JPH06326833A - Color picture reader - Google Patents

Abstract

PURPOSE:To provide a color picture reader capable of performing a reading with less color slurring by devising the reader such that color plural picture information on the same line are read simultaneously and all of plural light rays subjected to color separation are focused accurately onto plural line sensors. CONSTITUTION:This color picture reader in which an original 3 is illuminated by a light source 1 and the light reflected on the original 3 is converged on plural photodetectors 6 having plural linear picture element arrays 61, 62, 63 by an image forming lens 4 is provided with a multiple dichroic mirror 5 by which the light reflected on the original 3 and converged through the image forming lens 4 by the plural reflecting films 51, 54, 55 is reflected while being splitted into plural color component lights and the image is formed onto respective linear picture element arrays 61, 62, 63 of the photodetectors 6. The length of each optical path of each color component light between the image forming lens 4 and the photodetector 6 is defined as a focal distance of the image forming lens 4 with respect to each color component light.

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 reading device for reading a color image by separating it into three primary colors.

[0002]

2. Description of the Related Art Heretofore, there has been known a color original reading apparatus which separates a color image into three primary colors and photoelectrically converts the color-separated light in each wavelength range by a light receiving element.

For example, the apparatus shown in FIG. 6 uses white light including the entire desired wavelength range as a light source 1, and an image forming lens 4 for forming an image of reflected light from a document 3 placed on a platen glass 2. And G (green light), B (blue light), R on one chip
A color image is provided while scanning in the sub-scanning direction by including a light-receiving element 6 in which three one-dimensional pixel rows 61, 62, 63 set to have spectral sensitivity characteristics of three colors (red light) are arranged in the sub-scanning direction. Is to read.

Further, as shown in FIG. 7, white light including the entire desired wavelength range is used for the light source 1, and it is provided in the optical path between the image forming lens 4 and the light receiving element 6 for forming an image of the reflected light from the original 3. A color separation means including a beam splitter 8 in which a dichroic film 81 that reflects only a desired wavelength region is laminated via a transparent layer 82 is arranged, and the reflected light is color-separated by the beam splitter 8 to obtain a plurality of one-dimensional pixels. Rows 61, 62, 63
The device that makes the image sensor with ...
It is known from JP-A-3-201861.

Further, as shown in FIG. 8, a white light including the entire desired wavelength range is used for the light source 1, and it is formed in the optical path between the image forming lens 4 and the light receiving element 6 for forming an image of the reflected light from the original 3. A plurality of line sensors 61 are color-separated into parallel rays by using beam splitters 9 and 10 in which dichroic films 91 and 101 are laminated via transparent layers 92 and 102, respectively, as color separation means for reflecting only a desired wavelength range. , 62, 63
A configuration in which an image sensor that integrally includes ... Receives light is also disclosed in Japanese Patent Laid-Open Nos. 1-237619 and 2-
It is known from the description of Japanese Patent No. 180465.

[0006]

However, the above-mentioned conventional color image reading apparatus has the following problems.

First, in the color image reading apparatus shown in FIG. 6, since the three line sensors 61, 62, 63 sequentially read, a delay memory is required to perform color processing of a color image in real time. There is a problem that the processing becomes complicated and the cost becomes high. Furthermore, it is difficult to obtain a clear image due to color misregistration due to mechanical scanning misalignment during sub-scanning.

Further, in the color image reading apparatus shown in FIG. 7, since the light path length of the light flux of each color is different, it is necessary to use an imaging lens having a sufficiently deep depth of focus in order to obtain a clear image. There are difficulties. Further, if an attempt is made to adjust the optical path length by inclining the light receiving surface of the sensor, it is necessary to increase the angle, which causes a problem that the light receiving sensitivity is lowered.

Further, in the color image reading apparatus shown in FIG. 8, the light path lengths of the light fluxes of the respective colors are equal, but they have a complicated structure and their adjustment is difficult.

Further, in any of the above-mentioned color image reading devices, the light beams of the three primary colors are detected by a plurality of line sensors 6.
It is desirable to accurately focus on each of 1, 62, 63, ... However, due to the chromatic aberration of the imaging lens 4, the rays of each color are not imaged on the same plane. For this reason, the resolution is different for each color and a color shift occurs. As a countermeasure against this, it is conceivable to use a lens with little chromatic aberration, but it is extremely difficult in terms of lens design and manufacturing to completely eliminate chromatic aberration of the imaging lens 4 in a desired wavelength range.

The present invention has been made in view of the above problems, and an object of the present invention is to read color image information on the same line at the same time, and
An object of the present invention is to provide a color image reading device capable of reading with little color shift by accurately focusing all of a plurality of color-separated light rays on a plurality of line sensors.

[0012]

A color image reading apparatus according to the present invention comprises a light source, an imaging lens for collecting reflected light from a document illuminated by the light source, and a first lens provided in parallel at a predetermined interval. A light-receiving element having one one-dimensional pixel array and a second one-dimensional pixel array; and a first reflective film that selectively reflects the first color component light on both planes of a transparent layer having parallel planes. And a second reflection film that reflects at least a part of the specific color component light as the second color component light from the light that has passed through the first reflection film, and the first reflection film and the second reflection film. The reflection film separates the reflected light from the document condensed by the imaging lens into the first color component light and the second color component light, and reflects the light.
Color separation means for forming an image on a first one-dimensional pixel row and a second one-dimensional pixel row of the light receiving element, respectively, and the first color component between the imaging lens and the light receiving element. The lengths of the optical paths of the light and the second color component light are respectively defined as a first focal length of the imaging lens for the first color component light and a second focal length of the second color component light for the second color component light. It is characterized by doing.

Further, in the color image reading apparatus of the present invention, the light source, the imaging lens for collecting the reflected light from the original illuminated by the light source, and the first lens provided in parallel on the plane at a predetermined interval. A light-receiving element having a one-dimensional pixel array and a second one-dimensional pixel array, and a first focal length for the first color component light of the imaging lens with respect to the optical axis of the imaging lens. And a second focal length for the second color component light, the transparent layer is disposed so as to form a predetermined angle based on the ratio between the distance between both focal points and the predetermined distance of the light receiving element, and has a parallel plane. A first reflection film that selectively reflects the first color component light on both planes and at least a part of the specific color component light from the light that has passed through the first reflection film is reflected as the second color component light. And a second reflective film for controlling the thickness of the transparent layer to the predetermined angle. A color separation unit set based on a predetermined distance of the optical element, and the plane of the light receiving element is perpendicular to the reflected light from the document condensed by the imaging lens reflected by the color separation unit. Is arranged so as to receive light, and the reflected light from the document condensed by the imaging lens is split into the first color component light and the second color component light, and the first light component of the light receiving element is separated. An image is formed on each of the one-dimensional pixel row and the second one-dimensional pixel row.

[0014]

With the above arrangement, when reading a color image, the image information of a single line with no positional deviation can be read. Further, the image information of this single line is separated by the optical means at an interval corresponding to the array pitch of the line sensors arranged for each color component, and at the same time, each color light ray has a different optical path length for each color component. After that, it is guided to the line sensor. At this time, the thickness of the transparent layer laminated between the dichroic films, the beam splitter, and the line so that the difference in the optical path length for each color component in the color separation means matches the amount of deviation of the focal position due to the longitudinal chromatic aberration of the imaging lens. By setting the installation angle of the sensor, it is possible to accurately focus all of the plurality of color-separated light rays on the plurality of line sensors.

[0015]

1 is an explanatory view of an optical system showing an embodiment of a color image reading apparatus of the present invention. In the figure, 1 is a white slit light source whose emitted light flux includes almost the entire visible wavelength range, 2 is a platen glass for placing an original 3, and white light emitted from the light source 1 is emitted from the platen glass 2. The light is transmitted and reflected by the original 3, and the reflected light is formed by the imaging lens 4.
Is collected at. Reference numeral 5 denotes a multiple dichroic mirror as color separation means for separating the reflected light from the original 3 into information of three primary colors. The reflected light color-separated by the multiple dichroic mirror 5 enters a light receiving element 6 which is an image sensor. . The light receiving element 6 has three one-dimensional pixel rows, and
The reflected light reflected by is received and the image information of the original 3 is output as an electric signal.

In the multiple dichroic mirror 5 of this embodiment, a dichroic film 51 for reflecting a G (green) light component is coated on the outermost surface on the side where a light beam enters, and 2
The transparent surfaces 52 and 53 of the layers are coated with a dichroic film 54 that reflects a B (blue) light component, and R that has passed through the dichroic films 51 and 54, respectively.
The total reflection film 55 that reflects the (red) light component is the transparent film 53.
Is formed on the back surface of.

As described above, the color separation means in this embodiment is a multiplex structure in which the two dichroic films 51 and 54 and the one total reflection film 55 are laminated via the two transparent layers 52 and 53. It is the dichroic mirror 5.

Further, the light receiving element 6 is, as shown in FIG.
Predetermined pitches P1 and P2 on one chip, for example, 80
Three one-dimensional pixel rows 6 arranged in parallel at intervals of μm 6
1, 62, 63, wherein each of the components G, B, R of the three primary color lights color-separated by the multiple dichroic mirror 5 is a one-dimensional pixel array 61, 62, 63.
It is arranged so that it collects light.

The chromatic aberration characteristics of a normal imaging lens designed so that the chromatic aberration becomes small as a whole tend to have a longer focal length in the order of green (G), blue (B), and red (R). Therefore, each one-dimensional pixel array 61, 62, 63 is
The green light reading light receiving element, the blue light reading light receiving element, and the red light reading light receiving element are arranged in this order. In addition,
A filter for removing unnecessary component light may be attached to the light receiving element of each color. Further, the intervals of the array of one-dimensional pixel columns do not necessarily have to be the same.

Here, the thickness of each layer of the multiple dichroic mirror 5 and the inclination angle θ of the imaging lens 4 with respect to the optical axis 7.
Is determined by the amount of longitudinal chromatic aberration of the imaging lens 4 and the pitches P1, P2 between the three one-dimensional pixel rows 61, 62, 63 on the light receiving element 6, and the additional amount of the optical path length of the light flux of each color component is The amount of longitudinal chromatic aberration of the imaging lens 4 is adjusted by the multiple dichroic mirror 5 which is a color separation means.

The amount of change in the optical path length of each color ray due to the tilt angle θ of the multiple dichroic mirror 5 with respect to the optical axis 7 of the imaging lens 4, that is, the amount of shift of the image forming position due to the change in optical path length, and the interval between reflected lights, that is, beam separation. Figure 3 shows the width relationship
Shown in. The horizontal axis represents the incident angle θ (see FIG. 1), and the vertical axis represents the relative value.

In FIG. 3, the multiple dichroic mirror 5 is shown.
Both of the transparent layers 52 and 53 have a refractive index of N = 1.52, a broken line A indicates a change in the shift amount of the image forming position due to a change in the optical path length, and a solid line B indicates a change in the beam separation width.

From the relationship shown in FIG. 3, the transparent layers 52 and 53 of the optimum multiple dichroic mirror 5 are optimized based on the characteristics of the image forming lens 4 and the shape and size of the light receiving element 6 actually used.
The thickness and the inclination angle θ to be installed were designed.

As shown in FIG. 4, the shift amount of the image forming position of each color component light due to the longitudinal chromatic aberration of the image forming lens 4 used in this embodiment is as follows with respect to the image forming position 41 of the G (green) component light. The image forming position 42 of the B (blue) component light is about 50 μm, and the image forming position 43 of the R (red) component light is about 100 μm farther from the image forming lens 4. That is, FIG. 4 shows that the position 41 is the image forming position of the G component light because the MTF (modulation transfer function) value of the imaging lens 4 is the largest at the position 41 for the G component light. It is shown that the positions 42 and 43 where the MTF value is maximum for the component light and the R component light are the respective imaging positions.

Therefore, in this embodiment, in order to image each color component light at the same position, the optical path length of the B component light is made longer than the optical path length of the G component light, and the optical path length of the B component light is further increased. On the other hand, the optical path length of the R component light is increased. In order to add the optical path length in this way, both the first transparent layer 52 and the second transparent layer 53 of the multiple dichroic mirror 5 have a thickness of 0.1.
The thickness was set to 1 mm.

The procedure for determining the thickness of the first transparent layer 52 and the second transparent layer 53 will be described below with reference to FIG.

Transparent layer 5 of multiple dichroic mirror 5
FIG. 5 shows the relationship among the thicknesses of ₂ , 53 (refractive index n ₁ , n ₂ , film thickness t ₁ , t ₂ ), reflection angles θ ₁ , θ ₂ , beam separation width d ₁ , and optical path length difference Δl. As shown.

Now, consider the G component light reflected on the uppermost surface of the multiple dichroic mirror 5 and the B component light reflected on the intermediate surface.

Of the white light incident on the multi-dichroic mirror surface at an angle θ ₁ at a point O, the G component light is reflected at an angle θ ₁ ′ which is symmetrical with respect to the normal of the surface, while the light other than the G component light is refracted at an angle θ. _It refracts at ₂ and goes to the next surface. At this time, the relationship between the angles θ ₁ and θ ₂ is expressed by the refraction formula n ₁ sin θ ₁ = n ₂
It is determined by sin θ ₂ .

Of the light refracted at the point O, the B component light is reflected at the point P at an angle θ ₂ ′ (= −θ ₂ ), and from the point Q to the refraction angle θ ₁ ′ (= −θ ₁ ). And then travels in parallel with the G component light reflected by the first surface at an interval d ₁ .

Here, d ₁ is represented by OQ · cos θ ₁ . However, OQ is the distance between the point O and the point Q. The same applies to OP, PQ, and OR described later. OQ is 2t
_{Since 1} · tan θ ₂ , d ₁ = 2 · t ₁ · tan θ
₂ × cos θ ₁ .

The effective optical path length difference between the optical path length of the G component light from the point O to the point R and the optical path length of the B component light from the point O to the point P to the point Q, that is, The optical path length difference Δl converted into the vacuum is expressed by the following equation.

Δl = {(OP + PQ) / n ₂ }-(OR / n ₁ ) = {(2 · t ₁ ) / (n ₂ · cos θ ₂ )}-{(2 · t ₁ · tan θ ₂ × sin θ ₁ ) / N ₁ } Therefore, when n ₁ = 1 and n ₂ = 1.525,
When θ ₁ ≈ 58.0 degrees and t ₁ ≈ 113 μm, d ₁ ≈
It can be set to 80 μm and Δl≈50 μm.

As shown in FIG. 3, when the beam separation width: light amount length shift amount is 80 μm: 50 μm (= 1.6: 1), the ray incident angle θ is 58 °, and the transparent layer at this time is The thickness is 0.11 mm.

The first of the multiple dichroic mirrors 5 is
Both of the transparent layer 52 and the second transparent layer 53 of which the refractive index N is N = 1.52 to 1.53 in the visible wavelength range are used for the multiple dichroic mirror 5 with respect to the optical axis 7 of the imaging lens 4. The inclination angle θ is set to 58 degrees for the reason described above.

With the above settings, the deviation of the image forming positions of the component lights G, B, and R due to the aberration is canceled by making the optical path lengths of the component lights G, B, and R different from each other, and the color separation is performed. The respective component lights G, B, and R of the three primary colors thus formed are imaged on the respective one-dimensional pixel rows without defocusing.

The tilt angle θ of the multiple dichroic mirror 5 with respect to the optical axis 7 of the imaging lens 4 can be easily set.
Even if the first transparent layer 52 and the second transparent layer 53 are both set to a thickness of 0.115 mm, the B (blue) component light and the R (red) component light with respect to the G (green) component light are set to 0 degrees. The optical path length differences are about 46 μm and about 92 μm, respectively, which are values close to the respective shift amounts, 50 μm and 100 μm, and the effect of adjusting the imaging position can be expected sufficiently from FIG.

In the color image reading apparatus according to the present invention, the two dichroic films 5 which are color separation means.
The tilt angle θ formed by the planes of the total reflection films 55 and the optical axis 7 of the imaging lens 4 is determined by the row pitch of the light receiving elements and the optical path length adjustment width as described above.
If it is less than 70 degrees, the position of the light receiving element interferes with the light beam from the imaging lens, and if it exceeds 70 degrees, the spectral reflection characteristics deteriorate due to the characteristics of the dichroic film. It is set to the range of.

The thickness of the two transparent layers 52, 53 with the dichroic films 51, 54 and the total reflection film 55 interposed therebetween is
The range is not limited to the above range, and is usually set in the range of 50 to 300 μm.

The image forming lens 4 is constructed so that the image forming position of the blue light due to the amount of longitudinal chromatic aberration is located approximately at the midpoint between the image forming position of the green light and the image forming position of the red light.
The two transparent films of the multiple dichroic mirror can be made to have the same thickness, and the columns of the light receiving elements having the same pitch can be used.

In the color image reading apparatus of this embodiment, the optical path length difference of the color-separated G, B, and R component light is adjusted according to the chromatic aberration of the imaging lens 4, but the color separation is reversed. It is also possible to design the chromatic aberration of the imaging lens 4 in accordance with the optical path length difference between G (green) component light, B (blue) component light and R (red) component light of the system. The degree of freedom in design is increased.

For example, by using an image forming lens whose optical path lengths are short in the order of R, G, and B component light, the B component light can be reflected on the surface of the multiple dichroic mirror. Therefore, the absorption of the B component light can be reduced, and a light source with a small B component light can be effectively used.

[0043]

According to the color image reading apparatus of the present invention,
Even when an imaging lens with chromatic aberration is used, the optical path length of the color-separated light flux of each color can be canceled by the color separation means in accordance with the longitudinal chromatic aberration amount of the imaging lens, and all of the plurality of light rays can be canceled out. It is possible to accurately focus on each of the plurality of one-dimensional pixel rows on the light receiving element. As a result, the reading performance of the color image reading device can be improved, and reading with less color misregistration can be performed. Further, the design and manufacture of the imaging lens can be facilitated, and the cost of the entire device can be reduced.

[Brief description of drawings]

FIG. 1 is a side view of a color image reading apparatus showing an embodiment of the present invention.

FIG. 2 is a plan view of a light receiving element in this embodiment.

FIG. 3 is a correlation diagram showing the relationship between the tilt angle θ of the multiple dichroic mirror, the shift amount of the optical path length, and the beam separation width in the present embodiment.

FIG. 4 is a correlation diagram showing a relationship between an image formation position of GBR component light of three primary colors and an MTF value in the present embodiment.

FIG. 5 is a diagram illustrating an optical path length in a multiple dichroic mirror.

FIG. 6 is a configuration diagram of a conventional color image reading device.

FIG. 7 is a configuration diagram of a conventional color image reading device.

FIG. 8 is a configuration diagram of a conventional color image reading device.

[Explanation of symbols]

1 ... Light source, 2 ... Platen glass, 3 ... Original, 4 ... Imaging lens, 5 ... Multiple dichroic mirror, 6 ... Light receiving element,
7 ... Optical axis, 41, 42, 43 ... Imaging position, 51, 54 ...
Dichroic film, 52, 53 ... Transparent layer, 55 ... Total reflection film, 61, 62, 63 ... One-dimensional pixel array

Claims (2)

[Claims] 1. A light source, an imaging lens for collecting reflected light from a document illuminated by the light source, a first one-dimensional pixel array and a second one-dimensional pixel arranged in parallel at a predetermined interval. At least one of a light receiving element having columns and a first reflecting film that selectively reflects the first color component light on both planes of the transparent layer having parallel planes, and at least one of the light transmitted through the first reflecting film. And a second reflection film for reflecting the specific color component light of the part as a second color component light, respectively, and the light is condensed by the imaging lens by the first reflection film and the second reflection film. The reflected light from the document is split into the first color component light and the second color component light and reflected, and is reflected by the first one-dimensional pixel row and the second one-dimensional pixel row of the light receiving element, respectively. Color separation means for forming an image, and the first image sensor between the image forming lens and the light receiving element.
The lengths of the respective optical paths of the color component light and the second color component light are respectively defined by a first focal length of the imaging lens for the first color component light and a second focal length for the second color component light. A color image reading device having a focal length. 2. A light source, an imaging lens for condensing reflected light from a document illuminated by the light source, a first one-dimensional pixel array and a second one-dimensional pixel array arranged in parallel on a plane at a predetermined interval. A light-receiving element having a one-dimensional pixel array; a first focal length for the first color component light and a second focal length for the second color component light, which the imaging lens has, with respect to the optical axis of the imaging lens; The first color component is formed on both planes of the transparent layer having parallel planes, which are arranged so as to form a predetermined angle based on the ratio between the distance between the two focal points and the predetermined distance of the light receiving element. A first reflective film that selectively reflects light, and a second reflective film that reflects at least a part of the specific color component light as the second color component light from the light that has passed through the first reflective film, respectively. The thickness of the transparent layer is set based on the predetermined angle and the predetermined distance between the light receiving elements. Fixed color separation means, and the flat surface of the light receiving element is arranged so as to vertically receive the reflected light from the document condensed by the imaging lens reflected by the color separation means. The reflected light from the original collected by the image lens is combined with the first color component light and the second light.
Of the color component light and forms an image on each of the first one-dimensional pixel row and the second one-dimensional pixel row of the light receiving element.