JPS62116063A - Original reading device - Google Patents

Abstract

PURPOSE:To effectively use the dynamic range of a picture signal processing circuit by correcting the output level of respective color picture signals outputted from an image sensor to the prescribed reference level at the time of reading the black picture of an original. CONSTITUTION:When a CCD chip reds the black part of an original, the output signal of white balance correcting part 140 is corrected by a black level correcting part 150 so that the black level of respective colors and the black level between respective CCD chips can be the minimum level of an A/D converter 161, respective original color signals of the black level corrected B, G and R are further amplified to the dynamic range of the A/D converter 161 by a buffer amplifier 160 and continuously, converted to the digital value by the A/D converter 161. Then, the reference electric potential of a reference electric potential generating circuit 153 is set beforehand so that the black level of the black color can be coincident to the minimum reference level of the A/D converter 161 when the black color of the original is read, and the black level is corrected and the clamping of the output signal is simultaneously executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a document reading device that reads image information of a color document.

[Prior Art] There are demands for high resolution, miniaturization, and colorization (enabling color image reading) for document reading devices that read documents containing image information by photoelectric conversion. A solid-state scanning method is one of the promising technologies that can meet these demands. Generally, in this method, a photodiode array and MO
A solid-state image sensor combined with an S switch or a solid-state image sensor using a semiconductor functional element that has both pixel decomposition function and optical information storage function are used.

[Problems to be solved by the invention] In order to read images of trees, trees, etc. using such a solid-state image sensor, the original is exposed to light from a light source, and the reflected scene of the original 8i is exposed. is detected by a solid-state image sensor and converted into electricity. In this case, the white portion of the document must be accurately converted into an image signal with a predetermined white level, and the component portion must be accurately converted into an image signal with a predetermined black level before being output.

Further, in the case of reading a color original, each color image signal obtained by reading needs to be at a level indicating the corresponding image density.

Normally, in signal IA processing of each color image signal output from a photoelectric conversion element array such as a COD, the output signal level when the optical input to the photoelectric conversion element array is ; and a predetermined reference level of the image signal processing circuit (for example, (ground level), and the dynamic range of the signal level of the processing circuit is determined accordingly. However, there is a slight difference between the output signal level when the optical input to the photoelectric conversion element array is 7 and the output signal level when the black portion of the original is actually read. Therefore, when the dynamic range is determined using the method described above, the output signal level when reading the black part of the document will float from the reference level of the processing circuit, and the dynamic range of the processing circuit It narrows down.

In view of the above points, the present invention improves the dynamic range of an image signal processing circuit by correcting the output level of each color image signal output from an image sensor to a predetermined reference level when reading a black image of a document. It is an object of the present invention to provide a document reading device that can be used effectively and can obtain each color image signal suitable for image density.

[Means for Solving the Problems] In order to achieve the object, the present invention includes a light source, a plurality of color filters that select the wavelength of light reflected from a document irradiated by the light source, and a color filter selected by the filter. The present invention includes an image sensor that photoelectrically converts reflected light from an original, and a correction means that corrects the output level of each color image signal output from the image sensor to a predetermined reference level when reading a black image of the original. Features.

[Function] In the present invention, since the correction means corrects each color m-image signal level when reading a black image so that it reaches a predetermined reference level of the processing circuit, the dynamic range of the processing circuit can be improved. It becomes possible to use it effectively.

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

A. 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, numeral 1 indicates the entire document reading device. 2 is an original platen, 3 is an original on the original platen 2, 4 is a linear light source (exposure lamp) that illuminates the original from below, 5 is a reflective shade that focuses the irradiated light from the light source 4 onto the original 3, and 6 is a A7, which is a convergent rod lens array that guides the reflected light from the original 3 in a ratio of 1=1, is a close-contact color image that converts the erect real image guided by the rod lens array 6 into an electrical signal (image signal) through photoelectric conversion. In this example, a CCD 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. It is equipped with a rod lens array 6, a density type color image sensor (hereinafter referred to as 'IBM color CCD sensor) 7, etc., and is reciprocated in the sub-scanning direction of arrow A in this figure by a drive source (motor) not shown. do.

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, lO 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 section (described later) on the buffer amplifier board 11. 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 of FIG. 1. Here, 13 is an infrared absorption filter that absorbs infrared rays, and the focusing rod lens array 6 and 'IE
It is placed in the optical path between it and the B-type color CCD sensor 7.

