JP2000165680A - Binary image companding method, image compressor and image expander - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently compress/expand a binary image where a ratio of black and white mean code lengths is about 50%/ SOLUTION: A run length conversion section 12 detects a run length of respective binary data received from a data input section 10. A coding section 14 assigns a code from a code table storage section 16 to respective run lengths to encode the binary data. In this case, on the occurrence of a black run length 1, the code is skipped and white codes before and after the code are consecutively outputted. In the case of expanding coded data, parts where white codes are consecutive are detected and omitted black data are inserted to the parts to recover the original binary data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binary image compression / expansion method, an image compression apparatus, and an image expansion apparatus.
In particular, the present invention relates to a binary image compression / expansion method, an image compression apparatus, and an image expansion apparatus used for recording or transmitting an image.

[0002]

2. Description of the Related Art Conventionally, as a compression encoding method applied to a binary image transmission apparatus such as a facsimile apparatus,
For example, MH (Modified Huffuman) code and MMR (Modified
Run-length coding such as MR (modified READ) coding is known.

The run-length coding is a method of coding a continuous length of white and black of a binary image. In the case of a binary image, white and black are assigned to the values "0" and "1", so there is no redundancy in each value.
However, in a space called a screen, information is compressed using the fact that each value has a continuous length or width.

For example, as shown in FIG. 7, as an example of the MH code, for example, "Image Information Compression"
(Edited by the Society of Television Engineers, supervised by Hiroshi Harashima). This code is composed of a terminating code (T code) representing a run length of 0 to 63 and a make-up code (M code) representing a run length that is an integral multiple of 64.
It is composed of different types and used in combination according to the length of the run. The T code and the M code are assigned to the same code space, and the code alone can be used to determine whether the code is the T code or the M code. In this case, since there is a difference in the distribution of the run length between white and black in the binary image, a code for white run is assigned to a white run and a code for black run is assigned to a black run to shorten the overall code length. I was planning.

[0005]

However, in the above-mentioned prior art, the above-mentioned codes are assigned to the respective run lengths. Therefore, if the image handles a character document such as a facsimile, it is suitable for image compression. Although this method is used, there is a problem that compression may not be performed well in some cases, such as when a multi-valued image is decomposed into bitmaps and each bit plane is image-compressed. In some cases, the data after encoding rather than compression may increase. In particular, in the case of a multi-valued image, a phenomenon is seen in which the compression ratio deteriorates in the bit plane lower in the bit plane number. This is a bit plane
Since the appearance ratio of white and black appears in a random manner on the lower side, the average run length and the ratio of black and white are 50%
The encoding efficiency is degraded due to the nearby appearance rate.

The present invention solves such disadvantages of the prior art, and can improve the compression efficiency even for a binary image in which black and white appear randomly and the appearance rate is about 50%. It is an object of the present invention to provide a binary image compression / expansion method, an image compression apparatus, and an image expansion apparatus capable of improving the image compression efficiency even on a screen such as a text.

[0007]

In order to solve the above-mentioned problems, the binary image compression / expansion method according to the present invention converts the binary image information to the compression side with the same length of the same binary data. In the binary image compression / expansion method of decoding the encoded data to the original binary data on the expansion side and reproducing the original binary image information, the binary image information is encoded on the compression side. Are sequentially determined, and when a predetermined code is assigned to each run length and encoded, a predetermined run of data consisting of predetermined binary data is determined. For all other run lengths except the length,
A code in the same code space is assigned so that it is possible to determine which of the two values of data is the run length, and the encoded data is sequentially encoded to output encoded data. Upon receiving, while sequentially detecting which of the two-valued data codes each code is, the respective codes are decoded, and when the binary data codes of the same value continue, During this period, the original binary image information is reproduced by compensating for the run length data omitted on the compression side.

In this case, on the compression side and the decompression side, a code table indicating codes assigned to all run lengths other than a predetermined run length of data of one of two values is prepared. Good to put.

When encoding is performed on the compression side, the run length distribution of each data is measured over the entire screen of the image, the run length indicating the maximum value of the distribution is detected, and the run length is excluded. It is advantageous to encode all other run lengths sequentially.

In this case, the compression side adds the omitted data and the information indicating the run length to the encoded data and sends the encoded data, and the decompression side transmits the binary value based on the information added to the encoded data. It is preferable to detect the portion where the code of the data having the same number is continuous, supplement the run length data omitted on the compression side between them, and reproduce the original binary image information.

