JP2005260420A - Data compression apparatus and data compression program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data compression apparatus for compressing data such as image data the compression rate of which is enhanced. <P>SOLUTION: The data compression apparatus obtains a difference between adjacent numerical values in consecutive numerical values configuring data to be compressed and codes only a particular numerical value "YY" among the numerical values appearing in the difference data. In the case of carrying out coding, coding representing a consecutive number Z whose number of bits differs depending on whether the consecutive number Z of the numeral "YY" is Z<128 or Z≥128 is carried out. Huffman coding is applied further to data obtained by the coding by using a Huffman table in accordance with the type of images. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a data compression apparatus that compresses data such as image data, and a data compression program that causes an information processing apparatus such as a computer to operate as a data compression apparatus.

  2. Description of the Related Art Conventionally, techniques for compressing data such as image data have been widely adopted in order to reduce storage capacity and communication volume.

  For example, in Patent Document 1, when a representative color is selected from an original image and a CLUT (color look-up table) is configured, color numbers are assigned so that continuous color numbers have color data of close values, When a bitmap corresponding to the CLUT is created to obtain the difference in color number between adjacent pixels, and the difference takes a large value, the color number of the bitmap is changed within a range that does not cause image quality degradation, and the difference is set to a small value. A technique is disclosed in which run length encoding is applied to biased and differential data.

  Further, Patent Document 2 encodes image data configured by irreversibly compressing a plurality of data assigned to each color and assigning one of the data to a transparent color, The transparent color is reversible, and the image data is composed of an immediate value (the first value at the time of differential encoding) and a plurality of differential values (the previous value at the time of differential encoding) following the immediate value. When encoding a value by irreversible compression, the immediate value representing the transparent color and the difference value are made reversible, and the immediate value representing the transparent color is set to an intermediate value between the data values of each color, or the transparent color is changed. A technique has been proposed in which the difference value to be expressed is set to “0”.

  Patent Document 3 proposes that the number is encoded by the difference between the predicted number (s' (j)) and the actual number (s (j)).

  Further, Patent Document 4 recognizes the distribution status of the same pixel data in the sub-scanning direction and the distribution status of the same pixel data in the main scanning direction with respect to the n-th pixel data column. Based on this recognition result, there has been proposed an image compression device that determines whether to compress the same pixel data continuous in the sub-scanning direction or to compress the same pixel data continuous in the main scanning direction.

  Here, one system to which the data compression technology is applied is introduced.

  FIG. 1 is a diagram illustrating an example of a print system to which a data compression technique is applied, and FIG. 2 is a diagram illustrating a flow of data processing in the print system.

  As shown in FIG. 1, the print system includes a host controller 100, an interface device 200, and a printer 300. A general-purpose interface cable 150 such as SCSI is used between the host controller 100 and the interface device 200. Further, the interface device 200 and the printer 300 are connected by a dedicated interface cable 250.

  In the host controller 100, as shown in FIG. 2, character and image data 11 described in various languages and formats such as PDF, PS, and TIFF are image (CT) data, characters and lines. Etc. (LW; Line Work) data, RIP (Raster Image Processing) is performed for each to generate bitmap data 12A and 13A, and further, data compression processing is performed for each, and CT is performed. Generates irreversible compressed data 14 and reversible compressed data 15 for LW. These compressed data 14 and 15 are transferred from the host controller 100 to the interface device 200 via the general-purpose interface cable 150 shown in FIG. In the interface device 200, the compressed data 14 and 15 transferred are subjected to data decompression processing, and the bitmap data 12B and 13B corresponding to the bitmap data 12A and 13A in a state before the host controller 100 performs the data compression processing. Is generated. Here, since the CT data is subjected to lossy compression processing at the time of data compression by the host controller 100, the CT data (bitmap data 12B) after data decompression is completely CT data before data compression ( Although it does not return to the bitmap data 12A), almost the same bitmap data is restored. Since the LW data is subjected to lossless compression processing at the time of data compression by the host controller 100, the LW data (bitmap data 13B) after data expansion is the LW data (bitmap data 13A) before data compression. Is restored to the same data.

  In the interface device 200, CT data (bitmap data 12B) after data expansion and LW data (bitmap data 13B) are combined, and halftone dot information and the like are added as tags and sent to the printer 300. In the printer 300, an image is printed out according to the bitmap data received from the interface device 200 and the tag information added thereto.

  For example, when the host controller 100 and the interface device 200 are separated from each other, or when the interface device 200 is a system that receives image data from a plurality of host controllers, the host controller 100 and the interface device 200 are separated from each other. 2, the host controller 100 compresses data, transfers the data to the interface device 200, and decompresses the data using the interface device, as shown in FIG. Data transfer time to the interface device 200 can be shortened, and print productivity is improved.

  Here, generally, a compression method such as JPEG which is irreversible but has a high compression rate is adopted for CT data, and a reversible compression method such as PackBits is adopted for LW data.

  Hereinafter, for comparison with an embodiment of the present invention described later, an encoding method using PackBits will be described.

  FIG. 3 is an explanatory diagram of the PackBits encoding method.

  The original data is “01 02 02 02 03 03 03 03 04 05” arranged in the upper row. In this case, it is assumed that all are expressed in hexadecimal notation, the first numerical value of the original data is “01”, the next is “02”, and the next is “02”, and “02” is the same. Since the numerical values of are consecutive, there is only one numerical value “01” that is not continuous.

  Therefore, here, a numerical value “00” obtained by subtracting 1 from the number of numerical values that are not continuous (here, 1) is set (the first numerical value “00” in the lower part of FIG. 3). Subsequently, the discontinuous numerical value itself (here, “01”) is placed (the second numerical value “01” in the lower row). That is, here, “01” of the original data is replaced with “00 01” by PackBits encoding.

  Next, since “02” of the original data is continuous, the number (−2) obtained by subtracting 1 (here 2) from the consecutive number (here 3) minus 1 is expressed in hexadecimal. Is placed (the third numerical value “FE” in the lower row), and the continuous numerical value itself (here, “02”) is placed behind it (the fourth numerical value “02” in the lower row). ). That is, here, “02 02 02” of the original data is replaced with “FE 02” by PackBits encoding.

  Next, since “03” is consecutive in the original data, the number (−3) in which the number 3 obtained by subtracting 1 from the number 4 is negative is expressed in hexadecimal as in the above. “FD” and the continuous numerical value “03” are placed. That is, here, “03 03 03 03” of the original data is replaced with “FD 03”.

