JPH0638048A - Data compressing method for image and code - Google Patents

Abstract

PURPOSE:To compress both of image data and code data at high compressibility with simple device configuration by encoding the image data and the code data with one arithmetical encoding means. CONSTITUTION:Since an arithmetical code is a known encoding system suitable for the image data (a,) high compression effects can be obtained. When compressing character code data (b,) in a reference symbol possessing means 3, input data are parallelly arranged for the unit of 8 bits as the code length of one character, and respective bit data around an attention bit are extracted. Since correlation between the attention bit and the peripheral bits is made strong as a result, the hitting rate of predicting symbol appearance probability is improved. Therefore, the high compression effects can be obtained even to the character code data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image and code data compression method for selectively compressing binary image data and code data such as characters.

[0002]

2. Description of the Related Art Data compression is often performed when transmitting or storing data. As an encoding method for performing data compression, an arithmetic code, which is one of the predictive encoding methods, or Ziv-Lempe (Ziv-Lempe) is used.
The universal code of l) is known.

Since the arithmetic code is suitable for the data of the Markov information source and can be adapted according to the characteristics of the data, it is often adopted for the data compression of the binary image data. On the other hand, since the universal code has a high compression effect on data in which long data having the same symbol pattern appears repeatedly, it is often adopted for data compression of code data such as a character code.

By the way, there are cases where it is desired to arbitrarily select either image data or coded data for data compression.

In this case, conventionally, generally, two types of encoding methods, such as the arithmetic code and the universal code, have been used properly. For this reason, it is necessary to provide two types of encoding means in the device, which complicates the device.

On the other hand, as disclosed in, for example, Japanese Patent Laid-Open No. 3-70268, there has been proposed one in which image data and character code data are compressed by one encoding means.

In this proposal, character code data is compressed in bytes by a universal code.
Further, the image data is MH (Modified Huf).
fman), MR (Modified Relativ)
e Element Address Design
te) or MMR (Modified MR) system, and then assigns a fixed length code to the run length code and mode information obtained by the encoding,
The fixed length code is data-compressed by the universal code. By this processing, the periodicity of each data of the character code and the fixed length code is absorbed, and the compression effect becomes relatively high.

However, in the above proposal, MH, MR
Alternatively, since another encoding means called MMR is required, the device is complicated as in the above case.

Further, in the case of the universal code, the compression effect is enhanced when long data of the same symbol series appears repeatedly in the data to be processed, but the data length of the same symbol series is short or the number of appearances is small. If
The compression effect was reduced.

[0010]

As described above, the prior art is as follows.
If a high compression effect is to be obtained for both image data and coded data, a plurality of coding means are required, and the device becomes complicated.

The present invention solves the above problems and provides a method for compressing both image data and code data with a simple device configuration, and a method of compressing image and code data that provides a high compression effect. To aim.

[0012]

To this end, according to the present invention, a fixed number of input data are arranged in parallel, the symbol appearance probability of the target bit is predicted from the state of each bit around the target bit, and the predicted value The known arithmetic coding means for compressing data by coding the correspondence with the actual symbol is 1
In the case of compressing binary image data, when the number of pixels of one image line is set as the above-mentioned fixed number and the data is compressed by the arithmetic coding means, the code data is compressed by theta. Sets the number of bits per code data unit as the above-mentioned fixed number and compresses the data by the arithmetic coding means.

[0013]

Since only one encoding means is required, the device structure becomes simple. Further, since the image data is compressed by the arithmetic coding means as usual, a high compression effect can be obtained. In addition, since the code data are arranged in parallel one by one when the symbol appearance probability is predicted, the correlation between the target bit and each surrounding bit becomes strong. As a result, the prediction accuracy is improved, and a high compression effect can be obtained even for coded data.

