JP6154588B2 - Image encoding apparatus, image decoding apparatus, and program - Google Patents

Description

  The present invention relates to an image encoding device, an image decoding device, and a program that perform quantization control.

  MPEG (Moving Picture Experts Group) -2, H.M. In a compression encoding method such as H.264 / AVC (Advanced Video Coding) or HEVC (High Efficiency Video Coding) under standardization, each frame of a video signal is divided into rectangular areas called blocks.

  In these compression coding systems, transform coding is used in which an image signal is converted into a frequency domain signal in units of blocks. The converted signal in the frequency domain is replaced with a representative value by quantization, and the degree of compression of video information is controlled by the degree of replacement of the representative value.

  Quantization is realized by dividing the input signal by a certain numerical value. The numerical value to be divided is controlled by the quantization parameter. The quantization parameter is changed and controlled in units of blocks, thereby determining the overall compression rate and image quality.

  MPEG-2 and H.264 In the H.264 / AVC standard, processing is performed in units of 16 × 16 pixel size blocks called macroblocks, and the quantization parameter can be converted for each macroblock.

  On the other hand, in the HEVC standard, a variable size block called a CU (Coding Unit) is introduced, and frequency conversion and quantization are performed in units of small TUs (Transformation Units) obtained by hierarchically dividing the CU. A mechanism for controlling the quantization parameter in units of CU is currently under study (Non-patent Document 1).

K.Sato, M.Budagavi, M.Coban, H.Aoki, X.li, "Description of Core Experiment 4: Quantization", Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11 5th Meeting: Geneva, CH, 16-23 March, 2011

  Here, in the HEVC that is currently being standardized, as described above, frequency conversion and quantization are performed using a TU that is a unit of conversion smaller than a CU that is a unit of coding. However, since the quantization parameter is set in units of CU, the compression rate and the image quality cannot be controlled in units smaller than the encoding unit.

  Accordingly, the present invention has been made in view of the above problems, and provides an image encoding device, an image decoding device, and a program capable of controlling the compression rate and the image quality in units smaller than the encoding unit. Objective.

An image encoding apparatus according to an aspect of the present invention is an image encoding apparatus that divides an image into encoding units, generates a coefficient signal by performing frequency conversion on the encoding unit using a plurality of conversion units, and performs encoding. A quantization control unit that sets, for each transform unit, quantization control information that is logarithmically proportional to the quantization parameter based on the coefficient signal of the transform unit, and all of the coding units include The approximation unit that approximates the quantization control information of the transform unit with an approximation function that uses the position information of the transform unit in the coding unit as a variable, and the quantization control information approximated by the approximation unit And a quantization processing unit that quantizes the coefficient signal, and a parameter encoding unit that encodes the parameter of the approximation function generated by the approximation unit and includes the parameter in the stream .

Further, the approximation unit obtains the quantization control information of all the transform units included in the coding unit from three coefficients using the two-dimensional position information of the transform unit in the coding unit as a variable. Planar approximation may be performed using a linear function .

Further, the approximating unit obtains the quantization control information of all the transform units included in the coding unit from five coefficients using the two-dimensional position information of the transform unit in the coding unit as a variable. The curved surface may be approximated by a quadratic function .

Further, the approximating unit converts the quantization control information of all the transform units included in the coding unit based on the size of the transform unit into the two-dimensional position information of the transform unit in the coding unit. Is approximated by a plane using a linear function consisting of three coefficients with a variable, or a curved surface is approximated using a quadratic function consisting of five coefficients using the two-dimensional position information of the transform unit in the coding unit as a variable. You may decide.

An image decoding apparatus that decodes a stream encoded by the image encoding apparatus, wherein the decoding unit that decodes the stream, and quantization control information that approximates the transform unit is decoded by the decoding unit. And an inverse quantization unit that obtains the parameter using the approximate function and performs inverse quantization on the data decoded by the decoding unit using the quantization control information.

  According to the present invention, the compression rate and image quality can be controlled in units smaller than the encoding unit.

