JP3193153B2 - Encoding / decoding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding / decoding method for encoding a symbol sequence using an arithmetic code.

[0002]

2. Description of the Related Art For example, an encoding method for compressing the information amount of an image signal obtained by raster-scanning a document includes:
The MH code adopted as a standard encoding system of the group 3 facsimile machine, the MR code adopted as the optional encoding system, and the MMR code adopted as the standard encoding system of the group 4 facsimile machine are widely used. Although being used, other than such a standard encoding method, an encoding method with good encoding efficiency has been proposed.

For example, JPEG (Joint Photo)
The image data is encoded using an arithmetic code, such as a QM-coder adopted in an entropy encoding method of a color still image (natural image) encoding method for which international standardization work is being advanced in an "graphic Experts Group". Things have been proposed.

[0004]

However, in such a conventional method, the following inconvenience is caused because a well-known standard encoding method is used in any case.

That is, for example, when eavesdropping on the transmission data of the facsimile apparatus, it is easy to decode the transmission data, which may cause a disadvantage that the original image is known to others. there were.

The present invention has been made in view of the above circumstances, and has as its object to provide an encoding / decoding method capable of easily encrypting encoded code data.

[0007]

According to the present invention, there is provided an encoding / decoding method for encoding a symbol sequence by an arithmetic code, wherein a random data pattern randomly generated at the head of code data at the time of encoding, a predetermined keyword Data is added in this order, and at the time of decoding, code data is not decoded until keyword data added to the head of code data is detected, and when keyword data is detected, subsequent code data is decoded. It was done.

Further, in an encoding / decoding method for encoding a symbol sequence by an arithmetic code, at the time of encoding, additional data formed by sequentially arranging a randomly generated random data pattern and predetermined keyword data in code data. A plurality of markers are inserted and a predetermined marker code is arranged between the additional data and the code data. When the marker code is detected during decoding, the code data is removed while removing the additional data inserted subsequently. Is decrypted. The random data pattern may have a larger number of bits than the keyword data, and the random data pattern may not include the data pattern of the keyword data.

[0009]

Therefore, if it is not known that a random data pattern and a predetermined keyword data dummy bit have been added / inserted to the code data, the code data cannot be properly decoded, and the secret of the information cannot be obtained. Can be held.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a group 3 facsimile apparatus according to one embodiment of the present invention.

In FIG. 1, a control unit 1 performs a control process of each unit of the facsimile apparatus and a facsimile transmission control procedure process.
The control unit 1 stores a control processing program to be executed, various data necessary for executing the processing program, and the like, and constitutes a work area of the control unit 1. This is for storing various information unique to the facsimile machine.

The scanner 4 is for reading a document image at a predetermined resolution, the plotter 5 is for recording and outputting an image at a predetermined resolution, and the operation display unit 6 is a facsimile apparatus. To operate,
It consists of various operation keys and various indicators.

The encoding / decoding unit 7 is, for example, a QM-co
The encoding table storage unit 8 encodes and compresses the image signal and decodes the encoded and compressed image information into the original image signal according to the der encoding method.
Is for storing an encoding table which the encoding / decoding unit 7 refers to at the time of encoding / decoding. The reference line memory 9 stores the encoding table which the encoding / decoding unit 7 refers to at the time of encoding / decoding processing. The image storage device 10 is for temporarily storing the data of the reference line to be processed, and for storing a large number of image information in a coded and compressed state.

The group 3 facsimile modem 11 is for realizing a group 3 facsimile modem function, and is a low-speed modem function (V.21 modem) for exchanging transmission procedure signals, and mainly exchanging image information. High-speed modem function (V.29 modem,
V. 27 ter modem).

The network controller 12 is for connecting the facsimile apparatus to a public telephone line network, and has an automatic transmission / reception function.

These control unit 1, system memory 2,
The parameter memory 3, the scanner 4, the plotter 5, the operation display unit 6, the encoding / decoding unit 7, the reference line memory 9, the image storage device 10, the group 3 facsimile modem 11, and the network control device 12 are connected to the system bus 13. Data is exchanged between these elements mainly via the system bus 13.

Data exchange between the network controller 12 and the group 3 facsimile modem 11 is directly performed.