In this case, a code table indicating codes assigned to the same code space is prepared on the compression side and the expansion side in advance so as to be able to determine which of two values of data the code is. It is advantageous that the compression side adaptively assigns codes to all other run lengths except for the run lengths of unsigned data from the code table and encodes them.

On the other hand, an image compression apparatus according to the present invention is an image compression apparatus for compressing and encoding image information in which each pixel is represented by one of binary data, and sequentially inputs binary data representing each pixel. A data input means for detecting a value of each pixel from the data input means, and a run length for obtaining a run length representing the length of the continuous value of the same value of the binary data. Length detection means, code table storage means for storing at least codes assigned to the same code space so as to be able to discriminate which data code, and code table storage means for each run length from the run length detection means. Encoding means for sequentially encoding all run lengths except for a predetermined run length of predetermined binary data. Characterized in that it comprises a Goka means.

In this case, the image compression device according to the present invention
A run length measuring means for measuring a run length distribution of each data obtained by the run length detecting means over the entire screen of the image, and a maximum value detecting means for detecting a maximum value of the run length distribution; It is preferable that the encoding means assigns a code to data of a run length other than the run length and sequentially encodes the data without assigning a code to the run length data indicating the maximum value.

[0014] The encoding means may add the data to which no code is assigned and information indicating the run length to the encoded data and output the encoded data.

On the other hand, an image decompression device according to the present invention is an image decompression device for decompressing encoded data of image information encoded by an image compression device and reproducing original image information,
Data input means for sequentially inputting encoded data, code table storage means for storing codes assigned to the same code space so as to be able to determine at least which data code, and a code table for the code table storage means. Data determining means for determining which code the encoded data from the data input means is based on based on the code table of the code table storage means. Decoding means for decoding data having the same run length, code detecting means for detecting whether or not codes of binary data having the same value are continuous based on the result determined by the data determining means; Based on the result of the means, 2 of the same value
When data having a value has a continuous code, a data complementing means for complementing data omitted by the encoding means between data decoded by the decoding means is provided.

In this case, the image decompression device according to the present invention comprises:
Information detecting means for detecting the omitted data added to the encoded data and the information on the run length thereof, and the decoding means stores the code table of the code table storing means based on the information from the information detecting means. Each code may be decoded by assigning it according to the run length.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a binary image compression / expansion method, an image compression apparatus, and an image expansion apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 1 and 2 show an embodiment of an image compression apparatus and an image expansion apparatus to which a binary image compression / expansion method according to the present invention is applied. The image compression apparatus according to the present embodiment is an encoding apparatus that compresses and encodes image information in which each pixel is represented by a binary value of “0” or “1”. For example, the image information is read by a CCD image sensor or the like. This is a compression apparatus that compresses and encodes binary information for each bit plane into a binary bit string by developing a monochrome binary image or a multi-gradation natural image into a bit map. The image decompression device according to the present embodiment is a reproduction device that decodes the encoded data encoded by the image compression device and reproduces the original binary image information.

Particularly, in the present embodiment, for example,
When the value image is compression-encoded based on the respective continuous lengths, if there is only one black, no code is given, and other black continuous lengths and white continuous lengths are used. When white and black codes appear alternately when the coded data is decompressed and encoded, the code is decoded as it is. The main feature is that the original black and white binary image information is reproduced by inserting a single.

More specifically, as shown in FIG. 1, the image compression apparatus according to the present embodiment comprises a data input unit 10, a run-length conversion unit 12, an encoding unit 14, a code table storage unit 16, And an output unit 18. The data input unit 10 is a CCD (Charge C
Oupled Device) This circuit is connected to an image sensor or the like, and sequentially inputs, for example, binary data in which an image is read in the horizontal direction as a value of "1" for black and "0" for white. Each of the binary data is sequentially supplied to the run length conversion unit 12.

The run-length conversion unit 12 is a detection circuit for detecting a continuous length of white and black, respectively, and determines whether data to be sequentially input is "1" or "0", and Includes a counter that counts continuous length. Each count value is sequentially supplied to the encoding unit 14.

The encoding section 14 is a circuit for assigning a predetermined code to the count value representing each run length from the run length conversion section 12 and encoding the count value. In particular, in this embodiment, the black count value is 1 In the case of only the number, the coding circuit assigns a code to each of the white before and after the value without giving a code to the value.

