JPH10107952A - Color image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the color image reader by which a color image is read with high accuracy and a simple configuration and a loss in a luminous quantity is eliminated on a monolithic 3-line sensor face. SOLUTION: A color image is formed on a light receiving means 4 where a plurality of line sensors 5, 6, 7 are placed on the same board face by using an image optical system 10, the color image and the light receiving means are scanned relatively to allow the light receiving means to read the color image. In this case, the image forming optical system has an anamorphic optical system 2, the anamorphic optical system 2 collects the luminous flux from the color image within a subscanning cross section and forms an image, a divergent luminous flux is distributed into a plurality of sets of luminous flux in the subscanning direction by optical elements 3 arranged in an optical path and a plurality of sets of luminous flux distributed as above are imaged onto each corresponding line sensor face.

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 apparatus, and more particularly to an image forming optical system having an anamorphic optical system and a light receiving means provided with a plurality (three) of line sensors (light receiving elements) on the same substrate surface. By utilizing an optical element having a predetermined refractive power only in the sub-scanning direction,
The present invention relates to a color image reading apparatus capable of reading color image information on a document surface with high accuracy, and suitable for, for example, a color scanner or a color facsimile.

[0002]

2. Description of the Related Art Conventionally, color image information on a document surface is imaged on a line sensor (CCD) surface via an optical system, and color image information is converted using an output signal from the line sensor at this time. Various digital reading devices have been proposed.

[0003] For example, FIG. 4 is a schematic view of a main part of an optical system of a conventional color image reading apparatus. In the figure, when a light beam from a color image on the document surface 21 is condensed by an image forming lens 49 and formed on a line sensor surface described later, the light beam is, for example, red (R) and green through a 3P prism 40. (G) and blue (B) after being separated into three colors.
Light is guided on the surfaces 1, 42 and 43. The color image formed on each of the line sensors 41, 42, and 43 is line-scanned in the sub-scanning direction, and reading is performed for each color light.

FIG. 5 is a schematic view of a main part of an optical system of a conventional color image reading apparatus. In the figure, when a light beam from a color image on the document surface 21 is condensed by the imaging lens 59 and formed on a line sensor surface described later, a wavelength selective transmission film having dichroism is added to the light beam. The light is split into three light beams corresponding to three colors via two beam splitters 50 and 51 for color separation.

A color image based on the three color lights is formed on a so-called monolithic three-line sensor 52 provided with three line sensors on the same substrate surface. Thus, the color image is line-scanned in the sub-scanning direction, and reading is performed for each color light.

FIG. 6 is an explanatory view of the monolithic three-line sensor 52 shown in FIG. 5. The monolithic three-line sensor 52 includes three line sensors (CCDs) 45, 46, and 47 parallel to each other as shown in FIG. Are arranged at a finite distance from each other on the same substrate surface, and a color filter (not shown) based on each color light is provided on the line sensor surface.

The distances S1 and S2 between the line sensors 45, 46 and 47 are generally set to, for example, about 0.1 to 0.2 mm due to various manufacturing conditions. Are, for example, 7 μm × 7 μm,
It is set to about 10 μm × 10 μm.

[0008]

The color image reading apparatus shown in FIG. 4 requires three independent line sensors,
Further, high precision is required, and a 3P prism which is difficult to manufacture is required, so that the whole apparatus becomes complicated and expensive. In addition, it is necessary to perform matching adjustment between the imaged light beam and each line sensor three times independently, and there is a problem that assembly adjustment is troublesome.

In the color image reading apparatus shown in FIG. 5, when the plate thickness of the beam splitters 50 and 51 is x, the distance between each line of the line sensor is 2√2x. now,
When the distance between each line of the line sensor, which is preferable in manufacturing, is about 0.1 to 0.2 mm, the beam splitter 5
The thickness x of 0.51 is about 35 to 70 μm.

In general, it is very difficult to construct a beam splitter having such a small thickness and good optical flatness, and if a beam splitter having such a thickness is used, an image is formed on a line sensor surface. There is a problem that the optical performance of a color image is reduced.

On the other hand, as shown in FIG. 7, distances S1 and S2 between the other two lines 45 and 47 with respect to the center line 46 of the monolithic three-line sensor are generally equidistant in the opposite directions, respectively, and The pixel size in the scanning direction (see FIG. 6) is set to be an integral multiple of W2. This is for the following reasons.

That is, as shown in FIG. 7, when reading a color image with the above-described monolithic three-line sensor using only the normal imaging optical system 79, the three line sensors 45, 46, 47 simultaneously operate. Original surface 1 that can be read
The reading positions on the reference numeral 1 are three different positions 45 as shown in FIG.
', 46', 47 '.

For this reason, the signal components of the three colors (R, G, B) at an arbitrary position on the document surface 11 cannot be read at the same time. Come up.

To this end, the distances S1 and S2 between the lines of the three-line sensor are set so as to be an integral multiple of the pixel size W2, and a redundant line memory corresponding thereto is provided. By delaying each of the G and R signals (signal components based on the G and R color lights) with respect to the color light based signal components, a composite signal component of three colors can be obtained relatively easily.

Accordingly, as described above, the distances S1 and S2 between the other two line sensors 45 and 47 with respect to the center line sensor 46 of the three line sensors are set to be an integral multiple of the pixel size W2 in the sub-scanning direction. It is.

However, in the above-described color image reading apparatus, the use of the redundant line memory corresponding to the distance between the lines of the three-line sensor requires the provision of a plurality of expensive line memories, which is costly. There are problems such as being extremely disadvantageous, and the whole apparatus becoming complicated.

As another method, as shown in FIG. 8, a monolithic three-line sensor 52 is used as a light receiving means (light receiving element), and a predetermined power (refractive power) is provided only in the sub-scanning direction in the imaging optical system 90. Is arranged, an entire system is made an anamorphic optical system, and a light beam based on a color image in the sub-scanning direction is once imaged by the anamorphic optical system in front of the three-line sensor 52, and the image forming position A color image reading apparatus has been proposed in which a slit 84 that regulates a light beam in the sub-scanning direction is disposed in A to read the light beam based on the color image on the three-line sensor 52 surface in a defocused state. .

However, the color image reading apparatus shown in FIG. 8 has the following problems.

First, since the light beam in the sub-scanning direction is in a defocused state, each line sensor 45, 46, 4
The point is that the light amount loss in the non-sensor portion between the seven cannot be effectively used, so that the light amount loss is very large. Usually, the distance between the lines of the three-line sensor is about 10 to 20 times the pixel size of a single element, so that the loss in light quantity is very large.

Second, the width of the slit 84 for restricting the light beam in the sub-scanning direction becomes very narrow, and the arrangement accuracy thereof becomes very strict.

According to the present invention, when a color image on a document surface is read by a monolithic three-line sensor via an imaging optical system,
An anamorphic optical system is arranged in the image forming optical system, and a light beam in the sub-scanning direction is once formed in front of the monolithic three-line sensor, and the formed light beam has a predetermined refractive power only in the sub-scanning direction. After being divided into a plurality of optical elements by a plurality of diffractive optical elements having the following, an image is formed on the surface of the monolithic three-line sensor, so that the light amount can be effectively used on the surface of the monolithic three-line sensor. It is an object of the present invention to provide a color image reading apparatus capable of reading a color image with high accuracy with a simple configuration.

[0022]

According to the present invention, there is provided a color image reading apparatus comprising: (1) a color image is formed by an image forming optical system on a light receiving means surface on which a plurality of line sensors are arranged on the same substrate surface;
When the color image and the light receiving unit are relatively scanned and the color image is read by the light receiving unit, the imaging optical system has an anamorphic optical system, and the anamorphic optical system has In the above, after condensing the light beam from the color image and forming an image, the divergent light beam is divided into a plurality of light beams in the sub-scanning direction by an optical element arranged in the optical path, and the divided light beams are separated. It is characterized in that images are formed on the corresponding line sensor surfaces.

In particular, (1-1) the anamorphic optical system is a cylindrical lens having a refractive power only in the sub-scanning direction; (1-2) the anamorphic optical system is a toric lens; 1-3) The optical element comprises at least three diffractive optical elements having a refractive power only in the sub-scanning direction.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main portion in the sub-scanning direction showing a refractive power arrangement according to a first embodiment of the present invention.

In FIG. 1, reference numeral 11 denotes a document surface on which a color image is formed. Reference numeral 10 denotes an image forming optical system, which is a positive lens 1 having a common refractive power φ ₁ in the main scanning direction and the sub-scanning direction, and an anamorphic optical system (refracting optical system) having a predetermined refractive power φ ₂ only in the sub-scanning direction. And a cylindrical lens 2 as a system.

Reference numeral 3 denotes an optical element, which comprises three diffractive optical elements 3a, 3b and 3c having a common diffraction power (refractive power) φ ₃ only in the sub-scanning direction. 3b and 3c are juxtaposed in the sub-scanning direction, and are arranged in the vicinity of the light receiving means 4 described later. The optical element 3 in the present embodiment emits a light beam based on a color image once formed by the imaging optical system 10 in the sub-scanning section.
The three diffracted optical elements 3a, 3b, and 3c divide the light into three light beams in the sub-scanning direction, and form the focused three light beams on the corresponding line sensors 5, 6, and 7 (focusing).
Let me.

Reference numeral 4 denotes a light receiving means, which is a so-called monolithic three-line sensor (hereinafter, referred to as "CCD") in which three line sensors (CCD) 5, 6, and 7 are arranged on the same substrate surface at a finite distance so as to be parallel to each other. 3 line sensor ”).

In this embodiment, a color image on the document surface 11 is line-scanned by a scanning means (not shown) such as a mirror, and a light beam from the color image is condensed by the imaging optical system 10 in the main scanning direction. Are formed on the three-line sensor 4 surface only by the refractive power φ ₁ of the positive lens 1.
On the other hand, in the sub-scanning direction, the degree of convergence of the light flux based on the color image converged by the positive lens 1 is further increased by the cylindrical lens 2 as shown in FIG. after temporarily imaged point) a to form focal lines, caused to diverge, three diffractive optical element 3a having a common diffracting power phi ₃ a light beam having said divergent, 3
After being divided into three light beams by the optical element 3 composed of b and 3c, the three light beams are re-imaged on the corresponding line sensors 5, 6, and 7 respectively. Then, a color image based on each color light is digitally read by the three-line sensor 4.

Here, the image forming relationship in the sub-scanning direction of this embodiment will be described with reference to FIG.

In the figure, the distance between the original surface 11 and the positive lens 1 is e ₀ , the distance between the positive lens 1 and the cylindrical lens 2 is e ₁ , the distance between the cylindrical lens 2 and the imaging point A is e ₂ , The distance between the image point A and the optical element 3 is e ₃ , and the distance between the optical element 3 and the three-line sensor is e ₄ .

Now, consider the imaging relationship in the sub-scanning direction in a thin-walled system. The heights at which the peripheral luminous flux crosses the lenses 1 and 2 and the optical element 3 are defined as h ₁ , h ₂ and h ₃ , respectively.
The angles of the rays from 2 are α ′ ₁ and α ′ ₂ , respectively. Further, the peripheral light fluxes of the light rays imaged on the line sensor 6 at the center of the three-line sensor 4 are similarly denoted by h ₁₁ , h ₂₂ , and h ₂₂ , respectively.
_{33, α '11, α'} 22, think about the α _'33.

Here, since h ₁ = −α ₁ · e ₀ , when the distance e ₁ between the positive lens 1 and the cylindrical lens 2 is determined, all other values are obtained.

The equations obtained by ray tracing are as follows.

[0034] _{e 2 = h 22 / α '} 22 e 3 = d / 2α' 22 + 3h 22 / α '1 e 4 = -3h 33 / α' 1 φ 2 = (α '22 -α' 11) / h _{22 φ 3 = - (α '} 1/3 + α' 22) / h 33 h 11 = h 1/3 h 22 = h 11 -α '1/3 × e 1 h 33 = -d / 2 (1 + 3α' 22 / α ′ ₁ ) In this equation, d is the line interval of each line of the three-line sensor 4. In the above equation, the angle α ′ _{11 of the} light beam emitted from the positive lens 1 and the angle α ′ _{33 of the} light beam emitted from the optical element 3 have the same value with different signs (α ′ ₁₁
= −α ′ ₃₃ ). This is to match the imaging magnification in the main scanning direction and the sub-scanning direction.

In the above-described image forming relationship, the light beam in the sub-scanning direction is once formed on the image forming point A and then re-imaged on the surface of the three-line sensor 4 in a form of being split through the optical element 3. Is done. With such an image forming relationship, one line of color image information on the document surface 11 is divided into three zones (three lines).
By re-imaging the image on the line sensor 4, it is possible to eliminate the light amount loss caused when reading the color image information in a state where the light flux is defocused, which is a problem of the conventional example described above. Since a perfect imaging relationship is established also in the sub-scanning direction, a slit for regulating a light beam in the sub-scanning direction is not required.

In this embodiment, as a feature of the diffractive optical element, for example, if the above three zones correspond to the three primary colors R, G, and B of color reading, the respective color light R, G
By changing the grating pitch by adopting an element structure adapted to G and B, and thereby freely selecting the diffraction angle, the line interval d of each line of the three-line sensor 4 can be set to a free value. Can be.

In the element structure of the diffractive optical element 3b (corresponding to the line sensor 6) which is the central zone of the optical element 3, for example, in a Fresnel zone plate type, the phase function is φ (h).

[0038]

(Equation 1) Is required.

Here, λ is preferably the center wavelength of any one of the three primary colors R, G, and B.
Similarly, for each zone (diffractive optical element 3a, 3c) corresponding to each of the line sensors 5 and 7, the element structure is obtained in the same manner as described above, and each element is off-axis in the optical conjugate relationship. Only the point is different.

FIG. 2 shows a diffractive optical element having a Fresnel zone type element structure according to this embodiment. FIG. 3 shows a quantized stepwise so-called four-stage binary element (BOE) diffractive optical element. The basic effect of this embodiment is the same regardless of which diffractive optical element is used.

Next, a color image reading apparatus according to a second embodiment of the present invention will be described. This embodiment is different from the first embodiment in that the imaging optical system is configured by a toric lens having different refractive powers in the main scanning direction and the sub-scanning direction. Other configurations and optical functions are substantially the same as those in the first embodiment.

That is, the present embodiment can provide the same effects as those of the first embodiment also by forming an imaging optical system using a toric lens as an anamorphic optical system. In this embodiment, the use of the toric lens eliminates the need for the cylindrical lens 2 having a predetermined refractive power only in the sub-scanning direction used in the first embodiment.

Next, a color image reading apparatus according to a third embodiment of the present invention will be described. The present embodiment is different from the first embodiment in that the optical element and the cover glass for protecting the three-line sensor are integrally formed. Other configurations and optical functions are substantially the same as those of the first embodiment, and thus the same effects are obtained.

Normally, a cover glass is generally disposed on the upper surface of the three-line sensor for the purpose of dust prevention or the like. Therefore, in the present embodiment, the arrangement accuracy of the lens and the like is improved by integrally forming the cover glass and the optical element arranged near the three-line sensor based on the above-described calculation formula of the imaging relationship, and By reducing the number of parts by removing the fixing members, the overall size of the apparatus is reduced.

[0045]

According to the present invention, when a color image is read by a monolithic three-line sensor via an imaging optical system as described above, an anamorphic optical system is arranged in the imaging optical system, and The light beam is once formed into an image in the form of a focal line in front of the monolithic three-line sensor, and the formed light beam is formed into a plurality of light beams by an optical element including a plurality of diffractive optical elements having a predetermined refractive power only in the sub-scanning direction. By forming an image on the monolithic three-line sensor surface after division, the light amount can be effectively used on the monolithic three-line sensor surface and a color image can be read with high accuracy with a simple configuration. A color image reading device can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part in a sub-scanning direction showing a refractive power arrangement according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a principal part of the diffractive optical element according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a principal part of the diffractive optical element according to the first embodiment of the present invention.

FIG. 4 is a schematic view of a main part of an optical system of a conventional color image reading apparatus.

FIG. 5 is a schematic view of a main part of an optical system of a conventional color image reading apparatus.

FIG. 6 is an explanatory diagram of a monolithic three-line sensor.

FIG. 7 is a schematic view of a main part of an optical system of a conventional color image reading apparatus.

FIG. 8 is a schematic diagram of a main part of an optical system of a conventional color image reading apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Positive lens 2 Cylindrical lens 3 Optical element 3a, 3b, 3c Diffractive optical element 4 Light receiving means (monolithic three-line sensor) 5, 6, 7 Line sensor 10 Imaging optical system e ₀ Distance between original surface and positive lens e ₁ the refractive power of the positive lens and the cylindrical spacing e ₂ cylindrical lenses and spacing e ₄ optical element and the monolithic 3-line sensor to the interval phi ₁ positive lens between the distance e ₃ imaging point a and the lens of the imaging point a between the lens It focused on the angle alpha _'11 center line sensors' angular alpha _{to 1} peripheral light is emitted to the positive lens' ₂ peripheral light power alpha refractive power phi ₃ diffractive optical element of phi ₂ the cylindrical lens is emitted to the cylindrical lens angle α of _{33 '22} angle α marginal rays is emitted a cylindrical lens for focusing in the center of the line sensor' that the peripheral light is emitted to the positive lens High ambient light flux forms an image on the line sensor height h ₃ ambient light flux angle h ₁ ambient light flux emitted diffractive optical element height h ₂ marginal rays across the positive lens crosses cylindrical lens crosses the diffractive optical element H ₁₁ Height at which the peripheral luminous flux focused on the central sensor crosses the positive lens h ₂₂ Height at which the peripheral luminous flux focused on the central sensor traverses the cylindrical lens h ₃₃ Diffraction of the peripheral luminous flux focused on the central sensor Height across optical element A Image point d Line spacing

Claims (4)

[Claims] 1. A color image is formed by an imaging optical system on a light receiving means surface on which a plurality of line sensors are arranged on the same substrate surface, and the color image and the light receiving means are relatively scanned to form a color image. When the color image is read by the light receiving means, the imaging optical system has an anamorphic optical system, and the anamorphic optical system condenses a light beam from the color image in a sub-scanning cross section to form an image. After that, the divergent light beam is divided into a plurality of light beams in the sub-scanning direction by an optical element arranged in the optical path, and the divided light beams are imaged on the corresponding line sensor surfaces. Color image reading device. 2. The color image reading apparatus according to claim 1, wherein said anamorphic optical system is a cylindrical lens having a refractive power only in a sub-scanning direction. 3. An apparatus according to claim 1, wherein said anamorphic optical system is a toric lens. 4. The color image reading apparatus according to claim 1, wherein said optical element comprises at least three diffractive optical elements having refractive power only in a sub-scanning direction.