JP3131051B2 - Encoding / decoding method and apparatus therefor - 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, a method for encoding a symbol sequence using an arithmetic code, and decoding information encoded using an arithmetic code. And an encoding / decoding apparatus for forming an original symbol sequence.

[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]

SUMMARY OF THE INVENTION The present invention relates to an encoding / decoding method for encoding a symbol sequence by an arithmetic code and decoding information encoded by the arithmetic code to form an original symbol sequence. At the time of encoding, the initial value of the appearance probability width used at the beginning of encoding is set to a nonstandard arbitrary value, and at the time of decoding, the initial value of the appearance probability width used at the beginning of decoding is the same as at the time of encoding The value is used. Further, as the initial value of the appearance probability width, any positive rational number smaller than 1 may be used.

[0008] Further, in an encoding / decoding device which encodes a symbol sequence by an arithmetic code and decodes information encoded by the arithmetic code to form an original symbol sequence, it is used at the beginning of encoding / decoding. An encoding / decoding means capable of setting an initial value of the appearance probability width to an arbitrary value; and, when the standard mode is set, the encoding / decoding means sets the initial value of the appearance probability width to a predetermined standard value. And a control means for setting the initial value of the appearance probability width to a predetermined non-standard value for the encoding / decoding means when the non-standard mode is set. Further, as the initial value of the appearance probability width, any positive rational number smaller than 1 may be used.

[0009]

Therefore, if the initial value of the appearance probability width used at the beginning of encoding is not known, the encoded information cannot be properly decoded, and the information can be kept secret.

[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
This is for encoding and compressing an image signal by the der encoding method, and for decoding the encoded and compressed image information into the original image signal. The appearance probability used at the time of encoding / decoding is used. The initial value of the width A (described later) can be set from the outside. The encoding table storage unit 8 is for storing an encoding table which the encoding / decoding unit 7 refers to at the time of encoding / decoding.
This is for storing a large number of image information in a coded and compressed state.

The group 3 facsimile modem 10 realizes a group 3 facsimile modem function, and exchanges transmission procedure signals at a low speed (V.21 modem) and mainly exchanges image information. High-speed modem function (V.29 modem,
V. 27ter modem, V.I. 33 modems).

The network control device 11 is for connecting the facsimile machine to a public telephone line network and has an automatic transmission / reception function.

These control unit 1, system memory 2,
Parameter memory 3, scanner 4, plotter 5, operation display unit 6, encoding / decoding unit 7, image storage device 9, group 3 facsimile modem 10, and network control device 11
Are connected to a system bus 12, and data exchange between these elements is mainly performed through the system bus 12.

Data exchange between the network controller 11 and the group 3 facsimile modem 10 is directly performed.

Here, the arithmetic code which is the basis of the QM-coder coding method will be described. The arithmetic code is a corresponding section (appearance probability width; binary decimal [0.0... 0, 0.0...) On a number line of 0 or more and less than 1 ([0, 1)).
1)) is divided into unequal lengths according to the occurrence probabilities of the respective symbols, the target symbol sequence is assigned to the corresponding sub-interval, and is included in the interval obtained by repeating the division recursively. The coordinates of the point are expressed as a binary decimal number which can be distinguished from at least other sections, and are directly used as codes.

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 these number lines is A (= appearance probability width), and the probability of occurrence of the inferior symbol corresponding to the Markov state (state 0 in the initial state) at that time is Qe, the area after division is expressed by ).

[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. The initial value of the appearance probability width A is set to 1.

That is, when encoding the dominant symbol, the code C is not changed (process 101), and the value of the region (= appearance probability width) A is updated to a value smaller by the probability Qe corresponding to the Markov state at that time. (Step 102). At this time, it is checked whether or not the value of the area A is smaller than 0.75 (decision 103). When the result of the decision 103 is YES, the value of the area A and the code C are renormalized and the state transition is performed. (Step 104), the processing of one dominant symbol ends. If the result of the determination 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.

As described above, 1 is used as the initial value of the area (= appearance probability width) A. For example, if this initial value is changed during encoding, the initial encoding state changes. Therefore, an encoding result different from that when the initial value is set to 1 is obtained.

For example, the image signal obtained by reading the image of the type original shown in FIG. 4 by the scanner 4 is encoded by the encoding / decoding unit 7 in a state where the initial value of the area A is set to 0.6. The image information obtained by compression is decoded by the encoding / decoding unit 7 in a state where the initial value of the area A is also set to 0.6, and the image corresponding to the obtained image signal is plotted by the plotter 5. By recording and outputting, the same original as that shown in FIG. 4 can be recorded and output.

On the other hand, the image information obtained by encoding and compressing under the same conditions is decoded by the encoding / decoding unit 7 in a state where the initial value of the area A is set to 1 as a standard. When the image is recorded and output by the plotter 5, at this time, since the conditions at the time of encoding and the conditions at the time of decoding are different, an image almost in a noise state is obtained as shown in FIG.

