JP4000266B2 - Data encoding apparatus, data encoding method, and program thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data encoding device, a data encoding method, and a program thereof, and more specifically, compresses image data particularly efficiently based on a compression technique based on a dictionary-based method such as LZ77 and LZ88. The present invention relates to a data encoding device, a data encoding method, and a program thereof.
[0002]
[Prior art]
In recent years, in the field of handling images, such as scanners, printers, and digital cameras, the resolution has increased and the amount of data per image, the so-called number of pixels, has become enormous. In order to efficiently transfer such enormous data over a network or to store it in a storage medium such as a hard disk or memory, an efficient compression method is required in terms of processing speed and compression rate.
[0003]
As a method for efficiently compressing data, a method using a universal code has been put into practical use. This universal code is an information storage type data compression method, and since it does not presume the statistical nature of the information source at the time of data compression, it can be applied to data of various types (character code, object code, etc.). . A document image has similarities in character outlines and character spacings, and a halftone image has similar halftone dot periodicity, dot shape identity, and the like. Redundancy with this similarity can be reduced by universal codes, and effective compression can be performed.
[0004]
As a typical method of the universal code, there is a Ziv-Lempel code. In the Ziv-Lempel code, two algorithms of the universal type and the incremental decomposition type (Incremental parsing) have been proposed. As a practical method using the universal type algorithm, there is the LZSS code, and the incremental decomposition type algorithm. There is an LZW (Lempel-Ziv-Welch) code as a practical method using the code.
[0005]
The LZSS algorithm, which is the base of LZSS, is a method of encoding encoded data as a duplicate of a past sequence by dividing encoded data into a maximum length sequence that matches from any position in the past data sequence. Specifically, a moving window for storing encoded input data and a prefetch buffer for storing data to be encoded are provided, and a data sequence of the prefetch buffer and all partial sequences of the data sequence of the moving window are included. Collation is performed to find the maximum length subsequence that matches in the moving window.
[0006]
Then, in order to specify this maximum length subsequence in the moving window, a set of “start position of the maximum length subsequence”, “matching length”, and “next symbol that caused mismatch” Encode. Next, the encoded data sequence in the prefetch buffer is moved to the moving window, and a new data sequence for the data sequence encoded in the prefetch buffer is input. Thereafter, by repeating the same processing, the data is decomposed into partial series and encoded.
[0007]
In general, LZSS encoding requires detection of the longest match with the input data string by the number of moving windows that store the encoded input data. It is said that
[0008]
In addition, LZW encoding provides a rewritable dictionary, divides an input character string into different character strings, registers the numbers in the order in which the character strings appear, and registers the currently input character string. The encoding is performed by representing only the dictionary number of the longest matching character string registered in the dictionary. According to this LZW encoding, the compression rate is inferior to that of LZSS encoding, but it is simple, easy to calculate, and capable of high-speed processing, so that it is used for file compression, data transmission, etc. of a storage device.
[0009]
Further, according to “Data compression device” of Japanese Patent Application Laid-Open No. 11-168389, having a number of comparators in parallel corresponding to the number of moving windows has a large hardware load. The method considering the processing speed and the hardware scale has been proposed.
[0010]
According to “Pattern compression method and apparatus” of Japanese Patent Laid-Open No. 9-181610, a long repeating pattern that cannot be effectively compressed by the LZ method or the like is compressed with a small amount of calculation. A method has been proposed in which frequency components are extracted, thinned out, autocorrelation is calculated, pattern matching is performed based on the autocorrelation, and repetition is detected.
[0011]
[Problems to be solved by the invention]
When searching for matching data strings from past encoded data such as LZSS, which uses a moving window, the matching accuracy increases as the window size increases, but the amount of processing required for comparison increases accordingly. , Processing speed and hardware scale will be burdened.
