AU2015201329C1 - Method and apparatus for encoding residual block, and method and apparatus for decoding residual block - Google Patents

Abstract

Methods and apparatuses for encoding and decoding a residual block are provided. The method of encoding the residual block includes: generating a prediction block of a current block; generating a residual block based on a difference between the prediction block and the current block; generating a transformation residual block by transforming the residual block to a frequency domain; splitting the transformation residual block into frequency band units; and encoding effective coefficient flags indicating frequency band units, of the frequency band units, in which nonzero effective transformation coefficients exist.

Description

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 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 8x8.

Disclosure of Invention Technical Problem [31 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.

[5a] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for tile purpose; of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art. base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each-claim of this application.

[§b] Where the terms "comprise'-, "comprises", "comprised” Or "compisingf are used ii thisispeeificafibn (including the claims) they are to: he interpreted as specifying the presence of the stated features, integers, steps or component hut nofpeeluding the presence of one or more other features, integers, steps or components, or group thereof Brief Description of Drawings [6] MG. I is a block diagram of an apparatus for encoding a video, according to an exernpl ary enibo di i wentt [1] FIG. 2 is a block diagram of an apparatus for decoding a video, according to an exemplary embodiment; FIG. 34a diapbm fordescribing a concept of eodingpiils according to art exemplary embodiment; FIG. A is a block diagram of an image encoder based on coding units according to art exemplar)·· embodiment; FIG. 5 is a block diagram of an image decoder based on coding units according to ait exemplary embodiment; FIG. 6 is a diagram illustrating deeper coding units according to depths, and partitions according to an exemplary eni ixxlimont: FIG. 7 %·& diagram for describing a relationship between a eodmg unit and. transformation units, according to an exemplary embodiment;: FIG, 8 Is a diagram tor closer; ding encoding information or codmg units epr#--,>pood mg ίο a coded depth, according to an exemplary embodiment;: FIG, 9 is a diagram of deeper coding units aecoreling to depths, ae|pf§ih|:p;:£i| exemplary embodiment; FIGs, 10 through 12 are diagrams for describing a relationship between..coding, units, prediction units, and transformation units, according to one or more, exemplary embodiments ; FIG; 13 is a diagram for describing a relationship between a coding unit, a prediction unit or a pari ition, and a transformation unit, according to encoding mode information of exemplary Table 1 below, according to an exemplary embodiment; FIGs. 14A through I4C ore reference diagrams for describing a process of encoding a transformation residual block in a related technical field; FIG. 15 Is a block diagram of an apparatus for encoding a residual block, according to an exemplary embodiment; FIGs. 16Λ through 16J are diagrams for describing splitting of a tmnsfoimaridn residual block into predetermined frequency band units, according to one (>r pore exemplary embodiments; FIGs. 17 A and 17 B are reference diagrams for describing a process of ebixiSing an effective transformation coefficient, according to one or more exemplary embodiments; FIGs. 18A and 18B are reference diagrams for describing in detail a process of encoding a residual block, according to an exemplary embodiment; FIGs. 19A and 19B are reference diagrams for describing encoding information of a transformation residual block, which is generated by an effective coefficient encoder, according to one or more exemplary embodiments; FIG. 20 is a flowchart illustrating a. method of encoding a resifhgl block, |eeording to an exemplary embodiment; FIG. 21 is a block diagram of an apparatus for decoding a residual block, according to an exemplary embodiment; FIG. 21 is a block diagram of an apparatus for decoding a residual block, according to an exemplary embodiment; and 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

According to a first aspect, the present invention provides a method for decoding an image, the method comprising: extracting information about a maximum size of a coding unit from a bitstream; splitting the image into a plurality of maximum coding units based on the information about the maximum size of the coding unit; hierarchically splitting a maximum coding unit among the plurality of maximum coding units into a plurality of coding units; determining one or more transformation residual blocks from a coding unit among the plurality of coding units, wherein the one or more transformation residual blocks includes frequency band units; obtaining an effective coefficient flag of a frequency band unit among the frequency band units from the bitstream, the effective coefficient flag of the frequency band unit indicating whether at least one non-zero effective transformation coefficient exists in the frequency band unit; when the effective coefficient flag indicates that at least one non-zero transformation coefficient exists in the frequency band unit, obtaining transformation coefficients of the frequency band unit based on location information of the non-zero transformation coefficient and level information of the non-zero transformation coefficient obtained from the bitstream; and inverse-transforming on a transformation residual block including the frequency band unit based on the transform coefficients of the frequency band unit, wherein the transformation coefficients of the frequency band unit are a subset of transformation coefficients of the transformation residual block, and wherein, when the frequency band unit is not a first frequency band unit having a lowest frequency, the effective coefficient flag of the frequency band unit is obtained , and wherein, when the frequency band unit is the first frequency band unit having the lowest frequency, the effective coefficient flag of the frequency band unit is not obtained.

There may be provided 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; 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.

The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises splitting the transformation residual block such that a unit size split in a low frequency band is smaller than a unit size split in a high frequency band.

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.

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.

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.

The method of the exemplary embodiment, wherein the splitting the transformation residual block comprises: determining an image characteristic of the transformation residual block by using transformation coefficients of the transformat ion 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 residua! block according to the determined split size.

Tire 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.

The method of the exemplary embodiment, wherein the encoding the effective coefficient flags comprises not separately encoding an effective coefficient flag with respect to a smallest low frequency band unit from among the frequency band units.

The method of the exemplary embodiment, further comprising encoding a significance map indicating locations of the effective transfonnaiion coefficients existing in the frequency band units having the nonzero effective transformation coefficients, from among the frequency band units.

The method of the exemplary embodiment, wherein the. encoding die 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.

The method of the exemplary embodiment, when·in the encoding the significance map comprises encoding a flag indicating the locations of the. effective transformation coefficients existing in the frequency band units having die nonzero effective transformation coefficients by reading ail of the effective transformation coefficients in the transformation residual block according to a predetermined scanning order.

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 band 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.

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 Conns is added to an encoded bitstream comprising the effective coefficient flags.

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 subtractor 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.

According to an aspect of another exemplary embodiment, there is provided a method of decoding a residual block, the method including; extracting effective coefficient flags from an encoded bitstream, the effective coefficient flags indicating frequency band units in which nonzero effective transformation coefficients exist, from among split frequency band units obtained bv splitting a transformation residual block 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 fern among the split frequency bpptaits obtained by splitting the transformation residual block, by. using the extracted effective coefficient flags.

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 uun. size splii in a high frequency band,;

The method of the another exemplary embodiment, wherein the spiining the transformation residual blrtck comprises quadrisectiug the translbrmation residual block, and quadriseciiog a lowest frequency band of the quadriseeled transformation residual blocks.

The method of the another exemplary embodiment wherein the splitting the transformation residual block comprises splitting the transformation residual block into frequency baud units having a same size.

The method of the another exemplary embodiment, wherein the splitting the trans-ίυιτηηύυη residual block comprises splitting the transformation residual block by connecting a horizontal .frequency and a vertical frequency having a. same value at. pre-deteimined intervals.

The method of the another exemplary embodiment, wherein the splitting the information residual block comprises: extracting split form index information from the encoded bitstream, the split form index information indicating a spin form used to split the transformation residual block, from among a plurality of split forms that are predetermined according to sizes and shapes of the frequency band units; and splitting the transformation residual block into the frequency band units according to the extrapsd splir form index information.

The method of the another exemplary embodiment, fudher comprising: extracting a significance map from the encoded bitstream, the significance map indicating locations of nonzero effective transforrnation eoefficionrs existing in frequency hand units having the nonzero effective transformation coefficients, from among the frequency band units; and determining the locations of the nonzero effective trtosfematkM coefficients existing in the frequency band units having the .nonzero effective· truns·· i'oi'n:avion coefficients by using the significance map.

The method of the another exemplary embodiment, wherein the significance map indicates the locations of the effective transformation coefficients in the frequency hand units according to a predetermined scanning order independent for each of the frequency band units.

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 transformation residual block.

The method of the another exemplary embodiment, wherein the significance map comprises a flag indicating a last effective transformation coefficient existing in a frequency band 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 a flag indicating a last effective transformation coefficient existing in the transformation residual block.

According to an aspect of another exemplary embodiment, there is provided an apparatus for decoding a residual block, the apparatus including: a parser which ex#acts effective coeftlcieni flags from an encoded bitstream, the effective coefficient flags indicating frequency band units in which nonzero effective transformation coefficients exist, from among split frequency band units obtained by splitting a transformation residual block of a current block; and an entropy decoder which splits did transformation residual block into the split frequency band units, and determines a frequency band unit having an effective transformation coefficient.from among the split frequency band units obtained by splitting the transformation residual block, by using the extracted effective coefficient ii|0||

According to an aspect of another exemplary embodiment, there is provided a method of encoding a residual block, the method including: generating a transformation residual block by trmsform||0:q:r|sidual block to a frequency domain; splitting the transformation residual block into frequency band :unlts||||ineq||hg effective coefficient flags indk.a t i n g frequency band units, of the frequency band units, in which nonzero effective transformation eoeffideniy J^f|f Mode for the Invention

Hereinafter, exemplary embodiments will be described more fully 'with reference to foe accompanying drawings, it is understood that expressions such as :'at least one off· when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

In the exemplary embodiments, 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! encoded image data is decoded at a decoder side, iAlso, a coded depth refcm to a depth where a coding unit is encoded.

FIG. ! is a block diagram of a video encoding apparatus ! 00, according to an exemplary embodiment, Referring to FFG. 1, the video encoding apparatus JUO deludes a maximum coding uni· splitter 110, a coding unit determiner 120, and an output uni: 130.

The maximum coding unit splitter 1:.1.0 may split a current picture of an linage based on a maximum coding unit for the current picture. If the current picture is larger than the maximum coding unit,; image data of the current, picture may he split into the «t least one maximum coding unit. The maximum coding unit according to an exemplary embodiment may be a data unit having a size of 32x32. 64x64. 128x128, 256x256, etc., wherein a shape of lire data unit is a square having a width and length in squares of 2, The image data may be output to the coding unit determiner 120 according to t|| maximum coding unit. A coding unit according to an exemplary embodiment may be characterized by a maximum size and a depth. The depth denotes a number of times the coding unit is spatially split from the maximum coding unit, and as the depth deepens, deeper encoding units according to depths may be split from tbs maximum coding unit to a minimum-coding unit, A depth of the maximum coding unit is an uppermost depth and: -a depth of the minimum coding unit is a lowermost depth. .Since a size of a coding unit corresponding to each depth decreases as the depth of the maximum coding unit deepens, a coding unit corresponding to an upper depth may include a piuraiity of coding units corresponding to Lower depths.

