JPH1028266A - Image encoding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain encoding by encoding amounts less than set encoding amounts at the time of operating encoding, using variable length encoding in an image encoding device. SOLUTION: Weighting is operated by quantizing circuits 41 and 43 by using two kinds of initial quantization steps, generated encoding amounts at the time of variable length encoding are measured by encoding amount measuring circuits 42 and 44, a semi-optimal function coefficient value is calculated by an encoding amount characteristic function calculating circuit 47, and a quasi-optimal quantization step is calculated by a quantization step calculating circuit 48. Then, quantization is operated by a quantizing circuit 45 by using the quasi-optimal quantization step, the generated encoding amounts are measured by an encoding amount measuring circuit 46, and the generated encoding amounts closest to target encoding amounts 117 and two kinds of the quantization steps at that time are selected by a selecting circuit 49. An optimal function coefficient value is calculated by an encoding amount characteristic function calculating circuit 50, the quasi-optimal function coefficient value, and the optimal function coefficient value are adaptively selected by a characteristic function selecting circuit 51, the target encoding amounts are corrected, and the quantization step at the time of encoding is calculated by a quantization step calculating circuit 52.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus for compressing and encoding an input image signal to a predetermined code amount or less.

[0002]

2. Description of the Related Art An image coding apparatus using variable length coding can perform image signal coding with a target code amount or less.
It is necessary that stable image quality be obtained.

In general, in order to control the generated code amount at the time of encoding, a method of controlling using a quantization step is used. This utilizes the characteristic that when the quantization step value is increased, the appearance probability of the invalid coefficient value is increased, so that the code amount can be reduced. Conversely, when the quantization step value is reduced, the code amount increases.

However, in the variable length coding, since the generated code amount does not change linearly with respect to the quantization step, it is difficult to estimate the generated code amount. If the variable length coding is not actually performed, the generated code amount is reduced. There is a problem of not knowing.

Therefore, code amount control is the most important technique when performing image coding using variable length coding. However, the relationship between the quantization step for controlling the generated code amount and the generated code amount is as follows. Therefore, it is difficult to estimate a quantization step capable of performing encoding at a target code amount or less.

[0006] In the conventional code amount control method, in the case of a storage medium or the like that does not consider the encoding delay, a feedback loop is formed and the quantization step is calculated by changing the quantization step to obtain the target code amount or less. When it is necessary to perform encoding within a certain period of time such as video equipment, the quantization circuit and the encoding measurement circuit are driven in parallel using a plurality of initial quantization steps, and the number of encoded signals is set to a value closest to the target code amount. A point or a plurality of points are selected, modeling is performed using an approximate function such as a linear function or a spline function, a code amount characteristic function is calculated, and a quantization step used for coding is calculated.

An example of this method is described in detail in Reference 1: Masahiko Enari and Soichi Kashida, "HDTV Codec Supporting 60 to 140 Mbps", Video Information, January 1992, pages 51 to 58. I have.

[0008]

As described above, in the conventional code amount control method, when encoding is performed within a fixed time, encoding is performed with a stable code amount for various input images having different statistical characteristics. In order to be able to perform the quantization, it is necessary to perform quantization using about eight types of initial quantization steps and measure the generated code amount of each. Since both the quantization circuit and the code amount measurement circuit perform complicated calculations and processes, the use of a plurality of these circuits makes the entire encoding device large and expensive.

Furthermore, in such a code amount control system,
Because the code amount characteristic function cannot sufficiently approximate the characteristics of the input image due to the setting value of the initial quantization step, when the quantization step used for coding is estimated and coding is performed, the generated code amount is equal to or larger than the target code amount. Or when re-encoding already encoded / decoded image data, the variation of the generated code amount with respect to the quantization step becomes more complicated than normal image data, Code amount control cannot be performed with high accuracy.

[0010] In addition, since the quantization performs multiplication and division, the coefficient value may be shifted by several bits in order to secure the operation accuracy. This process is performed when the amount of information of the input image is large. When quantization is performed using the quantization step estimated without considering the bias, the overflow of the coefficient value occurs even though the generated code amount is lower than the target code amount,
There are problems such as deterioration of image quality.

