JP2003274115A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader which quickly reads a black-andwhite image without degrading the quality of color images and black-and-white images. <P>SOLUTION: The image reader is provided with a read means which reads an image of a document by using a 4-line CCD sensor 16 having three color line sensors and one black-and-white line sensor and a CPU 31 which controls the operation of the entire image reader including the read means. The CPU 31 is provided with a read color mode selection function for selecting one of a color mode to be applied to read a color image and a black-and-white mode to be applied to a black-and-white image as an image read color mode of the read means and an exposure period varying function for changing the exposure period of the black-and-white line sensor in accordance with the read color mode selected by the read color mode selection function. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for optically reading an image on a document.

[0002]

2. Description of the Related Art In recent years, as an image reading device used in a copying machine, a scanner device, or the like, a device capable of reading a color image has become widespread. In this type of image reading device,
The three primary colors of light: R (red), G (green), B
CCD with 3 lines corresponding to each color component of (blue)
It is known to use a (Charge Coupled Device) sensor to read both a color image and a monochrome image.

Generally, when an image of an original is read by an image reading apparatus, high-quality reading quality is required for a color image, whereas high-speed reading is often required for a monochrome image. However, when the image of the original is read using the CCD sensor of the three-line configuration as described above, black-and-white image data is generated from the output signal of each color component obtained from the CCD sensor, so that the image of the original to be read is read. Even if it is a black and white image, the reading speed will be the same as when reading a color image. Therefore, it is not possible to sufficiently meet the demand for reading a monochrome image at high speed.

Therefore, in recent years, in addition to the three color line sensors corresponding to the respective RGB color components, a 4-line CCD sensor provided with a single black-and-white line sensor is used to read a black-and-white image at high speed. The technology to make it is proposed. As an example, Japanese Patent Laid-Open No. 2001-
In Japanese Laid-Open Patent Publication No. 144900, the image sensor having the above-mentioned four-line structure is adopted, the number of pixels of the monochrome line sensor is set to be twice the number of pixels of the color line sensor, and the exposure cycle of the monochrome line sensor is set to the exposure cycle of the color line sensor. There is proposed a technique for reading a black and white image at a high resolution and at a high speed by setting it to 1/2.

[0005]

However, in the technique described in the above publication, the exposure cycle of the black and white line sensor is set to 1/2 of the exposure cycle of the color line sensor, so that the exposure cycle of the color line sensor is almost halfway between the exposure cycles. The signal charge of the black-and-white line sensor is vertically transferred in the section. For this reason, unnecessary noise from the black-and-white line sensor side may wrap around in the output signal from the color line sensor, which may deteriorate the reading quality of the color image.

Further, in order to read both a black-and-white image and a color image at high speed by using a CCD sensor having a 4-line structure,
As shown in FIG. 8, shift pulses (pulses for vertical transfer) BW-SH for reading charges corresponding to the black and white line sensor
, And the charge read shift pulse (vertical transfer pulse) CL-SH corresponding to the color line sensor may be output at individual timings. In such a case, the exposure cycle Ta and the color line sensor of the monochrome line sensor The exposure cycle Tb of is not synchronized. Therefore, the noise due to vertical transfer on the color line sensor side wraps around in the output signal BW-OUT from the black and white line sensor, and the noise due to vertical transfer on the black and white line sensor side appears in the output signal CL-OUT from the color line sensor. There is a risk that the quality of reading the black and white image and the quality of reading the color image are both reduced by going around. In the timing chart of FIG. 8, the transfer clock BW-CLK frequency F1 corresponding to the monochrome line sensor and the transfer clock BW-CLK corresponding to the color line sensor are used.
The CL-CLK frequency F2 is the same.

The present invention has been made to solve the above problems, and an object of the present invention is to read a monochrome image at high speed without deteriorating the reading quality of a color image or a monochrome image. An object is to provide an image reading device that can do this.

[0008]

An image reading apparatus according to the present invention includes a reading unit for picking up an image of an original using an image pickup unit having a color line sensor and a black and white line sensor, and an image reading unit for reading the image. As a reading color mode, a reading color mode selecting unit that selects either one of a color mode applied when reading a color image and a monochrome mode applied when reading a monochrome image, and the reading color mode selecting unit The exposure cycle changing means for changing the exposure cycle of the black-and-white line sensor according to the read color mode selected by.

In the image reading apparatus having the above structure, the exposure cycle changing means changes the exposure cycle of the black-and-white line sensor according to the read color mode (black and white mode, color mode) selected by the read color mode selecting means. When the monochrome mode is selected, the vertical transfer of the color line sensor is executed during the same period as the vertical transfer period of the monochrome line sensor.
When the color mode is selected, the vertical transfer of the color line sensor can be executed in synchronization with the vertical transfer period of the monochrome line sensor.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration example of an image reading apparatus according to an embodiment of the present invention. The illustrated image reading apparatus 1 includes an apparatus main body 2 having a built-in reading unit, and an original pressing portion 3 supported on the apparatus main body 2 so as to be openable and closable by a hinge mechanism or the like. A first document table (platen glass) 4 and a second document table 5 are juxtaposed on the upper surface of the apparatus main body 2. These first and second manuscript tables 4,
5 is made of glass (transparent glass or the like) having optical transparency.

The document pressing section 3 is opened and closed by a user when pressing a document placed on the first document table 4 from above. The document pressing section 3 is provided with a document setting section 6, a document discharging section 7, and a document conveying section 8. The document setting section 6 is a part on which a document (a bundle of documents) to be read according to a second reading method (described later) is set. The document discharge section 7 is a part for discharging a document read by the second reading method. The document setting unit 6 and the document discharging unit 7 are arranged in a vertical positional relationship in the document pressing unit 3.

The original conveying section 8 conveys the originals set in the original setting section 6 one by one along the conveying path R, and after moving the conveyed originals on the second original table 5, Finally, the document is discharged toward the document discharge unit 7. The document conveying section 8 is provided with a feeding roller 9, a first conveying roller 10, a registration roller 11, a second conveying roller 12, and a discharge roller 13.

The delivery roller 9 delivers the document set in the document setting section 6 onto the conveyance path R. The first transport roller 10 transports the document delivered by the delivery roller 9 along the transport path R to the registration roller 11 side. The registration roller 11 sends out the document conveyed by the first conveying roller 10 onto the second document table 5. The second transport roller 12 is
When the registration roller 11 is sent out, the second document table 5
The original that has passed above is received and conveyed to the discharge roller 13 side. The discharge roller 13 receives the document conveyed by the second conveyance roller 12 and receives the document from the document discharge section 7
To be discharged to.