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 according to an exemplary embodiment is spilt according to depths, the image data, of a spatial domain included in the maximum coding unit may be hierarchically classified according to depths, A maximum depth and a maximum size of a coding unit, which limit the total number of times a height and a width of the maximum coding unit can be hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split region obtained bv splitting a region of the maximum coding unit according to depths, and determines a dentil to output encoded image data 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 current picture, and selecting a depth having the least encoding error. Thus, the encoded Image dans o! the coding unit corresponding to the determined coded depth is output to the output unit 130. Also, the coding units epjpspoatingie the coded depth may be regarded as encoded coding units.

Tire determined coded depth and the dr-tedded imisgetiaia accorlihg to the determined c(x!ed depth are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deeper coding units corresponding to at 'seas: one depth equal to or below the. maximum depth, and results of encoding the image data are compared based on each of the deeper coding units, A depth having the least encoding error may he selected after comparing encoding1·, errors of the deeper coding units. At least one coded depth may be selected for each maximum coding unit.

The size of the maximum coding unit is split as a coding unit is hierarchically split according to depths, and as the number of coding units increases. Also, evert if coding units correspond to a same depth in one maximum coding unit, it is determined whether to split, each of the coding units corresponding to the same depth to a lower depth by-measuring an encoding error of the image data of each coding unit, separately. Accordingly, even when image data is included in one maximum coding unit, the image data is split urregionis according to the depths and the encodingerrors may· differ according to regions in the one maximum coding unit, and thus the codfed depths may differ according to regions in the image data, Therefore, one or more coded depths may be determined in one maximum coding unit, and the image data of the maximum coding unit may be u i v ided accord its g to coding units oi at least one coded depth.

Aiitirdingly, the coding unit determiner 120 may determine coding units having a tree structure included in the maximum coding unit. The. coding units having a tree SfHteture according to an exemplary embodiment include coding units corresponding to a depth determined to be the coded depth, from among deeper coding units included in the maximum coding unit. A coding unit of a coded depth may be hierarchically determined. according to depths in the same region of the maximum coding unit, and may be independently determined in different regions. Similarly, addded depth in a current region may be independently determined from a coded depth in another region. A maximum depth according to an exemplary embodiment is ail index related ip a number of splitting times from a maximum coding unit to a minimum coding unit. A first maximum depth according to an exemplary embodiment may denote a total hpiber of splitting times from the maximum coding unit to the minimum codinjpnit. A second maximum depth according to an exemplary embodiment may denote a total number of depth levels from the maximum coding unit to lie minimum coding unit. For example, when a depth of the maximum coding unit is 0, a df|th of a coding unit in which the maximum coding unit is spilt Price friay he set to i, and a depth of a coding unit in which the maximum coding uni t is split twice may he set to 2. Here, if the minimum coding unit is a coding unit in which the maximum coding unit' is split four times, 5 depth levels of depths 0, 1.2, 3 aril 4 exist. Tims, the first maximum depth may be set to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may he performed according to the maximum coding unit. The prediction encoding and the transformation are also performed based on the deeper coding units according to a depth equal to or depths less than the maximum depth, based on the maximum coding unit. Transformation may be performed according to a method of orthogonal, transformation or integer transformation.

Since the 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, Tor convenience of description , the prediction encoding and the transformation Wifi hereinafter be described based on a coding unit of a current depth, in a maxim um coding unit.

The video encoding apparatus:fOO may variously select at least one of a size and a shape of a data unit, for encoding the image data. In order to encode the image data, operations,: such as prediction encoding, mans formation, and entropy encoding,;: oily be peilbiMei, and at this time, the same data unit may be used for all operations or urfiereni data units may be used for each operation.

For example, die Video encoding apparatus 100 may select a coding unit ft®|l||||tg the image data and a|ii& unit different from the coding tpi|8rf:afsp perform the prediction encoding on the image data in the coding unit. hi order to perform prediction encoding in the maximum coding unit, the prediction encoding may be performed based on a coding unit corresponding to a coded depth, i.e„ based on a coding unit that is no longer split to coding units corresponding to a lower depth. Hereinafter, the coding unit that is no longer split, and becomes a basis unit for prediction encoding will be referred 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 prediction unit.

For example, when a coding unit of 2Nx2N (where N is a posi tive integer) is no longer split and becomes a prediction unit of:INx2N, a. size of a. partition maybe 2Nx2N, 2NxN, Nx2N, or NxN. Examples of a partition type include symmetrical partitions that are obtained by symmetrically splitting at least one of a height and a width of the prediction unit, partitions obtained by asymmetrically splitting die height op the width of the prediction unit (such as Imor n:l), partitions that are obtained by geometrically splitting the prediction unit, and partitions having arbitrary shapes. Λ prediction inode of the prediction unit may be at leal! one of au infra mode, a inter mode, and a skip mode. For example, the intra mode or the inter inode may be performed on the partition of 2Nx2N, 2NxN, Nx2N, or NxN. In this case, the skip mode may be performed only on the partition of 2Nx2N, The encoding is independently performed oh one prediction unit in a coding unit. thereby sefocung a prediction mode having t least encoding error.

The video encoding apparatus 100 may also perform the frassfoaliation 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 codfhgpmiv. in order to perform the transformation in the coding unit, the transformation may be performed based on a data unit having a size smaller than or equal So She coding unit. For example, the data unit .for fee iimtsformatiem may include a dplfotif folia intra rruxie and a data unit for an inter mode. 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 fvidth of the coding unit may also be set. in the transformation unit. For example, in a current coding unit of 2Nx2N, a transformation depth may be 0 when the size of a transformation unit is also 2Nx2N„ may he I when each of the height and width of the current coding unit is split into two equal pasts, totally split into 4Ai transformation units, and the size of the iranslonnadon unit is thus NxHy:hidimay be 2 when each, of the height and width of the current coding unit is split into four equal parts, totally split Into 4Λ2 transformation units, and the size of the transformatjon unit is thus N/2xN/2. For example, the transformation an it.may be set according to a hierarchical tree stnieutre, in which a transformation unit of an upper transformation depth is split into tour transformation units pf|& lower transformation depthiceordin| to hierarchical characteristics of a transformation depth,:

Similar to the coding unit, the transformation unit in the coding unit may be recursively split i||f|fjnaller sizedsmgfonsv s° that the transformation unit may be d6W iermined independently in units of regions. Thus, residua] data in the coding unit may besdivided according to the ttahKibrmatien having the tree structure according to transs formation deptlst

Encoding information according to coding units corresponding to a coded depth uses mformaiion about the coded depth shlahfonmtion related to prediction, encoding anti transformation. Accofolngly, tie coding unit determiner 120 determines a cocks] depth living 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 foansformation.

Coding units according to a tree structure in a maximum coding unit and a niedipdpf determining a partition, according to exemplary embodiments, will be described m detail 3.ater with reference to FTGs, 3 through 12,

The coding unit determiner 120 \Wfy measure an encoding error of deeper eodi% units according to dbpths by using Rate-Distortion Optimization based on Lagrangian multipliers.

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

The encoded image data may beobiained by encoding residual date of an image.

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

The information about the coded depth may be defined by using split information according to depths, which indicates whether encoding is performed on coding units of a lower depth instead of a current depth. If the current depth of the current coding unit is the coded depth, image data in the current coding unit is encoded and output. In this case, me split information may be defined to not split the current, coding unit to a lower depth. Aifelftiliy, 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 litis case, the split information may be defined to split the current coding unit to obtain the coding units of the lower depth.

If the current depth is not the coded depth, encoding Is performed on the coding unit that is split into the coding unit of the lower depth, 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 for the coding unite having the same depth.

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

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

The minimum unit according to an exemplary embodiment is a rectangular· data unit obtained by splitting the minimum etKiing unit of the lowermost depth by 4-, Alter· nauvciy, the minimum unit may be a maximum rectangular data unif|j|f:i|§y;be included in ail of the coding units., prediction units, partition units, and transformation «nits included in the maximurn coding unit.

For example, the encoding information output through the output uniildlidhuy hes classified into encoding information according to coding units and encoding information according to prediction units. The encoding information according to the coding units may include the information about the prediction mode and the size of the partitions. The encoding information according to the prediction units may include information about an estimated direction of an inter mode, a reference image index of the inter mode, a motion vector, a chroma component of an intra mode, and an interpolation method of the intra mode. Also, information about a maximum size of the coding unit defined according to pictures, slices, or GOPs, and information about a maximurn depth may be inserted into at least one of a Sequence Parameter Set (SI’S) or a header of a bitstream. in the v ideo encoding apparatus 1(50, 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 an 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 of the coding unit of the lower depth may 1¾ NxN. Also, the coding unit of the current depth having the size of 2Nx2N may include maximum 4 of the coding unit of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coiling units having fee tree .structure by determining coding units having an optimum shape and an optimum size for each maximum coding unit, based on the si/e of the maximum coding unit ars:i::: the maximum depth determined considering characteristics of the current picture. Also, since encoding may be performed on each maximum coding unit bym|fh|::§«y one of various prediction modes and trun'dbnnadons, an optimum encoding mode, may be determined considering characteristics of the coding unit of various image sizes,

Thus, if an imaphaving high resolution or a large amount of data is encoded in a related an rnacroblock, a number of macrobioekx per picture excessively increases, Accordingly, ai iiumber of pieces of compressed information generated:for each macroblock increases, and thus it is difficult: to transmit the compressed information and data, compression efficiency decreases, ilovyever, by using the video encoding apparatus 100 adebMing to an exemplary embodiment, image compression efOciency may be increased since a coding unit is adjusted while considering chtirac tens tics of an image and increasing a maximum size of a coding unit while considering a size of fee image, FIG. 2 is a block diagram of a video decoding apparatus 200, according to as Exemplary ernbt )di ment.

Referring to FIG. 2, the video decoding apparatus 200 includes a receiver 210, an image data and encoding information extractor 220, and an image data decoder 230. Definitions of various terms, such as a coding unit, a depth, a prediction unit, and a transformation unit, and information about various encoding modes for various operations of the video decoding apparatus 200 are similar to those described above with reference, to FIG. I.