[0014]

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

FIG. 1 is a block diagram of an encoding apparatus according to an embodiment of the present invention. In the figure,
The P / S conversion means 1 converts character code data of a parallel signal into data of a serial signal. The input switching means 2 switches between inputting image data and character code data. The reference symbol acquisition means 3 arranges a fixed number of input data in parallel and determines the state of each bit around the target bit. The reference symbol acquisition means 3 is provided with a 1-line bit number switching means 3a for switching the above-mentioned fixed number of input data arranged in parallel in two steps.

The probability table 4 is a data table that stores various probability values indicating the appearance probability of symbols.
The prediction value / probability data selection table 5 is a data table that stores a prediction value of a symbol and a pointer that points to one probability value in the probability table 4, corresponding to each of the determined bit states. is there. The prediction determination means 6 determines whether or not the predicted value of the symbol matches the actual value, that is, whether or not the prediction is correct. In addition, in other words, the determination result indicates whether the data symbol is the MPS (dominant symbol) or the LPS (inferior symbol). The arithmetic code generation means 7 generates an arithmetic code based on the determination result and the read probability value.

The table rewriting means 8 rewrites the pointer in the predicted value / probability data selection table 5 in accordance with the hit state of the symbol prediction. The identification code inserting means 9 inserts an identification code indicating which data is prior to each encoded data of an image and a character.

FIG. 2 is a block diagram showing the configuration of a decoding device that restores the encoded data generated by the encoding device to the original data. In the figure, an identification code detecting / removing means 10 detects an identification code of input encoded data and removes the identification code. The arithmetic code decoding means 11 determines whether the data symbol is MPS or LP depending on the encoded data and the probability value.
Whether or not it is S is determined.

The reference symbol acquisition means 3, probability table 4, predicted value / probability data selection table 5, prediction determination means 6 and arithmetic code generation means 7 have the same functions as in FIG. In this case, the prediction determination means 6 uses the MPS.
The data symbol is reproduced according to the LPS discrimination result and the symbol prediction value.

The output switching means 12 switches the signal path depending on whether the image data is reproduced or the character code data is reproduced. The S / P converter 13 converts serial signal data into parallel signals.

Next, the operation of the encoding apparatus of the present embodiment having the above configuration will be described.

Image data or character code data is arbitrarily input to the encoding device together with the data type signal. The data type signal indicates whether the input data is image data or character code data. The image data is binary data obtained by reading the original image by performing main scanning and sub-scanning at a constant resolution, and is sequentially input line by line. The character code data is character string information such as alphanumeric characters and is sequentially input in the ASCII code format.

As shown in FIG. 3, when the data type signal is input, this encoding device determines the type of data input by the signal (process 101). Now, for example, if the input data is image data (process 1
01 "image"), the input switching means 2 selects the image data side (processing 102), and the identification code inserting means 9 outputs an identification code indicating that it is an image (processing 103).
Then, the 1-line bit number switching means 3a sets the bit number of 1 line to the number of pixels of the original image in the main scanning direction (process 104).

On the other hand, if the input data is character code data (“character” in processing 101), the input switching means 2 selects the P / S conversion means 1 side (processing 105) and the identification code insertion means 9 is used. An identification code indicating a character is output (process 106). Then, the 1-line bit number switching means 3a sets the bit number of 1 line to 8 bits which is one unit of the ASCII code (process 107).

Then, a predetermined encoding process is started. That is, when the image data is input, the image data is directly input to the reference symbol acquisition means 3. If character code data is entered, P / S
It is converted into a serial signal by the conversion means 1 and input to the reference symbol acquisition means 3.

In the reference symbol acquiring means 3, as shown in FIG. 4, the input data is sequentially arranged in parallel by the set number of 1-line bits. Then, paying attention to each input bit, according to the preset template T,
10-bit data at a fixed position with respect to the target bit X is taken out. That is, the bits to be extracted are 2-bit data D1 and D2 on the same line, 5-bit data D2 to D6 on the previous line, and 3-bit data D7 to D9 on the line before the previous line.

