JP2502509B2 - Document reader - Google Patents

Description

The present invention relates to a document reading device for reading image information of a document by an image sensor.

[Prior Art] For a document reading device that reads a document containing image information by photoelectric conversion, there is a demand for high resolution, miniaturization, and colorization (color image readable). The solid-state scanning method is one of the leading technologies that can meet such demands. Generally, this method requires a photodiode array and MO
A fixed image sensor combined with an S switch, a solid-state image sensor using a semiconductor functional element that has both a pixel resolution function and an optical information storage function by the device itself are used.

[Problems to be Solved by the Invention] In order to read an image of an original such as a book or a document with such a solid-state image sensor (solid-state image sensor), the original is exposed by a light source and the reflected light of the original is converted into a solid-state image. It is detected by a sensor and photoelectrically converted. Then, in order to record an image based on the output signal of this solid-state image sensor, analog processing is required to make the analog output signal of the solid-state image sensor into a form suitable for image recording. Therefore, it is necessary to transmit the analog output signal of the solid-state image sensor to the analog processing circuit. For example, when the analog processing circuit is separated from the solid-state image sensor, the analog output is transmitted by a transmission line such as a coaxial cable. It In this transmission, if noise is present in the read analog output signal and is transmitted through the transmission line, the signal is affected by the permittivity of the transmission line and the like, and a proper signal is supplied to the analog processing circuit.

In addition, the output signal of the photoelectric conversion element array is sample-held (S /
H), if the output signal contains unnecessary high frequency components, accurate S / H cannot be performed.

The present invention relates to an image sensor for transmitting an image signal from a document scanning unit that moves relative to a document table to an image processing unit fixed to the document table via a transmission line capable of bending movement. It is an object of the present invention to provide a document reading device capable of stable signal transmission of an output signal from the device and capable of excellent image processing in an image processing unit.

[Means and Actions for Solving Problems] In order to achieve the above object, the document reading device of the present invention is
A light source, an image sensor for photoelectrically converting reflected light of a document on the platen illuminated by the light source, and a processing unit for removing high-frequency components of an output signal of the image sensor are provided relative to the platen. The output signal, which is arranged on the original scanning unit that moves to the right side, and in which the high-frequency component is removed by the processing means, can be flexibly moved from the original scanning unit to the image processing unit fixed to the original table. It is characterized in that it is transmitted via a wire.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

A. Internal Configuration of Document Reading Device FIG. 1 shows the internal configuration of a document reading device using a contact type color image sensor according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes the entire document reading device. Two
Is a document table, 3 is a document on the document table 2, 4 is a linear light source (exposure lamp) for irradiating the document from below, 5 is a reflection shade for converging the light emitted from the light source 4 onto the document 3, and 6 is a document. It is a converging rod lens array that guides the reflected light from 3 in a ratio of 1: 1. Reference numeral 7 denotes a contact type color image sensor that converts an erect real image guided by the rod lens array 6 into an electric signal (image signal) by photoelectric conversion. In this embodiment, a CCD (charge coupled device) array is used as an example. ing. Reference numeral 8 denotes an original scanning unit for scanning the original 3, which includes the above-described light source 4 and reflection shade.
5, a rod lens array 6, a contact type color image sensor (hereinafter referred to as a contact type color CCD sensor) 7, etc. are mounted, and an arrow A in this figure is provided by a drive source (motor) not shown.
Reciprocates in the sub-scanning direction.

FIG. 2 shows details of the document scanning unit 8 shown in FIG.
Here, 9 is a moving body of the document scanning unit 8, 10 is a sensor drive board on the moving body 9, 11 is a buffer amplifier board on the moving body 9, and 12 is a signal transmission unit (described later) on the buffer amplifier board 11. It is a coaxial flat cable for connection with an electric circuit (described later) of the main body.

FIG. 3 shows details of an optical system such as the rod lens array 6 shown in FIG. Here, 13 is an infrared absorption filter that absorbs infrared rays, and is arranged in the optical path between the converging rod lens array 6 and the contact color CCD sensor 7. In this embodiment, a linear halogen lamp is used as the light source 4.

FIG. 4 shows the appearance of the contact color CCD sensor 7 of FIG. The contact type color CCD sensor 7 has a side 6
Five pixels of 1024 pixels are arranged in a staggered pattern along the main scanning direction with 2.5 μm (1/16 mm) as one pixel, and each pixel is divided into three parts of 15.5 μm x 62.5 μm. Cy (cyan), G (green), and Ye (yellow) color filters are arranged in close contact with each pixel.