The receiver 210 receives and parses a bitstream of an encoded video. The image data and encoding information extractor 220 extracts encoded image data for each coding unit from the parsed bitstream, wherein the coding units have a tree structure according to each, maximum coding unit, and outputs the extracted image data to the image data decoder 230. The image data and encoding information extractor 220 may extract information about a maximum size of a coding unit of a current picture from a header about the current picture or an SPS,

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

The ivsforrnation about the coded depth and th|':eilb|iig mode according to the maximum coding unit may be set fos information about a?. least one cod·tig unit corresponding to the coded depth, and information about an encoding mode may include information about at least one of a partition type of a corresponding coding unit corresponding ίο the coded depth, a prediction mode, and a size of a transformation unit. Also, splitting information according to depths may be extracted as the information about the coded depth. ihl information alxaii the coded depth and the encoding mode according to each maximum coding unit esiracted by the image data and encoding infos mutton extractor 220 is infosmation about a coded depth and an encoding mode dcicrmmed to generate a minimum encoding error when an encoder, such as a video eneodissg appas’atus : (30 according to an exemplary embodiment, repeatedly performs encoding for each deeper coding unit based on. depths according to each maximum coding unit. Accordingly, the video decoding apparatus 200 may restore an image by decoding the image data according to a coded depth and an encoding mode that generates die minimum encoding error, infestation about die coded depth gasp the encoding mode may be assigned to a predetermined data unit from among a corresponding coding unit, a prediction unit, and a minimum unit, the image data and encoding information extractor 220 may extract the information about the coded depth and the encoding mode according to the predetermined data units. The· predetermined data units to which the same information about the coded depth and the encoding mode is assigned may be the data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding the image data, «reach maximum coding unit based on the information about the coded depth and the encoding mode according to the maximum coding units. For example, the image data dMouer 230 may decode the encoded image data based on the extracted information about the partition type, the prediedon mode, and the transformation unit tor each coding unit from among the coding units having the tree structure included in each maximum coding unit, A decoding process may include a prediction including intra prediction and motion compensation, and an inverse transformation, inverse trans-formatioa may be performed according: to a method of inverse orthogonal tratm formation or in verse integer transformation.

The image data dec£sdOr :230 may perform at least one of infra prediction and motion compensation according to a partition and a prediction mtjde of each coding unit, based on the information about the partition type and the prediction mode of the prediction unit of the coding unit according to coded depths.

Also, the image data decoder 230 may perform inverse iranrtorm&tion according to each transformation unit in die. coding unit, based on the information about tipsmiiof the transformation unit of the coding unit according to coded depths, so as to perform the inverse Iransionnation according to maximum coding units.

The image data decoder 230 may determine at least one aided depth of a current maximum coding unit by using split information according to depths. If the split information indicates that:image data is no longer split in the current depth, the current depth is a coded depth. Accordingly, the image data decoder 230 may decode encoded data of at least one coding unit corresponding to the each coded :||||i:||s||ecurrent maximum coding unit by using at least tine of the information about the partition type of the prediction unit, ^prediction mode, and the size of the transformation unit for each coding unit corresponding to the coded depth, and output the image data of the current maximum coding unit.

For example, data units including the encoding information having die same split information may be gathered by observing the encoding information set assigned for the predetermined data unit from among the coding unit, the prediction unit, and the minimum unit, and the gath^eetttaiiHH^m^h^tmsidered to be «MiBeit to be decoded by die image data decoder 230 in the same encoding mode.

The videmdecoding apparatus 2¾} may obtain unit -::01 generates the minimum encoding errtir when encoding is recursively performed tor each maximum coding unit, and may use the information to decode the current picture. That is, the coding units having the tree structure determined to be the optimum coding units in each maximum coding unilipijiy'lsi^ oiaxinrurn size oi the coding unit may be determined considering at least one- of resolution and an amount of image data.

Accordingly, even if iinageidatahashigh resolution and a large amount of data, the :image data may be efficientif decoded and restored by using a size of a coding unit and an encoding mode, wM|h are adaptively determined according to characteristics of the image data, and information about an optimum encoding mode received from an encoder. A method of litetmlningeodlng units having a tree structure, a prediction unit, and a trahSformatfon unit, according to one or more exemplary embodiments, will now be described with reference to FIG.s, 3 through 13. EIG..3 is a diagram for describing a concept of coding units according to an exemplary embodi meat, 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 parti lions of 64x64, 64x32, 32x64, or 32x32, and a coding unit of 32x32 may be split into partitions of 3lx3l,i3liilj 16x32, or 16x16, a coding unit of 16x16 pray be split into partitbins of !6xi6, 16x8,8x1.6, or 8x8, and a coding unit oi 8x8 may be split into partitions of 8x8, 8x4, 4x8, or 4x4.

Referring to PIG. 3, there is exemplariiy provided first video data 310 with a resolution of 1920>: 1080, and a coding unit with a maximum size of' 64 and a maximum depth of 2. Furthermore, there is exempknly provided second video data 320 with a resolution of 1920.x 108(), and a coding unit with a maximum size of 64 snd a maximum depth of 3, Also, there i|; exemplariiy provided third video data 330 wish | resolution of 352x288, and a.coding unit with a maximum size of 16 and a maximum depth of i. The maximum depth shown in FIG. 3 denotes a vital number of splits from a maximum, coding unit to a minimum decoding unit.

If a resolution is high ora data amount is large, a maximunrslxe ofra coding nnit 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 data 310 and 320 having the higher resolution than the third video data: 330 may be 64,

Since the maximum depth of the first video data 310 is 2, coding units 315 of the first video data 310 may include a maximum coding unit having a long axis size of 64, and coding units having long axis sizes of 32 and 16 since depths are deepened to two layers by spin ting tits maximum coding unit twice. Meanwhile, since the maximum depth of ώε third video data 330 is 1, coding units 335 of the third video data 3'30 may: include u maximum coding unit having a long axis size of 16, and coding rants having a long axis size of 8 since depths are deepened to one layer by splitting the maximum coding unit once, jSjhefe the maximum depth of the second video data 320 is 3. coding: units 325 of the sseeond video data 320 may include a maximum coding unit having a long axis size of 64, and coding units having long axis sizes of 32,16, and 8 since the depths are deepened to 3 layers by splitting the maximum coding unit three limes. As a depth deepens, detailed information may be precisely expressed. FIG. 4 is a block diagram of an image encoder 400 based on coding units, according to an exemplary embodiment.

The image encoder 400 may perform operations of a coding unit determiner 320 of a video encoding apparatus 100 according to an exemplary embodiment to encode image data. That is, referring to PIG, 4, an intra predictor 4!0 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 compensation on coding units, from among the current frame, in an inter mode by using the current frame 405 and a reference frame-495.

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

In order lor the image encoder 400 to be applied in the video encoding apparatus 100, eiemsms of the image encoder 400, i.e., fh·::· intra predictor 410, ihe motion estimator 420, the motion compensator 425. the transformer 430, the quantizer 440, the entropy encoder 450, the inverse quantizer 460, the inverse t/ansfonner 470, the deblocking unit 480, and the loop filtering unit 490, perform operations based on each coding unit flom among coding units having a tree structure while considering the maximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and the motion com- pensmoj 415 determine partitions and a prediction mode of each coding unit from among the coding units having a tree structine while considering a maximum ipge and . a maximum depth of a current maximum coding unit, and the transformer 430 determines the sire of the transformation nnii in each coding unit from among the coding units having a tree structure.: FIG. 5 is a block diagram of an image· decoder 500 based on coding units, according to an exemplary embodiment.

Referring to FIG. 5, a parser 510 parses encoded linage data to be decoded and information about encoding used for decoding from a bitstream 505. The encoded image data is output as inverse quantized data through an entropy decoder 520 and an inverse quantizer 530, and the inverse quantized data is restored to image data in a spatial domain through an .inverse transformer 540.

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

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

In 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 5.10.

In order lor die Image decoder 500 to be applied in the video decoding apparatus 200, elements of the hbage decoder 500, i.e., the parser 510, the entropy decode·· 520, the inverse quani;/.cr 530, the iι1verse transformer 540, the intra predictor 550, the motion compensator 560, the deblocking unit 570, and the loop filtering unit 580, perform operations based on coding units having a tree structure for each maximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560 perform operations based on partitions and a prediction mode for each of the coding units having a tree structure, add the inverse transformer 540 performs operations based on a size of a transformation unit for each coding unit, FIG·. 6 is a diagram, illustrating deeper coding units according to depths, and partitions, according to an exemplary embodiment. A video encoding apparatus 100 and a video decoding apparatus 200 according to exemplary embodiments use hieraichical coding units so as to consider characteristics of an image. A maximum height. a maximum width, and a maximum depth of coding units ma.y be asI;A:>= i vdy deternii ned according to the- eha? aeterisiks of the image, or may be differently set by a user. Sizes of deeper coding units according Its depths may be determined according: to the predetermined maximum size of the coding urni.

Referring a> FIG, 6, in a hierarchical structure 600 of eroding units, a§|*«phg to tin exemplary embodiment, the maximum height and the mHxirrrurn width of the coding units are each 64, and the maximum depth is 4. Since a depth deepens along a vertical axis of the hierarchical structure 600, a height and. a width of a deeper coding unit art-each split. Also, a prediction unit and partitions, which art bases for prediction encoding of each deeper coding unit, are shown along a horizontal axis of the hierarchical structure 600,

Thai is,: a first coding miitbli) is a maximum coding unit in the hierarchical structure 600, where!n a depth is 0 attd a size, ie„ a height:by width, is 64x64. The depth deepepshiong the vertical 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 16xi 6 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 unit 650 having the size of 4x4 and the depth of 4 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arranged along the horizontal axis according to each depth. That, is, if the 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 u size ol 64x64. partitions 612 having a size of 64x32. partitions 614 having a size of 32x64, or partitions 616 having a size of 32x32.

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, ie., a partition 620 having a size of 32x32, partitions 622 having a size of 32x16, partitions 624 having a size of 16x32, and partitions 626 having a size of 16x16.

Similarly, a. prediction unit of the third coding unit 630 having the size of 16x16 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 8x 16, and partitions 636 havingp* size of 8x8.

