JPS62115963A - Original reading device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an original reading device for reading image information of a color original.

[Prior Art] A document reading device that reads a document containing image information by photoelectric conversion is required to have high resolution, miniaturization, and color image reading (ability to read color images). A solid-state scanning method is one of the promising technologies that can meet these demands. Generally, this method uses a photodiode array and M
A solid-state image sensor combined with an OS switch or a solid-state image sensor using a semiconductor functional element that has both a pixel resolution function and an optical information storage function are used.

[Problems to be Solved by the Invention] In order to read a color document using such a solid-state image sensor (solid-state image sensor), reflected light from the document exposed by a light source is reflected by a dichroic mirror, a color filter, etc. For example, R (red).

Perform color separation # (color separation) of the three colors G (green) and B (blue),
The color-separated optical image is detected and read using a solid-state image sensor.

In reading such a color original, it is necessary to accurately set each color signal to a predetermined black level signal and white level signal when reading a black image and a white image, respectively. For this reason, it is necessary to correct the black level and white balance of each color signal.

Further, the dynamic range of the A/D converter is determined by both the white balance correction means and the black level correction means, so that the level from black to white of the original can be effectively used. There is a correlation between white balance correction and black level correction, and when the output level of a color signal is varied by white balance correction, the black level also changes.

In view of the above-mentioned points, the present invention provides a white balance correction means that performs white balance correction of color signals from a photoelectric conversion element array (line sensor). An object of the present invention is to provide a document reading device that can always perform reading with a wide dynamic range by feeding back the following information.

[Means for Solving the Problems] In order to achieve the present object, the present invention includes a light source, a plurality of color filters that select the wavelength of reflected light from the light source irradiated by the light source, and a color filter that selects the wavelength of reflected light from the light source. Sah Ta IJX ffl
an image sensor that photoelectrically converts the reflected light of the image sensor, a separation unit that separates each color signal from the output signal of the image sensor, a white balance correction unit that performs white balance correction on each color signal separated by the separation unit, and a black image It has a black level correction means for correcting the black mark 71/'t M+ of each color signal after white balance correction when reading, and each color signal whose black level has been corrected by the black level correction means is sent to the white balance correction means. It is characterized by giving feedback.

[Function] In the present invention, since the above-mentioned white balance correction means and black level correction means are placed in the feedback system, it is possible to accurately fix the white level and black level at the predetermined reference level in the palm of the hand, and the output It becomes possible to effectively A/D convert the dynamic range of the signal.

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

^, Internal structure of document reading device FIG. 1 shows the internal structure of a document reading device using a contact type color image sensor according to an embodiment of the present invention.

In FIG. 1, l indicates the entire document reading device, 2 is the document table, 3 is the document on the document table 2, 4 is a linear light source (exposure lamp) that illuminates the document from below, and 5 is the light source 4. A reflecting shade 6 focuses the irradiated light on the original 3, and 6 is a focusing rod lens array that guides the reflected light from the original 3 at a ratio of 1:1. 7 is a close-contact color image sensor that converts the erect real image guided by the rod lens array 6 into an electrical signal (image signal) through photoelectric conversion, and in this embodiment, COD is used as an example.
(charge-coupled device) array. 8 is a document scanning unit for scanning the document 3, and the light source 41 described above is
Reflective hat 5. Rod lens array 6, contact type color image sensor (hereinafter referred to as contact type color CCD sensor)
7, etc., and is reciprocated in the sub-scanning direction in the direction of the arrow in this figure by a drive source (motor) not shown.

FIG. 2 shows details of the document scanning unit 8 of FIG. 1. Here, 9 is a moving body of the document scanning unit 8, IO is a sensor drive board on the moving body 9, 11 is a buffer 7 amplifier board on the moving body 9, and 12 is a signal transmission section on the buffer amplifier board 11 (described later). This is a coaxial flat cable for connection to the main unit's electrical circuit (described later).

FIG. 3 shows details of the optical system such as the rod lens array 6 shown in FIG. placed in the optical path between the Also,
In this embodiment, a linear halogen lamp is used as the light source 4.