In the above configuration, in order to read the image of the document 3 on the document table 2, the document scanning unit 8 is moved and scanned in the direction of arrow A perpendicular to the main scanning direction, and at the same time, the halogen in the document scanning unit 8 is read. When the lamp 4 is turned on,
The reflected light from the original 3 is guided to the converging rod lens array 6 arranged near the side surface of the lamp 4, passes through the infrared absorption filter 13, and is condensed on the contact color CCD sensor 7.

At this time, the light emitted from the lamp 4 of the linear light source is condensed by the reflection shade 5 and irradiates the original 3, and the converging rod lens array 6 does not reduce the reflected light from the original 3 in a pair. Due to the relationship of 1, the positive color image is formed on the plurality of CCD chips of the contact color CCD sensor 7. Contact color C
The light receiving portion of the CD sensor 7 has a length sufficient to cover the length of one end of the document. The optical image formed on the CCD chip is converted into electric charges by the photoelectric conversion capability of the CCD. This charge is sequentially transferred as an image signal by the charge transfer capability of the CCD.

B. Contact Color CCD Sensor Next, the contact color CCD sensor 7 of FIG. 1 will be described in detail.

As shown in FIGS. 5 and 6, the contact color CCD sensor 7 includes five CCD chips 21 to 25 arranged in a zigzag pattern.
A ceramic substrate (26) for integrally holding these CCD chips (21-25), a cover (27) covering the upper part of the ceramic substrate (26), and a connecting lead wire (28) for the CCD chips (21-25).

Each of the CCD chips 21 to 25 has a light receiving portion made of a pn type Si photodiode, and the size of the light receiving portion for each color of one pixel is 62.5 μm × 15.5 μm. As shown in FIG. 7, the light receiving portion of each CCD chip has dummy pixels (areas) D1 to D12 that are not connected to the photosensitive pixels, and light shield pixels (areas) D13 to D36 that are shielded with aluminum Al. , Dummy pixels (area) D37 to D72, effective signal pixels (area) S1 to S3072,
And the rear end dummy pixels (areas) D73 to D76, which are 3168 bits in total.

In this embodiment, the CCD chips 21 to 25 are arranged in two rows in a staggered pattern as shown in FIG. As shown in FIG. 6, two adjacent CCD chips (for example, 21 and 22) are arranged in parallel with each other while keeping a predetermined distance 1 from the center of the light receiving portion of each CCD chip.

 In this embodiment, the distance is l = 4 pixels.

Further, these CCD chips 21 to 25 are arranged along the arrangement direction while allowing them to overlap with each other. That is, including the 3072-bit effective pixel areas S1 to S3072, the CCD chips 21 to
Each CCD chip 21 so that the total effective reading area of 25 is 304mm
~ 25 are arranged to allow overlapping.

In the light receiving portions of the CCD chips 21 to 25, it is necessary to dispose a color filter on the above Si photodiode in order to receive a color signal. This arrangement method includes color filters and Si
There are a method of adhering the photodiode element with an adhesive and a method of directly laminating the color filter on the Si photodiode element.

In the former filter bonding method, the color filter may be manufactured on the glass substrate, but an extra step of bonding is required when combining the color filter with the Si photodiode element, and a positioning error is likely to occur. In this case, it is actually quite difficult to suppress the adhesion error to several μm or less, which may cause deterioration in color reproducibility and shading characteristics.

On the other hand, the latter filter stacking method simply uses color filters as Si
A color light receiving element is completed by stacking and manufacturing the color light receiving element according to the position of the pixel of the photodiode element by a vapor deposition method or the like. Therefore, the manufacturing process thereof is extremely simple, and the positioning accuracy can be greatly improved. Therefore, the color filter of the CCD chip in this embodiment is manufactured by the latter filter laminating method.

C. Color Filter Next, a specific array of color filters will be described.

As shown in FIG. 8, in this embodiment, cyan (Cy) 3
As a filter array of 1, green (G) 32, and yellow (Ye) 33, one set of 3 bits of Cy, G, and Ye is configured as one pixel at the time of reading. The repeating pitch of one pixel is 62.5 μm.