It is an object of the present invention to accurately approximate a code amount characteristic function used for obtaining an optimum quantization step used for encoding by performing logarithmic approximation, and to achieve high accuracy within a given time with a smaller number of processing devices. An object of the present invention is to provide a coding device for a high-quality image signal by controlling a code amount.

[0012]

A block dividing circuit for dividing an input image into blocks each having a small area composed of a plurality of pixels, and a block dividing circuit for dividing the input image into blocks having a plurality of pixels. An orthogonal transformation circuit that performs orthogonal transformation on the block data that has been converted to transform coefficient values that are frequency data, and a code amount control circuit that calculates a quantization step such that the transform coefficient value is encoded at a target code amount or less. A quantization circuit that quantizes the transform coefficient value using the quantization step and outputs a quantized coefficient value, and a variable length encoding circuit that encodes the quantized coefficient value into a variable length codeword. An image coding apparatus comprising a modulation circuit for adding a synchronization signal, an error correction code, and the like to the quantization step and the variable-length codeword and transmitting modulated data to a transmission path and a recording / reproducing apparatus. The code amount control circuit weights a transform coefficient value using two types of predetermined initial quantization steps and outputs a quantized coefficient value; and the two types of initial quantization steps A code amount measuring circuit that measures the accumulated code amount as a generated code amount when performing the variable length coding on the quantized coefficient value calculated by using the logarithmic values of the two types of initial quantization steps and A code amount characteristic function calculating circuit for obtaining a code amount characteristic function near the target code amount from the logarithmic value of the generated code amount measured using the two types of initial quantization steps and outputting a function coefficient value; An image coding apparatus including a quantization step calculation circuit for obtaining an optimum quantization step capable of performing coding at a target code amount or less from a logarithmic value of a numerical value and a target code amount is conceivable.

As a high-quality image encoding apparatus, a block dividing circuit for dividing an input image into small-area blocks composed of a plurality of pixels, and an orthogonal transform of the block data divided by the block dividing circuit are performed. An orthogonal transform circuit that converts the transform coefficient value into a transform coefficient value that is the applied frequency data, a code amount control circuit that calculates a quantization step such that the transform coefficient value is encoded at a target code amount or less, and using the quantization step A quantization circuit that quantizes the transform coefficient value and outputs a quantized coefficient value; a variable length coding circuit that encodes the quantized coefficient value into a variable length codeword; the quantization step and the variable length In an image coding apparatus comprising a modulation circuit for adding a synchronization signal, an error correction code and the like to a code word and transmitting modulation data to a transmission path and a recording / reproducing apparatus, the code amount control circuit A quantization circuit that weights the transform coefficient value using two types of predetermined initial quantization steps and outputs a quantized coefficient value, and the quantized coefficient value calculated using the initial quantization step A code amount measuring circuit for measuring a generated code amount when variable length coding is performed, and a pair of a logarithmic value of the two types of initial quantization steps and a generated code amount measured using the two types of initial quantization steps. A code amount characteristic function calculating circuit for determining a code amount characteristic function for searching for a quantization step near the target code amount from the numerical value and outputting a sub-optimal function coefficient value; A quantization step calculation circuit that obtains a quasi-optimal quantization step from a logarithmic value of; a quantization circuit that quantizes the transform coefficient value using the quasi-optimal quantization step and outputs a quantized coefficient value; Most A code amount measuring circuit for measuring a generated code amount when the quantized coefficient value calculated by the quantization step is subjected to variable length coding; and a generated code amount measured by using the two types of initial quantization steps. From the generated code amounts measured using the sub-optimal quantization step, two types of generated code amounts closest to the target code amount and a quantization step used for calculation of the two types of generated code amounts closest to the target code amount are selected. From the logarithmic value of the two selected quantization steps, which are the outputs of the selection circuit, and the logarithmic value of the generated code amount measured using the two selected quantization steps. A code amount characteristic function calculating circuit for obtaining an optimal function coefficient value of the code amount characteristic function in the vicinity of the code amount; and an optimal code amount capable of performing encoding at a target code amount or less from the logarithmic value of the target code amount and the optimal function coefficient value. Quantization step An image coding apparatus including a quantization step calculating circuit for obtaining a loop is conceivable.