FIG. 4 shows the appearance of the contact type color 〇〇D sensorf of FIG. 1. Close-contact color CD sensor 7 (as described later, one pixel is 82.5 μm (1718 mm) on a side)
Five 024-pixel CCD chips are arranged in a staggered manner along the main scanning direction, and each pixel has a 15.5μlx
It is divided into three parts each having a size of 62.5 μm, and color filters of Cy (cyan), G (green), and Ye (yellow) 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 the arrow perpendicular to the main scanning direction, and at the same time, the halogen in the document scanning unit 8 is scanned. When the lamp 4 is turned on, the reflected light from the original 3 is guided to the focusing rod lens array 6 arranged near the side of the lamp 4, and then passed through the infrared absorption filter 1.
3 and is focused on a contact type color CCD sensor 7.

At this time, the light emitted from the linear light source lamp 4 is reflected by the reflective shade 5.
The light is focused and irradiated onto the document 3, and the focusing rod lens array 6 illuminates the plurality of CCo chips of the contact type color CCD sensor 7 in a one-to-one relationship without reducing the reflected light from the document 3 in any way. Form a positive real image. The light receiving section of the contact type color CCD sensor 7 has a length that sufficiently covers the length of one end of the document. The optical image formed on the CCD chip mentioned above is converted into an electric charge by the photoelectric conversion tTh capability of the CCD. This charge is sequentially transferred as an image by the charge transfer ability of the COD and becomes an image signal.

B. Contact type color CCD sensor Next, the contact type color 〇〇D sensor 7 shown in Fig. 1 will be explained in detail.

The close-contact color CD sensor 7 has five CCD chips 21 arranged in a row, as shown in FIGS. 5 and 6.
25, a ceramic substrate 26 that holds these CCD chips 21 to 25 together, and this ceramic substrate 26.
It consists of a cover 27 that covers the top of the CCD chips 21 to 25, and lead wires 28 for connecting the CCD chips 21 to 25.

The CCD chips 21 to 25 have p-n type S
The size of the light receiving portion for each color of one pixel is 62.5 μm×15.5 μm. Each CC
As shown in FIG. 7, the light-receiving part of the D chip includes air-feeding pixels (area) DI~012 that are not connected to photosensitive pixels, and light shield pixels (area) DI3~D36 that are shielded with aluminum^1. ．． Dummy pixel (area) D37~
D72, effective signal pixels (area) S1 to 53072, and rear end dummy pixels (area) D73 to D76, total 31
It consists of 68 bits.

In this embodiment, the CCD chips 21 to 25 are arranged in two rows in a staggered manner, as shown in FIG. Two adjacent CCDs
The chips (e.g. 21 and 22) are as shown in FIG.
The CCD chips are arranged parallel to each other while maintaining a predetermined distance @X from the center of the light receiving section of each CCD chip.

In this embodiment, a distance of 1=4 pixels is provided.

Further, these CCD chips 21 to 25 are arranged along the arrangement direction so as to overlap with each other. That is, 30
Including the 72-bit effective pixel area S1 to 53072,
The total effective reading area of CCD chips 21 to 25 is 304 mm.
The CCD chips 21 to 25 are arranged such that they overlap each other.

In the light receiving portions of the CCD chips 21 to 25, color filters must be placed on the above-mentioned Si photodiodes in order to receive color signals. This arrangement method includes a method of bonding the color filter and the Si photodiode element with an adhesive, and a method of laminating the color filter directly on the Si photodiode element.

In the former filter bonding method, the color filters can be fabricated on a glass substrate, but an extra step of adhesion is required when combining them with the Si photodiode element, and alignment errors are likely to occur. In practice, it is quite difficult to suppress the adhesion error to a few μm or less, which may cause deterioration of color reproducibility and shading characteristics.

On the other hand, the latter filter stacking method simply stacks color filters on Si.
A color light-receiving element is completed by laminating layers using a vapor deposition method or the like in accordance with the positions of the pixels of the photodiode element, so the manufacturing process is extremely simple and alignment accuracy can be greatly improved.

Therefore, the color filter of the CCO chip in this embodiment is manufactured by the latter filter lamination method.

C9 color filter Next, a specific arrangement of color filters will be explained.

As shown in FIG. 8, in this embodiment, shea...(Cy)
3 l, green (G) 32, yellow (Ye)
As a filter array of 33, one set of Cy, G, Ye is 3
A bit is configured as one pixel when reading. The repetition pitch of one pixel is 62.5 μm.

