JPH08316846A - Image coder, image decoder, image coding method and image decoding method - Google Patents

Abstract

PURPOSE: To attain image coding/decoding by efficient variable length coding and vector quantization even when a quantization level number of an input image is revised. CONSTITUTION: The method uses a quantization circuit 21 quantizing an input image by a decided quantization level number, a reference code table 22 representing cross reference between an input series and a variable length code word, a code word table conversion circuit 23 converting the reference code word table by an identifier corresponding to the quantization level number used by the quantization circuit, a variable length coding circuit 25 applying variable length coding to an output image of the quantization circuit by using the code word table 24 converted by the code word table conversion circuit and a CPU 26 controlling the image coder. Thus, a code word or a quantization vector is easily allocated and the code word or the quantization table corresponding to the input series is retrieved in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding method and an image decoding method for compressing image signal data.

[0002]

2. Description of the Related Art In recent years, various digital image data compression encoding techniques have been developed, some of which are image encoding devices,
It has been commercialized as a decryption device. This is because a high-efficiency image compression coding technique is required for transmitting and recording image data having a huge amount of information.

The conventional image coding apparatus and image decoding apparatus described above will be described below with reference to the drawings.

FIG. 7 is a diagram showing the configuration of a typical conventional image coding apparatus. In FIG. 7, reference numeral 71 is an image series conversion circuit, which converts an input image by prediction difference, orthogonal transformation, or the like in order to improve coding efficiency. Reference numeral 72 is a code word table, which shows the correspondence between the input sequences to the variable length coding circuit 73 and the variable length code words. Reference numeral 73 is a variable-length coding circuit, which uses the codeword table 72 to perform variable-length coding on the output of the image sequence conversion circuit.

[0005] The operation of the image coding apparatus configured as described above will be described below. First, the image signal
1 into the image series conversion circuit. The input image is a digital image obtained by sampling and quantizing an analog signal. The number of image quantization levels is often predetermined, and MPEG (Moving Pictu
re Coding Experts Group) inputs an image with a quantization level number of 8 bits.

The image sequence conversion circuit 71 reduces the spatial and temporal redundancy of the image. Specifically, in MPEG, spatial redundancy is reduced by the discrete cosine transform (DCT), and temporal redundancy is reduced by the difference between frames.

Next, the output of the image sequence conversion circuit 71 is changed to 73
Input to the variable length coding circuit of. Generally, there is a bias in the appearance probability of a pixel series of an image, and this is the entropy redundancy of the image. The variable-length coding circuit 73 assigns short codewords to those having a high appearance probability and long codewords to those having a low occurrence probability, thereby reducing the entropy redundancy of the image. In MPEG, two-dimensional variable length coding is performed in which a variable length code word is assigned to a set of a run length of a pixel value 0 of an input sequence of a variable length coding circuit and a pixel value other than 0 following it. The variable length coding circuit 73 selects and codes a variable length codeword from the codeword table 72 for the combination of the 0 run length and the pixel value of the input sequence. The code word table is created from the input image by entropy coding such as Huffman coding. In actual coding, however, a code table is often created in advance and used for all input images. In MPEG, entropy coding is used and the number of quantization levels is 8 bits
A codeword table is prepared in advance so that the input image can be efficiently coded, the codeword is coded according to the codetable, and the codeword sequence is output from the coding device.

The above-described image coding apparatus reduces the redundancy of the image and codes the image at a high compression rate.

FIG. 8 is a diagram showing a configuration of a decoding device for decoding an image coded by the above coding device. FIG.
In 81, a code word table 81 is the same as the code word table of the encoding device. A variable length decoding circuit 82 decodes the input codeword sequence using a codeword table. Reference numeral 83 denotes an image sequence inverse conversion circuit, which performs inverse conversion of the image sequence conversion in the encoding device.