Here, an image encoding apparatus according to a first aspect of the present invention includes a block dividing circuit for dividing an input image into small-area blocks each including a plurality of pixels, and a block dividing circuit for dividing the input image into blocks. An orthogonal transformation circuit that performs orthogonal transformation on the block data that has been converted to a transformation coefficient value that is frequency data, and a code amount control circuit that calculates a quantization step such that the transformation coefficient value is encoded at a target code amount or less. A quantization circuit that quantizes the transform coefficient value using the quantization step and outputs a quantized coefficient value, a variable length coding circuit that encodes the quantized coefficient value into a variable length codeword, An image coding apparatus comprising a quantization step and a modulation circuit for adding a synchronization signal, an error correction code, and the like to the variable-length codeword and transmitting modulation data to a recording / reproducing apparatus. The signal amount control circuit uses a predetermined two types of initial quantization steps to weight the transform coefficient value and outputs a quantized coefficient value, and the two types of initial quantization steps. A code amount measuring circuit for measuring, as a generated code amount, the accumulation of the code amount when the quantized coefficient value calculated by the variable length coding is performed, a logarithmic value of the two types of initial quantization steps, and A code amount characteristic function for obtaining a code amount characteristic function for searching for a quantization step near the target code amount from the logarithmic value of the generated code amount measured using the initial quantization step, and outputting a sub-optimal function coefficient value A calculating circuit, a quantization step calculating circuit for obtaining a sub-optimal quantization step from the logarithmic value of the sub-optimal function coefficient value and a target code amount, and performing the quantization of the transform coefficient value using the sub-optimal quantization step. quantum A quantization circuit that outputs a coefficient value; and a code amount measurement circuit that measures a generated code amount when the quantized coefficient value obtained by using the sub-optimal quantization step is subjected to variable length coding. From the generated code amount measured using the initial quantization step and the generated code amount measured using the sub-optimal quantization step, the two generated code amounts closest to the target code amount are selected as the generated code amounts. A selection circuit for selecting the quantization step used for calculating the two types of selection code amounts as two types of selection quantization steps, a logarithmic value of the two types of selection quantization steps, and the two types of selection generation codes A code amount characteristic function calculating circuit for obtaining an optimal function coefficient value of the code amount characteristic function in the vicinity of the target code amount from the logarithmic value of the amount; Threshold If it is larger, the optimum function coefficient value is selected as the selection function coefficient value, and the selected code amount is output as the selected target code amount without correcting the target code amount. If smaller, the sub-optimal function coefficient value is selected as a selection function coefficient value, and using the generated code amount measured using the sub-optimal quantization step, the target code amount is corrected and the selected target code amount is set. A quantization function that calculates a quantization step capable of performing encoding at a target code amount or less as an optimum quantization step from a characteristic function selection circuit to be output, and a logarithmic value of the selected target code amount function and the selection function coefficient value. And a conversion step calculation circuit.

According to a second aspect of the present invention, there is provided the image encoding apparatus according to the first aspect of the present invention, wherein the code amount control circuit performs quantization using two kinds of preset initial quantization steps. A quantization coefficient measuring circuit for measuring a maximum value of the quantization coefficient value to obtain a maximum quantization coefficient value by using any one of the quantization coefficient values, and calculating the maximum quantization coefficient value. A minimum quantization step calculation circuit for calculating a minimum quantization step which is a quantization step when the transform coefficient value can be quantized without overflowing from the used quantization step and the maximum quantization coefficient value. And the minimum quantization step and the step value of the optimum quantization step obtained by the code amount control circuit are compared, and a quantization step having a large step value is selected, and encoding can be performed with a target code amount or less. And further comprising a quantization step selection circuit for selecting the quantization step does not occur the overflow of the quantized coefficient values.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

FIG. 5 is a block diagram showing an outline of an image coding apparatus using the code amount control system of the present invention.

First, an input image signal 160 is digitized image data, and is composed of a multi-valued black-and-white image, an RGB primary color signal, luminance and two kinds of color difference signals, etc., and is a small area block composed of a plurality of pixels. The data is divided into data 161 by the block dividing circuit 71. In the orthogonal transformation circuit 72,
The orthogonal transform is performed on the block data 161 to output a transform coefficient value 162.

