JP2000350045A - Coding/decoding method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coding/decoding method by which the capacity of a decoding table is reduced and the memory space can be used efficiently. SOLUTION: A decoded image is generated (step SA11) on the basis of read run length information respectively, by using values of 5-bits in succession to a level '1' of the most significant bit, using values of remaining 8-bits, except the most significant bit when the most significant bit is '0' and the value of the high-order 8-bits is '2' or large, using remaining 4-bits when the received 8-bits are '1' in the case that modified Huffman MH coded data are white data, using the high-order 6-bits, when the high-order 4-bits are '1' and using the remaining 9-bits when the high-order 4-bits are '0', in the case that modified Huffman MH coded data are black data as the reference address of a decoded conversion table respectively (steps SA6-SA10). In the case that the decoded code is a terminate code, a value denoting a white/black level is inverted (step SA14), and coding decoding processing is conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decoding and decoding variable-length codes, and more particularly to a modified Huffman code (hereinafter referred to as MH code) used for encoding white / black binary image information. The encoding and decoding of
The present invention relates to a code decoding method and apparatus suitable for software processing in a general-purpose CPU.

[0002]

2. Description of the Related Art Conventionally, encoding of image information using a variable length code has been used for compression of image information in various devices such as a facsimile and an image filing device. Here, as the variable length code, for example, there is an MH code widely used in facsimile communication.

[0003] First, the MH code will be briefly described.
The MH code replaces the number of pixels of the same color (white or black) (referred to as run length) that are continuous for each horizontal line of the white / black binary image data with a corresponding MH code. There are two types of make-up codes and terminate codes. This is a method of expressing the quotient and remainder when the run length is divided by 64, and the quotient is a makeup code (hereinafter, referred to as an M code), and the remainder is a termination code (hereinafter, referred to as a M code). (Referred to as a T code). Therefore, assuming that the quotient is M and the remainder is T, the run length (RL) can be represented by RL = M × 64 + T.

FIGS. 13 and 14 show a terminating code in the MH code, and FIGS. 15 to 17 (FIGS. 15 and 16 show the case for the standard paper width, and FIG. 17 shows the case for the extended paper width). The make-up code in the code is shown. The terminating code corresponds to a run length from "0" to "63", and the make-up code corresponds to a run length up to an integer multiple of "64" and up to "2560". Further, the MH code is divided into those representing "white" and "black". Further, as shown in FIG. 11, the MH code has a maximum of seven “0” s before the first “1” appears.
And the number of code bits following the first "1" is a maximum of seven codes, and the code length is a variable length code of a maximum of 13 bits.

At the time of encoding, a terminating code is assigned to a run length of less than 64 pixels, and a make-up code and a terminating code are assigned to a run length of 64 pixels or more in combination. For example, a horizontal line having binary image data of white / black is shown in FIG.
In the case where white pixels and black pixels are arranged as shown in FIG. 8, if four first white pixels continue, the run length (RL) becomes “4”. Looking at the code for white run of run length 4 from the terminating code table of the MH code shown in FIGS. 13 and 14, a code “1011” can be obtained. That is, run lengths in the range from “0” to “63” pixels are encoded using only the termination code.

[0006] A run length of 64 pixels or more is first coded using a makeup code table shown in FIGS. Thereafter, a terminating code representing a difference between the actual run length and the run length represented by the make-up code has a code configuration (see the code corresponding to the run length of “white 139” in FIG. 18).
Note that the coding of the head of the horizontal line is performed from the white run, and when the image data of the actual horizontal line starts from the black pixel, it is assumed that there are 0 (run length 0) virtual white pixels at the head. Always start with a code for white pixels. Also, in the MR system and the MMR system, which are two-dimensional coding systems, the above-described MH coding process is used in a horizontal mode or the like.

Next, a conventional MH code decoding method will be described. Conventionally, as a method of decoding a variable-length code at high speed regardless of the code length, a decoding table of variable-length code data is configured in a memory, and a fixed-length code corresponding to input data is referred to by referring to the decoding table. A so-called table lookup method for reading data is known.