Similarly, an image signal obtained by reading the image of the handwritten document shown in FIG.
Is encoded and compressed by the encoding / decoding unit 7 in a state where the initial value is set to 0.6, and the image information obtained thereby is encoded and decoded in a state where the initial value of the area A is also set to 0.6. When the image corresponding to the image signal obtained by decoding by the converting unit 7 is recorded and output by the plotter 5, FIG.
The same original can be recorded and output.

On the other hand, image information obtained by encoding and compressing under the same conditions is decoded by the encoding / decoding unit 7 in a state where the initial value of the area A is set to the standard value of 1. When the image is recorded and output by the plotter 5, at this time, since the conditions at the time of encoding and the conditions at the time of decoding are different, an image almost in a noise state is obtained as shown in FIG.

If the initial value of the area A at the time of encoding differs from the initial value of the area A at the time of decoding, significant data cannot be obtained when decoding. That is, the image information to be transmitted can be encrypted by using a different value from the standard value for the initial value of the area A. In this embodiment, the initial value of the area A is set to a specific value as described above. And an encryption mode that uses the encoded and compressed image information.

When transmitting the image information, if the partner terminal has the same encryption mode, the initial value of the area A is set to a predetermined encryption mode value (for example, 0.6) to encode the image signal. The image is compressed to form image information. When the other terminal does not have the same encryption mode, the initial value of the area A is set to a standard value (that is, 1), and the image signal is encoded and compressed.

In the above configuration, when the group 3 facsimile apparatuses mutually transmit data, as shown in FIG. 8, 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 calling terminal TX receives these signals,
When the function of the destination terminal RX is confirmed, and it is known that the destination terminal RX has an encryption mode function, a non-standard function setting for notifying various transmission functions used for transmitting image information at that time, including the encryption mode, is set. It sends out a signal NSS, and then sends out a training check signal TCF to perform a 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 calling terminal TX reads the image of the transmission original set on the scanner 4 at that time, and sets the code of the state where the initial value of the area A is set to 0.6. The encoding / decoding unit 7 encodes and compresses the image signal obtained by reading by the scanner 4, and transmits the obtained image information PIX to the destination terminal RX. When the transmission of the image information PIX is completed, at this time, since there is no subsequent transmission image information, a procedure end signal EOP is transmitted.

At this time, since the encryption mode is set at the destination terminal RX, the image information P received by the encoding / decoding unit 7 with the initial value of the area A set to 0.6 is set.
IX is decoded into an original image signal, and the image signal obtained thereby is transferred to the plotter 5 to record and output a received image. In this case, a message confirmation signal MCF indicating that the image information PIX has been normally received is returned to the procedure end signal EOP.

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.

As described above, since the image information transmitting operation of the image information PIX in the encrypted state is performed, a third party who eavesdrops on the image information transmission and intercepts the image information PIX can obtain the image information PIX. Even if an attempt is made to restore the original image from the PIX, an appropriate image cannot be obtained because the initial value of the area A at the time of decryption is not known, and therefore, the purpose of the encryption mode can be achieved.

The initial encryption mode value of the area A is
The value is not limited to 0.6 as described above, as long as it is determined in advance on the transmitting side and the receiving side. Basically, an appropriate value can be used as long as it is a positive rational number less than 1.

FIG. 9 shows a processing example at the time of transmission.

First, a designated destination is called (processing 10).
1) Receive the called station identification signal CED, digital identification signal DIS, and non-standard function identification signal NSF from the called terminal (process 102).

The non-standard function identification signal NSF
It is checked whether or not the same encryption mode as that of the terminal itself is included (decision 103). If the result of decision 103 is YES, the encryption mode is set and the encoding / decoding section 7 sets the initial value of the area A As the value, the above-described predetermined encryption mode value (for example, 0.6) is set (Step 10).
4) If the result of the determination 103 is NO, the non-encryption mode is set, and the above-described predetermined standard value (1) is set in the encoding / decoding unit 7 as the initial value of the area A (processing). 105).

When the process related to the setting of the encryption mode is executed in this way, a non-standard device setting signal NSS for notifying the encryption mode and the other transmission function set at that time is formed, and transmitted to the destination terminal. Send (Process 10
6). Then, a modem training procedure is executed at the modem speed set at that time (process 107), and the modem speed used at the time of transmitting the image is determined.

Next, the scanner 4 sends one of the transmitted originals.
The image for the page is read and input (process 108), and the image signal obtained thereby is sequentially transferred to the encoding / decoding unit 7, and is encoded and compressed by the encoding / decoding unit 7, and the image information obtained thereby is obtained. Is transferred to the group 3 facsimile modem 10 and the image information is transmitted (process 109).

