond to RpRefPicAvailFlag  32 , and the third information may correspond to iv_res_pred_weight_idx[x0][y0]  39   a.    
     Referring to  FIG. 3D , based on a condition  38 , the video decoding apparatus  10  may determine whether to acquire the third information  39   a  from a bitstream. In a condition  45 , the controller  11  may acquire the third information  39   a  based on the second information  32  indicating whether a reference picture is available in residual prediction. For example, when the second information of RpRefPicAvailFlag indicates that a reference picture is available in residual prediction, the video decoding apparatus  10  may acquire the third information of iv_res_pred_weight_idx[x0][y0]  39   a  from a bitstream based on the second information. 
     According to an embodiment, the video decoding apparatus  10  may perform residual prediction based on the third information acquired from a bitstream. For example, when the third information represents a non-zero value, the video decoding apparatus  10  may perform residual prediction, and when the third information represents a value of 0, the video decoding apparatus  10  may not perform residual prediction.  FIG. 3D  illustrates semantics  39   b  of iv_res_pred_weight_idx[x0][y0] as the third information. Referring to  FIG. 3D , when a value of iv_res_pred_weight_idx[x0][y0] indicates a non-zero value, the controller  11  may perform residual prediction in a current coding unit and may determine a weight index value in a residual prediction process based on iv_res_pred_weight_idx[x0][y0]. When a value of iv_res_pred_weight_idx[x0][y0] indicates 0, the controller  11  may not perform residual prediction in a current coding unit. 
     According to an embodiment, based on the second information, the video decoding apparatus  10  may determine whether to perform illumination compensation (IC) in a current coding unit. In more detail, based on the first information, the video decoding apparatus  10  may determine whether a disparity vector is available in a current coding unit. Even when a disparity vector may not be derived from a neighboring block, when a reference picture available in inter-layer prediction is included in a reference picture list, the video decoding apparatus  10  may set a disparity vector of a current coding unit by using a default disparity vector and may set the first information as a value of 1. When the first information indicates a value of 1, the video decoding apparatus  10  may set the second information to indicate that a reference picture is available in a residual prediction process. When the second information indicates that a reference picture available in an inter-layer prediction process is included in a reference picture list, the video decoding apparatus  10  may acquire information indicating whether to perform illumination compensation in a current coding unit. 
     According to an embodiment, since the video decoding apparatus  10  always refers to a view-direction reference picture available in an inter-layer prediction process in the case of performing illumination compensation, the video decoding apparatus  10  may first determine whether a view-direction reference picture available in an inter-layer prediction process exists in a reference picture list of a slice including a current coding unit. 
     According to an embodiment, when the second information indicates that a view-direction reference picture available in an inter-layer prediction process is not included in a reference picture list, the video decoding apparatus  10  may not acquire the information indicating whether to perform illumination compensation from a bitstream. When the second information indicates that a view-direction reference picture available in an inter-layer prediction process is included in a reference picture list, the video decoding apparatus  10  may acquire the information indicating whether to perform illumination compensation from a bitstream. 
     According to an embodiment, based on the first information indicating whether a disparity vector is available in a current coding unit, the controller  11  of the video decoding apparatus  10  may control the information acquirer  12  to acquire fourth information indicating whether a depth-based block partitioning (DBBP) technique is available from a bitstream. The DBBP technique may include a method of splitting a texture image and perform prediction by using depth information included in a multilayer image including a plurality of layers. 
     The fourth information may indicate whether inter-sample prediction may be performed to split a block and perform prediction based on depth information in a current coding unit. When the fourth information is 0, the video decoding apparatus  10  may not perform inter-sample prediction, and when the fourth information is 1, the video decoding apparatus  10  may perform inter-sample prediction. 
     Referring to  FIG. 3D , the video decoding apparatus  10  may determine whether a value of DispAvailFlag  30   b  indicating whether a disparity vector is available in a current coding unit is 0 in a condition  36 , and may determine whether to acquire dbbp_flag[x0][y0]  37  indicating whether DBBP is available from a bitstream based on the value of DispAvailFlag  30   b . In more detail, even when a disparity vector may not be derived from a neighboring block, when a reference picture available in inter-layer prediction is included in a reference picture list, the video decoding apparatus  10  may set a disparity vector of a current coding unit by using a default disparity vector and may set the first information as a value of 1. When the first information indicates a value of 1, the video decoding apparatus  10  may acquire the fourth information indicating whether DBBP is available from a bitstream. 
     According to an embodiment, the value of DispAvailFlag  30   b  may indicate 0 when a disparity vector is not available in a current coding unit, and the video decoding apparatus  10  may fail to acquire dbbp_flag[x0][y0]  37  from a bitstream because the condition  36  may fail to be satisfied when the value of DispAvailFlag  30   b  is 0. That is, since a disparity vector is necessary to use a DBBP technique, when a disparity vector is not available in a current coding unit, it is not necessary to acquire the syntax  37  related to the DBBP technique from a bitstream. According to this embodiment, efficient video decoding may be performed by skipping an unnecessary syntax acquiring process. 
       FIG. 1B  illustrates a block diagram of a video encoding apparatus  15  for encoding a video including a multilayer, according to an embodiment. 
     Referring to  FIG. 1B , the video encoding apparatus  15  may include a controller  16  that may perform image processing for encoding a video including a multilayer and a bitstream generator  17  that may generate a bitstream including information necessary to encode a video. 
     According to an embodiment, the controller  16  may determine whether a reference picture for inter-layer prediction is included in a reference picture list. Various types of reference pictures may be included in the reference picture list. For example, pictures having temporally different reproduction orders may be included as pictures available for performance of inter prediction, and pictures having different layer identifiers for layer identification may be included as pictures available for performance of inter-layer prediction. 
     According to an embodiment, the controller  16  of the video encoding apparatus  15  may determine whether a reference picture for inter-layer prediction is included in a reference picture list. In addition, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  16  of the video encoding apparatus  15  may set first information to indicate that a disparity vector is available. This process may include the feature of a process corresponding to operation S 210  of the video decoding apparatus  10 . 
     According to an embodiment, in order to determine whether a reference picture available for inter-layer prediction is included among at least one picture included in the reference picture list, the controller  16  may determine whether a view index that is layer identification information of the reference pictures included in the reference picture list is equal to a view index of a reference picture candidate group that is available in inter-layer prediction of a current picture. The controller  16  may determine index values smaller than a view index of the current picture as a view index of the reference picture candidate group. For example, the view index of the reference picture candidate group may be included in the range of 0 to a value smaller by 1 than a value of the view index. 
     The controller  16  may determine whether a view index of at least one picture in the reference picture list of the current picture is equal to the view index of the reference picture candidate group. When there is a reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture, the controller  16  may determine that the reference picture available in inter-layer prediction is included in the reference picture list. 
     According to an embodiment, in order to determine whether a reference picture for inter-layer prediction is included in the reference picture list, the controller  16  may determine whether there is a reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture. In addition, the controller  16  may compare an index representing the reproduction order of the current picture with an index representing the reproduction order of the reference picture having the same value as the view index of the reference picture candidate group. For example, the controller  16  may compare a POC of the current picture with a POC of the reference picture having the same value as the view index of the reference picture candidate group. That is, the controller  16  may determine whether a POC of the reference picture having a view index equal to the view index of the reference picture candidate group among at least one reference picture included in the reference picture list of the current picture is equal to a POC of the current picture and may determine that the reference picture for inter-layer prediction is included in the reference picture list, when the POCs are equal to each other. 
       FIG. 3A  illustrates semantics for a process of determining whether a reference picture available in inter-layer prediction is included in a reference picture list. The semantics illustrated in  FIG. 3A  may be related to a process of determining whether a reference picture available in inter-layer prediction is included in a reference picture list by the video decoding apparatus  10  according to an embodiment, and this process may correspond to the result of reversely performing an encoding process performed on an original image by the video encoding apparatus  15 . Detailed contents thereof may be the contents corresponding to the above description in which the video decoding apparatus  10  operates according to the semantics of  FIG. 3A , and thus redundant descriptions thereof will be omitted for conciseness. According to the semantics of  FIG. 3A , the controller  16  of the video encoding apparatus  15  may determine whether a reference picture available in inter-layer prediction is included in a reference picture list. 
     According to an embodiment, when a reference picture exists in a reference picture list, the controller  16  of the video encoding apparatus  15  may set the first information to indicate that a disparity vector is available. According to an embodiment, when it is determined in operation S 210  that a reference picture for inter-layer prediction is included in a reference picture list, the controller  16  may set the first information to indicate that a disparity vector is available. Herein, whether a disparity vector is available may be determined based on a predetermined data unit, for example, a current coding unit. According to an embodiment, by acquiring information about a disparity vector from a neighboring block of a current coding unit, the controller  16  may determine whether the disparity vector is available in the current coding unit. According to another embodiment, even when information about a disparity vector fails to be acquired from a neighboring block of a current coding unit, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  16  may determine a disparity vector of the current coding unit by using a default disparity vector. In this way, even when a disparity vector of a current coding unit is determined based on a default disparity vector, the controller  16  may set the first information to indicate that a disparity vector is available. According to an embodiment, a default disparity vector may represent a value indicating a layer including a current picture. For example, the default disparity vector may have a value of (0,0). 
       FIG. 3C  illustrates semantics for a process of using a default disparity vector when a disparity vector is not to be derived from a neighboring block of a current coding unit by the controller  16  of the video encoding apparatus  15 , according to an embodiment. 
     According to an embodiment, the controller  16  of the video encoding apparatus  15  may determine whether a disparity vector is to be derived from a neighboring block of a current coding unit. When it is determined that a disparity vector is to be derived from a neighboring block, the controller  16  may set the first information to indicate that a disparity vector is available and may set a disparity vector for a current coding unit as a disparity vector of neighboring blocks. In addition, when it is determined that a disparity vector is to be derived from a neighboring block, the controller  16  may set a reference picture available for inter-layer prediction in a current coding unit as a reference picture available for inter-layer prediction in a neighboring block. 
     Referring to  FIG. 3C , according to an embodiment, by acquiring information about a disparity vector from a neighboring block of a current coding unit, the controller  16  may determine whether a disparity vector of the current coding unit is to be derived. A disparity vector using process performed by the controller  11  of the video encoding apparatus  15  according to the semantics illustrated in  FIG. 3C  may correspond to a process of using a disparity vector by the controller  16  of the video decoding apparatus  10  according to the semantics of  FIG. 3C  when a disparity vector may not be derived from a neighboring block of a current coding unit, and thus redundant descriptions thereof will be omitted for conciseness. 
     According to an embodiment, based on whether a reference picture for inter-layer prediction is included in a reference picture list and whether information about a disparity vector may be acquired from a neighboring block of a current coding unit, the controller  16  may determine a disparity vector of a current coding unit by using a default disparity vector. For example, when a disparity vector of a current coding unit may not be determined by using a disparity vector of samples around a current coding unit and a reference picture for inter-layer prediction is included in a reference picture list, the controller  16  may determine a disparity vector of a current coding unit by using a default disparity vector. That is, even when a disparity vector fails to be derived from a neighboring block of a current coding unit, when a reference picture for inter-layer prediction is included in a reference picture list, the controller  16  may set the first information to indicate that a disparity vector is available. 
     According to an embodiment, in principle, when a disparity vector may not be derived from a neighboring block, the first information related to a current coding unit may have different values according to the case where a disparity vector fails to be derived from a neighboring block and thus a disparity vector of a current coding unit is set as a default disparity vector value and the case where a reference picture available for inter-layer prediction is included in a reference picture list. However, in the related art, the syntax for inter-layer prediction may be acquired only when the first information indicates that a disparity vector may be derived from a neighboring block. However, even when a disparity vector may not be derived from a neighboring block, when a disparity vector of a current coding unit is set as a default disparity vector value, since inter-layer prediction may be performed, it may be efficient to acquire the syntax for inter-layer prediction. Thus, according to an embodiment, not only in the case where a disparity vector may not be derived from a neighboring block but also in the case where a disparity vector fails to be derived from a neighboring block and thus a disparity vector of a current coding unit is set as a default disparity vector value, the controller  16  may set the first information to indicate that a disparity vector is available and may determine whether a reference picture for residual prediction in inter-layer prediction is available, based on the set first information. This will be described below in more detail with reference to various embodiments. 
     According to an embodiment, the controller  16  of the video encoding apparatus  15  may set, based on the set first information, second information to indicate that a reference picture is available in a residual prediction process. 
     According to an embodiment, when a reference picture for inter-layer prediction is included in a reference picture list related to a current picture and thus the first information indicates that a disparity vector is available, the video encoding apparatus  15  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. That is, when the first information does not indicate that a disparity vector is available in a current coding unit, the controller  16  may set the second information to indicate that a reference picture in a reference picture list is not available in a residual prediction process. In addition, when the first information indicates that a disparity vector is available in a current coding unit and other predetermined conditions are satisfied, the controller  16  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. According to an embodiment, the controller  16  may check not only the first information but also a predetermined condition in the process of setting the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process, and the predetermined condition may include whether a temporal reference picture available in an inter prediction process exists in a reference picture list. In more detail, when the current coding unit is included in a P or B slice, one or two reference picture lists may be provided. The controller  16  may determine whether at least one temporal reference picture available in inter prediction exists in at least one reference picture list available in a current coding unit for inter prediction. When at least one temporal reference picture available in inter prediction exists in a reference picture list and the first information indicates that a disparity vector is available in a current coding unit, the controller  16  may set the second information to indicate that a reference picture in a reference picture list is available in a residual prediction process. 
       FIG. 3B  illustrates semantics for a process of setting second information, according to an embodiment. 
     Referring to  FIG. 3B , according to an embodiment, the controller  16  of the video encoding apparatus  15  may set a value of RpRefPicAvailFlag  32  as the second information. RpRefPicAvailFlag  32  may be determined based on whether a temporal reference picture exists in a reference picture list. When a slice related to a current coding unit is a P slice, one reference picture list may be provided, and when the slice is a B slice, two reference picture lists may be provided. The controller  16  may determine ( 33   a ) whether a temporal reference picture exists in at least one reference picture list related to a current coding unit, and may also determine ( 30   b ) whether the first information indicates that a disparity vector is available. According to an embodiment, when a disparity vector related to a current coding unit may be derived from a neighboring block or may be set as a default disparity vector, the first information may have a value greater than 0. Thus, when a temporal reference picture exists in at least one reference picture list related to a current coding unit and the first information indicates that a disparity vector is available, the controller  16  may set the second information of RpRefPicAvailFlag  32  as a value greater than 0. The second information may be used to determine whether to perform residual prediction. This will be described below in more detail with reference to various embodiments. 
     According to an embodiment, based on the set first information, the video encoding apparatus  15  may generate a bitstream including third information indicating whether to perform residual prediction in a current coding unit. 
     According to an embodiment, when the first information indicates that a disparity vector is available, the controller  16  of the video encoding apparatus  15  may control the bitstream generator  17  to generate a bitstream including the third information indicating whether to perform residual prediction in a current coding unit. That is, when a disparity vector is available and a reference picture available in residual prediction is included in a reference picture list, the video encoding apparatus  15  may generate a bitstream including the third information that is information for performing residual prediction in inter-layer prediction in a current coding unit. 
     According to an embodiment, the video encoding apparatus  15  may set the second information based on the first information and may generate a bitstream including the third information indicating whether to perform residual prediction in a current coding unit, based on the set second information. In more detail, when the first information indicates that a disparity vector is available and the second information indicates that a reference picture is available in a residual prediction process, the controller  16  of the video encoding apparatus  15  may control the bitstream generator  17  to generate a stream including the third information indicating whether to perform residual prediction in a current coding unit. That is, when a disparity vector is available and a reference picture available in residual prediction is included in a reference picture list, the video encoding apparatus  15  may generate a bitstream including the third information to perform residual prediction in inter-layer prediction in a current coding unit. Based on the acquired third information, the controller  16  may determine whether to perform residual prediction. 
