JP6682594B2 - Encoding method and decoding method - Google Patents

Description

  Embodiments of the present invention relate to an encoding method, a decoding method, and encoded data.

  2. Description of the Related Art In recent years, an image coding method that greatly improves coding efficiency has been developed in cooperation with ITU-T (International Telecommunication Union Telecommunication Standardization Sector) and ISO (International Organization for Standardization) / IEC (International Electrotechnical Commission). T REC. H. H.264 and ISO / IEC 14496-10 (hereinafter referred to as “H.264”).

  H. H.264 discloses an inter-prediction coding scheme that eliminates temporal redundancy and realizes high coding efficiency by performing fractional-accuracy motion compensation prediction using a coded picture as a reference picture. ing.

  Also, a scheme has been proposed in which a moving picture including a fade and a dissolve effect is encoded with higher efficiency than the inter prediction encoding scheme in ISO / IEC MPEG (Moving Picture Experts Group) -1, 2, and 4. In this method, as a framework for predicting a change in lightness in the time direction, motion compensation prediction with fractional accuracy is performed on an input moving image having luminance and two color differences. Then, using the reference image, the luminance and the weighting coefficient for each of the two color differences, and the offset for each of the luminance and the two color differences, the predicted image is multiplied by the weighting coefficient, and the offset is added. The weighting factor can express a fractional value with a predetermined precision by a parameter indicating fixed-point precision, and it becomes possible to perform weighted motion compensation prediction with a finer precision on pixel value changes between images. There is.

JP-A-2004-7377

  In the conventional technique as described above, the reference image, the weight coefficient, the offset, and the like are coded as an index, but since the index is defined to be expressed with a predetermined bit precision, the weight coefficient cannot be expressed. There is. The problem to be solved by the present invention is to provide an electronic device, a decoding method, and a program capable of improving a coding efficiency while allowing a weighting coefficient to be expressed with a predetermined bit precision.

  The encoding method of the embodiment uses the same value as the step of encoding the first fixed-point precision of the luminance weighting factor, and the difference between the first fixed-point precision and the second fixed-point precision of the color difference weighting factor. A step of encoding a first difference value, a first reference value which is the same value as the value obtained by left-shifting "1" by the number of bits determined by the first fixed point precision, and the luminance Encoding a second difference value of the luminance weighting coefficient, which has the same value as the difference between

FIG. 1 is a block diagram illustrating an example of an encoding device according to a first embodiment. FIG. 3 is an explanatory diagram showing an example of a predictive coding order of pixel blocks according to the first embodiment. FIG. 6 is an explanatory diagram showing another example of the predictive coding order of the pixel block according to the first embodiment. FIG. 3 is a diagram illustrating an example of a block size of a coding tree block according to the first embodiment. FIG. 3 is a diagram illustrating a specific example of a coding tree block according to the first embodiment. FIG. 3 is a diagram illustrating a specific example of a coding tree block according to the first embodiment. FIG. 3 is a diagram illustrating a specific example of a coding tree block according to the first embodiment. FIG. 2 is a block diagram illustrating an example of a predicted image generation unit according to the first embodiment. The figure which shows the example of the relationship of the motion vector of the motion compensation prediction in the bidirectional prediction of 1st Embodiment. FIG. 3 is a block diagram illustrating an example of a multi-frame motion compensation unit according to the first embodiment. A reference diagram for explaining a weighting factor. H. FIG. 12 is a reference diagram showing a selection range of H.264 weighting coefficients. Explanatory drawing which shows the example of the selection range of the weighting coefficient of 1st Embodiment. Explanatory drawing which shows the specific example of the selection range of the weighting coefficient of 1st Embodiment. Explanatory drawing which shows the specific example of the selection range of the weighting coefficient of 1st Embodiment. H. The reference diagram which shows the minimum value of the weighting coefficient of H.264, and the maximum value. Explanatory drawing which shows the example of the minimum value and maximum value of a weighting coefficient of 1st Embodiment. FIG. 3 is a diagram illustrating an example of WP parameter information according to the first embodiment. FIG. 3 is a diagram illustrating an example of WP parameter information according to the first embodiment. 6 is a flowchart showing an example of a process of deriving a selection range of weighting factors according to the first embodiment. The figure which shows the example of the syntax of 1st Embodiment. FIG. 4 is a diagram illustrating an example of a picture parameter set syntax according to the first embodiment. FIG. 4 is a diagram illustrating an example of slice header syntax according to the first embodiment. FIG. 4 is a diagram illustrating an example of a spread weight table syntax according to the first embodiment. Explanatory drawing which shows the example of the relationship of the value of the syntax element of 1st Embodiment. FIG. 13 is a block diagram illustrating a configuration example of a decoding device according to a second embodiment. Explanatory drawing which shows the example of the selection range of the offset of the modification 1. FIG. 9 is a flowchart illustrating an example of a process of deriving a selection range of offset according to the first modification. Explanatory drawing which shows the example of the selection range of the weighting factor of the modification 2. 9 is a flowchart showing an example of a process of deriving a selection range of weighting factors according to the second modification. FIG. 8 is an explanatory diagram showing an example of a range of difference values of weighting coefficients to be encoded according to the modified example 3. FIG. 10 is an explanatory diagram showing an example of a relationship between values of syntax elements according to Modification 3; Explanatory drawing which shows the example of the range of the difference value of the weighting coefficient of the modification 4. FIG. 11 is an explanatory diagram showing an example of a selection range of weighting coefficients after decoding according to the modified example 4. 9 is a flowchart showing an example of a wrapping process of a difference value of weighting factors according to the modified example 5. 9 is a flowchart showing an example of restoration processing of a difference value of weighting factors according to the fifth modification.

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. The encoding device and the decoding device according to the following embodiments can be realized by hardware such as an LSI (Large-Scale Integration) chip, a DSP (Digital Signal Processor), or an FPGA (Field Programmable Gate Array). In addition, the encoding device and the decoding device according to each of the following embodiments can be realized by causing a computer to execute a program, that is, by software. Note that in the following description, the term "image" can be appropriately replaced with a term such as "video", "pixel", "image signal", "picture", or "image data".

(First embodiment)
In the first embodiment, an encoding device that encodes a moving image will be described.

  FIG. 1 is a block diagram illustrating an example of a configuration of the encoding device 100 according to the first embodiment.

  The encoding device 100 divides each frame or each field constituting the input image into a plurality of pixel blocks, and uses a coding parameter input from the coding control unit 111 to perform prediction coding on the divided pixel blocks. To generate a predicted image. Then, the encoding device 100 subtracts the input image and the predicted image divided into a plurality of pixel blocks to generate a prediction error, orthogonally transforms and quantizes the generated prediction error, and further performs entropy coding to perform coding. Generate and output data.

  The encoding device 100 performs predictive encoding by selectively applying a plurality of prediction modes in which at least one of a block size of a pixel block and a method of generating a predicted image is different. The methods of generating a predicted image are roughly classified into two types: intra prediction for performing prediction in a current frame to be encoded, and inter prediction for performing motion compensation prediction using one or more temporally different reference frames. Intra prediction is also referred to as intra-picture prediction or intra-frame prediction, and inter-prediction is also referred to as inter-picture prediction, inter-frame prediction, motion compensation prediction, or the like.

  FIG. 2A is an explanatory diagram showing an example of a predictive coding order of pixel blocks in the first embodiment. In the example illustrated in FIG. 2A, the encoding device 100 performs predictive encoding from the upper left to the lower right of the pixel block, and in the frame f to be encoded, the left side and the left side of the encoding target pixel block c. The encoded pixel block p is located on the upper side.

  FIG. 2B is an explanatory diagram illustrating another example of the predictive coding order of the pixel block according to the first embodiment. In the example illustrated in FIG. 2B, the encoding device 100 divides the screen into a plurality of tiles or slices in advance, and then performs predictive encoding from the upper left to the lower right of the pixel block in each tile or each slice. The encoded pixel block p is located on the left side and the upper side of the encoding target pixel block c in the encoding target frame f. The tile means an area obtained by cutting out the screen in an arbitrary rectangular area, and the slice means an area cut out in an arbitrary number of large coding tree blocks described later according to the predictive coding order.

  As in the example shown in FIG. 2B, after the screen is divided into a plurality of tiles or a plurality of slices, encoding processing is performed for each tile or each slice, thereby enabling decoding processing for each tile or each slice. Become. Therefore, by performing the decoding processing of the high resolution video in parallel, it is possible to disperse the calculation amount required for the decoding. That is, in the case of the example shown in FIG. 2B, it is possible to speed up the encoding process and the decoding process.

  Hereinafter, for simplification of description, the coding apparatus 100 performs the predictive coding in the order shown in FIG. 2A, but the predictive coding order is not limited to this.

  The pixel block indicates a unit for processing an image, and corresponds to, for example, an M × N size block (M and N are natural numbers), a coding tree block, a macro block, a sub block, or one pixel. In the following description, a pixel block is basically used as a coding tree block, but may be used in other meanings. For example, in the description of the prediction unit, a pixel block is used in the meaning of the pixel block of the prediction unit. A block may be called by a name such as a unit. For example, a coding block is called a coding unit.

  FIG. 3A is a diagram illustrating an example of a block size of a coding tree block according to the first embodiment. The coding tree block is typically a 64 × 64 pixel block as shown in FIG. 3A. However, the present invention is not limited to this, and may be a 32 × 32 pixel block, a 16 × 16 pixel block, an 8 × 8 pixel block, a 4 × 4 pixel block, or the like. Further, the coding tree block may not be a square, and may be, for example, a pixel block of M × N size (M ≠ N).

  3B to 3D are diagrams illustrating specific examples of the coding tree block according to the first embodiment. FIG. 3B shows a coding tree block having a block size of 64 × 64 (N = 32). N represents the size of a coding tree block serving as a reference, and the size when divided is defined as N, and the size when not divided is defined as 2N. FIG. 3C shows a coding tree block obtained by dividing the coding tree block of FIG. 3B into quadtrees. The coding tree block has a quad tree structure as shown in FIG. 3C. When the coding tree block is divided, the four pixel blocks after the division are numbered in the Z-scan order as shown in FIG. 3C.

  Note that the coding tree block can be further divided into quadtrees within one quadtree number. Thus, the coding tree block can be divided hierarchically. In this case, the depth of division is defined by Depth. FIG. 3D shows one of the coding tree blocks obtained by dividing the coding tree block of FIG. 3B into quadtrees, and has a block size of 32 × 32 (N = 16). The depth of the coding tree block shown in FIG. 3B is 0, and the depth of the coding tree block shown in FIG. 3D is 1. Note that the coding tree block having the largest unit is called a large coding tree block, and the input image signal is encoded in raster scan order in this unit.

  In the following description, the encoding target block or the coding tree block of the input image may be referred to as a prediction target block or a prediction pixel block. Note that the coding unit is not limited to a pixel block, and may be at least one of a frame, a field, a slice, a line, and a pixel.

  As shown in FIG. 1, the encoding device 100 includes a subtraction unit 101, an orthogonal transformation unit 102, a quantization unit 103, an inverse quantization unit 104, an inverse orthogonal transformation unit 105, an addition unit 106, and a prediction unit. An image generation unit 107, an index setting unit 108, a motion evaluation unit 109, and an encoding unit 110 are provided. The encoding control unit 111 shown in FIG. 1 controls the encoding device 100, and can be realized by, for example, a CPU (Central Processing Unit).

  The subtraction unit 101 subtracts a corresponding prediction image from an input image divided into pixel blocks to obtain a prediction error. The subtraction unit 101 outputs a prediction error and inputs the prediction error to the orthogonal transformation unit 102.

  The orthogonal transformation unit 102 performs an orthogonal transformation such as a discrete cosine transform (DCT) or a discrete sine transform (DST) on the prediction error input from the subtraction unit 101 to obtain a transform coefficient. The orthogonal transformation unit 102 outputs the transformation coefficient and inputs it to the quantization unit 103.

  The quantization unit 103 performs a quantization process on the transform coefficient input from the orthogonal transform unit 102 to obtain a quantized transform coefficient. Specifically, the quantization unit 103 performs quantization according to quantization information such as a quantization parameter and a quantization matrix specified by the encoding control unit 111. More specifically, the quantization unit 103 divides the transform coefficient by the quantization step size derived from the quantization information to obtain the quantized transform coefficient. The quantization parameter indicates the degree of quantization. The quantization matrix is used to weight the fineness of the quantization for each component of the transform coefficient. The quantization unit 103 outputs the quantized transform coefficient, and inputs it to the inverse quantization unit 104 and the encoding unit 110.

  The inverse quantization unit 104 performs an inverse quantization process on the quantized transform coefficient input from the quantization unit 103 to obtain a restored transform coefficient. Specifically, the inverse quantization unit 104 performs inverse quantization according to the quantization information used in the quantization unit 103. More specifically, the inverse quantization unit 104 multiplies the quantization transform coefficient by the quantization step size derived from the quantization information to obtain a restored transform coefficient. The quantization information used in the quantization unit 103 is loaded from an internal memory (not shown) of the encoding control unit 111 and used. The inverse quantization unit 104 outputs the restored transform coefficient and inputs the same to the inverse orthogonal transform unit 105.

