JPH04334159A - Color picture reader - Google Patents

Abstract

PURPOSE:To realize the color picture reader able to read a highly accurate color picture by arranging properly the direction of a step shape of a blazed diffraction grating to correct color aberration of an image forming optical system for color picture read. CONSTITUTION:An original face 1 of a color picture is projected onto a face of a read means having plural line sensors 8, 9, 10 with a projection optical system and read by a read means 4. A linear blazed diffraction grating 3 separating an incident light into plural color lights and leading the result to each of the line sensors 8, 9, 10 is provided to the rear side of the projection optical system. Then the direction of a step shape of the diffraction grating 3 is set in a direction so that a color slurring or the like at each wavelength after the diffraction by a read picture angle of a color picture or a color aberration of the projection optical system is corrected to read the color picture with high accuracy.

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 that utilizes a reading means in which a color separation element consisting of a blazed diffraction grating and a line sensor such as three solid-state image sensor arrays are provided on the same substrate surface. The present invention relates to a color image reading device suitable for a color scanner, a color facsimile, etc., which can read color image information on a document surface with high precision by correcting the influence of chromatic aberration of an optical system.

0002

[Prior Art] Conventionally, color image information on the surface of a document is imaged on the surface of a line sensor such as a CCD through an optical system, and the output signal from the line sensor at this time is used to generate color image information. Various digital reading devices have been proposed.

For example, FIGS. 9 and 10 are schematic views of the main parts of a conventional color image reading device in the sub-scanning direction.

In FIG. 9, a light beam from a color image on a document surface 91 is condensed by an imaging lens 92, and when forming an image on a line sensor surface, which will be described later, the light beam is passed through a 3P prism 93 to produce, for example, a red color image. (R), green (G), blue (B) 3
After the light is separated into colors, the light is guided onto line sensors 94, 95, and 96, each consisting of a CCD or the like. The color images formed on the lines of the line sensors 94, 95, and 96 are then line-scanned and read for each color light.

In FIG. 10, a light beam from a color image on a document surface 91 is condensed by a condensing lens array (SLA) 97 and made incident on a blazed diffraction grating 98 as a color separation element. The blazed diffraction grating 98 separates the incident light into three colored lights, and the monolithic 3-line sensor (99
a, 99b, 99c) 99. A three-line sensor 99 reads a color image based on each color of light.

[0006]

Problem to be Solved by the Invention The color image reading device shown in FIG. 9 requires three independent line sensors.
In addition, high precision is required, and a 3P prism, which is difficult to manufacture, is required, making the entire device complex and expensive.
Furthermore, it is necessary to adjust the alignment between the imaging light beam and each line sensor three times independently, which causes problems such as troublesome assembly and adjustment.

In the color image reading device shown in FIG. 10, when a color image has a certain size, a difference occurs in the angle of incidence on the blazed diffraction grating, which causes color blurring. In order to correct this color blur, a condensing lens array (SLA) is used in FIG. 10, which is a telecentric system in which the entrance pupil is located at the front focal plane and the exit pupil is at infinity.

Generally, a condensing lens array is made by subjecting a cylindrical base glass material to ion exchange and providing an internal refractive index distribution to converge an incident light beam. This condensing lens array has an optical path length P depending on each wavelength of the incident light beam, where the refractive index distribution constant is A.

[0009]

[Equation 1] For this reason, the image formed on each line sensor of the 3-line sensor after passing through the blazed diffraction grating for color separation is out of focus, resulting in a problem that the quality of the read image deteriorates. was there.

[0010] The present invention aims at appropriately arranging the stepped shape of the one-dimensional blazed diffraction grating for color separation in accordance with the chromatic aberration of the optical system for reading color images, the color shift of the output wavelength due to the reading angle of view, etc. It is an object of the present invention to provide a color image reading device that can read color images with high precision by adjusting each wavelength after being diffracted by a diffraction grating, preventing deterioration of the image quality of a read image.

[0011]

[Means for Solving the Problems] A color image reading device of the present invention illuminates a color image on a document surface by an illumination means,
The color image is projected by a projection optical system onto a reading means surface in which a plurality of line sensors are arranged in parallel on the same substrate surface, and when the reading means reads the color image, the projection optical system projects the color image behind the projection optical system. A one-dimensional blazed diffraction grating that separates the light flux from the optical system into a plurality of colored lights in a direction perpendicular to the pixel arrangement direction of the line sensor and guides the light to each line sensor is arranged so that the direction of the staircase shape of the diffraction grating is It is characterized in that it is set to face in a direction that can correct the chromatic aberration of the projection optical system or the color shift of each wavelength after diffraction due to the reading angle of view of the color image.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of a main part in the sub-scanning direction of a first embodiment of the present invention, and FIG. 2 is an enlarged explanatory diagram of a portion of FIG.

Reference numeral 1 in the figure represents the original surface, on which a color image is formed. 2 is an imaging optical system, which is a condensing lens array. They are arranged in a plurality of rows in the main scanning direction, and are set to form a color image on the document surface 1 at the same magnification.

Reference numeral 3 denotes a color separation means, which is composed of a reflective one-dimensional blazed diffraction grating, and, as will be described later, is composed of a phase grating with a staircase shape upward to the right, and converts the incident light beam into three-color light, for example. Red light (R light) 5, green light (G light) 6
, is separated into blue light (B light) 7, and is reflected and diffracted. Reference numeral 4 denotes a reading means, which is a monolithic sensor 3 in which three line sensors 8, 9, and 10 each having a plurality of pixels arranged in one dimension are arranged on the same substrate surface so that the arrangement directions of the plurality of pixels are parallel to each other. It consists of a line sensor.

Reference numeral 11 denotes illumination means, which is comprised of, for example, a halogen lamp or a fluorescent lamp.

In this embodiment, the color image on one side of the document illuminated by the illumination means 11 is separated into three predetermined color lights by the imaging optical system 2 via the color separation means 3, and the separated color images are separated into three predetermined color lights. The images are formed on the corresponding line sensors 8, 9, and 10, respectively. A color image based on each color light is digitally read by the reading means 4.

In this embodiment, the imaging optical system 2 is constructed of a telecentric SLA with the same magnification so that the chief rays of all the light beams from the color image on the document surface 1 are incident on the diffraction grating 3 at the same angle. This corrects the color shift due to the viewing angle characteristics.

As shown in FIG. 2, the color separation means 3 of this embodiment has a phase section 103 that imparts a predetermined phase difference to the incident light beam on the substrate 102 and causes it to be reflected and diffracted, so that the stepped shape is upward to the right. It consists of a reflective one-dimensional blazed diffraction grating arranged in one-dimensional direction. 1 for this color separation
For dimensional blazed gratings, e.g. Appli
edOptics (Vol. 17, No. 15, P2273-P
2279, August 1, 1978).

That is, as for the basic optical properties, the substrate 102
A light beam incident at an angle θ0 is separated into three predetermined colored lights through a phase section 103 consisting of a step structure with a period (bitch) P provided so as to impart three phase differences and cause reflection and diffraction. It is reflected and diffracted.

One period length P of the condensing lens array as the imaging optical system 2 in this embodiment is expressed as P(C), P(D), P( F), the chromatic aberration of the condensing lens array is

[0021]

[Formula 2] exists. For this reason, for example, the respective optical path lengths at the wavelengths of F-line and C-line are determined as TC - TF (m
m) It varies depending on the degree.

As a result, the image formation state on the three line sensors 8, 9, and 10 of the reading means 4 shown in FIG. 1 is distorted due to the difference in optical path length, resulting in image deterioration.

Therefore, in this embodiment, in order to reduce the chromatic aberration of the condensing lens array in FIG. If it is closer to the side, the optical path length difference becomes TC' - TF', which is TC
Since -TF>TC'-TF' holds true, this is utilized to reduce the optical path length difference.

As a correction method at this time, in the blazed type diffraction grating of this embodiment, the step shape of the diffraction grating is set so as to reduce the chromatic aberration when the imaging optical system 2 having chromatic aberration is used.

That is, when the step shape of the diffraction grating 3 is upward to the right as shown in FIG. 2, each parameter is set as shown in FIG. 4, and m is a positive integer that satisfies 2h·cosθ=mλ0. However, h: the height of one stage of the diffraction grating λ0 is the zero-order wavelength, and θ is the diffraction angle.

[0026] Also, P=nL (where n is the number of stages of the diffraction grating)
Then, the wavelength after diffraction is

[0027]

[Formula 3] It can be expressed as (+1st order → m-1/n, -1st order → m+1/n). Similarly, in the case of a right-sloping diffraction grating

[0028]

[Math 4] (+1st order → m-1/n, -1st order → m+1/n).

Here, for example, i=30deg, d=909
．． 327nm, m=3, P=0.18mm......(
3).

When a right-sloping type is used as a diffraction grating, the wavelength is 0th order = 525 nm, +1st order = 589.9771n
m, -1st order = 472.9125 nm, and when using the right-down type, the wavelength is 0th order = 525 nm, +1st order = 59
1.2691 nm, −1st order=472.0856 nm. Comparing the above, the upward-sloping type has +1 order and is 1.29
It is on the short wavelength side of 2 nm, and is on the -1st order and on the long wavelength side of 0.8269 nm. Therefore, the total wavelength difference from the +1st order to the -1st order is narrowed by 2.1189 nm, and by using the upward-sloping diffraction grating, it is possible to reduce the chromatic aberration of the imaging optical system.

In the condensing lens array of this embodiment, it is difficult to control the ion exchange process during manufacture, and even if the base material glass is the same, there may be large variations in chromatic aberration depending on the lot. At this time, by using an upward-sloping diffraction grating, it is possible to reduce variations in chromatic aberration, thereby allowing highly accurate reading of color images.

FIGS. 5 and 6 are schematic views of main parts in the sub-scanning direction and the main scanning direction, respectively, of a second embodiment of the present invention, and FIG. 7 is an enlarged explanatory view of a portion of FIG. 5.

In the drawings, the same elements as those shown in the first embodiment are given the same reference numerals.

In FIGS. 5 and 6, reference numeral 21 denotes an imaging optical system, which is composed of a normal lens system, and separates the color image on the document surface 1 into three colored lights through the color separation means 3, and then the reading means 4. A reduced image is formed on each of the line sensors 8, 9, and 10.

In this embodiment, as shown in FIGS. 5 and 6, since there is a finite width for reading on the document surface 1, the imaging optical system 2
1, there is an angle of view α. As a result, in the main scanning section of FIG. 6, the light flux from outside the optical axis of the imaging optical system 21 is
Its chief ray enters the entrance pupil at an angle α, and from the exit pupil α
Inject at an angle of ´. If a light beam having an angle of view α≈α′ at this time is incident on the diffraction grating, the blazed wavelength may shift.

Now, when the grating thickness di of the diffraction grating is

003
7]

[Math 5] (i=1,2‥‥‥) holds true.

Here, φi is the phase difference (rad), and nλ is the refractive index of the medium of the diffraction grating with respect to the wavelength λ. That is, if the grating thickness di is constant, the wavelength λ for obtaining the desired phase difference φi will shift toward shorter wavelengths as the angle of view becomes larger. Therefore, in this embodiment, as shown in FIGS. 7 and 8, a diffraction grating with a stepped shape rising to the right is used to calculate the color shift from the above-mentioned equations (1), (2), and (3) and conditions.

That is, since the +1st order is shifted to the long wavelength side and the -1st order is shifted to the short wavelength side, the shift to the short wavelength side is corrected depending on the angle of view. As described above, in this embodiment, when an imaging optical system that is dependent on the angle of view is used, color shift is corrected using a step-shaped diffraction grating that slopes down to the right.

In each of the above embodiments, a reflection type diffraction grating is used as the color separation means, but the present invention can be similarly applied even if a transmission type diffraction grating is used.

[0041]

According to the present invention, as described above, the step shape of the one-dimensional blazed diffraction grating for color separation can be reduced to chromatic aberration of the optical system for reading color images, color shift of the output wavelength due to the reading angle of view, etc. By arranging them appropriately and adjusting each wavelength after diffraction with the diffraction grating, it is possible to prevent deterioration of the image quality of the read image and achieve a color image reading device that can read highly accurate color images. .

[Brief explanation of the drawing]

FIG. 1 A schematic diagram of main parts in the sub-scanning direction of Embodiment 1 of the present invention

[Figure 2] Enlarged explanatory diagram of the diffraction grating in Figure 1

[Figure 3]
An explanatory diagram of chromatic aberration of the imaging optical system according to the present invention

[Fig. 4] An explanatory diagram of diffracted light by the diffraction grating according to the present invention

FIG. 5 A schematic diagram of main parts in the sub-scanning direction of Embodiment 2 of the present invention

FIG. 6 A schematic diagram of main parts in the main scanning direction of Embodiment 2 of the present invention

[Figure 7] Enlarged explanatory diagram of the diffraction grating in Figure 5

[Figure 8]
Explanatory diagram of diffracted light by the diffraction grating in Figure 5

[Figure 9]
Schematic diagram of main parts of a conventional color image reading device

[Figure 1
0] Schematic diagram of main parts of conventional color image reading device

[Explanation of symbols]

1 Original surface 2 Imaging optical system 3
Color separation means (diffraction grating) 4
Reading means 8, 9, 10 Line sensor 11 Illumination means 12 Scanning means 102 Substrate 103 Phase section

Claims (1)

[Claims] 1. A color image on a document surface is illuminated by an illumination means, and the color image is projected by a projection optical system onto a reading means surface in which a plurality of line sensors are arranged in parallel on the same substrate surface, and the color image is When the color image is read by the means, the light beam from the projection optical system is color-separated into a plurality of colored lights in a direction perpendicular to the direction in which the pixels of the line sensor are lined up behind the projection optical system, and the light beams are sent to each line sensor. The one-dimensional blazed diffraction grating that guides the light is arranged so that the direction of the stepped shape of the diffraction grating can correct the chromatic aberration of the projection optical system or the color shift of each wavelength after diffraction due to the reading angle of the color image. A color image reading device characterized in that it is set to face the user.