JPH0671298B2 - Color image reader - Google Patents

Description

The present invention relates to an apparatus for reading a color image using a plurality of solid-state image sensor arrays, and in particular to a light flux having an angle of view that is incident on an imaging optical system at an angle from a subject. , A color image reader for forming an image on each corresponding solid-state image sensor array.

[Prior Art] Conventionally, an apparatus as shown in FIG. 7 has been known as an apparatus for line-scanning an object such as a document in a sub-scanning direction and reading the image with a solid-state image sensor (CCD sensor etc.) array in color. There is. In the figure, a part of the document surface 18 is illuminated with light from a light source for illumination (not shown), and a light flux containing information on this part enters a three-piece (3P) prism 20 via an imaging optical system 19. After being separated into three colors by the prism 20, images are formed on the three 1-line CCD sensors 21, 22 and 23. As a result, the information on the document surface 18 is read in color.

[Problems to be Solved by the Invention] However, in this conventional example, three independent sensors are required, and normally, high precision is required for manufacturing the 3P prism 20, resulting in high cost. Tsuku. Furthermore, there is a drawback in that it is necessary to adjust the condensed light flux and each of the sensors 21, 22, and 23 independently of each other, which makes the manufacturing difficult.

Therefore, the sensor array or solid-state image sensor array
3 lines, built in parallel on the same substrate with a finite distance, 3 lines as a monolithic 3 line sensor
It may be formed on the device.

This 3-line sensor 24 is shown in FIG. In the figure, the distances S ₁ and S ₂ between the three sensor arrays 25, 26 and 27 are, for example, about 0.1 to 0.2 mm due to various manufacturing conditions.
The widths W ₁ and W ₂ of the electrodes are, for example, about 7 μm × 7 μm and 10 μm × 10 μm. FIG. 9 shows a known structure as a color image reading apparatus using such a monolithic 3-line sensor as a light receiving element.

In the figure, when reading the information on the document surface 18 by line scanning in the sub-scanning direction (vertical direction in the drawing), the light from the document surface 18 is selected through the imaging optical system 19 to have dichroism. After entering the color separation beam splitters 30 and 31 to which a transparent film is added, the light beams are separated into three light fluxes of three colors, and then, corresponding sensor arrays 33 on the monolithic three-line sensor 32,
Focused on 34, 35.

However, as shown in FIG. 9, the beam splitters 30, 31
The distance between the arrays on the sensor 32 is And, as mentioned above, the distance between arrays Is about 0.1 to 0.2 mm, the plate thickness (x) is about 35 to 70 μm. This value is not easy to manufacture in consideration of the required flatness of the surface.

Further, a color image reading device having another structure using such a monolithic three-line sensor is also known. In this configuration, a blazed diffraction grating is used as a color separation means that can be used with the above-mentioned monolithic 3-line sensor.

However, in this configuration, consideration is given only to light from one point on the subject surface, and no consideration is given to the so-called angle-of-view characteristic due to the existence of a finite reading width in the main scanning direction on the subject surface. Not not.

Therefore, an object of the present invention is to provide a color image reading apparatus which solves the problems related to the above-mentioned field angle characteristics.

[Summary of the Invention] In order to achieve the above object, in a color image reading apparatus according to the present invention, light from a subject is detected by a plurality of light beams from an object in an optical path between an imaging optical system and a plurality of line sensors. 1D blazed diffraction gratings for arranging a plurality of color separations in the direction perpendicular to the array direction of the sensor array and guiding the color separation light to each corresponding sensor array, and a space between the sensor array of the sensors are arranged. However, a light flux having an angle of view that is incident on the imaging optical system at an angle from the subject is also changed corresponding to this angle of view so as to form an image on each corresponding sensor array.

With this configuration, the light from the image information of finite width is separated into a plurality of light fluxes in the freezing wavelength range, and then correctly imaged on the corresponding sensor arrays.

[Embodiment] FIG. 1 shows a three-line sensor 1 used in an embodiment of the present invention. On the substrate 1a of the sensor 1, a sensor array 2 corresponding to each color (for example, three primary colors of R, G, B),
3 and 4 are formed, and the intervals 5 and 6 between the arrays are determined corresponding to the angle of view as described later.