Since the fetched data D0 to D9 are 10 bits, as shown in FIG. 5A, each state of the symbol pattern is organized into 1024 types. The reference symbol acquisition unit 3 determines the symbol patterns of the extracted data D0 to D9 as states 0 to 1023.

The predicted value / probability data selection table 5 contains
As shown in (b) of the figure, the predicted value and pointer value of the MPS are stored corresponding to each of the states 0 to 1023 of the symbol pattern. The predicted value / probability data selection table 5 outputs a predicted value and a pointer value corresponding to the one determined state. The probability table 4 stores various probability values assigned serial numbers, as shown in FIG. The probability table 4 outputs the probability value of the number indicated by the pointer value.

Prediction judging means 6 compares the predicted value of the MPS with the symbol of the input data to judge whether the prediction is correct. In other words, this determination result indicates whether the symbol of the input data is MPS or LP.
S is shown. The arithmetic code generation means 7 generates an arithmetic code by a known operation based on the determination result and the probability value and outputs the arithmetic code to the outside (above, processing 10).
8).

In parallel with the above-mentioned encoding operation, the table rewriting means 8 counts the number of times the symbol prediction is correct and the number of times the symbol prediction is incorrect (process 109). Then, it is determined whether or not each of the counted numbers has reached a predetermined number (process 110). If the specified number of times has not been reached (N in process 110), it is then determined whether or not data switching is instructed by the data type signal (process 111). If the data switching is not instructed (N in process 111), it is determined whether the data has ended (process 112). If not (N in process 112), the operation is continued (to process 108).

Here, it is assumed that image data is being input. In this case, in the reference symbol acquisition means 3, as shown in FIG. 4, the image data are arranged line by line, and the template DO extracts the data DO to D9 around the target bit X. In the case of image data, it is well known that these data DO to D9 and the bit X of interest have a strong correlation. In the above encoding process,
The symbol of the bit of interest X is set to the data DO to D with strong correlation.
Since the prediction is performed based on 9, the prediction accuracy increases and the data compression rate also increases.

Next, it is assumed that character code data is being input. In this case, in the reference symbol acquisition means 3,
The character code data is arranged in order with 8 bits as one line, and each data DO to D9 around the target bit X is extracted in the same manner as above.

Now, for example, it is assumed that the input character code data is the data of the character string "ASCII ...". ASCII code is 8 bits per character,
When arranged in the reference symbol acquisition means 3, it becomes as shown in FIG. That is, “A” is “0100000
1 "and" S "are" 01010011 "and" C "is" 01 "
“000011” and “I” are data “01001001”, and most of the upper 3 to 4 bits of each character are the same. Therefore, the correlation between each data DO to D9 extracted by the template T and the target bit X is strong.

As a result, even when the character code data is encoded, the prediction accuracy is high and the data compression rate is high, as in the case of the image data.

On the other hand, when the number of hits or the number of misses of the symbol prediction reaches the specified number (Y in process 110), the pointer value stored in the predicted value / probability data selection table 5 is rewritten. That is, when the hit count reaches the specified count, the pointer value is rewritten so as to indicate a higher probability value in the probability table of the probability table 4. On the contrary, when the number of deviations reaches the specified number, the pointer value is rewritten so as to indicate a lower probability value (process 113). As a result, adaptation is performed according to the characteristics of the data being encoded, and the symbol prediction accuracy is further improved.

Next, it is assumed that data switching is instructed by the data type signal. In this case (Y in process 111), the data type is determined and the above process is executed similarly (to process 10). As a result, as shown in FIG. 7, the coded data of each of the image and the character is sequentially output together with the identification code indicating the data type. When there is no input data (Y in process 112), the above encoding process is terminated.

Next, the operation of the decoding apparatus of this embodiment will be described.

