Method for decoding video by considering skip and split order

[Technical Field]

0001Apparatuses and methods consistent with exemplary embodiments relate to decoding a video.

[Background Art]

0002As 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. In a related art video codec, a video is encoded according to a limited encoding method based on a macroblock having a predetermined size.

0003The international patent application <patcit id="pcit0001" dnum="WO2011019250A"><text>WO2011/019250</text></patcit>, having priority date 14 August 2009 and publication date 17 February 2011, discloses a method of encoding a video, the method including splitting a current picture into at least one maximum coding unit; determining a coded depth to output a final encoding result according to at least one split region obtained by splitting a region of the maximum coding unit according to depths, by encoding the at least one split region, based on a depth that deepens in proportion to the number of times the region of the maximum coding unit is split, and outputting image data constituting the final encoding result according to the at least one split region, and encoding information about the coded depth and a prediction mode, according to the at least one maximum coding unit.

0004The European patent application <patcit id="pcit0002" dnum="EP2106146A"><text>EP2106146</text></patcit> describes a method and apparatus for encoding/decoding motion vector information, in which a coding unit is divided into a plurality of subunits, predictive motion vectors (PMVs) of the subunits are predicted, it is determined whether the PMVs satisfy a predetermined condition, and coded motion vector data are generated, which include information indicating an omission of the motion vectors of the subunits, if the PMVs satisfy the predetermined condition.

0005The international patent application <patcit id="pcit0003" dnum="WO2009051719A"><text>WO2009/051719</text></patcit> describes methods and apparatus for video encoding and decoding geometrically partitioned super blocks. An apparatus includes an encoder for encoding image data for at least a portion of a picture. The image data is formed by a geometric partitioning that applies geometric partitions to picture block partitions. The picture block partitions are obtained from at least one of top-down partitioning and bottom-up tree joining.

[Disclosure]

[Technical Problem]

0006Exemplary embodiments provide decoding of a video by considering a skip and split order of a coding unit according to characteristics of a data unit.

[Technical Solution]

0007According to an aspect of an exemplary embodiment, there is provided a method as set out in accompanying claim 1.

[Advantageous Effects]

0008Coding units having the tree structure are formed by determining coding units having an optimum shape and an optimum size for each maximum coding unit, based on the size of the maximum coding unit and the maximum depth determined considering characteristics of the current picture. Also, since encoding may be performed on each maximum coding unit by using any one of various prediction modes and transformations, an optimum encoding mode may be determined considering characteristics of the coding unit of various image sizes.

0009An order of skip mode information and split information are determined by considering a data unit, an encoding mode, or the like. Also, the order of the skip mode information and the split information may be determined by considering a total bit number of the skip mode information and the split information, and a frequency of occurrence of a skip mode in encoding and decoding of video data. Since the order of the skip mode information and the split information of coding units according to depths may be set, encoded data transmission efficiency may be further improved.

[Description of Drawings]

0010<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a block diagram of an apparatus for encoding a video;</li><li><figref idref="f0001">FIG. 2</figref> is a block diagram of an apparatus for decoding a video;</li><li><figref idref="f0002">FIG. 3</figref> is a diagram for describing a concept of coding units;</li><li><figref idref="f0003">FIG. 4</figref> is a block diagram of an image encoder based on coding units;</li><li><figref idref="f0004">FIG. 5</figref> is a block diagram of an image decoder based on coding units;</li><li><figref idref="f0005">FIG. 6</figref> is a diagram illustrating deeper coding units according to depths, and a prediction unit;</li><li><figref idref="f0005">FIG. 7</figref> is a diagram for describing a relationship between a coding unit and transformation units;</li><li><figref idref="f0006">FIG. 8</figref> is a diagram for describing encoding information of coding units corresponding to a coded depth;</li><li><figref idref="f0007">FIG. 9</figref> is a diagram of deeper coding units according to depths;</li><li><figref idref="f0008 f0009">FIGS. 10 through 12</figref> are diagrams for describing a relationship between coding units, prediction units, and transformation units;</li><li><figref idref="f0010">FIG. 13</figref> is a diagram for describing a relationship between a coding unit, a prediction unit or a partition, and a transformation unit, according to encoding mode information of Table 1;</li><li><figref idref="f0011">FIG. 14</figref> is a flowchart illustrating a method of encoding a video;</li><li><figref idref="f0011">FIG. 15</figref> is a flowchart illustrating a method of decoding a video;</li><li><figref idref="f0012">FIG. 16</figref> is a block diagram illustrating an apparatus for encoding a video by considering a skip and split order;</li><li><figref idref="f0012">FIG. 17</figref> is a block diagram illustrating an apparatus for decoding a video by considering a skip and split order;</li><li><figref idref="f0012">FIG. 18</figref> illustrates coding units according to coded depths in a maximum coding unit;</li><li><figref idref="f0013 f0014 f0015">FIGS. 19 through 21</figref> are flowcharts illustrating methods of encoding and decoding skip information and split information, according to various exemplary embodiments;</li><li><figref idref="f0016">FIG. 22</figref> is a flowchart illustrating a method of encoding a video by considering a skip and split order; and</li><li><figref idref="f0016">FIG. 23</figref> is a flowchart illustrating a method of decoding a video by considering a skip and split order, according to an exemplary embodiment.</li></ul>

[Best Mode]

0011According to an aspect of an exemplary embodiment, there is provided a method as set out in accompanying claim 1.

0012A coding unit may be characterized by a maximum size and a depth. The depth denotes the number of times a coding unit is hierarchically split, and as the depth deepens, deeper coding units according to depths may be split from a maximum coding unit to a minimum coding unit. A depth of the maximum coding unit may be an uppermost depth, and a depth of the minimum coding unit may be a lowermost depth. Since sizes of coding units according to depths decrease as the depth of the maximum coding unit deepens, a coding unit of an upper depth may include a plurality of coding units of lower depths.

0013According to a maximum size of a coding unit, image data of a current picture may be split into maximum coding units, and each of the maximum coding units may include coding units split according to depths. Since a maximum coding unit is split according to depths, image data of a spatial domain included in the maximum coding unit may be hierarchically classified according to depths.

0014A maximum depth and a maximum size of a coding unit, which limit a total number of times a height and a width of the maximum coding unit are hierarchically split, may be predetermined.

0015The order of the split information and the skip mode information which is selectively determined for the coding units according to depths may be determined by at least one of an image sequence to which the coding units according to depths belong, a slice, a slice type according to a prediction direction, and a quantization parameter of a data unit.

0016The order of the split information and the skip mode information which is selectively determined for the coding units according to depths may be determined by the depths of the coding units in the maximum coding unit.

0017The order of the split information and the skip mode information of the coding units according to depths may be determined in such a manner that if a coding unit is the maximum coding unit, the skip mode information precedes the split information, and if the coding unit is not the maximum coding unit, the split information precedes the skip mode information.

0018The extracting may include: if a coding unit is the maximum coding unit, according to the order of the split information and the skip mode information, determining whether the maximum coding unit is predicted in a skip mode according to the skip mode information before determining whether the maximum coding unit is split according to the split information; if the coding unit is not the maximum coding unit, determining whether the coding unit is split according to the split information before determining whether the coding unit is predicted in a skip mode according to the skip mode information; and extracting the information about the coded depth and the encoding mode of the coded depth and the encoded video data according to coding units of the coded depth.

0019In the extracting, if one piece of split and skip information obtained by combining the split information and the skip mode information for coding unit according to depths is extracted, the coding units according to depths may be predicted in a skip mode without being split, and if the split information or the skip mode information for the coding units according to depths is extracted, the coding units according to depths may not be split or may not be predicted in a skip mode.

[Mode for Invention]

0020An apparatus for encoding a video, an apparatus for decoding a video, a method of encoding a video, and a method of decoding a video will be explained with reference to <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011 f0012 f0013 f0014 f0015 f0016">FIGS. 1 through 23</figref>. Herein-below, use of the term "example embodiment" or "exemplary embodiments" should be considered to relate to the invention only when said embodiments fall within the scope of the method of accompanying claim 1. Encoding and decoding of a video based on a spatially hierarchical data unit according to one or more exemplary embodiments will be explained with reference to <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011">FIGS. 1 through 15</figref>, and encoding and decoding of a video considering an order of skip and split according to one or more exemplary embodiments will be explained with reference to <figref idref="f0012 f0013 f0014 f0015 f0016">FIGS. 16 through 23</figref>.

0021Exemplary embodiments will now be described more fully with reference to the accompanying drawings.

0022Hereinafter, a 'coding unit' is an encoding data unit in which the image data is encoded at an encoder side, for example an encoding apparatus including a processor and an encoder, and an encoded data unit in which the encoded image data is decoded at a decoder side, for example a decoding apparatus including a processor and a decoder, according to the exemplary embodiments.

0023Hereinafter, an 'image' may denote a still image for a video or a moving image, that is, the video itself.

0024An apparatus for encoding a video, an apparatus for decoding a video, a method of encoding a video, and a method of decoding a video according to exemplary embodiments will be explained with reference to <figref idref="f0001 f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010 f0011">FIGS. 1 through 15</figref>.

0025<figref idref="f0001">FIG. 1</figref> is a block diagram of an apparatus 100 for encoding a video, according to an exemplary embodiment.

0026The apparatus 100 includes a maximum coding unit splitter 110, a coding unit determiner 120, and an output unit 130.

0027The maximum coding unit splitter 110 may split a current picture based on a maximum coding unit for the current picture of an image. If the current picture is larger than the maximum coding unit, image data of the current picture may be split into the at least one maximum coding unit. The maximum coding unit according to an exemplary embodiment may be a data unit having a size of 32x32, 64x64, 128x128, 256x256, etc., wherein a shape of the data unit is a square having a width and length in squares of 2. The image data may be output to the coding unit determiner 120 according to the at least one maximum coding unit.