  The inverse orthogonal transform unit 105 performs an inverse orthogonal transform such as an inverse discrete cosine transform (IDCT) or an inverse discrete sine transform (IDST) on the restored transform coefficient input from the inverse quantization unit 104, Obtain the restoration prediction error. Note that the inverse orthogonal transform performed by the inverse orthogonal transform unit 105 corresponds to the orthogonal transform performed by the orthogonal transform unit 102. The inverse orthogonal transform unit 105 outputs the restoration prediction error and inputs the error to the adding unit 106.

  The adding unit 106 adds the restored prediction error input from the inverse orthogonal transform unit 105 and the corresponding predicted image to generate a locally decoded image. The adding unit 106 outputs the locally decoded image and inputs the locally decoded image to the predicted image generating unit 107.

  The predicted image generation unit 107 stores the locally decoded image input from the addition unit 106 as a reference image in a memory (not shown in FIG. 1), outputs the reference image stored in the memory, and inputs the reference image to the motion evaluation unit 109. . The predicted image generation unit 107 also performs weighted motion compensation prediction based on the motion information and the WP parameter information input from the motion evaluation unit 109, and generates a predicted image. The predicted image generation unit 107 outputs a predicted image and inputs the predicted image to the subtraction unit 101 and the addition unit 106.

  FIG. 4 is a block diagram illustrating an example of a configuration of the predicted image generation unit 107 according to the first embodiment. As shown in FIG. 4, the prediction image generation unit 107 includes a multi-frame motion compensation unit 201, a memory 202, a unidirectional motion compensation unit 203, a prediction parameter control unit 204, a reference image selector 205, and a frame memory 206. And a reference image control unit 207.

  The frame memory 206 stores the locally decoded image input from the adding unit 106 as a reference image under the control of the reference image control unit 207. The frame memory 206 has a plurality of memory sets FM1 to FMN (N ≧ 1) for temporarily holding a reference image.

  The prediction parameter control unit 204 prepares a plurality of combinations of reference image numbers and prediction parameters as a table based on the motion information input from the motion evaluation unit 109. Here, the motion information indicates a motion vector indicating a displacement amount of motion used in motion compensation prediction, a reference image number, information on prediction modes such as unidirectional / bidirectional prediction, and the like. The prediction parameter indicates information on a motion vector and a prediction mode. Then, the prediction parameter control unit 204 selects and outputs a combination of the reference image number and the prediction parameter used for generating the prediction image based on the input image, inputs the reference image number to the reference image selector 205, Is input to the unidirectional motion compensation unit 203.

  The reference image selector 205 is a switch for switching which output terminal of the frame memories FM1 to FMN of the frame memory 206 is to be connected in accordance with the reference image number input from the prediction parameter control unit 204. For example, if the reference image number is 0, the reference image selector 205 connects the output terminal of FM1 to the output terminal of the reference image selector 205. If the reference image number is N-1, the reference image selector 205 refers to the output terminal of FMN. It is connected to the output terminal of the image selector 205. The reference image selector 205 outputs a reference image stored in a frame memory to which an output terminal is connected among the frame memories FM1 to FMN included in the frame memory 206, and outputs a unidirectional motion compensation unit 203 and a motion evaluation unit 109. Enter

  The unidirectional motion compensation unit 203 performs motion compensation prediction processing according to the prediction parameter input from the prediction parameter control unit 204 and the reference image input from the reference image selector 205 to generate a unidirectional prediction image.

  FIG. 5 is a diagram illustrating an example of a relationship between motion vectors of motion compensation prediction in bidirectional prediction according to the first embodiment. In motion-compensated prediction, interpolation processing is performed using a reference image, and a unidirectional predicted image is generated based on the amount of motion shift from the pixel block at the coding target position between the created interpolation image and the input image. . Here, the shift amount is a motion vector. As shown in FIG. 5, in a bidirectional prediction slice (B-slice), a predicted image is generated using two types of reference images and a set of motion vectors. As the interpolation processing, interpolation processing with 1/2 pixel precision, interpolation processing with 1/4 pixel precision, or the like is used, and the value of the interpolation image is generated by performing filtering processing on the reference image. For example, H.264 capable of performing interpolation processing up to 1/4 pixel accuracy for a luminance signal. In H.264, the shift amount is represented by four times the integer pixel precision.

  The unidirectional motion compensation unit 203 outputs the unidirectional predicted image and temporarily stores it in the memory 202. Here, when the motion information (prediction parameter) indicates bidirectional prediction, the multi-frame motion compensating unit 201 performs weighted prediction using two types of unidirectionally predicted images, so that the unidirectional motion compensating unit 203 The unidirectional predicted image corresponding to the first one is stored in the memory 202, and the unidirectional predicted image corresponding to the second is directly output to the multi-frame motion compensation unit 201. Here, the first unidirectional predicted image corresponding to the first is a first predicted image, and the second unidirectional predicted image corresponding to the second is a second predicted image.

  Note that two unidirectional motion compensating units 203 may be prepared, and each may generate two unidirectional predicted images. In this case, when the motion information (prediction parameter) indicates unidirectional prediction, the unidirectional motion compensating unit 203 may directly output the first unidirectional predicted image as the first predicted image to the multi-frame motion compensating unit 201. Good.

  The multi-frame motion compensation unit 201 uses the first predicted image input from the memory 202, the second predicted image input from the unidirectional motion compensation unit 203, and the WP parameter information input from the motion evaluation unit 109, Weighted prediction is performed to generate a predicted image. The multi-frame motion compensation unit 201 outputs the predicted image and inputs it to the subtraction unit 101 and the addition unit 106.

  FIG. 6 is a block diagram illustrating an example of a configuration of the multi-frame motion compensation unit 201 according to the first embodiment. As shown in FIG. 6, the multi-frame motion compensation unit 201 includes a default motion compensation unit 301, a weighted motion compensation unit 302, a WP parameter control unit 303, and WP selectors 304 and 305.

  The WP parameter control unit 303 outputs a WP application flag and weight information based on the WP parameter information input from the motion evaluation unit 109, inputs the WP application flag to the WP selectors 304 and 305, and weights the weight information. Input to the motion compensation unit 302. Specifically, when the WP parameter information is input from the motion evaluation unit 109, the WP parameter control unit 303 separates the WP parameter information into a first WP application flag, a second WP application flag, and weight information, and outputs the weight information. Then, the first WP application flag is input to the WP selector 304, the second WP application flag is input to the WP selector 305, and the weight information is input to the weighted motion compensation unit 302.

  Here, the WP parameter information includes a first WP applicable flag (specifically, flag information of the first WP applicable flag), a second WP adaptive flag (specifically, flag information of the second WP applicable flag), and a weight. Contains information of information. The first WP application flag and the second WP application flag are parameters that can be set for each corresponding reference image and signal component, and whether to perform default motion compensation prediction for prediction of the first prediction image and the second prediction image, respectively. It includes information on whether to perform weighted motion compensation prediction. Here, if the first WP application flag and the second WP application flag are both 0, it indicates that the default motion compensation prediction is performed, and if they are 1, it indicates that the weighted motion compensation prediction is performed. .

  The weight information includes a value w0C of the first weight coefficient, a value w1C of the second weight coefficient, a parameter LWD indicating fixed point precision of the first weight coefficient and the second weight coefficient (hereinafter, referred to as “fixed point precision LWD”). Yes), first offset o0C, and second offset o1C. The variable C means a signal component. For example, in the case of a YUV spatial signal, the luminance signal is represented by C = Y, the Cr color difference signal is represented by C = Cr, and the Cb color difference component is represented by C = Cb.

  The first weighting coefficient is a weighting coefficient corresponding to the first predicted image, and is a parameter whose value is determined (changes) by the fixed point precision LWD. The second weighting coefficient is a weighting coefficient corresponding to the second predicted image, and is a parameter whose value is determined (changes) by the fixed point precision LWD. The fixed point precision LWD is a parameter that controls the step size corresponding to the fractional precision of the first weighting coefficient and the second weighting coefficient. The fixed-point precision LWD may use different values for luminance and color difference, but here, for simplification, description will be made without explicitly dividing each color signal. For example, when w0C is expressed by a real number, 1.0 (1 in binary notation), when LWD is 5, the first weighting factor is 32 (100,000 in binary notation), and w1C is expressed by a real number. In this case, 2.0 (10 in binary notation), and when LWD is 5, the second weighting factor is 64 (1000000 in binary notation). The first offset o0C is an offset corresponding to the first predicted image, and the second offset o1C is an offset corresponding to the second predicted image.

  When the WP parameter information is input, the WP parameter control unit 303 checks whether the value of the weight information is within the specified range, and resets the value outside the range to the value within the range, The value of the WP applicable flag is changed. For example, when w0C is represented by a real number, 3.0, and when LWD is 7, the first weighting factor is 384. Here, 384 is outside the range of the first weighting factor and cannot be used, but 96 is within the range of the first weighting factor and can be used. In this case, the WP parameter control unit 303 sets the LWD to 5 and the first weighting factor to 96, so that the first weighting factor is set to 3.0 within the range when w0C is expressed as a real value. You may set it. Further, at this time, the WP parameter control unit 303 may perform a quantization process. For example, when LWD is 7 and the first weighting coefficient is 385, the WP parameter control unit 303 performs quantization processing to set the first weighting coefficient to 384, then sets LWD to 5 and w0C to real values. The first weighting factor may be reset to 96 by setting it to 3.0 when expressed. Further, the WP parameter control unit 303 may change the value of the first WP application flag from 1 to 0 so that the weighted motion compensation prediction is not used. Although not limited to these methods, the WP parameter control unit 303 controls such that the value of the weight information is not used beyond the prescribed range defined by the specifications and the like.

  The WP selectors 304 and 305 switch the connection end of each predicted image based on the WP application flag input from the WP parameter control unit 303. When each WP application flag is 0, the WP selectors 304 and 305 connect each output terminal to the default motion compensation unit 301. Then, the WP selectors 304 and 305 output the first prediction image and the second prediction image, and input them to the default motion compensation unit 301. On the other hand, when each WP application flag is 1, the WP selectors 304 and 305 connect each output end to the weighted motion compensation unit 302. Then, the WP selectors 304 and 305 output the first prediction image and the second prediction image, and input the weighted motion compensation unit 302.

  The default motion compensation unit 301 performs average value processing (default motion compensation prediction) based on the two unidirectional prediction images (first prediction image and second prediction image) input from the WP selectors 304 and 305 to obtain a prediction image. To generate. Specifically, when the first WP application flag and the second WP application flag are 0, the default motion compensation unit 301 performs an average value process based on Expression (1).

  P [x, y] = Clip1 ((PL0 [x, y] + PL1 [x, y] + offset2) >> (shift2)) (1)

  Here, P [x, y] is a predicted image, PL0 [x, y] is a first predicted image, and PL1 [x, y] is a second predicted image. offset2 and shift2 are parameters for rounding processing in the average value processing, and are determined by the internal calculation accuracy of the first predicted image and the second predicted image. Clip1 (X) is a function that clips the variable X within a specific bit precision, and here clips it within the bit precision of the prediction image. For example, when the bit precision of the predicted image is L = 8, a value outside the range of 0 to 255 is clipped to 0 to 255. More specifically, values less than or equal to 0 are set to 0, and values greater than 255 are set to 255.

  Assuming that the bit precision of the predicted image is L and the bit precisions of the first predicted image and the second predicted image are M (L ≦ M), shift2 is formulated by equation (2), and offset2 is formulated by equation (3). Is done.

  shift2 = (M−L + 1) (2)

  offset2 = (1 << (shift2-1) (3)

  For example, when the bit precision of the predicted image is 8, and the bit precisions of the first predicted image and the second predicted image are 14, shift2 = 7 from Expression (2), and offset2 = (1 <<) from Expression (3). 6).

  When the prediction mode indicated by the motion information (prediction parameter) is unidirectional prediction, the default motion compensation unit 301 uses only the first predicted image and calculates the final predicted image based on Expression (4). calculate.

  P [x, y] = Clip1 ((PLX [x, y] + offset1) >> (shift1)) (4)

  Here, PLX [x, y] indicates a unidirectional predicted image (first predicted image), and X is an identifier indicating either 0 or 1 in the reference list. For example, when the reference list is 0, it is PL0 [x, y], and when the reference list is 1, it is PL1 [x, y]. offset1 and shift1 are parameters of the rounding process, and are determined by the internal calculation accuracy of the first predicted image. If the bit precision of the predicted image is L and the bit precision of the first predicted image is M, shift1 is formulated by Equation (5) and offset1 is formulated by Equation (6).

  shift1 = (ML) (5)

  offset1 = (1 << (shift1-1) (6)

  For example, when the bit precision of the predicted image is 8 and the bit precision of the first predicted image is 14, shift1 = 6 from Expression (5), and offset1 = (1 << 5) from Expression (6).