The code table storage unit 16 allocates white and black codes to the same code space so that the numbers of white and black runs can be identified by the codes themselves, and stores a code table representing each code in advance. In this embodiment, as shown in FIG. 3, for example, a code table is formed in which no sign is set when the black run length is 1. The other codes of the black run length and the white run length are codes in the same code space. For example, the code “11” of white 1 does not appear in the upper two bits of those codes on the black run side. Sign. Similarly, the codes “10”, “0011”,... Of white 2, white 3,... Do not appear in the upper bits of the black run code, and the black run code “0”.
.. Are formed so as not to appear in the upper bits of the code on the white run side.

FIG. 3 shows run lengths up to 4, but these codes can be formed, for example, from black run codes of the MH code shown in FIG. The (makeup) code can also be formed by alternately assigning the black run code of the MH code to the white run and the black run. In this case, up to a run length of 1280 is assigned based on 32 codes. In the MH code, for example, the code "11" of black 2 appears in the upper bits of codes such as white 5 to white 7, and the black and white cannot be discriminated only by the code. In this embodiment, it is formed so that white and black can be distinguished only by the code.

Returning to FIG. 1, the data output section 18 is an output circuit for arranging the codes from the encoding section 14 in a time series and outputting them. Are continuously output. The encoded data is
For example, the data is transmitted via a transmission device or written in a storage device or a recording medium.

On the other hand, the image decompression device according to the present embodiment is a reproduction device for reproducing the binary image information encoded by the image compression device. For example, as shown in FIG. , A code table storage unit 32, an expansion unit 34, and a data output unit 36. The data input unit 30 is an input circuit connected to a transmission device or a storage device for sequentially inputting encoded data from the image compression device, and sequentially supplies the encoded data to the decompression unit 32.

The code table storage unit 32 is a storage circuit for storing a code table representing codes in which white and black run length codes are assigned to the same code space. The same code table as the code table is stored in advance.

The decompression unit 34 is a decoding circuit that decodes the encoded data from the data input unit 30 based on the code table of the code table storage unit 32. In this embodiment, the decompression unit 34 discriminates the white and black codes. This circuit decodes each code, and when the white codes continue, complements black between the decoded results to restore the original binary data.

More specifically, for example, as shown in FIG. 4, the decompression unit 34 of this embodiment includes a data determination unit 300, a previous data storage unit 302, a black decoding unit 304, a white decoding unit 306,
A black determining unit 308, a white determining unit 310, a white / white determining unit 312,
Black output switch (SW1) 314 and white output switch (SW2)
) 316 and a black insertion portion 318. The data determination unit 300 is a black-and-white determination circuit that receives the code Xi and determines whether the code is a white code or a black code, and stores the result in the previous data storage unit 302 and the determination units 308 to 308.
312, and supplies the determined code Xi to the black decoding unit 304 or the white decoding unit 306 sequentially.

The previous data storage unit 302 is provided with a data determination unit 300
Is a storage circuit for storing the determination result of the previous code for one code, and when the determination result of the current code is received, sequentially supplies the stored determination result of the previous code to the white / white determination unit 312.

The black decoding unit 304 is a decoding circuit that decodes the code Xi supplied via the data determination unit 300 with reference to the code table of the code table storage unit 32, and executes a black run represented by the code. Output long binary data "1". Similarly, the white decoding unit 306 is a circuit that decodes a white code Xi, and outputs binary data “0” for the white run length represented by the code.

The black discriminating unit 308 is a switch driving unit that turns on the black output switch 314 when the data discriminating unit 300 detects a black sign. In this embodiment, the black discriminating unit 308 is formed by a NAND element or the like. . The white discriminating unit 310 is a switch driving unit that turns on the white output switch 316 when the data discriminating unit 300 detects a white code. In the present embodiment, the white discriminating unit 310 is formed by an AND element or the like.

The white / white discriminating section 312 is formed by an AND element or the like which takes the logical product of the result of the current code determination from the data determination section 300 and the result of the previous code from the previous data storage section 302. In some cases, a drive output is supplied to the black insertion section 318.

The black insertion section 318 is a reproducing circuit for reproducing the binary data of the black run length 1 in response to the drive output from the white / white discriminating section 312. Is a data complement circuit that complements black data during the period. The decoded binary data Yi is output to the data output unit shown in FIG.
Supplied to 36.

Returning to FIG. 2, the data output unit 36 is connected to a display device or a printing device (not shown),
An output circuit for outputting the original binary image information expanded at 34.