A color reading optical system incorporating the sensor 1 is shown in FIGS. 2 and 3.

In the same figure, the image information on the document surface 8 is the document surface 8
Line scanning in the sub-scanning direction by a mirror (not shown) disposed between the image forming optical system 9 and the image forming optical system 9, and the image information light is transmitted through the image forming optical system 9 to a one-dimensional blazed diffraction grating for three-color separation. Guided to 10. Here, the information light is separated into light fluxes of three colors (for example, R, G, B) in so-called color reading, and this color separation light is imaged on each sensor array 2, 3, 4 of the monolithic three-line sensor 1. It The element surface of the sensor 1 is arranged parallel to the line scanning direction (sub scanning direction).

Applied Optic for 1D blazed gratings
S., Vol. 17, No. 15, pp. 2273-2279 (August 1, 1978 issue). The sub-scanning cross section of the shape is as shown in FIGS. 4 and 5.

Here, in order to understand the principle of the present invention, it will be described in detail what kind of problems will occur when the ordinary three-line sensor 24 shown in FIG. 8 is used in the color reading optical system shown in FIGS. 2 and 3. .

A finite reading width y as shown in FIG. 2 is necessary for constructing an actual reading device, and therefore an angle of view θ exists with respect to the coupling optical system 9. Therefore, in the main scanning cross section, a light flux from the optical axis of the imaging optical system 9 enters the entrance pupil of the imaging optical system 9 with its principal ray at an angle of θ, and FIGS. As shown in a), the light exits from the exit pupil 11 at an angle of θ '. Therefore, the distance from the blazed diffraction grating 10 to the 3-line sensor 1, as shown in 4 (a), although a 1 ₀ a axial ray, emitted from the exit pupil 11 at an off-axis ray of the incident angle θ 'since coming emitted _{by, 1 1 = 1 0 / cosθ} ' angle θ becomes. In an ordinary optical system, θ≈θ ′.

On the other hand, the diffraction angle α of the first-order diffracted light by the blazed diffraction grating 10 is Psin α = λ (P: grating pitch, λ: wavelength) in the configuration shown in FIG.

From the above, the separation distance Z shown in FIG. 4 between the color separation light of the sensor element surface (b) is, Z = 1 ₀ tan [alpha becomes the on-axis, the off-axis _{Z = 1 1 tanα = 1 0} tanα / cosθ ’ In this way, the two do not match, and as shown in FIG. 8, when the 3-line sensor 24 in which the distance between the sensor arrays 25, 26 and 27 does not change on-axis and off-axis and is constant, three colors of three colors are used. The light flux will not be properly imaged on each sensor array 25, 26, 27 over the entire angle of view.

For example, P = 60 μm, λ = 540 nm (green), angle of view θ
_{≒ θ '= 10deg, 1 0} = case of a 20 mm, displacement in the axial and off-axis separation distance Z becomes approximately 3 [mu] m, the aforementioned single element size 7 [mu] m × 7 [mu] m, when compared to 10 [mu] m × 10 [mu] m,
The image forming center of the light beam is largely deviated from the center of the element.
If the angle of view θ is made smaller, the above-mentioned deviation becomes smaller, but it cannot be made unnecessarily small because of the necessity of compacting the device.

Therefore, in this embodiment, the element spacing between the sensor arrays 2, 3 and 4 on and off the axis is set off-axis as shown in FIG. I have decided to spread it as I go.

Next, there is another problem caused by the angle of view θ≈θ ′. Blazed diffraction grating 10 having grating thicknesses d ₁ and d ₂ as shown in FIG.
In addition, when a light beam having an angle of view θ'is incident in the cross section perpendicular to the plane of the drawing in the figure, the actual optical path length in the grating 10 is different from that in the case of vertical incidence, and the blaze wavelengths of both may shift.

This is because the blaze wavelength λ and the thickness d ₁ have the following relationship.

Here, Φi is the phase difference (rad), and n _λ is the refractive index of the grating medium with respect to the light of wavelength λ. That is, the wavelength λ that achieves the desired phase difference Φi for diffracted light of a predetermined order is the grating thickness
If di is constant, the angle of view θ ′, that is, the angle of incidence on the grating, shifts to the short wavelength side. This means that when the image information on one line is read, the wavelength distribution in the wavelength range of the light captured by each sensor array deviates from on-axis to off-axis, resulting in a color shift. .