  The weighted motion compensation unit 302 is based on the two unidirectional prediction images (first prediction image and second prediction image) input from the WP selectors 304 and 305 and the weight information input from the WP parameter control unit 303. Weighted motion compensation (weighted motion compensation prediction) is performed.

  Here, the weighting factor will be further described. FIG. 7 is a reference diagram for explaining the weighting coefficient, and shows an example of the change in the gradation value of the moving image having the change in the pixel value in the time direction. In the example shown in FIG. 7, the encoding target frame is Frame (t), the temporally preceding frame is Frame (t−1), and the temporally succeeding frame is Frame (t + 1). As shown in FIG. 7, in a fade image that changes from white to black, the brightness (tone value) of the image decreases with time. The value of the weighting factor means the degree of pixel value change as described with reference to FIG. 7, and when there is no pixel value change (when the pixel value change is 0), a value of 1.0 is represented by a real value. I take the.

  Here, the case where the pixel value does not change will be further described. For example, assuming a moving image in which the same still image is temporally continuous, the luminance change between screens is zero. In this case, the weighted motion compensation unit 302 is equivalent to performing the default motion compensation prediction because the pixel value change is 0 even if the weighted motion compensation prediction is performed. In such a case, that is, when there is no pixel value change, the weighted motion compensation unit 302 implements the default motion compensation prediction by the weighted motion compensation prediction by selecting the reference value of the weighting coefficient. Here, the reference value of the weighting factor can be derived in accordance with the fixed point precision and becomes (1 << LWD).

  Further, in general, a pixel value change of a moving image such as a fade effect or a dissolve effect does not change so much for each frame, and therefore the value of the weighting factor is biased to around 1.0 when expressed by a real value. . In the first embodiment, the value of the weighting factor is quantized to the fixed point precision represented by a power of 2, so that even if a slight change in average pixel value occurs between two images, If the change is less than 128 precision, the value of the weighting coefficient is quantized to 1.0 when expressed by a real value. Therefore, in the first embodiment, it can be treated as a case where the pixel value does not substantially change even if the pixel value changes. In the following, in order to simplify the description, the description will be made assuming that there is no pixel value change, that is, the case where the value of the weighting coefficient is 1.0 when expressed by a real value. If there is no change in pixel value, it means that the change in pixel value is equal to or smaller than a predetermined value (a value sufficiently smaller than the accuracy of the weighting coefficient).

  Therefore, when the first WP application flag and the second WP application flag are 1, the weighted motion compensation unit 302 performs the weighting process based on Expression (7).

  P [x, y] = Clip1 (((PL0 [x, y] * w0C + PL1 [x, y] * w1C + ((o0C + o1C + 1) << LWD)) >> (LWD + 1))) ... (7)

  Note that the weighted motion compensation unit 302 implements the rounding process by controlling LWD as in Expression (8) when the calculation accuracy of the first predicted image and the second predicted image is different from that of the predicted image.

  LWD '= LWD + offset1 (8)

  The rounding process can be realized by replacing the LWD in Expression (7) with LWD ′ in Expression (8). For example, when the bit precision of the predicted image is 8 and the bit precision of the first predicted image and the second predicted image is 14, by resetting LWD, it is possible to obtain the same calculation precision as that of shift2 in Expression (1). It is possible to realize a batch rounding process.

  When the prediction mode indicated by the motion information (prediction parameter) is unidirectional prediction, the weighted motion compensator 302 uses only the first predicted image and calculates the final predicted image based on Expression (9). Is calculated.

  P [x, y] = Clip1 ((PLX [x, y] * wXC + (1 << (LWD-1))) >> (LWD) + oXC) (9)

  Here, PLX [x, y] indicates a unidirectional prediction image (first prediction image), wXC indicates a weighting factor corresponding to unidirectional prediction, and X indicates either 0 or 1 in the reference list. OXC indicates an offset corresponding to unidirectional prediction. For example, if the reference list is 0, PL0 [x, y], w0C, o0C, and if the reference list is 1, PL1 [x, y], w1C, o1C.

  Note that the weighted motion compensation unit 302 controls the LWD like Equation (8) as in bidirectional prediction when the first prediction image and the second prediction image have different calculation precisions from the prediction image. Achieve rounding processing.

  The rounding process can be realized by replacing the LWD in Expression (9) with LWD ′ in Expression (8). For example, when the bit precision of the predicted image is 8 and the bit precision of the first predicted image is 14, by resetting LWD, a batch rounding process with the same calculation precision as shift1 in Formula (4) is realized. It becomes possible to do.

  Note that in the case of unidirectional prediction, various parameters (second WP adaptation flag, second weighting coefficient, and second offset information) corresponding to the second predicted image are not used, so set to a predetermined initial value. It may have been done.

  Referring back to FIG. 1, the motion estimator 109 performs motion estimation between a plurality of frames based on the input image and the reference image input from the predicted image generator 107, outputs motion information and WP parameter information, and outputs the motion information. It is input to the predicted image generation unit 107 and the encoding unit 110, and the WP parameter information is input to the predicted image generation unit 107 and the index setting unit 108.

  The motion evaluator 109 calculates an error by calculating a difference value from a plurality of reference images corresponding to the same position as the input image of the pixel block to be predicted as a starting point, for example, and shifts the position with fractional accuracy to minimize the error. Optimum motion information is calculated by a method such as block matching for searching for a block. In the case of bidirectional prediction, the motion evaluator 109 performs block matching including default motion compensation prediction as shown in Expressions (1) and (4) using the motion information derived in unidirectional prediction. Thereby, motion information for bidirectional prediction is calculated.

  At this time, the motion evaluator 109 can calculate WP parameter information by performing block matching including weighted motion compensation prediction as shown in Expressions (7) and (9). Note that the WP parameter information may be calculated by using a method of calculating a weighting coefficient or offset using the pixel gradient of the input image, a method of calculating a weighting coefficient or offset by accumulating prediction errors at the time of encoding, or the like. Good. As the WP parameter information, a fixed value predetermined for each encoding device may be used.

  Here, referring to FIG. 7 again, a method of calculating the weighting coefficient, the fixed point precision of the weighting coefficient, and the offset from the moving image in which the pixel value changes temporally will be described. As described above, in the fade image that changes from white to black as shown in FIG. 7, the pixel value (gradation value) decreases with time. The motion evaluator 109 can calculate the weight coefficient by calculating the inclination.

  Further, the fixed point precision of the weighting factor is information indicating the precision of this inclination, and the motion evaluation unit 109 can calculate an optimum value from the temporal distance of the reference image and the degree of change of the image value. For example, in FIG. 7, when the value of the weighting coefficient between Frame (t−1) and Frame (t + 1) is expressed in real number precision as 0.75, it can be expressed as 3/4 in 1/4 precision. Therefore, the motion evaluation unit 109 sets the fixed-point precision to 2 (1 << 2). Since the value of the fixed-point precision affects the code amount when the weight coefficient is encoded, an optimum value may be selected in consideration of the code amount and the prediction accuracy. Note that the value of the fixed-point precision may be a predetermined fixed value.

  Further, when the inclinations do not match, the motion evaluation unit 109 can calculate the offset value by obtaining the correction value (deviation amount) corresponding to the intercept of the linear function. For example, in FIG. 7, when the value of the weighting coefficient between Frame (t-1) to Frame (t + 1) is expressed in real number precision, it is 0.60, and when the fixed point precision is 1 (1 << 1), It is highly possible that the weighting factor is set to 1 (that is, corresponds to 0.50 when the value of the weighting factor is expressed in real number precision). In this case, the decimal point precision of the weighting coefficient is shifted from the optimal value of 0.60 by 0.10, and therefore, the motion estimating unit 109 calculates the correction value for this value from the maximum value of the pixel, and sets Set. When the maximum value of the pixel is 255, the motion evaluator 109 may set a value such as 25 (255 × 0.1).

  In the first embodiment, the motion estimation unit 109 is exemplified as one function of the encoding device 100. However, the motion estimation unit 109 is not an essential component of the encoding device 100. It may be a device outside the chemical conversion device 100. In this case, the motion information and the WP parameter information calculated by the motion evaluation unit 109 may be loaded into the encoding device 100.

  The index setting unit 108 receives the WP parameter information input from the motion evaluation unit 109, checks the reference list (list number) and the reference image (reference number), outputs index information, and outputs the index information to the encoding unit 110. input. The index setting unit 108 maps the WP parameter information input from the motion evaluation unit 109 to a syntax element described below to generate index information. At this time, the index setting unit 108 derives the selection range of the weighting factor and confirms that the weighting factor is included in the selection range.

  Here, the derivation of the selection range of the weighting factor will be described.

  In the first embodiment, as described above, it is assumed that there is no pixel value change and the value of the weighting coefficient is 1.0 when expressed by a real value. In this case, the weighting coefficient / reference value of the weighting coefficient is assumed. = 1 is established. Since the reference value of the weighting factor is (1 << LWD) as described above, the weighting factor is (1 << LWD) in the first embodiment, which is the same value as the reference value of the weighting factor.

  By the way, H. In H.264 and the like, indexes such as weighting factors and offsets are specified to take signed 8-bit values from -128 to 127, and fixed-point precision is specified to take values from 0 to 7. . Therefore, in the first embodiment, the weighting factor may be out of the specified range.

  FIG. It is a reference diagram showing a selection range of the weighting coefficient in H.264, and shows the weighting coefficient (1 << LWD) when the fixed point precision LWD takes a value of 0 to 7, respectively. As is clear from FIG. 8, the weighting factor takes a positive value near 0 when the value of the fixed point precision LWD becomes small, but becomes 128 when the value of the fixed point precision LWD becomes 7, and H.264. It is outside the range specified by H.264.

  Thus, H.264. According to the H.264 standard, the range of the weighting coefficient to be used may be outside the specified range, which may not be practical. Further, in unidirectional prediction, even if a weighting coefficient corresponding to a negative direction is selected, the predicted pixel value output in unidirectional prediction is highly likely to be clipped to the bit range of the input image to 0, and The weighting factor corresponding to the direction of can not be selected substantially. On the other hand, in bidirectional prediction, in order to realize extrapolation prediction, it is possible to use one of the unidirectional prediction weighting factors as a negative value and the other weighting factor as a positive value. In many cases, the value on the negative side does not require the same accuracy as the value on the positive side as the range of the weighting coefficient.

  Therefore, in the first embodiment, the index setting unit 108 derives the selection range of the weighting factor by allocating the values in the negative direction and the positive direction with the reference value of the weighting factor as the center, and derives the derived weighting factor. Confirm that the weighting factor is included in the selection range of.

  FIG. 9 is an explanatory diagram showing an example of the selection range of the weighting factor according to the first embodiment. In the example shown in FIG. 9, unlike the weighting factor selection range described with reference to FIG. 8, the weighting factor reference value (1 << LWD) is arranged so as to be located substantially at the center of the selection range. The value obtained by subtracting 128 from the value (-128+ (1 << LWD)) becomes the minimum value of the selection range, and the value obtained by adding 127 to the reference value of the weighting factor (127+ (1 << LWD)) is the maximum of the selection range. It is a value.

  The index setting unit 108 uses Equations (10) and (11) to set the selection range of weighting factors. The minimum value of the selection range is formulated by the formula (10), and the maximum value of the selection range is formulated by the formula (11).

  min_wXC = -128 + (1 << LWD) (10)

  max_wXC = 127 + (1 << LWD) (11)

  10A and 10B are explanatory diagrams showing a specific example of the selection range of the weighting factor of the first embodiment, and FIG. 10A shows the selection range of the weighting factor when the value of the fixed point precision LWD is 7. FIG. 10B shows the selection range of the weighting factor when the value of the fixed point precision LWD is 5. In the example shown in FIG. 10A, the reference value 128 of the weighting coefficient is arranged so as to be located substantially at the center of the selection range, the minimum value of the selection range is 0, and the maximum value of the selection range is 255. In the example shown in FIG. 10B, the reference value 32 of the weighting factor is arranged so as to be located substantially at the center of the selection range, the minimum value of the selection range is −96, and the maximum value of the selection range is 159. .

  FIG. FIG. 12 is a reference diagram showing the minimum value and the maximum value of the selection range of the weighting coefficient in H.264, and FIG. 12 is an explanatory diagram showing an example of the minimum value and the maximum value of the selection range of the weighting coefficient of the first embodiment. As shown in FIG. In H.264, the minimum value and the maximum value of the selection range of the weight coefficient are constant without depending on the reference value of the weight coefficient. On the other hand, as shown in FIG. 12, in the first embodiment, the minimum value and the maximum value of the selection range of the weight coefficient fluctuate depending on the reference value of the weight coefficient.

