1 Description Title of Invention: METHOD AND APPARATUS FOR ENCODING RESIDUAL BLOCK, AND METHOD AND APPARATUS FOR DECODING RESIDUAL BLOCK The present application is a divisional application from Australian Patent Application No. 2014268181 which is a divisional of Australian Patent Application No. 2010313967 filed on 28 October 2010, the entire disclosure of which is incorporated herein by reference. Technical Field [1] Apparatuses and methods consistent with exemplary embodiments relate to encoding and decoding, and more particularly, to encoding and decoding of a residual block. Background Art [2] As hardware for reproducing and storing high resolution or high quality video content is being developed and supplied, a need for a video codec for effectively encoding or decoding the high resolution or high quality video content is increasing. In a related art video codec, a video is encoded according to a limited prediction mode based on a macroblock having a predetermined size. Also, the related art video codec encodes a residual block by using a transformation unit having a small size, such as 4x4 or W. Disclosure of Invention Technical Problem [3] The related art video codec encodes a residual block by using only a transformation unit having a small size, such as 4x4 or 8x8. Solution to Problem [4] Exemplary embodiments provide a method and apparatus for efficiently encoding and decoding effective transformation coefficient information in a transformation residual block having a large size. Advantageous Effects of Invention [5] According to one or more exemplary embodiments, an effective coefficient flag indicating existence of an effective transformation coefficient is generated according to frequency band units, so that a scanning process of a frequency hand skips a transformation residual block in which an effective transformation coefficient does not exist, and a number of bits generated to encode the effective transformation coefficient is reduced.
I a 5a] The discussion of documents, acts, materials devices. articles and the like is included in this specification solely for the purpose of providing a context for the present invention. it is not suggested or represented that any or a of these matters formed part of the prior ar base or were connon general knowledge in the field relevant to the present invention as it existed before the priority date of each clait of this application. [5b] Where the terms "comprise" "comprises", "comprised" or "comprising" are sed in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other|features, integers, steps or components, or group thereof Brief Description of Drawings [6] FIG. 1 is a block diarpam of an apparatus for encoding a video, according to an exemplary embodi ent; [7] FiG. 2 is a block diagram of an apparatus for decoding a video, according to an exemplary embodiment 2 8J FiG. 3 is a diagram for describing a concept of coding unsaccodng to an exemplary cembodinment; [9] FIG. 4 is a block diagram of an image encoder based on coding units according to an exemplary embodiment; 10] FIG. 5 is a block diagram of an image decoder based on coding units according to an exemplary embodiment; dI] FIG. 6 is a diagram ill ustrating deeper coding units according to depths, and partitions according to an exemplary embodiment; 1121 P. 7 is a diagram for describing a relationship between a coding unit and trans formation units, according to an exemplary embodiment; [13) FiG, 8 is a diagram for describing encoding information ot coding units corre sponding to a coded depth, according to an exemplary embodiment; [14] I. 9 is a diagram of deeper coding units according to depths, according to an exemplary embodiment; [l] FIGs. 10 through 12 are diagrams for describing a relationship between coding wits, prediction units, and transformation units, according to one or more exemplary em hod iments; 116] FIG. I 3 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 or exemplary Table I below, acrigto an exemplaryemoint [17] FIGs. l4A through 14C are reference diagrams for describing a process of encoding a transformation residual block in a related technical field; 1 8] FIG, 15 is a block dagram Of an apparatus for encoding a residual block, according to an exemplary embodiment; [19] FIGs 16A through 16J are diagrams for describing splitting of a transformation residual block into predetermined frequency band units, according to one or more exemplary embodiments; 20] FIGs, 17'A and 17 B are reference diagrams for describing a process of encoding an effective transformation coefticient, according to one or more exemplary cem bodi menms; [21] FiGs. i8A and 18B are reference diagrams for describing in detail a process of encoding a residual block 9 according to an exemplary embodiment; [22] FIGs. 19A and 19B are reference diagrams for describing encoding information of a transformation esidual block, whie is generted by an effective coefficient encoder. according to one or more exemplary embodiments; 23] PiG. 20 is a flowchartilustrating a method of encoding a residual block, according to an exemplary embodiment; [24] FIG. 21i is a block diagramf an apparatus for decoding a residual bock, according 3 to an exemplary embodiment; [24] FIG. 21 is it block diagram of an apparatus for decoding a residual block, according to an exemplary embodiment; and [25] FIG. 22 is a flowchart illustrating a method of decoding a residual block, according to an exemplary embodiment. Best Mode for Carrying out the Invention [26] According to an aspect of an exemplary embodiment, there is a method of decoding an image, the method comprising: splitting the image into a plurality of maximum coding units; hierarchically splitting a maximum coding unit among the plurality of maximum coding units into a plurality of coding units; determining one or more transform residual blocks from a coding unit of the plurality of coding units, wherein the transformation residual block includes sub residual blocks; obtaining an effective coefficient flag of a particular sub residual block among the sub residual blocks from a bitstream, the effective coefficient flag of the particular sub residual block indicating whether at least one nonzero effective transformation coefficient exists in the particular sub residual block; when the effective coefficient flag indicates that the at least one non-zero transformation coefficient exists in the particular sub residual block, obtaining transformation coefficients of the particular sub residual block based on location information of the at least one non-zero transformation coefficient and level information of the at least one non-zero transformation coefficient obtained from the bitstream; when the effective coefficient flag indicates that the non-zero transformation coefficient does not exist in the particular sub residual block, determining transformation coefficients of the particular sub residual block as zero; and performing inverse-transforming on the transform residual block including the particular sub residual block based on the transformation coefficients included in the transform residual block, wherein the transformation coefficients of the particular sub residual block are a part of the transformation coefficients included in the transform residual block. [27] The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises splitting the transformation residual block such that it unit size split in a low frequency band is smaller than a unit size split in it high frequency hand. [28] The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises quadrisecting the transformation residual block, and quadrisecting a lowest frequency band of the quadrisected transformation residual blocks. [29] The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises splitting the transformation residual block into frequency band units having a same size. [30] The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises splitting the transformation residual block by connecting a horizontal frequency and a vertical frequency having a same value at predetermined intervals.
4 [31] The method of the exempiry embodiment, wherein Lhe splicing the transformation residual block comprises: detennining an image characteristic of the transformation residual block by using transformation coefficients of the transformation residual block; determining a split size according to frequency bands of the transformation residual block by using the determined image characteristic; and splitting the transformation residual block according to the determined split size. 321 The method of the exemplary embodiment, wherein the determining the image characteristic comprises determining the image characteristic using at least one of a number and a distribution of transformation coefficients existing in each frequency band of the transformation residual block. [33 The method of the exemplary embodiment, wherein the the effective coefficient flags comprises not separately encoding an effective coefficient flag with respect to a smnai lest low frequency band unit from among the frequency band units. [3] The method of the exemplary embodiment, further comprising encoding a significance map indicating locations of the effective transformation coefficients existing in Lhe frequency band units having the nonzero effective transformation coefficients, from among the frequency band units. [35] The method of the exemplary embodiment, wherein the encoding the significance map comprises encoding a flag indicating the locations of the effective transformation coefficients existing in the frequency band units having the nonzero effective transformation coefficients by reading the effective transformation coefficients according to a predetermined scanning order independent for each of the frequency band units. [361 The method ofheeemplary embodiment wherein te encodingte sinicance ma comprises encoding a flag indicating the locations of the effective transformation coefficients existing in the frequency band units having the nonzero effective transformation coefficiens by reading all of tie effective transformation coefficients in the transformation residual block according to a predetermined scanning order. [7] The method of the exemplary embodiment, wherein the encoding the significance map comprises: setting a flag indicating a last effective transformation coefficient existing in a frequency hand unit, from among the frequency band units, by reading the effective transformation coefficients in the frequency band units according to a predetermined scanning order; and setting a flag indicating a last effective transformation coefficient existing in the transformation residual block. [38] The method of the exemplary embodiment, wherein: the splitting the transformation residual block comprises splitting the transformation residual block into the frequency band units according to a split form selected from a plurality of split forms that are predetermined according to sizes and shapes of the frequency band units; and split form index information indicating the selected split form from among the plurality of split forms is added to an encoded bitream comprising the effectve coefficient flags 4a [31] There may be provided an apparatus for encoding a residual block, the apparatus comprising: a predictor which generates a prediction block of a current block; a subtracter which generates a residual block based on a difference between the prediction block and the current block; a transformer which generates a transformation residual block by transforming the residual block to a frequency domain; an entropy encoder which splits the transformation residual block into sub residual blocks, and encodes an effective coefficient flag of the sub residual block indicating whether at least one nonzero effective transformation coefficient exists in a particular sub residual block among the sub residual blocks, wherein, when non-zero transformation coefficient exists in the particular sub residual block, the entropy encoder further encodes location information of the non-zero transformation coefficient and level information of the non-zero coefficient.
101 According to an aspect of another exemplary embodiment, there is provided a method of decoding a residual block, the method including' exrc -n fetv o efficient flags from an encoded bitstream, the effective coefficient flags indicating frequency band units in which nonzero effective trans fornmaion coefficients exiS firo among split frequency bnd units obtained by splittig a transformation resiul lci of 'a current block; splitting the transformation residual block into the split frequency band units; and determining a frequency band unit having an effective transformation coefficient from among the split frequency band units obtained by splitting the trans formation i'esidlual block,hby using the extracted effctive coefficient flags. [41] The method of the another exemplary embodiment, wherein the splitting the frequency band unit comprises splitting the transformation residual block such that a unit size split in a low frequency band is smaller than a Un. izspiinahg frequency band. [42] The method of the another exemplary embodiment, wherein the splitting the trans formnauon residual block comprises quadrisecting the transformation residual block, and quadrisecting a lowest frequency band of the quadrisected transformation residual blocks 1431 'The method of the unothier exemplary embodiment, wherein the splitting the trans formation residual block comprises splitting the transformation residual block into frequency band units baying a same size. [14 The method of the another exemplary embodiment, wherein the splitting the trans-' formation residual block comprises split ring the transformaion residual block by connecting a horizontal frequency and a vertical freu ency- having a same value at pre determined interval [151 The method of the another exemplary embodiment, wherein the splitting the trans formation residual block comprises: extracting split form index information from the encoded bitstream, the split form index information indicating a split form used to split the transformation residual block, from among a plurality of split forms that are prede termilned according to sizes and shapes of the frequency band units; and splitting the transformation residual block into the frequency band units according to the extracted split form index information. 1 6 ) The method of the another exemplary embodiment, further comprising: extracting a significance map from the encoded bitstream, the significance map indicating locations of nonzero effective transformation coefficients existing in frequency band units having the nonzero effective transformation coefficients, from among the frequency band units; and determining the locations of the nonzero effective transformation coef ficients existing in the frequency band units having the nonzero effective trans formation coefficients by using the significance map.
