JP2002077582A - Method and apparatus for reading image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently process to compress image data acquired by deviating a pixel by using the capacity of less buffer memories. SOLUTION: A method for reading the image comprises a step (S2) of shifting a imaged position on a photoelectric converter of an optical image on an original, a first imaging step (S3) of reading originals divided into a plurality of predetermined ranges at each predetermined range after shifting and outputting an image signal, a first compressing step (S4) of compressing and holding the signal, a step (S5) of further shifting the imaged position, a second imaging step (S6) of reading the same predetermined range as that of the first imaging step and outputting the signal, a second compressing step (S7) of compressing and holding the signal, a compositing step of compressing and compositing the compressed image signal and holding the image, and an outputting step (S24) of outputting the compressed composite image signal. In this method, the first compressing and outputting steps are executed at each reading of the predetermined range in the first imaging step. In the first imaging step, a next predetermined range is read after the process in the compositing step of the one predetermined range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-resolution image reading, and more particularly to control of an image reading device for efficiently compressing image information.

[0002]

2. Description of the Related Art Conventionally, various compression methods such as a run-length compression method used in facsimile and the like have been proposed for compressing image information. Further, a method of compressing image information in line units or block units has been proposed. I have.

[0003] As a video image compression technique, J.
Compression methods such as PEG have been proposed.

[0004]

However, in the above conventional example, when the resolution is increased by shifting the pixels,
Compression processing had to be performed after resolution conversion, which required a large buffer memory and was inefficient.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to efficiently perform compression processing of image data read by shifting pixels by using a smaller buffer memory capacity. .

[0006]

In order to achieve the above object, according to the present invention, there is provided an image reading apparatus for reading an original by using an image pickup means for converting an optical image of the original into an electric signal and outputting an image signal. The method includes the steps of: a first shift step of shifting an image forming position of the optical image of the document on the imaging unit in a predetermined direction by a first predetermined amount; and using the imaging unit after shifting by the first shifting step. A first imaging step of reading a document divided into a plurality of predetermined ranges by a predetermined range and outputting an image signal; a first compression step of compressing and holding the image signal of the predetermined range; A second shift step of shifting the image formation position of the optical image on the image pickup means in the predetermined direction by a second predetermined amount, and after the shift by the second shift step, the predetermined read in the first image pickup step Read the same area as the range A second image capturing step of outputting the image signal in the predetermined area, compressing and holding the image signal of the predetermined area output in the second image capturing step, and the first and second image capturing steps. A combining step of compressing and synthesizing the image signal compressed in the compression step, and an output step of outputting the image signal compressed and combined in the combining step; The first imaging step is performed every time a predetermined range is read. In the first imaging step, the next predetermined range is read after the processing in the synthesis step for one predetermined range.

According to another aspect of the present invention, there is provided an image reading apparatus which converts an optical image of a document into an electric signal and outputs an image signal, and sets an image forming position of the optical image of the document on the image capturing means in a predetermined direction. Shifting means for shifting by a first predetermined amount or a second predetermined amount, compression means for performing compression by a first compression method, synthesis means for performing compression and synthesis by a second compression method, the compression means and the synthesis means Storage means for storing an output of the means, output means for outputting the output of the synthesizing means stored in the storage means, and after a first predetermined amount shift and a second predetermined amount shift by the shift means, The document divided into a plurality of predetermined ranges is read by the predetermined range using the imaging unit, and the obtained image signals are compressed by the compression unit and stored in the storage unit, and the compression stored in the storage unit is performed. Control means for compressing and synthesizing the obtained image signal by the synthesizing means and storing the compressed image signal in the storage means, wherein the control means synthesizes a predetermined range of image signals by the synthesizing means, Control is performed so as to read the next predetermined range.

According to one preferred embodiment of the present invention, the first
In the compression step and the second compression step, compression is performed by the same compression method.

According to a preferred aspect of the present invention, in the first and second compression steps, a low-frequency component in the predetermined direction of the image signal and a low-frequency component in a direction perpendicular to the predetermined direction are included. And a high-frequency component in the predetermined direction of the image signal. The compression unit outputs a low-frequency component of the image signal in the predetermined direction, and a low-frequency component and a high-frequency component in a direction perpendicular to the predetermined direction.
Further, it outputs a high-frequency component of the image signal in the predetermined direction.