  As shown in FIG. 12, when the selection range of the weighting factor is set with the reference value of the weighting factor substantially at the center, the range of the weighting factor is -127 to 255, and 9-bit signed precision is required. . Therefore, in the first embodiment, the encoding unit 110, which will be described later, updates the weighting coefficient set as an index, that is, the value to be encoded, to the difference value between the weighting coefficient and the reference value of the weighting coefficient. As shown in FIG. 9, when the reference value of the weighting factor is subtracted from the derived selection range of the weighting factor, the range of the difference value of the weighting factor takes a signed 8-bit value from -128 to 127. In other words, when the weighting factor selection range is set with the reference value of the weighting factor substantially at the center, the weighting factor selection range varies depending on the weighting factor reference value. By subtracting the values, the range of the difference value of the weight coefficient becomes constant without depending on the reference value of the weight coefficient. As described above, in the first embodiment, since the weight coefficient is replaced with the difference value of the weight coefficient, the selection range of the weight coefficient can be expanded and the signed 8-bit precision selection range can be defined.

  If the index setting unit 108 confirms that the weighting factor is not included in the derived weighting factor selection range, the indexing unit 108 may perform clipping processing using the maximum value or the minimum value of the weighting factor selection range. Good. In this case, the index setting unit 108 may clip at the minimum value if the weight coefficient is smaller than the minimum value in the selection range, and at the maximum value if the weight coefficient is larger than the maximum value in the selection range. By introducing such a clipping process, the value to be encoded such as the difference value of the weighting coefficient takes a value within a predetermined bit precision even if a specific range constraint is not set. Can clarify the circuit scale configuration used by.

  Further, in the first embodiment, it is assumed that the selection range of the weighting coefficient has a precision of signed 8-bit, but the accuracy of the selection range of the weighting factor is not limited to this. The precision may be 9 bits. In this case, the selection range of the weighting coefficient is from -256 to 255, but -128 in Expression (10) may be replaced with -256, and 127 in Expression (11) may be replaced with 255.

  Further, in the first embodiment, the example in which the index setting unit 108 derives the selection range of the weighting factor has been described, but the present invention is not limited to this, and the encoding unit 110 may perform it. That is, the index setting unit 108 may be the derivation unit, and the coding unit 110 may be the derivation unit.

  13A and 13B are diagrams illustrating an example of WP parameter information input to the index setting unit 108 according to the first embodiment. An example of the WP parameter information at the time of P-slice is as shown in FIG. 13A, and an example of the WP parameter information at the time of B-slice is as shown in FIG. 13A and FIG. 13B. The list number is an identifier indicating the prediction direction, and takes a value of 0 in unidirectional prediction, and takes two values of 0 and 1 since two types of prediction can be used in bidirectional prediction. The reference numbers are values corresponding to 1 to N shown in the frame memory 206. Since the WP parameter information is held for each reference list and reference image, the information necessary for B-slice is 2N when the number of reference images is N.

  FIG. 14 is a flowchart showing an example of the derivation process of the selection range of the weighting factor according to the first embodiment. Here, description will be made assuming that the index setting unit 108 performs the derivation process of the selection range of the weighting coefficient, but as described above, the encoding unit 110 may perform it.

  First, the index setting unit 108 derives the fixed point precision LWD of the weighting factor (step S02). Here, the index setting unit 108 may derive the fixed point precision LWD of the weighting factor from the WP parameter information or the index information.

  Subsequently, the index setting unit 108 derives the reference value (1 << LWD) of the weighting factor using the derived fixed-point precision LWD (step S03).

  Subsequently, the index setting unit 108 subtracts 128 from the derived reference value (1 << LWD) of the weighting factor to derive the minimum value of the selection range of the weighting factor (step S04).

  Subsequently, the index setting unit 108 adds 127 to the derived reference value (1 << LWD) of the weighting factor to derive the maximum value of the selection range of the weighting factor (step S05).

  Then, the index setting unit 108 confirms that the weighting factor is included in the derived selection range of the weighting factor.

  Returning to FIG. 1, the encoding unit 110 selects the quantized transform coefficient input from the quantization unit 103, the motion information input from the motion evaluation unit 109, the index information input from the index setting unit 108, and the weighting coefficient. Encoding processing is performed on various encoding parameters such as the range and the quantization information designated by the encoding control unit 111 to generate encoded data. The encoding process corresponds to, for example, Huffman encoding or arithmetic encoding.

  The coding parameter is a parameter required for decoding prediction information indicating a prediction method and the like, information regarding a quantized transform coefficient, and information regarding quantization. For example, the encoding control unit 111 has an internal memory (not shown), and the encoding parameters are held in the internal memory. When encoding a pixel block, the encoding control unit 111 uses the encoding parameters of an adjacent already encoded pixel block. I can do it. For example, H.264. In the H.264 intra prediction, prediction information of a pixel block can be derived from prediction information of an encoded adjacent block.

  The encoding unit 110 outputs the generated encoded data according to an appropriate output timing managed by the encoding control unit 111. The output encoded data is multiplexed with various information by a multiplexing unit (not shown), for example, and temporarily stored in an output buffer (not shown). (Storage media) or a transmission system (communication line).

  The coding unit 110 includes an entropy coding unit 110A and an index reconstructing unit 110B.

  The entropy coding unit 110A performs coding processing such as variable length coding and arithmetic coding on the input information. For example, H.264. In H.264, context-based adaptive variable length coding (CAVLC) and context-based adaptive binary coding (CABAC) are used, and context-based adaptive variable length coding (CAVLC).

  In order to reduce the code length of the syntax element of the index information input from the index setting unit 108, the index reconstructing unit 110B performs prediction processing according to the characteristics of the parameter of the syntax element, and the value of the syntax element as it is (direct (Value) and the difference value between the prediction values and outputs the calculated value to the entropy coding unit 110A. A specific example of the prediction process will be described later. When the encoding unit 110 derives the selection range of the weighting coefficient, the index reconstructing unit 110B performs it.

  FIG. 15 is a diagram showing an example of the syntax 500 used by the encoding device 100 of the first embodiment. Syntax 500 indicates the structure of encoded data generated by encoding apparatus 100 by encoding an input image (moving image data). When decoding the encoded data, the decoding device described below refers to the same syntax structure as the syntax 500 and interprets the syntax of the moving image data.

  The syntax 500 includes three parts: a high-level syntax 501, a slice-level syntax 502, and a coding-tree-level syntax 503. The high-level syntax 501 includes syntax information of a layer higher than the slice. The syntax information includes, for example, the tiled division information described in the example illustrated in FIG. 2B. A slice refers to a rectangular area or a continuous area included in a frame or a field. Slice level syntax 502 contains the information needed to decode each slice. The coding tree level syntax 503 includes information necessary for decoding each coding tree (that is, each coding tree block). Each of these parts contains more detailed syntax.

  The high-level syntax 501 includes sequence and picture-level syntax such as a sequence parameter set syntax 504, a picture parameter set syntax 505, and an adaptation parameter set syntax 506.

  The slice level syntax 502 includes a slice header syntax 507, a spread weight table syntax 508, a slice data syntax 509, and the like. The pread weight table syntax 508 is called from the slice header syntax 507.

  The coding tree level syntax 503 includes a coding tree unit syntax 510, a transform unit syntax 511, a prediction unit syntax 512, and the like. The coding tree unit syntax 510 may have a quadtree structure. Specifically, the coding tree unit syntax 510 can be recursively called as a syntax element of the coding tree unit syntax 510. That is, one coding tree block can be subdivided by a quadtree. The transform tree syntax 511 is included in the coding tree unit syntax 510. The transform unit syntax 511 is called in each coding tree unit syntax 510 at the end of the quadtree. The transform unit syntax 511 describes information related to inverse orthogonal transform, quantization, and the like. Information on weighted motion compensation prediction may be described in these syntaxes.

  FIG. 16 is a diagram showing an example of the picture parameter set syntax 505 of the first embodiment. The weighted_pred_flag is, for example, a syntax element indicating the validity or invalidity of the weighted compensation prediction of the first embodiment relating to P-slice. When the weighted_pred_flag is 0, the weighted motion compensation prediction in the first embodiment in the P-slice is invalid. Therefore, the WP application flag included in the WP parameter information is always set to 0, and the WP selectors 304 and 305 connect their output terminals to the default motion compensation unit 301. On the other hand, when the weighted_pred_flag is 1, the weighted motion compensation prediction of the first embodiment in the P-slice is valid.

  As another example, when weighted_pred_flag is 1, in the syntax of a lower layer (slice header, coding tree block, transform unit, prediction unit, and the like), each local region within a slice is assigned The validity or invalidity of the weighted motion compensation prediction of one embodiment may be defined.

  weighted_bipred_idc is, for example, a syntax element indicating the validity or invalidity of the weighted compensation prediction of the first embodiment relating to B-slice. When weighted_bipred_idc is 0, the weighted motion compensation prediction according to the first embodiment in a B-slice becomes invalid. Therefore, the WP application flag included in the WP parameter information is always set to 0, and the WP selectors 304 and 305 connect their output terminals to the default motion compensation unit 301. On the other hand, when the weighted_bipred_idc is 1, the weighted motion compensation prediction of the first embodiment in the B-slice is valid.

  As another example, when weighted_bipred_idc is 1, in the syntax of a lower layer (slice header, coding tree block, transform unit, and the like), each local region in the slice according to the first embodiment is used. The validity or invalidity of the weighted motion compensation prediction may be defined.

  FIG. 17 is a diagram showing an example of the slice header syntax 507 of the first embodiment. slice_type indicates the slice type (I-slice, P-slice, B-slice, etc.) of the slice. pic_parameter_set_id is an identifier indicating which picture parameter set syntax 505 is referred to. num_ref_idx_active_override_flag is a flag indicating whether or not to update the number of valid reference images. When this flag is 1, num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1 that define the number of reference images in the reference list can be used. pred_weight_table () is a function indicating the pread weight table syntax used for weighted motion compensation prediction, and when weighted_pred_flag is 1 and P-slice, and when weighted_bipred_idc is 1 and B-slice, this function is Be called.

  FIG. 18 is a diagram showing an example of the pread weight table syntax 508 of the first embodiment. luma_log2_weight_denom represents the fixed-point precision (LWD) of the weighting factor of the luminance signal in the slice, and is a value corresponding to the LWD in Expression (7) or Expression (9). delta_chroma_log2_weight_denom represents the fixed point precision of the weighting coefficient of the color difference signal in the slice, and the derivation method will be described later. chroma_format_idc is an identifier representing a color space, and MONO_IDX is a value indicating a monochrome image. num_ref_common_active_minus1 indicates a value obtained by subtracting 1 from the number of reference images included in the common list in the slice.

  luma_weight_l0_flag and luma_weight_l1_flag indicate WP adaptation flags in the luminance signal corresponding to each of list 0 and list 1. When this flag is 1, the weighted motion-compensated prediction of the luminance signal of the first embodiment is effective in the entire slice. chroma_weight_l0_flag and chroma_weight_l1_flag indicate WP adaptation flags in the color difference signals corresponding to List 0 and List 1, respectively. When this flag is 1, the weighted motion compensation prediction of the chrominance signal of the first embodiment is valid in the entire area within the slice. luma_weight_l0 [i] and luma_weight_l1 [i] are weighting coefficients of the luminance signal corresponding to the reference number i-th managed in each of the list 0 and the list 1. luma_offset_l0 [i] and luma_offset_l1 [i] are offsets of the luminance signal corresponding to the reference number i-th managed in each of list 0 and list 1. These are values corresponding to w0C, w1C, o0C, and o1C in Equation (7) or Equation (9), respectively. However, C = Y.

  chroma_weight_l0 [i] [j] and chroma_weight_l1 [i] [j] are the weighting coefficients of the color difference signal corresponding to the reference number i-th managed in list 0 and list 1, respectively. chroma_offset_l0 [i] [j] and chroma_offset_l1 [i] [j] are offsets of the color difference signal corresponding to the reference number i-th managed in each of the list 0 and the list 1. These are values corresponding to w0C, w1C, o0C, and o1C in Equation (7) or Equation (9), respectively. However, C = Cr or Cb. j indicates a component of the color difference component. For example, in the case of a YUV 4: 2: 0 signal, j = 0 indicates a Cr component and j = 1 indicates a Cb component. In this notation, j = 0 may be used as a Cb component, and j = 1 may be used as a Cr component.

  Here, the details of the method of predicting each syntax element related to weighted prediction in the syntax configuration will be described. The prediction of the syntax element is performed by the index reconstructing unit 110B. In the example shown in FIG. 18, the syntax element to which prediction is introduced is shown with a prefix of delta.