Next, the binary image compression / expansion method according to this embodiment will be described together with the operation of the image compression apparatus and the image expansion apparatus. First, for example, a white and black binary image read by an image sensor or the like is read. When the binary data represented is sequentially supplied to the image compression device, the binary data is sequentially supplied to the run-length conversion unit 12 via the data input unit 10. As a result, the run length conversion unit 12 detects a run length indicating the number of continuous black and white pixels represented by the respective binary data, and outputs the result to the encoding unit 14.
Are supplied sequentially.

Encoding unit sequentially receiving white and black run lengths
The code 14 assigns a code from the code table storage unit 16 to each run length and encodes the code, and sequentially supplies the results to the data output unit 18. At this time, for example, as shown in FIG. 5, the encoding unit 14 firstly executes the run-length conversion unit in step S10.
Upon receiving the run length from step 12, it is determined in step S12 whether the run length is black or white. If the result is white, the process proceeds to step S14, where a code corresponding to the run length of the white is read from the code table, and the code is supplied to the data output unit 18.

If it is determined in step S12 that the run length is black, the flow advances to step S16 to determine whether or not the run length is 1. If the run length is 1, it is determined that there is no sign in step S18, and the process returns to step S12. Next, when the white run length is supplied again in step S10, the sign thereof is changed to step S1.
In step S14, a code is assigned to the white run length again, and the white run length is supplied to the data output unit 18.

Next, returning to step S10, when the black run length is supplied, the process proceeds to step S16 based on the result, and it is determined whether the run length is 1 or not. As a result, if the run length is not 1, the process proceeds to step S20, where the code from the code table storage unit 16 is assigned to the black run length, and the code is supplied to the data output unit 18.

Similarly, for example, as shown in FIG. 5A, when the white and black run lengths are alternately input, the white run length is added to the white code in the code table corresponding to the value. Is assigned and output, and when a black run length is input, it is determined whether or not the run length is 1, and if the run length is 1, it is omitted as unsigned and the black run length is omitted. If is not 1, the black code in the code table is assigned according to the value, and is sequentially supplied to the data output unit 18.

Thus, in the data output unit 18, the white and black codes from the encoding unit 14 are sequentially arranged in time series in step S22, for example, as shown in FIG. .. Are sequentially output to the transmission device or the storage device.

On the other hand, in the image decompression device, first, when the encoded data received from the transmission device or read from the storage device is input through the data input unit 30, the encoded data is sequentially sent to the decompression unit 34. Supplied. As a result, the decompression unit 34 converts each code into the data determination unit 300
Then, it is determined whether the code is white or black by referring to the code table of the code table storage unit 32. If the result of the determination is, for example, black, the determined code is
To the previous data storage unit
302 and the respective discriminating units 308 to 312.

As a result, the determination result representing black is stored in the previous data storage section 302, and an output for turning on the black output switch 314 is generated from the black determination section 308. Then
The black decoding unit 304 decodes the code from the data determination unit 300 with reference to the code table.
The value data is supplied to the data output unit 36 through the black output switch 314 turned on and via the black insertion unit 318 for the number of consecutive pixels.

Next, when a white code is determined by the data determination unit 300, the determination result is supplied to the previous data storage unit 302 and the determination units 308 to 312 in the same manner as described above, and the determined code is output. This is supplied to the white decoding unit 306. As a result, the determination result representing white is stored in the previous data storage unit 302, and an output for turning on the white output switch 316 from the white determination unit 310 is generated. Next, the white decoding unit 306 outputs the data
When the code from 0 is decoded with reference to the code table, the white binary data represented by the result is turned on by the white output switch 316 that has been turned on for the number of consecutive pixels sequentially, and via the black insertion unit 318. The data is supplied to the data output unit 36. At this time, the white code determination result of the current code is supplied to one input of the white / white determination unit 312, while the previous data storage unit is supplied to the other input.
Since the black determination result of the previous code from 302 is supplied, no drive output is generated.

Similarly, the next black code is the data judgment unit 300
, The black discriminating unit 308 turns on the black output switch 314 based on the result, and the binary black data decoded by the black decoding unit 304 is sequentially supplied to the data output unit 36.
Further, when the next white code is determined, the white discrimination unit 310 turns on the white output switch 316 and the white binary data decoded by the white decoding unit 306 is sequentially supplied to the data output unit 36. . Also in these cases, the white code determination result is supplied to one input of the white / white determination unit 312 as the previous code or current code determination result, but the black determination result is supplied to the other input. No drive output is generated. Accordingly, the decoding results of black and white are sequentially supplied to the data output unit 36.

