JP2017168985A - Encoding device and encoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoding device and an encoding method that can suppress buffer underflow with small processing amount.SOLUTION: An encoding device according to an embodiment is an encoding device that performs variable length encoding on a quantization value quantized on the basis of a quantization parameter of an input signal, the encoding device comprising a selection unit, an acquisition unit, a determination unit, a quantization unit, and an encoding unit. The selection unit selects a variable length encoding table of 1 on the basis of a characteristic of the input signal. The acquisition unit acquires a constant term of an equation which makes a function of a value based on the maximum code amount for any quantization parameter for the selected variable length encoding table as a reference code amount. The determination unit determines the quantization parameter on the basis of the reference code amount and an allocation code amount obtained by an occupied code amount. The quantization unit obtains a quantization value by quantizing using the quantization parameter. The encoding unit selects the variable length encoding table of 1 on the basis of the quantization parameter, and performs variable length encoding on the quantization value.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to an encoding device and an encoding method.

  For example, when transmitting various signals such as images, audio, video, sensor data, and other one-dimensional or multi-dimensional digital signals, generally, if the amount of signal information is larger than the communication capacity of a predetermined transmission path, By encoding these signals, transmission is performed while reducing the amount of information. In this case, as a coding method, for example, various processes such as predictive coding, transform coding, quantization, or variable length coding, or a process using any two or more of these is generally used. Among these, when the variable length coding method is used, the amount of code generated when a predetermined processing unit is coded may not be constant. In this case, a configuration is generally used in which a reception buffer is provided in the preceding stage of the decoding device, and an encoded signal (code) input from the encoding device via a transmission path is temporarily stored. In such a configuration, a reception buffer having a sufficiently large capacity with respect to the fluctuation range of the code amount of the code output from the encoding device is prepared, and the code amount of the code accumulated in the reception buffer is equal to the capacity of the reception buffer. Decoding processing is started after accumulation to a predetermined ratio. As a result, it is possible to suppress a situation in which the code accumulated in the reception buffer is insufficient, that is, the occurrence of buffer underflow, at the timing when the decoding apparatus starts decoding.

  In general, when the capacity of the reception buffer increases, buffer underflow can be suppressed even if the fluctuation range of the code amount of the code output from the encoding apparatus increases. On the other hand, since the time (initial delay time) until the reception buffer is first stored up to a predetermined ratio of the capacity becomes long, there is a problem that the delay time of the entire transmission system becomes large. Therefore, from the viewpoint of the initial delay time, the capacity of the reception buffer is desirably as small as possible.

  Based on the above viewpoint, as a method of suppressing the occurrence of buffer underflow while reducing the capacity of the reception buffer, the fluctuation amount of the code amount is controlled by controlling the code amount output by the encoding device, and the occurrence of buffer underflow. There are known ways to prevent this. As an example of such a method, for example, in video encoding, a method of encoding a frame group to be encoded twice is known. In this method, the amount of code output is controlled by determining the quantization parameter used in the second encoding using the statistical values collected in the first encoding, and the occurrence of buffer underflow is suppressed. Yes. As another example of the method, when the amount of code when a certain processing unit is encoded exceeds the allocated amount of code, the generated amount of code is suppressed by skipping the encoding of the portion that exceeded the amount. Is also known.

  However, the above-described method of encoding the frame group twice has a problem that the amount of processing required for the encoding process is large because the encoding process needs to be performed twice. Also, since encoding is performed by determining the quantization parameter based on the estimated value of the code amount, there is a possibility that a divergence may occur between the estimated value and the actually generated code amount. If it is small, there is a possibility that the occurrence of buffer underflow cannot be suppressed.

  In addition, in the method of suppressing the generated code amount by skipping the above-described encoding, there is a problem that the quality of the decoded signal is greatly deteriorated in the portion where the encoding is skipped.

Japanese Patent No. 5096342 JP 2001-169281 A

  The present invention has been made in view of the above, and an object of the present invention is to provide an encoding device and an encoding method that can suppress buffer underflow with a small amount of processing.

  An encoding apparatus according to an embodiment is an encoding apparatus that performs variable length encoding on a quantized value obtained by quantizing an input signal based on a quantization parameter, and includes a selection unit, an acquisition unit, a determination unit, A quantization unit and an encoding unit. The selection unit selects one variable length coding table based on the characteristics of the input signal. The acquisition unit acquires, as the reference code amount, a constant term of an expression obtained by functionalizing a value based on the maximum code amount for an arbitrary quantization parameter for the selected variable length encoding table. The determination unit determines the quantization parameter based on the reference code amount and the allocated code amount obtained from the occupied code amount. The quantization unit quantizes the input signal using the quantization parameter to obtain a quantization value. The encoding unit selects one variable length encoding table based on the quantization parameter, and performs variable length encoding on the quantized value.

It is a figure which shows an example of the whole structure of the transmission system which concerns on 1st Embodiment. It is a figure which shows an example of the hardware constitutions of the encoding apparatus which concerns on 1st Embodiment. It is a figure which shows an example of the block configuration of the encoding apparatus which concerns on 1st Embodiment. It is a figure explaining control of the occupation code amount of a receiving buffer. It is a figure which shows an example of the graph which shows the worst code amount with respect to each quantization parameter. It is a flowchart which shows an example of the encoding process of the encoding apparatus which concerns on 1st Embodiment. It is a figure which shows an example of the block configuration of the encoding apparatus which concerns on 2nd Embodiment.

  Hereinafter, an encoding device and an encoding method according to each embodiment of the present invention will be described in detail with reference to the drawings. However, since the drawings are schematic, a specific configuration should be determined in consideration of the following description.

(First embodiment)
FIG. 1 is a diagram illustrating an example of the overall configuration of the transmission system according to the first embodiment. The overall configuration of the transmission system 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the transmission system 1 according to the present embodiment includes an encoding device 10, a decoding device 20, and a reception buffer 30. A signal (a code stream described later) output from the encoding device 10 is accumulated in the reception buffer 30 via the network 40. The transmission path transmitted from the encoding apparatus 10 to the reception buffer 30 is not limited to a wired transmission path such as the network 40, and a signal is transmitted from the encoding apparatus 10 to the network 40 by wireless communication. It is good also as a thing. In addition, the configuration of the transmission system 1 illustrated in FIG. 1 illustrates a configuration in which the decoding device 20 and the reception buffer 30 are separate from each other. However, the configuration is not limited thereto. May include the reception buffer 30, and the reception buffer 30 may be arranged before the decoding process by the decoding device 20.

  The encoding device 10 is a device that encodes an input signal input from the outside and outputs the code to the outside (for example, the network 40). Specifically, the encoding device 10 quantizes the input signal, performs variable length encoding on the quantized value that is the quantized signal, and outputs the result.

  Here, examples of the input signal include voice, image, video, three-dimensional volume data, output signals from various sensors (one-dimensional or multi-dimensional signals), and transmission signals (baseband signals) in a wireless or wired transmission path. Etc. Note that the input signal is not limited to any of the above signals. For example, various signals having a small entropy with respect to the number of input bits, or a signal whose entropy has been reduced by predictive coding or transform coding described later. May be used as an input signal.