C [47] The method of the another exemplary embodiment, where th significance map indicates the locations of the effective transformation coefficients in the frequency band units according to a predetermined scanning order independent for each of the frequency band units. [IX] The method of the another exemplary embodiment, wherein the significance map indicates the locations of the effective transformation coefficients in the frequency band units according to a predetermined scanning order for an entirety of the nans formation residual block. [49] The method of the another exemplary embodiment, wherein the significance map comprises a flag indicating a last effective transformation coefficien existing in a frequency band unit, from anona the freguency band units, by readmg the effectve nsformadon coefficiemt in the frequency band units according to a predetermined scanning order, and a flag indicaung a last effective transformation coefficient existing in the transformation residual block. :501 According to an aspect of another exemplary embodiment, the is provided an apparatus for decoding a residual block, the apparatus including: a parser which extracts etFective coefficient flags from an encoded bitstrean, the effective coefficient flags indicating frequency band units in which nonmero efTective transformation coe ficients exist, from among split frequency band unis obuinei by splitting a trans formation residual block of a current block; and an entropy decoder which splits the transformation residual block into the spilt frequency band units, and determines a frequency band unit having an effective transfonmaton coefficient from among the split frequency band units obtained by splittng the transformation residual block. by using the extracted effective coefficient flags. [511 According to an aspect of another exemplary embodiment, there is provided a od encoding a r lbotk, the method including: generanga tans formaton residual block by transforming a residual block to a frequency domain; splitting the transformation residual block into frequency band units; and encoding effective coefficient flags indicating frequency band units, ot the frequency baud units, in vwhic nonzero effective transformation coefficients exist. Mode for the Invention [52] Hereinafter, exemplary embodiments will be described more fully with reference to the accompanying drawings, it is understood that expressions such as at least one of," when preceding a it of elements, modify the entire list of elemems and do not modify the indiviual elements of thelit i53] In the exemplary embodimems, a coding unit is an encoding data unit in which the image data is encoded at an encoder side and an encoded data unit in which the 7 encoded image data is deoded at a deoder side, Also, a coded depfh rfers to a depth where a coding unit is encoded. 541 IG. is a block diagram of a video encoding apparatus 100, according to an exemplary embodiment Referring to FIG. 1, the video encoding apparatus 100 includes a maximum coding uni splitter 110, a coding unit determiner 120, and an output unit 1.30. 15] The maxi mum coding unit splitter 1 10 may split a current picture of an image based on a maximum codine unit for the current picture. If the cument picture is larger than the maximum coding unit, image data 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 32x3 2 , 64x64, i28x 128, 256x256, etc. wherein a shape of the daa unit is a square having a width and length in sq uares of 2. The image data may be output to the coding unit deterniner 120 according to the at least one Inaxiniun coding unit. 1561 A coding unit according to an exemplary embodiment may be characterized by a niaximun size and a depth. The depth denotes a number of times the coding unit is spatially spit from the maximum coding unit, and as the depth deepens, deeper encoding 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 tpper depth may include a plurality of coding units corresponding to lower depths, [571 As 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 accoaling 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. 1581 A maximum depth and a maximum size oF a coding unit, which limit the total number of times a height and a width of the maximum coding unit can be hierar chicaliy split, may be predetermined. 591 The coding unit determiner 120 encodes ar least one split region obtained by splitting a legion of the maximum coding unit according to depths, and determines a depth output encoded image dat according to the at least one split region. That is, the coding unit determiner 120 determines a coded depth by encoding the image data in the deeper coding units according to depths, based on the maximum coding unit of the curtenw picture. and selecting a depth having the cast encoding error. Thus, the encoded image data of the codingamni corresponding to the determined coded depth is output to the output unit 130. Also, the coding units corresponding to the coded depth may be regarded as encoded coding units. 601 The determined coded depth and the cododed image dataaccording to the determined codec depth are output to the output unit 130. [1] The image data in the maximum coding unit is encoded based on the deeper coding unit corresponding to at least one depth equal to or below the maxinun depth, and results of encoding the inwge data are compared based on each of the deeper coding units. A depth having the least encoding error may he selected after comparing encoding errors of the deeper coding units. At least one coded depth may be selected for each maximum coding unit. N2] The size of the maximum ceding unit is split as a coding unit is hierarchically split according to depths, and as the number of coding units increases. Also, even if coding units correspond to a same depth in one maximurn coding unit. i is determined whether to split each of the coding units corresponding to the same depth to a lower depth by measuring an encoding error of the image data of 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 and the encoding errors may differ according to regions in the one maximum coding unit, and thus the coded depths may differ according to regions in the image data, Therefore, one or more coded depths may be determined in one naxnnum coding unit, and the image data of the maximum coding unit may be divided according to coding units of at least one coded depth. 63] Accordingly, the coding unit determiner 120 may determine coding units having a tree structure included in the maximum coding unit. The oding units having a tree structure accordingto an exemplary embodiment include nts corresponding to a depth determined to be the coded depth, from among deeper coding units included in the naxmumcoding unit. A coding unit ofi a coded deptn a eheacial e 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 [6} Amaximum det- corigt an exemplary embodimient is an index related to a j63dphaccordinguso WT!, i; lil-x toa number of splitting times from a maximum coding unit to a minimum coding unit A first maximuml depth according to an exemplary embodiment may denote a total number o spiting times from the mnaxium coding unit to the minimum coding unit A second maximum depth according to an exemplary embodiment may denote a total number of depth levels from the maximum coding unit to the minimum coding unit. For example, when a depth of the maximum coding umt is 0 a depth of a coding unit p in which the maximum coding unit is spit once may be set to , and a depth of a coding unit in which the maxumum coding uni is split twice may he set to 2. iHee. ii 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. Thus the first mnxmum depth may be set to 4, and the second maximum depth may be set to 5. [65 Prediction encoding and transformation may be performed according to the maximum codin noit. 'The prediction encoding and The transformation are also performed based on the deeper coding tnits according to a depth equal to or depths les than the maximum depth, based on the maximum conng unit Transformation may be performed according to a method of orthogonal transfonnation or integer transformation. Since lhe number of deeper coding units increases whenever the maximum coding unit is split according to depths, encoding such as 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 trans formation will hereinafter be described based on a coding unit of a current depth, in a maximum coding unit [67] The video encoding apparatus l00 may variously select at least one of a size and a shape of a data unit for encoding the image dIa. in order to encode the image data, op eratons, such as prediction encoding transformation, and entropy encoding, may be performed, and at this ume, the same data unit may be used tor all operatons or differentdata units maybe used freach operation. [681 For example, the deo encoding apparatus 100 mayselet acdingun for encoding the image data and a aa uni different fon the coding unio as to perforn h prediction encoding on the image data In the codingunit 691 In 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 wil be refermd to as a prediction unit, A partition obtained by splitting the prediction unit may include a prediction unit or a data unit obtained by splitting at least one of a height and a width of the predicton unit 170 For example, when a coding unit of 2Nx2N (where N is a positive integer) is no longer spit and becomes a prediction unit of Nx2N, a ie of a partition may he 2Nx2N, 2NxN, Nx2N, or NxN. Examples of a partition type include symmetrical partitons that are obtained by symmetrically splitting at least one of a height and a width of the prediction unit paRitions obtained by asymmetrically spiling the height or the width of the prediction unit (such as I:n or n It pariuons tat are obtained bv 10 geometrically splitting the prediction unit and partitions having arbitrary shapes, 711 diction mode of the prediction unit may be at least one of an intra mode, a inter node, and a skip mode, For example, the intra nmde or the inter mode may be performed on the partition of 2Nx2N, 2NxN, Nx2N, or NxN. In tbis case, the skem mode may be performed only on the partition of 2Nx2N, The encoding is inde pendentLy performed on one prediction unit in a coding unit, thereby selecting a prediction mde having a least encoding erm. 72n The video encoding apparatus 100 may also perform the transformation on the image data in a coding unit based on the coding unit for encoding the image data and on a data unit that is different from the coding unit 731 In order to perform the transformation th coding nit the transformation maybe performed based on a data unit having a size smaller than or equai to the coding unit For example. the data unit for the transfonnation may include a data unit for an intra mode and a data unit for an inter mode. [-41 A data unit used as a base of the transformation will hereinafter be referred to as a transformation unit. A transformation depth indicating a number of splitting times to reach the transformation unit by splitting the height and the width of the coding unit may also lie set in the transfonnation unit. For example, in a current coding unit of 2Nx2N, a transfonnation depth may be 0 when the size of a transformation ut is also 2Nx2N, may be I when each of the height and width of the current coding unit is split into two equal parts, totally split ito 4^I transformation units, and the size of the transformation unit is thus NaN, ard may be 2 when each of the height and width of the current coding unit is split into four equal parts, totally split into 4^2 transformation units, and the size of the transformation unit is thus N/2xN/2. For example, the trans formnation unit may be set accordng to a hierarchical tree structure, in which a trans formation unt of an upper transformation depth is split into four transformation units of a lower transformation depth according to hierarchical characteristics of a trans formation depth. [75] Similar to the coding unit the transformation unit in the coding unit may he re cursively split into smaller sized regions, so that the transformation unit may be de terumined 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 trans formation depths. 76] Encoding in formation according to coding units corresponding to a coded depth uses information about the coded depth and information related to prediction encoding and transformation. Accordingly, the coding unit determiner 120 determines a c oded depth having a least encoding error and determines a partition type in a prediction unit, a prediction mode according to prediction units, and a size of a transformation unit for 11 transformation. [R71 Coding units according to a tree structure in a nmaximumi coding unit and a method of determining a partition, according to exemplary ernbodinments, will be descibed in detai later with reference to FIGs. 3 through 12. 78The coding unit determiner 120 may treasure an encoding error of deeper coding units according to depths by using Rate-Distortion Optimization based on Lagrangian mulitip]lers. [ 79] The output unit 130 outputs the image data of the mnaxinmum coding unit, which is encoded based on the at least one coded depth determined by the coding un it de terminer 120, and information about the encoding mode according to the coded depth, in bitsreans, [80] The encoded image data may be obtained by encoding residual dat of an image. 