Subsequently, if the data determination unit 300 detects, for example, a white code following the previous data,
The determination result is supplied to the previous data storage unit 302 and the determination units 308 to 312 in the same manner as described above. Accordingly, the white / white determination unit 312 receives the white determination result of the current code from the data determination unit 300 and the white code determination result of the previous code from the previous data storage unit 302, and outputs the drive output to the black insertion unit 318. Supply.
As a result, the black insertion unit 318 inserts one black binary data after the white binary data obtained by decoding the previous code from the white decoding unit 306 and supplies the black binary data to the data output unit 36. Subsequently, the white discriminator 310 turns on the white output switch 316 in the same manner as described above, and the white binary data, which is the decoded output of the current data from the white decoder 306, is output via the black inserter 318. It is supplied to the unit 36.

Similarly, when black and white codes are supplied alternately, the black discriminating unit 308 or the white discriminating unit 310 turns on the black output switch 314 or the white output switch 316 to turn on the black decoding unit 304 or the black decoding unit 304, respectively. The binary data of the pixel decoded by the white decoding unit 306 is sequentially switched 314 or 316.
Is supplied from the black insertion unit 318 to the data output unit 36. When white codes appear successively, the drive output is supplied from the white / white discriminating unit 312 to the black insertion unit 318, and after the white binary data obtained by decoding the previous code from the white decoding unit 306, Binary data having a black run length of 1 is inserted, and then white binary data obtained by decoding the current code is sequentially output.

When the original binary data is decoded by the decompression unit 34, the binary data is supplied to a display device or a printing device via the data output unit 36, and is displayed or printed and displayed. Is reproduced.

As described above, according to the binary image compression / expansion method, the image compression apparatus, and the image expansion apparatus according to the present embodiment, the code is not assigned to the black run length 1 data,
Since the value image information is encoded, it is possible to improve the compression efficiency by an amount corresponding to the decrease in the code. At this time, codes of white and black run lengths other than black having a run length of 1 were assigned to the same code space and coded, so that the decoding side detects continuous white codes, and Decoding can be performed efficiently only by inserting black data. In particular, it can be effectively applied to a binary image in which the average value of the run length or the ratio of black and white is close to 50%. For example, it is more effective to apply multi-value data representing a natural character such as a character or a photograph of a text such as a personal computer with a large number of 1-dot display to a bit plane developed by a bit map. For example, in an experimental example of an 8-bit multivalued image, the compression could be reduced to about 60%.

In this case, the value of the 8-bit luminance data is B
Then, the data is bit-mapped based on the following equation (1).

[0050]

## EQU1 ## B = c7x2 ⁷ + c6x2 ⁶ + c5x2 ⁵ + c4x2 ⁴ + c3x2 ³ + c2x22 ² + clx2 ¹ + cOx2 ⁰ (1) In this equation (1), the value of the brightness (brightness) is 2 to be B
The coefficients cO to c7 of the exponent are expressed by "1" or "0" so that the sum of the right side becomes B. Do this operation for each pixel, then at the same index, e.g. c7
Are arranged in pixel order over the entire screen is a bit plane. The bit plane is a binary image. A bitmap is created by similarly creating a bit plane for each index and forming one set. Therefore, the binary bit string from each bit plane can be compression-encoded by the image compression device, and the encoded data can be decompressed by the image decompression device, and the decompression result is stored in the original bit plane. The original multi-value data can be reproduced by arranging. In particular, when the bitmap is developed, the appearance rates of "0" and "1" are random in the lower bit planes, and the binary image compression / expansion method and apparatus of this embodiment can be effectively applied. it can.

FIGS. 8 and 9 show another embodiment of the image compression apparatus and the image expansion apparatus to which the binary image compression / expansion method according to the present invention is applied. This embodiment is different from the above embodiment in that the image compression apparatus is provided with a run length distribution measuring unit 50 for measuring the distribution of the run lengths of black and white over the entire screen, and based on the result, an encoding unit.
At 52, the code of the other run length is encoded without assigning a code to the white or black run length data indicating the maximum value of the distribution, and the run length data to be omitted and the encoded data of the other run length are encoded. This is the point that the correspondence table is transmitted, and the encoded data is decompressed by the image decompression device based on the correspondence table. In FIGS. 8 and 9, the same parts as those in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

That is, in the image compression apparatus shown in FIG. 8, the run length distribution measuring unit 50 obtains the distribution of each run length detected by the run length conversion unit 12 and calculates the appearance rate of each run length. And a maximum value detection circuit that detects a run length with the maximum distribution from the operation result. In this case, it is preferable to detect some of the higher occurrence rates and supply the result to the encoding unit 52.