Further, in this embodiment, a linear halogen lamp is used as the light source 4.

FIG. 4 shows the appearance of the contact type color ○○○ sensor 7 shown in FIG. The close-contact color CCD sensor 7 has 1 pixel (62.5 μm (1716 mm) on each side as described later).
Five 024-pixel CCD chips are arranged in a staggered pattern along the main scanning direction, and each pixel is 15.5 μm×
It is divided into three parts each having a size of 62.5 μl, 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 a focusing rod lens array 6 placed near the side of the lamp 4, passes through an infrared absorption filter 13, and is focused on a contact type color CCD sensor 7. do.

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 original 8I3, and the focusing rod lens array 6 directs the light reflected from the original 3 onto the plurality of CCD chips of the contact type color CCD sensor 7 in a 1:1 relationship without reducing the reflected light from the original 3 in any way. Form a positive real image. The light receiving portion of the contact type color 〇〇D sensor 7 has a length that sufficiently covers the length of one end of the document. The optical image formed on the above-mentioned CCD chip is converted into an electric charge by the photoelectric conversion 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.

8. Contact type color CCD sensor Next, the contact type color CCD sensor 7 shown in FIG. 1 will be explained in detail.

As shown in FIGS. 5 and 6, the close-contact color CCD sensor 7 includes five CCD chips 21 to 21 arranged in a staggered manner.
25, a ceramic substrate 26 that holds these CCD chips 21-25 together, a cover 27 that covers the top of this ceramic substrate 26, and lead wires 28 for connecting the CCD chips 21-25.

The CCD chips 21 to 25 have p-n type S light receiving parts.
It consists of an i-photodiode, and the size of the light receiving part 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-fed pixels (areas) 01 to 012 that are not connected to photosensitive pixels, and light shield pixels (areas) 013 to D36 that are shielded with aluminum at 8°C. ．． Dummy pixel (area) 037~
D72, effective signal pixel (area) Sl-53072, and rear end dummy pixels (area) D73 to 07B, 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 (for example 2! and 22) are as shown in Figure 6.
A predetermined distance 1III from the center of the light receiving area of each CCD chip
Keep L and arrange them in parallel.

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 Sl~53072,
The total effective reading area of CCD chips 21 to 25 is 304n+
The CCD chips 21 to 25 are arranged so as to overlap with each other so that the number of chips is m.

In the light receiving portions of the CCD chips 21 to 25, a color filter must be placed on the photodiode 51 mentioned above 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.

The former method of bonding with a film or glue only requires producing a color filter on a glass substrate, but requires an extra step of adhesion when combining it with a Si photodiode element.
Moreover, it causes positioning errors. In this case, it is actually 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 CCD chip in this embodiment is manufactured by the latter filter lamination method.

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

As shown in FIG. 8, in this example, cyan (Cy)
31, Green (G) 32, Yellow (Ye) 3
As a filter array of 3, a set of 3 bits of Cy, G, and Ye is configured as 1EJ element at the time of 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 50OnI11, as shown by the chain line (a). The transmittance of the cy filter 31 peaks near the wavelength of 480r+a+, as shown by the solid line (b), and increases again beyond the wavelength of 700r+a+. Furthermore, since the G filter 32 is obtained by superposing the Cy filter 31 and the Ye filter 33 in this embodiment, its transmittance is determined by the broken line (c
As shown by l, it shows a peak around a wavelength of 500 nm. As can be seen from Figure 9, these filters: +
1. :+Z, :+:+ spectroscopy, the important point in the +1 property is that each transmittance does not become zero even for a wavelength of about 700 nm, which is outside the human visual sensitivity range.

However, in order to obtain accurate color information, three types of color filters 31 are required.
33 and the CCD chips 21 to 25 must perform the same identification function as the human eye. CCD chip 21
The spectral sensitivity characteristics (relative sensitivity) of the light receiving parts of ~25 are the 10th
As shown in the figure, the maximum occurs at a wavelength of about 550 nm,
It has a finite relative sensitivity up to 11000n 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 only a drop for wavelengths of 700 nm or more. Therefore, simply the CCD chips 21 to 25 and Cy,
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, & bundle 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 1=4 pixels (4 lines) as shown in FIG. Since it is a tree, 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 im; see 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 an original fA Flil tear-off is the ability to read colors on the same level as the human eye.

Figure 11 shows Thomson-Wr.
The basic curve of light) is shown. This curve shows the visibility characteristics of the human eye according to color, that is, the relationship between brightness sensitivity to red, green, and blue color light and the wavelength of light.

