JP2584745B2 - Image reading device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reading device.

[Prior Art] Various image reading apparatuses for photoelectrically reading a document image have been proposed.

There is also known a licensor in which a plurality of light receiving elements made of amorphous silicon or the like are arranged in a line in the width direction of a document to be read in order to photoelectrically read the density of a document image.

Now, the short side direction (about 210 mm) of an A4 size document is 16 pixels /
When reading at the same magnification with a resolution of mm, one line sensor having about 3500 light receiving elements on a substrate of about 300 mm is required. However, it is difficult to form such a large number of light receiving elements on the same substrate without dropping them and to have a substantially uniform sensitivity. Therefore, unless the yield and the like are improved, the cost is not practical.

Therefore, it is conceivable that a plurality of line sensors including about 1000 light receiving elements are arranged in the scanning direction and an image of one line is divided and read by each line sensor. In this case, the number of light receiving elements to be formed on the same substrate is not so large, so that the yield can be improved and the cost problem described above can be solved to some extent.

However, variations in the sensitivity among the line sensors are presently about 10 to 20%.

When a color original is separated into three primary colors and read photoelectrically, one pixel needs image signals for three colors, so that the signal amount is three times as large as that of a black and white image. ,
In order to perform high-speed processing, the processing speed is three times as high as that of a monochrome image, and it is difficult to perform high-speed processing as in the case of monochrome.

[Means for solving the problem]

SUMMARY An advantage of some aspects of the invention is to provide a color sensor that converts light from a subject into an image signal of a plurality of colors and outputs the image signal and outputs a plurality of color image signals output from the color sensor. A common amplifying means for amplifying up to the voltage level of, a reference white portion, and, when reading the reference white portion, only the image signal of the color having the maximum output level among the image signals of the plurality of colors from the color sensor. Control means for controlling the amplifying means to amplify the image signals of the plurality of colors based on the image signal.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a color contact sensor is used for reading a document. This color contact sensor is shown in FIG.
As shown in (b), a sensor unit 11 equipped with a plurality of CCD chips, a focusing rod lens array 12 and a focusing rod lens array arranged on the sensor unit.
The linear light source 13 and the reflection gas 14 provided in the vicinity of the side surface of the unit 12 form an integral structure. The light from the linear light source 13 is reflected from the original, and the reflected light is passed through the converging rod lens array 12 without any reduction to a plurality of CCD chips as erect real images in a one-to-one relationship. Be combined.

In addition, sensor unit 11, focusing rod lens array
As shown in FIG. 1B, the signal processing board 17, the sensor unit 11 and the signal processing board 16,
Are mounted on the moving body 15 together with the flexible electric wires 18 for connecting the moving body 15 and the flexible electric wires 19 for connecting the moving body 15 to the main body.

The optical image formed on the CCD chip as described above is converted into electric charges by the photoelectric conversion capability of the CCD. This charge is sequentially transferred by the charge transfer capability of the CCD to become an image signal.

Each part will be described in detail. As shown in FIGS. 2 and 3, a contact type color CCD sensor (sensor unit) 11 includes a ceramic substrate 26 provided with five CCD chips 21 to 25 arranged in a staggered manner, and a ceramic substrate 26 provided with the ceramic substrate. The cover 27 covers the board 26, and includes flexible electric wires 28a to 28f for connection. In the CCD chips 21 to 25, the light receiving portion is formed of a pn photodiode, and the size of the light receiving portion is 62.5 μm × 15.5 μm. As shown in FIG. 4, the corner CCD chip photosensitive pixels are light-shielded pixels D13 to D36 and dummy pixels D37 to Shield of idle feed pixels D1 to D12Al which are not connected to the photosensitive pixels.
The light receiving section is composed of a total of 3168 bits of D72, valid signal pixels S1 to S3072, and rear end dummy pixels D73 to D76.

Further, as described above, the CCD chips 21 to 25 are arranged in two rows in a staggered manner as shown in FIG. In this case, as shown in FIG. 3, adjacent CCD chips are provided in parallel with a distance 1 (l = 4 pixels in this embodiment) from the center of the light receiving section. These CCD chips 21 to 25 are arranged so as to overlap each other in the arrangement direction.

As described above, the light receiving sections of the CCD chips 21 to 25 include the idle feed areas D1 to D12, the light shield areas D13 to D36, the dummy areas D37 to D72, the effective pixel areas S1 to S3072, and the rear end dummy area D7 from the left end.
3 to D3072, of which the regions except for the 3072-bit effective pixel region S1 to S3072 are arranged so as to be overlapped with each other, and the reading effective region is a short width 29 of A3 size.
320mm which is slightly longer than 7mm.