The spectral characteristics of these color filters 31, 32, 33 are shown in FIG. As shown in this figure, the transmittance of the Ye filter 33 sharply increases from around the wavelength of 500 nm as shown by the chain line (a). The transmittance of the Cy filter 31 has a peak near the wavelength of 480 nm as shown by the solid line (b), and the transmittance again increases from the point of exceeding the wavelength of 700 nm. Further, since the G filter 32 is obtained by superimposing the Cy filter 31 and the Ye filter 33 in this embodiment, the transmittance thereof has a peak near the wavelength of 500 nm as shown by the broken line (c). As can be seen in FIG. 9, these filters 31, 32,
An important point in the spectral characteristics of 33 is that each transmittance does not become zero even at a wavelength of about 700 nm outside the human visual sensitivity range.

However, in order to obtain accurate color information, three types of color filters 31
~ 33 and CCD chips 21 to 25 must perform the same discrimination function as human eyes. The spectral sensitivity characteristics (relative sensitivity) of the light receiving parts of the CCD chips 21 to 25 are as shown in FIG.
It has a maximum at a wavelength of about 550 nm, and has a finite relative sensitivity up to 1000 nm or more.

That is, the CCD chip 2 with the color filters 31 to 33 attached
The light receiving units 1 to 25 have a response to light having a wavelength of 700 nm or more. On the other hand, the visual sensitivity of the human eye is zero for wavelengths above 700 nm. Therefore, the combination of the CCD chips 21 to 25 and the Cy, G, and Ye color filters 31 to 33 cannot fulfill the same function as human eyes. Therefore, in this embodiment, the spectral sensitivity is corrected by an optical filter, for example, the infrared absorption filter 13, as described later.

D. Focusing Rod Lens Array Next, the focusing rod lens array 6 will be described.

As shown in FIG. 3 described above, in the converging rod lens array 6 of this embodiment, the document surface 41 is located at the focal length on the light incident side, and the two rows of CCDs are located at the focal length on the light emitting side. There is a chip row 42. By arranging the converging rod lens array 6 in this way, the document surface 41 and the CCD chip array 42 are in an image forming relationship. That is, the image on the document surface is formed on the CCD chip row 42 as a one-to-one erect image. However, as shown in FIG. 6, the CCD chips 21 to 25 are arranged in a zigzag pattern with an interval of l = 4 pixels (4 lines), whereas the focusing rod lens array 6 has a length of 1 Since it is a book, the erect image formed on the CCD chip array 42 in the present embodiment is an image with a four-line interval on the document surface 41. Therefore, in this embodiment, this problem is solved by using the line memories mounted in the CCD chips 21 to 25 as described later.

E. Light Source Next, the light source 4 will be described.

As described above, the halogen lamp is used as the light source 4 in this embodiment. The function required of the contact-type color image sensor as the document reading device is a function of reading a color of the same level as human eyes.

Figure 11 shows the Thomson-Wright basic curve. This curve shows the relationship between the luminosity characteristics of the human eye according to color, that is, the brightness sensitivity for red, green, and blue color light and the wavelength of light. R (red), G (green), B
As is clear from each curve in (blue), the human eye is 700 nm
I do not feel the above long-wavelength light.

On the other hand, the light receiving parts of the CCD chips 21 to 25 and the color filters 31 to 33
As described above, the spectral characteristic of has a finite sensitivity value even for light having a long wavelength of 700 nm or more (see FIGS. 9 and 10), and has such color filters 31 to 33. When white light is made incident on the light receiving parts of the CCD chips 21 to 25, 700n
You will feel even light with a long wavelength longer than m.

Further, the halogen lamp used as the light source 4 has a spectral characteristic that its light energy increases in the longer wavelength region, as shown in FIG.

Therefore, in this embodiment, in order to block the light energy in the long wavelength region of 700 nm or more, the infrared absorption filter 13 is arranged on the contact color CCD sensor 7 as shown in FIG. FIG. 13 shows the spectral transmission characteristics of the infrared absorption filter 13. Further, in this embodiment, the halogen lamp 4 is lit by direct current in order to prevent a light amount ripple due to normal alternating current lighting.

F. Overall Circuit Configuration of Electric System Next, the electric system of the image reading apparatus 1 of FIG. 1 will be described.

FIG. 14 shows a schematic configuration example of the electric system. In FIG. 14, 100 is a drive circuit section for driving the CCD chips 21 to 25, and 110 is an output signal (image signal) from the CCD chips 21 to 25.
To the next stage, 120 is the signal transmission unit 1
An analog processing unit that converts the analog output signals from the CCD chips 21 to 25 input from 10 into a form suitable for image information, and further converts the converted signals into digital signals.
170 is B converted into a digital signal by the analog processing unit 120
(Blue), G (green), R (red) signals are a memory unit for temporarily storing B, G, R signals in order to connect them to one line for image signal output, and 180 is each of the above units 100, 120, 170
Is a timing pulse generator that controls the operation timing of. An electric system of the image reading apparatus 1 of the present embodiment is constituted by these constituent elements 100, 110, 120, 170 and 180.