8i] The infonnation about the encoding mode according to the coded depth may include ax least one of information about the coded depth, the partition type in the prediction unit, the prediction mode, and the size of the transformation unit, [82] TIhe information about the coded depth may he defined by using split information according to depths, which indicates whether encoding is pcrformecd 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. In this case, the split information may be defined to not split the current coding unit to a lower depth. Aiternatively, 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. In this case, the split information may be defined to split the current coding unit to obtain the coding units of the lower depth, 831 If the current deph is not the coded depth, encoding is performed on the coding unit that is split into the coding unit of the lower depth, In this case, 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 fohr the coding units having the same depth, I 84j Since 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 de termined for one mnaxinmumi coding unit. Also, a coded depth of the image data of the maximum coding unit may he different according to locations since the image data is hierarchicaly spilt according to depths, and thus information about the coded depth and the encoding mode may be set for the image data. [85 Accordingly, the output unit 130 may assign encoding information about a corre sponding coded depth and an encoding mode to at least one of the coding unit, the prediction unit and a minumn unt incu ded in the maximum coding unit 86 The minimum unit according to an exemIay emhodiment is a rectangular data unit obtained by splitting the minimum coding unit of the lowermost depth by 4, Alter natively, the minimum uit may be a maximum rectangular data unit that may he included in all of the coding units preiction units, partition units, and transformation units included in the maximum coding unit, 871 For example, the encodIng information output through the output unit 1130 may be classified into encoding information according to coding units and encoding in fornmation according to prediction units. The r-ncoding information according to the coding units may include the information about the prediction mode and the size of the partitions, The encoding information according to the prediction units may include in formation about an estimated direction of an inter node. a reference image index of the inter mode, a motion vector, a chroma comonent of an intra node, and an inter polation method of the ica mode. Also, information about a maximum size of the coding untdefined .codn topctures, slices, or GOPs, and information about a maximuo depth may be inserted into at least One of a Sequence Parameter Set (SPS) or a header oi- a bitstream. .88] in the video encodig apparatus 100, the deeper coding unit may be a coding unit obtained by dividing at least one of a height and a width of a coding unit of ai upper depth, which is one layer above, by two, For example, when the size of the coding unit of the current depth is 2Nx2N, the size ot the coding unit of the lower depth may be NxN. Also, te coding unit of the current depth having the size of 2Nx2N may include maximum 4 of the coding unit of the lower depth. 9] Accordingly, the video encoding apparatus 100 may fon 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 codmg unit and the maximum depth detenrined considering characteristics of the current picture. Also, since encoding may be performed on each maximum coding unit by using any one of various predicton modes and transfonnations, an optimum encoding mode may he de tennined considering characteristic of the coding unit of various imae sizes, !90i 'hus, if an image having high resolution or a large amount of data is encoded in a related an macrobloci, a number of macrmbicks per picture excessively mnceases, Accordingly, a number of pieces of compressed information generated for each macrohiock increase and thus it is difficult to transmit the compressed information and data compression efficiency decreases. loweven by using the video encoding apparatus 100 according to an exemplu-y embodiment. image compression efficiency may be increased since a coding unit is adjusted while considering characteristics of an image and increasing a maxmuin size of a coding unit while considering a size of the 12 image. 9l TiIG. 2 is a block diagram of a video decoding apparatus 200, according to an exemplary emubodirnent. [9[ Referring to FIG, 2, the video decoding apparamus 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, and a transformation unit, and information about various encoding modes for various oY erations of the video decoding apparatus 200 are similar to those described above with reference to MG. . [93] The receiver 210 receives and parses a bitstream of an encoded video. The image data and encoding mtomotion extractor 220 extrets encoded image data for each coding unit rnm the parsed bitstream, wherein the coding units have a tnee structure according to each maximum coding unit, and outputs the extracted iuage data to the image data decoder 230. The iuage 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 an SPS. )4 Also,the image taand encoding information extractor 220 extracts information coded depth and n encoding mode for the coding units ha g a t stuur according to each maxhumn coding unit, from the parsed hirstream. The extracted in formation about the coded depth and the encoding models output to the image data decoder 230. That is, the image data in a bit stream is split into the naximum coding unit so that the image data decoder 230 decodes the image data for each maximum coding unit. [3] The information about the coded depth and the encoding rode according to the maximum coding unit may be set for intforation about at least one coding unit corre sponding to the coded depth, and information about an encoding mode may include im formation about at least one of a partition type of a corresponding coding unit core sponding to the coded depth, a prediction mode, and a size of a transformation unit. Also, spitting information according to depths may be extracted as the information about the coded depth, [9%1 The 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 detenined to generate a minimum encoding error when an encoder, such as a video encoding apparatus 100 according to an exemplary embodiment, repeatedly performs encoding for each deeper coding unit based on depths according to each nmaximumt coding unit. A accordingly, the video decodingappaaus 200 may restore an iae by decoding the image data according to a coded depth and an encoding mode that generates the minimum 14 enicodingu erroin .7! Since 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 dat units. The predetermined data units to which the same information about the coded depth and the encoding mode is assigned may be the data units included in the same maximum coding unit. 98j The image data decoder 230 restores the current picture by decoding the image data. in each maximum coding unit based on the information abom the coded depth and the encoding mode according to the maxinm coding units, For example, the image data decoder 230 may decode the encoded image data based on the extraeled information about the patiton type, the prediction mode, a ththe transformation unit for each coding unit from among the codnig units having the tree structure included in each maximum coding tinit. A decoding process may include a predictim including intra prediction and motion compensation, and an inverse transformation. Inverse trants fonmation may he performed according to a rmetnod of inverse orthogonal trans formation or inverse integer transformation. [991 The image data decoder 230 may perform at least one of intra prediction and motion compensation according to a partition and a prediction mode ofeach coding unit, based on the information abom the partition type and the prediction mode of the prediction unit of the caing unit according to coded depths, [10 Also, the image data decoder 230 may perform inverse transformation according to each transformation unit in the coding unit, based on the infonnation about the size of the transformaton unit of the coding unit according to coded depths, so as to peitorm the inverse transformation according to maximum coding umts. 11i The image data decoder 230 may determine at least one coded depth of a current mnaximum coding unit by using split information according to depths, if the split in fornation indicates th 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 naxinn coding unit by using at least one of 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 codingit. [102] For example, data units including the encoding information having the same split in formation may be gathered by observing the encoding information set assigned for ithe predetermined data unit trom among the coding unit, the prediction unit, and the minimum unVit, and the gathered data uns may be considered to be one data unit to be decoded by the image data decoder 230 in the same encoding mode. [031 'The video decoding apparatus 200 may obtain information about at [east one coding unit that generates the mninimumr encoding error when encomding isreusvl performed for each maximurn coding unit, and may use the information to decode the current picture. That is, the coding units having the tree structure determined to be the optinmn coding units in eaeb maximum ing ng unit may he decoded. Also, the maxinum sie of the -odin ni y be determined considering at least one of resolution and an amlounit or image data. 1043 Accordingly, 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 arc adaptively determined according to characteristics of the image data, and information about an optimum encoding mode received from an encoder. [1051 A method of determining coding units Havng a tree structure, a prediction unit, and a transtornation unit, according to one or more exemplary embodiments, wil now be described with reference to FIGs, 3 through 13. [061 FIG, 3 is a diagram for describing a concept of coding units according to an exemplary embodiment. 107 A size of a coding unit may be expressed in width x height. For example, the size of the coding unit may be 64x64, 32x32, 16x16, or 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. 32x 16, 16x32, or 16x16, a coding unit of 16xi6 may be split into partitions of 16x16, 16x, 8x16, or 8x8, and a coding unit of 8xS may be split into partitions of 8x8, 8x4, 4x8, or 4x4, ~8E Referring to HG, 3, there is exemplarily provided first video data 310 with a resolution of 1920x1080, and a coding unit with a miaxinu size of 64 and a maximum depth of 2. Futhermore, there is exempiarly provided second video data 320 with a resolution of 1920x1080, and a coding unit with a maximum size of 64 and a maximum depth of 3, Also, there is exemplarily provided third video data 330 with a resolution of 352x28, and a coding unit with a maximum size of 16 and a maximum depth of 1 The maximum depth shown in FIG. 3 denotes a total number of splits from a maximum coding unit to a minimum decoding unit 109] If a resolution is high or a daa amount is large, a maximum size of a coding unit may be large so as to increase encoding efficiency and to accurately reflect characteristics of an image. Accordingly, the maximum size of the coding unit of the first and the second video d ala 310 and 32) having the higher resolution than the third video data 330 may be 64, is1 Since the raximum depth of the first video data 310 is 2, coding units 315 of the first video data 310 ay include a maxinum coding uni having a long axis SIZc of 64, and coding unis having long axis sizes of 32 and 16 since depths are deepened to two layers 'by splitting the maximum coding uni twice, Meanwhile, since the maximum depth of the third video data 330 is , coding units 335 of the third 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 maxiinun coding unit once. Since the maximum depth of the second video daa 20 is 3. oding units 325 of the second video data 320 may include a maximum coding unit having a long axis size of 64, and coding units having long axs sizes of 32, 16, and 8 since the depths arc deepened to 3 layer by splicing the maximum coding unit three imes. As a depth deepens. detailed intbrmation may be precisely expressed. [112 H. 4 is a block diagram of an image encoder 400 based on coding units, according to an exemplary embodiment. [3 The image encoder 400 may perform operations of a coding unit determiner 120 of a video encoding apparatus 100 according to an exemplary embodiment to encode image data. That is, referring to FIG. 4, an intra predictor 410 performs intra prediction on coding units, from among a current frame 405, in an intra mode, and a motion estimator 420 and a motion compensator 425 perform inter estimation and motion comnpensationonn coding units, front among the current frame, in an inter mode by using the current frame 405 and a reference frame 495. [1141 Data output from the nra predictor 410, the motion estimator 420, and the motion compensator 425 is output as a quantized transformation coefficiet 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 twit 480 and a loop filtering unt 490. The quantized transformation coefficient may he outpu as a bitstream 455 through an entropy encoder 450, 5 in order for the image encoder 400 to be applied in the video encoding apparatus 100, elements of the image encoder 400, i.e. the intra predictor 410, the notion estimator 420, the motion compensator 425, the transformer 430, the quantizer 440, the entmopy encoder 450, the inverse quantize 460, the inverse transformer 470, the de blocking unit 48S, 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. [6] Specifically, the intra predictor 410, the motion estimator 420, and the motion comnpensaror 425 determine partitions and a predicton mode of each coding Unit from among the coding units having a tree structure while considering a maximum size and a maximum depth of a current maximum coding unit, and the tAnsformer 430 de ermines the size of the transformation unit in each ceding unit fm among the coding units having a tree structure. 1171 FIG. 5 is a block diaram of an image decoder 500 based on coding units, according to an exemplary embodiment. 