According to another aspect of the present invention, there is provided an image reading apparatus for converting an optical image of an original into an electric signal and outputting an image signal by reading the original. The control method according to the present invention for the reading apparatus includes a first shift step of shifting an image forming position of the optical image of the document on the imaging unit by a first predetermined amount in a predetermined direction, and a shift by the first shift step. Later, using the imaging means,
A first imaging step of reading a document divided into a plurality of predetermined ranges by a predetermined range and outputting an image signal; a compression step of compressing and holding the image signal of the predetermined range; and The image forming position on the imaging means is shifted in a predetermined direction
A second shift step of shifting by a predetermined amount, and a second imaging step of reading the same area as the predetermined range read in the first imaging step and outputting an image signal after the shift by the second shift step. A synthesizing step of compressing and synthesizing the image signal compressed in the first compression step and the image signal of the predetermined area output in the second imaging step, and
An output step of outputting an image signal compressed and synthesized in the synthesis step, wherein the first compression step to the output step are performed every time a predetermined range is read in the first imaging step. In the imaging step, after the processing in the synthesizing step for one predetermined range, the next predetermined range is read.

According to another aspect of the present invention, there is provided an image reading apparatus for converting an optical image of a document into an electric signal to output an image signal, and for setting an image forming position of the optical image of the document on the imaging means in a predetermined direction. Shifting means for shifting by a first predetermined amount or a second predetermined amount, compression means for performing compression by a first compression method, synthesis means for performing compression and synthesis by a second compression method, the compression means and the synthesis means Storage means for storing the output of the means, output means for outputting the output of the synthesizing means stored in the storage means, and, after a first predetermined amount of shifting by the shifting means, a plurality of One predetermined range of the document divided into a predetermined range is read, and the obtained image signal is compressed by the compression unit and stored in the storage unit. After the shift unit shifts by a second predetermined amount, the image pickup unit To A predetermined range identical to the predetermined range read before the shift is read, and the obtained image signal and the compressed image signal stored in the storage unit are compression-synthesized by the synthesis unit and stored in the storage unit. Control means for performing control so that the image signal of one predetermined range is synthesized by the synthesizing means,
Control is performed so as to read the next predetermined range.

According to a preferred aspect of the present invention, in the compression step, a low-frequency component in the predetermined direction of the image signal and a low-frequency component and a high-frequency component in a direction perpendicular to the predetermined direction are held. In the synthesizing step, the image signal further holds a high-frequency component in the predetermined direction and a low-frequency component and a high-frequency component in a direction perpendicular to the predetermined direction. Also,
The compression unit outputs a low-frequency component of the image signal in the predetermined direction, and a low-frequency component and a high-frequency component of a direction perpendicular to the predetermined direction, and the synthesizing unit further outputs the image signal in the predetermined direction. Output the high frequency component of

According to a preferred aspect of the present invention, the direction perpendicular to the predetermined direction is a sub-scanning direction, and more preferably, the document is divided in a direction perpendicular to the predetermined direction. Further, the predetermined direction is a main scanning direction.

According to a preferred aspect of the present invention, the difference between the first predetermined amount and the second predetermined amount is a half pixel.

Further, according to a preferred aspect of the present invention, the first predetermined amount is zero.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a block diagram showing a configuration of an image reading apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an original, reference numeral 2 denotes an original platen glass for holding the original, and reference numeral 3 denotes a contact sensor (C
IS), and is a line sensor in the first embodiment. 4 is a piezoelectric element for shifting the CIS 3 in the main scanning direction, 5 is a carriage unit configured to shift the CIS 3 in the main scanning direction by the piezoelectric element 4, and 6 is a driving unit for driving the carriage unit 5 in the sub scanning direction. With a carriage drive mechanism, a guide rail, a drive pulley 61,
It consists of a dependent pulley 62, a reduction gear and a belt 63. Reference numeral 7 denotes a stepping motor for moving the carriage unit 5 through the carriage driving mechanism 6 to perform sub-scanning. Reference numeral 8 denotes a motor drive circuit for driving the stepping motor 7, and reference numeral 9 denotes sequence control and interface of the scanner. CPU 13 for performing communication control and image processing control via the CIS 13 is a CIS driving circuit for driving the CIS 3, 14 is a piezoelectric element 4 for moving the CIS 3 in the main scanning direction to perform pixel shift
, A reference numeral 15 denotes an A / D converter for converting an image signal read from the CIS 3 into digital data, a reference numeral 16 denotes an image processing circuit for performing shading correction and gradation processing, and a reference numeral 18 denotes reading. A compression circuit for compressing the compressed image;
A memory control circuit that controls image data by controlling 0
Reference numeral 20 denotes a buffer memory for temporarily storing image data, 21 denotes an interface control circuit for controlling communication with a host computer, transmission of image data, and the like, and 22 denotes a host computer.

