JP2013223051A - Arithmetic decoding device, image decoding device, arithmetic coding device, and image coding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a memory amount related to coding and decoding of transform coefficients, and improve throughput.SOLUTION: A coefficient presence flag context derivation unit 124z provided in a coefficient level decoding unit 124 derives a context index to be allocated to each transform coefficient presence flag belonging to a target sub-block by referring to the value of a decoded transform coefficient.

Description

  The present invention relates to an arithmetic decoding device that decodes encoded data that has been arithmetically encoded, and an image decoding device that includes such an arithmetic decoding device. The present invention also relates to an arithmetic encoding device that generates encoded data that has been arithmetically encoded, and an image encoding device that includes such an arithmetic encoding device.

  In order to efficiently transmit or record a moving image, a moving image encoding device (image encoding device) that generates encoded data by encoding the moving image, and decoding the encoded data A video decoding device (image decoding device) that generates a decoded image is used.

  As a specific moving picture encoding method, for example, H.264 is used. H.264 / MPEG-4. Examples include AVC and a method proposed by HEVC (High-Efficiency Video Coding) as a successor codec (Non-patent Document 1).

  In such a moving image coding system, an image (picture) constituting a moving image is a slice obtained by dividing the image, a coding unit (Coding Unit) obtained by dividing the slice. And is managed by a hierarchical structure composed of blocks and partitions obtained by dividing an encoding unit, and is normally encoded / decoded block by block.

  In such an encoding method, a predicted image is usually generated based on a locally decoded image obtained by encoding and decoding an input image, and a difference image between the predicted image and the input image (“residual”). A transform coefficient obtained by performing frequency transform such as DCT (Discrete Cosine Transform) transform for each block is encoded.

  As a specific coding method for transform coefficients, context-adaptive binary arithmetic coding (CABAC) is known.

  In CABAC, binarization processing is performed on various syntaxes representing transform coefficients, and binary data obtained by the binarization processing is arithmetically encoded. Here, the various syntaxes include a flag indicating whether or not the transform coefficient is 0, that is, a flag significant_coeff_flag (also referred to as a transform coefficient presence / absence flag) indicating the presence or absence of a non-zero transform coefficient, and the last in the processing order. Syntax last_significant_coeff_x and last_significant_coeff_y indicating the position of the non-zero transform coefficient.

  In CABAC, when one symbol (1 bit of binary data, also referred to as Bin) is encoded, a context index assigned to a frequency component to be processed is referred to, and a context variable designated by the context index is referred to. Is subjected to arithmetic coding according to the occurrence probability indicated by the probability state index included in. The occurrence probability specified by the probability state index is updated every time one symbol is encoded.

  Non-patent distribution 1 discloses a method of deriving a context index that is determined according to the number of non-zero coefficients in frequency components around the frequency component, using a transform coefficient presence / absence flag.

  In Non-Patent Document 2, as a method for integrating the transform coefficient presence / absence flag and level decoding, the context index of the transform coefficient presence / absence flag and the level decoding are performed using the sum of absolute levels of the frequencies around the frequency component. A method for obtaining the context index is known.

`` High Efficiency Video Coding (HEVC) text specification draft 6 (JCTVC-H1003_dK) '', Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11 6th Meeting: San Jose , US, 1-10 Feburary, 2012 (released February 17, 2012) "Non-CE11: Proposed Cleanup for Transform Coefficient Coding (JCTVC-H0228v1)", Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11 6th Meeting: San Jose, US, 1-10 Feburary, 2012 (released January 20, 2012)

  However, in the technique of Non-Patent Document 1 described above, since the transform coefficient presence / absence flag and the level decoding are not integrated, there is a problem in that individual mounting is necessary and the mounting scale increases.

  In the technique of Non-Patent Document 2, the transform coefficient presence / absence flag and the level decoding are integrated, but problems arise in high throughput and memory size. Specifically, in the technique of Non-Patent Document 2, in order to obtain the absolute value sum of the levels in the frequency components around the frequency component with high throughput, it is necessary to arrange the absolute value of the level in a high-speed memory. Therefore, there is a problem that a large amount of memory is required to hold the absolute value of the level as it is. On the other hand, when it cannot be arranged in a high-speed memory, the throughput decreases.

  Furthermore, in the technique of Non-Patent Document 2, it is necessary to refer to the level of the surrounding frequency component for the conversion coefficient located at a high frequency, so that the conversion located at a high frequency as in the technique of Non-Patent Document 1 is required. Compared to the case where the coefficients are derived in the position context, there is a problem that the throughput is reduced.

  The present invention has been made in view of the above problems, and its object is to reduce the amount of memory related to coding and decoding of transform coefficients and to improve throughput as compared with the conventional configuration. It is intended to realize an arithmetic decoding device and an arithmetic encoding device that can be used.

  In order to solve the above-described problem, the arithmetic decoding device according to the present invention uses various syntaxes representing transform coefficients for transform coefficients obtained for each frequency component by performing frequency transform on the target image for each unit region. An arithmetic decoding device for decoding encoded data obtained by arithmetic encoding, a sub-block dividing means for dividing a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size, and the sub For each subblock divided by the block dividing means, subblock coefficient presence / absence flag decoding means for decoding a subblock coefficient presence / absence flag indicating whether or not the subblock includes at least one non-zero transform coefficient; Presence / absence of non-zero transform coefficient for decoding a non-zero transform coefficient presence / absence flag indicating whether or not each transform coefficient in the sub-block is zero Lag decoding means, coefficient value decoding means for decoding the size of each transform coefficient in each sub-block, and context index derivation means for deriving a context index by referring to the value of the decoded transform coefficient It is characterized by providing.

  According to the above configuration, the context index is derived for each sub-block by referring to the value of each transform coefficient in the sub-block.

  Thus, by using the value of each transform coefficient in the sub-block for derivation of the context index, it becomes possible to classify the context with higher accuracy than when using the number of non-zero transform coefficients. There is an effect that the amount of codes is reduced. In addition, since the value of each transform coefficient in the sub-block is used in the derivation of the context index, the amount of memory related to encoding and decoding of the transform coefficient can be reduced compared to the conventional configuration, and the throughput can be improved. .

  As a result, it is possible to reduce the amount of memory related to encoding and decoding transform coefficients and improve the throughput as compared with the conventional configuration.

  In the arithmetic decoding device according to the present invention, it is preferable that the context index deriving unit derives a context index by using a sum of values obtained by clipping absolute values of decoded transform coefficients with a predetermined value.

  In the above configuration, since the absolute value of the decoded transform coefficient clipped with a predetermined value is used, the memory size for storing the absolute value of the decoded transform coefficient can be reduced.

  The arithmetic decoding apparatus according to the present invention further includes a counting unit that counts the number of non-zero transform coefficients decoded in the sub-block, and the context index deriving unit includes a predetermined number of the non-zero transform coefficients. In the following cases, it is preferable to derive the context index using the absolute value of the decoded transform coefficient.

  In the above configuration, since the context index is derived using the decoded transform coefficient only when the number of decoded non-zero transform coefficients is equal to or less than a predetermined number, the amount of processing necessary for derivation of the context index is reduced and the throughput is reduced. Has the effect of improving.

  The arithmetic decoding apparatus according to the present invention further includes a counting unit that counts the number of non-zero transform coefficients decoded in the sub-block, and the context index deriving unit includes a non-zero number before the target transform coefficient. When the number of the non-zero transform coefficients at the time when the transform coefficient presence / absence flag is decoded is equal to or smaller than a predetermined number, it is preferable to derive a context index using the absolute value of the decoded transform coefficient.

  In the above configuration, since the derivation of the context index does not depend on the decoded value of the non-zero transform coefficient presence / absence flag before the target transform coefficient, there is an effect that the throughput of the context index is improved.

  In the above configuration, the absolute value of the decoded transform coefficient when the number of the non-zero transform coefficients at the time of decoding the previous non-zero transform coefficient presence flag before the target transform coefficient is equal to or less than a predetermined number. The context index may be derived using

  In the arithmetic decoding apparatus according to the present invention, it is preferable that the non-zero transform coefficient presence / absence flag is decoded in a loop in the sub-block, and the code of the transform coefficient is decoded in a loop in a sub-block different from the loop.

  In the above configuration, the transform coefficient presence / absence flag and the transform are obtained by decoding the encoded data in which the individual transform coefficient presence / absence flags and the syntax indicating the size of the transform coefficient are sequentially arranged in one sub-block. A context index of syntax indicating the size of the coefficient can be determined using the value of the transform coefficient that has already been decoded, and the code amount of the syntax is reduced. At the same time, by continuously decoding the codes of the transform coefficients collected as a set in one sub-block by bypass, there is an effect that the amount of codes that can be decoded at a time is increased and the throughput is improved.

  An image decoding apparatus according to the present invention includes the arithmetic decoding apparatus, an inverse frequency converting unit that generates a residual image by performing inverse frequency conversion on a transform coefficient decoded by the arithmetic decoding apparatus, and the inverse frequency transform. It is desirable to include decoded image generation means for generating a decoded image by adding the residual image generated by the means and the predicted image predicted from the generated decoded image.

  An image decoding apparatus configured in this way is also within the scope of the present invention, and in this case as well, the same operations and effects as those of the arithmetic decoding apparatus can be obtained.

  In order to solve the above-described problems, the arithmetic coding apparatus according to the present invention includes various syntaxes representing transform coefficients for transform coefficients obtained for each frequency component by subjecting a target image to frequency transform for each unit region. An arithmetic encoding device for generating encoded data by arithmetically encoding a sub-block dividing means for dividing a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size, and the sub-block For each subblock divided by the dividing means, subblock coefficient presence / absence flag decoding means for decoding a subblock coefficient presence / absence flag indicating whether or not the subblock includes at least one non-zero transform coefficient; A non-zero transform coefficient presence / absence flag for encoding a non-zero transform coefficient presence / absence flag indicating whether each transform coefficient in the block is zero or not. Encoding means, coefficient value encoding means for encoding the size of each transform coefficient in each of the sub-blocks, and context index derivation for deriving a context index by referring to the value of the encoded transform coefficient And means.

  The image coding apparatus according to the present invention further includes transform coefficient generation means for generating a transform coefficient by frequency-converting a residual image between an encoding target image and a predicted image for each unit region, and The arithmetic encoding device generates encoded data by arithmetically encoding various syntaxes representing the transform coefficients generated by the transform coefficient generating means. It is desirable that there is.

  The arithmetic coding apparatus and the image coding apparatus configured as described above are also within the scope of the present invention, and in this case, the same operation and effect as the arithmetic decoding apparatus can be obtained.

  The arithmetic decoding device according to the present invention is obtained by arithmetically encoding various syntaxes representing the transform coefficients for each transform coefficient obtained for each frequency component by performing frequency transform on the target image for each unit region. An arithmetic decoding device that decodes encoded data, comprising: a sub-block division unit that divides a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size; and each sub-block divided by the sub-block division unit Subblock coefficient presence / absence flag decoding means for decoding a subblock coefficient presence / absence flag indicating whether or not at least one non-zero transform coefficient is included in the subblock, and each transform coefficient in each subblock is 0 A non-zero transform coefficient presence / absence flag decoding means for decoding a non-zero transform coefficient presence / absence flag indicating whether or not A coefficient value decoding means for decoding the magnitude of each transform coefficient in the lock, and context index deriving means for deriving a context index by referring to the value of decoded transform coefficients, a structure comprising a.

  The arithmetic coding apparatus according to the present invention performs coding by arithmetically coding various syntaxes representing the transform coefficients for each transform coefficient obtained for each frequency component by frequency transforming the target image for each unit region. An arithmetic coding apparatus for generating data, the sub-block dividing means for dividing a target frequency region corresponding to a unit area to be processed into sub-blocks of a predetermined size, and each sub-block divided by the sub-block dividing means A sub-block coefficient presence / absence flag decoding means for decoding a sub-block coefficient presence / absence flag indicating whether or not at least one non-zero transform coefficient is included in the sub-block, and each transform coefficient in each sub-block is 0 A non-zero transform coefficient presence / absence flag encoding means for encoding a non-zero transform coefficient presence / absence flag indicating whether or not each of the sub A coefficient value coding means for coding the size of each transform coefficient in the lock, and context index deriving means for deriving a context index by referring to the value of coded transform coefficients is configured to include.

  Therefore, it is possible to reduce the amount of memory related to encoding and decoding transform coefficients and improve the throughput as compared with the conventional configuration.

It is a block diagram which shows the 1st-3rd structural example of the coefficient level decoding part contained in the moving image decoding apparatus which concerns on embodiment of this invention. It is a figure which shows the data structure of the encoding data produced | generated by the moving image encoder which concerns on embodiment of this invention, and decoded by a moving image decoder, (a)-(d) is respectively a picture layer, It is a figure which shows a slice layer, a tree block layer, and a CU layer. (A)-(h) is a figure which shows the pattern of PU division | segmentation type, and PU division | segmentation type is 2NxN, 2NxnU, 2NxnD, 2NxN, 2NxnU, and 2N, respectively. The partition shape in the case of xnD is shown. (I)-(o) is a figure shown about the division | segmentation system which divides a square node into a square or a non-square by quadtree division. (I) is a square division, (j) is a horizontal rectangular division, (k) is a vertical rectangular division, (l) is a horizontal division of a horizontal node, and (m) is horizontal (N) shows the vertical division of the vertically long node, and (o) shows the square division of the vertical node. It is a figure which shows the first half part of the syntax table which shows the syntax contained in the quantization residual information of the coding data which concerns on a comparative example. It is a figure which shows the second half part of the syntax table which shows the syntax contained in the quantization residual information of the coding data which concerns on a comparative example. It is a figure which shows the first half part of the syntax table which shows the syntax contained in the quantization residual information of the coding data which concerns on embodiment. It is a figure which shows the second half part of the syntax table which shows the syntax contained in the quantization residual information of the coding data which concerns on embodiment. It is a figure which shows the relationship between a block and a subblock. (A) shows an example in which 4 × 4 TU is composed of one sub-block composed of 4 × 4 components. (B) shows an example in which 8 × 8 TU is composed of four sub-blocks composed of 4 × 4 components. (C) shows an example in which 16 × 16 TU is composed of 16 sub-blocks composed of 4 × 4 components. It is a figure for demonstrating the scanning order of the decoding process and encoding process which concern on embodiment, Comprising: (a) has shown the case where a subblock scan is a forward scan, (b) is in a subblock. The case where the scan is a forward scan is shown, (c) shows the case where the sub-block scan is a reverse scan, and (d) shows the case where the intra-sub-block scan is a reverse scan. . It is a figure for demonstrating the decoding process of the non-zero conversion coefficient in embodiment, Comprising: (a) is when the block whose TU size is 8x8 is divided | segmented into the subblock of 4x4 size, The scan order when each frequency component is scanned in the forward scan is shown, and (b) shows a non-zero transform coefficient (non-zero change coefficient) in the frequency domain composed of frequency components with a TU size of 8 × 8. (C) shows each value of the subblock coefficient presence / absence flag significant_coeff_group_flag decoded for each subblock when the transform coefficient to be decoded is the one shown in (b), and (d) ) Shows each value of the syntax significant_coeff_flag indicating the presence or absence of non-zero transform coefficients when the transform coefficients to be decoded are those shown in FIG. 10B, and (e) shows the transform to be decoded. Coefficient is (B) indicates the absolute value of each transform coefficient obtained by decoding the syntax coeff_abs_level_greater1_flag and coeff_abs_level_remaining in the case shown in (b), and (f) indicates that the transform coefficient to be decoded is (b) The syntax coeff_sign_flag in the case shown in FIG. It is a figure which shows the structural example of the quantization residual information QD of this embodiment. It is a block diagram which shows the structure of the moving image decoding apparatus which concerns on embodiment. It is a block diagram which shows the structure of the variable-length code decoding part with which the moving image decoding apparatus which concerns on embodiment is provided. It is a figure shown about the direction of the intra prediction which can be utilized in the moving image decoding apparatus which concerns on embodiment. It is a figure which shows intra prediction mode and the name matched with the said intra prediction mode. It is a block diagram which shows the structure of the quantization residual information decoding part with which the said variable length code decoding part is provided. It is a table | surface which shows the example of the scan index scanIdx designated with each value of intra prediction mode index IntraPredMode and log2TrafoSize-2. FIG. 6 is a diagram for explaining a scan index, where (a) shows a scan type ScanType specified by each value of the scan index scanIdx, and (b) shows a case where the TU size is 4 × 4. , (C) shows a vertical fast scan when the TU size is 4 × 4, and (d) shows a TU size of 4 An example of the scan order of each scan of the up-right diagonal scan when × 4 is shown. The horizontal direction priority scan shown in (b) is characterized in that the coefficient is scanned for each diagonal row in the horizontal direction in small sub-block units obtained by dividing the sub-block into upper and lower halves, and the vertical direction shown in (c). The direction-first scan is characterized in that the coefficient is scanned for each diagonal column in the vertical direction in small sub-block units obtained by dividing the sub-block into left and right halves. It is a figure shown about the scanning order of a block and a subblock. (A)-(c) shows an example of the scan order of each scan type specified by the scan index scanIdx when the TU size is 8 × 8 and the sub-block size is 4 × 4. . Moreover, the arrow in each example shown to (a)-(c) has shown the forward scan direction. The horizontal direction priority scan shown in (a) is characterized in that the coefficient is scanned for each diagonal row in the horizontal direction in small sub-block units obtained by dividing the sub-block into upper and lower halves, and the vertical direction shown in (b). The direction-first scan is characterized in that the coefficient is scanned for each diagonal column in the vertical direction in small sub-block units obtained by dividing the sub-block into left and right halves. It is a block diagram which shows the structure of the subblock coefficient presence / absence flag decoding part which concerns on embodiment. It is a figure for demonstrating the decoding process by the subblock coefficient level decoding part which concerns on embodiment, Comprising: (a) is an adjacent subblock adjacent to the lower side of an object subblock (xCG, yCG) and an object subblock (XCG, yCG + 1), and (b) shows the target subblock (xCG, yCG) and the adjacent subblock (xCG + 1, yCG) adjacent to the right side of the target subblock, (c ) Includes a target subblock (xCG, yCG), an adjacent subblock (xCG, yCG + 1) adjacent to the lower side of the target subblock, and an adjacent subblock (xCG + 1, yCG) adjacent to the right side of the target subblock. Show. It is a figure for demonstrating the subblock coefficient presence / absence flag encoding and decoding process which concerns on embodiment, Comprising: (a) has shown the transformation coefficient which exists in the frequency domain of 16x16TU, (b), A sub-block coefficient presence / absence flag assigned to each sub-block is shown. It is a figure which shows the context derivation process in a coefficient level decoding part. (A) to (c) correspond to the first to third configuration examples of the coefficient level decoding unit, respectively. It is a figure for demonstrating the reference frequency component referred when the decoding process is performed in reverse scanning order by the coefficient presence / absence flag context deriving unit included in the coefficient level decoding unit according to the embodiment, where (a) is a frequency (B) shows the relative position of the reference frequency components c1, c2, c3, c4, and c5 with the target frequency component x, and (c) shows the relationship between the position on the component and the template to be selected. , Reference frequency components c 1, c 2, c 4, c 5 and the target frequency component x, and (d) shows the relative positions of the reference frequency components c 1, c 2, c 4, c 5 and the target frequency component x. (E) represents the scan order (reverse scan order) of the oblique scan in the 4 × 4 sub-block. It is a flowchart which shows the flow of the transform coefficient decoding process by the transform coefficient decoding part which concerns on embodiment. It is a flowchart which shows the flow of the process which decodes the subblock coefficient presence / absence flag by the transform coefficient decoding part which concerns on embodiment. It is a flowchart which shows operation | movement of the 1st structural example of the coefficient level decoding part which concerns on embodiment. It is a flowchart for demonstrating more specifically the process (step S26 of FIG. 25) which decodes the code | symbol of each nonzero transform coefficient in a subblock. It is a flowchart for demonstrating more specifically the process (step S2507 of FIG. 27) which decodes the code | symbol of each non-zero transform coefficient in the subblock in the coefficient level decoding part which concerns on embodiment. It is a block diagram which shows the structure of the moving image encoder which concerns on embodiment. It is a block diagram which shows the structure of the variable-length code encoding part with which the moving image encoder which concerns on embodiment is provided. It is a block diagram which shows the structure of the quantization residual information encoding part with which the moving image encoder which concerns on embodiment of this invention is provided. It is a block diagram which shows the 1st structural example of the coefficient level encoding part which concerns on embodiment. It is a block diagram which shows the structure of the subblock coefficient level encoding part which concerns on embodiment. It is the figure shown about the structure of the transmitter which mounts the said moving image encoder, and the receiver which mounts the said moving image decoder. (A) shows a transmitting apparatus equipped with a moving picture coding apparatus, and (b) shows a receiving apparatus equipped with a moving picture decoding apparatus. It is the figure shown about the structure of the recording device which mounts the said moving image encoder, and the reproducing | regenerating apparatus which mounts the said moving image decoder. (A) shows a recording apparatus equipped with a moving picture coding apparatus, and (b) shows a reproduction apparatus equipped with a moving picture decoding apparatus.