0028A coding unit according to an exemplary embodiment may be characterized by a maximum size and a depth. The depth denotes a number of times the coding unit is spatially split from the maximum coding unit, and as the depth deepens or increases, deeper coding units according to depths may be split from the maximum coding unit to a minimum coding unit. A depth of the maximum coding unit is an uppermost depth and a depth of the minimum coding unit is a lowermost depth. Since a size of a coding unit corresponding to each depth decreases as the depth of the maximum coding unit deepens, a coding unit corresponding to an upper depth may include a plurality of coding units corresponding to lower depths.

0029As described above, the image data of the current picture is split into the maximum coding units according to a maximum size of the coding unit, and each of the maximum coding units may include deeper coding units that are split according to depths. Since the maximum coding unit according to an exemplary embodiment is split according to depths, the image data of a spatial domain included in the maximum coding unit may be hierarchically classified according to depths.

0030A maximum depth and a maximum size of a coding unit, which limit the total number of times a height and a width of the maximum coding unit are hierarchically split may be predetermined.

0031The coding unit determiner 120 encodes at least one split region obtained by splitting a region of the maximum coding unit according to depths, and determines a depth to output a finally encoded image data according to the at least one split region. In other words, the coding unit determiner 120 determines a coded depth by encoding the image data in the deeper coding units according to depths, according to the maximum coding unit of the current picture, and selecting a depth having the least encoding error. Thus, the encoded image data of the coding unit corresponding to the determined coded depth are finally output. Also, the coding units corresponding to the coded depth may be regarded as encoded coding units.

0032The determined coded depth and the encoded image data according to the determined coded depth are output to the output unit 130.

0033The image data in the maximum 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 are compared based on each of the deeper coding units. A depth having the least encoding error may be selected after comparing encoding errors of the deeper coding units. At least one coded depth may be selected for each maximum coding unit.

0034The size of the maximum 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 corresponding to same depth in one maximum coding unit, each of the coding units corresponding to the same depth may be split 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 maximum coding unit, the image data is split to regions according to the depths, the encoding errors may differ according to regions in the one maximum coding unite, and thus the coded depths may differ according to regions in the image data. Thus, one or more coded depths may be determined in one maximum coding unit, and the image data of the maximum coding unit may be divided according to coding units of at least one coded depth.

0035Accordingly, the coding unit determiner 120 may determine coding units having a tree structure included in the maximum coding unit. The 'coding units having a tree structure' according to an exemplary embodiment include coding units corresponding to a depth determined to be the coded depth, from among all deeper coding units included in the maximum coding unit. A coding unit of a coded depth may be hierarchically determined according to depths in the same region of the maximum coding unit, and may be independently determined in different regions. Similarly, a coded depth in a current region may be independently determined from a coded depth in another region.

0036A maximum depth according to an exemplary embodiment is an index related to the number of splitting times from a maximum coding unit to a minimum coding unit. A first maximum depth according to an exemplary embodiment may denote the total number of splitting times from the maximum coding unit to the minimum coding unit. A second maximum depth according to an exemplary embodiment may denote the total number of depth levels from the maximum coding unit to the minimum coding unit. For example, when a depth of the maximum coding unit is 0, a depth of a coding unit, in which the maximum coding unit is split once, may be set to 1, and a depth of a coding unit, in which the maximum coding unit is split twice, may be set to 2. Here, if the minimum coding unit is a coding unit in which the maximum coding unit is split four times, 5 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.

0037Prediction encoding and transformation may be performed according to the maximum 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 maximum coding unit. Transformation may be performed according to method of orthogonal transformation or integer transformation.

0038Since the number of deeper coding units increases whenever the maximum coding unit is split according to depths, encoding including the prediction encoding and the transformation is performed on all of the deeper coding units generated as the depth deepens. For convenience of description, the prediction encoding and the transformation will now be described based on a coding unit of a current depth, in a maximum coding unit.

0039The apparatus 100 may variably 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.

0040For example, the apparatus 100 may select not only a coding unit for encoding the image data, but also a data unit different from the coding unit so as to perform the prediction encoding on the image data in the coding unit.

0041In order to perform prediction encoding in the maximum coding unit, the prediction encoding may be performed based on a coding unit corresponding to a coded depth, i.e., based on a coding unit that is no longer split to coding units corresponding to a lower depth. Hereinafter, the coding unit that is no longer split and becomes a basis unit for prediction encoding will now be referred to as a 'prediction unit'. A partition obtained by splitting the prediction unit may include a data unit obtained by splitting at least one of a height and a width of the prediction unit.

0042For example, when a coding unit of 2Nx2N (where N is a positive integer) is no longer split and becomes a prediction unit of 2Nx2N, and a size of a partition may be 2Nx2N, 2NxN, Nx2N, or NxN. Examples of a partition type include symmetrical partitions that are obtained by symmetrically splitting a height or width of the prediction unit, partitions obtained by asymmetrically splitting the height or width of the prediction unit, such as 1:n or n:1, partitions that are obtained by geometrically splitting the prediction unit, and partitions having arbitrary shapes.

0043A prediction mode of the prediction unit may be at least one of an intra mode, a inter mode, and a skip mode. For example, the intra mode or the inter mode may be performed on the partition of 2Nx2N, 2NxN, Nx2N, or NxN. Also, the skip mode may be performed only on the partition of 2Nx2N. The encoding is independently performed on one prediction unit in a coding unit, thereby selecting a prediction mode having a least encoding error.

0044The apparatus 100 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.

0045In 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 data unit for the transformation may include a data unit for an intra mode and a data unit for an inter mode.

0046A data unit used as a base of the transformation will now be referred to as a 'transformation unit'. 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 2Nx2N, a transformation depth may be 0 when the size of a transformation unit is also 2Nx2N, may be 1 when each of the height and width of the current coding unit is split into two equal parts, totally split into 4¹ transformation units, and the size of the transformation unit is thus NxN, and may be 2 when each of the height and width of the current coding unit is split into four equal parts, totally split into 4² transformation units and the size of the transformation unit is thus N/2xN/2. For example, the transformation unit may be set according to a hierarchical tree structure, in which a transformation unit of an upper transformation depth is split into four transformation units of a lower transformation depth according to the hierarchical characteristics of a transformation depth.

0047Similarly to the coding unit, the transformation unit in the coding unit may be recursively split into smaller sized regions, so that the transformation unit may be determined independently in units of regions. Thus, residual data in the coding unit may be divided according to the transformation having the tree structure according to transformation depths.

0048Encoding information according to coding units corresponding to a coded depth requires not only information about the coded depth, but also information related to prediction encoding and transformation. Accordingly, the coding unit determiner 120 not only determines a coded depth having a least encoding error, but also determines a partition type in a prediction unit, a prediction mode according to prediction units, and a size of a transformation unit for transformation.

0049Coding units according to a tree structure in a maximum coding unit and a method of determining a partition, according to exemplary embodiments, will be described in detail later with reference to <figref idref="f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009">FIGS. 3 through 12</figref>.

0050The 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.

0051The output unit 130 outputs the image data of the maximum coding unit, which is encoded based on the at least one coded depth determined by the coding unit determiner 120, and information about the encoding mode according to the coded depth, in bitstreams.

0052The encoded image data may be obtained by encoding residual data of an image.

0053The information about the encoding mode according to coded depth may include information about the coded depth, about the partition type in the prediction unit, the prediction mode, and the size of the transformation unit.

0054The information about the coded depth may be defined by using split information according to depths, which indicates 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 the coded depth, image data in the current coding unit is encoded and output, and thus the split information may be defined not to split the current coding unit to a lower depth. Alternatively, if the current depth of the current coding unit is not the coded depth, the encoding is performed on the coding unit of the lower depth, and thus the split information may be defined to split the current coding unit to obtain the coding units of the lower depth.

0055If the current depth is not the coded 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.

0056Since the coding units having a tree structure are determined for one maximum coding unit, and information about at least one encoding mode is determined for a coding unit of a coded depth, information about at least one encoding mode may be determined for one maximum coding unit. Also, a coded depth of the image data of the maximum coding unit may be different according to locations since the image data is hierarchically split according to depths, and thus information about the coded depth and the encoding mode may be set for the image data.

0057Accordingly, the output unit 130 may assign encoding information about a corresponding coded depth and an encoding mode to at least one of the coding unit, the prediction unit, and a minimum unit included in the maximum coding unit.

0058The minimum unit according to an exemplary embodiment is a rectangular data unit obtained by splitting the minimum coding unit constituting the lowermost depth by 4. Alternatively, the minimum unit may be a maximum rectangular data unit that may be included in all of the coding units, prediction units, partition units, and transformation units included in the maximum coding unit.

0059For example, the encoding information output through the output unit 130 may be classified into encoding information according to coding units, and encoding information according to prediction units. The encoding information according to the 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 of 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 of the intra mode. Also, 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 SPS (Sequence Parameter Set) or a header of a bitstream.

0060In the 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 by two. In other words, when the size of the coding unit of the current depth is 2Nx2N, the size of the coding unit of the lower depth is NxN. Also, the coding unit of the current depth having the size of 2Nx2N may include maximum 4 of the coding unit of the lower depth.

0061Accordingly, the 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 maximum coding unit, based on the size of the maximum coding unit and the maximum depth determined considering characteristics of the current picture. Also, since encoding may be performed on each maximum coding unit by using any one of various prediction modes and transformations, an optimum encoding mode may be determined considering characteristics of the coding unit of various image sizes.

0062Thus, if an image having high resolution or large data amount is encoded in a conventional macroblock, a number of macroblocks per picture excessively increases. Accordingly, a 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 apparatus 100, 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.

0063<figref idref="f0001">FIG. 2</figref> is a block diagram of an apparatus 200 for decoding a video, according to an exemplary embodiment.