The CIS 3 includes an LED 31 for illuminating the original 1, a light guide 32 for guiding the illumination light of the LED 31 to a reading range of the original 1, a cell hook lens 33 for forming an image of the original, and a photoelectric converter. It includes a conversion element 34, a substrate 35 for holding the photoelectric conversion element 34 and the LED 31.

FIG. 2 is a view of the carriage unit of the image reading apparatus according to the first embodiment of the present invention as viewed from the document surface side. The same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, reference numeral 36 denotes a spring for urging the CIS 3 in the direction of the piezoelectric element, and 37 and 38 denote holding members for the piezoelectric element 4.

FIG. 3 is a diagram showing a document reading range and a unit block for performing a pixel shifting process. In FIG.
25 is the image readable range on the platen, 26 is the designated image reading range, S is the tip of the image reading range,
E is the rear end of the image reading range, P is the number of pixels of the image reading range at the basic resolution in the main scanning direction, L is the number of lines of the image reading range at the basic resolution in the sub-scanning direction, B1 to B
Reference numeral 5 denotes a block determined as a unit of processing by the CPU 9 based on the size of the image reading range 26, the storage capacity of the buffer memory 20, and the reading resolution, and BL denotes the number of lines of B1.

FIG. 4 is a block diagram showing an example of the configuration of a conversion circuit used for the compression processing, which is included in the compression circuit 18 of FIG. In FIG. 4, reference numeral 41 denotes a first filter having a conversion characteristic 1, 42 denotes a second filter having a conversion characteristic 2, 43 denotes a third filter having a conversion characteristic 3, and 44 denotes a filter for selecting filter outputs having different conversion characteristics. Selector, KSE
L is a selection signal for selecting a parameter for determining the conversion characteristic, Din is input data to the conversion circuit, and output data of the Dout conversion circuit.

As an example of the conversion characteristic, in the first embodiment of the present invention, the first filter 41 performs conversion such that output data corresponding to a low-frequency component is obtained in both the main scanning and the sub-scanning, and Filter 42 performs conversion such that output data corresponding to a low-frequency component in the main scanning and high-frequency components in the sub-scanning are obtained, and a third filter 43 obtains output data corresponding to a high-frequency component in the main scanning direction. Perform such a conversion.

The selection signal KSEL is supplied by the CPU 9 so that the first filter, the second filter, and the third filter are sequentially selected in order to obtain frequency characteristic data required for the compression processing.

FIG. 5 is a block diagram showing another example of the construction of the conversion circuit used for the compression processing. Reference numeral 51 denotes a conversion filter capable of setting conversion characteristics, 52 denotes a selector for selecting a parameter for determining the conversion characteristics, and K0 Is a parameter corresponding to the conversion characteristic 0, K1 is a parameter corresponding to the conversion characteristic 1, K2 is a parameter corresponding to the conversion characteristic 2,
K3 is a parameter corresponding to the conversion characteristic 3, KSEL is a selection signal for selecting a parameter for determining the conversion characteristic,
Din is input data of the conversion circuit and output data of the Dout conversion circuit.

The parameters K0 to K3 are preset and supply a selection signal KSEL for selecting the parameters of the conversion characteristics in order for the CPU 9 to sequentially obtain the data of the characteristics required for the compression processing.

The conversion characteristics are determined by parameters K0 to K3.
It is also possible to return according to the image by the setting of, and it is possible to cope with non-conversion processing depending on the setting of the parameters K0 to K3.

FIG. 6 is a flow chart showing the sequence of the main processing when compression and pixel shift are performed.

Image reading is started, and in step S1, preparations for scanning, such as setting of reading resolution and reading area, moving speed of the carriage, calculation of the optimal number of lines BL of the block, and the like are performed. Then, step S2
In order to realize the pixel-shifted reading, when a predetermined position of the CIS 3 in the main scanning direction is set as a main scanning reference position, the difference between the main scanning reference position and the position of the CIS 3 when reading is actually performed is calculated. The first shift amount shown is set. In step S3, the reading start position in the main scanning direction is shifted by an amount corresponding to the first shift amount, and the scanning for the BL lines is performed at the basic resolution in the main scanning direction and twice the basic resolution in the sub-scanning direction. I do.