  For example, as a preprocessing for the input signal, the encoding apparatus 10 predicts the input signal based on adjacent samples, obtains a difference value (prediction residual) from the predicted value (prediction process), and inputs the prediction residual. The signal may be quantized and variable-length coded (so-called predictive coding). For example, in the case of an output signal from a temperature sensor or the like, it is highly possible that signals that are close in time have similar values, and the amount of information (entropy) can be reduced by prediction processing.

  Also, the encoding device 10 performs a conversion process such as discrete Fourier transform, discrete cosine transform, or discrete wavelet transform on the input signal or the above-described prediction residual, and the converted signal is quantized and variable as an input signal. Long coding may be used (so-called transform coding). For example, in an image signal, particularly a natural image, the signal tends to concentrate in a region having a low spatial frequency. By performing frequency conversion processing, it is possible to reduce entropy in a region having a high spatial frequency. In the case of an image signal, a method for further reducing entropy with higher efficiency by using a combination of prediction processing and conversion processing is generally known.

  In this way, entropy is reduced by performing appropriate prediction processing or conversion processing according to the input signal, and highly efficient coding is realized by variable-length coding this signal (or its quantized value). The In the present embodiment, for the sake of convenience, an encoding device that assumes an input signal (for example, a prediction residual) having a low entropy with respect to the number of input bits and outputs the signal after quantization and variable length encoding will be described.

  The decoding device 20 is a device that subtracts a predetermined unit of code at a decoding timing every predetermined time from the reception buffer 30 in which the encoded signal output from the encoding device 10 is accumulated, and decodes the extracted code. is there.

  The reception buffer 30 is a storage device that accumulates the encoded signal output from the encoding device 10 at a constant rate. In addition, the reception buffer 30 is arranged in the preceding stage of the decoding function of the decoding device 20, and a predetermined unit of code is pulled out for decoding by the decoding device 20 at a decoding timing every predetermined time.

  The network 40 is a wireless or wired transmission path that connects the encoding device 10 and the reception buffer 30.

  FIG. 2 is a diagram illustrating an example of a hardware configuration of the encoding device according to the first embodiment. A hardware configuration of the encoding apparatus 10 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 2, the encoding apparatus 10 according to the present embodiment includes an input I / F 501, an encoding processor 502, a cache 502a, a RAM (Random Access Memory) 503, an output I / F 504, and an auxiliary device. A storage device 505. The input I / F 501, the encoding processor 502, the RAM 503, the output I / F 504, and the auxiliary storage device 505 are connected to each other via a bus 506 such as an address bus and a data bus.

  The input I / F 501 is an interface for inputting an input signal from the outside.

  The encoding processor 502 is an arithmetic device that controls the overall operation of the encoding device 10 shown in FIG. The encoding processor 502 executes an encoding process.

  The cache 502a is a memory that temporarily stores data when the encoding processor 502 performs processing as a work area.

  The RAM 503 is a volatile storage device that temporarily stores a code stream or the like generated by the encoding process of the encoding processor 502. The RAM 503 is, for example, an SRAM (Static RAM) or a DRAM (Dynamic RAM).

  The output I / F 504 is an interface for outputting the code stream generated by the encoding process of the encoding processor 502 to the outside.

  The auxiliary storage device 505 is a storage device that stores a variable-length coding table and the like to be described later. The auxiliary storage device 505 is a storage device capable of electrical, magnetic, or optical storage such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), a flash memory, or an optical disk. The auxiliary storage device 505 is included in the encoding device 10, but is not limited thereto, and may be installed outside the encoding device 10, and in this case, the auxiliary storage device The data stored in 505 may be communicated with the encoding device 10 via the interface. Further, the information stored in the auxiliary storage device 505 described above may be incorporated as a processing method (logic circuit or program) instead of being stored in the auxiliary storage device 505.

  Note that the hardware configuration of the encoding device 10 illustrated in FIG. 2 is an example, and may be realized by other configurations.

  FIG. 3 is a diagram illustrating an example of a block configuration of the encoding device according to the first embodiment. FIG. 4 is a diagram for explaining control of the occupied code amount of the reception buffer. The block configuration and operation of the encoding apparatus 10 according to this embodiment will be described with reference to FIGS.

  As illustrated in FIG. 3, the encoding device 10 according to the present embodiment includes a table selection unit 101 (selection unit), a code amount acquisition unit 102 (acquisition unit), a parameter determination unit 103 (determination unit), a quantum A coding unit 104, a coding unit 105, a code amount control unit 106, and a storage unit 107.

  The table selection unit 101 receives an input signal from the outside and, based on the characteristics of the input signal for each predetermined processing unit, from one or more variable length coding tables stored in advance in the storage unit 107, This is a functional unit that selects one variable length coding table. Here, the characteristics of the input signal may be, for example, the absolute value sum or variance of the signal values of the input signal. The variable length coding table is a table for converting (variable length coding) an input signal into a known code such as a Golomb-Rice code or an exponential Golomb code. The table selection unit 101 is a variable length coding table that reduces the code amount when variable length coding is performed on an input signal from one or more variable length coding tables stored in advance in the storage unit 107. select. For example, in the case of a variable-length coding table of Golomb-Rice codes, the table selection unit 101, when the variance of the input signal is small, is a variable-length code having a short suffix length that is a parameter for specifying the variable-length coding table of Golo-Mrice codes By selecting a coding table, it is possible to reduce the amount of code when coding is performed using the variable length coding table. On the other hand, when the variance of the input signal is large, the table selection unit 101 selects a variable length coding table having a long suffix length, thereby reducing the amount of codes when coding is performed using the variable length coding table. I can do it.

  The table selection unit 101 sends information indicating the selected variable-length coding table (hereinafter sometimes referred to as a table index) to the code amount acquisition unit 102 and the coding unit 105, respectively. For example, in the case of a variable length coding table of Golomb-Rice codes, the suffix length may be used as a table index. The table selection unit 101 is realized by the encoding processor 502 shown in FIG.

  Note that a correspondence relationship between the characteristics (absolute value sum or variance) of the input signal and the variable-length coding table is determined in advance, and information (for example, a mathematical expression or a lookup table) that defines the correspondence relationship is stored in the storage unit 107. The table selection unit 101 may select the variable-length coding table by referring to the information defining the correspondence relationship. For example, in the case of the Golomb-Rice code, since the absolute value sum of the input signal and the suffix length are in a logarithmic relationship, the table selection unit 101 uses the mathematical formula for calculating the suffix length from the absolute value sum as information defining the correspondence relationship. And the variable length coding table may be selected based on the suffix length calculated from the characteristic value (absolute value sum).

