JPH0775101A - Device and method for encoding image - Google Patents

Abstract

PURPOSE:To provide the image encoding device which can efficiently allocate a data amount. CONSTITUTION:When a zero detection part 101 detects zero in an output from a quantizing part, the increment of a threshold value is instructed to a quantizing threshold value update part 102. When zero is detected in a quantized DCT coefficient by the zero detection part 101, at this quantizing threshold value update part 102, the quantizing threshold value is incremented. On the other hand, when any one quantizing DCT coefficient exceeds the threshold value and the zero detection part 101 detects any quantizing output value excepting for zero, the quantizing threshold value is returned to the initial value by the quantizing threshold value update part 102.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus and method for quantizing transform coefficients obtained by orthogonally transforming input image information in pixel block units.

[0002]

2. Description of the Related Art Conventionally, in a quantizer of an image coding apparatus, an input DC is input with a step size selected according to a quantization characteristic control signal from the image coding controller.
The T coefficient is quantized. At the time of this quantization, DCT coefficients below a certain threshold value are rounded down to zero so that the zero run in the quantized data string becomes long.

Regarding the quantization characteristic, generally, if the quantization step size is set to be small, the image quality is improved, but significant data increases and the number of transmission bits increases, and the quantization step size is increased. If set, the amount of data will decrease but the image quality will deteriorate. Further, according to the CCITT recommendation, the upper limit is defined for the number of bits generated when encoding one frame, and there is a limit to the significant improvement of the quantization characteristic for high definition of an image. Then, in consideration of the deterioration of the image quality due to the movement, it is also necessary to perform processing such as dropping frames (frame skip). In other words, higher definition image quality means an increase in the number of transmission bits, which leads to a reduction in the frame rate.

Image quality (spatial resolution) and motion followability (temporal resolution) are contradictory, and pursuing high image quality inevitably greatly deteriorates motion followability. Therefore, the quantization step size needs to be set efficiently according to not only the characteristics of the input image but also the amount of data accumulated in the buffer. Figure 11
FIG. 9 is a diagram showing an operation example of updating a quantization threshold for a DCT coefficient in a conventional image encoding device. here,
The quantization step size is g, the increment amount at the time of updating is 1, and the upper limit of the threshold is set to the quantization step size g,
The case of 1.5 g is shown as an example. Further, the initial value of the quantization threshold is set equal to the quantization step size.

As shown in the figure, when the DCT coefficient input from the DC component to the high frequency component is less than the threshold value, the threshold value is incremented by 1. However, the threshold has an upper limit (1.5 g) and is not updated beyond that. When the DCT coefficient data exceeding the threshold is input, the threshold returns to the initial value (quantization step size g).

By the above operation, generation of zero is promoted, zero run is easily generated, and the amount of data to be transmitted is suppressed.
In general, the spectrum of an image has very few high-frequency components and is concentrated in the low-frequency region. Also, considering the visual characteristics that the visual spatial frequency decreases in the high range, the encoded data amount For the purpose of reduction, it is also practiced to cut off the high frequency component in the DCT coefficient and not transmit it.

[0007]

However, in the above-mentioned conventional image coding apparatus, when the actual image is directly DCT processed (INTRA mode), the interframe difference is DCT processed (INTER mode). Is
A large amount of DCT coefficient power is distributed in the high frequency region.
Further, the high frequency component is essentially important, and if the high frequency region of the DCT coefficient is cut off, a fine change is lost, resulting in a blurred image.

The present invention has been made in view of the above problems, and it is an object of the present invention to efficiently cut off an important high frequency component of a DCT coefficient and unnecessarily lower the quantization characteristic. It is an object of the present invention to provide an image encoding device capable of allocating a data amount to the.

[0009]

In order to achieve the above object, the present invention provides an image coding apparatus for quantizing a transform coefficient obtained by orthogonally transforming an input image in pixel block units, and searching for the value of the transform coefficient. Search means for setting, when the conversion coefficient includes a specific value as a result of the search, setting means for varying the update width of the quantization threshold for the quantization, and the quantization threshold set by the setting means. Quantizing means for performing quantization in accordance with.