  First, a prediction method between signals of luma_log2_weight_denom and chroma_log2_weight_denom indicating fixed-point precision of a weight coefficient will be described. The index reconstructing unit 110B performs the prediction process between the signals of luma_log2_weight_denom and chroma_log2_weight_denom using Formula (12), and performs the restoration process using Formula (13). Here, as shown in FIG. 18, since luma_log2_weight_denom is defined first, chroma_log2_weight_denom is predicted from the value of luma_log2_weight_denom.

  delta_chroma_log2_weight_denom = (chroma_log2_weight_denom-luma_log2_weight_denom)… (12)

  chroma_log2_weight_denom = (luma_log2_weight_denom + delta_chroma_log2_weight_denom) (13)

  In general, the fade effect rarely causes different temporal changes for each color space, so that the fixed point precision of each signal component has a strong correlation between the luminance component and the color difference component. For this reason, by performing prediction in the color space in this way, the amount of information indicating fixed-point precision can be reduced.

  Note that in the formula (12), the luminance component is subtracted from the color difference component, but the color difference component may be subtracted from the luminance component. In this case, the equation (13) may be modified according to the equation (12).

  Next, a method of predicting luma_weight_lx [i] and chroma_weight_lx [i] [j] representing the weight coefficients of the luminance and color difference signals will be described. Here, x is an identifier indicating 0 or 1. The values of luma_weight_lx [i] and chroma_weight_lx [i] [j] change according to the values of luma_log2_weight_denom and chroma_log2_weight_denom, respectively. For example, when the value of luma_log2_weight_denom is 3, luma_weight_lx [i] when there is no pixel value change is (1 << 3). On the other hand, when the value of luma_log2_weight_denom is 5, the luma_weight_lx [i] is (1 << 5) assuming that there is no change in brightness.

  Therefore, the index reconstructing unit 110B performs the prediction process by using the weighting coefficient when there is no pixel value change as the reference coefficient (default value). Specifically, the index reconstructing unit 110B performs the prediction process of luma_weight_lx [i] using Formulas (14) to (15), and performs the restoration process using Formula (16). Similarly, the index reconstructing unit 110B performs the prediction process of chroma_weight_lx [i] using Formulas (17) to (18), and performs the restoration process using Formula (19).

  delta_luma_weight_lx [i] = (luma_weight_lx [i]-default_luma_weight_lx) (14)

  default_luma_weight_lx = (1 << luma_log2_weight_denom) (15)

  luma_weight_lx [i] = (default_luma_weight_lx + delta_luma_weight_lx [i]) (16)

  delta_chroma_weight_lx [i] [j] = (chroma_weight_lx [i] [j]-default_chroma_weight_lx) (17)

  default_chroma_weight_lx = (1 << chroma_log2_weight_denom) (18)

  chroma_weight_lx [i] [j] = (default_chroma_weight_lx + delta_chroma_weight_lx [i] [j]) (19)

  Here, default_luma_weight_lx and default_chroma_weight_lx are reference values (default values) with no change in pixel value in the luminance component and the color difference component, respectively.

  An image including a fade effect fades at a specific fade change point, and the other images are usually natural images or images without a fade effect. In this case, the weighting factor is often taken when there is no change in pixel value. Therefore, it is possible to reduce the code amount of the weighting coefficient by deriving the initial value when there is no pixel value change from the fixed-point precision and using it as the predicted value.

  Next, a method of predicting chroma_offset_lx [i] [j] representing the offset of the color difference signal will be described. In the YUV color space, the color difference component expresses a color with an amount of deviation from the median value. For this reason, the amount of change from the pixel value change considering the median can be used as the predicted value using the weighting coefficient. Specifically, the index reconstructing unit 110B performs the prediction process of chroma_offset_lx [i] [j] using Formulas (20) to (21), and performs the restoration process using Formula (22).

  delta_chroma_offset_lx [i] [j] = (chroma_offset_lx [i] [j] + ((MED * chroma_weight_lx [i] [j]) >> chroma_log2_weight_denom)-MED) (20)

  MED = (MaxChromaValue >> 1)… (21)

  Here, MaxChromaValue indicates the maximum pixel value at which the color difference signal can be obtained. For example, in the case of an 8-bit signal, MaxChromaValue is 255 and MED is 128.

  chroma_offset_lx [i] [j] = (delta_chroma_offset_lx [i] [j]-((MED * chroma_weight_lx [i] [j]) >> chroma_log2_weight_denom) + MED) (22)

  By using the signal characteristics of the color difference signal to introduce a predicted value that takes into account the amount of deviation from the median, the amount of code for the offset value of the color difference signal is reduced as compared to the case where the offset value is directly encoded it can.

  FIG. 19 is an explanatory diagram illustrating an example of the relationship between the values of the syntax elements according to the first embodiment, and illustrates the relationship between the values of luma_log2_weight_denom, default_luma_weight_lx, luma_weight_lx [i], and delta_luma_weight_lx [i]. As shown in FIG. 19, delta_luma_weight_lx [i], which is a syntax element coded by the entropy coding unit 110A, that is, a range in which a difference value of weighting factors can be taken is fixed in a range of −128 to 127. , Signed 8-bit precision.

  As described above, in the first embodiment, the selection range of the weighting factor is derived by allocating the values in the negative direction and the positive direction with the reference point of the weighting factor at which the pixel value change is 0 as the approximate center. Confirm that the weighting factor is included in the selection range of the weighting factor. Therefore, according to the first embodiment, H.264. Compared with H.264 or the like, it is possible to expand the selection range of the weighting coefficient and make it easier to take a positive value that is frequently selected. Further, according to the first embodiment, since the difference value of the weighting coefficient to be encoded is a signed 8-bit value from −128 to 127, a fixed value is added while expanding the selection range of the weighting coefficient. An 8-bit precision selection range can be defined.

  As described above, in the first embodiment, the range of syntax (difference value of weighting factor) to be encoded can be set to a fixed value, so that the specification can be compared with the configuration in which the encoder dynamically changes these ranges. Can be simplified. For example, when the syntax to be encoded is a weighting coefficient and the selection range of the weighting coefficient fluctuates according to the reference value of the weighting coefficient, the reference value of the weighting coefficient is associated with the minimum value and the maximum value of the selection range of the weighting coefficient. It is necessary to prepare a table and refer to it each time after deriving the selection range of the weighting coefficient, or to calculate and derive the selection range of the weighting coefficient each time. In such a case, a configuration in which the table is loaded in the memory and referred to each time and an arithmetic circuit for calculating the selection range of the weighting coefficient each time are required, which increases the hardware scale. On the other hand, in the first embodiment, the range of syntax to be coded (difference value of weighting factor) can be set to a fixed value, so that the hardware scale is reduced without being restricted by the hardware configuration as described above. be able to.

  Furthermore, in the first embodiment, the difference value of the weighting coefficient whose range is fixed to signed 8-bit precision is encoded, but the difference value of the weighting coefficient takes a value near the center of the range (near 0). Therefore, the code length at the time of encoding can be shortened and the encoding efficiency can be improved. H. In H.264 or the like, the weighting factor is encoded by a signed exponential Golomb code (se (v)), which is a valid code for a symbol whose value to be encoded increases exponentially with 0 as a reference. For this reason, it is common to set the most frequently used reference value as the center of the range. In the first embodiment, the case where the pixel value change between pictures in a general moving image is 0 is set as the reference value of the weighting coefficient, and the prediction from the reference value is also introduced in the prediction of the selection range of the weighting coefficient. ing. As a result, the exponential Golomb code and the selection range of the prediction and weighting coefficients match, so that the code amount reduction effect is high and the coefficient range is determined around the reference value. The distance from the reference value of the negative value becomes approximately the same, and there is an effect that encoding can be performed with a shorter code length as compared with the conventional method.

  It should be noted that syntax elements not defined in the present embodiment may be inserted between the rows of the syntax table illustrated in FIGS. 16 to 18 of the first embodiment, and description regarding other conditional branches is included. May be. Further, the syntax table may be divided into a plurality of tables, or a plurality of syntax tables may be integrated. The term of each syntax element exemplified can be arbitrarily changed.

(Second embodiment)
In the second embodiment, a decoding device that decodes the encoded data encoded by the encoding device according to the first embodiment will be described. In the second embodiment, as in the first embodiment, description will be made assuming that there is no pixel value change, that is, the case where the value of the weighting coefficient is represented by a real value is 1.0.

  FIG. 20 is a block diagram showing an example of the configuration of the decoding device 800 according to the second embodiment.

  The decoding device 800 decodes encoded data stored in an input buffer (not shown) or the like into a decoded image and outputs the decoded image to an output buffer (not shown) as an output image. The encoded data is output from, for example, the encoding device 100 in FIG. 1 or the like, and is input to the decoding device 800 via a storage system, a transmission system, or a buffer (not shown).

  As illustrated in FIG. 20, the decoding device 800 includes a decoding unit 801, a dequantization unit 802, an inverse orthogonal transformation unit 803, an addition unit 804, a predicted image generation unit 805, and an index setting unit 806. Prepare The inverse quantization unit 802, the inverse orthogonal transformation unit 803, the addition unit 804, and the predicted image generation unit 805 are respectively the inverse quantization unit 104, the inverse orthogonal transformation unit 105, the addition unit 106, the predicted image generation unit 107, Are substantially the same or similar elements. The decoding control unit 807 shown in FIG. 20 controls the decoding device 800 and can be realized by, for example, a CPU.

  The decoding unit 801 performs decoding on a frame-by-frame or field-by-field basis based on syntax for decoding encoded data. The decoding unit 801 includes an entropy decoding unit 801A and an index reconstruction unit 801B.

  The entropy decoding unit 801A sequentially performs entropy decoding on the code string of each syntax, and calculates motion information including a prediction mode, a motion vector, and a reference number, index information for weighted motion compensation prediction, and quantization transform coefficients. The encoding parameters of the encoding target block are reproduced. Note that entropy decoding is also called parsing processing or the like. Here, the coding parameters are all parameters other than those described above that are necessary for decoding information such as transform coefficient information and quantization information.

  Specifically, the entropy decoding unit 801A has a function of performing decoding processing such as variable-length decoding processing and arithmetic decoding processing on input encoded data. For example, H.264. In H.264, context-based variable-length coding (CAVLC), context-based arithmetic coding (CABAC), and the like are used to input context-based adaptive coded data (CABAC). Is decoded into a meaningful syntax element. These processes are also called decryption processes.

  The index reconstructing unit 801B restores the decrypted index information and reconstructs the index information. Specifically, in order to reduce the code length of the syntax element of the decoded index information, the index reconstructing unit 801B performs prediction processing according to the characteristics of the syntax element parameter, restores the syntax element, Reconstruct information. A specific example of the prediction process will be described later.

  The decoding unit 801 outputs the motion information, the index information, and the quantized transform coefficient, inputs the quantized transform coefficient to the inverse quantization unit 802, inputs the index information to the index setting unit 806, and outputs the motion information to the prediction image. Input to the generation unit 805.

  The inverse quantization unit 802 performs an inverse quantization process on the quantized transform coefficient input from the decoding unit 801 to obtain a restored transform coefficient. Specifically, the inverse quantization unit 802 performs inverse quantization according to the quantization information used in the decoding unit 801. More specifically, the inverse quantization unit 802 multiplies the quantized transform coefficient by a quantization step size derived from the quantization information to obtain a restored transform coefficient. The inverse quantization unit 802 outputs the restoration transform coefficient and inputs it to the inverse orthogonal transform unit 803.

  The inverse orthogonal transform unit 803 performs an inverse orthogonal transform corresponding to the orthogonal transform performed on the encoding side on the restored transform coefficient input from the inverse quantization unit 802, and obtains a restored prediction error. The inverse orthogonal transformation unit 803 outputs the restoration prediction error and inputs it to the addition unit 804.

  The addition unit 804 adds the restoration prediction error input from the inverse orthogonal transform unit 803 and the corresponding prediction image to generate a decoded image. The addition unit 804 outputs the decoded image and inputs the decoded image to the predicted image generation unit 805. The addition unit 804 outputs the decoded image to the outside as an output image. The output image is then temporarily stored in an external output buffer (not shown) or the like, and is output to a display device system such as a display or monitor (not shown) or a video device system in accordance with the output timing managed by the decoding control unit 807, for example. Is output.

  The index setting unit 806 receives the index information input from the decoding unit 801, converts the index information into WP parameter information, outputs the WP parameter information, and inputs the WP parameter information to the predicted image generation unit 805. Specifically, the index setting unit 806 receives the index information decoded by the entropy decoding unit 801A and reconstructed by the index reconstructing unit 801B. Then, the index setting unit 806 checks the reference image list and the reference number, converts the reference image list into the WP parameter information, and outputs the converted WP parameter information to the predicted image generation unit 805. The index setting unit 806 derives the selection range of the weighting factor when converting the index information into the WP parameter information, and confirms that the weighting factor is included in the selection range. The derivation of the selection range of the weighting factor is the same as in the first embodiment, and thus detailed description will be omitted. Moreover, the derivation of the selection range of the weighting factor may be performed not by the index setting unit 806 but by the index reconstructing unit 801B. That is, the index setting unit 806 may be the derivation unit, or the index reconstruction unit 801B (decoding unit 801) may be the derivation unit.