Similarly, a prediction unit, of the fourth coding unit 640 havi ng the size of 8x8 and the depth of 3 may he split into partitions included in the fourth coding unit 640, i.e.. a partition having a size of 8x8 included in die fourth coding unit 640, partitions 642 having a size of 8x4, partitions 644 having a size of 4x8, and partitions 646 havii^p size of 4x4. ΐ% ifth coding tmit 650 having the sizeof 4x4 and the depth of 4nis the minimum coding unit and a coding unit of the lowermost depth, A prediction unit of the fifth coding unit 650 is only assigned to a partition having a size of 4x4. in order to determine the at least one coded depth of the Citing unite of the maximum coding unit 6 SO, a coding unit determiner 120 tflp video encoding apparatus 100 performs encoding for coding units corresponding to each depth included in the maximum coding unit 6 i ft. A number of deeper coding units according to depths including data in the same range and. the same, size increases as the depth deepens, lor example, four coding units corresponding to a depth of 2 are used to cover data that is included in one coding unit eOrrespondisg to & depth of 1, Accordingly, in order to compare encoding results of the same data according to depths, the coding unit corresponding to the depth of 1 and four lading units corresponding to the depth of 2 are each encoded. in order to perform encoding for a current:depth from among the depths, a least encoding error may be selected for the current depth by performing encoding for each prediction unit in the coding units coiTespphding it) the current depth, along the horizontal axis erf the hierarchical structure ;§(.)(), Alternatively, the minimum encoding error may be searched for by comparing the least encoding errors according to depths, by performing encoding for each depth as the depth deepens along the vertical axis of the hierarchical structure 600. A depth arid 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 codiug unit 610. FIG, 7 is a diagram for describing a relationship between a coding g|fif7:|i|:iftd trans-forma! ion units 720, according to an exemplary embodiment. A video encoding or decoding apparatus 100 or 200 according to exemplary embodiments encodes or decodes an image according to coding units having sizes smaller than or equal to a maximum coding unit for each maximum coding unit. Sizes of. transformation units for Uimsformation during encoding may be selected based on data units tfiaf are not larger than a correspond.!ng coding unit.

For example, in the video encoding or decoding apparatus 100 or 200, if a size erf the coding unit 7ft! is 64x64, transform;)lion maybe performed by using the transformation units 720 having a size of 32x32.

Also, date-of the coding uilit 710 having the size of 64x64 may be encoded by .performing the transformation on each of the transformation unirs having the size ot 32x32,11x16, 8x8, and 4x4. which are smaller than 64x64, such that a transformation nmhhaving the least coding error may be selected. FIG, 8 iS a diagram for describing encoding in formation of coding units ^responding to a coded depth, according to an exemplary embodiment.

Referring to F!G. 8, an output unit 130 of a video encoding apparatus 100 according temsi exemplary embodiment may encode and transmit information 800 about a partition type, information 8)0 about a prediction mode, and information 820 about a size of a transformation unit for each coding unit arrresponding to a coded depth, as information about an encoding mode.

The information 800 about the partition type is information about a shape of a partition obtained by splitting a prediction unit of a current coding unit, wherein tie partition is a data unit for prediction encoding the current coding unit, For exalapte:*: a current coding unit CU..0 having a size of 2Nx2N may be split into any one of a partition 802 having a size of 2Nx2N, a partition 804 having a size of 2NxN, a partition: 806 having a size of Nx2N, and a partition 808 having a size of NxN, Here, lire information 800 about the partition type- is set to indicate· one of the partition 804 having a. size of 2NxN, tie partition 806 having a size of Nx2N. and the partition 808 having a size of NxN

The information 810 about the prediction mode indicates a predicrion mode o|§afif partition. For example, "he information 810 about the prediction mode may indicate a mode of prediction encoding performed on a partition indicated by the information 800 about the partition type. i.e„ an imru mode 8 i 2. an Inter mode 814, or a skip mode 816,

The information 820 about the size of a transformation unit indicates a transformation unit to be based on when transformation is performed on a current coding unit For example, the hmsibimarion unit may be a first intra transformation unit 822, a second inira transformation unit 824, a first inter transformation unit 826, or a second intra transformation unit 828;

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 800, 81:0:, and 820 for decoding, according to each deeper coding unit FIG. 9 is a diagram of deeper coding units according to depths, according to art e xem pi a ry smbt >4 i men t,

Split information may be used to indicate a change of a depth. The split information indicates whether a coding unit of a cunent depth is split into coding unit.1·; of a lower depth.

Referring to FIG. 9, a prediction unit 910 for prediction encoding a coding unit 900 having a depth of 0 and a size of 2N.J)x2N_0 may include partitions of a partition type 912 'having a size of 2N„ 0x2N_0, a partition type 914 having a size of 2\ 0xN...0, a partition type 916 having a size of NJ)x2N_0, and a partition type 918 having a size of N„0xN 0. Alhough FiC. 9 only illustrates the partition types 912 through 918 which are obtained by symmetrically splitting the prediction unit 91.0, it is understood that a partition type is not limited thereto. For example, according to another exemplary Hi :'bodiment, the partitions of the prediction unit 910 may include- asymmetrical ^partitions, partitions having & predetermined shape, and partitions having a geometrical shape,

Prediction encoding is repeatedly performed on one partition having a size of 2N. 0x2N 0, two partitions having a size of 2I| J§|N. 0, two partitions having a s$p: of N. 0x2 N...(), eptifour partitions having a size of X_.0xN 0, according to each partition type. The pfeliction encoding in an intra mode arid an inter mode may be peril>rmed Οη1:®©: parti lions h a v i n g the sixes of 2N ,.0x2N. .0, N. ...0x2 M ..0,2N„OxNj3, and N_0xN_0. The prediction encoding in a skip mode is performed only on the partition having the size of 2N J)x2N„0.

Errors of encoding including the prediction encoding in the partition types 912 through 918 are compared, and the least encoding error is determined among the partition types, if an encoding error is smallest In one of the partition types 912 through 916, the prediction unit 910 may nor be split into a lower depth.

For example, if the encoding error is the smallest in the partition type 918, a depth is changed from 0 to j to split the partition type 918 in operation 920, and encoding is repeatedly performed on coding units 930 having a depth of 2 and a size of N_._0xN. 0 to search for a minimum encoding error, A prediction -unit 94(3 for prediction encoding the ceding unit 930 having a depth of i and a size of 2N... 1 x2N_J (~N __QxN_0) may include partitions of a partition type 942 "having a size of 2N !x2N...i, a partition iii;ii:i:5 h partition type 946 having a size of N„ix2N_l, and a partition type 948 having a size of N ixN 1.....

As an example, if an encoding error is tlpplal^ depth is changed from 1 to 2 to split the partition type 948 in operation 950, and encoding is repeatedly performed on coding units 960, which have a depth of 2 and a size of K 2xN .2 to search for a minimum encoding error.

When a maximum depth is <i, split operpay he performed up to when a depth becomes d-i, and split information may be encoded as up to when a depth is one of 0 to d-2. for example, when encoding is performed up to when the depth is d-i after a coding unit corresponding to a depth of d-2 is split in operation 970, a prediction unit 990 for prediction encoding a coding unit 980 having a depth of d-1 and a size of 2N_(d-l)x2N_(d-l) may include partitions of a partition type 992 having a size of 2N._(d-1 )x2N_(d-1), a partition type 994 having a size of 2NJ'd-1 )xN_(d-1), a partition type 996 having a size of N_(d-1 )x2N_(d-1), and a partition type 998 having a size of N_(d-l)xN_(#-l).

Prediction encoding may be repeatedly performed on one partition having a size of 2iyirl)x2hya~ 0? two partitions havmg a size of 2N...(d-l)xN..(d-l). two partitions having a size of N„(d-1 )x2N.„(d - 1), four fprtidons having a size of NJd-1 )xN_(d-1 j; front among tits partition types 992 through 998 to search tor a partition type having a minimum encoding error.

Even when the partition type 998 has the minimum encoding error, since a. maximum depth is d,;» coding unit CU_(d-1) having a depth of d-1 is no longer split to a lower depth. In this case, a coded depth for the coding units of a current maximum coding unit 900 is determined to be. d-1 and a partition type of the current maximum coding unit 900 may be determined to be N_(d-l)xN„(d-l). Also, since the maximum depth is d and a minimum coding unit. 980 having a lowermost depth of d-1 is no longer split to a lower depth, split information for the minimum coding unit 980 is not set. A data unit 999 may be a minimum unit for tire curpSht maximum, coding unit. A minimum unit according to an exemplary embodiment may be a rectangular data unit oltahtod. by splitting a minimum coding unit 980 by 4, By performing the encoding repeatedly, 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 partition type and a prediction mode as an encoding mode of the coded depth.

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

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

FlGs. 10 through 12 are diagrams for describing a relationship between coding units KMC), prediction units 1060, |nd transformation units 1070, according to one or more exemp lary embodiments.

Referring to FIG. 30, dteooiing units 1010 am 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; Jfofbmng to FlGs, ί 1 and 12, the prediction units 1060 are partitions of prediction units of each of the coding nnits 10.10. and die transformation units 1070 are transformation units of each oithe boding units 10if).

When a depth of a maximum coding unit is 0 in the coding units 1010, depths of coding units JO 12 and 1054 are 1, depths of coding units 1014, 1016, 1018, 1028, 1050. and 1052 arc 2, depths of coding units 1020, 1022, J024,1026,1030,1032, and 10i| are; 3.,. and:depths of taxiing units 11)40, 1042, 104%:;$hd'5::t66 are 4.

In the· prediction units 1060, some encoding urn Is 1014, 1016, 1022,1032,1048, 1050, 1032, and '054 are obtained by splitting coding units of the encoding units 10:10. In particular, partition types in ihe coding units 1014, 1022, 4050, and 1054 have a size of 2NxN, partition types inrthe coding units 1016, 1048, $$$4052 have a size#

Nxll, and a partition type of the coding unit 1032 has a size of NxM, Prediction units and. partitions of the coding units 1.010 are smaller than or equal to each coding unit.

Transformation or inverse transfornialkm is performed on image data.of the coding:; unit 1.052 in the rpnsfoitkitioaunits 1070 in a data unit that is smaller than the e||ing unit .1052. Also, the coding units 1014, 1016, 1()22 , 1032, 1048, 1050, and 1052 of the Transformation units 1070 a!'piiil||ffenliip|B those of hie prediction units 1060 in verms of and shapes. 1'hat is, the video encoding, and decoding apparatuses 10<S and 200 according to exemplary embodiments may perform intra prediction, motion estimation, motion compensation, transformation, and inverse transformation individually on a data unit in the .same coding unit.

Accordingly, encoding is recursively performed on each of coding units having a hierarchical structure In each region of a maximum coding unit to determine an optimum coding unit, and thus coding units having a recursive tree structure may be obtained. Encoding information may include split information about, a coding unit, information about a partition type, information about a prediction mode, and information a bout a size of a transformation unit. Exemplary Table 1 shows the encoding intormatioh that may be set by the video encoding and decoding apparatuses KK) and 200.

Table 1 [Table 11 [Table |

Α·ι output unit i 30 of the video encoding apparatus 100 rni| output the encoding information about the coding units having a tree structure, and an ili|ge data and encoding information extractor 220 of the video decoding apparatus 200 may extract the encoding information about the eodttlg:units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split into coding units of a lower depth. If spilt information of a current depth d is 0, a depth in which a current coding unit is no longer Split into a lower depth, is a taxied depth. Information about a partition type, prediction mode, and a size of a transformation unit may he defined for the coded depth, if the current coding unit is further split according to the split information, encoding is independently performed on split coding units of a lower depth,: A prediction mode may he one of an infra inode, an inter mode, and a skip .mode. The infra mode and the Inter mode may be defined in all partition types, and the skip mode may be defined in only a partition type having a size of 2Nx2N.

