JP2014096638A - Image encoder, image encoding method, image encoding program, image decoder, image decoding method and image decoding program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve encoding efficiency when introducing a group flag into a significant coefficient flag for use in arithmetic coding.SOLUTION: An image encoder performing CABAC includes a specification unit for specifying an area having the last non-zero coefficient value in a predetermined scanning order, for a plurality of divided areas of a block to be transformed orthogonally, an estimation unit for estimating a first area group having a group flag indicating the fact that at least one significant coefficient flag is included, using the position of a specified area, for a group flag indicating whether or not a significant coefficient flag, included in a syntax element, is a value indicating a coefficient value of zero, and an arithmetic coding unit performing arithmetic coding of a significant coefficient flag of an area indicating the fact that the position of the last non-zero coefficient value, a group flag of an area other than the first area group, and at least one significant coefficient flag indicating a non-zero coefficient value of group flag other than the first area group are included, and an area of the first area group.

Description

  The present invention relates to an image encoding device, an image encoding method, an image encoding program, an image decoding device, an image decoding method, and an image decoding program that perform arithmetic encoding.

  In recent years, with the advance of multimedia, there are many opportunities to handle moving images. Image data has a large amount of information, and a moving image, which is a set of images, has an information amount exceeding 1 Gbit / sec in high-definition (1920 × 1080) broadcasting, which is the mainstream of television broadcasting.

  Therefore, the moving image data is H.264. H.264 / AVC (Advanced Video Coding) (see, for example, Non-Patent Document 1) and HEVC (High Efficiency Video Coding) being standardized, etc. Has been done.

  In these coding techniques, a technique called context-adaptive binary arithmetic coding (CABAC) is used. In CABAC, various syntax elements are used and arithmetic coding is performed.

  A significant coefficient flag (significant_coeff_flag), which is one of the syntax elements, is set for each position of each coefficient value in the conversion target block. This significant coefficient flag is a flag having a value indicating whether each coefficient value is 0 or not. For example, a significant coefficient flag of 1 indicates a non-zero coefficient value, and a significant coefficient flag of 0 indicates a 0 coefficient value.

  There is a technique for reducing the amount of data when arithmetically coding the significant coefficient flag. For example, in HEVC, when the size of a transform block (TU: Transform Unit) is 16 × 16 or 32 × 32, introduction of the concept of grouping significant coefficient flags in each region obtained by dividing TU into 16 is being studied. Yes. Specifically, a group flag (significant_coeffgroup_flag) indicating whether or not at least one significant coefficient flag having a value of 1 is included in each region is introduced (see Non-Patent Document 1).

Nguyen Nguyen, Tianying Ji, Dake He, Gaelle Martin-Cocher, and Lin Song, "Multi-level significance maps for Large Transform Unit", JCT-VC of ITU-T SG16 WP3 and ISO / IEC JTC1 / WG11 JCTVC-G644 ( Nov.2011)

  FIG. 1 is a diagram illustrating an example of a relationship between a significant coefficient flag and a group flag. In the example illustrated in FIG. 1, a conversion block tu101 (size 16 × 16) to be converted is divided into regions each having 4 × 4 as one group. One square indicates one pixel position, and the values “1” and “0” in the conversion block tu101 indicate the values of the significant coefficient flags.

  Here, when the group flag is not introduced, 217 significant coefficients included in the range ar100 shown in FIG. 1 are encoded. Note that the significant coefficient flag included in the range ar101 illustrated in FIG. 1 is not encoded because the coefficient position is after the last non-zero significant coefficient (last_significant_coeff).

  On the other hand, when a group flag is introduced as described in Non-Patent Document 1, a group flag in each region and a significant coefficient flag in a region where the group flag is 1 are encoded. An area block gr101 shown in FIG. 1 is a block of an area obtained by dividing the transform block tu101 into 4 × 4 groups.

  The value in the area block gr101 indicates the value of the group flag. In the example shown in FIG. 1, when the group flag is 1, it indicates that at least one significant coefficient flag having a value of 1 is included in the area. When the group flag is 0, all significant coefficient flags in the area are all included. Indicates a value of 0.

  Since the group flag of the region included in the range ar102 is a region including last_significant_coeff, it is assumed that the group flag is 1, and thus is not encoded. In addition, since the group flag of each region included in the range ar103 is assumed to be 1, it is not encoded. This is because the group flags in the areas adjacent to the right side and the lower side are both 1, and therefore the group flag in the range ar103 is assumed to be 1 in consideration of the coefficient characteristics after frequency conversion. is there.

  As a result, the data encoded when the group flag is introduced is shown in FIG. FIG. 2 is a diagram illustrating an example of encoded data when a group flag is introduced. In the example shown in FIG. 2, 148 significant coefficient flags included in the range ar104 and 10 group flags included in the range ar105 are encoded data.

  In the technique of Non-Patent Document 1, 59 (= 217− (148 + 10)) encoded data is reduced from 217 encoded data when the group flag is not introduced in the examples shown in FIGS. Can do.

  However, even when a group flag is introduced, there is still room for improving the coding efficiency.

  Therefore, the present invention provides an image coding apparatus, an image coding method, an image coding program, and an image decoding that can improve coding efficiency when a group flag is introduced into a significant coefficient flag used in arithmetic coding. It is an object to provide an apparatus, an image decoding method, and an image decoding program.

  An image encoding device according to an aspect of the present invention is an image encoding device that performs context-adaptive binary arithmetic encoding (CABAC). A plurality of regions into which a target block for orthogonal transformation is divided are assigned to a predetermined region. Whether the specific part for specifying the region having the last non-zero coefficient value in the scanning order and the significant coefficient flag included in the CABAC syntax element are values indicating a coefficient value of 0 in all of the regions. A first region group having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included using the position of the region specified by the specifying unit with respect to a group flag indicating whether or not An estimation unit for estimation, a position of the last non-zero coefficient value, a group flag of an area other than the first area group, and a coefficient value of a group flag other than the first area group indicating a non-zero coefficient value Significant coefficient flag of the area and the first area group region indicating that the meaning coefficient flag comprising at least one, and comprising an arithmetic coding unit for arithmetic coding.

  Further, the specifying unit specifies a position of the last non-zero coefficient value in the specified region, and the estimation unit uses the position of the coefficient value specified by the specifying unit, One region group may be expanded.

  Further, the estimation unit uses the position of the region specified by the specifying unit among the plurality of regions, and uses the position of the first region group and a group flag indicating that all significant coefficient flags have coefficient values of 0. And the arithmetic encoding unit arithmetically encodes the position of the last non-zero coefficient value and the significant coefficient flag of the region of the first region group, and the first region group And the group flag of the second region group may not be arithmetically encoded.

  The determination unit further includes a determination unit that determines whether to estimate the second region group based on a group flag value of a region other than the first region group, and the arithmetic encoding unit includes the determination unit It is possible to determine whether or not the group flag of the second region group is arithmetically encoded based on the use flag indicating the determination content of the second region group, and to include the use flag as an encoding target and not perform the arithmetic encoding .