[0010]

In the above configuration, when the transform coefficient obtained by orthogonally transforming the input image in pixel block units is quantized, the update width of the quantization threshold is made variable, and the quantization is performed using the quantization threshold. To realize efficient encoding of image information.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 1 is a block diagram of CCITT Recommendation H.264 that employs an image coding apparatus according to an embodiment of the present invention.
FIG. 261 is a schematic block diagram showing a circuit configuration of an image communication telephone according to H.261. In FIG. 1, reference numeral 301 is one of image input means in this apparatus, a camera input section for inputting a self-portrait and the like, and 302 is one of image input means in this apparatus, a drawing, a map, A document camera input unit 303 for inputting an image such as a document is a display unit for displaying an input image from the camera input unit 301 or the document camera input unit 302, an image received from a communication partner, an operation screen, or the like. Reference numeral 304 denotes an image input interface unit that performs the switching process of the image input unit and the like according to an instruction from a system control unit 314 described later, and 305 is an image output interface unit that performs the switching process of the image output unit and the like.

Reference numeral 306 is an image editing unit for performing picture-in-picture processing, screen freeze processing, etc. according to an instruction from the system control unit 314, and 307 is a transmission image signal encoding process and a reception image signal decoding process. Reference numeral 307a denotes an image encoding / decoding unit that performs processing, and 307a denotes an image encoding unit that configures the image encoding / decoding unit 307.
An image decoding unit 307b is included in the image encoding / decoding unit 307.

Reference numeral 308 is a handset unit which is one of the voice input / output means of the present apparatus, 309 is a microphone section which is one of the voice input means of the present apparatus, and 310 is a voice output section of the present apparatus. It is a speaker unit which is one of the above. Further, 311 is a voice input for performing an echo canceling process, a tone generating process such as a dial tone, a ringing tone, a busy tone, a ringing tone or the like, or a switching process of the voice inputting / outputting means according to an instruction of the system control section 314. The output interface unit.

Reference numeral 312 is a voice encoding / decoding unit that performs a transmission voice signal encoding process and a reception voice signal decoding process according to an instruction from the system control unit 314.
Reference numeral 2a is a voice encoding unit in the voice encoding / decoding unit 312, and reference numeral 312b is a voice decoding unit in the voice encoding / decoding unit 312. Reference numeral 313 is an operation unit having a keyboard, a touch panel, etc. used for inputting control information to this apparatus.

Reference numeral 315 is an image encoding / decoding unit 30.
7, the audio signal from the audio encoding / decoding unit 312, and the control signal from the system control unit 314 are multiplexed in a transmission frame unit, and the reception frame is an image signal, an audio signal, and a control signal. It is a demultiplexing / multiplexing unit that separates the signal and transfers it to each unit. Reference numeral 314 includes a CPU, a ROM, a RAM, an auxiliary storage device, and the like (not shown), monitors the states of the above-mentioned units, controls the entire apparatus, creates an operation / display screen according to the state, and further an application program. This is a system control unit that executes, for example. Reference numeral 316 is a line interface unit for controlling the line according to the ISDN user network interface, 31
7 is a communication line.

Next, the operation of the image communication telephone having the above configuration will be described. An input image from the camera input unit 301 or the document camera input unit 302 is input to the image coding unit 307a via the image input interface unit 304 and the image editing unit 306. Also, the handset unit 3
08 or the voice input from the microphone unit 309 passes through the voice input / output interface unit 311 and the voice encoding unit 3
12a is input. Then, the input image encoded by the image encoding unit 307a and the input voice encoded by the voice encoding unit 312a are multiplexed by the demultiplexing and multiplexing unit 315, and the communication circuit 317 is passed through the line interface unit 316.
Sent to.

On the other hand, the received signal from the communication line 317 is
Demultiplexing and multiplexing unit 315 via line interface unit 316
Then, it is separated into an image signal and an audio signal, and each is input to the image encoding unit 307b and the audio encoding unit 312b. Among them, the received image decoded by the image decoding unit 307b is
It is displayed on the display unit 303 via the image editing unit 306 and the image output interface unit 305, and also the audio decoding unit 31.
The received voice decoded in 2b is output to the handset unit 308 or the speaker unit 310 via the voice input / output interface unit 311.

FIG. 2 is a schematic block diagram showing the configuration of the image encoding unit 307a which constitutes the image communication telephone according to this embodiment. In FIG. 2, reference numeral 201 denotes an encoding mode selection unit, and here, the input pixel value data, the prediction value data from the reference frame (previous frame), and the difference value (prediction error) of the input pixel value data The inter-frame difference value (prediction error value) is encoded with respect to the pixel value data input in macroblock units according to the energy comparison result between the two and the instruction from the image encoding control unit 215 (INTE).
R mode) or the input pixel value is directly encoded (INTRA mode). And INT
When RA mode is selected, input pixel value
When the TER mode is selected, the prediction error value is output.