[0012]
Further, in the method disclosed in Japanese Patent Application Laid-Open No. 11-168389, the comparison processing is small, but storing a place with a high degree of coincidence eventually increases the buffer size as the window size. In the method of the above-mentioned Japanese Patent Laid-Open No. 9-181610, this method requires a large number of steps in order to find a long repetitive pattern that exceeds the buffer. It can be said that there is.
[0013]
In the method of the present invention, setting the window size as small as possible reduces the number of comparison processes, and has the advantages of improving the processing speed and reducing the hardware scale. In addition, by increasing the size of the comparison target unit (encoding unit), it is possible to convert a long pattern into a short pattern, and it is possible to find a repeated pattern at a short distance.
[0014]
The present invention utilizes the fact that the period of the encoding target data is generated as a repetition of a symbol sequence, and efficiently compresses the data by run-length encoding it. Further, by making the encoded data immediately before the symbol string to be encoded a comparison target, it becomes possible to reduce the comparison range, improve the processing speed, and reduce the hardware scale. A first object is to provide an encoding device, a data encoding method, and a program thereof.
[0015]
In addition, when the data subjected to the processing for generating the cycle such as dither is the data to be encoded, the present invention is efficient in obtaining the cycle of the original image by setting the encoding unit based on this cycle. A data encoding device, a data encoding method, and a program thereof that can obtain a good period, that is, can reduce the comparison range, improve processing speed, and reduce the hardware scale are provided. This is the second purpose.
[0016]
The present invention also provides a data encoding apparatus, a data encoding method, and the like that can cope with a case in which the cycle changes in the middle of the encoding target data (for example, in the case of image data, a mixture of dithers). And a third object thereof is to provide the program.
[0017]
In addition, the present invention provides a data encoding device and a data code that can prevent a reduction in compression rate and increase encoding efficiency when a continuous number is encoded by providing a lower threshold for the continuous number. A fourth object is to provide a computerization method and a program therefor.
[0018]
In addition, the present invention provides a data code that can limit the bit length of a code when encoding the continuous number by providing an upper limit threshold value for the continuous number, and can increase the encoding efficiency. It is a fifth object to provide an encoding device, a data encoding method, and a program therefor.
[0019]
In addition, the present invention provides a data encoding apparatus, a data encoding method, and a program thereof that can improve compression efficiency by performing different encoding on consecutive events that occur recursively. This is the sixth purpose.
[0020]
Further, according to the present invention, when the difference is large with respect to the target predetermined compression rate as a result of the progress of encoding, it cannot be said that the optimum processing is performed. As a countermeasure for such a problem, a data encoding device, a data encoding method, and a program thereof that can increase the compression effect optimal in terms of compression rate and processing speed by adaptively changing the comparison range It is the seventh object to provide.
[0021]
Further, according to the present invention, if the compression rate in a certain predetermined range does not satisfy the predetermined value with respect to the target predetermined compression rate as a result of proceeding with the encoding, the comparison range is widened to increase the continuous pattern. It is an eighth object of the present invention to provide a data encoding device, a data encoding method, and a program thereof that can increase the probability of occurrence and increase the compression efficiency.
[0022]
Further, according to the present invention, if the compression rate in a certain predetermined range satisfies a predetermined value with respect to the target predetermined compression rate as a result of the encoding, it can be said that the comparison range is sufficient. At this time, it is a ninth object to provide a data encoding device, a data encoding method, and a program thereof that can speed up the comparison process by further narrowing the comparison range.
[0023]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 is characterized in that, in a symbol sequence, M encoded symbol sequences adjacent to the current encoding time point, M symbol sequences before encoding, Are determined to match, and if it is determined that they match, whether the M symbol sequences before encoding and the M symbol sequences that are consecutive match the encoded symbol sequences Instead of a comparing means for repeatedly determining whether or not, a run determining means for counting the number of matches determined to be matched by the comparing means, and a plurality of symbol sequences determined to be matched by the comparing means, the value of M And an encoding means for encoding the number of matches.The data encoding apparatus further includes: a compression rate calculation unit that calculates a compression rate of a predetermined processing range; and a determination unit that determines whether or not the compression rate has achieved a target value. The upper limit value of the number of symbols to be compared by the comparing means is changed according to whether or not the determining means determines that the compression ratio has achieved the target value.A data encoding device characterized by that.