  Embodiments of a decoding apparatus and an encoding apparatus according to the present invention will be described below with reference to the drawings. Note that the decoding apparatus according to the present embodiment decodes a moving image from encoded data. Therefore, hereinafter, this is referred to as “moving image decoding apparatus”. In addition, the encoding device according to the present embodiment generates encoded data by encoding a moving image. Therefore, hereinafter, this is referred to as a “moving image encoding device”.

However, the scope of application of the present invention is not limited to this. That is, as will be apparent from the following description, the features of the present invention can be realized without assuming a plurality of frames. That is, the present invention can be applied to a general decoding apparatus and a general encoding apparatus regardless of whether the target is a moving image or a still image.
[Configuration of Encoded Data # 1]
A configuration example of encoded data # 1 generated by the moving image encoding device 2 and decoded by the moving image decoding device 1 will be described with reference to FIG. The encoded data # 1 exemplarily includes a sequence and a plurality of pictures constituting the sequence.

  In the sequence layer, a set of data referred to by the video decoding device 1 is defined in order to decode the sequence to be processed. The sequence layer includes a sequence parameter set SPS, a picture parameter set PPS, and a picture PICT.

  FIG. 2 shows a hierarchical structure below the picture layer in the encoded data # 1. 2A to 2D are included in the picture layer that defines the picture PICT, the slice layer that defines the slice S, the tree block layer that defines the tree block TBLK, and the tree block TBLK, respectively. It is a figure which shows the CU layer which prescribes | regulates a coding unit (Coding Unit; CU).

(Picture layer)
In the picture layer, a set of data referred to by the video decoding device 1 for decoding a picture PICT to be processed (hereinafter also referred to as a target picture) is defined. As shown in FIG. 2A, the picture PICT includes a picture header PH and slices S _{1 to} S _NS (NS is the total number of slices included in the picture PICT).

Note that, hereinafter, when it is not necessary to distinguish each of the slices S _{1 to} S _NS , the reference numerals may be omitted. The same applies to other data with subscripts included in encoded data # 1 described below.

  The picture header PH includes a coding parameter group that is referred to by the video decoding device 1 in order to determine a decoding method of the target picture.

(Slice layer)
In the slice layer, a set of data referred to by the video decoding device 1 for decoding the slice S to be processed (also referred to as a target slice) is defined. As shown in FIG. 2B, the slice S includes a slice header SH and tree blocks TBLK _{1 to} TBLK _NC (where NC is the total number of tree blocks included in the slice S).

  The slice header SH includes an encoding parameter group that is referred to by the video decoding device 1 in order to determine a decoding method of the target slice. Slice type designation information (slice_type) for designating a slice type is an example of an encoding parameter included in the slice header SH.

  The slice types that can be specified by the slice type specification information include (1) I slice that uses only intra prediction at the time of encoding, (2) P slice that uses single prediction or intra prediction at the time of encoding, ( 3) B-slice using single prediction, bi-prediction, or intra prediction at the time of encoding may be used.

In addition, the slice header SH includes a filter parameter FP that is referred to by a loop filter included in the video decoding device 1. The filter parameter FP includes a filter coefficient group. The filter coefficient group includes (1) tap number designation information for designating the number of taps of the filter, (2) filter coefficients a _{0 to} a _NT-1 (NT is the total number of filter coefficients included in the filter coefficient group), and , (3) offset is included.

(Tree block layer)
In the tree block layer, a set of data referred to by the video decoding device 1 for decoding a processing target tree block TBLK (hereinafter also referred to as a target tree block) is defined.

The tree block TBLK includes a tree block header TBLKH and coding unit information CU _{1 to} CU _NL (NL is the total number of coding unit information included in the tree block TBLK). Here, first, a relationship between the tree block TBLK and the coding unit information CU will be described as follows.

  Tree block TBLK is divided into units for specifying a block size for each process of intra prediction or inter prediction and transformation.

  The unit of the tree block TBLK is divided by recursive quadtree division. The tree structure obtained by this recursive quadtree partitioning is hereinafter referred to as a coding tree.

  Hereinafter, a unit corresponding to a leaf which is a node at the end of the coding tree is referred to as a coding node. In addition, since the encoding node is a basic unit of the encoding process, hereinafter, the encoding node is also referred to as an encoding unit (CU).

That is, the coding unit information CU _{1 to} CU _NL is information corresponding to each coding node (coding unit) obtained by recursively dividing the tree block TBLK into quadtrees.

  Also, the root of the coding tree is associated with the tree block TBLK. In other words, the tree block TBLK is associated with the highest node of the tree structure of the quadtree partition that recursively includes a plurality of encoding nodes.

  Note that the size of each coding node is half of the size of the coding node to which the coding node directly belongs (that is, the unit of the node one level higher than the coding node).

  In addition, the size that each coding node can take depends on the size designation information and the maximum hierarchical depth of the coding node included in the sequence parameter set SPS of the coded data # 1. For example, when the size of the tree block TBLK is 64 × 64 pixels and the maximum hierarchical depth is 3, the coding nodes in the hierarchy below the tree block TBLK have four sizes, that is, 64 × 64. It can take any of a pixel, 32 × 32 pixel, 16 × 16 pixel, and 8 × 8 pixel.

(Tree block header)
The tree block header TBLKH includes an encoding parameter referred to by the video decoding device 1 in order to determine a decoding method of the target tree block. Specifically, as shown in FIG. 2C, tree block division information SP_TBLK that designates a division pattern of the target tree block into each CU, and a quantization parameter difference that designates the size of the quantization step. Δqp (qp_delta) is included.

  The tree block division information SP_TBLK is information representing a coding tree for dividing the tree block. Specifically, the shape and size of each CU included in the target tree block, and the position in the target tree block Is information to specify.

  Note that the tree block division information SP_TBLK may not explicitly include the shape or size of the CU. For example, the tree block division information SP_TBLK may be a set of flags (split_coding_unit_flag) indicating whether or not the entire target tree block or a partial area of the tree block is divided into four. In that case, the shape and size of each CU can be specified by using the shape and size of the tree block together.

  The quantization parameter difference Δqp is a difference qp−qp ′ between the quantization parameter qp in the target tree block and the quantization parameter qp ′ in the tree block encoded immediately before the target tree block.

(CU layer)
In the CU layer, a set of data referred to by the video decoding device 1 for decoding a CU to be processed (hereinafter also referred to as a target CU) is defined.

  Here, before describing specific contents of data included in the coding unit information CU, a tree structure of data included in the CU will be described. The encoding node is a node at the root of a prediction tree (PT) and a transform tree (TT). The prediction tree and the conversion tree are described as follows.

  In the prediction tree, the encoding node is divided into one or a plurality of prediction blocks, and the position and size of each prediction block are defined. In other words, the prediction block is one or a plurality of non-overlapping areas constituting the encoding node. The prediction tree includes one or a plurality of prediction blocks obtained by the above division.

  Prediction processing is performed for each prediction block. Hereinafter, a prediction block that is a unit of prediction is also referred to as a prediction unit (PU).

  Broadly speaking, there are two types of division in the prediction tree: intra prediction and inter prediction.

  In the case of intra prediction, there are 2N × 2N (the same size as the encoding node) and N × N division methods.

  In the case of inter prediction, there are 2N × 2N (the same size as the encoding node), 2N × N, N × 2N, N × N, and the like.

  In the transform tree, the encoding node is divided into one or a plurality of transform blocks, and the position and size of each transform block are defined. In other words, the transform block is one or a plurality of non-overlapping areas constituting the encoding node. The conversion tree includes one or a plurality of conversion blocks obtained by the above division.

  The conversion process is performed for each conversion block. Hereinafter, a transform block that is a unit of transform is also referred to as a transform unit (TU). The size of the TU is represented by the horizontal width and logarithm log2TrafoWidth of the transform block and the logarithmic value log2TrafoHeight of the vertical width. The size of the TU is also represented by a value log2TrafoSize obtained by the following equation.

log2TrafoSize = (log2TrafoWidth + log2TrafoHeight) >> 1
Hereinafter, a TU having a size of horizontal width W × longitudinal width H is referred to as W × HTU (example: 4 × 4 TU).

(Data structure of encoding unit information)
Next, specific contents of data included in the coding unit information CU will be described with reference to FIG. As shown in FIG. 2D, the coding unit information CU specifically includes a skip mode flag SKIP, CU prediction type information Pred_type, PT information PTI, and TT information TTI.

[Skip flag]
The skip flag SKIP is a flag indicating whether or not the skip mode is applied to the target CU. When the value of the skip flag SKIP is 1, that is, when the skip mode is applied to the target CU, the code The PT information PTI in the unit information CU is omitted. Note that the skip flag SKIP is omitted for the I slice.

[CU prediction type information]
The CU prediction type information Pred_type includes CU prediction method information PredMode and PU partition type information PartMode. The CU prediction type information may be simply referred to as prediction type information.

  The CU prediction method information PredMode specifies whether intra prediction (intra CU) or inter prediction (inter CU) is used as a predicted image generation method for each PU included in the target CU. Hereinafter, the types of skip, intra prediction, and inter prediction in the target CU are referred to as a CU prediction mode.

  The PU partition type information PartMode designates a PU partition type that is a pattern of partitioning the target coding unit (CU) into each PU. Hereinafter, dividing the target coding unit (CU) into each PU according to the PU division type in this way is referred to as PU division.

  For example, the PU partition type information PartMode may be an index indicating the type of PU partition pattern, and the shape, size, and position of each PU included in the target prediction tree may be It may be specified.

  The selectable PU partition types differ depending on the CU prediction method and the CU size. Furthermore, the PU partition types that can be selected differ in each case of inter prediction and intra prediction. Details of the PU partition type will be described later.

[PT information]
The PT information PTI is information related to the PT included in the target CU. In other words, the PT information PTI is a set of information on each of one or more PUs included in the PT. As described above, since the generation of the predicted image is performed in units of PUs, the PT information PTI is referred to when the moving image decoding apparatus 1 generates a predicted image. As shown in FIG. 2D, the PT information PTI includes PU information PUI _{1 to} PUI _NP (NP is the total number of PUs included in the target PT) including prediction information in each PU.

  The prediction information PUI includes an intra prediction parameter PP_Intra or an inter prediction parameter PP_Inter depending on which prediction method is specified by the prediction type information Pred_mode. Hereinafter, a PU to which intra prediction is applied is also referred to as an intra PU, and a PU to which inter prediction is applied is also referred to as an inter PU.

  The inter prediction parameter PP_Inter includes a coding parameter referred to when the video decoding device 1 generates an inter prediction image by inter prediction.

  Examples of the inter prediction parameter PP_Inter include a merge flag (merge_flag), a merge index (merge_idx), an estimated motion vector index (mvp_idx), a reference image index (ref_idx), an inter prediction flag (inter_pred_flag), and a motion vector residual (mvd). ).

  The intra prediction parameter PP_Intra includes a coding parameter that is referred to when the video decoding device 1 generates an intra prediction image by intra prediction.

  Examples of the intra prediction parameter PP_Intra include an estimated prediction mode flag, an estimated prediction mode index, and a residual prediction mode index.

  The intra prediction parameter may include a PCM mode flag indicating whether to use the PCM mode. When the PCM mode flag is encoded and the PCM mode flag indicates that the PCM mode is used, the prediction process (intra), the conversion process, and the entropy encoding process are omitted. .

[TT information]
The TT information TTI is information regarding the TT included in the CU. In other words, the TT information TTI is a set of information regarding each of one or a plurality of TUs included in the TT, and is referred to when the moving image decoding apparatus 1 decodes residual data. Hereinafter, a TU may be referred to as a block.

As shown in FIG. 2D, the TT information TTI includes TT division information SP_TU for designating a division pattern of the target CU into each transform block, and TU information TUI _{1 to} TUI _NT (NT is assigned to the target CU. The total number of blocks included).

  Specifically, the TT division information SP_TU is information for determining the shape and size of each TU included in the target CU and the position within the target CU. For example, the TT division information SP_TU can be realized from information (split_transform_flag) indicating whether or not the target node is to be divided and information (trafoDepth) indicating the depth of the division.

  For example, when the size of the CU is 64 × 64, each TU obtained by the division can take a size from 32 × 32 pixels to 4 × 4 pixels.

The TU information TUI _{1 to} TUI _NT are individual information regarding each of one or more TUs included in the TT. For example, the TU information TUI includes a quantized prediction residual (also referred to as a quantized residual) (hereinafter, information related to the quantized predictive residual is referred to by the quantized residual information QD).

  Each quantization prediction residual is encoded data generated by the moving image encoding device 2 performing the following processes 1 to 3 on a target block that is a processing target block.

Process 1: Frequency conversion (for example, DCT transform (Discrete Cosine Transform)) of the prediction residual obtained by subtracting the prediction image from the encoding target image;
Process 2: Quantize the transform coefficient obtained in Process 1;
Process 3: Variable length coding is performed on the transform coefficient quantized in Process 2;
The quantization parameter qp described above represents the magnitude of the quantization step QP used when the moving image coding apparatus 2 quantizes the transform coefficient (QP = 2 ^{qp / 6} ).

(PU split type)
In the PU division type, if the size of the target CU is 2N × 2N pixels, there are the following eight patterns in total. That is, 4 symmetric splittings of 2N × 2N pixels, 2N × N pixels, N × 2N pixels, and N × N pixels, and 2N × nU pixels, 2N × nD pixels, nL × 2N pixels, And four asymmetric splittings of nR × 2N pixels. N = 2 ^m (m is an arbitrary integer of 1 or more). Hereinafter, an area obtained by dividing a symmetric CU is also referred to as a partition.

  3A to 3H specifically show the positions of the boundaries of PU division in the CU for each division type.

  FIG. 3A illustrates a 2N × 2N PU partition type that does not perform CU partitioning. Moreover, (b), (c), and (d) of FIG. 3 show the shapes of partitions when the PU partition types are 2N × N, 2N × nU, and 2N × nD, respectively. . Also, (e), (f), and (g) of FIG. 3 show the shapes of the partitions when the PU partition types are N × 2N, nL × 2N, and nR × 2N, respectively. . Moreover, (h) of FIG. 3 has shown the shape of the partition in case PU partition type is NxN.

  The PU partition types shown in FIGS. 3A and 3H are also referred to as square partitioning based on the shape of the partition. Further, the PU partition types shown in FIGS. 3B to 3G are also referred to as non-square partitions.

  In FIGS. 3A to 3H, the numbers assigned to the respective regions indicate the region identification numbers, and the regions are processed in the order of the identification numbers. That is, the identification number represents the scan order of the area.

[Partition type for inter prediction]
In the inter PU, seven types other than N × N ((h) in FIG. 3) are defined among the above eight division types. The six asymmetric partitions are sometimes called AMP (Asymmetric Motion Partition).

  A specific value of N is defined by the size of the CU to which the PU belongs, and specific values of nU, nD, nL, and nR are determined according to the value of N. For example, a 128 × 128 pixel inter-CU includes 128 × 128 pixels, 128 × 64 pixels, 64 × 128 pixels, 64 × 64 pixels, 128 × 32 pixels, 128 × 96 pixels, 32 × 128 pixels, and 96 × It is possible to divide into 128-pixel inter PUs.

[Partition type for intra prediction]
In the intra PU, the following two types of division patterns are defined. A division pattern 2N × 2N in which the target CU is not divided, that is, the target CU itself is handled as one PU, and a pattern N × N in which the target CU is divided into four PUs symmetrically.