The spectral characteristics of these color filters 31, 32, and 33 are
As shown in the figure. As shown in this figure, the transmittance of the Ye filter 33 rapidly increases from around the wavelength of 50On11, as shown by the slope (a). The transmittance of the Cy filter 31 is
As shown by the solid line (b), the transmittance shows a peak near the wavelength of 480 nm, and increases again beyond the wavelength of 700 nm. Furthermore, in this embodiment, the G filter 32 is obtained by superposing the Cy filter 31 and the Ye filter 33, so its transmittance peaks around the wavelength of 5001, as shown by the broken line (C). As can be seen from FIG. 9, the important point in the spectral characteristics of these filters 31, 32, and 33 is that
The point is that each transmittance does not become zero even for a wavelength of about 00no+.

However, to get accurate color information, use 3f! kind of color filter 3
1 to 33 and CCD chips 21 to 25 must perform the same identification function as the human eye. CCD chip 2
The spectral sensitivity characteristics (relative sensitivity) of the light receiving sections 1 to 25 are the first
As shown in Figure 0, it reaches a maximum at a wavelength of about 550 nm, and has a finite relative sensitivity up to 1000 n+a or more.

That is, the light receiving parts of the CCD chips 21 to 25 provided with the color filters 31 to 33 respond even to light having a wavelength of 700 nm or more. On the contrary,
The visibility of the human eye is zero for wavelengths of 700 nm or more. Therefore, simply a CCO chip of 21 to 25 gy,
Only in combination with G and Ye color filters 31 to 33,
It cannot perform the same functions as the human eye.

Therefore, in this embodiment, the spectral sensitivity is corrected using an optical filter, for example, the infrared absorption filter 13, as will be described later.

D. Focusing rod lens array Next, the convergent rod lens array 6 will be explained.

As shown in FIG. 3 above, the convergent rod lens array 6 in this embodiment has an original surface 41 at the focal length on the light incident side, and two rows of CCDs at the focal length on the light exit side. A chip row 42 exists. By arranging the convergent rod lens array 6 in this manner, the document surface 41 and the CCD chip array 42 are in an imaging relationship. That is, the image on the document surface is formed on the CCD chip array 42 as a one-to-one erect image. However, while the CCD chips 21 to 25 are arranged in a staggered manner with an interval of β=4 pixels (4 lines) as shown in FIG. Since it is a book, the erect image formed on the CCD chip array 42 in this embodiment is an image spaced apart by four lines on the document surface 41. Therefore, in this embodiment, the CCD chip 21
This problem is solved by using the line memory installed in the ~25.

E, light source Next, the light source 4 will be explained.

As mentioned above, a halogen lamp is used as the light source 4 in this embodiment. The function required of a contact type color image sensor as a document reading device is the ability to read colors on the same level as the human eye.゛Figure 11 shows the Thomson Wright (ThIlson-fr)
This curve shows the visibility characteristic of the human eye according to color, that is, the relationship between the brightness sensitivity and the wavelength of light for red, green, and blue color light.

As is clear from the R (red), G (green), and B (blue) curves, the human eye does not sense long wavelength light of 700 nm or more.

On the other hand, the light receiving parts of the CCD chips 21 to 25 and the color filter 3
As mentioned above, the spectral characteristics of color filters 31 to 33 have a finite sensitivity value even to light with a long wavelength of 700 nm or more (see Fig. 9 and Fig. 1θ). 3
When white light is made incident on the light receiving portions of the CtD chips 21 to 25 having a wavelength of 3, it will be perceived as light with a long wavelength of 700n+c or more.

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

Therefore, in this embodiment, an infrared absorption filter 13 is disposed on the contact type color CCD sensor 7, as shown in FIG. 3, in order to block optical energy in a long wavelength range of 700 nIm or more. . Figure 13 shows the infrared absorption filter 13.
shows the spectral transmission characteristics of Furthermore, in this embodiment, the halogen lamp 4 is lit with direct current to prevent ripples in the amount of light caused by normal alternating current lighting.

-F. Overall circuit configuration of electrical system Next, the electrical system of the image reading device 1 shown in FIG. 1 will be explained.

FIG. 14 shows an example of a schematic configuration of the electrical system.

In FIG. 14, 100 is a drive circuit section for driving the CCD chips 21 to 25, and 110 is a drive circuit section for driving the CCD chips 21 to 25.
A signal transmission unit for transmitting the output signal (image signal) from the signal transmission unit 110 to the next stage;
This is an analog processing section that converts the analog output signals from the D chips 21 to 25 into a form suitable for image information, and further converts the converted signals into digital signals. 170 connects the B (blue), G (green), and R (red) signals converted into digital signals by the analog processing unit 120 to one line for image signal output. 180 is a memory section for temporary storage, and 180 is the above-mentioned section 100.
, 120, 170. These components 100, 11
0, 120, 170, and 180 constitute the electrical system of the image reading device 1 of this embodiment.