  An image coding method according to another aspect of the present invention is an image coding method in an image coding apparatus that performs context adaptive binary arithmetic coding (CABAC), in which a target block for orthogonal transformation is divided. A specific step of specifying a region having the last non-zero coefficient value in a predetermined scanning order for a plurality of regions, and a significant coefficient flag included in the syntax element of the CABAC is 0 in all of the regions A group indicating that the group flag indicating whether or not the value indicates a coefficient value includes at least one significant coefficient flag indicating a non-zero coefficient value by using the position of the region specified by the specifying step. An estimation step of estimating a first region group having a flag, a position of the last non-zero coefficient value, a group flag of a region other than the first region group, and the first An arithmetic encoding step for arithmetically encoding a region other than the region group indicating that the group flag includes at least one significant coefficient flag indicating a non-zero coefficient value and a significant coefficient flag of the region of the first region group; Have

  An image encoding program according to another aspect of the present invention provides a computer for performing context-adaptive binary arithmetic encoding (CABAC) with respect to a plurality of regions into which a target block for orthogonal transformation is divided. The specific step of specifying the region having the last non-zero coefficient value in the scan order and the significant coefficient flag included in the CABAC syntax element are values indicating coefficient values of 0 in all of the areas A first region group having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included using the position of the region specified in the specifying step with respect to the group flag indicating whether or not An estimation step to estimate, a position of the last non-zero coefficient value, a group flag of a region other than the first region group, and a group flag other than the first region group. Pufuragu significant coefficient flag of the area and the first area group of the indicated area that contains at least one significant coefficient flag indicating coefficient values of the non-0, the executing the arithmetic coding step of arithmetic coding.

  An image decoding apparatus according to another aspect of the present invention is an image decoding apparatus that decodes a stream on which context adaptive binary arithmetic coding (CABAC) has been performed, and includes blocks to be orthogonally transformed among the streams. On the other hand, a position decoding unit that decodes the position of the last non-zero coefficient value in a predetermined scanning order, and a plurality of regions in which the target block is divided based on the position of the decoded coefficient value, Based on the specified area that specifies the region having the last non-zero coefficient value, and the significant coefficient flag included in the syntax element of the CABAC sets a coefficient value of 0 in all the regions. A first flag decoding unit for decoding a group flag indicating whether or not the value is a value to be indicated, and a value of the decoded group flag is at least a significant coefficient flag indicating a non-zero coefficient value Comprising a second flag decoding unit for decoding the significant coefficient flag of the region to be a value indicating that it contains One, a.

  An image decoding method according to another aspect of the present invention is an image decoding method in an image decoding apparatus for decoding a stream on which context adaptive binary arithmetic coding (CABAC) has been performed. A position decoding step for decoding the position of the last non-zero coefficient value in a predetermined scanning order with respect to the target block for orthogonal transform, and a plurality of blocks in which the target block is divided based on the position of the decoded coefficient value A step of specifying the region having the last non-zero coefficient value for the region of the region, and a significant coefficient flag included in the syntax element of the CABAC based on the specified region is all in the region. A first flag decoding step of decoding a group flag indicating whether the coefficient value is 0 or not, and the decoded value of the group flag is: 0 significant coefficient flag indicating coefficient values has a second flag decoding step of decoding the significant coefficient flag of the region to be a value indicating that it contains at least one.

  In addition, an image decoding program according to another aspect of the present invention provides a computer for decoding a stream subjected to context adaptive binary arithmetic coding (CABAC) to an orthogonal transform target block in the stream. A position decoding step for decoding the position of the last non-zero coefficient value in a predetermined scanning order, and a plurality of regions into which the target block is divided based on the position of the decoded coefficient value. A specifying step for specifying a region having a non-zero coefficient value, and a value indicating that a significant coefficient flag included in the syntax element of the CABAC indicates a coefficient value of 0 in all the regions based on the specified region. A first flag decoding step for decoding a group flag indicating whether or not the value is present, and the decoded group flag value indicates a non-zero coefficient value. Coefficient flag to execute a second flag decoding step of decoding the significant coefficient flag of the value range that indicates that at least one.

  According to the present invention, when a group flag is introduced into a significant coefficient flag used in arithmetic coding, the coding efficiency can be improved.

The figure which shows an example of the relationship between a significant coefficient flag and a group flag. The figure which shows an example of the coding data at the time of introducing a group flag. 1 is a block diagram illustrating an example of a schematic configuration of an image encoding device according to Embodiment 1. FIG. FIG. 3 is a block diagram illustrating an example of a configuration of an entropy encoding unit in the first embodiment. FIG. 3 is a block diagram illustrating an example of a configuration of a reduction unit according to the first embodiment. The figure for demonstrating a 1st area | region group. The figure which shows an example of a conversion block and an area | region. The figure which shows the example 1 of estimation. The figure which shows the example 2 of an estimation. The figure which shows the estimation example 3. FIG. The figure which shows the example 4 of an estimation. 5 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag in the first embodiment. FIG. 9 is a block diagram illustrating an example of a configuration of a reduction unit according to the second embodiment. The figure which shows the example 5 of estimation. 9 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag in the second embodiment. FIG. 10 is a block diagram illustrating an example of a configuration of a reduction unit according to a third embodiment. The figure which shows the example of the group flag of each area | region. 10 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag in the third embodiment. FIG. 10 is a block diagram illustrating an example of a schematic configuration of an image decoding device according to a fourth embodiment. FIG. 10 is a block diagram illustrating an example of a configuration of an entropy decoding unit according to a fourth embodiment. 10 is a flowchart illustrating an example of a decoding process related to a significant coefficient flag in the fourth embodiment. FIG. 10 is a block diagram illustrating an example of a configuration of an image processing apparatus 80 according to a fifth embodiment.

  In the following, each embodiment capable of further improving the coding efficiency when a group flag is introduced into a significant coefficient flag used in arithmetic coding will be described in detail with reference to the accompanying drawings.

[Example 1]
In the first embodiment, the region existing in the upper left direction from the region including last_significant_coeff which is the last non-zero coefficient value in the orthogonal transformation target block is encoded by estimating the group flag as 1 and not performing the encoding. Improve efficiency.

<Configuration>
FIG. 3 is a block diagram illustrating an example of a schematic configuration of the image encoding device 10 according to the first embodiment. In the example illustrated in FIG. 3, the image encoding device 10 includes a preprocessing unit 100, a prediction error signal generation unit 101, an orthogonal transformation unit 102, a quantization unit 103, an entropy encoding unit 104, an inverse quantization unit 105, and an inverse orthogonal. A conversion unit 106, a decoded image generation unit 107, a loop filter unit 109, a decoded image storage unit 110, an intra prediction unit 111, an inter prediction unit 112, a motion vector calculation unit 113, and a predicted image selection unit 115 are included. An outline of each part will be described below.

  The preprocessing unit 100 rearranges the pictures in accordance with the picture type, and sequentially outputs the picture type and the frame image for each frame. The preprocessing unit 100 also performs block division and the like.

  The prediction error signal generation unit 101 acquires block data obtained by dividing an encoding target image of input moving image data into blocks such as 32 × 32, 16 × 16, and 8 × 8 pixels.

  The prediction error signal generation unit 101 generates a prediction error signal based on the block data and the block data of the prediction image output from the prediction image selection unit 115. The prediction error signal generation unit 101 outputs the generated prediction error signal to the orthogonal transformation unit 102.