As is clear from the R (red), G (green), and B (blue) curves, the human eye is not sensitive to 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 70θnm or more (see FIGS. 9 and 10). 3
When white light is made incident on the light-receiving portions of the CCD chips 21 to 25 having CCD chips 21 to 25, they will be sensitive to light with a long wavelength of 700 nm 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, in order to block light energy in a long wavelength region of 700 nm or more, as shown in FIG.
An infrared absorption filter 13 is arranged on the contact type color CCD sensor 7. FIG. 13 shows the spectral transmission characteristics of the infrared absorption filter 13. Furthermore, in this embodiment, the halogen lamp 4 is lit with direct current in order 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 apparatus 1 shown in FIG. 1 will be described.

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.
120 is a CC input from the signal transmission unit 110.
This is an analog processing section that converts the analog output signals of the LI chips 1 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 primary storage, and 180 is the above-mentioned section 10.
This is a timing pulse generator that controls the operation timings of 0, 120, and 170. These components 100.1
10, 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 φI^.

φ2A, final stage transfer lock φ2B, scanning synchronization signal S
I+, reset signal R5, vertical transfer lock φ□
-φ92. Only the output signal O5 will be handled.

An inverter 101 is connected to the input terminal of one clock signal φ1A of the two-phase clock, and the inverter! A resistor 102 and a speed-up capacitor 1 are connected to the output terminal of 01.
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 10.4 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-mentioned clock signals φ and A. Also, scan synchronization terminal SN, reset signal R5, vertical transfer lock φ
9. 〜φv7 also has two-phase clock φl A + φ
Similarly to 2^, an inverter 101, a resistor 102. A capacitor 103 and a MOS clock driver 104 are 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. Also, CCD chip 2
The power supply voltage +V of 1 is connected to C through capacitors 108 and 109.
It is connected to the OD terminal of the CD chip 21.

Two-phase clock φlA + φ2A is CCD chip 2
This is a signal necessary to sequentially transfer the charges generated in each bit of 1 to the output terminal side. The scan synchronization signal 5+1 is a signal that distinguishes one scan in the transfer of charges of the CCD chip 21, and the reset signal nS is a signal that erases the pixel signal after the charges have been transferred.

The final stage transfer lock φ2A is a so-called high-speed transfer pulse, and as shown in FIG. 15, charges are transferred to the CCD horizontal analog shift register at the final stage. The vertical transfer locks φv1 to φv7 are so-called line shift pulses and transfer charges in the vertical direction. This line shift pulse φ9. ~The seven line shift gates ■~■ controlled by φV7 can each store charge for one line, and charge is transferred line by line, so these gates are controlled appropriately with line shift pulses. This makes it possible to configure a line memory with a maximum of 7 lines.

Therefore, in this embodiment, the line shift gate pulse φ9
, ~φv7 is controlled to provide a staggered arrangement of CCD sensors 21 to 2.
The distance between the light receiving parts of 5 alt I-=4 lines is corrected.

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.
D. This is for separating the analog system and the digital system in order to reduce the influence of power supply noise and radiation noise caused by drive pulses on the signal transmission section 110.

H0 signal transmission section Next, the color code transmission section 110 is explained in i)2.

FIG. 17 shows the circuit configuration of the signal transmission section 110. The signal transmission section 110 connects each COD chip 21 as shown in FIG.
~ 25, but below we will use C as a representative.
The signal transmission circuit 110a for the CD 21 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 DC (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 115 into 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 111-115.

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 two-layer lock φIAv φ2+
Let the frequency of 1 be 9 [1z. 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 a capacitor 112, and the DC level varies in an AC (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 No. 15 of a solid-state image sensor such as a CCD 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. C
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 a bending motion,
Capacity fluctuations between conductors and insulators and electrostatic noise have a strong influence on the above-mentioned high frequency components other than image signal components.

Therefore, the low-pass filter 114 removes unnecessary high frequency components and stabilizes the signal during analog transmission.

In this way, the low-pass filter 114 has a passband of 20M1lz in this embodiment, which can remove high frequency components included in the CCD output signal and extract changes in the signal.
The high cutoff frequency is selected. 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 of the CCD chips 21 to 25 similarly to the signal transmission section 110. The analog processing circuit 120a for the CCD 21 will be described below as a representative.