As a variable length code decoding apparatus using this method, for example, as described in Japanese Patent Application Laid-Open No. Sho 61-265927, a decoding table in which variable length data corresponding to the longest code length is directly used as a memory address. And outputs the corresponding fixed-length data and code length. However, in the above variable length code decoding device, fixed length data corresponding to each variable length code is held in the decoding table for all code patterns having the longest code length, and thus input data is used for decoding the MH code. Two tables for an address “13 bits” and 11 bits for output are required for white and black, and 213 × 11 × 2 =
A memory capacity of 176K bits is required.

Further, for a variable length code shorter than the longest code length, the same data must be stored in duplicate for all code patterns of an invalid portion except for a portion corresponding to an upper variable length code. That much memory space is wasted. In order to eliminate such disadvantages of the prior art, Japanese Patent Publication No. 2687926 focuses on the features of the MH code described above and counts the number of “0” before the first “1” appears in a code string. Thus, the decoding table is divided into two tables: a table for reading 8-bit information including a run length value at an 11-bit address, and a table for reading a 3-bit code length using the read 8-bit information as an address. A method has been proposed for reducing the memory capacity of the device to reduce the redundancy.

The above-described code decoding process can be performed at high speed by using dedicated hardware as in the above-described conventional device. However, in consideration of versatility, cost reduction, miniaturization, easy change of processing contents, and the like, it is desirable to realize such processing by software processing using a general-purpose CPU.

Next, the operation of the conventional code decoding method will be described with reference to the flowchart shown in FIG. In the conventional code decoding method, first, consecutive MHs to be decoded are stored in a code input register (not shown).
The first 8 bits of the code are input (step SB
1). Next, up to seven consecutive “0” s are counted until “1” first appears in the input code sequence in the code input register (0 counting process) (step SB2).

Next, the contents of the sign input register are shifted to the left by a value obtained by adding "1" to the count value, and the next sign bit is input to the sign input register by the number of bits shifted to the left ( Step SB3). As a result, up to seven sign bits following the first appearing "1" are set in the sign input register.

Next, the value of the code input register, the value indicating white / black of the target image, and the “0” count value are
The decoding conversion table is referred to using 11 bits of the format shown in FIG. 12A as an address value (step SB4). From the decoding conversion table, as shown in FIG. 12B, information (1 bit) indicating the color (white / black) of the target image and a termination code (T) or a makeup code ( M) T / M bits indicating whether
Information of a total of 8 bits of the run length (RL) (6 bits) to be actually decoded is obtained.

Next, a restored image is generated based on the read 8-bit information (step SB5). Next, the 8-bit information (white / black, T / M, RL) read from the decoding conversion table is referred to as a code length table as an address value in a format as shown in FIG. (Step SB6). The data referred to is shown in FIG.
As shown in (c), the number of remaining code bits after “1” detected after consecutive “0” in one code is shown, and information for determining the head position of the code to be decoded next is shown. Becomes

Next, the contents of the code input register are shifted to the left by the read code bit number, and the code bits are input to the code input register by the shift number (step SB).
7). As a result, the code to be decoded next is set in the code input register.

Next, information indicating whether the code is a terminating code (T) or a makeup code (M) read from the decoding conversion table previously is determined (step SB).
8) If the decoded code is a terminating code, the value indicating white / black is inverted because the color of the image to be decoded next is inverted (step SB9).
Finally, it is determined whether or not there is a code to be decoded next in the code input register (step SB10), and the above-described processing from step SB2 to step SB10 is repeatedly executed until there is no more code input. I do.