The original conveying section 8 constituted by the plurality of rollers 9 to 13 conveys the original by the rotation of each roller, and at the time of the conveyance, the original is placed on the second original table 5. In addition to the basic transport function of moving, the reversing function of reversing the document surface for double-sided reading, and the alignment of reversing the document surface reversed by this reversing function and ejecting it to the document ejection unit 7 It has a function. However, since the inversion function and the matching function are not directly related to the gist of the present invention, detailed description thereof will be omitted.

An optical scanning system 14, an imaging lens 15 and a CCD sensor 16 are provided inside the apparatus body 2 as a reading means for optically reading an image of a document. Each of the optical scanning systems 14 has a sub-scanning direction Y (left-right direction in the drawing).
A full-rate carriage 17 and a half-rate carriage 18 that are movably supported are used. The full rate carriage 17 has a lamp 19 and a first mirror 2
0 is mounted, and the second mirror 21 and the third mirror 22 are mounted on the half rate carriage 18.

The full-rate carriage 17 and the half-rate carriage 18 move in the sub-scanning direction Y by using a common carriage moving motor as a drive source.
At this time, the half-rate carriage 18 moves with a movement amount (moving speed) that is half that of the full-rate carriage 17, so that even if the carriages 17, 18 move to any position in the sub-scanning direction Y, The optical path length from the document surface on the document table 4 to the light receiving surface of the CCD sensor 16 is always kept constant.

The lamp 19 serves as a light source for irradiating light (illumination light) toward a document to be read, and is composed of, for example, a xenon lamp that emits white light of three wavelengths. The light reflected on the original surface by the light irradiation from the lamp 19 is sequentially reflected by the first mirror 20, the second mirror 21, and the third mirror 22. The imaging lens 15 allows the light reflected by the third mirror 22 to CC at a predetermined reduction ratio.
An image is formed on the light receiving surface of the D sensor 16. CCD
The sensor 16 is an image sensor (image sensor) for optically reading an image of a document.

In the image reading apparatus 1 having the above structure, the first
When the image of the original document placed on the original platen 4 is read according to the first reading method, the optical scanning system 14 is moved from the preset home position (the left end in FIG. 1) to the first original platen 4. By moving in the sub-scanning direction Y along
An image of a document placed on the first document table 4 is optically read and scanned by the optical scanning system 14, the imaging lens 15 and the CCD sensor 16. This first reading method is
Also called "platen scan method" or "flat bed scan method".

When the image of the document set on the document setting section 6 is read according to the second reading method,
The optical scanning system 14 is stopped at a predetermined position in the sub-scanning direction Y (home position or in the vicinity thereof), and the originals are conveyed one by one from the original setting section 6 by the conveying operation of the original conveying section 8 to generate a second original. An image of a document fed onto the table 5 and moving on the second document table 5 at a constant speed is optically read and scanned by the optical scanning system 14, the imaging lens 15 and the CCD sensor 16. This second reading method is
It is also called a "CVT (Constant Velocity Transfer) method" or "original flow reading method". In this case, the position just above the first mirror 20 mounted on the full rate carriage 17 is the reading position of the original image.

FIG. 2 is a schematic diagram showing the configuration of an image reading sensor adopted in the embodiment of the present invention. As shown,
The CCD sensor 16 has a configuration including four line sensors (four-line configuration). That is, the CCD sensor 1
The black-and-white line sensor 23 and the three color line sensors 24, 25, and 26 are provided in the light receiving unit 6 of FIG. These four line sensors 23, 24, 25,
26 are arranged in parallel to each other along the main scanning direction (left and right direction in the drawing). The main scanning direction is a direction orthogonal to the sub scanning direction.

The black and white line sensor 23 is the main sensor in the black and white mode applied when reading a black and white image. The color line sensors 24, 25, 26 are main sensors in the color mode applied when reading a color image. That is, when the image of the original is read in the monochrome mode, the monochrome image data read by the monochrome line sensor 23 is adopted as the reading result,
When the image of the original is read in the color mode, the color image data read by the color line sensors 24, 25 and 26 is adopted as the reading result. However,
Whether the reading color mode is the black-and-white mode or the color mode, the image of the original is read by both the black-and-white line sensor 23 and the color line sensors 24, 25, and 26 at substantially the same time.

Three color line sensors 24, 25, 2
6 corresponds to each color component of R (red), G (green), and B (blue). Each of the black and white and color line sensors 23, 24, 25, and 26 is configured by arranging a plurality of pixels (photosensitive pixels) of a predetermined size in a straight line at a predetermined pitch. One pixel corresponds to one light receiving element (photodiode or the like).

The three line sensors 24, 25, 26 are
They have different color separation characteristics. That is, the line sensor (hereinafter, also referred to as R line sensor) 24 corresponding to the red component has a color filter (color separation filter) that transmits only the light of the red component on the pixel row, and a line corresponding to the green component. The sensor (hereinafter, also referred to as a G line sensor) 25 has a color filter that transmits only the green component light on the pixel row, and the line sensor (hereinafter, also referred to as the B line sensor) 26 corresponding to the blue component 26.
Has a color filter on the pixel column that transmits only the blue component light. On the other hand, the black-and-white line sensor 23 has a color filter that transmits only the green component light on the pixel row. That is, the monochrome line sensor 23 has the same color separation characteristic as the G line sensor 25.

The reason why the black and white line sensor 23 has the same color separation characteristics as the G line sensor 25 is as follows. First, when considering the black-and-white line sensor 23 alone, a configuration without a color filter may be considered, but in such a case, the sensor sensitivity of the black-and-white line sensor 23 becomes larger than that of the other three line sensors 24, 25, 26.
Therefore, with the white illumination light required for reading a color image, only the output of the black-and-white line sensor 23 may be saturated. In order to avoid this, if the amount of illumination light is reduced, the other three line sensors 24, 2
5 and 26, the amount of received light is insufficient, and RGB output SN (Signal-
to-Noise) deteriorates. Therefore, it is very difficult to design the sensor sensitivity of each line sensor 23, 24, 25, 26.

Further, in the reading of an image by the second reading method, if foreign matter such as dust adheres to the second platen 5, the foreign matter is continuously read and black streaks occur. Sometimes. In order to prevent the occurrence of such black stripes, the image of the original sent by the original conveying unit 8 onto the second original table 5 is read by the black-and-white line sensor 23 and the RGB line sensors 24, 25 and 26 almost at the same time. It is conceivable that the read image data is relatively compared with each other to perform the generation of black streaks and the correction for removing the black streaks. In such a case, if the sensor sensitivities of the line sensors to be compared with the read image data are different, the sensor outputs will differ even if the same image is read, making relative level comparison difficult.