  The orthogonal transform unit 102 performs orthogonal transform processing on the input prediction error signal. The orthogonal transform unit 102 outputs a signal indicating the transformed coefficient value to the quantization unit 103.

  The quantization unit 103 quantizes the output signal from the orthogonal transform unit 102. The quantization unit 103 reduces the code amount of the output signal by quantization, and outputs this output signal to the entropy encoding unit 104 and the inverse quantization unit 105.

  The entropy coding unit 104 entropy codes and outputs the output signal from the quantization unit 103, the motion vector information output from the motion vector calculation unit 113, the filter coefficient from the loop filter unit 109, and the like. Entropy coding is a method of assigning variable-length codes according to the appearance frequency of symbols. Details of the entropy encoding unit 104 will be described later with reference to FIG.

  The inverse quantization unit 105 dequantizes the output signal from the quantization unit 103 and then outputs the output signal to the inverse orthogonal transform unit 106. The inverse orthogonal transform unit 106 performs an inverse orthogonal transform process on the output signal from the inverse quantization unit 105 and then outputs the output signal to the decoded image generation unit 107. By performing decoding processing by the inverse quantization unit 105 and the inverse orthogonal transform unit 106, a signal having the same level as the prediction error signal before encoding is obtained.

  The decoded image generation unit 107 adds the block data of the image subjected to motion compensation by the inter prediction unit 112 and the prediction error signal decoded by the inverse quantization unit 105 and the inverse orthogonal transform unit 106. The decoded image generation unit 107 outputs the decoded image block data generated by addition to the loop filter unit 109.

  The loop filter unit 109 is, for example, an ALF (Adaptive Loop Filter) or a deblocking filter, and may include either or both.

  For example, the loop filter unit 109 divides the input image into groups for each predetermined size, and generates an appropriate filter coefficient for each group. The loop filter unit 109 divides the filtered decoded image into groups for each predetermined size, and performs filter processing for each group using the generated filter coefficients. The loop filter unit 109 outputs the filter processing result to the decoded image storage unit 110 and accumulates it as a reference image. The predetermined size is, for example, an orthogonal transformation size.

  The decoded image storage unit 110 stores the input block data of the decoded image as new reference image data, and outputs the data to the intra prediction unit 111, the inter prediction unit 112, and the motion vector calculation unit 113.

  The intra prediction unit 111 generates block data of the predicted image from the already-encoded reference pixels for the processing target block of the encoding target image. The intra prediction unit 111 performs prediction using a plurality of prediction directions and determines an optimal prediction direction.

  The inter prediction unit 112 performs motion compensation on the reference image data acquired from the decoded image storage unit 110 with the motion vector provided from the motion vector calculation unit 113. Thereby, block data as a motion-compensated reference image is generated. The inter prediction unit 112 outputs information on the prediction block used for motion compensation to the orthogonal transform unit 102.

  The motion vector calculation unit 113 obtains a motion vector using the block data in the encoding target image and the reference image acquired from the decoded image storage unit 110. The motion vector is a value indicating a spatial deviation in units of blocks obtained using a block matching technique or the like that searches for a position most similar to the processing target block from the reference image in units of blocks.

  The motion vector calculation unit 113 outputs the obtained motion vector to the inter prediction unit 112, and outputs motion vector information including information indicating the motion vector and the reference image to the entropy coding unit 104.

  The block data output from the intra prediction unit 111 and the inter prediction unit 112 are input to the predicted image selection unit 115.

  The predicted image selection unit 115 selects one of the block data acquired from the intra prediction unit 111 and the inter prediction unit 112 as a predicted image. The selected prediction image is output to the prediction error signal generation unit 101.

  The configuration of the image encoding device 10 illustrated in FIG. 3 is an example, and the configurations may be combined or the configurations may be appropriately changed as necessary.

<Configuration of entropy encoding unit>
Next, the configuration of the entropy encoding unit 104 will be described. FIG. 4 is a block diagram illustrating an example of the configuration of the entropy encoding unit 104 according to the first embodiment. The entropy encoding unit 104 illustrated in FIG. 4 includes a variable length encoding unit 200 and a binary arithmetic encoding unit 201.

  The variable length coding unit 200 uses, for example, a context adaptive variable length coding method called CAVLC (Context-Adaptive Variable Length Coding), and obtains necessary coefficient values from among quantized DCT coefficient values. Encode. The encoded coefficient value is included in the stream.

  The binary arithmetic encoding unit 201 arithmetically encodes syntax elements and the like using, for example, CABAC. The binary arithmetic encoding unit 201 includes a binarizing unit 202, a reduction unit 203, a context calculation unit 204, and an arithmetic encoding unit 205.

  The binarization unit 202 converts the syntax element of the multilevel signal into a binary signal. The binarization method may be different depending on syntax elements.

  The reduction unit 203 reduces the encoded data for the group flag (significant_coeffgroup_flag) for the significant coefficient flag among the binarized syntax elements. Details of the reduction unit 203 will be described later with reference to FIG.

  The context calculation unit 204 holds a plurality of binary signal occurrence probabilities, and switches the occurrence probabilities according to the current encoding target and the surrounding situation (context) to give to the arithmetic encoding unit 205.

  The arithmetic encoding unit 205 arithmetically encodes the input signal using the given binary signal occurrence probability. The arithmetically encoded data is included in the stream.

<Reduction Department>
Next, the configuration of the reduction unit 203 will be described. FIG. 5 is a block diagram illustrating an example of the configuration of the reduction unit 203a according to the first embodiment. The reduction unit 203a illustrated in FIG. 5 includes a specifying unit 301 and an estimation unit 302. Since the reduction unit 203a sets the group flag for the significant coefficient flag as a reduction target, other syntax elements are not mentioned.

  Based on the binarized significant coefficient flag, the specifying unit 301 has an area having the last non-zero coefficient value (last_significant_coeff) in a predetermined scanning order with respect to a plurality of areas in which the orthogonal transformation target block is divided Is identified. Hereinafter, the target block for orthogonal transform is also referred to as a transform block, and a region having last_significant_coeff is also referred to as a last region.

  Further, the specifying unit 301 may include a position specifying unit 311, and the position specifying unit 311 may specify which position in the last region has the last non-zero coefficient value. Hereinafter, the position where the last non-zero coefficient value is also referred to as the last position. The identifying unit 301 outputs the identified last region and last position to the estimating unit 302.

  The estimation unit 302 performs the following estimation on the group flag indicating whether or not the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all the regions. The estimation unit 302 estimates a region having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included in the region, using the position of the region specified by the specifying unit 301. Hereinafter, the region estimated by the estimation unit 302 is also referred to as a first region group.

  For example, the group flag indicates “0” when all the significant coefficient flags in the region are “0”, and indicates “1” when the significant coefficient flag in the region includes at least one “1”. And

  The estimation unit 302 estimates the first region group including the region where the group flag is “1” using the position of the last region.

  The estimation unit 302 includes a first region group estimation unit 321 and an unnecessary region determination unit 322. For example, the first region group estimation unit 321 estimates, as a first region group, a region located in the upper left direction of the last region among the regions in the transform block. Moreover, the 1st area group estimation part 321 may expand a 1st area group using the last position, when the last position is acquired. That is, the first region group estimation unit 321 may increase the number of regions included in the first region group using the last position.