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 a quantization unit according to the first embodiment. The figure which shows the example of a setting of a quantization parameter. 3 is a flowchart illustrating an example of a quantization control process according to the first embodiment. FIG. 3 is a block diagram illustrating an example of a configuration related to a quantization process in the first embodiment. The figure which shows an example of LUT. 9 is a flowchart illustrating an example of a quantization control process and an encoding process in the second embodiment. FIG. 10 is a block diagram illustrating an example of a configuration related to a quantization process in the third embodiment. 10 is a flowchart illustrating an example of a quantization control process and an encoding process according to the third embodiment. The flowchart which shows an example of the quantization control process in a modification, and an encoding process. 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 schematic configuration of an image processing apparatus according to a fifth embodiment.

  First, an encoding unit, a prediction unit, and a conversion unit in HEVC will be described. HEVC does not simply divide the screen into blocks that are encoding units from the upper left as in the conventional encoding technique, but newly adopts hierarchical division to enable block division of a plurality of hierarchies. A coding unit divided into a plurality of blocks is also called a CU (Coding Unit). In HEVC, an image can be divided into 8 × 8, 16 × 16, 32 × 32, etc. as a CU and encoded. The quantization parameter is set in units of CU.

  In HEVC, in order to efficiently express the prediction error signal, the CU can be divided into layers and divided into conversion units. The conversion unit is also called TU. For example, for a 32 × 32 CU, a TU with zero layer division is the same block as a CU of 32 × 32, and a TU with one layer division is a block divided into 16 × 16. In addition, a TU with two hierarchical divisions is a block divided into 8 × 8.

  In HEVC, a CU is divided into prediction units that are a plurality of types of rectangular areas, and prediction processing is performed in each prediction unit. This prediction unit is also called PU (Prediction Unit).

  Hereinafter, each example will be described in detail with reference to the accompanying drawings. Each example is an improvement of the function of the quantization unit in the HEVC configuration.

[Example 1]
<Configuration>
FIG. 1 is a block diagram illustrating an example of a schematic configuration of an image encoding device 10 according to the first embodiment. In the example illustrated in FIG. 1, the image encoding device 10 includes a preprocessing unit 100, a prediction error signal generation unit 101, an orthogonal transform unit 102, a quantization unit 103a, 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 deblocking filter unit 108, 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 prediction image selection unit 115 Have. 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 for encoding 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 for each TU. The orthogonal transform unit 102 outputs the coefficient signal separated into horizontal and vertical frequency components by the orthogonal transform process to the quantization unit 103a.

  The quantization unit 103a quantizes the coefficient signal output from the orthogonal transform unit 102. The quantization unit 103 a reduces the code amount of the coefficient signal by performing quantization, and outputs the coefficient signal to the entropy encoding unit 104 and the inverse quantization unit 105. The quantization unit 103a sets the quantization parameter for each TU, not the CU, and performs quantization. This quantization control process will be described later.

  The entropy encoding unit 104 entropy-encodes and outputs the quantized coefficient signal output from the quantization unit 103a, the motion vector information output from the motion vector calculation unit 113, the filter coefficient from the loop filter unit 109, and the like. To do. Entropy coding is a method of assigning variable-length codes according to the appearance frequency of symbols.

  The inverse quantization unit 105 performs inverse quantization on the output signal from the quantization unit 103 a and 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 the addition to the deblocking filter unit 108.

  The deblocking filter unit 108 applies a filter for reducing block distortion to the decoded image output from the decoded image generation unit 107 and outputs the filtered image to the loop filter unit 109.

  The loop filter unit 109 is, for example, an ALF (Adaptive Loop Filter), and performs a filtering process using a decoded image subjected to the deblocking filtering process and an input image. For example, a Wiener filter is used for the filter processing, but other filters may be used.

  In addition, 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 decoded image subjected to the deblocking filter processing 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 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 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 for searching 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 above-described configuration of the image encoding device 10 is merely an example, and the configuration may be changed depending on the mounting method. For example, a plurality of units may be configured together.