  In the above description, one or more variable-length coding tables are stored in the storage unit 107 in advance. However, the present invention is not limited to this, and the table selection unit 101 determines the input signal as a characteristic (absolute value). Based on the appearance frequency of the input signal classified into each group, a variable length coding table for coding into a specific code (for example, Huffman code) may be created. . This makes it possible to create a variable-length coding table that is optimal for the input signal, and to realize highly efficient coding. In the above description, the one or more variable length coding tables are stored in the storage unit 107 in advance. However, the present invention is not limited to this, and one or more variable length coding processing methods are prepared in advance. You may keep it. For example, in the case of a Golomb-Rice code, variable length coding can be performed by calculating each parameter of a prefix length and a suffix value from an input signal and constructing a variable length code based on these values. When using a variable-length encoding method that can be defined as the predetermined arithmetic processing in this way, instead of storing the variable-length encoding table in the storage unit 107 by preparing this arithmetic logic in the encoding device. It can be.

  In the above description, the sum of absolute values and the variance are exemplified as the characteristics of the input signal. However, the present invention is not limited to these, and the average value of the input signal may be used as the characteristics of the input signal. In general, when predictive coding is performed on speech or an image, the predicted signal tends to be distributed around 0. However, when an input signal that is distributed around the center other than 0 is input to the encoding device 10, the variable length encoding table is selected based on the average value of the input signal, so that higher efficiency can be achieved. Encoding may be realized.

  The table selection unit 101 selects one variable length coding table from one or more variable length coding tables stored in the storage unit 107 based on the characteristics of the input signal. The variable length coding table stored in the storage unit 107 is not limited, and may be a single table. When the characteristics of the input signal hardly change, even if a single variable length coding table is used, highly efficient coding may be performed. In this case, since it is not necessary to select one variable length coding table from one or more variable length coding tables, the encoding device 10 does not need to have the table selection unit 101. In this case, the code amount acquisition unit 102 and the encoding unit 105 may perform the processing described later on the assumption that this single variable-length encoding table is selected.

  The code amount acquisition unit 102 is a functional unit that receives a table index from the table selection unit 101 and acquires a reference code amount based on the table index. The reference code amount acquisition method by the code amount acquisition unit 102 will be described later. The code amount acquisition unit 102 sends the acquired reference code amount to the parameter determination unit 103. The code amount acquisition unit 102 is realized by the encoding processor 502 shown in FIG.

  The parameter determination unit 103 is a functional unit that receives the reference code amount from the code amount acquisition unit 102, receives the assigned code amount from the code amount control unit 106, and determines the quantization parameter based on the reference code amount and the assigned code amount. is there. A method for determining the quantization parameter by the parameter determination unit 103 will be described later. The parameter determination unit 103 sends the determined quantization parameter to the quantization unit 104 and the encoding unit 105, respectively. The parameter determination unit 103 is realized by the encoding processor 502 shown in FIG.

  The quantization unit 104 is a functional unit that receives an input signal from the outside, receives a quantization parameter from the parameter determination unit 103, quantizes the input signal with the quantization parameter, and obtains a quantization value. For example, the quantization unit 104 performs quantization based on the following equation (1).

x1 = round (x0 / 2 ^q ) (1)

In the above equation (1), x0 represents an input signal, x1 represents a quantized value, and q represents a quantization parameter. In addition, round () indicates a function that rounds off after the decimal point. By performing the process using the function round (), it is possible to reduce the error of the decoded signal when decoding the code encoded by the decoding device 20 as compared with the case where rounding is not performed. Further, since the quantized value quantized by the above equation (1) becomes small according to the quantization width (2 ^{q in the} equation (1)), the dispersion becomes small. The quantization unit 104 sends the quantized value obtained by the quantization to the encoding unit 105. The quantization unit 104 is realized by the encoding processor 502 shown in FIG.

  Note that the quantization unit 104 is not limited to performing quantization using the above equation (1), and may perform quantization based on other methods. For example, H.M. Processing similar to quantization in H.264 / MPEG-4 AVC (Advanced Video Coding) may be performed.

  The encoding unit 105 receives a table index from the table selection unit 101, receives a quantization parameter from the parameter determination unit 103, receives a quantization value from the quantization unit 104, and performs variable length encoding on the quantization value. It is a functional part. Specifically, the encoding unit 105 selects one variable length encoding table from one or more variable length encoding tables stored in the storage unit 107 based on the table index and the quantization parameter. Then, the variable length coding is performed on the quantized value by the variable length coding table. As described above, since the quantized value becomes smaller in accordance with the quantization width, the variance becomes smaller. Therefore, the encoding unit 105 uses the variable length code corresponding to the quantized value whose variance is smaller than that of the input signal. By performing variable length encoding using the conversion table, the amount of generated code can be reduced.

  Here, a case where quantization is performed using the above-described equation (1) and a variable length coding table of Golomb-Rice codes is used will be considered. Further, as described above, the suffix length of the Golomb-Rice code is considered as a table index of the variable length coding table. The encoding unit 105 does not perform quantization on the variable-length encoding table selected by the table selection unit 101 described above. That is, for example, in the equation (1), it is optimal when the quantization parameter q = 0. Therefore, when the received quantization parameter q is “0”, variable length coding may be performed using the variable length coding table selected by the table selection unit 101. Further, when the quantization parameter q determined by the parameter determination unit 103 is “1”, according to the above equation (1), the quantized value is approximately ½ of the input signal, and thus the variance is A variable-length coding table corresponding to a 1/2 signal (quantized value) is optimal. In the case of the variable length coding table of the Golomb-Rice code, this corresponds to a variable length coding table whose suffix length is 1 smaller. From this, assuming that the table index of the variable-length coding table selected by the table selection unit 101 is k, the coding unit 105 stores the Golomb-Rice code stored in the storage unit 107 and having a suffix length kq. Variable length encoding may be performed using a variable length encoding table. Since the suffix length of the Golomb-Rice code is greater than or equal to 0, for example, when k-q is less than 0, the encoding unit 105 is variable using the variable-length encoding table of the Golomb-Rice code with a suffix length of 0. What is necessary is just to perform long encoding. For example, when quantization is performed by a method other than Equation (1), a variable-length coding table corresponding to the degree of change in variance corresponding to each quantization parameter may be selected as described above.

  Note that when variable length coding is performed using the variable length coding table of the Huffman code, the variable length coding table may be selected and encoded by the same method. When using a variable length coding table of Huffman codes, a table corresponding to a plurality of characteristic values (absolute value sum or variance of signals) is prepared in advance, and the table selection unit 101 selects one of them. Similar to the case of using the variable length coding table of the Golomb-Rice code, the encoding unit 105 distributes the quantized value (or the absolute value) based on the table index of the variable length coding table of the Huffman code and the quantization parameter. Sum) is obtained, and variable length coding may be performed on the quantized value using a variable length coding table corresponding to or closest to this. The Huffman code variable-length coding table used here may be created in advance based on the frequency of appearance of signals classified for each variance or absolute value sum.

  Also, for example, when performing variable-length encoding using a variable-length encoding table that assumes an unsigned integer such as a Golomb-Rice code, and when the quantized value is a signed integer, the encoding unit 105 is: It is also possible to perform variable length coding after converting the quantized value to an unsigned integer according to equation (2).

x2 = −2 · x1 (if x1 ≦ 0)
x2 = 2 · x1 + 1 (if x1> 0) (2)

  In the above equation (2), x1 represents a signed quantized value, and x2 represents a value converted to an unsigned integer. Instead of performing the conversion according to the above equation (2), the code bit may be separately encoded, and the absolute value of the quantized value may be subjected to variable length encoding using the variable length encoding table of the Golomb-Rice code.