After the scanning for the BL lines is completed in step S3, the compression circuit 18 applies the filter 1 and the filter 2 of the conversion characteristics 1 and 2 to the image data for the BL lines in step S4. A first conversion is performed to perform an operation of extracting image information of a low-frequency component in the scanning direction and a low-frequency component in the sub-scanning direction and image information of a low-frequency component in the main scanning direction and a high-frequency component in the sub-scanning direction. The image data corresponding to the first shift amount and the data after the first conversion are stored in the first block of the memory 20.

Next, in step S5, the image data is returned by BL lines in the sub-scanning direction, and a second shift amount indicating the difference between the main scanning reference position and the position of CIS3 is set. This second shift amount is
The position shifted by a half pixel pitch from the first shift amount is set to be the position of CIS3. In step S6, again
Scanning for BL lines is performed at a basic resolution in the main scanning direction and twice the basic resolution in the sub-scanning direction.

When the scanning for the BL lines is completed in step S6, the first conversion is performed on the image data for the BL lines by the compression circuit 18 using the filter 1 and the filter 2 in step S7. The image data corresponding to the second shift amount and the data after the first conversion are stored in the second block of the memory 20.

At this point, the first block and the second block of the buffer memory 20 have image data shifted by a half pixel pitch from each other, and have a low frequency component in the main scanning direction and a low frequency component in the sub scanning direction of each image. The data of the high-frequency component is completed.

Next, in step S8, it is checked whether the third block of the buffer memory 20 has sufficient free space.
If there is sufficient free space, the process proceeds to step S10, and if not, the process proceeds to step S9.

In step S9, it is checked whether an error such as a timeout has occurred. If an error has occurred, the process is interrupted. If no error has occurred, the process proceeds to step S9.
Return to 8.

On the other hand, if there is sufficient free space, the compression circuit 18 in step S10
The high-frequency component in the main scanning direction is extracted from the data stored in the first block and the second block using the filter 3 of the conversion characteristic 3, and based on the image data extracted for each frequency component, A second conversion for performing a compression process is performed, and the data after compression is stored in a third block of the buffer memory 20.

When the data storage in the third block is completed, the flow advances to step S11 to set a data ready flag. In a data transfer task described later, when the data ready flag is set, the data stored in the third block is transferred.

In step S12, it is determined whether or not the scanning has been completed. If the scanning has been completed, the process proceeds to step S13. If not, the process returns to step S2.

In step S13, it is confirmed whether or not the data transfer has been completed, and when the data transfer has been completed, the process is terminated.

FIG. 7 shows a task process for performing data transfer. When the data transfer task is started, it waits until the data transfer mode is set in step S21.
In the data transfer mode, the process proceeds to step S22.

In step S22, the data ready flag is monitored, and the process waits until the data ready flag is set. When the data ready flag is set, the process proceeds to step S23, where the data ready flag is cleared and the process proceeds to step S24.

In step S24, the data stored in the third block of the buffer memory 20 is transferred. When the data transfer ends, the process returns to step S21.

FIG. 8 shows steps S3 and S6.
FIG. 4 is a diagram illustrating the concept of a method of combining image data obtained by shifting a reading start position by a half pixel and combining the image data with high-resolution image data. In the figure, P1 is the first
Is the first image data output from the CIS 3 when the shift amount is set, the image data becomes the first pixel after the composition, and P2 is the image data when the second shift amount is set.
The first image data output from IS3.
The image data that becomes the pixel, P3 is the image data that is output second from the CIS3 at the first shift amount, the image data that becomes the third pixel after synthesis, and P4 is the image data that becomes the second pixel from the CIS3 at the second shift amount. P5 is the image data output fourth from the CIS3 when the first shift amount is set, and image data which becomes the fifth pixel after synthesis is obtained. P6 is the third image data output from CIS3 at the second shift amount, which is the sixth pixel after synthesis, and P7 is the fourth image data output from CIS3 at the first shift amount. , P8 is the fourth image data output from CIS3 at the time of the second shift amount, P8 is the image data of the eighth pixel after synthesis, and P9 is the first shift amount. At the time of CI After synthesis in the image data output from 3 to 5 th image data to be 9 th pixel, P10 is the second
Is the fifth image data output from the CIS 3 when the shift amount is, and becomes the tenth pixel after combination.