[0017]

However, the above-mentioned conventional code decoding method has the following problems. A first problem is that a memory capacity of 17,152 bits is required as a reference table used for the decoding process, and the memory space is wasted.
The reason is that 3 bits indicating the number of “0” s before the first “1” appears in the code string of the MH code, 7 bits of the longest code length following the first “1”, and white / black , A run length value corresponding to the MH code of 6 bits, a white / black color bit, and a terminate code / make-up code of 1 bit. Two tables, a decoding conversion table having 8-bit information and a code length table having 3-bit code length data for the 8-bit information of the coding conversion table, are required. The total capacity of the two tables is as follows. , 211 × 8 + 28 × 3 = 17,152 (bits). As for the decoding conversion table, for codes having a length of less than 7 bits following the first appearing “1” in the code string, all code patterns of invalid portions except for portions corresponding to the codes are duplicated. This is because the same data must be stored, and the memory space is used wastefully.

The second problem is that when code decoding is performed by software, the processing speed is reduced. The reason is that arithmetic processing for counting the number of “0” is necessary, and it is necessary to refer to a decoding conversion table for reading out the run-length value and a code length table for reading out the code length.

In recent data communication systems, it has become necessary to increase the speed of code decoding processing, to expand functions, and to realize many multimedia processing, and to increase the memory used for these processing. The lack of memory has become serious. Also, due to the low cost of the set, it is important to use the memory efficiently and reduce the amount of mounted memory.

The present invention has been made in view of such a background, and reduces the capacity of a decoding conversion table used for decoding an MH code, efficiently uses a memory space, and performs a code decoding process. An object of the present invention is to provide a code decoding method that can be executed at high speed.

Further, the present invention provides a code capable of reducing the capacity of a decoding conversion table used for decoding an MH code, enabling efficient use of a memory space, and speeding up a code decoding process. It is an object to provide a decoding device.

[0022]

In order to achieve the above object, a code decoding method according to the present invention is arranged such that an MH code is divided into a plurality of groups according to the relationship between the color of a target image, the upper common bit portion of the code, and the code length. A plurality of decoding conversion tables storing code lengths and run-length information corresponding to decoding-related bit portions excluding the upper common bit portion of the MH code of each group, and decoding target of the MH code. A step of selecting one corresponding decoding conversion table from a plurality of decoding conversion tables by determining a color and a common part bit of a part of code data; A step for reading out the code length and run length information of the target code by referring to the decoding conversion table with the code-related bits excluding the common bit portion as address information. Characterized in that it comprises and. Therefore, paying attention to the characteristic that the MH code has a higher-order common bit portion related to the code length, the MH code is classified into a plurality of groups by the higher-order common bit portion, and the decoding-related bit portion excluding the higher-order common bit portion Is used to determine the color to be decoded and some bits of the code data, and select one of the corresponding decoding conversion tables from the plurality of decoding conversion tables. However, since each decoding conversion table refers to the code length and the run length information using the code-related bits as address information, the decoding conversion table is read for the decoding process of one code of the target code. It can be performed only once, and the capacity of the decoding conversion table used for decoding can be reduced, and the memory space can be used efficiently. In addition, since the table needs to be referred to only once, the processing speed of code decoding is improved.

Further, the code decoding apparatus according to the present invention has a MH
The codes are classified into a plurality of groups based on the relationship between the color of the target image, the upper common bit portion of the code, and the code length, and the code length corresponding to the decoding-related bit portion excluding the upper common bit portion of the MH code of each group. A plurality of decoding conversion tables storing run-length information are provided. By determining the color of the image to be decoded of the MH code and a common part bit of a part of the code data, the plurality of decoding conversion tables correspond to each other. Means for selecting one decoding conversion table to be decoded, and each decoding conversion table refers to the decoding conversion table as address information using code-related bits excluding the upper common bit portion of the MH code, thereby obtaining the code of the target code. A means for reading the length and the run length information is provided. Therefore, paying attention to the characteristic that the MH code has a higher common bit portion in relation to the code length, the MH code is classified into a plurality of groups by the higher common bit portion,
Using a plurality of decoding conversion tables associated with the decoding-related bit portions excluding the upper common bit portion, the selecting means determines the color to be decoded and some bits of the code data, and performs a plurality of decoding. Means for selecting one of the corresponding decoding tables from the conversion table and reading the data so that each decoding conversion table refers to the code length and the run length information using the code-related bits as address information. The capacity of the decoding conversion table used for decoding can be reduced, the memory space can be used efficiently, and the speed of the code decoding process can be increased.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a code decoding method and a code decoding apparatus according to the present invention. The MH code applied to the present invention can be applied to various types of devices that handle images, such as facsimile and image filing devices.
As an example, an embodiment of a code decoding method and apparatus according to the present invention will be described by taking application to facsimile as an example.