  The encoding unit 105 also encodes the table index and the quantization parameter for use in the decoding process by the decoding device 20. In this case, the table index and the quantization parameter may be encoded with a fixed length by, for example, a predetermined number of bits, or may be variable length encoded using a predetermined variable length encoding table. Also good. The table index and the quantization parameter may be subjected to predictive encoding. When the characteristics of the table index and the quantization parameter do not change significantly, these values are predicted using values encoded in the past (for example, the values encoded immediately before) (for example, 0th-order prediction or primary prediction). The amount of code generated by encoding the prediction residual can be reduced.

  As described above, the encoding unit 105 encodes the table index, the quantization parameter, and the quantization value, and outputs the encoded code stream to the outside (for example, the network 40 or the like). In addition, the encoding unit 105 sends the code amount (generated code amount) of the encoded code to the code amount control unit 106. The encoding unit 105 is realized by the encoding processor 502 shown in FIG.

  The code amount control unit 106 is a functional unit that receives the generated code amount from the encoding unit 105 and sets the assigned code amount. The code amount control unit 106 models the amount of code occupied in the reception buffer 30 (hereinafter referred to as the occupied code amount), and the generated code amount in the encoding unit 105 so that no buffer underflow occurs in the reception buffer 30. The assigned code amount is set so that

  For example, the code amount control unit 106 may be a VBV (Video Buffer Verifier) in MPEG-2 or M.264. An allocation code amount that does not cause buffer underflow in the reception buffer 30 may be set by performing modeling that is the same as or similar to a buffer model such as HRD (Hypothetical Reference Decoder) in H.264 / MPEG-4 AVC.

  Specifically, for example, the occupation code amount of the reception buffer 30 as shown in FIG. 4 may be modeled. In FIG. 4, the vertical axis represents the code amount occupied by the reception buffer 30 (occupied code amount), and the horizontal axis represents time. As shown in FIG. 4, the reception buffer 30 is in a state where the occupied code amount is “0” in the initial state, and from this, the code output from the encoding device 10 at a constant bit rate is accumulated. Thereafter, when a predetermined initial delay time elapses, the decoding device 20 starts decoding, and a code corresponding to the code amount in the first processing unit is pulled out of the reception buffer 30 by the decoding device 20. Thereafter, the accumulation of the code output from the encoding device 10 and the removal of the code by the decoding device 20 are repeated for each predetermined processing unit. In the model shown in FIG. 4, a buffer underflow occurs when the occupied code amount falls below “0”. That is, in each processing unit, a buffer underflow occurs when the code amount (generated code amount) of the code output from the encoding unit 105 is larger than the occupied code amount at the timing of code removal by the decoding device 20. .

  Therefore, the code amount control unit 106 sets a code amount that is the same as or smaller than the occupied code amount at the timing of code removal in each processing unit as the assigned code amount. The encoding device 10 can suppress the occurrence of buffer underflow by performing variable length encoding on the quantized value of an input signal in a certain processing unit so that the code amount is smaller than the allocated code amount. It becomes. Here, the allocated code amount may be set as the same code amount as the occupied code amount at the time of code removal in each processing unit, but is not limited thereto, and the code amount smaller than this May be set as

  Further, when the amount of code occupied by the reception buffer 30 is greater than a certain value, that is, when there is a margin in the amount of code that can be generated by the encoding unit 105, this margin is consumed at a time in a certain processing unit. If the margin is divided by a plurality of subsequent processing units, the generated code amount is more stable. From this, it is possible to stabilize the quality of the signal decoded by the decoding device 20 by setting the code amount smaller than the occupied code amount as the assigned code amount, particularly when the occupied code amount is large. .

  The code amount control unit 106 sends the set assigned code amount to the parameter determination unit 103. The code amount control unit 106 is realized by the encoding processor 502 shown in FIG.

  The storage unit 107 is a functional unit that stores one or more variable-length encoding tables and the like that are referenced by the table selection unit 101 and the encoding unit 105. The storage unit 107 is realized by the auxiliary storage device 505 illustrated in FIG.

  The table selection unit 101, the code amount acquisition unit 102, the parameter determination unit 103, the quantization unit 104, the encoding unit 105, the code amount control unit 106, and the storage unit 107 illustrated in FIG. It is shown and it is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in FIG. 3 may be configured as one functional unit. On the other hand, the function of one functional unit in FIG. 3 may be divided into a plurality of units and configured as a plurality of functional units.

  Also, the table selection unit 101, the code amount acquisition unit 102, the parameter determination unit 103, the quantization unit 104, the encoding unit 105, and the code amount control unit 106 illustrated in FIG. However, the present invention is not limited to this. That is, a program stored in a storage medium such as a storage device (for example, the auxiliary storage device 505 shown in FIG. 2) is executed by a CPU (Central Processing Unit) at least one of the functional units described above. It is good also as what is realized by.

  FIG. 5 is a diagram illustrating an example of a graph indicating the worst code amount for each quantization parameter. Details of the reference code amount acquisition method by the code amount acquisition unit 102 and the quantization parameter determination method by the parameter determination unit 103 will be described with reference to FIGS.

  As described above, the table selection unit 101 is a variable length code that reduces the amount of code when variable length coding is performed on an input signal based on the absolute value sum or variance of the input signal received from the outside. Select a conversion table. In other words, when a variable length coding table indicated by a certain table index is given, possible values of the corresponding input signal are limited to a certain finite range. For example, when a variable length coding table is a table corresponding to the sum of absolute values of input signals ≦ 128, if this variable length coding table is given, the values that can be taken by the input signal in the processing unit are the absolute values. It is limited to an arbitrary numerical value group whose value sum is 128 or less (an arbitrary integer when the input signal is an integer value). If the input signals are limited, it is possible to obtain the generated code amount when these input signals are encoded by the corresponding variable length encoding table. For example, this variable length encoding can be performed by a brute force method or the like. The maximum code amount when the input signal is encoded by the table can be acquired. This acquired code amount is the maximum code amount when quantization is not performed, but the maximum code amount when encoded can be acquired in the same manner for the quantized value. is there. This maximum code amount may be acquired in advance.

  When the quantization parameter and the quantization width are in a monotonically increasing relationship, the larger the quantization parameter, the smaller the code amount when the quantized value quantized with the quantization parameter is encoded. For example, when the quantization width is expressed as an exponential function of the quantization parameter as in the above equation (1), the encoded code amount can be approximated by a linear expression for the quantization parameter. This property is the same for the maximum code amount described above. Therefore, as shown in FIG. 5, the maximum code amount is modeled in advance by a linear expression. Specifically, when encoding is performed using a variable-length encoding table indicated by a certain table index, the maximum code amount when an arbitrary quantization parameter is used is acquired (for example, by brute force), and FIG. As shown, a linear expression exceeding all of these maximum code amounts is set (the following expression (3)).