  The unnecessary region determination unit 322 determines a region included in the first region group in which the group flag is estimated as 1 as a region that does not require encoding. The estimation unit 302 sends the final position, the group flag other than the first region group, and the significant coefficient flag in the region where the group flag is “1” (including the estimated “1”) to the arithmetic coding unit 205. Output. Thereby, the arithmetic encoding unit 205 does not encode the group flag of the first region group.

  Therefore, the arithmetic encoding unit 205 arithmetically encodes the position of the last non-zero coefficient value (last position) and the group flag of the area other than the first area group. If there is an area to be scanned after the last area, the arithmetic encoding unit 205 sets this area and the area of the first area group as an encoding unnecessary area, and sets group flags for areas other than the encoding unnecessary area. Is arithmetically encoded.

  Further, the arithmetic encoding unit 205 includes a significant coefficient flag in an area indicating that a group flag of an area other than the first area group includes at least one significant coefficient flag indicating a non-zero coefficient value, and the first Arbitrarily encodes the significant coefficient flag in the region of the region group. That is, the arithmetic encoding unit 205 arithmetically encodes the significant coefficient flag in the region where the group flag is “1” (including the estimated “1”).

  The arithmetic encoding unit 205 arithmetically encodes the group flag and the significant coefficient flag scanned in a predetermined scanning order (for example, zigzag scanning). At this time, the decoder side can recognize where the unencoded group flag and significant coefficient flag are located. This is because the decoder can identify the last region by decoding the last position, and if the last region is known, it can recognize which region group flag is not encoded in the same manner as the encoder. .

<Example of first region group>
Next, an example of the first region group will be described. FIG. 6 is a diagram for explaining the first region group. FIG. 6A is a diagram illustrating an example of a transform block represented by a significant coefficient flag. A significant coefficient flag fr201 illustrated in FIG. 6A is a significant coefficient flag at the last position in a zigzag scan, for example.

  As shown in FIG. 6A, the group flag in the range ar201 including the significant coefficient flag in the upper left direction at the last position is estimated to be “1”. This estimation is based on the tendency for non-zero coefficient values to gather in the upper left direction with respect to coefficient values frequency-converted by DCT (Discrete Cosine Transform), for example.

  FIG. 6B is a diagram showing the group flag for each region of FIG. As shown in FIG. 6B, if at least one significant coefficient flag is “1” in the area, the group flag is “1”, and if all the area is “0”, the group flag is “group”. The flag is “0”.

  Here, FIG. 6B shows the first region group when the last region and the last position are used. The estimation unit 302 uses the last region and the last position to estimate the region in the range ar202 as the region whose group flag is “1”. A detailed estimation method will be described later with reference to FIGS.

  Thereby, the arithmetic encoding unit 205 encodes the group flags in the ranges ar203 and ar204 without encoding the group flags in the first region group. For example, the arithmetic encoding unit 205 scans in a predetermined scanning order and encodes only the group flag to be encoded. The lower right region is not encoded because the group flag is estimated to be 0 based on the last position.

<Estimation process>
Next, the estimation process by the estimation unit 302 will be described using a specific example. FIG. 7 is a diagram illustrating an example of transform blocks and regions. FIG. 7A shows a conversion block. In the example shown in FIG. 7A, the conversion block is described using 16 × 16, but 32 × 32 or the like may be used. In the example shown in FIG. 7A, a region obtained by dividing the transform block is represented as A [k] [l] (k = 0 to 3, l = 0 to 3).

  FIG. 7B shows pixel positions in the region. In the example illustrated in FIG. 7B, the pixel position in the region is represented as B [n] [m] (n = 0 to 3, m = 0 to 3).

(Estimation example 1)
FIG. 8 is a diagram illustrating a first estimation example. In FIG. 8, the specifying unit 301 specifies the last area as A [2] [3] (FIG. 8A).

  At this time, the estimation unit 302 sets the group flag of the region (A [0-1] [0-2]) in the range ar302 existing in the upper left direction from the last region A [2] [3] to “1”. And the region in the range ar302 is estimated as the first region group. The estimation unit 302 also includes A [2] [3], which is the last region, in the first region group because the group flag is “1”.

  The example shown in FIG. 8 is an estimation process in the case where the last position is B [0] [0] (FIG. 8B), and the last position is not specified and only the last area is the first area group. It is also an estimation process when estimating.

  Thereby, the arithmetic encoding unit 205 only has to encode the group flags of the regions in the ranges ar303 and ar304.

(Estimation example 2)
FIG. 9 is a diagram illustrating a second estimation example. In FIG. 9, the identifying unit 301 identifies the last area as A [2] [3] (FIG. 9A) and identifies the last position as one of B [0] [1-3]. Yes (FIG. 9B).

  At this time, the estimation unit 302 estimates the group flag of the area (A [0-1] [0-2]) existing in the upper left direction from the last area A [2] [3] as “1”. The estimation unit 302 also estimates that there is a significant coefficient flag of “1” in the upward direction at the last position, and includes the regions A [0] [3] and A [1] [3] in the first region group. . Therefore, the estimation unit 302 estimates the area within the range ar402 as the first area group. The estimation unit 302 also includes A [2] [3], which is the last region, in the first region group because the group flag is “1”.

  Thereby, the arithmetic encoding unit 205 only has to encode the group flag of the region in the range ar403.

(Estimation example 3)
FIG. 10 is a diagram illustrating a third estimation example. In FIG. 10, the identifying unit 301 identifies the last area as A [2] [3] (FIG. 10A) and identifies the last position as one of B [1-3] [0]. (FIG. 10B).

  At this time, the estimation unit 302 estimates the group flag of the area (A [0-1] [0-2]) existing in the upper left direction from the last area A [2] [3] as “1”. The estimation unit 302 also estimates that there is a significant coefficient flag of “1” in the left direction of the last position, and the regions A [2] [0], A [2] [1], A [2] [2 ] Are included in the first region group. Therefore, the estimation unit 302 estimates the area within the range ar502 as the first area group. The estimation unit 302 also includes A [2] [3], which is the last region, in the first region group because the group flag is “1”.

  Thereby, the arithmetic encoding unit 205 only has to encode the group flags of the areas in the ranges ar503 and ar504.

(Estimation example 4)
FIG. 11 is a diagram illustrating a fourth estimation example. In FIG. 11, the specifying unit 301 specifies the last area as A [2] [3] (FIG. 11A) and specifies the last position as one of B [1-3] [1-3]. This is the case (FIG. 11B).

  At this time, the estimation unit 302 estimates the group flag of the area (A [0-1] [0-2]) existing in the upper left direction from the last area A [2] [3] as “1”. The estimation unit 302 also estimates that there are significant coefficient flags of “1” in the upward and left directions of the last position, and the regions A [0] [3], A [1] [3], and A [2 ] [0], A [2] [1], A [2] [2] are included in the first region group. Therefore, the estimation unit 302 estimates the area within the range ar602 as the first area group. The estimation unit 302 also includes A [2] [3], which is the last region, in the first region group because the group flag is “1”.

  Thereby, the arithmetic encoding unit 205 only has to encode the group flag of the area within the range ar603.