The operation of the image decoding apparatus configured as described above will be described below. The codeword sequence encoded by the encoding device is first input to the variable length decoding circuit 82. Decoding is possible by obtaining the 0 run length and the pixel value from the variable length codeword using the codeword table of 81. Further, the output of the variable length decoding is inversely converted by the image series inverse conversion circuit 83, so that the image can be decoded.

There have also been attempts to apply vector quantization to image coding. FIG. 9 is a diagram showing an example of an encoding device to which vector quantization is applied. In FIG. 9, 91
Is a codebook showing the quantized output vector.
Reference numeral 92 is a vector quantization circuit, which performs vector quantization of the input image using the codebook of 91.

The operation of the image coding apparatus configured as described above will be described below. First, the image is input to 92 vector quantization circuits. The vector quantization circuit of 92 vector-quantizes the input image using the codebook of 91.

In vector quantization, a plurality of pixels are collectively quantized as a quantized output vector to reduce image redundancy. A codeword sequence can be obtained by outputting an index indicating each quantization vector. A variable length codeword may be assigned to the index according to its appearance probability. The codebook is composed of a set of quantized output vectors, and the input vector composed of a plurality of pixels of the input image is quantized to the closest quantized output vector in the codebook. Vector quantization enables efficient coding depending on the codebook structure.
The LBG algorithm has been developed as a method for generating an efficient codebook.

FIG. 10 is a diagram showing the configuration of a decoding device for decoding an image coded by the above-mentioned coding device using vector quantization. In FIG. 10, 101 is a codebook, which is the same as the codebook of the encoding device. 102 is a vector quantization decoding circuit, which decodes the input codeword sequence using the codebook of 101.

The operation of the image decoding apparatus configured as described above will be described below. The codeword sequence encoded by the encoding device is first input to the vector quantization decoding circuit 102. Using the codebook 101, the quantized output vector can be obtained from the index of the quantized output vector indicated by the codeword. An image is decoded by this quantized output vector.

[0016]

The number of quantization levels of an image greatly affects the image quality. If the number of quantization levels is increased, the image quality is improved, but the amount of information is also increased accordingly, which imposes a heavy burden on image transmission and recording. Conversely, if the number of quantization levels is reduced, the amount of image information is reduced, but the image quality is reduced. Image users have different requirements for image quality and information amount, and the number of quantization levels of an image should be changeable according to the user's application.

However, in the above configuration, the codeword table for variable length coding and the codebook for vector quantization are considered only when the number of quantization levels of the input image is one, and the input image is not considered. When the number of quantization levels of s is different, the codeword table and the codebook do not match and the compression efficiency is reduced. Further, if it is attempted to deal with a large number of quantization levels, the code word table and the code book become huge, which adversely affects code word allocation and code word search.

In view of the above problems, the present invention provides an image coding method and an image coding method capable of efficiently performing variable length coding and vector quantization even when the number of quantization levels of an input image is changed. The present invention provides an image decoding method for decoding a signal encoded by the above.

[0019]

In order to solve the above problems, the image coding apparatus of the present invention is a quantizing means for inputting an image signal and quantizing the image signal with a predetermined number of quantization levels. A codeword selecting means for selecting one codeword table from the set of codeword tables by an identifier corresponding to the number of quantization levels; and the image signal quantized by using the selected codeword table. It is provided with a variable-length coding means for performing variable-length coding and outputting the codeword sequence as a result of the variable-length coding and the identifier.

Another image coding apparatus of the present invention is a quantizing means for inputting an image signal and quantizing the image signal with a predetermined number of quantization levels, and an identifier corresponding to the number of quantization levels. A codeword table converting means for converting the reference codeword table according to the above, variable length encoding the quantized image using the converted reference codeword table, and a codeword sequence which is the result of the variable length encoding. A variable length coding means for outputting the above-mentioned identifier is provided.

A decoding device of the present invention is an image decoding device for inputting a code word sequence and an identifier output from the above image coding device, wherein one of a plurality of code word tables is selected according to the above identifier. A control means for selecting one codeword table and a variable length decoding means for decoding the codeword sequence using the selected codeword table are provided.