G. Drive Circuit First, the drive circuit section 100 will be described in detail.

However, in the following description, the driving circuit 100a of the CCD chip 21 is representatively shown. As shown in FIG. 15, the drive circuit 110a includes a two-phase clocks φ _1A and φ _2A , a final stage transfer clock φ _2B , a scan synchronization signal SH, a reset signal RS, vertical transfer clocks φ _{V1 to} φ _V7 , and output signals. Only the OS will be handled.

An inverter 101 is connected to an input terminal of one clock signal φ _1A of the two-phase clock, a resistor 102 and a speed-up capacitor 103 are connected in parallel to an output terminal of the inverter 101, and a MOS (metal oxide silicon) is further provided.
Of the clock driver 104. This M
Output terminal of OS clock driver 104 is φ _{1A of} CCD chip 21
Connected to the terminal. The other clock signal φ _2A of the two-phase clock is the same as the above-mentioned clock signal φ _1A .
Further, the scan synchronization terminal SH, the reset signal RS, and the vertical transfer clocks φ _{V1 to} φ _V7 are also connected with the inverter 101, the resistor 102, the capacitor 103, and the MOS clock driver 104 as in the case of the two-phase clocks φ _1A and φ _2A . .

An emitter follower including an npn transistor 105, a collector resistance 106, and an emitter resistance 107 is connected to the terminal of the output signal OS. Also, the power supply voltage of the CCD chip 21 + V
Is connected to the OD terminal of the CCD chip 21 via capacitors 108 and 109.

The two-phase clocks φ _1A and φ _2A are signals necessary for sequentially transferring the charges generated in each bit of the CCD chip 21 to the output end side. The scan synchronization signal SH is a signal that distinguishes one scan in the charge transfer of the CCD chip 21, and the reset signal RS.
Is a signal for erasing the pixel signal after the charge is transferred.

The final stage transfer clock φ _2A is a so-called high-speed transfer pulse, and transfers the charge of the CCD horizontal analog shift register at the final stage as shown in FIG. The vertical transfer clocks φ _{V1 to} φ _V7 are so-called line shift pulses, which transfer charges in the vertical direction. This line shift pulse φ _V1
~ ₇ line shift gates controlled by φ _V7 ~ can store charge for 1 line each and transfer charge line by line, so control this gate appropriately by line shift pulse. This makes it possible to construct a line memory of up to 7 lines. Therefore, in this embodiment, the line shift gate pulses φ _{V1 to} φ _V7 are controlled so that the distance l between the light receiving portions of the staggered CCD sensors 21 to 25 is 1 =
4 lines are corrected.

The output signal OS is an output signal output from the CCD chip 21, and as shown in FIG.
In addition to the 3072 bits of the effective signal of S3072, a dummy signal, an idle feed signal, and a reference black level signal are included. The bit positions of these output signals OS are accurately defined, and the reference level signal is a dark signal of the light receiving portion (optical seal portion) of the CCD chip 21, which is used to obtain a true output according to color.
FIG. 16 shows an example of the timing of each signal described above.

The drive circuit section 100 is mounted on the sensor drive board 10 shown in FIG. 2 described above, and the sensor drive board 10 is separated from the buffer amplifier board 11 on which the signal transmission section 110 is mounted. These substrates 10 and 11 separate the analog system and the digital system in order to reduce the influence of the power supply noise and the radiation noise generated by the high-speed and large-amplitude CCD drive pulse in the drive circuit 100 on the signal transmission unit 110. It is for.

H. Signal Transmission Unit Next, the signal transmission unit 110 will be described.

FIG. 17 shows the circuit configuration of the signal transmission unit 110. The signal transmission unit 110 is provided for each CCD chip 21 to 25 as shown in FIG. 14, but the signal transmission circuit 110a for the CCD 21 will be described below as a representative.

In FIG. 17, 111 is a buffer circuit that temporarily stores the output signal from the CCD chip 21, 112 is a capacitor that removes the DC component of the output signal of the buffer circuit 111, and 113 is an output that is AC-coupled with the capacitor 112. An amplifier that amplifies the signal to a specified level, 114 was amplified by amplifier 113
A low-pass filter (LPF) 115 that removes high-frequency components included in the CCD output signal and extracts only the change in the signal. 115 is an analog signal processing unit that outputs the output signal of the low-pass filter 115.
The signal transmission unit 110 is an output amplifier that amplifies the signal to be transmitted to the signal transmission unit 110. The signal transmission unit 110 includes these elements 111 to 115.