On the other hand, when the black and white line sensor 23 is provided with a color filter that transmits light of the green component, the sensor sensitivity (sensor output characteristic) becomes equal to that of the G line sensor 25, so that the amount of illumination light is increased. It is possible to avoid saturation of the output of the black-and-white line sensor 23 without lowering. Further, as a measure for preventing the occurrence of black stripes, since relative level comparison can be performed using image data read by the line sensors 23 and 25 having the same color separation characteristics, it is possible to appropriately detect the occurrence of black stripes and perform correction processing. It becomes possible to do.

Further, when the color filter corresponding to the green component among the color filters corresponding to the RGB color components is adopted for the monochrome line sensor 23, the color corresponding to the other color components (red component, blue component) Compared with the filter, the spectral characteristic region is wider and a larger output signal can be obtained. Therefore, the image of the original can be read with a good SN ratio over almost the entire visible light region (about 400 to 700 nm). However, when the sensor sensitivity levels are properly adjusted, the black-and-white line sensor 23 is configured without a color filter or with a color filter corresponding to another color component (red component, blue component). It doesn't matter.

In the CCD sensor 16 having the 4-line structure, as shown in FIG. 3, each line sensor 23,
A charge transfer register (hereinafter, abbreviated as a transfer register) for reading and transferring the signal charges generated by photoelectric conversion at 24, 25, and 26 is provided. here,
When the number of transfer registers corresponding to the RGB line sensors 24, 25, and 26 is M, the number of transfer registers of the monochrome line sensor 23 is 2M. In other words, the monochrome line sensor 23 is the color line sensor 2
It has twice as many transfer registers as 4, 25 and 26.

Specifically, for the R line sensor 24, two transfer registers 27A and 27B are provided on one side (between the black and white line sensor 23) and for the G line sensor 25, the R line sensor. Two transfer registers 28A and 28B are provided on the side opposite to 24 through the B line sensor 26.
Two transfer registers 29A and 29B are attached to the B line sensor 26 on the side opposite to the G line sensor 25 via the transfer registers 28A and 28B. Further, the black and white line sensor 23 is provided with four transfer registers 30A, 30B, 30C and 30D on one side thereof (on the side opposite to the R line sensor 24).
In this case, the color line sensors 24, 25, and 26 are arranged adjacent to each other at intervals of one line, and the black and white line sensor 23 and the G line sensor 25 are arranged at intervals of 12 lines.

As a result, in the R line sensor 24, odd-numbered (ODD) pixels and even-numbered (EVEN) pixels are included.
Pixels can be distributed to the two transfer registers 27A and 27B and output in parallel. Similarly, in the G line sensor 25, the odd-numbered pixels and the even-numbered pixels can be distributed to the two transfer registers 28A and 28B and output in parallel, and the B-line sensor 26 can also output the odd-numbered pixels. And even-numbered pixels can be distributed to the two transfer registers 29A and 29B and output in parallel. On the other hand, in the monochrome line sensor 23, odd-numbered pixels are distributed to two transfer registers (for example, transfer registers 30A and 30C), while even-numbered pixels are distributed to the other two transfer registers (for example, transfer register 30).
B, 30D) and output in parallel.

At this time, four transfer registers 30A, 30B, 30C, 30D attached to the black and white line sensor 23
About 10 kinds of shift pulses SH for respectively shifting (reading) the signal charges are required. The transfer registers 27A, 27B, 28A, 28B, 29A, 2 attached to the color line sensors 24, 25, 26 are also provided.
About 10 kinds of shift pulses SH for shifting the signal charges to 9B are required.

Further, each transfer register 27A, 27
B, 28A, 28B, 29A, 29B, 30A, 30
A transfer clock for sequentially transferring the signal charges read to B, 30C, and 30D in the line direction is also required. According to this transfer clock, the transfer register 3
Black-and-white output signals BW1, BW2, BW3, BW4 are output in parallel from 0A, 30B, 30C, 30D via an amplifier. The transfer registers 27A and 27B output the red component output signals R1 and R2 in parallel through the amplifier, and the transfer registers 28A and 28B output the green component output signals G1 and G2 in parallel through the amplifier. Then, the transfer registers 29A and 28B output the blue component output signals B1 and B2 in parallel through the amplifiers.

From the above, assuming that the number of pixels of the R line sensor 24 is N, the two transfer registers 27A and 27B attached thereto are N / 2 per line, respectively.
The signal charge of each pixel will be transferred. This point is
The same applies to the G line sensor 25 and the B line sensor 26. On the other hand, assuming that the number of pixels of the black-and-white line sensor 23 is the same as the number of pixels of the R line sensor 24, that is, four transfer registers 30A, 30B, 30C, 3 attached thereto.
OD will transfer the signal charges of N / 4 pixels per line. As a specific example, the number of pixels of each line sensor 23, 24, 25, 26 is 1
If the line has 7600 pixels, the transfer registers 27A, 27B, 28A, 28B corresponding to the respective RGB color components are
29A and 29B transfer signal charges of 3800 pixels per line, and transfer registers 30A, 30B, 30C and 30D corresponding to black and white transfer signal charges of 1900 pixels per line, respectively.

By attaching a plurality of transfer registers to one line sensor in this manner, reading of the original image can be performed at a higher speed than in the case where one transfer register is attached to one line sensor. it can. Also,
By setting the number of transfer registers of the black and white line sensor 23 to twice the number of transfer registers of the RGB line sensors 23, 24, 25, the number of stages when the signal charges obtained from the black and white line sensor 23 are transferred by the transfer registers. Is less. Therefore, the efficiency of transfer of the signal charges obtained from the black-and-white line sensor 23 can be improved, and the black-and-white image can be read at higher speed.

FIG. 4 is a block diagram showing the functional arrangement of the image reading apparatus according to the embodiment of the present invention. In FIG.
A CPU (Central Processing Unit) 31 controls the processing operation of the entire image reading apparatus 1 according to a control program given in advance. The CPU 31 has a reading color mode selection function, an exposure cycle variable function, and a resolution variable function as main processing functions. Details of each function will be described later in detail. A plurality of sensors (not shown) are connected to the CPU 31, and a detection signal necessary for controlling the operation of the entire image reading apparatus 1 is given from each sensor.

Among the above-mentioned plural sensors, for example, an open / close detection sensor for detecting the open / closed state of the original pressing portion 3, an original size detection sensor for detecting the original size of the original to be read, and an original set on the original setting portion 6. A first document presence / absence sensor for detecting whether or not a document is present (also usable as a document size detection sensor), and a second document presence / absence sensor for detecting whether or not a document is placed on the first document table 4. (Can also be used as a document size detection sensor), carriage 1 in the sub-scanning direction
A carriage position detecting sensor for detecting the positions of 7 and 18,
Various sensors are included, such as a jam sensor that detects a document jam in the document transport unit 8.