<Quantization>
Next, the quantization process in Embodiment 1 will be described. In the first embodiment, the compression rate and image quality can be controlled for each TU by controlling the quantization parameter (Qp) for each TU instead of the CU.

  FIG. 2 is a block diagram illustrating an example of the configuration of the quantization unit 103a according to the first embodiment. The quantization unit 103a illustrated in FIG. 2 includes a quantization control unit 201 and a quantization processing unit 203.

  The quantization control unit 201 sets quantization control information for each transform unit based on the coefficient signal of the transform unit (TU) acquired from the orthogonal transform unit 102. The quantization control information is also called a quantization step. The quantization control unit 201 sets quantization control information for each transform unit according to the bit rate and desired image quality based on the transform unit coefficient signal.

  The quantization control unit 201 sets, for example, quantization control information according to the characteristics of the coefficient signal and the like after converting a preset information amount into an allocation amount to one TU. The setting of the quantization control information is not limited to this method.

  The quantization control unit 201 obtains a quantization parameter (Qp) from the set quantization control information (quantization step). For example, the quantization parameter and the logarithm of the quantization step are in a proportional relationship. The quantization control unit 201 outputs quantization control information for the set transform unit to the quantization processing unit 203.

  FIG. 3 is a diagram illustrating a setting example of the quantization parameter. In the example shown in FIG. 3, the CU is 16 × 16 and the TU is 4 × 4. As shown in FIG. 3, the set quantization parameter is expressed as Qp (i, j) (0 ≦ i ≦ 3, 0 ≦ j ≦ 3).

  The quantization processing unit 203 quantizes the coefficient signal for each transform unit using the transform control information of the transform unit acquired from the quantization control unit 201. For example, quantization is described in H.264. A known technique such as H.264 or HEVC may be used. The quantization processing unit 203 outputs the quantized coefficient signal to the entropy encoding unit 104 and the inverse quantization unit 105.

  Note that the quantization parameter for each transform unit may be encoded by the entropy encoding unit 104 to reduce the amount of information.

<Operation>
Next, the operation of the image encoding device 10 in the first embodiment will be described. FIG. 4 is a flowchart illustrating an example of the quantization control process according to the first embodiment. In step S101 illustrated in FIG. 4, the quantization control unit 201 sets a quantization parameter for the TU.

  In step S102, the quantization control unit 201 converts the set quantization parameter into quantization control information.

  In step S103a, the quantization control unit 201 determines whether or not the processed TU is the last unit (TU) of the macroblock (or CU). If the TU is the last unit (step S103-YES), the process proceeds to step S104. If the TU is not the last unit (step S103-NO), the process returns to step S101, and quantization parameters of other TUs are set.

  In step S104, the quantization processing unit 203 quantizes the coefficient signal using the quantization control information based on the quantization parameter.

  As described above, according to the first embodiment, since the quantization parameter can be set for each TU of the conversion unit, the compression rate and the image quality can be accurately controlled for each TU.

[Example 2]
Next, an image coding apparatus according to the second embodiment will be described. In the second embodiment, the amount of information is reduced by using the approximation of the quantization parameter information increased by setting the quantization parameter for each TU.

<Configuration>
The configuration of the image encoding device in the second embodiment is basically the same as the schematic configuration shown in FIG. Hereinafter, the quantization unit different from that in the first embodiment will be mainly described.

<Quantization>
Next, the quantization process in Example 2 will be described. In the second embodiment, the quantization parameter (Qp) is controlled for each TU, not the CU, so that the compression rate and the image quality are controlled for each TU, and the quantization control information is approximated. Reduce the amount of control information.

  FIG. 5 is a block diagram illustrating an example of a configuration related to the quantization process according to the second embodiment. In the example illustrated in FIG. 5, the quantization unit 103 b includes a quantization control unit 301, an approximation unit 303, and a quantization processing unit 305, and the entropy encoding unit 104 includes a parameter encoding unit 307.