The output signal output from the CCD chip 21 is output by the buffer circuit 111 with low output impedance. In this case, in this embodiment, the frequencies of the two-layer clocks φ _1A and φ _2B are
9MHz The output signal from the CCD chip 21 has an offset of about 4V, so that the output signal of the buffer circuit 111 also has a voltage offset. The DC component of the CCD output signal with this offset is removed by the capacitor 112, and the DC level becomes AC depending on the output level.
It fluctuates (exchange). The output signal thus AC-coupled is amplified to a designated output level by the amplifier 113 and input to the low pass filter 114.

Generally, an output signal of a solid-state image sensor such as a CCD includes an image signal component synchronized with a transfer pulse, a frequency component due to a reset pulse, and a high-frequency component generated by each clock pulse in order to drive the solid-state image sensor. There is. Such an output signal is analog-transmitted by an electric wire such as a coaxial wire such as the coaxial flat cable 12 of the present embodiment, and when the electric wire is bent, the capacitance fluctuation between the conductor and the insulator is caused. And electrostatic noise greatly affect the above high frequency components other than the image signal components. Therefore, the low-pass filter 114 removes unnecessary high-frequency components to stabilize the signal during analog transmission.

As described above, in the low-pass filter 114, the high-frequency cutoff frequency of 20 MHz is selected as the pass band in which the high-frequency component included in the CCD output signal is removed and the variation of the signal can be extracted. . The signal from which unnecessary high frequency components have been removed by the low pass filter 114 is output by the output amplifier.
The signal is transmitted from the output terminal 116 through the coaxial flat cable 12 to the analog processing unit 120.

I. Analog Processing Unit Next, the analog processing unit 120 will be described.

FIG. 18 shows a circuit configuration of the analog processing unit 120. As shown in FIG. 14, the analog processing section 120 is provided for each CCD chip 21 to 25 as in the signal transmission section 110.
In the following, the analog processing circuit 120 for the CCD 21 is representatively shown.
Explain a.

In FIG. 18, reference numeral 121 denotes a variable amplifier which can input the CCD output signal from the signal transmission unit 110 and freely change the output voltage of the CCD output signal to a predetermined output voltage set in advance. Reference numeral 122 denotes a multiplexer that separates the output signal of the variable amplifier 121 into each color signal, and 123 is a buffer amplifier that amplifies the signal separated into each color signal by the multiplexer 122 by a certain factor. 124 is a buffer amplifier 123
Connected to the output side of the low-pass filter for extracting the change of the above-mentioned color-separated signal, 125 is connected to the output side of the low-pass filter 124, each color-separated signal (Cy, G ,
Ye) to the operation signals −Cy, −G, −Ye for producing the primary color signals of blue (B), green (G), and red (R).
It is an inverting amplifier that makes. Further, 126 is the operation signal Cy, G, -Ye generated by the inverting amplifier 125 from the operation signal Cy, G, -Ye.
It is an inverting amplifier that makes Ye.

130 is a matrix amplifier which outputs R, G, B primary color signals from the above-mentioned −Cy, −G, −Ye and Cy, G, Ye operation signals, 140
Is the R, G, B primary color signal, and the R, G, B
White balance correction unit that adjusts the output level of R, G and B to the same level, 150 is the A / D (analog / digital) converter that outputs the output level of R, G and B when a black original is read by the R, G and B primary color signals Black level correction unit that matches the reference level of 161, 160
Is white balance corrected and black level corrected R, G,
It is a buffer amplifier that amplifies the B signal to the dynamic range of the A / D converter 161. The analog processing unit 120 is composed of the above-mentioned constituent elements 121 to 126, 130, 140, 150, 160, 161.

The multiplexer 122 is an S / H (sample hold) circuit 122a that separates the output signal from the variable amplifier 121 for each color.
It consists of ~ 122c. The inverting amplifiers 125 and 126 are respectively inverting amplifiers 125a, 125b, 125c and 126a, 126b, 12 for each color.
6c, the level of the reference black level signal in the color-separated Cy, G, Ye signals is detected, and the inverting amplifiers 125a, 125b, 125c and 126a, 126 are set so that the level becomes a predetermined ground level.
It is composed of clamp circuits 125d, 125e, 125f and 126d, 126e, 126f for correcting the output signals of b and 126c with reference to the ground level.