The UI (User Interface) 32 is
It is configured by an operation panel (control panel) including an input unit such as buttons and switches and a display unit, and operation information for operating the image reading apparatus 1, such as reading start, reading magnification, reading range, and document size. It is used when the user specifies the document color, document color discrimination, and the like. The designation of the document color is a designation of whether the image of the document to be read is black and white or color, and the designation of the document color discrimination is a designation of whether or not to perform the document color discrimination processing. .

The crystal oscillator 33 generates a reference clock serving as a reference when driving the CCD sensor 16.
This reference clock is given to a timing generator for black and white (hereinafter abbreviated as TG) 34 and a timing generator for color (hereinafter abbreviated as TG) 35, respectively. The TGs 34 and 35 generate a drive signal for driving the CCD sensor 16 using the reference clock given from the crystal oscillator 33.

The black-and-white line sensor 23 is included in this drive signal.
A timing signal for reading out the signal charge accumulated in the signal line, a timing signal for reading out the signal charge accumulated in each of the RGB line sensors 24, 25, 26, and an output signal obtained by reading out the signal charge are selected. A switching signal for resetting, a reset signal for resetting the charge after output, and the like are included. Also, TG
The timing signals generated by 34 and 35 include the above-described shift pulse SH and transfer clock, respectively.

The CPU 32 is provided in the two TGs 34 and 35.
A control command is individually given from the TGs 34 and 35, and the TGs 34 and 35 generate drive signals in accordance with the control commands. As a result, the image reading operation by the black-and-white line sensor 23 (a series of operations including signal charge accumulation, shift, transfer, output, etc.) and the color line sensors 24, 25, 26 are performed.
The image reading operation by the CPU 31 is independently controlled by the CPU 31.

From the CCD sensor 16, the black and white output signals BW1, BW2, BW3, BW4 and the color (R
GB) output signals R1, R2, G1, G2, B1, B2
Are output in separate systems. Of these, the black and white output signals BW1, BW2, BW3B and BW4 are analog-processed by the analog processing circuits 36-1 and 36-2, and then A /
D-converter (analog-to-digital Converter) 37-1, 3
At 7-2, an analog signal is converted into a digital signal.
Incidentally, the analog processing circuits 36-1, 36-2 and A
In the D / D converters 37-1 and 37-2, the output signals W1 and BW3 output from the even-numbered pixels of the pixel row of the monochrome line sensor 23 and the output signals from the odd-numbered pixels are output. Output signal BW2
The BW 4 is configured to be processed separately.

On the other hand, the output signals R1 and R2 of the red component are analog-processed by the analog processing circuit 38, and then A / D.
The converter 39 converts the analog signal into a digital signal. Similarly, the output signals G1 and G2 of the green component are analog-processed by the analog processing circuit 40 and then converted from an analog signal to a digital signal by the A / D converter 41, and the output signals B1 and B2 of the blue component are analog-processed. Circuit 42
After being analog-processed by, the A / D converter 43 converts the analog signal into a digital signal. Each of the analog processing circuits 36, 38, 40 and 42 includes a sample hold circuit, a gain control circuit, an offset control circuit and the like.

The black-and-white and color image signals thus digitized are supplied to the image processing circuit 44. The image processing circuit 44 performs various image processing on the black and white and color image signals input thereto, and outputs BW which constitutes a black and white image signal and R output, G output and B which constitute a color image signal. Produces output. The image processing performed by the image processing circuit 44 includes shading correction for correcting variations in the output signal due to uneven sensitivity of the CCD sensor 16 and uneven illumination of the illumination system, and correction of the reading position corresponding to the line sensor interval of the CCD sensor 16. In addition to (gap correction), γ correction using a look-up table, etc., it is determined whether the image of the document to be read is black and white or color (in other words, the document to be read is a black and white document. Whether it is a color document or a color document), so-called document color discrimination (ACS; Auto Color Selection)
It is possible to detect the occurrence of black streaks caused by foreign matter such as dust adhering to the second platen 5 when processing or reading an image of a document by the second reading method (CVT method), and Processing for correcting (removing) streaks and the like are included.

The reading color mode selection function, the exposure cycle changing function and the resolution changing function of the CPU 31 will be described in order. First, the reading color mode selection function is a function of automatically selecting the image reading color mode in accordance with preset mode selection conditions. The image reading color mode includes a color mode applied when reading a color image and a monochrome mode applied when reading a monochrome image. The color mode is a mode for reading an image of a document as a color image, and the monochrome mode is a mode for reading an image of a document as a monochrome image.

Of these two reading color modes, the CPU
The reference numeral 31 selects one of the reading color modes (black and white mode or color mode) according to the mode selection condition input via the UI 32. Specifically, when the image of the document is designated as black and white by the user's input operation of the UI 32 or the like, the monochrome mode is selected, and when the image is designated as color, the color mode is selected. Further, when it is necessary to determine whether the image of the document to be read is monochrome or color by the document color determination process, that is, when the user specifies execution of the document color determination process through the UI 32, Since the image of the original needs to be read on the premise of a color image, the CPU 31 selects the color mode and executes the reading of the original image, and the image processing circuit 44 determines whether the image of the original is a color image or a monochrome image. Determine.

The exposure cycle variable function is used for the black and white line sensor 2
3 of the exposure cycle and the exposure cycle of the color line sensors 24, 25, 26, the color line sensors 24, 25, 26
Black-and-white line sensor 2 with the exposure cycle of as a reference (fixed)
3 is a function of automatically changing the exposure cycle according to the reading color mode. The read color mode in this case refers to the read color mode (black and white mode or color mode) selected by the read color mode selection function. The CPU 31 variably controls the exposure cycle of the black-and-white line sensor 23 using the exposure cycle changing function so as to switch between the black-and-white mode and the color mode.

Specifically, when the monochrome mode is selected by the read color mode selection function, the exposure cycle of the monochrome line sensor 23 is set to the first cycle. When the color mode is selected by the reading color mode selection function, the exposure cycle of the monochrome line sensor 23 is set to the second cycle which is longer than the first cycle. In the exposure cycle variable function of the CPU 31, the first cycle becomes half of the second cycle, and the second cycle
The exposure cycle changing condition is set in advance so that the cycle becomes the same as the exposure cycle of the color line sensors 24, 25, 26.