  The quantization control unit 301 is the same as the quantization control unit 201 of the first embodiment in basic processing. In addition, the quantization control unit 301 acquires approximate quantization control information described later from the approximation unit 303. The quantization control unit 301 recalculates the encoded information amount of the CU generated by the approximation of the quantization control information, and reflects it in the quantization control of the processing block of the next encoding unit (CU). Good.

  The approximation unit 303 approximates the quantization control information of the transform unit (TU) included in the coding unit (CU) acquired from the quantization control unit 301. Further, the approximation unit 303 may approximate the quantization parameter. In the example shown below, a case where quantization control information is approximated will be described. As an approximation method, two examples are given: (1) using an approximation function and (2) using a lookup table (LUT).

(1) Using approximate function The approximating unit 303 approximates the quantization control information using an approximate function of the position of the transform unit, for example. The approximating unit 303 expresses the quantization control information based on the quantization parameter set for each TU as the following function.
Qs (i, j) = f (i, j) Expression (1)
Qs (i, j): TU quantization control information at position (i, j) The approximation unit 303 approximates the function f (i, j) as a formula (2) and approximates a quadratic surface as a plane approximation. Then, it is set as Formula (3).
f (i, j) = a × i + b × j + c (2)
f (i, j) = a × i ² + b × j ² + c × i + d × j + e (3)
As a result, three parameters (a, b, c) are used for plane approximation using equation (2), and five parameters (a, b, c) are used for quadratic surface approximation using equation (3). b, c, d, e), and the number of parameters is smaller than 16 as shown in FIG. This parameter is a parameter for representing the approximated quantization control information.

  As the approximation method, for example, a numerical calculation method such as a least square method can be used. Further, as an approximate function, a trigonometric function such as a sin function or a cos function, a log function, or the like may be used.

  The approximation unit 303 uses a linear function (planar approximation) as an approximation function or a quadratic function (quadratic surface), for example, based on the size of the conversion unit, since the approximation becomes more complex as the number of parameters increases. It may be determined whether to use approximation.

  For example, the approximating unit 303 may determine that a linear function is used if the hierarchical division from the CU is once, and a quadratic function is used if the hierarchical division is twice or more. In addition, the approximating unit 303 may determine that a linear function is used if the size of the TU is divided into four from the CU, and a quadratic function is used if the size is divided into 16 or more from the CU. .

  The approximation unit 303 outputs the approximated quantization control information (also referred to as approximate quantization control information) to the quantization processing unit 305 for each TU. Further, the approximating unit 303 outputs the parameter of the approximating function (also referred to as an approximating parameter) to the parameter encoding unit 307.

(2) When LUT is Used The approximating unit 303 holds an LUT in which a table number (Tb number) is associated with each quantization control information, and each quantization control most similar to each set quantization control information Look for tables with information. The table number is a parameter for representing the approximate quantization control information.

  FIG. 6 is a diagram illustrating an example of the LUT. The example shown in FIG. 6 is an example when there are 16 TUs. Typical quantization control information is set in Qs101 to Qsn16 shown in FIG.

  The approximating unit 303 selects the table number having the smallest sum of absolute difference and least square error between each quantization control information and each Qsi01 to Qsi16 of the LUT.

  The approximating unit 303 outputs the table number having the most similar quantization control information to the parameter encoding unit 307 as an approximate parameter. The approximating unit 303 also outputs the most similar quantization control information to the quantization processing unit 305.

  Returning to FIG. 5, the quantization processing unit 305 quantizes the coefficient signal using the approximate quantization control information acquired from the approximation unit 303. The quantization processing unit 305 outputs the quantized coefficient signal to the entropy encoding unit 104 and the inverse quantization unit 105.

  The parameter encoding unit 307 encodes approximation parameters for representing the quantization control information approximated by the approximation unit 303. The parameter encoding unit 307 is, for example, MPEG-2 or H.264. VLC (Variable Length Coding) used in H.264, H.264, etc. The encoding may be performed by CABAC (Context-based Adaptive Binary Arithmetic Coding) used in H.264 or HEVC. The encoded approximate parameter is included in the stream.