In FIG. 18, 121 indicates C from the signal transmission section 110.
This is a variable amplifier that inputs a CD output signal and can freely vary the output voltage of the CCD output signal up to a predetermined output voltage. 122 is a variable amplifier 12
a multiplexer that separates the output signal of 1 into each color signal;
23 is a buffer amplifier that amplifies the signal separated into each color signal by the multiplexer 122 by a certain magnification. 1
24 is a low-pass filter connected to the output side of the buffer amplifier 123 and used to extract the changes in the color-separated signals described above; 125 is connected to the output side of the low-pass filter 124, and a low-pass filter is used to extract the changes in the color-separated signals described above; Blue (B) from signals (Cy, G, Ye).

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 an inverting amplifier that generates operational signals Cy, G, and Ye from the operational signals -Gy, -G, and -Ye generated by the inverting amplifier 125.

130 is the above-mentioned -Cy, -G, -Ye and Gy, G,
A matrix amplifier 140 outputs R, G, and B primary color signals from the Ye calculation signal, and adjusts the output levels of n, a, and u to the same level when reading a white plate using the R, G, and B primary color signals. white balance correction section, 1
504fR,G.

When a black original is read using the B primary color signal, the n, G, and β output levels are converted to ^/D (analog/digital) W
black level correction unit for matching the reference level of 161;
60 is a buffer amplifier that amplifies the white balance corrected and black level corrected Il, G, and B signals to the dynamic range of the A/D converter 181. The analog processing section 120 includes the above components 121 to 126.130.
, 140, 150, 160, 161.

The multiplexer 122 includes S/H (sample and hold) circuits 122a to 122c that separate the output signal from the variable amplifier 121 for each color. Also, inversion amplification i 1
25 and 126 are inverting amplifiers 125a for each color, respectively;
125b, 125c and 126a, 126b, 126
Inverting amplifiers 125a, 125b,
A clamp circuit 12 that corrects the output signals of 125c, 126a, 126b, and 126c with reference to the ground level.
5d, 125e, 125f and 126d, 126c,
126f.

In the above configuration, the signal transmission section 1 of the CCD chip 21
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 CCD chip 21 to 25 matches when reading a white plate. Ru.

After the output variation between each CCD chip is corrected by the variable amplifier 12+, the S/1 in the multiplexer 122
Cy, G in one circuit 122a, 122b, 122c
, Ye from the variable amplifier 121 in the order of Cy, Ye at the timing shown in FIG.
The signals are separated into G and Ye color signals and amplified by a buffer amplifier 123 having the same gain. In reality, considering the attenuation by the next-stage low-pass filter 124, approximately 6d[l
Each buffer amplifier 123 has a gain of .

Next, the multiplexer 1 is processed by the low-pass filter 124.
'14122a, 122b, L22 in S/11th of 22
The frequency component of the sampling pulse in the S/11 output signal (color-separated signal) generated at c is removed, and only the change in the sampled S/11 output signal is extracted. Therefore, the low-pass filter 124 has a second
It has frequency characteristics as shown in Figure 0. That is, the input signals of the S/11 circuits 122a, 122b, and 122c are CCD output signals of 9Ml1z, and by holding the output pulses by the S/11 circuits 122a, 122b, and 122c, the input signals are 11 of 3MIIz of 1/3 the frequency. It becomes a defeatist signal. By inputting this discrete signal to the low-pass filter 124 having frequency characteristics as shown in FIG. 20, only the changing components of the signal are extracted, and the frequency bandwidth of the subsequent signal processing system is kept low. becomes possible.

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,
Positive and negative calculation input signals are created by passing each color No. 48, from which only the changing components of each color signal are extracted by the low-pass filter 124, to inverting amplifiers 125 and 126. By the way, in the matrix amplifier 130, the matrix I! When performing ii calculation, each calculation manual signal needs to have the same reference value. Therefore, in this embodiment, clamp circuits 125d, 125e, 125f and 126d, 1
26e and 126f, the inverting amplifiers 125a and 125b are arranged so that the output level of the optical shield section in the CCD output signal (the output level of the reference black level signal) becomes a predetermined reference level (ground level in this embodiment).

The output levels of 125c, 128a, +26b, and 126c are corrected.

J, matrix amplifier clamp circuits 125d, 125e, 125f and 12
6d, 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 130 and are expressed by the following equation (1).
The calculations shown in (2) and (3) are performed, and the primary color signal B,
G and R are output from the matrix amplifier 130.