G, drive circuit First, the drive circuit section 100 will be explained in detail.

However, in the following explanation, the CCD chip 21 will be used as a representative.
A drive circuit 100a is assumed. This drive circuit 110a is
As shown in FIG. 15, the two-phase clock φlA+φ2A+
Final stage transfer lock φ23. Scanning synchronization signal S]1. Only the reset signal R5, vertical transfer locks φv1 to φV7+output signal O5 will be handled.

An inverter 101 is connected to the input terminal of one clock signal φIA of the two-phase clock, and a resistor 102 and a speed-up capacitor 1 are connected to the output terminal of the inverter 101.
03 are connected in parallel, and further connected to an input terminal of a MOS (metal oxide silicon) clock driver 104. The output terminal of this MOS clock driver 104 is connected to the φ terminal of the CCD chip 21. The other clock signal φ2A of the two-phase clock is also similar to the above-described clock signal φIA. Also, a scan synchronization terminal SH, a reset signal RS, a vertical transfer lock φ9. ~φ
For v7 as well, the inverter 101, resistor 102, . Capacitor 103, M
An OS clock driver 104 is connected.

An emitter follower consisting of an npn transistor 105, a collector resistor 106, and an emitter resistor 107 is connected to the terminal of the output signal O5. Further, the power supply voltage +V of the CCD chip 21 is connected to the OD terminal of the CCD chip 21 via capacitors 108 and 109.

The two-phase clocks φ, φ, and A are necessary signals to sequentially transfer 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 transfer of charges of the CCD chip 21, and the reset signal R5 is a signal that erases the pixel signal after the charges have been transferred.

The final stage transfer lock φn is a so-called high-speed transfer pulse, and the vertical transfer locks φday to φv7, which transfer the charge of the final stage CCD horizontal analog shift register, are so-called line shift pulses, as shown in FIG. and
The seven line shift gates ■ to ■, which are controlled by line shift pulses φv1 to φv7 and which transfer charges in the vertical direction, can each accumulate charges for one line, and transfer charges in line units. Therefore, by appropriately controlling this gate with a line shift pulse, it is possible to configure a line memory with a maximum of 7 lines. Therefore, in this embodiment, the line shift gate pulse φ9. ~
φ9. is controlled to correct the distance 1111-4 line between the light receiving parts of the CCO sensors 21 to 25 arranged in a staggered manner.

The output signal O5 is an output signal output from the CCD chip 21, and as shown in FIG. and a reference black level signal. The bit positions of these output signals O5 are accurately defined, and the reference level signal is a dark signal of the light receiving section (light seal section) of the CCD chip 21, and is used to obtain a true output corresponding to the color.

FIG. 16 shows an example of the timing of each of the above-mentioned signals.

Further, the drive circuit section 100 is mounted on the sensor drive board 10 shown in FIG. 2 described above, and this sensor drive board 10 is separated from the buffer amplifier board 11 on which the signal transmission section 110 is mounted. These substrates 10.1
1 is a high-speed and large-amplitude CC in the drive circuit section 100.
This is to separate the analog system and the digital system in order to reduce the influence of power supply noise and radiation noise caused by the D drive pulse on the signal transmission section 110.

H6 signal transmission section Next, the signal transmission section 110 will be explained.

FIG. 17 shows the circuit configuration of the signal transmission section 110. The signal transmission section +10 connects each C (D chip 21) as shown in FIG.
~ 25, but below we will use C as a representative.
(: The signal transmission circuit 110a for D21 will be explained.

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 OC (direct current) 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, 1
14 is a low-pass filter (LPF) that removes high frequency components included in the CCD output signal amplified by the amplifier 113 and extracts only changes in the signal; 115 is an analog signal processing unit that converts the output signal of the low-pass filter + 15 to an analog signal processing unit; It is an output amplifier that performs amplification for transmission to signal transmission section 120.
10 is composed of these elements 111 to N115.

The output signal output from the CCD chip 21 is output with low output impedance by the buffer circuit 111.