     A process of generating a bitstream including predetermined information based on the first information related to the availability of a disparity vector in a current coding unit by the video encoding apparatus  15 , according to an embodiment, will be described below. 
     Referring to  FIG. 3D , based on the condition  38 , the video encoding apparatus  15  may determine whether to generate a bitstream including the third information  39   a . In the condition  45 , the controller  16  may generate a bitstream including the third information  39   a  based on the second information  32  indicating whether a reference picture is available in residual prediction. For example, when the second information of RpRefPicAvailFlag indicates that a reference picture is available in residual prediction, the video encoding apparatus  15  may generate a bitstream including the third information of iv_res_pred_weight_idx[x0][y0] based on the second information. A process of generating a bitstream including the third information by the controller  16  of the video encoding apparatus  15  may correspond to a process of acquiring the third information from a bitstream by the controller  11  of the video decoding apparatus  10  in association with  FIG. 3D , and thus redundant descriptions thereof will be omitted for conciseness. 
     According to an embodiment, based on the second information, the video encoding apparatus  15  may determine whether to perform illumination compensation in a current coding unit. In more detail, based on the first information, the video encoding apparatus  15  may determine whether a disparity vector is available in a current coding unit. Even when a disparity vector may not be derived from a neighboring block, when a reference picture available in inter-layer prediction is included in a reference picture list, the video encoding apparatus  15  may set a disparity vector of a current coding unit by using a default disparity vector and may set the first information as a value of 1. When the first information indicates a value of 1, the video encoding apparatus  15  may set the second information to indicate that a reference picture is available in a residual prediction process. When the second information indicates that a reference picture available in an inter-layer prediction process is included in a reference picture list, the video encoding apparatus  15  may generate a bitstream including information indicating whether to perform illumination compensation in a current coding unit. 
     According to an embodiment, since the video encoding apparatus  15  always refers to a view-direction reference picture available in an inter-layer prediction process in the case of performing illumination compensation, the video encoding apparatus  15  may first determine whether a view-direction reference picture available in an inter-layer prediction process exists in a reference picture list of a slice including a current coding unit. 
     According to an embodiment, when the second information indicates that a view-direction reference picture available in an inter-layer prediction process is not included in a reference picture list, the video encoding apparatus  15  may not include the information indicating whether to perform illumination compensation in a bitstream. When the second information indicates that a view-direction reference picture available in an inter-layer prediction process is included in a reference picture list, the video encoding apparatus  15  may generate a bitstream including the information indicating whether to perform illumination compensation. 
     According to an embodiment, based on the first information indicating whether a disparity vector is available in a current coding unit, the controller  16  of the video encoding apparatus  15  may control the bitstream generator  17  to generate a bitstream including fourth information indicating whether a DBBP technique is available. The DBBP technique may include a method of splitting a texture image and perform prediction by using depth information included in a multilayer image including a plurality of layers. 
     The fourth information may indicate whether inter-sample prediction may be performed to split a block and perform prediction based on depth information in a current coding unit. When the fourth information is 0, the video encoding apparatus  15  may not perform inter-sample prediction, and when the fourth information is 1, the video encoding apparatus  15  may perform inter-sample prediction. 
     Referring to  FIG. 3D , the video encoding apparatus  15  may determine whether a value of DispAvailFlag  30   b  indicating whether a disparity vector is available in a current coding unit is 0 in the condition  36 , and may determine whether to generate a bitstream including dbbp_flag[x0][y0]  37  indicating whether DBBP is available based on the value of DispAvailFlag  30   b . In more detail, even when a disparity vector may not be derived from a neighboring block, when a reference picture available in inter-layer prediction is included in a reference picture list, the video encoding apparatus  15  may set a disparity vector of a current coding unit by using a default disparity vector and may set the first information as a value of 1. When the first information indicates a value of 1, the video encoding apparatus  15  may generate a bitstream including the fourth information indicating whether DBBP is available. 
     According to an embodiment, the value of DispAvailFlag  30   b  may indicate 0 when a disparity vector is not available in a current coding unit, and the video encoding apparatus  15  may generate a bitstream including dbbp_flag[x0][y0]  37  because the condition  36  may fail to be satisfied when the value of DispAvailFlag  30   b  is 0. That is, since a disparity vector is necessary to use a DBBP technique, when a disparity vector is not available in a current coding unit, it is not necessary to include the syntax  37  related to the DBBP technique in a bitstream. According to this embodiment, efficient video encoding may be performed by skipping an unnecessary syntax encoding process. 
       FIG. 4A  illustrates a block diagram of an inter-layer video decoding apparatus  40  according to an embodiment. The inter-layer video decoding apparatus  40  according to an embodiment may include a first layer decoder  42  and a second layer decoder  44 . The inter-layer video decoding apparatus  40  of  FIG. 4A  may correspond to the video decoding apparatus  10  of  FIG. 1A . In addition, the operations performed by the first layer decoder  42  and the second layer decoder  44  of  FIG. 4A  may be performed by the controller  11  of  FIG. 1A . 
     The inter-layer video decoding apparatus  40  according to an embodiment may receive bitstreams on a layer-by-layer basis according to a scalable encoding method. The number of layers of the bitstreams received by the inter-layer video decoding apparatus  40  is not limited. However, for convenience of description, an embodiment in which the first layer decoder  42  of the inter-layer video decoding apparatus  40  receives and decodes a first layer stream and the second layer decoder  44  receives and decodes a second layer stream will be described below. 
     For example, the inter-layer video decoding apparatus  40  based on spatial scalability may receive a stream generated by encoding image sequences of different resolutions in different layers. The first layer stream may be decoded to reconstruct a low-resolution image sequence, and the second layer stream may be decoded to reconstruct a high-resolution image sequence. 
     As another example, a multiview video may be decoded according to a scalable video coding method. When a stereoscopic video stream is received in a plurality of layers, the first layer stream may be decoded to reconstruct left view images. The right view images may be reconstructed by further decoding the second layer stream in addition to the first layer stream. 
     Alternatively, when a multiview video stream is received in a plurality of layers, the first layer stream may be decoded to reconstruct center view images. The left view images may be reconstructed by further decoding the second layer stream in addition to the first layer stream. The right view images may be reconstructed by further decoding the third layer stream in addition to the first layer stream. 
     As another example, a scalable video coding method based on temporal scalability may be performed. The first layer stream may be decoded to reconstruct base frame rate images. The high frame rate images may be reconstructed by further decoding the second layer stream in addition to the first layer stream. 
     Also, when there are three or more second layers, the first layer images may be reconstructed from the first layer stream, and the second layer images may be further reconstructed by further decoding the second layer stream with reference to the first layer reconstruction images. The Kth layer images may be further reconstructed by further decoding the Kth layer stream with reference to the second layer reconstruction image. 
     The inter-layer video decoding apparatus  40  may acquire the encoded data of the first layer images and the second layer images from the first layer stream and the second layer stream and may further acquire the motion vector generated by inter prediction and the prediction information generated by inter-layer prediction. 
     For example, the inter-layer video decoding apparatus  40  may decode inter-predicted data in each layer and decode inter-layer-predicted data between a plurality of layers. The reconstruction may be performed through the motion compensation and the inter-layer decoding based on the encoding unit or the prediction unit. 
     Regarding each layer stream, images may be reconstructed by performing motion compensation for a current image by referring to reconstructed images predicted via inter prediction with respect to the same layer. The motion compensation may refer to an operation of reconstructing the reconstruction image of the current image by synthesizing the residual component of the current image and the reference image determined by using the motion vector of the current image. 
     Also, in order to reconstruct the second layer image predicted through inter-layer prediction, the inter-layer video decoding apparatus  40  may perform inter-layer decoding with reference to the first layer images. The inter-layer decoding may refer to an operation of reconstructing the reconstruction image of the current image by synthesizing the residual component of the current image and the reference image of another layer determined to predict the current image. 
     According to an embodiment, the inter-layer video decoding apparatus  40  may perform inter-layer decoding for reconstructing the third layer images predicted with reference to the second layer images. An inter-layer prediction structure thereof will be described below in detail with reference to  FIG. 5A . 
     However, the second layer decoder  44  according to an embodiment may decode the second layer stream even without reference to the first layer image sequence. Thus, it should be noted that the second layer decoder  44  is not limited as performing inter-layer prediction to decode the second layer image sequence. 
     The inter-layer video decoding apparatus  40  performs decoding on each block of each image of a video. Among the coding units according to a tree structure, the block may be a largest coding unit, a coding unit, a prediction unit, a transformation unit, or the like. 
     The first layer decoder  42  may decode the first layer image by using parsed encoding symbols of the first layer image. When the inter-layer video decoding apparatus  40  receives streams encoded based on coding units of a tree structure, the first layer decoder  42  may perform decoding based on the coding units of the tree structure according to a largest coding unit of the first layer stream. 
     The first layer decoder  42  may acquire encoding information and encoded data by performing entropy decoding per largest coding unit. The first layer decoder  42  may reconstruct a residual component by performing inverse quantization and inverse transformation on encoded data acquired from a stream. According to another embodiment, the first layer decoder  42  may directly receive a bitstream of quantized transformation coefficients. Residual components of images may be reconstructed by performing inverse quantization and inverse transformation on the quantized transformation coefficients 
     The first layer decoder  42  may reconstruct the first layer images by combining the prediction image and the residual component through motion compensation between same layer images. 
     According to an inter-layer prediction structure, the second layer decoder  44  may generate a second layer prediction image by using samples of a first layer reconstruction image. The second layer decoder  44  may acquire a prediction error according to inter-layer prediction by decoding a second layer stream. The second layer decoder  44  may generate a second layer reconstruction image by combining a second layer prediction image and the prediction error. 
     The second layer decoder  44  may determine a second layer prediction image by using a decoded first layer reconstruction image decoded by the first layer decoder  42 . According to an inter-layer prediction structure, the second layer decoder  44  may determine a block of the first layer image which is to be referred to by a block such as a prediction unit or a coding unit of the second layer image. For example, a reconstruction block of a first layer image whose position corresponds to a position of a current block of the second layer image may be determined. The second layer decoder  44  may determine a second layer prediction block by using a first layer reconstruction block corresponding to the second layer block. 
     The second layer decoder  44  may use the second layer prediction block determined by using the first layer reconstruction block according to an inter-layer prediction structure, as a reference image for inter-layer prediction of the second layer original block. In this case, the second layer decoder  44  may reconstruct the second layer block by synthesizing the residual component according to the inter-layer prediction and the sample value of the second layer prediction block determined by using the first layer reconstruction image. 
     According to a spatial scalable video coding method, when the first layer decoder  42  reconstructs the first layer image of the different resolution from the second layer image, the second layer decoder  44  may interpolate the first layer reconstruction image for size adjustment to the same resolution as the second layer original image. The interpolated first layer reconstruction image may be determined as the second layer prediction image for inter-layer prediction. 
     Thus, the first layer decoder  42  of the inter-layer video decoding apparatus  40  may reconstruct the first layer image sequence by decoding the first layer stream and reconstruct the second layer image sequence by decoding the second layer stream. 
     Hereinafter, an inter-layer decoding apparatus  40  using a particular encoding tool according to a particular condition, according to an embodiment of the inventive concept, will be described. 
     The first layer decoder  42  reconstructs a first layer image based on the encoding information of the first layer image acquired from a bitstream. 
     The second layer decoder  44  splits the largest coding unit of the second layer image into one or more coding units based on the split information of the second layer image acquired from a bitstream. The second layer decoder  44  splits the coding unit into prediction units for prediction decoding. 
     The second layer decoder  44  may determine a structure of the coding unit by splitting the coding unit into one or more prediction units based on at least one of the prediction mode information and the partition mode information of the coding unit acquired from a bitstream. 
     Based on at least one of the prediction mode information, the size information, and the color depth information of the current prediction unit, the second layer decoder  44  determines whether to use a predetermined encoding tool and performs decoding on the current prediction unit by using the predetermined encoding tool. 
     When the prediction unit has the same size as the coding unit, the second layer decoder  44  may perform decoding by using a predetermined encoding tool. Herein, the predetermined encoding tool may be a tool for performing encoding on the prediction unit by using the first layer image. The predetermined encoding tool may include at least one of MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), DDD (Disparity Derived Depth), VSP (View Synthesis Prediction), IC (Illumination Compensation), SDC (Segment-wise DC Coding), DMM (Depth Modeling Mode), DBBP (Depth-Based Block Partitioning), and ARP (Advanced Residual Prediction). 
     The inter-layer video decoding apparatus  40  according to an embodiment may include a central processor (not illustrated) for collectively controlling the first layer decoder  42  and the second layer decoder  44 . Alternatively, each of the first layer decoder  42  and the second layer decoder  44  may be operated by its own processor (not illustrated), and the inter-layer video decoding apparatus  40  may be operated as a whole when the processors (not illustrated) operate organically with respect to each other. Alternatively, the first layer decoder  42  and the second layer decoder  44  may be controlled by an external processor (not illustrated) of the inter-layer video decoding apparatus  40  according to an embodiment. 
     The inter-layer video decoding apparatus  40  according to an embodiment may include one or more data storages (not illustrated) for storing the input/output data of the first layer decoder  42  and the second layer decoder  44 . The inter-layer video decoding apparatus  40  may include a memory controller (not illustrated) for controlling the data input/output of a data storage (not illustrated). 
     According to an embodiment, in order to reconstruct the video through video decoding, the inter-layer video decoding apparatus  40  may perform a video decoding operation including inverse transformation by operating in conjunction with an external video decoding processor or an internal video decoding processor thereof. The internal video decoding processor of the inter-layer video decoding apparatus  40  according to an embodiment may be a separate processor. However, in some cases, the inter-layer video decoding apparatus  40 , the central operation apparatus, or the graphic operation apparatus may include a video decoding processing module to implement a basic video decoding operation. 
       FIG. 4B  illustrates a block diagram of an inter-layer video encoding apparatus  45  according to an embodiment. The inter-layer video encoding apparatus  45  according to an embodiment may include a first layer encoder  46  and a second layer encoder  48 . The inter-layer video encoding apparatus  45  of  FIG. 4B  may correspond to the video encoding apparatus  15  of  FIG. 1B . In addition, the operations performed by the first layer encoder  46  and the second layer encoder  48  of  FIG. 4B  may be performed by the controller  16  of  FIG. 1B . 
     According to an embodiment, the inter-layer video encoding apparatus  45  may classify and encode a plurality of image sequences on a layer-by-layer basis according to a scalable video coding method and may output a separate stream including the data encoded on a layer-by-layer basis. The inter-layer video encoding apparatus  45  may encode a first layer image sequence and a second layer image sequence in different layers. 
     The first layer encoder  46  may encode first layer images and may output a first layer stream including the encoding data of the first layer images. 
     The first layer encoder  48  may encode second layer images and may output a second layer stream including the encoding data of the second layer images. 
     For example, according to a scalable video coding method based on spatial scalability, low-resolution images may be encoded as first layer images, and high-resolution images may be encoded as second layer images. The encoding result of the first layer images may be output as a first layer stream, and the encoding result of the second layer images may be output as a second layer stream. 
     As another example, a multiview video may be encoded according to a scalable video coding method. When two-view images are to be encoded, left view images may be encoded as first layer images and right view images may be encoded as second layer images. Alternatively, when three-view images are to be encoded, center view images, left view images, and right view images may be respectively encoded, wherein the center view images may be encoded as first layer images, the left view images may be encoded as second layer images, and the right view images may be encoded as third layer images. The inventive concept is not limited to this configuration, and the reference layer and the layers in which center view, left view, and right view images are encoded may vary according to embodiments. 
     As another example, a scalable video coding method may be performed according to temporal hierarchical prediction based on the temporal scalability. A first layer stream including the encoded information generated by encoding the images of a base frame rate may be output. A temporal layer (temporal level) may be classified with respect to each frame rate, and each temporal layer may be encoded as each layer. The images of a high frame rate may be further encoded with reference to the images of the base frame rate, and a second layer stream including the encoded information of the high frame rate may be output. 
     Also, scalable video coding may be performed on a first layer and a plurality of second layers. When there are two or more second layers, the first layer images, the first second layer images, the second second layer images, . . . , the Kth second layer images may be encoded. Accordingly, the encoding result of the first layer images may be output as the first layer stream, and the encoding results of the first, second, . . . , Kth second layer images may be output as the first, second, . . . , Kth second layer streams respectively. 