  Further, “04 05” follows on the original data, but these “04” and “05” are each independent and the same numerical value is not continuous. Therefore, here, 1 is subtracted from the number (in this case, 2) of the non-consecutive numerical values (“04”, “05”) to place “01”, followed by the non-contiguous numerical value itself “04”. 05 ”. That is, here, “04 05” of the original data is replaced with “01 04 05” by PackBits encoding.

In PackBits, encoding is performed according to the above rules.
JP-A-5-328142 Japanese Patent Laid-Open No. 10-164620 Japanese translation of PCT publication No. 2001-5-20822 Japanese Patent Laid-Open No. 9-200540

  In the case of the PackBits encoding described above, values that can be taken as consecutive numbers of the same numerical value are −1 to −127. That is, up to 128 can be expressed as a continuous number. Since this is expressed by 2 bytes (8 bits × 2), the maximum compression rate that can be realized in principle is 2/128 = 1/64.

  Such PackBits encoding has a problem that the compression rate is small although there is an advantage that the original data can be completely restored because it is lossless compression. For this reason, conventionally, as shown in FIG. 2, lossless compression is performed only for LW data that tends to have a noticeable deterioration in image quality in lossy compression, and CT data may be lossy compared to LW data. Since degradation of image quality is relatively inconspicuous, JPEG, which is a type of lossy compression, is used.

  However, in recent years, there has been an increasing demand for higher image quality, and it has been studied to perform lossless compression of CT data so as not to cause deterioration of image quality.

  In view of the above circumstances, the present invention provides a data compression apparatus capable of performing a reversible compression process with a higher compression ratio than the conventional lossless compression method, and an information processing apparatus such as a computer as such a data compression apparatus. An object of the present invention is to provide a data compression program that can be operated.

A data compression apparatus of the present invention that achieves the above object is a data compression apparatus that performs data compression processing on data to be compressed consisting of a series of numerical values represented by a predetermined unit bit number.
Among the data to be compressed, numerical values other than one or a plurality of predetermined numerical values to be compressed are output as they are, and for the numerical values to be compressed, the numerical values to be compressed and the continuous number of the numerical values to be compressed that are the same as the numerical values to be compressed A first data compression unit that encodes and outputs a numerical value representing
A second data compression unit that performs entropy coding on the data that has been encoded by the first data compression unit using a table that associates codes and numerical values according to the type of data to be compressed; It is characterized by that.

  Here, in the data compression apparatus of the present invention, the second data compression unit may perform Huffman encoding using a Huffman table corresponding to the type of data to be compressed, as a typical example. .

  The second data compression unit preferably includes a type determination unit that determines the type of the data to be compressed based on the data encoded by the first data compression unit. The second data compression unit includes a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and the type determination unit is obtained by the histogram calculation unit. It is preferable that the type of data to be compressed is determined based on the obtained histogram.

  Further, the compressed data is data representing one of a continuous tone image and a linework image, and the type determining unit is the compressed data representing the continuous tone image or representing the linework image. It is preferable to determine whether the data is compressed data.

  Further, the second data compression unit is based on a histogram calculation unit for obtaining a histogram of numerical values appearing in the data encoded by the first data compression unit, and a histogram obtained by the histogram calculation unit. A table according to the type of data to be compressed, including a code assigning unit that assigns a code having a shorter code length to a numerical value with a higher appearance frequency, and using the table in which a code is assigned to the numerical value by the code assigning unit. It is preferable to perform entropy coding.

  Moreover, it is preferable that the first data compression unit performs encoding that expresses the continuous number with a different number of bits in accordance with the continuous number of the same numerical value to be compressed. When the number of consecutive compression values of the same compression target is less than or equal to a predetermined number, the number of consecutive numbers is expressed by one unit bit number, and when the number of consecutive values exceeds the predetermined number, it is expressed by two unit bit numbers. Encoding may be performed.

  Further, in the data compression apparatus according to the present invention, the first stage of the first data compression unit is made up of a series of numerical values representing the difference by obtaining a difference between adjacent numerical values for a series of numerical values constituting the compressed data. It is preferable to include a third data compression unit that generates new compressed data and passes it to the first data compression unit. In this case, the third data compression unit outputs the first numerical value for each segment when the sequence of the numerical values constituting the compressed data is sequentially segmented, and adjoins other than the first numeric value. It is more preferable to output a numerical value represented by the lower unit bit number of the difference between the numerical values.

The data compression program of the present invention that achieves the above object is executed in an information processing apparatus that executes the program, and converts the information processing apparatus into compressed data consisting of a series of numerical values represented by a predetermined number of unit bits. A data compression program that operates as a data compression device that performs data compression processing,
The information processing apparatus is
Among the data to be compressed, numerical values other than one or a plurality of predetermined compression target values are output as they are, and for the compression target numerical value, the compression target numerical value and the continuous number of the compression target numerical values that are the same as the compression target numerical value are displayed. A first data compression unit that encodes and outputs a numerical value to be represented;
A second data compression unit that performs entropy coding on the data that has been encoded by the first data compression unit using a table that associates codes and numerical values according to the type of data to be compressed; It is characterized by operating as a data compression device.

  Here, in the data compression program of the present invention, the second data compression unit may perform Huffman coding using a Huffman table corresponding to the type of data to be compressed.

  In the data compression program of the present invention, the second data compression unit includes a type determination unit that determines the type of data to be compressed based on the data encoded by the first data compression unit. In this case, the second data compression unit includes a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and The type determining unit is preferably operated as a data compression device that determines the type of the data to be compressed based on the histogram obtained by the histogram calculating unit.

  Further, the compressed data is data representing one of a continuous tone image and a linework image, and the type determining unit is the compressed data representing the continuous tone image or representing the linework image. It is preferable to determine whether the data is compressed data.

  Further, the second data compression unit is based on a histogram calculation unit for obtaining a histogram of numerical values appearing in the data encoded by the first data compression unit, and a histogram obtained by the histogram calculation unit, The table according to the type of data to be compressed has a code assigning unit that assigns a code having a shorter code length to a numerical value with a higher appearance frequency. It is preferable to operate as a data compression device that performs processing.

  Furthermore, in the data compression program of the present invention, it is preferable that the first data compression unit performs encoding to express the continuous number with a different number of bits according to the continuous number of the same numerical value to be compressed. As an example, the first data compression unit expresses the continuous number as a unit bit number when the number of consecutive consecutive numerical values to be compressed is a predetermined number or less, and the continuous number exceeds the predetermined number. May be one that performs encoding expressed in 2 unit bits.