0064The apparatus 200 includes a receiver 210, an image data and encoding information extractor 220, and an image data decoder 230. Definitions of various terms, such as a coding unit, a depth, a prediction unit, a transformation unit, and information about various encoding modes, for various operations of the apparatus 200 are identical to those described with reference to <figref idref="f0001">FIG. 1</figref> and the apparatus 100.

0065The 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 maximum 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 or SPS.

0066Also, the image data and encoding information extractor 220 extracts information about a coded depth and an encoding mode for the coding units having a tree structure according to each maximum coding unit, from the parsed bitstream. The extracted information about the coded depth and the encoding mode is output to the image data decoder 230. In other words, the image data in a bit stream is split into the maximum coding unit so that the image data decoder 230 decodes the image data for each maximum coding unit.

0067The information about the coded depth and the encoding mode according to the maximum coding unit may be set for information about at least one coding unit corresponding to the coded depth, and information about an encoding mode may include information about a partition type of a corresponding coding unit corresponding to the coded depth, about a prediction mode, and a size of a transformation unit. Also, splitting information according to depths may be extracted as the information about the coded depth.

0068The information about the coded depth and the encoding mode according to each maximum coding unit extracted by the image data and encoding information extractor 220 is information about a coded depth and an encoding mode determined to generate a minimum encoding error when an encoder, such as the apparatus 100, repeatedly performs encoding for each deeper coding unit according to depths according to each maximum coding unit. Accordingly, the apparatus 200 may restore an image by decoding the image data according to a coded depth and an encoding mode that generates the minimum encoding error.

0069Since encoding information about the coded 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 information about the coded depth and the encoding mode according to the predetermined data units. The predetermined data units to which the same information about the coded depth and the encoding mode is assigned may be inferred to be the data units included in the same maximum coding unit.

0070The image data decoder 230 restores the current picture by decoding the image data in each maximum coding unit based on the information about the coded depth and the encoding mode according to the maximum coding units. In other words, the image data decoder 230 may decode the encoded image data based on the extracted information about the partition type, the prediction mode, and the transformation unit for each coding unit from among the coding units having the tree structure included in each maximum coding unit. A decoding process may include a prediction including intra prediction and motion compensation, and a inverse transformation. Inverse transformation may be performed according to method of inverse orthogonal transformation or inverse integer transformation.

0071The 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 coded depths.

0072Also, the image data decoder 230 may perform inverse transformation according to each transformation unit in the coding unit, based on the information about the size of the transformation unit of the coding unit according to coded depths, so as to perform the inverse transformation according to maximum coding units.

0073The image data decoder 230 may determine at least one coded depth of a current maximum 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 coded depth. Accordingly, the image data decoder 230 may decode encoded data of at least one coding unit corresponding to the each coded depth in the current maximum coding unit by using the information about the partition type of the prediction unit, the prediction mode, and the size of the transformation unit for each coding unit corresponding to the coded depth, and output the image data of the current maximum coding unit.

0074In other words, 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.

0075The apparatus 200 may obtain information about at least one coding unit that generates the minimum encoding error when encoding is recursively performed for each maximum coding unit, and may use the information to decode the current picture. In other words, the coding units having the tree structure determined to be the optimum coding units in each maximum coding unit may be decoded. Also, the maximum size of coding unit is determined considering resolution and a amount of image data.

0076Accordingly, even if image data has high resolution and a large amount of data, the image data may be efficiently decoded and restored by using a size of a coding unit and an encoding mode, which are adaptively determined according to characteristics of the image data, by using information about an optimum encoding mode received from an encoder.

0077A method of determining coding units having a tree structure, a prediction unit, and a transformation unit, according to an exemplary embodiment, will now be described with reference to <figref idref="f0002 f0003 f0004 f0005 f0006 f0007 f0008 f0009 f0010">FIGS. 3 through 13</figref>.

0078<figref idref="f0002">FIG. 3</figref> is a diagram for describing a concept of coding units according to an exemplary embodiment.

0079A size of a coding unit may be expressed in width x height, and may be 64x64, 32x32, 16x16, and 8x8. A coding unit of 64x64 may be split into partitions of 64x64, 64x32, 32x64, or 32x32, and a coding unit of 32x32 may be split into partitions of 32x32, 32x16, 16x32, or 16x16, a coding unit of 16x16 may be split into partitions of 16x16, 16x8, 8x16, or 8x8, and a coding unit of 8x8 may be split into partitions of 8x8, 8x4, 4x8, or 4x4.

0080In video data 310, a resolution is 1920x1080, a maximum size of a coding unit is 64, and a maximum depth is 2. In video data 320, a resolution is 1920x1080, a maximum size of a coding unit is 64, and a maximum depth is 3. In video data 330, a resolution is 352x288, a maximum size of a coding unit is 16, and a maximum depth is 1. The maximum depth shown in <figref idref="f0002">FIG. 3</figref> denotes a total number of splits from a maximum coding unit to a minimum decoding unit.

0081If a resolution is high or a data amount is large, a maximum size of a coding unit may be 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 the higher resolution than the video data 330 may be 64.

0082Since the maximum depth of the video data 310 is 2, coding units 315 of the video data 310 may include a maximum 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 maximum coding unit twice. Meanwhile, since the maximum depth of the video data 330 is 1, coding units 335 of the video data 330 may include a maximum 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 maximum coding unit once.

0083Since the maximum depth of the video data 320 is 3, coding units 325 of the video data 320 may include a maximum 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 maximum coding unit three times. As a depth deepens, detailed information may be precisely expressed.

0084<figref idref="f0003">FIG. 4</figref> is a block diagram of an image encoder 400 based on coding units, according to an exemplary embodiment.

0085The image encoder 400 performs operations of the coding unit determiner 120 of the apparatus 100 to encode image data. In other words, an intra predictor 410 performs intra prediction on coding units in an intra mode, from among a current frame 405, and a motion estimator 420 and a motion compensator 425 performs inter estimation and motion compensation on coding units in an inter mode from among the current frame 405 by using the current frame 405, and a reference frame 495.

0086Data output from the intra predictor 410, the motion estimator 420, and the motion compensator 425 is output as a quantized transformation coefficient through a transformer 430 and a quantizer 440. The quantized transformation coefficient is restored as data in a spatial domain through an inverse quantizer 460 and an inverse transformer 470, and the restored data in the spatial domain is output as the reference frame 495 after being post-processed through a deblocking unit 480 and a loop filtering unit 490. The quantized transformation coefficient may be output as a bitstream 455 through an entropy encoder 450.

0087In order for the image encoder 400 to be applied in the apparatus 100, all elements of the image encoder 400, i.e., the intra predictor 410, the motion estimator 420, the motion compensator 425, the transformer 430, the quantizer 440, the entropy encoder 450, the inverse quantizer 460, the inverse transformer 470, the deblocking unit 480, and the loop filtering unit 490 perform operations based on each coding unit from among coding units having a tree structure while considering the maximum depth of each maximum coding unit.

0088Specifically, the intra predictor 410, the motion estimator 420, and the motion compensator 425 determines partitions and a prediction mode of each coding unit from among the coding units having a tree structure while considering the maximum size and the maximum depth of a current maximum coding unit, and the transformer 430 determines the size of the transformation unit in each coding unit from among the coding units having a tree structure.

0089<figref idref="f0004">FIG. 5</figref> is a block diagram of an image decoder 500 based on coding units, according to an exemplary embodiment.

0090A parser 510 parses encoded image data to be decoded and information about encoding required for decoding from a bitstream 505. The encoded image data is output as inverse quantized data through an entropy decoder 520 and an inverse quantizer 530, and the inverse quantized data is restored to image data in a spatial domain through an inverse transformer 540.

0091An intra predictor 550 performs intra prediction on coding units in an intra mode with respect to the image data in the spatial domain, and a motion compensator 560 performs motion compensation on coding units in an inter mode by using a reference frame 585.

0092The image data in the spatial domain, which passed through the intra predictor 550 and the motion compensator 560, may be output as a restored frame 595 after being post-processed through a deblocking unit 570 and a loop filtering unit 580. Also, the image data that is post-processed through the deblocking unit 570 and the loop filtering unit 580 may be output as the reference frame 585.

0093In order to decode the image data in the image data decoder 230 of the apparatus 200, the image decoder 500 may perform operations that are performed after the parser 510.

0094In order for the image decoder 500 to be applied in the apparatus 200, all elements of the image decoder 500, i.e., the parser 510, the entropy decoder 520, the inverse quantizer 530, the inverse transformer 540, the intra predictor 550, the motion compensator 560, the deblocking unit 570, and the loop filtering unit 580 perform operations based on coding units having a tree structure for each maximum coding unit.

0095Specifically, the intra predictor 550 and the motion compensator 560 perform operations based on partitions and a prediction mode for each of the coding units having a tree structure, and the inverse transformer 540 perform operations based on a size of a transformation unit for each coding unit.

0096<figref idref="f0005">FIG. 6</figref> is a diagram illustrating deeper coding units according to depths, and partitions, according to an exemplary embodiment.

0097The apparatus 100 and the apparatus 200 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 differently set by a user. Sizes of deeper coding units according to depths may be determined according to the predetermined maximum size of the coding unit.

0098In a hierarchical structure 600 of coding units, according to an exemplary embodiment, the maximum height and the maximum width of the coding units are each 64, and the maximum depth is 4. Since a depth deepens along a vertical axis of the hierarchical structure 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 600.

0099In other words, a coding unit 610 is a maximum coding unit in the hierarchical structure 600, wherein a depth is 0 and a size, i.e., a height by width, is 64x64. The depth deepens along the vertical axis, and a coding unit 620 having a size of 32x32 and a depth of 1, a coding unit 630 having a size of 16x16 and a depth of 2, a coding unit 640 having a size of 8x8 and a depth of 3, and a coding unit 650 having a size of 4x4 and a depth of 4 exist. The coding unit 650 having the size of 4x4 and the depth of 4 is a minimum coding unit.