For example, in the blazed diffraction grating 10 having a two-step structure in FIG. 5, d ₁ = 3100 nm, d ₂ = 6200 nm, n _λ =
When set to 1.5, Φ ₁ = 6π, Φ on the axis (θ ′ = 0)
_{When 2} = 12π, the blaze wavelength of the first-order diffracted light is 516.7 nm, but at the off-axis (θ '= 20 °), the wavelength is 492.3 nm, which is about 24n.
m shift. However, off-axis (θ '= 10 °), the blaze wavelength is 511.2 nm, which is a shift of about 5 nm, which is a level that can be captured by image processing. Therefore, in the present embodiment using the blazed diffraction grating 1 shown in FIG. 1, it is desirable that the angle of view θ be such that θ ′ = 10 (deg) or less.

In the above embodiment, the spacing element between the sensor array in the axial and off-axis, separation distance Z = 1 ₀ tanα / cosθ 'is continuously altering to accommodate, in the light flux having an angle of view The image was correctly formed on the surface of the sensor array element over the entire angle of view. However, it is considerably difficult in manufacture to change the interval for each element. For example, when a 1000-bit CCD is used as a sensor array, the amount of change in the inter-array spacing for each CCD element chip is several nm.

Therefore, a second embodiment using the 3-line sensor 12 having the structure shown in FIG. 6 can be considered. In this sensor 12, several tens of chips of the sensor arrays 13, 14 and 15 are set as one block, and the inter-array intervals 5 and 6 of each block are such that one element in the block is the separation distance Z = 1 ₀ in the above embodiment. tan α / co
Determine so that sθ ′ is satisfied. If you do this,
The target 3-line sensor 12 can be manufactured relatively easily. Therefore, it is possible to improve the production efficiency and reduce the cost. The number of elements in one block may be appropriately determined in consideration of the total number of ticks of the sensor array, the interval between the arrays, and the like.

[Advantages of the Invention] According to the present invention having the above-described configuration, the spacing between a plurality of line elements is adjusted according to the angle of view, so that even image information having a reading width can be satisfactorily color-separated without displacement of the image formation position. A separate and image-formed, compact and inexpensive color image reader can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a three-line sensor of a first embodiment of the present invention, FIGS. 2 and 3 are diagrams showing a reading optical system of the first embodiment, and FIG. 4 is a diagram for explaining the function of a blazed diffraction grating. Figure to
FIG. 5 is a partially enlarged view of the blazed diffraction grating, FIG. 6 is a view showing the 3-line sensor of the second embodiment, FIG. 7 is a view showing a conventional color image reading optical system, and FIG. 8 is a normal view. FIG. 9 is a diagram showing a configuration of a monolithic 3-line sensor, and FIG. 9 is a diagram showing another conventional color image reading optical system. 1,12 …… 3 line sensor 2,3,4,13,14,15
...... Sensor array, 8 ... Subject, 9 ... Imaging optical system, 10 ... One-dimensional blazed diffraction grating

Claims (3)

[Claims] 1. A one-dimensional sensor array forms a plurality of line sensors at a right angle to the array direction on a same substrate with a plurality of lines separated by a finite distance and an image of an object on the sensor. A color image reading apparatus having an image forming optical system for controlling the light from a subject into a plurality of colors in a direction perpendicular to the array direction in an optical path between the image forming optical system and the sensor. A one-dimensional blazed diffraction grating for disassembling and guiding the color-separated light to each corresponding sensor array is arranged, and the intervals between the plurality of sensor arrays of the sensor are incident on the imaging optical system at an angle from a subject. A color image reading device characterized in that a light flux having an angle of view is also changed corresponding to this angle of view so as to form an image on each corresponding sensor array. 2. The color image reading apparatus according to claim 1, wherein the distance between the plurality of sensor arrays is continuously changed. 3. The color image reading apparatus according to claim 1, wherein the interval between the plurality of sensor arrays is such that several tens of chips of the sensor are one block, and the intervals vary discontinuously for each block.