The conversion coefficient value 162 is calculated by the code amount control circuit 73.
Quantization step 16 that can be encoded with a target code amount or less
3 is output to the quantization circuit 74 and the modulation circuit 76.

The quantization circuit 74 uses the quantization step 163 estimated by the code amount control circuit 73 to convert the transform coefficient value 16
2 and outputs a quantized coefficient value 164 to the variable length coding circuit 75. The variable length coding circuit 75 converts the quantization coefficient value 164 into variable length data, and outputs a variable length code word 165 corresponding to the quantization coefficient value 164 to the modulation circuit.

In the modulation circuit 76, the quantization step 163
Then, a synchronization signal, an error correction code, and the like are added to the variable-length codeword 165 and output as output data 166 to a transmission path, a recording / reproducing device, or the like.

FIG. 1 is a block diagram showing a first example of the code amount control circuit 73. In this code amount control circuit, the transform coefficient value 162 is weighted by the quantizing circuits 1 and 3 using the two types of preset initial quantization steps 101 and 102, and the quantized coefficient value 103,
As 104, it is output to the code amount measuring circuits 2 and 4. In the code amount measuring circuits 2 and 4, quantization coefficient values 103 and 1 are respectively provided.
It measures the accumulation of the code amount necessary to encode the code 04 into variable-length data, and outputs it to the code amount characteristic function calculation circuit 5 as the generated code amounts 105 and 106. The code amount characteristic function calculation circuit 5 obtains logarithmic values of the two types of initial quantization steps 101 and 102 and logarithmic values of the generated code amounts 105 and 106, and easily models the relationship between the quantization step and the generated code amount. Therefore, the coefficient value of the function is obtained using a linear function, and the function coefficient value 108 is output to the quantization step calculation circuit 6. In the quantization step calculation circuit 6, the target code amount 1
An optimum quantization step 163 capable of performing encoding at a target code amount or less is calculated from the logarithmic value of 07 and the function coefficient value 108, and is output to the quantization circuit 74 and the modulation circuit 76 in FIG.

The code amount characteristic function will be described with reference to FIGS. FIG. 6 illustrates the relationship between the amount of generated code and the quantization step. Such a relationship often occurs in a general input image, and finding a complicated approximate relationship is not used because of an increase in the amount of arithmetic processing, and the quantization of the transform coefficient value is performed using a plurality of initial quantization steps. , Measure the generated code amount when performing variable length coding, and perform linear approximation using the two types of generated code amounts closest to the target code amount and the quantization step used for calculating the generated code amount, A quantization step that can perform encoding with a target code amount or less is estimated. However, when a logarithmic value is obtained for each of the quantization step and the generated code amount, and the relationship between the quantization step and the generated code amount is obtained, approximation can be performed with a substantially linear line as shown in FIG. Quantization of the transform coefficient value using the conversion step, and the complexity of checking the amount of code generated when performing variable-length coding can be greatly reduced. Can be obtained.

FIG. 2 is a block diagram showing a second example of the code amount control circuit 73. In this code amount control circuit, the transform coefficient value 162 is obtained by using two types of initial quantization steps 111 and 112 set in advance.
Weights the transform coefficient value 162 to calculate the quantized coefficient value 11
3, 114 are output to the code amount measuring circuits 22 and 24. The code amount measurement circuits 22 and 24 measure the code amount required when the quantization coefficient values 113 and 114 are encoded into variable length data, and generate the generated code amounts 115 and 116 to the code amount characteristic function calculation circuit 27. Output. In the code amount characteristic function calculation circuit 27, two types of initial quantization steps 11
The logarithmic value of 1,112 and the logarithmic value of the generated code amount 115,116 are obtained, and a function coefficient value 118 is obtained using a linear function,
Output to the quantization step calculation circuit 28.

In the quantization step calculation circuit 28, the semi-optimal quantization step 11 which is a quantization step near the target code amount is determined from the logarithmic value of the target code amount 117 and the function coefficient value 118.
9 is output to the quantization circuit 25 and the selection circuit 29.

The quantization circuit 25 quantizes the transform coefficient value 162 using the sub-optimal quantization step 119, and outputs the quantization coefficient value 120 to the code amount measurement circuit 26.