     Also, multiview video coding may be performed on a first layer and a plurality of layers. When there are K view images, first layer images, second layer images, third layer images, . . . , Kth layer images may be encoded. Accordingly, the encoding result of the first layer images may be output as a first layer stream, and the encoding result of the Kth layer images may be output as a Kth layer stream. 
     A multiview scalable bitstream includes sub-streams corresponding to different viewpoints in one bitstream. For example, in a stereoscopic image, a bitstream includes a left image and a right image. Also, a scalable bitstream may include sub-streams related to a multiview image and encoded data of a depth map. The viewpoint scalability may also be classified into different dimensions according to different viewpoints. 
     Different scalable expansion types may be combined with each other. That is, a scalable video bitstream may include sub-streams in which image sequences of a multilayer including images, wherein at least one of temporal, spatial, quality, and multiview scalabilities are different from each other, are encoded. 
     According to an embodiment, the first layer image sequence, the second layer image sequence, and the nth layer image sequence may be image sequences that are different in at least one of resolution, image quality, and view. Also, when a first layer image sequence is a base layer image sequence, other layer image sequences may be defined as enhancement layer image sequences. An enhancement layer may be defined as a layer that may be predicted with reference to one or more neighboring view images. However, a base layer may be determined as one of a plurality of layers, and the base layer is not limited to the first layer. 
     As an example, the first layer image sequence may be the first view images, the second layer image sequence may be the second view images, and the nth layer image sequence may be the nth view images. As another example, the first layer image sequence may be the left view images of the base layer, the second layer image sequence may be the right view images of the base layer, and the nth layer image sequence may be the right view images of the enhancement layer. However, the inventive concept is not limited thereto, and the image sequences having different scalable extension types may be respectively image sequences having different image attributes. 
     According to an embodiment, the inter-layer video encoding apparatus  45  may perform inter prediction for predicting the current image with reference to the images of a single layer. A motion vector representing motion information between the current image and the reference image and a residual component between the current image and the reference image may be generated through the inter prediction. 
     Also, the inter-layer video encoding apparatus  45  may perform inter-layer prediction for predicting the second layer images with reference to the first layer images. 
     Also, according to an embodiment, when the inter-layer video encoding apparatus  45  allows three or more layers such as the first layer, the second layer, and the third layer, the inter-layer prediction between a first layer image and a third layer image and the inter-layer prediction between a second layer image and a third layer image may be performed according to a multilayer prediction structure. 
     A position difference component between the current image and the reference image of another layer and a residual component between the current image and the reference image of another layer may be generated through the inter-layer prediction. 
     According to an embodiment, the inter-layer video encoding apparatus  45  encodes each block of each image of a video in each layer. A block may have a square shape, a rectangular shape, or an arbitrary geometrical shape, and is not limited to a data unit having a predetermined size. The block may be a largest coding unit, a coding unit, a prediction unit, or a transformation unit, among coding units according to a tree structure. The largest coding unit including the coding units of a tree structure may be called differently, such as a coding block tree, a block tree, a root block tree, a coding tree, a coding root, or a tree trunk. Video encoding and decoding schemes based on the coding units according to a tree structure will be described later with reference to  FIGS. 7 through 20 . 
     Inter prediction and inter-layer prediction may be performed based on a data unit of a coding unit, a prediction unit, or a transformation unit. 
     According to an embodiment, the first layer encoder  46  may generate symbol data by performing source coding operations including inter prediction or intra prediction on the first layer images. The symbol data represents a sample value of the residual and a sample value of each encoding parameter. 
     For example, the first layer encoder  46  may generate symbol data by performing inter prediction or intra prediction, transformation, and quantization on the samples of the data unit of the first layer images and may generate a first layer stream by performing entropy encoding on the symbol data. 
     The second layer encoder  48  may encode the second layer images based on the coding units of a tree structure. The second layer encoder  48  may generate symbol data by performing inter/intra prediction, transformation, and quantization on the samples of the data unit of the second layer images and may generate a second layer stream by performing entropy encoding on the symbol data. 
     According to an embodiment, the second layer encoder  48  may perform inter-layer prediction for predicting a second layer image by using a reconstruction sample of a first layer image. In order to encode a second layer original image among the second layer image sequence through an inter-layer prediction structure, the second layer encoder  48  may generate a second layer prediction image by using a first layer reconstruction image and may encode a prediction error between the second layer original image and the second layer prediction image. 
     The second layer encoder  48  may perform inter-layer prediction on a second layer image with respect to each block such as a coding unit or a prediction unit. A block of the first layer image to be referenced by a block of the second layer image may be determined. For example, a reconstruction block of a first layer image whose position corresponds to a position of a current block of the second layer image may be determined. The second layer encoder  48  may determine a second layer prediction block by using a first layer reconstruction block corresponding to the second layer block. 
     The second layer encoder  48  may use the second layer prediction block determined by using the first layer reconstruction block according to an inter-layer prediction structure, as a reference image for inter-layer prediction of the second layer original block. By using the first layer reconstruction image, the second layer encoder  48  may entropy-encode an error between the sample value of a second layer prediction block and the sample value of a second layer original block, that is, a residual component according to inter-layer prediction. 
     As described above, the second layer encoder  48  may encode the current layer image sequence with reference to the first layer reconstruction images through the inter-layer prediction structure. However, according to an embodiment, the second layer encoder  48  may encode the second layer image sequence according to the single-layer prediction structure without reference to other layer samples. Thus, it should be noted that the second layer encoder  48  is not limited as performing inter-layer prediction to encode the second layer image sequence. 
     The first layer encoder  46  generates a bitstream including the encoded information generated by encoding the first layer image. 
     The second layer encoder  48  may split the largest coding unit of a second layer image into one or more coding units and may split the coding unit into one or more prediction units for prediction encoding. The second layer encoder  48  encodes the prediction units split according to a plurality of prediction modes or partition modes, and determines an optimal prediction mode or partition mode based on a rate-distortion cost. The second layer decoder  48  may determine a structure of the coding unit by splitting the coding unit into one or more prediction units by using the determined prediction mode or partition mode of the coding unit. 
     The second layer encoder  48  determines whether to use a predetermined encoding tool based on at least one of the prediction mode, the size, and the color depth of the prediction unit, and encodes a current prediction unit according to the determination. 
     When the determined prediction unit has the same size as the coding unit, the second layer encoder  48  may perform encoding by using a predetermined encoding tool. The predetermined encoding tool used in the second layer encoder  48  may be a tool for performing encoding on the prediction unit by using the first layer image. The predetermined encoding tool may include at least one of MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), DDD (Disparity Derived Depth), VSP (View Synthesis Prediction), IC (Illumination Compensation), SDC (Segment-wise DC Coding), DMM (Depth Modeling Mode), DBBP (Depth-Based Block Partitioning), and ARP (Advanced Residual Prediction). 
       FIG. 5A  illustrates an inter-layer prediction structure according to an embodiment. 
     According to an embodiment, the inter-layer video encoding apparatus  45  may prediction-encode base view images, left view images, and right view images according to a reproduction order  50  of a multiview video prediction structure illustrated in  FIG. 5A . Information about the respective view images described below may be information included in each layer of a multilayer image. For example, information about a base view image may be information included in a base layer of the multilayer image, and information about a left view image or a right view image may be information included in an enhancement layer of the multilayer image. 
     According to the reproduction order  50  of a multiview video prediction structure according to the related art, same view images are arranged in a horizontal direction. Thus, the left view images represented by ‘Left’ are arranged in a line in the horizontal direction, the base view images represented by ‘Center’ are arranged in a line in the horizontal direction, and the right view images represented by ‘Right’ are arranged in a line in the horizontal direction. The base view images may be center view images in comparison with the left view/right view images. 
     Also, the images having the same POC order are arranged in the vertical direction. The POC order of the image may represent the reproduction order of the images constituting a video. “POC X” indicated in the multiview video prediction structure  50  may represent the relative reproduction order of the images located in a relevant column, wherein the reproduction order may be earlier as the number of X decreases, and the reproduction order may be later as the number of X increases. 
     Thus, according to the reproduction order  50  of a multiview video prediction structure according to the related art, the left view images represented by ‘Left’ are arranged in the horizontal direction according to the POC order (reproduction order), the base view images represented by ‘Center’ are arranged in the horizontal direction according to the POC order (reproduction order), and the right view images represented by ‘Right’ are arranged in the horizontal direction according to the POC order (reproduction order). Also, the left view images and the right view images located in the same column as the base view images are images that have the same POC order (reproduction order) while having different views. 
     In each view, four consecutive images constitute a Group of Pictures (GOP). Each GOP includes one anchor picture (key picture) and images between consecutive anchor pictures. 
     The anchor picture corresponds to a random access point. When a reproduction position is selected among the arranged images according to the POC order, that is, the reproduction order of an image in the process of reproducing a video, the anchor picture having the most adjacent POC order is reproduced at the reproduction position. The base view images include base view anchor pictures  51 ,  52 ,  53 ,  54 , and  55 , the left view images include left view anchor pictures  151 ,  152 ,  153 ,  154 , and  155 , and the right view images include right view anchor pictures  251 ,  252 ,  253 ,  254 , and  255 . 
     The multiview images may be reproduced and predicted (reconstructed) in the GOP order. First, according to the reproduction order  50  of a multiview video prediction structure, in each view, images included in GOP  0  may be reproduced and then images included in GOP  1  may be reproduced. That is, the images included in each GOP may be reproduced in the order of GOP  0 , GOP  1 , GOP  2 , and GOP  3 . Also, the coding order of a multiview video prediction structure, in each view, the images included in GOP  0  may be predicted (reconstructed) and then the images included in GOP  1  may be predicted (reconstructed). That is, the images included in each GOP may be predicted (reconstructed) in the order of GOP  0 , GOP  1 , GOP  2 , and GOP  3 . 
     According to the reproduction order of a multiview video prediction structure, both inter-view prediction (inter-layer prediction) and inter prediction are performed on images. In the multiview video prediction structure, an image at which an arrow starts corresponds to a reference image, and an image at which an arrow ends corresponds to an image predicted by using the reference image. 
     The prediction result of base view images may be encoded and then output in the form of a base view image stream, and the prediction result of additional view images may be encoded and then output in the form of a layer bitstream. Also, the prediction encoding result of left view images may be output as a first layer bitstream, and the prediction encoding result of right view images may be output as a second layer bitstream. 
     Only inter prediction may be performed on the base view images. That is, I-picture type anchor pictures  51 ,  52 ,  53 ,  54 , and  55  refers to other images, but B-picture type and b-picture type merged images are predicted with reference to other base view images. The B-picture type images may be predicted with reference to the following I-picture type anchor picture and the preceding I-picture type anchor picture having a preceding POC order. The B-picture type images may be predicted with reference to the following B-picture type image and the preceding I-picture type anchor picture having a preceding POC order, or may be predicted with reference to the following I-picture type anchor picture and the preceding B-picture type image having a preceding POC order. 
     Inter-view prediction (inter-layer prediction) referring to different view images and inter prediction referring to the same view images may be performed on the left view image and the right view image. 
     Inter-view prediction (inter-layer prediction) may be performed on the left view anchor pictures  151 ,  152 ,  153 ,  154 , and  155  with reference to the base view anchor pictures  51 ,  52 ,  53 ,  54 , and  55  having the same POC order. Inter-view prediction may be performed on the right view anchor pictures  251 ,  252 ,  253 ,  254 , and  255  with reference to the left view anchor pictures  151 ,  152 ,  153 ,  154 , and  155  or the base view images  51 ,  52 ,  53 ,  54 , and  55  having the same POC order. Also, inter-view prediction (inter-layer prediction) may be performed on the merged images (not the anchor pictures  151 ,  152 ,  153 ,  154 ,  155 ,  251 ,  252 ,  253 ,  254 , and  255 ) among the left view images and the right view images with reference to other view images having the same POC order. 
     The merged images (not the anchor pictures  151 ,  152 ,  153 ,  154 ,  155 ,  251 ,  252 ,  253 ,  254 , and  255 ) among the left view images and the right view images may be predicted with reference to the same view images. 
     However, the left view images and the right view images may not be predicted with reference to the anchor pictures having the preceding reproduction order among the same view additional view images. That is, a current left view image may be inter-predicted with reference to the left view images other than the left view anchor pictures having the preceding reproduction order than the current left view image. Likewise, a current right view image may be inter-predicted with reference to the right view images other than the right view anchor pictures having the preceding reproduction order than the current right view image. 
     Also, a current left view image may be inter-predicted with reference to the left view image that belongs to the current GOP but is to be reconstructed earlier than the current left view image, without reference to the left view image that belongs to the previous GOP preceding the current GOP to which the current left view image belongs. The same is true of the case of right view images. 
     According to an embodiment, the inter-layer video decoding apparatus  40  may reconstruct the base view images, the left view images, and the right view images according to the reproduction order  50  of a multiview video prediction structure illustrated in  FIG. 5A . 
     The left view images may be reconstructed by inter-view disparity compensation referring to the base view images and inter-image motion compensation referring to the left view images. The right view images may be reconstructed by inter-view disparity compensation referring to the base view images and the left view images and inter-image motion compensation referring to the right view images. The reference images should be first reconstructed for disparity compensation and motion compensation of the left view images and the right view images. 
     For inter-image motion compensation of the left view image, the left view images may be reconstructed by inter-image motion compensation referring to the reconstructed left view reference image. For inter-image motion compensation of the right view image, the left view images may be reconstructed by inter-image motion compensation referring to the reconstructed right view reference image. 
     Also, a current left view image may be inter-image motion compensated with reference to only the left view image that belongs to the current GOP but is to be reconstructed earlier than the current left view image, without reference to the left view image that belongs to the previous GOP preceding the current GOP to which the current left view image belongs. The same is true of the case of right view images. 
       FIG. 5B  is a diagram illustrating multiview video frames acquired through a multiview camera and depth map frames acquired through a depth camera. 
     Referring to  FIG. 5B , a depth map frame  58  of a first view ‘view  0 ’ corresponding to a color video frame  56  of the first view ‘view  0 ’, a depth map frame  58  of a second view ‘view  1 ’ corresponding to a color video frame  56  of the second view ‘view  1 ’, and a depth map frame  58  of a third view ‘view  2 ’ corresponding to a color video frame  56  of the third view ‘view  2 ’ are illustrated. Although  FIG. 5 b    illustrates a multiview color video frame  56  and a corresponding depth map frame  58  at three views ‘view  0 , view  1 , and view  2 ’, the number of views may vary according to embodiments. Also, in  FIG. 5B , the multiview color video frame  56  may be one of a luminance component video frame (Y) and a chrominance component video frame (Cb,Cr). 
     Referring to  FIG. 5B , between the depth map frame and the color video frames of the same view, since an image at the same view is represented by color and depth, there is a correlation therebetween. That is, when comparing the multiview color video frame  56  with the corresponding depth map frame  58 , there is a predetermined correlation, for example, the fact that a contour of a subject may be identified. Thus, according to an embodiment, the inter-layer video encoding apparatus  45  and the inter-layer video data decoding apparatus  20  may improve the compression efficiency of multiview video data by prediction-encoding the corresponding depth map frame  58  from the multiview color video frame  56  through depth intra prediction in consideration of the correlation between the multiview color video frame  56  and the corresponding depth map frame  58 . In particular, according to an embodiment of the inventive concept, the inter-layer video encoding apparatus  45  and the inter-layer video decoding apparatus  40  may split the block of the multiview color video frame  56  into partitions based on pixel values, split the block of the corresponding depth map frame  58  into partitions like the block of the multiview color video frame  56 , acquire a parameter representing the correlation between the block partitions of a multiview color video frame and the block partitions of a depth map frame by using the neighboring pixel values of the block partitions of the multiview color video frame  56  and the neighboring pixel values of the block partitions of the depth map frame, and predict a block partition of the corresponding depth frame from the partition of the block of the multiview color video frame  56  by using the correlation determined by using the acquired parameter. 
       FIGS. 6A and 6B  illustrate the contents related to a prediction mode using color information and depth information in a method of predicting a multiview video as a multilayer video. 
       FIG. 6A  is a diagram illustrating an encoding tool used in a decoding process of the inter-layer video decoding apparatus  40 , according to an embodiment. 
     In the present embodiment, the inter-layer video decoding apparatus  40  such as a single view decoder  61 , a depth map decoder  62 , a multiview decoder  63 , and a multiview depth map decoder  64  may be physically divided; however, those of ordinary skill in the art may easily understand that one inter-layer video decoding apparatus  40  may be functionally divided. 
     Referring to  FIG. 6A , encoding information of a color image of View  0  may be decoded by using the single view decoder  61 . In the case of the single view decoder  61 , a tool used for decoding may perform decoding without using a depth map image or other view images. 