Here, the arithmetic code which is the basis of the QM-coder coding method will be described. Arithmetic code means that a corresponding section (a binary decimal number [0.0 ... 0, 0.0 ... 1)) on a number line of 0 or more and less than 1 ([0, 1)) according to the occurrence probability of each symbol. The target symbol sequence is assigned to the corresponding subsections, and the coordinates of the points included in the section obtained by repeating the division recursively are distinguished at least from other sections. It is represented by a binary decimal number that can be used as a code as it is.

For example, in the binary arithmetic coding for the coded symbol sequence 0100, coding as shown in FIG. 2 is performed.

In FIG. 1, for example, when encoding the first symbol, the entire interval is divided into A (0) and A (1) according to the ratio of the occurrence probabilities of the 0 and 1 symbols. A (0) is selected. Next, when encoding the second symbol, A (0) is further divided by the occurrence probability ratio of both symbols in that state, and A (01) is selected as a section corresponding to the generated symbol sequence. Coding is advanced by repeating such division and selection processing.

This arithmetic code is a so-called non-block code, and is particularly suitable for coding in which the appearance probability of a symbol changes according to a state number (context) as in a predictive coding method. Compared with run-length codes such as codes, there are advantages in that hardware such as an encoder scale and a required memory amount can be reduced, higher efficiency can be expected, and applied coding is easier.

The above-described QM-coder implements this arithmetic coding using less hardware resources and enables higher-speed processing. Normally, image data is not directly subjected to arithmetic coding, but pre-processing is performed by predictive coding to determine whether each pixel of the image data is a lesser symbol or a more significant symbol.

Next, an encoding / decoding algorithm of QM-coder will be described.

At the beginning of encoding, a number line from 0 to less than 1 is considered. Assuming that the interval between the number lines is A, and the probability of occurrence of inferior symbols corresponding to the Markov state (state 0 in the initial state) at that time is Qe, the area after division is represented by the following equation (I).

[0026]

A = A × (1−Qe) (a: area size of dominant symbol) b = A × Qe (b: area size of inferior symbol) (I)

Here, if the first symbol is 0 (dominant symbol), a is set as a new A, and if it is 1 (inferior symbol), b is set as a new A and further division is performed. The encoding table stores a set of a relationship between a Markov state number and a probability Qe, information on a state transition when a renormalization process occurs (described later), and the like.

However, performing the multiplication operation at the time of encoding is disadvantageous in terms of the apparatus scale and the operation speed. Further, when encoding an infinite-length symbol sequence, an infinite-length operation register is required to operate a reduced area.

Therefore, the QM-coder operates so that the new A after the division always has a size of 0.75 or more and less than 1.5, so that A can be approximated to 1 and the above-mentioned equation (I ) Is approximated by the following equation (II).

[0030]

## EQU2 ## a = A-Qe b = Qe (II)

In accordance with this approximation, when the value of A becomes less than 0.75, renormalization processing in which A is bit-shifted to the left and enlarged until A becomes a value of 0.75 or more and less than 1.5. Perform By this renormalization processing, an operation requiring multiplication can be realized by subtraction, and an operation can be performed using a finite length register. When the renormalization process is performed, the state changes to the next Markov state according to the Markov state at that time and the distinction between the superior / inferior of the symbol to be processed.

The encoding process of the superior symbol is performed, for example, as shown in FIG. 3A, and the encoding process of the inferior symbol is performed, for example, as shown in FIG. Here, C represents a code, and its initial value is 0.

That is, when encoding the dominant symbol, the code C is not changed (process 101), and the value of the area A is updated to a value smaller by the probability Qe corresponding to the Markov state at that time (process 102). At this time, it is checked whether or not the value of the area A is smaller than 0.75 (determination 10
3) When the result of the judgment 103 is YES, the value of the area A and the code C are renormalized and the state is changed (processing 104), and the processing of one dominant symbol is ended. When the result of the judgment 103 is NO,
The process 104 is not performed, and the Markov state at that time is maintained.

When coding the inferior symbol, the value of code C is increased by (A-Qe) (step 20).
1) Update the value of the area A to the value of the probability Qe (Process 20)
2) The region A and the code C are re-normalized and the state is changed (process 203).