According to a second aspect of the present invention, in the data encoding device according to the first aspect, when the determination unit determines that the compression ratio has not achieved the target value, the comparison unit compares the compression rate. The upper limit value of the number of symbols is increased, and when it is determined that the compression ratio has achieved the target value, the upper limit value of the number of symbols to be compared by the comparing means is decreased.
[0024]
  Claim3The described invention is claimed.1 or 2The data encoding device according to claim 1, further comprising: a symbol generating unit that generates the symbol string from the encoding target data, and determining the number of bits per symbol based on a period of the encoding target data. And
[0025]
  Claim4The described invention is claimed.3In the data encoding device described above, the symbol creation unit includes a cutout unit that cuts out data of a plurality of bits from the encoding target data based on a cycle of the encoding target data, and M that extracts the data cut out by the cutout unit. conversion means for obtaining the symbol by conversion by the oveToFront method.
[0026]
  Claim5The described invention is claimed.4In the data encoding device described above, the symbol creation unit further includes a cycle detection unit that detects a cycle from the encoded data, and the cutout unit changes the number of cutout bits based on the detected cycle. It is characterized by that.
[0027]
  Claim6The described invention is claimed.Any one of 1 to 5In the data encoding device described above, the encoding unit encodes the value of M and the number of matches when the number of matches counted by the run determination unit is equal to or greater than a predetermined number, If the number of matches counted by the run determination means is less than a predetermined number, the symbol string before encoding is encoded.
[0028]
  Claim7The described invention is claimed.Any one of 1 to 6In the data encoding device described above, the encoding means includes the first symbol determined to be inconsistent with the value of M to be encoded and the number of matches, and the value of M encoded immediately before If the number of matches is equal between the number of matches and the first symbol determined not to match, encoding is performed without the number of matches.
[0031]
  Claim8The described invention determines whether or not the encoded M symbol sequences adjacent to the current encoding point in the symbol sequence coincide with the M symbol sequences before encoding. A comparison step that repeats the determination as to whether or not the M symbol sequences that are consecutive with the M symbol sequences that have been encoded coincide with the M symbol sequences that have been encoded, in addition to the M symbol sequences before the encoding. A run determination step for counting the number of matches determined to be matched by the comparison means, and encoding the value of M and the number of matches in place of a plurality of symbol strings determined to be matched by the comparison means An encoding step;A compression rate calculation step of calculating a compression rate of a predetermined processing range, a determination step of determining whether or not the compression rate has achieved a target value, and And changing the upper limit value of the number of symbols to be compared in the comparison step according to whether or not the compression step is determined to achieve the target value.This is a data encoding method.
[0032]
  Claim9The described invention determines whether or not the encoded M symbol sequences adjacent to the current encoding point in the symbol sequence coincide with the M symbol sequences before encoding. If it is determined, a comparison process that repeats determination of whether or not M consecutive symbol sequences match the encoded symbol sequence in addition to the M symbol sequences before encoding, A run determination process for counting the number of matches determined to be matched by the comparison means, and an encoding process for encoding the value of M and the number of matches in place of the plurality of symbol sequences determined to be matched by the comparison means And let the computer runA data encoding program, further comprising: a compression ratio calculation process for calculating a compression ratio of a predetermined processing range; a determination process for determining whether or not the compression ratio has achieved a target value; and the determination process And causing the computer to execute a process of changing the upper limit value of the number of symbols to be compared by the comparison process according to whether or not the compression rate is determined to have achieved the target value.This is a data encoding program.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0035]
A first embodiment of the present invention will be described. First, the basic configuration is shown in the block diagram of FIG. The input data in FIG. 1 may be text data or binary data. Here, an example is shown in which image data subjected to halftone processing such as 1 bit / pixel dither processing is used as input data. First, the multi-bit cutout unit 101 cuts out input data as one data by collecting several bits. Next, the intermediate data creation unit 102 converts each data into N-bit data by a method such as MTF (MoveToFront) and outputs the data as intermediate data.