  Further, the data compression program according to the present invention comprises a series of numerical values representing the difference by obtaining a difference between adjacent numerical values for a series of numerical values constituting the data to be compressed before the first data compression unit. It is preferable to operate as a data compression apparatus including a third data compression unit that generates new compressed data and passes the data to the first data compression unit.

  In this case, the third data compression unit outputs the first numerical value for each delimiter when the sequence of numerical values constituting the compressed data is sequentially delimited, and adjoins other than the first numerical value. It is more preferable to output a numerical value represented by the lower unit bit number of the difference between the numerical values.

  According to the data compression apparatus or data compression program of the present invention described above, only the numerical value to be compressed is encoded into the numerical value representing the numerical value to be compressed and the continuous number in the first data compression unit. As described with reference to the above, a situation in which the redundancy is higher than that of the original data is avoided, and the compression rate is improved.

  Further, according to the data compression apparatus or data compression program of the present invention, the data compressed in the first data compression unit as described above is further processed in the second data compression unit according to the type of the data. Since entropy coding using a table, typically Huffman coding, is performed, the entropy is appropriately selected according to the type of data such as CT data representing a continuous tone image and LW data representing a linework image. Encoding is performed, and the compression rate is greatly improved.

  Here, in determining the data type, for example, CT data and LW data can be appropriately determined by providing the above-described histogram calculation unit and determining the type based on the histogram.

  Further, the second data compression unit obtains the above histogram, and assigns a code length that is shorter to a numerical value with a higher appearance frequency to a table corresponding to the data type based on the histogram, and the numerical value is assigned in that way. If the table is used to perform entropy coding, the compression rate is higher than that of entropy coding (for example, Huffman coding) using a table that has a fixed numerical value assignment, although it depends on the type of data. Further improvement can be achieved.

  Further, the first data compression unit is configured to perform encoding that expresses the continuous number with different bit numbers according to the continuous number of the same compression target numerical value, for example, the continuous number of the same compression target numerical value is predetermined When the number of consecutive numbers is less than the number, the number of consecutive numbers is expressed by one unit bit number, and when the number of consecutive numbers exceeds a predetermined number, the number of consecutive numbers of the same compression target numerical value is encoded. When the number is a large number, compression is performed at a high compression rate, and the compression rate is further improved.

  Further, when the third data compression unit is provided, if the same numerical value continues, the difference becomes a numerical value zero, the appearance probability of the numerical value zero increases, and the combination with the first and second data compression units The compression rate can be further improved.

  Here, when the numerical difference is obtained, for example, when the numerical value is expressed by 1 byte (8 bits), the difference is expressed by 9 bits including the sign. As shown in the embodiment described later, by storing the first numerical value as it is, by omitting 1 bit of the MSB as a numerical value representing the difference and storing the lower 8 bits (1 byte), The numerical value can be restored.

  Therefore, the third data compression unit outputs the first numerical value for each delimiter when the series of numerical values constituting the compressed data are sequentially delimited, and the adjacent numerical values other than the first numerical value. By adopting a configuration that outputs a numerical value represented by the number of lower unit bits among the differences, it is possible to prevent one difference from increasing by one bit due to the difference, which helps to further improve the compression rate.

  Hereinafter, embodiments of the present invention will be described.

  The embodiment described below is a data compression apparatus incorporated in the host controller 100 in the entire system shown in FIG. 1, and more specifically, CT bitmap data 12A in the host controller shown in FIG. Further, the present invention relates to a process for compressing data of the LW bitmap data 13A. Therefore, here, it is understood that the data compression processing for CT data and LW data described with reference to FIGS. 1 and 2 is replaced with processing as an embodiment of the present invention described below, and is shown in FIG. Duplicate illustrations and duplicate descriptions of the overall system and the processing flow shown in FIG. 2 are omitted.

  FIG. 4 is a block diagram showing an embodiment of the data compression apparatus of the present invention.

  The data compression apparatus 500 shown in FIG. 4 includes a differential encoding unit 510, a run length encoding unit 520, a data scanning unit 530, an image determination unit 540, a table storage unit 550, a code allocation unit 560, A Huffman encoder 570. Although details of the respective units 510 to 570 will be described later, the flow of image data in the data compression apparatus 500 is as follows.

  An input image file (in this embodiment, a file storing CT data 12A or LW data 13A expanded in a bitmap as shown in FIG. 2) is differentially encoded by the data compression apparatus 500 shown in FIG. Input to unit 510 to generate a differential encoding process, that is, to obtain a difference between adjacent numerical values for a series of numerical values constituting the input data, thereby generating image data composed of a series of numerical values representing the difference. Processing is performed. The differential encoding unit 510 corresponds to an example of a third data compression unit referred to in the present invention. More specifically, the differential encoding unit 510 outputs the first numerical value for each segment when the sequence of the numerical values constituting the input data is sequentially segmented, and also outputs other than the first numeric value. Is processed to output a numerical value represented by the number of lower unit bits of the difference between adjacent numerical values.

  The data that has been differentially encoded by the differential encoding unit 510 is input to both the run-length encoding unit 520. In the run-length encoding unit 520, first, the presence of one or a plurality of compression target numerical values and the continuous number of the same compression target numerical values are detected from the input data. Next, the run-length encoding unit 520 receives the detection result and outputs the numerical values excluding the numerical values to be compressed in the data input from the differential encoding unit 510 as it is. An encoding process is performed in which a numerical value to be compressed and a numerical value representing a continuous number of numerical values to be compressed that are the same as the numerical value to be compressed are encoded and output. In the run-length encoding unit 520, in the encoding process, encoding is performed to express the continuous number with a different number of bits according to the continuous number of the same numerical value to be compressed. More specifically, when the number of consecutive compression target numerical values is less than or equal to a predetermined number, the number of consecutive numbers is expressed by one unit bit number, and when the number of consecutive values exceeds the predetermined number, it is expressed by two unit bit numbers. Encoding to represent is performed. In the present embodiment, this run-length encoding unit 520 corresponds to the first data compression unit referred to in the present invention.