  Therefore, in the intra PU, the division patterns (a) and (h) can be taken in the example shown in FIG.

  For example, an 128 × 128 pixel intra CU can be divided into 128 × 128 pixel and 64 × 64 pixel intra PUs.

(TU split type)
Next, the TU partition type will be described with reference to FIGS. The TU partition pattern is determined by the CU size, the partition depth (trafoDepth), and the PU partition type of the target PU.

  The TU partition pattern includes a square quadtree partition and a non-square quadtree partition.

  (I) to (k) in FIG. 3 show a division method for dividing a square node into a square or a non-square by quadtree division. More specifically, (i) of FIG. 3 shows a division method in which a square node is divided into quadtrees into squares. Further, (j) in the figure shows a division method in which a square node is divided into quadrants into horizontally long rectangles. And (k) of the same figure has shown the division | segmentation system which divides a quadrilateral tree into a vertically long rectangle by quadtree.

  Further, (l) to (o) of FIG. 3 show a dividing method for dividing a non-square node into a square or a non-square by quadtree division. More specifically, (l) of FIG. 3 shows a division method for dividing a horizontally long rectangular node into a horizontally long rectangle by quadtree division. Further, (m) in the figure shows a division method in which horizontally long rectangular nodes are divided into quadtrees into squares. In addition, (n) in the figure shows a division method in which a vertically long rectangular node is divided into quadrants into vertically long rectangles. And (o) of the figure has shown the division | segmentation system which divides a vertically long rectangular node into a quadtree in a square.

(Comparative example of configuration of quantization residual information QD)
4 and 5 show each syntax included in the quantization residual information QD (indicated as residual_coding_cabac () in FIGS. 4 and 5) in the comparative example.

  FIG. 4 is a diagram illustrating a first half portion of a syntax table indicating syntax included in the quantized residual information QD. FIG. 5 is a diagram illustrating the second half of the syntax table indicating the syntax included in the quantized residual information QD.

  In the comparative example, the syntax significant_coeff_flag indicating the presence / absence of a non-zero transform coefficient, the syntax coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag, coeff_abs_level_remaining (coeff_abs_level_minus3) indicating the magnitude of the transform coefficient, and the sign of the sign of the transform coefficient _ It is characterized by continuous decoding in a loop in the block (shaded portion shown in FIGS. 4 and 5). Another feature is that a context index used for decoding significant_coeff_flag is derived using the sum of absolute values of already decoded transform coefficients.

(Configuration of quantization residual information QD)
6 and 7 are diagrams illustrating syntaxes included in the quantization residual information QD (denoted as residual_coding () in FIGS. 6 and 7).

  FIG. 6 is a diagram illustrating a first half portion of a syntax table indicating syntax included in the quantized residual information QD. FIG. 7 is a diagram illustrating the second half of the syntax table indicating the syntax included in the quantized residual information QD.

  As shown in FIGS. 6 and 7, the quantization residual information QD includes syntax last_significant_coeff_x, last_significant_coeff_y, significant_coeff_group_flag, significant_coeff_flag, coeff_abs_level_greater1_flag, coeff_sign_flag, and coeff_abs_level_remaining.

  Each syntax included in the quantized residual information QD is encoded by context adaptive binary arithmetic coding (CABAC).

  The conversion coefficient is sequentially scanned from the low frequency side to the high frequency side. This scan order may be referred to as a forward scan. On the other hand, a scan from the high frequency side to the low frequency side is also used, contrary to the forward scan. This scan order is sometimes called reverse scan.

  The syntaxes last_significant_coeff_x and last_significant_coeff_y are syntaxes indicating the position of the last non-zero transform coefficient along the forward scan direction.

  The syntax significant_coeff_flag is a syntax indicating whether or not there is a non-zero transform coefficient for each frequency component along the reverse scan direction starting from the non-zero transform coefficient. The syntax significant_coeff_flag is a flag that takes 0 for each xC, yC if the conversion coefficient is 0, and 1 if the conversion coefficient is not 0. The syntax significant_coeff_flag is also referred to as a conversion coefficient presence / absence flag or coefficient presence / absence flag. Note that significant_coeff_flag may not be treated as an independent syntax but may be included in a syntax (for example, coeff_abs_level) representing an absolute value of a transform coefficient. In this case, the first bit of the syntax coeff_abs_level corresponds to significant_coeff_flag, and the process of deriving the context index of the following significant_coeff_flag corresponds to the process of deriving the context index of the first bit of the syntax coeff_abs_level.

  The variable length code decoding unit 11 included in the video decoding device 1 divides the transform block into a plurality of sub blocks, and decodes significant_coeff_group_flag using the sub blocks as processing units. The quantization residual information QD includes a flag (subblock coefficient presence / absence flag significant_coeff_group_flag) indicating whether or not at least one non-zero transform coefficient exists in the subblock in units of subblocks.

  Hereinafter, the decoding process will be described with reference to FIGS.

  FIG. 8 is a diagram illustrating the relationship between blocks and sub-blocks. FIG. 8A shows an example in which 4 × 4 TU is composed of one sub-block composed of 4 × 4 components. FIG. 8B shows an example in which 8 × 8 TU is composed of four sub-blocks composed of 4 × 4 components. FIG. 8C shows an example in which 16 × 16 TU is composed of 16 sub-blocks composed of 4 × 4 components. Note that the relationship between the TU size and the sub-block size and the division method are not limited to this example.

  FIG. 9A is a diagram showing the scan order for a plurality of (4 × 4 = 16 in FIG. 9A) sub-blocks obtained by dividing a block. Hereinafter, scanning in units of sub-blocks is also referred to as sub-block scanning. When scanning is performed on the sub-block as shown in FIG. 9A, scanning is performed on each frequency region in the sub-block in the scanning order shown in FIG. 9B. The scan order shown in FIGS. 9A and 9B is also referred to as “forward scan”.

  FIG. 9C is a diagram showing a scan order for a plurality of sub-blocks (4 × 4 = 16 in FIG. 9B) obtained by dividing a block. When scanning is performed on the sub-block as shown in FIG. 9C, scanning is performed on each frequency region in the sub-block in the scanning order shown in FIG. 9D. The scan order shown in FIGS. 9C and 9D is also referred to as “reverse scan”.

  10A to 10F, the horizontal axis represents the horizontal frequency xC (0 ≦ xC ≦ 7), and the vertical axis represents the vertical frequency yC (0 ≦ yC ≦ 7). In the following description, among the partial areas included in the frequency domain, the partial areas specified by the horizontal frequency xC and the vertical frequency yC are also referred to as frequency components (xC, yC). Further, the conversion coefficient for the frequency component (xC, yC) is also expressed as Coeff (xC, yC). The conversion coefficient Coeff (0, 0) indicates a DC component, and the other conversion coefficients indicate components other than the DC component. In this specification, (xC, yC) may be expressed as (u, v).

  FIG. 10A is a diagram illustrating a scan order when each frequency component is scanned in a forward scan when a block having a TU size of 8 × 8 is divided into sub-blocks of 4 × 4 size. It is.

  FIG. 10B illustrates a non-zero transform coefficient (non-zero transform coefficient) in the frequency domain composed of 8 × 8 frequency components. In the case of the example shown in FIG. 10B, last_significant_coeff_x = 6 and last_significant_coeff_y = 0.

  FIG. 10C is a diagram illustrating each value of the subblock coefficient presence / absence flag significant_coeff_group_flag decoded for each subblock when the transform coefficient to be decoded is the one shown in FIG. Significant_coeff_group_flag related to a sub-block including at least one non-zero transform coefficient takes 1 as a value, and significant_coeff_group_flag related to a sub-block including no non-zero transform coefficient takes 0 as a value.

  FIG. 10D is a diagram illustrating each value of syntax significant_coeff_flag indicating the presence or absence of a non-zero transform coefficient when the transform coefficient to be decoded is the one illustrated in FIG. For a subblock with significant_coeff_group_flag = 1, significant_coeff_flag is decoded in reverse scan order, and for a subblock with significant_coeff_group_flag = 0, it is included in the subblock without performing decoding processing of significant_coeff_flag for the subblock Significant_coeff_flag for all frequency components to be transmitted is set to 0 (lower left subblock of FIG. 10D).

  FIG. 10 (e) shows the absolute value of each transform coefficient obtained by decoding the syntax coeff_abs_level_greater1_flag and coeff_abs_level_remaining when the transform coefficients to be decoded are those shown in FIG. 10 (b). .

  FIG. 10F is a diagram illustrating the syntax coeff_sign_flag when the transform coefficient to be decoded is the one illustrated in FIG.

  The decoding of the syntaxes coeff_abs_level_greater1_flag, coeff_abs_level_greater2_flag, and coeff_abs_level_remaining indicating the value of each transform coefficient varies depending on the mode (high throughput mode). At the start of the sub-block, the high-throughput mode is off, and the high-throughput mode is turned on when the number of non-zero coefficients numSigCoeff in the sub-block becomes equal to or greater than a predetermined constant. In the high throughput mode, decoding of a part of syntax is skipped.

  The syntax coeff_abs_level_greater1_flag is a flag indicating whether or not the absolute value of the transform coefficient exceeds 1, and is encoded for a frequency component having a syntax significant_coeff_flag value of 1. When the absolute value of the transform coefficient exceeds 1, the value of coeff_abs_level_greater1_flag is 1, otherwise, the value of coeff_abs_level_greater1_flag is 0. Note that the decoding of coeff_abs_level_greater1_flag is skipped in the high throughput mode.

  The syntax coeff_abs_level_remaining is a syntax for designating the absolute value of the transform coefficient when the absolute value of the transform coefficient is a predetermined base level baseLevel. When decoding of coeff_abs_level_greater1_flag is skipped, and coeff_abs_level_greater1_flag is In the case of 1, it is encoded. The value of the syntax coeff_abs_level_remaining is obtained by subtracting baseLevel from the absolute value of the transform coefficient. For example, coeff_abs_level_remaining = 1 indicates that the absolute value of the transform coefficient is baseLevel + 1. BaseLevel is determined as follows.

baseLevel = 1 (when decoding of coeff_abs_level_greater1_flag is skipped)
baseLevel = 2 (other than above, when coeff_abs_level_greater1_flag is 1)
The syntax coeff_sign_flag is a flag indicating the sign of the transform coefficient (whether positive or negative), and is encoded for frequency components whose syntax significant_coeff_flag value is 1, except when sign hiding is performed. The The syntax coeff_sign_flag takes 1 when the transform coefficient is positive, and takes 0 when the transform coefficient is negative.

  Note that sign hiding refers to a method of calculating by calculation without explicitly encoding the sign of the transform coefficient.

  The variable length code decoding unit 11 included in the video decoding device 1 decodes the syntax last_significant_coeff_x, last_significant_coeff_y, significant_coeff_flag, coeff_abs_level_greater1_flag, coeff_abs_level_remaining, and coeff_sign_flag to generate transform coefficients Ceff (Ceff for each frequency component) be able to. Here, coeff_abs_level_remaining and coeff_sign_flag are syntaxes encoded by an arithmetic code called bypass that does not use a context.

  FIG. 11 is a diagram illustrating a configuration example of the quantization residual information QD according to the present embodiment. As illustrated in FIG. 11, the quantization residual information QD of the present embodiment is exemplarily defined as information having a hierarchical structure that is generated in units of TUs (transform_unit).

  As shown in FIG. 11, the configuration of the quantized residual information QD according to the present embodiment includes a syntax last_coefficient_pos (last_coefficient_pos_x, last_coefficient_pos_y) indicating the last position of a transform coefficient included in a TU and a subblock of encoded data in subblock units. It consists of.

  The coded data subblock in units of subblocks is a set of coded data coeff_level (coeff_level # M-1 ... coeff_level # 0) indicating the value of the transform coefficient and a set of syntax coeff_sign (coeff_sign # M) indicating the sign of the transform coefficient. -1 ... coeff_sign # 0).

  The encoded data coeff_level indicating the value of the transform coefficient includes a transform coefficient presence / absence flag significant_coeff_flag, and syntaxes coeff_abs_level_greater1_flag and coeff_abs_level_remaining indicating the value of the transform coefficient.

  In the encoded data of the present embodiment, a transform coefficient presence / absence flag and a syntax indicating the size of the transform coefficient are arranged as a set of subblock units (coeff_level # M-1... Coeff_level # 0), and further, transform coefficients Is characterized by being arranged after the previous set as a set of sub-block units (coeff_sign # M-1... Coeff_sign # 0). In this configuration, unlike the configuration of the comparative example shown in FIGS. 4 and 5, the sign of the transform coefficient is arranged as a set different from the transform coefficient presence / absence flag and the syntax indicating the size of the transform coefficient. The flow of decoding the encoded data of this configuration will be described later with reference to FIG.

  A set of non-zero transform coefficients in a specific area (for example, TU) may be referred to as a significance map.

Details of the decoding processing of various syntaxes will be described later, and the configuration of the moving image decoding device 1 will be described subsequently.
[Moving picture decoding apparatus 1]
Below, the moving image decoding apparatus 1 which concerns on this embodiment is demonstrated with reference to FIG. 16, FIG. 12-FIG. The moving picture decoding apparatus 1 is an H.264 video camera. This is a decoding device that implements a technique proposed in HEVC (High-Efficiency Video Coding), which is a successor codec of the H.264 / MPEG-4 AVC standard.

  FIG. 12 is a block diagram illustrating a configuration of the video decoding device 1. As illustrated in FIG. 12, the video decoding device 1 includes a variable length code decoding unit 11, a predicted image generation unit 12, an inverse quantization / inverse conversion unit 13, an adder 14, a frame memory 15, and a loop filter 16. I have. As illustrated in FIG. 12, the predicted image generation unit 12 includes a motion vector restoration unit 12a, an inter predicted image generation unit 12b, an intra predicted image generation unit 12c, and a prediction method determination unit 12d. The moving picture decoding apparatus 1 is an apparatus for generating moving picture # 2 by decoding encoded data # 1.

(Variable-length code decoding unit 11)
FIG. 13 is a block diagram illustrating a main configuration of the variable-length code decoding unit 11. As shown in FIG. 13, the variable-length code decoding unit 11 includes a quantization residual information decoding unit 111, a prediction parameter decoding unit 112, a prediction type information decoding unit 113, and a filter parameter decoding unit 114.

  In the variable length code decoding unit 11, the prediction parameter decoding unit 112 decodes the prediction parameter PP related to each partition from the encoded data # 1, and supplies it to the prediction image generation unit 12. Specifically, for the inter prediction partition, the prediction parameter decoding unit 112 decodes the inter prediction parameter PP_Inter including the reference image index, the estimated motion vector index, and the motion vector residual from the encoded data # 1, and these Is supplied to the motion vector restoration unit 12a. On the other hand, for the intra prediction partition, the intra prediction parameter PP_Intra including the estimated prediction mode flag, the estimated prediction mode index, and the residual prediction mode index is decoded from the encoded data # 1, and these are supplied to the intra predicted image generation unit 12c. To do.

  Further, the variable length code decoding unit 11 decodes the prediction type information Pred_type for each partition from the encoded data # 1 in the prediction type information decoding unit 113, and supplies this to the prediction method determination unit 12d. Further, the variable length code decoding unit 11 uses the quantization residual information decoding unit 111 to convert the quantization residual information QD related to the block and the quantization parameter difference Δqp related to the TU including the block from the encoded data # 1. These are decoded and supplied to the inverse quantization / inverse transform unit 13. In the variable length code decoding unit 11, the filter parameter decoding unit 114 decodes the filter parameter FP from the encoded data # 1 and supplies this to the loop filter 16. Note that a specific configuration of the quantized residual information decoding unit 111 will be described later, and a description thereof will be omitted here.

(Predicted image generation unit 12)
The predicted image generation unit 12 identifies whether each partition is an inter prediction partition that should perform inter prediction or an intra prediction partition that should perform intra prediction, based on prediction type information Pred_type for each partition. In the former case, the inter prediction image Pred_Inter is generated, and the generated inter prediction image Pred_Inter is supplied to the adder 14 as the prediction image Pred. In the latter case, the intra prediction image Pred_Intra is generated, The generated intra predicted image Pred_Intra is supplied to the adder 14. Note that, when the skip mode is applied to the processing target PU, the predicted image generation unit 12 omits decoding of other parameters belonging to the PU.

(Motion vector restoration unit 12a)
The motion vector restoration unit 12a restores the motion vector mv for each inter prediction partition from the motion vector residual for the partition and the restored motion vector mv ′ for the other partition. Specifically, (1) an estimated motion vector is derived from the restored motion vector mv ′ according to the estimation method specified by the estimated motion vector index, and (2) the derived estimated motion vector and the motion vector residual are A motion vector mv is obtained by addition. It should be noted that the restored motion vector mv ′ relating to other partitions can be read from the frame memory 15. The motion vector restoration unit 12a supplies the restored motion vector mv to the inter predicted image generation unit 12b together with the corresponding reference image index RI.

(Inter prediction image generation unit 12b)
The inter prediction image generation unit 12b generates a motion compensated image mc related to each inter prediction partition by inter-screen prediction. Specifically, using the motion vector mv supplied from the motion vector restoration unit 12a, the motion compensated image from the adaptive filtered decoded image P_ALF ′ designated by the reference image index RI also supplied from the motion vector restoration unit 12a. Generate mc. Here, the adaptive filtered decoded image P_ALF ′ is an image obtained by performing the filtering process by the loop filter 16 on the decoded image that has already been decoded for the entire frame. 12b can read out the pixel value of each pixel constituting the adaptive filtered decoded image P_ALF ′ from the frame memory 15. The motion compensated image mc generated by the inter predicted image generation unit 12b is supplied to the prediction method determination unit 12d as an inter predicted image Pred_Inter.

(Intra predicted image generation unit 12c)
The intra predicted image generation unit 12c generates a predicted image Pred_Intra related to each intra prediction partition. Specifically, first, a prediction mode is specified based on the intra prediction parameter PP_Intra supplied from the variable length code decoding unit 11, and the specified prediction mode is assigned to the target partition in, for example, raster scan order.