  With the above estimation process, the number of group flags to be encoded can be reduced as compared with the prior art shown in FIG. 2, and the encoding efficiency can be improved.

<Operation>
Next, the operation of the image encoding device 10 in the first embodiment will be described. FIG. 12 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag that is one of syntax elements in the first embodiment. The process shown in FIG. 12 shows the arithmetic coding process with respect to a significant coefficient flag and a group flag.

  In step S101, the specifying unit 301 specifies a region (last region) including the last non-zero coefficient value for a plurality of regions in the transform block. Further, the specifying unit 301 may further specify the position (last position) of the last non-zero coefficient value in the region.

  In step S102, the estimation unit 302 uses the position of the last region to estimate a first region group including a region where the group flag is likely to be “1” (see, for example, FIG. 8). When the last position is specified, the estimation unit 302 may expand the area of the first area group using the last position (see, for example, FIGS. 9 to 11).

  In step S103, the estimation unit 302 determines the first area group as an encoding unnecessary area. Therefore, the estimation unit 302 outputs the group flags of the regions other than the encoding unnecessary region including the first region group to the arithmetic encoding unit 205. The encoding unnecessary area includes an area of the first area group and an area scanned after the last area.

  In step S104, the arithmetic encoding unit 205 determines the significance of the last position, the group flag of the region other than the region that does not require encoding, and the region where the group flag indicates “1” (including the estimated “1”). Coefficient flags are arithmetically encoded.

  Note that the encoding unnecessary determination process in step S103 can be determined in advance not to output the group flag of the first region group, and is not necessarily a necessary process.

  As described above, according to the first embodiment, when a group flag is introduced into a significant coefficient flag used in arithmetic coding, it is possible to improve coding efficiency. Further, according to the first embodiment, it is possible to further improve the coding efficiency by specifying the last position and expanding the first region group.

[Example 2]
Next, an image coding apparatus according to the second embodiment will be described. In the second embodiment, by estimating the region where the group flag is “0” using the position of the last region, it is not necessary to encode the group flag, and the encoding efficiency can be further improved.

<Configuration>
The configurations of the image encoding device and the entropy encoding unit in the second embodiment are the same as the configurations illustrated in FIGS. 3 and 4 of the first embodiment, and therefore, description will be made using the same reference numerals. In the second embodiment, the processing of the reduction unit 203 is different from that of the first embodiment. Therefore, in the second embodiment, the reduction unit 203b is described, and the reduction unit 203b will be mainly described below.

<Reduction Department>
FIG. 13 is a block diagram illustrating an example of the configuration of the reduction unit 203b according to the second embodiment. Among the configurations of the reduction unit 203b illustrated in FIG. 13, the same components as those illustrated in FIG. Hereinafter, the estimation unit 401 will be mainly described.

  The estimation unit 401 includes a first region group estimation unit 411, a second region group estimation unit 412, and an unnecessary region determination unit 413. The first region group estimation unit 411 performs the same process as the first region group estimation unit 321 in the first embodiment, and estimates the first region group.

  The second region group estimation unit 412 uses the position of the last region identified by the identifying unit 301 to determine a region having the above-described first region group and a group flag in which all significant coefficient flags have coefficient values of 0. The second region group to be included is estimated. For example, the second region group estimation unit 412 estimates a region other than the first region group as the second region group.

  The unnecessary area determination unit 413 determines the first area group and the second area group as encoding unnecessary areas, and does not output the group flags of the first area group and the second area group. Thereby, the group flag is not encoded at all, and the encoding efficiency can be improved.

  Here, it is considered that the image quality is not so much affected even if the second region group actually includes a region whose group flag is “1”. This is because the second region group is a region in the right direction and the lower direction of the transform block, and is not a region that greatly affects the image quality in consideration of the characteristic of the coefficient value after frequency conversion. .

<Estimation process>
Next, the estimation process by the estimation unit 401 will be described using a specific example.

(Estimation example 5)
FIG. 14 is a diagram illustrating a fifth estimation example. In FIG. 14, the specifying unit 301 specifies the last area as A [2] [3] (FIG. 14A).

  At this time, the estimation unit 401 sets the group flag of the region (A [0-1] [0-2]) in the range ar702 existing in the upper left direction from the last region A [2] [3] to “1”. And the region within the range ar702 is estimated as the first region group. The estimation unit 401 also includes A [2] [3], which is the last region, in the first region group because the group flag is “1”.

  In addition, the estimation unit 401 estimates the areas in the ranges ar703 and ar704 as the second area group. For example, the estimation unit 401 estimates a region other than the first region group as the second region group.

  The example shown in FIG. 14 is an estimation process in the case where the last position is B [0] [0] (FIG. 14 (B)), and the first area group is determined only by the last area without specifying the last position. This is an estimation process when estimating.

  Thereby, the arithmetic encoding unit 205 does not need to encode the group flag, and can further improve the encoding efficiency.

  In addition, when specifying the last position with the specification part 301, the estimation part 401 estimates area | regions other than a 1st area group to a 2nd area group by the example shown to FIGS.

<Operation>
Next, the operation of the image encoding device 10 according to the second embodiment will be described. FIG. 15 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag having one syntax element according to the second embodiment. The process shown in FIG. 15 shows an arithmetic encoding process for the significant coefficient flag and the group flag.

  The processing in step S201 is the same as the processing in step S101 shown in FIG.

  In step S202, the estimation unit 401 uses the position of the last region to estimate a first region group including a region where the group flag is likely to be “1”. The estimation unit 401 uses the position of the last region to estimate a second region group including a region where the group flag is likely to be “0” (see, for example, FIG. 14). When the last position is specified, the estimation unit 302 may expand the area of the first area group using the last position.

  In step S203, the estimation unit 401 determines the first region group and the second region group as encoding-unnecessary regions. Therefore, the estimation unit 401 outputs the last position and the significant coefficient flag in the region with the group flag “1” to the arithmetic coding unit 205.

  In step S204, the arithmetic encoding unit 205 arithmetically encodes the last position and the significant coefficient flag in the region where the group flag indicates “1” (including the estimated “1”).

  Note that the encoding unnecessary determination process in step S203 can be determined in advance not to output the group flag of the encoding unnecessary area, and is not necessarily a necessary process.

  As described above, according to the second embodiment, when a group flag is introduced into a significant coefficient flag used in arithmetic coding, it is not necessary to perform coding by estimating the group flag, thereby further improving coding efficiency. it can.

[Example 3]
Next, an image coding apparatus according to the third embodiment will be described. In the third embodiment, whether to apply the estimation processing of the first embodiment or the estimation processing of the second embodiment is determined using a flag, and adaptive estimation processing can be performed. Improvements can be made.

<Configuration>
Since the configurations of the image encoding device and the entropy encoding unit in the third embodiment are the same as the configurations illustrated in FIGS. 3 and 4 of the first embodiment, the description will be made using the same reference numerals. In the third embodiment, the processing of the reduction unit 203 is different from those of the first and second embodiments. Therefore, in the third embodiment, the reduction unit 203c is described, and the reduction unit 203c will be mainly described below.

