JPH07105861B2 - Color image reader - Google Patents

Description

The present invention relates to a color image reader, and more particularly to a color image reading device provided with a color separation means composed of a reflective one-dimensional blazed diffraction grating and three line sensors on the same substrate surface. The present invention relates to a color image reading apparatus suitable for a color scanner, a color facsimile, etc., which can read color image information on the surface of a document with high accuracy by using the means.

(Prior art) Conventionally, color image information on the original surface is CC-processed via an optical system.
Various devices have been proposed in which an image is formed on the surface of a line sensor such as D, and color image information is digitally read using an output signal from the line sensor at this time.

For example, FIG. 4 is a schematic view of a conventional color image reading apparatus. In the figure, when a light flux from a color image on the original surface 1 is condensed by an imaging lens 20 and is imaged on a line sensor surface described later, the light flux is, for example, red (R) through a 3P prism 21. , Green (G), and blue (B) are separated, and the light is guided to the surface of the line sensor 22, 23, 24 made of CCD or the like. The color images formed on the surfaces of the line sensors 22, 23, 24 are line-scanned and read for each color light.

FIG. 5 is a schematic view of a main part of a color image reading device proposed in Japanese Patent Laid-Open No. 62-234106.

In the figure, when a light flux from a color image on the original surface 1 is condensed by an imaging lens 25 and is imaged on a line sensor surface described later, the light flux is added with a selective transmission film having dichroism. 3 via two color separation beam splitters 26, 27
It is divided into three light fluxes corresponding to the colors. Then, a color image based on the three color lights is generated by the three line sensors 28a,
So-called monolithic 3 in which 28b and 28c are provided on the same substrate surface
An image is formed on each line sensor surface of the line sensor 28. Thus, the color image is line-scanned to read each color light.

FIG. 3 shows the monolithic align sensor shown in FIG.
28 is an explanatory view of the monolithic align sensor 28. FIG.
Shows three line sensors (CCD) 28a, 2 as shown in the figure.
8b and 28c are arranged on the same substrate surface so as to be parallel to each other at a finite distance, and all filters (not shown) based on the respective color lights are provided on the line sensor surface.

The spacing S1 and S2 between the line sensors 28a, 28b and 28c is generally 0.1 to 0.2 mm, for example, due to various manufacturing conditions, and the pixel width W1 and W2 of each single element 28. Is 7
It is set to about μm × 7 μm, 10 μm × 10 μm.

A color separation means using a transmission type blazed diffraction grating is proposed in, for example, Japanese Patent Publication No. 62-43594.

This publication discloses a light flux from one point on the subject surface, but does not disclose that there is a finite reading width in the main scanning direction at the time of image reading, that is, so-called angle of view characteristics by line scanning. .

(Problems to be Solved by the Invention) The color image reading apparatus shown in FIG. 4 requires three independent line sensors, requires high accuracy, and requires a 3P prism which is difficult to manufacture. However, there are problems that the entire apparatus becomes complicated and expensive, and that it is necessary to perform matching adjustment between the image forming light beam and each line sensor independently three times, which makes assembly and adjustment troublesome.

Further, in the color image reading apparatus shown in FIG. 5, when the plate thickness of the beam splitters 26 and 27 is X, the distance between each line of the line sensor is Becomes Now, the beam splitter if the distance between each line of the line sensor, which is preferable in manufacturing, is about 0.1 to 0.2 mm.
The plate thickness X of 26 and 27 is about 34 to 70 μm.

Generally, it is very difficult to construct a beam splitter having such a thin thickness and maintaining a good optical flatness, and using a beam splitter having such a thickness makes it possible to form a color image on a line sensor surface. There is a problem that the optical performance is deteriorated.

Further, no specific disclosure is made about how to read a color image when the color separation means proposed in Japanese Patent Publication No. 62-43594 is used, and particularly a transmission type diffraction grating is used. Therefore, when applied to a color image reading device, the size of the entire device becomes large.

The present invention uses a reflective one-dimensional blazed diffraction grating as the color separation means, and appropriately configures the configuration of the imaging optical system and the color separation means to simplify the entire apparatus, for example,
It is an object of the present invention to provide a color image reading device capable of reading a color image digitally with high precision with three color lights of R, G, and B.

(Means for Solving Problems) In the color image reading apparatus of the present invention, a color image is formed on a reading means surface in which three line sensors are arranged on the same substrate surface by an imaging optical system, and the reading is performed. When the color image is read by means, a color separation means including a reflection type one-dimensional blazed diffraction grating for color-separating an incident light beam into three color lights is provided in an optical path between the imaging optical system and the reading means surface. The color image based on the color light color-separated by the color separation unit is read by the reading unit.

In particular, in the present invention, the three line sensors are arranged so as to be parallel to each other, the image forming optical system is composed of an emission type telecentric system, and the color separation means detects the incident light flux of the line sensor. The feature is that color separation is performed in the direction orthogonal to the pixel arrangement direction.

In addition, in the present invention, when the image forming optical system is composed of a normal optical system, the grating pitch of the reflection type one-dimensional blazed diffraction grating is set so as to be gradually increased from the optical axis center to the periphery. I am trying.

(Embodiment) FIGS. 1A and 1B are a plan view (main scanning cross section) and a side view (sub scanning cross section) of an essential part of a first embodiment of the present invention.

In the figure, reference numeral 1 is a document surface on which a color image is formed.
Reference numeral 2 denotes an image forming optical system, which is configured to be a so-called emission type telecentric system in which the principal ray on the emission side is emitted in parallel with the optical axis. 3 is a color separation means, which is a reflection type 1
It is composed of a three-dimensional blazed diffraction grating, and makes the incident light flux into three color lights, for example, red light (R light) 5 and green light (G light).
6, blue light (B light) 7 is color separated and reflected and diffracted. A reading unit 4 is a monolithic 3 in which three line sensors 8, 9 and 10 having a plurality of pixels arranged in a one-dimensional direction are arranged on the same substrate surface such that the arrangement directions of the plurality of pixels are parallel to each other. Made of line sensor.

In this embodiment, a color image on the surface of the original 1 illuminated by an illumination system (not shown) is separated into three predetermined color lights by the image forming optical system 2 through the color separation means 3, and the separated color images are respectively separated. The images are formed on the corresponding line sensors 8, 9 and 10. Then, the reading unit 4 digitally reads a color image based on each color light.

As shown in FIG. 2, the color separation means 3 of this embodiment is a substrate 102.
A reflection type one-dimensional blazed diffraction grating formed by arranging in the one-dimensional direction a phase portion 103 which gives a predetermined phase difference to the incident light beam and reflects and diffracts it. For the one-dimensional blazed diffraction grating for color separation, see Appl.
ied Optics (Vol. 17, No. 15, P2273 to P2279, August 1, 1978 issue).

That is, as shown in Fig. 10, the basic optical properties of the substrate
A period (pitch) P provided so as to reflect and diffract a light beam incident on 102 at an angle θ ₀ with three phase differences.
The light is separated into three predetermined color lights and reflected and diffracted through the phase portion 103 having the step structure.

As shown in FIG. 1 (A), in the main scanning section, the original 1
There is a finite reading width on the surface, and this width forms an angle of view α with respect to the imaging optical system 2.

Now, it is assumed that the light flux incident at the angle of view α is emitted at the exit side by the imaging optical system 2 at an angle α ′ as shown in FIG. 6, for example.
At this time, the light is reflected and diffracted by the reflective one-dimensional blazed diffraction grating, and the distance to one line sensor 4 of the reading means 4 is l ₀ on the axis and l ₁ off the axis of the emission angle α ′. Where l ₁ = l ₀ / cos α '. (In FIG. 6, the optical path is expanded as indicated by the broken line. In an ordinary optical system, α≈α ′.) On the other hand, the first order by the reflection type one-dimensional blazed diffraction grating Z is the separation distance from the 0th-order light on the line sensor surface according to the reflection diffraction of, and is shown using the symbols in FIG. 6 and FIG. Becomes

Where λ is wavelength, θ _{0 is} incident angle, P is grating pitch, and l ₀ orl
₁ and ± sign correspond to ± 1st order.

(1) not separation distance Z is constant at from = l ₀ orl ₁ therefore alpha '= 0 except expression, i.e., the light flux of the predetermined wavelength to each line sensor plane aligned parallel to the straight line is not correctly imaged.

For example, period P = 180 μm, wavelength λ = 540 nm (green), θ ₀ =
When the angle of view is 30 degrees, l ₀ = 45 mm, and the angle of view α ≈ α '= 20 degrees, the deviation between the on-axis and off-axis directions in the Z direction is about 24 μm. Then, the line sensor comes off from the light receiving surface. When α≈α ′, it becomes difficult to make the entire apparatus compact.

Therefore, in the present embodiment, the imaging optical system is configured so that the exit angle α ′ is always 0 degrees regardless of the incident angle α, that is, the exit type telecentric system, and the separation distance Z in the equation (1) is constant. I am trying.

If the other angle of view α ≈ α ', as shown in Fig. 10, the phase part
When the chief ray is incident on the diffraction grating at an angle α ′ in the cross section perpendicular to the plane of the drawing with respect to the grating thicknesses d ₁ and d _{2 of} 103, the actual optical path length depends on this angle α ′. The wavelength is shifting.

That is, the wavelength λ for obtaining the desired phase difference φi shifts for off-axis light (α ′ ≠ 0) when the grating thickness di is constant. This means that the wavelength distributions captured on the line sensor deviate depending on the angle of view, resulting in color misregistration.

For example, when the grating thickness d ₁ = 909.3 nm and d ₂ = 1818.6 nm,
When the incident angle is θ ₀ = 30 degrees, φ ₁ = 6π, and φ ₂ = 12π, the 0th-order diffracted light blazed wavelength is α ′ = 0 (on axis) and λ = 52.
It becomes 5 nm.

As a means for solving these problems, in this embodiment, the image forming optical system is an emission type telecentric system as described above.

That is, the image forming optical system (emission type telecentric system) in this embodiment has an entrance pupil on the front focal plane, the exit pupil is located at infinity in the direction of one surface of the original, and the exit angle of the off-axis chief ray is on the optical axis. On the other hand, α ′ is always 0.

Next, features of the one-dimensional blazed diffraction grating of this embodiment when it is constructed of a reflection type will be described.

The relationship between the phase difference φ ₁ and the grating thickness di as a diffraction grating for a transmission type diffraction grating is as follows.

(However, vertical incidence in the Z direction, that is, θ ₀ = 0) As is clear from the equation (2), the refractive index of the medium is n
When λ≈1.5 and α ′ = 0, in order to obtain the 0th-order diffracted light blazed wavelength λ = 525 nm shown in the above example with the phase difference φ ₁ = 6π required to obtain a predetermined diffraction efficiency, the grating thickness d ₁ =
3150 nm, similarly phase difference φ ₂ = 12π, grating thickness d ₂ = 6300
The actual required lattice thickness is 4.6 times thicker. This is extremely difficult to manufacture the diffraction grating. That is, in the grating manufacturing method of this type which is generally known at present such as lithography technology or die manufacturing in the replica method, the grating thickness becomes difficult when a large amount is supplied at low cost.

On the other hand, if the diffraction grating is a reflection type, the grating thickness is d ₂
= 1818.6 nm, for example, in optical disc manufacturing
A thickness that can be positioned on the extension line by a method such as the 2P method is preferable. In consideration of diffraction efficiency, it is sufficient to set the phase difference φ ₁ to about 6π or more.

FIG. 7 is a schematic view of the essential parts of an optical system according to the second embodiment of the present invention. In this embodiment, by forming the reflection type blazed diffraction grating of the color separation means into a cylindrical shape, the imaging optical system becomes a normal optical system (here, not the telecentric system but the aforementioned angles α and α'are α≈ Optical system with α'relationship)
It is made up of.

That is, as shown in the figure, the substrate on which the reflective blazed diffraction grating 3 is mounted due to the existence of the exit angle α'in the main scanning section (finite angle of view) is a cylinder whose center is the exit pupil of the imaging optical system. It is configured as a surface so that the emitted principal rays corresponding to each angle of view always enter the diffraction grating 3 vertically. This effectively prevents the shift of the blazed wavelength due to the incident angle dependence in the cross section.

On the other hand, the optical path length reaching the line sensor surface after being reflected / diffracted by the diffraction grating 3 is l ₀ = − on the axis (α ′ = 0).
R, off-axis (α ′ ≠ 0), l ₁ ′ = / cos α′-R,
Both are not constant, and the reflected diffracted light is not correctly imaged on each line sensor due to the same contents as in the above formula (1). In order to eliminate this, by increasing the period (pitch) P of the diffraction grating from the on-axis to the off-axis chief ray according to the equation (1) (P → P ′ in FIG. 8), the primary reflection The diffraction angle is changed, and as a result, the image is correctly formed on the linear line sensor from the on-axis to the off-axis.

FIG. 9 is a schematic view of the reading means 4 according to the third embodiment of the present invention. In the second embodiment, the substrate of the reflection type diffraction grating is a cylindrical surface in the main scanning section, but conversely, for example, the two line sensors 8 and 10 on both sides sandwiching the center line of the monolithic three-line sensor are removed from parallel to each other. With the configuration shown in FIG. 9, the Z-direction shift according to the equation (1) can be absorbed by the position shift of each pixel of the light receiving portion of the line sensor while the diffraction grating substrate is a flat plate.

(Effects of the Invention) According to the present invention, when a color image is read by a reading unit including a monolithic three-line sensor via a color separation unit,
By using the reflection-type one-dimensional blazed diffraction grating having the above-mentioned configuration as the color separation means, the thickness of the grating for imparting a phase difference can be made sufficiently thin, which facilitates the production, and the optical path bending effect by reflection makes the device easier. (EN) A color image reading device that can downsize the whole and separately form color images separated into predetermined three color lights on a line sensor surface and can digitally read a color image with high accuracy. be able to.

[Brief description of drawings]

1 (A) and 1 (B) are a plan view and a side view of an essential part of a first embodiment of the present invention, FIG. 2 is an explanatory view of a part of FIG. 1, and FIG. 3 is a monolithic three-line sensor. 4 and 5 are schematic diagrams of a conventional color image reading apparatus, FIGS. 6 and 10 are schematic diagrams for comparative explanation with the configuration of the present invention, and FIGS. 7 and 8 are schematic diagrams of the present invention. FIG. 9 is a schematic view of the essential parts of the second embodiment of the present invention, and FIG. 9 is a schematic view of the essential parts of the third embodiment of the present invention. In the figure, 1 is a document, 2 is an image forming optical system, 3 is a color separation means, 4
Is a reading means, 5,6,7 are luminous flux, 8,9,10 are line sensors, 1
02 is a substrate and 103 is a phase part.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 1/04

Claims (1)

[Claims] 1. A color image is formed by an image forming optical system on a surface of a reading means having three line sensors arranged on the same substrate surface, and the image forming optical system is used when the color image is read by the reading means. And a grating pitch in the optical path between the reading means surface and the reading means surface are set to be gradually increased from the optical axis center to the periphery,
A color separation means including a reflection type one-dimensional blazed diffraction grating for color-separating an incident light beam into three color lights is provided, and a color image based on the color light separated by the color separation means is read by the reading means. A color image reading device characterized by the above.