JPH0421256A - Color picture reader - Google Patents

Abstract

PURPOSE:To keep the S/N among three color lights with well balance by providing optical filter means onto the faces of other two line sensors except a line sensor whose output signal level is minimum. CONSTITUTION:The ratio of unbalance in an output ratio from three CCDs is decreased by forming a G filter and an R filter on a chip to G-CCD102, an R-CCD103 without provision of a filter for correcting luminous quantity to a B-CCD101 whose output level is minimum to compensate the deterioration in the S/N caused due to unbalanced output ratio from the B-CCD101, G-CCD102, R-CCD103 receiving B, G, R lights decomposed by a blazed diffraction grating. Thus, the rate of unbalance of the output ratio from the three CCDs is decreased. Thus, the color picture is read from the three color lights with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a color image reading device, and particularly to a color image reading device that utilizes a detection means in which a color separation element made of a blazed diffraction grating and three line sensors are provided on the same substrate surface. The present invention relates to a color image reading device suitable for a color scanner, a color facsimile, etc., which can separate color image information on a document surface into, for example, blue light, green light, and red light and read it with high precision.

(Prior art) Conventionally, detailed color images on the document surface are transmitted through an optical system.
Various devices have been proposed that digitally read color image information by forming an image on the surface of a line sensor such as a CD and using an output signal from the line sensor at this time.

Generally, when reading information on a document as color information, conventionally, as shown in FIG. 11, R (red), G (green), and B (blue) are ) color filters in order,
There is a method of forming a color image on the R, G, and H color filters using a projection optical system and reading color information. In addition, as shown in Figure 12, three line sensor CCDs are arranged in a row, and R, G, and B color filters are placed on each line sensor surface, and a color image is projected onto the line sensor surface by a projection optical system. There is a method of forming the image and reading the color information.

In addition, in Japanese Patent Publication No. 62-43594, as shown in FIG. A color image detection device is proposed in which color-separated color image information is made incident on a three-line sensor 131 and the color image information is detected.

(Problems to be Solved by the Invention) A color image reading device using a single line sensor shown in FIG. It is not possible to perform color separation for each color of light, and for example, when reading an A3 size document at a reading density of 400 DPI, approximately 14,000 pixels need to be configured on one line sensor.

Generally, it is very difficult to configure such a large number of pixels with uniform sensitivity, dimensions, etc.

On the other hand, there are methods such as connecting multiple line sensors, but this method has problems such as requiring extremely high-precision correction due to the differences in the characteristics of each line sensor. .

In addition, a color image reading device using three R, G, and B line sensors as shown in FIG. 12 has a physical distance between the line sensors, similar to the line sensor in FIG. It is not possible to separate and read the same point on the image surface. Therefore, the electrically read signal is usually delayed by the distance between the line sensors and used.

However, there is a problem in that ghosts and the like occur at color boundaries due to unevenness in the relative moving speed of the document and the line sensor, resulting in image deterioration.

On the other hand, in the color image reading device shown in FIG. 13, one point on the document surface is separated into three color lights by the color separation element 132. No positional deviation occurs when reading with the line sensor shown in FIG. 12.

However, since there is a large difference in the intensity of the three colored lights separated by the blazed diffraction grating, there has been a problem that it is very difficult to read a color image in a well-balanced manner using the three colored lights.

Next, technical problems when using the blazed diffraction grating shown in FIG. 13 will be explained.

Figure 15 shows 3 when using a one-dimensional blazed diffraction grating.
Spectral characteristics of color separation system FIG. 14 shows the spectral characteristics of a color separation system in which R, G, and H on-chip color filters are formed on the conventional line sensor surface. 14th. As shown in FIG. 15, the color separation system using a blazed diffraction grating has a narrower band than the color separation system using an on-chip color filter.

In addition, the spectral sensitivity characteristics of the line sensor (CCD) (16th
), the spectral energy distribution of the illumination light source (halogen lamp) (Figure 17), and the spectral transmittance characteristics of the infrared cut filter (Figure 18) The spectral characteristics of the light output ratio are the first
As shown in Figure 9, each color light (R, G, B) is extremely different. For example, in FIG. 19, R:G:B=3:6:1. When signals based on three colored lights with different output values are processed by the signal processing circuit shown in Fig. 20, the S/N ratio will vary greatly for each colored light, and finally color correction processing such as masking is required. Doing so will cause a significant deterioration in image quality.

In FIG. 20, 100 is a 3-line sensor as a detection means, and a B-line sensor (B-CCD) that receives blue light color-separated by a blazed diffraction grating.
) 101, G line sensor (G-C
CD) 102, R line sensor (R
-CCD) 103 formed on the same substrate surface. 2001, 2002, and 2003 respectively amplify the output signals from the respective CCDs 10I, 102, and 103 to a voltage level corresponding to the reference level of the A/D converters 2004, 2005, and 2006. Note that since the signal processing units 2002 and 2003 have the same configuration as the signal processing unit 2001, their contents are omitted in the figure.

In FIG. 20, 2001a is the first amplifier, and 2001a is the first amplifier.
01b is the second amplifier and 2001C is the S/H circuit, which shields the inner light receiving section of the output signal from the CCD shown in Fig. 21 from aluminum light, and outputs the dark current component of the light receiving section as a dark output signal. The output level of the section is sampled and held.

A comparator circuit 2001d compares the S/H dark output signal level with a reference level. The second amplifier 2001b, the S/H circuit 2001C, and the comparator circuit 2001d constitute a feedback ramp circuit for keeping constant the reference level of the output signal from each CCD amplified by the first. Second amplifier 2001a
.

2001b, each CCD output signal is amplified to the dynamic range of the A/D converter.

By the way, B-CCD 101. G-CCD102, R-
The output signal ratio of the CCD 103 is different, for example, each output value is 100 mV.

600mV, 300mV, A/D converter 2004.
If the dynamic range of 2005 and 2006 is 2V, the total amplification factor in the signal processing section of each color is B: 2V/1
00mV=20. G: 2V/600mV=3. 3
．． R: 2V/300mV46.6, each C
Since the noise level output from the CD is constant, the noise level of B and R with respect to the G signal is B:20/3.3
Gradient 6. R: 6.6/3.3 = 2 times, relative S/N
The ratio will deteriorate.

The present invention uses a one-dimensional blazed diffraction grating as a color separation element to separate a color image into three predetermined color lights, and when the color image is read by a detection means consisting of a three-line sensor, an appropriate optical filter means is provided in the detection means. S between three colored lights
An object of the present invention is to provide a color image reading device capable of reading color images with high precision by maintaining a well-balanced /N ratio.

(Means for Solving the Problems) The color image reading device of the present invention illuminates a color image on a document surface using an illumination means, and uses a projection optical system to project three line sensors in parallel on the same substrate surface. When the color image is projected onto the detection means surface disposed above and the color image is read by the detection means, the light flux from the projection optical system is directed behind the projection optical system in a direction perpendicular to the direction in which the pixels of the line sensor are arranged. A one-dimensional blazed diffraction grating that separates the light into three color lights and guides the light to each line sensor is arranged, and the detection means is provided with an optical filter means for adjusting the output signal level from the three line sensors. It is characterized by the fact that it has been established.

In particular, the present invention is characterized in that the optical filter means is provided on the surfaces of two line sensors other than the line sensor with the minimum output signal level among the three line sensors.

(Embodiment) FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a document surface on which a color image is formed. Reference numeral 11 denotes illumination means, which is comprised of, for example, a Herokane lamp or a fluorescent lamp. Reference numeral 12 denotes a scanning means, which is composed of a mirror or the like, and performs line scanning of the document surface 1 in a sub-scanning direction 13 within the paper surface. 2 is a projection optical system. 3 is a one-dimensional blazed diffraction grating as a color separation element, and the light beam from the projection optical system 2 is directed in the sub-scanning direction 13 as shown in the figure.
It is separated into predetermined color light, for example, 3R color light 6, 7.8 of R (red), G (green), and B (blue). 100
is a detection means, for example, as shown in FIG.
It consists of a so-called monolithic three-line sensor in which line sensors 101, 102, 103 such as OD are arranged parallel to each other on the same substrate 107 surface. As will be described later, color filters (not shown) as optical filter means based on each color light are arranged on two line sensor surfaces of each line sensor, and the distance between each line sensor is 11.12. are set to values corresponding to the color separation directions of the color separation element 3. Note that one pixel of each line sensor has a dimension of aXa.

In this embodiment, the scattered reflected light from the color image on the document surface 1 is scanned by the scanning means 12, the light beam from the scanning means 12 is condensed by the projection optical system 2, and the light beam is condensed by the projection optical system 2, and then transmitted through the one-dimensional blazed diffraction grating 3. After color separation into three color lights, the color image on the document surface 1 is sent to three line sensors 101, 102,
The images are respectively formed on 103 planes. As a result, the color images on the document surface 1 are sequentially digitally read by the detection means 100.

Next, the specifications of the one-dimensional blazed diffraction grating 3 for color separation in this embodiment will be explained with reference to FIG.

As shown in the figure, the structure consists of a structure in which the grating is periodically turned around in steps in the color separation direction, for example, the periodic pitch P
= 60 μm, grating thickness d = d2 = 3100 nm, and refractive index of the medium n = approximately 1.5. At this time, as shown in the figure, the incident light is transmitted and diffracted and is mainly separated into three directions: +1st order, 0th order, and 11th order.

Next, the configuration of the detection means 100 of this embodiment will be explained. FIG. 3 is a schematic diagram of an embodiment showing the configuration of the three-line sensor shown in FIG. 2. 101, 102, 10 in the diagram
Line sensors 3 each include a silicon (Si) photodiode (PD). The line sensor 101 is for blue color (B-CCD), the line sensor 102 is for green color (G-CCD), and the line sensor 103 is for red color (R-CCD).
CCD). There is no color filter on the line sensor 101 surface, a green filter (G) is formed on the line sensor 102 surface, and a red filter (R) is formed on the line sensor 103 surface.
, corresponds to 3yX colors of R color. Incidentally, the color filter consists of a stripe filter made of organic dye.

204a, 204b, 205a, 205b.

Reference numerals 206g and 206b are CCD shift registers for transferring the charges accumulated in the B color light receiving section 101, the G color light receiving section 102, and the R color light receiving section 103 to the output section, respectively. It is composed of two CCD registers indicated by suffixes a and b in order to separate and transfer the charge for each pixel from 101, 102, and 103 to the left and right for each pixel. Further 207a, 207b.

208a, 208b, 209a, and 209b are an output capacitance section called a floating diffusion (FD) that detects the charge from the light receiving sections 101, 102, and 103 that are separated and transferred to the left and right, and converts it into a voltage. This is a floating diffusion amplifier (FDA) consisting of an amplifier that receives and outputs a signal.

In addition, the light receiving section 101 and the CCD shift registers 204a, 2
B-CCD consisting of 04b, FDA2D7a, 207b
Sensor, light receiving section 102, and CCD shift register 205a
, 205b, FDA208a, GC consisting of 208b
CD sensor, light receiving section 103 and CCD shift register 20
R consisting of 6a, 206b, FDA209a, 209b
- The CCD sensors are formed on the same silicon Si wafer, and each CCD sensor can be driven separately.

Now, FIG. 4 is an explanatory diagram that describes in detail the B-CCD in FIG. 3 as an example, and the operation thereof will be described next using the diagram.

The light receiving unit 101 includes a charging conversion unit Iota, an accumulation unit 301a,
301b, and the charges accumulated in the light receiving section 101 are transferred to the CCD shift registers 204a and 204b by a shift gate pulse φ5G applied to the shift gates 302a and 302b.

At this time, the charges accumulated in even-numbered pixels are equal to those of even-numbered CC
The charges accumulated in the D shift register 204b and the odd numbered pixels are transferred to the odd numbered CCD shift register 204a.

The period of this shift gate pulse φsa corresponds to the accumulation time CC]) The shift registers 204a and 204b convert the charge sent from the light receiving section 101 into two-phase clock φ0.
．． It is transferred to the output parts FDA 207a and 207b according to φ2.

FDA207a, 207b are output gates (OG) 303
a, 303b and output capacitance section (FD) 304a, 304b
and amplifier section 305a.

305b, and an output gate (OG) 3
03a, 303b are CCD shift registers 204a, 2
04b is transferred to the capacitor portions 304a and 304b.
04b, and serves as an output gate 303a.

The charge transferred beyond 303b is transferred to the output capacitor section 30.
4a and 304b, the voltage is converted into a voltage corresponding to the amount of charge, and the impedance is converted by two stages of source follower amplifiers, ie, amplifier sections 305a and 305b, and output.

In this embodiment, the color image formed on the CCD surface is read by using the detection means configured as described above.

Next, in this example, three line sensors B-CC are used when a halogen lamp is used as a light source and an infrared cut filter is used to prevent the influence of sensitivity on the long wavelength side.
D 101. The overall spectral characteristics of the output levels from G-CCD 102 and R-CCD 103 are as shown in Figure 14, where the spectral transmittance characteristics of the B, G, and R filters are
An R filter is formed on-chip to the R-CCD. ), the spectral characteristics of the blazed diffraction grating are the 15th
If the spectral sensitivity characteristics of the light receiving part of the CCD are shown in FIG. 16, the spectral characteristics of the halogen lamp are shown in FIG. 17, and the spectral transmittance characteristics of the infrared cut filter are shown in FIG. 18, then FIG. It becomes as shown in .

From Figure 6, B-CCDIOI, G-CCD102, R-
When the output ratio from the CCD 103 is determined, it is, for example, approximately B:G:R=1:3:2.5.

Now, if the output values of B-CCD, G-CCD, and R-CCD are 200 mV, 600 mV, and 500 mV, and the dynamic range of the A/D converter is 2 V, each color light B, G,
The total amplification factor in the signal processing section of R is B: 2V/200mV=10 G: 2V/600mV= 3.3R2
2V1500mV=4. Since the noise level output from the CCD of each color is constant, the noise levels of the B signal and R signal with respect to the G signal are B; 10/3.3 #3 R; 4/3.3 to 1.2.

That is, in the conventional case (noise level of B signal and R signal with respect to G signal B; 20/3.3 to 6, R; 6.6/3
．． 3 = 2 times), the noise levels of the B signal and R signal in this example are B: 3/6 = 0.5 R: 1.2/3 = 0.6, and the noise levels are relative. , and the S/N ratio improves.

In this embodiment, the B-CCDI receives the B, G, and R color lights separated by the blazed diffraction grating.
OI, G-CCD102. The deterioration of the S/N ratio caused by the unbalance of the output ratio from the R-CCD 103 is suppressed by not providing a filter for light intensity correction in the B-CCD 101 whose output level is the minimum value, but in the G-CCD 102. R-CCD1
By forming on-chip G filters and R filters shown in FIG. 14 in FIG. This allows color images to be read with high precision using three colored lights.

FIG. 7 is a sectional view of a main part of a second embodiment of the detection means 100 according to the present invention. In this embodiment, the G-CCD 102 is equipped with an ND filter (
Neutral Density Filter)70
1 and the R-CCD 103 are provided with an ND filter 702, respectively.

FIG. 8 shows a curve 801 of the spectral characteristics of the ND filter 701.
and a curve 802 of the spectral characteristics of the ND filter 702, respectively.

In this embodiment, two such ND filters 701.
702 to adjust the balance of transmittance of each color light incident on C0DIOI, 102°103, the output ratio from each CCDIOI, 102°103 is approximately B:G:R=1:1:1. I'm trying to make it happen.

For example, in the conventional example, B-CCD/G-CCD, R-C
The output signal values from the CD are 100mV and 600mV, respectively.
Assume that the voltage is 300mV. At this time, in order to make the output ratios from each CCD approximately equal, the transmittance ratio of the ND filters 801 and 802 for green light and red light with respect to B color light is set to B/G = 100 mV/600 mV, respectively, 0.17 B/R = 1
G-CCD102.00mV/300mV:0.33. It is placed on the light receiving surface of the R-CCD 103.

As a result, the output ratio from each COD is kept well balanced, and the same effect as in the first embodiment is obtained.

Figure 3g9 is a sectional view of a main part of a third embodiment of the detection means 100 according to the present invention. In this embodiment, the same magenta (Mg) filter 901 is formed on-chip on the surfaces of the G-CCD 102 and the R-CCD 103 as light amount correction filters. Note that no optical filter is provided on the B-COD 101 surface.

's10 Figure shows the magenta (Mg) filter 9 of this example.
FIG. 2 is a schematic diagram of the spectral characteristics of No. 01. According to the spectral characteristics shown in the same figure, the transmittance is about 37% for G-CCD 102 and about 37% for R-CCD.
103 is about 53%.

In the conventional example, the output values from B-CCD, G-CCD, and R-CCD are 100 mV, 600 mV, and 300 mV, respectively.
Therefore, the output values from B-CCD, G-CCD, and R-CCD are 100 mV and 600 mV x 0.3742, respectively.
20mV.

300mVxO, 534160mV. In this way, this embodiment achieves the same effect as the first embodiment described above.

The optical filter means according to the present invention is not limited to the color filter or ND filter used in each of the above embodiments, but can substantially reduce the amount of light incident on the G-CCD and R-CCD. Any filter with any spectral characteristics may be used as long as it maintains the balance of output values from each CCD.

(Effects of the Invention) According to the present invention, when a color image is color-separated and read using a seven-line 3-line sensor as a detection means and a one-dimensional blazed diffraction grating as a color separation element, the colors are separated by the blazed diffraction grating. By using the above-mentioned optical filter means, the difference in the S/N ratio due to the difference in the light intensity ratio of each color light is reduced, and it is possible to read a color image with high precision, effectively preventing deterioration of the read image quality. A possible color image reading device can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention, and FIG. Third. 4 is a schematic diagram of the main parts of the detection means according to the present invention, FIG. 5 is an explanatory diagram of a one-dimensional blazed diffraction grating, FIG. 6 is a comprehensive spectral characteristic of the color image reading device of the present invention, and FIG. FIG. 9 shows the second embodiment of the present invention. 8. A cross-sectional view of main parts of the detection means of the third embodiment. FIG. 10 shows the spectral characteristics of an ND filter and a magenta filter as optical filter means according to the present invention. Fig. 12 is a schematic diagram of a conventional detection means, Fig. 13 is a schematic diagram of a conventional color image reading device, and Fig. 13 is a schematic diagram of a conventional color image reading device.
Figure 4 shows the spectral characteristics of R, G, and B filters, and Figure 15 shows 1.
Spectral characteristics during color separation of dimensional blazed diffraction gratings, Part 1
Figure 6 shows the spectral characteristics of a line sensor, Figure 17 shows the spectral characteristics of a halogen lamp, Figure 18 shows the spectral characteristics of an infrared cut filter, Figure 19 shows the overall spectral characteristics using a conventional one-dimensional blazed diffraction grating, and Figure 19 shows the spectral characteristics of a conventional one-dimensional blazed diffraction grating. FIG. 20 is an explanatory diagram of a signal processing section of a conventional color image reading device, and FIG. 21 is an explanatory diagram of output timing of each signal of a conventional line sensor. In the figure, 1 is a document surface, 2 is a projection optical system, 3 is a blazed diffraction grating, 11 is an illumination means, 12 is a scanning means, 100 is a detection means, 101, 102°, 103 are line sensors, 107 is a substrate, 701. 702 is an ND filter 9
01 is a magenta filter. Wavelength λ [nm] Wavelength input [nm] Figure wavelength input [nml Sensitivity characteristics miscellaneous diagram Wavelength input [nml [% Coho V ρK CLAMP'] -

Claims (4)

[Claims] (1) Illuminating the color image on the document surface with the illumination means,
The color image is projected by a projection optical system onto a detection means surface in which three line sensors are arranged in parallel on the same substrate surface, and when the color image is read by the detection means, the projection optical system projects the color image behind the projection optical system. A one-dimensional blazed diffraction grating that separates the light flux from the optical system into three colored lights in a direction perpendicular to the direction in which the pixels of the line sensor are arranged and guides the light to each line sensor is disposed, and a one-dimensional blazed diffraction grating is arranged in the detection means. A color image reading device comprising an optical filter means for adjusting the output signal level from a three-line sensor. (2) The color image reading device according to claim 1, wherein the optical filter means is provided on two line sensor surfaces other than the line sensor having the minimum output signal level among the three line sensors. . (3) The three colored lights are blue light, green light, and red light, and the line sensor into which the green light enters is provided with a green filter, and the line sensor into which the red light enters is provided with a red filter. A color image reading device according to claim 1. (4) The three colored lights are blue light, green light, and red light, and as the optical filter means, ND filters with different transmittances are used for the green light and red light, or magenta color is used for both. 3. The color image reading device according to claim 2, further comprising a filter.