JPH04101556A - Color image reader - Google Patents

Abstract

PURPOSE:To make a color image reader possible to read a highly accurate color image by making the magnification of image formation in the direction perpendicular to a direction of an array of line sensor picture elements in a projecting optical system. CONSTITUTION:At a position distant by Xs from the surface 1 of original, a slit 5 is installed having a predetermined opening. An outer point of axis is defined so that an image hs' (length of L1') on the surface of an inspection means 4 prepared by a projecting optical system 2 for a half shadow terminal hs (length of L1) on the surface of original 1 determined by this slit 5 is less than a predetermined size. For example, light from light source point P1 enters line sensors 4a and 4c that receive + or - primary diffracted light to protect the light from becoming noise light. When reading color image information by means of line scanning using a monolithic line sensor 3, a primary brazed diffraction grating as color separation element and a slit that satisfies the aforementioned condition. With this, a flux of light from the outer point of axis is protected effectively from entering the line sensor to cause noise light, thereby enabling the color image reader to read a highly accurate digital color image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a color image reading device, and particularly to a color image reading device that utilizes a detection means in which a color separation element consisting of a blazed diffraction grating and three line sensors are provided on the same substrate surface. By W,
The present invention relates to an image reading device suitable for color scanners, color facsimiles, etc., which can remove unnecessary noise light and read color image information on the M4 surface with high illuminance.

(Prior art) Conventionally, color image information on the document surface is transmitted through an optical system.
Various devices have been proposed that digitally read color image information by forming an image on the surface of a line sensor such as a CD and using an output signal from the line sensor at this time.

For example, a light beam from a color image on the document surface is condensed by an imaging lens, and the light beam is passed through a 3P prism, for example, in red color (
After color separation into three colors: R), green (G), and blue (B),
A color image reading device has been proposed that guides light onto three line sensor surfaces each composed of a CCD or the like, scans the color images formed on the three line sensor surfaces, and reads each color light separately. There is.

In addition, the present applicant has filed Japanese Patent Application No. 1-35692 and Japanese Patent Application No. 122
No. 2535, etc., a color image on the document surface is illuminated by an illumination means, and the color image is projected by a projection optical system onto a detection means surface in which three line sensors are arranged in parallel on the same substrate surface. When the color image is read by the means, the light beam from the projection optical system is color-separated into three 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. We have proposed a color image reading device configured with a one-dimensional blazed diffraction grating for guiding light.

(Problems to be Solved by the Invention) The color image reading device proposed in the above-mentioned Japanese Patent Publication No. 62-43594 handles only the light flux from one point on the document surface when reading a color image. ,
For example, when reading a reflective original, so-called off-axis light may pass through a blazed diffraction grating and then be incident on each line sensor as noise light of other color components.

In contrast, the color image reading device proposed in Japanese Patent Application No. 222535 uses a one-dimensional blazed diffraction grating to perform color separation and read a color image, when a predetermined condition is established between the document surface and the projection optical system. By arranging a slit that satisfies the following, it effectively prevents light from an off-axis point from entering the line sensor and becoming noise light. It is being read with high accuracy.

The present invention more effectively eliminates the noise light generated when a color image is separated and read using a one-dimensional blazed diffraction grating by using the aforementioned slit and appropriately setting the lens configuration of the projection optical system. The object of the present invention is to provide a color image reading device that can read color images with high precision.

(Means for Solving the Problems) The color image reading device of the present invention projects a color image on a document surface onto a detection means surface in which a plurality of line sensors are arranged in parallel on the same substrate surface using a projection optical system. When the color image is read by the detection 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 arranged, and each A diffraction grating that guides light to the line sensor is arranged, and the projection optical system is configured such that the imaging magnification is different in the direction in which the pixels of the line sensor are lined up and in the direction orthogonal to the line sensor. .

In particular, the present invention is characterized in that the projection optical system is configured such that the imaging magnification in a direction perpendicular to the pixel arrangement direction of the line sensor is smaller than that in the pixel arrangement direction of the line sensor.