In this case, in this embodiment, the frequency of the two-layer locks φ, A, φ, 8 is set to 9 MHz. The output signal from the CCD chip 21 has an offset of about 4V, so the output signal from the buffer circuit 111 also has a voltage offset. The DC component of the CCD output signal having this offset is removed by the capacitor 112, and the DC level varies in a C (alternating current) manner depending on the output level. The AC-coupled output signal is amplified to a specified output level by the amplifier 113 and input to the low-pass filter 114.

In general, the output signal of a solid-state image sensor such as a CCO includes an image signal component synchronized with a transfer pulse, a frequency component caused by a reset pulse, and a high-frequency component generated by each clock pulse in order to drive the solid-state image sensor. There is. When such an output signal is analog-transmitted using an electric wire such as a coaxial line such as the coaxial flat cable 12 of this embodiment, and the electric wire is subjected to bending motion, capacitance fluctuation between the conductor and the insulator occurs. and electrostatic noise greatly affect the above-mentioned 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.

In this way, in this embodiment, the low-pass filter 114 selects a high cutoff frequency of 20 Hz as a passband that can remove high-frequency components included in the CCD output signal and extract changes in the signal. . The signal from which unnecessary high frequency components have been removed by the low-pass filter 114 is transmitted from the output terminal 116 through the output amplifier 115 to the analog processing section 120 through the coaxial flat cable 12.

■, Analog processing section Next, the analog processing section 120 will be explained.

FIG. 18 shows the circuit configuration of the analog processing section 120. As shown in FIG. 14, this analog processing section 120 is provided for each COD chip 21 to 25 similarly to the signal transmission section 110. The analog processing circuit 120a for the CfD 21 will be described below as a representative.

In the vJta diagram, 121 is a variable amplifier that manually inputs the CCD output signal from the signal transmission section 110 and can freely vary the output voltage of the CCD output signal up to a predetermined output voltage. 122 is variable amplifier 1
a multiplexer that separates the 21 output signals into each color signal;
Reference numeral 123 denotes a buffer amplifier that amplifies the signals separated into each color signal by the multiplexer H2 by a certain magnification.
124 is connected to the output side of the buffer amplifier 123 and is a low-pass filter for extracting the variation of the color-separated signals mentioned above; 125 is connected to the output side of the low-pass filter 124 and is a low-pass filter for extracting the changes in the color-separated signals described above; From the signal (cy, c, ye),
Blue (B).

This is an inverting amplifier that produces operational signals -Cy, -G, and -Ye for producing primary color signals of green (G) and red (R).

Further, 126 is a calculation signal f:y, G, Ye generated from the calculation signals -Gy, -G, -Ye produced by the inverting amplifier 125.
It is an inverting amplifier that makes.

! 30 is the above-mentioned -Cy, -G, -Ye and Gy, G,
A matrix amplifier 140 outputs R, G, and B primary color signals from the Ya calculation signal, and adjusts the R, G, and B output levels to the same level when reading a white board using the R, G, and B primary color signals. white balance correction section, 150 is R
,G.

a black level correction unit 16 that matches the output levels of R, G, and B with the reference level of the ^/D (analog-digital) converter 161 when a black original is read using the B primary color signal;
0 is R with white balance correction and black level correction
, G, and B signals to the dynamic range of the D/D converter 161. The analog processing circuit 120 includes the above components 121 to 128, 130,
It consists of 140, 150, 160, 161.

The multiplexer 122 is an S/H (sample hold) that separates the output No. 3 from the variable amplifier 121 for each color.
Consists of circuit +22a-122c. Also, the inverting amplifier 1
25 and 126 are inverting amplifiers 125a for each color, respectively;
125bj25c and 126a, 126b, 126c
The inverting amplifiers 125a, 125b, 12 detect the level of the reference black level signal in the color-separated Cy, G, and Ye signals, and adjust the level to a predetermined ground level.
A clamp circuit 125d corrects the output signals of 5c, 126a, 126b, and 126c based on the ground level.
, 125g, 125f and 126d, 126e, 12
It consists of 6f.

In the above configuration, the signal transmission section 1 of the CCD chip z1
The CCD output signal output from the analog processing section 120a is amplified to a predetermined output voltage by the variable amplifier 121 of the analog processing section 120a. This variable amplifier 121 is for correcting output variations between other CCD chips 22 to 25, and the gain is set so that the output signal level of each CCp chip 21 to 25 matches when reading a white plate. Ru.