WB = C ₁ xq + C ₂ (C ₁ <0, C ₂ > 0) (3)

In the above equation (3), C ₁ is the slope of the linear equation and is a negative value because the amount of code decreases as the quantization parameter q increases. C ₂ is an intercept of a linear expression. WB indicates a code amount calculated by a linear expression, and is hereinafter referred to as a worst code amount. That is, Expression (3) is a linear expression indicating the worst code amount for each quantization parameter.

For each table index, the slope C ₁ and the intercept C ₂ of the linear expression shown in the above equation (3) are acquired in advance. That is, when the table index is determined, a linear expression indicating the worst code amount is determined. Thereby, the worst code amount for a specific quantization parameter can be easily calculated for each table index. Further, the information on the correspondence between the table index and the linear expression indicating the worst code amount (that is, the gradient C ₁ and the intercept C ₂ ) may be stored in the storage unit 107 in advance, for example. Then, code amount obtaining unit 102 refers to the storage unit 107 to identify the primary expression showing the worst amount of codes corresponding to the table index received from the table selection unit 101, for example, sections C ₂ of the linear expression And obtained as a reference code amount. Incidentally, may be common between the table index for the slope C ₁ of the primary type, this case may be previously stored only sections C ₂ each table index.

  The parameter determination unit 103 identifies a primary expression indicating the worst code amount having the reference code amount acquired by the code amount acquisition unit 102, so that the worst code amount does not exceed the allocated code amount received from the code amount control unit 106. Determine the quantization parameter. As a result, the occurrence of buffer underflow in the reception buffer 30 can be suppressed. Specifically, since the worst code amount WB is modeled by the above equation (3), the following equation (4) only needs to be satisfied for the allocated code amount B.

B ≧ C ₁ xq + C ₂ (4)

  Further, when the quantization parameter q is arranged from the equation (4), the following equation (5) is obtained.

q ≧ (B−C ₂ ) / C ₁ (5)

  The parameter determination unit 103 only needs to determine the quantization parameter q that satisfies the equation (5). For example, the parameter determination unit 103 determines the minimum quantization parameter q that satisfies the equation (5) and sends the determined quantization parameter q to the quantization unit 104. For the purpose of stabilizing the quality of the decoded signal of the decoding apparatus 20, in order to suppress the fluctuation of the quantization parameter q, a value similar to the previous quantization parameter is quantized within a range that satisfies the above-described equation (5). It may be determined as a parameter.

  The primary expression indicating the worst code amount shown in the above equation (3) is set to a linear expression exceeding all of the maximum code amounts corresponding to each quantization parameter, as shown in FIG. However, the present invention is not limited to this. For example, it is a graph that connects two points of the maximum code amount corresponding to each quantization parameter, and is set to a linear expression indicating a graph in which the absolute value sum of the difference between the other maximum code amount and the difference is minimum. Also good. Further, the graph represented by the linear equation set as described above may be a linear equation indicating a graph in which the intercept is shifted within a predetermined range (for example, a range of 1 to 2 times the intercept of the original graph). .

  FIG. 6 is a flowchart illustrating an example of the encoding process of the encoding device according to the first embodiment. With reference to FIG. 6, the flow of the encoding process of the encoding apparatus 10 according to the present embodiment will be generally described.

<Step S11>
The table selection unit 101 receives an input signal from the outside. Then, the process proceeds to step S12.

<Step S12>
The table selection unit 101 has one or more variables stored in advance in the storage unit 107 on the basis of the characteristics of the input signal (for example, the absolute value sum or variance of the signal values of the input signal) for each predetermined processing unit. One variable length coding table is selected from the long coding table. The table selection unit 101 sends information indicating the selected variable-length coding table (hereinafter sometimes referred to as a table index) to the code amount acquisition unit 102 and the coding unit 105, respectively. Then, the process proceeds to step S13.

<Step S13>
The code amount acquisition unit 102 receives a table index from the table selection unit 101, and acquires a reference code amount based on the table index. Specifically, the code amount acquisition unit 102 refers to the storage unit 107, identifies a primary expression indicating the worst code amount corresponding to the table index received from the table selection unit 101, and, for example, an intercept of the primary expression the C _2, to obtain as the reference code amount. The code amount acquisition unit 102 sends the acquired reference code amount to the parameter determination unit 103. Then, the process proceeds to step S14.

<Step S14>
The parameter determination unit 103 receives the reference code amount from the code amount acquisition unit 102, receives the assigned code amount from the code amount control unit 106, and determines the quantization parameter based on the reference code amount and the assigned code amount. Specifically, the parameter determination unit 103 specifies a primary expression indicating the worst code amount having the reference code amount acquired by the code amount acquisition unit 102, and the assigned code received by the worst code amount from the code amount control unit 106 The quantization parameter is determined so as not to exceed the amount. The parameter determination unit 103 sends the determined quantization parameter to the quantization unit 104 and the encoding unit 105, respectively. Then, the process proceeds to step S15.

<Step S15>
The quantization unit 104 receives an input signal from the outside, receives a quantization parameter from the parameter determination unit 103, quantizes the input signal with the quantization parameter, and obtains a quantization value. The quantization unit 104 sends the quantized value obtained by the quantization to the encoding unit 105. Then, the process proceeds to step S16.

<Step S16>
The encoding unit 105 receives a table index from the table selection unit 101, receives a quantization parameter from the parameter determination unit 103, receives a quantization value from the quantization unit 104, and performs variable length encoding on the quantization value. . For example, assuming that the table index of the variable length coding table selected by the table selection unit 101 is k, the coding unit 105 stores the variable length of the Golomb-Rice code stored in the storage unit 107 and having a suffix length k−q. Variable length coding is performed using a coding table. Then, the process proceeds to step S17.

<Step S17>
The code amount control unit 106 receives the generated code amount from the encoding unit 105 and sets the allocated code amount. The code amount control unit 106 models the occupied code amount occupied in the reception buffer 30 and assigns the assigned code amount so that the generated code amount in the encoding unit 105 does not cause a buffer underflow in the reception buffer 30. Set.

  As shown in steps S11 to S17 above, the encoding apparatus 10 performs an encoding process on the input signal that has been input.

  As described above, in the encoding device 10 according to the present embodiment, the quantization parameter that becomes the code amount equal to or less than the allocated code amount by modeling the worst code amount for each table index indicating the variable-length encoding table. Can be obtained and encoded with a small amount of processing. As a result, it is possible to realize signal encoding that suppresses the occurrence of buffer underflow in the reception buffer 30 with a small amount of processing. In addition, since occurrence of buffer underflow is suppressed, it is not necessary to include means for avoiding buffer underflow such as skip in the encoding process, thereby reducing local SNR (Signal-to-Noise Ratio). Can be suppressed.