FIG. 3 is a block diagram showing the configuration of a facsimile applied to the first embodiment of the code decoding method and apparatus according to the present invention. The facsimile is a device that takes in image data, encodes the information, transmits the information to a communication line, and decodes and prints the code data received from the communication line. The facsimile shown in FIG. It has the function of a chemical conversion device. Some facsimile machines have a copy function for printing the captured image data as it is, but this copy function is not directly related to the present invention and will not be described below.

In FIG. 3, a facsimile includes a CPU (Central Processing Unit) 2 for controlling the entire apparatus,
, A memory for storing information such as a program for driving the scanner and image data, a scanner 7 for reading image data from a document and converting it into electrical information, a scanner controller 6 for reading data from the scanner 7, and printing images and the like. A printer 9, a printer control unit 8 for sending data to the printer 9, a communication control unit 5 for adjusting a communication procedure with a communication partner through a communication line and transmitting and receiving data, and inputting a transmission destination. And an operation panel control unit 3 for controlling the operation panel 4. In such a configuration, the CPU 2 executes a process of encoding image data into MH code data and a process of decoding MH code data into image data according to a predetermined program.

Now, in such a facsimile,
When sending image data to a communication partner from a communication line, the image data read by the scanner 7 is held in the memory 1,
The image data in the memory 1 is compressed by being encoded into an MH code by the CPU 2 and transmitted from the communication control unit 5 to the communication line. Here, an encoding method for the MH code is realized by, for example, a conventional technique disclosed in Japanese Patent Application Laid-Open No. Sho 59-117375, and is not directly related to the present invention. No particular description is given.
When receiving the image data sent from the communication partner, the MH code data received from the communication line is held in the memory 1 via the communication control unit 5 and the Mh code data stored in the memory 1 is stored.
The H code data is restored to the original image data by code decoding by the CPU 2, and is sent to the printer 9 through the printer control unit 8 to perform printing.

Next, the code decoding process of the MH code data performed by the CPU 2 will be described. This code decoding process is performed using the memory 1. Here, how to use the memory 1 in this process will be described. FIG. 2 shows the contents of the memory 1 when the code decoding process is executed. In FIG. 2, a memory area includes a program area 11 for controlling each process of facsimile, a code data area 13 for storing code data to be decoded, and a code decoding conversion table used when converting the code data into image data. It is divided into a decoding table area 12 for storing and an image data storage area 14 for storing decoded image data.

In the first embodiment of the code decoding method according to the present invention, as shown in FIGS. 6 to 9, the relationship between the color of the target image of the code, the upper common bit portion of the code, and the code length is shown in FIGS. Are classified into five code groups a to e. 6 shows code groups b and c, and FIG. 7 shows code group a.
8 shows the case of code group e, and FIG. 9 shows the case of code groups d and e. 6 and 7 show a code group correspondence table for white runs, and FIGS. 8 and 9 show a code group correspondence table for black runs.

In the decoding table area 12, the value of the maximum length of the decoding-related bit portion excluding the group common bit portion from the MH code of each code group is set as the bit length of the table reference address, and the MH code corresponding to the address information is set. 1 bit indicating a termination code / makeup code (T / M) and a run length value (R
L) and 4 indicating the number of bits (code length) of the code.
Five decoding conversion tables of code groups a to e in which information of a total of 11 bits is stored in the format shown in FIG. 4 are stored. FIG. 5 shows the configuration of the decoding conversion table, taking the decoding conversion table corresponding to the code group a as an example.