<Reduction Department>
FIG. 16 is a block diagram illustrating an example of the configuration of the reduction unit 203c according to the third embodiment. Among the configurations of the reduction unit 203c illustrated in FIG. 16, the same components as those illustrated in FIG. Below, the estimation part 501 is mainly demonstrated.

  The estimation unit 501 includes a first region group estimation unit 511, a determination unit 512, a second region group estimation unit 513, and an unnecessary region determination unit 514. The first region group estimation unit 411 performs the same process as the first region group estimation unit 321 in the first embodiment, and estimates the first region group.

  The determination unit 512 determines whether or not to estimate the second region group based on the value of the group flag of the region other than the first region group. For example, the determination unit 512 counts the number of areas other than the first area where the group flag is “1”, and determines that the second area group is estimated if the number is equal to or less than the threshold. The threshold may be set in advance. Moreover, the determination part 512 determines the use flag which shows the determination content. The usage flag is expressed as significant_coeffgroup_flag_use, for example.

  When the threshold value is set to 0, the determination unit 512 determines to perform estimation of the second region group when all the group flags of the regions other than the first region group are “0”. For example, significant_coeffgroup_flag_use = 0 is set. . Further, when the counted number is 1 or more, the determination unit 512 determines not to estimate the second region group, and sets, for example, significant_coeffgroup_flag_use = 1. The determination unit 512 outputs the set use flag to the second region group estimation unit 513 and the unnecessary region determination unit 514.

  By setting the threshold value to 0, the determination unit 512 can improve the coding efficiency without deterioration of image quality. In addition, when the threshold is set to a value of 1 or more, the determination unit 512 may improve the coding efficiency although there may be some degradation in image quality.

  FIG. 17 is a diagram illustrating an example of the group flag of each region. In this example, the threshold value used by the determination unit 512 is set to 0. In the example shown in FIG. 17A, the determination unit 512 sets the use flag to 0 because the group flags of the areas other than the first area group ar801 are all 0 (number ≦ threshold). In the example shown in FIG. 17B, the determination unit 512 sets the use flag to 1 because the group flag of the area other than the first area group ar802 is 1 (number> threshold).

  Returning to FIG. 16, the second region group estimation unit 513 performs the second region group estimation process when the use flag is 0, and performs the second region group estimation process when the use flag is 1. Not performed.

  If the use flag is 1, the unnecessary area determination unit 514 determines the first area group as an encoding unnecessary area as described in the first embodiment, and if the use flag is 0, the unnecessary area determination section 514 is described in the second embodiment. As described above, the first region group and the second region group are determined as the encoding unnecessary regions.

  Thereby, in the third embodiment, it is possible to adaptively select the processing in the first embodiment and the processing in the second embodiment using the use flag.

<Operation>
Next, the operation of the image encoding device 10 according to the third embodiment will be described. FIG. 18 is a flowchart illustrating an example of an encoding process related to a significant coefficient flag having one syntax element according to the third embodiment. The process shown in FIG. 18 shows the arithmetic coding process for the significant coefficient flag and the group flag.

  The processing in steps S301 to S302 is the same as the processing in steps S101 to S102 shown in FIG.

  In step S303, the determination unit 512 sets a use flag indicating whether or not to estimate the second region group based on the group flag values of regions other than the first region group. The determination unit 512 counts the number of group flag values of “1” in regions other than the first region group, and sets the use flag by comparing this number with a threshold value.

  In step S304, the second region group estimation unit 513 determines whether or not the use flag is “1”. If the use flag is “1” (step S304—YES), the process proceeds to step S306, and if the use flag is “0” (step S304—NO), the process proceeds to step S305.

  In step S305, the second region group estimation unit 513 estimates the second region group in the same manner as in the second embodiment.

  In step S306, if the use flag is “1”, the unnecessary area determination unit 514 determines the first area group as an encoding unnecessary area, and if the use flag is “0”, the first area group and the second area group. Is determined as an encoding unnecessary area. Therefore, the estimation unit 501 uses the sign when the last position, the use flag, the significant coefficient flag in the region where the group flag is “1” (including the estimated “1”), and the use flag is “1”. The group flags other than the conversion unnecessary area are output to the arithmetic encoding unit 205.

  In step S307, the arithmetic encoding unit 205 determines that the last position, the use flag, the significant coefficient flag of the area where the group flag indicates “1” (including the estimated “1”), and the use flag is “1”. In the case of, the group flags other than the encoding unnecessary area are arithmetically encoded.

  Note that the encoding unnecessary determination process in step S306 can be determined in advance not to output the group flag of the encoding unnecessary area, and is not necessarily a necessary process.

  As described above, according to the third embodiment, the encoding efficiency can be improved by adaptively selecting the processing of the first embodiment and the processing of the second embodiment.

[Example 4]
Next, the image decoding apparatus 60 in Example 4 is demonstrated. The image decoding device 40 according to the fourth embodiment is a device that decodes the bitstream encoded by the image encoding device 10 according to the first to third embodiments.

<Configuration>
FIG. 19 is a block diagram illustrating an example of a schematic configuration of the image decoding device 60 according to the fourth embodiment. As illustrated in FIG. 19, the image decoding device 60 includes an entropy decoding unit 601, an inverse quantization unit 602, an inverse orthogonal transform unit 603, an intra prediction unit 604, a decoding information storage unit 605, an inter prediction unit 606, and a prediction image selection unit. 607, a decoded image generation unit 608, a loop filter unit 610, and a frame memory 611. An outline of each part will be described below.

  When the bit stream is input, the entropy decoding unit 601 performs entropy decoding corresponding to the entropy encoding of the image encoding device 10. The prediction error signal decoded by the entropy decoding unit 601 is output to the inverse quantization unit 602. Also, the decoded filter coefficient, the decoded motion vector when inter prediction is performed, and the like are output to the decoded information storage unit 605.

  Further, in the case of intra prediction, the entropy decoding unit 601 notifies the intra prediction unit 604 to that effect. Further, the entropy decoding unit 601 notifies the predicted image selection unit 607 whether the decoding target image is inter predicted or intra predicted. Decoding processing related to the significant coefficient flag for the entropy decoding unit 601 will be described later with reference to FIG.

  The inverse quantization unit 602 performs inverse quantization processing on the output signal from the entropy decoding unit 601. The inversely quantized output signal is output to the inverse orthogonal transform unit 603.

  The inverse orthogonal transform unit 603 performs an inverse orthogonal transform process on the decoded block of the output signal from the inverse quantization unit 602 to generate a residual signal. The residual signal is output to the decoded image generation unit 608.

  The intra prediction unit 604 generates a predicted image using a plurality of prediction directions from the peripheral pixels already decoded of the decoding target image acquired from the frame memory 611.

  The decoding information storage unit 605 stores decoding information such as filter coefficients, motion vectors, and division modes of the decoded loop filter.

  The inter prediction unit 606 performs motion compensation on the reference image data acquired from the frame memory 611 using the motion vector and the division mode acquired from the decoded information storage unit 605. Thereby, block data as a motion-compensated reference image is generated. The inter prediction unit 606 notifies the information of the prediction block to the inverse orthogonal transform unit 603.

  The predicted image selection unit 607 selects either the intra predicted image or the inter predicted image. The selected block data is output to the decoded image generation unit 608.