Incidentally, the exposure cycle of the black-and-white line sensor 23 is determined by the output timing of the charge read (vertical transfer) shift pulse SH corresponding to the black-and-white line sensor 23, and the color line sensors 24, 25, 2 are selected.
The exposure cycle of 6 is the color line sensor 24, 25,
It is determined by the output timing of the charge read (vertical transfer) shift pulse SH corresponding to 26. From this, the CPU 31 variably controls the exposure cycle of the black-and-white line sensor 23 by changing the output timing (output cycle) of the shift pulse SH for reading charges corresponding to the black-and-white line sensor 23.

The variable resolution function is provided by the black and white line sensor 23.
This is a function of automatically switching the reading resolution in the sub-scanning direction (hereinafter abbreviated as the sub-scanning resolution) and the reading resolutions in the sub-scanning direction of the color line sensors 24, 25, 26 according to the reading color mode. The read color mode in this case also refers to the read color mode (monochrome mode or color mode) selected by the read color mode selection function. The CPU 31 variably controls the sub-scanning resolution of the black-and-white line sensor 23 and the sub-scanning resolutions of the color line sensors 24, 25 and 26 by using this resolution changing function so as to switch between the black-and-white mode and the color mode.

Specifically, when the monochrome mode is selected by the reading color mode selection function, the sub-scanning resolution of the monochrome line sensor 23 is set to be higher than the sub-scanning resolutions of the color line sensors 24, 25 and 26. Also, if you select a color mode by the reading color mode selection function,
The sub-scanning resolution of the monochrome line sensor 23 and the sub-scanning resolutions of the color line sensors 24, 25, 26 are set to be the same. In the variable resolution function of the CPU 31,
When the monochrome mode is selected, the sub-scanning resolution of the monochrome line sensor 23 becomes twice the sub-scanning resolution of the color line sensors 24, 25, 26, and when the color mode is selected, the sub-scanning resolution of the monochrome line sensor 23. The resolution changing conditions are set in advance so that the black and white line sensor and the color line sensor are the same.

Incidentally, the sub-scanning resolution is the physical scanning speed (hereinafter referred to as the reading scanning speed) when reading and scanning the image of the original in the sub-scanning direction by the optical scanning system 14 and the signal charge to the transfer register. It depends on the read timing of. The interval of the signal charge read timing to the transfer register corresponds to one line cycle. Also,
Since the signal charge is accumulated in each pixel of the line sensor within this one line period, the one line period corresponds to the exposure period of the line sensor. On the other hand, the reading scanning speed is set as follows when reading an image of a document placed on the first document table 4.
That is, in the case of the first reading method (platen scan method), it is determined by the moving speed of the carriages 17 and 18 of the optical scanning system 14, and when reading the image of the original set in the original setting section 6, that is, in the second reading. In the case of the method (CVT method), it is determined by the moving speed of the original moving on the second original table 5 by driving the original conveying unit 8.

Therefore, in the case of the first reading method, the CPU 31 moves the carriage, which is the drive source of the optical scanning system 14, together with the timing of reading the signal charges to the transfer register (exposure cycle of the line sensor). By changing the number of rotations of the motor, each line sensor 23, 2
In the case of the second reading method, the sub-scanning resolutions of 4, 25, and 26 are variably controlled, and in the case of the second reading method, the driving source of the document conveying unit 8 is matched with the reading timing of the signal charges to the transfer register (exposure cycle of the line sensor). By changing the number of rotations of the original feeding motor, the line sensors 23, 24,
The sub-scanning resolutions of 25 and 26 are variably controlled.

Next, the operation of the image reading apparatus 1 based on the control processing of the CPU 31 will be described. First, when the user places an original on the first original table 4 and presses the reading start button of the UI 32, the CPU 31 receives this and selects the first reading method as the reading method of the original image. The control command based on is given to various driver circuits (for example, driver circuits for lighting control, carriage movement control, etc.). When the user sets a document on the document setting section 6 and presses the reading start button of the UI 32, the CP is received in response to this.
The U31 selects the second reading method as the reading method of the original image and gives a control command based on the second reading method to various driver circuits (driver circuits for original document conveyance control, illumination control, carriage movement control, etc.).

Further, the CPU 31 selects the reading color mode (black and white mode, color mode) based on the input information from the UI 32 in addition to the selection of the reading method. That is, when the reading start button of the UI 32 is pressed, if the original document color is designated in black and white by the user's input operation prior to that, the monochrome mode is selected, and the original color is designated in color. When the execution of the document color discrimination processing is designated, the color mode is selected. When the monochrome mode is selected, the monochrome sensor 23 is used as a main sensor and the color line sensors 24, 25 and 26 are used as sub-sensors to control the driving of the CCD sensor 16. When the color mode is selected, the color line sensor 24 is used. , 2
The driving of the CCD sensor 16 is controlled by using 5, 26 as main sensors and the black and white line sensor 23 as sub sensors. Further, when the monochrome mode is selected, the sensor output signals from the color line sensors 24, 25, and 26, which are sub-sensors, are used as the sensor output signals for detecting and correcting the occurrence of black stripes, and when the color mode is selected, the black-and-white line which is a sub-sensor is used. The sensor output signal from the sensor 23 is used as a sensor output signal for detecting and correcting the occurrence of black stripes.

First, when the CPU 31 selects the monochrome mode, as shown in FIG. 5, the shift pulse BW-SH1 for reading charges corresponding to the monochrome line sensor 23 is output from the TG 34 at a predetermined line cycle T1. , Transfer clock BW for charge transfer corresponding to the black and white line sensor 23
-CLK1 is output from TG34 at frequency F1. Also,
A shift pulse CL-SH for reading charges corresponding to the color line sensors 24, 25, 26 is output from the TG 35 at a reference line period T2, and a charge transfer pulse corresponding to the color line sensors 24, 25, 26 is transferred. The transfer clock CL-CLK is output from the TG 35 at the frequency F2.
Further, as the above-mentioned reading method, when the first reading method is selected, the reading scanning speed of the image due to the movement of the carriages 17 and 18, and when the second reading method is selected, the reading scanning of the image due to the movement of the document is performed. The speeds are each set to the first speed.