  Here, the prediction mode based on the intra prediction parameter PP_Intra can be specified as follows. (1) The estimated prediction mode flag is decoded, and the estimated prediction mode flag indicates that the prediction mode for the target partition to be processed is the same as the prediction mode assigned to the peripheral partition of the target partition. If the target partition is indicated, the prediction mode assigned to the partition around the target partition is assigned to the target partition. (2) On the other hand, when the estimated prediction mode flag indicates that the prediction mode for the target partition to be processed is not the same as the prediction mode assigned to the partitions around the target partition, The residual prediction mode index is decoded, and the prediction mode indicated by the residual prediction mode index is assigned to the target partition.

  The intra predicted image generation unit 12c generates a predicted image Pred_Intra from the (local) decoded image P by intra prediction according to the prediction method indicated by the prediction mode assigned to the target partition. The intra predicted image Pred_Intra generated by the intra predicted image generation unit 12c is supplied to the prediction method determination unit 12d. Note that the intra predicted image generation unit 12c can also be configured to generate the predicted image Pred_Intra from the adaptive filtered decoded image P_ALF by intra prediction.

  The definition of the prediction mode will be described with reference to FIG. FIG. 14 shows the definition of the prediction mode. As shown in the figure, 36 types of prediction modes are defined, and each prediction mode is specified by a number (intra prediction mode index) from “0” to “35”. Further, as shown in FIG. 15, the following names are assigned to the respective prediction modes. That is, “0” is “Intra_Planar (planar prediction mode, plane prediction mode)”, “1” is “Intra DC (intra DC prediction mode)”, and “2” to “34” are “ "Intra Angular (direction prediction)" and "35" is "Intra From Luma". “35” is unique to the color difference prediction mode, and is a mode for performing color difference prediction based on luminance prediction. In other words, the color difference prediction mode “35” is a prediction mode using the correlation between the luminance pixel value and the color difference pixel value. The color difference prediction mode “35” is also referred to as an LM mode. The number of prediction modes (intraPredModeNum) is “35” regardless of the size of the target block.

(Prediction method determination unit 12d)
The prediction method determination unit 12d determines whether each partition is an inter prediction partition for performing inter prediction or an intra prediction partition for performing intra prediction based on prediction type information Pred_type for the PU to which each partition belongs. To do. In the former case, the inter prediction image Pred_Inter generated by the inter prediction image generation unit 12b is supplied to the adder 14 as the prediction image Pred. In the latter case, the inter prediction image generation unit 12c generates the inter prediction image Pred_Inter. The intra predicted image Pred_Intra that has been processed is supplied to the adder 14 as the predicted image Pred.

(Inverse quantization / inverse transform unit 13)
The inverse quantization / inverse transform unit 13 (1) inversely quantizes the transform coefficient Coeff decoded from the quantized residual information QD of the encoded data # 1, and (2) transform coefficient Coeff_IQ obtained by the inverse quantization. Are subjected to inverse frequency transformation such as inverse DCT (Discrete Cosine Transform) transformation, and (3) the prediction residual D obtained by the inverse frequency transformation is supplied to the adder 14. Note that when the transform coefficient Coeff decoded from the quantization residual information QD is inversely quantized, the inverse quantization / inverse transform unit 13 performs quantization from the quantization parameter difference Δqp supplied from the variable length code decoding unit 11. Deriving step QP. The quantization parameter qp can be derived by adding the quantization parameter difference Δqp to the quantization parameter qp ′ relating to the TU that has just been inversely quantized and inversely frequency transformed immediately before, and the quantization step QP can be derived from the quantization parameter qp, for example QP = 2 ^{pq / 6} . The generation of the prediction residual D by the inverse quantization / inverse transform unit 13 is performed in units of blocks obtained by dividing TUs or TUs.

  For example, when the size of the target block is 8 × 8 pixels, the inverse DCT transform performed by the inverse quantization / inverse transform unit 13 sets the pixel position in the target block to (i, j) (0 ≦ i ≦ 7, 0 ≦ j ≦ 7), and the value of the prediction residual D at the position (i, j) is represented as D (i, j), and the frequency component (u, v) (0 ≦ u ≦ 7, When the inversely quantized transform coefficient in 0 ≦ v ≦ 7) is expressed as Coeff_IQ (u, v), it is given by, for example, the following formula (1).

Here, (u, v) is a variable corresponding to (xC, yC) described above. C (u) and C (v) are given as follows.

・ C (u) = 1 / √2 (u = 0)
・ C (u) = 1 (u ≠ 0)
・ C (v) = 1 / √2 (v = 0)
・ C (v) = 1 (v ≠ 0)
(Adder 14)
The adder 14 generates the decoded image P by adding the prediction image Pred supplied from the prediction image generation unit 12 and the prediction residual D supplied from the inverse quantization / inverse conversion unit 13. The generated decoded image P is stored in the frame memory 15.

(Loop filter 16)
The loop filter 16 includes (1) a function as a deblocking filter (DF) that performs smoothing (deblocking processing) on an image around a block boundary or partition boundary in the decoded image P, and (2) a deblocking filter. It has a function as an adaptive filter (ALF: Adaptive Loop Filter) which performs an adaptive filter process using the filter parameter FP with respect to the image which the blocking filter acted on.

(Quantization residual information decoding unit 111)
The quantization residual information decoding unit 111 decodes the quantized transform coefficient Coeff (xC, yC) for each frequency component (xC, yC) from the quantization residual information QD included in the encoded data # 1. It is the structure for doing. Here, xC and yC are indexes representing the position of each frequency component in the frequency domain, and are indexes corresponding to the above-described horizontal frequency u and vertical frequency v, respectively. Hereinafter, the quantized transform coefficient Coeff may be simply referred to as transform coefficient Coeff.

  FIG. 16 is a block diagram illustrating a configuration of the quantized residual information decoding unit 111. As illustrated in FIG. 16, the quantized residual information decoding unit 111 includes a transform coefficient decoding unit 120 and an arithmetic code decoding unit 130.

(Arithmetic Code Decoding Unit 130)
The arithmetic code decoding unit 130 is configured to decode each bit included in the quantized residual information QD with reference to the context. As illustrated in FIG. 16, the context recording update unit 131 and the bit decoding unit 132 are provided. I have.

(Context record update unit 131)
The context recording / updating unit 131 is configured to record and update the context variable CV managed by each context index ctxIdx. Here, the context variable CV includes (1) a dominant symbol MPS (most probable symbol) having a high occurrence probability and (2) a probability state index pStateIdx for designating the occurrence probability of the dominant symbol MPS.

  The context recording update unit 131 updates the context variable CV by referring to the context index ctxIdx supplied from each unit of the transform coefficient decoding unit 120 and the Bin value decoded by the bit decoding unit 132, and updated. Record the context variable CV until the next update. The dominant symbol MPS is 0 or 1. Further, the dominant symbol MPS and the probability state index pStateIdx are updated every time the bit decoding unit 132 decodes one Bin.

  The context index ctxIdx may directly specify the context for each frequency component, or may be an increment value from the context index offset set for each TU to be processed (the same applies hereinafter). ).

(Bit decoding unit 132)
The bit decoding unit 132 refers to the context variable CV recorded in the context recording update unit 131 and decodes each bit (also referred to as Bin) included in the quantization residual information QD. Further, the Bin value obtained by decoding is supplied to each unit included in the transform coefficient decoding unit 120. Further, the value of Bin obtained by decoding is also supplied to the context recording update unit 131 and is referred to in order to update the context variable CV.

(Transform coefficient decoding unit 120)
As shown in FIG. 16, the transform coefficient decoding unit 120 includes a last coefficient position decoding unit 121, a scan order table storage unit 122, a coefficient decoding control unit 123, a coefficient level decoding unit 124, a coefficient code decoding unit 125, and a decoded coefficient storage unit. 126, and a sub-block coefficient presence / absence flag decoding unit 127.

(Last coefficient position decoding unit 121)
The last coefficient position decoding unit 121 interprets the decoded bit (Bin) supplied from the bit decoding unit 132, and decodes the syntax last_significant_coeff_x and last_significant_coeff_y. The decoded syntax last_significant_coeff_x and last_significant_coeff_y are supplied to the coefficient decoding control unit 123. Further, the last coefficient position decoding unit 121 calculates a context index ctxIdx for determining a context used for decoding the bins of the syntax last_significant_coeff_x and last_significant_coeff_y in the arithmetic code decoding unit 130. The calculated context index ctxIdx is supplied to the context recording update unit 131.

(Scan order table storage unit 122)
The scan order table storage unit 122 uses as arguments the size of the TU (block) to be processed, the scan index representing the type of scan direction, and the frequency component identification index given along the scan order. A table for giving a position in the frequency domain is stored.

  An example of such a scan order table is ScanOrder shown in FIGS. 6 and 7. In ScanOrder shown in FIGS. 6 and 7, log2TrafoWidth represents the width of the TU to be processed, log2TrafoHeight represents the height of the TU to be processed, and scanIdx represents the scan index. , N represent frequency component identification indexes given along the scan order. 6 and 7, xC and yC represent the positions of the frequency components to be processed in the frequency domain.

  The table stored in the scan order table storage unit 122 is specified by the scan index scanIdx associated with the size of the TU (block) to be processed and the prediction mode index of the intra prediction mode. When the prediction method used for the TU to be processed is intra prediction, the coefficient decoding control unit 123 creates a table specified by the scan index scanIdx associated with the size of the TU and the prediction mode of the TU. The scanning order of the frequency components is determined with reference to it.

  FIG. 17 illustrates an example of the scan index scanIdx specified by the intra prediction mode index IntraPredMode and the value log2TrafoSize specifying the TU size. In FIG. 17, log2TrafoSize-2 = 0 indicates that the TU size is 4 × 4 (corresponding to 4 × 4 pixels), and log2TrafoSize-2 = 1 indicates that the TU size is 8 × 8 (8 × 8 Corresponding to a pixel). As shown in FIG. 17, for example, when the TU size is 4 × 4 and the intra prediction mode index is 1, the scan index = 0 is used, the TU size is 4 × 4, and the intra prediction mode index is When 6, scan index = 2 is used.

  FIG. 18A shows the scan type ScanType specified by each value of the scan index scanIdx. As shown in FIG. 18A, when the scan index is 0, an up-right diagonal scan is designated, and when the scan index is 1, a horizontal fast scan is performed. When specified and the scan index is 2, a vertical fact scan is specified.

  In addition, when the CU prediction method information PredMode is inter prediction, a scan index can be derived using the TU size. When the TU size matches the width and height of the TU size, a scan order other than horizontal priority and vertical priority (scan index = 0) is used. If the width and height of the TU size do not match and the width of the TU size is larger than the height, the horizontal priority scan order (scan index = 1) is used. On the other hand, when the height of the TU size is larger than the width, the scan order with priority (scan index = 2) is used.

  18B to 18D show the scan types (horizontal fast scan) and vertical direction priority scan (specified by the scan index scanIdx) when the TU size is 4 × 4. An example of the scan order of vertical fast scan) and diagonal scan (Up-right diagonal scan) is shown. In addition, each example illustrated in FIGS. 18B to 18D indicates the forward scan direction. The horizontal direction priority scan shown in FIG. 18B is characterized in that a coefficient is scanned for each diagonal row in the horizontal direction in units of small sub-blocks obtained by dividing the sub-block into upper and lower halves. It is suitable when the concentration is concentrated. Further, the vertical priority scan shown in FIG. 18C is characterized in that the coefficient is scanned diagonally for each column in the vertical direction in small sub-block units obtained by dividing the sub-block into left and right halves. This is suitable when the coefficients are concentrated.

  FIGS. 19A to 19C show an example of the scan order of each scan type specified by the scan index scanIdx when the TU size is 8 × 8 and the sub-block size is 4 × 4. ing. Each example shown in FIGS. 19A to 19C indicates the forward scan direction. The horizontal direction priority scan shown in FIG. 19 (a) is characterized in that a coefficient is scanned for each diagonal row in the horizontal direction in small sub-block units obtained by dividing the sub-block into upper and lower halves. It is suitable when the concentration is concentrated. Further, the vertical priority scan shown in FIG. 19B is characterized in that the coefficient is scanned for each diagonal column in the vertical direction in small sub-block units obtained by dividing the sub-block into left and right halves. This is suitable when the coefficients are concentrated.

(Sub-block scan order table)
The scan order table storage unit 122 stores a sub-block scan order table for designating the scan order of sub-blocks. The sub-block scan order table is specified by the scan index scanIdx associated with the size of the TU (block) to be processed and the prediction mode index (prediction direction) of the intra prediction mode. When the prediction method used for the TU to be processed is intra prediction, the coefficient decoding control unit 123 creates a table specified by the scan index scanIdx associated with the size of the TU and the prediction mode of the TU. The scanning order of the sub-blocks is determined with reference to it.

(Coefficient decoding control unit 123)
The coefficient decoding control unit 123 is configured to control the order of decoding processing in each unit included in the quantization residual information decoding unit 111.

  The coefficient decoding control unit 123 refers to the syntaxes last_significant_coeff_x and last_significant_coeff_y supplied from the last coefficient position decoding unit 121, identifies the position of the last non-zero transform coefficient along the forward scan, and identifies the identified last non-zero The position of each sub-block (xCG) in the scan order starting from the position of the sub-block including the transform coefficient and in the reverse scan order of the scan order given by the sub-block scan order table stored in the scan order table storage unit 122 , YCG) is supplied to the sub-block coefficient presence / absence flag decoding unit 127. Further, the coefficient decoding control unit 123 supplies the scan index scanIdx associated with the size of the TU and the prediction mode of the TU to the coefficient level decoding unit 124.

  Also, the coefficient decoding control unit 123 includes the subblocks to be processed in the reverse scan order of the scan order given by the scan order table stored in the scan order table storage unit 122 for the subblocks to be processed. The position (xC, yC) of each frequency component is supplied to the coefficient level decoding unit 124 and the decoded coefficient storage unit 126. Here, as the scan order of each frequency component included in the sub-block to be processed, in the case of intra prediction, the scan index scanIdx specified by the intra prediction mode index IntraPredMode and the value log2TrafoSize specifying the TU size In the case of inter prediction, an oblique scan (Up-right diagonal scan) may be used.

  Thus, when the prediction scheme applied to the unit region (block, TU) to be processed is intra prediction, the coefficient decoding control unit 123 determines the sub-block scan order according to the prediction direction of the intra prediction, In addition, the scan order within the sub-block is set.

  In general, the intra prediction mode and the bias of the transform coefficient are correlated with each other. Therefore, by switching the scan order according to the intra prediction mode, a scan suitable for the bias of the subblock coefficient presence / absence flag and the coefficient presence / absence flag is performed. It can be carried out. As a result, the coding amount of the subblock coefficient presence / absence flag and coefficient presence / absence flag to be encoded and decoded can be reduced, so that the processing amount is reduced and the coding efficiency is improved.

(Subblock coefficient presence / absence flag decoding unit 127)
The subblock coefficient presence / absence flag decoding unit 127 interprets each Bin supplied from the bit decoding unit 132, and decodes the syntax significant_coeff_group_flag [xCG] [yCG] specified by each subblock position (xCG, yCG). Also, the sub-block coefficient presence / absence flag decoding unit 127 calculates a context index ctxIdx for determining a context used for decoding Bin of the syntax significant_coeff_group_flag [xCG] [yCG] in the arithmetic code decoding unit 130. The calculated context index ctxIdx is supplied to the context recording update unit 131. Here, the syntax significant_coeff_group_flag [xCG] [yCG] is 1 when the subblock specified by the subblock position (xCG, yCG) includes at least one nonzero transform coefficient, and is nonzero. This is a syntax that takes 0 when no conversion coefficient is included. The decoded syntax significant_coeff_group_flag [xCG] [yCG] value is stored in the decoded coefficient storage unit 126.

  Note that a more specific configuration of the sub-block coefficient presence / absence flag decoding unit 127 will be described later.

(Coefficient level decoding unit 124)
The coefficient level decoding unit 124 according to the present embodiment decodes the syntax significant_coeff_flag [xC] [yC], coeff_abs_level_greater1_flag, and coeff_abs_level_remaining specified by each coefficient position (xC, yC), and transform coefficient level transCoeffLevel [xC] [ yC] is derived. The value of the decoded transform coefficient level transCoeffLevel [xC] [yC] is stored in the decoded coefficient storage unit 126. Also, the coefficient level decoding unit 124 calculates a context index ctxIdx for determining a context used for decoding Bin of the syntax significant_coeff_flag [xC] [yC] in the arithmetic code decoding unit 130. The calculated context index ctxIdx is supplied to the context recording update unit 131. A specific configuration of the coefficient level decoding unit 124 will be described later.

(Coefficient code decoding unit 125)
The coefficient code decoding unit 125 interprets each Bin supplied from the bit decoding unit 132, decodes the syntax coeff_sign_flag, and, based on the decoding result of these syntaxes, transform coefficients (more than Specifically, the value of the non-zero conversion coefficient is derived. Also, the context index ctxIdx used for decoding various syntaxes is supplied to the context recording update unit 131. The derived transform coefficient value is stored in the decoded coefficient storage unit 126.

(Decoding coefficient storage unit 126)
The decoding coefficient storage unit 126 is a configuration for storing each value of the transform coefficient decoded by the coefficient code decoding unit 125. In addition, each value of the syntax significant_coeff_flag decoded by the coefficient level decoding unit 124 is stored in the decoding coefficient storage unit 126. Each value of the transform coefficient stored in the decoded coefficient storage unit 126 is supplied to the inverse quantization / inverse transform unit 13.

(Configuration example of subblock coefficient presence / absence flag decoding unit 127)
Hereinafter, a specific configuration example of the sub-block coefficient presence / absence flag decoding unit 127 will be described with reference to FIG.

  FIG. 20 is a block diagram illustrating a configuration example of the sub-block coefficient presence / absence flag decoding unit 127. As shown in FIG. 20, the sub-block coefficient presence / absence flag decoding unit 127 includes a sub-block coefficient presence / absence flag context deriving unit 127a, a sub-block coefficient presence / absence flag storage unit 127b, and a sub-block coefficient presence / absence flag setting unit 127c. .

  Hereinafter, a case where the sub-block coefficient presence / absence flag decoding unit 127 is supplied with sub-block positions (xCG, yCG) from the coefficient decoding control unit 123 in the reverse scan order will be described as an example. In this case, in the configuration on the encoding device side corresponding to the sub-block coefficient presence / absence flag decoding unit 127, the sub-block positions (xCG, yCG) are supplied in the forward scan order.