Another decoding device of the present invention is an image decoding device for inputting a codeword sequence output by another image coding device and an identifier, and a reference codeword table according to the identifier. And a variable length decoding means for decoding the codeword sequence using the converted reference codeword table.

[0023]

According to the present invention, the codeword table for variable-length coding or the codebook for vector quantization can be changed according to the number of quantization levels of the input image by the above-mentioned configuration,
Even when the number of quantization levels is changed, efficient encoding and decoding can be performed.

Further, according to the present invention, according to the above-mentioned structure,
Since each codeword table or codebook does not become huge, allocation of codewords or quantized vectors becomes easy, and retrieval of codewords or quantized vectors corresponding to input sequences can be performed in a short time.

[0025]

【Example】

(Embodiment 1) FIG. 1 shows the configuration of an image coding apparatus according to the first embodiment of the present invention. In FIG. 1, 1
Reference numeral 1 is a quantization circuit, 12 is a set of code word tables, 13 is a code word table selection circuit, 14 is a variable length coding circuit, and 15 is a CPU which is a control device.

Further, in the present embodiment, it is assumed that a variable length code word is given to a set of 0 run length of the input sequence and subsequent pixel values other than 0 to perform two-dimensional variable length coding. It is assumed that the set of 12 codeword tables is composed of a total of N codeword tables of the first to Nth codeword tables (N is a natural number).

The operation of the image coding apparatus configured as described above will be described below. In this embodiment, 11
Number of quantization levels nbit (nbit (n
Is a natural number). The code word table selection circuit of 13 is 1
One codeword table is selected from the set of codeword tables by the identifier from the CPU of 5. An identifier is associated with the number of quantization levels in order to select the codeword table according to the number of quantization levels of the input image. In this embodiment, the number of quantization levels n itself is used as an identifier. In the encoding device, a codeword table of variable length encoding suitable for encoding an image of each quantization level number is prepared and prepared in advance by entropy encoding or the like. An identifier is associated with each code word table. Here, the code word table for the quantization level number nbit is the n-th code word table in FIG. 1, and the identifier n is associated. Since the number of quantization levels is nbit, the codeword table selection circuit 13 selects the nth codebook. The variable length coding circuit 14 has a set of 0 run length and pixels as an input sequence, and performs variable length coding using the n-th codeword table. When the number of quantization levels of the input image is changed, the codeword table for repeatedly selecting the same operation as above is changed. Finally, the image coding apparatus outputs the variable-length coded codeword sequence and the identifier.

As described above, according to this embodiment, the code table can be automatically changed even when the number of quantization levels of the input image is changed, and efficient coding can be performed.

Although a quantizing circuit is provided in the present embodiment, the digital image and its quantizing level number or identifier may be directly input without the quantizing circuit.

The input image may be quantized after conversion of an image sequence such as DCT or image difference. However, the code table prepared is for the converted image.

As an output of the encoding device, the method of selecting the code word table may be described as an operation program of the CPU or an operation program of the code word table selection circuit, encoded, and sent to the decoding device. The codeword table selection method includes a method of associating the identifier with the codeword table, a method of selecting the CPU identifier, and the like.

The codeword table itself selected as the output of the encoder may be sent to the decoder. In this case, the identifier need not be sent.

In this embodiment, the identifiers and the code tables correspond one to one, but one code table may correspond to a plurality of identifiers.

In this embodiment, the variable length codeword is assigned to the set of 0 run length and the pixel value other than 0 following it. However, the variable length codeword may be assigned to only the pixel value.

Only when the number of quantization levels is 1 bit, coding suitable for binary images such as run length, MR, and MH coding may be performed.

In this embodiment, a set of codebooks is used instead of the set of 12 codeword tables, a codebook selecting circuit is used instead of the codeword table selecting circuit 13 and a variable length coding circuit is used instead of the variable length coding circuit 14. An input image may be encoded by vector quantization using a vector quantization circuit. In the case of vector quantization, the codebook selection circuit selects a codebook with an identifier corresponding to the number of quantization levels, and vector quantization is performed using the codebook.