  Note that the encoding unit 105 performs encoding on the table index and the quantization parameter in addition to the quantization as described above. In this case, the parameter determination unit 103 may determine the quantization parameter in consideration of these code amounts. Specifically, for example, when encoding these parameters with a fixed number of bits, the quantization parameter is calculated for each processing unit after adding the number of bits to the right side in the above equation (4). You may go. Alternatively, for example, when predictively encoding a table index and a quantization parameter, the code amount in each value of the table index and the quantization parameter may be calculated for each processing unit and reflected in the above equation (4). Or, more simply, the maximum code amount that can be generated in the case of predictive encoding is obtained in advance, and the quantization parameter may be calculated after adding the maximum code amount.

  Also, the encoding apparatus 10 according to the present embodiment performs encoding using a variable length encoding table corresponding to a signal having a small variance as the quantization parameter increases. However, if the quantization parameter is greater than or equal to a predetermined value, it may be difficult to reduce the code even if the quantization parameter increases. For example, in the case of using the Golomb-Rice code, if the quantization parameter exceeds the suffix length as the table index of the variable length coding table selected by the table selection unit 101, a table with a smaller variance is not prepared. Therefore, even if the quantization parameter is increased, the code is not easily reduced. Therefore, the variable length coding table selected by the table selection unit 101 (that is, the variable length coding table used when quantization is not performed) is a plurality of predetermined variable length coding tables. You may limit to the variable-length encoding table corresponding to a signal with big dispersion | distribution. For example, when using a variable length coding table of Golomb-Rice codes, the table selection unit 101 selects only a variable length coding table whose suffix length is larger than a predetermined value. In this case, the table selection unit 101 selects a suffix length k that is greater than the predetermined value k0. The encoding unit 105 performs encoding using a variable length encoding table with a suffix length kq when the quantization parameter is q, but there is no problem even if kq is less than k0. When the variable length coding table used for coding by the coding unit 105 is not prepared by the selection of the variable length coding table by the table selection unit 101 (that is, k−q <0. The worst code amount can be modeled more accurately.

  Further, when modeling the worst code amount shown in the above equation (3), a linear expression that exceeds all the maximum code amounts corresponding to each quantization parameter is set. However, the worst code amount is not necessarily a straight line. It may not be modeled correctly. In such a case, the maximum code amount corresponding to a part of the quantization parameters may be regarded as an outlier, and modeling may be performed using a linear expression that is less than this. In this case, when a quantization parameter corresponding to the maximum code amount regarded as an outlier is used, a buffer underflow may occur in the reception buffer 30, but other parts are accurately modeled. As a result, the coding efficiency can be improved as a whole. In this case, since it is impossible to completely avoid the occurrence of buffer underflow, when buffer underflow occurs, it is necessary to perform processing such as skipping subsequent encoding. Here, in the portion regarded as the outlier of the above-mentioned worst code amount model, if the protruding portion of the maximum code amount for the model is sufficiently small, the number of insufficient bits when the buffer underflow occurs is sufficiently small (for example, , Several bits). For example, when the encoding unit 105 performs encoding, if the quantization parameter and the table index are encoded first, and then the quantized value is encoded, the portion where the buffer underflow occurs is Since this corresponds to the last few bits of the processing unit, even if a buffer underflow occurs, the influence can be limited to a small part (for example, the last few symbols) in the processing unit. Further, with regard to the quantization value encoding method, if the code information of each quantization value or the information of the upper bit part in the processing unit is first encoded and then the information of the lower bit is encoded, the buffer underflow Therefore, it is possible to prevent the signal from being completely lost and decode it to a certain extent. For example, when a variable length coding table of Golomb-Rice codes is used, encoding may be performed in the order of signal code information, code prefix portion, and suffix portion. In this case, since the range of the absolute value of the decoded signal is limited based on the length of the prefix portion of the code, decoding can be performed with a certain degree of accuracy from this information. Such an encoding method can prevent a significant decrease in SNR when a buffer underflow occurs.

  Further, when a buffer underflow occurs, the encoding unit 105 may perform encoding up to a code amount at which the buffer underflow just occurs in the reception buffer 30 and discard the subsequent codes in the processing unit. Thereafter, the encoding unit 105 restarts encoding from the next processing unit. The decoding device 20 reads all codes in the reception buffer 30 and decodes up to a portion that can be decoded within the processing unit. A signal that cannot be decoded may be replaced with a predetermined value (for example, “0” or the like). Thereafter, the decoding device 20 can read the code from the head of the reception buffer 30 and resume decoding in the next processing unit.

  In addition, with regard to the encoding by the encoding unit 105 described above, the method for suppressing the occurrence of buffer underflow in the reception buffer 30 has been described. However, the occurrence of buffer overflow can also be suppressed by the same or similar method. Is possible. Specifically, the code amount control unit 106 outputs a minimum code amount that does not cause a buffer overflow, instead of the allocated code amount. Instead of the worst code amount, the encoding device 10 models in advance a code amount that is generated at the minimum in each variable-length encoding table for each processing unit. Based on this model, the parameter determination unit 103 sets a quantization parameter based on the table index and the code amount output from the code amount control unit 106. In order to suppress the occurrence of the buffer overflow, the upper limit value of the quantization parameter can be obtained because the mathematical expression in the form obtained by inverting the inequality sign in the above equation (4) can be obtained. Select a parameter. Note that the upper limit value of the quantization parameter may be lower than a predetermined minimum value (for example, “0” in the case of performing the quantization of the above formula (1)). This means that there is still a possibility of buffer overflow. If the amount of code actually generated is insufficient and buffer overflow is likely to occur, adding a surplus code to the end of the code of the processing unit can increase the amount of generated code and suppress the occurrence of buffer overflow Good (so-called bit stuffing process).

  Further, the method for suppressing the occurrence of the buffer overflow described above may be used in combination with the method for suppressing the occurrence of the buffer underflow described above. In this case, the parameter determination unit 103 calculates the upper limit value and the lower limit value of the quantization parameter from the allocated code amount, the minimum code amount, and the table index, and sets the quantization parameter that falls within this range. .

  In the encoding device 10 according to the present embodiment, the table index and the quantization parameter are determined for each processing unit, but are not limited thereto. For example, the quantization parameter may be determined for each first processing unit, and the table index may be selected for each second processing unit that is smaller than the first processing unit. For example, when transform coding is performed, the code variance may be different for each transform coefficient position. In such a case, for example, different table indexes are selected for the first half coefficient (for example, a signal having a low spatial frequency in the case of an image) and the latter half coefficient (for example, a signal having a high spatial frequency in the case of an image). Thus, it is possible to increase the encoding efficiency. In this case, the parameter determination unit 103 models the worst code amount for each second processing unit in the first processing unit so that the sum of the worst code amounts corresponding to the quantization parameter is less than the allocated code amount. The quantization parameter may be set in.

(Second Embodiment)
The encoding apparatus according to the second embodiment will be described focusing on differences from the encoding apparatus 10 according to the first embodiment. In the first embodiment, the operation of performing variable length encoding by selecting a variable length encoding table for each predetermined processing unit has been described. In the present embodiment, an operation of reusing information of the previously selected variable length coding table will be described. Note that the overall configuration of the transmission system according to the present embodiment and the hardware configuration of the encoding device are the same as those described in the first embodiment.