In the above configuration, the signal transmission section 110a of the CCD chip 21
The CCD output signal output from is amplified to a predetermined output voltage by the variable amplifier 121 of the analog processing unit 120a. This variable amplifier 121 is for correcting the output variation between the other CCD chips 22 to 25, and each CC when reading the white plate.
The gain is set so that the output signal levels of the D chips 21 to 25 match.

After the output variation between the CCD chips is corrected by the variable amplifier 121, the S / H circuit 122a, 1 in the multiplexer 122 is corrected.
In 22b, 122c, Cy, G, and Ye are separated into color signals Cy, G, and Ye at the CCD output signal continuously output from the variable amplifier 121 in the order shown in FIG. It is amplified by the buffer amplifier 123. In practice, each buffer amplifier 123 is given a gain of about 6 dB in consideration of the attenuation by the low pass filter 124 in the next stage.

Next, the low pass filter 124 causes the multiplexer 122 to
S / H circuit 122a, 122b, 122c of the S / H output signal (color separated signal) generated in the S / H output signal (color separated signal) is removed, and only the change of the sampled S / H output signal is removed. Extract. For this reason, the low-pass filter 124 is given the frequency characteristic shown in FIG. That is, the input signal of the S / H circuits 122a, 122b, 122c is a CCD output signal of 9MHz, and the output pulse is held by the S / H circuits 122a, 122b, 122c, and the discrete frequency of 3MHz of 1/3 frequency is used. Become a target signal. By inputting this discrete signal into the low-pass filter 124 having a frequency characteristic as shown in FIG. 20, only the change component of the signal is extracted, and the frequency bandwidth of the signal processing system thereafter is kept low. It becomes possible.

In order to convert the complementary color system signals of Cy, G, and Ye into the primary color system signals of R, G, B in the matrix amplifier 130, each color signal in which only the change component of each color signal is extracted by the low-pass filter 124 is an inverting amplifier. By passing through 125 and 126, positive and negative operation input signals are created. By the way, when performing matrix calculation in the matrix amplifier 130, each calculation input signal must have the same reference value. Therefore, in this embodiment, the clamp circuits 125d, 125e, 125f and 126d, 1
Inverting amplifiers 125a, 125b, 125c and 26e, 126f so that the output level of the optical shield section (output level of the reference black level signal) in the CCD output signal becomes a predetermined reference level (ground level in this embodiment). The output level of 126a, 126b, 126c is corrected.

J. Matrix amplifier Positive and negative operation signals (Cy, G, Ye, −Cy, −G, −Ye) clamped to the ground level by the clamp circuits 125d, 125e, 125f and 126d, 126e, 126f are input to the matrix amplifier 130. Then, the operations shown in the following equations (1), (2), and (3) are performed, and the primary color signals B, G, and R are output from the matrix amplifier 130.

B = Cy-a ₁ · G (1) B = Ga ₂ · Cy-a ₃ · Ye (2) R = Ye-a ₄ · G (3) where a _{1 to} a ₄ are spectra of the CCD chip 21. Sensitivity characteristics (No. 10
(See the drawing) and the spectral transmittance characteristics (see FIG. 9) of the Cy, G, and Ye filters 31, 32, and 33 (see FIG. 9) and the like, which are calculation coefficients (constants) in advance.

The matrix amplifier 130 is, for example, an inverting addition amplifier using resistors R _{1 to} Rn, R _FB as shown in FIG. Here, R ₁ , R ₂ , and Rn are input resistors, R _FB is a feedback resistor, and 131 is an operational amplifier provided with a non-inverting input terminal. Input resistance
R ₁ , R ₂ ... Rn are connected in parallel to the inverting input terminal of the operational amplifier 131, and one end of the feedback resistor R _FB is also connected to the inverting input terminal. Now, assuming that the input voltages input corresponding to the input resistors R ₁ , R ₂ ... Rn are V ₁ , V ₂ ... vn respectively, the inverting summing amplifier 13
Output voltage V _O of 0 is a value of the following equation (4).

That is, V ₁ , V ₂ ... vn are positive and negative operation signals V _O are R, G, B
Corresponding to the signal, -R _FB , R ₁ , R ₂ ... Rn is the above-mentioned operation signal a
Determined from _{1 to} a ₄ .

The primary color signals B, G, R of the respective outputs of the matrix amplifier 130 thus obtained are the white balance correction unit 140 of the next stage.
To input white balance correction.