[0036]
Here, the meaning of converting to intermediate data is the reason for removing redundancy of input data. For example, when the chunk cut out by the multi-bit cutout unit 101 is relatively small, for example, when it is about 4 bits, there are at most 16 patterns of data to be cut out. In such a case, it is good. However, for example, when the number of bits to be cut out is 20 bits, the number is 2 to the 20th power.
[0037]
In this case, the generation pattern becomes enormous, which causes problems in terms of processing speed on software and hardware scale. However, the image data that has been subjected to the dither process originally has periodicity. If the period of the dither is 20 bits, if 20 bits are converted into one data based on the period, the distribution should be considerably biased. Using this, 20-bit data is converted into N bits having a relatively small number of bits by MTF (MoveToFront), and output as intermediate data.
[0038]
The MTF will be described with reference to FIG. Here, it is assumed that data input to the MTF is 8-bit character data. First, when there is an input symbol “A” as shown in (1) in FIG. 2, conversion is performed with the index number “2” of the dictionary storing “A” as an output value. Next, as shown in (2), the input symbol “A” is moved to the top of the dictionary to update the dictionary.
[0039]
As the processing proceeds, frequently appearing symbols gather at the position of a small index number, so that an input having an arbitrary distribution shape can be changed to a distribution having 0 as a peak. The number of registrations in this dictionary can be limited to an arbitrary number. When a symbol other than those registered is input, it can be handled by outputting it as “ESC code + raw data” and newly registering the symbol at the top of the dictionary.
[0040]
Returning to FIG. 1, intermediate data that has been subjected to processing such as MTF is input to the comparator 103 (hereinafter, this intermediate data is referred to as a character). The comparator 103 will be described with reference to FIGS. Assume that the buffer size is 16 characters (n = 16), and 8 characters have already been encoded (FIG. 3a). Eight lengths of characters starting from the encoding start position (dotted line position in the figure) in the buffer (right side of dotted line) and the left side of the dotted line immediately before the encoding start position of the encoded character string in the buffer Is compared with the character string of and the longest match is searched (step S1).
[0041]
In this case, “abc” is determined to be the longest match (step S1 / YES), but here, the head address, that is, “3” representing the character string length is temporarily stored without outputting the code. Next, the characters in the buffer are shifted to the left so that the three matched character strings are at the end of the encoded buffer portion, and the encoding start position is shifted (FIG. 3b). Looking at the next encoding start position, the character string “abc” is the longest match as before, and the address “3” is determined again.
[0042]
Here, in the run determination unit 104 shown in FIG. 1, it can be seen that it is the same value as compared with the address temporarily stored (step S2 / YES). Here, the run is incremented by 1 (step S3). Again, no sign is output. Next, it is shifted to the left by three characters as in the previous description (step S5). There is no matching character string between the current encoding start character string and the encoded character string (step S1 / NO). In this way, the characters that do not match the current run are output as codes only when they do not match (step S8). At this time, the start position of “abc”, that is, the character length “3”, the run “2”, and the code “d” are output (FIG. 3c). The details of the processing by the comparator 103 are shown in the flowchart of FIG.
[0043]
In this way, we want to generate a run to increase the compression efficiency. That is, the intermediate data is created based on the period of the original image so that the character string is repeated. For example, it is assumed that the data to be encoded is 8 bit / pixel data, and is dithered with a dither matrix size of 20 × 20 and subjected to halftone processing to 1 bit / pixel. At this time, the data after halftone processing can be expected to be repeated in 20 cycles in the X direction. When the period “20” is known, the multi-bit cutout unit 101 in FIG. 1 cuts the input data in units of 20 bits and passes it to the intermediate data creation unit 102. As a result, the similarity increases with the cut out data, so that the matching accuracy can be improved in the comparator 103.