(Embodiment 2) FIG. 2 shows the structure of an image coding apparatus according to the second embodiment of the present invention. Figure 2
, 21 is a quantization circuit, 22 is a reference codeword table, 2
3 is a code word table conversion circuit, 24 is a code word table, 25 is a variable length coding circuit, and 26 is a CPU.

The operation of the image coding apparatus configured as described above will be described below. In this embodiment, 21
The input image is quantized to the number of quantization levels nbit by the quantization circuit of. In this embodiment, a variable length code word is given to a set of 0 run length of the input sequence and the pixel value other than 0 following it. The code word table conversion circuit 23 converts the reference code word table 22 into the code word table 24 according to the identifier from the CPU 26. In this embodiment, the number of quantization levels n itself is used as an identifier, and the reference codeword table is converted into a codeword table for nbit for the number of quantization levels nbit of the input image. The conversion method will be described later. The 25 variable-length coding circuits perform variable-length coding using the 24 codeword tables. When the number of quantization levels of the input image is changed, the same operation as described above is repeatedly converted into a code word table according to the number of quantization levels. Finally, the image coding apparatus outputs the variable-length coded codeword sequence and the identifier.

As described above, according to this embodiment, it is possible to perform encoding corresponding to a change in the number of quantization levels of an input image with one reference codeword table.

Although a quantizing circuit is provided in this embodiment, the digital image and the number of quantizing levels or the identifier thereof may be directly input without the quantizing circuit.

The input image may be quantized after conversion of an image sequence such as DCT or image difference. However, the code table prepared is for the converted image.

The code word table conversion method may be described as an output of the encoding device by the operation program of the CPU or the operation program of the code word table conversion circuit, encoded, and sent to the decoding device.

The codeword table itself selected as the output of the encoder may be sent to the decoder. In this case, the identifier need not be sent.

In the present embodiment, the variable length code word is assigned to the set of 0 run length and the pixel value other than 0 following it. However, variable length coding may be used in which the variable length code is assigned only to the pixel value.

When the number of quantization levels is 1 bit, run length, MR (Modified Read), MH (Modified H)
It is also possible to perform coding suitable for a binary image such as (uffman) coding.

In this embodiment, a reference codebook is replaced by the reference codebook 22; a codebook conversion circuit is replaced by the codeword table selection circuit 23; a codebook is replaced by the codeword table 24; A vector quantization circuit may be used in place of the variable length coding circuit of No. 3, and the input image may be coded by vector quantization. In the case of vector quantization, the codebook conversion circuit converts the codebook using the identifier corresponding to the number of quantization levels, and vector quantization is performed using the codebook.

(Embodiment 3) FIG. 3 shows the configuration of an image decoding apparatus according to a third embodiment of the present invention. FIG.
In the figure, 31 is a set of code word tables, 32 is a code word table selection circuit, 33 is a variable length code decoding circuit, 34 is an inverse quantization circuit, and 35 is a CPU.

The operation of the image decoding apparatus configured as above will be described below. In this embodiment, the first
The codeword sequence coded by the coding device of the embodiment of
3 to the variable length decoding circuit. Further, the identifier output from the encoding device is input to the CPU 35. The set of 31 code word tables is the same as that of the coding device that has performed the coding, and the code word selection method is also the same as that of the coding device. The CPU of 35 selects one codeword table by the codeword table selection circuit of 32 according to the identifier. The variable length decoding circuit 33 decodes the codeword sequence using the selected codeword table.
The CPU 35 obtains the number of quantization levels from the input identifier, and the inverse quantization circuit inversely quantizes and decodes the image decoded by the number of quantization levels.