The encoding unit 52 of this embodiment sets the run length data indicating the maximum value of the distribution detected by the run length distribution measuring unit 50 as unsigned, and adapts the code to the run length with the highest appearance rate. A correspondence table generation circuit for generating a correspondence table by dynamically assigning the code table, replacing the code of the code table in the encoding storage unit 34 based on the generated correspondence table, and performing a run-length conversion based on the code table with the replaced code. This is a circuit for encoding data from the unit 12.

For example, when the appearance rate as shown in FIG. 10 is detected, the encoding unit 52 assigns the codes of the code table in order of the code length from the higher run length. Then, in the code table, the run lengths of the code data that are omitted in the code table because the code data is used in the correspondence table, the run data of the run length of the code table are arranged in order from the top at the code data of the run length. Selected and assigned in order of arrangement. The correspondence table is added to the encoded data and output. It should be noted that the output correspondence table includes run lengths (white or black) for which encoding is omitted and their data.

On the other hand, in the image decompression device shown in FIG.
The decompression unit 60 is a decoding circuit that decodes the encoded data by adaptively changing the code of the code table based on the correspondence table added to the encoded data, and at least the same color code as in the above embodiment. It is a data complementing unit that complements the run length specified in the correspondence table between them when they appear consecutively.

More specifically, the white / white discriminating unit 312 of the circuit shown in FIG. 4 applied in the above-described embodiment is provided with a code table in which the sequence of white or black codes is replaced based on a correspondence table. , And selectively replaces the drive output with a black-and-white / black-and-white discriminating section that supplies the driving output to the inserting section 318, and further sets the number of bits to be inserted and its value in the black inserting section 318 as desired. The unit 326 may be connected to form a circuit for detecting a sequence of desired white or black codes and inserting binary data having a desired run length therebetween.

In the above configuration, in the image compression apparatus, when the white and black run lengths detected by the run length conversion unit 12 are sequentially supplied to the run length distribution measurement unit 50, the run length distribution measurement unit At 50, the distribution of their run lengths is measured over the entire screen. At this time, for example, as shown in FIG. 10, some of the higher occurrence rates are detected and supplied to the encoding unit 52.

Next, upon receiving the respective run lengths from the run length converting unit 12, the encoding unit 52 selects and assigns the codes from the code table storage unit 16 in order of appearance frequency in ascending order of code length. In this case, a code is assigned to each run length except for the black run length 1 whose appearance rate indicates the maximum value, and the coding is performed. At this time, a correspondence table is generated which indicates at least the omitted black and the code assigned to the higher rank of the appearance rate including the information of the run length 1. For example, when the code table of FIG. 3 applied in the above embodiment is used, the appearance rate of FIG.
, "11" and "10" are assigned to upper white 2 and white 3, and "011" is assigned to black 4. In this case, in FIG. 3, white 1 and white 3 are switched, and black 2 and black 4 are switched. The information is generated as a correspondence table. The generated correspondence table is added to the encoded data,
The data is output via the data output unit 18.

On the other hand, in the image decompression device, upon receiving the encoded data and the correspondence table, the decompression unit 32 replaces the codes of the encoding storage unit 34 based on the correspondence table, and converts the encoded data to be sequentially input. Each is decrypted. At this time, when continuous white codes are detected, the original binary image information is reproduced by complementing the data of the black run length 1 specified in the correspondence table between the data obtained by decoding those codes.

In this case, the black run length 1 is omitted as in the above embodiment. For example, if any of the white run lengths is omitted, the circuit shown in FIG. When receiving the table, the white / white discriminating unit 312
The black / white / black / black discriminating unit that replaces
The drive output is supplied to the insertion section 318 to be driven. Next, the run length is set in the bit number setting unit 326 from the information in the correspondence table,
And the value of the insertion bit is set. Thereby, the number of bits of the binary data corresponding to the desired run length of white is
Insert at 318.

As described above, according to the binary image compression / expansion method, the image compression apparatus, and the image expansion apparatus according to the present embodiment, the run-length appearance frequency is measured for each image, and the run-length having the maximum value is measured. Since the sign of is omitted,
The compression ratio can be more reliably and stably increased. Also, since the white and black codes are assigned to the same code space, they can be assigned in the order of appearance frequency without considering black and white, and compared to conventional MH coding, only white codes and only black codes are used. There is no waste and the compression ratio can be improved more effectively.