The subtraction unit 202 performs a subtraction process between the input pixel value data and the reference data. In addition, the DCT unit 203
Performs a DCT (discrete cosine transform) process, which is a kind of orthogonal transform, on the input pixel value data, and the quantizer 204 selects a quantization step size according to an instruction from the image coding controller 215. And input DCT
Quantize coefficient data. Then, the quantization threshold setting unit 2
Reference numeral 05 sets a quantization threshold for increasing the zero run in the quantized output of the quantizer 204.

Here, the image coding control unit 215 is used.
Is set, the update width of the quantization threshold is set and controlled.
The variable length coding unit 206 performs variable length coding on the quantized DCT coefficient data. The transmission buffer unit 207 also stores transmission data. Inverse quantizer 208
Then, the quantized DCT coefficient data is dequantized and I
The DCT unit 209 is the ID of the input DCT coefficient data.
Perform CT (Inverse Discrete Cosine Transform) processing. Then, the addition unit 210 adds the predicted value to the data processed in the INTER mode.

The frame memory unit 211 is a frame memory for motion-compensated inter-frame prediction, and the motion vector detection unit 212 detects a motion vector for the previous frame of the processing macroblock of the current frame. In addition, the motion compensation unit 213 includes a motion vector detection unit 212.
According to the motion vector detected in, the pixel value data of the corresponding macroblock unit in the previous frame is selected.

The filter unit 214 is a low-pass filter for a block for performing motion-compensated inter-frame prediction, and the image coding control unit 215 stores the image quality signal from the system control unit 314 and the buffer storage of the transmission buffer unit 207 shown in FIG. Coding mode selection, quantization step size selection, variable threshold control, significant block judgment,
Performs various encoding controls such as frame drop (frame skip).

The data input to the coding mode selection unit 201 of the main image coding unit 307a is CCITT Recommendation H.264. 261 is a common intermediate format (CIF or QCIF). 4 to 7 are diagrams showing the configuration of the CIF format, and FIG. 8 is a diagram showing the configuration of the QCIF format. In the CIF format image, one frame shown in FIG. 4 is composed of 12 blocks called GOB (group of blocks) shown in FIG. 5, and one GOB is called a block called 33 macro blocks. Composed of. Further, as shown in FIG. 6, one macroblock is composed of six blocks (one for each of four Y blocks, Cb blocks, and Cr blocks), and one block is 8 pixels × 8 lines. (See FIG. 7).

The encoding process here is performed within a frame.
The order of GOBs 1 to 12 in FIG.
In B, the macroblocks 1 to 33 in FIG. 5 are arranged in that order, and in each macroblock, Y (luminance) blocks 1 to 4, Cb (color difference) blocks, and Cr (color difference) in FIG. Perform in the order of blocks. In addition, the QCIF format, as shown in FIG.
The number of pixels in the F format and the number of lines are each halved. Coded transmission is performed on a GOB basis, motion compensation and quantization step sizes are selected on a macroblock basis, and DCT (discrete cosine transform) and filter processing are performed on a block basis.

Therefore, the image coding unit 3 having the above configuration
The operation of 07a will be described. The pixel value data in macroblock units and the prediction value data of the previous frame are input to the subtraction unit 202 of FIG. 2, and the difference value (prediction error) between the pixel value data and the prediction value data is input to the encoding mode selection unit 2
Output to 01. Further, the pixel mode data and the difference value between the pixel value data and the prediction value are input to the encoding mode selection unit 201 in macroblock units, and the input pixel value data, the pixel value data and the prediction value are input. Energy comparison with the difference value (prediction error value) of. Then, the coding mode is selected according to the energy comparison result and the coding mode control signal from the image coding control unit 215. When the INTER mode is selected, the input pixel value is selected, and in the INTRA mode, the prediction error is selected. Value is DCT
It is output to the unit 203.

The DCT unit 203 performs a DCT (discrete cosine transform) process, which is a kind of orthogonal transform, on the pixel value data from the coding mode selection unit 201 in block units, and the resulting DCT coefficient data is obtained. Quantizer 20
Output to 4. Here, the output of the DCT unit 203 is, as shown in FIG. 9, from the upper left (DC component) to the lower right (high frequency component).
It is a data string that is scanned in a zigzag pattern.