In this black and white mode, the exposure cycle of the black and white line sensor 23 is set to the first cycle "T1" in accordance with the output timing of the shift pulse BW-SH1, and
The exposure cycle of the color line sensors 24, 25, 26 is set to the reference cycle “T
Set to 2 ". In this case, the relationship between the two is T2 = T1 ×
2, that is, the exposure cycle T1 of the monochrome line sensor 23 is 1/2 of the exposure cycle T2 of the color line sensors 24, 25, and 26. The exposure cycle T1 of the black and white line sensor 23 and the exposure cycle T2 of the color line sensors 24, 25, 26 are synchronized with each other. On the other hand, the black and white line sensor 2
3 corresponding to transfer registers 30A, 30B, 30C, 3
The charge transfer frequency 0D (frequency of the transfer clock BW-CLK1) F1 corresponds to the transfer registers 27A, 27B, 28A, 28B, 2 corresponding to the color line sensors 24, 25, 26.
It has the same relationship as the charge transfer frequency (frequency of transfer clock CL-CLK) F2 of 9A and 29B.

Therefore, when the CPU 31 selects the monochrome mode, in the monochrome line sensor 23, the signal charge accumulated in each pixel within the exposure cycle T1 is transferred to the four transfer registers according to the shift pulse BW-SH1. 30A,
After being read by 30B, 30C, 30D, they are sequentially transferred in the line direction in accordance with the transfer clock BW-CLK1 by the respective transfer registers 30A, 30B, 30C, 30D.
Therefore, assuming that the number of pixels of the black line sensor 23 is N, each of the transfer registers 30A and 30 within the exposure cycle T1.
Signal charges of 1 / 4N each are transferred by B, 30C, and 30D. Therefore, the signal charges of N pixels in total are output within the exposure cycle T1.

In the color line sensor 24 corresponding to the red component, the signal charge accumulated in each pixel within the exposure cycle T2 is read out to the two transfer registers 27A and 27B according to the shift pulse CL-SH. After being
Transfer clock CL-C in each transfer register 27A, 27B
It is sequentially transferred in the line direction according to LK. Therefore, if the number of pixels of the color line sensor 24 is N,
Within the exposure cycle T2, ½N signal charges are transferred by the transfer registers 27A and 27B. Therefore, the signal charges of N pixels in total are output in the exposure cycle T2. The same applies to the color line sensor 25 corresponding to the green component and the color line sensor 26 corresponding to the blue component.

From the above, when the CPU 31 selects the monochrome mode, the two-line cycle (T1 × 2) of the monochrome line sensor 23 is 1 of the color line sensors 24, 25, 26.
Since the line cycle (T2) is set, the color line sensor 2
The black and white line sensor 23 outputs the signal charges for two lines while the signal charges for one line are output for 4, 25 and 26.

When the level of the output signal BW-OUT1 of the monochrome line sensor 23 when the monochrome mode is selected is "V1" and the level of the output signal CL-OUT of the color line sensor 25 corresponding to the green component is "V2". , The relationship of the magnitudes of these output levels (the relationship of high and low) is as follows:
From the difference, V1≅V2 / 2, that is, the output level V1 of the monochrome line sensor 23 becomes almost half of the output level V2 of the color line sensor 25.

The sub-scanning resolution when the monochrome mode is selected is such that the line period T1 of the monochrome line sensor 23 is 1/2 of the line period T2 of the color line sensors 24, 25, 26.
Therefore, the sub-scanning resolution of the monochrome line sensor 23 is twice the sub-scanning resolution of the color line sensors 24, 25, 26. Therefore, when the monochrome mode is selected, the sub-scanning resolution of the monochrome line sensor 23 is set to 600 dp.
If i, the color line sensors 24, 25, 26
Sub-scanning resolution is 300 dpi.

In this way, when the CPU 31 selects the black and white mode, the vertical transfer of the black and white line sensor 23 (reading of signal charges to the transfer register) is performed at approximately the middle of the exposure cycle T2 of the color line sensors 24, 25 and 26. ) Is performed, the vertical transfer of the main black-and-white line sensor 23 is performed in the same period as the vertical transfer of the color lines 24, 25, 26, and the exposure cycle T1 of the black-and-white line sensor 23 is
The vertical transfer of the color line sensors 24, 25, 26 is not performed inside. Therefore, the black and white line sensor 2
Noise due to vertical transfer on the side of the color line sensors 24, 25 and 26 does not wrap around to the black and white sensor output signal mainly composed of 3. Therefore, when the monochrome mode is selected, the monochrome image can be read with high quality using the monochrome line sensor 23.

Further, four transfer registers 30A, 30B, 30C and 30D are attached to the black and white line sensor 23,
By transferring the signal charges read out from the respective pixels in parallel, a black-and-white image can be read at high speed. Further, the resolution variable function of the CPU 31 allows a black-and-white image to be read with high resolution. However, since the output signal of the line sensor 25 corresponding to the green component having the same color separation characteristic as the black and white line sensor 23 is used in the detection and correction processing of the black streak, the output signal from this line sensor 25 is used. It is desirable to consider the sneak of noise from the black and white line sensor 23 side.

On the other hand, when the CPU 31 selects the color mode, as shown in FIG. 6, the charge read shift pulse BW-SH2 corresponding to the black and white line sensor 23 is output from the TG 34 at a predetermined line cycle T3. , Transfer clock for charge transfer corresponding to the black and white line sensor 23
BW-CLK2 is output from the TG 34 at the frequency F1. Further, the shift pulse CL-SH for reading charges corresponding to the color line sensors 24, 25, 26 is output from the TG 35 at the reference line period T2, and the charge transfer corresponding to the color line sensors 24, 25, 26 is performed. The transfer clock CL-CLK for is output from the TG 35 at the frequency F2.

Further, as the above-mentioned reading method, when the first reading method is selected, the reading scanning speed of the image due to the movement of the carriages 17 and 18, and when the second reading method is selected, the image due to the movement of the document is selected. The scanning speeds for reading are set to second speeds slower than those in the monochrome mode (first speed). Specifically, the second speed is set so as to be half the speed of the first speed.

In this color mode, the exposure cycle of the black-and-white line sensor 23 is set to the second cycle "T3" in accordance with the output timing of the shift pulse BW-SH2, and the color line sensors 24, 25, 26 are exposed. The exposure cycle is set to "T2" according to the output timing of the shift pulse CL-SH. In this case, the relationship between them is T3 = T2, that is, the exposure cycle T3 of the monochrome line sensor 23 is the same as the exposure cycle T2 of the color line sensors 24, 25, 26. The exposure cycle T3 of the black and white line sensor 23 and the exposure cycle T2 of the color line sensors 24, 25, 26 are synchronized with each other. Further, the exposure cycle (second cycle) T3 of the monochrome line sensor 23 in the color mode is the exposure cycle (second cycle) of the monochrome line sensor 23 in the monochrome mode described above.
Longer than T1 and the relationship between them is T1 = T3 / 2, that is, the exposure cycle of the monochrome line sensor 23 in the monochrome mode.
The relationship of T1 is 1/2 of the exposure cycle T3 of the monochrome line sensor 23 in the color mode.