[0044]
Further, the period of the encoding target data is automatically detected. FIG. 5 shows a processing block diagram. A cycle detection unit 501 is added to the head of the process shown in FIG. FIG. 6 shows an example of the period detection method. If such an automatic cycle detector 501 is provided, different cycles can be found even in one line depending on the determination range. For example, depending on the image processing, the image portion and the graphic portion may be dithered differently. That is, even if different periods occur in one line, it is possible to cope with it.
[0045]
Cutting out using the period of the data to be encoded as described above increases the compression effect, but of course, a predetermined effect can be obtained without such processing.
[0046]
Next, a second embodiment will be described. In the example shown in the first embodiment, the run determination unit 104 in FIG. 1 sets a threshold value for a run. As shown in FIG. 6, when a run is not created, assuming that there is a character string “ab”, and “a” has a 3-bit code and “b” has a 4-bit code, “ab” Becomes 7 bits.
[0047]
For example, if the run code is ESC2 code = 5 bits, address = 5 bits, and run length = 8 bits, 18 bits are used. When creating a run, since it is premised that the compression efficiency is higher than the normal one-character encoding, in this example, “ab” is 14 bits for 2 times and 21 bits for 3 times. The effect of creating a run cannot be obtained unless it is more than once. Therefore, a threshold value (A) that is the minimum value of the run is required.
[0048]
Next, an upper threshold (B) for the run length is set. That is, the number of bits representing the run length is limited. In general, run-length encoding of binary data that is subject to compression increases the compression efficiency the longer the run length, but if the bit length as a run code is fixed as in this case, the bit of the code representing the run length The length needs to be limited to some extent. This is because if only a short run length actually occurs, useless bits are output.
[0049]
In the above example, the lower threshold for the run length is determined from the run value only, but the number of bits actually generated is determined by the bit length of each character constituting the character string and the number of runs. Therefore, it is possible to set a threshold value at which the compression efficiency does not decrease considering all of them.
[0050]
Next, a third embodiment will be described with reference to FIG. Assume that the data to be encoded as shown in FIG. 7 is in the buffer. When this data is encoded by the processing shown in the first embodiment, “A code + ESC2 code + address (1) + run (3)” followed by “B code + ESC2 code + address (1)”. + Run (3) ”,“ C code + ESC2 code + address (1) + run (3) ”.
[0051]
However, as can be seen, these three types of codes have the same configuration, and only the character types are different. In order to encode this efficiently, the output of “BBB” is replaced with “B code + ESC3 code” in the present embodiment. Similarly, the next “CCC” is “C code + ESC3 code”. Thus, the compression efficiency can be further improved by creating two stages of runs. In this example, a sequence of one character is given, but it can also be applied to a case where three characters such as “ABCABCABCDEFDEFDEF” are repeated N times.
[0052]
Next, a fourth embodiment will be described. In the present embodiment, the comparator 103 in FIG. 1 adaptively changes the buffer size in the comparison process based on a certain reference. FIG. 8 shows a flowchart. When a certain predetermined processing range is set and the processing range ends (step S23 / YES), the compression rate (M) is calculated as the coding efficiency up to that point (step S24), and a predetermined target compression rate is achieved. (Step S25), if not achieved (step S25 / NO), the comparison range (= window size) is expanded (step S26).
[0053]
The window size possessed by the normal LZ method, etc., especially the buffer for storing the encoded data, requires a considerably large size. This is to increase the compression efficiency, but depending on the size, the processing speed and circuit scale are greatly affected.
[0054]
In the present invention, the buffer size used in the description from the first embodiment is originally assumed to be a very small size sufficient to satisfy the processing speed and the circuit scale, and the purpose is to extract local repetitions. Yes. Therefore, if there is actually a repetition of a period longer than the window size, this may not be detected. In order to avoid this, the window size is increased and the process proceeds. By setting an upper limit for the size to be expanded, it is possible to suppress a decrease in processing speed.