The data signal encoded by the above encoding device is input to the decoding device. As shown in FIG. 8, when the decoding device receives a data signal, the identification code detecting / removing means 10 reads the identification code and determines the data type (process 201).

If the data signal is image data ("image" in step 202), the 1-line bit number switching means 3a sets the bit number of 1 line to the number of pixels in the main scanning direction of the original image ( Process 203). If it is character code data (“character” in process 202), the 1-line bit number switching means 3a sets the bit number of 1 line to 8 bits (process 204). Then, in the case of image data, the output switching means 12 selects the image output signal line, and in the case of character data, the S / P conversion means 13 side is selected (process 205).

Then, a predetermined decoding process is executed. That is, the arithmetic code decoding means 11 decodes into the information whether the original data symbol is MPS or LPS based on the input coded data and the probability value output from the probability table 4. The prediction determination means 6 restores the symbol of the original data based on the information and the predicted value output from the predicted value / probability data selection table 5.
In the case of image data, the restored data is output as it is. Further, in the case of character code data, it is converted into a parallel signal by the S / P conversion means 13 and output. In addition,
The reference symbol acquisition unit 3, the predicted value / probability data selection table 5, the probability table 4, and the arithmetic code generation unit 7 operate in the same manner as in the above-described encoding device (above,
Process 206).

In parallel with the above decoding operation, as in the case of FIG. 3, the prediction result of the symbol is determined, and the pointer value of the prediction value / probability data selection table 5 is rewritten according to the determination result (process). 109, process 110 and process 1
13).

During the above operation, the identification code of the input data is monitored (process 207). If the identification code is not detected (N in process 207), it is determined whether the input data is completed (process 208). If not (N in process 208), the decoding operation is continued (process 206).
What). When there is no input data (Y in process 208), the above decoding process is terminated.

As described above, the coding apparatus of this embodiment is
One arithmetic code encoding means is provided, and the image data and the character code data are both compressed by the one encoding means.

As a result, since it is not necessary to provide two types of encoding means as in the conventional case, the device structure is simplified.
Further, since the decoding device only needs to be provided with one decoding means for the corresponding arithmetic code, the device configuration is similarly simplified.

Since the arithmetic code is a known coding method suitable for image data, a high compression effect can be obtained.
Further, when the character code data is compressed by the data, the input data is arranged in parallel in the reference symbol acquisition means 3 in units of 8 bits which is the code length of one character, and each bit data around the target bit is taken out. I have to.

In the case of character code data, even if the characters are different, the bits at the same position are likely to be the same, so the correlation between the target bit and the peripheral bits becomes strong. As a result, the accuracy of the prediction of the symbol appearance probability increases, so that a high compression effect can be obtained for the character code data.

According to the experiments of the inventor, it was confirmed that the data amount was compressed to 40% or less when the character string information of the C language source program was data-compressed by the encoding apparatus of this embodiment. There is.

In the case of a C language source program,
The same character string appears frequently, but for example, "0.1258
6 2.13658 5.23698 ... ”, even in the case of real-valued data in which the same character string rarely appears, the upper bits of each character match, so that the encoding apparatus according to the present embodiment , High data compression effect can be obtained.

Further, in this embodiment, the identification code indicating the data type of the image and the character is inserted at the beginning of the generated encoded data. As a result, the decryption device can determine the data type by the identification code at the time of decryption and automatically execute the predetermined operation.

In the above embodiment, an example of encoding character string information of ASCII code as the code data has been described, but other character string codes may be used, and various code information other than characters may be encoded in the same manner. can do.
In that case, the reference symbols are arranged in parallel in the reference symbol acquisition means 3.
The number of line bits may be set to one code length.
For example, in the case of JIS code, one character is 2 bytes,
Set the number of 1 line bits to 2 bytes. Further, the number of 1 line bits is not limited to one code length, and may be set to an integral multiple of the code length.

Although the identification code inserted into the encoded data is shown only for the data type, it may be shown for the number of 1-line bits.