In this case, the CPU 31 changes the exposure cycle of the monochrome line sensor 23 in the monochrome mode and the color mode by changing the number of transfer clocks in one line cycle corresponding to the monochrome line sensor 23. . Specifically, the number of transfer clocks in one line period corresponding to the black and white line sensor 23 is changed so as to be twice as large in the color mode as in the black and white mode. Exposure cycle (first
Change the relationship between the cycle (1) and the second cycle) such that T1 = T3 / 2.

On the other hand, the charge transfer frequency F1 of the transfer registers 30A, 30B, 30C and 30D corresponding to the black and white line sensor 23 is the transfer registers 27A, 27B, 28A and 28B corresponding to the color line sensors 24, 25 and 26.
It has the same relationship as the charge transfer frequency F2 of 29A and 29B. In addition, each line sensor 2 in the color mode
The charge transfer frequencies F1, F2 of 3, 24, 25, 26 are the same as those of the line sensors 23, 24, 2 in the monochrome mode described above.
It is the same as the charge transfer frequencies F1 and F2 of 5 and 26.

From this, when the CPU 31 selects the color mode, in the black-and-white line sensor 23, the signal charge accumulated in each pixel within the exposure period T3 is transferred to the four transfer registers according to the shift pulse BW-SH2. Thirty
After being read by A, 30B, 30C and 30D, they are sequentially transferred in the line direction in accordance with the transfer clock BW-CLK2 by the respective transfer registers 30A, 30B, 30C and 30D. At this time, since the charge transfer frequency F1 in the color mode is set to be the same as that in the monochrome mode, the signal charges read in the transfer registers 30A, 30B, 30C, 30D are stored in the middle portion of the exposure cycle T3. Will be all transferred. Therefore, in the latter half of the exposure cycle T3, a black level signal whose signal charge is substantially zero is output due to idle transfer in the transfer register. Further, assuming that the number of pixels of the black and white line sensor 23 is N, within the exposure cycle T3, each transfer register 30A, 30B, 30C, 30D has 1 / 4N.
Signal charges (excluding dummy signals) are transferred individually. Therefore, in the exposure cycle T3, the signal charges of N pixels in total are output.

In the color line sensor 24 corresponding to the red component, the signal charge accumulated in each pixel within the exposure cycle T2 follows the shift pulse CL-SH, as in the case of the black and white mode described above. After being read by the two transfer registers 27A and 27B, they are sequentially transferred in the line direction in accordance with the transfer clock CL-CLK by the respective transfer registers 27A and 27B. Therefore, assuming that the number of pixels of the color line sensor 24 is N, in the exposure cycle T2, ½N signal charges are transferred by the transfer registers 27A and 27B. Therefore, in the exposure cycle T2, the signal charges of the N pixels in total (black and white line sensor 2
The same number of signal charges as in the case of 3 will be output.
This point is due to the color line sensor 2 corresponding to the green component.
The same applies to the color line sensor 26 corresponding to 5 or blue component.

From the above, when the CPU 31 selects the color mode, the one-line cycle (T3) of the black and white line sensor 23 becomes the one-line cycle (T2) of the color line sensors 24, 25, 26. Sensor 24,2
During the period of outputting the signal charge for one line at 5, 26,
The black and white line sensor 23 also outputs the signal charge for one line.

Further, when the color mode is selected, the level of the output signal BW-OUT2 of the monochrome line sensor 23 is set to "V3",
When the level of the output signal CL-OUT of the color line sensor 25 corresponding to the green component is "V2", the magnitude relationship (high-low relationship) of these output levels is the above-mentioned exposure cycle T3, T.
Due to the commonality of 2, the relationship of V3≈V2, that is, the output level V3 of the monochrome line sensor 23 becomes substantially the same level as the output level V2 of the color line sensor 25.

The output level V3 of the black and white line sensor 23 when the color mode is selected is higher than the output level V1 of the black and white line sensor 23 when the black and white mode is selected, and in the relative comparison between the two, V3≈V1 × 2. Become involved. Further, the sub-scanning resolution when the color mode is selected is the same as the sub-scanning resolution of the monochrome line sensor 23 because the exposure cycle T3 of the monochrome line sensor 23 is the same as the exposure cycle T2 of the color line sensors 24, 25 and 26. The sub-scanning resolutions of the color line sensors 24, 25, 26 are also the same.

Further, since the reading scanning speed is 1/2 of that in the monochrome mode, the sub-scanning resolution of the color line sensors 24, 25, 26 is twice as high as that in the monochrome mode. Therefore, when the color mode is selected, the sub-scanning resolution of the monochrome line sensor 23 is set to 600d.
In the case of pi, the color line sensors 24, 25, 2
The sub-scanning resolution of 6 is also 600 dpi.

In this way, when the CPU 31 selects the color mode, the main color line sensor 24,
Since the vertical transfer of 25 and 26 is performed in the same period as the vertical transfer of the black-and-white line sensor 23, and the vertical transfer of both is performed in synchronization, the color line sensors 24, 25 and 26.
The vertical transfer of the black-and-white line sensor 23 is not performed within the exposure cycle T2. Therefore, the color line sensor 2
Noise due to vertical transfer on the side of the black-and-white line sensor 23 does not wrap around the color sensor output signals mainly including 4, 25, and 26. Therefore, when the color mode is selected, the color line sensor 24, 25, 26 can be used to read a color image with high quality.

Further, the color image can be read with high resolution by the variable resolution function of the CPU 31. Further, in detecting the occurrence of black stripes and in the correction processing, the output signal of the black and white line sensor 23 having the same color separation characteristics as the color line sensor 25 corresponding to the green component can be used. In this case, the output signal CL-OUT of the color line sensor 25 and the output signal BW-OUT2 of the monochrome line sensor 23 have the same output level (V3≈V1).
The relative comparison between the two enables highly accurate detection and correction of black streaks.

In the above embodiment, the CPU 31 changes the number of transfer clocks in one line period corresponding to the black and white line sensor 23, so that the exposure of the black and white line sensor 23 in the black and white mode and the color mode is performed. Although the cycle is changed, the present invention is not limited to this, and by changing the frequency of the transfer clock within one line cycle corresponding to the black-and-white line sensor 23, the black-and-white mode and the color mode can be changed. In some cases, the exposure cycle of the monochrome line sensor 23 may be changed. Specifically, when the CPU 31 selects the color mode, as shown in FIG. 7, the frequency F3 of the transfer clock BW-CLK3 in one line cycle in the monochrome line sensor 23 is set to 1 in the monochrome mode (frequency F1). By setting / 2, the relationship between the exposure cycle (first cycle and second cycle) of the monochrome line sensor 23 is changed to be T1 = T3 / 2.