[0055]
On the other hand, when the target compression rate is achieved, the window size is reduced. By reducing the size, the processing speed of the comparator 103 can be improved. Similarly, it is not necessary to make it unnecessarily small in balance with the processing speed, and it is possible to set a limit that does not lower the compression efficiency.
[0056]
The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there.
[0057]
The present invention can be realized by causing a computer to execute a program. The program is provided by being recorded on an optical recording medium, a magnetic recording medium, a magneto-optical recording medium, or a semiconductor IC recording medium, or is provided by being downloaded from a program server via a network such as FTP or HTTP. The
[0058]
【The invention's effect】
As is clear from the above description, the following effects can be obtained according to the present invention. Using the fact that the period of the data to be encoded is generated as a repetition of the data sequence, it can be efficiently compressed by run-length encoding it. In addition, since the encoded data immediately before the symbol string to be encoded is used as a comparison target, the processing speed can be improved and the hardware scale can be reduced by reducing the comparison range.
[0059]
  Also,BookAccording to the invention, for example, when the data subjected to the process of generating a cycle such as dither is the data to be encoded, by setting the encoding unit based on this cycle, the efficiency in obtaining the cycle of the original image is obtained. The period can be obtained well, that is, the comparison range can be made smaller, the processing speed can be improved, and the hardware scale can be reduced.
[0060]
  Also,BookAccording to the invention, it is possible to cope with a case where the period changes in the middle of the encoding target data (for example, in the case of image data, a mixture of dithers).
[0061]
  Also,BookAccording to the invention, by providing a lower limit threshold value for the continuous number, when encoding the continuous number, it is possible to prevent the compression rate from being lowered and to increase the encoding efficiency.
[0062]
  Also,BookAccording to the invention, by providing an upper limit threshold value for the continuous number, the bit length of the code can be limited when encoding the continuous number, and the encoding efficiency can be increased.
[0063]
  Also,BookAccording to the invention, when a continuous event occurs recursively, the compression efficiency can be increased by performing different coding on this event.
[0064]
  Also,BookAccording to the invention, if the difference is large with respect to the target predetermined compression rate as a result of the progress of encoding, it cannot be said that the optimum processing is performed. By adaptively changing the comparison range as a countermeasure against such problems, it is possible to obtain optimum conditions in terms of compression rate and processing speed.
[0065]
  Also,BookAccording to the invention, as a result of advancing the encoding, when the compression rate in a certain predetermined range does not satisfy the predetermined value with respect to the target predetermined compression rate, the comparison range is expanded to generate a continuous pattern. The establishment can be improved and the compression efficiency can be increased.
[0066]
  Also,BookAccording to the invention, as a result of advancing the encoding, if the compression rate in a certain predetermined range satisfies a predetermined value with respect to the target predetermined compression rate, it can be said that the comparison range is sufficient. At this time, since the comparison process can be reduced by further narrowing the comparison range, the comparison process can be speeded up.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of the present invention.
FIG. 2 is a diagram for explaining an MTF.
FIG. 3 is a diagram for explaining a comparator 103;
FIG. 4 is a flowchart for explaining processing of the comparator 103;
FIG. 5 is a block diagram showing a configuration of a variation of the present invention.
FIG. 6 is a diagram illustrating a configuration example for automatically detecting a cycle.
FIG. 7 is a diagram for explaining a third embodiment;
FIG. 8 is a flowchart for explaining a fourth embodiment;
[Explanation of symbols]
101 Multi-bit cutout unit
102 Intermediate data creation unit
103 comparator
104 Run determination unit
501 Period detector

Claims (9)

In the symbol string, it is determined whether or not the encoded M symbol strings adjacent to the current encoding point coincide with the M symbol strings before encoding.