<Operation>
Next, the operation of the image encoding device 10 according to the second embodiment will be described. FIG. 7 is a flowchart illustrating an example of the quantization control process and the encoding process according to the second embodiment. The process shown in FIG. 7 shows the quantization control process and encoding process in one CU.

  In step S201 illustrated in FIG. 7, the quantization control unit 301 sets a quantization parameter for the TU.

  In step S202, the quantization control unit 301 converts the set quantization parameter into quantization control information.

  In step S203, the quantization control unit 301 determines whether the processed TU is the last unit (TU) of the macroblock (or CU). If the TU is the last unit (step S203—YES), the process proceeds to step S204. If the TU is not the last unit (step S203—NO), the process returns to step S201, and the quantization parameters of other TUs are set.

  In step S204, the approximation unit 303 approximates the quantization parameter (or quantization control information). As an approximation method, an approximation function or an LUT may be used.

  In step S205, the quantization processing unit 305 quantizes the coefficient signal of the transform unit using the quantization control information approximated for each transform unit.

  In step S206, the entropy encoding unit 104 performs entropy encoding on the approximated quantization parameter and the quantized transform coefficient.

  In step S207, the quantization control unit 301 reflects the approximated quantization parameter (or approximate quantization control information) acquired from the approximation unit 303 to the quantization control of the TU in the next CU.

  As described above, according to the second embodiment, since the quantization parameter can be set for each TU of the conversion unit, it is possible to accurately control the compression rate and the image quality for each TU. Further, according to the second embodiment, the number of parameters related to the quantization parameter can be reduced by approximating the quantization parameter, and the encoding efficiency can be improved.

[Example 3]
Next, an image coding apparatus according to the third embodiment will be described. In the third embodiment, the amount of information is reduced by using the mode value of the quantization parameter information increased by setting the quantization parameter for each TU.

<Configuration>
The configuration of the image coding apparatus according to the third embodiment is basically the same as the schematic configuration illustrated in FIG. Hereinafter, the quantization unit different from the first and second embodiments will be mainly described.

<Quantization>
Next, the quantization process in Example 3 will be described. In the third embodiment, the quantization parameter (Qp) is controlled for each TU, not the CU, so that the compression rate and the image quality are controlled for each TU, and the mode value is used to control the quantization control information. Reduce the amount of information.

  FIG. 8 is a block diagram illustrating an example of a configuration related to a quantization process according to the third embodiment. In the example illustrated in FIG. 8, the quantization unit 103 c includes a quantization control unit 401, a parameter setting unit 403, and a quantization processing unit 405, and the entropy encoding unit 104 includes a parameter encoding unit 407.

  The quantization control unit 401 is the same as the quantization control unit 201 of the first embodiment in basic processing. The quantization control unit 401 outputs the set quantization parameter (or quantization control information) to the parameter setting unit 403 and the quantization processing unit 405.

  The parameter setting unit 403 represents the quantization control information of the transform unit included in the coding unit as a mode value of the quantization control information and a parameter indicating a difference between the mode values. The parameter setting unit 403 outputs the obtained mode value and the difference value in a predetermined scanning order to the parameter encoding unit 407.

  The quantization processing unit 405 quantizes the coefficient signal for each transform unit using the quantization control information acquired from the quantization control unit 401. The quantization processing unit 405 outputs the quantized coefficient signal to the entropy coding unit 104 and the inverse quantization unit 105.

  The parameter encoding unit 407 encodes the mode value of the quantization parameter and the difference value from the mode value of each quantization parameter as a parameter relating to the quantization parameter, and includes it in the stream.

<Operation>
Next, the operation of the image encoding device 10 according to the third embodiment will be described. FIG. 9 is a flowchart illustrating an example of the quantization control process and the encoding process according to the third embodiment. The process shown in FIG. 9 shows a quantization control process and an encoding process in one CU.