Next, the operation of the first embodiment of the code decoding method according to the present invention will be described. In describing this operation, FIG. 1 shows a procedure of the code decoding process in the reception process of the facsimile code data shown in FIG. 3 having the function of the code decoding device of the present invention applied to execute this operation. This will be described with reference to the flowchart shown in FIG. Here, it is assumed that the received code data has already been stored in the code data area 13 of the memory 1.

First, the first 16 bits of a continuous MH code to be decoded are read out from the code data area 13 to a code input register (not shown) (step SA in FIG. 1).
1). Here, the CPU 2 reads a 16-bit code data from a general 16-bit or 32-bit CPU, and a data width corresponding to a given instruction out of 8-bit, 16-bit, or 32-bit. Assuming that the data in the memory 1 can be accessed by
The data is read out at a convenient size with a maximum bit length of 13 bits or more of the MH code. An access mechanism using such different data widths is provided in a general 16-bit or 32-bit CPU.

Next, it is determined whether the read code data to be decoded is white or black (step SA2). If the result of this determination is white, it is determined whether the most significant bit of the code input register is "1" (step SA3). If the result of this determination is "1", since the code length is at most 6 bits, the data is read using the 5-bit value following "1" as the reference address of the decoding conversion table a (step SA6). .

If the most significant bit is "0" at step SA3, it is determined whether or not the value of the upper 8 bits of the code input register is "1" (step SA3).
5). If the value of the upper 8 bits is “2” or more, the code length is 9 bits at the maximum, so that the remaining 8 bits excluding the most significant bit are read as reference addresses of the decoding conversion table b (step SA7). . If the value of the upper 8 bits of the code input register is "1", the code length is 12 bits at the maximum, and the data is read using the remaining 4 bits as reference addresses of the decoding conversion table c (step SA8). .

Similarly, if the decoding target is black in step SA2, it is determined whether the upper 4 bits of the code input register are "0" (step SA4). If the result of this determination is “1” or more, the code length is at most 6
The data is read out using the upper 6 bits as the reference address of the decoding conversion table d (step S).
A9). If the upper 4 bits are "0", the code length is 13 bits at the maximum, and thus the remaining 9 bits are read as the reference address of the decoding conversion table e (step SA10).

Next, a restored image is generated from the current color (white / black) information to be decoded and the run-length information read out by any of steps SA6 to SA10, and stored in the image data area 14. Yes (step SA1
1). Next, by the number of code bits (code length) read in any of steps SA6 to SA10,
The contents of the code input register are shifted to the left, and the code data following the number of shifts is input from the code data area 13 to the code input register (step SA12). As a result, the code to be decoded next is set in the code input register.

Next, from step SA6 to step SA1
It is determined whether the value indicating the termination code / make-up code (T / M) read by any one of 0 is a termination code (step SA13). As a result of this decision,
If it is determined that the decoded code is a terminating code, the value indicating white / black is inverted because the color of the image to be decoded next is inverted (Step S).
A14).

Finally, it is determined whether or not there is a code to be decoded next in the code input register (step SA15).
If it is determined that there is a code to be decoded next in the code input register, the above-described processing from step SA2 to step SA15 is performed to repeatedly execute the code input in step SA15 until there is no code input. Thus, a code decoding process is performed. Step SA15
In, when there is no code input, a series of processing ends.

Next, the above-described code decoding processing according to the present invention will be described using a specific example. For example, in the code data storage area 13 shown in FIG.
MH code data ““ 1011 ”,“ 000 ”corresponding to the run length of“ white 4, black 15, white 139,.
011000 "," 10010 01000 "..." are stored, first, the 16-bit code data "1011000011000100" from the top is input to the code input register (step SA1).