L1 is the value for the first shift amount and the value for the second shift amount.
L2 is the image data of the first line of each read block at the shift amount of, and L2 is the image data of the second line of each read block at the time of the first shift amount and the second shift amount.

Scanning is performed at the basic resolution in the main scanning direction and at twice the basic resolution in the sub-scanning direction, and the same sub-scanning area is shifted by 1/2 pixel in the main scanning direction in each block. By reading and combining, the CI
An image having twice the resolution of the basic resolution of S3 can be obtained. According to the present invention, synthesis is performed for each block of a plurality of lines while performing compression processing, and the result of compression and synthesis is output to a PC for each block.

As described above, according to the first embodiment, pixel shifting is performed for each block, and at the time of image reading with the first shift amount, compression processing for low-frequency components is performed. When the image with the shift amount is read, the compression processing for the high-frequency component is performed. Therefore, the required capacity of the buffer memory is small, and the compression processing can be performed efficiently.

<Second Embodiment> Next, a second embodiment will be described.

Since the configuration of the image reading apparatus used in the second embodiment is the same as that described in the first embodiment, the description is omitted here.

In the first embodiment, every time an image is read from the image reading start position obtained by shifting the same block by a different shift amount, the same conversion is performed on the read image data to extract a low frequency component. , And calculate the high-frequency components later. On the other hand, in the second embodiment, the conversion method is changed between the first shift and the second shift to perform the conversion efficiently.

FIG. 9 is a flowchart showing the sequence of the main process in the case where the pixel is shifted while being compressed. The process is the same as the process shown by the same step numbers in FIG. 6 except for steps S7 'and S10'.

In the second embodiment, step S
After scanning is performed with the second shift amount in step S6, step S7 '
, The data stored in the first block obtained by performing the first conversion on the image at the first shift amount by the compression circuit 18 and the image data for the BL lines of the second shift amount On the other hand, the second conversion including the conversion corresponding to the high-frequency component in the main scanning direction is performed using the filter having the conversion characteristic 3, and the conversion result is stored in the second block of the buffer memory.

By the above processing, the data of the low frequency component and the data of the high frequency component of the image are aligned in the second block when step S7 'is completed.

In the next step S8, the buffer memory 20
It is checked whether the third block has enough free space. If there is enough free space, the process proceeds to step S10 ′, and if not, the process proceeds to step S9.

In step S10 ', the compression circuit 18
The data stored in the second block of the buffer memory 20 is subjected to a third conversion by a run-length compression method or the like, and the compressed data is stored in the third block of the buffer memory 20.

The subsequent processing is the same as the processing described with reference to FIG. 6, and the data transfer processing is performed in the same procedure as the flowchart shown in FIG.

As described above, according to the second embodiment, the first
Although the reproducibility is slightly inferior to that of the embodiment, the data can be compressed more efficiently.

In this embodiment, the CIS3
Is shifted in the main scanning direction by the piezoelectric element 4, thereby shifting the reading start position of the original. However, the present invention is not limited to this, and the original can be moved or reflected light from the original and CIS 3 Any configuration may be used as long as the position at which the optical image of the document is formed on the CIS 3 can be shifted, for example, a unit for changing the optical path of the reflected light is provided between the two.

Further, in the present embodiment, the image reading apparatus for reading a reflection original has been described. However, it is needless to say that the present invention is not limited to this and can be applied to, for example, reading a transparent original.

In this embodiment, the CIS3
Is described as a line sensor, but it is also possible to use an area sensor.

In the present embodiment, a so-called close contact type line sensor using a cell hook lens is used. However, the present invention is not limited to this, and a fixed image pickup device is used, and the image of the original is different. The optical image at the position may be configured to be guided onto the image sensor using an optical system.

[0062]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Further, an object of the present invention is to supply a storage medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (a computer) of the system or the apparatus. Or a CPU or MPU) reads out and executes the program code stored in the storage medium,
Needless to say, this is achieved. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
In addition, by the computer executing the readout program code, not only the functions of the above-described embodiments are realized, but also based on the instructions of the program code,
The operating system (OS) running on the computer performs part or all of the actual processing,
It goes without saying that a case where the functions of the above-described embodiments are realized by the processing is also included.