  In step S301 illustrated in FIG. 9, the quantization control unit 401 sets a quantization parameter in the TU.

  In step S302, the quantization control unit 401 converts the set quantization parameter into quantization control information.

  In step S303, the quantization control unit 401 determines whether the processed TU is the last unit (TU) of the macroblock (or CU). If the TU is the last unit (step S303—YES), the process proceeds to step S304. If the TU is not the last unit (step S303—NO), the process returns to step S301, and the quantization parameters of other TUs are set.

  In step S304, the parameter setting unit 404 obtains the mode value of the quantization parameter (or quantization control information) and the difference value between the mode value and each quantization parameter.

  In step S305, the parameter encoding unit 407 encodes a parameter including the mode value and the difference value.

  In step S306, the quantization processing unit 405 quantizes the coefficient signal of the transform unit using the quantization control information for each transform unit.

  In step S307, the entropy encoding unit 104 entropy encodes the quantized transform coefficient.

  As described above, according to the third embodiment, since the quantization parameter can be set for each TU of the conversion unit, the compression rate and the image quality can be accurately controlled for each TU. Further, according to the third embodiment, it is possible to reduce the amount of information using the mode value with respect to the quantization parameter, and it is possible to improve the encoding efficiency.

<Modification>
As a modification of each of the above embodiments, the quantization unit 103 can execute the quantization control process according to the first to third embodiments, and can set which quantization control process is performed. The quantization unit 103 has a configuration in which the quantization units 103a to 103c of the embodiments are combined. The quantization unit 103 executes the set quantization control process. This process will be described with reference to FIG.

  FIG. 10 is a flowchart illustrating an example of the quantization control process and the encoding process in the modification. The process shown in FIG. 10 shows a quantization control process and an encoding process in one CU.

  The processes in steps S401 to S403 shown in FIG. 10 are the same as the processes in steps S101 to S103 shown in FIG.

  In step S404, the quantization unit 103 determines whether approximation of the quantization parameter is set. If approximation is set (step S404—YES), the process proceeds to step S405, and if approximation is not set (step S404—NO), the process proceeds to step S409.

  The processing in steps S405 to S408 is the same as the processing in steps S204 to S207 shown in FIG. 7 described in the second embodiment.

  In step S409, the quantization unit 103 determines whether the mode value and difference value representation of the quantization parameter are set. If the mode value and difference value expression are set (step S409-YES), the process proceeds to step S410, and if the mode value and difference value expression is not set (step S409-NO), the process proceeds to step S414.

  The processing of steps S410 to S413 is the same as the processing of S304 to S307 shown in FIG. 9 described in the third embodiment.

  In step S414, the entropy encoding unit 104 encodes the quantization parameter using a known technique.

  As described above, according to the modification, the quantization control process in the first to third embodiments is included, and which process is performed can be changed according to the image. Which quantization control process is to be performed may be set in the quantization unit 103 in advance.

[Example 4]
Next, an image decoding apparatus according to the fourth embodiment will be described. In the fourth embodiment, the stream encoded in the first to third embodiments is decoded. In the fourth embodiment, the same quantization control processing as in the first to third embodiments is performed, and inverse quantization is performed using the same quantization control information as that of the encoding device.

<Configuration>
FIG. 11 is a block diagram illustrating an example of a schematic configuration of the image decoding device 50 according to the fourth embodiment. As illustrated in FIG. 11, the image decoding device 50 includes an entropy decoding unit 501, an inverse quantization unit 502, an inverse orthogonal transform unit 503, an intra prediction unit 504, a decoded information storage unit 505, an inter prediction unit 506, and a predicted image selection unit. 507, a decoded image generation unit 508, a deblocking filter unit 509, a loop filter unit 510, and a frame memory 511. An outline of each part will be described below.

  When the bit stream is input, the entropy decoding unit 501 performs entropy decoding corresponding to the entropy encoding of the image encoding device 10. The prediction error signal decoded by the entropy decoding unit 501, parameters related to quantization, and the like are output to the inverse quantization unit 502. In addition, a decoded motion vector or the like when inter prediction is performed is output to the decoded information storage unit 505.