(Subblock coefficient presence / absence flag context deriving unit 127a)
The subblock coefficient presence / absence flag context deriving unit 127a included in the subblock coefficient presence / absence flag decoding unit 127 derives a context index to be allocated to the subblock specified by each subblock position (xCG, yCG). The context index assigned to the sub-block is used when decoding Bin indicating the syntax significant_coeff_group_flag for the sub-block. Further, when the context index is derived, the value of the decoded sub-block coefficient presence / absence flag stored in the sub-block coefficient presence / absence flag storage unit 127b is referred to. The sub-block coefficient presence / absence flag context deriving unit 127a supplies the derived context index to the context recording / updating unit 131.

  In the derivation of the context index to be assigned to the sub-block, the sub-block coefficient presence / absence flag of the sub-block (xCG + 1, yCG) (see FIG. 21B) located immediately to the right of the sub-block position (xCG, yCG) and the sub-block The sub block coefficient presence / absence flag of the sub block (xCG, yCG + 1) (see FIG. 21B) located below the position (xCG, yCG) is referred to.

  That is, the context index to be assigned to the sub-block is specifically determined by using the sub-block position (xCG, yCG) and the value of the decoded sub-block coefficient presence / absence flag stored in the sub-block coefficient presence / absence flag storage unit 127b. Derived.

  More specifically, the context index is a decoded subblock coefficient presence / absence flag significant_coeff_group_flag [xCG + 1] [yCG decoded for a subblock (xCG + 1, yCG) located to the right of the subblock position (xCG, yCG). ] And the value of the decoded subblock coefficient presence / absence flag siginificant_coeff_group_flag [xCG] [yCG + 1] decoded for the subblock (xCG, yCG + 1) located below the subblock position (xCG, yCG) It is set as follows with reference.

ctxIdx = ctxIdxOffset + Min ((significant_coeff_group_flag [xCG + 1] [yCG] + significant_coeff_group_flag [xCG] [yCG + 1]), 1)
Note that the initial value ctxIdxOffset is determined by cIdx indicating a color space. When there is no decoded sub-block located at (xCG + 1, yCG) or (xCG, yCG + 1), the value of the sub-block coefficient presence / absence flag located at (xCG + 1, yCG) or (xCG, yCG + 1) is set. Treat as zero.

(Subblock coefficient presence / absence flag storage unit 127b)
Each value of the syntax significant_coeff_group_flag decoded or set by the subblock coefficient presence / absence flag setting unit 127c is stored in the subblock coefficient presence / absence flag storage unit 127b. The subblock coefficient presence / absence flag setting unit 127c can read the syntax significant_coeff_group_flag allocated to the adjacent subblock from the subblock coefficient presence / absence flag storage unit 127b.

(Subblock coefficient presence / absence flag setting unit 127c)
The sub-block coefficient presence / absence flag setting unit 127c interprets each Bin supplied from the bit decoding unit 132, and decodes or sets the syntax significant_coeff_group_flag [xCG] [yCG]. More specifically, the subblock coefficient presence / absence flag setting unit 127c includes a subblock position (xCG, yCG) and a subblock adjacent to the subblock specified by the subblock position (xCG, yCG) (adjacent subblock). Also, the syntax significant_coeff_group_flag [xCG] [yCG] is decoded or set. Further, the value of the syntax significant_coeff_group_flag [xCG] [yCG] decoded or set is supplied to the coefficient level decoding unit 124.

  The sub-block coefficient presence / absence flag setting unit 127c, as shown in FIG. 21 (c), sub-block coefficient presence / absence flag significant_coeff_group_flag [xCG + assigned to the sub-block (xCG + 1, yCG) adjacent to the sub-block (xCG, yCG). 1] Referring to the value of [yCG] and the value of subblock coefficient presence / absence flag significant_coeff_group_flag [xCG] [yCG + 1] assigned to the subblock (xCG, yCG + 1), subblock coefficient presence / absence flag significant_coeff_group_flag [xCG] [ The context index used for decoding yCG] is derived.

  Note that in a block in which the sub-block coefficient presence / absence flag is set to 0, the coefficient level decoding unit 124 can skip decoding of the coefficient presence / absence flag significant_coeff_flag, thereby simplifying the decoding process.

  A specific example using FIG. 22 is as follows. When transform coefficients are distributed as shown in FIG. 22 (a), the sub-block coefficient presence / absence flags assigned to the respective sub-blocks are as shown in FIG. 22 (b). That is, among the 4 × 4 sub-blocks, the non-zero coefficient exists in the sub-block in the first row, but the non-zero coefficient does not exist in the sub-blocks after the second row.

  Therefore, in the example illustrated in FIG. 22B, the coefficient level decoding unit 124 can skip decoding of the coefficient presence / absence flag significant_coeff_flag in decoding of the sub-blocks in the second and subsequent rows.

<First Configuration Example of Coefficient Level Decoding Unit 124>
Below, the 1st structural example of the coefficient level decoding part 124 is demonstrated with reference to FIG. 1, FIG. 23 (a). In the first configuration example of the coefficient level decoding unit 124 described below, regarding the context index derivation of the coefficient presence / absence flag, the reference position of the coefficient used for the peripheral reference context (the shape of the template) according to the scan index and the position of the coefficient ).

  FIG. 1 is a block diagram illustrating a configuration example of the coefficient level decoding unit 124. In the following, only the members shown in FIG. 1 that are necessary for the description of the first configuration example will be referred to. That is, FIG. 1 illustrates the non-zero transform coefficient count unit 124y, but the non-zero transform coefficient count unit 124y can be omitted in the coefficient level decoding unit 124 according to the first configuration example.

  As shown in FIG. 1, the coefficient level decoding unit 124 includes a coefficient presence / absence flag context deriving unit 124z, a coefficient level storage unit 124d, a coefficient presence / absence flag setting unit 124e, and a coefficient level decoding processing unit 124f.

(Coefficient presence / absence flag context deriving unit 124z)
The coefficient presence / absence flag context deriving unit 124z derives the context index ctxIdx for the frequency component to be decoded based on the decoded absolute value sumAbsLevel for the frequency components around the frequency component. More specifically, the coefficient presence / absence flag context deriving unit 124z, when the position of the target frequency component (xC, yC) or the position of the sub-block to which the target frequency component belongs (xCG, yCG) satisfies the following condition: A decoded absolute value sum sumAbsLevel is derived using a reference position (template) that differs depending on the scan index scanIdx and the position of the transform coefficient.

  Under the above conditions, the coefficient presence / absence flag context deriving unit 124z derives a decoded absolute value sum sumAbsLevel using a reference position (template) that differs depending on the scan index scanIdx and the position of the transform coefficient. Also, the coefficient presence / absence flag context deriving unit 124z derives the context index ctxIdx based on the decoded absolute value sum sumAbsLevel derived in this way.

  The coefficient presence / absence flag context deriving unit 124z derives a decoded absolute value sum sumAbsLevel using a reference position (template) that differs depending on the scan index scanIdx and the position of the transform coefficient as follows. FIG. 24A is a diagram illustrating a position on a frequency component in a sub-block and a relationship between templates to be selected when the scan index scanIdx indicates oblique scan. In the 4 × 4 component sub-block, when the notation shown in the position is (b), the template shown in FIG. 24B is used, and when the notation is (c), the template shown in FIG. 24C is used. Is used. 24B and 24C show the shape of the template. That is, it indicates the relative position between the reference frequency component (for example, c1, c2, c3, c4, c5) and the target frequency component x. FIG. 24E is a diagram illustrating the scan order (reverse scan order) of the oblique scan in the 4 × 4 sub-block.

  Processing is performed when the position of the transform coefficient (xC, yC) satisfies the following equation (eq.A3), that is, the position of the transform coefficient is at the upper left of the sub-block, or the position of the transform coefficient is at the right of the sub-block. There is a difference between the case above the one below and the other cases.

((xC & 3) == 0 && (yC & 3) == 0) || ((xC & 3) == 3 && (yC & 3) == 2) (eq.A3)
In the above equation (eq.A3), the operator “&” is a bitwise OR operator, “&&” is a logical product operator, and “||” is a logical operator. It is an operator indicating the sum (the same applies hereinafter).

  The equation (eq.A3) can also be expressed by the equation (eq.A3 ′).

((xC% 4) == 0 && (yC% 4) == 0) || ((xC% 4) == 3 && (yC% 4) == 2) (eq.A3 ')
In the above equation (eq.A3 ′), “%” is an operator for calculating the remainder (the same applies hereinafter).

(Derivation of sum of absolute values sumAbsLevel)
(If the expression (eq.A3) is satisfied)
When the position (xC, yC) of the transform coefficient satisfies the equation (eq.A3), the reference frequency components (c1, c2, c4, c5) shown in FIG.
The absolute value sum sumAbsLevel of the decoded transform coefficients is derived by the following equation (eq.A4).

sumAbsLevel = clipAbsCoeff [xC + 1] [yC] // c1
+ clipAbsCoeff [xC + 2] [yC] // c2
+ clipAbsCoeff [xC + 1] [yC + 1] // c4
+ clipAbsCoeff [xC] [yC + 2] // c5 ・ ・ ・ (eq.A4)
Here, clipAbsCoeff [xC] [yC] is the absolute value of the decoded transform coefficient after clipping with the predetermined value LevelTH by the following equation.

clipAbsCoeff [xC] [yC] = Min (abs (transCoeffLevel [xC] [yC]), LevelTH)
As will be described later, when the level of the decoded transform coefficient stored in the coefficient level storage unit 124d is already a value after clipping, the coefficient presence / absence flag context deriving unit 124z does not perform the clipping process. It doesn't matter.

(If the expression (eq.A3) is not satisfied)
When the position (xC, yC) of the transform coefficient does not satisfy the equation (eq.A3), the following equation (eq.A5) is used by using the reference frequency components c1 to c5 shown in FIG. The absolute value sum sumAbsLevel is calculated.

sumAbsLevel = clipAbsCoeff [xC + 1] [yC] // c1
+ clipAbsCoeff [xC + 2] [yC] // c2
+ clipAbsCoeff [xC] [yC + 1] // c3
+ clipAbsCoeff [xC + 1] [yC + 1] // c4
+ clipAbsCoeff [xC] [yC + 2] // c5 ・ ・ ・ (eq.A5)
(Derivation of context index ctxIdx)
Subsequently, the coefficient presence / absence flag context deriving unit 124z derives a context index ctxIdx using the following equation (eq.A6), which is also indicated by the reference number A6 in FIG. ctxIdx is supplied to the context recording update unit 131.

ctxIdx = Min (sumAbsLevel, 5) + baseCtx (eq.A6)
(Coefficient presence / absence flag setting unit 124e)
The coefficient presence / absence flag setting unit 124e interprets each Bin supplied from the bit decoding unit 132, and sets the syntax significant_coeff_flag [xC] [yC]. The set syntax significant_coeff_flag [xC] [yC] is supplied to the decoding coefficient storage unit 126.

  When the target frequency region is divided into sub-blocks, the coefficient presence / absence flag setting unit 124e refers to the syntax significant_coeff_group_flag [xCG] [yCG] assigned to the target sub-block, and the value of significant_coeff_group_flag [xCG] [yCG] Is 0, significant_coeff_flag [xC] [yC] is set to 0 for all frequency components included in the target sub-block.

(Coefficient level decoding processing unit 124f)
The coefficient level decoding processing unit 124f decodes the syntax coeff_abs_greater1_flag and coeff_abs_remaining indicating the level of the transform coefficient for the non-zero coefficient. Specifically, the coefficient level decoding processing unit 124f derives a context index with the syntax coeff_abs_greater1_flag and coeff_abs_remaining and supplies the context index to the bit decoding unit 132. Next, the coefficient level decoding processing unit 124f interprets each Bin supplied from the bit decoding unit 132, and derives a transform coefficient level transCoeffLevel [xC] [yC]. The coefficient level decoding processing unit 124 f supplies the derived syntax transform coefficient level transCoeffLevel [xC] [yC] to the decoded coefficient storage unit 126. At the same time, the coefficient level decoding processing unit 124f also stores the transform coefficient level transCoeffLevel [xC] [yC] in the coefficient level storage unit 124d.

  The coefficient level decoding processing unit 124f derives the context index of the syntax coeff_abs_greater1_flag indicating the level of the transform coefficient in accordance with the value obtained by clipping the level of the already decoded transform coefficient. Specifically, the context index ctxIdx_c1 is derived using the decrypted absolute value sum sumAbsLevel and the number of transform coefficients cnt.

sumAbsLevel = clipAbsCoeff [xC + 1] [yC] // c1
+ clipAbsCoeff [xC + 2] [yC] // c2
+ clipAbsCoeff [xC] [yC + 1] // c3
+ clipAbsCoeff [xC + 1] [yC + 1] // c4
+ clipAbsCoeff [xC] [yC + 2] // c5 ・ ・ ・ (eq.A5)
cnt = (transCoeffLevel [xC + 1] [yC]! = 0) // c1
+ transCoeffLevel [xC + 2] [yC]! = 0) // c2
+ transCoeffLevel [xC] [yC + 1]! = 0) // c3
+ transCoeffLevel [xC + 1] [yC + 1]! = 0) // c4
+ transCoeffLevel [xC] [yC + 2]! = 0) // c5
ctxIdx_c1 = Min (sumAbsLevel-cnt, 4) + baseCtx_c1
Note that sumAbsLevelM1 (= sumAbsLevel-cnt) may be obtained by the following equation.

sumAbsLevel = clipAbsCoeffM1 [xC + 1] [yC] // c1
+ clipAbsCoeffM1 [xC + 2] [yC] // c2
+ clipAbsCoeffM1 [xC] [yC + 1] // c3
+ clipAbsCoeffM1 [xC + 1] [yC + 1] // c4
+ clipAbsCoeffM1 [xC] [yC + 2] // c5 ・ ・ ・ (eq.A5)
clipAbsCoeffM1 [xC] [yC] = transCoeffLevel [xC] [yC] == 0? 0: Min (abs (transCoeffLevel [xC] [yC]-1), LevelTH)
The coefficient level decoding processing unit 124f derives a parameter r of the Golomb-Rice code used when decoding the syntax coeff_abs_remainin indicating the level of the transform coefficient, and by bypass that is arithmetic code decoding without using the context using the parameter r, Decode the syntax coeff_abs_remaining. The parameter r is obtained by the following expression using the decoded absolute value sum sumAbsLevel and the number of transform coefficients cnt. This equation can also be realized by a table indicating the correspondence between the decoded absolute value sum sumAbsLevel and the number of transform coefficients cnt and r.

r = 0 (0 ≦ Min (sumAbsLevel-cnt) <4)
1 (4 ≦ Min (sumAbsLevel-cnt) <10)
2 (10 ≦ Min (sumAbsLevel-cnt) <21)
3 (21 ≦ Min (sumAbsLevel-cnt)
(Coefficient level storage unit 124d)
The coefficient level storage unit 124d stores each value of the level of transform coefficient transCoeffLevel [xC] [yC] after clipping. That is, the value of Min (abs (transCoeffLevel [xC] [yC]), LevelTH) is stored. Each value of transCoeffLevel [xC] [yC] stored in the coefficient level storage unit 124d is referred to by the coefficient presence / absence flag context deriving unit 124z.

  In the above configuration, the coefficient presence / absence flag context deriving unit 124z derives a context index according to the clipped value of the level of the already decoded transform coefficient. By using the level of transform coefficients, context classification can be performed with higher accuracy than when the number of non-zero transform coefficients is used, and the code amount of transform coefficients is reduced. In addition, since the product of the level of the transform coefficient that has already been decoded and a predetermined mask is used, the memory size required for the coefficient level storage unit 124d is reduced.

<Second Configuration Example of Coefficient Level Decoding Unit 124>
Hereinafter, a second configuration example of the coefficient level decoding unit 124 will be described with reference to FIG. The second configuration example of the coefficient level decoding unit 124 described below uses the same configuration as the first configuration example of the coefficient level decoding unit 124 except that the coefficient level decoding unit 124 includes the non-zero transform coefficient counting unit 124y illustrated in FIG. .

  Based on the decoding result of the coefficient presence / absence flag, the non-zero transform coefficient counting unit 124y counts the number of non-zero transform coefficients numSigCoeff in the target sub-block, and supplies it to the coefficient presence / absence flag context deriving unit 124z.

  FIG. 23B is a diagram showing context derivation processing in the second configuration example of the coefficient level decoding unit 124.

  As indicated by A7 in FIG. 23 (b), when the number of transform coefficients numSigCoeff in the target sub-block is less than a predetermined threshold TH, a context index ctxIdx is derived using the sum of the levels of transform coefficients that have already been decoded. To do. On the other hand, when the value is equal to or greater than the predetermined threshold TH, the context index lastCtxIdx used last in the target sub-block is used. Note that the derivation of the context index can also reduce the memory size by using the sum of the transformation coefficients transCoeffLevel [xC] [yC] after clipping, as in the first embodiment. Further, as described below, a transform coefficient transCoeffLevel [xC] [yC] without a clip may be used.

sumAbsLevel = | Coeff [xC + 1] [yC] |
+ | Coeff [xC + 2] [yC] |
+ | Coeff [xC] [yC + 1] |
+ | Coeff [xC + 1] [yC + 1] |
+ | Coeff [xC] [yC + 2] |
This configuration can be suitably used for the context index derivation of the coefficient presence / absence flag significant_coeff_flag already described and the context index derivation of the syntax coeff_abs_greater1_flag indicating the level of the transform coefficient.

  On the other hand, when the value is equal to or greater than the predetermined threshold TH, the maximum value of the context index used in the target subblock before decoding the target transform coefficient, instead of using the last context index lastCtxIdx used in the target subblock. May be used. Further, the context index may be derived using the maximum value of sumAbsLeve used before decoding the target transform coefficient. Conversely, when the threshold is equal to or higher than the predetermined threshold TH, a dedicated fixed context index may be used. When the threshold value is equal to or higher than the predetermined threshold TH, the appearance probability is estimated with high accuracy by using a dedicated context because the appearance probability of a non-zero coefficient is high or a conversion coefficient having a large level is likely to appear. be able to.

  In addition, the same method can be used when deriving the parameter r used when decoding the syntax indicating the level of the transform coefficient (for example, coeff_abs_remaining) regardless of the context index. That is, the parameter r last used in the target sub-block, the maximum value of r used in the target sub-block before decoding the target transform coefficient, the maximum value of sumAbsLevel used before decoding the target transform coefficient, a predetermined threshold A fixed value can be used when it is greater than or equal to TH.