A comparison unit that repeats the determination of whether or not the M symbol sequences before encoding and the M symbol sequences that are consecutive match the encoded symbol sequence when it is determined that they match ; instead before symbol comparison means run judgment means for counting the number of matches that have been determined to match, prior symbol plurality of symbol columns which are determined to match the comparison means, for coding the match count value of the M a chromatic data encoding device and the encoding means, and
Furthermore, a compression rate calculation means for calculating a compression rate of a predetermined processing range;
Determining means for determining whether or not the compression ratio has achieved a target value,
A data encoding apparatus , wherein the upper limit value of the number of symbols to be compared by the comparing means is changed according to whether or not the determining means determines that the compression rate has achieved a target value . By the determination means,
  If it is determined that the compression ratio has not reached the target value, the comparison means increases the upper limit value of the number of symbols to be compared,
  2. The data encoding apparatus according to claim 1, wherein when it is determined that the compression ratio has achieved the target value, the upper limit value of the number of symbols to be compared by the comparing means is lowered. A symbol creating means for creating the symbol string from the encoding target data;
3. The data encoding apparatus according to claim 1, wherein the number of bits per symbol is determined based on a period of the encoding target data. The symbol creating means includes:
Based on the cycle of the encoding target data, a cutting means for cutting out a plurality of bits of data from the encoding target data;
4. The data encoding apparatus according to claim 3 , further comprising conversion means for converting the data cut out by the cut-out means by the MoveToFront method to obtain the symbol. The symbol creating means includes:
Further comprising a period detecting means for detecting a period from the encoded data;
5. The data encoding apparatus according to claim 4 , wherein the cutout unit changes the number of cutout bits based on the detected cycle. The encoding means includes
If the number of matches counted by the run determination means is greater than or equal to a predetermined number, encode the value of M and the number of matches,
If the match count counted by the run-determining means is less than a predetermined number of times, according to any one of claims 1-5, characterized in that for encoding the symbol string before encoding Data encoding device. The encoding means includes
The first symbol determined to be inconsistent with the value of M to be encoded and the number of matches, and the first symbol determined to be inconsistent with the value of M encoded immediately before and the number of matches 7. The data encoding device according to claim 1, wherein the encoding is performed when the number of matches is equal to each other . In the symbol string, it is determined whether or not the encoded M symbol strings adjacent to the current encoding point coincide with the M symbol strings before encoding.
A comparison step of repeatedly determining whether or not consecutive M symbol sequences match the encoded M symbol sequences in addition to the M symbol sequences before encoding when it is determined that they match If, before symbol run determination step of counting the number of matches that have been determined to match the comparison means, before symbol instead plurality of symbol columns which are determined to match the comparison means and the match count value of the M An encoding step for encoding, and a data encoding method comprising:
Furthermore, a compression ratio calculation step for calculating a compression ratio of a predetermined processing range;
A determination step of determining whether or not the compression ratio has achieved a target value;
Changing the upper limit value of the number of symbols to be compared in the comparison step according to whether or not the compression rate is determined to have achieved the target value in the determination step. Method. In the symbol string, it is determined whether or not the encoded M symbol strings adjacent to the current encoding point coincide with the M symbol strings before encoding.
A comparison process for repeatedly determining whether or not consecutive M symbol sequences match the encoded symbol sequence in addition to the M symbol sequences before encoding when it is determined that they match . instead before symbol comparison means by the run determination processing for counting the number of matches that have been determined to match, before symbol plurality of symbol columns which are determined to match the comparison means, for coding the match count value of the M A data encoding program for causing a computer to execute encoding processing ,
Furthermore, a compression ratio calculation process for calculating a compression ratio of a predetermined processing range;
A determination process for determining whether or not the compression ratio has achieved a target value;
And causing the computer to execute a process of changing an upper limit value of the number of symbols to be compared by the comparison process according to whether or not the compression rate is determined to have achieved the target value by the determination process. A data encoding program.

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