K. White Balance Correction Unit Next, the white balance correction unit 140 will be described.

The white balance correction unit 140 is composed of, for example, a multiplication type D / A converter 141 and a current / voltage amplifier 142 as shown in FIG. 22, and digital data D ₀ input to the multiplication type D / A converter 141 is input.
According to D _7, it is possible to make the output voltage Vout to the variable. Reference numeral 143 is a feedback resistor of the current / voltage amplifier 142. As a result, when the CCD chip 21 reads the reference white plate of the document cover (not shown), the input terminal of the multiplication type D / A converter 141
The output relative Vout of each primary color B, G, R input to Vin has the same value, that is, the output value of each primary color signal B, G, R so that it becomes the maximum level of the A / D converter 161 in FIG. To control.

Next, when the CCD chips 21 to 25 read the black portion of the original 3, the white balance correction unit is set so that the black level of each color and the black level between the CCD chips become the minimum level of the A / D converter 161. The output signal of 140 is corrected by the black level correction unit 150, and each of the black-level-corrected B, G, and R primary color signals is further amplified by the buffer amplifier 160 to the dynamic range of the A / D converter 161. Then, it is converted into a digital value by the A / D converter 161. At that time, the A / D converter 161 performs an A / D conversion operation based on one function as described later.

L. Black Level Correction Unit Next, the black level correction unit 150 will be described in more detail with reference to FIG.

In FIG. 23, 151 is a black level detection circuit, 152 is an error amplification circuit, 153 is a reference potential generation circuit, and 154 is a clamp circuit. The primary color signals B, G, R (B in FIG. 23) color-converted by the matrix amplifier 130 as described above are
Through the clamp circuit 154, the white balance correction unit 140,
It is input to the A / D converter 161 via the buffer amplifier 160.

To effectively perform A / D conversion by the A / D converter 161,
The dynamic range of the A / D converter 161 must be used to the maximum. Therefore, in the output of the buffer amplifier 160, the output levels of the light shield pixels D13 to D36 shown in FIG.
P (see FIG. 16) is detected, and this detection signal is compared with the reference potential of the reference potential generation circuit 153 in the error amplification circuit 152 as clamp voltage setting means and converted into a clamp voltage of DC voltage. Is input to the clamp circuit 154 to clamp the color-converted primary color signals R, G, B based on the level of the light shield pixel, that is, the level of the light-shielded portion. Further, at that time, by setting the reference potential of the reference potential generation circuit 153 in advance so that the black level of black matches the minimum reference level of the A / D converter 161, when the black of the original is read. The output signal is clamped at the same time as the black level is corrected.

M.A / D Converter Next, the A / D converter 161 will be described.

In this embodiment, the A / D converter 161 is, as shown in FIG.
It is composed of an A / D converter 161a and a ROM (Read Only Memory) 161b, and achieves the function of the following expression (5).

D = −log R (5) where D is the optical reflection density and R is the reflectance. That is, by the A / D converter 161a, first, the voltage a applied to the reference voltage setting terminal V _IN is not divided into equal parts, and b in FIG.
It is approximated by the one-dot broken line shown in. Next, the output data b
The data is input to the addresses A _{0 to} A ₇ of the ROM 161b, and the conversion data written in the addresses is used to perform correction using the curve shown in C of FIG. 25 so as to approximate the function of the above equation (5). In this way, the primary color signals B, G, R input from the buffer amplifier 160 to the A / D converter 161 are converted into digital density data D _R , D.
It becomes _G and D _B and is output to the memory unit 170.

The color signals D _B , D _G , and D _R of the above digital density data are
It is output to each CCD chip 21-25. Further, as described above, since the photodiode parts of the CCD chips 21 to 25 are arranged in a staggered pattern to allow overlapping in the main scanning direction,
The density data D _B , D _G , and D _R output from the D chips 21 to 25 are also C
Duplication of data will occur between the CD chips 21 to 25.
Therefore, in the memory section 170 shown in FIG. 14, data duplication between the CCD chips 21 to 25 is removed, and parallel-serial conversion is performed so that the sensor outputs of 5 lines are connected to 1 line and output. Is going.

N. Modified Example In the above-described present embodiment, the contact type color CCD sensor was used as the photoelectric conversion element, but the present invention is not limited to this.
A solid-state image sensor such as an i (amorphous silicon) sensor or a Cd-Se sensor may be used as long as it can read one pixel by dividing it with a plurality of color filters. Further, as a color filter, in this embodiment, cyan (Cy), green (G),
The yellow (Ye) filter was used, but the blue (B),
Other color filters such as green (G), red (R), cyan (Cy), white (W), and yellow (Ye) may be used.