0100The prediction unit and the partitions of a coding unit are arranged along the horizontal axis according to each depth. In other words, if the coding unit 610 having the size of 64x64 and the depth of 0 is a prediction unit, the prediction unit may be split into partitions include in the coding unit 610, i.e. a partition 610 having a size of 64x64, partitions 612 having the size of 64x32, partitions 614 having the size of 32x64, or partitions 616 having the size of 32x32.

0101Similarly, a prediction unit of the coding unit 620 having the size of 32x32 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 32x32, partitions 622 having a size of 32x16, partitions 624 having a size of 16x32, and partitions 626 having a size of 16x16.

0102Similarly, a prediction unit of the coding unit 630 having the size of 16x16 and the depth of 2 may be split into partitions included in the coding unit 630, i.e. a partition having a size of 16x16 included in the coding unit 630, partitions 632 having a size of 16x8, partitions 634 having a size of 8x16, and partitions 636 having a size of 8x8.

0103Similarly, a prediction unit of the coding unit 640 having the size of 8x8 and the depth of 3 may be split into partitions included in the coding unit 640, i.e. a partition having a size of 8x8 included in the coding unit 640, partitions 642 having a size of 8x4, partitions 644 having a size of 4x8, and partitions 646 having a size of 4x4.

0104The coding unit 650 having the size of 4x4 and the depth of 4 is the minimum coding unit and a coding unit of the lowermost depth. A prediction unit of the coding unit 650 is only assigned to a partition having a size of 4x4, as opposed to being partitioned into partitions 652 having a size of 4x2, partitions 654 having a size of 2x4, and partitions 656 having a size of 2x2.

0105In order to determine the at least one coded depth of the coding units constituting the maximum coding unit 610, the coding unit determiner 120 of the apparatus 100 performs encoding for coding units corresponding to each depth included in the maximum coding unit 610.

0106A 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 encoding results of the same data according to depths, the coding unit corresponding to the depth of 1 and four coding units corresponding to the depth of 2 are each encoded.

0107In order to perform encoding for a current depth from among the depth, a least encoding error may be selected for the current depth by performing encoding for each prediction unit in the coding units corresponding to the current depth, along the horizontal axis of the hierarchical structure 600. Alternatively, the minimum encoding error may be searched for by comparing the least encoding errors according to depths, by performing encoding for each depth as the depth deepens along the vertical axis of the hierarchical structure 600. A depth and a partition having the minimum encoding error in the coding unit 610 may be selected as the coded depth and a partition type of the coding unit 610.

0108<figref idref="f0005">FIG. 7</figref> is a diagram for describing a relationship between a coding unit 710 and transformation units 720, according to an exemplary embodiment.

0109The apparatus 100 or 200 encodes or decodes an image according to coding units having sizes smaller than or equal to a maximum coding unit for each maximum coding unit. Sizes of transformation units for transformation during encoding may be selected based on data units that are not larger than corresponding coding unit.

0110For example, in the apparatus 100 or 200, if a size of the coding unit 710 is 64x64, transformation may be performed by using the transformation units 720 having a size of 32x32.

0111Also, data of the coding unit 710 having the size of 64x64 may be encoded by performing the transformation on each of the transformation units having the size of 32x32, 16x16, 8x8, and 4x4, which are smaller than 64x64, and then a transformation unit having the least coding error may be selected.

0112<figref idref="f0006">FIG. 8</figref> is a diagram for describing encoding information of coding units corresponding to a coded depth, according to an exemplary embodiment.

0113The output unit 130 of the apparatus 100 may encode and transmit information 800 about a partition type, information 810 about a prediction mode, and information 820 about a size of a transformation unit for each coding unit corresponding to a coded depth, as information about an encoding mode.

0114The 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 2Nx2N may be split into any one of a partition 802 having a size of 2Nx2N, a partition 804 having a size of 2NxN, a partition 806 having a size of Nx2N, and a partition 808 having a size of NxN. Here, the information 800 about a partition type is set to indicate one of the partition 804 having a size of 2NxN, the partition 806 having a size of Nx2N, and the partition 808 having a size of NxN

0115The information 810 indicates a prediction mode of each partition. For example, the information 810 may indicate a mode of prediction encoding performed on a partition indicated by the information 800, i.e., an intra mode 812, an inter mode 814, or a skip mode 816.

0116The information 820 indicates a transformation unit to be based on when transformation is performed on a current coding unit. For example, the transformation unit may be a first intra transformation unit 822, a second intra transformation unit 824, a first inter transformation unit 826, or a second inter transformation unit 828.

0117The image data and encoding information extractor 220 of the apparatus 200 may extract and use the information 800, 810, and 820 for decoding.

0118<figref idref="f0007">FIG. 9</figref> is a diagram of deeper coding units according to depths, according to an exemplary embodiment.

0119Split information may be used to indicate a change of a depth. The spilt information indicates whether a coding unit of a current depth is split into coding units of a lower depth.

0120A prediction unit 910 for prediction encoding a coding unit 900 having a depth of 0 and a size of 2N_0x2N_0 may include partitions of a partition type 912 having a size of 2N_0x2N_0, a partition type 914 having a size of 2N_0xN_0, a partition type 916 having a size of N_0x2N_0, and a partition type 918 having a size of N_0xN_0. <figref idref="f0007">FIG. 9</figref> only illustrates the partition types 912 through 918 which are obtained by symmetrically splitting the prediction unit 910, but a partition type is not limited thereto, and the partitions of the prediction unit 910 may include asymmetrical partitions, partitions having a predetermined shape, and partitions having a geometrical shape.

0121Prediction encoding is repeatedly performed on one partition having a size of 2N_0x2N_0, two partitions having a size of 2N_0xN_0, two partitions having a size of N_0x2N_0, and four partitions having a size of N_0xN_0, according to each partition type. The prediction encoding in an intra mode and an inter mode may be performed on the partitions having the sizes of 2N_0x2N_0, N_0x2N_0, 2N_0xN_0, and N_0xN_0. The prediction encoding in a skip mode is performed only on the partition having the size of 2N_0x2N_0.

0122Errors of encoding including the prediction encoding in the partition types 912 through 918 are compared, and the least encoding error is determined among the partition types. If an encoding error is smallest in one of the partition types 912 through 916, the prediction unit 910 may not be split into a lower depth.

0123If the encoding error is the smallest in the partition type 918, a depth is changed from 0 to 1 to split the partition type 918 in operation 920, and encoding is repeatedly performed on coding units 930 having a depth of 2 and a size of N_0xN_0 to search for a minimum encoding error.

0124A prediction unit 940 for prediction encoding the coding unit 930 having a depth of 1 and a size of 2N_1x2N_1 (=N_0xN_0) may include partitions of a partition type 942 having a size of 2N_1x2N_1, a partition type 944 having a size of 2N_1xN_1, a partition type 946 having a size of N_1x2N_1, and a partition type 948 having a size of N_1xN_1.

0125If an encoding error is the smallest in the partition type 948, a depth is changed from 1 to 2 to split the partition type 948 in operation 950, and encoding is repeatedly performed on coding units 960, which have a depth of 2 and a size of N_2xN_2 to search for a minimum encoding error.

0126When a maximum depth is d, split operation according to each depth may be performed up to when a depth becomes d-1, and split information may be encoded as up to when a depth is one of 0 to d-2. In other words, 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)x2N_(d-1) may include partitions of a partition type 992 having a size of 2N_(d-1)x2N_(d-1), a partition type 994 having a size of 2N_(d-1)xN_(d-1), a partition type 996 having a size of N_(d-1)x2N_(d-1), and a partition type 998 having a size of N_(d-1)xN_(d-1).

0127Prediction encoding may be repeatedly performed on one partition having a size of 2N_(d-1)x2N_(d-1), two partitions having a size of 2N_(d-1)xN_(d-1), two partitions having a size of N_(d-1)x2N_(d-1), four partitions having a size of N_(d-1)xN_(d-1) from among the partition types 992 through 998 to search for a partition type having a minimum encoding error.

0128Even when the partition type 998 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 to a lower depth, and a coded depth for the coding units constituting a current maximum coding unit 900 is determined to be d-1 and a partition type of the coding unit 900 may be determined to be N_(d-1)xN_(d-1). Also, since the maximum depth is d and a minimum coding unit 980 having a lowermost depth of d-1 is no longer split to a lower depth, split information for a coding unit 980 is not set.

0129A data unit 999 may be a 'minimum unit' for the current maximum coding unit. A minimum unit according to an exemplary embodiment may be a rectangular data unit obtained by splitting a minimum coding unit 980 by 4. By performing the encoding repeatedly, the apparatus 100 may select a depth having the least encoding error by comparing encoding errors according to depths of the coding unit 900 to determine a coded depth, and set a corresponding partition type and a prediction mode as an encoding mode of the coded depth.

0130As such, the minimum encoding errors according to depths are compared in all of the depths of 1 through d, and a depth having the least encoding error may be determined as a coded depth. The coded depth, the partition type of the prediction unit, and the prediction mode may be encoded and transmitted as information about an encoding mode. Also, since a coding unit is split from a depth of 0 to a coded depth, only split information of the coded depth is set to 0, and split information of depths excluding the coded depth is set to 1.

0131The image data and encoding information extractor 220 of the apparatus 200 may extract and use the information about the coded depth and the prediction unit of the coding unit 900 to decode the partition 912. The apparatus 200 may determine a depth, in which split information is 0, as a coded depth by using split information according to depths, and use information about an encoding mode of the corresponding depth for decoding.

0132<figref idref="f0008 f0009">FIGS. 10 through 12</figref> are diagrams for describing a relationship between coding units 1010, prediction units 1060, and transformation units 1070, according to an exemplary embodiment.