The code C generated at this time matches the binary decimal value indicating the lowermost part of the area. In the re-normalization process, the code C is shifted to the left by the same number of digits as the area A and enlarged, and the value of the code C exceeding 1 is output as code data.

FIG. 3C shows an example of the decoding process.

First, it is checked whether or not the code C is smaller than the value (A-Qe) (decision 301). If the result of the decision 301 is YES, the target pixel to be decoded is set as the dominant symbol. Judgment is made (step 302), and the value of the area A is updated to a value reduced by the probability Qe corresponding to the current Markov state (step 303). Then, it is checked whether or not the updated value of the area A has become smaller than 0.75 (determination 304). When the result of the determination 304 is YES, the area A and the code C are renormalized and the Markov state is changed. After the transition (process 305), the decoding process of this one symbol ends. When the result of the determination 304 is NO, the process 305 is not performed, and the Markov state at that time is maintained.

If the result of determination 301 is NO, the pixel of interest is determined to be the inferior symbol (step 30).
6) Update the value of code C to a value smaller by (A-Qe) (process 307), update region A to the value of probability Qe (process 308), and renormalize region A and code C. Together with the Markov state (process 309).
The decoding process for one symbol is completed.

As described above, when encoding the QM-coder, the code C does not change when a superior symbol appears, and there is little possibility that renormalization processing will be performed. The re-normalization process is performed and code data is formed.

Therefore, if the predictive coding process, which is the pre-processing, is performed so that the appearance frequency of the inferior symbol becomes small, the coding efficiency is improved and the processing speed is also improved.

FIG. 4 shows the format of encrypted code data according to one embodiment of the present invention. In this case, random data RD and a predetermined keyword KW are added to the head of the code data CD. However, the random data RD does not include the same data pattern as the data pattern of the keyword KW. Further, the keyword KW can be set in advance in the group 3 facsimile apparatus.

In the QM-coder, as described above,
Since the code is determined sequentially from the beginning of the code data CD,
Thus, the random data RD is added to the head of the code data CD.
When the random data RD and the keyword KW are added, the random data RD and the keyword KW are also decoded as a part of the code data CD. Therefore, unless the random data RD and the keyword KW are removed, an appropriate decoding process is performed. Can not do. That is, in this case, the code data CD can be encrypted by adding the random data RD and the keyword KW.

Therefore, in this case, when encoding is performed on the transmission side of the group 3 facsimile apparatus, the encoded data CD
, A random facsimile transmission operation can be performed by adding the random data RD and the keyword KW to the head of the received code data and removing the random data RD and the keyword KW at the head of the received code data.

At the same time, even if such transmission data is intercepted by another person, the random data R
Since D and the keyword KW cannot be removed, for example,
A noise-like image is obtained, the original image cannot be reproduced properly, and the secret of information can be kept.

FIG. 5 shows a processing example at the time of encoding the encoded data.

First, a preset keyword (for example, 32 bits) is input (process 401), and random data having a predetermined number of bits (for example, 128 bits) is generated (process 402). Next, when the random data generated at that time includes the data pattern of the keyword, the data pattern is deleted,
Form a modified random data pattern (process 40)
3). The modified random data pattern thus formed is output as code data (step 40).
4) Output the keyword as code data (Process 4)
05).

Then, one bit of data to be encoded is input (process 406), and the above-described encoding process is performed (process 4).
07). It is checked whether or not a code is output in this encoding process (decision 408). If the result of decision 408 is YES, the code is output (decision 409).

Next, it is checked whether or not the data to be encoded has been completed (decision 410), and the result of decision 410 is NO.
, The process returns to step 406 to input the next data. When the result of determination 410 is YES, the encoding process has ended, and this process ends.

FIG. 6 shows an example of a process at the time of decoding the encoded data of FIG.

First, a preset keyword is input (process 501), and code data to be decoded is sequentially read until a keyword KW is detected, and random data RD and RD added to the head of the code data CD are read. Skip keyword KW (process 502, judgment 5
03 NO loop).

Random data RD and keyword KW
Is skipped, and if the result of determination 503 is YES, one bit of subsequent code data CD is input (process 504), and decoding processing is performed on the one-bit input data (process 505).