  In addition, the WP parameter information includes the information of the first WP application flag, the second WP adaptation flag, and the weight information, as in the first embodiment. In addition, the weight information includes the first weighting coefficient value w0C, the second weighting coefficient value w1C, the fixed-point precision LWD of the first weighting coefficient and the second weighting coefficient, the first offset o0C, and the first weighting coefficient w0C, as in the first embodiment. Two offsets o1C information is included.

  The predicted image generation unit 805 generates a predicted image using the motion information input from the decoding unit 801, the WP parameter information input from the index setting unit 806, and the decoded image input from the addition unit 804.

  Here, the details of the predicted image generation unit 805 will be described with reference to FIG. Like the predicted image generation unit 107, the predicted image generation unit 805 includes a multi-frame motion compensation unit 201, a memory 202, a unidirectional motion compensation unit 203, a prediction parameter control unit 204, a reference image selector 205, and a frame memory 206. And a reference image control unit 207.

  The frame memory 206 stores the decoded image input from the adding unit 106 as a reference image under the control of the reference image control unit 207. The frame memory 206 has a plurality of memory sets FM1 to FMN (N ≧ 1) for temporarily holding a reference image.

  The prediction parameter control unit 204 prepares a plurality of combinations of reference image numbers and prediction parameters as a table based on the motion information input from the decoding unit 801. Here, the motion information indicates a motion vector indicating a displacement amount of motion used in motion compensation prediction, a reference image number, information on prediction modes such as unidirectional / bidirectional prediction, and the like. The prediction parameter indicates information on a motion vector and a prediction mode. Then, the prediction parameter control unit 204 selects and outputs a combination of a reference image number and a prediction parameter used for generation of a predicted image based on the motion information, inputs the reference image number to the reference image selector 205, Is input to the unidirectional motion compensation unit 203.

  The reference image selector 205 is a switch for switching which output terminal of the frame memories FM1 to FMN of the frame memory 206 is to be connected in accordance with the reference image number input from the prediction parameter control unit 204. For example, if the reference image number is 0, the reference image selector 205 connects the output terminal of FM1 to the output terminal of the reference image selector 205. If the reference image number is N-1, the reference image selector 205 refers to the output terminal of FMN. It is connected to the output terminal of the image selector 205. The reference image selector 205 outputs a reference image stored in a frame memory to which an output terminal is connected among the frame memories FM1 to FMN of the frame memory 206, and inputs the reference image to the unidirectional motion compensation unit 203. In the decoding device 800, the reference image is not used except for the predicted image generation unit 805, and thus the reference image does not have to be output to the outside of the predicted image generation unit 805.

  The unidirectional motion compensation unit 203 performs motion compensation prediction processing according to the prediction parameter input from the prediction parameter control unit 204 and the reference image input from the reference image selector 205 to generate a unidirectional prediction image. The motion compensation prediction has already been described with reference to FIG.

  The unidirectional motion compensation unit 203 outputs the unidirectional predicted image and temporarily stores it in the memory 202. Here, when the motion information (prediction parameter) indicates bidirectional prediction, the multi-frame motion compensating unit 201 performs weighted prediction using two types of unidirectionally predicted images, so that the unidirectional motion compensating unit 203 The unidirectional predicted image corresponding to the first one is stored in the memory 202, and the unidirectional predicted image corresponding to the second is directly output to the multi-frame motion compensation unit 201. Here, the first unidirectional predicted image corresponding to the first is a first predicted image, and the second unidirectional predicted image corresponding to the second is a second predicted image.

  Note that two unidirectional motion compensating units 203 may be prepared, and each may generate two unidirectional predicted images. In this case, when the motion information (prediction parameter) indicates unidirectional prediction, the unidirectional motion compensating unit 203 may directly output the first unidirectional predicted image as the first predicted image to the multi-frame motion compensating unit 201. Good.

  The multi-frame motion compensation unit 201 uses the first predicted image input from the memory 202, the second predicted image input from the unidirectional motion compensation unit 203, and the WP parameter information input from the motion evaluation unit 109, Weighted prediction is performed to generate a predicted image. The multi-frame motion compensation unit 201 outputs a prediction image and inputs the prediction image to the addition unit 804.

  Here, the details of the multi-frame motion compensation unit 201 will be described with reference to FIG. The multiple-frame motion compensation unit 201 includes a default motion compensation unit 301, a weighted motion compensation unit 302, a WP parameter control unit 303, and WP selectors 304 and 305, similarly to the predicted image generation unit 107.

  The WP parameter control unit 303 outputs the WP application flag and weight information based on the WP parameter information input from the index setting unit 806, inputs the WP application flag to the WP selectors 304 and 305, and weights the weight information. It is input to the motion compensation unit 302.

  Specifically, when the WP parameter information is input from the index setting unit 806, the WP parameter control unit 303 separates and outputs the WP parameter information into a first WP application flag, a second WP application flag, and weight information. , The first WP application flag is input to the WP selector 304, the second WP application flag is input to the WP selector 305, and the weight information is input to the weighted motion compensation unit 302.

  When the WP parameter information is input, the WP parameter control unit 303 checks whether the value of the weight information is within the specified range. For example, when w0C is represented by a real number, 3.0, and when LWD is 7, the first weighting factor is 384. Here, 384 is out of the range of the first weighting coefficient and cannot be used. In this case, since the WP parameter control unit 303 is data that violates the standard, the WP parameter control unit 303 may notify the decoding control unit 807 of information indicating that the standard has been violated, and stop the decoding process. Further, the WP parameter control unit 303 may perform the clipping process within the range of the first weighting coefficient and proceed with the decoding process. Further, the WP parameter control unit 303 may change the value of the first WP application flag from 1 to 0 and perform the default motion compensation prediction.

  The WP selectors 304 and 305 switch the connection end of each predicted image based on the WP application flag input from the WP parameter control unit 303. When each WP application flag is 0, the WP selectors 304 and 305 connect each output terminal to the default motion compensation unit 301. Then, the WP selectors 304 and 305 output the first prediction image and the second prediction image, and input them to the default motion compensation unit 301. On the other hand, when each WP application flag is 1, the WP selectors 304 and 305 connect each output end to the weighted motion compensation unit 302. Then, the WP selectors 304 and 305 output the first prediction image and the second prediction image, and input the weighted motion compensation unit 302.

  The default motion compensation unit 301 performs an average value process based on two unidirectional predicted images (first predicted image and second predicted image) input from the WP selectors 304 and 305, and generates a predicted image. Specifically, when the first WP application flag and the second WP application flag are 0, the default motion compensation unit 301 performs an average value process based on Expression (1).

  When the prediction mode indicated by the motion information (prediction parameter) is unidirectional prediction, the default motion compensation unit 301 uses only the first predicted image and calculates the final predicted image based on Expression (4). calculate.

  The weighted motion compensation unit 302 is based on the two unidirectional prediction images (first prediction image and second prediction image) input from the WP selectors 304 and 305 and the weight information input from the WP parameter control unit 303. Perform weighted motion compensation. Specifically, when the first WP application flag and the second WP application flag are 1, the weighted motion compensation unit 302 performs a weighting process based on Expression (7).

  Note that the weighted motion compensation unit 302 performs rounding processing by controlling LWD, which is fixed-point precision, as in Expression (8) when the calculation accuracy of the first predicted image and the second predicted image is different from that of the predicted image. To realize.

  In addition, when the prediction mode indicated by the motion information (prediction parameter) is unidirectional prediction, the weighted motion compensation unit 302 uses only the first prediction image and makes a final prediction image based on Expression (9). To calculate.

  Note that the weighted motion compensation unit 302 sets the LWD, which is the fixed-point precision, to the formula (8) as in the bidirectional prediction when the calculation accuracy of the first prediction image and the second prediction image is different from that of the prediction image. The rounding process is realized by controlling to.

  Since the fixed-point precision of the weight coefficient has already been described with reference to FIG. 7, the description is omitted. Note that in the case of unidirectional prediction, various parameters (second WP adaptation flag, second weighting coefficient, and second offset information) corresponding to the second predicted image are not used, so set to a predetermined initial value. It may have been done.

  The decoding unit 801 uses the syntax 500 shown in FIG. The syntax 500 shows the structure of encoded data to be decoded by the decoding unit 801. The syntax 500 has already been described with reference to FIG. 15, so description thereof will be omitted. Further, the picture parameter set syntax 505 has already been described with reference to FIG. 16 except that the encoding is decoding, and therefore description thereof will be omitted. Also, the slice header syntax 507 has already been described with reference to FIG. 17 except that the encoding is decoding, and thus the description thereof will be omitted. Further, the description of the pred weight table syntax 508 has also been omitted because it has already been described with reference to FIG. 18 except that the encoding is decoding.

  Here, the details of the method of predicting each syntax element related to weighted prediction in the syntax configuration will be described. The prediction of the syntax element is performed by the index reconstructing unit 801B. The syntax configuration explicitly showing the prediction method of the second embodiment is the same as that of the first embodiment.

  Regarding the prediction method between the signals of luma_log2_weight_denom and chroma_log2_weight_denom, which indicate the fixed-point precision of the weighting coefficient, the restoration process is performed using Expression (13).

  With respect to the prediction method of luma_weight_lx [i] and chroma_weight_lx [i] [j] that represent the weighting factors of the luminance and color difference signals, the restoration process is performed using Equations (16) and (19).

  Note that the above-described plurality of prediction methods can be used not only alone but also in combination. For example, by combining Expression (13), Expression (15), Expression (19), and the like, it is possible to efficiently reduce the code amount of the syntax element in the index information.

  As described above, in the second embodiment, the selection range of the weighting factor is derived and derived by allocating the values in the negative direction and the positive direction with the reference point of the weighting factor at which the pixel value change is 0 as the center. Confirm that the weighting factor is included in the selection range of the weighting factor. Therefore, according to the second embodiment, H.264. Compared with H.264 or the like, it is possible to expand the selection range of the weighting coefficient and make it easier to take a positive value that is frequently selected. Further, according to the second embodiment, since the difference value of the weighting coefficient to be decoded is a signed 8-bit value from −128 to 127, the weighting coefficient selection range is expanded and A bit precision selection range can be defined.

  As described above, in the second embodiment, since the range of syntax (difference value of weighting factor) to be decoded can be set to a fixed value, the decoder determines whether the decoded encoded data is within the range of the predetermined specifications. Can be checked easily and the specifications can be simplified. For example, when the syntax to be decoded is a weighting coefficient and the selection range of the weighting coefficient varies according to the reference value of the weighting coefficient, a table that associates the reference value of the weighting coefficient with the minimum value and the maximum value of the selection range of the weighting coefficient. Must be prepared and referred to each time after the selection range of the weighting factor is derived. In such a case, it is necessary to load the table in the memory and refer to the table each time, which increases the hardware scale. On the other hand, in the second embodiment, the range of syntax (difference value of weighting coefficient) to be decoded can be set to a fixed value, so that the hardware scale can be reduced without being restricted by the hardware configuration as described above. You can

  Furthermore, in the second embodiment, the difference value of the weighting coefficient whose range is fixed to signed 8-bit precision is decoded, but the difference value of the weighting coefficient takes a value near the center of the range (near 0). The code length at the time of decoding can be shortened, and the decoding efficiency can be improved. H. In H.264 and the like, the weighting coefficient is decoded by a signed exponential Golomb code (se (v)), but this code is effective for a symbol whose value to be decoded increases exponentially with 0 as a reference. , It is common to set the most frequently used reference value as the center of the range. In the second embodiment, when the pixel value change between pictures in a general moving image is 0, the reference value of the weighting coefficient is used, and the prediction from the above reference value is also introduced in the prediction of the selection range of the weighting coefficient. ing. As a result, the exponential Golomb code and the selection range of the prediction and weighting coefficients match, so that the code amount reduction effect is high and the coefficient range is determined around the reference value. The distance from the reference value of the negative value becomes approximately the same, and there is an effect that decoding can be performed with a shorter code length as compared with the conventional method.

(Modification 1 of the first embodiment)
In the first embodiment, the derivation of the selection range of the weighting coefficient in the encoding device 100 has been described, but in the first modification, the derivation of the selection range of the offset in the encoding device 100 will be described.

  As described in the formulas (20) to (22), in the YUV color space, the color difference component expresses a color by the amount of deviation from the median value. For this reason, the amount of change from the pixel value change considering the median can be used as the predicted value using the weighting coefficient. This predicted value indicates the reference value of the offset when the influence of the weighting coefficient is eliminated. That is, the index setting unit 108 can derive the offset selection range by allocating a range of possible values around the predicted value (offset reference value), and the offset is included in the derived offset selection range. Can be confirmed.

  For example, when the LWD is 2 and the value of the weighting coefficient is 5, the reference value of the weighting coefficient is (1 << 2), that is, 4. On the other hand, since the value of the weighting factor is 5, the pixel value changes. Since the color difference signal expresses the color by the amount of deviation from the median value, the index setting unit 108 eliminates the influence of the weighting coefficient to obtain the offset reference value. The reference value of the offset is formulated by Equation (23).