The information about the partition type may indicate symmetrical partition types having sizes of 2Nx2N, 2NxN, Nx2N, and NxN, which are obtained by symmetrically splitting a height or a width of a prediction unit, and asymmetrical partition types having sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N, which ate obtained by asymmetrically splitting the height or the width of the prediction unit. The asymmetrical partition types having the sizes of 2N’xnO and SNxnD may be respectively obtained by splitting die height of thf pr|dictk>n unit ih ratios of. 1:3 and 3:1, and the asymmetrical partition types having the sizes of nLxfhf and nRx2N may be respectively obtained by splittingJbe width of the prediction unit in ratios of 1:3 and 3:1 He size: of the transformation unit may be set to be two types in the inira mode and two typos in the inter mode. For example, it split information ot the transformation unit is 0. the size of the transformation unit:may be 2Mx2N. which is rhe siz« of the current coding unit. If split information of the transformulion unit is 1, the transformation units may be obtained by spllning the current coding unit. Also, if a partition type of the current coding unit having the size of 2Nx2N is a symmetrical partition type, a size of as|-ansfbim:Sti|!Tinh may he NxN, end if the partition type of the current coding unitls an asymmetrical partition type, the size of the transform;* lion unit may be N/2xN/2.

The encoding information about coding units having a tree structure may include at "least one of a coding unit corresponding to a coded depth, a cod mg umi ourresponumg 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 ot h prediction unit and a .minimum, unit including the same encoding information.

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

Accordingly, if a current coding unit is predicted based on encoding intOMMidn 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.

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 die current coding unit me searched using encoding information oi tite data units, and the searched adjacent coding units may be referred for predicting the current coding U’UL FIG. 13 is a diagram for describing a relationship between a coding:mm, a prediction unit or a partition, and a transformation unit, according to encoding mode information of exemplary Table I, according to an exemplary embodiment.

Referring to FIG. 13, a maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312, 13:1:4, 1:316, and 1318 of coded depths. Here, since the coding unit 1318 is a cpling unitfof a; coded depth, split information may be set to 0. Information a bout I* partition type of the coding unit 1318 having a size of 2Mx2N may be set to he one of|: partition type 1322 having a size of 2Nx2N, a. partition type 13:24 having a size of 2NxN. a partition type 1326 having a size of Nx2M, a partition type 1328 having a sizes of ffkN, a partition type 1332 having a size of 2NxnU, a partition type 1334 having a size of 2NxnEL a partition typo 1336 having a size of ttLx2N, anti a partition type4338 haSin|il::Si:^sOf nR>;2N,

When the partition type is set robe symmetrical, i.o„ the partition type 1.122, 1324, i 32f·, or 1328, a transformation unit 1342 having a size of 2Nx2N is set if split information (TU size flag! of a transfonaation unit is 0, and a traasfarmaiioD unit 1344 having a size of NxN is set if a TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partition: type 1332,1334, 1336, or 1338, a transformation unit ; 352 having a size of 2N>;2N is serif a TU size flag is 0, and a transformation unit .1354 having a size ofN/2xN/2 is set if a TU size flag is 1.

Referring to FIG. 13, the TU size flag is a. flag having a value of 0 or 1, although it is understood that the TU size flag is not limited to 1 bit, and a transformation unit may be hierarchically split having a tree structure while the TU size flag increases from 0.

In this ease, the size of a tt’&amp;nstormation unit that has been actually used may be ex-pnessed by using a TU size flag of a transformation unit, according lo an exemplary; embodiment, together with a maximum size and minimum size of the transformation: unit. According to an exemplary embodiment, a video encoding apparatus 100 is capable of encoding maximum transformation unit size information, minimum trans-forvnation unit size information, and a maximum TU .size flag, The result ot encoding the maximum transformation unit size information, the minimum transformation unit §ize information, and the maximum TU size flag may be inserted into an SPS, According to an exemplary embodiment, a video decoding apparatus 200 may decode video by using the maximum transformation unit size information, the minimum t$ms-formation uhlt size information, and the maximum TU size illj&amp; 1 <.)·, example, if the size of a current coding unit is 64x64 and a maximum transformation unit size is 32x32, the size of a transformation unit may be 32x32 when: a TU size flag is 0, may be 16x!6 when the TU size flag is i, and may be 8x8 when the TU size flag is 2,

As another example, if the size oft.be current coding tuifls JpxSS and a mini mum transformation unit size is 32x32, the size of the transformation unit may be 32x32 when the TU size flag is 0, Here, the TU size flag cannot be set to a value other than 0, since the size of the transformation unit cannot be less than 32x32.

As another example, if the size of the current coding unit is 64x64 and. a maximum *fU size flag is 1, the TU size flag may be 0 or 1. Here·, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it Is defined that the maximum '1U size flag Is MaxTransiormSizelndex, a minimum transformation unit size is MinTransformSize. and. a transformation unit size is Root'lu Size when the TU size flag is 0, a current minimum transformation unit size CiuTMi.nTuS.ize that can be determined in a current coding unit, may be defined by Equation |1|«:::

CiurMinTuSize - maxiMinTransformSize, RootTuSize/ (2AMaxTransformSizeIndex)).,. (I).

Compared to the current minimum transformation unit size CumMinThSIze that catr be determined in the current coding unit, a transformation unit size RoofTuSIze wlrpf the TU size flag is 0 may denote a maximum transformation unit size that can be selected in the system. In Equation (i), RootTuSize/(2AMaxTransfbttii&amp;izelndex) denotes a mansformation unit size when the transformation unit size RootTuSize, when the TU size flag is 0, is split a number of times corresponding to the maximum TU size Hag. Furthermore, MinTransformSize denotes a minimum transformation size. Thus*# smaller value from among RootTuSize/(2AMaxTranstbrmSizeIndex) and MinTratis-formSize may be the current minimum transformation unit size CurrMinTuSIze that can be determined In the current coding unit.

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

For example, if a current prediction mode is an inter mode, then RwrtTuSize may ;|g determined by using Equation (2) below, in Equation (2), MaxTranstbrmSize denotes a maximum transformation unit size, and PUSize denotes a current prediction unit Size,

RootTuSize - minCMaxTransformSize, PUSize).........(2).

That is, if the current prediction mode is the inter mode, the transformation tmilsize RootTuSize when the TU size flag Is 0. may be a smaller value from among the maximum transformation unit size and the current prediction unit size,

If a prediction mode of a current partition unit is an intra mode, RootTuSize may b® determined by using liquation (2.) below. In Equation (3), PartitionSize denotes the size of the current partition unit.

RootTuSize - miniMuxTrausionnSwe, Pa||iis||Si|e):x:.,,.,(3)1

That is, If the current predict ion mode is tbeUlfa: mode, the transformation mot size RootTuSize when the TU size flag is 0 may be a smaller value from among the maximum iransformaioirpnit size and the size of the current partition unit.

However, the current maximum transformation unit size RooiTuSize that varies according: to the type of!,prediction mode in a partition unit is merely exemplary, and: another exemplary embodiment is not limited thereto.

Hereinafter, encoding and decoding of residual block performed by tire entropy encoder 450 of the video encoding apparatus 4U0 illustrated in FIG, 4 and the entropy decoder 520 of Ok; video decoding apparatus 500 iiiuslnned in FIG. 5 will be described in detail, hr the fblkuvirtg description, an encoding unit denotes a current encoded block in an encoding process of an image, and a decoding unit denotes a current decoded 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 skill in the art would understand by the present disclosure that an intra prediction method and apparatus according to an exemplary embodiment may also be applied to perform iitrk prediction in a. general video codec. FIGs. 14A through l4C are reference diagrams for describing a process of encoding; a transformation residual block in a related technical field.

Referring to FIG. 14A, when a transformation residual block 1410 is generated by transforming a residual block, a significance map, which indicates a location of a nonzero effective transformation coefficient in the transformation, residual block 1410 while scanning transformation coefficients in the transformation residual block 1410;; according to a zigzag scanning order. After scanning the transformation coefficients in the transformation residual block 1410, level information of an effective transformation coefficient are encoded. For example, a process of encoding a transformation residual block 1420 having a. size of 4x4, as illustrated in FIG. 14B, will now be described, hi FIG. 14B, it is assumed that transformation coefficients at locations indicated by X arc nonzero effective transformation coefficients. Here, a significance map indicates an effective transformation coefficient as 1 and a 0 transformation coefficient as 0 from among transformation coefficients In a residual block 1430, as shown in FIG. 14C. Hie .significance map is scanned according to a pnedcr termitied scanning order, while context adaptive binary arithmetic coding is performed thereon. For example, when the significance map of FIG. 14C is encoded aecofoingdo 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 corresponding to an binary string of "1 ilillllOlllUdlc Level information of an nttect.ive coefficient,keg a sign and an absolute value of the effective coefficient, is encoded after the significance map is encoded, .Such a process in the related technical held may he utilized for encoding a iran.s-foi /nation residua] block having a small sizeyisuehsas 4x4 or 8x8, but may not be suitable for encoding a transformation rest dial block havisig a large size., such as 16x16, 32x32. or 64x64. In particular, if ali transformation coefficients in a transformation residual block are scanned and encoded according to the process oi MGs, 14A through 14C with respect to a transformation residual block having a large size, a length of a binary string corresponding to a significance map may increase and encoding efficiency may deteriorate#

Accordingly, a method anil apparatus for encoding a residual block according to exemplary embodiments are capable of efficiently encoding a transformation residual block by splitting ihe transformation residusillock into pnGeiurmineu frequency band units and i'lag according to ihe frequency band units,

which indicates whether a nonzero effective, transformation coefficient exists for each frequency band unit, while encoding effective: transfonnation coefficient iη formatioii, i.e., u significance map ami level information of an effective coefficient, in a frequency ianlln which an effective coefficient, flag according to frequency band units has a value of L FIG. 15 is a block diagram of an apparatus 1500 tor encoding a residual block, according to an exemplary embodiment. While not restricted thereto, the apparatus 1.500 may correspond to the entropy encoder 450 of FIG, 4, or may be included in the entropy encoder 450.

Referring to FIG. 15, the apparatus 1500 includes a frequency band splitter 1510, an effective coefficient flag generator 1520, and an effective coefficient encoder 1530.

The frequency band splitter 1510 splits a transformation residual block into predetermined frequency band units, Referring back to FIG. 14A, in the exemplary transformation residual block 141.0, an upper left transformation coefficient has alow frequency component, and a lower right transformation coefficient has a high frequency component. Most of the effective transformation coefficients of the transformation resiuuai block 1410 may exist in Sow frequency bands, and the; transformation coefficients having high frequency components may mostly have a value of 0. in this case, a nonzero effective transformation coefficient from among the transformation coefficient* of tire high frequency component is sparse, ipeliilly;,......|iS-:i tribution of effective transformation coefficients of high frequency components may be sparser when a uansfonnauoi· resiluklPqclls generated by formation with a transionrunion unit having a size of ] 6x 10,:3ik32f ρηΑϊΙβΐ which is huger than a related art transformation unit having -a size of 4x4 or 8x8, as in the image encoder 400. Accordingly, the frequency band splitter 1510 may split the transfer?.?.»lion residual block into th&amp;plfpehey bund units while considering distribution characteristics according to the frequency bands of the transfonnation coefficients in the transformation residual block. FIGs, 16A through f 6J are diagrams for describing splitting of a transformation residual block into predetermined frequency band units, according to one or more exemp 1 a ry emhodime n ts,

Referring to FIG. 16A, the frequency band splitter 1510 generates frequency pnd units 1611 through 1614 by splitting a transformation residual block 1610 at pede-termined frequency intervals from a low frequency band lo a horizontal frequency H 1 and a vertical frequency VI. In FIG. 16A, horizontal sides and. vertical sides of the frequency band units 1611 through 1614 have the same length, although it is understood that the lengths of the horizontal and vertical sides may differ from each other. If a length of a remaining frequency band from the hors vernal frequency Hi to a rnaximum frori/ontu 1 frequency is less than a frequency interval corresponding to a length of the horizontal side of each of the. frequency band units 16 i 1.....through i 6 i 4, or if a length of a remaheng frequency hand from the vertical 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 16.] 1 through 1614, the frequency band splitter 1510 no longer splits the franslormacion residual block .1610, : arid generates a frequency band unit 1615 corresponding to a.high frequency component. Effective transfomiation coefficients may be intensively distributed in the frequency band quits; 1611 through 1614 corresponding to low frequency components, and distribution of effective transformation coefficients of high frequency components may be sparse. Accordingly, even when the entire remaining high frequency components, aside from die frequency band units 1611 through 1614 generated by splitting the transformation residual block 1610 at predetermined frequency intervals, are generated in one frequency band unit 1615, an overhead while encoding trans--formation coefficients in the frequency band unit 3615 may not remarkably increase.

In another exemplary embodiment, as shown in FIG. 16B, the frequency band splitter 1510 may generate frequency baud units 1621 through i 624 by splitting^, transformation residual block 162U fr om, a low frequency band to a horizontal frequency H2 and a vsrii|f| frequency ¥2, and gene|||| frequency band units 1625 through i 627 by splitting remaining high frequency components of the transformation, residual block 1620 based on the horizontal frequency H2 and the vertical Irequency V2, similarly to the description with reference: to FIG, 16A,

Moreover, according to another exemplary embodiment, as shown in FIG. J6C, the;;; frequency band splitter 1510 may generate frequency band units 1631 through 1634 by splitting a transformation residua! block 1630 from a low frequency band to a horizontal frequency H3 and a vertical frequency V3, and generate frequency hand units 1635 and 1636 of high frequency components by splitting remaining high frequency components of the transformation residual block 1630 into two based on the vertical frequency V3, similarly to the description with reference id FIG,; 16A.

Referring to FIG, 16D, according to another exemplary embodiment, the frequency band splitter 1510 may generate frequency band units 1641 through 1644 by splitting a transformation residual block 1640 from a low frequency band to a horizontal frequency H4 and a vertical frequency Y4. and generate frequency band units 1645 and 1640 of high frequency components by splitting remaining high frequency component of the transformation residua] block 1630 into two based on the horizontal frequency H4, similarly to the description witbreferenee to

As described above, distribution of effective transformation coefficients is concentrated in a low frequency band, and is sparse toward a high frequency band. Aa§? eordingly, as shown in FIG. 16E. 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 -triburion characteristic of the effective transformation coefficients. In other words, the frequency band splitter 1510 splits the transformation reskiuil block 1650 minutely in the low frequency band and relatively large in the high frequertey bahl so that the effective transformation coefficients (hat are 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 split units .1651 through 1657 by splitting the framki formation residual block 1650 based on a horizontal frequency H5, vertical frequency V5, a horizontal frequency H6 having a larger value than a multiple of the horizontal frequency H5, and a vertical frequency V6 having a larger value than a multiple of the vertical frequency V5. Thus, when A1651 through A1657 respectively denote sizes of he frequency band split units 1651 through 1657, the transformation residual block 1650 is split in such a way that A1651 has a minimum size and A1657 has a maximum size.

Referring: (OiM. 16F, according to another exemplary embodiment, the frequency band spbuer 1510 may split a transformation residual block 1660 into frequency bpd units 1661 having the same size.

Moreover, referring to FIG. 16G, according to another exemplary embodiment, the frequency band splitter 1510 may quadriseet a transformation residua! block i67i$ and again quadrisect a smallest low frequency band unit 1671 from among quadrisected frequency band units to generate frequency band units. The frequency band .splitter 1510 may ag*in quadrisect a smallest low frequency band unit 1672 from among frequency band units obtained by quadrisecting the smallest low frequency band unit 1671. Such a splitting process may be repeated until sizes of quadrisected frequency band units are equal to orlelow a predetenrn rsed sure.

According to another exemplary embodiment, referring to FIG. 16H, tire fr equency-band splitter 1510 srusy generate a frequency hand unit 1681 pf a IqwTrequeney component from:alow frequency to a horizontal frequency H7 and a vertical frequency V7, and generate frequency band units 1682 and 1683 by diagonally splitting remaining high frequency components of a transformation residual block 1680.

Referring to FIGs. 161 and I.6J, according tiispue or mMeother exemplary em- bodiiSeats, fhefislae^ band splitter 1510 may split transformation residu# b|pks 1690 and 1695 by eoineetuig a horizontal frequency and a vertical frequency, which have predetermined values. In FIG. 161, the transformation residual block 1690 is split by connecting She. horizontal frequency and the vertical frequency at uniform frequency intervals, in F!G< 16,1, the transformants residual block 1695 is split so that frequency intervals increase: toward, a high frequency, i.e., by connecting ai and |:f,: || and b2, a3 and b3, and ad and fj|, wherein al <a2<a3<a4 and bl<b2<b3<b4.

According to another exempf|^*embodiment, instead of using a pretleterniined split form as shown in PIGs. 16A through 161, the frequency band splitter I510 may determine image characteristics of a transformation residual block by using distribution eharactoristies of effective transforaiation coefficients of tire transformation residual block or a number of I he effective transformation coc Oleic u Is in each frequency bund, and determine a size of a ireqtsency unit tu spilt the trahlforphtion 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 H8 and a vertical frequency V8 and do not exist in a frequency band larger than the horizontal frequency H8 and the vertical frequency V8, the frequency band splitter 1510 may set the entire transformation, residual block fan. a low frequency band to the horizontal frequency H8 and the vertical frequency V8 as one frequency band unit. Alternatively, the frequency band splitter I S 10 split the transiormatiou residual block into frequency band units having the saute size, and set a-remaining frequency band larger than the horizontal frequency Fib and the vertical frequency V'8 as one frequency band unit.

It is understand that the splitting of a transformation residual block into predetermined: frequency band units is not limited toslle exemplary embodiments described above with reference to PIGs. 16A through 16J, and that a transformation residual blcekmay be split into various forms in onetor snore c#er exemplary embodiments.

Mtewhlfaplit forms of a transliaroaipm residual block by the frequency band isipliftffir;: 15 SO may be idemieally set in an encoder and a decoder. However, it is understood that another exemplary embodiment is not issued thereto, lor example* according to another exemplary embodiment, a predetermined split index may be determined for each of various split form, such as shown in FlGs. 16A through 16J, and the encoder may insert the split index about spill inhumation used while encoding a transformation residual block info an encoded bitstream. For example, when integer values from split index idivjndex) 0 to 9 respectively denote split forms of HGs, 16A through 16.1, and a split form used to encode a current transtormafion residual block is divjndcx=5 corresponding to the form shown in FIG, 16.F, such split information may be added to encoding information of the current tmnsformation residual block.

Referring back ίο FIG. i 5, after the frequency band splitter 1510 splits the transformation residual block into the frequency baud units, the effective coefficient flag generator 1520 generates an effective coefficient flag indicating whether an effective transformation coefficient, exists in each frequency band unit. Tlere, the effective coefficient fag generator 1520 may not generate a separate effective coefficient flag for a smallest low frequency band unit. For example, when the transformation residual bl||§r 1610 of FIG. 1 <:·A is split, the etlecfive coefficient flag generator 1520 may generate effective coefficient flags indicating whether effective transformation coefficients e$f§|::: for the frequency band units 1612 through 16f|, other than the frequency hand unit fill: of a smallest low frequency band unit. When Coefl„exist„l612. §iHfoexistJ6i3, Coeff.exist_.l614, and Cocff_exisi..l6i5 respectively denote foci effective coefficient flags of the frequency band units 1612 through 1615. and efle||||:: coefficients exist only in the frequency band milts and 1613 from among rite frequency band units 1612 through 16|5i thes|®eeive coefficient flag generator If|§| geleijates the effective coefficient flags of each frequency band unit, for example, generates Coeff_exist_1612=1, CoefLexist_1613=1, and Coeff_exist_l 614=0,

Cdefi.exist.. 1615-0, As described above, since an dfeetive iransfoi matron coefficient may exist in the frequency band unit fil l of the smallest low frequency band unit, an effective coefficient flag indicating existence of the effective transformation axdfleient may not be separately generated for the frequency band unit 161 ]. Moreover, instead of separately generating the effective coefficient flag for the frequency band unit 1611, a related art eoded_bloekJlag field indicating whether an effective transformation coefficient exists in a residual block may be used to indicate the existence of the effective lansfermifriqnfel® band unit 1611. Such a process of generating the effective coefficient flag is not limited to the slit form of FIG. 16A, and may be applied to other split forms in one or more other exemplary embodiments, such as those of FIGs, 16B through 16J,

Meanwhile, transformation process or inverse-transformation process may be performed i|diyi||hfiydh::ii|| frequency band unit by use of different transformation or invei-se-transfonnation method. Funner, transformation process or in verse-transformation may be performed only in the frequency band uni;, having an effective coefficient Hag I, and may be skipped in the frequency band unit having an effective coefficient flag 0.