At that time, it is checked whether or not the code data CD has been completed (decision 506). If the result of decision 506 is NO, the process returns to step 504 to process the next bit. Also, the result of decision 506 is YES
, The decoding process ends.

With the above configuration, when the group 3 facsimile apparatuses mutually transmit data, as shown in FIG. 7, first, when the calling terminal TX calls the called terminal RX, the called terminal RX becomes the own terminal. A digital identification signal DIS for notifying of a standard device function provided in the own terminal while responding with a called station identification signal CED for indicating that the terminal is a non-voice terminal; A non-standard function identification signal NSF for notifying the specified non-standard device function is returned.

The originating terminal TX receives these signals,
After confirming the function of the destination terminal RX and knowing that the destination terminal RX has a function of receiving the encrypted code data, various transmission functions including the encrypted code data mode and used at the time of transmitting the image information are performed. Non-standard function setting signal NSS
Is transmitted, and then a training check signal TCF is transmitted to perform the modem training procedure at the transmission rate set at that time.

The destination terminal RX receives the non-standard function setting signal NSS
The transmission rate specified by the above is set to the group 3 facsimile modem 10, and the training check signal TCF is received. If the reception result of the training check signal TCF at that time is good, the reception preparation confirmation signal CFR is responded.

Upon receiving the reception preparation confirmation signal CFR, the originating terminal TX reads the image of the transmission original set on the scanner 4 at that time, and executes the above-described encoding processing of the encrypted code data. As shown in FIG. 4, random data RD and a keyword KW are added to the head of the code data CD to form encrypted code data, and the encrypted code data is transmitted as image information PIX. Image information PI
When the transmission of X is completed, at this time, since there is no subsequent transmission image information, a procedure end signal EOP is transmitted.

The destination terminal RX executes the above-described decryption processing of the encrypted code data of the received image information PIX to obtain the random data RD and the keyword added to the head of the code data CD. After removing the KW, the code data CD is decoded, and the image signal obtained thereby is transferred to the plotter 5 to record and output the received image. In this case, the procedure end signal EOP
In response to a message confirmation signal MCF indicating that the image information PIX has been normally received.

The calling terminal TX sends a message confirmation signal MCF
Is received, a disconnection command signal DCN is sent out to restore the line, and a series of image information transmission operations ends. Further, upon receiving the disconnection command signal DCN, the destination terminal RX restores the line and ends a series of image information receiving operations.

Thus, the image information transmission operation is performed.

In the above-described embodiment, the random data RD and the keyword K are added to the head of the code data CD.
The code data CD is encrypted by adding W, but the encryption method is not limited to this.

For example, as shown in FIG.
D, the random data RD and the keyword KW are added to the beginning, and the random data R
The code data CD can also be encrypted by appropriately inserting D and the keyword KW. In this case, between the inserted random data RD and the code data CD immediately before it, a marker code MK indicating a break of the code data CD is inserted.

FIGS. 9A and 9B show an example of an encoding process for forming the encoded data of FIG.

First, a preset keyword is input (process 601), and random data having a predetermined number of bits is generated (process 602). Next, when the random data generated at that time includes the data pattern of the keyword, the data pattern is deleted to form a corrected random data pattern (step 60).
3). The modified random data pattern thus formed is output as code data (step 60).
4) Output the keyword as code data (Process 6)
05).

Then, the counter i for managing the number of processed encoded data is cleared to 0 (processing 6).
06). Next, one bit of data to be encoded is input (process 607), and the above-described encoding process is performed (process 60).
8).

It is checked whether or not a code is output in this encoding process (decision 609). If the result of decision 609 is YES, the code is output to a predetermined code buffer (process 610). Next, the value of the counter i is increased by one (process 611), and it is checked whether or not the value of the counter i is equal to N at that time (decision 612).

When the result of decision 612 is NO,
Since the processing for one unit of the data to be encoded has not been completed, the process returns to the step 607 to execute the encoding processing of the next encoded data. When the result of the determination 612 is YES, the processing for one unit of the data to be encoded has been completed, so that the contents of the code buffer at that time are output as the code data CD, The contents are deleted (step 613), and it is checked whether or not the processing of all data to be encoded has been completed (decision 61)
4).