Further, after the program code read from the storage medium is written into the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the functions of the above-described embodiments are realized by the processing is also included.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts shown in FIGS. 6 or 9 and F described above.

[0066]

As described above, according to the present invention, it is possible to efficiently perform compression processing of image data read by shifting pixels by using a smaller capacity of the buffer memory.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image reading device according to a first embodiment of the present invention.

FIG. 2 is a diagram of a carriage unit of the image reading apparatus according to the first embodiment of the present invention as viewed from a document surface side.

FIG. 3 is a diagram for explaining a relationship between a document reading range and a pixel shift processing block.

FIG. 4 is a configuration example of a conversion circuit used in compression processing.

FIG. 5 is another configuration example of the conversion circuit used in the compression processing.

FIG. 6 is a flowchart illustrating a sequence of a main process when performing compression and pixel shift according to the first embodiment of the present invention.

FIG. 7 is a flowchart illustrating a task process for performing data transfer.

FIG. 8 is a diagram illustrating the concept of image data read by pixel shifting and a synthesizing process thereof.

FIG. 9 is a flowchart illustrating a sequence of a main process when performing compression and pixel shift according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original 2 Original platen glass 3 Contact sensor (CIS) 4 Piezoelectric element 5 Carriage unit 6 Carriage drive mechanism 7 Stepping motor 8 Motor drive circuit 9 CPU 13 CIS drive circuit 14 Piezoelectric element drive circuit 15 A / D converter 18 Compression circuit 19 Memory Control circuit 20 Buffer memory 21 Interface control circuit 22 Host computer 31 LED 32 Light guide 33 Cell hook lens 34 Photoelectric conversion element 35 Substrate

 ──────────────────────────────────────────────────の Continued on the front page F term (reference) 5B047 BB02 BC16 CA11 5C051 AA01 DA03 DC07 DE09 DE12 EA03 FA01 5C072 AA01 BA16 MA10 MB08 UA08 WA03 XA01 5C076 AA01 AA19 AA36 BA01 BA03 BA06 CA08

Claims (20)