     Encoding information of a depth image of View  0  may be input as an input of the depth map decoder  62 . Unlike the single view decoder  61 , the depth map decoder  62  may use a decoded color image of View  0 . The depth image may be reconstructed by additional information, in which distance information of a subject and a camera is stored with respect to a certain pixel of a color image, and then virtual view images may be synthesized together with the color image. A 3D stereoscopy may be represented by the virtual view images. 
     Thus, in the color and depth images encoded for 3D stereoscopy, tools for encoding color images by using depth images, tools for encoding depth images by using color images, tools for encoding color images without using depth images, or tools for encoding depth images without using color images will be referred to as 3D encoding tools. In particular, not only encoding tools used to decode depth images without using color images but also tools used to decode only depth images may be referred to as 3D encoding tools because they may be used together with the encoding information of color images to generate a 3D image. 
     The tools used to encode/decode depth images may include SDC (Segment-wise DC Coding) and DMM (Depth Modeling Mode). The SDC (Segment-wise DC Coding) may be a tool or mode used to decode a residual signal of a depth image in a DC form. The DMM (Depth Modeling Mode) may be a tool or mode for splitting and decoding a depth image. Examples of the tools used to decode other depth images may include MPI (Motion Parameter Inheritance) and DDD (Disparity Derived Depth). In this case, the MPI (Motion Parameter Inheritance) may refer to an encoding tool or mode that uses the motion information of a color image for decoding of a depth image as it is. In this case, the DDD (Disparity Derived Depth) may refer to an encoding tool or mode that uses the motion information of a color image as a reconstruction sample value of a depth image as it is. 
     Encoding information of a color image of View  1  may be input as an input of the multiview decoder  63 . The multiview decoder may perform decoding by using the encoding information of a depth image of View  0  as well as a color image of View  0 . In this case, a tool used to perform decoding with reference to at least one of the color image of View  0  and the depth image of View  0  may be included in a 3D encoding tool as a tool used to generate a multiview image. 
     Examples of the 3D encoding tool may include ARP (Advanced residual prediction), IC (Illumination Compensation), VSP (View Synthesis Prediction), DBBP (Depth-Based Block Partitioning), and IVMP (Inter-view Motion Parameter Prediction). The ARP (Advanced residual prediction) may be a tool used to predict a residual signal from a multiview image. The IC (Illumination Compensation) may be a tool for compensating the luminance of a current image from the images of a neighboring view. The VSP (View Synthesis Prediction) may be a tool or mode for performing prediction encoding by using a synthesized image or a depth image as a reference image by using the color or depth image of a neighboring view. The IVMP (Inter-view Motion Parameter Prediction) may be an encoding tool of mode for copying motion information in an image of an adjacent view by using a depth image. The DBBP (Depth-Based Block Partitioning) may refer to an encoding tool for performing prediction by splitting a color image into depth images. Also, the 3D encoding tool may include an encoding tool used in an image of an enhancement layer or a depth image representing depth information. 
     Encoding information of a depth image of View  1  may be input as an input of the multiview depth map decoder  64 . The multiview decoder may perform decoding by using a depth image of View  0  as well as a color image of View  0 . Also, it may perform decoding by using a color image of View  1 . An encoding tool for performing decoding by using depth images and color images of View  0  and color images of View  1  may be included in a 3D encoding tool used to generate a multiview image. 
     Although an example performed in the inter-layer video decoding apparatus  40  has been described above, those of ordinary skill in the art may easily understand that it may also be performed in the inter-layer video encoding apparatus 
       FIG. 6B  is a diagram illustrating the contents of using an encoding tool according to prediction unit size, prediction mode, and color depth information by the inter-layer video decoding apparatus  40 , according to an embodiment. 
     Referring to  FIG. 6B , a coding unit  65  is divided into various prediction units according to sizes  66 . The inter-layer video decoding apparatus  40  may receive partition mode information from a bitstream to determine the size of a prediction unit. For example, when receiving PART 2N×2N information as partition mode information about the coding unit  65 , the inter-layer video decoding apparatus  40  may set the prediction unit to have the same size as the coding unit  65 . Herein, N may represent the half of the height or width of the coding unit. The partition mode information may include information such as PART 2N×2N, PART 2N×N, PART N×2N, PART N×N, PART 2N×nU PART 2N×Nd, PART nL×2N, and PART nR×2N. Herein, each of nU, nD, nL, and nR may represent the position of a portion corresponding to ¼ of the coding unit. 
     According to an embodiment of the inventive concept, in the inter-layer video decoding apparatus  40 , the size of the prediction unit split according to the prediction mode may be restricted. For example, when the prediction mode determined in the inter-layer video decoding apparatus  40  is an intra prediction mode, the partition mode information may include only PART 2N×2N and PART N×N. 
     The partition mode information acquired from a bitstream may represent only the relative size with respect to the coding unit  65 . Thus, the size of the coding unit should be first determined in order to determine the absolute size of the prediction unit. The inter-layer video decoding apparatus  40  may determine the size of the coding unit based on the coding unit information of the largest size and the split information representing the split degree. 
     For example, when the coding unit information of the largest size represents 65×65 pixels and the split information represents two-time splitting, since it correspond to the case of two-time quad-split, it may be determined that the size of the coding unit is 16×16. Also, when the partition mode information is PART N*N, it corresponds to ¼ of the coding unit and thus the size of the prediction unit is 8*8. Thus, the size of the prediction unit may be determined based on the partition mode information and the split size of the coding unit  65  determined. However, the inventive concept is not limited thereto, and information about the size of the prediction unit may be acquired based on various types of information. 
     According to an embodiment of the inventive concept, when the size of the coding unit and the size of the prediction unit are equal to each other, that is, when the partition mode information of the coding unit represents PART 2N*2N, the inter-layer video decoding apparatus  40  may perform decoding the prediction unit by using a predetermined encoding tool. In this case, the predetermined encoding tool may be a 3D encoding tool. Thus, an operation load may be reduced by using the predetermined encoding tool to perform prediction decoding in the unit corresponding to the case where the coding unit is not further split. Also, according to an embodiment of the inventive concept, the inter-layer video decoding apparatus  40  may not perform decoding on the prediction unit by using a predetermined encoding tool with respect to the block having a predetermined size or less. For example, the inter-layer video decoding apparatus  40  may perform decoding by using a predetermined encoding tool only when the size of the prediction unit is greater than or equal to 8×8. Also, the inter-layer video decoding apparatus  40  may perform decoding by using a predetermined encoding tool only when the prediction unit has a size other than greater than 8×4 and 4×8. Also, the inter-layer video decoding apparatus  40  may perform decoding by using a predetermined encoding tool only in the case of other than an AMP (Asymmetric Motion Partition) form, for example, forms such as PART 2N×nU PART 2N×Nd, PART nL×2N, and PART nR×2N. 
     Also, the inter-layer video decoding apparatus  40  may perform decoding by using a predetermined encoding tool only when the size of the prediction unit is greater than or equal to 8×8. However, the prediction unit is not limited to such sizes, and the inter-layer video decoding apparatus  40  may determine whether to use a predetermined encoding tool according to various sizes and may perform decoding on the prediction unit according to the determination. For example, MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), or DDD (Disparity Derived Depth) may be used to perform decoding only when the prediction unit has a size other than 8×4 and 4×8. For example, MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), VSP (View Synthesis Prediction), or DDD (Disparity Derived Depth) may be used to perform decoding only when the prediction unit has a size other than 8×4 and 4×8. For example, ARP (Advanced Residual Prediction) IC(Illumination Compensation), or SDC(Segment-wise DC Coding) may be used to perform decoding only when the partition mode information is PART 2N*2N. 
     Referring to  FIG. 6B , the prediction mode of the coding unit  65  may vary. The prediction mode may generally include an inter prediction mode that is an inter-picture prediction mode and an intra prediction mode that is an intra-picture prediction mode. 
     In the present embodiment, the inter prediction mode may include a mode for performing prediction by using different-view images. The inter prediction mode may include Skip, Merge, and AMVP (Advanced motion vector Predictor). 
     The merge mode may refer to a mode for predicting the prediction unit by deriving a reference direction, a reference picture index, a disparity vector, and a motion vector prediction value by merging a current prediction unit with an adjacent data unit. The skip mode may refer to a mode for transmitting only neighboring block selection information without transmission of a residual image. The AMVP is technology for deriving only a motion vector prediction value from a neighboring block, wherein a differential motion vector, reference picture identification information, and a reference picture index are included and transmitted in a bitstream. 
     The information about the prediction mode may include information about the prediction mode for the coding unit  65  including the prediction unit. For example, when the prediction mode for the coding unit  65  is an intra prediction mode, the prediction mode for the prediction unit included in the coding unit  65  may also be an intra prediction mode. 
     According to an embodiment of the inventive concept, when the prediction mode of the prediction unit is a particular mode, the inter-layer video decoding apparatus  40  may be restricted to use a predetermined encoding tool. Alternatively, the inter-layer video decoding apparatus  40  may perform decoding on the prediction unit by using a predetermined encoding tool only when the prediction mode of the prediction unit is the merge mode. Also, when the prediction mode of the prediction unit is the skip mode, the inter-layer video decoding apparatus  40  may perform decoding on the prediction unit by using a predetermined encoding tool. For example, as one of the predetermined encoding tool, VSP (View synthesis Prediction) may be used to perform decoding in the case of the merge mode. For example, MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), DDD (Disparity Derived Depth), or VSP (View Synthesis Prediction) may be used to perform decoding in the case of the merge mode. By using the 3D encoding tool to perform decoding on the prediction mode having a relatively small operation load, the operation load in the inter-layer video decoding apparatus  40  may be reduced. 
     Referring to  FIG. 6 b   , the prediction unit may include color information or depth information (hereinafter referred to as color depth information). Herein, the color information may include luminance information and chrominance information. The depth information may represent distance information of a subject and a camera of the block corresponding to the color information. The inter-layer video decoding apparatus  40  may determine the depth information or the color information of the prediction unit by acquiring the depth information or the color information about the unit including a prediction unit such as a frame unit from a bitstream. 
     According to an embodiment of the inventive concept, when the prediction unit includes depth information, the inter-layer video decoding apparatus  40  may perform decoding by using a predetermined encoding tool. Alternatively, when the prediction unit includes color information, the inter-layer video decoding apparatus  40  may perform decoding by using another predetermined encoding tool. 
     As described above, the inter-layer video decoding apparatus  40  according to an embodiment of the inventive concept may determine whether to perform decoding by using a predetermined encoding tool according to one condition among the size and the prediction mode or color depth information acquired from a bitstream. However, the inventive concept is not limited thereto, and whether to perform decoding a predetermined encoding tool may be determined according to whether a plurality of conditions are satisfied. For example, when the prediction mode of the prediction unit is the merge mode and the size of the prediction unit is equal to the size of the coding unit, the inter-layer video decoding apparatus  40  may determine whether to perform decoding by using a predetermined encoding tool. Also, for example, when the prediction unit includes depth information and the size of the prediction unit is equal to the size of the coding unit, the inter-layer video decoding apparatus  40  may determine whether to perform decoding a predetermined encoding tool. Also, for example, when the prediction mode of the prediction unit is the merge mode and the size of the prediction unit is greater than or equal to 8×8, the inter-layer video decoding apparatus  40  may determine whether to perform decoding by using a predetermined encoding tool. For example, MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), or DDD (Disparity Derived Depth) may be used to perform decoding only when the prediction mode is the merge mode and the prediction unit has a size other than 8×4 and 4×8. For example, MPI (Motion Parameter Inheritance), IVMP (Inter-View Motion Parameter Prediction), VSP (View Synthesis Prediction), or DDD (Disparity Derived Depth) may be used to perform decoding only when the prediction mode is the merge mode and the prediction unit has a size other than 8×4 and 4×8. 
     The inter-layer video decoding apparatus  40  according to an embodiment of the inventive concept has been mainly described above. The inter-layer video decoding apparatus  40  determines whether to use a predetermined encoding tool by acquiring the color depth information, the size information, and the prediction mode information about the prediction unit from a bitstream, while the inter-layer video encoding apparatus  45  performs encoding on the prediction unit by applying various prediction modes or sizes, determines the prediction mode or size according to the calculated rate-distortion cost, and splits the same into one or more prediction units according to the determined prediction mode or size. The inter-layer video encoding apparatus  45  is different from the inter-layer video decoding apparatus  40  only in that it determines whether to use a predetermined encoding tool based on the color depth, size, and prediction mode of the split prediction unit, and an operation of determining whether to use a predetermined encoding unit is the same as that of the inter-layer video decoding apparatus  40 . Thus, redundant descriptions of the operation of an encoder will be omitted for conciseness. 
       FIG. 7  illustrates a block diagram of a video encoding apparatus based on coding units of a tree structure  100 , according to various embodiments. The video encoding apparatus  100  of  FIG. 7  may correspond to the video encoding apparatus  15  of  FIG. 1B . Also, the operations performed by a largest coding unit splitter  110  and a coding unit determiner  120  of  FIG. 7  may be performed by the controller  16  of  FIG. 1 b   , and the operation performed by an output unit  130  of  FIG. 7  may be performed by the bitstream generator  17  of  FIG. 1B . 
     The video encoding apparatus involving video prediction based on coding units of the tree structure  100  includes a coding unit determiner  120  and an output unit  130 . Hereinafter, for convenience of description, the video encoding apparatus involving video prediction based on coding units of the tree structure  100  is referred to as the ‘video encoding apparatus  100 ’. 
     The coding unit determiner  120  may split a current picture based on a largest coding unit that is a coding unit having a maximum size for a current picture of an image. If the current picture is larger than the largest coding unit, image data of the current picture may be split into the at least one largest coding unit. The largest coding unit according to an embodiment may be a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc., wherein a shape of the data unit is a square having a width and length in squares of 2. 
     A coding unit according to an embodiment may be characterized by a maximum size and a depth. The depth denotes the number of times the coding unit is spatially split from the largest coding unit, and as the depth deepens, deeper coding units according to depths may be split from the largest coding unit to a smallest coding unit. A depth of the largest coding unit may be defined as an uppermost depth and a depth of the smallest coding unit may be defined as a lowermost depth. Since a size of a coding unit corresponding to each depth decreases as the depth of the largest coding unit deepens, a coding unit corresponding to an upper depth may include a plurality of coding units corresponding to lower depths. 
     As described above, the image data of the current picture is split into the largest coding units according to a maximum size of the coding unit, and each of the largest coding units may include deeper coding units that are split according to depths. Since the largest coding unit according to an embodiment is split according to depths, the image data of a spatial domain included in the largest coding unit may be hierarchically classified according to depths. 
     A maximum depth and a maximum size of a coding unit, which limit the total number of times a height and a width of the largest coding unit are hierarchically split, may be predetermined. 
     The coding unit determiner  120  encodes at least one split region obtained by splitting a region of the largest coding unit according to depths, and determines a depth to output a finally encoded image data according to the at least one split region. That is, the coding unit determiner  120  determines a final depth by encoding the image data in the deeper coding units according to depths, according to the largest coding unit of the current picture, and selecting a depth having the minimum encoding error. The determined final depth and image data according to largest coding units are output to the output unit  130 . 
     The image data in the largest coding unit is encoded based on the deeper coding units corresponding to at least one depth equal to or below the maximum depth, and results of encoding the image data based on each of the deeper coding units are compared. A depth having the minimum encoding error may be selected after comparing encoding errors of the deeper coding units. At least one final depth may be selected for each largest coding unit. 
     The size of the largest coding unit is split as a coding unit is hierarchically split according to depths, and as the number of coding units increases. Also, even if coding units correspond to the same depth in one largest coding unit, it is determined whether to split each of the coding units corresponding to the same depth to a lower depth by measuring an encoding error of the image data of the each coding unit, separately. Accordingly, even when image data is included in one largest coding unit, the encoding errors may differ according to regions in the one largest coding unit, and thus the final depths may differ according to regions in the image data. Thus, one or more final depths may be determined in one largest coding unit, and the image data of the largest coding unit may be divided according to coding units of at least one final depth. 
     Accordingly, the coding unit determiner  120  according to the embodiment may determine coding units having a tree structure included in the largest coding unit. The ‘coding units having a tree structure’ according to an embodiment include coding units corresponding to a depth determined to be the final depth, from among all deeper coding units included in the largest coding unit. A coding unit of a final depth may be hierarchically determined according to depths in the same region of the largest coding unit, and may be independently determined in different regions. Equally, a final depth in a current region may be independently determined from a final depth in another region. 
     A maximum depth according to an embodiment is an index related to the number of splitting times from a largest coding unit to a smallest coding unit. A first maximum depth according to an embodiment may denote the total number of splitting times from the largest coding unit to the smallest coding unit. A second maximum depth according to an embodiment may denote the total number of depth levels from the largest coding unit to the smallest coding unit. For example, when a depth of the largest coding unit is 0, a depth of a coding unit, in which the largest coding unit is split once, may be set to 1, and a depth of a coding unit, in which the largest coding unit is split twice, may be set to 2. Here, if the smallest coding unit is a coding unit in which the largest coding unit is split four times, depth levels of depths 0, 1, 2, 3, and 4 exist, and thus the first maximum depth may be set to 4, and the second maximum depth may be set to 5. 