1181 Referring to FIG. 5, a parser 510 parses encoded image data to be decoded and in formation about encoding used for decoding from a bitstream 505. The encoded image data is output as inverse quantized data through an entupy decoder 520 and an inverse quantzer 530, and the inverse quantized data is restored to image data in a spatial domain through an inverse transiforner 540. [t 19] An intra predictor 550 performs intra prediction on coding units in anintra mode with resNpect to the image data in the spatial domain, and a motion compensatory 560 performs motion compensation on coding units in an inter mode by using a reference frame 585. [01 The image data in the spatial domain, which passed through the intra predictor 550 and the motion Tcmpensator 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. [211 i order to decode the image data in an image data decoder 230 of a video decoding apparatus 200 according to an exemplary embodiment, the image decoder 500 may perform operations that are performed after the parser 510. [1221 In order for the image decoder 500 to be applied in the video decoding apparatus 200, elements of thgeae decoder 50, i.e the parser 510, the entropy decoder 520, the inverse quantizer 530, the inverse transformer 540, the intra predictor 550, the motion compensatory 560, the debiocking unit 570, and the loop filtering unit 580, perform operations based on coding units having a tree structure for each maxinmmr coding unit, 23] Specificaliy, the intra prediction 550 and the motion compensator 560 perform op erations based on partitions and a prediction mode for each of the coding units having a tree structure, and the inerse transformer 540 performs operations based on a size 01 a transformation unit for each coding unit. 1241 IG 6 is a diagram iliustraing deeper codingauits according to depths. and partitions, according to an exemplary cmbodinent. [1251 A video encoding appartus 1|00 and a video decoding apparau 200acodingt exemplary embodimentsuse hieachical coding units so as to consider chamateristics ot an image, A maximnum height, a maximum width, and a maximum depth of coding units may be adaptively determined according to the characteristics of the image, or may he differently set by a user, Sizes of deeper coding units according to depths may be determined according to the rredetermned maximum size of the coding uni. 26] Referring to FIG. 6, in 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 naxiun depth is 4. Since a depth deepens along a vertical axis of the hierarchical structure 600, a height and a width of a deeper coding unit are each split. Also, w prediction unit and partitions, which are bases for prediction encoding of each deeper coding unit, are shown along a horizomal axis of the hier archical structure 600. ,27] That. is, a first coding unit 610 is a maximum coding unit in the hierarchical stucture 600. where a depth is 0 and a size, i.e, a height by width, is 64x64. The depth deepens al"ng the venical axis, and a second coding unit 620 having a size of 32x32 and a depth of 1, a third coding unit 630 having a size of -6x16 and a depth of 2,a fourth coding unit 640 having a size of 8x8 and a depth of 3, and a fifth coding unit 650 having a size of 4x4 and a depth of 4 exist, The fifth coding un 650 having the size of 4x4 and the depth of 4 is a minimum coding unit. [28] The prediction unit and the partitions of a coding unit are arranged along the horizontal axis according to each depth. That is, if the first 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 included in the first coding unit 610, i.e, a partition 610 having a size of 64x64, partitions 612 having a size of 64x32, partitions 614 having a size of 32x64, or partitions 616 having a size of 32x32. 129] Similarly, a prediction unit of the second coding unit 620 having the size of 32x32 and the depth of 1 may be split into partitions included in the second coding unit 620, i.e, a partition 620 having a size of 3232, partitions 622 having a size of 32x16, partitions 624 having asize of 16x32. and partitions 626 having a size of 16xi6. [01 Similarly, a prediction unit of the third coding unit 630 having the size of 16xi6 and the depth of 2 may be split into partitions included in the third coding unit 630, ie. a partition having a size of 16x16 included in the third 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. Si31 Similarly, a prediction unit of the fourth coding unit 640 having the size of Xx8 and the depth of 3 may be split into partitions included in the forth coding unit 640, i.e. a partition having a size of 8x8 included in the fourth coding unit 640, partitions 642 having a size of 8x4. petitions 644 having a size of 4x8 and partitions 646 having a sWe of 44 [132] the fifth coding unit 650 having the size oif 4x4 and the de pth of 4 is the minimum coding unit and a coding unit of the lowenost depth. A prediction unit of the fifth coding unit 650 is only assigned to a partition having a size of 4x4. S1331 In order to determine the at least one coded depth of the coding units of the maximum coding unit 610, a coding unit determiner 120 of the video encoding apparatus 100 performs encoding for coding units corresponding to each depth included in the maxinmum coding unit 610. [1341 A number of deeper coding units according to depths including data in the same range and the same size increase as the depth deepens, For example, four coding units corresponding to a depth of 2 are used to cover data that is included in one coding unit conwesponding to a depth of 1. Accordinglv, in order to compare encoding results of the same data according to depths, the coding unit coresponding to the depth of I and four coding units corresponding to the depth of 2 are each encoded. 135 In order to perform encoding for a current depth from among the depths, a least encoding error may he 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 perforning 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 first coding unit 610 may be selected as the coded depth and a partition type of the first coding unit 610. [136] IG7 isadiagram fordescrbing a relationshpbetween a codingunit 70|arnd trans formation nis 720 acordingto ant exempay embodiment f371 A video encoding or deoding apparatus 100 or 200 according to exemplar em bed iments 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 traus formation units for transformation during encoding may be selected based on data units that are not larger than a corresponding coding unit. 138 For example, in the video encoding or decoding aUpparatus 100 or 200, if a size of the coding unit 710 is 64x64, transformation may be performed by using the trans formation units 720 having a size of 32x32. [139] Also, data of the coding unit 710 having the size of 64x64 may be encoded by performing the transformation on each of the transformation nits having the size of 32x32, 16x16. 8x8, and 4x4, which are smaller than 64x64, such that a transformation unit having the least coding error may be selected. 140] HWG. S is a diagram for describing encoding information of coding units corme sponding to a coded depth, according to an exemplary embodiment.
20 141] Referring to FIG 8, an output unit 130 of a video encoding apparatus 100 according to ani exemplary emibodimnent may encode and tansmit information 800 about a partition type, infomation 810 about a prediction mode, and information 820 about a size of a transtomtion unit or each coding unit corresponding to a coded depth, as information about an encoding mode. 42] he information 800 about the partition type is formation about a shape of a partition obtained by splitting a Irdiction unit of a currem ecding unit, wherein the parition is a data unit Qor prediction encoding the current coding unit For example, a current coding unit CUO having a size of 2Nx2N may he spit into any one of a partion 802 having a size of 2Nx2N, a panition 801 having a size of 2NxN, a partitin 806 having a size of Nx2N, and a parttion 808 having a size of NxN. Here, the information 800 about the partiion type is set Lu indicate one of the partilon 804 having a size of 2NxN, the partition 806 having a size of Nx2N, and the partton 808 having a size of NxN 143] The information 810 about the prediction mode indicates a predicton mode of each parttion, For exarnple, the information 810 about the prediction mode may indicate a node of prediction encoding performed on a partilon indicated by the information 800 about the portion type, ie, an inmra mode 812, an inter node 814, or a skip rmode 816. [1441 The intormaion 820 abot the size of a transformation ui indicates a trans formation unit to be based on when tranormation is performed on a currem coding unit. For example, the transfonnaton unit may be a tirst intra transformation unit 822, a second intra transfonnaton urt1 824, a first inter transformatin unit 826 or a second intra transformation unit 828. [14] An image data and encoding information exractor 220 of a video decoding apparatus 200 according to an exemplary embodiment may extract and use the intbrmation 800, 810, and 820 for decoding, according to each deeper coding unit 4 FIG. 9 is a diagram of deeper coding units according to depths, according to an exemplary embodiment [47] Split information may beu sed to indicate a change of a depth. The split information indicates whether a coding unit of a current depth is split into coding units of a lower dep di 148] Referring to FIG. 9, a prediction unit 910 for prediction encoding a coding unit 0 having a depth of 0 and a size of 2N Ox2N-- n( may include parttions of a partiton ty pe 92 having a se of 21OxN 0, a partition type 914 having a size of 2NOxN.I, a partition type 916 having a size of N..x2N_0, and a partition type 918 having a size of N_.0xNA. Aihough P1G. 9 only illustrates the partion types 912 through 91.8 which are obtained by asymmetrical splitting die prediction unit 910, it is understood that a partition type is not limited thereto. For exmlacring to another exemplary cmbodiMent, the partitions of the prediction unit 910 may include asymmetrical partitions, partitions having a predetermined shape, and partitions having a geometrical shape. 1 49] Prediction encoding is repeatedly performed on one partition having a size of 2N- x2N_, two partitions having a size of 2NxN_, two partitions having a :ize of N Ox2N_0, and four partitions having a size of N_xN_0, according to each partition type. The prediction encoding in an intra mode and an inter mode may be performed on the pardtions having the sizes of 2NOx2N_0, N_0x2N_0, 2N-0xN_0, and NOxN . The prediction encoding in a skip mode is performed only on the partiton having the size of 2N_0x2N 0. 1501j Errors of encoding including the prediction encoding in the partition types 912 through 918 are compared, and the least encoding error is deerinned among the partition types, if an encoding error is smallest in one of the partition types 912 through 916, the prediction unit 910 nay nor be spt into a lower depth. 151] For example, if the encoding error is the smallest in the partition type 918, a depth is changed from 0 to I to spit the partition type 918 in operation 920, and encoding is re peatedly perirmed on coding units 930 having a depth of 2 and a size of N N to search for a minmum encoding errors 1521 A prediction unit 940 for prediction encoding the codiwn unit 930 hain a dept of and a size of 2N I x2N. (=N_ xN_) may include partitions of a partition Type 942 having a size of 2Nx2N_ 1, a partition type 944 having a size of 2NixNi, a partition type 946 having a site of Nx2N,!, and a parition type 948 havig a size of N IxN , [153] As an example, if 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 repeatey performed on coding units 960, which have a depth of 2 and a size of N 2xN-2 to search for a mninimtum encoding error. [154]| When a maximum depth is d, split operations according to each depth many be performed up to when a depth becomes d-i, and split information may be encoded as up to when a depth is one or 0 to d-2. For example, when encoding is performed up to when the depth is d-i alter a coding uni 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-I and a size of 2N_(d-I)x2Nd- 1) may include partidons of a partition type 992 having a size of 2N (d-1x2N(d~ 1), partition type 994 having a size of 2N_(di-1)N-(d-1), a panition type 996 having a size of N_(d-l)x2Nd-1), and a partition type 998 having a size of N(d-1)xN_(d-i), [15] Prediction encoding may be repeatedly performed on one partition having a size of 2N_(d-i1x2Nt (d~-i), two partitions having a size of 2N_(d-1I)xN_ (d-i), tw o partitions having a size of N.d- 1c)x2N(d -I), four partitions having a size of Nd-1)xNId-) fri among the partition types 992 through 998 to search for a partition type having a minimum encoding error. 561 Even when the partition type 998 has the minimum encoding error, since a maimum depth is d, a coding unit CU - 1) having a depth of U-I is no longer spli to a lower depth. In this case, a coded depth for the coding units of a current naximun coding unit 900 s determined to he d-i and a partition type of the cunient maximum coding unit 900 may be determined to be N d-)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 spur to a lower depth, split information for the minimum coding unit 980 is not set. 157] A data unit 999 may be a minimum unit for the current mnaximn coding umi A miim m nt according to an exemplary embodiment may be a recangular data unit obtained by spliting a nnimUm coding unit 980 by 4. By performing the encodin re peatedly, a video encoding apparatus 100 according to an exemplary embodiment 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 partiton type and a predicion mode as an encoding mode of the coded depth, [381 As such, the minimum encoding errors according to depths are compared in al of the depths of I through d, and a depth having the least encxing error may be determined as a coded depth, The coded depth, the partiten type of the prediction unit, and the prediction eode 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, split in formanton of the coded depth is set to 0, and split formation of depths exuding the coded depth is set to 1. [1t 591 An image data and encoding information extractor 220 of a video decoding apparatus 200 according to an exemplary embodiment may extract and use the information about the coded depth and the prediction unit of the coding uiniit 900 to decode the partition 912. The video decoding apparatus 200 may determine a depth, in which split in formation is 0, as a coded depth by using split information according to depths 5 and use information about an encoding mode of the corresponding depth for decoding, 160l FIGs, 10 through 12 are diagrams for describing a relationship between coding units 1010, prediction units 1060, and transformation units 1070. according to one or more exemplary embodiments. 