When the result of decision 614 is YES, this encoding process ends. When the result of the determination 614 is NO, after outputting the marker code MK as the code data CD (process 615), the process 604
After outputting the modified random data pattern and the keyword, the processing of the next data to be encoded is executed.

FIG. 10 shows a processing example at the time of decryption of the encoded data of FIG.

First, a preset keyword is input (step 701), and code data to be decoded is sequentially read until a keyword KW is detected, and random data RD and RD added to the head of the code data CD are read. Skip the keyword KW (processing 702, judgment 7
03 NO loop).

When the skipping of the random data RD and the keyword KW at the head is completed and the result of the judgment 703 is YES, one bit of the following code data CD is input (processing 704), and the input of the one bit is performed. The decoding process is performed on the data (process 705).

In the decoding process, the marker code M
It is checked whether or not K has been detected (judgment 706).
If the result of step 06 is YES, the process returns to step 702, where the subsequent random data RD and keyword KW
Is skipped, the processing of the next code data CD is executed.

When the result of the judgment 706 is NO, it is checked whether or not the code data CD is completed at that time (decision 707). When the result of the judgment 707 is NO, the process returns to the process 704, and The next bit is processed. On the other hand, when the result of determination 707 is YES, the decoding process ends.

As described above, in the above-described embodiment, since the code data is encrypted, the secrecy of the communication can be maintained.

In the above-described embodiment, a keyword is set in advance for the group 3 facsimile apparatus, but the method of setting this keyword is not limited to this. For example, a password set at the time of confidentiality can be used as a keyword. Further, the number of bits of the keyword and the number of bits of the random data are not limited to those described above. Further, the above-described random data can be generated by giving dummy data to an arithmetic decoder in the encoding / decoding unit, for example.

In the above-described embodiment, encrypted code data is always transmitted. However, whether to transmit encrypted code data or unencrypted code data is set before transmission. You can negotiate by procedure.

In the above-described embodiment, the present invention is applied to the group 3 facsimile apparatus. However, the present invention can be applied to an encoding / decoding unit of other terminal apparatuses.

In the above-described embodiment, the present invention is applied to the transmission system. However, the present invention can be similarly applied to the storage system.

[0078]

As described above, according to the present invention,
If it is not known that a random data pattern and a predetermined keyword data dummy bit are added / inserted to the code data, the code data cannot be properly decoded. The effect that can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a group 3 facsimile apparatus according to one embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the principle of an arithmetic code.

FIG. 3 is a flowchart showing an example of an encoding algorithm and a decoding algorithm of QM-coder.

FIG. 4 is a schematic diagram showing an example of encrypted encoded data.

FIG. 5 is a flowchart showing an example of an encoding process for forming the encoded encoded data shown in FIG. 4;

FIG. 6 is a flowchart illustrating an example of a decoding process of the encrypted encoded data illustrated in FIG. 4;

FIG. 7 is a time chart showing an example of a procedure of image information transmission of the apparatus shown in FIG. 1;

FIG. 8 is a schematic view showing another example of the encrypted code data.

FIG. 9 is a flowchart illustrating an example of an encoding process of the encoded encoded data illustrated in FIG. 8;

FIG. 10 is a flowchart illustrating an example of a decoding process of the encrypted encoded data illustrated in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control part 2 System memory 7 Encoding / decoding part 8 Encoding table storage part

Claims (3)

(57) [Claims] 1. An encoding / decoding method for encoding a symbol sequence using an arithmetic code, comprising: a random data pattern randomly generated at the head of code data during encoding;
Predetermined keyword data is added in this order, and at the time of decryption,
An encoding / decoding method characterized in that decoding of encoded data is not performed until keyword data added to the head of the encoded data is detected, and subsequent encoded data is decoded when keyword data is detected. 2. An encoding / decoding method for encoding a symbol sequence by an arithmetic code, wherein at the time of encoding, additional data obtained by sequentially arranging a randomly generated random data pattern and predetermined keyword data in code data. A plurality of markers are inserted and a predetermined marker code is arranged between the additional data and the code data. When the marker code is detected during decoding, the code data is removed while removing the additional data inserted subsequently. An encoding / decoding method characterized by decoding. 3. The random data pattern has a larger number of bits than the keyword data, and the random data pattern does not include the data pattern of the keyword data. Encoding / decoding method according to any one of the preceding claims.