  Pred ＝ (MED − ((MED * chroma_weight_lx [i] [j]) >> chroma_log2_weight_denom))… (23)

  Pred indicates the reference value of the color difference signal offset, MED indicates the median value of the color difference signal (128 at 8 bits), and the term on the right side means the amount of deviation from the median value due to the influence of the weighting coefficient. Expression (23) corresponds to a value obtained by inverting the sign of the rightmost term of expression (20). As shown in Expression (23), the reference value of the offset of the color difference signal is determined according to the weighting coefficient of the color difference signal and the fixed point precision.

  The formula (23) can be transformed into the formula (24).

  Pred = ((1 << (BitDepth − 1)) − ((chroma_weight_lx [i] [j]) << (BitDepth − 1 − chroma_log2_weight_denom))… (24)

  Here, BitDepth represents the pixel depth of the color difference signal, and BitDepth is 8 if it is an 8-bit signal. Since the MED in Expression (23) is a value expressed by a power of 2, it can be expressed as Expression (24) if the shift on the right side is rewritten using BitDepth.

  FIG. 21 is an explanatory diagram showing an example of the selection range of the offset of the color difference signal of the first modification. In the example shown in FIG. 21, Pred is arranged so as to be located substantially at the center of the selection range, and (Pred)-(1 << OR) becomes the minimum value of the selection range, and (Pred) + (1 << OR ) -1 is the maximum value of the selection range. OR means the bit precision of the offset, for example, H.264. In H.264, it becomes 8. As shown in FIG. 21, the selection range of the offset of the color difference signal is defined within a predetermined bit precision centering on the reference value of the offset of the color difference signal. Although detailed description is omitted, the offset difference value of the color difference signal to be encoded (the difference value between the color difference signal offset and the color difference signal offset reference value) is defined as a fixed value of the offset bit precision. it can. For example, with 8-bit precision, the difference value of the offset of the color difference signal is an 8-bit fixed value of -128 to 127. Further, for example, with 9-bit precision, the difference value of the offset of the color difference signal is a fixed value of 9-bit from -256 to 255.

  This can solve the problem that the range of values to be encoded cannot be determined unless the reference value is restored. In addition, in the first modification, an example in which the index setting unit 108 derives the selection range of the offset of the color difference signal has been described, but the present invention is not limited to this, and the encoding unit 110 may perform it.

  FIG. 22 is a flowchart illustrating an example of the derivation process of the offset selection range of the color difference signal according to the first modification. Here, description will be made assuming that the index setting unit 108 performs the process of deriving the offset selection range of the color difference signals, but as described above, the encoding unit 110 may perform it.

  First, the index setting unit 108 derives the fixed point precision LWD of the weighting factor (step S12). Here, the index setting unit 108 may derive the fixed point precision LWD of the weighting factor from the WP parameter information or the index information.

  Subsequently, the index setting unit 108 derives the weighting coefficient Wxc (S13). Here, the index setting unit 108 may derive the weighting coefficient Wxc from the WP parameter information or the index information.

  Subsequently, the index setting unit 108 derives the reference value of the offset of the color difference signal from the mathematical expression (23) using the fixed point precision LWD and the weighting coefficient Wxc of the derived weighting coefficient (step S14).

  Subsequently, the index setting unit 108 subtracts (1 << OR) from the derived reference value of the offset of the color difference signal to derive the minimum value of the selection range of the offset of the color difference signal (step S15).

  Subsequently, the index setting unit 108 adds (1 << OR) -1 to the derived reference value of the offset of the color difference signal to derive the maximum value of the selection range of the offset of the color difference signal (step S16).

  Then, the index setting unit 108 confirms that the offset of the color difference signal is included in the derived selection range of the offset of the color difference signal. In addition, when the index setting unit 108 confirms that the offset of the color difference signal is not included in the selection range of the offset of the color difference signal, the clip setting process is performed using the maximum value or the minimum value of the selection range of the offset of the color difference signal. You may go. In this case, if the offset of the color difference signal is smaller than the minimum value of the selection range, the index setting unit 108 clips at the minimum value, and if the offset of the color difference signal is larger than the maximum value of the selection range, the index setting unit 108 clips at the maximum value. Good. By introducing such a clipping process, the value to be encoded such as the difference value of the offset of the color difference signal takes a value within a predetermined bit precision without providing a specific range constraint. The structure of the circuit scale used by the hardware can be clarified.

  Note that, as described with reference to FIG. 18, since the value of the weighting factor and the information on the fixed point precision are encoded before the information on the offset, the value of the weighting factor can be derived when deriving the reference value of the offset. .

  Further, the selection range of the first offset and the second offset with respect to the color difference signal described in the first modification may be applied separately from the selection range of the first weighting coefficient and the second weighting coefficient described in the first embodiment. . For example, the selection range of the first weighting coefficient and the second weighting coefficient is H.264. The selection range of the first offset and the second offset with respect to the color difference signal may be the same as that of the first modification.

  According to the first modification, the range of syntax (difference value of offset) to be encoded can be set to a fixed value, so that the specification can be simplified as compared with the configuration in which the encoder dynamically changes these ranges. . In addition, when the syntax to be decoded is an offset and the selection range of the offset varies according to the reference value of the offset, a table in which the reference value of the offset and the minimum value and the maximum value of the selection range of the offset are associated is prepared, It is necessary to have a configuration that refers to the offset selection range each time after derivation and a configuration that calculates and derives the offset selection range each time. In such a case, a configuration in which the table is loaded into the memory and referred to each time and a calculation circuit for calculation are required, which increases the hardware scale. On the other hand, when the range of syntax (offset difference value) to be encoded is fixed as in the first modification, the hardware scale can be reduced because the hardware configuration is not restricted.

(Modification 1 of the second embodiment)
In the second embodiment, the derivation of the selection range of the weighting factor in the decoding device 800 has been described, but in the first modification of the second embodiment, the derivation of the selection range of the offset in the decoding device 800 will be described. In the first modification of the second embodiment, the index setting unit 806 can derive the offset selection range and derive the offset by allocating the range of possible values with the predicted value (reference value of the offset) as the approximate center. You can confirm that it is included in the offset selection range. The derivation of the offset selection range is the same as in the first modification of the first embodiment, and thus detailed description thereof is omitted. Further, the derivation of the offset selection range may be performed by the index reconstructing unit 801B instead of the index setting unit 806.

  According to the first modification of the second embodiment, the range of syntax (offset difference value) to be encoded can be set to a fixed value, and therefore, as compared with a configuration in which the decoder dynamically changes these ranges, The specifications can be simplified. In addition, when the syntax to be decoded is an offset and the selection range of the offset varies according to the reference value of the offset, a table in which the reference value of the offset and the minimum value and the maximum value of the selection range of the offset are associated is prepared, It is necessary to have a configuration that refers to the offset selection range each time after derivation and a configuration that calculates and derives the offset selection range each time. In such a case, a configuration in which the table is loaded into the memory and referred to each time and a calculation circuit for calculation are required, which increases the hardware scale. On the other hand, when the range of the syntax (the difference value of the offset) to be encoded is fixed as in the first modification, the hardware scale can be reduced because the hardware configuration is not restricted.

(Modification 2 of the first embodiment)
In the first embodiment, the derivation of the weighting factor selection range in the encoding device 100 has been described, but in the second modification, the weighting factor selection is performed when the weighting factor selection range is derived in the encoding device 100. An example of shifting the range will be described.

  In the first embodiment, as described with reference to FIG. 9, the approximate center of the selection range of the weight coefficient is used as the reference value of the weight coefficient. Further, as described with reference to FIG. 7 and the like, when there is no average pixel value change between images, the value of the weighting coefficient is 1.0 when expressed by a real value, and the range where the weighting coefficient is negative is unidirectional. Not selected in weighted prediction. From this, it can be seen that the selection range of the weighting factor in actual operation has the highest selection frequency near the reference value, and the negative range is rarely used. For this reason, in the second modification, the index setting unit 108 shifts the weighting factor selection range to the positive side when deriving the weighting factor selection range.

  FIG. 23 is an explanatory diagram showing an example of the selection range of the weighting factor of the second modification. In the example shown in FIG. 23, unlike the selection range of the weighting factor described in FIG. 9, a new reference value ((1 << LWD) + SHFT) obtained by adding the shift value SHFT to the reference value (1 << LWD) of the weighting factor. ) Is arranged so as to be located substantially at the center of the selection range, and the value obtained by subtracting 128 from this value (-128+ (1 << LWD) + SHFT) becomes the minimum value of the selection range, and 127 is added to this value. The value (127+ (1 << LWD) + SHFT) is the maximum value of the selection range. At this time, the maximum value may become larger than 255 depending on the value of the fixed-point precision LWD, but the index setting unit 108 may perform the clipping process with the maximum value at 255, or the SHFT that can be taken for each fixed point. The value of may be changed. In Modification 2, the example in which the index setting unit 108 derives the selection range of the weighting factor has been described, but the present invention is not limited to this, and the encoding unit 110 may perform it.

  FIG. 24 is a flowchart illustrating an example of the derivation process of the selection range of the weighting factor of the second modification. Here, description will be made assuming that the index setting unit 108 performs the derivation process of the selection range of the weighting coefficient, but as described above, the encoding unit 110 may perform it.

  First, the index setting unit 108 derives the fixed point precision LWD of the weighting factor (step S22). Here, the index setting unit 108 may derive the fixed point precision LWD of the weighting factor from the WP parameter information or the index information.

  Then, the index setting unit 108 derives the reference value ((1 << LWD) + SHFT) of the weighting factor using the derived fixed-point precision LWD and shift value SHFT (step S23).

  Subsequently, the index setting unit 108 subtracts 128 from the derived reference value ((1 << LWD) + SHFT) of the weighting factor to derive the minimum value of the selection range of the weighting factor (step S24).

  Subsequently, the index setting unit 108 adds 127 to the derived reference value ((1 << LWD) + SHFT) of the weighting factor to derive the maximum value of the selection range of the weighting factor (step S25).

  Then, the index setting unit 108 confirms that the weighting factor is included in the derived selection range of the weighting factor. If the index setting unit 108 confirms that the weighting factor is not included in the derived weighting factor selection range, the indexing unit 108 may perform clipping processing using the maximum value or the minimum value of the weighting factor selection range. Good. In this case, the index setting unit 108 may clip at the minimum value if the weight coefficient is smaller than the minimum value in the selection range, and at the maximum value if the weight coefficient is larger than the maximum value in the selection range. By introducing such a clipping process, the value to be encoded such as the difference value of the weighting coefficient takes a value within a predetermined bit precision even if a specific range constraint is not set. Can clarify the circuit scale configuration used by.

  As described above, in the second modification, the weighting factor selection range is assigned values in the negative direction and the positive direction around the reference point shifted by a predetermined value in consideration of the variation of the weighting factor. By this, the range of values to be encoded can be fixed.

(Modification 2 of the second embodiment)
In the second embodiment, the derivation of the selection range of the weighting factor in the decoding device 800 has been described. However, in the modification 2 of the second embodiment, the weighting is performed in the derivation of the selection range of the weighting factor in the decoding device 800. An example of shifting the selection range of the coefficient will be described. In the second modification of the second embodiment, the index setting unit 806 shifts the weighting factor selection range to the positive side when deriving the weighting factor selection range. The derivation of the selection range of the weighting factor is the same as in the second modification of the first embodiment, and thus detailed description will be omitted. Moreover, the derivation of the selection range of the weighting factor may be performed not by the index setting unit 806 but by the index reconstructing unit 801B.

  As described above, in the modified example 2 of the second embodiment, the selection range of the weighting factor is negative and positive with respect to the reference point that is shifted by a predetermined value in consideration of the change amount of the weighting factor. By assigning a value to, the range of values to be decoded can be fixed.

(Modification 3 of the first embodiment)
In Modification 3, a derivation method different from the derivation method of the selection range of the weighting coefficient in the encoding device 100 of the first embodiment will be described.

  In Modification 3, luma_weight_lx [i] in Expressions (14) to (16) has a fixed selection range, and delta_luma_weight_lx [i] has a dynamic selection range according to LWD. The selection range of the weighting factor (luma_weight_lx [i]) of the modification 5 is the same as that of FIG.

  FIG. 25 is an explanatory diagram showing an example of the range of the difference value of the weighting coefficient to be encoded in Modification 3. In the example shown in FIG. 25, the difference value of the weighting factors (delta_luma_weight_lx [i]) is a signed 9-bit value because addition / subtraction of a signed 8-bit signal is performed. On the other hand, since the reference value of the weighting coefficient takes a value that increases according to the fixed point precision, the difference value of the weighting coefficient tends to be biased toward the negative side as the value of the fixed point precision increases.