0133The coding units 1010 are coding units having a tree structure, corresponding to coded depths determined by the apparatus 100, in a maximum coding unit. The prediction units 1060 are partitions of prediction units of each of the coding units 1010 , and the transformation units 1070 are transformation units of each of the coding units 1010.

0134When a depth of a maximum coding unit is 0 in the 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.

0135In the prediction units 1060, some coding units 1014, 1016, 1022, 1032, 1048, 1050, 1052, and 1054 are split into partitions for prediction encoding. In other words, partition types in the coding units 1014, 1022, 1050, and 1054 have a size of 2NxN, partition types in the coding units 1016, 1048, and 1052 have a size of Nx2N, and a partition type of the coding unit 1032 has a size of NxN. Prediction units and partitions of the coding units 1010 are smaller than or equal to each coding unit.

0136Transformation 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, and 1052 in the transformation units 1070 are different from those in the prediction units 1060 in terms of sizes and shapes. In other words, the apparatuses 100 and 200 may perform intra prediction, motion estimation, motion compensation, transformation, and inverse transformation individually on a data unit in the same coding unit.

0137Accordingly, encoding is recursively performed on each of coding units having a hierarchical structure in each region of a maximum coding unit to determine an optimum coding unit, and thus coding units having a recursive tree structure may be obtained. Encoding information may include split information about a coding unit, information about a partition type, information about a prediction mode, and information about a size of a transformation unit. Table 1 shows the encoding information that may be set by the apparatuses 100 and 200. <tables id="tabl0001" num="0001"><table frame="all"><title>[Table 1]</title><tgroup cols="6"><colspec colnum="1" colname="col1" colwidth="20mm" /><colspec colnum="2" colname="col2" colwidth="23mm" /><colspec colnum="3" colname="col3" colwidth="25mm" /><colspec colnum="4" colname="col4" colwidth="31mm" /><colspec colnum="5" colname="col5" colwidth="31mm" /><colspec colnum="6" colname="col6" colwidth="37mm" /><thead><row><entry namest="col1" nameend="col5" align="left" valign="middle">Split Information 0 (Encoding on Coding unit having Size of 2Nx2N and Current Depth of d)</entry><entry valign="middle">Split Information 1</entry></row></thead><tbody><row><entry valign="middle">Prediction Mode</entry><entry namest="col2" nameend="col3" align="left" valign="middle">Partition Type</entry><entry namest="col4" nameend="col5" align="left" valign="middle">Size of Transformation Unit</entry><entry morerows="6" valign="middle">Repeatedly Encode Coding Units having Lower Depth of d+1</entry></row><row rowsep="0"><entry valign="middle">Intra,</entry><entry morerows="1" rowsep="1" valign="middle">Symmetrical Partition Type</entry><entry morerows="1" rowsep="1" valign="middle">Asymmetrical Partition Type</entry><entry morerows="1" rowsep="1" valign="middle">Split Information 0 of Transformation Unit</entry><entry morerows="1" rowsep="1" valign="middle">Split Information 1 of Transformation Unit</entry></row><row><entry rowsep="0" valign="middle">Inter,</entry></row><row rowsep="0"><entry morerows="3" rowsep="1">Skip (Only 2Nx2N)</entry><entry valign="middle">2Nx2N,</entry><entry valign="middle">2NxnU,</entry><entry morerows="3" rowsep="1" valign="middle">2Nx2N</entry><entry morerows="1" valign="middle">NxN (Symmetrical Type),</entry></row><row rowsep="0"><entry valign="middle">2NxN,</entry><entry valign="middle">2NxnD,</entry></row><row rowsep="0"><entry valign="middle">Nx2N,</entry><entry valign="middle">nLx2N,</entry><entry morerows="1" rowsep="1" valign="middle">N/2xN/2 (Asymmetrical Type)</entry></row><row><entry valign="middle">NxN</entry><entry valign="middle">nRx2N</entry></row></tbody></tgroup></table></tables>

0138The output unit 130 of the apparatus 100 may output the encoding information about the coding units having a tree structure, and the image data and encoding information extractor 220 of the apparatus 200 may extract the encoding information about the coding units having a tree structure from a received bitstream.

0139Split information indicates 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 coded depth, and thus information about a partition type, prediction mode, and a size of a transformation unit may be defined for the coded depth. If the current coding unit is further split according to the split information, encoding is independently performed on four split coding units of a lower depth.

0140A 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 types, and the skip mode is defined only in a partition type having a size of 2Nx2N.

0141The information about the partition type may indicate symmetrical partition types having sizes of 2Nx2N, 2NxN, Nx2N, and NxN, which are obtained by symmetrically splitting a height or a width of a prediction unit, and asymmetrical partition types having sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N, which are obtained by asymmetrically splitting the height or width of the prediction unit. The asymmetrical partition types having the sizes of 2NxnU and 2NxnD may be respectively obtained by splitting the height of the prediction unit in 1:3 and 3:1, and the asymmetrical partition types having the sizes of nLx2N and nRx2N may be respectively obtained by splitting the width of the prediction unit in 1:3 and 3:1

0142The size of the transformation unit may be set to be two types in the intra mode and two types in the inter mode. In other words, if split information of the transformation unit is 0, the size of the transformation unit may be 2Nx2N, 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 type of the current coding unit having the size of 2Nx2N is a symmetrical partition type, a size of a transformation unit may be NxN, and if the partition type of the current coding unit is an asymmetrical partition type, the size of the transformation unit may be N/2xN/2.

0143The encoding information about coding units having a tree structure may include at least one of a coding unit corresponding to a coded depth, a prediction unit, and a minimum unit. The coding unit corresponding to the coded depth may include at least one of a prediction unit and a minimum unit containing the same encoding information.

0144Accordingly, it is determined whether adjacent data units are included in the same coding unit corresponding to the coded depth by comparing encoding information of the adjacent data units. Also, a corresponding coding unit corresponding to a coded depth is determined by using encoding information of a data unit, and thus a distribution of coded depths in a maximum coding unit may be determined.

0145Accordingly, 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.

0146Alternatively, if a current coding unit is predicted based on encoding information of adjacent data units, data units adjacent to the current coding unit are searched using encoded information of the data units, and the searched adjacent coding units may be referred for predicting the current coding unit.

0147<figref idref="f0010">FIG. 13</figref> is a diagram for describing a relationship between a coding unit, a prediction unit or a partition, and a transformation unit, according to encoding mode information of Table 1.

0148A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312, 1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318 is a coding unit of a coded depth, split information may be set to 0. Information about a partition type of the coding unit 1318 having a size of 2Nx2N may be set to be one of a partition type 1322 having a size of 2Nx2N, a partition type 1324 having a size of 2NxN, a partition type 1326 having a size of Nx2N, a partition type 1328 having a size of NxN, a partition type 1332 having a size of 2NxnU, a partition type 1334 having a size of 2NxnD, a partition type 1336 having a size of nLx2N, and a partition type 1338 having a size of nRx2N.

0149When the partition type is set to be symmetrical, i.e. the partition type 1322, 1324, 1326, or 1328, a transformation unit 1342 having a size of 2Nx2N is set if split information (TU size flag) of a transformation unit is 0, and a transformation unit 1344 having a size of NxN is set if a TU size flag is 1.

0150When the partition type is set to be asymmetrical, i.e., the partition type 1332, 1334, 1336, or 1338, a transformation unit 1352 having a size of 2Nx2N is set if a TU size flag is 0, and a transformation unit 1354 having a size of N/2xN/2 is set if a TU size flag is 1.

0151Referring to <figref idref="f0010">FIG. 13</figref>, the TU size flag is a flag having a value or 0 or 1, but the TU size flag is not limited to 1 bit, and a transformation unit may be hierarchically split having a tree structure while the TU size flag increases from 0.

0152In this case, the size of a transformation unit that has been actually used may be expressed by using a TU size flag of a transformation unit, according to an exemplary embodiment, together with a maximum size and minimum size of the transformation unit. According to an exemplary embodiment, the video encoding apparatus 100 is capable of encoding maximum transformation unit size information, minimum transformation unit size information, and a maximum TU size flag. The result of encoding the maximum transformation unit size information, the minimum transformation unit size information, and the maximum TU size flag may be inserted into an SPS. According to an exemplary embodiment, the video decoding apparatus 200 may decode video by using the maximum transformation unit size information, the minimum transformation unit size information, and the maximum TU size flag.

0153For example, if the size of a current coding unit is 64x64 and a maximum transformation unit size is 32x32, then the size of a transformation unit may be 32x32 when a TU size flag is 0, may be 16x16 when the TU size flag is 1, and may be 8x8 when the TU size flag is 2.

0154As another example, if the size of the current coding unit is 32x32 and a minimum transformation unit size is 32x32, then the size of the transformation unit may be 32x32 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 less than 32x32.

0155As another example, if the size of the current coding unit is 64x64 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.

0156Thus, 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): <maths id="math0001" num="(1)"><math display="block"><mi>CurrMinTuSize</mi><mo>=</mo><mi>max</mi><mfenced><mi>MinTransformSize</mi><mo>,</mo><mspace width="1ex" /><mi>RootTuSize</mi><mo>/</mo><mfenced><msup><mn>2</mn><mo>∧</mo></msup><mi>MaxTransformSizeIndex</mi></mfenced></mfenced></math><img file="EP3032829B1_D0001.tif" /></maths>

0157Compared 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. In Equation (1), 'RootTuSize/(2^MaxTransformSizeIndex)' denotes a transformation unit size when the transformation unit size 'RootTuSize', when the TU size flag is 0, is split a number of times corresponding to the maximum TU size flag, and 'MinTransformSize' denotes a minimum transformation size. Thus, a smaller value from among 'RootTuSize/(2^MaxTransformSizeIndex)' and 'MinTransformSize' may be the current minimum transformation unit size 'CurrMinTuSize' that can be determined in the current coding unit.

0158According to an exemplary embodiment, the maximum transformation unit size RootTuSize may vary according to the type of a prediction mode.