In each of the above embodiments, the code table storage unit 1
Although the code table shown in FIG. 3 using the MH code for black run is stored in 6, 34 in the present invention, in the present invention, another code in which a white code and a black code are assigned to the same space is applied. Good.
For example, the code applied to the present invention is shown below (2)
Or a code may be created in consideration of the condition that the expression (5) and the continuation of one code appear but there is no continuation of the other code. First, Kraft's inequality (2) is known as the existence condition of codes that can be instantaneously decoded.

[0063]

(Equation 2) Here, li is the code length, i is the symbol number, and k is the number of symbols. A combination of code lengths can be obtained from this equation (2). Further, the average code length L is obtained by Expression (3), where Pi is the symbol appearance probability.

[0064]

(Equation 3) The code that gives the smallest L is called the compact code for that source. Average code length L for compact codes
And the entropy H of the information source has the relationship of equation (4).

[0065]

## EQU4 ## From the above concept, for example, a code table shown in FIG. 11 can be created.

Further, in each of the above embodiments, an example in which the image compression apparatus and the image decompression apparatus are separately configured has been described. However, in the present invention, both apparatuses are provided in the same housing and a transmission apparatus such as a facsimile or a recording apparatus is provided. You may comprise as a reproduction | regeneration apparatus. Further, in each of the above embodiments, the binary image is described using expressions of white and black. However, in the present invention, for example, red and yellow may be used, or any symbol that can be discriminated into two may be used. Can also be applied.

Further, an example of an 8-bit image has been described as an example of multi-value data, but the number of bits of the multi-value data may be arbitrary. The multi-valued image may be monochrome or color. Either "0" or "1" may be used for white or black.

On the other hand, in the embodiment of FIG. 1 and FIG.
Although the case where the code of the black run length 1 is omitted has been described as an example, in the present invention, which run length code is omitted is arbitrary.

Further, in the embodiment of FIGS. 8 and 9, the case where a correspondence table of codes having higher appearance frequencies is created and transmitted has been described as an example. For example, a code is given to black run 1. A fixed code table determined in advance may be used, and information on only the omitted run length may be sent without sending the code correspondence table. Alternatively, a code correspondence table in the order of appearance frequency representing only the currently coded run length code may be created and sent. In the case of a natural image or the like, a code correspondence table for each bit plane may be used, or a code correspondence table for the entire bitmap may be used.

Further, in the case of multi-valued image information such as a natural image, even if arithmetic coding used in JBIG (Joint Bi-level Image Experts Group) or the like and binary image coding according to the present invention are applied in combination. Good.

[0071]

As described above, according to the binary image compression / expansion method, the image compression apparatus, and the image expansion apparatus of the present invention,
When compressing and encoding the binary image information, the code is omitted and the code is omitted from the run length of either white or black, so that the compression efficiency can be improved. When decompressing the coded data, it is possible to detect portions where codes of the same color are continuous and complement data omitted between them, so that decoding can be performed easily and easily. . In particular, this method is effective when binary-coding and decoding of an image in which black and white are random and the ratio is close to 50%, for example, multi-valued image information such as a text image of a personal computer or a natural image, for each bit plane. And the like.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image compression apparatus to which a binary image compression / expansion method according to the present invention is applied.

FIG. 2 is a block diagram showing an embodiment of an image decompression device to which a binary image compression / decompression method according to the present invention is applied.

FIG. 3 is a diagram showing an example of a code table applied to the embodiment of FIGS. 1 and 2;

FIG. 4 is a block diagram showing an example of the internal configuration of a decompression unit applied to the image decompression device according to the embodiment of FIG.

FIG. 5 is a flowchart for explaining the operation of the image compression apparatus according to the embodiment of FIG. 1;

FIG. 6 is a diagram showing a code string for explaining the operation of the image compression device according to the embodiment of FIG. 1;

FIG. 7 is a diagram illustrating an example of an MH code.

FIG. 8 is a block diagram showing another embodiment of an image compression apparatus to which a binary image compression / expansion method according to the present invention is applied.

FIG. 9 is a block diagram showing another embodiment of the image decompression device to which the binary image compression / decompression method according to the present invention is applied.

FIG. 10 is a diagram illustrating an example of an appearance rate of a run length detected by the image compression device according to the embodiment of FIG. 8;

FIG. 11 is a diagram illustrating another example of a code table applied to the binary image compression / expansion method, the image compression device, and the image expansion device according to the present invention.