The quantizing unit 204 includes an image coding control unit 21.
Quantize the input DCT coefficient with a step size selected according to the quantization characteristic control signal from 5. At the time of this quantization, DCT coefficients below a certain threshold value are rounded down to zero so that the zero run in the quantized data string becomes long. Further, in the quantization threshold setting unit 205,
If zero occurs in the quantized output, the threshold is updated to a higher value.

Here, the update width of the quantization threshold is variable and is set by the threshold update width setting signal from the image coding control unit 215. In the variable length coding unit 206, a significant block determination or the like is performed based on the coding control signal from the image coding control unit 215, and the quantized DCT coefficient is C
CITT Recommendation H.264 The variable length coding is performed according to H.261 and is output to the transmission buffer unit 207. The transmission buffer unit 207 is composed of a buffer memory, buffers the variable-length coded data and outputs the variable-length coded data to the demultiplexing and multiplexing unit 315, and at the same time, stores the buffer storage amount in the image coding control unit 215.
Notify to.

On the other hand, the inverse quantizer 208 includes the quantizer 2
The DCT coefficient quantized output from 04 is input, inverse quantization is performed using the quantization step size selected in the quantization unit 204, and the DCT coefficient is output. IDC
The T unit 209 performs IDCT (inverse discrete cosine transform) processing on the DCT coefficient output from the inverse quantization unit 208, and outputs it to the addition unit 210.

For the data of the macroblock processed in the INTER mode, the addition unit 210 adds the corresponding prediction value to the output from the IDCT unit 209 and outputs it, and also, the macro processed in the INTRA mode. For block data, the output from the IDCT unit 209 is output as it is. The frame memory unit 211 is a frame memory for motion-compensated inter-frame prediction, which is composed of a frame memory for at least two frames. The frame memory unit 211 accumulates the pixel value output from the addition unit 210 and simultaneously performs motion-compensated inter-frame prediction. Therefore, the pixel value data of the previous frame is output according to an instruction from the motion compensation unit 213. In addition, the motion vector detection unit 212 calculates the previous frame pixel value data near the processing macroblock position of the current frame as
A motion vector search window is read from the frame memory unit 211, and a block matching operation is performed to detect a motion vector.

The motion compensation unit 213 reads out pixel value data of the corresponding macroblock unit of the previous frame from the frame memory unit 211 according to the motion vector detected by the motion vector detection unit 212 and outputs it. The filter unit 214 is a low-pass filter for the purpose of alleviating the discontinuity at the block boundary due to the motion compensation, and performs the filtering process on the motion-compensated data, The predicted value data is output to the subtraction unit 202.

The image coding control section 215 controls the timing of the entire image coding section, and at the same time, it always controls the entire image coding section 307a or the system control section 31.
4 (FIG. 1), the image quality signal and the writing mode signal are monitored, and changes in the input image based on the amount of data accumulated in the transmission buffer unit 207 are monitored so that the transmission buffer unit 207 does not overflow. Depending on the scene change or the like, or according to the image quality setting by the communication operator, the quantization step size is adaptively selected by the quantization characteristic control signal, the quantization step size is controlled, the variable threshold is controlled, and the encoding mode control signal is used. Encoding mode determination control in the encoding mode selection unit 201, significant block determination in the variable length encoding unit 206 based on the encoding control signal, or encoding control such as frame dropping (frame skip) is performed.

Next, the encoding control in the image encoding controller 215 according to the embodiment shown in FIG. 2 will be described.
As for the encoding mode, there are an INTER mode in which the difference from the previous frame (predicted value) is encoded and an INTRA mode in which the difference is encoded without any difference. Therefore, in an image with little movement or change, the current frame and the previous frame are very similar to each other.
By using the NTER mode, the temporal redundancy is reduced, and when an image with a large motion or a scene change has a small correlation between frames, the coding within the same frame is effective. Therefore, two modes are adaptively switched, such as encoding as it is without taking the difference from the previous frame and using the INTRA mode.

