JPH089101A - Color image reader - Google Patents

Abstract

PURPOSE:To obtain the color image reader in which three color luminous flux is separated with a small separation width, color registration compensation precision is improved and on-axis color aberration of an image forming lens is compensated. CONSTITUTION:Information on an original is formed on a line sensor 2 through an image forming lens, the image in the main scanning direction is read by electric scanning of the line sensor 2 and the image in the sub scanning direction is read by moving relatively the image forming position of the line sensor 2 in this-color image reader. A 3-color dispersion element 1 that has two sets of 2-color separate means to divide a received image into 3-color luminous flux is provided in an optical path of an image forming ray L, and each of the two color separate means is made up of a dichroic plane 3(4) and a reflecting plane 5(6) arranged with a gap by a spacer. A sensor selectively receiving a light of each one color separated into three colors by an on-chip color filter 20 or the like is adopted for the line sensor 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reading device, and more particularly to a color image reading device having an improved reading accuracy of an optical image in a device for reading a color image by color separation into three primary colors.

[0002]

2. Description of the Related Art Conventionally, the following four methods have been used to scan and read a color image using a line sensor. (1) A method of switching the read color by switching the color of the monochrome image sensor + light source / filter. (2) A method in which color filters are attached in sequence of three color points on a pixel line of one line of the image sensor. (3) A method in which a reading line for three colors is provided on one chip of the image sensor. (4) Color separation into 3 optical paths with a dichroic prism
A method of reading with a book image sensor.

Of these, the method (1) is not suitable for increasing the speed. In the method (2), when considering high image quality and high resolution, the pixel density becomes high, so that the method uses a long contact sensor and has a structure in which a plurality of CCDs are arranged. In this case, there is a weak point that the boundary of the reading area of each chip is likely to be conspicuous on the read image due to the characteristic mismatch between the chips.

As shown in a part of the optical path in FIG. 18, the reading optical path is color-separated into three optical paths by a dichroic prism.
In the method (4) of reading with three black and white CCDs, strict alignment of the three image sensors is required, which requires a lot of adjustment man-hours.

On the other hand, in the method (3), since a 3-line RGB pixel array is formed on the semiconductor substrate,
There is no need for alignment for matching the registrations of the three colors, and since the reading line for each color is composed of one chip, there is no point of change in the reading characteristics within the reading area.

However, since the three reading lines do not read the same position on the document surface at the same time during reading and scanning, the memory is used to delay the previously read color information, It becomes necessary to perform digital correction such that the same position is read at the same time.

The high-speed FIFO memory and the memory control circuit required for this correction are costly, which is a bottleneck in the case of inexpensively supplying a color image reading apparatus. Further, in order to perform this correction (gap correction), since the reading position shift is replaced with the reading time shift and the correction is performed, it is premised that the reading scanning speed is completely constant. For this reason, when scanning speed unevenness is present due to vibration of the mechanism system or the like, local color misregistration occurs. Therefore, the requirement for stability of the scanning speed of the mechanism system becomes strict, and an expensive scanning mechanism system is required.

Further, in this method, since the image is formed on the three-line sensor with the same conjugate length, the MTF of RGB when the original is floated from the platen glass due to the influence of the axial residual chromatic aberration of the imaging lens. There is a problem in that the changing method becomes unbalanced, the sharpness of the thin line changes for each RGB, and black characters are colored.

Regarding this point, the method of (4) is shown in FIG.
As shown in FIG. 8, since the three image sensors (CCD) can be independently adjusted in focus, the MTFs of RGB can be adjusted in good balance.

Further, in the method (3), the read original is floated from the platen glass because the reading positions of the three colors are different and the sharply focused illumination is performed to increase the illumination efficiency. In this case, the light amount of each read color changes unbalanced among the three colors, so that the color balance of the read data changes and becomes yellowish, resulting in an unsightly image.

Among these, as a countermeasure against the fact that 3 lines do not read the same point at the same time, 3 line color C
Improvements have been made to reduce the spacing between the three color read pixel columns of a CD. As one of them, as shown in FIG. 19, a method is proposed in which the horizontal transfer electrodes are not provided between the three-color reading pixel columns and the signal of the pixel column at the center of three lines is read out through the pixel columns on both sides. Has been done. In this method, the distance between adjacent lines can be reduced to about 1 to 2 lines.

However, in order to read the signal of the pixel column at the center of the three lines by passing it through the outer pixel column, there is a phenomenon in which the exposed signal is slightly superimposed on the passing read line. Therefore, it is not appropriate to bring a low output line to the inner reading line. For example, in the case of halogen lamp illumination, if B with a small light quantity is brought to the read color of the center line, there is a problem that the S / N ratio with the noise signal that is superimposed while passing through the outer pixel row becomes worse.

However, even such a measure for reducing the distance between the pixel columns does not completely read the image information on the same line at the same time, and is not a complete measure.

In order to solve the problem, a proposal has been made for forming image information by optically separating three lines of image information of the same line into three reading lines provided on one image sensor chip.

As one of them, as shown in FIG. 20, a white light source including a desired wavelength region is used for a lamp of a light source, and an image forming lens for forming an image of reflected light from an original and a black and white three line which is a light receiving element. In the optical path with the CCD, two layers of dichroic film (dichroic film) that reflects only a desired wavelength range and a reflective film that reflects light over all wavelengths, a total of three layers, through a transparent layer. Using a beam splitter consisting of dichroic mirrors stacked together, three parallel light beams (R
There has also been proposed a structure in which color separation is performed according to GB) and an image pickup device integrally provided with a plurality of black and white line sensors receives light (Japanese Patent Laid-Open No. 3-201861).

Further, the present inventor has proposed to correct the occurrence of the optical path difference for each color of the beam splitter in which the dichroic film is laminated, which is a difficulty of the above method, by using the axial chromatic aberration of the lens ( Japanese Patent Application No. 5-111818
issue). There is also a proposal to integrate a beam splitter laminated via a dichroic film with a monochrome line sensor. Here, as the three-layer film, a film formed by vapor-depositing a dichroic film / reflection film on a thin glass plate is laminated and laminated on the glass substrate.

However, in these methods, there is a concern that crosstalk may occur in which signal light other than the point on the document line that is being read is mixed into the read pixel row.

That is, in FIG. 20, R of the white light emitted from the line 1 is the second light of the laminated dichroic film.
B of the white light emitted from line 2 is reflected by hitting the first layer of the laminated dichroic film, while being reflected by the layer and reaching the central pixel line in the read line of 3 lines. The central pixel row of the read pixel rows of 3 lines is reached. Therefore, the R information of the line 1 and the B information of the line 2 are mixed.

As a countermeasure against this, it is necessary to provide a slit as shown in the drawing at a position close to the document surface to cut off the light from the line 2 to eliminate crosstalk. However, considering the adjustment margin, the opening width of this slit is 1 m.
A width of about m is required. Therefore, in order to eliminate crosstalk, the size of the gap between pixel columns of the 3-line sensor needs to be 16 lines (16 pixels) or more and about 20 lines ( Assume a read resolution of 16 dots / mm.). Further, in this way, the sensor having a large line gap has a special specification.

When the line spacing of the sensor is widened in this manner, it is necessary to increase the thickness of the transparent layer between the dichroic films, but if this thickness is adjusted to 20 line correction, it becomes 3
In order to satisfactorily correct the registration between colors to about 1/4 line, the accuracy of the thickness of the transparent layer must be created with an accuracy of 1/80 of the thickness. Since the thickness of this transparent layer is originally about 0.2 mm, it must be adjusted to about 3 μm by polishing.
The accuracy of will be very difficult.

On the contrary, even if a narrow slit is formed and the gap between lines is shortened and the number of correction lines can be reduced, when the thickness of the transparent layer becomes 0.1 mm or less, this thin glass is stable. Then, it becomes very difficult to deposit the dichroic film. Further, since the dichroic film is vapor-deposited on such thin glass, there is a concern in terms of flatness of the reflecting surface for reading with high definition.

Further, by arranging the slits as described above, the illumination luminous flux of the lamp is disturbed, so that the reduction of the illumination efficiency becomes a problem.

Further, when a full rate / half rate mirror scanning system is combined, the position of the line read by the sensor and the relative position of the slit fixed to the full rate unit are displaced during scanning of the document surface. However, as a countermeasure against this, it is necessary to strictly adjust the angle of 90 ° between the two half rate mirrors in the scanning optical system.

On the other hand, Japanese Patent Laid-Open No. 3-96063 mentions the drawbacks of such a three-layer type three-color spectroscopic element and proposes that two two-layer type two-color spectroscopic elements separate three colors. In this embodiment, "a spacer is provided between the dichroic surface and the reflecting surface to regulate the distance between the two surfaces."
And "combined with a 3-line color sensor."

However, the reason why the 3-line color sensor is used instead of the 3-line black-and-white sensor is not described, and the above-mentioned problem of crosstalk is not considered. This is because the gap between the three reading lines of 128 μm in the embodiment is such that R.
Crosstalk occurs due to color mixing between G, but no measures are taken for this. Although the optical path difference caused by the three-color spectroscopic element is taken into consideration, an attempt is made to correct the optical path difference by inclining the sensor surface to a large extent, which causes side effects such as a decrease in sensor sensitivity. In addition, the proposed optical system is large, which is disadvantageous in cost.

In addition, Japanese Patent Application No. 5-28 was filed by the present inventor.
A method has also been proposed in which the color dispersion member proposed in No. 4860 is inserted into the optical path and the spectrally dispersed light is read in combination with an on-chip color filter formed on the sensor.

In this system, the width of chromatic dispersion is reduced by using a sensor having a short gap interval to generate the above crosstalk, and light of other wavelengths is mixed as crosstalk due to the effect of the on-chip color filter. It is preventing it from coming.

However, in this method, the problem that "the resolution is slightly lowered due to the spread of chromatic dispersion" and "the separation width of RGB differs depending on the nature of chromatic dispersion, so that a sensor with special specifications is required. There is still a problem. Further, the above-mentioned problem of axial chromatic aberration of the imaging lens cannot be solved.

[0029]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and an object thereof is to enable separation of three-color light flux with a small separation width without using a slit. It is another object of the present invention to provide a color image reading apparatus that minimizes the influence of crosstalk between reading lines, improves the accuracy of color registration correction, and corrects the axial chromatic aberration of the imaging lens. More specifically, it is to enable the following.

(1) The accuracy of optical color registration correction in the conventional laminated dichroic mirror system is improved, and the light flux can be separated with a small separation width which was not possible in the conventional laminated dichroic mirror system. (2) The problem is eliminated by eliminating the slits from the three-color separation optical system and using the slits together in the conventional laminated dichroic mirror system, and at the same time, the influence of the above-mentioned crosstalk is minimized. (3) Correct the axial chromatic aberration of the imaging lens. (4) A combination with a general-purpose color CCD sensor is possible. (5) It becomes unnecessary to adjust the position of the three-color separation optical system. (6) Reduce the cost by downsizing the three-color separation optical system.

[0031]

A color image reading apparatus of the present invention which achieves the above object forms an image of information on a surface to be read on a line image sensor by an image forming optical system,
In a color image reading device that reads the main scanning direction by electrical scanning of a line image sensor and reads the sub-scanning direction by relatively moving an image forming position on the line image sensor, an imaging light beam from an imaging optical system is read. Two sets of two-color separating means are arranged in the optical path to provide a three-color separating means for dividing an incident light beam into three-color light beams, and the two-color separating means is provided with a dichroic reflecting surface and a gap provided by a spacer on the dichroic reflecting surface. And a three-line color image sensor that selectively receives light of one color among the three colors separated, is used as the line image sensor. is there.

In this case, the distance between the three read pixel rows of the three-line color image sensor can be set to 4 times or less than the sensor sampling pitch determined by the pixel interval in the main scanning direction. Then, the arrangement order of the read pixel rows of three colors of the three-line color image sensor is R, G, B or G.
The order of R and B can be set.

Further, in the structure of the reflection color and the reflection angle from each of the two-color separating means of the above-mentioned three-color separating means, the optical path difference for each color determined by the structure corrects the axial chromatic aberration of the imaging optical system. It is preferable that the light beams divided by the three-color separation means are shifted in parallel with each other.

The three-color separating means can be integrally provided on the package sealing glass of the three-line color image sensor.

As a means for separating three colors, a dichroic reflecting mirror is coated on the upper and lower surfaces of a parallel plate glass,
A glass member having a reflecting surface may be arranged so that the reflecting surfaces face each other with a spacer interposed between the dichroic reflecting surfaces.

The two dichroic reflecting surfaces of the three-color separating means can be composed of B-reflecting and R / G-transmitting ones and G / B-reflecting and R-transmitting ones. In addition, G reflection, BR
It can be configured with a transparent one, a G / R reflection, and a B transmission.

Further, as the spectral characteristics of the 3-line color image sensor, the common part of the G output light of the 3-color separating means and the B spectral sensitivity characteristic of the 3-line color image sensor, and the B output light of the 3-color separating means. It is desirable to set the spectral characteristics such that the common part of the G spectral sensitivity characteristics of the three-line color image sensor becomes small.

More specifically, as a three-color separating means, a first dichroic coat is applied to both surfaces of a plane-parallel glass.
Second and third glass members having reflection surfaces formed around the glass member 1 so as to face the dichroic surface, and fifth and fourth glass members serving as light guide paths for entering and exiting the first glass member. It can be made by bonding members.

As a method for producing a glass member in which the upper and lower surfaces of such parallel flat glass are coated with dichroic reflecting mirrors, a long parallel flat glass whose upper and lower surfaces are coated with dichroic reflecting mirrors is cut into strips. Can be created with.

As another three-color separating means, two two
The color separation means are arranged in series so that the optical axes of the respective incident light beams are deflected in the clockwise direction and reflected.
The dichroic reflection surfaces of the two two-color separating means may be composed of G / B reflection and R transmission, and G / R reflection and B transmission.

Further, as color separation means, a first surface on which the image-forming light beam is incident, a second surface composed of the first dichroic reflection surface, and a third surface composed of the second dichroic reflection surface,
A prism having a fourth surface from which the image-forming light flux is emitted and two glass members having a reflecting surface may be provided so as to face the two dichroic reflecting surfaces and via a spacer.

In this case, it can be integrally provided on the fourth surface side of the three-color separating means on the package sealing glass of the three-line color image sensor.

In the three-color separating means, the angle formed by the optical axis of the light flux incident on the three-color separating means and the optical axis of the light flux emitted from the three-color separating means is perpendicular to the angle from the imaging lens. It is also possible to incline the aperture angle of the emitted light beam.

Further, the vertical line of the sensor surface of the three-line color image sensor is inclined with respect to the optical axis of the incident light beam to the three-color separating means, and two dichroic reflecting surfaces are formed as the three-color separating means. It is composed of a parallel plate glass and a parallel plate glass with a reflecting surface formed on the flat surface of the parallel plate glass facing each other via a spacer, and this dichroic reflecting surface and a part of the reflecting surface are made to be a transmitting surface. You can also do it.

[0045]

In the present invention, two sets of two-color separating means are arranged in the optical path of the image-forming light beam from the image-forming optical system to provide the three-color separating means for dividing the incident light beam into three-color light beams. The separating means is composed of a dichroic reflecting surface and a reflecting surface arranged with a gap therebetween by a spacer, and as a line image sensor, selectively receives light of each one of the three colors separated. Since the 3-line color image sensor is used, the following effects can be obtained.

(1) In the conventional type, since the three-color separating means is a three-layer type, the dichroic reflection surface and the reflection surface are formed on both surfaces of a thin glass plate of 0.1 mm or more, so the flatness is poor and Since the glass plate cannot have a thickness of 0.1 mm or less, the separation width of the optical path is large, and the color registration correction accuracy cannot be sufficiently obtained. However, in the present invention, since it is a two-layer type, it is dichroic reflection on the glass flat surface. By forming the surface and the reflecting surface, the plane accuracy of each surface can be improved. Also, with this configuration, the spacer simply serves to separate the two color mirrors from each other.
Since the thickness can be made as thin as 0.1 mm or less and the light beam separation width is narrow, the accuracy of the separation amount can be increased.

(2) A 3-line color image sensor having an on-chip color filter on the sensor is used as a 3-line color image sensor for selectively receiving light of one color among the three colors. By combining with the above-mentioned three-color separating means, the crosstalk generated in the three-color separating means can be cut by the on-chip color filter. In addition, by narrowing the interval between 3 lines,
It is possible to minimize the influence of crosstalk that cannot be completely cut by the on-chip color filter, and it is possible to make the spacer of (1) thinner.

(3) By combining two two-layer two-color separation means, it is possible to intentionally generate an optical path difference for each color, and cancel the axial residual chromatic aberration of the imaging lens. (4) Since the spacer of (1) above can be arbitrarily set to a thickness of 0.1 mm or less, the three-color registration can be corrected in accordance with the general-purpose three-line color image sensor. (5) By integrating the three-line color image sensor, it is possible to eliminate the need for adjustment. (6) The cost can be reduced by reducing the area of the dichroic reflecting surface.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The color image reading apparatus of the present invention will be described below based on several embodiments. [Embodiment 1] FIG. 1 is a cross-sectional view of the main part of the first embodiment.
It is provided on the D sensor 2. Further, FIG. 2 is a diagram showing the configuration and optical path of the three-color spectroscopic element 1, and FIG. 3 is an enlarged optical path diagram.

As will be described in detail later, the three-color spectroscopic element 1
Is composed of five glass members 11 to 15, in which the first glass member 11 at the center has both surfaces parallel to each other, and the first dichroic film 3 and the second dichroic film 4 are provided on those surfaces. The second glass member 12 and the third glass member 13 are arranged so as to face the films 3 and 4 through the thin air layers 7 and 8, and the fourth glass member 14 is closely attached to both sides of the first glass member 11. , 5th glass member 1
5 are arranged, and the cross section of the block in which these glass members 11 to 15 are combined has a rectangular shape as illustrated. Then, a second reflection film 6 and a first reflection film 5 are provided on the surfaces of the second glass member 12 and the third glass member 13 facing the dichroic films 3 and 4, respectively.

As shown in FIG. 2, assuming that the first dichroic surface 3 is the B (blue) reflecting surface 3 and the second dichroic surface 4 is the BG (green) reflecting surface 4, an imaging lens (not shown) is formed. The incident light ray L that has passed through the fifth glass member 15
Incident on the first glass member 11 and passes through the boundary between the fifth glass member 15 and the first glass member 11 as it is,
Next, it hits the first dichroic reflecting surface 3 that reflects only B, and is separated into B rays and GR rays. The G and R rays are first emitted to the air layer 7, and then the first rays of the third glass member 13 are emitted.
It is reflected by the reflecting surface 5 and returns to the first glass member 11 again.
At this time, the B ray and the GR rays are shifted parallel to each other. Next, the B and G / R rays are transmitted through the first glass member 11
And hits the second dichroic reflecting surface 4 which reflects B and G, and reflects B and G. Only the R ray passes through the second dichroic reflecting surface 4 and once exits the air layer 8. Then, the R ray hits the second reflecting surface 6 of the second glass member 12, is reflected, and returns to the first glass member 11 again. G ・
The R ray is separated into G and R rays, becomes a ray shifted in parallel to three colors, travels in the first glass member 11, and enters the fourth glass member 14 as it is. Finally, the fourth glass member 14 is emitted and an image is formed on the corresponding on-chip color filter 20 of the 3-line color CCD sensor 2 located therebelow.

The three-color spectroscopic element 1 thus combined with the three-line color CCD sensor 2 is arranged so as to receive the image-forming light flux from the image-forming lens (not shown), and The reading system is relatively moved in the sub-scanning direction, and the main scanning direction is read by electrical scanning of the 3-line color CCD sensor 2. The reading in the sub-scanning direction is performed at the image forming position on the 3-line color CCD sensor 2. Performed by relative movement.

By the way, as shown in FIG. 3, when the first dichroic reflecting surface 3 is provided at an angle of, for example, 67.5 ° with respect to the incident light ray L traveling through the first glass member 11, the incident white light is incident. The light L is separated into B rays reflected by the reflecting surface 3 and G rays and R rays transmitted therethrough. The B ray reflected by the dichroic surface 3 is reflected in the direction of 45 ° with respect to the incident ray L. The transmitted G and R rays are
The glass medium 11 is refracted by coming out of the air layer 7 and then reflected by the reflecting surface 5 provided in parallel to the dichroic reflecting surface 3, and again passes through the dichroic surface 3 to enter the glass medium 11. At this time, the rays of G and R are
The position of the luminous flux for the ray of B is sin (67.5 °) × 2 × d × tan {sin ^-1 (n ・ sin (90 ° -6
7.5 °)} = 1.30 × d will be shifted in parallel. At this time, d is the distance between the dichroic reflecting surface 3 and the reflecting surface 5, and n is the refractive index of the glass 11, which is simply calculated here as 1.5.

Here, since the G and R rays are large rounds with respect to the B ray, 2 × d ÷ cos {sin ⁻¹ (n · sin (90 ° -67.5 °)} −
An optical path difference of 1.30 × d ÷ tan (67.5 °) ÷ n = 2.44 × d−0.36 × d = 2.08 × d occurs.

Thus, the G and R rays parallel-shifted with respect to the B ray enter the next dichroic reflecting surface 4. On this surface 4, G and B are reflected and only R is transmitted. Here, the dichroic reflecting surface 4 is formed by vapor-depositing the dichroic film 4 on both surfaces of the parallel flat plate glass as described later, and is parallel to the first dichroic reflecting surface 3. Therefore, the same amount of light beam shift and optical path difference as that between B and G · R occurs between the G and R rays that have not been separated so far.

Thus, the three parallel light fluxes of G, R and B are split into light fluxes shifted by 1.30 × d. These light fluxes enter a three-line color CCD sensor 2 provided directly below the three-color spectroscopic element 1.

Assuming that the 3-line color CCD sensor 2 has an interline distance of 28 μm (a pixel has a gap of 2 lines for 14 μm), the dichroic reflection surfaces 3 and 4 and the reflection surface 5 are used. , The distance of 6 d
Is 21.5 μm. The number of 28 μm is the number of an off-the-shelf sensor that uses the intra-pixel transfer method.

Here, as shown in FIG. 4, in order to form the thin air layers 7 and 8 between the dichroic reflecting surfaces 3 and 4 and the reflecting surfaces 5 and 6 facing each other, the spacers 1 are formed at both ends.
6 and 16 are provided, and by adjusting the thickness thereof, it is possible to correspond to a 3-line color sensor having an arbitrary interline distance. At this time, if the correction accuracy of the distance between lines is 1/4 line, the thickness of the spacer 16 may be made with an accuracy of ± 1/8. In this case, since the ratio of the tolerance to the thickness is small, the accuracy of ± 1/8 to the thickness can be easily achieved.

In the method of forming dichroic films on both sides of a thin glass plate used in an existing three-color spectroscopic element,
It is difficult to obtain this line correction accuracy. Originally, in order to prevent the above-mentioned crosstalk, in order to completely separate the three colors by combining the three-color spectroscopic element and the slit, it is necessary to make the three-line separation width large for 20 lines or more. It is very difficult to suppress this separation width to 1/80 accuracy as described above (1/80 = 1/4/2).
0). On the contrary, when the glass thickness becomes thin, it becomes very difficult to form a dichroic film on this glass plate by vapor deposition, and the glass plate is distorted by the stress of the vapor deposition film when vapor deposition.

FIG. 5 shows the structure of the glass block of the three-color spectroscopic element 1 of the present invention. Four glass members 1 are provided around the first glass member 11 having the dichroic films 3 and 4 on both sides.
2 to 15 are pasted together. Among them, the second and third glass members 12 and 13 have the role of forming the reflecting surfaces 5 and 6 facing the dichroic surfaces 3 and 4, and the dichroic surfaces 3 and 4 of the first glass member 11 are the same. Reflective films 5 and 6 are provided on the surfaces facing each other. Then, spacers 16 as shown in the drawing are arranged at both ends between the dichroic surfaces 3 and 4 and the reflecting surfaces 5 and 6 so that the distance between the two surfaces can be maintained at a desired distance. Also, the fourth and fifth glass members 14, 15 are 3
The fourth glass member 1 plays a role of causing a light beam entering and exiting the color spectroscopic element 1 to enter the entrance surface and the exit surface vertically.
The entrance surface of No. 4 and the exit surface of the fifth glass member 15 are perpendicular to the optical axis. The surfaces of the glass members 14 and 15 that come into contact with the glass member 11 are treated so that light rays are not refracted or diffusely reflected, and are bonded together with an optical adhesive.

The surface between the glass member 14 and the glass member 12 and the surface between the glass member 15 and the glass member 13 are misaligned by about ± 10 minutes in angle when the other surfaces are bonded accurately. Although it occurs, by filling the gap with a flexible material such as tar, this mismatch is absorbed and fixed.

Here, FIG. 6 shows a method of forming the first glass member 11 having the dichroic films 3 and 4 on both surfaces. Dichroic films 3 and 4 on both sides of a long parallel flat glass plate 17.
The first glass member 11 can be produced several times at a time by cutting the product subjected to the step as shown in the drawing. In this way, the parallel flat plate glass 17 having originally high surface accuracy
By using, the two dichroic surfaces 3 and 4 can be manufactured with high precision.

By the way, when such a three-color spectroscopic element 1 is used, as described in the conventional problem, light other than the color to be read from different reading lines on the original causes crosstalk. This is shown in FIG. As in the case of FIG. 20, the lights emitted from different lines 1 and 2 on the original document follow the optical path shown in FIG. 7, and the G light emitted from the line 1 and the B light emitted from the line 2 are C
An image is formed on the same reading line G on CD2. Here, by providing an on-chip color filter 20 for reading each reading color on each of the three reading lines of the CCD 2, it is possible to block noise light that comes in as crosstalk. In FIG. 7, B input from line 2 other than the line to be read
Light can be blocked with a G filter on the G line.

At this time, the effect of this block is between R and G and between B and G like the spectral characteristic of each reading line of the on-chip filter 20 on the 3-line color CCD sensor 2 shown in FIG. Not perfect due to some color mixture present. Among the mixed colors, the mixed color of R and G is unavoidable in order to bring the spectral characteristics of the sensor close to the spectral characteristics of human eyes.

However, if the 3-line color CCD sensor 2 that uses the intra-pixel transfer system and the gap between the reading lines is reduced as described above, blurring between adjacent lines will occur as blurring caused by aberration of the imaging lens. Since crosstalk exists, the crosstalk due to this color mixture is inconspicuous.

If R and B, which do not mix colors with each other, are arranged on both sides of the three lines of the three-line color CCD sensor 2 apart from each other, the distance between the lines becomes the largest and the influence of crosstalk should be noticeable. Interference between read lines can be prevented.

By the way, when the three colors are separated by the two two-layer surfaces in this way, as described above, a difference in optical path occurs between the three colors, and axial chromatic aberration occurs. On the other hand, the uncorrected axial chromatic aberration also remains in the imaging lens itself (not shown) that gives the incident light ray L. FIG. 9 shows how the axial chromatic aberration of the imaging lens is corrected. In the case of a single lens, due to the difference in the refractive index depending on the wavelength, as shown in FIG.
It has chromatic aberration in which B light having a short wavelength is imaged further toward the front. This is based on the property that the refractive index of glass increases as the wavelength decreases, as shown in FIG.
In order to correct this aberration, a convex lens with a small difference in refractive index depending on wavelength (small chromatic dispersion) (for example, B in FIG. 10) is used.
It is common practice to correct the axial chromatic aberration by combining a lens (made of K7) with a concave lens (made of F2 in FIG. 10) having a large difference in refractive index depending on wavelength (large chromatic dispersion). The aberration correction amount is determined by the power distribution of these two lenses.

At this time, the glass having a large color dispersion is shown in FIG.
As shown in the above example, the inclination of the refractive index change curve has a strong tendency to become steeper as the wavelength becomes shorter than that of glass having a small chromatic dispersion. Therefore, in the process of relatively increasing the power of the concave lens having large chromatic dispersion, the image forming positions of G and R are changed as shown in FIG. 9 (b) → FIG. 9 (c) → FIG. 9 (d) → FIG.
9B, the image forming position of B moves rapidly, and in FIG. 9A, {distance of image forming point of B−G}> {image forming of G−R> The relationship of the distance of the point} is that the distance of the image forming point of BG = {G in FIG. 9B.
−R distance of image forming point}, the image forming point of B is located between R and G in FIG. 9C, and B and R in FIG. 9D.
Overlap each other, and in FIG. 9E, the image forming point of B is farther from the lens than R is. Normally, RGB comes closest to FIG.
The imaging lens is designed in the settings near (c) and FIG. 9 (d).

Here, if the setting of FIG. 9B which is an intermediate process of the axial chromatic aberration correction is made, {distance of image point of B-G} = {distance of image point of G-R} } And the distance of the image formation point from the lens is R>G> B.
This setting exactly cancels the properties of the axial chromatic aberration of the three-color spectroscopic element 1 in which the two reflecting films of two layers are combined.

The amount of axial chromatic aberration generated by the three-color spectroscopic element 1 can be adjusted by changing the inclination of the reflected ray with respect to the incident ray L. FIG.
Figure 1 shows the adjustment process. Here, the horizontal axis represents the angle formed by the incident ray L and the perpendicular of the reflecting surface 3. The vertical axis is
This is the amount of axial chromatic aberration when the separation shift amount for the three colors is fixed at 28 μm. In this way, the correction amount of the axial chromatic aberration of the imaging lens can be adjusted by setting the angle of the three-color spectroscopic element 1. With the above configuration, it is possible to provide the three-color spectroscopic element 1 that achieves the above object.

[Embodiment 2] In the embodiment 1, the arrangement order of the three-line color CCD sensor 2 is the order of R, G, B, but when the axial chromatic aberration is in this order, FIG. 9), the amount of chromatic aberration of the lenses from B to R becomes larger than that in FIG. 9C because the lens is combined with an imaging lens in which the amount of axial chromatic aberration is weakly corrected. Therefore, when the axial chromatic aberration of the imaging lens is large, the axial chromatic aberration amount of the three-color spectroscopic element 1 may not be able to cancel it.

In this case, the aberration correction amount can be further reduced by changing the arrangement order of the pixel rows of the CCD and changing the order of separating the three lines by the three-color spectroscopic element 1.
Here, considering the case where the chromatic aberration of the imaging lens of FIG. 9C is small, when the amount of axial chromatic aberration of the three-color separation element 1 is canceled out, the following two problems occur.

(1) When G and R are at both ends of the three lines, the influence of crosstalk becomes large (these two colors need to have a large color mixture due to their spectral characteristics, so they should be placed at distant positions. Absent.). (2) In the case of an intra-pixel transfer type sensor, when the signal charges of the central pixel row of three lines are read out, they pass through the reading pixel row of another color. At this time, a phenomenon occurs in which signals of other colors are mixed under the influence of being exposed to light while passing through the pixel columns of other colors. Under this influence, if B having a small amount of reading light and a relatively small amount of signal charges is set to the central pixel row, the ratio of R and G signals mixed in when passing through pixels of other two colors having a large reading light amount. It gets bigger.

From these two points, the arrangement order of the colors of the three lines combined with the lens of FIG. 9C is not preferable. Therefore,
In some cases, the B reading line is not positioned at the center of the three lines, and the axial chromatic aberration of the imaging lens is combined with the case of FIG. 9E. In this case, as shown in FIG. 12, the first dichroic mirror 3 is for G reflection and R / B transmission, and the second dichroic mirror 4 is for R / G reflection and B / B reflection.
Keep it transparent. By doing so, color separation can be performed in the order of G, R, and B. At this time, the optical path lengths are G, R, and B in ascending order. With this structure, FIG.
It becomes possible to cancel the axial chromatic aberration in combination with the image forming lens of (e). In the case of FIG. 9E, the correction amount by the concave lens having a large chromatic dispersion is larger than that of the case of FIG. 9B used in the first embodiment, so that the axial chromatic aberration between R and G becomes smaller. The amount corrected by the three-color spectroscopic element 1 becomes small.
Therefore, even if the axial chromatic aberration amount of the original imaging lens is large, the axial chromatic aberration can be corrected without having to make the angle between the perpendicular of the reflecting surface and the optical axis close to 0 ° in the first embodiment. . In Example 1, it is not preferable to set the angle between the perpendicular line of the reflecting surface and the optical axis too close to 0 °, because the optical path becomes difficult to take.

By the way, the problem with the structure of this embodiment is that since the B and G photosensitive pixel rows are located at the two ends of the three lines, crosstalk will occur if there is a color mixture between these two colors. Is to end up. As a countermeasure against this, as shown in FIG. 13, the spectral characteristic of the on-chip color filter of the color sensor is set to a filter that causes no color mixture between B and G. By doing so, the characteristics of the dichroic reflection film used here are set to 500 nm as shown in FIG. 14A showing the characteristics of the dichroic reflection surface 3 and FIG. 14B showing the characteristics of the dichroic reflection surface 4. At the boundary, since the characteristics of reflection and transmission are interchanged, "G light of the dichroic mirror must pass through the B filter of the CCD.""B light of the dichroic mirror passes through the B filter of the CCD. It is possible to suppress the occurrence of crosstalk between distant pixel rows.

As described above, it is possible to provide a three-color spectroscopic element capable of correcting chromatic aberration even when the axial chromatic aberration of the imaging lens is large as compared with the first embodiment.

[Embodiment 3] Another embodiment of FIG.
As shown in FIG. FIG. 15 is a sectional view of a main part of this embodiment corresponding to FIG. 1, and FIG. 16 is an enlarged optical path diagram corresponding to FIG. With this configuration, the imaging light flux is converted into a 3-line color CC.
The three-color spectroscopic element 1'which is incident from the side surface side of the D sensor 2 and deflects the optical axis of the outgoing light ray by 90 degrees with respect to the optical axis of the incident light ray L by the two surfaces of the three-color spectroscopic element 1 '. The three-line color CCD sensor 2 has an image formed on the on-chip color filter.

The structure of the dichroic reflecting portion of the three-color spectroscopic element 1'is similar to that of the first and second embodiments in that the dichroic reflecting surface and the ordinary reflecting surface are separated by a spacer (not shown). That is, this three-color spectroscopic element 1 '
Is composed of three glass members 31 to 33, of which the first glass member 31 at the center has a pentagonal shape as shown in the drawing, and the entrance glass surface 34 and the exit glass surface 3 intersect each other.
The second dichroic surface 4 on each of the two surfaces adjacent to 5,
The 1st dichroic surface 3 is provided, and the 2nd glass member 32 and the 3rd glass member 33 are arrange | positioned facing these dichroic surfaces 3 and 4 through the thin air layers 7 and 8. Then, the second glass member 32 and the third glass member 33
A first reflecting surface 5 and a second reflecting surface 6 are provided on the surfaces facing the dichroic surfaces 3 and 4, respectively. In addition,
The second glass member 32 and the third glass member 33 do not necessarily need to be made of glass.

Here, in order to reduce the size of the three-color spectroscopic element 1'and integrate it on the cover glass 21 of the CCD sensor 2, as shown in FIG. Tilt to the axis by 10 ° (CCD sensor 2
The vertical line of the sensor surface and the optical axis of the incident light intersect at 100 ° as shown in FIG. ), The image forming light flux that converges at the exit aperture angle of the image forming lens is detected by the CCD sensor 2
The sensor surface does not cause vignetting. By doing so, even in the optical system according to the present embodiment that guides the light beam through the path that traverses the incident light beam, this optical system can be integrated in the vicinity of the pixel row of the CCD sensor 2, and the size can be reduced.

By the way, as shown in FIG. 16, the incident light beam L is first incident on the incident glass surface 34 which is perpendicular to the optical axis.
Is incident on the first dichroic surface 3 and the first reflecting surface 5, and is reflected in the direction of 40 °. At this time, the first dichroic surface 3 is a dichroic reflection surface that reflects R and G and transmits B, and only B light reaches the air layer 7,
It is folded back at the reflecting mirror surface 5 behind. Here, the B light has a light beam shift and an optical path difference with respect to the R and G lights. These light fluxes are incident on the upper left second dichroic surface 4 and the second reflecting surface 6 and are reflected again in the direction of 40 °. At this time, the G and B lights are reflected on the second dichroic surface 4, only the R light is transmitted, reach the air layer 8, and are reflected by the reflection mirror surface 6 behind. Here, the R light has a light beam shift and an optical path difference with respect to the B and G lights.

As a result, due to the light beam shift, BG
The colors are separated into three colors in the order of less R crosstalk, and the optical path difference is that B and R have the same optical path length, and only G has the short optical path length. When the thickness of the spacers forming the air layers 7 and 8 is d, the luminous flux is sin (70 °) × 2 × d × tan {sin ⁻¹ (n · sin (90 ° -70
°)} = 1.12 × d will be shifted in parallel. At this time, n is the refractive index of the glass 31, which is simply calculated here as 1.5.
Here, if the line gap of the 3-line color CCD sensor 2 is 28 μm, the thickness d of the spacer is 2
It becomes 5 μm.

Further, here, since the transmitted ray becomes a large circle with respect to the reflected ray, 2 × d ÷ cos {sin ⁻¹ (n · sin (90 ° -70 °)} − 1.
An optical path difference of 12 × d ÷ tan (70 °) ÷ n = 2.33 × d−0.41 × d = 1.92 × d occurs. The thickness of the spacer at this time is 25μ
When m, the optical path difference is 48 μm.

As described above, the direction of deflection due to reflection in the two two-color spectroscopic elements (two-color spectroscopic element composed of the dark-colored mirror surface 3 or 4 and the reflection mirror surface 5 or 6) as in the present embodiment, In both cases, by deflecting in the clockwise direction and by making one of the three colors always reflected by the dichroic mirror surface, the optical paths of the two colors (B and R) are equal in length, and the dichroic mirror is always used. It is possible to make the optical path of the other color (G) reflected by the surface shorter than the other two colors.

In this way, the optical path difference is such that the G optical path is shorter than the R and B optical paths, and when combined with the imaging lens in the case of FIG. 9D, a suitable structure is obtained. FIG. 9 (c)
9 (d) is a design objective of a normal lens, and in particular, FIG. 9 (d) is a case where the axial chromatic aberration between the three colors is the smallest. However, even if the axial chromatic aberration is designed to be small in this way, unless the three-color achromatism is performed by using an expensive optical material such as fluorite, the RG of the lens
The axial chromatic aberration between B does not completely disappear, and the axial chromatic aberration between B and R is made uniform as shown in FIG. 9D, and the image forming point of G is shifted from that to the lens side of 50 μm to 100 μm. It is in a state. By combining such a normal imaging lens with the spectroscopic optical element 1'of Example 3, it is possible to surely correct the axial chromatic aberration of the imaging lens to a small value, even if it cannot be completely reduced to zero.

Here, the dichroic reflecting surface is
The first was R / G reflective surface 3, and the second was G / B reflective surface 4,
The first may be the G / B reflecting surface, and the second may be the R / G reflecting surface.
At this time, the arrangement order of the three colors of the sensor 2 is BG from the right.
Although it changes from R to R / G / B, the relationship of optical path difference does not change.

Furthermore, by adopting the configuration of this embodiment, 3
The number of parts forming the color spectroscopic element 1'is reduced to facilitate fabrication, and the three-color spectroscopic elements are integrated so that the color spectroscopic element 1'can be downsized and integrated, and the cost of the optical system can be reduced.

In the prior art Japanese Patent Laid-Open No. 3-96063, a similar optical system is used in which the optical paths of R and B are the same and only G has an optical path difference, but the dichroic film has a structure. Since G is transparent on both surfaces, the optical path of G is longer than that of the other two colors, which is opposite to the axial chromatic aberration of the imaging lens.
Further, in Japanese Patent Laid-Open No. 3-96063, there is no problem within the depth of focus, but since it is in the direction of expanding the chromatic aberration of the imaging lens, a problem arises when attempting high-definition reading.

[Embodiment 4] FIG. 17 shows a sectional view of an essential portion corresponding to FIG. 1 of Embodiment 4. The optical path of this embodiment is the first embodiment.
Same as, but the surface of 3 line color CCD sensor 2
By inclining by 2.5 °, the structure of the three-color spectroscopic element 1 ″ is changed to a parallel structure in which the first glass member 41 made of parallel plate glass on which the dichroic reflection films 3 and 4 are vapor deposited and the reflection mirrors 5 and 6 are formed. This is an embodiment in which the number of the second and third glass members 42 and 43 made of flat glass is reduced to three.

At this time, the dichroic surfaces 3 and 4 and the reflecting surfaces 5 and 6 are provided in order to secure a window for entering and exiting light.
As shown in FIG. 17, the part that forms the
Is limited to the left half of the upper surface and the right half of the lower surface. This structure can be easily manufactured by masking only the part where the film is not applied at the stage of applying the film to the glass members 41 to 43.

Further, air spaces 7 and 8 are formed between the dichroic films 3 and 4 and the reflecting surfaces 5 and 6 by the spacers as in the previous embodiment, and the gaps in the portions where the films 3 to 6 are not attached are made optically. Fill with glue.

With the above configuration, the structure of the three-color spectroscopic element 1 "can be simplified. Further, with this structure, the right and left lines of the three-line color CCD sensor 2 of FIG. The optical path difference between and can be increased by the inclination of the sensor 2, and the chromatic aberration correction amount of the imaging lens can be increased.

In the above four embodiments, the space between the dichroic surfaces 3 and 4 and the reflecting surfaces 5 and 6 is the air layers 7 and 8 by sandwiching the spacers 16 at both ends. It may be filled with a transparent medium such as an optical adhesive.
Further, as the spacer, a transparent spacer such as a thin transparent filter may be sandwiched.

The color image reading apparatus of the present invention has been described above based on the embodiments, but the present invention is not limited to these embodiments and various modifications can be made.

[0094]

As is apparent from the above description, according to the color image reading apparatus of the present invention, two sets of two-color separating means are arranged in the optical path of the image-forming light beam from the image-forming optical system to make the incident light beam. A three-color separating means for dividing light into three-color light flux is provided, and the two-color separating means is composed of a dichroic reflecting surface and a reflecting surface provided with a gap therebetween by a spacer. Since the three-line color image sensor that selectively receives the light of each one of the separated lights is used, the following effects are obtained.

(1) One line on the original can be imaged on the three-line color image sensor by highly accurate color registration correction by the three-color separating means of the present invention. It is possible to eliminate the color registration correction error that was present in 1. (2) The three-color separating means in the present invention can be integrated with a three-line color image sensor such as a CCD.
Color registration adjustment between lines becomes unnecessary. (3) The axial chromatic aberration originally possessed by the image forming lens can be corrected by the three-color separating means in the present invention, so that a higher quality image can be read.

(4) Since the correction amount of registration can be adjusted by the thickness of the spacer according to the 3-line color image sensor, the existing small gap 3-line color image sensor can be used.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a first embodiment of a color image reading apparatus of the present invention.

FIG. 2 is a diagram showing a configuration and an optical path of a three-color spectroscopic element of Example 1.

FIG. 3 is an enlarged optical path diagram of the three-color spectroscopic element of Example 1.

FIG. 4 is a diagram showing an arrangement of spacers for forming an air layer.

FIG. 5 is a diagram showing a configuration of a glass block of the three-color spectroscopic element of Example 1.

FIG. 6 is a diagram showing a method of manufacturing the first glass member of Example 1.

FIG. 7 is a diagram showing how crosstalk occurs in the first embodiment.

FIG. 8 is a diagram showing spectral characteristics of an on-chip filter on a 3-line color CCD sensor.

FIG. 9 is a diagram showing how axial chromatic aberration of an imaging lens is corrected.

FIG. 10 is a diagram showing the wavelength dependence of the refractive index of two types of glass.

FIG. 11 is a diagram showing a relationship between an angle and an optical path difference when the parallel shift amounts of the optical paths of three colors are constant.

12 is an enlarged optical path diagram of the three-color spectroscopic element of Example 2. FIG.

FIG. 13 is a diagram showing the spectral characteristics of the on-chip filter on the 3-line color CCD sensor of the second embodiment.

FIG. 14 is a diagram showing the spectral characteristics of the dichroic reflecting surface of the second embodiment.

FIG. 15 is a cross-sectional view of a main part of a three-color spectroscopic element of Example 3.

16 is an enlarged optical path diagram of the three-color spectroscopic element of Example 3. FIG.

FIG. 17 is a cross-sectional view of the main parts of the three-color spectroscopic element of Example 4.

FIG. 18 is a diagram showing a part of an optical path of one conventional example.

FIG. 19 is a diagram for explaining one reading method of a conventional 3-line color CCD.

FIG. 20 is a view for explaining the configuration and operation of another conventional example.

[Explanation of symbols]

L ... Incident light ray, 1 ... 3-color spectroscopic element, 1 '... 3-color spectroscopic element, 1 "... 3-color spectroscopic element, 2 ... 3-line color CCD sensor, 3 ... First dichroic surface (film), 4 ... Second Dichroic surface (film), 5 ... First reflection film, 6 ... Second reflection film, 7, 8 ... Air layer, 11 ... First glass member, 12 ... Second glass member, 13 ... Third glass member, 14 ... Fourth glass member, 15 ... Fifth glass member, 16 ... Spacer, 17
... parallel flat glass, 20 ... on-chip color filter,
21 ... Cover glass, 31 ... 1st glass member, 32 ... 2nd glass member, 33 ... 3rd glass member, 34 ... Incident glass surface, 35 ... Exit glass surface, 41 ... 1st glass member, 4
2 ... 2nd glass member, 43 ... 3rd glass member

Claims (1)

[Claims] 1. An image forming optical system forms an image of information on a surface to be read on a line image sensor, the main scanning direction is read by electrical scanning of the line image sensor, and the sub-scanning direction is connected to the line image sensor. In a color image reading apparatus which reads an image by moving an image position relatively, two color separation means are provided in an optical path of an image forming light beam from an image forming optical system.
A three-color separating unit for arranging the incident light beams into three-color light beams is provided, and the two-color separating unit is composed of a dichroic reflecting surface and a reflecting surface provided with a gap therebetween by a spacer. A color image reading apparatus, wherein a 3-line color image sensor that selectively receives light of one color of each of the three colors separated is used as the line image sensor.