In the code amount measuring circuit 26, the quantization coefficient value 1
Measure the code amount required to perform 20 variable length codings,
The generated code amount 121 is output to the selection circuit 29.

In the selection circuit 29, the two kinds of generated code amounts closest to the target code amount 117 are generated code amounts 115, 116,
121, and the quantization step used to calculate the quantization coefficient value of the selected generated code amount is the quantization step 11
1, 12 and 119, and selected quantization step 12
2, 124, and output 123 and 125, respectively.

The code amount characteristic function calculation circuit 30 uses the logarithmic values of the selective quantization steps 122 and 124 and the logarithmic values of the selected generated code amounts 123 and 125 to obtain a function coefficient value 1
26 is output.

The quantization step calculation circuit 31 calculates an optimum quantization step 163 capable of performing coding at a target code amount or less from the logarithmic value of the target code amount 117 and the function coefficient value 126, and calculates the quantization circuit 74 in FIG. Is output to the modulation circuit 76.

FIG. 3 is a block diagram showing an example of the code amount control circuit 73 according to the first embodiment of the present invention. In this code amount control circuit, the transform coefficient value 162 is weighted by the quantizing circuits 41 and 43 using two kinds of preset initial quantization steps 131 and 132, and the quantized coefficient value 133 is obtained. , 134 to the code amount measuring circuits 42 and 44. The code amount measurement circuits 42 and 44 measure the code amounts required when the quantization coefficient values 133 and 134 are encoded into variable length data, and the generated code amounts 135 and 136 are transmitted to the code amount characteristic function calculation circuit 47. Output. The code amount characteristic function calculation circuit 47 obtains logarithmic values of the two types of initial quantization steps 131 and 132 and logarithms of generated code amounts 135 and 136, obtains a function coefficient value 138 using a linear function, and performs a quantization step. Output to the calculation circuit 48.

The quantization step calculation circuit 48 calculates a sub-optimal quantization step 139 for obtaining the target code amount from the logarithmic value of the target code amount 137 and the function coefficient value 138, and sends it to the quantization circuit 45 and the selection circuit 49. Output.

The quantization circuit 45 quantizes the transform coefficient value 162 using the sub-optimal quantization step 139, and outputs a quantized coefficient value 140.

In the code amount measuring circuit 46, the quantization coefficient value 1
The code amount when the variable-length coding of 40 is performed is measured, and the generated code amount 141 is supplied to the selection circuit 49 and the characteristic function selection circuit 51.
Is output.

In the selection circuit 49, the two types of generated code amounts closest to the target code amount 117 are generated code amounts 135, 136,
141, the quantization step at that time is selected from the quantization steps 131, 132, and 139, and the selected quantization steps 142 and 144, and the selected generated code amounts 143 and 14 are selected.
Output as 5.

The code amount characteristic function calculation circuit 50 obtains logarithmic values of the selective quantization steps 142 and 144 and logarithms of the selected generated code amounts 143 and 145, and obtains a function coefficient value 146 of the code amount characteristic function.

In the characteristic function selection circuit 51, the function coefficient value 146 obtained from the initial analysis and the function coefficient value 146 representing the code amount characteristic near the target code amount are adapted by comparing the function coefficient value 146 with the threshold value. And the selected function coefficient value 148 is output.

The characteristic function selection circuit 51 further includes:
If the generated code amount 141 measured using the sub-optimal quantization step 139 is larger than the target code amount 137, the target code amount is corrected and the corrected target code amount 147 is output.

This is because, when an image that has already been subjected to encoding and decoding processing is used as an input image, the change in the generated code amount with respect to the change in the quantization step shows a large variation in the function coefficient value when viewed in a small section. The problem arises because accurate modeling cannot be performed, and by calculating the quantization step used for encoding using the function coefficient value in a larger section, the variation of the function coefficient value in a small section is calculated. This is because absorption can be performed and stable encoding can be performed.

The quantization step calculation circuit 52 calculates an optimum quantization step 163 capable of performing coding with a target code amount or less from the logarithmic value of the corrected target code amount 147 and the selected function coefficient value 148. 5 to the quantization circuit 74 and the modulation circuit 76.