  The decoded image generation unit 608 adds the predicted image output from the predicted image selection unit 607 and the residual signal output from the inverse orthogonal transform unit 403 to generate a decoded image. The generated decoded image is output to the loop filter unit 610.

  The loop filter unit 610 applies a filter for reducing block distortion to the decoded image output from the decoded image generation unit 608, and outputs the decoded image after the loop filter processing to the frame memory 611. Note that the decoded image after the loop filter may be output to a display device or the like.

  The frame memory 611 stores a decoded image that serves as a reference image. The decoded information storage unit 605 and the frame memory 611 are configured separately, but may be the same storage unit.

<Configuration of entropy decoding unit>
Next, the configuration of the entropy decoding unit 601 will be described. FIG. 20 is a block diagram illustrating an example of the configuration of the entropy decoding unit 601 according to the fourth embodiment. The entropy decoding unit 601 illustrated in FIG. 20 includes a position decoding unit 701, a specifying unit 702, a first flag decoding unit 703, a second flag decoding unit 704, and a coefficient value decoding unit 705. Below, the decoding process regarding a significant coefficient flag is demonstrated.

  The position decoding unit 701 decodes the position (last position) of the last non-zero coefficient value in a predetermined scanning order (for example, zigzag scan) with respect to the target block for orthogonal transformation in the input stream.

  Based on the position of the coefficient value decoded by the position decoding unit 701, the specifying unit 702 specifies a region (last region) having the last non-zero coefficient value for a plurality of regions into which the target block is divided. Thereby, the last area similar to that of the image encoding device 10 can be specified.

  The first flag decoding unit 703 determines whether the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all of the areas based on the last area specified by the specifying unit 702. Is decoded.

  For example, the first flag decoding unit 703 estimates and acquires the group flag in the upper left direction from the last region as “1”, decodes the encoded group flag included in the stream, and performs group flag of the remaining region To get. In this case, the process of acquiring the group flag of each area of the target block is referred to as a group flag decoding process.

  In addition, when the encoded group flag is not included in the stream, the first flag decoding unit 703 estimates the region having the group flag “1” and the region “0” based on the last region. get.

  Further, when the use flag is decoded, the first flag decoding unit 703 adaptively changes the group flag decoding process according to the value of the use flag.

  The second flag decoding unit 704 applies a group flag value decoded by the first flag decoding unit 704 to a region having a value indicating that there is at least one significant coefficient flag indicating a non-zero coefficient value. Decode the significant coefficient flag of the region.

  For example, the second flag decoding unit 704 decodes the significant coefficient flag in the region where the group flag indicates “1”.

  Note that the position decoding unit 701, the first flag decoding unit 703, and the second flag decoding unit 704 perform a decoding process corresponding to the arithmetic encoding of the image encoding device 10.

  The coefficient value decoding unit 705 decodes the coefficient value corresponding to the pixel position whose significant coefficient flag is “1”. The coefficient value decoding unit 705 performs a decoding process corresponding to the variable length encoding of the image encoding device 10. The decoded coefficient value is output to the inverse quantization unit 602.

  Thereby, the stream encoded by the image encoding device 10 according to the first to third embodiments can be appropriately decoded.

<Operation>
Next, the operation of the image decoding device 60 will be described. FIG. 21 is a flowchart illustrating an example of a decoding process related to a significant coefficient flag in the fourth embodiment.

  In step S401, the position decoding unit 701 decodes the position (last position) of the last non-zero coefficient value in a predetermined scanning order (for example, zigzag scan) with respect to the target block for orthogonal transformation in the input stream. To do.

  In step S402, the specifying unit 702, based on the position of the coefficient value decoded by the position decoding unit 701, has the last non-zero coefficient value for the plurality of areas into which the target block is divided (last area). Is identified.

  In step S403, the first flag decoding unit 703 is based on the last region specified by the specifying unit 702, and the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all the regions. A group flag indicating whether or not there is present is decoded.

  In step S404, the second flag decoding unit 704 has a value indicating that the value of the group flag decoded by the first flag decoding unit 703 has at least one significant coefficient flag indicating a non-zero coefficient value. On the other hand, the significant coefficient flag of this area is decoded.

  In step S405, the coefficient value decoding unit 705 decodes the coefficient value corresponding to the pixel position whose significant coefficient flag is “1”.

  As described above, according to the fourth embodiment, the bitstream encoded by the image encoding device 10 according to the first to third embodiments can be appropriately decoded.

[Example 5]
FIG. 22 is a block diagram illustrating an example of the configuration of the image processing apparatus 80 according to the fifth embodiment. An image processing apparatus 80 illustrated in FIG. 22 is an example of an apparatus in which the image encoding process described in the first to third embodiments or the image decoding process described in the fourth embodiment is implemented by software.

  As illustrated in FIG. 22, the image processing apparatus 80 includes a control unit 801, a main storage unit 802, an auxiliary storage unit 803, a drive device 804, a network I / F unit 806, an input unit 807, and a display unit 808. These components are connected to each other via a bus so as to be able to transmit and receive data.

  The control unit 801 is a CPU (Central Processing Unit) that controls each device, calculates data, and processes in a computer. The control unit 801 is an arithmetic device that executes an image encoding processing program or an image decoding processing program stored in the main storage unit 802 or the auxiliary storage unit 803. The control unit 801 receives data from the input unit 807 and the storage device, calculates and processes the data, and then outputs the data to the display unit 808 and the storage device.

  Also, the control unit 801 can realize the processing described in each embodiment by executing a program for image encoding processing or image decoding processing.

  The main storage unit 802 is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like. The main storage unit 802 is a storage device that stores or temporarily stores programs and data such as an OS (Operating System) and application software that are basic software executed by the control unit 801.

  The auxiliary storage unit 803 is an HDD (Hard Disk Drive) or the like, and is a storage device that stores data related to application software and the like.

  The drive device 804 reads the program from the recording medium 805, for example, a flexible disk, and installs it in the storage unit.

  A predetermined program is stored in the recording medium 805, and the program stored in the recording medium 805 is installed in the image processing apparatus 80 via the drive device 804. The installed predetermined program can be executed by the image processing apparatus 80.

  The network I / F unit 806 has a communication function connected via a network such as a LAN (Local Area Network) or a WAN (Wide Area Network) constructed by a data transmission path such as a wired and / or wireless line. This is an interface between the device and the image processing apparatus 80.

  The input unit 807 includes a keyboard having cursor keys, numeric input, various function keys, and the like, a mouse, a slide pad, and the like for selecting keys on the display screen of the display unit 808. The display unit 808 is configured by an LCD (Liquid Crystal Display) or the like, and displays according to display data input from the control unit 801.

  The decoded image storage unit 111 illustrated in FIG. 3 is realized by, for example, the main storage unit 802 or the auxiliary storage unit 803, and the configuration other than the decoded image storage unit 111 illustrated in FIG. 3 includes, for example, a control unit 801 and a work memory. This can be realized by the main storage unit 802.

  Further, the decoding information storage unit 405 and the frame memory 411 illustrated in FIG. 19 are realized by, for example, the main storage unit 802 or the auxiliary storage unit 803, and configurations other than the decoding information storage unit 405 and the frame memory 411 illustrated in FIG. It can be realized by the control unit 801 and the main storage unit 802 as a work memory.