     Prediction encoding and transformation may be performed according to the largest coding unit. The prediction encoding and the transformation are also performed based on the deeper coding units according to a depth equal to or depths less than the maximum depth, according to the largest coding unit. 
     Since the number of deeper coding units increases whenever the largest coding unit is split according to depths, encoding, including the prediction encoding and the transformation, has to be performed on all of the deeper coding units generated as the depth deepens. Hereinafter, for convenience of description, the prediction encoding and the transformation will be described based on a coding unit of a current depth in at least one largest coding unit. 
     The video encoding apparatus  100  according to the embodiment may variously select a size or shape of a data unit for encoding the image data. In order to encode the image data, operations, such as prediction encoding, transformation, and entropy encoding, are performed, and at this time, the same data unit may be used for all operations or different data units may be used for each operation. 
     For example, the video encoding apparatus  100  may select not only a coding unit for encoding the image data, but may also select a data unit different from the coding unit so as to perform the prediction encoding on the image data in the coding unit. 
     In order to perform prediction encoding in the largest coding unit, the prediction encoding may be performed based on a coding unit of a final depth, i.e., based on the coding unit that is no longer split. A partition obtained by splitting a prediction unit may include a coding unit and a data unit obtained by splitting at least one selected from a height and a width of the coding unit. A partition may include a data unit where a coding unit is split and a data unit having the same size as the coding unit. A partition that is a base of prediction may be referred to as a ‘prediction unit’. 
     For example, when a coding unit of 2N×2N (where N is a positive integer) is no longer split and becomes a prediction unit of 2N×2N, and a size of a partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partition mode may include symmetrical partitions obtained by symmetrically splitting a height or width of the prediction unit, and may selectively include partitions obtained by asymmetrically splitting the height or width of the prediction unit, such as 1:n or n:1, partitions obtained by geometrically splitting the prediction unit, and partitions having arbitrary shapes. 
     A prediction mode of the prediction unit may be at least one of an intra mode, an inter mode, and a skip mode. For example, the intra mode and the inter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, or N×N. Also, the skip mode may be performed only on the partition of 2N×2N. The encoding may be independently performed on one prediction unit in a coding unit, thereby selecting a prediction mode having a minimum encoding error. 
     The video encoding apparatus  100  according to the embodiment may also perform the transformation on the image data in a coding unit based not only on the coding unit for encoding the image data, but also based on a data unit that is different from the coding unit. In order to perform the transformation in the coding unit, the transformation may be performed based on a data unit having a size smaller than or equal to the coding unit. For example, the transformation unit may include a data unit for an intra mode and a transformation unit for an inter mode. 
     The transformation unit in the coding unit may be recursively split into smaller sized regions in the similar manner as the coding unit according to the tree structure, thus, residual data of the coding unit may be divided according to the transformation unit having the tree structure according to a transformation depth. 
     A transformation depth indicating the number of splitting times to reach the transformation unit by splitting the height and width of the coding unit may also be set in the transformation unit. For example, in a current coding unit of 2N×2N, a transformation depth may be 0 when the size of a transformation unit is 2N×2N, may be 1 when the size of the transformation unit is N×N, and may be 2 when the size of the transformation unit is N/2×N/2. That is, with respect to the transformation unit, the transformation unit having the tree structure may be set according to the transformation depths. 
     Split information according to depths requires not only information about a depth but also requires information related to prediction and transformation. Accordingly, the coding unit determiner  120  may determine not only a depth generating a minimum encoding error but may also determine a partition mode in which a prediction unit is split to partitions, a prediction mode according to prediction units, and a size of a transformation unit for transformation. 
     Coding units according to a tree structure in a largest coding unit and methods of determining a prediction unit/partition, and a transformation unit, according to embodiments, will be described in detail later with reference to  FIGS. 9 through 19 . 
     The coding unit determiner  120  may measure an encoding error of deeper coding units according to depths by using Rate-Distortion Optimization based on Lagrangian multipliers. 
     The output unit  130  outputs, in bitstreams, the image data of the largest coding unit, which is encoded based on the at least one depth determined by the coding unit determiner  120 , and information according to depths. 
     The encoded image data may correspond to a result obtained by encoding residual data of an image. 
     The split information according to depths may include depth information, partition mode information of the prediction unit, prediction mode information, and the split information of the transformation unit. 
     Final depth information may be defined by using split information according to depths, which specifies whether encoding is performed on coding units of a lower depth instead of a current depth. If the current depth of the current coding unit is a depth, the current coding unit is encoded by using the coding unit of the current depth, and thus split information of the current depth may be defined not to split the current coding unit to a lower depth. On the contrary, if the current depth of the current coding unit is not the depth, the encoding has to be performed on the coding unit of the lower depth, and thus the split information of the current depth may be defined to split the current coding unit to the coding units of the lower depth. 
     If the current depth is not the depth, encoding is performed on the coding unit that is split into the coding unit of the lower depth. Since at least one coding unit of the lower depth exists in one coding unit of the current depth, the encoding is repeatedly performed on each coding unit of the lower depth, and thus the encoding may be recursively performed for the coding units having the same depth. 
     Since the coding units having a tree structure are determined for one largest coding unit, and at least one piece of split information has to be determined for a coding unit of a depth, at least one piece of split information may be determined for one largest coding unit. Also, a depth of data of the largest coding unit may vary according to locations since the data is hierarchically split according to depths, and thus a depth and split information may be set for the data. 
     Accordingly, the output unit  130  according to the embodiment may assign encoding information about a corresponding depth and an encoding mode to at least one of the coding unit, the prediction unit, and a minimum unit included in the largest coding unit. 
     The minimum unit according to an embodiment is a square data unit obtained by splitting the smallest coding unit constituting the lowermost depth by 4. Alternatively, the minimum unit according to an embodiment may be a maximum square data unit that may be included in all of the coding units, prediction units, partition units, and transformation units included in the largest coding unit. 
     For example, the encoding information output by the output unit  130  may be classified into encoding information according to deeper coding units, and encoding information according to prediction units. The encoding information according to the deeper coding units may include the information about the prediction mode and about the size of the partitions. The encoding information according to the prediction units may include information about an estimated direction during an inter mode, about a reference image index of the inter mode, about a motion vector, about a chroma component of an intra mode, and about an interpolation method during the intra mode. 
     Information about a maximum size of the coding unit defined according to pictures, slices, or GOPs, and information about a maximum depth may be inserted into a header of a bitstream, a sequence parameter set, or a picture parameter set. 
     Information about a maximum size of the transformation unit permitted with respect to a current video, and information about a minimum size of the transformation unit may also be output through a header of a bitstream, a sequence parameter set, or a picture parameter set. The output unit  130  may encode and output reference information, prediction information, and slice type information, which are related to prediction. 
     According to the simplest embodiment for the video encoding apparatus  100 , the deeper coding unit may be a coding unit obtained by dividing a height or width of a coding unit of an upper depth, which is one layer above, by two. That is, when the size of the coding unit of the current depth is 2N×2N, the size of the coding unit of the lower depth is N×N. Also, a current coding unit having a size of 2N×2N may maximally include four lower-depth coding units having a size of N×N. 
     Accordingly, the video encoding apparatus  100  may form the coding units having the tree structure by determining coding units having an optimum shape and an optimum size for each largest coding unit, based on the size of the largest coding unit and the maximum depth determined considering characteristics of the current picture. Also, since encoding may be performed on each largest coding unit by using any one of various prediction modes and transformations, an optimal encoding mode may be determined by taking into account characteristics of the coding unit of various image sizes. 
     Thus, if an image having a high resolution or a large data amount is encoded in a conventional macroblock, the number of macroblocks per picture excessively increases. Accordingly, the number of pieces of compressed information generated for each macroblock increases, and thus it is difficult to transmit the compressed information and data compression efficiency decreases. However, by using the video encoding apparatus according to the embodiment, image compression efficiency may be increased since a coding unit is adjusted while considering characteristics of an image while increasing a maximum size of a coding unit while considering a size of the image. 
       FIG. 8  illustrates a block diagram of a video decoding apparatus based on coding units of a tree structure  200 , according to various embodiments. The video decoding apparatus  200  of  FIG. 8  may correspond to the video decoding apparatus  10  of  FIG. 1A . Also, the operations performed by an image data and encoding information extractor  220  and an image data decoder  230  of  FIG. 8  may be performed by the controller  11  of  FIG. 1A , and the operation performed by a receiver  210  of  FIG. 8  may be performed by the information acquirer  12  of  FIG. 1A . 
     The video decoding apparatus involving video prediction based on coding units of the tree structure  200  according to the embodiment includes a receiver  210 , an image data and encoding information extractor  220 , and an image data decoder  230 . Hereinafter, for convenience of description, the video decoding apparatus involving video prediction based on coding units of the tree structure  200  according to the embodiment is referred to as the ‘video decoding apparatus  200 ’. 
     Definitions of various terms, such as a coding unit, a depth, a prediction unit, a transformation unit, and various types of split information for decoding operations of the video decoding apparatus  200  according to the embodiment are identical to those described with reference to  FIG. 7  and the video encoding apparatus  100 . 
     The receiver  210  receives and parses a bitstream of an encoded video. The image data and encoding information extractor  220  extracts encoded image data for each coding unit from the parsed bitstream, wherein the coding units have a tree structure according to each largest coding unit, and outputs the extracted image data to the image data decoder  230 . The image data and encoding information extractor  220  may extract information about a maximum size of a coding unit of a current picture, from a header about the current picture, a sequence parameter set, or a picture parameter set. 
     Also, the image data and encoding information extractor  220  extracts, from the parsed bitstream, a final depth and split information about the coding units having a tree structure according to each largest coding unit. The extracted final depth and the extracted split information are output to the image data decoder  230 . That is, the image data in a bit stream is split into the largest coding unit so that the image data decoder  230  may decode the image data for each largest coding unit. 
     A depth and split information according to each of the largest coding units may be set for one or more pieces of depth information, and split information according to depths may include partition mode information of a corresponding coding unit, prediction mode information, and split information of a transformation unit. Also, as the depth information, the split information according to depths may be extracted. 
     The depth and the split information according to each of the largest coding units extracted by the image data and encoding information extractor  220  are a depth and split information determined to generate a minimum encoding error when an encoder, such as the video encoding apparatus  100 , repeatedly performs encoding for each deeper coding unit according to depths according to each largest coding unit. Accordingly, the video decoding apparatus  200  may reconstruct an image by decoding data according to an encoding method that generates the minimum encoding error. 
     Since encoding information about the depth and the encoding mode may be assigned to a predetermined data unit from among a corresponding coding unit, a prediction unit, and a minimum unit, the image data and encoding information extractor  220  may extract the depth and the split information according to the predetermined data units. If a depth and split information of a corresponding largest coding unit are recorded according to each of the predetermined data units, predetermined data units having the same depth and the split information may be inferred to be the data units included in the same largest coding unit. 
     The image data decoder  230  reconstructs the current picture by decoding the image data in each largest coding unit based on the depth and the split information according to each of the largest coding units. That is, the image data decoder  230  may decode the encoded image data, based on a read partition mode, a prediction mode, and a transformation unit for each coding unit from among the coding units having the tree structure included in each largest coding unit. A decoding process may include a prediction process including intra prediction and motion compensation, and an inverse transformation process. 
     The image data decoder  230  may perform intra prediction or motion compensation according to a partition and a prediction mode of each coding unit, based on the information about the partition type and the prediction mode of the prediction unit of the coding unit according to depths. 
     In addition, for inverse transformation for each largest coding unit, the image data decoder  230  may read information about a transformation unit according to a tree structure for each coding unit so as to perform inverse transformation based on transformation units for each coding unit. Due to the inverse transformation, a pixel value of a spatial domain of the coding unit may be reconstructed. 
     The image data decoder  230  may determine a depth of a current largest coding unit by using split information according to depths. If the split information indicates that image data is no longer split in the current depth, the current depth is a depth. Accordingly, the image data decoder  230  may decode the image data of the current largest coding unit by using the information about the partition mode of the prediction unit, the prediction mode, and the size of the transformation unit for each coding unit corresponding to the current depth. 
     That is, data units containing the encoding information including the same split information may be gathered by observing the encoding information set assigned for the predetermined data unit from among the coding unit, the prediction unit, and the minimum unit, and the gathered data units may be considered to be one data unit to be decoded by the image data decoder  230  in the same encoding mode. As such, the current coding unit may be decoded by obtaining the information about the encoding mode for each coding unit. 
     The image decoding apparatus  30  described above with reference to  FIG. 3A  may include the video decoding apparatuses  200  corresponding to the number of views, so as to reconstruct first layer images and second layer images by decoding a received first layer image stream and a received second layer image stream. 
     When the first layer image stream is received, the image data decoder  230  of the video decoding apparatus  200  may split samples of the first layer images, which are extracted from the first layer image stream by an extractor  220 , into coding units according to a tree structure of a largest coding unit. The image data decoder  230  may perform motion compensation, based on prediction units for the inter-image prediction, on each of the coding units according to the tree structure of the samples of the first layer images, and may reconstruct the first layer images. 
     When the second layer image stream is received, the image data decoder  230  of the video decoding apparatus  200  may split samples of the second layer images, which are extracted from the second layer image stream by the extractor  220 , into coding units according to a tree structure of a largest coding unit. The image data decoder  230  may perform motion compensation, based on prediction units for the inter-image prediction, on each of the coding units of the samples of the second layer images, and may reconstruct the second layer images. 
     The extractor  220  may obtain, from a bitstream, information related to a luminance error so as to compensate for a luminance difference between the first layer image and the second layer image. However, whether to perform luminance compensation may be determined according to an encoding mode of a coding unit. For example, the luminance compensation may be performed only on a prediction unit having a size of 2N×2N. 
     Thus, the video decoding apparatus  200  may obtain information about at least one coding unit that generates the minimum encoding error when encoding is recursively performed for each largest coding unit, and may use the information to decode the current picture. That is, the coding units having the tree structure determined to be the optimum coding units in each largest coding unit may be decoded. 
     Accordingly, even if an image has high resolution or has an excessively large data amount, the image may be efficiently decoded and reconstructed by using a size of a coding unit and an encoding mode, which are adaptively determined according to characteristics of the image, by using optimal split information received from an encoding terminal. 
       FIG. 9  illustrates a concept of coding units, according to various embodiments. 
     A size of a coding unit may be expressed by width×height, and may be 64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split into partitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32 may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a coding unit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8, and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8, or 4×4. 
     In video data  310 , a resolution is 1920×1080, a maximum size of a coding unit is 64, and a maximum depth is 2. In video data  320 , a resolution is 1920×1080, a maximum size of a coding unit is 64, and a maximum depth is 3. In video data  330 , a resolution is 352×288, a maximum size of a coding unit is 16, and a maximum depth is 1. The maximum depth shown in  FIG. 10  denotes the total number of splits from a largest coding unit to a smallest coding unit. 
     If a resolution is high or a data amount is large, it is preferable that a maximum size of a coding unit is large so as to not only increase encoding efficiency but also to accurately reflect characteristics of an image. Accordingly, the maximum size of the coding unit of the video data  310  and  320  having a higher resolution than the video data  330  may be selected to 64. 
     Since the maximum depth of the video data  310  is 2, coding units  315  of the video data  310  may include a largest coding unit having a long axis size of 64, and coding units having long axis sizes of 32 and 16 since depths are deepened to two layers by splitting the largest coding unit twice. On the other hand, since the maximum depth of the video data  330  is 1, coding units  335  of the video data  330  may include a largest coding unit having a long axis size of 16, and coding units having a long axis size of 8 since depths are deepened to one layer by splitting the largest coding unit once. 
     Since the maximum depth of the video data  320  is 3, coding units  325  of the video data  320  may include a largest coding unit having a long axis size of 64, and coding units having long axis sizes of 32, 16, and 8 since the depths are deepened to 3 layers by splitting the largest coding unit three times. As a depth deepens, an expression capability with respect to detailed information may be improved. 
       FIG. 10  illustrates a block diagram of an image encoder  400  based on coding units, according to various embodiments. 