(Embodiment) FIG. 1 is a schematic diagram of the main part of an optical system according to a first embodiment of the present invention in a main scanning section.

In the figure, reference numeral 1 denotes a document surface on which a color image is formed. Reference numeral 101 denotes illumination means, which is made up of, for example, a heat lamp, a fluorescent lamp, or the like.

Reference numeral 102 denotes a scanning means, which consists of a mirror, etc., and scans the original surface 1.
is line-scanned in the sub-scanning direction 103 within the plane of the paper. 2
is a projection optical system, which has different imaging magnifications in the main scanning direction (the direction in which the pixels of the line sensor described later are arranged) and the sub-scanning direction (the direction perpendicular to the direction in which the pixels are arranged).

The projection optical system 2 has a lens system 21 and a lens system 22. The lens system 21 has the same imaging magnification in the main scanning direction and the sub-scanning direction. The lens system 22 has different imaging magnifications in the main scanning direction and the sub-scanning direction.

In this embodiment, the lens system 22 includes negative and positive cylindrical lenses 11 and 12 having refractive power only in the sub-scanning direction in order to change the imaging magnification in the sub-scanning direction.

Reference numeral 3 denotes a one-dimensional blazed diffraction grating as a color separation element, which converts the light beam from the projection optical system 2 into predetermined colored light 5 in the sub-scanning direction 103, for example, the three primary colors of R, G, and B, as shown in the figure. , 7.8. 4 is a detection means and 9
For example, as shown in FIG. 4, there are three line sensors 4a such as CCDs.

It consists of a so-called monolithic 3-line sensor in which 4b and 4c are arranged parallel to each other on the same substrate 20 surface. A color filter (not shown) based on each color light is arranged on each line sensor surface, and the interval 11 and fi2 between each line sensor correspond to the color separation direction of the color separation element 3 and are different from each other. is set to the specified value. A slit 5 has a long opening in the direction perpendicular to the page (main scanning direction), which is the direction in which the pixels of the line sensors 4a, 4b, and 4c are lined up. are arranged so as to satisfy the conditions described below. Further, the slit 5 is set to be movable in the sub-scanning direction 103.

In this embodiment, among the scattered reflected light from the color image on the yX'M4 surface 1, the light flux that has passed through the opening of the slit 5 is scanned by the scanning means 102, and the light flux from the scanning means 102 is scanned by the projection optical system 2. After condensing the light and color-separating it into three color lights through a one-dimensional blazed diffraction grating 3, a color image on the document surface 1 is formed on three line sensors 4a, 4b, and 4c, respectively. As a result, the color images on the document surface 1 are sequentially digitally read by the detection means 4.

At this time, the lens system 22 increases the reduction magnification in the sub-scanning direction compared to the main scanning direction (by decreasing the projection magnification), and adjusts the line spacing of the 3-line sensors 4a, 4b, and 4c on the iM plane 1. This is expanded compared to the case where the system 22 is not used. In other words, the color image reading lines on the document surface are separated from each other to prevent light flux from off-axis points (images that are not being read, the same applies hereinafter) from entering the line sensor and becoming noise light. I'll do it.

Next, the optical function of the slit 5, which prevents light beams from off-axis points (points other than image reading points) from entering the line sensor and becoming noise light in this embodiment, will be explained.

In this embodiment, as shown in FIG. 1, a slit 5 having a predetermined opening is provided at a distance of 1 m x s from the document surface 1, for example. The original M4 determined by this slit 5 is transformed into an image h8' (length L1) on the surface of the detection means 4 by the projection optical system 2 of the penumbra edge hs (length L1) on the surface.
') or less than a predetermined size, and prevent the light from, for example, point P, or ±1st-order diffracted light from entering the line sensors 4a and 4c that receive the light and becoming noise light. are doing.