Regarding the quantization characteristic, if the quantization step size is set to be small, the image quality is improved, but significant data is increased, which leads to an increase in the number of transmission bits and a decrease in frame rate. Further, if the quantization step size is set large, the data amount decreases but the image quality deteriorates. Therefore, it is necessary to constantly monitor the amount of data stored in the transmission buffer and set it appropriately and efficiently. Furthermore, depending on the number of encoded bits generated, dropping frames (frame
Processing such as skip).

As a pre-processing of the quantization, the amount of data to be generated is reduced by truncating the DCT coefficient which is below a certain level (quantization threshold value) to zero by stepping to zero and facilitating the generation of zero run. Is decreasing. Here, the threshold value for rounding down to zero is the Variable Threshold value that is updated to a higher value due to occurrence of zero.
(Variable threshold).

Next, the operation of updating the quantization threshold and setting the threshold update width will be described. FIG. 3 is a schematic block diagram showing the configuration of the quantization threshold setting unit 205 according to this embodiment. In FIG. 3, reference numeral 101 is a zero detector,
Zero is detected in the output from the quantization unit 204 shown in FIG. 2, and the quantization threshold updating unit 102 in the subsequent stage is instructed to increment the threshold. The quantization threshold updating unit 102 increments the quantization threshold when the zero detecting unit 101 detects zero in the quantized DCT coefficient. Also,
When even one quantized DCT coefficient exceeds the threshold value and the zero detection unit 101 detects a quantized output value other than zero, the quantization threshold updating unit 102 returns the quantization threshold value to the initial value.

The counter 103 counts the number of quantized DCT coefficients (including zero), and the threshold update width setting unit 104 selectively sets the update width of the threshold according to the output from the counter 103. The quantization threshold updating unit 102 and the counter 103 are reset to initial values by the block synchronization signal from the image coding control unit 215. Next, the operation of the quantization threshold setting unit 205 in this embodiment will be described.

The DCT coefficient data quantized by the quantizer 204 (see FIG. 2) is the zero detector 1 shown in FIG.
01 and the counter 103. Here, the output from the quantization unit 204 is a data string scanned in zigzag from the DC component to the high frequency component, as shown in FIG. When the zero detection unit 101 detects a zero coefficient in the input quantized DCT coefficient data, the zero detection unit 101 instructs the quantization threshold updating unit 102 at the subsequent stage to increment the quantization threshold. When a coefficient other than zero is detected, the initialization of the quantization threshold is instructed.

The quantizing threshold updating unit 102 increments the quantizing threshold when the zero detecting unit 101 in the preceding stage detects the coefficient zero. Here, the increment amount (threshold update width) is set by the threshold update width setting unit 104.
However, the quantization threshold has an upper limit. Also,
If at least one DCT coefficient exceeding the quantization threshold is input to the quantizer 204 of FIG. 1 and a quantized coefficient other than zero is generated and the zero detector 101 in the previous stage detects a coefficient other than zero, As described above, the quantization threshold value is reset to the initial value.

The counter 103 counts the quantized coefficients including the zero coefficient, and informs the threshold update width setting unit 104 at the subsequent stage of which DCT coefficient in the processing block is quantized. Threshold update width setting unit 10
Reference numeral 4 instructs the quantization threshold updating unit 102 on the threshold updating width according to the threshold updating width control signal from the image coding control unit 215 and the output of the counter 103.

The threshold update width control signal is a signal for controlling whether the update width of the threshold is variable or fixed according to the output of the counter 103. In addition, the counter 103 receives the block synchronization signal from the image encoding control unit 215.
The counter value in and the threshold in the quantization threshold updating unit 102 are initialized. Furthermore, the quantization threshold updating unit 102
And the quantization step size instruction signal from the image coding control unit 215, the quantization unit 204 performs a quantization process on the input DCT coefficient.

Next, the operation of setting the quantization threshold value in this embodiment will be described with reference to a concrete example. Figure 10
FIG. 6 is a diagram showing a specific operation of updating a quantization threshold value in the image coding apparatus according to the present embodiment. Here, the initial value of the threshold is a quantization step size (given), and the upper limit of the quantization threshold is 1.5 g. Further, as will be described later, the increment amount (update width) of the threshold value is determined by the counter output at the 32nd coefficient from the DC component as a boundary.
It is assumed that "1" and "3" are switched.