After the output variation between each COD chip is corrected by the variable amplifier 121, the S/H in the multiplexer 122
In the circuits 122a, 122b, 122c, Gy, G,
The CCD output signals successively outputted from the variable amplifier 121 in the order of Ye are converted to Gy and G at the timing shown in FIG.
, Ye, and amplified by a buffer amplifier 123 having the same gain. In reality, each buffer amplifier 123 has a gain of about 6 dB in consideration of the attenuation caused by the low-pass filter 124 in the next stage.

Next, the multiplexer 1 is processed by the low-pass filter 124.
The frequency components of the sampling pulses in the S/H output signals (color-separated signals) generated in the 22 S/H circuits 122a, 122b, and 122c are removed, and only the changes in the sampled S/H output signals are removed. Extract. For this reason, the low-pass filter 124 is provided with frequency characteristics as shown in FIG. That is, S/H circuit 1
The input signals of 22a, 122b, 122c are 9 M) Iz
This is the CCO output signal of S/H circuits 122a, 122.
By holding the output pulses by 122c and 122c, it becomes a 3 MHz discrete signal with 1/3 the frequency. By inputting this discrete signal to a low-pass filter 124 having frequency characteristics as shown in FIG.
Only the changing components of the signal are extracted, and the frequency bandwidth of the subsequent signal processing system can be kept low.

In order to convert complementary color signals of Cy, G, and Ye into primary color signals of R, G, and B in the matrix amplifier 130,
By passing each color signal from which only the change component of each color signal has been extracted by the low-pass filter 124 to inverting amplifiers 125 and 126, positive and negative calculation input signals are generated. By the way, when performing matrix calculation in the matrix amplifier 130, each calculation input signal needs to have the same reference value. Therefore, in this embodiment, the clamp circuit 12
5d, 125e, 125f and +21id, 126e
, 126f, the inverting amplifiers 125a, 125b are arranged so that the output level of the optical shield part (the output level of the reference black level signal) in the CCO output signal becomes a predetermined reference level (ground level in this embodiment).

The output levels of 125c, 126a, 126b, and 126c are corrected.

J, matrix amplifier clamp circuits 125d, 125e, 125f and 12
6'd, 126e.

The positive and negative operation signals (Cy, G, Ye, -Cy, -G, -Ye) clamped to the ground level by 126f are input to the matrix amplifier 13G, and are expressed by the following equation (1).
(2) The calculations shown in (:l) are performed, and the primary color signal B
, G, and R are output from the matrix amplifier 130.

B=Cy-al ・G(1) B=G-a2-Cy-83Ye
(2) R=Ye-84・a
(3) Here, a1 to a4 are CCD
Spectral sensitivity characteristics of chip 21 (see Figure 10) and Gy, G
, are calculation coefficients (constants) obtained in advance from the spectral transmittance characteristics (see FIG. 9) of the Ye filters 31, 32, and 33.

The matrix amplifier 130 is composed of an inverting summing amplifier using resistors R1 to Rn and 'RFll as shown in FIG. 21, for example. Here, J, R2, Rn are human resistances, 1i
ra is a feedback resistor, and 131 is an operational amplifier provided with a non-inverting input terminal. The input resistors ttl, R2...Rn are connected in parallel to the inverting input terminal of the operational amplifier 131, and one end of the feedback resistor R6 is also connected to the inverting input terminal. Now, the manually input voltages corresponding to the human resistors R1, R2...Rn are set to V1. V2...vn, the output voltage vo of the inverting summing amplifier 130 has the value of the following equation (4).

That is, Vl, V2...VQ are positive and negative operation signals ■o
corresponds to rl, G, B signals, RrR,J, R2+
+Rjl is determined from the above-mentioned calculation signals a1 to a4.

The primary color signals B, G, and R output from the matrix amplifier 130 thus obtained are input to a white balance correction section 140 at the next stage, where white balance correction is performed.

K. White balance correction section Next, the white balance correction section 140 will be explained.

For example, as shown in FIG. 22, the white balance correction unit 140 is composed of a multiplication type D/A converter 141 and a current/voltage amplifier 142, and according to digital data DO to D7 input to the multiplication type D/A converter 141, Its output voltage V
out can be made variable. 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 output relative Vout of each primary color B, G, and R input to the input terminal Vin of the multiplication type D/A converter 141 is mutually The output values of the primary color signals B, G, and R are controlled so that they have the same value, that is, the maximum level of the A/D converter 161 in FIG. 18.