As described above, according to this embodiment, the code word sequence of the first embodiment can be decoded. The code word table selection method may be input to the CPU from the encoding device, and the code word table may be selected according to the input code word table selection method.
Then, even if the method of selecting the code word table of the decoding device is changed, the decoding device can cope.

In the present embodiment, a set of codebooks is replaced with a set of 31 codeword tables, a codebook selection circuit is replaced with a codeword table selection circuit 32, and a variable length decoding circuit is replaced with a variable length decoding circuit 33. An input image may be decoded by vector quantization using a vector quantization circuit. In the case of vector quantization decoding, the codebook selection circuit selects a codebook according to the identifier, and vector quantization is performed using the codebook.

(Embodiment 4) FIG. 4 shows the arrangement of an image decoding apparatus according to the fourth embodiment of the present invention. FIG.
In the figure, 41 is a reference codeword table, 42 is a codeword table conversion circuit, 43 is a codeword table, 44 is a variable length decoding circuit, 45 is an inverse quantization circuit, and 46 is a CPU.

The operation of the image decoding apparatus configured as described above will be described below. In this embodiment, the third
Of the codeword sequence encoded by the encoding device of the embodiment of FIG.
4 to the variable length decoding circuit. Also, the identifier output from the encoding device is input to the 45 CPU. The code word table conversion circuit 42 uses the same encoding device as the encoding device, and the reference code word converting method is also the same as the encoding device. The CPU of 46 converts the reference codeword table of 41 by the codeword table conversion circuit of 42 according to the identifier. The variable length decoding circuit 44 decodes the code word sequence using the converted code word table. The CPU of 46 obtains the number of quantization levels from the inputted identifier, and the image decoded by the number of quantization levels is inversely quantized by the inverse quantization circuit of 45.

As described above, according to this embodiment, the code word sequence of the second embodiment can be decoded. The code word table conversion method may be input to the CPU from the encoding device, and the code word table may be converted according to the input code word table conversion method.
Then, even if the conversion method of the code word table of the encoding device is changed, the decoding device can cope.

In the present embodiment, the vector quantization decoding circuit may be used instead of the variable length code decoding circuit to perform the vector quantization decoding. In the case of vector quantization, the same codebook as the coding device is prepared instead of the codeword table, and the codebook is converted according to the identifier.

(Embodiment 5) FIG. 5 shows a processing flow of a code word table conversion circuit in a fifth embodiment of the present invention. This process is used in the third embodiment, and the reference code word table is converted into the code word table used in the variable length coding circuit.

The reference codeword table of this embodiment is a codeword table suitable for encoding an image having a quantization level number mbit (m is a natural number), and is assumed to be created by entropy encoding or the like. It is also assumed that the number of quantization levels of the image before input to the quantization circuit is also mbit. The number of quantization levels of the quantizer is nbit.
And n <m in the present embodiment.

In this embodiment, the run length of the input sequence is 0 (hereinafter ru
It is assumed that two-dimensional variable-length coding is performed in which a variable-length code is assigned to a set of a pixel value other than 0 (hereinafter referred to as “n”) and a pixel value other than 0 (hereinafter referred to as level).

The operation of the above codeword table conversion circuit will be described below with reference to FIG. First, in the process of 51 of FIG. 5, the level of the reference codeword table is quantized to nbit. This operation corresponds to quantizing the input image. 51 in next 52 processes
The quantization result in the process of is stored as the converted level as the converted level value. The processes of 51 and 52 are repeated for all level values in the codeword table. Next, since some levels have the same post-conversion level due to quantization, as a process of 53, the levels having the same post-conversion level and run are grouped into one group.

Next, in the process of 54, the same codeword is assigned in the group. Here, the shortest code word in the group can be assigned as the same code word.
Also, a new codeword can be assigned to each group. In step 55, the newly assigned codeword is registered in the codeword table after conversion together with the run and level of the group.

As described above, the code word table conversion circuit can convert the reference code word table into the code word table by the above processing.