  FIG. 7 is a diagram illustrating an example of a block configuration of an encoding device according to the second embodiment. The block configuration and operation of the encoding device 10a according to this embodiment will be described with reference to FIG.

  As illustrated in FIG. 7, the encoding device 10a according to the present embodiment includes a table selection unit 101a (selection unit), a code amount acquisition unit 102 (acquisition unit), a parameter determination unit 103a (determination unit), a quantum The encoding unit 104, the encoding unit 105 a, the code amount control unit 106, and the storage unit 107. The operations of the code amount acquisition unit 102, the quantization unit 104, the code amount control unit 106, and the storage unit 107 are the same as those described in the first embodiment.

  The table selection unit 101a receives an input signal from the outside and, based on the characteristics of the input signal for each predetermined processing unit, from one or more variable length coding tables stored in advance in the storage unit 107, This is a functional unit that selects one variable length coding table. Note that the method for selecting the variable-length coding table based on the characteristics of the input signal may be the same or similar operation as the table selection unit 101 of the first embodiment. The table selection unit 101a further generates selection information. Here, the selection information indicates which variable-length encoding table is used among the variable-length encoding table selected in the processing unit and the variable-length encoding table selected before (for example, immediately before). Information.

  When the characteristics (such as variance or sum of absolute values) of the input signal are the same as or similar to the previous one, it is necessary to encode the table index in the encoding unit 105a by using the previously selected variable length encoding table. It is possible to reduce the amount of codes. On the other hand, when the characteristics of the input signal are different from the previous ones, the table selection unit 101a can improve the encoding efficiency by selecting a new variable length encoding table.

  The selection information is set by the table selection unit 101a as follows, for example. First, the table selection unit 101a acquires a characteristic value (a variance value or an absolute value sum) of an input signal in order to select a variable length coding table in each processing unit. The table selection unit 101a compares the acquired characteristic value with the characteristic value corresponding to the previously selected variable length coding table, and if the difference is less than a predetermined threshold, the previously selected variable length coding Select the table again. When the difference is larger than the predetermined threshold, the table selection unit 101a newly selects a variable length coding table based on the characteristic value of the input signal in the processing unit. In the characteristic value comparison process, instead of comparing the characteristic values themselves, threshold determination may be performed for the difference between the logarithmic values. In general, the amount of generated code at the time of encoding correlates with the logarithm of the characteristic value, so that it becomes possible to select a variable-length encoding table with high encoding efficiency by performing comparison in this way.

  The table selection unit 101a sends a table index indicating the selected variable-length coding table to each of the code amount acquisition unit 102 and the coding unit 105a, and sends the generated selection information to each of the parameter determination unit 103a and the coding unit 105a. send. The table selection unit 101a is realized by the encoding processor 502 shown in FIG.

  The parameter determination unit 103a is a functional unit that receives a reference code amount from the code amount acquisition unit 102, receives an assigned code amount from the code amount control unit 106, receives selection information from the table selection unit 101a, and determines a quantization parameter. . The parameter determination unit 103a is realized by the encoding processor 502 shown in FIG. The quantization parameter determination method by the parameter determination unit 103a includes the operation of the parameter determination unit 103 according to the first embodiment when the selection information indicates that a variable length coding table is newly selected by the table selection unit 101a. The quantization parameter may be determined by the same or similar method. On the other hand, when the selection information indicates that the previously selected variable length coding table has been selected by the table selection unit 101a, the parameter determination unit 103a determines the quantization parameter by the following operation.

  In the first embodiment, the parameter determination unit 103 specifies the primary expression indicating the worst code amount shown in the above equation (3), which has the reference code amount acquired by the code amount acquisition unit 102. If the selection information indicates that the variable length coding table previously selected by the table selection unit 101a is selected, the parameter determination unit 103a uses the variable length coding table previously selected by the table selection unit 101a. . In this case, the code amount may be larger than when encoding is performed using the variable length coding table (optimal variable length coding table) newly selected by the table selection unit 101a. In this case, when the linear expression indicating the worst code amount shown in the above equation (3) is used, there is a problem that the prediction accuracy of the worst code amount is deteriorated, and as a result, the encoding efficiency is lowered. Therefore, as shown in the following formula (6), the increase in the code amount due to the difference in the variable-length coding table is added as another term to model the worst code amount.

WB = C ₁ xq + C ₂ + dif [t ₁ , t ₂ ] (C ₁ <0, C ₂ > 0) (6)

In the above formula (6), C ₁ and C ₂ may be the same or similar values as the corresponding values in the above formula (3). t ₁ represents a table index of the variable length coding table corresponding to the characteristic value (absolute value sum or variance) of the input signal, and t ₂ represents the variable length coding table previously selected by the table selection unit 101a. Indicates the table index. Then, dif [t ₁ , t ₂ ] indicates a difference in code amount encoded between the case where the table index is t ₁ and the case where the table index is t ₂ . dif [t ₁ , t ₂ ] may be “0” when t ₁ = t ₂ , and increases as the variances of the variable length coding tables of t ₁ and t ₂ differ. The value of dif [t ₁ , t ₂ ] is obtained by encoding an input signal corresponding to an arbitrary table index t ₁ with a variable length coding table corresponding to the table index t ₂ , for example, brute force coding. Can be acquired. Encoding is performed brute force for each t ₁ and t ₂ to obtain the worst code amount, and the difference from the worst code amount in the case of t ₁ = t ₂ is obtained as dif [t ₁ , t ₂ ]. Become. If the worst code amount is modeled by the above equation (6), the subsequent method of determining the quantization parameter by the parameter determination unit 103a is similar to the operation of the parameter determination unit 103 of the first embodiment. Specifically, for the allocated code amount B, the following equation (7) may be satisfied.

B ≧ C ₁ xq + C ₂ + dif [t ₁ , t ₂ ] (7)

  Further, when the quantization parameter q is arranged from the equation (7), the following equation (8) is obtained.

q ≧ (B−C ₂ −dif [t ₁ , t ₂ ]) / C ₁ (8)

  The parameter determination unit 103a only needs to determine the quantization parameter q that satisfies the equation (8). For example, the parameter determination unit 103a determines the minimum quantization parameter q that satisfies the equation (8) and sends it to the quantization unit 104.

As described above, the difference in the worst code amount when the table indexes are different is modeled as the difference dif [t ₁ , t ₂ ] for the two-dimensional table. However, a variable length coding table prepared in advance is used. Depending on the characteristics, it is possible to model with a one-dimensional table. For example, when a variable length coding table of Golomb-Rice codes is used, a certain variable length coding table (for example, suffix length = k) and its adjacent variable length coding table (for example, suffix length = k + 1, k−1). Corresponds to an input signal whose absolute value sum is double or ½ times. This relationship holds for any variable-length coding table with a suffix length of 2 or more. Therefore, the difference in the worst code amount when using a different variable-length coding table is almost dependent on the absolute value of each suffix length. Without relying on that difference. From this, it is possible to reduce the amount of information held in the encoding device 10a by modeling as in the following expression (9) instead of the expression (7).