  In the above configuration, when the number of transform coefficients in the target sub-block is large, the context index is derived for the transform coefficients of a predetermined number or more without using the peripheral reference (transformed coefficients that have already been decoded). There is an effect of improving the throughput. In addition, even with a predetermined number of transform coefficients or more, a suitable context index can be derived based on the value of a transform coefficient that has already been decoded or based on a fixed value, so that encoding efficiency is maintained. It is possible to decode transform coefficients with high throughput. The same effect can be obtained not only in the context index but also in the derivation of parameters for decoding the value of the transform coefficient.

<Third Configuration Example of Coefficient Level Decoding Unit 124>
Hereinafter, a third configuration example of the coefficient level decoding unit 124 will be described with reference to FIG. The second configuration example of the coefficient level decoding unit 124 described below uses the same configuration as the first configuration example of the coefficient level decoding unit 124 except that the coefficient level decoding unit 124 includes the non-zero transform coefficient counting unit 124y illustrated in FIG. .

  Based on the decoding result of the coefficient presence / absence flag, the non-zero transform coefficient counting unit 124y counts the last value lastNumSigCoeff of the number of non-zero transform coefficients in the target sub-block and supplies the counted value to the coefficient presence / absence flag context deriving unit 124z.

  FIG. 23C is a diagram illustrating context derivation processing in the second configuration example of the coefficient level decoding unit 124.

  As indicated by A8 in FIG. 23C, when the last value lastNumSigCoeff of the number of transform coefficients in the target sub-block is less than a predetermined threshold TH, the context index is calculated using the sum of the levels of transform coefficients that have already been decoded. Derive ctxIdx. On the other hand, when the value is equal to or less than the predetermined threshold, the context index lastCtxIdx used last in the target sub-block is used. Note that the derivation of the context index can also reduce the memory size by using the sum of the transformation coefficients transCoeffLevel [xC] [yC] after clipping, as in the first embodiment. Further, as described below, a transform coefficient transCoeffLevel [xC] [yC] without a clip may be used.

  With the above configuration, when there are a large number of transform coefficients in the target sub-block, the context index is derived without using the peripheral reference (already decoded transform coefficients), so that the throughput is improved. Further, since lastNumSigCoeff does not depend on the decoding result of the coefficient presence / absence flag decoded immediately before, decoding of the coefficient presence / absence flag and the context index of the next coefficient presence / absence flag can be executed in parallel, thereby further improving the throughput. Details of a method for deriving the last value lastNumSigCoeff of the number of transform coefficients in the target sub-block will be described later with reference to FIG.

  Further, in the above configuration, the last value lastNumSigCoeff of the number of transform coefficients in the target sub-block, that is, the number of non-zero transform coefficients at the time of decoding the non-zero transform coefficient presence flag before the target transform coefficient is used. Although it was a structure, it is not restricted to this.

  It may be configured to use a value immediately before lastNumSigCoeff. In other words, the number of non-zero transform coefficients at the time of decoding the non-zero transform coefficient presence / absence flag that is a predetermined number before the target transform coefficient may be used. lastlastNumSigCoeff is an example.

<Processing Flow by Transform Coefficient Decoding Unit 120>
Hereinafter, the flow of transform coefficient decoding processing by the transform coefficient decoding unit 120 will be described with reference to FIG.

  FIG. 25 is a flowchart showing the flow of transform coefficient decoding processing by the transform coefficient decoding unit 120.

(Step S21)
First, the coefficient decoding control unit 123 included in the transform coefficient decoding unit 120 selects a scan type ScanType.

(Step S22)
Subsequently, the last coefficient position decoding unit 121 included in the transform coefficient decoding unit 120 decodes the syntaxes last_significant_coeff_x and last_significant_coeff_y indicating the position of the last transform coefficient along the forward scan.

(Step S23)
Subsequently, the coefficient decoding control unit 123 starts a loop in units of sub blocks. Note that a sub-block having a last coefficient is set as a loop start position, and decoding processing in units of sub-blocks is performed in reverse scan order of sub-block scan.

(Step S24)
Subsequently, the subblock coefficient presence / absence flag decoding unit 127 included in the transform coefficient decoding unit 120 decodes the subblock coefficient presence / absence flag significant_coeff_group_flag.

(Step S25)
Subsequently, the coefficient level decoding unit 124 included in the transform coefficient decoding unit 120 decodes each non-zero transform coefficient presence / absence flag significant_coeff_flag and the magnitude of the non-zero transform coefficient in the target sub-block. The magnitude of the non-zero transform coefficient is determined by decoding coeff_abs_level_greater1_flag and coeff_abs_level_remaining. coeff_abs_level_remaining is decoded by bypass, which is an arithmetic code that does not use a contest.

(Step S26)
Subsequently, the coefficient code decoding unit 125 included in the transform coefficient decoding unit 120 decodes the code coeff_sign_flag of the non-zero transform coefficient in the target subblock. coeff_sign_flag is decoded by bypass, which is an arithmetic code that does not use a contest.

(Step S27)
This step is the end of the loop in units of sub-blocks. (End of loop in units of sub-blocks in step S23)
In the flow from S23 to S27, the loop in the sub-block is composed of two loops: a transform coefficient presence / absence flag, a loop for decoding the syntax indicating the magnitude of the transform coefficient, and a loop for decoding the code.

In the above configuration, the transform coefficient presence / absence flag and the transform are obtained by decoding the encoded data in which the individual transform coefficient presence / absence flags and the syntax indicating the size of the transform coefficient are sequentially arranged in one sub-block. A context index of syntax indicating the size of the coefficient can be determined using the value of the transform coefficient that has already been decoded, and the code amount of the syntax is reduced. At the same time, by successively decoding the codes of the transform coefficients collected as a set in one sub-block by bypass, the amount of codes that can be decoded at a time increases, and the throughput is improved.
<< Decoding processing of subblock coefficient presence / absence flag >>
FIG. 26 is a flowchart for more specifically explaining the process of decoding the subblock coefficient presence / absence flag (step S24).

  The sub-block coefficient presence / absence flag decoding unit 127 initializes the value of the sub-block coefficient presence / absence flag significant_coeff_group_flag included in the target frequency region before starting the sub-block loop. In this initialization process, the sub block coefficient presence / absence flag of the sub block including the DC coefficient and the sub block coefficient presence / absence flag of the sub block including the last coefficient are set to 1, and the other sub block coefficient presence / absence flags are set to 0. Is done by doing.

(Step S244)
The subblock coefficient presence / absence flag decoding unit 127 acquires the position of the subblock.

(Step S247)
The sub-block coefficient presence / absence flag decoding unit 127 determines whether the target sub-block is a sub-block including the last coefficient or a DC coefficient.

(Step S248)
When the target subblock is not a subblock including the last coefficient or a DC coefficient (No in step S247), the coefficient presence / absence flag decoding unit 124 decodes the subblock coefficient presence / absence flag significant_coeff_group_flag.
<< Decoding processing of coefficient presence / absence flag and transform coefficient >>
FIG. 27 is a diagram for more specifically explaining the process (step S25 in FIG. 25) for decoding the non-zero transform coefficient presence / absence flag significant_coeff_flag and the magnitude of the non-zero transform coefficient in the sub-block in the coefficient level decoding unit 124. It is a flowchart.

(Step S2501)
Subsequently, the coefficient level decoding unit 124 initializes the number numSigCoeff of transform coefficients in the target sub-block to 0. Also, the immediately preceding value lastNumSigCoeff of the number of transform coefficients in the target sub-block is initialized to zero. When the lastlastNumSigCoeff immediately before the number of transform coefficients in the target sub-block is used, lastlastNumSigCoeff is initialized to 0.

(Step S2502)
The coefficient level decoding unit 124 starts a loop in the target subblock. The loop is a loop having a frequency component as a unit.

(Step S2503)
The coefficient level decoding unit 124 determines whether or not the position of the transform coefficient is the last position.

(Step S2504)
When the position of the transform coefficient is not the last position (No in step S2504), the coefficient level decoding unit 124 decodes the transform coefficient presence / absence flag significant_coeff_flag.

(Step S2505)
The number of transform coefficients numSigCoeff is substituted for the last value lastNumSigCoeff of the number of transform coefficients in the target sub-block. Note that this process (updating the last value lastNumSigCoeff) needs to be performed before the process of updating the number of transform coefficients numSigCoeff in the target sub-block (step S2507). In addition, as long as it processes before numSigCoeff, you may process in another order. When the immediately preceding value lastlastNumSigCoeff of the immediately preceding value of the number of transform coefficients in the target sub-block is used, lastNumSigCoeff is updated before updating the immediately preceding value lastNumSigCoeff.

(Step S2506)
The coefficient level decoding unit 124 determines whether or not the transform coefficient is a non-zero coefficient.

(Step S2507)
When the position of the transform coefficient is a non-zero coefficient (Yes in step S2506), the number of transform coefficients numSigCoeff is incremented by 1.

(Step S2508)
When the position of the transform coefficient is a non-zero coefficient (Yes in step S2506), the coefficient level decoding unit 124 decodes the magnitude of the transform coefficient following step S2506.

(Step S2509)
This step is the end of the loop in units of frequency components. (End of loop in units of frequency components in step S2502)
<< Decoding processing of transform coefficient code >>
FIG. 28 is a flowchart for more specifically explaining the process (step S26 in FIG. 25) for decoding the code of each non-zero transform coefficient in the sub-block.

(Step S2601)
The coefficient code decoding unit 125 starts a loop in the target subblock. The loop is a loop having a frequency component as a unit.

(Step S2602)
The coefficient code decoding unit 125 determines whether or not the transform coefficient is a non-zero coefficient.

(Step S2603)
When the transform coefficient is a non-zero coefficient (Yes in step S2602), the coefficient code decoding unit 125 determines whether or not to perform sign hiding.

(Step S2604)
When the coefficient code decoding unit 125 does not perform sign hiding (No in step S2603), the coefficient code decoding unit 125 decodes the code of the transform coefficient.

(Step S2605)
This step is the end of the loop in units of frequency components. (End of loop in units of frequency components in step S2601)
<< Decoding processing of transform coefficient size >>
FIG. 29 is a flowchart for more specifically explaining the process (step S2507 in FIG. 27) for decoding the code of each non-zero transform coefficient in the sub-block in the coefficient level decoding unit 124.

(Step S2507A)
The coefficient level decoding unit 124 determines whether the number of transform coefficients numSigCoeff is less than a predetermined threshold TH. In this determination, lastNumSigCoeff may be used instead of the number of transform coefficients numSigCoeff so as not to depend on the value of the transform coefficient presence / absence flag decoded immediately before. When lastNumSigCoeff is used, numSigCoeff described below is replaced with lastNumSigCoeff.

(Step S2507B)
When the number of transform coefficients numSigCoeff is less than the predetermined threshold TH (Yes in step S2507A), the coefficient level decoding unit 124 decodes coeff_abs_greater1_flag.

(Step S2507C)
When the number of transform coefficients numSigCoeff is equal to or greater than a predetermined threshold TH (No in step S2507A), the coefficient level decoding unit 124 sets coeff_abs_greater1_flag to 0. When the number of transform coefficients numSigCoeff is equal to or greater than a predetermined threshold value TH, this corresponds to the high throughput mode.

(Step S2507D)
The coefficient level decoding unit 124 derives baseLevel by the sum of 1 and coeff_abs_greater1_flag.

(Step S2507E)
The coefficient level decoding unit 124 determines whether or not baseLevel matches a predetermined value. The predetermined value is 2 when the number of conversion coefficients numSigCoeff is less than the predetermined threshold TH, and 1 otherwise.

(Step S2507F)
When the baseLevel matches a predetermined value (Yes in step S2507E), the coefficient level decoding unit 124 decodes coeff_abs_remaining.

(Step S2507G)
The coefficient level decoding unit 124 sets coeff_abs_remaining to 0 when baseLevel does not match a predetermined value (No in step S2507E).

(Step S2507H)
The coefficient level decoding unit 124 derives the transform coefficient magnitude transCoeffLevel by the sum of coeff_abs_remaining and baseLevel.

  As described above, the moving image decoding apparatus 1 arithmetically encodes various syntaxes representing transform coefficients for transform coefficients obtained for each frequency component by performing frequency transform on the target image for each unit region. The encoded data obtained by this is decoded. In addition, the video decoding device 1 includes a variable length code decoding unit 11 that divides a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size, and a non-blocking sub-block for each sub-block. A subblock coefficient presence / absence flag setting unit 127c for decoding a subblock coefficient presence / absence flag indicating whether or not at least one 0 transform coefficient is included, and non-representation indicating whether each transform coefficient in each subblock is 0 or not. Refer to the coefficient presence / absence flag setting unit 124e for decoding the 0 transform coefficient presence / absence flag, the coefficient level decoding processing unit 124f for decoding the size of each transform coefficient in each sub-block, and the value of the transformed transform coefficient. And a coefficient presence / absence flag context deriving unit 123z for deriving a context index.

According to the above configuration, it is possible to reduce the amount of memory related to encoding and decoding transform coefficients and improve the throughput while maintaining the encoding efficiency as compared with the conventional configuration.
[Moving picture encoding apparatus 2]
A configuration of the moving picture encoding apparatus 2 according to the present embodiment will be described with reference to FIGS. 30 to 34. The moving image encoding apparatus 2 is an H.264 standard. It is an encoding device that implements the technology adopted in the H.264 / MPEG-4 AVC standard and the technology proposed in HEVC (High-Efficiency Video Coding) as a successor codec. In the following, the same parts as those already described are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 30 is a block diagram illustrating a configuration of the moving image encoding device 2. As illustrated in FIG. 30, the moving image encoding apparatus 2 includes a predicted image generation unit 21, a transform / quantization unit 22, an inverse quantization / inverse transform unit 23, an adder 24, a frame memory 25, a loop filter 26, a variable A long code encoding unit 27 and a subtracter 28 are provided. In addition, as illustrated in FIG. 30, the prediction image generation unit 21 includes an intra prediction image generation unit 21 a, a motion vector detection unit 21 b, an inter prediction image generation unit 21 c, a prediction method control unit 21 d, and a motion vector redundancy deletion unit. 21e. The moving image encoding device 2 is a device that generates encoded data # 1 by encoding moving image # 10 (encoding target image).

(Predicted image generation unit 21)
The predicted image generation unit 21 recursively divides the processing target LCU into one or a plurality of lower-order CUs, further divides each leaf CU into one or a plurality of partitions, and uses an inter-screen prediction for each partition. A predicted image Pred_Inter or an intra predicted image Pred_Intra using intra prediction is generated. The generated inter prediction image Pred_Inter and intra prediction image Pred_Intra are supplied to the adder 24 and the subtracter 28 as the prediction image Pred.

  Note that the predicted image generation unit 21 omits encoding of other parameters belonging to the PU for the PU to which the skip mode is applied. Also, (1) the mode of division into lower CUs and partitions in the target LCU, (2) whether to apply the skip mode, and (3) which of the inter predicted image Pred_Inter and the intra predicted image Pred_Intra for each partition Whether to generate is determined so as to optimize the encoding efficiency.

(Intra predicted image generation unit 21a)
The intra predicted image generation unit 21a generates a predicted image Pred_Intra for each partition by intra prediction. Specifically, (1) a prediction mode used for intra prediction is selected for each partition, and (2) a prediction image Pred_Intra is generated from the decoded image P using the selected prediction mode. The intra predicted image generation unit 21a supplies the generated intra predicted image Pred_Intra to the prediction method control unit 21d.

  In addition, the intra predicted image generation unit 21a determines an estimated prediction mode for the target partition from the prediction modes assigned to the peripheral partitions of the target partition, and the estimated prediction mode and the prediction mode actually selected for the target partition Are supplied to the variable-length code encoding unit 27 via the prediction scheme control unit 21d as a part of the intra-prediction parameter PP_Intra, and the variable-length code encoding unit 27 Is configured to include the flag in the encoded data # 1.

  In addition, when the estimated prediction mode for the target partition is different from the prediction mode actually selected for the target partition, the intra predicted image generation unit 21a sets a residual prediction mode index indicating the prediction mode for the target partition, As a part of the intra prediction parameter PP_Intra, the prediction method control unit 21d supplies the variable length code encoding unit 27 to the variable length code encoding unit 27. The variable length code encoding unit 27 includes the residual prediction mode index in the encoded data # 1. And

  In addition, when generating the predicted image Pred_Intra, the intra predicted image generation unit 21a selects and applies a prediction mode that further improves the coding efficiency from the prediction mode illustrated in FIG.

(Motion vector detection unit 21b)
The motion vector detection unit 21b detects a motion vector mv regarding each partition. Specifically, (1) by selecting an adaptive filtered decoded image P_ALF ′ used as a reference image, and (2) by searching for a region that best approximates the target partition in the selected adaptive filtered decoded image P_ALF ′, A motion vector mv related to the target partition is detected. Here, the adaptive filtered decoded image P_ALF ′ is an image obtained by performing an adaptive filter process by the loop filter 26 on a decoded image that has already been decoded for the entire frame, and is a motion vector detection unit. The unit 21b can read out the pixel value of each pixel constituting the adaptive filtered decoded image P_ALF ′ from the frame memory 25. The motion vector detection unit 21b sends the detected motion vector mv to the inter-predicted image generation unit 21c and the motion vector redundancy deletion unit 21e together with the reference image index RI designating the adaptive filtered decoded image P_ALF ′ used as a reference image. Supply.

(Inter prediction image generation unit 21c)
The inter prediction image generation unit 21c generates a motion compensated image mc related to each inter prediction partition by inter-screen prediction. Specifically, using the motion vector mv supplied from the motion vector detection unit 21b, the motion compensated image mc from the adaptive filtered decoded image P_ALF ′ designated by the reference image index RI supplied from the motion vector detection unit 21b. Is generated. Similar to the motion vector detection unit 21b, the inter prediction image generation unit 21c can read out the pixel value of each pixel constituting the adaptive filtered decoded image P_ALF ′ from the frame memory 25. The inter prediction image generation unit 21c supplies the generated motion compensated image mc (inter prediction image Pred_Inter) together with the reference image index RI supplied from the motion vector detection unit 21b to the prediction method control unit 21d.