1161 Referring to FG, 10, the coding units 1010 are coding units having a tree structure, corresponding to coded depths determined by a video encoding apparatus 100 according to an exemplary embodiment, in a maximum coding unit. Referring to EGs. 11 and 12, 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 23 of thec oding un 101 162 When a depth of a maximum coding unit is 0 in the coding units 1I ,lepths o' coding units 1012 and 1054 are 1, depths of coding units 1014, 1016, 1018 1028, 1050, and 1052 are 2, depths of coding units 2 10, 1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units 1040, 1042, 1044, and 1046 are 4. [1631 In the prediction units 1060, some encodmg unis 1014, 1016, 1022, 1032, 1048, 1050. 1052, and 1054 are obtained by spiinng coding Dnits of the encoding un its 1010. In particular, partition types in the coding units 1014, 1022, 1050, and 1054 have a size or 2NxN, paitiion 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 ot the coding units 1010 are smaller than or equal to each codig unit 164] Transformation or inverse transformatilon 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 untit 1014. 1016, 1022, 1032, 1043, 1050, and 1052 of the transformation units 1(170 are different from those of the prediction units 1060 in terms of sizes and shapes. That is, the video encoding and decoding apparatuses 100 and 200 according to exemplary embodiments may perform imra prediction, motion estimation. motion compensation, transformation, and inverse transformation idividualiy on a data unit in the samte coding unit 65] Accordingly, encoding is recursively performed on each of coding units having a hi erarchical mrucoe in each region of a maximum coding unit to determine an optimum uding unit and thus coding units having a recursive Uee structure may be obtained, Encoding information may include split information about a coding unit, information about a partition tye. information about a prediction mode, and information about a size of a transtormation unit, Exemplary Table 1 shows the encoding information that may be set by the video encoding and decodig apparatuses 100 and 201. 1661 167] Table 1 24 [table Ui [Table Spit information 0 (Ecodng on Coding Unit having Se of Nx2N Sp In and Current Depth of di formation I Prediction Partiton Ty pe Size of Transformation Unit Repeatedly Mode Encode lrtriter Syinmetdai Asymmnehnc Sph ~tIn- iSpUt in- oig nt \kic. artd io Prmian fortmaion A of fornat ion 1 of having Ud' Type Tpc Tansformatio uTsfrato Lower Depth Nx2'Nni Unitofd'i 1 Nx2N2Nx 1 zNxnU2: Nxr \NxN INx>MSymmetr N. 2NNxN Dnht 2NR ca 1 2N Type)N/2xN/2 (Asyummtriedl Putuni 1 t tfhenie enQodngIap U2 100 may output the encoding in formation about the coding units having a tree structure, and an image data and encoding information extractor 220 of the video decoding apparatus 200 may extract the encoxding information about the coding units having a tree sn'rucure from a received b)lts tream. 169] Split information indicates whether a current coding unit is split into coding units of a lowerr depth, if spit information of a current depth d is 0, a depth in which a current coding unit is no longer split into a tower depth, is a coded depth. Iuformnation 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 spli according to the split in formation, en coding is independently perfbrnned on split coding units of a lower depth, ~170] A prediction mode rmay be one of an intra mode, an inter mode, and a skip mode. The intra mode arl the inter mode may be defined in all parition types and the skip mode may be defined in only a partition type having a size of 2Nx2N. [17l The information about the partition type may indicate symmnetrical partition types having sizes of 2Nx2N, 2NxN. Nx2N, and NxN, w hich are obtained by syrmnetrically spiitting a height or a width of prediction unit, and asymmetriaI partition types having sizes of 2N xnU,. 2NxniD. nLx2N, and nRx2N, which aro obtained by asyrn metrically splitting the height or the width of the prediction unit. The asymnmetrical partition types having the sizes of 2NxnU and 2NxnD may be respectively obtained by spitting the height of the prediction unit in ratios of 1:3 and 3: 1. and the ammetrical 25 partition types havng the sizes of n'x2N and nRx2N may be respectively obtained by spliting the width of the prediction unit i ratios of 1:3 and 3:1 172] The side of the transformation uni may be set to be two types in the intra mode and two types in the imer mode. For example, if split information of te transformation unit is 0, the size of the transformation unit may be 2Nx2N. which is the sie of the current coding unit if split inforn-union of the transformtation unit is 1, the transformation units may be obtained by splintin the current coding unit. Also, if a partalon type of the cunt oding u hing he size or is etrical partition type, a size of a transformation unit may he NxN, and if the partition type of the current coding unit is an asynmmetrical partition type, the size of the transformation unit may be N/2xN/2. .3 The encoding information about coding umts having a tree structure may include at least one of a coding uni corresponding to a coded depth, a coding unit corresponding to a prediction unit, and a coding unit corresponding to a minimum unit, The coding unit corresponding to the coded depth may include at least one of a prediction unit and a mnmmunit inldn-tesm encodng mftonnation, a Imnruan including the same 74] Accordingly, it is determmed whether adjacent data Lnits are included in the same coding unit corresponding to the coded depth by comparing encoding information of the adjacent da its Alo a corresponding coding un onspondng to a ced depth is determined by using encoding information of a data unit and thus a dis tribution of coded depths in a maximum coding unit may be determined. L75] Accordingly, if a current coding unit is predicted based on encoding intornation 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. [76 However, it is understood that another exemplary embodiment is not limited thereto. For example, according to another exemplary embodiment, 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 encoding information of the data units. and the searched adjacent coding units may be referred for predicting the current codmng unit 177] Fi 13 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 exemplary Table 1, according to an exemplary embodiment. [1781 Referring to FIG. 13, a maximum codmig unit 1300 includes coding units 1302, 1304, 306, 1312. 134, 1316. and 11 8 of coded depths. Here. since the coding unit 1318 is a coding unit of a coded depth, split information nay be set to 0, Information about a partion type of the coding unit 1318 having a size of 2Nx2N may be set to be one of a panition type 1322 having a size of 2Nx2N, a pu rtion type 1324 having a size of 2NxN. a partitin type 1326 having a size of Nx2N, a partition type 1328 having a size 26 of NN, 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 n Rx-2N, 11791 When the partition type is ser to be symmetrical, i.e, the partition type 1 322, 1324, 1326, or 1328, a transformation ui 1342 hing a size of 2Nx2N is set if split in formation (TU size flag) of a transfonation unit is 0, and a transformation unit 1344 havinA a size of NxN is set if a TU size flag is 1 [801 When the partition type is set to be asymmetrica[, i.e, the partition type 1332, 1334, 1336, or 1338, a transfornation unit 1352 having a size of 2Nx2N is set if anTU size flag is 0, and a transformation unit 1354 having a size of N/2xN/2 is set if a TIU size flag is& [81 Referring vo F)I 13, the TU size flag is a lag having a value of 0 or L, alhough it is understood that the TU size flag is not limited to I bit, and a transformation unit may be hierarchical spit having a tree structure while the TU size flag increases from 0. 182] In this case, the size of a transformation unit that has been actually used may be expressed by using a (T size lag of a transformation unit, according to an exemplary embodiment together with a maximum size and miimunum size of the transformation unit. According to an exemplary embodiment, a video encoding apparaus 100 is capable of encoding maximum transformation unit size infoaio, ininnun iran formation unit size information, and a maximum TI) size flag. The resut of encoding the maximnun transformation unit size information, the minimum transformation unit sie information, and the maximum TU size flag may be inserted imo an SPS. According to an exemplary embodinmemr. a video decoding apparatus 200 may decode video by using the maximum transformation unit size information, the mi ii trans formation unit size information and the Waximum TU size flag, [1831 For example, if the size of a current coding unit is 64x64 and a maximum trans formation unit size is 32x32, the size of a transformation unit may be 32x32 when a TU size lg 0, may be 16x 6 when the T size flag is i, and may be 8x8 when the TU size flag is 2, 184] As another example, if the size of the current coding uni is 32x32 and a minimum transformation unit size is 32x32, the size of the transformation unit may be 32x32 when the T U size flag is 0, Here, the TU sie flag cannot be set to a value other than 0, since the size of the transformation unit cannot be less than 32x32. [851 As another example if the size of the current coding unit is 64x64 and a maximum TU size lag is 1, the TU size lag may be 0 or 1 Here, theU size flag cannot be set to a value other than 0 or I. [186] Ths, i f it is defined that the maximum TO size flagi Maxransform izelndex a minimum transformation unit size is MifransfonnSize and a transformation unit sie 27 isW ootluSie when the ' size flag is 0, a current minimum transformation unitsze CurrMinTuSize that can be determined in a current coding unit, may be defined by Equation (): [i $7 CurrMi nTuSi ze =L max( MinTra nsformSize, RootTuSize/! (2^MaxTransforrnSize Index)). - (I'). 881 Compared to the current minimum transformation unit size CrrMinTuSize that can be determined in the current coding unit, a transformation unit size RootTuSize when the Tn size flag is o may denote a maximum transformation unit size that can be selected in the system. hn Equation (U), RootuSize!(2^MaxTransformS izelndex) denotes a transformation unit size when the transformation unit size RootluSize, whten the T U size flag is 0, is spit a number of times corresponding to the maximum T1U size flagt. Furthermont, MinlransformnSize denotes a minimum transformation size. Thus, a smaller value from among RootTusize/(2^Maxlransformnsizeindex) and MintTrants formSize may be the current minimum transformation unit size CurrMinuize that c an he determined in the current coding unit. 189] According to an exemplary embodiment, the maximum transformation unit size RootTuSize may vary according to the type of a prediction mode. 190] N example, if a current prediction mode is an inter mode, then RootluSize 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, [191]j RootTuSize = min(MaxlransformrSize, PUS ize) -- ,,, (2), 192] Thaat 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. [1931 if a prediction mode of a current partition unit is an intra mode, RootTuSize may be determined by using Equation (3) below, In Equation (3), PartitionSize denotes the size of die current partition unit, 194] RootTuSize = min(MaxransformSie, PartitionSize) . . 195 That is, iA the current predictin mode i the intra mode, the transformation unit size RootTuSize when the 'EL size flag is 0 may be a smaller value from among the maximum transformation unit size and the size of the ement partition unit, 196] 1-owever, the current maximum transformation unit size RootluSize that varies according to the type of a prediction mode in a partition unit is merely exemplary, and another exemplary embodiment is not luited thereto. [197 Hereinafter, encoding and decoding of residual block perfonned by the entropy encoder 450 of the video encoding apparatus 400 lustrated in FlG. 4 and the entropy decoder 520 of the video decoding apparaus 500 illustrate in FIG. 5 will be described in detail in the following description, an encoding unit denotes a current encoded 28 block in an encoding process of an image, and a decoding unit denotes a cunrent decodedi block in a decoding process of an image, The encoding unit and the decoding unit are different in that the encoding unit is used in the encoding process and the decoding unit is used in the decoding. For the sake of consistency, except for a particular case, the encoding unit and the decoding unit are referred to as a coding unit in both the encoding and decoding processes, Also, one of ordinary skil in the art would understand by the present disclosure that an irtra prediction method and aDparatus acCording to an exemplary embodiment may also be applied to perform intra prediction in a general video code. [98 FIGs. 14A through 14C are reference diagrams for describing a process of encoding a transformation residual block in a related technical field. 