In the present embodiment, the two-dimensional variable-length coding is performed in which the variable-length codeword is assigned to the set of 0 run length and the pixel value. It can be converted in the same way.

If the input image is subjected to image conversion such as DCT conversion or prediction difference, a reference code word table is created for the converted image, and the reference code word table is converted into the above-mentioned conversion code. Convert in a way.

(Embodiment 6) FIG. 6 shows a processing flow of a codebook conversion circuit according to a sixth embodiment of the present invention. This codebook conversion circuit is used in the third embodiment of the present invention and converts the reference codebook into a codebook.

The operation of the above codebook conversion circuit will be described below with reference to FIG. The reference codebook of the present embodiment is a codebook suitable for encoding an image with a quantization level number of mbit. It is also assumed that the number of quantization levels of the image before input to the quantization circuit is also mbit. Further, it is assumed that the number of quantization levels of the quantization circuit is nbit and that n <m in this embodiment.

First, in the processing of 61 in FIG. 6, the components of the quantized output vector in the reference codebook are quantized into n bits.
This operation corresponds to quantizing the input image. In the next step 62, the quantization result in the step 61 is stored as the quantized output vector after conversion. The processing of 61 and 62 is repeated for all the quantized output vectors. Next, because some quantization output vectors have the same quantized output vector after conversion, as a process of 63, those having the same quantized output vector after conversion are combined into one group.

Next, in the process of 64, the same codeword is assigned to the quantized output vectors in the group. Here, if the code indicating the quantized output vector is variable-length coded,
The shortest codeword in the group can be assigned as the same codeword. Further, any codeword in the group may be assigned, or a new codeword may be assigned again. In the process of 65, the code word newly assigned to the converted code word table is registered together with the run and level of the group.

With the above processing, the codebook conversion circuit can convert the reference codebook into a codebook.

If the input image is subjected to image conversion such as DCT conversion or prediction difference, a reference codebook is created for the converted image and the reference codebook is converted by the above conversion method. Convert.

[0069]

As described above, the image coding apparatus of the present invention inputs the image signal, and quantizes the image signal with a predetermined number of quantization levels, and the quantization level number. 1 from the set of codewords according to the corresponding identifier
Code word selecting means for selecting one code word table, variable length coding the quantized image signal using the selected code word table, and the code word sequence and the identifier which are the result of the variable length coding. The variable length coding means for outputting is provided. Another image encoding device of the present invention is configured to receive an image signal, quantize the image signal with a predetermined number of quantization levels, and an identifier corresponding to the number of quantization levels. Codeword table conversion means for converting the reference codeword table, variable-length coding the quantized image using the converted reference codeword table, the codeword sequence is the result of the variable-length coding and the identifier The variable length coding means for outputting is provided. Therefore, the codeword table for variable length coding can be changed according to the number of quantization levels of the input image, and efficient coding can be performed even when the number of quantization levels is changed. In addition, since each codeword table does not become huge, the codewords can be easily assigned and the codewords corresponding to the input sequence can be searched in a short time.

The decoding device of the present invention is an image decoding device for inputting the codeword sequence output by the image coding device and an identifier, and one of a plurality of codeword tables is selected according to the identifier. A control means for selecting one codeword table and a variable length decoding means for decoding the codeword sequence using the selected codeword table are provided.

Another decoding apparatus of the present invention is an image decoding apparatus for inputting a codeword sequence output by another image coding apparatus and an identifier, and a reference codeword table according to the identifier. And a variable length decoding means for decoding the codeword sequence using the converted reference codeword table. Therefore,
Efficient encoding and decoding can be performed. In addition, since each codebook does not become huge, it is easy to allocate the quantized vector and the quantized vector corresponding to the input sequence can be searched in a short time.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image coding apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an image coding apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an image decoding apparatus according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an image decoding apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a processing flow of a codeword table conversion circuit according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a processing flow of a codebook conversion circuit according to a sixth embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a conventional image coding apparatus using variable length coding.