[Explanation of symbols]

 10 Data input unit 12 Run length conversion unit 14, 52 Encoding unit 16 Code table storage unit 18 Data output unit 30 Data input unit 32 Code table storage unit 34, 60 Decompression unit 36 Data output unit 50 Run length distribution measurement unit

Claims (10)

[Claims] 1. Binary image information is converted into two
The same value of the value data is encoded based on the continuous length,
In a binary image compression / expansion method for decoding the encoded data into original binary data on the expansion side and reproducing the original binary image information, the method comprises the steps of: When the run lengths indicating the lengths of the same values of the binary data are successively obtained are sequentially obtained, and when a predetermined code is assigned to each run length for encoding,
Codes in the same code space are assigned to all run lengths other than the predetermined run length of the predetermined binary data except for the predetermined run length so that it can be determined which of the two values the data has. When the encoded data is received from the compression side on the decompression side, the decompression side sequentially detects which of the two-valued data is the code of the binary data. Decoding the respective codes to reproduce the original binary image information by compensating for the run length data omitted on the compression side between them when the codes of the same binary data continue. A binary image compression / expansion method. 2. A method for compressing and expanding a binary image according to claim 1, wherein said method further comprises removing a predetermined run length of one of binary data on said compression side and expansion side in advance. A code table representing codes assigned to all run lengths of the binary image. 3. The binary image compression / expansion method according to claim 1, wherein, when encoding is performed on the compression side, a distribution of run lengths of respective data is measured over the entire screen of the image, and the maximum of the distribution is measured. A binary image compression / expansion method comprising detecting a run length indicating a value and sequentially encoding all run lengths other than the run length. 4. The binary image compression / expansion method according to claim 3, wherein the compression side adds the information representing the omitted data and its run length to the encoded data and transmits the encoded data, and the expansion side transmits the encoded data. Based on the information added to the coded data, a portion where the code of the data having the same binary value is continuous is detected, and the data of the run length omitted on the compression side between them is complemented. And reproducing the original binary image information. 5. The binary image compression / expansion method according to claim 4, wherein said method uses the same code on said compression side and expansion side in advance so as to be able to determine which of two-valued data code. A code table representing codes assigned to a space is prepared, and codes are adaptively allocated to all other run lengths except for run lengths of data for which codes are not given from the code table on the compression side. A binary image compression / expansion method. 6. An image compression apparatus for compressing and encoding image information in which each pixel is represented by one of binary data, said apparatus comprising: data input means for sequentially inputting binary data representing each pixel Run length detecting means for detecting which value of each pixel from the data input means is binary data, and obtaining a run length representing each continuous length of the same value of the binary data. And code table storage means for storing a code assigned to the same code space so as to be able to determine at least which code of the data, and a code length of the code table storage means for each run length from the run length detection means. An encoding means for allocating and encoding a code, wherein said encoding means sequentially encodes all run lengths other than a predetermined run length of predetermined binary data. Image compression apparatus which comprises a. 7. An image compression apparatus according to claim 6, wherein said apparatus comprises a run length measuring means for measuring a run length distribution of each data obtained by said run length detecting means over an entire screen of an image. And a maximum value detecting means for detecting the maximum value of the distribution of the run length, wherein the encoding means does not assign a code to the data of the run length indicating the maximum value, and executes other run except the run length. An image compression apparatus characterized in that a code is assigned to long data and sequentially encoded. 8. An image compression apparatus according to claim 7, wherein said coding means adds data to which no code is assigned and information indicating a run length thereof to the coded data and outputs the coded data. Compression device. 9. An image decompression device for decompressing encoded data of image information encoded by the image compression device according to claim 6 to reproduce original image information. Data input means for sequentially inputting coded data; code table storage means for storing at least codes assigned to the same code space so as to be able to determine which data is the code; Data determining means for determining which code the encoded data from the data input means is based on the code table of the storage means; and each code determined by the data determining means is provided in the code table. Decoding means for decoding the data into the original run length based on the code table of the storage means, and whether the binary codes of the same value are continuous based on the result determined by the data determination means Code detecting means for detecting whether the code of binary data having the same value is continuous based on the result of the code detecting means; An image decompression device comprising: data complementing means for complementing data omitted by the converting means. 10. The image decompression device according to claim 9, wherein said device includes information detection means for detecting omitted data added to said encoded data and information on its run length, and said decoding means. Is an image decompressing apparatus for allocating a code table of the code table storage means based on information from the information detection means in accordance with a run length of each data, and decoding each code.