[Claims] 1. An image reading method for reading an original using an imaging unit that converts an optical image of the original into an electric signal and outputs an image signal, comprising: forming an optical image of the original on the imaging unit. A first shift step of shifting a position in a predetermined direction by a first predetermined amount, and after the shift in the first shift step, reading the document divided into a plurality of predetermined ranges by the predetermined range using the imaging unit. A first imaging step of outputting an image signal; a first compression step of compressing and holding the image signal in the predetermined range; and an image forming position of the optical image of the document on the imaging unit in a predetermined direction. A second shift step of shifting by a second predetermined amount; and a second imaging step of, after shifting by the second shift step, reading an area same as the predetermined range read in the first imaging step and outputting an image signal. The step; A second compression step of compressing and holding the image signal of the predetermined area output in the imaging step of 2, and a combining step of compressing and combining the image signals compressed in the first and second compression steps. And an output step of outputting an image signal compressed and synthesized in the synthesis step. The first compression step to the output step are performed every time a predetermined range is read in the first imaging step. In the first imaging step, an image reading method is characterized in that after the processing in the synthesizing step for one predetermined range, the next predetermined range is read. 2. The image reading method according to claim 1, wherein in the first compression step and the second compression step, compression is performed by the same compression method. 3. In the first and second compression steps, a low-frequency component in the predetermined direction of the image signal and a low-frequency component and a high-frequency component in a direction perpendicular to the predetermined direction are held.
3. The image reading method according to claim 2, wherein the synthesizing step further holds a high-frequency component of the image signal in the predetermined direction. 4. An image reading method for reading an original using an imaging unit that converts an optical image of the original into an electric signal and outputs an image signal, comprising: forming an optical image of the original on the imaging unit. A first shift step of shifting a position in a predetermined direction by a first predetermined amount, and after the shift in the first shift step, reading the document divided into a plurality of predetermined ranges by the predetermined range using the imaging unit. A first imaging step of outputting an image signal, a compression step of compressing and holding the image signal in the predetermined range, and a second step of setting an image formation position of the optical image of the document on the imaging means in a predetermined direction. A second shift step of shifting by a predetermined amount; a second imaging step of reading an area that is the same as the predetermined range read in the first imaging step and outputting an image signal after the shift in the second shift step; The first pressure A combining step of compressing and combining the image signal compressed in the compression step and the image signal of the predetermined area output in the second imaging step, and outputting the image signal compressed and combined in the combining step An output step, wherein the first compression step to the output step are performed each time a predetermined range is read in the first imaging step, and in the first imaging step, one of the predetermined ranges is An image reading method for reading a next predetermined range after the processing of (1). 5. The compression step holds a low-frequency component of the image signal in the predetermined direction, and a low-frequency component and a high-frequency component of a direction perpendicular to the predetermined direction. A high frequency component of the signal in the predetermined direction;
5. The image reading method according to claim 4, wherein a low frequency component and a high frequency component in a direction perpendicular to the predetermined direction are held. 6. The image reading method according to claim 3, wherein the direction perpendicular to the predetermined direction is a sub-scanning direction. 7. The image reading method according to claim 1, wherein the document is divided in a direction perpendicular to the predetermined direction. 8. The image reading method according to claim 1, wherein the predetermined direction is a main scanning direction. 9. The method according to claim 1, wherein a difference between a first predetermined amount in the first shift step and a second predetermined amount in the second shift step is a half pixel. The image reading method according to any one of the above. 10. The image reading method according to claim 1, wherein the first predetermined amount is zero. 11. An image pickup means for converting an optical image of a document into an electric signal and outputting an image signal, and an image forming position of the optical image of the document on the image pickup means for a first predetermined amount or a predetermined amount in a predetermined direction. Shift means for shifting by a predetermined amount of 2, compression means for performing compression by a first compression method, synthesis means for performing compression and synthesis by a second compression method, and storage means for storing outputs of the compression means and the synthesis means. An output unit that outputs an output of the synthesizing unit stored in the storage unit; and a plurality of shifts using the imaging unit after a first predetermined amount shift and a second predetermined amount shift by the shift unit. A document divided into a predetermined range is read by a predetermined range, and the obtained image signals are compressed by the compression means and stored in the storage means, and the compressed image signals stored in the storage means are combined by the synthesis means. And control means for performing control so that the image signals are compressed and synthesized by the storage means and stored in the storage means. The control means performs reading of the next predetermined range after synthesizing image signals of one predetermined range by the synthesis means. An image reading apparatus characterized in that the control is performed in such a manner. 12. An image pickup means for converting an optical image of a document into an electric signal and outputting an image signal, and an image forming position of the optical image of the document on the image pickup means in a predetermined direction by a first predetermined amount or a predetermined amount. Shift means for shifting by a predetermined amount of 2, compression means for performing compression by a first compression method, synthesis means for performing compression and synthesis by a second compression method, and storage means for storing outputs of the compression means and the synthesis means. Output means for outputting an output of the synthesizing means stored in the storage means; and after shifting by a first predetermined amount by the shift means, a document divided into a plurality of predetermined ranges using the imaging means One predetermined range is read, the obtained image signal is compressed by the compression unit and stored in the storage unit, and after the shift of the second predetermined amount by the shift unit, read using the imaging unit before the shift. Control for reading the same predetermined range as the predetermined range, controlling the obtained image signal and the compressed image signal stored in the storage means to be compression-synthesized by the synthesis means and stored in the storage means. An image reading device, comprising: a control unit configured to perform a read operation in a next predetermined range after the image signal in one predetermined range is synthesized by the synthesis unit. 13. The compression unit outputs a low-frequency component in the predetermined direction of the image signal, and a low-frequency component and a high-frequency component in a direction perpendicular to the predetermined direction, and the synthesizing unit further outputs the image signal. The image reading apparatus according to claim 11, wherein a high-frequency component of the signal in the predetermined direction is output. 14. The image reading apparatus according to claim 13, wherein the direction perpendicular to the predetermined direction is a sub-scanning direction. 15. The image reading apparatus according to claim 11, wherein the document is divided in a direction perpendicular to the predetermined direction. 16. The image reading apparatus according to claim 11, wherein the predetermined direction is a main scanning direction. 17. The image reading apparatus according to claim 11, wherein a difference between the first predetermined amount and the second predetermined amount is a half pixel. 18. The image reading apparatus according to claim 11, wherein the first predetermined amount is zero. 19. A storage medium storing a program code for realizing the image reading method according to claim 1. Description: A program for realizing the image reading method according to any one of claims 1 to 10.