FIG. 4 is a block diagram showing an example of the code amount control circuit 73 according to the second embodiment of the present invention. In this code amount control circuit, the transform coefficient value 162 is quantized using a quantization step 150 set in advance by the quantization circuit 60, and is output as a quantized coefficient value 151. Here, the quantization circuit 60 can be shared with a quantization circuit that performs quantization using the initial quantization step of FIG. 1, FIG. 2, or FIG.

The quantization coefficient measuring circuit 61 measures the maximum value of the quantization coefficient value 151 and outputs the maximum quantization coefficient value 152. The minimum quantization step calculation circuit 62 obtains the minimum quantization step at which the quantization coefficient value does not overflow due to the quantization, and outputs the minimum quantization step to the quantization step selection circuit 63.

For example, when the maximum value of the quantized coefficient value 151 is measured using the quantization step Q1, a coefficient value of 721 is obtained, and the maximum coefficient value at which quantization can be performed is 2047. Minimum quantization step QM
Can be calculated using the following equation.

In the quantization step selection circuit 63, QM = 721 × Q1 / 2047, a minimum quantization step 153,
By comparing the quantization step 154 obtained by the code good control circuit of FIGS. 1, 2 and 3, and selecting the one with the larger step value and outputting it as the quantization step at the time of encoding,
Even if the code amount is equal to or less than the target code amount, it is possible to prevent image quality deterioration due to overflow of the quantization coefficient value.

[0045]

As described above, according to the code amount control circuit of FIG. 1, the code amount characteristic function can be efficiently modeled by taking a logarithmic value when obtaining the code amount characteristic function. The input image signal is analyzed using only two types of initial quantization steps set in advance, and the input image signal can be subjected to variable-length encoding, thereby enabling encoding within a fixed time. In addition, since the number of quantization circuits and code amount measurement circuits can be reduced, the device can be reduced in size and weight, and can be provided at low cost.

According to the code amount control circuit of FIG. 2, even if the generated code amount measured by using the sub-optimal quantization step obtained from the first-stage analysis exceeds the target code amount, By calculating the quantization step using the code amount characteristic function near the code amount, the code amount characteristic function can be modeled more accurately, and the target code amount does not exceed the target at the time of encoding. Therefore, a surplus buffer can be reduced, coding can be performed with a code amount very close to the target code amount below the target code amount, and a coding apparatus capable of obtaining a high-quality image can be configured.

According to the first aspect of the present invention, even for an image signal that has already been encoded and decoded, encoding can be stably performed with the target code amount. The effect is that it can be prevented.

Further, according to the second aspect of the present invention, it is possible to prevent the image quality from being degraded due to the overflow of the quantization coefficient value even when the information amount of the input image signal is small and the bias is large. Therefore, there is an effect that a high-quality encoded image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining the present invention.

FIG. 2 is a block diagram for explaining the present invention.

FIG. 3 is a block diagram showing an embodiment of a configuration of a code amount control circuit according to the first invention of the present invention.

FIG. 4 is a block diagram showing one embodiment of a configuration of a code amount control circuit according to a second invention of the present invention.

FIG. 5 is a block diagram of an image encoding device using the code amount control method of the present invention.

FIG. 6 is a diagram illustrating a relationship between a generated code amount and a quantization step.

FIG. 7 is a diagram illustrating a relationship between a generated code amount and a quantization step.

[Explanation of symbols]

1,3,21,23,25,41,43,45,60,
74 quantization circuit 2,4,22,24,26,42,44,46 code amount measurement circuit 5,27,30,47,50 code amount characteristic function calculation circuit 6,28,31,48,52 quantization step Calculation circuits 29, 49 Selection circuit 51 Characteristic function selection circuit 61 Quantization coefficient measurement circuit 62 Minimum quantization step calculation circuit 63 Quantization step selection circuit 71 Block division circuit 72 Orthogonal transformation circuit 73 Code amount control circuit 75 Variable length coding circuit 76 Modulation circuit 101, 102, 111, 112, 131, 132, 1
50 Initial quantization step 103, 104, 113, 114, 120, 133, 1
34, 140, 151, 164 Quantized coefficient values 105, 106, 115, 116, 121, 135, 1
36, 141 Generated code amount 107, 117, 137 Target code amount 108, 118, 126, 138, 146 Function coefficient value 119, 139 Sub-optimal quantization step 122, 124, 142, 144 Selected quantization step 123, 125 , 143, 145 Selected generated code amount 147 Modified target code amount 148 Selected function coefficient value 152 Maximum quantization coefficient value 153 Minimum quantization step 154 Optimal quantization step 160 Input image 161 Block data 162 Transformation coefficient value 163 quantization step 165 variable-length codeword 166 modulated data