Next, the color of the image to be decoded is determined (step SA2). Since the head is always white, it is determined whether the most significant bit of the code input register is "1" (step SA3). In this case, since the most significant bit is “1”, data is read using the 5-bit value “01100” following “1” as a reference address of the decoding conversion table a (step SA6). Referring to the decoding conversion table a shown in FIG. 5, for the address value "01100", "1" indicating that T / M is a termination code.
, A code length “4”, and a run length value (RL) “4”.

Next, the current color to be decoded is white,
Since the read run length value is "4",
A restored image of four white pixels is generated and stored in the image data area 14 of the memory 1 (step SA11). next,
Since the read code length is “4”, the contents of the code input register are shifted left by 4 bits, and the code data area 1 is shifted.
The code data following 3 is input to the code input register by 4 bits (step SA12). As a result, the code “000” to be decoded next is stored in the code input register.
0110001001001 "is set.

Next, it is determined whether the value indicating the termination code / makeup code (T / M) of the target code is a termination code (step SA13), and the read value is "1" indicating the termination code. Then, the color information of the target image of the code to be decoded next is inverted to a value indicating black (step SA14). Next, it is determined whether or not there is a code to be decoded next in the code input register (step SA).
15) Since there is a code to be decoded next, the flow returns to step SA2 again to determine the color of the target image to be decoded.

Here, since the color information of the target image has a value indicating black, it is determined whether the upper 4 bits of the code input register are "0" (step SA4).
Since the upper 4 bits are “0000”, “0000”
Then, the data is read using the 9-bit value “110001001” subsequent to the above as the reference address of the decoding conversion table e (step SA10). Here, the address value “110”
For “001001”, “1” indicating that the T / M is a terminated code, a code length “9”, and a run length value (RL) “15” are read (not shown).

Next, the current color to be decoded is black,
Since the read run-length value is "15", a restored image of 15 black pixels is generated and stored in the image data area 14 of the memory 1 (step SA11). next,
Since the read code length is “9”, the content of the code input register is shifted to the left by 9 bits, and the code data area 1 is shifted.
The code data subsequent to 3 is input to the code input register for 9 bits (step SA12).

Next, it is determined whether the value indicating the termination code / makeup code (T / M) of the target code is a termination code (step SA13), and the read value is "1" indicating the termination code. Then, the color information of the target image of the next code to be decoded is inverted to a value indicating white again (step SA14). Next, it is determined whether or not there is a code to be decoded next in the code input register (step SA15). The code decoding process is performed by executing the above operation until there is no code input.

As described above, in the first embodiment of the code decoding method in the facsimile code data receiving process according to the present invention, the MH codes are classified into a plurality of groups by the upper common bit portion, By preparing a plurality of decoding tables corresponding to the decoding-related bit parts excluding the part, overlapping data is reduced with respect to the decoding tables used in the conventional code decoding method. The capacity of the conversion table can be reduced, and the memory space can be used efficiently. Further, the decoding conversion table is referred to by the above procedure, and the run length value corresponding to the MH code, code length data and T / M
Since the restored image can be generated by directly referring to the information, the number of times of reading the memory of the decoding table from the conventional decoding process can be reduced, so that the decoding speed can be improved. . It goes without saying that the above-described code decoding processing method of the present invention can also be used in horizontal mode code decoding processing in the MR method or the MMR method.

As described above, in the first embodiment of the present invention, by preparing a plurality of decoding conversion tables corresponding to decoding-related bit portions excluding the common bit portion of the code, the decoding used for decoding is performed. Since the capacity of the decoding conversion table is reduced, the capacity of the decoding conversion table used for decoding can be reduced, and the memory space can be used efficiently. In the first embodiment, the capacity of the five decoding conversion tables is (2 ⁵ +2 ⁸ +2 ⁴ +2 ⁶ +2 ⁹ ) × 11 = 9680 (bits) (1). Is about 17K bits in the table area of the conventional code decoding device shown in FIG.
The memory capacity has been reduced by about half.