B ≧ C ₁ xq + C ₂ + dif [t ₁ −t ₂ ] (9)

  Even when a variable length coding table for codes other than the Golomb-Rice code is used, modeling similar to the above equation (9) can be performed depending on the prepared variable length coding table. For example, when a variable-length coding table based on a Huffman code is prepared, the probability distribution that is the basis of the variable-length coding table may be a distribution that is changed at a predetermined rate for each table index. Specifically, for example, if a normal distribution is prepared in which the variance is doubled every time the table index increases by “1”, and a variable length coding table of Huffman codes is configured based on this distribution, the formula ( 9) can be modeled.

  The parameter determination unit 103a sends the determined quantization parameter to each of the quantization unit 104 and the encoding unit 105a.

  The encoding unit 105a receives a table index and selection information from the table selection unit 101a, receives a quantization parameter from the parameter determination unit 103a, receives a quantization value from the quantization unit 104, and receives a variable length code for the quantization value It is a functional part that performs the conversion. Specifically, when the selection information indicates that the variable-length coding table previously selected by the table selection unit 101a has been selected, the encoding unit 105a can change the previously encoded variable stored therein. The quantization value is variable-length encoded using the long encoding table. Note that the encoding unit 105a uses the table index (the variable length encoding table previously selected by the table selection unit 101a) for the variable length encoding table that is actually used, as in the encoding unit 105 of the first embodiment. The table index may be selected based on the quantization parameter. On the other hand, when the selection information indicates that the variable length coding table is newly selected by the table selection unit 101a, the coding unit 105a is variable by the same or similar operation as the coding unit 105 of the first embodiment. What is necessary is just to perform long encoding. The encoding unit 105a internally stores information on the table index so that it can be used in subsequent processing units. The encoding unit 105a is realized by the encoding processor 502 shown in FIG.

  The encoding unit 105a performs the encoding of the table index by a method different from the same method of the encoding unit 105 of the first embodiment. Specifically, the encoding unit 105a first encodes selection information (for example, a flag), and then changes only when the selection information selects a variable-length encoding table selected in the processing unit. Encode the table index of the long encoding table. As a result, the amount of code when the table index is encoded is reduced. In other operations, the encoding unit 105a performs the same or similar operation as the encoding unit 105 of the first embodiment. As described above, the encoding unit 105a encodes the selection information, the table index (if necessary), the quantization parameter, and the quantization value, and outputs the encoded stream to the outside (for example, the network 40 or the like).

  As described above, the encoding device 10a according to the present embodiment, like the encoding device 10 according to the first embodiment, is a quantization parameter that suppresses the occurrence of buffer underflow in the reception buffer 30 with a small amount of processing. Can be set and encoding can be performed. As a result, the amount of processing required for the encoding process can be reduced, and it is not necessary to include means for avoiding buffer underflow due to skipping or the like, and local SNR degradation of the decoded signal can be suppressed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example 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 are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Transmission system 10, 10a Encoding apparatus 20 Decoding apparatus 30 Reception buffer 40 Network 101, 101a Table selection part 102 Code amount acquisition part 103, 103a Parameter determination part 104 Quantization part 105, 105a Encoding part 106 Code quantity control part 107 Storage unit 501 Input I / F
502 Encoding processor 502a Cache 503 RAM
504 Output I / F
505 Auxiliary storage device 506 Bus

Claims (11)

An encoding device that performs variable length encoding on a quantized value obtained by quantizing an input signal based on a quantization parameter,
A selection unit that selects one variable-length coding table from two or more variable-length coding tables based on the characteristics of the input signal;
An acquisition unit that acquires, as a reference code amount, a constant term of an expression obtained by functionalizing a value based on the maximum code amount for any of the quantization parameters for the variable length coding table selected by the selection unit;
A determination unit that determines the quantization parameter based on the reference code amount and an assigned code amount determined by an occupied code amount of a reception buffer;
Using the quantization parameter determined by the determination unit, a quantization unit that quantizes the input signal to obtain the quantization value;
Based on the quantization parameter determined by the determination unit, one variable length encoding table is selected from the two or more variable length encoding tables, and the quantization value is determined by the variable length encoding table. An encoding unit for performing variable length encoding on
An encoding device comprising:   The encoding apparatus according to claim 1, wherein the selection unit selects one variable-length encoding table based on a variance or a sum of absolute values of the input signal as a characteristic of the input signal.   A code that sets the allocated code amount so that the code amount of the variable-length encoded code by the encoding unit is smaller than the occupied code amount at the timing when the code of the reception buffer is removed by the decoding device The encoding device according to claim 1, further comprising a quantity control unit.   The encoding unit has a variable length encoding table corresponding to a variance smaller than a variance corresponding to the variable length encoding table selected by the selection unit, as the quantization parameter determined by the determination unit is larger. The encoding device according to claim 1 to select.   The encoding apparatus according to claim 4, wherein the variable length encoding table selected by the selection unit and the encoding unit is a table based on a Golomb-Rice code.   The encoding unit selects a variable length encoding table indicated by an index obtained by subtracting the quantization parameter determined by the determination unit from the suffix length of the variable length encoding table selected by the selection unit. The encoding device according to claim 5.   The encoding device according to claim 6, wherein the selection unit selects a variable-length encoding table having a suffix length larger than a predetermined value. The quantization width of the quantization by the quantization unit is an exponential function of the quantization parameter,
The encoding apparatus according to claim 1, wherein the function expression is expressed by a linear expression of the quantization parameter. The selection unit, when the difference between the value indicating the characteristic of the input signal and the value of the characteristic corresponding to the previously selected variable length coding table is less than a predetermined threshold, the previously selected variable length coding Select the table again,
When the previously selected variable length coding table is selected by the selection unit, the encoding unit may change the variable length code for the quantized value using the variable length coding table previously used for encoding. The encoding apparatus according to claim 1, wherein the encoding is performed.   When the selection unit reselects the variable length coding table previously selected by the selection unit, the acquisition unit is based on the maximum code amount corresponding to the reselected variable length coding table and the characteristics of the input signal. The encoding apparatus according to claim 9, wherein a value obtained by adding a difference from a maximum code amount corresponding to a variable-length encoding table to a constant term of the function expression is acquired as the reference code amount. An encoding method of an encoding device that performs variable length encoding on a quantized value obtained by quantizing an input signal based on a quantization parameter,
A selection step of selecting one variable length coding table from two or more variable length coding tables based on the characteristics of the input signal;
An acquisition step of acquiring, as a reference code amount, a constant term of an expression obtained by functionalizing a value based on the maximum code amount for any of the quantization parameters for the selected variable length coding table;
A determination step of determining the quantization parameter based on the reference code amount and an assigned code amount determined by an occupied code amount of a reception buffer;
Using the determined quantization parameter, a quantization step for quantizing the input signal to obtain the quantized value;
Based on the determined quantization parameter, one variable length coding table is selected from the two or more variable length coding tables, and the variable length coding table is used to select a variable length for the quantized value. An encoding step for encoding;
An encoding method comprising:

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