(Prediction method controller 21d)
The prediction scheme control unit 21d compares the intra predicted image Pred_Intra and the inter predicted image Pred_Inter with the encoding target image, and selects whether to perform intra prediction or inter prediction. When the intra prediction is selected, the prediction scheme control unit 21d supplies the intra prediction image Pred_Intra as the prediction image Pred to the adder 24 and the subtracter 28, and sets the intra prediction parameter PP_Intra supplied from the intra prediction image generation unit 21a. This is supplied to the variable length code encoding unit 27. On the other hand, when the inter prediction is selected, the prediction scheme control unit 21d supplies the inter prediction image Pred_Inter as the prediction image Pred to the adder 24 and the subtracter 28, and the reference image index RI and motion vector redundancy described later. The estimated motion vector index PMVI and the motion vector residual MVD supplied from the deletion unit 21e are supplied to the variable length code encoding unit 27 as an inter prediction parameter PP_Inter. Further, the prediction scheme control unit 21 d supplies prediction type information Pred_type indicating which prediction image is selected from the intra prediction image Pred_Intra and the inter prediction image Pred_Inter to the variable length code encoding unit 27.

(Motion vector redundancy deleting unit 21e)
The motion vector redundancy deletion unit 21e deletes redundancy in the motion vector mv detected by the motion vector detection unit 21b. Specifically, (1) an estimation method used for estimating the motion vector mv is selected, (2) an estimated motion vector pmv is derived according to the selected estimation method, and (3) the estimated motion vector pmv is subtracted from the motion vector mv. As a result, a motion vector residual MVD is generated. The motion vector redundancy deleting unit 21e supplies the generated motion vector residual MVD to the prediction method control unit 21d together with the estimated motion vector index PMVI indicating the selected estimation method.

(Transformation / quantization unit 22)
The transform / quantization unit 22 (1) performs frequency transform such as DCT transform (Discrete Cosine Transform) for each block (transform unit) on the prediction residual D obtained by subtracting the prediction image Pred from the encoding target image, (2) The transform coefficient Coeff_IQ obtained by frequency transform is quantized, and (3) the transform coefficient Coeff obtained by quantization is supplied to the variable length code encoding unit 27 and the inverse quantization / inverse transform unit 23. The transform / quantization unit 22 (1) selects a quantization step QP to be used for quantization for each TU, and (2) sets a quantization parameter difference Δqp indicating the size of the selected quantization step QP. The variable length code encoding unit 28 is supplied, and (3) the selected quantization step QP is supplied to the inverse quantization / inverse transform unit 23. Here, the quantization parameter difference Δqp is the quantization parameter qp related to the TU that has been frequency converted and quantized immediately before, from the value of the quantization parameter qp (for example, QP = 2 ^{pq / 6} ) related to the frequency conversion and quantization TU. The difference value obtained by subtracting the value of '.

  Note that the DCT transform performed by the transform / quantization unit 22 is, for example, when transforming coefficients before quantization for the horizontal frequency u and the vertical frequency v when the size of the target block is 8 × 8 pixels. Coeff_IQ (u, v) (0 ≦ u ≦ 7, 0 ≦ v ≦ 7) is given by, for example, the following formula (2).

Here, D (i, j) (0 ≦ i ≦ 7, 0 ≦ j ≦ 7) represents the prediction residual D at the position (i, j) in the target block. C (u) and C (v) are given as follows.

・ C (u) = 1 / √2 (u = 0)
・ C (u) = 1 (u ≠ 0)
・ C (v) = 1 / √2 (v = 0)
・ C (v) = 1 (v ≠ 0)
(Inverse quantization / inverse transform unit 23)
The inverse quantization / inverse transform unit 23 (1) inversely quantizes the quantized transform coefficient Coeff, and (2) inverse DCT (Discrete Cosine Transform) transform or the like on the transform coefficient Coeff_IQ obtained by the inverse quantization. (3) The prediction residual D obtained by the inverse frequency conversion is supplied to the adder 24. When the quantized transform coefficient Coeff is inversely quantized, the quantization step QP supplied from the transform / quantization unit 22 is used. Note that the prediction residual D output from the inverse quantization / inverse transform unit 23 is obtained by adding a quantization error to the prediction residual D input to the transform / quantization unit 22. Common names are used for this purpose. A more specific operation of the inverse quantization / inverse transform unit 23 is substantially the same as that of the inverse quantization / inverse transform unit 13 included in the video decoding device 1.

(Adder 24)
The adder 24 adds the predicted image Pred selected by the prediction scheme control unit 21d to the prediction residual D generated by the inverse quantization / inverse transform unit 23, thereby obtaining the (local) decoded image P. Generate. The (local) decoded image P generated by the adder 24 is supplied to the loop filter 26 and stored in the frame memory 25, and is used as a reference image in intra prediction.

(Variable-length code encoding unit 27)
The variable length code encoding unit 27 (1) the quantized transform coefficient Coeff and Δqp supplied from the transform / quantization unit 22, and (2) the quantization parameter PP (interpolation) supplied from the prediction scheme control unit 21d. Prediction parameter PP_Inter and Intra prediction parameter PP_Intra), (3) Prediction type information Pred_type, and (4) Variable parameter coding of filter parameter FP supplied from loop filter 26, thereby encoding encoded data # 1. Generate.

  FIG. 31 is a block diagram showing a configuration of the variable length code encoding unit 27. As shown in FIG. 31, the variable-length code encoding unit 27 includes a quantization residual information encoding unit 271 that encodes the quantized transform coefficient Coeff, and a prediction parameter encoding unit 272 that encodes the prediction parameter PP. A prediction type information encoding unit 273 that encodes the prediction type information Pred_type, and a filter parameter encoding unit 274 that encodes the filter parameter FP. Since the specific configuration of the quantization residual information encoding unit 271 will be described later, the description thereof is omitted here.

(Subtractor 28)
The subtracter 28 generates the prediction residual D by subtracting the prediction image Pred selected by the prediction method control unit 21d from the encoding target image. The prediction residual D generated by the subtracter 28 is frequency-transformed and quantized by the transform / quantization unit 22.

(Loop filter 26)
The loop filter 26 includes (1) a function as a deblocking filter (DF: Deblocking Filter) that performs smoothing (deblocking processing) on an image around a block boundary or partition boundary in the decoded image P; It has a function as an adaptive filter (ALF: Adaptive Loop Filter) which performs an adaptive filter process using the filter parameter FP with respect to the image which the blocking filter acted on.

(Quantization residual information encoding unit 271)
The quantization residual information encoding unit 271 performs quantum adaptive encoding (CABAC: (Context-based Adaptive Binary Arithmetic Coding)) on the quantized transform coefficient Coeff (xC, yC). Generated residual information QD. The syntaxes included in the generated quantization residual information QD are the syntaxes shown in FIGS. 6 and 7 and significant_coeff_group_flag.

  Note that, as described above, xC and yC are indexes representing the position of each frequency component in the frequency domain, and are indexes corresponding to the above-described horizontal frequency u and vertical frequency v, respectively. Hereinafter, the quantized transform coefficient Coeff may be simply referred to as a transform coefficient Coeff.

(Quantization residual information encoding unit 271)
FIG. 32 is a block diagram illustrating a configuration of the quantization residual information encoding unit 271. As illustrated in FIG. 32, the quantization residual information encoding unit 271 includes a transform coefficient encoding unit 220 and an arithmetic code encoding unit 230.

(Arithmetic Code Encoding Unit 230)
The arithmetic code encoder 230 is configured to generate the quantized residual information QD by encoding each Bin supplied from the transform coefficient encoder 220 with reference to the context, and is shown in FIG. As described above, a context recording update unit 231 and a bit encoding unit 232 are provided.

(Context record update unit 231)
The context recording / updating unit 231 is configured to record and update the context variable CV managed by each context index ctxIdx. Here, the context variable CV includes (1) a dominant symbol MPS (most probable symbol) having a high occurrence probability and (2) a probability state index pStateIdx for designating the occurrence probability of the dominant symbol MPS.

  The context recording update unit 231 updates the context variable CV by referring to the context index ctxIdx supplied from each unit of the transform coefficient encoding unit 220 and the Bin value encoded by the bit encoding unit 232, and The updated context variable CV is recorded until the next update. The dominant symbol MPS is 0 or 1. The dominant symbol MPS and the probability state index pStateIdx are updated every time the bit encoding unit 232 encodes one Bin.

  The context index ctxIdx may directly specify the context for each frequency component, or may be an increment value from the context index offset set for each TU to be processed (the same applies hereinafter). ).

(Bit Encoding Unit 232)
The bit encoding unit 232 refers to the context variable CV recorded in the context recording / updating unit 231, and encodes each Bin supplied from each unit of the transform coefficient encoding unit 220, thereby quantizing residual information. Generate a QD. The encoded Bin value is also supplied to the context recording update unit 231 and is referred to in order to update the context variable CV.

(Transform coefficient coding unit 220)
As shown in FIG. 32, the transform coefficient coding unit 220 includes a last position coding unit 221, a scan order table storage unit 222, a coefficient coding control unit 223, a coefficient level coding unit 224, a coefficient code coding unit 225, An encoding coefficient storage unit 226, a sub-block coefficient presence / absence flag 227, and a syntax derivation unit 228 are provided.

(Syntax derivation unit 228)
The syntax deriving unit 228 refers to each value of the transform coefficients Coeff (xC, yC), and syntaxes for identifying these transform coefficients in the target frequency domain, last_significant_coeff_x, last_significant_coeff_y, significant_coeff_flag, coeff_abs_level_greater1_flag, level_great_main_flag_, coeff_sign_flag_ Deriving each value. Each derived syntax is supplied to the coding coefficient storage unit 226. Of the derived syntax, last_significant_coeff_x and last_significant_coeff_y are also supplied to the coefficient coding control unit 223 and the last position coding unit 221. Further, significant_coeff_flag in the derived syntax is also supplied to the coefficient level encoding unit 224. In addition, since the content which each syntax shows was mentioned above, description is abbreviate | omitted here.

(Last position encoding unit 221)
The last position encoding unit 221 generates Bin indicating the syntax last_significant_coeff_x and last_significant_coeff_y supplied from the syntax deriving unit 228. Further, each generated Bin is supplied to the bit encoding unit 232. Also, the context record update unit 231 is supplied with a context index ctxIdx that designates a context to be referred to in order to encode Bin of the syntax last_significant_coeff_x and last_significant_coeff_y.

(Scan order table storage unit 222)
The scan order table storage unit 222 uses the size of the TU (block) to be processed, the scan index indicating the type of scan direction, and the frequency component identification index given along the scan order as arguments. A table for giving a position in the frequency domain is stored. An example of such a scan order table is ScanOrder shown in FIGS. 6 and 7.

  The scan order table storage unit 222 stores a sub-block scan order table for designating the scan order of sub-blocks. Here, the sub-block scan order table is specified by the scan index scanIdx associated with the size of the TU (block) to be processed and the prediction mode index of the intra prediction mode.

  The scan order table and the sub-block scan order table stored in the scan order table storage unit 222 are the same as those stored in the scan order table storage unit 122 included in the moving image decoding apparatus 1, and will be described here. Is omitted.

(Coefficient encoding control unit 223)
The coefficient encoding control unit 223 is a configuration for controlling the order of encoding processing in each unit included in the quantization residual information encoding unit 271.

(When TU size is less than or equal to the specified size)
When the TU size is equal to or smaller than a predetermined size (for example, 4 × 4 TU or the like), the coefficient encoding control unit 223 refers to the syntax last_significant_coeff_x and last_significant_coeff_y supplied from the syntax deriving unit 228, and performs the last along the forward scan. The scan order specified by the scan order table stored in the scan order table storage unit 222 is specified in the scan order starting from the position of the last specified non-zero transform coefficient. The position (xC, yC) of each frequency component is supplied to the coefficient level encoding unit 224 in the reverse scan order.

  Also, the coefficient coding control unit 223 supplies the size of the TU to be processed to each unit included in the transform coefficient coding unit 220 (not shown).

  The coefficient encoding control unit 223 displays the position (xC, yC) of each frequency component in the order of the scan order given by the scan order table stored in the scan order table storage unit 222, as a coefficient level encoding unit. It is good also as a structure supplied to 224.

  The coefficient coding control unit 223 refers to the syntax last_significant_coeff_x and last_significant_coeff_y supplied from the syntax deriving unit 228, identifies the position of the last non-zero transform coefficient along the forward scan, and identifies the identified last non-zero The position of each sub-block (xCG) in the scan order starting from the position of the sub-block including the transform coefficient and in the reverse scan order of the scan order given by the sub-block scan order table stored in the scan order table storage unit 222 , YCG) is supplied to the sub-block coefficient presence / absence flag encoding unit 227.

  Further, the coefficient encoding control unit 223 includes the subblocks to be processed in the reverse scan order of the scan order given by the scan order table stored in the scan order table storage unit 222 for the subblocks to be processed. The position (xC, yC) of each frequency component is supplied to the coefficient level encoding unit 224. Here, as the scan order of each frequency component included in the sub-block to be processed, in the case of intra prediction, the scan index scanIdx specified by the intra prediction mode index IntraPredMode and the value log2TrafoSize specifying the TU size In the case of inter prediction, an oblique scan (Up-right diagonal scan) may be used. Also, the coefficient coding control unit 223 supplies the scan index scanIdx associated with the size of the TU and the prediction mode of the TU to the coefficient level coding unit 224.

  Thus, the coefficient encoding control unit 223 is configured to switch the scan order for each intra prediction mode. In general, the intra prediction mode and the bias of the transform coefficient are correlated with each other. Therefore, by switching the scan order according to the intra prediction mode, a scan suitable for the bias of the subblock coefficient presence / absence flag and the coefficient presence / absence flag is performed. It can be carried out. As a result, the coding amount of the sub-block coefficient presence / absence flag and coefficient presence / absence flag to be encoded and decoded can be reduced, and the coding efficiency is improved.

(Coefficient Code Encoding Unit 225)
The coefficient code encoding unit 225 generates Bin indicating the syntax coeff_sign_flag supplied from the syntax deriving unit 228. Further, each generated Bin is supplied to the bit encoding unit 232. In addition, a context index ctxIdx that specifies a context to be referred to in order to encode Bin of these syntaxes is supplied to the context recording update unit 231.

(Coefficient level encoding unit 224)
The coefficient level coding unit 224 according to the present embodiment codes the syntax significant_coeff_flag [xC] [yC], coeff_abs_level_greater1_flag, and coeff_abs_level_remaining specified by each position (xC, yC). More specifically, the coefficient level encoding unit 224 generates Bin indicating the syntax significant_coeff_flag [xC] [yC] specified by each position (xC, yC). Each generated Bin is supplied to the bit encoding unit 232. Also, the coefficient level encoding unit 224 calculates a context index ctxIdx for determining a context used for encoding the Bin of the syntax significant_coeff_flag [xC] [yC] in the arithmetic code encoding unit 230. The calculated context index ctxIdx is supplied to the context recording update unit 231.

(First Configuration Example of Coefficient Level Encoding Unit 224)
FIG. 33 is a block diagram illustrating a first configuration example of the coefficient level encoding unit 224 according to the present embodiment. As shown in FIG. 33, the coefficient level encoding unit 224 includes a coefficient presence / absence flag context deriving unit 224z, a coefficient presence / absence flag setting unit 224e, and a coefficient level encoding processing unit 224f.

(Coefficient presence / absence flag context deriving unit 224z)
The coefficient presence / absence flag context deriving unit 224z derives the context index ctxIdx for the frequency component to be encoded based on the number cnt of non-zero transform coefficients that have been encoded for the frequency components around the frequency component. More specifically, the coefficient presence / absence flag context deriving unit 224z, when the position of the target frequency component (xC, yC) or the position of the sub block to which the target frequency component belongs (xCG, yCG) satisfies a predetermined condition, The number cnt of encoded non-zero transform coefficients is derived using a reference position (template) that differs depending on the scan index scanIdx and the position of the transform coefficient.

  Specific processing by the coefficient presence / absence flag context deriving unit 224z is the same as that of the coefficient presence / absence flag context deriving unit 124z included in the video decoding device 1, and thus the description thereof is omitted here.

(Coefficient presence / absence flag setting unit 224e)
The coefficient presence / absence flag setting unit 224e generates Bin indicating the syntax significant_coeff_flag [xC] [yC] supplied from the syntax deriving unit 228. The generated Bin is supplied to the bit encoding unit 232. In addition, the coefficient presence / absence flag setting unit 224e refers to the value of significant_coeff_flag [xC] [yC] included in the target subblock, and when all the significant_coeff_flag [xC] [yC] included in the target subblock is 0, That is, when a non-zero transform coefficient is not included in the target subblock, the value of significant_coeff_group_flag [xCG] [yCG] related to the target subblock is set to 0, otherwise significant_coeff_group_flag [ Set the value of xCG] [yCG] to 1. The significant_coeff_group_flag [xCG] [yCG] to which the value is added in this way is supplied to the sub-block coefficient presence / absence flag encoding unit 227.

(Coefficient level encoding processing unit 224f)
The coefficient level encoding processing unit 224f generates a Bin indicating the syntax coeff_abs_greater1_flag [xC] [yC] and coeff_abs_remaining [xC] [yC] supplied from the syntax deriving unit 228 and a context index used for encoding. The coefficient level encoding processing unit 224 f supplies the generated Bin to the bit encoding unit 232. Further, the coefficient level encoding processing unit 224f supplies the generated context index to the context recording update unit 231.

(Subblock coefficient presence / absence flag encoding unit 227)
The subblock coefficient presence / absence flag encoding unit 227 encodes syntax significant_coeff_group_flag [xCG] [yCG] specified by each subblock position (xCG, yCG). More specifically, Bin indicating the syntax significant_coeff_group_flag [xCG] [yCG] specified by each sub-block position (xCG, yCG) is generated. Each generated Bin is supplied to the bit encoding unit 232. In addition, the sub-block coefficient presence / absence flag encoding unit 227 determines a context index ctxIdx for determining a context used for encoding Bin of the syntax significant_coeff_flag [xC] [yC] in the arithmetic code encoding unit 230. calculate. The calculated context index ctxIdx is supplied to the context recording update unit 231.

  FIG. 34 is a block diagram showing a configuration of the sub-block coefficient presence / absence flag encoding unit 227. As shown in FIG. 34, the sub-block coefficient presence / absence flag encoding unit 227 includes a context deriving unit 227a, a sub-block coefficient presence / absence flag storage unit 227b, and a sub-block coefficient presence / absence flag setting unit 227c.

  Hereinafter, the case where the sub block position (xCG, yCG) is supplied to the sub block coefficient presence / absence flag encoding unit 227 from the coefficient encoding control unit 223 in the order of the forward scan will be described as an example. In this case, it is preferable that the sub-block coefficient presence / absence flag decoding unit 127 included in the video decoding device 1 supplies the sub-block positions (xCG, yCG) in reverse scan order.

(Context deriving unit 227a)
The context deriving unit 227a included in the subblock coefficient presence / absence flag encoding unit 227 derives a context index to be allocated to the subblock specified by each subblock position (xCG, yCG). The context index assigned to the sub-block is used when decoding Bin indicating the syntax significant_coeff_group_flag for the sub-block. Further, when the context index is derived, the value of the subblock coefficient presence / absence flag stored in the subblock coefficient presence / absence flag storage unit 227b is referred to. The context deriving unit 227a supplies the derived context index to the context record updating unit 231.

(Subblock coefficient presence / absence flag storage unit 227b)
Each value of the syntax significant_coeffgroup_flag supplied from the coefficient level encoding unit 224 is stored in the sub-block coefficient presence / absence flag storage unit 227b. The subblock coefficient presence / absence flag setting unit 227c can read the syntax significant_coeffgroup_flag assigned to the adjacent subblock from the subblock coefficient presence / absence flag storage unit 227b.

(Subblock coefficient presence / absence flag setting unit 227c)
The sub-block coefficient presence / absence flag setting unit 227c generates the Bin indicating the syntax significant_coeff_group_flag [xCG] [yCG] supplied from the coefficient level encoding unit 224. The generated Bin is supplied to the bit encoding unit 232.
[Appendix 1]
Application examples of the moving image encoding device 2 and the moving image decoding device 1 will be described with reference to FIGS. 35 and 36. The above-described moving image encoding device 2 and moving image decoding device 1 can be used by being mounted on various devices that perform transmission, reception, recording, and reproduction of moving images. The moving image may be a natural moving image captured by a camera or the like, or may be an artificial moving image (including CG and GUI) generated by a computer or the like.

  First, it will be described with reference to FIG. 35 that the above-described moving image encoding device 2 and moving image decoding device 1 can be used for transmission and reception of moving images.

  FIG. 35A is a block diagram illustrating a configuration of a transmission apparatus PROD_A in which the moving image encoding apparatus 2 is mounted. As illustrated in (a) of FIG. 35, the transmission device PROD_A modulates a carrier wave with an encoding unit PROD_A1 that obtains encoded data by encoding a moving image, and the encoded data obtained by the encoding unit PROD_A1. Thus, a modulation unit PROD_A2 that obtains a modulation signal and a transmission unit PROD_A3 that transmits the modulation signal obtained by the modulation unit PROD_A2 are provided. The moving image encoding apparatus 2 described above is used as the encoding unit PROD_A1.

  The transmission device PROD_A is a camera PROD_A4 that captures a moving image, a recording medium PROD_A5 that records the moving image, an input terminal PROD_A6 that inputs the moving image from the outside, as a supply source of the moving image input to the encoding unit PROD_A1. An image processing unit A7 that generates or processes an image may be further provided. FIG. 35A illustrates a configuration in which the transmission apparatus PROD_A includes all of these, but some of them may be omitted.

  The recording medium PROD_A5 may be a recording of a non-encoded moving image, or a recording of a moving image encoded by a recording encoding scheme different from the transmission encoding scheme. It may be a thing. In the latter case, a decoding unit (not shown) for decoding the encoded data read from the recording medium PROD_A5 according to the recording encoding method may be interposed between the recording medium PROD_A5 and the encoding unit PROD_A1.

  FIG. 35B is a block diagram illustrating a configuration of the receiving device PROD_B in which the video decoding device 1 is mounted. As illustrated in (b) of FIG. 35, the reception device PROD_B includes a reception unit PROD_B1 that receives a modulation signal, a demodulation unit PROD_B2 that obtains encoded data by demodulating the modulation signal received by the reception unit PROD_B1, and a demodulation A decoding unit PROD_B3 that obtains a moving image by decoding the encoded data obtained by the unit PROD_B2. The moving picture decoding apparatus 1 described above is used as the decoding unit PROD_B3.

  The receiving device PROD_B has a display PROD_B4 for displaying a moving image, a recording medium PROD_B5 for recording the moving image, and an output terminal for outputting the moving image to the outside as a supply destination of the moving image output by the decoding unit PROD_B3. PROD_B6 may be further provided. FIG. 35B illustrates a configuration in which the reception apparatus PROD_B includes all of these, but a part of the configuration may be omitted.

  The recording medium PROD_B5 may be used for recording a non-encoded moving image, or may be encoded using a recording encoding method different from the transmission encoding method. May be. In the latter case, an encoding unit (not shown) for encoding the moving image acquired from the decoding unit PROD_B3 according to the recording encoding method may be interposed between the decoding unit PROD_B3 and the recording medium PROD_B5.

  Note that the transmission medium for transmitting the modulation signal may be wireless or wired. Further, the transmission mode for transmitting the modulated signal may be broadcasting (here, a transmission mode in which the transmission destination is not specified in advance) or communication (here, transmission in which the transmission destination is specified in advance). Refers to the embodiment). That is, the transmission of the modulation signal may be realized by any of wireless broadcasting, wired broadcasting, wireless communication, and wired communication.

  For example, a terrestrial digital broadcast broadcasting station (such as broadcasting equipment) / receiving station (such as a television receiver) is an example of a transmitting device PROD_A / receiving device PROD_B that transmits and receives a modulated signal by wireless broadcasting. Further, a broadcasting station (such as broadcasting equipment) / receiving station (such as a television receiver) of cable television broadcasting is an example of a transmitting device PROD_A / receiving device PROD_B that transmits and receives a modulated signal by cable broadcasting.

  Also, a server (workstation or the like) / client (television receiver, personal computer, smartphone, etc.) such as a VOD (Video On Demand) service or a video sharing service using the Internet transmits and receives a modulated signal by communication. This is an example of PROD_A / reception device PROD_B (usually, either a wireless or wired transmission medium is used in a LAN, and a wired transmission medium is used in a WAN). Here, the personal computer includes a desktop PC, a laptop PC, and a tablet PC. The smartphone also includes a multi-function mobile phone terminal.

  Note that the client of the video sharing service has a function of encoding a moving image captured by a camera and uploading it to the server in addition to a function of decoding the encoded data downloaded from the server and displaying it on the display. That is, the client of the video sharing service functions as both the transmission device PROD_A and the reception device PROD_B.

  Next, it will be described with reference to FIG. 36 that the above-described moving image encoding device 2 and moving image decoding device 1 can be used for recording and reproduction of moving images.

  FIG. 36A is a block diagram showing a configuration of a recording apparatus PROD_C in which the above-described moving picture encoding apparatus 2 is mounted. As shown in (a) of FIG. 36, the recording apparatus PROD_C has an encoding unit PROD_C1 that obtains encoded data by encoding a moving image, and the encoded data obtained by the encoding unit PROD_C1 on the recording medium PROD_M. A writing unit PROD_C2 for writing. The moving image encoding apparatus 2 described above is used as the encoding unit PROD_C1.

  The recording medium PROD_M may be of a type built in the recording device PROD_C, such as (1) HDD (Hard Disk Drive) or SSD (Solid State Drive), or (2) SD memory. It may be of a type connected to the recording device PROD_C, such as a card or USB (Universal Serial Bus) flash memory, or (3) DVD (Digital Versatile Disc) or BD (Blu-ray Disc: registration) Or a drive device (not shown) built in the recording device PROD_C.

  In addition, the recording device PROD_C serves as a moving image supply source to be input to the encoding unit PROD_C1. The unit PROD_C5 and an image processing unit C6 that generates or processes an image may be further provided. In FIG. 36A, a configuration in which the recording apparatus PROD_C includes all of these is illustrated, but a part of the configuration may be omitted.

  The receiving unit PROD_C5 may receive a non-encoded moving image, or may receive encoded data encoded by a transmission encoding scheme different from the recording encoding scheme. You may do. In the latter case, a transmission decoding unit (not shown) that decodes encoded data encoded by the transmission encoding method may be interposed between the reception unit PROD_C5 and the encoding unit PROD_C1.

  Examples of such a recording device PROD_C include a DVD recorder, a BD recorder, and an HDD (Hard Disk Drive) recorder (in this case, the input terminal PROD_C4 or the receiving unit PROD_C5 is a main supply source of moving images). . In addition, a camcorder (in this case, the camera PROD_C3 is a main source of moving images), a personal computer (in this case, the receiving unit PROD_C5 or the image processing unit C6 is a main source of moving images), a smartphone (in this case In this case, the camera PROD_C3 or the receiving unit PROD_C5 is a main supply source of moving images) is also an example of such a recording device PROD_C.

  FIG. 36 (b) is a block diagram illustrating a configuration of a playback device PROD_D in which the above-described video decoding device 1 is mounted. As shown in (b) of FIG. 36, the playback device PROD_D reads the moving image by decoding the reading unit PROD_D1 that reads the encoded data written on the recording medium PROD_M and the encoded data read by the reading unit PROD_D1. And a decoding unit PROD_D2 to be obtained. The moving picture decoding apparatus 1 described above is used as the decoding unit PROD_D2.

  Note that the recording medium PROD_M may be of the type built into the playback device PROD_D, such as (1) HDD or SSD, or (2) such as an SD memory card or USB flash memory, It may be of a type connected to the playback device PROD_D, or (3) may be loaded into a drive device (not shown) built in the playback device PROD_D, such as DVD or BD. Good.

  In addition, the playback device PROD_D has a display PROD_D3 that displays a moving image, an output terminal PROD_D4 that outputs the moving image to the outside, and a transmission unit that transmits the moving image as a supply destination of the moving image output by the decoding unit PROD_D2. PROD_D5 may be further provided. FIG. 36B illustrates a configuration in which the playback apparatus PROD_D includes all of these, but a part of the configuration may be omitted.

    The transmission unit PROD_D5 may transmit an unencoded moving image, or transmits encoded data encoded by a transmission encoding method different from the recording encoding method. You may do. In the latter case, it is preferable to interpose an encoding unit (not shown) that encodes a moving image with an encoding method for transmission between the decoding unit PROD_D2 and the transmission unit PROD_D5.

Examples of such a playback device PROD_D include a DVD player, a BD player, and an HDD player (in this case, an output terminal PROD_D4 to which a television receiver or the like is connected is a main supply destination of moving images). . In addition, a television receiver (in this case, the display PROD_D3 is a main supply destination of moving images), a digital signage (also referred to as an electronic signboard or an electronic bulletin board), and the display PROD_D3 or the transmission unit PROD_D5 is the main supply of moving images. Desktop PC (in this case, the output terminal PROD_D4 or the transmission unit PROD_D5 is the main video image supply destination), laptop or tablet PC (in this case, the display PROD_D3 or the transmission unit PROD_D5 is a moving image) A smartphone (which is a main image supply destination), a smartphone (in this case, the display PROD_D3 or the transmission unit PROD_D5 is a main moving image supply destination), and the like are also examples of such a playback device PROD_D.
[Appendix 2]
Each block of the moving picture decoding apparatus 1 and the moving picture encoding apparatus 2 described above may be realized in hardware by a logic circuit formed on an integrated circuit (IC chip), or may be a CPU (Central Processing Unit). ) May be implemented in software.

  In the latter case, each device includes a CPU that executes instructions of a program that realizes each function, a ROM (Read Only Memory) that stores the program, a RAM (Random Access Memory) that expands the program, the program, and various types A storage device (recording medium) such as a memory for storing data is provided. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program for each of the above devices, which is software that realizes the above-described functions, is recorded so as to be readable by a computer. This can also be achieved by supplying each of the above devices and reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU).

  Examples of the recording medium include tapes such as magnetic tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks / hard disks, and disks including optical disks such as CD-ROM / MO / MD / DVD / CD-R. IC cards (including memory cards) / optical cards, semiconductor memories such as mask ROM / EPROM / EEPROM / flash ROM, PLD (Programmable logic device), FPGA (Field Programmable Gate Array), etc. Logic circuits can be used.

  Further, each of the above devices may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited as long as it can transmit the program code. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication network, and the like can be used. The transmission medium constituting the communication network may be any medium that can transmit the program code, and is not limited to a specific configuration or type. For example, even with wired lines such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, and ADSL (Asymmetric Digital Subscriber Line) line, infrared rays such as IrDA and remote control, Bluetooth (registered trademark), IEEE 802.11 wireless, HDR ( It can also be used by radio such as High Data Rate (NFC), Near Field Communication (NFC), Digital Living Network Alliance (DLNA), mobile phone network, satellite line, and digital terrestrial network.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used for an arithmetic decoding device that decodes arithmetically encoded data and an arithmetic encoding device that generates arithmetically encoded data.

1 video decoding device (image decoding device)
11 Variable length code decoding unit (sub-block dividing means)
111 Quantization residual information decoding unit (arithmetic decoding device)
120 transform coefficient decoding unit 123 coefficient decoding control unit 124 coefficient level decoding unit 124d coefficient level storage unit 124e coefficient presence / absence flag setting unit (non-zero transform coefficient presence / absence flag decoding means)
124f Coefficient level decoding processing unit (coefficient value decoding means)
124y non-zero conversion coefficient count unit (counting means)
124z Coefficient presence / absence flag context deriving unit (context index deriving means)
125 coefficient code decoding unit 127 subblock coefficient presence / absence flag decoding unit 127a subblock coefficient presence / absence flag context deriving unit 127b subblock coefficient presence / absence flag storage unit 127c subblock coefficient presence / absence flag setting unit (subblock coefficient presence / absence flag decoding unit)
130 Arithmetic Code Decoding Unit 131 Context Recording Update Unit 132 Bit Decoding Unit 2 Video Coding Device (Image Coding Device)
27 Variable length code encoding unit (sub-block dividing means)
271 Quantization residual information encoding unit (arithmetic encoding device)
220 transform coefficient encoding unit 223 coefficient encoding control unit 224 coefficient level encoding unit 224z coefficient presence / absence flag context deriving unit (context index deriving unit)
224e Coefficient presence / absence flag setting unit (non-zero conversion coefficient presence / absence flag encoding means)
224f Coefficient level encoding processing unit (coefficient value encoding means)
225 Coefficient code encoding unit 227 Subblock coefficient presence / absence flag encoding unit (subblock coefficient presence / absence flag encoding means)
227a Context deriving unit 227b Subblock coefficient presence / absence flag storage unit 227c Subblock coefficient presence / absence flag setting unit 228 Syntax deriving unit 230 Arithmetic code coding unit 231 Context recording update unit 232 Bit coding unit

Claims (8)

Arithmetic decoding apparatus that decodes encoded data obtained by arithmetically encoding various syntaxes representing transform coefficients for transform coefficients obtained for each frequency component by performing frequency transform on the target image for each unit region Because
Sub-block dividing means for dividing a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size;
Subblock coefficient presence / absence flag decoding means for decoding a subblock coefficient presence / absence flag indicating whether or not at least one non-zero transform coefficient is included in the subblock for each subblock divided by the subblock division means;
Non-zero transform coefficient presence / absence flag decoding means for decoding a non-zero transform coefficient presence / absence flag indicating whether or not each transform coefficient in each sub-block is 0;
Coefficient value decoding means for decoding the magnitude of each transform coefficient in each sub-block;
An arithmetic decoding apparatus comprising: context index deriving means for deriving a context index by referring to a value of a decoded transform coefficient.   2. The arithmetic decoding apparatus according to claim 1, wherein the context index deriving unit derives a context index by using a sum of values obtained by clipping absolute values of decoded transform coefficients by a predetermined value. Counting means for counting the number of non-zero transform coefficients decoded in the sub-block,
The context index deriving means derives a context index using an absolute value of a decoded transform coefficient when the number of the non-zero transform coefficients is equal to or less than a predetermined number. Arithmetic decoding device. Counting means for counting the number of non-zero transform coefficients decoded in the sub-block,
The context index deriving means, when the number of the non-zero transform coefficients at the time of decoding the non-zero transform coefficient presence flag that is a predetermined number before the target transform coefficient is equal to or less than the predetermined number, The arithmetic decoding apparatus according to claim 1, wherein a context index is derived using an absolute value.   2. The arithmetic decoding apparatus according to claim 1, wherein a non-zero transform coefficient presence / absence flag is decoded in a loop in the sub-block, and a sign of the transform coefficient is decoded in a loop in a sub-block different from the loop. The arithmetic decoding device according to any one of claims 1 to 5,
Inverse frequency transforming means for generating a residual image by inverse frequency transforming transform coefficients decoded by the arithmetic decoding device;
Decoded image generating means for generating a decoded image by adding the residual image generated by the inverse frequency transform means and the predicted image predicted from the generated decoded image;
An image decoding apparatus comprising: An arithmetic encoding device that generates encoded data by arithmetically encoding various syntaxes representing transform coefficients for each transform coefficient obtained by performing frequency transform on a target image for each unit region. And
Sub-block dividing means for dividing a target frequency region corresponding to a unit region to be processed into sub-blocks of a predetermined size;
Subblock coefficient presence / absence flag decoding means for decoding a subblock coefficient presence / absence flag indicating whether or not at least one non-zero transform coefficient is included in the subblock for each subblock divided by the subblock division means;
Non-zero transform coefficient presence / absence flag encoding means for encoding a non-zero transform coefficient presence / absence flag indicating whether or not each transform coefficient in each sub-block is 0;
Coefficient value encoding means for encoding the magnitude of each transform coefficient in each of the sub-blocks;
An arithmetic coding apparatus comprising: context index deriving means for deriving a context index by referring to a value of an encoded transform coefficient. Transform coefficient generating means for generating a transform coefficient by frequency transforming the residual image between the encoding target image and the predicted image for each unit region;
The arithmetic encoding device according to claim 7,
With
The arithmetic encoding device generates encoded data by arithmetically encoding various syntaxes representing transform coefficients generated by the transform coefficient generating means.
An image encoding apparatus characterized by that.

Images