Even when the CCD sensor 16 is driven according to the timing chart shown in FIG. 7, the vertical transfer of the main color line sensors 24, 25, 26 is performed by the black and white line sensor 23 when the color mode is selected in the same manner as described above. The black-and-white line sensor 2 is used within the exposure cycle T2 of the color line sensors 24, 25 and 26 because the vertical transfer is performed in the same period as the vertical transfer and the vertical transfer is performed in synchronization with each other.
No vertical transfer of 3 is performed. For this reason, noise due to vertical transfer on the side of the black and white line sensor 23 does not wrap around to the color sensor output signal mainly using the color line sensors 24, 25, 26. Therefore, when the color mode is selected, the color line sensors 24, 25,
26, a color image can be read with high quality. Further, the color image can be read with high resolution by the resolution variable function of the CPU 31. Further, in detecting the occurrence of black stripes and in the correction processing, the output signal CL- of the color line sensor 25 is used by using the output signal of the monochrome line sensor 23 having the same color separation characteristic as the color line sensor 25 corresponding to the green component. Since the output signal BW-OUT3 of OUT and the black-and-white line sensor 23 have the same output level (V4≅V1), it is possible to perform the black stripe occurrence detection and the correction processing with high accuracy by the relative comparison between the both.

[0080]

As described above, according to the present invention, the exposure cycle of the black-and-white line sensor is changed by the exposure cycle changing means according to the reading color mode selected by the reading color mode selecting means. When selected, the vertical transfer of the color line sensor can be executed in the same period as the vertical transfer period of the monochrome line sensor, and when the color mode is selected, the vertical transfer of the color line sensor can be executed in synchronization with the vertical transfer period of the monochrome line sensor. . As a result, it becomes possible to speed up the reading of the monochrome image without deteriorating the reading quality of the color image or the monochrome image. As a result, it is possible to maintain and improve the reading quality when reading a color image and improve the productivity when reading a monochrome image.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a sensor configuration for image reading adopted in an embodiment of the present invention.

FIG. 3 is a diagram showing details of a sensor configuration adopted in the embodiment of the present invention.

FIG. 4 is a block diagram showing a functional configuration of the image reading apparatus according to the embodiment of the present invention.

FIG. 5 is a timing chart showing an example of a sensor drive timing and a sensor output signal in a monochrome mode.

FIG. 6 is a timing chart showing an example of a sensor drive timing and a sensor output signal in a color mode.

FIG. 7 is a timing chart showing another example of the sensor drive timing and the sensor output signal in the color mode.

FIG. 8 is a timing chart showing an example of a conventional sensor drive timing and a sensor output signal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image reading device, 8 ... Original conveying part, 14 ... Optical scanning system, 15 ... Imaging lens, 16 ... CCD sensor, 23 ... Monochrome line sensor, 24, 25, 26 ... Color line sensor, 27A, 27B, 28A , 28B, 29A, 29
B, 30A, 30B, 30C, 30D ... Transfer register,
31 ... CPU, 32 ... UI, 34, 35 ... TG (timing generator), 44 ... Image processing circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/19 H04N 1/04 102 1/46 1/46 A 1/48 C F term (reference) 5B047 AA01 AB04 BB03 BC05 BC09 BC11 BC14 CA05 CB05 CB17 5C051 AA01 BA03 DA03 DB01 DB08 DB12 DB22 DB24 DB28 DC03 DE02 EA01 FA01 5C072 AA01 BA03 BA11 CA02 DA02 DA04 EA05 FA07 FA08 FB23 QA10 TA04 XA01 5C079 HA11 NA13 HA13 HA13 HA13 HA13 HA13 HA13 HA13 HA13 HA13 HA13 HA13

Claims (11)

[Claims] 1. A reading unit for drawing an image of an original using an image pickup unit having a color line sensor and a monochrome line sensor, and a reading color mode of an image read by the reading unit, which is applied when reading a color image. Read color mode selecting means for selecting one of a color mode and a monochrome mode applied when reading a monochrome image, and the black and white line according to the read color mode selected by the reading color mode selecting means. An image reading apparatus comprising: an exposure cycle changing means for changing an exposure cycle of a sensor. 2. The exposure cycle changing means sets the exposure cycle of the monochrome line sensor to a first cycle when the monochrome mode is selected by the reading color mode selecting means, and the reading color mode selecting means. The image reading apparatus according to claim 1, wherein when the color mode is selected by, the exposure cycle of the monochrome line sensor is set to a second cycle that is longer than the first cycle. 3. The number of charge transfer registers attached to the black-and-white line sensor is twice the number of charge transfer registers per line sensor attached to the color line sensor. Image reading device. 4. A resolution varying means for switching the reading resolution of the monochrome line sensor in the sub-scanning direction and the reading resolution of the color line sensor in the sub-scanning direction according to the reading color mode selected by the reading color mode selecting means. The image reading apparatus according to claim 1, further comprising: 5. The color line sensor comprises a plurality of line sensors each having a different color separation characteristic, and the black and white line sensor has the same color separation characteristic as one of the plurality of line sensors. The image reading apparatus according to claim 1. 6. The exposure cycle changing means sets the exposure cycle of the monochrome line sensor to be the same as the exposure cycle of the color line sensor when the color mode is selected by the reading color mode selecting means. The image reading apparatus according to claim 1, wherein: 7. The exposure period changing means changes the exposure period of the black-and-white line sensor by changing the number of clocks in one line period corresponding to the black-and-white line sensor. Image reading device. 8. The exposure cycle changing means changes the exposure cycle of the black-and-white line sensor by changing a clock frequency within one line cycle corresponding to the black-and-white line sensor. Image reading device. 9. The exposure cycle changing means changes the exposure cycle of the black-and-white line sensor under the condition that the first cycle is ½ of the second cycle. Image reading device. 10. The resolution changing means sets the reading resolution of the monochrome line sensor in the sub-scanning direction to the reading resolution of the color line sensor in the sub-scanning direction when the monochrome mode is selected by the reading color mode selecting means. If the color mode is selected by the reading color mode selecting means, the reading resolution in the sub-scanning direction of the monochrome line sensor is set to be the same as the reading resolution in the sub-scanning direction of the color line sensor. The image reading apparatus according to claim 4, wherein: 11. The exposure cycle varying means synchronizes the exposure cycle of the monochrome line sensor with the exposure cycle of the color line sensor when the color mode is selected by the reading color mode selecting means. The image reading device according to claim 6.