19] Referning a, FIG. 14A when a trans formation residual block 1410 is generated by transoinn a residual block, a significance map, which indicates a location of a nonzero effective transformion coefficient in the transformation residual block 141 0 while scanning transformation coefficients in the transformation residual block 1410 according to a zintag scanning order. After scanning the transformation coefficients in the transformation residual block i14!0. level information of an effective trait formation coefficient are encoded. For example, a process of encoding a trams formation residual block 1420 having a size of 4x4. as illustrated in IG. 14B, will now be described, in IG. 1 4B, it is assumed that trnsformation coefficients at locations indicated by X are nonzero effective transformation coefficients. Here, a sig nificance map indicted. an effective transfornmaton coefficient as I and a 0 trans formation coefficient as 0 from among transformation coefficients in a residual block 1430, as shown in FIG. 14(2. The significance map is scanned according to a prede termined scanning order, while context adaptive binary arithmetic coding is performed thereon. F-or example, when the significance map of HIG. 1 4C is encoded according to a raster scanning order, and scanning is performed from left to right and top to bottom, context adaptive binary arithmetic coding is performed on the significance map corre spond ing to an binary Thing of 1111111 ii 10101000." Level information of an effective coefficient, i.e a sign and an absolute value of the effective coefficient. is enicodedi [200] Such a process in the related technical field may he utilized for encoding a trans formation residual block having a small size, such as 4x4 or 8x8, but may not be suitable for encoding a transformatin residual block having a large size, such as 16x 16, 32x32, or 64x64. In particular, if all transformation coefficients in a trans fornatron residual block are scanned and encoded according to the process of PIGs, 4 A through 14C2 withn expect to a transformation residual block having a large size, a length of a binary sting corresponding to a significance map mray increase and 29 encoding efficiency may deteriorate. Accordingly, a method and apparatus for encoding a residual block according to exemplary embodimens are capable of efficiently encoding a transformation residual block by splitting the Irnmsfornation residual block into predetermined frequency band units and encoding an effective coefficient lag according to the frequency band units, which indicates whether a nonzero effective transformaion coefficent exists for each frequency band unit, while encoding effective transfornation coefficient inufornnati on, i.e., a significance map and level infonnation of an effective coefficient, in a frequency hand iwn kviiich an efctive efficienflag according to equency band units hasa value of L 2021 FiG.|5is a block diagramonappartus 150 folencoding A residual black according Lu an. exemplary emabodimnt While not restricted thereto, the apparatus 1500 may correspond to the entropy encoder 450 of FIG, 4, or may be included in the entropy encoder 450. 2031 Referring to FIG. 15, the apparatus 1500 includes a frequency band splitter 1510, an effective coefficient hflg generator 1520, and an effective coefficient encoder 1530. [204] The frequency band splitter 1510 splits a transformaiion residual block into piede terrnined frequency band units. Referring back to I.FIG, 4A the exemplary trans formation residual block 1410, an upper left tansformaion coefficient has a low frequency component, and a lower right transformation coefficient has a high frequency component Most of the elective transformation coefficients of the trans formation residual blocks 1410 may exist in low frequency bands, and the trans formation coefficiets having high frequency components may mostly have a value of 0. In this case, a nonzero effective transformation coefficient tromt among the trans formation coefficients of the high. frequency component is sparse. Specifically, dis tri bution of effective transformation coefficients of high frequency components tmay he sparser when a ausfonnation residual block is gene ated by performing trans formation with a transfonrmation unit having a si ze of i 6ix 16, 32x32, 64x64, or above, which is larger than a related art transformation unit having a size of ex4 or 8x8. as in the image encoder '100, Accordingly, the frequency band splitter 1510 may split the transformation residual block into the frequency band units while considermg dis tribution characteristics according to the frequency bands of the tran sformarion coef ficients in the transtornation residual block. [2(15 FIGs. i 6A through 161 are diagrams for describing splitting of a transformation residual block into predetermined frequency band units, according to one or more exemplary embodiments. [206] Referring to FIG. 16A., the frequency band splitter 1510 generates frequency band units 1611 through 1614 by splitting a transformation residual block 1610 at prede- 30 term ed frequnency intervals from a low frequency band to a horizomtalfequency I II and a vertical frequency Vl. In FIG. 16A, horizontal sides and vertical sides of die fequency band units 1611 ih gh 1614 have the same length, although it is un iertOd that the len gls of the horizntal and vertical sides may differ from each other, if a length of a remaining frequency band from the horizontal frequency Hli to a maximum horizontal frequency is less than a frequency interval corresponding to a lenth of the horizontal side of each of the frequency band umts 16 11 through 1614, or if a length of a remaining frequency band from the verucal frequency Vi to a maximum vertical frequency is less than a frequency interval corresponding to a length of the vertical side of each of the frequency band units 1611 through 1614, the frequency band splitter 1510 no longer splits the transformation residual block 1610, and generates a frequency band unit 1615 corresponding to a high frequency componem. Effective transformation coefficients may be intensively distributed the frequency band units 1611 through 1614 corresponding to low frequency components. anid distribution of effective transformation coefficients of high frequency components may be sparse, Accordingly, even when the etire remaking high frequency component aside from the frequency band units 1611 through 1614 generated by splicing the transformation residual block 1610 at predetermined frequency intervals, are generaed in one frequency band unit 1615, an overhead while encoding trans fomation coefficients in the frequency band unit 161:5 may not remarkably increase, 2071 in another exemplary embodiment, as shown n FIG. 16B, the frequency band s litter 1510 fay generate frequency band units 1621 through 1624 by spiin g a trans formation residual block 1620 from a low frequency band to a horizontal frequency H2 and a vertical frequency V2 and genenat frequency band units 1625 through 1627 by splitting remaining high frequency components of the transformation residual block 1620 based on the horizontal frequency H2 and the vertical frequency V, similarly to the description with reference to FIG. 16A, [2081 Moreover, accordmgs to another exemplary embodimem, as shown in FIG. 16C. the frequency hand spliner 1510 may generate frequency band unis 1631 through 1.634 b splicing a transformation residual block 1631) from a o frequency band to a horizontal frequency [13 and a vertical frequency V3, and general frequency band units 1635 and 1636 of high frequency components by splicing remaining high frequency components of the transformation residual block 1630 into two based on the vertical frequency V3, similarly to the descriptin with reference to FiG. 1A. 209] Referring to FIG. 16D, accoiing to another exemplary embodiment, the frequency band splitter 1510 may generate frequency band units 1641 Through 1644 by sp hitting a transformation residual block 1640 from a low frequency band to a horizontal frequency PH and a vertical frequency V4. and generate frequency band units 1645 and 31 S646 of high frequency components by splitting remnaining high frequency components of the transfrmaton residual block 1630 ino iwo based on the hozontal frequency H4, similarly to the description with reference to FIG. !6A. 2(10] As described above, distribution of effective transformation coefficients is con centrated in a low frequency band, and is sparse toward a high frequency band. Ac cordinglv. as shown in FIG. 1RE. the frequency band splitter 1510 splits a trans formation residual block 1650 in such a way that a unit size split in the low frequency band is smaller than a unit size split in the high frequency band. by considering a dis tribution characteristic of the effective transformation coefficient. in other words, the frequency band splitter 1510 splits the transfor-ation residual block 1650 minuely in the low frequency band and relatively lrge in the high frequency band so that the effective transformatilon coefficients that ar concentrated in the low frequency band are precisely encoded. For example, as shown in FIG, 16E. the frequency band splitter 1510 may generate frequency band spiN units 1651 through 1657 by splitting the trms formation residual block 1650 based on a horizotal frequency 115, vertical frequency V5, a horizmnal frequency H6 having a larger value than a multiple of the horizonal frequency 5, and a vertical frequency V6 having a larger value than a multiple of the vertcal frequency VS Thus, when A1651 through A 1657 respectively denote sizes of the frequency baud split units 1651 through 1657, the transformation residual block 1650 is split in such a way that A 1651 has a minimum size and A 1657 has a maximum size. [21 Refening to FIG. 16F, according to another exemplary embodiment the frequency band splitter [510 may split a transformation residual block 1660 into frequency band units i661 having the same size, 12121 Moreover, referring to FIG. 16G, according to another exemplary embodiment, the frequency band splitter 1510 may quadrisect a transformation residual block 1670, and again quadrisect a smallest low frequency band unit 167: irom among quadrisected frequency band units to generate frequency band units. The frequency band splitter 1510 may again quadriseci a smallest low frequency band unit 1672 from among frequency band units obtained by quadrisecring the smallest ow frequency band unit 1671. Such a splitting process may be repeated until sizes of quadrisected frequency band units are equal to or below a predetermined size, 2 131 According to another exemplary embodiment, referring to FIG. L6H, the frequency hand splitter 1510 may generate a frequency band unit 1681 of a low frequency component from a low frequency to a horizontal frequency H7 and a verical frequency V7, and generate frequency band units 1682 and 1683 by diagonaly splitting remaining high frequency cOmponents of a transformation residual block 1680, [214] Referring to FIGs. 161 and 1.63, according to one or more other exmiary em- 32 bodiments, the frequency band splier 1510 may splt transformation residue blocks 1 690 and 1695 by connecting a horizontal frequency and a vertical freqnoy, which have predetermined values. in FIG. 161, the transformation residual block 1690 is split by connecting the horizontal frequency and the vertical frequenicy at uniform frequency intervals, In Fi. 163y, the transformation residual block 1695 is split so that frequency intervals increase toward a high frcqucncy, ie. by connecting a I and hi, a2 and b2, a3 and bad al and b4. wherein al<a2<a3<ad and bi<b2<b3<b4. [2151 According to another exemplary embodiment, instead of using a predetermined split form as shown in Fis I6A through 16, the frequency hand splitter 1 5 10 may determine image characteristics of a transformation residual bloci by using distribution characteristics oQ effective transformation coefficients of the ransformatton residual bkck or a number of the effective nmsformation coefficients in each frequency hand and determine a size of a frequency unit to splt the transformation residual block according to each frequency band by using the determined image characteristics. For example, when effective transformation coefficients in a transformation residual block exist only in a frequency band smaller than a horizontal frequency H-8 and a vertical frequency V and do not eXist in a frequency band larger than the horizontal fe c HI and the vertiti frequency VS, the frequency band spitter 1510 may set the entire transformation residual block fron a low frequency band to the horizontal frequency H8 and the vertical frequency V8 as one frequency band unit. Alternatively, the frequency band sitter i0 split the transfomationesidal block into frequency band units having the same size, and set a remaining frequency hand larger than the horizontal frequency U8 and the vertical frequency VS as one frequency band unit. 121] it is undemand that the splitting of a transfonnation residual block into prede termined frequency hand units is not limited to the exemplary embodiments described above with reference to Gs. 1 6A through 13 and that a transformation residual block may be split into various forms in one or more other exemplary emibodintts. 21 7] Meanwhile, split forms of a uransformation residual bloc< bv the frequency band spiter 15 1( may be idemicaly set in an encoder and a decoder. However, it is un derstood that another exemplary embodiment is not limited thereto, For example, according 1o another exemplary embodimem, a predetermined split index may be de termined for each of various split fonn, such as shown in FG(. ;6A through 16, and the encoder may insert the spilt index about spt information used while encoding a transfonnation residual block into an encoded bitstream. For example, when integer values from split index (divjndex) 0 to 9 respectively denote split rms of FIGs. I6A through 1 (. and a split form used to encode a current transformation residual block is div.index=5 corresponding to the fonn shown in FIG. 16F, such split information nay be added to encoding information of the current transformation residual block.