EFFECTS OF THE INVENTION As described above, according to the present invention, a transmission line capable of bending movement from a document scanning unit moving relatively to a document table to an image processing unit fixed to the document table. When the image signal is transmitted through the image sensor, by removing the high frequency component of the output signal from the image sensor before the transmission through the transmission line, for example, when the document scanning unit is moved, the conductor and the insulator are removed. It is possible to prevent adverse effects of capacitance variation and electrostatic noise on the high frequency component, and stable signal transmission and good image processing in the image processing unit are possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view showing a schematic internal structure of a document reading apparatus according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view showing a structure of a document scanning unit shown in FIG. 3 is a sectional view showing the arrangement of the optical system shown in FIG. 1, FIG. 4 is a perspective view showing the external appearance of the optical system shown in FIG. 1, and FIG. 5 is an external view of the contact type color CCD sensor shown in FIG. FIG. 6 is a front view showing the arrangement of the contact color CCD sensor of FIG. 5, FIG. 7 is an arrangement of the CCD chip shown in FIG. 6, and FIG. FIG. 7 is a plan view showing the arrangement of the color filters stacked on the CCD chip in FIG. 7, FIG. 9 is a view showing the spectral transmittance characteristics of the color filter in FIG. 8, and FIG. 10 is a graph showing the CCD chip in FIG. Fig. 11 shows the spectral sensitivity characteristics of the light receiving part. Fig. 11 shows the basic curve of Thomson light showing human visual sensitivity to color. Fig. 12 shows Fig. 13 is a diagram showing the spectral characteristics of the halogen lamp (light source), Fig. 13 is a diagram showing the spectral transmission characteristics of the infrared absorption filter of Fig. 8, and Fig. 14 is the entire electrical system of the document reading device of Fig. 1. 15 is a circuit diagram showing the circuit configuration of the drive circuit unit of FIG. 14, FIG. 16 is a waveform diagram showing the timing of the output signal of the drive circuit unit of FIG. 15, and FIG. FIG. 14 is a circuit diagram showing the circuit configuration of the signal transmission unit of FIG. 14, FIG. 18 is a circuit diagram showing the circuit configuration of the analog processing unit of FIG. 14, and FIG. 19 is the timing of the S / H signal of the multiplexer of FIG. FIG. 20 is a waveform diagram, FIG. 20 is a diagram showing the frequency characteristics of the low-pass filter of FIG. 18, FIG. 21 is a circuit diagram showing the circuit configuration of the matrix amplifier of FIG. 18, and FIG. 22 is a white of FIG. FIG. 23 is a circuit diagram showing the circuit configuration of the balance correction unit, and FIG. 23 is a circuit diagram showing the circuit configuration of the black level correction unit of FIG. FIG. 24 is a circuit diagram showing the circuit configuration of the A / D converter of FIG. 23, and FIG. 25 is a diagram showing the relationship between the density change and the output value showing the operation of the A / D converter of FIG. . 3 ... Original, 4 ... Light source (halogen lamp), 6 ... Focusing rod lens array, 7 ... Contact color CCD sensor, 8 ... Original scanning unit, 12 ... Coaxial flat cable, 13 ... Red External absorption filter, 21 to 25 …… CCD chip, 31 to 33 …… Color filter, 100 …… Drive circuit, 101 ……
Inverter, 104 ... Clock driver, 110 ... Signal transmission unit, 111 ... Buffer circuit, 114 ... Low-pass filter, 120 ... Analog processing unit, 121 ... Variable amplifier, 122
…… Multiplexer, 123 …… Buffer amplifier, 124 ……
Low pass filter, 125,126 …… Inversion amplifier, 130 …… Matrix amplifier, 140 …… White balance correction unit, 1
50: Black level correction unit, 151: Black level detection circuit, 152
…… Error amplification circuit, 153 …… Reference potential generator, 154 …… Clamp circuit, 160 …… Buffer amplifier, 161 …… A / D converter.

Claims (1)

(57) [Claims] 1. A platen including a light source, an image sensor for photoelectrically converting reflected light of a document on the platen illuminated by the light source, and processing means for removing a high frequency component of an output signal of the image sensor. Is arranged on a document scanning unit that moves relative to the image scanning unit, and the output signal from which the high frequency component has been removed by the processing unit is sent from the document scanning unit to an image processing unit fixed to the document table. An original reading device characterized by transmitting data through a transmission line capable of bending movement.