  The program executed by the image processing apparatus 80 has a module configuration including each unit described in the first to fourth embodiments. As actual hardware, when the control unit 801 reads a program from the auxiliary storage unit 803 and executes the program, one or more of the above-described units are loaded on the main storage unit 802, and one or more of the units are main. It is generated on the storage unit 802.

  As described above, the image encoding processing described in the first to third embodiments and the image decoding processing described in the fourth embodiment may be realized as a program for causing a computer to execute. The processing described in each embodiment can be realized by installing this program from a server or the like and causing the computer to execute the program.

  It is also possible to record the program in the recording medium 805 and cause the computer or portable terminal to read the recording medium 805 on which the program is recorded to realize the above-described processing. The recording medium 805 is a recording medium that records information optically, electrically, or magnetically, such as a CD-ROM, a flexible disk, or a magneto-optical disk, and information is electrically stored such as a ROM or flash memory. Various types of recording media such as a semiconductor memory for recording can be used. Further, the processes described in the above embodiments may be implemented in one or a plurality of integrated circuits.

  Note that the image processing device 80 according to the fifth embodiment functions as the image encoding device 10 and the image decoding device 60 as described above.

  Each embodiment has been described in detail above. However, the present invention is not limited to the specific embodiment, and various modifications and changes other than the above-described modification are possible within the scope described in the claims. .

DESCRIPTION OF SYMBOLS 10 Image encoding apparatus 60 Image decoding apparatus 80 Image processing apparatus 101 Predictive image generation part 102 Orthogonal transformation part 103 Quantization part 104 Entropy encoding part 201 Binary arithmetic encoding part 202 Binarization part 203 Reduction part 204 Context calculation part 205 Arithmetic coding unit 301 Identification unit 302, 401, 501 Estimation unit 601 Entropy decoding unit 701 Position decoding unit 702 Identification unit 703 First flag decoding unit 704 Second flag decoding unit 705 Coefficient value decoding unit

Claims (9)

An image coding apparatus that performs context adaptive binary arithmetic coding (CABAC),
A specifying unit for specifying a region having the last non-zero coefficient value in a predetermined scanning order for a plurality of regions obtained by dividing the target block of the orthogonal transform;
For the group flag indicating whether or not the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all the areas, the position of the area specified by the specifying unit is set. An estimation unit for estimating a first region group having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
It includes at least one position of the last non-zero coefficient value, a group flag of an area other than the first area group, and a significant coefficient flag indicating a non-zero coefficient value other than the first area group. An image encoding device comprising: an arithmetic encoding unit that arithmetically encodes a signifying region and a significant coefficient flag of the region of the first region group. The specific part is:
Locating the last non-zero coefficient value in the identified region;
The estimation unit includes
The image encoding device according to claim 1, wherein the first region group is expanded using the position of the coefficient value specified by the specifying unit. The estimation unit includes
Among the plurality of regions, using the position of the region specified by the specifying unit, the first region group and a second region group having a group flag in which all significant coefficient flags indicate coefficient values of 0 Estimate
The arithmetic encoding unit is
The position of the last non-zero coefficient value and the significant coefficient flag of the region of the first region group are arithmetically encoded, and the group flag of the first region group and the second region group is not arithmetically encoded. 3. The image encoding device according to 1 or 2. A determination unit that determines whether to estimate the second region group based on a value of a group flag of a region other than the first region group;
The arithmetic encoding unit is
A determination is made as to whether or not the group flag of the second region group is arithmetically encoded based on a usage flag indicating the determination content of the determination unit, and the arithmetic flag is included in the encoding target to perform arithmetic encoding. Item 4. The image encoding device according to Item 3. An image coding method in an image coding apparatus that performs context adaptive binary arithmetic coding (CABAC),
A specifying step for specifying a region having the last non-zero coefficient value in a predetermined scanning order with respect to the plurality of regions obtained by dividing the target block for orthogonal transformation;
With respect to the group flag indicating whether or not the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all the areas, the position of the area specified by the specifying step is set. Using the estimation step of estimating a first region group having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
It includes at least one position of the last non-zero coefficient value, a group flag of an area other than the first area group, and a significant coefficient flag indicating a non-zero coefficient value other than the first area group. An arithmetic encoding step of arithmetically encoding a significant coefficient flag between the region indicating the above and the region of the first region group. A computer for performing context adaptive binary arithmetic coding (CABAC);
A specifying step for specifying a region having the last non-zero coefficient value in a predetermined scanning order with respect to the plurality of regions obtained by dividing the target block for orthogonal transformation;
With respect to the group flag indicating whether or not the significant coefficient flag included in the CABAC syntax element is a value indicating a coefficient value of 0 in all the areas, the position of the area specified by the specifying step is set. Using the estimation step of estimating a first region group having a group flag indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
It includes at least one position of the last non-zero coefficient value, a group flag of an area other than the first area group, and a significant coefficient flag indicating a non-zero coefficient value other than the first area group. An image encoding program for executing an arithmetic encoding step for arithmetically encoding a significant coefficient flag between the area indicating the above and the area of the first area group. An image decoding apparatus for decoding a stream subjected to context adaptive binary arithmetic coding (CABAC),
A position decoding unit that decodes the position of the last non-zero coefficient value in a predetermined scanning order with respect to the orthogonal transformation target block in the stream;
Based on the position of the decoded coefficient value, for a plurality of areas into which the target block is divided, a specifying unit that specifies an area having the last non-zero coefficient value;
A first flag for decoding a group flag indicating whether or not the significant coefficient flag included in the syntax element of the CABAC is a value indicating a coefficient value of 0 in all the areas based on the specified area. A decryption unit;
A second flag decoding unit that decodes a significant coefficient flag in a region in which the decoded group flag value is a value indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
An image decoding apparatus comprising: An image decoding method in an image decoding apparatus for decoding a stream subjected to context adaptive binary arithmetic coding (CABAC),
A position decoding step for decoding the position of the last non-zero coefficient value in a predetermined scanning order with respect to a target block for orthogonal transformation in the stream;
A specifying step of specifying a region having the last non-zero coefficient value for a plurality of regions into which the target block is divided based on the position of the decoded coefficient value;
A first flag for decoding a group flag indicating whether or not the significant coefficient flag included in the syntax element of the CABAC is a value indicating a coefficient value of 0 in all the areas based on the specified area. A decryption step;
A second flag decoding step of decoding a significant coefficient flag in a region where the value of the decoded group flag is a value indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
An image decoding method comprising: A computer for decoding a stream subjected to context adaptive binary arithmetic coding (CABAC);
A position decoding step for decoding the position of the last non-zero coefficient value in a predetermined scanning order with respect to a target block for orthogonal transformation in the stream;
A specifying step of specifying a region having the last non-zero coefficient value for a plurality of regions into which the target block is divided based on the position of the decoded coefficient value;
A first flag for decoding a group flag indicating whether or not the significant coefficient flag included in the syntax element of the CABAC is a value indicating a coefficient value of 0 in all the areas based on the specified area. A decryption step;
A second flag decoding step of decoding a significant coefficient flag in a region where the value of the decoded group flag is a value indicating that at least one significant coefficient flag indicating a non-zero coefficient value is included;
An image decoding program for executing

Images