Next, when the CCD chips 21 to 25 read the black part of the document 3, the white balance correction unit adjusts the black level of each color and the black level between each CCD chip to the minimum level of the A/D converter 161. 140 is corrected by a black level correction section 150, and this black level corrected B
, G, and H are further amplified by a buffer amplifier 160 to the dynamic range of an A/D converter 161, and then converted into digital values by the A/D converter 161. At this time, the A/D converter 161 performs a ^10 conversion operation based on one function as described later.

L. Black Level Correction Section Next, the black level correction section 150 will be explained in more detail with reference to FIG. 23.

In FIG. 23, 151 is a black level detection circuit, 152
153 is an error amplifier circuit, 153 is a reference potential generation circuit, and 1
54 is a clamp circuit. The primary color signals B, G, R (
In FIG. 23, signal B) passes through the clamp circuit 154, passes through the white balance correction section 140, and the buffer amplifier 160, and is input to the A/D converter 1[il.

In order to effectively perform ^/D conversion by the A/D converter 161, the dynamic range of the A/D converter 161 must be utilized to the maximum. Therefore, in the output of the buffer amplifier 180, the light shield pixel 01 in FIG.
The output levels of 3 to 03B are detected by the black level detection pulse CP (see FIG. 16) in the black level detection circuit 151, and this detection signal is sent to the reference potential generation circuit 153 in the error amplification circuit 152 as a clamp voltage setting means. It is compared with a reference potential and converted into a DC voltage clamp voltage, and this clamp voltage is input to the clamp circuit 154, and the above-mentioned color-converted primary color signals R, G, and B are applied to the level of the light shield pixel, that is, the light shielded portion. Clamp based on the level of .

In addition, at this time, by setting the reference potential of the reference potential generation circuit 153 in advance so that when the black of the original is read, it matches the lowest reference level of the black The level is corrected and the output signal is clamped at the same time.

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

In this embodiment, the A/D converter 161 is composed of an A/D converter 161a and a ROM (read only memory) 1Blb, as shown in FIG. 24, and achieves the function of the following equation (5). There is.

D--1og R(5) where D is optical reflection density and R is reflectance. That is, the A/D converter 161a first divides the voltage a applied to the reference voltage setting terminal VIN into equal parts, but divides the voltage a into a second voltage.
The output data b is approximated by the one-dot broken line shown in Fig. 5 b, and the output data b is set to the address ^0~^ of the ROM 161b.
7, and the conversion data written to that address is used to approximate the function of equation (5) above.
Perform correction using the curve shown in . In this way, each of the primary color signals B, G, and R input from the buffer amplifier 180 to the D/D converter 161 is converted into digital density data D scale, oc.
, , DB are outputted to the memory section 170.

Date of each color signal for the above digital density data.

D, , DR are output to each CCD chip 21-25.

Furthermore, as described above, since the photodiode portions of each CCD chip 21 to 25 are arranged in a staggered manner to permit a melon in the main scanning direction, the density data DB, DC output from each CCD chip 21 to 25 is ,, DR also causes duplication of data between the CCD chips 21 to 25.

Therefore, in the memory section 170 shown in FIG.
Parallel-to-serial conversion is performed so that the outputs of the line sensors are connected to one line and output.

N Modification Example Although a contact type color 〇〇D sensor was used as the photoelectric conversion element in this embodiment described above, the present invention is not limited to this.
-5i (amorphous silicon) sensor and Cd-5e
Any solid-state image sensor such as a sensor that reads one pixel by dividing it with a plurality of color filters may be used. In this example, cyan (Cy) is used as a color filter.
, green (G), and yellow (Ye) filters were used, but blue (B), green (G), red (R), cyan (Cy), and white (W) filters were used.

Other color filters such as yellow (Ye) may also be used.