  In the case of intra prediction, the entropy decoding unit 501 notifies the intra prediction unit 504 to that effect. In addition, the entropy decoding unit 501 notifies the prediction image selection unit 507 whether the decoding target image is inter predicted or intra predicted.

  The inverse quantization unit 502 performs inverse quantization processing on the output signal from the entropy decoding unit 501. At this time, the inverse quantization unit 502 performs processing reverse to the processing described in the first to third embodiments. For example, when the inverse quantization unit 502 holds an approximation function or an LUT, the inverse quantization unit 502 acquires the quantization control information from the approximation parameters, or acquires the quantization control information from the parameters related to the quantization (mode value and difference value). Then, inverse quantization is performed. The inversely quantized output signal is output to the inverse orthogonal transform unit 503.

  The inverse orthogonal transform unit 503 performs an inverse orthogonal transform process on the decoded block of the output signal from the inverse quantization unit 502 to generate a residual signal. The residual signal is output to the decoded image generation unit 508.

  The intra prediction unit 504 generates a prediction image from the already decoded peripheral pixels acquired from the frame memory 511 using a filter notified from the filter control unit 510 described later.

  The decoded information storage unit 505 stores a filter coefficient of a decoded loop filter, a decoded motion vector, and the like.

  The inter prediction unit 506 performs motion compensation on the reference image data acquired from the frame memory 511 using the motion vector acquired from the decoded information storage unit 505. Thereby, block data as a motion-compensated reference image is generated.

  The predicted image selection unit 507 selects either one of the intra predicted image and the inter predicted image. The selected block data is output to the decoded image generation unit 508.

  The decoded image generation unit 508 adds the predicted image output from the predicted image selection unit 507 and the residual signal output from the inverse orthogonal transform unit 503 to generate a decoded image. The generated decoded image is output to the deblocking filter unit 509.

  The deblocking filter unit 509 applies a deblocking filter for reducing block distortion to the decoded image output from the decoded image generation unit 508 and outputs the result to the loop filter unit 510.

  The loop filter unit 510 performs filter processing for each predetermined size of the decoded image using the filter coefficient acquired from the decoded information storage unit 505. The predetermined size is, for example, an inverse orthogonal transform size. The decoded image after the loop filter processing is output to the frame memory 511. Note that the decoded image after the loop filter may be output to a display device or the like.

  The frame memory 511 stores a decoded image that serves as a reference image. The decoded information storage unit 505 and the frame memory 511 are configured separately, but may be the same storage unit. Note that the configuration of the image decoding device 50 illustrated in FIG. 11 is merely an example, and the configuration may be changed depending on the implementation.

  As described above, according to the fourth embodiment, it is possible to appropriately decode the streams encoded in the first to third embodiments.

[Example 5]
Next, an image processing apparatus in Embodiment 5 will be described. In the image processing apparatus of the above embodiment, the image encoding apparatus and the image decoding apparatus are collectively referred to as an image processing apparatus. In the fifth embodiment, a case where each process of the above-described embodiment is implemented by software will be described.

<Configuration>
FIG. 12 is a block diagram illustrating an example of a schematic configuration of the image processing device 60 according to the fifth embodiment. An image processing device 60 illustrated in FIG. 12 includes at least a control unit 601, a main storage unit 602, an auxiliary storage unit 603, a communication unit 604, and a recording medium I / F unit 605. Each unit is connected via a bus so that data can be transmitted / received to / from each other.

  The control unit 601 is a CPU (Central Processing Unit) that controls each device, calculates data, and processes in a computer. The control unit 601 is an arithmetic device that executes programs stored in the main storage unit 602 and the auxiliary storage unit 603. The control unit 601 receives data from the communication unit 604 and each storage unit, calculates, processes, and outputs the data. And output to each storage unit.

  In addition, the control unit 601 can execute the above-described processing by executing a program for performing any of the processing of the above-described embodiment stored in the auxiliary storage unit 603, for example.