3 [218 Referring back to HG. 15, after the frequency band splitter 1510 spits the trans tormatin residual block into the frequency band units the effective coefficient flag generator 1520 generates an effective coeficien flag indicating wheTer an efecuive transformation coefficient exists in each frequency band unit, Here, the effective co efficient flag generator 1520 may not generate a separate effective coefficient flag for a smallest lov frequency band unit. For example, when the transformaion residual block 1610 of FIG. jA is split, the effective coefficient flag generator 1520 may generate effective coefficient flags indicating whether effective transfonmaton coefficients exist for the frequency band units 1612 through 1615, other than the frequency band unit 1611 of a smallest low frequency band unit. When Coeff.exist_1612, Coett.exist.1613, Coeff..exist .1614 and Coeffexist 1615 respeetvely denote the ef'ectise coefficient flags of the frequency band units 1612 Through 1615, and effecive coefficients exist only in the frequency band units 1612 and 1613 from among the frequency band units 1612 though 1615, the effective coefficient flag generator 1520 generates the effective coefficient flags of each frequency band unit, for examille, generates Coeff..exist..1612=1, Coeff_exist_i 613=1, and Coeff..exist..14=0, Coeff.exist 1615=0, A s described above, since an elective transformation coefficient may exit in the frequency band unit 16) 1 of the smalest low frequency band unit, an effective coefficient iiag indicAing existence of the effective transformation coefficie may not be separately generated for the frequency hand unit 1611 Moreover instead of separately generating the effective coefcat flag for the frequency band unit i 6 1, a related art coded_biociflag field indicating whether an effective transformation co efficient exists in a residual block may be used to indicate the existence of the effective transformation coefficient in the frequency band unit 1611. Such a process of generating the effective coefficient flag is not limited to the slit form of FIG. i 6A. and nay be applied to other splt forms in one or more other exemplary embodimems such as those of FIGs, 16B through 161 [2 i 91 Meanwhile, transformation process or inverse-transformation process may be performed individually in each frequency hand unit by use of different transformation or inverse-transformation meto . Further, transformation process or inverse transformation may be performed only in the frequency band unit having an effective nag and may be slipped in te frequency band unit having an effective coefficient flag 0, [22Q] RMeferring hack to FIG. 15, the effective coefficient encoder 1530 encodes a sig nificance map and level information of the effective transformation coefficient The significance map indicates locations of the effective transformation coefficients existing in the frequency band unit, in which a value of the effective coefficient flag generated by the effective coefficient flag generator 1520 is 1, i.e, the frequency band 34 unit having the effective transformation coetncient. [221] FIGs. 1?A and 17B3 are reference diagrams for describing a process of encoding an effective transformation coefficient, according to one or more exemplary em bodiments. FIGs. V7A and 17B illustrate split forms corresponding to the split form of FIG. I6E, whemin frequency band units are generated by quadisecting a trans-. formation residual block, and again quadrisecting a low freq uency band, it is tun derstood that the process descri bed with reference to F IGs I A and I 7B may also be applied to the frequency band units having other split fonms, such as any one of the split fonts of FIs inA thmuih 16J r222] The effective coefficient encoder 1530 may encode an effective transformation co efficient by scanning an entire transformation residual block, or encode an effective transfourmnation coefficiem tin a frequency band unit by perfonning scanning inde pendently for each frequency band unit, in detaili. referring to FIG, 17A. the effective coefficient encoder 1530 may encode a significance map indicating locations of effective zranstormation coefficients existing in a transformation residu~ai block Vi10, and size and sign information of each effective transformation coefficient while scanning the entire transformation esicial block ! 710 according to a predetermxined scanning order, fexamp, a rast scanning may be skipped in a freqpuency band unit in which an effective coefficient flag has a value of 0, i.e., a frequency band unit that does not have an effective trans formation coefficient. 223] According to another exemplary embodiment, referring lo FIG. 17W the ef fective Co efficient encoder 1530 may encode significance rnap and level information of an effective transtorma tion coefficiemt for each frequency band unit according to a split form of a transformation residual block 1720 split by the frequency band splitter 1510. 122h! FGs, I18A and 1813 are reference diagrams for describing in detail a process of enicoding a r-es idual block, according to an exemplary embodiment. In FIGs. ISA and 1 8B, a transformation coefficient indicated with x is an effective transformation co efficient and a transfonnation coefficient without any indication has a varue of (1 12251 Referring to FIG. I8A, the frequency band splitter 1 510 splits a transformation residual block 1810 according to a split form, such as one of the split forms shown in fiGs, 16A through 161L FIG. 'I8A shows a split form corresponding to the split form of IG. 16E,. though it is understood that the process with reference to FIG, I8A may also he applied to other split forms. The effective coefficient flag generator 1520 re spectively sets effective coefficient flags of frequency band units 1811 through 1813 including effective transformation coefficients as 1, and respectively sets effectie co efficient flags of freuunency band units 1814 through 13R17 thaI. do not include an effective transformation coefficient as 0, The effectave coefficient encoder 1530 encodes a significance map indiceating locations of the effective transformation coef ficiens while scanning the enure transformation residual block 1810. As described above, the significance map indicates whether a transfonnation coeffcient according to each scan inaex is an effective transformation coefficient or 0. A fter encoding the significance map, the effective coefficient enconer 1530 encodes level information of each effective transformation coefficient ihe level information of the effective trans formation coefficient includes sign and absolute value information of the effective transformation coefficient. For example, the significance map of the frequency band Units 181 1 through 11I3 including the effective transformation coefficient ay hae binary string value, such as "10001000101011 10100100100010001 when scanning is performed according to a raster scanning order as shown I FIG. 18A. ~226] Also, when information about the ef fective transformation coefficient is encoded while scanning threenr transoination residual block 1810 as show In IG, I8A, an end-of-block OB) flag indicating whether an effective transforation coefficient is the last effective transformation coefficient may be set for the entire tnansformaation residual block 1810 or each frequency band unit When an LOB flag is set for the entre transformation residual bkick 810, only' an FOB flag of a transformation co efficient 1802 of the last effective transformation coeffiient according to the scanning order from among tramforation coefficients of FIG. ISA may have a value of 1, For example, as described above, if the signifcance map according to FIG 18 A has a value of " O 001000i010110100100100010001, an FOB flag corresponding to such a significance mapO has a value of "000000000001 since only the last effective trans formation coefticient from among 12 effective transformation coefficients included in "100010001010i10100100100010001" has a value of 1. In oher words, a total of 12 bits are used to express dTe EOB Oag corresponding to the significance map of FIG, 18A, [227j Aitematively, in order to reduce a number of bits used to express an lOB flag, the effective coefficient encoder 1530 may deine a flag ('ast) indicating whether a last effective transformation coetticient exists according to each frequency band unit, set Tast as 1 if the last effective transformation coefficient according to each frequency band unit exists and as 0 i the last effective transformation coefficient does not exist, and ses an EOB flag for only a frequency band unit where Tast is . thereby reducing a number of bits used to identify locamions of effective transformaion coefficients in the entire transformation residual block and the last effective transformation co efficient In detail referring to FIG. ISA. the effective coefficient encoder 1530 may check the existence ot a last effectve transformation coefficient for each of the frequency band units 181 1 through 1813 including the effectve transformation coef ficienN and set Tiast as I in the frequency band un it 1812 including the last effective transformation coefficient, and set Tiast as 0 in the remaining frequency band units i8i t and 1813. If each hit of 'Ilast indicates the existence of the las effective trans formation coefficient in each of the frequency band units 1211 through 1813 according to an order of scanning the transfarmation coefficients, a most signiicant hit QMSB) of THart may indicate whether the effective transformation coefficient exists in a lowest frequency band unit, and a least significant bit (LSB) of Tlast may indicate whether the las effective transfWrmation coefficient exists in the frequency hand unit 1812. That is, a bit value of 4001" is set since Tiast has a value of 0 for the frequency band unit 1811, 0 for the frequency band unit 1813, and i for the frequency hand unit 1812. Here, since an effective trnsformation coefficient in a transformation residual block may end at the frequency band unit 1811 that is the lowest, a lst valUe may not be separately assigned for the frequency band unit 1811. That is, iast may be set only for the frequency bands 1812 and 1813 excluding the frequency band 181 i front among the frquency band units 1211 through 1813 that are scanned according to a scanning order. Here, two bit values of '01" are set as Tiast. "0" that is the MSB of "01 indicates that the last effective transformation coeffIcient of the transformation residual block does not exist in the frequency band unit 1813, and "1" that is the LSB of "01 indicates that the last effective transformation coefficient of the transformation residual block exists in the frequency hand unit 1812. Tiast may have a value of "00" if the last effective transformation coefficient of the transformation residual block exists in the frequency band 181 i of the lowest frequency band unit Thus, when al bits of Mast are 0, it may be determined that the last eff(eive transformation efficient of the transformation residual block exists in the frequency baud unit 18 81. [22] in the present exemplary embodiment, the effective coefficient encoder 1530 sets an EOB lng only for the frequency band unit in which Tiast is 1, i.e. the frequency band unit inclMg the last effective transformation coeffcient of the transformation residual block, Referr ing to FIG. iSA. the effective coefficient encoder 1530 sets an EMB lag only for each effective transformation coetficient existing in the frequency hand unit 1312 in which TiAst is I. Since a total four effective transf3rm ia tio n co-ef ficients exist in the frequency band unit 1812, the EOB fag has four bits of "0001, According to another exemplary mibodiment, a tol of six to seven bits are used to identify the location of the effective transformation coefficients in the transformation residual block, and the last effective transformation coefficient, since two to three bits a;e set for Ant nd fin hi set for the FOB flag. Here, five to six bits are saved compared to the previously described exemplary embodiment in which a total of 12 bits are used to set the EOB flag, such as "O0000QO0000 ." [229] According to another exemplary embodiment when an EOB flag is set for each frequency hand unit. EOB flags of a transformation coefficient 1801 in the frequency 37 band uitl1811 a transformation coefficient 1802 in thefrequeniyband unit 8 and a transfornation coefficient 1803 in the frequency band unit 1813 ar set to F, EOB flags are not set for the frequency band units 1814 through 1817 that do not include the effective transformaion coefficieniw As such when an FOB ag is set for each frequency band unit including an effective transformation coefficient, an effective transformation coefyicient in a predetermined frequency band unit is banned, and then an effecuve transformation coefficient in a following frequency band unit may be scanned. For example, a transtformration coefficient in the frequency band unit 1812 may he scanned after the transformation coefficient 1803 of the frequency band unit 1813 is scanned. Referring to F1G. ISB, effective transfomation coefficient in tormation is encoded independently tbr each frequency band Unit. The effective co eficeient encoder 1530 encodes a significance map indicating locations of effective transformation coefficients, and level information of each effective transformation co efficient while independently scanning each frequency band unit of a transformation residual block 1820, For example, a significance map of a frequency band unit 1821 has a binary string value such as "100010001001 " when scanned accordmg to a raster scanning order as shown in FIG. 18B Also, the ef fective coefficient encoder 1530 sets an EOB flag of an effective transformnion coefficient 1831 corresponding to a last effective transformma ion coefficient from anmonga effective transtormation coeffice ns of the frequency band unit 1821 as 1, Simiarly, the effective coeffcient encoder 1530 generates a binary string value, such as "101010001," as a significance map ofa frequency band unit 1822. Also, the effective coeffici eneder 1530 ses an FOB of an effective transformation coefficient 1832 fror anong effective tmnsformation coef ficiens in the frequency band unit 1822 as 1. Similarly, the effective coefficient encoder 1530 generates a binary swing value. such as "I 001," as a significance map of a frequency band unit1823, and set nOB flag of an effectivetrasforaion co efficent 1833 a 1, 12301 Meanwhile, the effective coeffcient encoder 1530 may separately encode an End Of WhoIBlock flag indicating a last effective transformation coefficient of the transformation residual block 1820, aside from dhe EGS flag indicating that the effective transformation coefficients 1331 through 1833 -are the last effective trans formaion coefficiens in a corresponding frequency band unit, Referring to FQI, I8B, if the frequency band units 1821 through 1827 are independently scanned in the stated order, the effective transformation coefficient 1833 is the las effective transformation coefficient of the frequency band unit 1823 and, at the same time, tie last effective transformation coefficient of the transformation residual block 1820. Accordingly, an FOB flag and an End_Of_WholeBlock flag of the effecdye transformation coefficient 1833 both bae a value of 1. In the effective transformation coefficients 1831 and 1832, which are the ias effective transformation coefficients of the frequency hand unt14821 and 182.2 LOB fags have a value of I, but EndOfXWholeBiock flags have a value of 0. 