By the way, since the encoded data of the arithmetic code is pseudo random data, there is no data pattern that does not appear. Therefore, the specific code cannot be fixedly defined as the identification code. Therefore, for example, the first to third various codes are set, and the identification code is defined as a series of the first and second codes, while the first code is added to the encoded data at the time of encoding. If appears, the third code is arranged to be inserted after that. Thus, when encoding, the first code is detected, and when the second code is further detected, it can be determined that the code is the identification code.

[0053]

As described above, according to the present invention, since both the image data and the code data are coded by one arithmetic coding means, the device configuration is simplified and the code data is In the data compression, the number of bits per code data unit is arranged in parallel, and the appearance probability of the target symbol is predicted based on the pattern of each bit symbol around the target bit. Since the hit rate of the prediction result is high, a high compression effect can be obtained for both the image data and the coded data.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an encoding device according to an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a decoding device according to an embodiment of the present invention.

FIG. 3 is an operation flowchart of encoding processing.

FIG. 4 is an explanatory diagram showing an operation of arranging input data and extracting each bit data.

FIG. 5 is an explanatory diagram showing a symbol prediction operation.

FIG. 6 is an explanatory diagram showing an arrangement method of character code data.

FIG. 7 is an explanatory diagram of output data of the encoding device.

FIG. 8 is an operation flowchart of a decoding process.

[Description of Codes] 1 P / S conversion means 2 Input switching means 3 Reference symbol acquisition means 3a 1 Line bit number switching means 4 Probability table 5 Predicted value / probability data selection table 6 Prediction determination means 7 Arithmetic code generation means 8 Table rewriting Means 9 Identification code insertion means 10 Identification code detection / removal means 11 Arithmetic code decoding means 12 Output switching means 13 S / P conversion means

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[Procedure amendment]

[Submission date] December 4, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an encoding device according to an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a decoding device according to an embodiment of the present invention.

FIG. 3 is an operation flowchart of encoding processing.

FIG. 4 is an explanatory diagram showing an operation of arranging input data and extracting each bit data.

FIG. 5 is an explanatory diagram showing a symbol prediction operation.

FIG. 6 is an explanatory diagram showing an arrangement method of character code data.

FIG. 7 is an explanatory diagram of output data of the encoding device.

FIG. 8 is an operation flowchart of a decoding process.

[Description of Codes] 1 P / S conversion means 2 Input switching means 3 Reference symbol acquisition means 3a 1 Line bit number switching means 4 Probability table 5 Predicted value / probability data selection table 6 Prediction determination means 7 Arithmetic code generation means 8 Table rewriting Means 9 Identification code insertion means 10 Identification code detection / removal means 11 Arithmetic code decoding means 12 Output switching means 13 S / P conversion means

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 4]

[Figure 5]

[Figure 6]

[Figure 7]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 8]

Claims (4)

[Claims] 1. A method of compressing an image and a code for selectively inputting binary image data having a constant number of pixels of one line and code data having a constant number of bits of one unit for data compression. , Input data is arranged in parallel by a fixed number, the symbol appearance probability of the bit of interest is predicted from the state of each bit around the bit of interest, and data is compressed by encoding the correspondence between the predicted value and the actual symbol. 1
When two binary image data are compressed, the number of pixels of one line is set as the fixed number of the data arranged in parallel, and the binary coding is performed by the arithmetic coding means. On the other hand, when compressing the image data while compressing the code data, the number of bits per unit of the code data is set as the fixed number, and the code data is compressed by the arithmetic coding means. Image and code data compression method characterized by. 2. The image and code data compression method according to claim 1, wherein the code data is a character code. 3. When the data compression of the binary image data and the coded data is started, the coded data is output after outputting the identification code indicating the type of each data. Image and code data compression method described. 4. The image and code data compression method according to claim 3, wherein the identification code includes information indicating the fixed number of the data arranged in parallel.