Referring hack to FIG, 15, the effective coefficient encodes' 1530 encodes a significance 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 i, i,e„ the frequency band unit having· the effective transformation coefficient. FIGs. 17A and 17B are reference diagrams for describing a process ot encoding pa effective transformation coefficient, according to one or more exemplary embodiments. FIGs, 17A and L7B illustrate split forms corresponding to fee split form, of PiG. I6E, whesoir; frequency band units are generated by quadfiseetisgg trans* formation residual block, and again quadrlsectirtg a low irequeney bsitirlfls un-iderstood that the process described with reference to FIGs. 17A and i 7B may also be applied to the frequency band units having other split forms, such as any onetof the split forms of FIGs. i 6A through I6J,

The effective coefficient encoder 1530 may encode an co efficient by seamtingfM entire transformation residual block, oiihcode'ii effective transformation coefficient, in a irequency band null by performing scanning independently for eaefi frequency band unit in detail, referring to FIG, 17A, the effective coefficient encoder 1530 may encode a significance map indicating hxations of effective transformation coefficients existing in a transformation residual block 1710, and size and sign information of each effective transformation coefficient, while scanning the entire transformation residua! block 1710 according to a predetermined scanning order, for example, a raster scanning order as shown in FIG. 17A, Here, scanning may be skipped in a frequency band unit in which an effective coefficient Hag has a value of 0, i.e., a frequency band unit that does not have an effective transformation coefficient.

According to another exemplary embodiment, referring to FIG. 17B, the effective coefficient encoder 1530 iSaf encode significance map and level information of an effective transformation coefficient for each frequency band bit according to a split form of a transformation residual block 1720 spin by fee frequency band splitter lfl|,: FIGs, 18A and 18B are reference diagram^: for describing iri detail a process of encoding a residual block, according to an exemalary em.bssdiraent. In FIGs. 18A and i SB, a transformation coefficient indicated with x Is an effective transformation coy1 efficient, and a insnsfomiaiioa coefficient v/irho»! any indication lias a value of 0.

Referring to FIG. 18A, the frequency band splitter 151b splits a transformation residual block 1.810 according to a split form, such as one of the split forms shown in FIGs. 16A through 16J. FIG. ISA shows a split form corresponding to the split, form of FIG. 16E, though it is understood feat the process with reference to FIG. 18Λ may also be applied to other split, forms. The effective coefficient flag generator 1520 respectively sets effective coefficient flags of frequency band units 1811 through 1813 including effective transformation ebeificibitx as 1, and respectively sets effective coefficient flags of frequency band units 1814 through 1817 that do rah include an effective transformation coefficient as 0. The effective coefficient encoder 1530 encodes a significance map indicating locations of the effective translramiation coefficients while scanning the entire transformation residua] block 1110, As described above, the Significance map indicates whether a tranafonnation coefficient according to each scan index is an effective transformation coefficient or ff After encoding the sipifieatteemap, the effective coefficient encoder 1530 encode|]evgi information of each effective tninsformatidi coiffiefenff The level information if the effective transformation coefficient includes aign and absolute value information of die effective transformation coefficient. For example, the significance map of the frequency band units 1811 through 1813 including the effective transformation coefficients may have a binary string value, such as " 1000100010101110100i00100010001,“ when scanning is performed according to a raster scanning order as shown in FIG. I SA,

Also, when information about the effective transformation coefficient is encoded while scanning the entire transformation residual block 1810 as shpt|n in FIG. 18A, an end-of-block (BOB) flag indicating whether an effective transformation coefficient is the last effective transformation coefficient may be set for the entire- transformation residual biock 1810 or each frequency band unit. When art HOB flag is set for the entire traiisM‘fls®ttion residual block. 1810, only an BOB flag of a iPsformatioa eo-efficient 1802 of the last effective transformation coefficient according to the scanning order from among transformation coefficients of FIG. 18A may have a value of 1, For example, as described above, if the significance map according to FIG. 18A has a value of ” 1000!000 10101 11010010010001000.1an HOB flag corresponding to such a significance map has a value of ΤΧ500ϋϋϋίίθ00Γ: since only the lari effective iratsv forntrstion c<scfticies\1 from among 12 effective transformation coefficient* Included In ’’KKXHOOOlOlOll 10100100100010001” has a value of 1. in other words, a total of 12 bits are used to express the EOB flag correspond!!® *° significance map of FIG, ISA.

Alternatively, in order to reduce a number of bits; used to express an EOB flag^ the effective coefficient encoder 1530 may define afpg (Tlast) indicating whether a last; effective transfesinarionicoeffieient exists according to each frequency band unit, set Tlast as 1 if tire last cfi'ecti ve transforma- U·>π coef fici etit accordIng to each frequency battd unit exists and as 0 if fee last effective transformation coefficient does not exist, and sets an HOB flag for only a frequency band unit where Tlast is S, thereby reducing a number of bits used to identify locations of effective transformation coefficients in the entire transformation residual block and the last effective tra.fisfbrma.tion eqp efficient In detail, inferring to FIG, 18A, the effective coefficient encoder 1530 may check flse existence of a last effective transformation coefficient for each of the frequency baid units» 1811 through 1813 including the effective transformation coefficients, and set Tlast as 1 in the frequency band unit 1812 including the last effective transformation coefficient, and set Tlast as 0 in the remaining frequency band units 1811 aud '1813. If each bit of Tlast indicates the existence oflfeeTast effective trans* formation coefficient in each of the frequency band units 18 i! through 1813 according to an ortler of scanning the transformation coefficients, a most significant bit (MSB) of Tlast may indicate whether the effective transformation coefficient exists in a lowest frequency band unit, and a least significant bit (LSB) of Hast may indicate whether the last effective transformation coefficient, exists in the frequency band unit 1812. Thai is, a bit value of ''00Γ is set since Tlast has a value of 0 for the frequency band unit 1811, 0 for the frequency band un it 1813, and 1 for the frequency band unit 1812.1 Sere., si nee an effective· transformation coefficient in a transformation residual block may end at the frequency band unit 1811 that is the lowest, a Tlast value may not be separately assigned for the frequency band unit 1811. Thai is, Tlast may be set only for the frequency bauds 1812 and 1813 excluding the frequency band 1811 from among the frequency band units 1811 through 1813 that are scanned according to a scanning order. Here, two bit values of "0Γ are set as Tlast, "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 band unit 1812. Tlast may have a value of "00" if the last-effective transformation coefficient of the transformation residual block exists in the frequency band 1811 of the lowest frequency band unit. Thus, when all bits of Tlast are 0, it may be determined that the last effective transformation coefficient of the transformation residual block exists in the frequency band unit 1811.

In the present exemplary embodiment, the effective coefficient encoder 1530 sets an BOB fl ag only for the frequency band unit in which Tlast Is 1, i.e„ the frequency band unit including the last effective transformation coefficient of the transformation residual block. Referring to FIG, 18A, the effective coefficient encoder 1530 sets an BOB flag only for each effective transformation coefficient existing in the frequency band unit 1.812 in which Tlast Is 1. Since a total four effective transformation coefficients exist in the frequency band unit 1812, the EOB flag has four bits of ”000 i According to another exemplary embodiment, a total oisix to seven bits are used to identify the location of the effective transformation coefficients in the transformation residual block, and the Iasi effective transformation coefficient, since two to three bits are seLfor Tlast andibehiis are set for the EOB 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 "(XXXXKXiOOOOl."

According to another exemplary embodiment, when an EOB flag is seifrwreach frequency hand unit. EOB flags of a transformation coefficient 1.801 in the frequency band unit 1811 1802 in the frequency band unit ί 8 i 2, anl a transformatioa coefficient 1803 La the frequency band unit 1813 are set to 1, EOB flags are not set for the frequency band units 1814 through 1817 that do not include the effective traits forma lion coefficients. As such when an EOB flag is set for each frequency band unit including an effective transformation coefficient, an effective transformation coefficient in a predetermined frequency band unit is scanned, and then an effective transformation coefficient in a following frequency band unit may be scanned. For example, a transformation coefficient in the frequency band unit 1812 may fie scanned after the transformation coefficient 1803 of the frequency band unit 1813 is scanned. Referring to HG. 18B, effective transformation coefficient information is encoded independently for each frequency bmtdSnit. The effective coefficient encoder 1530 encodes a significance map indicating locations of effective transformation coefficients, and level information of each effective transformation coefficient whi te 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 !Ί00010001003 3 " when scanned according to a raster scanning order as shown in HG, 18B, Also, the effective coefficient encoder 1530 sets an EOB flag of an effective transformation coefficient 1831 corresponding to a last offer. Live transforms don coefficient from among effective (mnsfbmtation coefficients of the frequency band unit 1821 as i. Similarly, the effective coefficient encoder 1530 generates a binary string value, such as" lOLUiOUOl," as a significance map of a frequency band unit .1822. Also, the effective coefficient encoder 1530 sets an BOB of an effective transformation coefficient 1832 from among effective translbrmatioa coef-ficfehtilfrithe frequency baidihifr:::i822 aa 1- Similifrlpiifhihtie^ encoder 1530 generates a binary string value, such as "11001," as a:;s|||i|||iiebsmap^ of a frequency band; unit 1 823, and sets an BOB flag of an effective transformation coefficient 1833 as 1,,

Meanwhile, the effective· coefficient encoder IS30 may separately encode an E»d_Of_WholeRiock flag indicating a last, effective transformation coefficient of the transformation residual block )820, aside from the BOB flag indicating that the effective transformation coefficients 1831 through 1833 are the last effective transformation coefficients in a corresponding frequency band unit, Referring to FlG. 18B, if the frequency band units 1821 through ll2|ll|e independently scahhed:||i:i||ei|tat^ order, the effective transformation coefficient 1833 is the last, effective transformation coefficient of the frequency band unit 1823 and, at the same time, the last effective traitsformatian coefficient of the transformation residual block 1820. Accordmglp an; EOB flag lock flag of the effective transformation coefficient 1833 both have a value-of .1, In the effective transformation coefficients 1831 and J'p2i which are the Iasi effective uaurs format ion coeffici^nus of the frequency band diilS;i<s2i add.....1822, BOB flags have a value of 1 ,hut End..Of WhGcBRck flags have a value of 0.