0159For 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. <maths id="math0002" num="(2)"><math display="block"><mi>RootTuSize</mi><mo>=</mo><mi>min</mi><mfenced><mi>MaxTransformSize</mi><mo>,</mo><mspace width="1ex" /><mi>PUSize</mi></mfenced></math><img file="EP3032829B1_D0002.tif" /></maths>

0160That 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.

0161If 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. <maths id="math0003" num="(3)"><math display="block"><mi>RootTuSize</mi><mo>=</mo><mi>min</mi><mfenced><mi>MaxTransformSize</mi><mo>,</mo><mspace width="1ex" /><mi>PartitionSize</mi></mfenced></math><img file="EP3032829B1_D0003.tif" /></maths>

0162That 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.

0163However, the current maximum transformation unit size 'RootTuSize' that varies according to the type of a prediction mode in a partition unit is just an example and is not limited thereto.

0164<figref idref="f0011">FIG. 14</figref> is a flowchart illustrating a method of encoding a video, according to an exemplary embodiment.

0165In operation 1210, a current picture is split into at least one maximum coding unit. A maximum depth indicating the total number of possible splitting times may be predetermined.

0166In operation 1220, a coded depth to output a final encoding result according to at least one split region, which is obtained by splitting a region of each maximum coding unit according to depths, is determined by encoding the at least one split region, and a coding unit according to a tree structure is determined.

0167The maximum coding unit is spatially split whenever the depth deepens, and thus is split into coding units of a lower depth. Each coding unit may be split into coding units of another lower depth by being spatially split independently from adjacent coding units. Encoding is repeatedly performed on each coding unit according to depths.

0168Also, a transformation unit according to partition types having the least encoding error is determined for each deeper coding unit. In order to determine a coded depth having a minimum encoding error in each maximum coding unit, encoding errors may be measured and compared in all deeper coding units according to depths.

0169In operation 1230, encoded image data constituting the final encoding result according to the coded depth is output for each maximum coding unit, with encoding information about the coded depth and an encoding mode. The information about the encoding mode may include information about a coded depth or split information, information about a partition type of a prediction unit, a prediction mode, and a size of a transformation unit. The encoded information about the encoding mode may be transmitted to a decoder with the encoded image data.

0170<figref idref="f0011">FIG. 15</figref> is a flowchart illustrating a method of decoding a video, according to an exemplary embodiment.

0171In operation 1310, a bitstream of an encoded video is received and parsed.

0172In operation 1320, encoded image data of a current picture assigned to a maximum coding unit, and information about a coded depth and an encoding mode according to maximum coding units are extracted from the parsed bitstream. The coded depth of each maximum coding unit is a depth having the least encoding error for the each maximum coding unit. In encoding each maximum coding unit, the image data is encoded based on at least one data unit obtained by hierarchically splitting the each maximum coding unit according to depths.

0173According to the information about the coded depth and the encoding mode, the maximum coding unit may be split into coding units having a tree structure. Each coding unit of the coding units having the tree structure is determined as a coding unit corresponding to a coded depth, optimally encoded as to output the least encoding error. Accordingly, encoding and decoding efficiency of an image may be improved by decoding each piece of encoded image data in the coding units after determining at least one coded depth according to coding units.

0174In operation 1330, the image data of each maximum coding unit is decoded based on the information about the coded depth and the encoding mode according to the maximum coding units. The decoded image data may be reproduced by a reproducing apparatus, stored in a storage medium, or transmitted through a network.

0175Encoding and decoding of a video considering an order of skip and split according to exemplary embodiments will now be explained with reference to <figref idref="f0012 f0013 f0014 f0015 f0016">FIGS. 16 through 23</figref>.

0176<figref idref="f0012">FIG. 16</figref> is a block diagram illustrating an apparatus 1400 for encoding a video by considering a skip and split order, according to an exemplary embodiment.

0177Referring to <figref idref="f0012">FIG. 16</figref>, the apparatus 1400 includes a maximum coding unit splitter 1410, a coding unit and encoding mode determiner 1420, and an output unit 1430.

0178The apparatus 1400 of <figref idref="f0012">FIG. 16</figref> may be an example of the apparatus 100 of <figref idref="f0001">FIG. 1</figref>, and the maximum coding unit splitter 110, the coding unit determiner 120, and the output unit 130 of the apparatus 100 of <figref idref="f0001">FIG. 1</figref> may correspond to the maximum coding unit splitter 1410, the coding unit and encoding mode determiner 1420, and the output unit 1430 of <figref idref="f0012">FIG. 16</figref>, respectively.

0179The maximum coding unit splitter 1410 splits a picture of an input image into maximum coding units having predetermined sizes, and image data according to the maximum coding units is output to the coding unit and encoding mode determiner 1420.

0180The coding unit and encoding mode determiner 1420 hierarchically splits regions of each of the maximum coding units input from the maximum coding unit splitter 1410 as a depth deepens, and individually performs encoding based on coding units according to depths corresponding to split numbers for every independent region hierarchically split. The coding unit and encoding mode determiner 1420 determines an encoding mode and a coded depth to output an encoding result according to each region. The encoding mode may include information about a partition type of a coding unit corresponding to the coded depth, about a prediction mode, and about a size of a transformation unit.

0181In order to determine an encoding mode and a coded depth to output an encoding result for every independent region of a maximum coding unit, the coding unit and encoding mode determiner 1420 may perform encoding based on coding units according to depths, and may search for a coded depth having a least encoding error in original image data and an encoding mode related to the coded depth. Accordingly, the coding unit and encoding mode determiner 1420 may determine the coding units having the tree structure by determining coding units corresponding to coded depths for each maximum coding unit of the current picture

0182Information about the coded depth and the encoding mode determined by the coding unit and encoding mode determiner 1420 and a corresponding encoding result are output to the output unit 1430.

0183The output unit 1430 outputs information about a coded depth and an encoding mode according to a maximum coding unit, and encoded video data. An encoding mode includes skip mode information indicating whether a prediction mode of a coding unit is a skip mode, and split information indicating whether the coding unit is split to a lower depth. Since a prediction mode of a coding unit may be determined in a coding unit of a coded depth which is not further split, skip mode information may be encoded in the coding unit of the coded depth.

0184The output unit 1430 may selectively determine an order in which skip mode information and split information of coding units according to depths are output.

0185The output unit 1430 may output information indicating a selectively determined order in which skip mode information and split information are output. Accordingly, the output unit 1430 may output information about an order in which skip mode information and split information are output, the information about an encoding mode including the skip mode information and the split information which are arranged in the selectively determined order, and encoded video data.

0186The order of the skip mode information and the split information which is selectively determined for every coding unit according to depths may be determined according to at least one of an image sequence to which a coding unit corresponding to each depth belongs, a slice, a slice type according to a prediction direction, and a quantization parameter (QP) of a data unit.

0187Also, the order of the skip mode information and the split information which is selectively determined for every coding unit according to depths may be individually determined according to depths of coding units in a maximum coding unit.

0188For example, the order of the skip mode information and the split information may be determined in such a manner that the skip mode information precedes the split information for a maximum coding unit, and the split information precedes the skip mode information for coding units of lower depths other than the maximum coding unit.

0189The output unit 1430 may perform encoding by combining the split information and the skip mode information as one piece of split and skip information. Also, the output unit 1430 may assign different bit numbers to the split and skip information according to a frequency of occurrence of a combination of the split information and the skip mode information.

0190For example, if both split information indicating that a corresponding coding unit is split and skip mode information indicating that a prediction mode of the corresponding coding unit is not a skip mode are encoded, the split and skip information may be assigned one bit. Also, in cases other than the case where both the split information indicating that the corresponding coding unit is split and the skip mode information indicating that the prediction mode of the corresponding coding unit is not the skip mode are encoded, the split and skip information may be assigned two bits and output.

0191The output unit 1430 may not encode a transformation coefficient and prediction-related information such as a prediction direction and a motion vector, for a coding unit that is predicted in a skip mode. Selectively, the output unit 1430 may encode motion vector predictor index information about a prediction unit adjacent to a current coding unit. Also, the output unit 1430 may output information about a maximum size of the coding units.

0192<figref idref="f0012">FIG. 17</figref> is a block diagram illustrating an apparatus 1500 for decoding a video by considering a skip and split order, according to an exemplary embodiment.

0193Referring to <figref idref="f0012">FIG. 17</figref>, the apparatus 1500 includes a receiver 1510, a data extractor 1520, and a decoder 1530. The apparatus 1500 of <figref idref="f0012">FIG. 17</figref> may be an example of the apparatus 200 of <figref idref="f0001">FIG. 2</figref>. The receiver 210, the image data and encoding information extractor 220, and the image data decoder 230 of the apparatus 200 of <figref idref="f0001">FIG. 2</figref> may correspond to the receiver 1510, the data extractor 1520, and the decoder 1530 of the apparatus 1500 of <figref idref="f0012">FIG. 17</figref>, respectively.

0194The receiver 1510 receives and parses a bitstream of an encoded video.

0195The data extractor 1520 receives the parsed bitstream from the receiver 1510, and extracts encoded video data and information about a coded depth and an encoding mode for each maximum coding unit from the bitstream. Also, the data extractor 1520 may extract information about a maximum size of the coding units from the bitstream. The data extractor 1520 extracts, from the bitstream, information about an order of skip mode information and split information of coding units according to depths.

0196The data extractor 1520 may read the skip mode information and the split information from the information about the encoding mode based on the extracted information about the order of the skip mode information and the split information, and extract the encoded video data in coding units according to depths based on the skip mode information and the split information.

0197The order of the skip mode information and the split information may be selectively set according to at least one of an image sequence to which a coding unit corresponding to each depth belongs, a slice, a slice type according to a prediction direction, and a QP of a data unit. Also, the order of the skip mode information and the split information may be selectively set according to depths of coding units according to depths in a maximum coding unit.