FIG. 8 is a diagram showing a configuration of a conventional image coding apparatus using vector quantization.

FIG. 9 is a diagram showing a configuration of a conventional image decoding device using variable length coding.

FIG. 10 is a diagram showing a configuration of a conventional image decoding device using vector quantization.

[Explanation of symbols]

 11, 21 Quantization circuit 12, 31 Codeword table set 22, 41 Reference codeword table 13, 32 Codeword table selection circuit 23, 42 Codeword table conversion circuit 24, 43 Codeword table 14, 25 Variable length coding Circuits 15, 26, 35, 46 CPU 33, 44 Variable length decoding circuit 34, 45 Dequantization circuit

Claims (24)

[Claims] 1. A quantizer for inputting an image signal and quantizing the image signal with a predetermined number of quantizing levels, and an identifier corresponding to the number of quantizing levels to select one from among a set of code word tables. Code word selecting means for selecting one code word table, variable length coding the quantized image signal using the selected code word table, and the code word sequence and the identifier which are the result of the variable length coding. An image coding apparatus having a variable length coding means for outputting. 2. A reference codeword table is converted in accordance with a quantizing means for inputting an image signal and quantizing the image signal with a predetermined number of quantization levels, and an identifier corresponding to the number of quantization levels. Code word table conversion means, variable length coding means for variable length coding the quantized image using the converted reference code word table, and outputting a code word sequence as a result of the variable length coding and the identifier An image coding apparatus including. 3. An image decoding device for inputting a codeword sequence and an identifier output by the image encoding device according to claim 1,
An image including control means for selecting one code word table from a plurality of code word tables according to the identifier and variable length decoding means for decoding the code word sequence using the selected code word table Decoding device. 4. An image decoding apparatus for inputting a codeword sequence and an identifier output by the image encoding apparatus according to claim 2,
Image decoding including second codeword table conversion means for converting the reference codeword table according to the identifier, and variable length decoding means for decoding the codeword sequence using the converted reference codeword table. Device. 5. A sequence registered in a reference codeword table with the number of quantization levels is quantized, sequences having the same quantized result are combined into one group, and the one group is newly added to one sequence. 3. The image coding apparatus according to claim 2, wherein the shortest variable-length codeword in the group is assigned to the group, and the reference codeword table is converted. 6. A sequence registered in a reference codeword table with the number of quantization levels is quantized, sequences having the same quantized result are combined into one group, and the one group is newly added to one sequence. 4. The image decoding apparatus according to claim 3, wherein the shortest variable-length codeword in the group is assigned to the group, and the reference codeword table is converted. 7. A quantizer for inputting an image signal and quantizing the image signal with a predetermined number of quantization levels, and one codebook among a plurality of codebooks according to the number of quantization levels. And a variable length for outputting the codeword sequence as the result of the vector quantization and the number of quantization levels, by vector quantizing the quantized image signal using the codebook selecting means for selecting An image coding apparatus including a coding means. 8. A quantizing means for inputting an image signal and quantizing the image signal with a predetermined number of quantization levels, and a code block converting means for converting a reference codebook according to the number of quantization levels. , Image coding using variable-length coding means for vector-quantizing the quantized output using the converted codebook, and outputting the codeword sequence resulting from the vector quantization and the number of quantization levels apparatus. 9. An image decoding apparatus for inputting a codeword sequence and the number of quantization levels output from the image encoding apparatus according to claim 7, wherein a plurality of codebooks are selected according to the number of quantization levels. An image decoding apparatus comprising codebook selecting means for selecting one codebook from among the codebooks, and variable length decoding means for decoding the codeword sequence using the selected codebook. 10. An image decoding device for inputting a codeword sequence and a quantization level number output from the image encoding device according to claim 8, wherein the reference codebook is converted according to the quantization level number. An image decoding device comprising codebook conversion means and variable length decoding means for decoding the codeword sequence using the converted codebook. 11. A quantized output vector registered in a reference codebook with the number of quantization levels is quantized, and vectors having equal quantized results are combined into one group, and one group is quantized as one quantized output. Vector and