As such, when an EOB Hag and an End_Of_Who1eBlock flag are set for a Iasi effective transformation coefficient according to each frequency band, existence of an effective transformation coefficient in a coiresponding frequency band unit may be first determined by using an above-described effective coefficient Hag during decoding so as to skip scanning of a frequency band unit, in which an effective coefficient, flag is 0. Furthermore, when a transformation coefficient, in which an FOB flag is 1. is scanned while scanning transformation coefficients in a frequency band unit, in which coefficient flag J§ |, i.e„ a frequency band unit having an effective transformation coefficient, a following frequency band unit may be scanned. When an effective transformation coefficient, in which an EOB flag is 1 and an End„Of_ WholeBlock flag is 1, is scanned, effective transformation coefficients of an entire transformation residual block are scan ned, and thus scanning of the wit formation residua! block is ended, FIGs. 19A and 19B are reference diagrams for #|§ribing encoding information of a transformation residual block, which is generated by the effective coefficient encoder 1530, according to one or more exemplary' embodiments.

Referring to FIG. J9A. the effective coefficient encoder 1530 may sequdbhfiiy encodc :significarsi|e maps and:|!bces of effective coblticipf flag infemafian generated according l u frequency bands. When a first frequency band is a smallest frequency band of a transformation residual block, only a significance snap 19.11 of-he fliik frequency band rnay be encoded and a flag of the first" l||||h|| band, which indicates whether an effective· transformation coefficient exists in the first frequency band, may not be separately encoded, as shown in HG. 19A, According to another exemplary embodiment, referring to RG, 19B. eil Active coefficient flags i 921 pleach frequency:: band rnay be first encoded, and then significance maps 1925 of each frequency band may be encoded, PIG. 20 is a flowchart illustrating a method of encoding a residua! block, aec||i|p|:i io an exemplary embodiment

Referring to RG, 20, die intra predictor 410 or the motion compensate 425 of FIG. 4 generates a prediction block via inter prediction or intra prediction by using a current block ;n operation 2010.

In operation 2020, a substractor generates a residual block that is a difference between the prediction block and the current block.

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 frequenc^iiiniam via di screte cosine "^sforni^IMT).

In operation 2040, the frequency band splitter .3.5.10 splits the ti^^ormaiioii residual block into predetermined frequency band units. As described ab<ite|:ihe frequency band splitter 1510 may split the transfomuition residual block infoone of various split, forms, for example as shown in PIQs, 16A through 16J, In detail, the frequency band splitter 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 high frequency band, split the transformation residual block by qaadrisecting the transformation residual block and repeatedly qaadrisecting a smallest: low frequency hand, in the quadrisected trass-formation residual block, split the transformation residual block into frequency bgal units having the same size, 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 the transformation residual block by using image characteristics of the fransformatioo residual, block determined by using transformation coefficients of the transformation residual block, and split the transformation residual block according to the determined split size according to frequency bands,

In operation 2050. the effective coefficient flog generator 1520 generates an effective coefficient Hag according to frequency band units, wherein the effective coefficient flag indicates whether a nonzero effective transformation coefficient exists in each frequency band unit. The effective coefficient flag may not be separately generated for a smallest frequency band unit, from among the frequency band units of the transformation residual block. Also, the elleciive coefficient encoder 1530 encodes a significance map indicating locations of the effective transformation coefficients and level inf tarnation 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 transfoosation coefficients, while scanning the transformation residual block according to a predetermined scanning order or independently scanning each frequency band unit, as described above with reference to FIGs. 17A, 17B. 18Λ, and 18B.

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 efficiently encoded according to distribution characteristics of the effective transfomuition coefficient in a transformation residual block having a size that is greater than or equal to 16x16, by splitiing 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 Coefficient flag indicating an existence of the effective transformation coefficient is generated according to frequency land units; Jgifoolingly, a scanning process of a frequency band, in which an effective transformation coefficient does not exist in the Uansrornmtion residual Mock, may be skipped and a number of bits generated to encode the effective transformation coefficient may be reduced, FIG. 2! is a block diagram of an apparatus 21.00 iV;r decoding a residual block, according to an exemplary embodiment, While not restricted thereto, the apparatus 2100 may correspond to the- entropy decoder 520 of FIG. 5 or be included in the entropy decoder 520.

Referring to FIG. 21, the apparatus 2.100 includes a frequency band splitter 2110, an effective frequency band determiner 2120, and an effective coefficient decoder 2130.

The frequency band splitter 2110 splits a transformation residual block into predetermined frequency band units. In. detail, as described with reference to FIGs. 16A through 16H, the frequency band splitter 2110 may split the transformation residual block In such a way that a unit size split in a low frequency band is smaller titan a unit size split in a high frequency band, split the transformation residual block by quadrisecting the trattsformation residual block and repeatedly quadrisecting a smallest Sow frequeney bind in the quadriseeted transformation residua! block, split the transformation residual block into frequency band units ha ving the same size, split the transformation residual block by connecting a horizontal frequency and a vertical frequency haying the same value, or determine a split size according to frequency bands of the transformation residual block by using image characteristics of the tfaiis-formation residual block determined by using transformation coefficients of the transformation residual block, and split the transformation residua] block, according to the determined split size according to frequency bands, j, split form of the transformation residual block may be predetermined by an encoder and a decoder, though it is understood that another exemplary embodiment is not limitedfherifo. For example, aceoiding 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 transformation residual block is added to a bitstream during encoding, the frequency band splitter 2110 may determine which split form was used to split the current transformation residual block based on the information about ihe split index included in the bitstream.

The effective frequently band determiner 2120 extracts an effective coefficient flag from a bitstream, wherein the effective coefficient flag indicates whether an effective transformation coefficient exists according to the frequency band units obtained by splitting the transformation residual block. The effective frequency band determiner 2120 may determine a frequency band unit including an effective transformation coefficient from among the frequency bund units by using the eiiectiyeiCoefficient flag. For example, when the transformation residual block 1.820 of FIG. 18B is used, the effective coefficient flags of the frequency band unites 1§2d fefough 1823 have a valise of i, and she effective coefficient flags of tire frequency band units 1824 through1822 have a value of 0. Thus., the effective frequency band, determiner 2120 may deteonine: the frequency hand units including the effective transformation coefficients front the extracted effective coefficient flags according to the frequency bands,

The effective coefficient decoder 2130 decodes the effective transfonnation coefficients in the. frequency band units that are determined to include the effective transformation coefficients by the effective frequency band determiner 2120. In detail* lie effective coefficient decoder 2130 extracts a significance map indicating ibeiiionkdf the effective transformation coefficients and level information of the effective, transformation coefficients, from the bitstream, Also, as described above with reference to FIGs. 17A and. 17B, the effective coefficient decoder 2130 determines the locations of the effective transformation coefficients in the transformation residual block by using the significance map, and restores values of the effective transformation coefficients by using the level information while scanning the entire transformation residual block or scanning each frequency band unit according to a predetermined scanning order that is ...independent for each frequency band unit, FIG, 22 is a flowchart illustrating a method of decoding a residual block, according to an exemplary embodiment.

Referring to FIG. 22, in operation 2210, the. effective frequency baud determiner 212U extracts an effective coefficient flag from an encoded bitstream, wherein the effecti ve coefficient flag indicates whether an effective transformation coefficient exists: according to frequency band units obtained 'by splitting a transformation residual block of a current block.

In operation 2220. the frequency band splitter 2110 splits the transformation residual block into the frequency band units. As described above with reference to HGs, 16A through i 6.1, tiie frequency bend splitter 2110 may spit the transformation residual block in such a way that a unit size split in a low frequency band is smaller than guif i size spin in a high frequency band, split the transforms!ion residual block, by quadnseeting the iranv.l·.srmation residual block and repealedly quadrisecthtg a smallest low frequency baud in the quadriseeted transformation residual block, split the transformation residual block into frequency band units having the same size, 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 the transformation residual block by using linage characteristics of the transformation residual block determined by using transformation coefficients of the transformation residual block, and split the lransfo.rma!.ion residual block according to the determined split size according to .frequency bands. Such a split form may be prede-tenmhediwiih an encoder. or may be determined by u&amp;n^;%formath>fea&amp;>ut a split index separately added to the encoded bitstream, Moreover, it is understood that operational fi and 2220 may be switched in order or performed simultaneously or substantially simultaneously.

In opemtion 2230, the frequency band splitter 2110 determines a frequency band unit including aaefective transformation coefficient front among the frequency band units, by using the extracted effective coefficient flag. The effective, coefficient decoder 2130 restores the effective transfermation coefficient by using a significance map about the frequency band unit determined to include the effective transformation coefficient, and level feformbibn of the effective transformation coefficient.

Acebrdingdo one or more exemplary embodiments, an effective coefficient flag indicating existence of an effective Uunsformation cOefficielf:·^ gUBiitMl according to frequency band units, so that a scanning process of a frequency band skips a transformation residual block in which an effective transformation coefficient does β exist, and a number of bits generated to encode the effective transformation coefficient is reduced.

While not restiiited thereto, an exemplary embodiment can also be embodied as;: computer readable code on a computer readable recording medium. The computet readable recording medium is airy data storage device that can store· data winch can le thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CP* ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Whifeexemplary embodiments have been particularly shown and described, it will be understood by one of ordinary skill in the art that various changes in formaud details may be made therein without departing from the spill and scope of the inventive concept as defined by the following claims. The exemplary embodiments should 1! considered in a descriptive sense only and not for purposes of limitation. Therefore, fie scope of the inventive concept is defined not by the detailed description Of the exemplary embodiments, but by the following claims, and all differences within fee scope v|llbe construed as being included in the prsifet inventive eqrfegpt.

Claims (2)

1. The claims defining the invention are as follows
2. 1. A method for decoding an image, the method comprising: extracting information about a maximum size of a coding unit from a bitstream; splitting the image into a plurality of maximum coding units based on the information about the maximum size of the coding unit; hierarchically splitting a maximum coding unit among the plurality of maximum coding units into a plurality of coding units; determining one or more transformation residual blocks from a coding unit among the plurality of coding units, wherein the one or more transformation residual blocks includes frequency band units; obtaining an effective coefficient flag of a frequency band unit among the frequency band units from the bitstream, the effective coefficient flag of the frequency band unit indicating whether at least one non-zero effective transformation coefficient exists in the frequency band unit; when the effective coefficient flag indicates that at least one non-zero transformation coefficient exists in the frequency band unit, obtaining transformation coefficients of the frequency band unit based on location information of the non-zero transformation coefficient and level information of the non-zero transformation coefficient obtained from the bitstream; and inverse-transforming on a transformation residual block including the frequency band unit based on the transform coefficients of the frequency band unit, wherein the transformation coefficients of the frequency band unit are a subset of transformation coefficients of the transformation residual block, and wherein, when the frequency band unit is not a first frequency band unit having a lowest frequency, the effective coefficient flag of the frequency band unit is obtained, and wherein, when the frequency band unit is the first frequency band unit having the lowest frequency, the effective coefficient flag of the frequency band unit is not obtained.