0198For example, if a coding unit is a maximum coding unit, according to the order of the skip mode information and the split information, whether the coding unit is predicted in a skip mode according to the skip mode information may be determined before determining whether the coding unit is split according to the split information. Also, if a coding unit is not a maximum coding unit, whether the coding unit is split according to the split information may be determined before determining whether the coding unit is predicted in a skip mode according to the skip mode information.

0199The data extractor 1520 may extract one piece of split and skip information obtained by combining the skip mode information and the split information for the coding units according to the depths. For example, if one bit of split and skip information is extracted, a corresponding coding unit may be predicted in a skip mode without being split, and if two bits of split and skip information is read, whether a corresponding coding unit is split may be determined based on the split information and whether the corresponding coding unit is predicted in a skip mode may be determined based on the skip mode information.

0200The data extractor 1520 may extract only the split information and the skip mode information for a coding unit that is predicted in a skip mode, and may not extract information for prediction decoding such as a transformation coefficient and prediction-related information such as a prediction direction and a motion vector. Motion vector predictor index information for a coding unit that is predicted in a skip mode may be selectively extracted. Accordingly, the decoder 1530 may perform prediction decoding on a current coding unit by borrowing motion information of a prediction unit adjacent to the current coding unit that is predicted in a skip mode, or inferring motion information of the current coding unit from motion information of the adjacent prediction unit.

0201The decoder 1530 decodes encoded video data according to a coding unit of at least one coded depth for every maximum coding unit of the encoded video data based on the information about the coded depth and the encoding mode.

0202Decoded and restored video data may be transmitted to various terminals which may reproduce the video data or may be stored in a storage device.

0203The apparatus 1400 of <figref idref="f0012">FIG. 16</figref> and the apparatus 1500 of <figref idref="f0012">FIG. 17</figref> may determine an order of skip mode information and split information by considering a data unit, an encoding mode, or the like. Also, the order of the skip mode information and the split information may be determined by considering a total bit number of the skip mode information and the split information, and a frequency of occurrence of a skip mode in encoding and decoding of video data. Since the order of the skip mode information and the split information of coding units according to depths may be set, encoded data transmission efficiency may be further improved.

0204<figref idref="f0012">FIG. 18</figref> illustrates coding units according to coded depths in a maximum coding unit, according to an exemplary embodiment.

0205In order to explain an order in which the data extractor 1520 reads an encoded bitstream output from the output unit 1430 by considering an order of skip mode information and split information, a maximum coding unit 1600 is exemplary illustrated.

0206Coding units included in the maximum coding unit 1600 include the maximum coding unit 1600 having a depth of 0, coding units 1610, 1620, 1630, and 1640 having a depth of 1, and coding units 1622, 1624, 1626, and 1628 having a depth of 2. Also, the coding units 1610, 1630, and 1640 having the coded depth of 1 and the coding units 1622, 1624, 1626, and 1628 having the coded depth of 2 are determined as coded depths of the maximum coding unit 1600. Also, it is assumed that prediction modes of the coding units 1610, 1630, and 1640 having the depth of 1 are set to skip modes, and prediction modes of the coding units 1622, 1624, 1626, and 1628 having the depth of 2 are not set to skip modes.

0207An example where the data extractor 1520 of the apparatus 1500 reads split information before reading skip mode information for the maximum coding unit 1600 of a current picture will be first explained. In this example where the split information precedes the skip mode information, if the split information is 1, split information of coding units of lower depths is recursively read, and if the split information is 0, skip mode information of a coding unit of a corresponding depth is read.

0208Accordingly, an order in which split information and skip mode information are set or read is as follows.

0209Split information 1 about the maximum coding unit 1600, split information 0 and skip information 1 about the coding unit 1610 having the depth of 1, split information 1 about the coding unit 1620 having the depth of 1, split information 0 and skip information 0 about the coding unit 1622 having the depth of 2, split information 0 and the skip information 0 about the coding unit 1624 having the depth of 2, split information 0 and skip information 0 about the coding unit 1626 having the depth of 2, split information 0 and skip information 0 about the coding unit 1628 having the depth of 2, split information 0 and skip information 1 about the coding unit 1630 having the depth of 1, and split information 0 and skip information 1 about the coding unit 1640 having the depth of 1 may be sequentially read. Accordingly, a total bit number of the split information and the skip mode information of the maximum coding unit 1600 is 16.

0210Also, another example where the data extractor 1520 of the apparatus 1400 reads skip mode information of the maximum coding unit 1600 of a current picture earlier than split information will be explained. In this example where the skip mode information precedes the split information, if the skip mode information is 1, split information of coding units having lower depths do not need to be set, and if the skip mode information is 0, the split information is set. Accordingly, an order in which the split information and the skip mode information are set or read is as follows.

0211Skip mode information 0 about the maximum coding unit 1600, skip mode information 1 about the coding unit 1610 having the depth of 1, skip mode information 0 and split information 1 about the coding unit 1620 having the depth of 1, skip mode information 0 and split information 0 about the coding unit 1622 having the depth of 2, skip mode information 0 and split information 0 about the coding unit 1624 having the depth of 2, skip mode information 0 and split information 0 about the coding unit 1626 having the depth of 2, skip mode information 0 and split information 0 about the coding unit 1628 having the depth of 2, skip mode information 1 about the coding unit 1630 having the depth of 1, and skip mode information 1 about the coding unit 1640 having the depth of 1 may be sequentially read. In this case, a total bit number of the split information and the skip mode information about the maximum coding unit 1600 is 14.

0212<figref idref="f0013 f0014 f0015">FIGS. 19 through 21</figref> are flowcharts illustrating methods of encoding and decoding skip information and split information, according to various exemplary embodiments.

0213If the output unit 1430 of the apparatus 1400 outputs an encoded bitstream in such a manner that split information precedes skip mode information according to a split first method, the data extractor 1520 of the apparatus 1500 reads encoded video data according to an order in which the skip mode information and the split information are read.

0214That is, in operation 1650, according to the split first method, the data extractor 1520 reads split information about a maximum coding unit having a depth of 0 and determines whether the maximum coding unit is split. If it is determined in operation 1650 that the maximum coding unit is not split, the method proceeds to operation 1652. In operation 1652, skip mode information is read and it is determined whether the maximum coding unit is predicted in a skip mode. If it is determined in operation 1650 that the maximum coding unit is split, the method proceeds to operation 1654. In operation 1654, split information of a coding unit having a depth of 1 is read. Similarly, in operation 1654, it is determined whether the coding unit having the depth of 1 is split. If it is determined in operation 1654 that the coding unit having the depth of 1 is not split according to split information of the coding unit having the depth of 1, the method proceeds to operation 1656. In operation 1656, skip mode information of the coding unit having the depth of 1 is read. If it is determined in operation 1654 that the coding unit having the depth of 1 is split, the method proceeds to operation 1658. In operation 1658, split information of a coding unit having a depth of 2 is read and it is determined whether the coding unit having the depth of 2 is split. If it is determined in operation 1658 that the coding unit having the depth of 2 is not split, the method proceeds to operation 1660. In operation 1660, skip mode information of the coding unit having the depth of 2 is read. If it is determined in operation 1658 that the coding unit having the depth of 2 is split, the method may proceed to a next depth.

0215If the output unit 1430 of the apparatus 1400 outputs an encoded bitstream in such a manner that skip mode information precedes split information according to a skip first method, the data extractor 1520 of the apparatus 1500 reads encoded video data according to an order in which the skip mode information and the split information are read.

0216That is, in operation 1670, according to the skip first method, the data extractor 1520 reads skip mode information about a maximum coding unit having a depth of 0. If it is determined from the reading that a prediction mode of the maximum coding unit is a skip mode, the decoder 1530 may decode the maximum coding unit in a skip mode. In operation 1670, if it is determined from the reading that the prediction mode of the maximum coding unit is not a skip mode, the method may proceed to operation 1672. In operation 1672, the data extractor 1520 may read split information of the maximum coding unit having the depth of 0. In operation 1672, if it is determined from the reading that the maximum coding unit is not split, the decoder 1530 may decode the maximum coding unit. In operation 1672, if it is determined from the reading that the maximum coding unit is split, the method proceeds to operation 1674. In operation 1674, the data extractor 1520 may read skip mode information of a coding unit having a depth of 1.

0217Similarly, in operation 1674, according to the skip mode information of the coding unit having the depth of 1, if it is determined from the reading that a prediction mode of the coding unit having the depth of 1 is a skip mode, the coding unit having the depth of 1 may be decoded in a skip mode. If it is determined from the reading in operation 1674 that a prediction mode of the coding unit having the depth of 1 is not a skip mode, the method proceeds to operation 1676. In operation 1676, split information of the coding unit having the depth of 1 may be read.

0218If the output unit 1430 of the apparatus 1400 performs encoding in such a manner that skip mode information precedes split information for a maximum coding unit and split information precedes skip mode information for coding units other than the maximum coding unit, the data extractor 1520 of the apparatus 1500 reads encoded video data according to an order in which the skip mode information and the split information are read.

0219That is, in operation 1680, according to a skip first method for a maximum coding unit having a depth of 0, the data extractor 1520 reads skip mode information about the maximum coding unit having the depth of 0. If it is determined from the reading that a prediction mode of the maximum coding unit is a skip mode, the decoder 1530 may decode the maximum coding unit in a skip mode. In operation 1680, if it is determined from the reading that the prediction mode of the maximum coding unit is not a skip mode, the method proceeds to operation 1682. In operation 1682, the data extractor 1520 may read split information of the maximum coding unit having the depth of 0. In operation 1682, if it is determined from the reading that the maximum coding unit is not split, the decoder 1530 may decode the maximum coding unit. In operation 1682, if it is determined from the reading that the maximum coding unit is split, the data extractor 1520 may read split information and skip mode information of a coding unit having a depth of 1 in operations 1684 and 1686.