  Further, the data encoded by the run-length encoding unit 520 is input to both the data scanning unit 530 and the Huffman encoding unit 570. The data scanning unit 530 scans all of the data after being encoded by the run length encoding unit 520, and obtains the appearance frequency (histogram) of all the numerical values appearing in the data. Here, in this embodiment, the data for obtaining the appearance frequency is the data after the input image file shown in FIG. 4 is encoded as a unit and encoded by the run-length encoding unit 520 for each input image file. Appearance frequency of the numerical value inside is calculated. The data histogram (numerical frequency appearance frequency) obtained by the data scanning unit 530 is input to the image determination unit 540 and the code allocation unit 560.

  The data canning unit 530 and the image determination unit 540 correspond to examples of the histogram calculation unit and the type determination unit, respectively, according to the present invention, and the image determination unit 540 is based on the histogram obtained by the data canning unit 530 this time. An image type determination is performed as to whether the input image data is CT data representing a continuous tone image or LW data representing a linework image.

  The table storage 550 stores a Huffman table 550a for CT data and a Huffman table 550b for LW data. From the table storage 550, the image determination unit 540 determines that the current image data is CT data. When this is done, the Huffman table 550a for CT data is read out and input to the code assignment unit 560. When the image type determination unit 540 determines that the current image data is LW data, the Huffman for LW data The table 550b is read and input to the code allocation unit 560.

  Based on the histogram obtained by the data scanning unit 530, the code assigning unit 560 assigns a code having a shorter code length to a Huffman table corresponding to the image type read from the table storage unit 550 with a higher appearance frequency. . The Huffman table in which a code is assigned to a numerical value by the code assigning unit 560 is passed to the Huffman coding unit 570, and the Huffman coding unit 570 is input to the Huffman coding unit 570 according to the passed Huffman table. An encoding process is performed in which the numerical values constituting the received data are replaced with a code according to the Huffman table, that is, a numerical value with a higher appearance frequency is replaced with a code represented by a shorter bit length.

  This Huffman coding is a kind of entropy coding. In this embodiment, the data scanning unit 530, the image determination unit 540, the table storage unit 550, the code allocation unit 560, and the Huffman coding unit 570 are combined. This corresponds to the second data compression unit referred to in the present invention.

  The data after the Huffman coding by the Huffman coding unit 570 is a compression including an assignment table assigned by the code assigning unit 560 to the values of the input data to the Huffman coding unit 570 and the values after Huffman coding. The information is attached and transferred to the interface device 200 via the general-purpose interface 150 such as SCSI shown in FIG. In the interface device 200, the received lossless compressed data is subjected to data decompression processing. In this data decompression processing, first, decoding processing for the encoding processing performed by the Huffman encoding unit 570 in FIG. 4 is performed. 4 is then performed, and the decoding process for the encoding process performed by the run-length encoding unit 520 in FIG. 4 is performed. Further, the decoding process for the encoding process performed by the differential encoding unit 510 in FIG. As a result, the same image data as the image data in the original input image file is restored.

  FIG. 5 is a hardware configuration diagram of the host controller shown in FIG.

  The host controller 100 shown in FIG. 1 is configured by a computer system having the configuration shown in FIG.

  5 includes a CPU 111, a RAM 112, a communication interface 113, a hard disk controller 114, an FD drive 115, a CDROM drive 116, a mouse controller 117, a keyboard controller 118, a display controller 119, And a communication board 120 are connected to each other via a bus 110.

  The hard disk controller 114 controls access to the hard disk 104 built in the host controller 100, and the FD drive 115 and the CDROM drive 116 are flexible disks (FD) loaded in the host controller 100 so as to be removable. Controls access to the 130 CD ROM 140. The mouse controller 117 and the keyboard controller 118 play a role of detecting operations of the mouse 107 and keyboard 108 provided in the host controller 100 and transmitting them to the CPU 111. Further, the display controller 119 plays a role of displaying an image on the display screen of the image display 109 provided in the host controller 100 based on the instruction of the CPU 111.

  The communication board 120 is responsible for communication conforming to a general-purpose interface protocol such as SCSI, and is responsible for transferring the compressed image data to the interface device 200 (see FIG. 1) via the interface cable 150.

  Furthermore, the communication interface 113 is responsible for general-purpose communication such as the Internet, and the host controller 100 can also capture image data via the communication interface 113.

  A program stored in the hard disk 104 is read into the RAM 112 and expanded for execution by the CPU 111, and the program expanded in the RAM 112 is read out and executed by the CPU 111.

  FIG. 6 is a schematic configuration diagram of the data compression processing program of the present invention.

  Here, the data compression program 600 is stored in the CDROM 140.

  The data compression program includes a differential encoding unit 610, a run length encoding unit 620, a data scanning unit 630, an image determination unit 640, a table storage unit 650, a code allocation unit 660, and a Huffman encoding unit 670. It consists of and. In addition to the data compression program 600 shown here, the CDROM 140 stores various programs for executing the series of processing shown in FIG. 2 in the host controller 100 shown in FIG. Therefore, illustration and description are omitted.

  The CDROM 140 shown in FIG. 6 is loaded into the host controller 100 shown in FIG. 5 and accessed by the CDROM drive 116, and the program stored in the CDROM 140 is uploaded to the host controller 100 and stored in the hard disk 104. When the program stored in the hard disk 104 is read out from the hard disk 104, loaded into the RAM 112, and executed by the CPU 111, the host controller 100 includes the data shown in FIG. It operates as a device that executes various processes as a controller.

  Here, the data compression program 600 shown in FIG. 6 is installed in the host controller 100 and executed by the CPU 111, thereby realizing the data compression apparatus 500 shown in FIG. The encoding unit 610, the run length encoding unit 620, the data scanning unit 630, the image determination unit 640, the table storage unit 650, the code allocation unit 660, and the Huffman encoding unit 670 are executed by the CPU 111 so that the host controller 100, respectively, which constitute the data compression apparatus 500 shown in FIG. 4, are a differential encoding unit 510, a run length encoding unit 520, a data scanning unit 530, an image determination unit 540, a table storage unit 550, a code allocation unit 560, and Operates as Huffman encoder 570 It is a program component to. The operations of the units 610 to 670 constituting the data compression program 600 of FIG. 6 when executed by the CPU 111 are the operations themselves of the units 510 to 570 constituting the data compression apparatus 500 of FIG. Therefore, the description up to now and the detailed description described below regarding the respective units 510 to 570 of the data compression apparatus 500 of FIG. 4 also serve as the description of the respective units 610 to 670 constituting the data compression program 600 of FIG. And

  FIG. 7 is a diagram illustrating the data structure of image data in the input image file input to the data compression apparatus 500 of FIG. 4 and the concept of differential encoding.