B=CV-al・a (t
)B=G-a2-Cy-a3-Yc
(2) R=Ye-a4 ・G
(3) Here, a1 to a4 are determined in advance from the spectral sensitivity characteristics of the CCD chip 21 (see Figure 1θ) and the spectral transmittance characteristics of the Cy, G, and Ye filters 31, 32, and 33 (see Figure 9), etc. This is the calculation coefficient (constant).

The matrix amplifier 130 is, for example, an inverting summing amplifier using resistors R1 to Rn and Rra as shown in FIG. Here, R1, R2, Rn are human resistances, RFf
1 is a feedback resistor, and 131 is an operational amplifier provided with a non-inverting input terminal. The input resistors R1, R2...Rn are connected in parallel to the inverting input terminal of the operational amplifier 131, and the feedback resistor R
One end of Ffi is also connected to its 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).

In other words, ■□, V2...vn are positive and negative operation signals vO
corresponds to It, G, B signals, RFII, J, R
2.=nn is determined from the above-mentioned calculation signals a□ to a4.

The primary color signals B, G, and It of the respective outputs of the matrix amplifier 130 obtained in this manner are manually subjected to white balance correction in a white balance correction section 140 at the next stage.

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

For example, as shown in FIG.
According to the digital data Do to D7 input to the multiplier type D/A converter 141, the output voltage Vo
ut 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 relative output Vout of each primary color B, G, and R input to the input terminal Vin of the multiplication type D/A converter 141 is determined. The output values of the primary colors No. 18 B, G, and R are controlled so that they are 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 nose level between each CCD chip to the minimum level of the A/D converter 161. 140 is corrected by the black level correction section 150, and the black level corrected [
1. Each of the G and R primary color signals is further processed by a buffer amplifier 160.
The signal is then amplified to the dynamic range of the 10 converter 151, and then converted into a digital value by the A/D converter 161. At this time, the A/D converter 161 is
A/D conversion operation is performed based on two functions.

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;
2 is an error amplifier circuit, 153 is a reference potential generation circuit, and 154 is a clamp circuit. The primary color signals Th, G, color-converted by the matrix amplifier 130 as described above
R (B in FIG. 23) passes through the clamp circuit 154,
White balance correction section 140, buffer amplifier 16
0 and then manually input to the A/D converter 161.

In order to effectively perform A/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 160, the light shield pixel 013 in FIG.
The output level of ~036 is detected by the black level detection pulse CP (see FIG. 16) in the black level detection circuit 151, and this detection signal is used as the reference of the reference potential generation circuit 153 in the error amplification circuit 152 as a clamp voltage setting means. The voltage is compared with the electric potential to convert it into a DC voltage clamp voltage, and this clamp voltage is manually applied to the clamp circuit 154, and the above-mentioned color-converted primary color signals n, G, and B are set at the level of the light shield pixel, that is, the light shielding part. Clamp based on the level. In addition, at this time, the reference potential of the reference potential generation circuit 153 described above should be set in advance so that when the black of the original is read, the black level of the black corresponds to the lowest reference level of A/[I RjA'a16x. This simultaneously corrects the black level and clamps the output signal.

M, 810 Metamorphosis I moxibustion body ( Next, the A/D converter 161 will be explained.

In this embodiment, as shown in FIG. 24, the A/D converter 161 is composed of a 10 converter 181a and a 10M (read only memory) 161b, and achieves the function of the following equation (5). .

D--1og R(5) where D is optical reflection density and R is reflectance. That is, the A/D converter 181a first divides the voltage a applied to the reference voltage setting terminal VAN into equal parts, and divides the voltage a into a second voltage.
It is approximated by the one-dot broken line shown in Fig. 5b. Next, the output data b is stored at addresses 8o to A 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 I (are digital density data oPL,
D, , DB are outputted to the memory section 170.

Each color signal DB of the above-mentioned digital density data.

[IG, OR are output to each CCD chip 21-25.

Further, as described above, since the photodiode portions of each of the CCD chips 21 to 25 are arranged in a staggered manner allowing overlap in the main scanning direction, the density data oB, D, , DR also causes data duplication between the CCD chips 21 to 25. Therefore, in the memory section 170 shown in FIG.
Duplication of data between the CD chips 21 to 25 is removed, and parallel-to-serial conversion is performed so that the outputs of five lines of sensors are connected to one line and output.