     The image encoder  400  according to an embodiment performs operations of a picture encoder  120  of the video encoding apparatus  100  so as to encode image data. That is, an intra predictor  420  performs intra prediction on coding units in an intra mode, from among a current image  405 , and an inter predictor  415  performs inter prediction on coding units in an inter mode by using the current image  405  and a reference image obtained from a reconstructed picture buffer  410  according to prediction units. The current image  405  may be split into largest coding units and then the largest coding units may be sequentially encoded. In this regard, the largest coding units that are to be split into coding units having a tree structure may be encoded. 
     Residue data is generated by removing prediction data regarding a coding unit of each mode which is output from the intra predictor  420  or the inter predictor  415  from data regarding an encoded coding unit of the current image  405 , and the residue data is output as a quantized transformation coefficient according to transformation units through a transformer  425  and a quantizer  430 . The quantized transformation coefficient is reconstructed as the residue data in a spatial domain through an inverse quantizer  445  and an inverse transformer  450 . The reconstructed residual image data in the spatial domain is added to prediction data for the coding unit of each mode which is output from the intra predictor  420  or the inter predictor  415  and thus is reconstructed as data in a spatial domain for a coding unit of the current image  405 . The reconstructed data in the spatial domain is generated as a reconstructed image through a deblocking unit  455  and an SAO performer  460  and the reconstructed image is stored in the reconstructed picture buffer  410 . The reconstructed images stored in the reconstructed picture buffer  410  may be used as reference images for inter predicting another image. The transformation coefficient quantized by the transformer  425  and the quantizer  430  may be output as a bitstream  440  through an entropy encoder  435 . 
     In order for the image encoder  400  to be applied in the video encoding apparatus  100 , all elements of the image encoder  400 , i.e., the inter predictor  415 , the intra predictor  420 , the transformer  425 , the quantizer  430 , the entropy encoder  435 , the inverse quantizer  445 , the inverse transformer  450 , the deblocking unit  455 , and the SAO performer  460 , may perform operations based on each coding unit among coding units having a tree structure according to each largest coding unit. 
     In particular, the intra predictor  420  and the inter predictor  415  may determine a partition mode and a prediction mode of each coding unit from among the coding units having a tree structure, by taking into account the maximum size and the maximum depth of a current largest coding unit, and the transformer  425  may determine whether to split a transformation unit according to a quad tree in each coding unit from among the coding units having a tree structure. 
       FIG. 11  illustrates a block diagram of an image decoder  500  based on coding units, according to various embodiments. 
     An entropy decoder  515  parses, from a bitstream  505 , encoded image data to be decoded and encoding information required for decoding. The encoded image data corresponds to a quantized transformation coefficient, and an inverse quantizer  520  and an inverse transformer  525  reconstruct residue data from the quantized transformation coefficient. 
     An intra predictor  540  performs intra prediction on a coding unit in an intra mode according to prediction units. An inter predictor  535  performs inter prediction by using a reference image with respect to a coding unit in an inter mode from among a current image, wherein the reference image is obtained by a reconstructed picture buffer  530  according to prediction units. 
     Prediction data and residue data regarding coding units of each mode, which passed through the intra predictor  540  or the inter predictor  535 , are summed, so that data in a spatial domain regarding coding units of the current image  405  may be reconstructed, and the reconstructed data in the spatial domain may be output as a reconstructed image  560  through a deblocking unit  545  and an SAO performer  550 . Reconstructed images stored in the reconstructed picture buffer  530  may be output as reference images. 
     In order for a picture decoder  230  of the video decoding apparatus  200  to decode the image data, operations after the entropy decoder  515  of the image decoder  500  according to an embodiment may be performed. 
     In order for the image decoder  500  to be applied in the video decoding apparatus  200  according to an embodiment, all elements of the image decoder  500 , i.e., the entropy decoder  515 , the inverse quantizer  520 , the inverse transformer  525 , the intra predictor  540 , the inter predictor  535 , the deblocking unit  545 , and the SAO performer  550  may perform operations based on coding units having a tree structure for each largest coding unit. 
     In particular, the intra predictor  540  and the inter predictor  535  may determine a partition mode and a prediction mode of each coding unit from among the coding units according to a tree structure, and the inverse transformer  525  may determine whether or not to split a transformation unit according to a quad tree in each coding unit. 
     The encoding operation of  FIG. 10  and the decoding operation of  FIG. 11  are described as a video stream encoding operation and a video stream decoding operation, respectively, in a single layer. Thus, if the image encoding apparatus  40  of  FIG. 4A  encodes a video stream of two or more layers, the image encoder  400  may be provided for each layer. Similarly, if the decoding apparatus  30  of  FIG. 3A  decodes a video stream of two or more layers, the image decoder  500  may be provided for each layer. 
       FIG. 12  illustrates deeper coding units according to depths, and partitions, according to various embodiments. 
     The video encoding apparatus  100  according to an embodiment and the video decoding apparatus  200  according to an embodiment use hierarchical coding units so as to consider characteristics of an image. A maximum height, a maximum width, and a maximum depth of coding units may be adaptively determined according to the characteristics of the image, or may be variously set according to user requirements. Sizes of deeper coding units according to depths may be determined according to the predetermined maximum size of the coding unit. 
     In a hierarchical structure of coding units  600  according to an embodiment, the maximum height and the maximum width of the coding units are each 64, and the maximum depth is 3. In this case, the maximum depth represents a total number of times the coding unit is split from the largest coding unit to the smallest coding unit. Since a depth deepens along a vertical axis of the hierarchical structure of coding units  600 , a height and a width of the deeper coding unit are each split. Also, a prediction unit and partitions, which are bases for prediction encoding of each deeper coding unit, are shown along a horizontal axis of the hierarchical structure of coding units  600 . 
     That is, a coding unit  610  is a largest coding unit in the hierarchical structure of coding units  600 , wherein a depth is 0 and a size, i.e., a height by width, is 64×64. The depth deepens along the vertical axis, and a coding unit  620  having a size of 32×32 and a depth of 1, a coding unit  630  having a size of 16×16 and a depth of 2, and a coding unit  640  having a size of 8×8 and a depth of 3. The coding unit  640  having the size of 8×8 and the depth of 3 is a smallest coding unit. 
     The prediction unit and the partitions of a coding unit are arranged along the horizontal axis according to each depth. That is, if the coding unit  610  having a size of 64×64 and a depth of 0 is a prediction unit, the prediction unit may be split into partitions included in the coding unit  610  having the size of 64×64, i.e. a partition  610  having a size of 64×64, partitions  612  having the size of 64×32, partitions  614  having the size of 32×64, or partitions  616  having the size of 32×32. 
     Equally, a prediction unit of the coding unit  620  having the size of 32×32 and the depth of 1 may be split into partitions included in the coding unit  620 , i.e. a partition  620  having a size of 32×32, partitions  622  having a size of 32×16, partitions  624  having a size of 16×32, and partitions  626  having a size of 16×16. 
     Equally, a prediction unit of the coding unit  630  having the size of 16×16 and the depth of 2 may be split into partitions included in the coding unit  630 , i.e. a partition having a size of 16×16 included in the coding unit  630 , partitions  632  having a size of 16×8, partitions  634  having a size of 8×16, and partitions  636  having a size of 8×8. 
     Equally, a prediction unit of the coding unit  640  having the size of 8×8 and the depth of 3 may be split into partitions included in the coding unit  640 , i.e. a partition  640  having a size of 8×8 included in the coding unit  640 , partitions  642  having a size of 8×4, partitions  644  having a size of 4×8, and partitions  646  having a size of 4×4. 
     In order to determine a depth of the largest coding unit  610 , the coding unit determiner  120  of the video encoding apparatus  100  has to perform encoding on coding units respectively corresponding to depths included in the largest coding unit  610 . 
     The number of deeper coding units according to depths including data in the same range and the same size increases as the depth deepens. For example, four coding units corresponding to a depth of 2 are required to cover data that is included in one coding unit corresponding to a depth of 1. Accordingly, in order to compare results of encoding the same data according to depths, the data has to be encoded by using each of the coding unit corresponding to the depth of 1 and four coding units corresponding to the depth of 2. 
     In order to perform encoding according to each of the depths, a minimum encoding error that is a representative encoding error of a corresponding depth may be selected by performing encoding on each of prediction units of the coding units according to depths, along the horizontal axis of the hierarchical structure of coding units  600 . Also, the minimum encoding error may be searched for by comparing representative encoding errors according to depths, by performing encoding for each depth as the depth deepens along the vertical axis of the hierarchical structure of coding units  600 . A depth and a partition generating the minimum encoding error in the largest coding unit  610  may be selected as a depth and a partition mode of the largest coding unit  610 . 
       FIG. 13  illustrates a relationship between a coding unit and transformation units, according to various embodiments. 
     The video encoding apparatus  100  according to an embodiment or the video decoding apparatus  200  according to an embodiment encodes or decodes an image according to coding units having sizes smaller than or equal to a largest coding unit for each largest coding unit. Sizes of transformation units for transformation during an encoding process may be selected based on data units that are not larger than a corresponding coding unit. 
     For example, in the video encoding apparatus  100  or the video decoding apparatus  200 , when a size of the coding unit  710  is 64×64, transformation may be performed by using the transformation units  720  having a size of 32×32. 
     Also, data of the coding unit  710  having the size of 64×64 may be encoded by performing the transformation on each of the transformation units having the size of 32×32, 16×16, 8×8, and 4×4, which are smaller than 64×64, and then a transformation unit having the minimum coding error with respect to an original image may be selected. 
       FIG. 14  illustrates a plurality of pieces of encoding information according to depths, according to various embodiments. 
     The output unit  130  of the video encoding apparatus  100  according to an embodiment may encode and transmit, as split information, partition mode information  800 , prediction mode information  810 , and transformation unit size information  820  for each coding unit corresponding to a depth. 
     The partition mode information  800  indicates information about a shape of a partition obtained by splitting a prediction unit of a current coding unit, wherein the partition is a data unit for prediction encoding the current coding unit. For example, a current coding unit CU_0 having a size of 2N×2N may be split into any one of a partition  802  having a size of 2N×2N, a partition  804  having a size of 2N×N, a partition  806  having a size of N×2N, and a partition  808  having a size of N×N. In this case, the partition mode information  800  about a current coding unit is set to indicate one of the partition  802  having a size of 2N×2N, the partition  804  having a size of 2N×N, the partition  806  having a size of N×2N, and the partition  808  having a size of N×N. 
     The prediction mode information  810  indicates a prediction mode of each partition. For example, the prediction mode information  810  may indicate a mode of prediction encoding performed on a partition indicated by the partition mode information  800 , i.e., an intra mode  812 , an inter mode  814 , or a skip mode  816 . 
     The transformation unit size information  820  represents a transformation unit to be based on when transformation is performed on a current coding unit. For example, the transformation unit may be one of a first intra transformation unit  822 , a second intra transformation unit  824 , a first inter transformation unit  826 , and a second inter transformation unit  828 . 
     The image data and encoding information extractor  220  of the video decoding apparatus  200  may extract and use the partition mode information  800 , the prediction mode information  810 , and the transformation unit size information  820  for decoding, according to each deeper coding unit. 
       FIG. 15  illustrates deeper coding units according to depths, according to various embodiments. 
     Split information may be used to represent a change in a depth. The spilt information specifies whether a coding unit of a current depth is split into coding units of a lower depth. 
     A prediction unit  910  for prediction encoding a coding unit  900  having a depth of 0 and a size of 2N_0×2N_0 may include partitions of a partition mode  912  having a size of 2N_0×2N_0, a partition mode  914  having a size of 2N_0×N_0, a partition mode  916  having a size of N_0×2N_0, and a partition mode  918  having a size of N_0×N_0. Only the partition modes  912 ,  914 ,  916 , and  918  which are obtained by symmetrically splitting the prediction unit are illustrated, but as described above, a partition mode is not limited thereto and may include asymmetrical partitions, partitions having a predetermined shape, and partitions having a geometrical shape. 
     According to each partition mode, prediction encoding has to be repeatedly performed on one partition having a size of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, two partitions having a size of N_0×2N_0, and four partitions having a size of N_0×N_0. The prediction encoding in an intra mode and an inter mode may be performed on the partitions having the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. The prediction encoding in a skip mode may be performed only on the partition having the size of 2N_0×2N_0. 
     If an encoding error is smallest in one of the partition modes  912 ,  914 , and  916  having the sizes of 2N_0×2N_0, 2N_0×N_0 and N_0×2N_0, the prediction unit  910  may not be split into a lower depth. 
     If the encoding error is the smallest in the partition mode  918  having the size of N_0×N_0, a depth is changed from 0 to 1 and split is performed (operation  920 ), and encoding may be repeatedly performed on coding units  930  of a partition mode having a depth of 2 and a size of N_0×N_0 so as to search for a minimum encoding error. 
     A prediction unit  940  for prediction encoding the coding unit  930  having a depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include a partition mode  942  having a size of 2N_1×2N_1, a partition mode  944  having a size of 2N_1×N_1, a partition mode  946  having a size of N_1×2N_1, and a partition mode  948  having a size of N_1×N_1. 
     If an encoding error is the smallest in the partition mode  948  having the size of N_1×N_1, a depth is changed from 1 to 2 and split is performed (in operation  950 ), and encoding is repeatedly performed on coding units  960  having a depth of 2 and a size of N_2×N_2 so as to search for a minimum encoding error. 
     When a maximum depth is d, deeper coding units according to depths may be set until when a depth corresponds to d-1, and split information may be set until when a depth corresponds to d-2. That is, when encoding is performed up to when the depth is d-1 after a coding unit corresponding to a depth of d-2 is split (in operation  970 ), a prediction unit  990  for prediction encoding a coding unit  980  having a depth of d-1 and a size of 2N_(d-1)×2N_(d-1) may include partitions of a partition mode  992  having a size of 2N_(d-1)×2N_(d-1), a partition mode  994  having a size of 2N_(d-1)×N_(d-1), a partition mode  996  having a size of N_(d-1)×2N_(d-1), and a partition mode  998  having a size of N_(d-1)×N_(d-1). 
     Prediction encoding may be repeatedly performed on one partition having a size of 2N_(d-1)×2N_(d-1), two partitions having a size of 2N_(d-1)×N_(d-1), two partitions having a size of N_(d-1)×2N_(d-1), four partitions having a size of N_(d-1)×N_(d-1) from among the partition modes so as to search for a partition mode generating a minimum encoding error. 
     Even when the partition type  998  having the size of N_(d-1)×N_(d-1) has the minimum encoding error, since a maximum depth is d, a coding unit CU_(d-1) having a depth of d-1 is no longer split into a lower depth, and a depth for the coding units constituting a current largest coding unit  900  is determined to be d-1 and a partition mode of the current largest coding unit  900  may be determined to be N_(d-1)×N_(d-1). Also, since the maximum depth is d, split information for a coding unit  952  having a depth of d-1 is not set. 
     A data unit  999  may be a ‘minimum unit’ for the current largest coding unit. A minimum unit according to the embodiment may be a square data unit obtained by splitting a smallest coding unit having a lowermost depth by 4. By performing the encoding repeatedly, the video encoding apparatus  100  according to the embodiment may select a depth having the minimum encoding error by comparing encoding errors according to depths of the coding unit  900  to determine a depth, and set a corresponding partition type and a prediction mode as an encoding mode of the depth. 
     As such, the minimum encoding errors according to depths are compared in all of the depths of 0, 1, . . . , d-1, d, and a depth having the minimum encoding error may be determined as a depth. The depth, the partition mode of the prediction unit, and the prediction mode may be encoded and transmitted as split information. Also, since a coding unit has to be split from a depth of 0 to a depth, only split information of the depth is set to ‘0’, and split information of depths excluding the depth has to be set to ‘1’. 
     The image data and encoding information extractor  220  of the video decoding apparatus  200  according to the embodiment may extract and use a depth and prediction unit information about the coding unit  900  so as to decode the coding unit  912 . The video decoding apparatus  200  according to the embodiment may determine a depth, in which split information is ‘0’, as a depth by using split information according to depths, and may use, for decoding, split information about the corresponding depth. 
       FIGS. 16, 17, and 18  illustrate a relationship between coding units, prediction units, and transformation units, according to various embodiments. 
     Coding units  1010  are deeper coding units according to depths determined by the video encoding apparatus  100 , in a largest coding unit. Prediction units  1060  are partitions of prediction units of each of the coding units  1010  according to depths, and transformation units  1070  are transformation units of each of the coding units according to depths. 
     When a depth of a largest coding unit is 0 in the deeper coding units  1010 , depths of coding units  1012  and  1054  are 1, depths of coding units  1014 ,  1016 ,  1018 ,  1028 ,  1050 , and  1052  are 2, depths of coding units  1020 ,  1022 ,  1024 ,  1026 ,  1030 ,  1032 , and  1048  are 3, and depths of coding units  1040 ,  1042 ,  1044 , and  1046  are 4. 
     Some partitions  1014 ,  1016 ,  1022 ,  1032 ,  1048 ,  1050 ,  1052 , and  1054  from among the prediction units  1060  are obtained by splitting the coding unit. That is, partitions  1014 ,  1022 ,  1050 , and  1054  are a partition mode having a size of 2N×N, partitions  1016 ,  1048 , and  1052  are a partition mode having a size of N×2N, and a partition  1032  is a partition mode having a size of N×N. Prediction units and partitions of the deeper coding units  1010  are smaller than or equal to each coding unit. 
     Transformation or inverse transformation is performed on image data of the coding unit  1052  in the transformation units  1070  in a data unit that is smaller than the coding unit  1052 . Also, the coding units  1014 ,  1016 ,  1022 ,  1032 ,  1048 ,  1050 ,  1052 , and  1054  in the transformation units  1760  are data units different from those in the prediction units  1060  in terms of sizes and shapes. That is, the video encoding apparatus  100  and the video decoding apparatus  200  according to the embodiments may perform intra prediction/motion estimation/motion compensation/and transformation/inverse transformation on an individual data unit in the same coding unit. 
     Accordingly, encoding is recursively performed on each of coding units having a hierarchical structure in each region of a largest coding unit so as to determine an optimum coding unit, and thus coding units according to a recursive tree structure may be obtained. Encoding information may include split information about a coding unit, partition mode information, prediction mode information, and transformation unit size information. Table 1 below shows the encoding information that may be set by the video encoding apparatus  100  and the video decoding apparatus  200  according to the embodiments. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Split Information 0 
                   