As shown in FIG. 7, the image data input to the data compression apparatus 500 shown in FIG. 4 has M pixels arranged in a predetermined main scanning direction. For the Nth line when taught in the sub-scanning direction perpendicular to the main scanning direction, the pixel values of the pixels arranged in the main scanning direction are as follows:
Dn _{, 1} , Dn _{, 2} ,..., Dn _{, m-2} , Dn _{, m-1} , Dn _{, m}
It is expressed.

Similarly, for the (N + 1) th line in the sub-scanning direction, the pixel values of the pixels arranged in the main scanning direction are as follows:
Dn _{+ 1,1} , Dn _{+ 1,2} ,..., Dn _{+ 1, m-2} , Dn _{+ 1, m-1} , Dn _{+ 1, m}
It is expressed.

Here, in the differential encoding unit 510 constituting the data compression apparatus 500 shown in FIG. 4, the above-described image data is input, and a difference between pixels adjacent in the sub-scanning direction is obtained. That is, if the difference between the Nth line and the (N + 1) th line and the jth pixel lined up in the main scanning direction is Sn _{, j} , the difference _{Sn, j} is
S _{n, j} = D _{n + 1, j} −D _{n, j} (j = _{1 to m} )
It is expressed.

  This difference calculation will be specifically described.

  FIG. 8 is a diagram illustrating a differential encoding process in the differential encoding unit 510 constituting the data compression apparatus 500 of FIG.

Here, the pixel values in one vertical line arranged in the sub-scanning direction shown in FIG. 7 are “image data” in FIG.
As shown in the column
"12 01 02 FF 64 ... 40 40 3F ..."
Suppose that Here, each pixel value is represented by two hexadecimal digits (1 byte = 8 bits). Here, “line” indicates pixels arranged in the main scanning direction.

  First, the pixel value “12” on the first line is output as it is.

  Next, the pixel value “12” of the first line is subtracted from the pixel value “01” of the second line, and the result is output. Here, the result of subtracting “12” from “01” is a negative number and is expressed as “1EF” by 9 bits, but “1” that is 1 bit of the MSB is omitted and “8” is the lower 8 bits. Only “EF” is output.

  Next, the pixel value “01” of the second line is subtracted from the pixel value “02” of the third line, and the resultant value “01” is output.

  Next, the pixel value “02” of the third line is subtracted from the pixel value “FF” of the fourth line, and the resultant value “FD” is output.

  Next, the pixel value “FF” of the fourth line is subtracted from the pixel value “64” of the fifth line, and “1” that is 1 bit of the MSB is omitted from the resulting value, and the lower 8 bits. “65” is output.

  Hereinafter, by repeating the same operation, it is represented in the column of “differential encoding (lower 8 bits)” in FIG.

"(12) EF 01 FD 65 ... L0 00 FF ..."
Is output.

  In decoding the differentially encoded data, the interface device 200 shown in FIG. 1 performs the operation shown on the right side of FIG.

  First, the pixel value of the first line remains “12”.

  The pixel value of the second line is “01” represented by the lower 8 bits of the result of adding the pixel value “12” of the first line to the difference value “EF”.

  The pixel value of the third line is “02” obtained by adding the pixel value “01” of the second line obtained above to the difference value “01”.

  The pixel value of the fourth line is “FF” obtained by adding the pixel value “02” of the third line obtained above to the difference value “FD”.

  The pixel value of the fifth line is “64” represented by the lower 8 bits of the result obtained by adding the pixel value “FF” of the fourth line obtained above to the difference value “65”.

  Thereafter, the same calculation is repeated, whereby the same data as the data before differential encoding is decoded.

  Here, the calculation illustrated in FIG. 8 is performed with the pixel value of each pixel arranged in the first line in the main scanning direction as the first numerical value in the calculation. In other words, in the example shown here, one column in the sub-scanning direction is treated as “each delimiter when the sequence of numerical values constituting the input data is sequentially delimited” according to the present invention. The pixel value is handled as “the first numerical value for each segment”.

  Here, one column in the sub-scanning direction is defined as one segment, but the unit of segmentation is arbitrary. For example, one column in the sub-scanning direction may be segmented into a plurality of columns, and a plurality of columns in the sub-scanning direction are grouped together. It is good also as one division.

  FIG. 9 is a diagram for explaining the operation by differential encoding.

  FIG. 9A shows the concept of an image. Here, the vertical direction in the figure is the main scanning direction, the horizontal direction is the sub scanning direction, and each of the arrows A drawn in the sub scanning direction (horizontal direction) is shown in FIG. Focus is on the pixel value of the pixel. Here, the LW image is described as the compression target, but the same applies to the case where the CT image is the compression target.

  On this image, a straight line L1 having a density of pixel value “63” extending in the main scanning direction and a straight line L2 having a density of pixel value “FF” are drawn. There is a CT image area to be fitted. A region to which a CT image is fitted is represented by a pixel value “00”.

  As shown in FIG. 9B, the pixel values of the pixels arranged on the arrow A in FIG. 9A are, in order from the left, first “01”, followed by “63” on the straight line L1, and again “01 ”Continues to“ FF ”on the straight line L2, returns to“ 01 ”again,“ 00 ”continues in the area where the CT image is fitted, and“ 01 ”continues again when the CT image area ends. Here, the pixel value “01” represents an area in which nothing is drawn (paper area).

  When the difference calculation is performed on the original data shown in FIG. 9B, the difference data shown in FIG. 9C is obtained, and the appearance probability of “00” is greatly increased. In the differential encoding unit 510 of FIG. 4 described with reference to FIG. 8, 1 bit (code bit) of the MSB is omitted, so that the data output from the differential encoding unit 510 is as shown in FIG. become that way. Even in this case, as described with reference to FIG. 8, the original data is sequentially restored by transmitting the first pixel value (the pixel value “12” of the first line in the case of FIG. 8) as it is. be able to.

  The data after the above-described differential encoding process is performed by the differential encoding unit 510 shown in FIG. 4 is input to the run-length encoding unit 520 this time.

  Run-length encoding unit 520 performs an encoding process only on specific numerical values among a plurality of numerical values constituting the data received from differential encoding unit 510. In the run-length encoding unit 520, the specific numerical value detection unit 520 performs a run-length encoding process from the data received from the differential encoding unit 510 (here, this numerical value is referred to as a “compression target numerical value”). Then, the continuous number of the numerical values to be compressed is detected.

  In the present embodiment, the run-length encoding unit 520 in FIG. 4 uses, for example, three numerical values “01”, “FF”, and “00” as compression target numerical values.

  Since it is considered that the background of the LW image has a lot of “01” representing the color of the background of the paper, “01” is one of the numerical values to be compressed here.

  “FF” is a value representing the maximum density. The character portion of the LW image does not always have a pixel value of “FF”, but “FF” appears relatively frequently, so “FF” is also one of the numerical values to be compressed here.

  Further, “00” in the LW image is a value for instructing to select CT data instead of LW data in the synthesis / tag addition processing in the interface device internal processing shown in FIG. In the case where the LW image and the CT image are mixed in one image finally printed by the printer 300, “00” in the LW data is also a pixel value having a high appearance frequency. For this reason, here, “00” is also one of the numerical values to be compressed.

  Here, as described above, the three numerical values “01”, “FF”, and “00” are the compression target numerical values, but “FD” and “02” may also be specified as the compression target numerical values for the following reason. .

In the embodiment shown in FIG. 4, a differential encoding unit 510 is placed before the run length encoding unit 520 in FIG. 4. Therefore, when the difference between the above three frequently occurring numerical values “00”, “FF”, “01” is obtained, the sign bit is excluded,
FF-00 = FF
00-FF = 01
01-00 = 01
01-01 = FF
FF-01 = FE
02-FF = 0
Of these six difference values, “FF” and “01” have already been cited as compression target values for the above reasons, and the remaining “FE” and “02” are used as compression target values. In addition, five values “01”, “FF”, “00”, “FE”, and “02” may be set as the compression target numerical values.

  However, here, the description will be continued on the assumption that three of “01”, “FF”, and “00” are designated as compression target numerical values.

  FIG. 10 is an explanatory diagram of encoding in the run-length encoding unit 520 shown in FIG. The upper line in FIG. 10 is the data received from the differential encoding unit 510, and the lower line is the data after the encoding process is performed by the run length encoding unit 520.

Here, as shown in the upper line of FIG. 10, from the differential encoding unit 510,
"06 02 02 02 01 01 01 01 01 04 05 00 ..."
It is assumed that the following data is input. At this time, in the run-length encoding unit 520, the leading “06” is not the compression target value, and the subsequent “02 02 02” is not the compression target value, and next, the compression target value “01” is set. It is detected that there are four consecutive, and next, 32767 consecutive compression target numerical values “00” with “04” and “05” which are not compression target numerical values in between.

  FIG. 11 is a diagram illustrating an encoding algorithm for a numerical value to be compressed in the run-length encoding unit.

  In FIG. 11, Z is the continuous number of the same numerical values to be compressed, for example, Z = 4 for “01” in the upper line of FIG. 10, and Z = 32767 for “00”.

  In FIG. 11, “YY” represents the compression target numerical value itself represented by two hexadecimal digits. “0” or “1” following “YY” is “0” or “1” expressed by 1 bit, and “XX...” That follows “XY” represents one bit. This “XX...” Represents the value of Z.

  That is, FIG. 11 shows that when the compression target numerical value “YY” continues for Z <128, the compression target numerical value “YY” is expressed by the first byte, the first bit is “0”, and the subsequent byte is the subsequent one. Express the value of Z with 7 bits, and when the compression target numerical value “YY” continues Z ≧ 128, express the compression target numerical value “YY” with the first byte, followed by 2 bytes (16 bits) The first 1 bit of “1” is expressed as “1” to express that it is expressed over 2 bytes, and the subsequent 15 bits indicate that the value of Z is expressed.

  An example of the encoding shown in FIG. 10 will be described in accordance with the rules shown in FIG.

  Since the first numerical value “06” constituting the data (upper line) input from the differential encoding unit 510 in FIG. 4 is not a compression target numerical value, it is output as “06”. In addition, “02 02 02” that follows, “02” is not a numerical value to be compressed, and these three “02” are output as they are. Next, since “01”, which is a numerical value to be compressed, continues, it is encoded into “01 04”. Since the next “04” and “05” are not compression target numerical values, “04 05” is output as it is.

  Next, since there are 32767 consecutive “00s”, “00” is placed, the first 1 bit of the next 1 byte is set to “1”, and then 32767-128 is expressed by 15 bits. It represents that 32767 “00” s are consecutive in 3 bytes of “00 FF 7F”. That is, the consecutive number 128 is expressed as “00 00” except for the first bit “1”.

FIG. 12 is a diagram illustrating an example of an encoding process according to the number of consecutive steps in the run-length encoding unit 520 in FIG.
When “00” is 127 consecutive, it is encoded to “00 7E” using 2 bytes,
When “00” is 32767 consecutive, it is encoded into “00 FF 7E” using 3 bytes,
When “00” is 32895 consecutive, it is encoded into “00 FF FF” using 3 bytes,
When “00” is 128 consecutive, it is encoded to “00 80 00” using 3 bytes,
-When 4096 "FFs" are contiguous, they are encoded into "FF 8F 80" using 3 bytes.

  In the run length encoding unit 520 shown in FIG. 4, the encoding process as described above is performed.

  In this case, since the numerical values other than the compression target numerical values are output as they are, the situation of becoming redundant rather than the PackBits encoding described with reference to FIG. 3 is avoided. 3, the maximum compression rate is 1/64, but according to the run-length encoding unit 520 according to the present embodiment, the maximum compression rate is 3/32895 = 1/10. It improves to 965.

  The data after the above-described encoding processing is performed by the run-length encoding unit 520 in FIG. 4 is input to the data scanning unit 530 and the Huffman encoding unit 570 in FIG.

  In the data scanning unit 530, the appearance frequency (histogram) of the pixel value is obtained for the pixels constituting the entire LW image, and the histogram is transmitted to the image determination unit 540 and the code allocation unit 560.

  FIG. 13 is a diagram illustrating an example of a histogram obtained by the data scanning unit 530 of FIG. FIGS. 13A and 13B are histograms of LW data and CT data, respectively.

  In the case of LW data, even after the run length encoding unit 520 in FIG. 4 performs encoding, the frequency of some specific numerical values is high as shown in FIG. On the other hand, in the case of CT data, there are peaks in the vicinity of the value 0 and the value 256 (maximum value), but all numerical values are distributed evenly at a low frequency except for both ends.

  In the image determination unit in FIG. 4, using the above difference between the LW data and the CT data, for example, the sum of the frequencies of the values 0 to 9 and the values 247 to 256 accounts for 70% or more of the total number of pixels of the image. The case of occupancy is determined as CT data, and the case of less than 70% is determined as LW data.

  Here, the appearance frequency of “A1” is the strongest, and it is assumed that “A2”, “A3”, “A4”,. These “A1”, “A2” and the like do not directly represent numerical values, but are symbols representing numerical values. That is, “A1” is, for example, a numerical value “00”, “A2” is a numerical value “FF”, and the like. Here, for simplicity, the data sent from the run-length encoding unit 520 in FIG. 4 is expressed by any one of the 16 numerical values “A1” to “A16” for all pixels. Shall be.

  FIG. 14 is a diagram illustrating an allocation process in the code allocation unit 560 illustrated in FIG.

  Here, the code string “00 01 100 101 11000 11001...” Is a code string arranged on the Huffman table read from the table storage unit 550 based on the image type determination result in the image determination unit 540 of FIG. .

  Here, “A1” having the highest appearance frequency is assigned to the code “00” represented by 2 bits, and the next “A2” is assigned to the code “01” also represented by 2 bits. The next “A3” and the next “A4” are represented by 3 bits, respectively, assigned to “100” and “101”, and the next “A5” to “A8” are represented by 5 bits. Assigned to each numerical value, and similarly, a numerical value with a lower appearance frequency is assigned to a numerical value represented by a larger number of bits.

  In the Huffman encoding unit 570 of FIG. 4, each numerical value in the data input from the run-length encoding unit 520 is obtained by referring to the Huffman table to which the code assigning unit 560 has assigned a numerical value as described above. Converted to each code.

  15 and 16 are diagrams illustrating examples of the Huffman table. FIG. 15 shows an example of a Huffman table for encoding LW data, and FIG. 16 shows an example of a Huffman table for encoding CT data. Here, the numerical value on the right side of “,” in each code string means the bit length, and the binary code corresponding to the bit length from the left to the right of “,” is the actual code. Represents. For example, in the case of the Huffman table for encoding LW data in FIG. 15, the code of # 1 at the upper right is 2 bits of “00”, the code of the next # 2 is 3 bits of “010”, and the next # 3 The code is 3 bits of “111”, and the next code of # 4 is 8 bits of “11000000”.

  When the currently compressed data is LW data, the table storage unit 550 in FIG. 4 reads the Huffman table 550a for LW data encoding shown in FIG. 15 and inputs it to the code allocation unit 560. On the other hand, when the data currently compressed is CT data, the Huffman table 550b for CT data encoding shown in FIG. 16 is read and input to the code allocation unit 560. The code allocation unit 560 For the Huffman table corresponding to the type of image input as described above, based on the histogram obtained by the data scanning unit 530, as described with reference to FIG. A numerical value having a high frequency of appearance is assigned to the young code.

  FIG. 17 is a diagram illustrating an example of a data format of image data output from the data compression apparatus 500 illustrated in FIG.

  First, a code representing SOI (Start Of Image) indicating the beginning of the image data file is arranged, followed by a header in which information such as the size of the image is recorded, and then the data compression apparatus of FIG. In 500, compression information related to data compression processing performed on the image data in the current input image file is arranged. The compression information includes information indicating the distinction between CT data and LW data, the Huffman table used in the Huffman encoding unit 570 (see FIGS. 15 and 16), and each code and its code in the Huffman table. 1 includes all information necessary for decoding by the interface device 200 in FIG. 1, such as correspondence with the assigned numerical values.

  As shown in FIG. 16, the compressed image is followed by the actual image data after Huffman coding, and is finally concluded with a code of EOI (End Of Image).

  From the data compression apparatus 500 shown in FIG. 4, the image data file whose format is arranged as shown in FIG. 16 is transferred to the interface device 200 shown in FIG. 1, and the interface device 200 performs the encoding described above. The data is decompressed by decoding in the reverse order, and restored to the same image data as the image data in the input image file before being input to the data compression apparatus 500 shown in FIG.

The data compression apparatus 500 of FIG. 4 includes a code allocation unit 560. In the code allocation unit 560, the appearance frequency is displayed in the Huffman tables 550a and 550b corresponding to the image type read from the table storage unit 550. However, instead of providing the code allocating unit 560, each numerical value in the Huffman tables 550a and 550b may be fixedly allocated in advance. When the frequency of appearance of pixel values in image data does not differ greatly from one image to another, it is possible to perform higher speed processing by assigning a fixed numerical value. Alternatively, for example, the code allocating unit 560 associates a code with a numerical value for the LW data encoding Huffman table 550a, and the CT data encoding Huffman table 550b allocates a numerical value to the code in advance. In addition, the data compression apparatus 500 shown in FIG. 4 includes the differential encoding unit 510. When the differential encoding unit 510 is included, the appearance frequency of the numerical value “00” increases as described above. However, in the present invention, it is not always necessary to provide the differential encoding unit 510, and the run-length encoding unit 520 shown in FIG. 4 is directly performed without performing the differential encoding process on the input data. May be entered. Alternatively, instead of the differential encoding unit 510 that performs the above-described differential encoding, an encoding unit that performs other data compression processing may be arranged there.

1 is a diagram illustrating an example of a print system to which a data compression technique is applied. FIG. 6 is a diagram illustrating a flow of data processing in the print system. It is explanatory drawing of a PackBits encoding system. It is a block block diagram which shows one Embodiment of the data compression apparatus of this invention. It is a hardware block diagram of the host controller shown in FIG. It is a schematic block diagram of the data compression processing program of this invention. FIG. 5 is a diagram illustrating a data structure of image data in an input image file input to the data compression apparatus in FIG. 4 and a concept of differential encoding. It is a figure which illustrates and illustrates the differential encoding process in the differential encoding part which comprises the data compression apparatus of FIG. It is operation | movement explanatory drawing by difference encoding. It is explanatory drawing of the encoding in the run length encoding part shown in FIG. It is a figure which shows the algorithm of the encoding for the numerical value for compression in a run length encoding part. FIG. 5 is a diagram illustrating an example of an encoding process according to a continuous number in the run length encoding unit of FIG. 4. It is a figure which shows the example of the histogram calculated | required by the data scanning part of FIG. It is the figure which illustrated the allocation process in the code allocation part shown in FIG. It is a figure which shows an example of a Huffman table. It is a figure which shows the other example of a Huffman table. FIG. 5 is a diagram illustrating an example of a data format of image data output from the data compression apparatus illustrated in FIG. 4.

Explanation of symbols

11 data 12A, 12B, 13A, 13B, bitmap data 14 compressed data 15 LW lossless compressed data 100 host controller 140 CDROM
DESCRIPTION OF SYMBOLS 150 General-purpose interface 200 Interface apparatus 250 Dedicated interface 300 Printer 500 Data compression apparatus 510 Differential encoding part 520 Run length encoding part 530 Data scanning part 540 Image determination part 550 Table memory | storage part 560 Code allocation part 570 Huffman encoding part 600 Data compression Program 610 Differential encoding unit 620 Run length encoding unit 630 Data scanning unit 640 Image determination unit 650 Table storage unit 660 Code allocation unit 670 Huffman encoding unit

Claims (20)

In a data compression apparatus that performs data compression processing on data to be compressed consisting of a series of numerical values represented by a predetermined number of unit bits,
Among the data to be compressed, numerical values other than one or a plurality of predetermined numerical values to be compressed are output as they are, and for the numerical values to be compressed, the numerical values to be compressed and the continuous number of the numerical values to be compressed that are the same as the numerical values to be compressed A first data compression unit that encodes and outputs a numerical value representing
A second data compression unit that performs entropy coding on the data that has been encoded by the first data compression unit using a table that associates codes and numerical values according to the type of data to be compressed. A data compression apparatus characterized by that.   2. The data compression apparatus according to claim 1, wherein the second data compression unit performs Huffman coding using a Huffman table corresponding to a type of data to be compressed.   The second data compression unit includes a type determination unit that determines a type of data to be compressed based on data encoded by the first data compression unit. Data compression device.   The second data compression unit includes a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and the type determination unit is the histogram calculation unit. 4. A data compression apparatus according to claim 3, wherein the type of data to be compressed is determined based on the obtained histogram.   The compressed data is data representing one of a continuous tone image and a line work image, and the type determining unit is the compressed data representing the continuous tone image or the compressed data representing the line work image. 2. The data compression apparatus according to claim 1, wherein the data compression apparatus determines whether or not.   The second data compression unit is based on a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and a histogram obtained by the histogram calculation unit, A table according to the type of data to be compressed, and a code allocating unit that assigns a code having a shorter code length to a numerical value with a higher appearance frequency, and uses the table in which a code is allocated to the numerical value by the code allocating unit. 2. The data compression apparatus according to claim 1, wherein the data compression apparatus performs encoding.   2. The data compression apparatus according to claim 1, wherein the first data compression unit performs encoding to express the continuous number with a different number of bits according to the continuous number of the same numerical value to be compressed. .   The first data compression unit expresses the continuous number by one unit bit number when the number of consecutive identical numerical values to be compressed is equal to or smaller than a predetermined number, and two unit bits when the continuous number exceeds the predetermined number 8. The data compression apparatus according to claim 7, wherein encoding is performed by a number.   The first stage of the first data compression unit generates new compressed data consisting of a series of numerical values representing the difference by obtaining a difference between adjacent numerical values for a series of numerical values constituting the compressed data, and The data compression apparatus according to claim 1, further comprising a third data compression unit that passes to the first data compression unit.   The third data compression unit outputs the first numerical value for each delimiter when the sequence of the numerical values constituting the compressed data is sequentially delimited, and other than the first numerical value, 10. The data compression apparatus according to claim 9, wherein a numerical value represented by a lower unit bit number of the difference is output. A data compression program that is executed in an information processing apparatus that executes a program, and causes the information processing apparatus to operate as a data compression apparatus that performs data compression processing on data to be compressed consisting of a series of numerical values represented by a predetermined number of unit bits. There,
The information processing apparatus;
Among the data to be compressed, numerical values other than one or a plurality of predetermined numerical values to be compressed are output as they are, and for the numerical values to be compressed, the numerical values to be compressed and the continuous number of the numerical values to be compressed that are the same as the numerical values to be compressed A first data compression unit that encodes and outputs a numerical value representing
A second data compression unit that performs entropy coding on the data that has been encoded by the first data compression unit using a table that associates codes and numerical values according to the type of data to be compressed. A data compression program which is operated as a data compression apparatus.   12. The data compression program according to claim 11, wherein the second data compression unit performs Huffman coding using a Huffman table corresponding to a type of data to be compressed.   The said 2nd data compression part is provided with the classification determination part which determines the classification of to-be-compressed data based on the data after encoding by the said 1st data compression part. Data compression program.   The second data compression unit includes a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and the type determination unit is the histogram calculation unit. 14. The data compression program according to claim 13, wherein the data compression program is operated as a data compression apparatus that determines the type of data to be compressed based on the obtained histogram.   The compressed data is data representing one of a continuous tone image and a line work image, and the type determining unit is the compressed data representing the continuous tone image or the compressed data representing the line work image. 14. The data compression program according to claim 13, wherein the data compression program is for determining whether or not.   The second data compression unit is based on a histogram calculation unit that obtains a histogram of numerical values that appear in the data encoded by the first data compression unit, and a histogram obtained by the histogram calculation unit, The table according to the type of data to be compressed has a code assigning unit that assigns a code with a shorter code length to a numerical value with a higher appearance frequency, and uses the table in which a code is assigned to the numerical value by the code assigning unit. 14. The data compression program according to claim 13, wherein the data compression program is operated as a data compression device that performs processing.   12. The data compression program according to claim 11, wherein the first data compression unit performs encoding to express the continuous number with a different number of bits according to the continuous number of the same numerical value to be compressed. .   The first data compression unit expresses the continuous number by one unit bit number when the number of consecutive identical numerical values to be compressed is equal to or less than a predetermined number, and two unit bits when the continuous number exceeds the predetermined number 18. The data compression program according to claim 17, wherein the data compression program performs encoding expressed by a number.   The first stage of the first data compression unit generates new compressed data consisting of a series of numerical values representing the difference by obtaining a difference between adjacent numerical values for a series of numerical values constituting the compressed data, and 12. The data compression program according to claim 11, wherein the data compression program is operated as a data compression apparatus including a third data compression unit to be passed to the first data compression unit.   The third data compression unit outputs the first numerical value for each delimiter when the sequence of the numerical values constituting the compressed data is sequentially delimited, and the other numerical values other than the first numerical value are adjacent to each other. 20. The data compression program according to claim 19, wherein the data compression program outputs a numerical value represented by a lower unit bit number of the difference.

Images