In the description of the first embodiment, M
An example in which the H codes are classified into five groups and five decoding conversion tables are used has been described. For example, the code group e is further divided into two groups according to whether the upper 8 bits are “00000001”. By dividing the code groups in more detail, it is possible to reduce the capacity of the decoding conversion table, and the processing speed decreases due to the complexity of the selection processing of the decoding conversion table, and the reduced memory capacity Therefore, it is possible to select a code grouping appropriate for the system.

Further, the above-mentioned Patent Publication No. 2687926 is disclosed.
In order to reduce the capacity of the decoding conversion table, the conventional code decoding device shown in FIG. 1 uses “0” before the first “1” appears in the code sequence for each decoding process of one code. In contrast to the process of counting the number and the need to refer to the table twice for reading the run length value and the table for reading the code length, the code decoding method according to the first embodiment of the present invention requires: Since the count processing of “0” is unnecessary, and the corresponding run length value and code length are read by referring to the decoding conversion table once, the number of times of reading the memory is reduced, and the processing time is shortened. , In contrast to the conventional code decoding method,
High-speed encoding processing can be performed.

Next, when comparing the number of clocks of a different process between the conventional code decoding method in the decoding process of one code and the code decoding method according to the present invention, the external memory reference of the CPU, the branch instruction, The number of execution clocks of the shift instruction and the operation instruction is 18 clocks, 3 clocks,
When one clock is used, a processing time difference represented by the following equation occurs. Note that the process of generating a restored image from the run-length value is the same as in the related art, and thus will not be described in the following calculation of the difference in processing time.

"In the case of the conventional code decoding method" In the flowchart of FIG.
The total of the clocks corresponding to B3, step SB4, and step SB6 is 2 to 28 clocks + 20 clocks + 20
Clock + 18 clocks = 60-86 clocks.
"In the case of the code decoding method according to the present invention" In the flowchart of FIG. 1, steps SA2 to SA5,
The sum of the clocks corresponding to steps SA6 to SA10 is 6 to 8 clocks + 20 clocks = 26 to 28
Clock.

[0052]

As described above, according to the code decoding method and apparatus of the present invention, a plurality of decoding conversion tables are prepared which are associated with decoding-related bit portions excluding common bit portions of codes. By determining the color to be converted and the common part bit of a part of the code data, one corresponding decoding conversion table is selected from the plurality of decoding conversion tables, and each decoding conversion table determines the code-related bits. By reading the code length and run-length information of the target code by referring to the address information, the capacity of the decoding conversion table used for decoding is reduced, so that the memory space can be used efficiently. it can. Also,
Since the count processing of “0” is unnecessary and the corresponding run length value and code length are read by referring to one decoding conversion table, the number of times of reading the memory can be reduced, and the processing time can be shortened. High-speed encoding processing can be performed.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining an operation of a first embodiment of a code decoding method according to the present invention.

FIG. 2 is an explanatory diagram showing an example of use of a memory at the time of code decoding processing in a facsimile to which the first embodiment of the code decoding method according to the present invention is applied.

FIG. 3 is a block diagram showing a configuration of a facsimile to which the code decoding method according to the present invention is applied and which has the function of the code decoding apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing a specific example of a data format of a decoding conversion table applied to the first embodiment of the code decoding method according to the present invention;

FIG. 5 is an explanatory diagram showing a configuration of a decoding conversion table applied to the first embodiment of the code decoding method according to the present invention.

FIG. 6 is an explanatory diagram showing a white run code group correspondence table applied to the first embodiment of the code decoding method according to the present invention.

FIG. 7 is an explanatory diagram showing a white run code group correspondence table applied to the first embodiment of the code decoding method according to the present invention.

FIG. 8 is an explanatory diagram showing a black run code group correspondence table applied to the first embodiment of the code decoding method according to the present invention.

FIG. 9 is an explanatory diagram showing a black run code group correspondence table applied to the first embodiment of the code decoding method according to the present invention.

FIG. 10 is a flowchart for explaining the operation of a conventional code decoding method.

FIG. 11 is an explanatory diagram showing a format of an MH code.