               
               
                 (Encoding on Coding Unit having Size of 2N × 2N and Current Depth of d) 
                 Split Information 1 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Prediction Mode 
                 Partition Mode 
                 Size of Transformation Unit 
                 Repeatedly 
               
            
           
           
               
               
               
               
               
               
            
               
                 Intra 
                 Symmetrical 
                 Asymmetrical 
                 Split Information 
                 Split Information 
                 Encode Coding 
               
               
                 Inter 
                 Partition 
                 Partition Mode 
                 0 of 
                 1 of 
                 Units having 
               
               
                 Skip (Only 
                 Mode 
                   
                 Transformation 
                 Transformation 
                 Lower Depth of 
               
               
                 2N × 2N) 
                   
                   
                 Unit 
                 Unit 
                 d + 1 
               
               
                   
                 2N × 2N 
                 2N × nU 
                 2N × 2N 
                 N × N 
               
               
                   
                 2N × N  
                 2N × nD 
                   
                 (Symmetrical 
               
               
                   
                  N × 2N 
                 nL × 2N 
                   
                 Partition Mode) 
               
               
                   
                 N × N 
                 nR × 2N 
                   
                 N/2 × N/2 
               
               
                   
                   
                   
                   
                 (Asymmetrical 
               
               
                   
                   
                   
                   
                 Partition Mode) 
               
               
                   
               
            
           
         
       
     
     The output unit  130  of the video encoding apparatus  100  according to the embodiment may output the encoding information about the coding units having a tree structure, and the image data and encoding information extractor  220  of the video decoding apparatus  200  according to the embodiment may extract the encoding information about the coding units having a tree structure from a received bitstream. 
     Split information specifies whether a current coding unit is split into coding units of a lower depth. If split information of a current depth d is 0, a depth, in which a current coding unit is no longer split into a lower depth, is a depth, and thus partition mode information, prediction mode information, and transformation unit size information may be defined for the depth. If the current coding unit has to be further split according to the split information, encoding has to be independently performed on each of four split coding units of a lower depth. 
     A prediction mode may be one of an intra mode, an inter mode, and a skip mode. The intra mode and the inter mode may be defined in all partition modes, and the skip mode is defined only in a partition mode having a size of 2N×2N. 
     The partition mode information may indicate symmetrical partition modes having sizes of 2N×2N, 2N×N, N×2N, and N×N, which are obtained by symmetrically splitting a height or a width of a prediction unit, and asymmetrical partition modes having sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N, which are obtained by asymmetrically splitting the height or width of the prediction unit. The asymmetrical partition modes having the sizes of 2N×nU and 2N×nD may be respectively obtained by splitting the height of the prediction unit in 1:3 and 3:1, and the asymmetrical partition modes having the sizes of nL×2N and nR×2N may be respectively obtained by splitting the width of the prediction unit in 1:3 and 3:1. 
     The size of the transformation unit may be set to be two types in the intra mode and two types in the inter mode. That is, if split information of the transformation unit is 0, the size of the transformation unit may be 2N×2N, which is the size of the current coding unit. If split information of the transformation unit is 1, the transformation units may be obtained by splitting the current coding unit. Also, if a partition mode of the current coding unit having the size of 2N×2N is a symmetrical partition mode, a size of a transformation unit may be N×N, and if the partition mode of the current coding unit is an asymmetrical partition mode, the size of the transformation unit may be N/2×N/2. 
     The encoding information about coding units having a tree structure according to the embodiment may be assigned to at least one of a coding unit corresponding to a depth, a prediction unit, and a minimum unit. The coding unit corresponding to the depth may include at least one of a prediction unit and a minimum unit containing the same encoding information. 
     Accordingly, it is determined whether adjacent data units are included in the same coding unit corresponding to the depth by comparing encoding information of the adjacent data units. Also, a corresponding coding unit corresponding to a depth is determined by using encoding information of a data unit, and thus a distribution of depths in a largest coding unit may be inferred. 
     Accordingly, if a current coding unit is predicted based on encoding information of adjacent data units, encoding information of data units in deeper coding units adjacent to the current coding unit may be directly referred to and used. 
     In another embodiment, if a current coding unit is predicted based on encoding information of adjacent data units, data units adjacent to the current coding unit may be searched by using encoded information of the data units, and the searched adjacent coding units may be referred for predicting the current coding unit. 
       FIG. 19  illustrates a relationship between a coding unit, a prediction unit, and a transformation unit, according to encoding mode information of Table 1. 
     A largest coding unit  1300  includes coding units  1302 ,  1304 ,  1306 ,  1312 ,  1314 ,  1316 , and  1318  of depths. Here, since the coding unit  1318  is a coding unit of a depth, split information may be set to 0. Partition mode information of the coding unit  1318  having a size of 2N×2N may be set to be one of partition modes including 2N×2N  1322 , 2N×N  1324 , N×2N  1326 , N×N  1328 , 2N×nU  1332 , 2N×nD  1334 , nL×2N  1336 , and nR×2N  1338 . 
     Transformation unit split information (TU size flag) is a type of a transformation index, and a size of a transformation unit corresponding to the transformation index may be changed according to a prediction unit type or partition mode of the coding unit. 
     For example, when the partition mode information is set to be one of symmetrical partition modes 2N×2N  1322 , 2N×N  1324 , N×2N  1326 , and N×N  1328 , if the transformation unit split information is 0, a transformation unit  1342  having a size of 2N×2N is set, and if the transformation unit split information is 1, a transformation unit  1344  having a size of N×N may be set. 
     When the partition mode information is set to be one of asymmetrical partition modes 2N×nU  1332 , 2N×nD  1334 , nL×2N  1336 , and nR×2N  1338 , if the transformation unit split information (TU size flag) is 0, a transformation unit  1352  having a size of 2N×2N may be set, and if the transformation unit split information is 1, a transformation unit  1354  having a size of N/2×N/2 may be set. 
     The transformation unit split information (TU size flag) described above with reference to  FIG. 19  is a flag having a value of 0 or 1, but the transformation unit split information according to an embodiment is not limited to a flag having 1 bit, and the transformation unit may be hierarchically split while the transformation unit split information increases in a manner of 0, 1, 2, 3 . . . etc., according to setting. The transformation unit split information may be used as an example of the transformation index. 
     In this case, the size of a transformation unit that has been actually used may be expressed by using the transformation unit split information according to the embodiment, together with a maximum size of the transformation unit and a minimum size of the transformation unit. The video encoding apparatus  100  according to the embodiment may encode maximum transformation unit size information, minimum transformation unit size information, and maximum transformation unit split information. The result of encoding the maximum transformation unit size information, the minimum transformation unit size information, and the maximum transformation unit split information may be inserted into an SPS. The video decoding apparatus  200  according to the embodiment may decode video by using the maximum transformation unit size information, the minimum transformation unit size information, and the maximum transformation unit split information. 
     For example, (a) if the size of a current coding unit is 64×64 and a maximum transformation unit size is 32×32, (a-1) then the size of a transformation unit may be 32×32 when a TU size flag is 0, (a-2) may be 16×16 when the TU size flag is 1, and (a-3) may be 8×8 when the TU size flag is 2. 
     As another example, (b) if the size of the current coding unit is 32×32 and a minimum transformation unit size is 32×32, (b-1) then the size of the transformation unit may be 32×32 when the TU size flag is 0. Here, the TU size flag cannot be set to a value other than 0, since the size of the transformation unit cannot be smaller than 32×32. 
     As another example, (c) if the size of the current coding unit is 64×64 and a maximum TU size flag is 1, then the TU size flag may be 0 or 1. Here, the TU size flag cannot be set to a value other than 0 or 1. 
     Thus, if it is defined that the maximum TU size flag is ‘MaxTransformSizeIndex’, a minimum transformation unit size is ‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ when the TU size flag is 0, then a current minimum transformation unit size ‘CurrMinTuSize’ that can be determined in a current coding unit may be defined by Equation (1): 
       CurrMinTuSize=max(MinTransformSize,RootTuSize/(2*MaxTransformSizeIndex))   (1)
 
     Compared to the current minimum transformation unit size ‘CurrMinTuSize’ that can be determined in the current coding unit, a transformation unit size ‘RootTuSize’ when the TU size flag is 0 may denote a maximum transformation unit size that can be selected in the system. That is, in Equation (1), ‘RootTuSize/(2̂MaxTransformSizeIndex)’ denotes a transformation unit size when the transformation unit size ‘RootTuSize’, when the TU size flag is 0, is split by the number of times corresponding to the maximum TU size flag, and ‘MinTransformSize’ denotes a minimum transformation size. Thus, a smaller value from among ‘RootTuSize/(2̂MaxTransformSizelndex)’ and ‘MinTransformSize’ may be the current minimum transformation unit size ‘CurrMinTuSize’ that can be determined in the current coding unit. 
     According to an embodiment, the maximum transformation unit size RootTuSize may vary according to the type of a prediction mode. 
     For example, if a current prediction mode is an inter mode, then ‘RootTuSize’ may be determined by using Equation (2) below. In Equation (2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and ‘PUSize’ denotes a current prediction unit size. 
       RootTuSize=min(MaxTransformSize,PUSize)  (2)
 
     That is, if the current prediction mode is the inter mode, the transformation unit size ‘RootTuSize’, when the TU size flag is 0, may be a smaller value from among the maximum transformation unit size and the current prediction unit size. 
     If a prediction mode of a current partition unit is an intra mode, ‘RootTuSize’ may be determined by using Equation (3) below. In Equation (3), ‘PartitionSize’ denotes the size of the current partition unit. 
       RootTuSize=min(MaxTransformSize,PartitionSize)  (3)
 