  The main storage unit 602 is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like, and a storage device that stores or temporarily stores programs and data such as an OS and application software that are basic software executed by the control unit 601. It is.

  The auxiliary storage unit 603 is a hard disk drive (HDD) or the like, and is a storage device that stores data related to application software and the like. The auxiliary storage unit 603 may store a program acquired from the recording medium 606 or the like.

  The communication unit 604 performs wired or wireless communication. For example, the communication unit 604 may store a program transmitted from a server or the like in the auxiliary storage unit 603.

  A recording medium I / F (interface) unit 605 is an interface between the image processing apparatus 60 and a recording medium 606 (for example, a flash memory) connected via a data transmission path such as a USB (Universal Serial Bus).

  A predetermined program is stored in the recording medium 606, and the program stored in the recording medium 606 is installed in the image processing apparatus 60 via the recording medium I / F unit 605. The installed predetermined program can be executed by the image processing apparatus 60.

  For example, the decoded image storage unit 110 illustrated in FIG. 1, the decoded information storage unit 505, and the frame memory 511 illustrated in FIG. 11 can be realized by the main storage unit 602 or the auxiliary storage unit 603, for example. Each unit other than each storage unit illustrated in FIGS. 1 and 11 can be realized by, for example, the control unit 601 and the main storage unit 602 as a working memory.

  It is also possible to record the program on the recording medium 606 and cause the computer or portable terminal to read the recording medium 606 on which the program is recorded to realize the above-described processing.

  The recording medium 606 is a recording medium that records information optically, electrically, or magnetically, such as a CD-ROM, flexible disk, magneto-optical disk, etc., 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.

  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 50 Image decoding apparatus 60 Image processing apparatus 103 Quantization part 104 Entropy encoding part 201,301,401 Quantization control part 203,305,405 Quantization processing part 303 Approximation part 307,407 Parameter encoding part 403 Parameter setting unit 502 Inverse quantization unit 601 Control unit 602 Main storage unit

Claims (5)

An image encoding apparatus that divides an image into encoding units, performs frequency conversion on the encoding units by a plurality of conversion units, generates a coefficient signal, and performs encoding.
Based on the coefficient signal of the transform unit, a quantization control unit that sets quantization control information that is logarithmically proportional to the quantization parameter for each transform unit;
An approximation unit for approximating the quantization control information of all the transform units included in the coding unit with an approximation function having the position information of the transform unit in the coding unit as a variable;
A quantization processing unit that quantizes the coefficient signal using the quantization control information approximated by the approximation unit;
A parameter encoding unit that encodes the parameter of the approximation function generated by the approximation unit and includes the parameter in the stream;
An image encoding device comprising: The approximation is
Approximate the quantization control information of all the transform units included in the encoding unit with a linear function composed of three coefficients using the two-dimensional position information of the transform unit in the encoding unit as a variable. The image encoding device according to claim 1. The approximation is
Quantization control information of all the transform units included in the coding unit is approximated by a curved surface with a quadratic function consisting of five coefficients with the two-dimensional position information of the transform unit in the coding unit as a variable. The image encoding apparatus according to claim 1. The approximation is
Based on the size of the transform unit, the quantization control information of all the transform units included in the coding unit, and the three coefficients using the two-dimensional position information of the transform unit in the coding unit as a variable 2. It is determined whether to perform planar approximation with a linear function consisting of or a curved surface approximation with a quadratic function consisting of five coefficients whose variables are two-dimensional position information of the transform unit in the coding unit. 4. The image encoding device according to any one of items 1 to 3. An image decoding device for decoding a stream encoded by the image encoding device according to any one of claims 1 to 4,
A decoding unit for decoding the stream;
Quantization control information approximated by the transform unit is acquired using the parameters of the approximation function decoded by the decoding unit, and the data decoded by the decoding unit using the quantization control information is dequantized. An inverse quantization unit that
An image decoding apparatus comprising:

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