231] As such, when an E0B flag and an EndOfWholeBlock flag are set fow a last effective transformation coefficient according to eachi frequency band, existence of an effective transformation coefficient in a corresponding frequency band unit may be first determined by using an abov-described effective coefficient flag during decoding so as to skip scanning of a frequency band unit, in which an effective coefficient fla is 0. Futhermore, when a transformation coefficient, in which an FOB flag is 1, is scanned while scanning transformation coefficients in a frequency band unit, in which an effective coefficient flag is 1, i.e., a frequency band unit having an effective trans formation coefficient, a following frequency band unnit may be scanned. 'When an effective transformation coefficient, in which an EOB flag is 1 and an End-Of_WholeBlock flag is 1. is sc anned, effective transformation coefficients of an entire transfornation residual block are scanned, and thus scanning of the trans~ formation residual block is ended, f232 FIGs, 19A and 19B are reference diagrams lor describing encoding information of a tranusformation residual block, which is generated by the effective coefficient encoder 1530, according to one or more exemplary embodiments. 233! Referring to FIG. 19A. the effective coefficient encoder 1530 may sequentially encode significance maps and pieces of effective coefficient flag information generated according to frequency bands. When a first frequency band is a smallest frequency band of a transformatin residual block, only a significance map 1911i of the first frequency band mnay be encoded and a flag of the first frequency band, which indicates whether an effecuve u:ansformafion coefficient exiss in the first frequency band, may not be separately encoded, as shown in IG 19A. According to another exemphay em bodiment, referring to FIG. 19B, effective coefficient nags 1921 of each frequency band may be first encoded, and then signiFicance maps 1925 of each frequency band may be encoded, 234] FIG. 20 is a flowchart illustrating a method or encoding a residual bock, according to an exeniplary embodiment. 235J Referring to FIG, 20, the intra predictor 410 or the motion compensator 425 of F1G, 4 generates a prediction block via inter prediction or intra prediction by using a current block in operation 2010, [2361 In operation 2020, a substractor generates a residual block that is a difference between the prediction block and the current block. [2371 In operation 2030, the transformer 430 transforms the residual block into a frequency domain to generate a transformation residual block. For example, the residual block may be transformed to the frequency domain via d iscrete cosine transform (DC~T [238] in operation 2040, the frequency band splitter 1510 splits the transfonaion residual block into predetermined frequency band units, As described above, the frequency hand spliter 151 may split the wransformation residual block into one of various split forms., or example as shown in FGs. 16A through 16J. In detail, the frequency band splter 1510 may split the transformation residual block such that a unit size split in a low frequency band is smaller than a unit size split in a ligl frequency band, split the transformation residual block by quadrisecdrng the transformation residual block and repeatedly quadrisecti ng a smallest low frequency hand in the quadrisected trans formation residual block, split the transformation residual block into frequency band units having the same size, split the transformation residual block by connecting a horzontal frequency and a vertal l frequency having the same value, or determine a split size according to frequency bands of the transformation residual block by using image characteristics of the transformation residual block determined by using trans formation coefficieR s of the transformation residual block, and spit the transformation residual block according to the determined split sie according to frequency bands. [2391 in pecation 2050, the effective coefficient flag generator 1520 generates an effective coefficTent Mhag according to frequency band units wherein the effective coefficient flag indicates whether a nouzero effective transonmaion coefficient exists in each frequency band unit, le effective coefficiem flag may not be separtely generated for a smallest frequency band unit from among the frequency band units of the trans formation residul blockA Also, the eTac ive coefficient encoder 1530 encodes a sig nificance map indicating locations of the effective transformation coefficients and level information of the. effective transformation coefficients with respect to the frequency band units, in which the effective coefficient flags are not 0, i.e., the frequency band units including the effective transformaion coefficients, while scanning the trans formation residual bIock according to a predetennined scanning order or independently scanning each frequency band unit, as described above wih reference to Fi~O NA, 17B, 1A, and 18K. 2401 According to a method and an apparatus for encoding a residual block according to one or more exemplary embodiments as described above, information about an effective transformation coefficient may be effic~iently encoded according to dis tribution characteristics of the effective transformation coefficient in a transformation residual block having a size that is greater than oc equal to i !16 by spitting the transformation residual block into frequency band units. Thus a transformation residual block having a large size is split into frequency band units, and an effective coefficiem flag indicating an existence of the effective omsformation coefficiet is generated according to frequency band units, Accordingly, a scanning process of a 40 frequency band, in which an effective transformation coefficient does not exist in the transformation residual block, may be skipped and a number of bits gnredto encode the effective transformation coefficient may be reduced. 2411 FIG. 2 1 is a block diagram of an apparatus 2100 for decoding a residual block, according to an exemplary embodiment, While not restricted thereto, the apparatus 2100 may concspond to the entropy decoder 520 of PIG. 5 or be included in the entropy decoder 520. .2421 Referring to FKI 21 the apparmus 2100 includes a frequency band splitter 2110, an effecive frequency band determiner 2120, and an effective coefficient decoder 2130. 243] The frequency band spliter 2110 splits a transformation residual blK into prede termined frequency band units. In detail. as described with reference to JIGs, 16A through 1614, the frequency band splitter 2110 may split the transformation resdual block in such a way that a unit size split in a low frequency band is smaller than a unit size split in a high frequency band, split the transformation residual block by quadirisecting the transformation residual block and repeatedly quadrisecting a smallest low frequency band in the quadrisected transformation residual block, split the trans formatio residual block into frequency hand units having dhe same size, split the transformation residual block by connecting a horizontal frequency and a vertical frequency Paving the same value, or determine a split size according to frequency bands of the transformation residual block by using image characteristics of the trans formation residual block determined by using transformation coefficients of the trans formantin residual block, and split the transfmation residma block according to the determined split size according to frequency bands. A spit form of the transformation residual block may be predetermined by an encoder and a decoder, though it is un ders tood that another exemplary embodiment is not limited thereto. For example, according to another exemplary embodiment, when a predetermined split index is set for each split form and information about a split index used to split a current tras formation residual blAck is added to a bitsueam during encoding, the frequency band splitter 2J 1i0 may determine which snipT form was usd to split the current trans formation residual block based on the information about the split index included in the bitstream. t24j The effective frequency band determiner 2120 extracts an effective coefficient flag from a bitstream. wherein the effective coefficient flag indicates whether an effective transforation coefficient exists according to the frequency hand units obtained by spitting the transformation residual block. The effective frequency band determier 2120 may determine a frequency band unit including an effective transformation co efficient from among the frequency band units by using the effectve coefficient flag. For example, when the transformation residual block 1820 of IG. 18B is used, the 41 effective coefficient lags of the frNquene hand units 1821 through 1823 hue a vue of , and tie effective coefQient6flags of the |fequency hand units 1824 through 1827 have a value of 0. Thus. the effective frequency band determiner 2120 may determine the frequency hand units including the effective transformation coefficients from the extracted effective coefficient flags according to the frequency bands, 2451| The effective coefficient decoder 2130 decodes the effective transformation coef ficienus in the frequency band units that are determined to include the effective rans formation coefficiens by the effective frequency band determiner1 20. In detail, the effective coeffcient decoder 2130 extracts a significance map indicating locations of the effective transformnation coefficients and level information of the effective trans formation coefficiens, from the bitstream. Also, as described above with reference to FIGs, 17A and 17B, h effective coefficiem decoder 2130 determines the locations of the effective transformation coetticients in the transformation residual block by using the significance map, and restores values of the effective transonnion coefficients by usig the level information while scanning the enre transformation residual block or scanning each frequency band unit according to a predetermined scanning order that is independent for each fiequency' band unit [2461 FiG. 22 is a flowchart illustrating a method of decoding a residual block, according to an exemplary embodimem . 247 Referring to FI 22, in operation 2210, the effect e frequency band determiner 2120 extracts an effective coefficient flag from an encoded bitsweamn. wherein the effectve coeffiren flag indicates whether an effective transformation coefficiem exists according to frequency band units obtained by splitting a transformation residual blxck of a current bock. [2481 In operation 2220 the frequency band splitter 2110 splits the transformation residual bhok into the frequency band units As described above with reference to FGs, 16 A through 163 the frequency band splitter 21 10 may split the transformation residual block in such a way' that a unit size split in a low frequency band is smaller than a unit size split in a high frequency hand, split the transformation residual block by quadrisecting the transformation residual block and repeatedly quadrisecting a smallest low frequency band in the quadrisected transformation rsidual block, split the trans ornation residual block into frequency band units having the samesize, split the transformation residual block by connecting a horizontal frequency and a vertical frequency having the same value or determine a split size according to frequency bands of die transformation residual block by using image characteristics of the trans formation residual block determined by using transformation coefficients of the trans formation residual block, and split the transformation residual block according to the determined split size according to frequency bands. Such a split form may be prede- 42 termiined withn an encoder, or may be determined by usng information about a splt index separateiv added to the encoded bitstream Moreover. it is understud that up erations 2210 and 2220 may be switched in order or performed simltaneouasiy or sub stantially sirmulhaneously. [249] In operation 2230, the frequency band splitter 2 110 determines a frequency band unit including an effective transformation coefficient fronm among the frequency band units. by using the extracted effective coefficient flag, The effective coefficient decoder 2130 restores the effective transformation coefficient by using a significance map about the frequency band un it determined to include the effective transformation coefficient, and level information of the effective transformation coefficit. 250] According to one or more exemplary embodimets, an effective coefficient flag in dicating existence of an effective transiormation coefficient is generated according to frequency band units, so that a scanning process of a frequency band skips a trans formation residual block in which an effective transformation coefficient does not exist, and a number of bits generated to encode the effective transformation coefficient is reduced. [25!1 While not restricted thereto, an exemplary embodiment can also be embodied as computer readable code on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random- access memory (RAMt), CD ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer readable recording medium can also be distributed over network coupled counter systems so that the computer readable code is stored and executed in a distributed fashion, 252 While exemplary embodiments have been particularly shown and described, it wil be understood by one of ordinary skill in the art that various changes in form and details may be made her-ein without departng from the Tint and scope of the invenive concept as defined by the following chims, The exemplry embodiments should be considered in a descritive sense only and not for purposes of lImitation Therefore, the scope of the invenive concept is defined not by the detailed description of the exemplary embodiments, but by the flowing claims, and all differences within the scope will be construed as be included in the present inventve concept [253], J251]