When the transmission of the image information for one page is completed,
It is checked whether the next page is set in the scanner 4 (decision 110). If the result of the decision 110 is YES, the multi-page signal M is output as a post-message signal.
A PS is transmitted (step 111), a response signal from the destination terminal is received (step 112), and the process returns to step 108 to transmit the image information of the next page.

If the result of determination 110 is NO, a procedure end signal EOP is sent as a post-message signal (process 113), a response signal from the destination terminal is received (process 114), and a disconnection command signal DCN is sent. After the transmission (process 115), the line is restored (process 116), and a series of image information transmission operations is terminated.

FIG. 10 shows a processing example at the time of reception.

When an incoming call is detected, the line is closed (process 2).
01), called station identification signal CED, digital identification signal DI
S and the non-standard function identification signal NSF are transmitted (step 202), and the non-standard function setting signal NSS is received from the calling terminal (step 203).

At this time, it is checked whether or not the encryption mode is designated (decision 204), and the result of decision 204 is YE
When S is reached, the encryption mode is set, and the above-mentioned predetermined encryption mode value (for example, 0.6) is set in the encoding / decoding unit 7 as the initial value of the area A (processing 205). When the result of step 204 is NO, the non-encryption mode is set and the encoding / decoding unit 7
Then, the above-described predetermined standard value (1) is set as the initial value of the area A (step 206). Next, the modem training procedure is executed at the modem speed notified at that time (process 207), and the modem speed used at the time of receiving the image is determined.

In this way, when the preparation for receiving the image information is completed, the image information for one page is received (process 208), and the received image information is sequentially transferred to the encoding / decoding section 7 and is returned to the original. The image signal is decoded into an image signal, and the obtained image signal is sequentially transferred to the plotter 5 to record and output a received image (Process 2).
09).

When the reception of the image information for one page is completed,
It is checked whether there is a subsequent page (decision 210). When the result of determination 210 is YES, a response signal indicating the reception state at that time is sent to the calling terminal (processing 2).
11) Return to the process 208 to receive the image information of the next page.

When the result of determination 210 is NO, a response signal indicating the reception state at that time is sent to the calling terminal (process 212), and a disconnection command signal DCN is received (process 213). After recovery (process 214), a series of image receiving operations ends.

In the above embodiment, the case where the present invention is applied to a group 3 facsimile apparatus has been described. However, the present invention is applicable to other communication apparatuses.
The same can be applied.

In the above-described embodiment, the image information transmission operation in the encryption mode is executed when the partner terminal has the encryption mode. Can be executed. Further, the image information transmitting operation in the encryption mode can be always executed. Further, the encryption mode value of the area A is changed at a certain cycle or by a user setting.
It can be changed as appropriate.

The present invention can be applied not only to transmission systems but also to storage systems. Further, the present invention can be similarly applied to a coding / decoding method of an arithmetic coding method other than the above-described QM-coder.

[0072]

As described above, according to the present invention,
Unless the initial value of the appearance probability width used at the beginning of the encoding is known, the encoded information cannot be properly decoded, so that the effect of maintaining the secret of the information 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 a type document image.

FIG. 5 is a schematic diagram showing an example of an image obtained when the image of FIG. 4 is transmitted in the encryption mode and decrypted under standard conditions.

FIG. 6 is a schematic diagram showing an example of a handwritten document image.

FIG. 7 is a schematic diagram showing an example of an image obtained when the image of FIG. 5 is transmitted in the encryption mode and decrypted under standard conditions.

FIG. 8 is a time chart showing an example of a procedure at the time of transmitting image information in the apparatus of FIG. 1;

FIG. 9 is a flowchart illustrating a processing example at the time of transmission.

FIG. 10 is a flowchart illustrating a processing example at the time of reception.

[Explanation of symbols]

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

Claims (4)

(57) [Claims] An encoding / decoding method for encoding a symbol sequence using an arithmetic code and decoding information encoded using the arithmetic code to form an original symbol sequence. The initial value of the probability of occurrence width used for is set to any non-standard value, and the same value as at the time of encoding is used as the initial value of the probability of occurrence width used at the time of decoding and at the beginning of decoding. Encoding / decoding method. 2. The method according to claim 1, wherein the initial value of the appearance probability width is any positive rational number smaller than 1.
Encoding / decoding method according to any one of the preceding claims. 3. An encoding / decoding apparatus which encodes a symbol sequence by an arithmetic code and decodes information encoded by the arithmetic code to form an original symbol sequence is used at the beginning of the encoding / decoding. An encoding / decoding means capable of setting an initial value of the appearance probability width to an arbitrary value; and, when the standard mode is set, the encoding / decoding means sets the initial value of the appearance probability width to a predetermined standard value. And a control means for setting the initial value of the appearance probability width to a predetermined non-standard value for the encoding / decoding means when the non-standard mode is set. Decryption device. 4. The method according to claim 3, wherein the initial value of the appearance probability width is any positive rational number smaller than 1.
An encoding / decoding device according to claim 1.