0220In operation 1684, according to a split first method for the coding unit having the depth of 1, if it is determined from the reading that the coding unit having the depth of 1 is not split according to split information of the coding unit having the depth of 1, the method proceeds to operation 1686. In operation 1686, skip mode information of the coding unit having the depth of 1 is read. In operation 1684, if it is determined from the reading that the coding unit having the depth of 1 is split, the method proceeds to operation 1688, and split information of a coding unit having a depth of 2 may be read. In operation 1688, if the coding unit having the depth of 2 is not split according to the split information of the coding unit having the depth of 2, the method proceeds to operation 1690. In operation 1690, skip mode information of the coding unit having the depth of 2 may be read, and if the coding unit having the depth of 2 is split, the method may proceed to a next depth.

0221Total bit numbers of skip mode information and split information according to the exemplar embodiments of <figref idref="f0013 f0014 f0015">FIGS. 19 through 21</figref> will be compared with one another as follows.

0222In detail, if a maximum coding unit is encoded in a skip mode, total bit numbers of skip mode information and split information according to various exemplary embodiments are as shown in Table 2. <tables id="tabl0002" num="0002"><table frame="all"><title>[Table 2]</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="72mm" /><colspec colnum="2" colname="col2" colwidth="66mm" /><colspec colnum="3" colname="col3" colwidth="29mm" /><thead><row><entry valign="top">Embodiment</entry><entry valign="top">Skip mode information and split information</entry><entry valign="top">Total bit number</entry></row></thead><tbody><row><entry>Split first method (<figref idref="f0013">FIG. 19</figref>)</entry><entry>Split information 0, skip mode information 1</entry><entry>2 bits</entry></row><row><entry>Skip first method (<figref idref="f0014">FIG. 20</figref>)</entry><entry>Skip mode information 1</entry><entry>1 bit</entry></row><row><entry>Maximum coding unit skip first method (<figref idref="f0015">FIG. 21</figref>)</entry><entry>Skip mode information 1</entry><entry>1 bit</entry></row></tbody></tgroup></table></tables>

0223According to a split first method of Table 2, since split information of a maximum coding unit having a depth of 0 is encoded to be '0' and skip mode information of the maximum coding unit having the depth of 0 is encoded to be '1', the data extractor 1520 may read two bits of skip mode information and split information in total. According to a skip first method of Table 2, since skip mode information of the maximum coding unit having the depth of 0 is encoded to be '1', the data extractor 1520 may read one bit of skip mode information in total. According to a maximum coding unit skip first method of Table 2, since skip mode information of the maximum coding unit having the depth of 0 is encoded to be '1', the data extractor 1520 may read only one bit of skip mode information in total.

0224In detail, if a coding unit having a depth of 2 is encoded in a skip mode, total bit numbers of skip mode information and split information according to various exemplary embodiments are as shown in Table 3. <tables id="tabl0003" num="0003"><table frame="all"><title>[Table 3]</title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="50mm" /><colspec colnum="2" colname="col2" colwidth="91mm" /><colspec colnum="3" colname="col3" colwidth="26mm" /><thead><row><entry valign="top">Embodiment</entry><entry valign="top">Skip mode information and split information</entry><entry valign="top">Total bit number</entry></row></thead><tbody><row><entry>Split first method (<figref idref="f0013">FIG. 19</figref>)</entry><entry>Split information 1, split information 1, split information 0, skip mode information 1</entry><entry>4 bits</entry></row><row><entry>Skip first method (<figref idref="f0014">FIG. 20</figref>)</entry><entry>Skip mode information 0, split information 1, skip mode information 0, split information 1, skip mode information 1</entry><entry>5 bits</entry></row><row><entry>Maximum coding unit skip first method (<figref idref="f0015">FIG. 21</figref>)</entry><entry>Skip mode information 0, split information 1, split information 1, split information 0, skip mode information 1</entry><entry>5 bits</entry></row></tbody></tgroup></table></tables>

0225According to a split first method of Table 3, since split information of a maximum coding unit having a depth of 0 is encoded to be '1', split information of a coding unit having a depth of 1 is encoded to be '1', split information of a coding unit having a depth of 2 is encoded to be '0', and skip mode information of the coding unit having the depth of 2 is encoded to be '1', the data extractor 1520 may read four bits of skip mode information and split information in total. According to a skip first method of Table 3, since skip mode information of the maximum coding unit having the depth of 0 is encoded to be '0', split information of the maximum coding unit having the depth of 0 is encoded to be '1', skip mode information of the coding unit having the depth of 1 is encoded to be '0', split information of the coding unit having the depth of 1 is encoded to be '1', and skip mode information of the coding unit having the depth of 2 is encoded to be '1', the data extractor 1520 may read five bits of skip mode information and split information in total. According to a maximum coding unit skip first method of Table 3, since skip mode information of the maximum coding unit having the depth of 0 is encoded to be '0', split information of the maximum coding unit having the depth of 0 is encoded to be '1', split information of the coding unit having the depth of 1 is encoded to be '1', split information of the coding unit having the depth of 2 is encoded to be '0', and skip mode information of the coding unit having the depth of 2 is encoded to be '1', the data extractor 1520 may read five bits of skip mode information and split information in total.

0226As described above with reference to <figref idref="f0013 f0014 f0015">FIGS. 19 through 21</figref>, by changing an order of split information and skip mode information, a total bit number of skip mode information about coding units according to depths may be varied. For example, if a coding unit of an upper depth is predicted and encoded in a skip mode, since split information of a coding unit of a lower depth does not need to be encoded, if there are many regions predicted and encoded in a skip mode, it may be advantageous in terms of a bit rate that skip mode information precedes split information. However, in an image with a small number of skip modes, it may be advantageous in terms of a bit rate that split information precedes skip mode information.

0227Accordingly, a bit rate may be adjusted by adjusting an order of split information and skip mode information according to characteristics of an image, a sequence, a data unit level such as a slice, a QP, and a slice type. Also, like in the example explained with reference to <figref idref="f0015">FIG. 21</figref> where a skip first method is selected only for a maximum coding unit and a split first method is selected for coding units having depths other than the maximum coding unit, an order of split information and skip mode information may be changed according to depths.

0228In the exemplary embodiment described with reference to <figref idref="f0012">FIG. 18</figref>, skip mode information or split information is earlier read in units of pictures. The apparatus 1400 of <figref idref="f0012">FIG. 16</figref> and the apparatus 1500 of <figref idref="f0012">FIG. 17</figref> may variably determine an order in which skip mode information and split information are output or read according to a data unit, a depth, a QP, and a slice type according to a prediction direction without being limited to the exemplary embodiment of <figref idref="f0012">FIG. 18</figref>.

0229Also, split information and skip mode information may be combined and used as one piece of split and skip information. The apparatus 1400 of <figref idref="f0012">FIG. 16</figref> and the apparatus 1500 of <figref idref="f0012">FIG. 17</figref> may use split and skip information that is assigned 1 bit for a combination of split information and skip mode information having a high frequency of occurrence, and split and skip information that is assigned 2 bits for a combination having a low frequency of occurrence.

0230If split information precedes skip mode information, since split information of a coding unit of a lower depth is immediately read when split information of a coding unit of a current depth is 1, a skip mode of a current coding unit is not read. Accordingly, three combinations, that is, split information 1, a combination of split information 0 and skip mode information 0, and a combination of split information 0 and skip mode information 1, may occur. For example, a frequency of occurrence of the combination of split information 0 and skip mode information 1 is the highest, the combination is assigned 1 bit, and each of the split information 1 and the combination of split information 0 and skip mode information 0 may be assigned 2 bits.

0231<figref idref="f0016">FIG. 22</figref> is a flowchart illustrating a method of encoding a video by considering a skip and split order, according to an exemplary embodiment.

0232In operation 1710, a picture is split into maximum coding units having predetermined maximum sizes.

0233In operation 1720, for each of coding units having a tree structure, an encoding mode about a coded depth to output an encoding result and a coding unit of the coded depth is determined by performing encoding based on coding units according to depths, according to regions obtained by hierarchically splitting the maximum coding unit as a depth deepens.

0234In operation 1730, information indicating an order of skip mode information and split information which is selectively determined for every coding unit according to depths, information about the encoding mode including the skip mode information and the split information which are arranged according to the determined order, and encoded video data are output for every maximum coding unit.

0235Also, one piece of combined split and skip information obtained by combining the split information and the skip mode information may be set. Also, a bit number of the corresponding split and skip information may be assigned based on a frequency of occurrence of a combination of the split information and the skip mode information.

0236<figref idref="f0016">FIG. 23</figref> is a flowchart illustrating a method of decoding a video by considering a skip and split order, according to an exemplary embodiment.

0237In operation 1810, a bitstream of an encoded video is received and parsed.

0238In operation 1820, information about an order of skip mode information and split information of coding units according to depths is extracted from the bitstream, and according to the order of the skip mode information and the split information, information about a coded depth and an encoding mode and encoded video data are extracted according to a maximum coding unit from the bitstream.

0239Also, one piece of combined split and skip information obtained by combining the split information and the skip mode information may be read. The method of decoding the video of <figref idref="f0016">FIG. 23</figref> may read a combination of the split information and the skip mode information based on the split and skip information that is discriminatively assigned based on a frequency of occurrence of a combination of the split information and the skip mode information.

0240In operation 1830, encoded video data is decoded according to coding units having a tree structure for every maximum coding unit of encoded video data based on the information about the coded depth and the encoding mode.

0241Exemplary embodiments can be written as computer programs and can be implemented in general-use digital computers that execute the programs using a computer readable recording medium. Examples of the computer readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs). Moreover, one or more units of the apparatus 1400 and the apparatus 1500 can include a processor or microprocessor executing a computer program stored in a computer-readable medium, such as the local storage 220.