In the quantizing unit 204 shown in FIG. 2, when the DCT coefficient input from the DCT unit 203 from the DC component to the high frequency component is less than or equal to the threshold set by the quantization threshold setting unit 205, "Zero" as conversion factor
Is output to the zero detection unit 101 (FIG. 3) in the quantization threshold setting unit 205. Then, when the zero coefficient is detected by the zero detection unit 101, the quantization threshold is incremented.

As shown in FIG. 10, the update width of the threshold value is "1" for 32 coefficients from the DC component and "3" for the subsequent 32 coefficients. Also,
Since the upper limit of the threshold is 1.5 g, it is not updated any further. When the DCT coefficient exceeding the quantization threshold is input to the quantization unit 204 and even one coefficient other than zero is input to the zero detection unit 101, the threshold is reset to the initial value (quantization step size g). It When the processing of one block (64 DCT coefficients) is completed, the quantization threshold is initialized by the block synchronization signal.

As described above, according to this embodiment,
For the high frequency component, the update width of the quantization threshold is set larger than that of the direct current component and the low frequency component, and the threshold value is quickly raised by the occurrence of the coefficient zero, so that the high frequency component is not completely discarded, The DCT coefficient can be rounded down to zero only for a sufficiently small DCT coefficient, so that the generation of zero run can be efficiently promoted and the data to be transmitted can be suppressed.

In the above embodiment, two threshold update widths are prepared and the upper limit of the threshold is fixed, but the present invention is not limited to this. For example, a plurality of variable update widths may be set. Alternatively, the upper limit of the threshold may be variable. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0047]

As described above, according to the present invention, when a transform coefficient obtained by orthogonally transforming an input image in pixel block units is quantized, the quantization is performed in accordance with the quantization threshold value in which the update width is variably set. By performing the encoding, it is possible to perform efficient compression encoding processing of image information.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing a circuit configuration of an image communication telephone adopting an image encoding device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram showing a configuration of an image encoding unit 307a included in the image communication telephone according to the embodiment.

FIG. 3 is a schematic block diagram showing the configuration of a quantization threshold setting unit 205 according to the embodiment.

FIG. 4 is a diagram showing a configuration of a CIF format in the embodiment.

FIG. 5 is a diagram showing a structure of a CIF format in the embodiment.

FIG. 6 is a diagram showing a configuration of a CIF format in the embodiment.

FIG. 7 is a diagram showing a configuration of a CIF format in the embodiment.

FIG. 8 is a diagram showing a configuration of a QCIF format in the embodiment.

FIG. 9 is a matrix showing spatial frequencies.

FIG. 10 is a diagram showing a specific operation of updating a quantization threshold value in the image coding apparatus according to the embodiment.

FIG. 11 is a diagram showing a quantization threshold updating operation in a conventional image encoding device.

[Explanation of symbols]

 301 camera input unit 302 document camera input unit 303 display unit 304 image input interface unit 305 image output interface unit 306 image editing unit 307 image encoding / decoding unit 307a image encoding unit 307b image decoding unit 308 handset unit 309 microphone unit 310 speaker unit 311 voice input / output interface unit 312 voice encoding / decoding unit 312a voice encoding unit 312b voice decoding unit 313 operation unit 314 system control unit 315 demultiplexing unit 316 line interface unit 317 communication line

Claims (5)

[Claims] 1. An image coding apparatus for quantizing a transform coefficient obtained by orthogonally transforming an input image in pixel block units, a search means for searching a value of the transform coefficient, and as a result of the search, the transform coefficient is specified. If it contains a value,
An image coding apparatus comprising: a setting unit for varying an update width of a quantization threshold for the quantization; and a quantization unit for performing a quantization according to the quantization threshold set by the setting unit. 2. The image coding apparatus according to claim 1, wherein the setting unit makes the update width of the quantization threshold variable according to the frequency domain. 3. The image coding apparatus according to claim 2, wherein the setting unit increases the update width of the quantization threshold value in a high frequency region. 4. The setting means sets the quantization threshold value high when 0 is included in the transform coefficient, and the quantization threshold value when the coefficient other than 0 is included in the transform coefficient. The image encoding device according to claim 1, wherein the image encoding device is initialized. 5. An image coding method for quantizing a transform coefficient, which is obtained by orthogonally transforming an input image in pixel block units, in the step of searching the value of the transform coefficient, and as a result of the search, the transform coefficient has a specific value. Contains
An image coding method comprising: a step of varying an update width of a quantization threshold for the quantization; and a step of performing quantization according to a quantization threshold having the update width.