In the light receiving sections of the CCD chips 21 to 25, it is necessary to arrange a color filter on the Si photodiode in order to receive a color signal. As this method, there are a method of bonding the color filter and the Si element with an adhesive, and a method of laminating the color filter directly on the Si element. In the former case, the color filter may be manufactured on a glass substrate, but an extra step of bonding is required when combining with a Si element, and alignment errors are likely to occur. It is extremely difficult to reduce the bonding error to less than a few mm, and the color reproducibility and the shading characteristics may be degraded. On the other hand, in the latter case, simply producing a color filter according to the pixels of the Si element completes the color element,
The process is very simple, and the alignment accuracy can be greatly improved. Therefore, the color filter of the CCD chip used in this embodiment is the latter.

Next, a specific filter arrangement will be described. In this embodiment, as shown in FIG. 5, a filter array of yellow (Ye), green (G), and cyan (Cy) is used, and one pixel at the time of reading is constituted by three bits.

FIG. 6 shows the spectral characteristics of these filters. As shown in FIG. 6, the transmittance of the Ye filter rapidly increases from around 500 nm as shown by the curve 61. The transmittance of the Cy filter shows a peak near 500 nm as shown by curve 62. In this embodiment, the G filter is a Cy filter and a Ye filter.
Since the transmittance is obtained by overlapping the filters, the transmittance shows a peak near 500 nm as shown by a curve 63.

An important point in the spectral characteristics of these filters is that the transmittance does not become zero even at a wavelength of about 700 nm outside the human visibility range.

Here, the color filter and the CCD chips 21 to 25 must perform the same function as the human eye. CCD chip 2
The spectral characteristics of the light receiving sections 1 to 25 are 550 as shown in FIG.
It has a maximum relative wavelength of about nm and a finite relative sensitivity up to 1000 nm or more.

That is, the light receiving sections of the CCD chips (4a) to (4e) provided with the color filters in the present embodiment have a response even to light having a wavelength of 700 nm or more.

In contrast, the visibility of the human eye is zero for wavelengths above 700 nm. Therefore, only the CCD chips (4a) to (4
The combination of e) and the color filters of Cy, G and Ye alone cannot fulfill the same function as the human eye. Therefore, in the present embodiment, the above-described characteristics are corrected using a filter as described later.

Next, the focusing rod lens array will be described. The converging rod lens array 12 in this embodiment has a document surface 81 at the focal length on the light incident side and two rows at the focal length on the emission side.
There is a CCD chip row 82.

With this setting, the document surface 81 and the CCD chip row 82 have an image forming relationship. That is, the image on the original surface 81 is 1
The image is formed on the CCD chip row 82 as a one-to-one erect image. However, since there is only one focusing rod lens array 21, in this embodiment, the erect image formed on the CCD chip array 82 is an image spaced four lines apart on the document surface 81. . In order to solve this, in this embodiment, a dedicated memory is used as described later.

Next, the light source 13 will be described. In this embodiment, a halogen lamp is used as the light source 13.

The functions required for a contact type sensor as a reader are:
Like the human eye, this function reads colors.

FIG. 9 shows a Thomson-Wright basic curve. This curve shows the visibility characteristics of the human eye according to the color, that is, the relationship between the sense of brightness for colored light and the wavelength of light. P _1, P _2, P ₃ of the human eye as is apparent from the curve 700n
It does not feel for light with long wavelengths longer than m.

On the other hand, the spectral characteristics of the light receiving sections and the color filters of the CCD chips 21 to 25 have a finite sensitivity value even for light having a long wavelength of 700 nm or more, as described above.
When white light is incident on the light receiving sections of D chips 21 to 25, 7
It is felt even with light having a long wavelength of 00 nm or more.

Therefore, in this embodiment, an infrared cut filter having almost no spectral characteristics in a long wavelength region of 700 nm or more is used together with a halogen lamp. FIG. 10 shows the spectral characteristics of the above-described halogen lamp, and FIG. 11 shows the spectral characteristics of the infrared cut filter.

FIG. 12 is a configuration diagram of a color image reading apparatus 121 using the contact type color CCD sensor described above. Reference numeral 14 denotes a document scanning unit which moves and scans in the direction of arrow A to read the image of the document 123 on the document table, and simultaneously turns on the exposure lamp 13 in the document scanning unit 14 so that the reflected light from the document is collected by the converging unit. The light is guided to the drain lens array 12 and condensed on the contact type color CCD sensor 11 described above. Reference numeral 126 denotes a standard white plate which is read to obtain a reference signal.

As described above, the contact type color CCD sensor 11 is 62.5 μm (1
/ 16 mm) as one pixel, and 5 chips of 1024 pixels are arranged in a staggered pattern, and each pixel is 15.5 μm × 62.5 μm
, And color filters of Cy, G, and Ye are attached to each of them. As a result, a color original is photoelectrically read while color separation is performed for each line.

Next, the electric system will be described. The electrical system consists of a drive circuit that operates the CCD, an analog processing unit that converts the output signal of the CCD into a form suitable for image information, and a digital signal processing unit that converts the signal from the analog processing section into a signal suitable for the recording format It is configured.

First, the driving circuit will be described. However, in the following explanation, CC
The driving circuit of the D chip 21 is used. Similar driving circuits are provided for other CCD chips. As shown in FIG. 14, the driving circuit includes a two-phase clock φ ₁ , φ ₂ scanning synchronizing signal SH, a reset signal R
S, only the output signal OS is handled.

The clock signal phi ₁ input terminal inverter 141 is connected to the output of inverter 141 and resistor 142 and speed up-capacitor 143 is connected in parallel, further MOS
Is connected to the input terminal of the clock driver 144. This M
The output terminal of the OS clock driver 144 is connected to the φ terminal of the CCD chip 21. It is similar to the phi ₁ also clock signals phi _2. Further, ₁ is also phi to scan synchronization terminal SH, similarly to the phi ₂ inverter 141, resistor 142, capacitor 143, MOS black poke driver 144 is connected.

The output signal OS terminal is connected to an emitter follower including an npn transistor 145 and a collector resistor 146 and an emitter resistor 147. The power supply voltage + V of the CCD chip 21 is connected to the OD terminal of the CCD chip via the capacitors 148 and 149.

The two-phase clocks φ ₁ and φ ₂ are signals necessary for transferring the electric charge generated in each bit of the CCD chip 21.

The scan synchronizing signal SH is a signal for discriminating one scan in transferring the electric charge of the CCD chip 21, and the reset signal RS is a signal for erasing a bit after the electric charge is transferred.

The signal OS is an output signal from the CCD chip 21 and, as shown in FIG. 4, is equivalent to 3072 bits of the valid signal, and outputs a dummy signal, an idle feed signal and a reference black level signal.
The bit positions of these signals are accurately specified, and the reference black level signal is a dark signal of the light receiving section and is used to obtain a true output corresponding to the color.

Next, an analog processing section is shown in FIG. The analog processing unit is provided for each of the CCD chips 21 to 25. Here, a circuit for the CCD chip 21 will be described as a representative. Similar circuits are provided for other CCD chips.

The signal from the CCD 21 is input through a buffer circuit 131 to a multiplexer 132 for separating the signal for each color. Among the output signals of the respective colors from the multiplexer 132, the color output signal (Ye in this embodiment) having the maximum output voltage when the white plate 126 is illuminated before the original is scanned is
Automatic gain control (AGC) provided at a stage preceding the multiplexer 132 to amplify an output signal from the CCD 21 to a predetermined voltage value
The signal is input to an AGC control circuit 138 that controls the circuit 133. Then, at the time of white plate irradiation, the AGC voltage for amplifying the output signal from the CCD 21 to a predetermined voltage value is fixed.

Further, the output signal of each color obtains a true output corresponding to light by the first clamp circuit 134 based on the reference black level signal, and further includes an amplifier 135 for amplifying the output signal to a voltage to be inputted to the next stage color conversion unit. Output of each color from the amplifier 135 (C
(y, G, Ye) to blue (B), green (G), and red (R). The output signal from the color conversion circuit 139 is converted into a digital signal by the A / D conversion unit 136, and the signal from the A / D conversion unit is stored in the memory unit 140.

The multiplexer 132 is a first sample and hold (S / H) for separating Cy and G from the output signal from the buffer circuit 131.
The circuits 132a and 132b and the second S / H circuits 132c to 132e for separating Ye from the Cy and G signals sampled and held and the output signal from the buffer circuit 131 are output from the CCD 21 as described above. The serial signal of Cy, G, and Ye is converted into a parallel signal with the same synchronization by two sample-and-holds. By doing so, the actual signal processing time in the next-stage color conversion becomes three times the signal output period, and a sufficient margin can be provided for the circuit performance and the like.

At the stage before scanning of the original, the CCD 21 when the light source 13 illuminates the white plate 126 provided at the end of the contact glass 125
Are separated into Cy, G, and Ye by the multiplexer 132. The AGC control circuit 138 has a configuration as shown in FIG. 15, in which the color signal Ye having the maximum output signal among the respective color signals is input, and the DC signal smoothed through the LPF141 (Low Path Filter) is A / D converted. The data is converted into a digital value by the device 142, and the data is held by the latch circuit 143 until the next original scanning. This latch data is stored in the D / A converter 144.
Is converted again into an analog DC signal and input to the differential amplifier 145. A reference voltage Vret is input to the other input terminal of the differential amplifier 145, and a difference signal between the output signal of the D / A converter and the reference voltage Vref is amplified to a voltage necessary for operating the AGC. The signal is input to the AGC circuit 133 as an AGC voltage, and operates so that the output voltage of the CCD 21 becomes a constant value.

The color conversion circuit 139 includes differential amplifiers 139a to 139c for converting Cy, G, Ye to B, G, R, and outputs a color difference signal of a primary color.

The A / D converter 136 outputs B, G, and R output from the color conversion circuit 139.
After passing through an amplifier 1362 that amplifies the output signal of the A / D converter to the dynamic range of the A / D converter 1365 and a logarithmic conversion circuit 1363 that converts the output signal into a density value, the signal is sampled by an S / H circuit 1364 and A / D converted. It is converted to 8-bit digital data by the device 1365. Here, the S / H circuit 1364 exists immediately before the A / D converter 1365 because the A / D converter 1365 is a serial-parallel type and must temporarily hold an input signal.

The A / D converter 136 feeds back a digital value corresponding to the reference black level of the A / D converted digital data to the clamp circuit 1361 to control the black level to be constant. 1362 is a feedback circuit.

In this embodiment, the original scanning unit 14 is provided with a system up to the A / D converter 136, and is connected to the memory unit 140 and a main board 124 such as a digital signal processing unit by a flexible electric wire 19.

As described above, the corresponding density data Dy, Dm, and D corresponding to B, G, and R converted into 8-bit digital signals by the A / D converter 136.
c is latched by the latch circuit 1366, transmitted to the main board 124 by the flexible electric wire 19, and input to the memory unit 140.

The memory unit 140 is a storage area 14 provided for R, G, and B.
0a to 140c and a memory control unit 140d.
It has a function of performing connection processing as density data Dy, Dm, and Dc corresponding to R, G, and B as one-line image data and outputting the data to an output device such as a printer.

〔effect〕

As described above, the image reading apparatus according to the present invention includes a color sensor that converts light from a subject into image signals of a plurality of colors and outputs the signals, and converts the image signals of the colors output from the color sensor to a predetermined voltage. Common amplifying means for amplifying up to the level, a reference white portion, and based on only the image signal of the color having the maximum output level among the image signals of the plurality of colors from the color sensor when the reference white portion is read. The amplification means has a control means for controlling the image signals of the plurality of colors to be amplified.

With this configuration, even when the image signals of a plurality of colors are amplified using the common amplifying means, the amplified signal level does not saturate, and a color signal faithful to the color of the subject can be obtained. Now you can. In addition, since the circuit configuration is simplified by using a common amplifying unit, high-quality image reading can be performed at high speed.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) show the construction of a sensor unit, and FIG.
The figure shows the configuration of the color contact sensor. Fig. 3 shows the adjacent CCD.
FIG. 4 is a diagram showing the contents of the photosensitive pixels, FIG. 5 is a diagram showing the filter configuration, FIG. 6 is a characteristic diagram of the filter, FIG. 7 is a characteristic diagram of the photodiode, FIG. 9 is a diagram showing the configuration of an optical system, FIG. 9 is a characteristic diagram showing visibility, FIG. 10 is a spectral characteristic diagram of a halogen lamp, FIG. 11 is a spectral characteristic diagram of an infrared cut filter, and FIG. FIG. 13 is a block diagram of the image signal processing circuit, and FIG.
FIG. 15 is a block diagram of a CCD drive circuit, and FIG. 15 is a block diagram of an AGC control circuit. 11 is a sensor unit, 13 is a light source, 21 to 25 are CCD chips, 1
32 is a multiplexer, 132 is a sample and hold circuit, 133
Is an AGC circuit, 138 is an AGC control circuit, and 140 is a memory unit.

Claims (1)

(57) [Claims] A color sensor that converts light from a subject into image signals of a plurality of colors and outputs the image signals; a common amplifying unit that amplifies the image signals of the plurality of colors output from the color sensors to a predetermined voltage level; A reference white portion; and the amplifying unit detects the plurality of colors based on only the image signal having the maximum output level among the plurality of color image signals output from the color sensor when the reference white portion is read. Control means for controlling the image signal so as to amplify the image signal.