That is, in this embodiment, the length of the penumbra edge hs in the sub-scanning direction determined from the pupil diameter of the projection optical system 2 at the opening of the slit 5 in the sub-scanning direction 103 is Ll, and the half-shape having the length Ll is As shown in FIG.
a.

The shorter interval between 11 and 112 between 4b and 4c is L.
2, each element is set so as to satisfy the condition Ll'/2<L2).

Next, the slit width of the slit 5 and the distance m x s will be explained using the symbols shown in FIG.

Now, the shorter of the intervals between the L2.3 line sensors: the imaging magnification of the projection optical system 2 (here, it is assumed to be equal in the main scanning direction and the sub-scanning direction) xo; from the document surface to the projection optical system Mathe distance Z5: Coordinates of the penumbra edge (document surface) (distance at which the 0th-order diffracted light from the off-axis point enters the line sensor that receives the ±1st-order diffracted light) φ2: Entrance pupil diameter of the projection optical system 2 Then, zs = L 2 ×- Also, the distance 11xs becomes. Also, if xs is the position of Nislit 5, Ws is the width of Nislit 5 in the sub-scanning direction, then the slit width Ws is W5=! -'-x

becomes.

Now, L2=0.14 (mm), m=-1/6°25,
Xo ”400 (mm), φ, =20 (mm)
In other words, the pixel size is 10 with a resolution of 16 peu.
Focal length 1[[f=80m
m, when reading image information using a projection optical system with FNO=4.0, Zs=0.875 (mm), X5=16.
77 (mm), Ws=0.838 (mm).

In this embodiment, by arranging a slit having such a slit width WS so that the slit center and the line sensor have an appropriate positional relationship in the sub-scanning direction, the distance from the off-axis point P in the sub-scanning direction is This prevents the light from entering the line sensors 4a and 4c that receive the ±1st-order diffracted light and becoming noise light.

At this time, the slit needs to be correctly placed at a regular position, or in reality, errors in the shape and placement position of the slit occur due to assembly errors. For this reason, a small amount of noise light from the same building as mentioned above may be generated.

Therefore, in this embodiment, the generation of noise light at this time is effectively prevented by making the projection magnification of the projection optical system in the sub-scanning direction smaller than that in the main-scanning direction, as described above.

For example, of the above-mentioned magnification m (-1/6.25), the imaging magnification m' in the sub-scanning direction is reduced to m -1713.5, about 2 degrees.

At this time, with other parameters being the same, ZS ′;
Coordinates of penumbra edge xS: Distance between document surface and slit W5'; Width of slit in sub-scanning direction, each of the above parameters is Zs' = 1.778 (mm), Xs = 32°66 (mm) , VVs'=1.63 (mm). That is, the slit width WS' is 1.95 times, and the two coordinates Zs' into which the noise light due to the light beam from the off-axis point enters is approximately twice, and the parameters for generating the noise light are relaxed.

In this example, by making the projection magnification smaller in the sub-scanning direction than in the main-scanning direction, it is possible to efficiently prevent the light flux from off-axis points that could not be removed by the slit from entering the line sensor and becoming noise light. Removes well. This also allows for relaxation in terms of slit width dimension and placement accuracy.

In this example, the reading density PH, Pv (number of pixels per 1 mm) in the main scanning direction and sub-scanning direction on the document surface is D (mm); the size of one pixel of the line sensor S
R (mm/s); reader scanning speed Tc (S);
The drive cycle of the line sensor (CCD storage time) is 2・□, DP・−8,・T.

becomes. For example, the reading density P H - P v = 16 p
e It (number of pixels per mm), scanning speed SR
=100mm/s, pixel dimension D=10 (μm)
If it is 10 (μm), then n=-176,25Tc-625μs. Here, from the above equation, the reading density PV in the sub-scanning direction does not depend on the imaging magnification m of the projection optical system. In existing digital copying machines, for example, magnification (enlargement, reduction) in the sub-scanning direction is performed by keeping the driving cycle TC constant and changing the scanning speed SR of the reader.