9. The image coding apparatus according to claim 8, wherein the shortest variable-length codeword in the group is assigned to the group to transform the reference codebook. 12. A quantized output vector registered in a reference codebook with the number of quantization levels is quantized, and vectors having equal quantized results are combined into one group, and one group is quantized as one quantized output. Vector and
The image decoding device according to claim 10, wherein the shortest variable-length codeword in the group is assigned to the group, and the reference codebook is converted. 13. An image signal is input, the image signal is quantized by a predetermined number of quantization levels, and one codeword table is selected from a set of codeword tables by an identifier corresponding to the number of quantization levels. Image coding characterized by variable length coding the quantized image signal using the selected code word table and outputting the code word sequence and the identifier that are the result of the variable length coding Method. 14. An image signal is input, the image signal is quantized by a predetermined number of quantization levels, a reference code word table is converted according to an identifier corresponding to the number of quantization levels, and the converted reference is converted. An image coding method characterized in that the quantized image is variable-length coded using a codeword table, and a codeword sequence as a result of the variable-length coding and the identifier are output. 15. A codeword sequence output by the image coding method according to claim 13 and an identifier are input, one codeword table is selected from a plurality of codeword tables according to the identifier, and the selection is performed. An image decoding method, characterized in that the above codeword sequence is decoded using the codeword table. 16. A codeword sequence output by the image coding method according to claim 14 and an identifier are input, a reference codeword table is converted according to the identifier, and the converted reference codeword table is used to convert the reference codeword table. An image decoding method characterized by decoding a codeword sequence. 17. A sequence registered in a reference codeword table with the number of quantization levels is quantized, sequences having the same quantized result are combined into one group, and the one group is newly added to one sequence. 15. The image coding method according to claim 14, wherein the shortest variable-length codeword in the group is assigned to the group, and the reference codeword table is converted. 18. A sequence registered in a reference codeword table with the number of quantization levels is quantized, sequences having the same quantized result are combined into one group, and the one group is newly added to one sequence. 16. The image decoding method according to claim 15, wherein the shortest variable-length codeword in the group is assigned to the group, and the reference codeword table is converted. 19. An image signal is input, the image signal is quantized by a predetermined number of quantization levels, one codebook is selected from a plurality of codebooks according to the number of quantization levels, and An image coding method, characterized in that the quantized image signal is vector-quantized by using a selected codebook, and a codeword sequence and a quantization level number which are the result of the vector quantization are output. 20. An image signal is input, the image signal is quantized by a predetermined number of quantization levels, a reference codebook is converted according to the number of quantization levels, and the converted codebook is used, An image coding method characterized in that a quantized output is vector-quantized, and a codeword sequence as a result of the vector quantization and the number of quantization levels are output. 21. A codeword sequence output by the image coding method according to claim 19 and the number of quantization levels are input, and one codebook is selected from a plurality of codebooks according to the number of quantization levels. Then, the image decoding method is characterized in that the codeword sequence is decoded using the selected codebook. 22. A codeword sequence output by the image coding method according to claim 20 and the number of quantization levels are input, a reference codebook is converted according to the number of quantization levels, and the converted codebook is converted. An image decoding method, characterized in that the above codeword sequence is decoded. 23. The quantized output vector registered in the reference codebook is quantized by the number of quantization levels used in the quantization circuit, and the vectors having the same quantized result are grouped into one group. 21. The image coding method according to claim 20, wherein a single quantized output vector is used, the shortest variable-length codeword in the group is assigned to the group, and the reference codebook is converted. 24. The quantized output vector registered in the reference codebook is quantized by the number of quantization levels used in the quantization circuit, and the vectors having equal quantized results are grouped into one group. 23. The image decoding method according to claim 22, wherein one quantization output vector is used, the shortest variable-length codeword in the group is assigned to the group, and the reference codebook is converted.