[Effects of the Invention] As explained above, according to the present invention, the white balance correction means and the black level correction means are placed in the feedback system, so that the white level and black level can always be accurately adjusted to the predetermined standards. The dynamic range of the output signal can be fixed to a certain level, and the dynamic range of the output signal can be effectively /1/D converted, resulting in the effect that a good color image signal can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic internal configuration of a document reading device according to an embodiment of the present invention, FIG. tS2 is a vertical cross-sectional view showing the configuration of the document scanning unit shown in FIG. 1, and FIG. 4 is a perspective view showing the appearance of the optical system shown in FIG. 1; FIG. 5 is a perspective view showing the appearance of the contact type color CD sensor shown in FIG. 1; The figure is a front view showing the arrangement of the contact type color COD sensor in Fig. 5, Fig. 7 is an arrangement diagram showing the arrangement of the CCD chip in Fig. 6, and Fig. 8 is a front view showing the arrangement of the CCD chip in Fig. 7. FIG. 9 is a plan view showing the arrangement of the laminated color filters; FIG. 9 is a diagram showing the spectral transmittance characteristics of the color filter in FIG. 8; FIG. Figure 11 is a diagram showing the basic Thomson-Wright curve that shows human visual sensitivity to color, Figure 12 is a diagram showing the spectral characteristics of the halogen lamp (light source) in Figure 3, and Figure 13 is a diagram showing the spectral characteristics of the halogen lamp (light source) in Figure 3. Figure 8 is a diagram showing the spectral transmission characteristics of the infrared absorption filter, Figure 14 is a block diagram showing the entire electrical system of the document reading device in Figure 1, and Figure 15 is the circuit configuration of the drive circuit section in Figure 14. 16 is a waveform diagram showing the timing of the output signal of the drive circuit section in FIG. 15, FIG. 17 is a circuit diagram showing the circuit configuration of the signal transmission section in FIG. 14, and FIG. 18 is ' Figure 14 is a circuit diagram showing the circuit configuration of the analog processing section; Figure 19 is a waveform diagram showing the timing of the S/H signal of the multiplexer in Figure 18; Figure 20 is the frequency of the low-pass filter in Figure 18. Figure 21 is a circuit diagram showing the circuit configuration of the matrix amplifier in Figure 18. Figure 22 is a circuit diagram showing the circuit configuration of the white balance correction section in Figure 18. Figure 23 is the circuit diagram shown in Figure 18. 24 is a circuit diagram showing the circuit configuration of the black level correction section of FIG. 23, FIG. 25 is a circuit diagram showing the circuit configuration of the to/D converter of FIG. FIG. 3 is a diagram showing the relationship between density changes and output values shown in FIG. 3... Original document, 4... Light source (halogen lamp), 6... Focusing rod lens array, 7... Contact type color 〇〇D sensor, 8... Original scanning unit, 12... Coaxial flat cable, 13... Infrared absorption filter, 21-25... CCD chip, 31-33... Color filter, 100... Drive circuit, 101... Inverter, 104... Clock try 110... Signal transmission section, 111... Buffer circuit, 114... Low pass filter, 120... Analog processing section, 121... Variable amplifier, 122... Multiplexer, 123... -Buffer amplifier, 124...Low pass filter, 125.128...Inverting amplifier, +30...Matrix amplifier, 140...White balance correction section, 150...Black level correction section, 151... - Black level detection circuit, 152... Error amplification circuit, 153... Reference potential generator, 154... Clamp circuit, 160... Buffer amplifier, 161... 8/D converter. 'Q 4Z' [ΦOriginal light 4] Vertical V-plane view of the main body Figure 2 Cross-sectional view of the optical system in row A of the case Figure 3 Perspective view of the optical system of the column A Figure 4 ! Arrangement configuration of #ll color filter [shown in Fig. 8 Liquid stop (nm) Example 0 Spectral transmission characteristics of color filter + Lt National policy Fig. Spectral grade characteristics of the light receiving section Whistle 10 Bacterial solution length (nm) Thomson-Wright's basic curved edge dimensions Figure 11 Relative spectral power (% wavelength (nm) Infrared 9 absorption filter of the example Figure 1 shows the spectral transmission characteristics of
Figure 3 RFB: Circuit diagram of Matritsuta Matariba of Tora Shoes example Figure 21 Circuit diagram of white balanceless correction section of Example

Claims (1)

[Scope of Claims] A light source, a plurality of color filters that select the wavelength of the light reflected from the light source irradiated by the light source, and an image sensor that photoelectrically converts the light reflected from the document selected by the color filter, separation means for separating each color signal from the output signal of the image sensor; white balance correction means for performing white balance correction on each color signal separated by the separation means; and white balance correction means for performing white balance correction on each color signal separated by the separation means; What is claimed is: 1. A document reading device comprising: black level correcting means for correcting the black level of each color signal, and feeding back each color signal whose black level has been corrected by the black level correcting means to the white balance correcting means.