Claims (2)

[Claims] 1. A block dividing circuit for dividing an input image into blocks each having a small area composed of a plurality of pixels, and performing orthogonal transformation on the block data divided by the block dividing circuit to transform coefficient values which are frequency data. An orthogonal transform circuit for transforming, a code amount control circuit for obtaining a quantization step such that the transform coefficient value is encoded at a target code amount or less, and performing quantization of the transform coefficient value using the quantization step. A quantization circuit that outputs a quantization coefficient value; a variable length encoding circuit that encodes the quantization coefficient value into a variable length codeword; a synchronization signal, an error correction code for the quantization step and the variable length codeword; And a modulation circuit for transmitting modulation data to a transmission path and a recording / reproducing apparatus by adding the above-mentioned information. A quantization circuit that weights the transform coefficient value using a quantization step and outputs a quantization coefficient value; and performs variable-length encoding on the quantization coefficient value calculated using the two types of initial quantization steps. A code amount measurement circuit for measuring the accumulated code amount as a generated code amount, a logarithmic value of the two types of initial quantization steps, and a generated code amount measured using the two types of initial quantization steps. A code amount characteristic function calculation circuit for obtaining a code amount characteristic function for searching for a quantization step near the target code amount from the logarithmic value and outputting a sub-optimal function coefficient value; and the sub-optimal function coefficient value and a target code amount A quantization step calculation circuit that obtains a sub-optimal quantization step from a logarithmic value of: a quantization circuit that quantizes the transform coefficient value using the sub-optimal quantization step and outputs a quantization coefficient value; Optimal quantum The amount of generated code at the time of performing variable length coding on the quantized coefficient value obtained using the step is measured by a code amount measuring circuit, and the generated code amount measured using the two types of initial quantization steps is From the generated code amounts measured using the sub-optimal quantization step, two types of generated code amounts closest to the target code amount are selected as selected generated code amounts, and quantization used for calculating the two selected code amounts is performed. A selection circuit that selects a step as two types of selective quantization steps; and a code amount characteristic near a target code amount from a logarithmic value of the two types of selective quantization steps and a logarithmic value of the two types of selectively generated code amounts. A code amount characteristic function calculating circuit for obtaining an optimum function coefficient value of the function; and, if a change in the generated code amount with respect to a change in the quantization step is larger than a threshold value, the optimum function coefficient value is selected from the optimum function coefficient value. Person in charge Select as a numerical value and output it as a selected target code amount without modifying the target code amount. If the change in the generated code amount with respect to the change in the quantization step is smaller than a threshold value, the suboptimal function coefficient value is selected as a selection function. A characteristic function selecting circuit for selecting as a coefficient value, correcting the target code amount using the generated code amount measured by using the sub-optimal quantization step, and outputting the corrected target code amount, A logarithmic value of a function and the selection function coefficient value, and a quantization step calculation circuit that calculates a quantization step capable of performing encoding at a target code amount or less as an optimal quantization step. Image encoding device. 2. The image coding apparatus according to claim 1, wherein said code amount control circuit includes one of said quantized coefficient values quantized using two types of preset initial quantization steps. A quantizing coefficient measuring circuit for measuring a maximum value of the quantizing coefficient value to obtain a maximum quantizing coefficient value, a quantization step used when calculating the maximum quantizing coefficient value, and From the quantization coefficient value, a minimum quantization step calculation circuit that calculates a minimum quantization step that is a quantization step when the transform coefficient value can perform quantization without overflow, and the minimum quantization step The step value of the optimal quantization step obtained by the code amount control circuit is compared, a quantization step having a larger step value is selected, and encoding can be performed with a target code amount or less. Image encoding apparatus further comprising a quantization step selection circuit for selecting the quantization step does not occur with flow.