N. Modification Example Although a contact type color CCD sensor was used as the photoelectric conversion element in this embodiment described above, the present invention is not limited to this.
-5t (amorphous silicon) sensor, Cd-5,
Any solid-state image sensor such as an e-sensor may be used as long as one pixel is divided and read using a plurality of color filters. In this embodiment, cyan (Gy) is used as a color filter.
), green CG), and yellow (Ye) filters were used; however, blue (8), green (G), and let (
11), cyan (Cy), and white (W).

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

[Effects of the Invention] As explained above, according to the present invention, the output level of each color image signal output from the image sensor is corrected to a predetermined reference level when reading a black image of a document, so that the image The dynamic range of the signal processing circuit can be effectively used, and each color image signal suitable for the image density 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. 2 is a vertical cross-sectional view showing the configuration of a document scanning unit in FIG. 1, and FIG. FIG. 4 is a cross-sectional view showing the arrangement of the optical system in FIG. 1; and FIG. 4 is a perspective view showing the appearance of the optical system in FIG. Figure 5 is a perspective view showing the appearance of the contact type color CCO sensor in Figure 1, Figure 6 is a front view showing the arrangement and configuration of the contact type color CCD sensor in Figure 5, and Figure 7 is the Fig. 8 is a plan view showing the arrangement of the color filters laminated on the CCD chip of Fig. 7; Fig. 9 is the spectral transmission of the color filters of Fig. 8. Figure 10 is a diagram showing the spectral sensitivity characteristics of the light-receiving part of the CCD chip in Figure 7. Figure 11 is a diagram showing Tomsodz-Wright's basic curve showing human visual sensitivity to color. Figure 12 shows the spectral characteristics of the halogen lamp (light source) in Figure 3, Figure 13 shows the spectral transmission characteristics of the infrared absorption filter in Figure 8, and Figure 14 shows the original reading device in Figure 1. 15 is a circuit diagram showing the circuit configuration of the drive circuit section of FIG. 14; FIG. 16 is a waveform diagram showing the timing of the output signal of the drive circuit section of FIG. 15; 17 is a circuit diagram showing the circuit configuration of the signal transmission section in FIG. 14; FIG. 18 is a circuit diagram showing the circuit configuration of the analog processing section in FIG. 14; FIG. 19 is a circuit diagram showing the circuit configuration of the multiplexer in FIG. A waveform diagram showing the timing of the H signal, FIG. 20 is a diagram showing the frequency characteristics of the low-pass filter in FIG. 18, FIG. 21 is a circuit diagram showing the circuit configuration of the matrix amplifier in FIG. 18, and FIG. A circuit diagram showing the circuit configuration of the white balance correction section in FIG. 18, FIG. 23 is a circuit diagram showing the circuit configuration of the black level correction section in FIG. 18, and FIG. 24 is a circuit diagram of the 10 converter in FIG. t indicating the configuration
ill! ! 250 is a diagram showing the relationship between the 41 degree change and the output value, showing the operation of the D/D converter shown in FIG. 24. 3... Original, 4... Light source (halogen lamp), 6... Focusing rod lens array, 7... Close contact type color CCD 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 driver, 110... Signal transmission unit, ill... Buffer circuit, 114... Low pass filter, 120... Analog processing unit, 121... Variable amplifier, 122... Multiplexer, 123... Buffer Amplifier, 124...Low pass filter, 125.126...Inverting amplifier, 130...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... To/ro converter. Figure 2: Cross-sectional view of the optical system in row A of the housing Figure 3: Perspective view of the optical system of sugar roll 1 Figure 4: Color filter arrangement of the embodiment Diagram showing the configuration Figure 8 Umbrella (phantom 47) 0';00 fat
7θθ 80θ'? 00!
006 liquid length Cnrn) Fig. 10 shows the spectral grade characteristics of the light receiving part of the COD chip of the example (nm) Fig. 11 shows the basic curve 1 of total light Fig. 11 shows the relative power (%) ) 400 SOD 600 700
11001 Length (nm) Example cQ Spectral transmission characteristics of infrared absorption filter Binding diagram Figure 13 Circuit diagram of the matrices or amplifiers of the embodiments Circuit diagram of the white balance correction section of the embodiments Figure 22

Claims (1)

[Claims] A light source, a plurality of color filters that select the wavelength of light reflected from a document irradiated by the light source, and an image sensor that photoelectrically converts light reflected by the document selected by the color filter; A document reading device comprising: a correction means for correcting the output level of each color image signal output from the image sensor to a predetermined reference level when reading a black image of the document.