  FIG. 26 is an explanatory diagram showing an example of the relationship between the values of the syntax elements of the modified example 3, and shows the relationship between the values of luma_log2_weight_denom, default_luma_weight_lx, luma_weight_lx [i], and delta_luma_weight_lx [i]. As shown in FIG. 19, the delta_luma_weight_lx [i], which is a syntax element encoded by the entropy encoding unit 110, that is, the range in which the difference value of the weight coefficient can be taken, is such that the value of luma_log2_weight_denom representing the fixed-point precision becomes large. It turns out that there is a tendency to bias toward the negative side. On the other hand, it can be seen that the decoded weight coefficient value (luma_weight_lx [i]) is in a fixed range from -128 to 127.

  As described above, in Modification 3, by defining the range of the difference value to be encoded so that the value of the decoded weighting coefficient has a fixed selection range, even if the prediction method is changed, the H.264 codec is changed. It becomes possible to define the same selection range as H.264.

(Modification 3 of the second embodiment)
In the modified example 3 of the second embodiment, a derivation method different from the derivation method of the selection range of the weighting coefficient in the decoding device 800 of the second embodiment will be described. However, since the method of deriving the selection range of the weighting factor of the modified example 3 of the second embodiment is the same as that of the modified example 3 of the first embodiment, detailed description thereof will be omitted.

  As described above, in the modified example 3 of the second embodiment, the range of the difference value to be decoded is determined so that the value of the weighting coefficient has a fixed selection range. It becomes possible to define the same selection range as H.264.

(Modification 4 of the first embodiment)
In modification 4, an example of shifting the selection range of the weighting factor when deriving the selection range of the weighting factor of the modification 3 of the first embodiment will be described.

  In the modified example 4, the index setting unit 108 shifts the range of the difference value of the weighting factors to the positive side, which is substantially equivalent to shifting the selection range of the decoded weighting factors to the positive side. is there.

  FIG. 27 is an explanatory diagram showing an example of the range of the difference value of the weighting factor of the modified example 4. Compared with the modified example 3 of the first embodiment, the range of the difference value of the weighting coefficient that takes a value in the 8-bit range from −128 to 127 is shifted to the positive side by SHFT.

  FIG. 28 shows a selection range of the weighting coefficient after decoding in the modified example 4. From FIG. 28, it is understood that in Modification 4, the range of the weighting factor is shifted to the positive side by the shift amount of the difference value. Even with such a configuration, it becomes possible to select the reference value when the LWD is 7, which could not be selected conventionally.

(Modification 4 of the second embodiment)
In the modification 4 of the second embodiment, an example of shifting the selection range of the weight coefficient when deriving the selection range of the weight coefficient of the modification 3 of the second embodiment will be described. However, since the method of shifting the selection range of the weighting factor of the modified example 4 of the second embodiment is the same as that of the modified example 4 of the first embodiment, detailed description thereof will be omitted. Even with such a configuration, it becomes possible to select the reference value when the LWD is 7, which could not be selected conventionally.

(Modification 5 of the first embodiment)
In modification 5, an example in which the difference value of the weighting factors is subjected to the wrap processing in modifications 3 and 4 of the first embodiment will be described.

  As described with reference to FIG. 25, the difference value of the weighting coefficient is a signed 9-bit signal (-256 to 126) and is biased to the negative side when the fixed-point precision increases. Since the weighting factor is generally entropy-coded by using an exponential Golomb code or the like, if the positive and negative balance is biased, the coding efficiency may decrease. Although the range of the difference value of the weighting coefficient differs depending on the fixed point precision, the range when the fixed point precision is fixed is within 8 bits. For example, when LWD is 7, the range of the difference value is −256 to −1, and when it is shifted to the 0 standard, it becomes an 8-bit value from 0 to 255. Therefore, the index reconstructing unit 110B wraps signed 9 bits into unsigned 8 bits according to the fixed-point precision. In this case, the positive value has a conventional value, and the negative value is connected to the end of the positive value.

  FIG. 29 is a flowchart showing an example of the wrapping process of the difference value of the weighting factors of the modified example 5.

  First, the index reconstructing unit 110B derives the fixed point precision LWD of the weighting factor from the index information (step S32).

  Subsequently, the index reconstructing unit 110B derives a weighting factor from the index information (step S33).

  Subsequently, the index reconstructing unit 110B derives the reference value (1 << LWD) of the weighting factor using the derived fixed-point precision LWD (step S34).

  Subsequently, the index reconstructing unit 110B derives the difference value of the weighting factor from the mathematical expression (14) (step S35).

  Subsequently, the index reconstructing unit 110B performs the wrap processing based on the reference value (1 << LWD) of the weighting coefficient, and connects the negative value after the maximum positive value while keeping the positive value as it is. An unsigned 8-bit code is generated by (step S36).

  Then, the code generated by the index reconstructing unit 110B is entropy coded by the entropy coding unit 110A.

  As described above, in the modified example 5, by performing the wrap processing on the signed 9-bit value, it is possible to always encode with an unsigned 8-bit value, and the signed 9-bit exponential Golomb coding unit or the like can be used. Eliminates the need to have hardware

(Modification 5 of the second embodiment)
In the modified example 5 of the second embodiment, an example in which the difference value of the weighting factors in the modified examples 3 and 4 of the second embodiment is lapped will be described.

  As described with reference to FIG. 25, the difference value of the weighting coefficient is a signed 9-bit signal (-256 to 126) and is biased to the negative side when the fixed-point precision increases. Since the weighting factor is generally entropy-coded by using an exponential Golomb code or the like, if the positive and negative balance is biased, the coding efficiency may decrease. Although the range of the difference value of the weighting coefficient differs depending on the fixed point precision, the range when the fixed point precision is fixed is within 8 bits. For example, when LWD is 7, the range of the difference value is −256 to −1, and when it is shifted to the 0 standard, it becomes an 8-bit value from 0 to 255. Therefore, the index reconstructing unit 801B wraps signed 9 bits into unsigned 8 bits according to the fixed-point precision. In this case, the positive value has a conventional value, and the negative value is connected to the end of the positive value.

  FIG. 30 is a flowchart showing an example of the restoration process of the difference value of the weighting factors according to the modified example 5 of the second embodiment.

  First, the entropy decoding unit 801A decodes the encoded data to derive the fixed point precision LWD of the weighting factor (step S42).

  Subsequently, the entropy decoding unit 801A next decodes the encoded data to decode an unsigned 8-bit code indicating the difference value of the weighting factors (step S43).

  Subsequently, the index reconstructing unit 801B derives the reference value (1 << LWD) of the weighting factor using the derived fixed-point precision LWD (step S44).

  Subsequently, the index reconstructing unit 801B restores the unsigned 8-bit code into a signed 9-bit difference value by using the derived reference value (1 << LWD) of the weighting coefficient (step S45). Here, the value below the reference value is left unchanged from the decoded data, and the difference value is restored by connecting the code above the reference value to the negative side. As described above, the difference value of the restored weighting factor is derived, and the weighting factor is restored by the mathematical expression (15).

  As described above, in the modified example 5 of the second embodiment, by performing the wrap processing on the signed 9-bit value, it is possible to always encode the unsigned 8-bit value. There is no need to have hardware such as an encoding unit.

(Modification 6)
In the first and second embodiments, an example is described in which a frame is divided into rectangular blocks having a size of 16 × 16 pixels, and encoding / decoding is performed in order from the upper left block to the lower right. 2A). However, the encoding order and the decoding order are not limited to this example. For example, the encoding and decoding may be performed sequentially from the lower right side to the upper left side, or the encoding and decoding may be performed so as to draw a spiral from the center of the screen toward the screen edge. Furthermore, encoding and decoding may be performed in order from the upper right to the lower left, or encoding and decoding may be performed so as to draw a spiral from the edge of the screen toward the center of the screen. In this case, since the position of the adjacent pixel block that can be referred to changes depending on the encoding order, it may be changed to an appropriately usable position.

  The first to second embodiments have been described by exemplifying the prediction target block size such as the 4 × 4 pixel block, the 8 × 8 pixel block, and the 16 × 16 pixel block, but the prediction target block is a uniform block. It does not have to be a shape. For example, the prediction target block size may be a 16 × 8 pixel block, an 8 × 16 pixel block, an 8 × 4 pixel block, a 4 × 8 pixel block, or the like. Further, it is not necessary to unify all block sizes in one coding tree block, and a plurality of different block sizes may be mixed. When a plurality of different block sizes are mixed in one coding tree block, the code amount for coding or decoding the division information increases as the number of divisions increases. Therefore, it is desirable to select the block size in consideration of the balance between the code amount of the division information and the locally decoded image or the quality of the decoded image.

  In the first and second embodiments described above, for simplification, there is a part in which a comprehensive description is described regarding the color signal component without distinguishing between the prediction process and the selection range deriving method for the luminance signal and the color difference signal. . However, when the prediction process and the method of deriving the selection range are different between the luminance signal and the color difference signal, the same or different prediction method may be used. If different prediction methods are used between the luminance signal and the chrominance signal, the prediction method selected for the chrominance signal can be encoded or decoded in the same manner as the luminance signal.

  In the first and second embodiments, for simplicity, a comprehensive description has been given regarding the color signal components without distinguishing between the weighted motion compensation prediction processing on the luminance signal and the color difference signal. However, when the weighted motion compensation prediction processing differs between the luminance signal and the color difference signal, the same or different weighted motion compensation prediction processing may be used. If different weighted motion compensation prediction processes are used between the luminance signal and the color difference signal, the selected weighted motion compensation prediction process for the color difference signal can be encoded or decoded in the same manner as the luminance signal.

  In the first and second embodiments, syntax elements not defined in the present embodiment can be inserted between the rows of the table shown in the syntax configuration, and descriptions about other conditional branches are included. It does not matter. Alternatively, the syntax table can be divided into a plurality of tables and integrated. Further, it is not always necessary to use the same term, and the term may be arbitrarily changed depending on the form used.

  As described above, each embodiment and each modified example define a range of values that syntax elements can take when performing weighted motion compensation prediction, and set the accompanying value range within a predetermined bit precision range. By setting it and giving a short code length to a value that is frequently used, a highly efficient weighted motion compensation prediction process can be performed while solving the problem of encoding redundant information of syntax elements. To be realized. Therefore, according to each embodiment and each modification, the coding efficiency is improved and the subjective image quality is also improved.

  Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto.

  For example, a program that implements the processing of each of the above embodiments may be stored in a computer-readable storage medium and provided. The storage medium may be a computer-readable storage medium that can store a program, such as a magnetic disk, an optical disk (CD-ROM, CD-R, DVD, etc.), a magneto-optical disk (MO, etc.), a semiconductor memory, etc. The storage format may be any format.

  Further, a program for realizing the processing of each of the above embodiments may be stored on a computer (server) connected to a network such as the Internet, and downloaded to a computer (client) via the network.

REFERENCE SIGNS LIST 100 Encoding device 101 Subtraction unit 102 Orthogonal transformation unit 103 Quantization unit 104 Inverse quantization unit 105 Inverse orthogonal transformation unit 106 Addition unit 107 Predicted image generation unit 108 Index setting unit 109 Motion evaluation unit 110 Encoding unit 110A Entropy encoding unit 110B Index Reconstruction Unit 111 Encoding Control Unit 201 Multiple Frame Motion Compensation Unit 202 Memory 203 Unidirectional Motion Compensation Unit 204 Prediction Parameter Control Unit 205 Reference Image Selector 206 Frame Memory 207 Reference Image Control Unit 301 Default Motion Compensation Unit 302 Weighted Motion Compensation unit 303 WP parameter control unit 304, 305 WP selector 800 Decoding device 801 Decoding unit 801A Entropy decoding unit 801B Index reconstructing unit 802 Inverse quantization unit 803 Inverse orthogonal transform unit 804 Calculation unit 805 predicted image generator 806 index setting unit 807 the decoding control unit

Claims (2)

Encoding a first fixed point precision of luminance weighting factors used in weighted motion compensated prediction for an image;
Encoding a first difference value that is the same value as the difference between the first fixed-point precision and the second fixed-point precision of the color difference weighting coefficient used in the weighted motion compensation prediction;
The same value as the difference between the first reference value, which is the same value as the value obtained by left-shifting “1” by the number of bits determined by the first fixed-point precision, and the luminance weighting coefficient. Encoding the second difference value of the luminance weighting coefficient, which is a value that can take a range from -128 to +127 regardless of the first fixed point precision.
An encoding method including: Decoding a first fixed point precision of the luminance weighting factors used in the weighted motion compensated prediction for the image;
Decoding a first difference value that is the same value as the difference between the first fixed-point precision and the second fixed-point precision of the color difference weighting coefficient used in the weighted motion compensation prediction;
Determining the second fixed-point accuracy by adding the first fixed-point accuracy and the first difference value;
Determining the same value as the value obtained by left-shifting "1" by the number of bits determined by the first fixed-point precision as the first reference value of the luminance weighting factor;
Of the luminance weighting factor, which is the same value as the difference between the luminance weighting factor and the first reference value and can take a range of −128 to +127 regardless of the first fixed point precision. Decoding the second difference value;
Determining the weighting coefficient of the brightness by adding the first reference value and the second difference value;
A decoding method including: