JP2006352548A - Data compression apparatus and data compression program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data compression apparatus for carrying out novel and preferable compression processing capable of compressing CT data and LW data without distinguishing them. <P>SOLUTION: The data compression apparatus includes: a first lossless compression processing section for applying first lossless compression processing suitable for compression to be applied to one of the CT data and the WL data to data to be compressed; a second reversible compression processing section for applying second lossless compression processing suitable for compression to be applied to the other of the CT data and the WL data to the data to be compressed when the result of data compression by the first lossless compression processing section dose not reach a prescribed target compression rate; and an lossy compression processing section that applies lossy compression processing to the data to be compressed when the result of data compression by the second lossless compression processing section dose not reach the target compression rate. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 a 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 the state before the data compression processing is performed by the host controller 100. 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, the CT data (bitmap data 12B) after data expansion and the 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 performs data compression, 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.
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

  However, in a compression method such as JPEG, it takes time to perform compression processing by software, which causes a reduction in processing capacity of the entire compression processing system.

  In addition, JPEG and the like are irreversible compression processes, and therefore there is a inevitably deterioration in image quality. However, in recent years, there has been an increasing demand for higher image quality, and CT data will not deteriorate. It has been studied to perform lossless compression.

  In view of the above circumstances, an object of the present invention is to provide a data compression apparatus and a data compression program that perform a new preferable compression process that can compress CT data and LW data without distinguishing them.

The data compression apparatus of the present invention that achieves the above object provides:
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,
A first lossless compression processor that performs a first lossless compression process on the data to be compressed;
A second lossless compression processing unit that applies a second lossless compression process to the data to be compressed when a result of data compression by the first lossless compression processing unit does not reach a predetermined target compression rate;
An irreversible compression processing unit that performs irreversible compression processing on the data to be compressed when a result of data compression by the second lossless compression processing unit does not reach the target compression rate;
One of the first lossless compression processor and the second lossless compression processor is
A difference generating unit for generating new compressed data composed 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;
An offset unit for offsetting each numerical value constituting new compressed data generated by the difference generation unit by a predetermined value;
By dividing each numerical value of the compressed data whose numerical value is offset by the offset part into an upper bit part and a lower bit part at a predetermined divided bit number smaller than the unit bit number, the compressed data is A dividing unit that divides the upper data consisting of a continuation of the upper bit part in each numerical value and the lower data consisting of a continuation of the lower bit part of each numerical value;
An upper data compression unit that performs lossless compression processing on the upper data divided by the dividing unit;
A lower data compression unit that performs a lossless compression process on the lower data divided by the dividing unit,
The other of the first lossless compression processing unit and the second lossless compression processing unit with respect to the one is
In the large 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 values, the compression target numerical value and the same compression target numerical value as the compression target numerical value are output. A lossless compression process including an encoding process for encoding and outputting a numerical value representing the continuous number of
The lossy compression processing unit is
By periodically decimating a numerical value from a series of numerical values constituting the compressed data, a first compressed data consisting of a series of numerical values extracted from the compressed data by the thinning and a continuation of the remaining numerical values. A decimation processing unit for creating one compressed data;
A lossless compression unit that performs a lossless compression process on the first compressed data created by the thinning processing unit;
And an irreversible compression unit that performs irreversible compression processing on the second compressed data generated by the thinning processing unit.

  Here, “adjacent” in the above “by calculating the difference between adjacent numerical values for a series of numerical values constituting the compressed data” may be adjacent on the data stream, but is not necessarily limited thereto. It is not something. For example, if two-dimensional image data is handled as one-dimensional stream data, the two-dimensional images may be adjacent to each other when viewed on the two-dimensional image. Further, “difference between adjacent numerical values” means not only a one-dimensional difference but also a multi-dimensional difference of two or more dimensions. The same applies to the following.

This data compression apparatus of the present invention is
The reversible compression unit of the irreversible compression processing unit performs a reversible compression process equivalent to the reversible compression process in the one of the first reversible compression process unit and the second reversible compression process unit in the first It is preferable to apply it to the data to be compressed.

The data compression apparatus of the present invention
The irreversible compression unit of the irreversible compression processing unit is
Whether or not the numerical value constituting the second compressed data created by the thinning processing unit has a value between the numerical values thinned out before and after the numerical value by thinning out the thinning processing unit. If there is an intervening value, a sign indicating that it is an intervening value is output. If not, the numerical value is re-expressed with a smaller number of bits than the unit bit number. It may be in a form that outputs a numerical value that has been
The compressed data represents a continuous two-dimensional image of the numerical value represented by the number of unit bits,
The lossy compression processing unit includes a determination unit that determines an edge portion in the image,
When the irreversible compression unit of the irreversible compression processing unit is not the edge portion determined by the determination unit with respect to the numerical value constituting the second compressed data created by the thinning processing unit, the unit In a form that outputs a predetermined code having a bit number smaller than the number of bits and outputs a numerical value obtained by re-expressing the numerical value with a smaller number of bits smaller than the unit bit number in the case of an edge portion. There may be.

  Here, the predetermined code includes a 0-bit code (that is, a state in which substantially nothing is output). Decoding for the case where a 0-bit code is used in this way is performed, for example, in the following procedure. That is, based on the decoded TRUE pixel, it is confirmed whether or not it is an edge portion. If it is an edge portion, the FAKE pixel is decoded from the numerical value of the small number of bits. FAKE pixels are generated by interpolation processing using.

A data compression program of the present invention that achieves the above object is as follows.
In a data compression program that is incorporated in an information processing apparatus that executes a program and causes the information processing apparatus to execute data compression processing on data to be compressed consisting of a series of numerical values represented by a predetermined number of unit bits.
On the information processing apparatus,
A first lossless compression processor that performs a first lossless compression process on the data to be compressed;
A second lossless compression processing unit that applies a second lossless compression process to the data to be compressed when a result of data compression by the first lossless compression processing unit does not reach a predetermined target compression rate;
When the result of data compression by the second lossless compression processing unit does not reach the target compression rate, a lossy compression processing unit that performs lossy compression processing on the compressed data is constructed,
One of the first lossless compression processor and the second lossless compression processor is
A difference generating unit for generating new compressed data composed 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;
An offset unit for offsetting each numerical value constituting new compressed data generated by the difference generation unit by a predetermined value;
By dividing each numerical value of the compressed data whose numerical value is offset by the offset part into an upper bit part and a lower bit part at a predetermined divided bit number smaller than the unit bit number, the compressed data is A dividing unit that divides the upper data consisting of a continuation of the upper bit part in each numerical value and the lower data consisting of a continuation of the lower bit part of each numerical value;
An upper data compression unit that performs lossless compression processing on the upper data divided by the dividing unit;
A lower data compression unit that performs a lossless compression process on the lower data divided by the dividing unit,
The other of the first lossless compression processing unit and the second lossless compression processing unit with respect to the one is
In the large 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 values, the compression target numerical value and the same compression target numerical value as the compression target numerical value are output. A lossless compression process including an encoding process for encoding and outputting a numerical value representing the continuous number of
The lossy compression processing unit is
By periodically decimating a numerical value from a series of numerical values constituting the compressed data, a first compressed data consisting of a series of numerical values extracted from the compressed data by the thinning and a continuation of the remaining numerical values. A decimation processing unit for creating one compressed data;
A lossless compression unit that performs a lossless compression process on the first compressed data created by the thinning processing unit;
And an irreversible compression unit that performs irreversible compression processing on the second compressed data generated by the thinning processing unit.

  The data compression program referred to in the present invention is only shown in its basic form here, but this is only for avoiding duplication, and the data compression program referred to in the present invention includes only the above basic form. Instead, various forms corresponding to each form of the data compression apparatus described above are included.

  In addition, the element such as a difference generation unit configured on the computer by the data compression program of the present invention may be one element constructed by one program part, and one element by a plurality of program parts. It may be constructed, or a plurality of elements may be constructed by one program part. In addition, these elements may be constructed so as to execute such actions by themselves, or constructed by giving instructions to other programs and program components incorporated in the computer. May be.

  According to the data compression device or the data compression program of the present invention, each of the first lossless compression processing unit, the second lossless compression processing unit, and the irreversible compression processing unit described above is used so that the target compression rate is obtained. To compress uncompressed data. The compression processing in the first lossless compression processing unit, the second lossless compression processing unit, and the irreversible compression processing unit is a high-speed process including a simple processing procedure. Even if the compression is performed again by another compression process when it does not reach the above, the processing time is shorter than the conventional JPEG method or the like. In the first lossless compression processing unit and the second lossless compression processing unit, on the one hand, lossless compression processing suitable for CT data compression is executed, and on the other hand, lossless compression processing suitable for LW data compression is performed. Executed. Therefore, a large amount of image data is greatly compressed by either the first lossless compression processing unit or the second lossless compression processing unit, and the target compression rate is reached while the image quality of the original image data is completely maintained. It is expected. Then, irreversible compression is executed only when image data of a special type that does not reach the target compression rate in either lossless compression process becomes data to be compressed or when the compression target is particularly high. .

  In addition, the data to be compressed that does not reach the target compression rate by the above two lossless compression processes is considered to be a type close to CT data, and the lossless compression unit of the irreversible compression processing unit uses the CT data. If the above-described lossless compression process suitable for compression is performed, such type of compressed data is efficiently compressed.

  The embodiment described below is an image compression apparatus incorporated in a host controller in the overall system shown in FIG. 1, and more specifically, CT bitmap data 12A and LW in the host controller shown in FIG. The present invention relates to the data compression processing for the bitmap data 13A. Therefore, here, the data compression processing for the CT data and LW data described with reference to FIGS. 1 and 2 is replaced with the data compression processing according to the embodiment of the present invention described below, and the data in the interface device is replaced. It is understood that the decompression (decompression) process replaces the data decompression (decompression) process corresponding to the data compression process as the embodiment of the present invention, and the entire system shown in FIG. 1 and the process flow shown in FIG. 2 are duplicated. The illustration and repeated explanation are omitted.

  FIG. 3 is a block diagram showing an image compression apparatus corresponding to an embodiment of the data compression apparatus of the present invention.

  The image compression apparatus 500 illustrated in FIG. 3 includes a first lossless compression processing unit 501, a second lossless compression processing unit 502, an irreversible compression processing unit 503, and a determination unit 504. Although details of each of the units 501 to 503 will be described later, the flow of image data in the image compression apparatus 500 is as follows.

  The input image file D0 (in this embodiment, a file storing CT data 12A or LW data 13A expanded in a bitmap as shown in FIG. 2) is the first of the data compression apparatus 500 shown in FIG. The data is input to the lossless compression processing unit 501. In the first lossless compression processing unit 501, the first lossless compression processing is performed on the image data in the input image file D0. In the present embodiment, as the first lossless compression process, a lossless compression process suitable for CT data compression is performed, and the compression process is performed with 8 lines of the input image as one unit. The first lossless compression processing unit 501 corresponds to an example of a first lossless compression processing unit according to the present invention.

  The data for 8 lines subjected to the reversible compression processing by the first reversible compression processing unit 501 is input to the determination unit 504. The determination unit 504 is notified in advance of the requested compression rate, and the determination unit 504 determines whether or not the input compressed data is data that has been compressed to a level that satisfies the requested compression rate. . This determination is also performed with the input image 8 lines as a unit. When the compressed data for 8 lines has data that satisfies the required compression ratio, the compression ratio is satisfied at the stage of the lossless compression processing, and no further compression is required, and the data is output as it is as lossless compression data D10. . When the reversible compressed data D10 is output, a header describing the position of the reversible compressed data D10 on the input image, information necessary for subsequent decompression processing, and the like is added and output.

  When the determination unit 504 determines that the compressed data is data that does not satisfy the required compression rate, the determination result is notified to the second lossless compression processing unit 502, and the second lossless compression processing unit 502 A second lossless compression process is performed on the image data in the original input image file D0. In the present embodiment, as the second lossless compression process, a lossless compression process suitable for compression of LW data is performed, and again, the compression process is performed with 8 lines of the input image as one unit.

  The data for 8 lines subjected to the reversible compression processing by the second reversible compression processing unit 502 is also input to the determination unit 504, and whether or not the data is compressed to a level that satisfies the required compression rate. Determined. If there is data in which the compressed data for 8 lines at this time satisfies the required compression rate, the compression rate is satisfied at the stage of the lossless compression process, and no further compression is required, and the lossless compression data D20 is used as it is. Is output. The output of the lossless compressed data D20 is also appended with a header.

  If the determination unit 504 determines that the compressed data that has undergone the second lossless compression process is also data that does not satisfy the required compression rate, the determination result is notified to the lossy compression processing unit 503, and the lossy compression process is performed. In unit 503, lossy compression processing is performed on the image data in the original input image file D0. Again, compression processing is performed with 8 lines of the input image as one unit, and lossy compressed data D30 is output. A necessary header is also attached to the lossy compressed data D30.

  The compressed data D10, D20, D30 obtained as described above in the image compression apparatus 500 shown in FIG. 3 is 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, decoding processing corresponding to the various encoding processing described in FIG. The same or almost the same image data as the image data in the input image file is restored.

  FIG. 4 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.

  4 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. 130, controls access to the CDROM 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.

  Further, 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. 5 is a schematic configuration diagram of an image compression processing program corresponding to an embodiment of the data compression program of the present invention.

  Here, the image compression program 600 is stored in the CD ROM 140.

  The image compression program 600 includes a first lossless compression processing unit 610, a second lossless compression processing unit 620, an irreversible compression processing unit 630, and a determination unit 640. In addition to the image compression program 600 shown here, the CDROM 140 stores various programs for executing a series of processes in the host controller 100 shown in FIG. The description is omitted.

  The CD ROM 140 shown in FIG. 5 is loaded into the host controller 100 shown in FIG. 4 and accessed by the CD ROM drive 116, and the program stored in the CD ROM 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 from the hard disk 104, loaded into the RAM 112 and executed by the CPU 111, the host controller 100 includes a process as the image compression apparatus 500 shown in FIG. It operates as an apparatus that executes various processes.

  Here, the image compression program 600 shown in FIG. 5 is installed in the host controller 100 and executed by the CPU 111, thereby realizing the image compression apparatus 500 shown in FIG. The first reversible compression processing unit 610, the second reversible compression processing unit 620, the irreversible compression processing unit 630, and the determination unit 640 are executed by the CPU 111 so that the host controller 100 can perform image compression shown in FIG. These are program parts that operate as the first lossless compression processing unit 501, the second lossless compression processing unit 502, the irreversible compression processing unit 503, and the determination unit 504, respectively, constituting the device 500. That is, the components of the image compression apparatus 500 are substantially constructed on the host controller 100 by these program parts.

  The operations of the units 610 to 640 constituting the image compression program 600 of FIG. 5 when executed by the CPU 111 are the operations themselves of the units 501 to 504 constituting the image compression apparatus 500 of FIG. Accordingly, the description up to now and the detailed description to be described below regarding the respective units 501 to 504 of the image compression apparatus 500 in FIG. 3 also serve as the description of the respective units 610 to 640 constituting the image compression program 600 in FIG. And

  First, the first lossless compression processing unit 501 will be described.

  FIG. 6 is a block configuration diagram showing the first lossless compression processing unit 501.

  The first lossless compression processing unit 501 includes a differential encoding unit 510, an offset unit 520, a plane division unit 530, an L plane compression unit 540, and an H plane compression unit 550. Details of the processing in each of the units 510 to 550 will be described later. Here, the flow of data in the first lossless compression processing unit 501 will be described.

  The image data in the input image file D0 input to the first lossless compression processing unit 501 is input to the differential encoding unit 510 to perform differential encoding processing, that is, a series of numerical values constituting the input data. By calculating the difference between adjacent numerical values, a process of generating image data consisting of a series of 8-bit numerical values representing the difference is performed. The difference encoding unit 510 corresponds to an example of a difference generation unit referred to in the present invention.

  The image data composed of a series of numerical values representing the difference generated by the differential encoding unit 510 is input to the offset unit 520 and offset by a predetermined value. Thereafter, the plane division unit 530 divides each numerical value of 8 bits in the image data into lower 4 bits and upper 4 bits, so that the image data is converted into a lower subplane D1L composed of a sequence of lower 4 bits. It is divided into an upper subplane D1H consisting of a sequence of upper 4 bits. The offset unit 520 corresponds to an example of an offset unit according to the present invention, and the plane division unit 530 corresponds to an example of a division unit according to the present invention. Further, the lower subplane D1L and the upper subplane D1H correspond to examples of the lower data and the upper data according to the present invention, respectively.

  The lower subplane D1L and the upper subplane D1H divided by the plane division unit 530 are input to the L plane compression unit 540 and the H plane compression unit 550, respectively, and subjected to lossless compression. The L plane compression unit 540 and the H plane compression unit 550 correspond to examples of the lower data compression unit and the upper data compression unit according to the present invention, respectively.

  In the Huffman coding unit 541 of the L plane compression unit 540, in accordance with a fixed Huffman table that associates a numerical value with a code, the numerical value constituting the lower subplane D1L input to the Huffman coding unit 541 is displayed in the Huffman table. An encoding process for replacing with a code according to the above is performed. This Huffman coding is a kind of entropy coding. Note that a mode switching unit 542 is incorporated in the L plane compression unit 540, and the mode switching unit 542 is instructed by the user to switch between the high speed mode and the normal mode, and is performed by the Huffman coding unit 541. Switching between a normal mode that undergoes Huffman coding and a high-speed mode that omits Huffman coding and outputs the lower subplane D1L as it is. The L-plane compression unit 540 outputs lower-order compressed data D2L obtained by compressing the lower-order subplane D1L. In the high-speed mode, the lower-order compressed data D2L is the lower-order subplane D1L itself.

  On the other hand, the H plane compression unit 550 includes a run length encoding unit 551, a data scanning unit 552, and a Huffman encoding unit 553, and the upper subplane D1H is input to the run length encoding unit 551. .

  In the run-length encoding unit 551, 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 of the upper subplane D1H. Next, the run-length encoding unit 551 receives the detection result, and outputs the numerical values excluding the numerical values to be compressed in the data of the upper subplane D1H as they are, and the numerical values to be compressed with the numerical values to be compressed, An encoding process is performed in which the compression target numerical value is encoded and output as a numerical value representing the number of consecutive compression target numerical values. In the run-length encoding unit 551, in the encoding process, encoding is performed in which the continuous number is expressed by 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.

  The data encoded by the run-length encoding unit 551 is then input to both the data scanning unit 552 and the Huffman encoding unit 553. The data scanning unit 552 scans all of the data encoded by the run length encoding unit 551, and obtains the appearance frequency (histogram) of all the numerical values appearing in the data. Here, in the present embodiment, the processing for obtaining the appearance frequency is performed in units of one of the upper subplanes D1H illustrated in FIG. 3, and is encoded by the run length encoding unit 551 of each upper subplane D1H. The frequency of appearance of the numerical value in the data after being processed is obtained. Furthermore, the data scanning unit 552 assigns a code having a shorter code length to a Huffman table based on the obtained data histogram (numerical frequency appearance frequency).

  The Huffman table in which a code is assigned to a numerical value by the data scanning unit 552 is passed to the Huffman coding unit 553, and the Huffman coding unit 553 inputs the Huffman coding unit 553 according to the passed Huffman table. An encoding process is performed in which numerical values constituting the received data are replaced with codes according to the Huffman table, that is, codes represented by shorter bit lengths as numerical values having a higher appearance frequency.

  The data after the Huffman coding by the Huffman coding unit 553 is attached with compression information including an assignment table of numerical values and codes assigned by the data scanning unit 552, and the upper compressed data in which the upper subplane D1H is compressed. It is output from the H plane compression unit 550 as D2H.

  As described above, the set of the low-order compressed data D2L and the high-order compressed data D2H output from each of the L plane compression unit 540 and the H plane compression unit 550 is the lossless compression shown in FIG. 3 in which the original image data is reversibly compressed. Data D10 is configured. Although a detailed description of the header is omitted here, for example, a Huffman table used for Huffman coding is stored in this header.

  Details of the processing in each of the units 510 to 550 of the first lossless compression processing unit 501 will be further described later, and then the second lossless compression processing unit 502 shown in FIG. 3 will be described.

  FIG. 7 is a block configuration diagram showing the second lossless compression processing unit 502.

  The second lossless compression processing unit 502 includes a differential encoding unit 560, a run length encoding unit 570, and a Huffman encoding unit 580. Details of the processing in the respective units 560 to 580 of the second lossless compression processing unit 502 will also be described later together with the details of the processing in the respective units of the first lossless compression processing unit described above. The flow of data in the lossless compression processing unit 502 will be described.

  The image data in the input image file D0 input to the second lossless compression processing unit 502 is input to the differential encoding unit 560, and the same differential code as the differential encoding processing in the differential encoding unit 510 of FIG. Processing is performed. That is, a process of generating image data composed of a series of 8-bit numerical values representing the difference is obtained by obtaining a difference between adjacent numerical values for a series of numerical values constituting the input data.

  The data subjected to the differential encoding process is input to the run-length encoding unit 570, and the encoding process similar to the encoding process in the run-length encoding unit 551 of the H plane compression unit 550 in FIG. Then, the encoded data is input to the Huffman encoder 580 and subjected to an encoding process according to a predetermined Huffman table prepared in advance.

  The second lossless compression processing unit 502 generates and outputs the lossless compressed data D20 shown in FIG. 3 by these encodings.

  Next, the lossy compression processing unit 503 illustrated in FIG. 3 will be described.

  FIG. 8 is a block diagram showing the lossy compression processing unit 503.

  The lossy compression processing unit 503 includes a thinning processing unit 505, a differential encoding unit 510, an offset unit 520, a plane division unit 530, an L plane compression unit 540, an H plane compression unit 550, and a FAKE pixel compression unit 590. Yes. Also here, the flow of image data in the lossy compression processing unit 503 will be described first.

  The image data in the input image file D0 input to the lossy compression processing unit 503 is input to the thinning processing unit 505, and TRUE pixel data corresponding to a periodic pixel portion in the image is thinned out from the image data. . The remainder thinned out becomes FAKE pixel data. These TRUE pixel data and FAKE pixel data correspond to examples of the first compressed data and the second compressed data, respectively, according to the present invention.

  The TRUE pixel data is input to the differential encoding unit 510, and each process of the differential encoding unit 510, the offset unit 520, the plane division unit 530, the L plane compression unit 540, and the H plane compression unit 550 is performed, and the lower-order compressed data D2L The upper compressed data D2H is obtained. The flow of TRUE pixel data is exactly the same as the flow of image data in the first lossless compression processing unit 501 described with reference to FIG. Among the elements shown in FIG. 8, the same elements as those shown in FIG. 6 are given the same reference numerals as those shown in FIG. A set of the lower-order compressed data D2L and the higher-order compressed data D2H constitutes reversible compressed data obtained by reversibly compressing TRUE pixel data.

  On the other hand, the FAKE pixel data obtained by the thinning processing unit 505 is input to the FAKE pixel compression unit 560 and subjected to irreversible compression processing. The FAKE pixel compression unit 560 includes a bit shortening unit 561, a run length coding unit 562, and a Huffman coding unit 563, and the numerical values constituting the FAKE pixel data are 1 bit by the bit shortening unit 561. Alternatively, it is replaced with a 4-bit code. Then, the run length encoding unit 562 and the Huffman encoding unit 563 perform processing exactly the same as the processing in the H plane compression unit 550. As a result, the FAKE pixel compression unit 560 outputs lossy compressed data D3 obtained by irreversibly compressing the FAKE pixel data.

  A set of low-order compressed data D2L and high-order compressed data D2H that constitute reversible compressed data in which TRUE pixel data is reversibly compressed, and irreversible compressed data D3 in which FAKE pixel data is irreversibly compressed are as a whole input image file. The irreversible compression data D30 shown in FIG. 3 is configured in which the image data in D0 is irreversibly compressed.

  In the following, details of processing in each of the parts constituting the first lossless compression processing unit, the second lossless compression processing unit, and the lossy compression processing unit described above will be described.

  First, the processing of the differential encoding unit 510 of the first lossless compression processing unit 501 illustrated in FIG. 6 will be described.

  FIG. 9 is a diagram showing the data structure of the image data in the input image file input to the first lossless compression processing unit 501 shown in FIG. 6 and the concept of differential encoding.

As shown in FIG. 9, the image data input to the first lossless compression processing unit 501 shown in FIG. 6 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, the image data as described above is input to the difference encoding unit 510 included in the first lossless compression processing unit 501 illustrated in FIG. 6, 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. 10 is a diagram illustrating a differential encoding process in the differential encoding unit 510 included in the first lossless compression processing unit 501 illustrated in FIG.

Here, the pixel values in one vertical row arranged in the sub-scanning direction shown in FIG. 9 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, “(12) EF 01 FD 65... L0 00 FF...” Shown in the “difference encoding (lower 8 bits)” field of FIG.
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.

  In the differential encoding unit 510 of FIG. 6, the differential encoding as described above is performed on the image data. The data obtained by this differential encoding is input to the offset unit 520 in FIG. 6, and a predetermined offset value is added to each numerical value of the data.

  Here, the effects of such differential encoding and offset will be described using specific CT image data as an example.

  FIG. 11 is a diagram illustrating an example of CT image data.

  In part (A) of FIG. 11, a monochrome landscape image is shown as an example of a CT image represented by CT image data. In this embodiment, the color of each pixel of such a CT image is shown. Image data represented by numerical values having a density of 8 bits is used. Part (B) of FIG. 11 shows a histogram of data values in the image data representing the landscape image shown in Part (A). The horizontal axis of this histogram is the data value, and the vertical axis is the number of data (number of pixels). ). In general, in a CT image, the width of a histogram is wide, and even if there are peaks and valleys in the number of data in the histogram, it is extremely rare that an area with the number of data “0” occurs in the middle of the histogram.

  FIG. 12 is a diagram illustrating the effect of differential encoding and offset on CT image data.

  In part (A) of FIG. 12, a histogram of data obtained by performing differential encoding on the CT image data shown in FIG. 11 is shown. The vertical axis represents the appearance frequency. When the differential encoding described with reference to FIGS. 9 and 10 is performed on CT image data, the data histogram generally has a minimum data value and a maximum data as shown in part (A) of FIG. A histogram with sharp peaks on both data values. When such data is offset, the data histogram becomes a histogram having a sharp peak at the offset value as shown in part (B) of FIG. In the present embodiment, “8” is used as the offset value, and the frequency of data whose value is “16” or more is almost “0” as a result of the offset.

  In this way, the data whose histogram has been transformed by differential encoding and offset is divided into a lower subplane and an upper subplane by the plane dividing unit 530 of FIG.

  FIG. 13 is a diagram for explaining the effect of data division by the plane division unit 530.

  FIG. 13 shows a histogram in which the histogram shown in Part (B) of FIG. 12 is separated between the data value “15” and the data value “16”. The plane dividing unit 530 of FIG. Data division produces an effect equivalent to such a histogram division. In other words, in this embodiment, each 8-bit numerical value constituting the data is divided into upper 4 bits and lower 4 bits, so that the lower subplane and the upper 4 An upper subplane consisting of a series of numerical values represented by bits is obtained. Then, the 4-bit numerical value constituting the lower subplane directly represents the numerical values from the value “0” to the value “15”, and in the case of the 4-bit numerical value constituting the upper subplane, the value “16” is used. ”To“ 256 ”, the histogram of the lower subplane is substantially the same as the histogram shown on the left side of FIG. Is substantially the same as the histogram shown on the right side of FIG. However, for the histogram of the upper subplane, a peak having a height equal to the area of the histogram shown on the left side of FIG. 13 is added to the data value “16” of the histogram shown on the right side of FIG. It will be a thing.

  Such higher order subplanes are input to the run length encoding unit 551 constituting the H plane compression unit 550 shown in FIG.

  In this embodiment, for convenience of processing, the run-length encoding unit 551 treats two consecutive 4-bit numerical values constituting the upper subplane as one 8-bit numerical value, and displays the value “ The following encoding process is applied to a series of numerical values from “00” to the value “FF”.

  In this encoding process, the encoding process is performed only for a specific numerical value among a plurality of 8-bit numerical values. For this reason, in the run length encoding unit 551, a numerical value to be encoded from the received data (here, this numerical value is referred to as a “compression target numerical value”) and a continuous number of the compression target numerical value are obtained. Detected.

  In this embodiment, as an example, three numerical values “01”, “FF”, and “00” are set as compression target numerical values.

  FIG. 14 is an explanatory diagram of the run-length encoding process in the run-length encoding unit 551 shown in FIG.

  The upper line in FIG. 14 is data constituting the upper subplane, and the lower line is data after the run-length encoding process in the run-length encoding unit 551 is performed.

Here, as shown in the upper line of FIG. 14, from the quantization processing unit 551,
"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 551 in FIG. 6, the leading “06” is not a compression target value, and the subsequent “02 02 02” is not a compression target value but is a compression target value “ It is detected that four consecutive “01” s are present, and next, 32767 consecutive “00” s that are compression target values are inserted between “04” and “05” that are not compression target numerical values. Is done.

  FIG. 15 is a diagram illustrating an encoding algorithm for a numerical value to be compressed in the run-length encoding unit.

  In FIG. 15, Z is a continuous number of the same numerical values to be compressed, for example, Z = 4 for “01” in the upper line of FIG. 14, and Z = 32767 for “00”.

  In FIG. 15, “YY” represents the numerical value to be compressed 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, in FIG. 15, 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 encoding shown in FIG. 14 will be described in accordance with the rules shown in FIG.

  Since the first numerical value “06” constituting the upper subplane data (upper line) input from the plane dividing unit 530 in FIG. 6 is not a compression target numerical value, it is output as it is. Also, “02 02 02” that follows, “02” is not a compression target numerical value, 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. 16 is a diagram illustrating an example of an encoding process according to the number of consecutive steps in the run-length encoding unit 551 in FIG.
When “00” is 127 consecutive, it is encoded into “00 7F” 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 consecutive, they are encoded into "FF 8F 80" using 3 bytes.

  The run-length encoding unit 551 shown in FIG. 6 performs the encoding process as described above.

  According to the run-length encoding unit 551 according to the present embodiment, the maximum compression rate is improved to 3/32895 = 1 / 10,965. In addition, as described in the histogram of FIG. 13, most of the 4-bit numerical values represented the data value “16” in the upper subplane data that is the target of the encoding process by the run-length encoding unit 551. The numerical value is “0”, and many 8-bit numerical values created from the 4-bit numerical value are also “00” in hexadecimal notation. For this reason, significant data compression is expected by the encoding process in the run-length encoding unit 551.

  The data after the above-described encoding process is performed by the run-length encoding unit 551 in FIG. 6 is then input to the data scanning unit 552 and the Huffman encoding unit 553 that constitute the H-plane compression unit 550 in FIG. The

  In the data scanning unit 552, first, the entire data output from the run-length encoding unit 551 is scanned to determine the appearance frequency of the data value.

  FIG. 17 is a diagram illustrating an example of a scanning result by the data scanning unit 552.

  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. Further, here, for the sake of simplicity, the data sent from the run-length encoding unit 551 in FIG. 3 is any one of 16 numerical values “A1” to “A16”. It shall be. Then, the data scanning unit 552 assigns a code corresponding to the appearance frequency to each of these 16 numerical values to create a Huffman table. That is, “A1” having the highest appearance frequency is assigned the code “00” represented by 2 bits, and the next “A2” is assigned the code “01” also represented by 2 bits. The next “A3” and the next “A4” are each assigned a code “100” and a code “101” represented by 3 bits, and the next “A5” to “A8” Each code represented by 5 bits is assigned. Similarly, a code represented by a larger number of bits is assigned to a numerical value with a lower appearance frequency.

  FIG. 18 is a diagram illustrating an example of the Huffman table.

  This Huffman table is the same as that in FIG. 17, and the numerical values before encoding (before replacement) and the encodings are arranged so that the numerical values with higher appearance frequency are replaced with the codes represented by shorter bits. It is a correspondence table with a numerical value after (after replacement).

  In the Huffman coding unit 553 constituting the H plane compression unit 550 of FIG. 6, the numerical values of the data are encoded according to such a Huffman table, and as a result, many numerical values are replaced with codes having a short bit number. Thus, data compression is realized.

  As described above, the high-order subplane D1H input to the H-plane compression unit 550 in FIG. 6 is encoded by the run-length encoding unit 551 and the encoding by the Huffman encoding unit 553, thereby achieving a high compression rate. Is compressed into higher-order compressed data D2H.

  In the Huffman coding unit 541 of the L plane compression unit 540 in FIG. 6, as in the run length coding unit 551 of the H plane compression unit 550, two 4-bit numerical values are regarded as one 8-bit numerical value. Processed. In the encoding process by the Huffman encoding unit 541, the same process as the encoding process by the Huffman encoding unit 553 of the H plane compression unit 550 is executed except that a fixed Huffman table is used. . As a result, the lower subplane D1L becomes the lower compressed data D2L.

  Various processes as described above are executed by the respective units of the first lossless compression processing unit 501 shown in FIG. 6, so that the first lossless compression processing unit 501 can compress the image data by lossless compression. In particular, significant compression is realized for CT image data. Moreover, since various processes as described above are processes based on simple algorithms, high-speed processing is possible.

  Next, details of processing in each unit of the second lossless compression processing unit 502 illustrated in FIG. 7 will be described.

  The image data input to the second lossless compression processing unit 502 is input to the differential encoding unit 560 shown in FIG. This difference encoding unit 560 is exactly the same as the difference encoding unit 510 shown in FIG. 6, and the difference encoding unit 560 of the second lossless compression processing unit 502 also uses the difference described in FIGS. 9 and 10. An encoding process is executed. The data subjected to the differential encoding process is input to a run length encoding unit 570 shown in FIG. In the run-length encoding unit 570, an encoding process similar to the encoding process described with reference to FIGS.

  Unlike the first lossless compression processing unit, the second lossless compression processing unit 502 executes a run-length encoding process immediately after the differential encoding process. Such a processing procedure is particularly suitable for processing LW data. That is, in the LW image, the data after the differential encoding process is extremely concentrated on some specific values, and the run-length encoding process as described above is performed on such data. Is expected to achieve significant compression.

  The data that has been subjected to the run-length encoding process is input to the Huffman encoding unit 580 in FIG. The Huffman encoding unit 580 performs the data scanning and Huffman encoding described with reference to FIGS. 17 and 18, and further compresses the data.

  As described above, various processes are executed by the respective units of the second lossless compression processing unit 502 shown in FIG. 7, so that the second lossless compression processing unit 502 can compress image data by lossless compression. In particular, significant compression is realized for LW image data. Various processes in the second lossless compression processing unit 502 are also simple algorithm processes, and can be performed at high speed.

  Finally, details of processing in each unit of the lossy compression processing unit 503 illustrated in FIG. 8 will be described.

  The image data input to the irreversible compression processing unit 503 shown in FIG. 8 is input to the thinning processing unit 505 and subjected to thinning processing.

  FIG. 19 is a diagram showing the data structure of image data in the input image file input to the lossy compression processing unit 503 shown in FIG. 8 and the concept of thinning processing.

  Although the data structure has been described with reference to FIG. 9, here, for the purpose of explaining the concept of the thinning process, an expression different from the expression of the pixel value in the above description is used.

  As shown in FIG. 19, the image data input to the irreversible compression processing unit 503 shown in FIG. 8 includes a predetermined main scanning direction (horizontal direction in the figure) and a sub-scanning direction (see FIG. 19) perpendicular to the main scanning direction. Pixels in the vertical direction), and a column of pixels arranged in the main scanning direction is called a line. Here, pixels for 8 lines are shown, and the interval between the pixels corresponds to a resolution of 600 dpi.

The position of each pixel is represented by a subscript attached to codes T and F representing pixel values. For example, for the third line, the pixel values of the pixels arranged in the main scanning direction are
3_1, 3_2, 3_3, 3_4, ...
The subscript is attached.

  The thinning-out processing unit 505 constituting the irreversible compression processing unit 503 shown in FIG. 8 receives image data composed of pixel values arranged in this way, and classifies each pixel into a TRUE pixel and a FAKE pixel. Among the pixels shown in FIG. 19, the TRUE pixel has a pixel value represented by T, and the FAKE pixel has a pixel value represented by F. The TRUE pixel is a pixel that is periodically thinned out from the arrangement of the pixels. Here, as an example, for each line (odd-numbered line) every other line in the sub-scanning direction, one pixel in the main scanning direction. Every other pixel (odd-numbered pixel) is thinned out as a TRUE pixel. As a result, in the example shown in FIG. 19, the TRUE pixel corresponds to a pixel constituting an image that has been reduced from the original 600 dpi resolution to the 300 dpi resolution, and corresponds to a quarter of the original image data. Will be thinned out. The TRUE pixels thus thinned out constitute TRUE pixel data consisting of a series of such TRUE pixels, and the structure of the TRUE pixel data is similar to the original image data in the main scanning direction and the sub-scanning direction. It has a structure in which pixels are lined up. For FAKE pixels remaining after thinning out TRUE pixels, FAKE pixel data consisting of a series of the FAKE pixels is configured.

  In addition to the TRUE pixel decimation, for example, for every second line in the sub-scanning direction, every second pixel in the main scanning direction is thinned out to one-ninth of the original image data. A method of thinning out corresponding pixels or a method of different thinning-out cycles in the main scanning direction and the sub-scanning direction can be adopted. However, in the following, as shown in FIG. The explanation will be continued on the assumption that was thinned out.

  The TRUE pixel data obtained in this way is input to the differential encoding unit 510 constituting the irreversible compression processing unit 503 shown in FIG. 8, and the differential encoding unit 510, the offset unit 520, the plane division unit 530, L Each process of the plane compression unit 540 and the H plane compression unit 550 is performed. Details of the processing in these units 510 to 550 are exactly the same as the processing in each unit 510 to 550 shown in FIG. Note that when the processing in each of these units 510 to 550 is performed, the CT data is efficiently compressed as described above. If the two lossless compression processing units described above do not reach the target compression rate, the image represented by the image data may be a type of image that cannot be said to be a CT image or an LW image. In the case of image data and LW image data, the compression rate of the CT image data is less likely to increase. Therefore, when the two lossless compression processing units do not reach the target compression rate, the compression rate of the CT image data is often used. It is thought that there was a situation where there was a shortage. For this reason, it is expected that the TRUE pixel data is efficiently compressed when the compression process for the TRUE pixel data is each of the above processes suitable for the compression of the CT image data.

  On the other hand, the FAKE pixel data obtained by the thinning processing unit 505 shown in FIG. 8 is input to the FAKE pixel compression unit 590 and subjected to lossy compression.

The FAKE pixel data input to the FAKE pixel compression unit 590 is transferred to the bit shortening unit 591. The bit shortening unit 591 first adds the pixel value of each FAKE pixel constituting the FAKE pixel data to the original image data. The pixel values of the two TRUE pixels sandwiching the FAKE pixel are obtained, and the pixel values of the FAKE pixel are compared with the pixel values of these TRUE pixels. Here, each FAKE pixel shown in FIG. 19 is divided into three systems according to the positional relationship with the TRUE pixel. That is, when the pixel value of the TRUE pixel is expressed as T _{n_k} , the pixel value of the FAKE pixel is expressed in three types, F _{n_k + 1} , F _{n + 1_k} , and F _{n + 1_k + 1} . Among these three types of FAKE pixels, regarding the pixel value of the FAKE pixel whose pixel value is expressed as F _{n_k + 1} , the pixel values T _{n_k} and T of two TRUE pixels sandwiching the FAKE pixel in the main scanning direction. Compared with _{n_k + 2} . The pixel value for a pixel value of FAKE pixels is expressed as F _{n + 1_k,} compared the FAKE pixel pixel value T _{n_k} two TRUE pixels bounding the sub-scanning direction, and T n _{+ 2_k.} Further, the pixel value of the FAKE pixel whose pixel value is expressed as F _{n + 1_k + 1} is compared with the pixel values T _{n_k} and T _{n + 2_k + 2 of} two TRUE pixels sandwiching the FAKE pixel in an oblique direction. The

  Next, the bit shortening unit 591 encodes the pixel value of the FAKE pixel into a 4-bit code starting from a 1-bit code “0” or “1” according to the comparison result.

  FIG. 20 is a diagram illustrating the concept of encoding in the bit shortening unit.

Here, among the above-described three types of FAKE pixels, a FAKE pixel whose pixel value is expressed as F _{n + 1 — k} will be described as a representative. When the pixel value F _{n + 1_k} of the FAKE pixel is present in the regular FAKE pixel zone between the pixel values T _{n_k} and T _{n + 2_k} of the two TRUE pixels, the pixel value F _{n + 1_k} is present in the regular FAKE pixel zone. It is encoded into a 1-bit code “0” indicating that it is present. Further, when the pixel value F _{n + 1_k} of the FAKE pixel exists in the remaining irregular FAKE pixel zone excluding the regular FAKE pixel zone in the numerical range of 0 to 255 that can be expressed by 8 bits, The pixel value is encoded into a 4-bit code starting with “1” as described below.

  FIG. 21 is a diagram illustrating a first encoding method into a 4-bit code.

In this first encoding method, the lower five digits of the 8-bit bit value representing the pixel value F _{n_k + 1} are truncated in the pixel value F _{n_k + 1} of the FAKE pixel, and the remaining upper three digits start. When “1” is added to, the codes are encoded into codes “1000” to “1111”. Therefore, as shown in the table of this figure, among the values “0” to “255” before encoding, the values “0” to “31” are encoded to “1000”, and “22” to “63”. "Is encoded as" 1001 ". Similarly, “64” to “95”, “96” to “127”, “128” to “159”, “160” to “191”, “192” to “223”, “224” to “255”. Are encoded into “1010”, “1011”, “1100”, “1101”, “1110”, and “1111”, respectively. Such a first encoding method is realized by a very simple process of truncating the digit of the bit value.

  By such encoding in the bit shortening unit 591 of FIG. 8, the 8-bit pixel value of the FAKE pixel is shortened to 1 bit or 4 bits. In the case of a CT image, since the correlation between adjacent pixels is high, pixel values for many FAKE pixels exist in the regular FAKE pixel zone, and it is considered that significant compression is possible.

  In the present embodiment, the first encoding method described above is used for the encoding to the 4-bit code, but the bit shortening unit according to the present invention uses the second encoding method described below. May be adopted.

  FIG. 22 is a diagram illustrating a second encoding method into a 4-bit code.

In the second encoding method, the numerical range of the irregular FAKE pixel zone described above is divided into eight steps, and the above four 4-bit codes are allocated and encoded. For example, if the regular FAKE pixel zone is “36” to “128”,
{255- (128-36)} / 8 = 20.37, INT (20.38) = 20
As shown in FIG. 18, the numerical value of “0” to “20” is encoded as “1000” and the numerical values of “21” to “36” are “1001”. Is encoded. The numerical values “128” to “128 + 20” are encoded to “1010”, and similarly “128 + 21” to “128 + 40”, “128 + 41” to “128 + 60”, “128 + 61” to “128 + 80”, “128 + 81”. ”To“ 128 + 100 ”and“ 128 + 101 ”to“ 255 ”are encoded as“ 1011 ”,“ 1100 ”,“ 1101 ”,“ 1110 ”, and“ 1111 ”, respectively. Such a second encoding method is highly accurate because encoding is limited to a necessary numerical range.

  The data encoded by the bit shortening unit 591 in FIG. 8 is a mixture of 1-bit code and 4-bit code, but is divided into 8-bit units (byte packing) for subsequent processing, and FIG. The run-length encoding unit 592 and the Huffman encoding unit 593 perform processing exactly the same as the processing in the H-plane compression unit 550 shown in FIGS. Here, the Huffman encoding unit 593 also serves as both the data scanning unit 552 and the Huffman encoding unit 553 described above.

  In the case of a CT image, since many pixel values are encoded to “0” by the encoding of the bit shortening unit 591, it is expected that the run length encoding unit 592 further compresses the pixel value after that.

  The various processes as described above are executed by the respective units of the irreversible compression processing unit 503 shown in FIG. 8, so that the irreversible compression processing unit 503 can compress the image data by irreversible compression. The CT image data is compressed more greatly than the compression in the first lossless compression processing unit. Various processes in the irreversible compression processing unit 503 are also processes by a simple algorithm, and high-speed processing is possible.

  As described above, the image compression apparatus 500 illustrated in FIG. 3 includes various types of image data by including the first lossless compression processing unit 501, the second lossless compression processing unit 502, and the lossy compression processing unit 503. High speed and significant compression can be performed.

  In the above description, as an example of the first lossless compression processing unit according to the present invention, the first lossless compression processing unit 501 that performs processing suitable for compression of CT data is shown, and the second loss referred to in the present invention. As an example of the reversible compression processing unit, a second reversible compression processing unit 502 that performs processing suitable for compression of LW data is shown, but the first reversible compression processing unit according to the present invention and the first reversible compression processing unit according to the present invention. Even if the first lossless compression processing unit performs processing suitable for compression of LW data in the first lossless compression processing unit and performs processing suitable for compression of CT data in the second lossless compression processing unit. Good.

  Further, in the above description, as an example of the difference generation unit referred to in the present invention, the one that calculates the difference in the sub-scanning direction is shown, but the difference generation unit referred to in the present invention calculates the difference in the main scanning direction. There may be. Further, in the above description, as an example of the difference generation unit according to the present invention, the one for obtaining the difference by using a one-dimensional difference calculation is shown, but the difference generation unit according to the present invention is a vertical and horizontal image. In other words, the difference between the two may be calculated by using a two-dimensional difference calculation.

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 a block block diagram which shows the image compression apparatus corresponded to 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 image compression processing program equivalent to one Embodiment of the data compression program of this invention. It is a block block diagram which shows a 1st lossless compression process part. It is a block block diagram which shows a 2nd lossless compression process part. It is a block block diagram which shows an irreversible compression process part. It is a figure which shows the data structure of the image data in the input image file input into the 1st lossless compression process part shown in FIG. 6, and the concept of differential encoding. It is a figure which illustrates and illustrates the differential encoding process in the differential encoding part which comprises the 1st lossless compression process part shown in FIG. It is a figure which shows the example of the image data of CT. It is a figure which shows the effect of the differential encoding and offset with respect to the image data of CT. It is a figure explaining the effect of the data division by a plane division part. 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. It is a figure which shows the example of the encoding process according to the continuous number in the run length encoding part of FIG. It is a figure which shows the example of the scanning result by a data scanning part. It is a figure which shows an example of a Huffman table. It is a figure which shows the data structure of the image data in the input image file input into the lossy compression process part shown in FIG. 8, and the concept of a thinning process. It is a figure which shows the concept of the encoding in a bit shortening part. It is a figure showing the 1st encoding system to a 4-bit code | symbol. It is a figure showing the 2nd encoding system to a 4-bit code.

Explanation of symbols

11 Image data 12A, 12B, 13A, 13B Bitmap data 14 Lossy compression data 15 Lossless compression data 100 Host controller 140 CDROM
DESCRIPTION OF SYMBOLS 150 General-purpose interface cable 200 Interface apparatus 250 Dedicated interface cable 300 Printer 500 Image compression apparatus 501 1st lossless compression process part 502 2nd lossless compression process part 503 Lossy compression process part 504 Judgment part 505 Thinning process part 510 Difference encoding Section 520 Offset section 530 Plane division section 540 L plane compression section 541 Huffman coding section 542 Mode switching section 550 H plane compression section 551 Run length coding section 552 Data scanning section 553 Huffman coding section 560 Differential coding section 570 Run length Coding unit 580 Huffman coding unit 590 FAKE pixel compression unit 591 Bit shortening unit 592 Run length coding unit 593 Huffman coding unit 600 Image compression program 61 The first reversible compression processing unit 620 second lossless compression processing unit 630 lossy compression processing unit 640 determination unit

Claims (5)

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,
A first lossless compression processor that performs a first lossless compression process on the data to be compressed;
A second lossless compression processing unit that applies a second lossless compression process to the data to be compressed when a result of data compression by the first lossless compression processing unit does not reach a predetermined target compression rate;
An irreversible compression processing unit that performs irreversible compression processing on the data to be compressed when the result of data compression by the second lossless compression processing unit does not reach the target compression rate;
One of the first lossless compression processor and the second lossless compression processor is
A difference generating unit that generates new compressed data composed 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;
An offset unit for offsetting each numerical value constituting the new compressed data generated by the difference generation unit by a predetermined value;
By dividing each numerical value of the compressed data whose numerical value is offset by the offset unit into an upper bit part and a lower bit part at a predetermined number of divided bits smaller than the unit bit number, the compressed data is A dividing unit that divides the upper data consisting of a continuation of the upper bit part in each numerical value and the lower data consisting of a continuation of the lower bit part of each numerical value;
An upper data compression unit that performs a lossless compression process on the upper data divided by the dividing unit;
A lower data compression unit that performs a lossless compression process on the lower data divided by the dividing unit;
The other of the first lossless compression processing unit and the second lossless compression processing unit with respect to the one is:
In the large 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 values, the compression target numerical values and the same compression target numerical values as the compression target numerical values are output. A lossless compression process including an encoding process for encoding and outputting a numerical value representing the continuous number of
The irreversible compression processing unit
By periodically decimating a numerical value from a series of numerical values constituting the compressed data, the first compressed data consisting of a series of numerical values extracted from the compressed data by the thinning and a continuation of the remaining numerical values A decimation processing unit for creating first compressed data;
A lossless compression unit that performs a lossless compression process on the first data to be compressed created by the thinning processing unit;
A data compression apparatus comprising: an irreversible compression unit that performs irreversible compression processing on the second compressed data created by the thinning processing unit.   The lossless compression unit of the irreversible compression processing unit performs a lossless compression process equivalent to the lossless compression process in the one of the first lossless compression process unit and the second lossless compression process unit. 2. The data compression apparatus according to claim 1, wherein the data compression apparatus is applied to data to be compressed. The irreversible compression unit of the irreversible compression processing unit,
Whether or not the numerical value constituting the second compressed data created by the thinning processing unit has a value between the numerical values thinned out before and after the numerical value by thinning out the thinning processing unit. If there is an intermediate value, a sign indicating that it is an intermediate value is output, and if it is not an intermediate value, the numerical value is re-expressed with a smaller number of bits than the unit bit number. 2. The data compression apparatus according to claim 1, wherein the numerical value is output. The compressed data represents a continuous and two-dimensional image of a numerical value represented by the number of unit bits,
The lossy compression processing unit includes a determination unit that determines an edge portion in the image;
When the irreversible compression unit of the irreversible compression processing unit is not the edge portion determined by the determination unit with respect to the numerical value constituting the second compressed data created by the thinning processing unit, the unit A predetermined code having a smaller number of bits than the number of bits is output, and in the case of an edge portion, a numerical value obtained by re-expressing the numerical value with a smaller number of bits than the unit bit number is output. The data compression apparatus according to claim 1. In a data compression program that is incorporated in an information processing apparatus that executes a program and causes the information processing apparatus to execute data compression processing on data to be compressed consisting of a series of numerical values represented by a predetermined number of unit bits.
On the information processing apparatus,
A first lossless compression processor that performs a first lossless compression process on the data to be compressed;
A second lossless compression processing unit that applies a second lossless compression process to the data to be compressed when a result of data compression by the first lossless compression processing unit does not reach a predetermined target compression rate;
When a result of data compression by the second lossless compression processing unit does not reach the target compression rate, a lossy compression processing unit that performs lossy compression processing on the data to be compressed is constructed,
One of the first lossless compression processor and the second lossless compression processor is
A difference generating unit that generates new compressed data composed 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;
An offset unit for offsetting each numerical value constituting the new compressed data generated by the difference generation unit by a predetermined value;
By dividing each numerical value of the compressed data whose numerical value is offset by the offset unit into an upper bit part and a lower bit part at a predetermined number of divided bits smaller than the unit bit number, the compressed data is A dividing unit that divides the upper data consisting of a continuation of the upper bit part in each numerical value and the lower data consisting of a continuation of the lower bit part of each numerical value;
An upper data compression unit that performs a lossless compression process on the upper data divided by the dividing unit;
A lower data compression unit that performs a lossless compression process on the lower data divided by the dividing unit;
The other of the first lossless compression processing unit and the second lossless compression processing unit with respect to the one is:
In the large 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 values, the compression target numerical values and the same compression target numerical values as the compression target numerical values are output. A lossless compression process including an encoding process for encoding and outputting a numerical value representing the continuous number of
The irreversible compression processing unit
By periodically decimating a numerical value from a series of numerical values constituting the compressed data, the first compressed data consisting of a series of numerical values extracted from the compressed data by the thinning and a continuation of the remaining numerical values A decimation processing unit for creating first compressed data;
A lossless compression unit that performs a lossless compression process on the first data to be compressed created by the thinning processing unit;
A data compression program comprising: an irreversible compression unit that performs irreversible compression processing on the second compressed data created by the thinning processing unit.

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