     That is, if the current prediction mode is the intra mode, the transformation unit size ‘RootTuSize’ when the TU size flag is 0 may be a smaller value from among the maximum transformation unit size and the size of the current partition unit. 
     However, the current maximum transformation unit size ‘RootTuSize’ that varies according to the type of a prediction mode in a partition unit is just an embodiment, and a factor for determining the current maximum transformation unit size is not limited thereto. 
     According to the video encoding method based on coding units of a tree structure described above with reference to  FIGS. 7 through 19 , image data of a spatial domain is encoded in each of the coding units of the tree structure, and the image data of the spatial domain is reconstructed in a manner that decoding is performed on each largest coding unit according to the video decoding method based on the coding units of the tree structure, so that a video that is formed of pictures and picture sequences may be reconstructed. The reconstructed video may be reproduced by a reproducing apparatus, may be stored in a storage medium, or may be transmitted via a network. 
     The one or more embodiments may be written as computer programs and may be implemented in general-use digital computers that execute the programs by using a non-transitory computer-readable recording medium. Examples of the non-transitory computer-readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.), optical recording media (e.g., CD-ROMs, or DVDs), etc. 
     For convenience of description, the image encoding methods and/or the video encoding method, which are described with reference to  FIGS. 1A through 19 , will be collectively referred to as ‘the video encoding method’. Also, the image decoding methods and/or the video decoding method, which are described with reference to  FIGS. 1A through 19 , will be collectively referred to as ‘the video decoding method’. 
     Also, a video encoding apparatus including the image encoding apparatus  40 , the video encoding apparatus  100 , or the image encoder  400  which are described with reference to  FIGS. 1A through 19  will be collectively referred to as a ‘video encoding apparatus’. Also, a video decoding apparatus including the image decoding apparatus  30 , the video decoding apparatus  200 , or the image decoder  500  which are described with reference to  FIGS. 1A through 19  will be collectively referred to as a ‘video decoding apparatus’. 
     The non-transitory computer-readable recording medium such as a disc  26000  that stores the programs according to an embodiment will now be described in detail. 
       FIG. 20  illustrates a physical structure of the disc  26000  in which a program is stored, according to various embodiments. The disc  26000 , as a storage medium, may be a hard drive, a compact disc-read only memory (CD-ROM) disc, a Blu-ray disc, or a digital versatile disc (DVD). The disc  26000  includes a plurality of concentric tracks Tr that are each divided into a specific number of sectors Se in a circumferential direction of the disc  26000 . In a specific region of the disc  26000 , a program that executes the quantized parameter determining method, the video encoding method, and the video decoding method described above may be assigned and stored. 
     A computer system embodied using a storage medium that stores a program for executing the video encoding method and the video decoding method as described above will now be described with reference to  FIG. 22 . 
       FIG. 21  illustrates a disc drive  26800  for recording and reading a program by using the disc  26000 . A computer system  26700  may store a program that executes at least one of the video encoding method and the video decoding method according to an embodiment, in the disc  26000  via the disc drive  26800 . In order to run the program stored in the disc  26000  in the computer system  26700 , the program may be read from the disc  26000  and may be transmitted to the computer system  26700  by using the disc drive  26800 . 
     The program that executes at least one of the video encoding method and the video decoding method according to an embodiment may be stored not only in the disc  26000  illustrated in  FIGS. 20 and 21  but may also be stored in a memory card, a ROM cassette, or a solid state drive (SSD). 
     A system to which the video encoding method and the video decoding method according to the embodiments described above are applied will be described below. 
       FIG. 22  illustrates an overall structure of a content supply system  11000  for providing a content distribution service. A service area of a communication system is divided into predetermined-sized cells, and wireless base stations  11700 ,  11800 ,  11900 , and  12000  are installed in these cells, respectively. 
     The content supply system  11000  includes a plurality of independent devices. For example, the plurality of independent devices, such as a computer  12100 , a personal digital assistant (PDA)  12200 , a video camera  12300 , and a mobile phone  12500 , are connected to the Internet  11100  via an internet service provider  11200 , a communication network  11400 , and the wireless base stations  11700 ,  11800 ,  11900 , and  12000 . 
     However, the content supply system  11000  is not limited to as illustrated in  FIG. 22 , and devices may be selectively connected thereto. The plurality of independent devices may be directly connected to the communication network  11400 , not via the wireless base stations  11700 ,  11800 ,  11900 , and  12000 . 
     The video camera  12300  is an imaging device, e.g., a digital video camera, which is capable of capturing video images. The mobile phone  12500  may employ at least one communication method from among various protocols, e.g., Personal Digital Communications (PDC), Code Division Multiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA), Global System for Mobile Communications (GSM), and Personal Handyphone System (PHS). 
     The video camera  12300  may be connected to a streaming server  11300  via the wireless base station  11900  and the communication network  11400 . The streaming server  11300  allows content received from a user via the video camera  12300  to be streamed via a real-time broadcast. The content received from the video camera  12300  may be encoded by the video camera  12300  or the streaming server  11300 . Video data captured by the video camera  12300  may be transmitted to the streaming server  11300  via the computer  12100 . 
     Video data captured by a camera  12600  may also be transmitted to the streaming server  11300  via the computer  12100 . The camera  12600  is an imaging device capable of capturing both still images and video images, similar to a digital camera. The video data captured by the camera  12600  may be encoded using the camera  12600  or the computer  12100 . Software that performs encoding and decoding video may be stored in a non-transitory computer-readable recording medium, e.g., a CD-ROM disc, a floppy disc, a hard disc drive, an SSD, or a memory card, which may be accessed by the computer  12100 . 
     If video data is captured by a camera built in the mobile phone  12500 , the video data may be received from the mobile phone  12500 . 
     The video data may be encoded by a large scale integrated circuit (LSI) system installed in the video camera  12300 , the mobile phone  12500 , or the camera  12600 . 
     In the content supply system  11000  according to an embodiment, content data, e.g., content recorded during a concert, which has been recorded by a user using the video camera  12300 , the camera  12600 , the mobile phone  12500 , or another imaging device is encoded and is transmitted to the streaming server  11300 . The streaming server  11300  may transmit the encoded content data in a type of a streaming content to other clients that request the content data. 
     The clients are devices capable of decoding the encoded content data, e.g., the computer  12100 , the PDA  12200 , the video camera  12300 , or the mobile phone  12500 . Thus, the content supply system  11000  allows the clients to receive and reproduce the encoded content data. Also, the content supply system  11000  allows the clients to receive the encoded content data and decode and reproduce the encoded content data in real time, thereby enabling personal broadcasting. 
     The video encoding apparatus and the video decoding apparatus of the present disclosure may be applied to encoding and decoding operations of the plurality of independent devices included in the content supply system  11000 . 
     With reference to  FIGS. 23 and 24 , the mobile phone  12500  included in the content supply system  11000  according to an embodiment will now be described in detail. 
       FIG. 23  illustrates an external structure of the mobile phone  12500  to which a video encoding method and a video decoding method are applied, according to various embodiments. The mobile phone  12500  may be a smart phone, the functions of which are not limited and a large number of the functions of which may be changed or expanded. 
     The mobile phone  12500  includes an internal antenna  12510  via which a radio-frequency (RF) signal may be exchanged with the wireless base station  12000 , and includes a display screen  12520  for displaying images captured by a camera  12530  or images that are received via the antenna  12510  and decoded, e.g., a liquid crystal display (LCD) or an organic light-emitting diode (OLED) screen. The mobile phone  12500  includes an operation panel  12540  including a control button and a touch panel. If the display screen  12520  is a touch screen, the operation panel  12540  further includes a touch sensing panel of the display screen  12520 . The mobile phone  12500  includes a speaker  12580  for outputting voice and sound or another type of a sound output unit, and a microphone  12550  for inputting voice and sound or another type of a sound input unit. The mobile phone  12500  further includes the camera  12530 , such as a charge-coupled device (CCD) camera, to capture video and still images. The mobile phone  12500  may further include a storage medium  12570  for storing encoded/decoded data, e.g., video or still images captured by the camera  12530 , received via email, or obtained according to various ways; and a slot  12560  via which the storage medium  12570  is loaded into the mobile phone  12500 . The storage medium  12570  may be a flash memory, e.g., a secure digital (SD) card or an electrically erasable and programmable read only memory (EEPROM) included in a plastic case. 
       FIG. 24  illustrates an internal structure of the mobile phone  12500 . In order to systemically control parts of the mobile phone  12500  including the display screen  12520  and the operation panel  12540 , a power supply circuit  12700 , an operation input controller  12640 , an image encoder  12720 , a camera interface  12630 , an LCD controller  12620 , an image decoder  12690 , a multiplexer/demultiplexer  12680 , a recording/reading unit  12670 , a modulation/demodulation unit  12660 , and a sound processor  12650  are connected to a central controller  12710  via a synchronization bus  12730 . 
     If a user operates a power button and sets from a ‘power off’ state to a ‘power on’ state, the power supply circuit  12700  supplies power to all the parts of the mobile phone  12500  from a battery pack, thereby setting the mobile phone  12500  to an operation mode. 
     The central controller  12710  includes a CPU, a read-only memory (ROM), and a random access memory (RAM). 
     While the mobile phone  12500  transmits communication data to the outside, a digital signal is generated by the mobile phone  12500  under control of the central controller  12710 . For example, the sound processor  12650  may generate a digital sound signal, the image encoder  12720  may generate a digital image signal, and text data of a message may be generated via the operation panel  12540  and the operation input controller  12640 . When a digital signal is transmitted to the modulation/demodulation unit  12660  by control of the central controller  12710 , the modulation/demodulation unit  12660  modulates a frequency band of the digital signal, and a communication circuit  12610  performs digital-to-analog conversion (DAC) and frequency conversion on the frequency band-modulated digital sound signal. A transmission signal output from the communication circuit  12610  may be transmitted to a voice communication base station or the wireless base station  12000  via the antenna  12510 . 
     For example, when the mobile phone  12500  is in a conversation mode, a sound signal obtained via the microphone  12550  is converted to a digital sound signal by the sound processor  12650 , under control of the central controller  12710 . The generated digital sound signal may be converted to a transmission signal through the modulation/demodulation unit  12660  and the communication circuit  12610 , and may be transmitted via the antenna  12510 . 
     When a text message, e.g., email, is transmitted during a data communication mode, text data of the text message is input via the operation panel  12540  and is transmitted to the central controller  12710  via the operation input controller  12640 . By the control of the central controller  12710 , the text data is transformed to a transmission signal via the modulation/demodulation unit  12660  and the communication circuit  12610  and is transmitted to the wireless base station  12000  via the antenna  12510 . 
     In order to transmit image data during the data communication mode, image data captured by the camera  12530  is provided to the image encoder  12720  via the camera interface  12630 . The captured image data may be directly displayed on the display screen  12520  via the camera interface  12630  and the LCD controller  12620 . 
     A structure of the image encoder  12720  may correspond to that of the video encoding apparatus  100  according to an embodiment. The image encoder  12720  may transform the image data received from the camera  12530  into compressed and encoded image data according to the aforementioned video encoding method, and then output the encoded image data to the multiplexer/demultiplexer  12680 . During a recording operation of the camera  12530 , a sound signal obtained by the microphone  12550  of the mobile phone  12500  may be transformed into digital sound data via the sound processor  12650 , and the digital sound data may be transmitted to the multiplexer/demultiplexer  12680 . 
     The multiplexer/demultiplexer  12680  multiplexes the encoded image data received from the image encoder  12720 , together with the sound data received from the sound processor  12650 . A result of multiplexing the data may be transformed into a transmission signal via the modulation/demodulation unit  12660  and the communication circuit  12610 , and may then be transmitted via the antenna  12510 . 
     While the mobile phone  12500  receives communication data from the outside, frequency recovery and analog-to-digital conversion (ADC) are performed on a signal received via the antenna  12510  to transform the signal into a digital signal. The modulation/demodulation unit  12660  modulates a frequency band of the digital signal. The frequency-band modulated digital signal is transmitted to the image decoder  12690 , the sound processor  12650 , or the LCD controller  12620 , according to the type of the digital signal. 
     During the conversation mode, the mobile phone  12500  amplifies a signal received via the antenna  12510 , and obtains a digital sound signal by performing frequency conversion and ADC on the amplified signal. A received digital sound signal is converted to an analog sound signal via the modulation/demodulation unit  12660  and the sound processor  12650 , and the analog sound signal is output via the speaker  12580  by the control of the central controller  12710 . 
     When, during the data communication mode, data of a video file accessed at an Internet website is received, a signal received from the wireless base station  12000  via the antenna  12510  is output as multiplexed data via the modulation/demodulation unit  12660 , and the multiplexed data is transmitted to the multiplexer/demultiplexer  12680 . 
     In order to decode the multiplexed data received via the antenna  12510 , the multiplexer/demultiplexer  12680  demultiplexes the multiplexed data into an encoded video data stream and an encoded audio data stream. Via the synchronization bus  12730 , the encoded video data stream and the encoded audio data stream are provided to the image decoder  12690  and the sound processor  12650 , respectively. 
     A structure of the image decoder  12690  may correspond to that of the video decoding apparatus described above. The image decoder  12690  may decode the encoded video data to obtain reconstructed video data and provide the reconstructed video data to the display screen  12520  via the LCD controller  12620 , by using the aforementioned video decoding method. 
     Thus, the data of the video file accessed at the Internet website may be displayed on the display screen  12520 . At the same time, the sound processor  12650  may transform audio data into an analog sound signal, and provide the analog sound signal to the speaker  12580 . Thus, audio data contained in the video file accessed at the Internet website may also be reproduced via the speaker  12580 . 
     The mobile phone  12500  or another type of communication terminal may be a transceiving terminal including both a video encoding apparatus and a video decoding apparatus according to an embodiment, may be a transmitting terminal including only the video encoding apparatus according to an embodiment, or may be a receiving terminal including only the video decoding apparatus according to an embodiment. 
     A communication system according to an embodiment is not limited to the communication system described above with reference to  FIG. 24 . For example,  FIG. 25  illustrates a digital broadcasting system employing a communication system, according to various embodiments. The digital broadcasting system of  FIG. 25  may receive a digital broadcast transmitted via a satellite or a terrestrial network by using the video encoding apparatus and the video decoding apparatus according to the embodiments. 
     In more detail, a broadcasting station  12890  transmits a video data stream to a communication satellite or a broadcasting satellite  12900  by using radio waves. The broadcasting satellite  12900  transmits a broadcast signal, and the broadcast signal is transmitted to a satellite broadcast receiver via a household antenna  12860 . In every house, an encoded video stream may be decoded and reproduced by a TV receiver  12810 , a set-top box  12870 , or another device. 
     When the video decoding apparatus according to an embodiment is implemented in a reproducing apparatus  12830 , the reproducing apparatus  12830  may parse and decode an encoded video stream recorded on a storage medium  12820 , such as a disc or a memory card to reconstruct digital signals. Thus, the reconstructed video signal may be reproduced, for example, on a monitor  12840 . 
     In the set-top box  12870  connected to the antenna  12860  for a satellite/terrestrial broadcast or a cable antenna  12850  for receiving a cable television (TV) broadcast, the video decoding apparatus according to an embodiment may be installed. Data output from the set-top box  12870  may also be reproduced on a TV monitor  12880 . 
     As another example, the video decoding apparatus according to an embodiment may be installed in the TV receiver  12810  instead of the set-top box  12870 . 
     An automobile  12920  that has an appropriate antenna  12910  may receive a signal transmitted from the satellite  12900  or the wireless base station  11700 . A decoded video may be reproduced on a display screen of an automobile navigation system  12930  installed in the automobile  12920 . 
     A video signal may be encoded by the video encoding apparatus according to an embodiment and may then be recorded to and stored in a storage medium. In more detail, an image signal may be stored in a DVD disc  12960  by a DVD recorder or may be stored in a hard disc by a hard disc recorder  12950 . As another example, the video signal may be stored in an SD card  12970 . If the hard disc recorder  12950  includes the video decoding apparatus according to an embodiment, a video signal recorded on the DVD disc  12960 , the SD card  12970 , or another storage medium may be reproduced on the TV monitor  12880 . 
     The automobile navigation system  12930  may not include the camera  12530 , the camera interface  12630 , and the image encoder  12720  of  FIG. 26 . For example, the computer  12100  and the TV receiver  12810  may not include the camera  12530 , the camera interface  12630 , and the image encoder  12720  of FIG. 
       FIG. 26  illustrates a network structure of a cloud computing system using a video encoding apparatus and a video decoding apparatus, according to various embodiments. 
     The cloud computing system may include a cloud computing server  14000 , a user database (DB)  14100 , a plurality of computing resources  14200 , and a user terminal. 
     The cloud computing system provides an on-demand outsourcing service of the plurality of computing resources  14200  via a data communication network, e.g., the Internet, in response to a request from the user terminal. Under a cloud computing environment, a service provider provides users with desired services by combining computing resources at data centers located at physically different locations by using virtualization technology. A service user does not have to install computing resources, e.g., an application, a storage, an operating system (OS), and security software, into his/her own terminal in order to use them, but may select and use desired services from among services in a virtual space generated through the virtualization technology, at a desired point in time. 
     A user terminal of a specified service user is connected to the cloud computing server  14000  via a data communication network including the Internet and a mobile telecommunication network. User terminals may be provided cloud computing services, and particularly video reproduction services, from the cloud computing server  14000 . The user terminals may be various types of electronic devices capable of being connected to the Internet, e.g., a desktop PC  14300 , a smart TV  14400 , a smart phone  14500 , a notebook computer  14600 , a portable multimedia player (PMP)  14700 , a tablet PC  14800 , and the like. 
     The cloud computing server  14000  may combine the plurality of computing resources  14200  distributed in a cloud network and provide user terminals with a result of combining. The plurality of computing resources  14200  may include various data services, and may include data uploaded from user terminals. As described above, the cloud computing server  14000  may provide user terminals with desired services by combining video database distributed in different regions according to the virtualization technology. 
     User information about users who have subscribed for a cloud computing service is stored in the user DB  14100 . The user information may include logging information, addresses, names, and personal credit information of the users. The user information may further include indexes of videos. Here, the indexes may include a list of videos that have already been reproduced, a list of videos that are being reproduced, a pausing point of a video that was being reproduced, and the like. 
     Information about a video stored in the user DB  14100  may be shared between user devices. For example, when a video service is provided to the notebook computer  14600  in response to a request from the notebook computer  14600 , a reproduction history of the video service is stored in the user DB  14100 . When a request for reproducing the video service is received from the smart phone  14500 , the cloud computing server  14000  searches for and reproduces the video service, based on the user DB  14100 . When the smart phone  14500  receives a video data stream from the cloud computing server  14000 , a process of reproducing video by decoding the video data stream is similar to an operation of the mobile phone  12500  described above with reference to  FIG. 24 . 
     The cloud computing server  14000  may refer to a reproduction history of a desired video service, stored in the user DB  14100 . For example, the cloud computing server  14000  receives a request to reproduce a video stored in the user DB  14100 , from a user terminal. If this video was being reproduced, then a method of streaming this video, performed by the cloud computing server  14000 , may vary according to the request from the user terminal, i.e., according to whether the video will be reproduced, starting from a start thereof or a pausing point thereof. For example, if the user terminal requests to reproduce the video, starting from the start thereof, the cloud computing server  14000  transmits streaming data of the video starting from a first frame thereof to the user terminal. If the user terminal requests to reproduce the video, starting from the pausing point thereof, the cloud computing server  14000  transmits streaming data of the video starting from a frame corresponding to the pausing point, to the user terminal. 
     Here, the user terminal may include the video decoding apparatus according to an embodiment as described above with reference to  FIGS. 1A through 19 . As another example, the user terminal may include the video encoding apparatus according to an embodiment as described above with reference to  FIGS. 1A through 19 . Alternatively, the user terminal may include both the video encoding apparatus and the video decoding apparatus according to an embodiment as described above with reference to  FIGS. 1A through 19 . 
     Various applications of the image encoding method, the image decoding method, the image encoding apparatus, and the image decoding apparatus described above with reference to  FIGS. 1A through 19  are described above with reference to  FIGS. 20 through 26 . However, various embodiments of methods of storing the video encoding method and the video decoding method in a storage medium or various embodiments of methods of implementing the video encoding apparatus and the video decoding apparatus in a device described above with reference to  FIGS. 1A through 19  are not limited to the embodiments of  FIGS. 20 through 26 . 
     While the present disclosure has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the following claims. Therefore, the scope of the present disclosure is defined not by the detailed description of the present disclosure but by the appended claims, and all differences within the scope will be construed as being included in the present disclosure.