FIG. 12 is an explanatory diagram showing a reference address of a conversion table and a format of table data in a conventional code decoding method.

FIG. 13 is an explanatory diagram showing a termination code in the MH code.

FIG. 14 is an explanatory diagram showing a termination code in the MH code.

FIG. 15 is an explanatory diagram showing a makeup code in the case of a standard paper width in the MH code.

FIG. 16 is an explanatory diagram showing a makeup code in the case of a standard paper width in the MH code.

FIG. 17 is an explanatory diagram showing a makeup code in the case of an extended paper width in the MH code.

FIG. 18 is an explanatory diagram illustrating an example of a binary image of white / black.

[Explanation of symbols]

1 ... memory, 2 ... central processing unit (CPU), 3
... Operation panel control unit, 4 ... Operation panel, 5 ... Communication control unit, 6 ... Scanner control unit, 7 ... Scanner, 8 ...
... Printer controller 9, printer 11, program area 12, decoding table area 13, code data area 14, image data area.

Claims (12)

[Claims] 1. An MH code decoding method, wherein the MH codes are classified into a plurality of groups according to a relationship between a color of a target image, an upper common bit portion of the codes, and a code length, and the upper common MH codes of each group are classified. A plurality of decoding conversion tables storing code lengths and run-length information corresponding to decoding-related bit portions excluding bit portions; a common part of a color of an image to be decoded of the MH code and a part of code data; Selecting one corresponding decoding conversion table from the plurality of decoding conversion tables by judging the bits; each decoding conversion table addresses a code-related bit excluding the upper common bit portion of the MH code; Reading the code length and run-length information of the target code by referring to the decoding conversion table as the information. METHOD No. decoding. 2. The encoding / decoding method according to claim 1, wherein the decoding / conversion table only needs to read the decoding / conversion table once for the decoding process of one code. 3. The decoding conversion table according to claim 1, wherein a value of a maximum length of the code-related bit portion is a bit length of a table reference address, and one bit indicating a termination code / makeup code of an MH code corresponding to the address information. 2. The code decoding method according to claim 1, wherein information of a total of 11 bits of 6 bits of a run length value to be actually decoded and 4 bits indicating the number of bits of a code is formatted. 4. The code decoding method according to claim 1, wherein the MH codes are classified into five groups. 5. The code decoding method according to claim 1, wherein said MH codes are classified into two groups. 6. The code decoding method according to claim 1, wherein the decoding conversion table reads out the corresponding run length value and code length by one reference. 7. An MH code decoding apparatus, wherein the MH codes are classified into a plurality of groups according to the relationship between the color of the target image, the upper common bit portion of the codes, and the code length, and the upper MH codes of the respective groups are classified. A plurality of decoding conversion tables storing code lengths and run-length information corresponding to decoding-related bit portions excluding bit portions; a common part of a color of an image to be decoded of the MH code and a part of code data; Means for selecting one corresponding decoding conversion table from a plurality of decoding conversion tables by judging bits, and each decoding conversion table addresses a code-related bit excluding the upper common bit part of the MH code. Means for reading out the code length and run-length information of the target code by referring to the decoding conversion table as information. Decoder. 8. The code decoding apparatus according to claim 7, wherein the decoding conversion table only needs to read the decoding conversion table once for one code decoding process. 9. The decoding conversion table according to claim 1, wherein a value of a maximum length of the code-related bit portion is a bit length of a table reference address, and one bit indicating a termination code / makeup code of an MH code corresponding to the address information. 8. The code decoding apparatus according to claim 7, wherein a total of 11 bits of information of 6 bits of a run length value to be actually decoded and 4 bits indicating the number of bits of a code are formatted. 10. The code decoding apparatus according to claim 7, wherein said MH codes are classified into five groups. 11. The code decoding apparatus according to claim 7, wherein said MH codes are classified into two groups. 12. The code decoding apparatus according to claim 7, wherein the decoding conversion table reads out the corresponding run length value and code length by one reference.