From the above, in the present invention, even if the imaging magnification in the sub-scanning direction is made smaller than the imaging magnification determined from the main scanning direction, the reading density in the sub-scanning direction does not change unless the scanning speed SR of the retarder system is changed.

Furthermore, since the imaging magnification m' in the sub-scanning direction is small, the resolution in the sub-scanning direction does not deteriorate.

In this example, the dimension of one pixel of the line sensor is 10XIO (μm), which is the same in the main scanning direction and the sub-scanning direction, but the imaging magnification in the sub-scanning direction is smaller than that in the main scanning direction. Therefore, the pixel size in the sub-scanning direction may be made smaller than that in the main-scanning direction.

For example, (main scanning direction)
m) may also be used. According to this, the resolution (contrast) of the reading system in the sub-scanning direction can be improved.

That is, in a system that reads images by line scanning using a line sensor as in this embodiment, the reading density in the sub-scanning direction is determined by the accumulation time for -line, and is determined by the amount of charge integrated within a predetermined accumulation time. This is the output of each pixel.

For example, when reading an image in which a white part exists within a black part as shown in Fig. 3 (A), the output from the line sensor is obtained every predetermined accumulation time as shown in Fig. 3 (B). For example, even if the resolution of the projection optical system decreases,
As shown in the same figure (C), position X and position X+ in the sub-scanning direction
An output is generated at pixel No. 4, and the output at positions X+1 and X+3 decreases, resulting in a signal that looks like the resolution has decreased. Furthermore, if the resolving power of the projection optical system is reduced, the signal deterioration (abortion) at this edge portion will increase.

Therefore, in the present invention, the size of the pixel of the line sensor in the sub-scanning direction is made small as described above, thereby reducing signal deterioration (rounding) at this edge portion and improving resolution as a result.

In the embodiment shown in FIG. 1, the imaging magnification in the main scanning direction and the imaging magnification in the sub-scanning direction are changed by using two cylindrical lenses. You can also use it. For example, as shown in FIG. 2, a plurality of prisms 21a to 21d may be combined to change the imaging magnification.

Further, the present invention can be similarly applied to a one-dimensional blazed diffraction grating not only of a transmission type but also of a reflection type.

(Effects of the Invention) According to the present invention, when reading color image information by line scanning using a monolithic 3-line sensor, a one-dimensional blazed diffraction grating as a color separation element and a slit satisfying the above-mentioned conditions are used. By configuring the projection optical system as described above, we have created a color image reading device that can effectively prevent the light flux from an off-axis point from entering the line sensor and becoming noise light, and can read highly accurate digital color images. can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the main parts of the optical system of the first embodiment of the present invention, Fig. 2 is an explanatory diagram of a part of Fig. 1 of another embodiment, and Fig. 3 is an image reading and line FIG. 4 is an explanatory diagram of the output signal from the sensor, and FIG. 4 is an explanatory diagram of the detection means of FIG. 1. In the figure, 1 is a document, 2 is a projection optical system, 3 is a one-dimensional blazed diffraction grating, 4 is a detection means, and 4a. 4b and 4c are line sensors, 5 is a slit, 6,
7.8 are G color light, B color light, and R color light, 101 is an illumination means, and 102 is a scanning means.

Claims (4)

[Claims] (1) When a color image on the document surface is projected by a projection optical system onto a detection means surface in which a plurality of line sensors are arranged in parallel on the same substrate surface, and the color image is read by the detection means, the projection optical system A diffraction grating is arranged behind the system to separate the light beam from the projection optical system into a plurality of colored lights in a direction perpendicular to the direction in which the pixels of the line sensor are arranged, and guide the light to each line sensor. 1. A color image reading device, characterized in that the system is configured such that the imaging magnification is different in the direction in which the pixels of the line sensor are arranged and in the direction orthogonal to the direction in which the pixels are arranged. (2) The color imager according to claim 1, wherein the projection optical system is configured such that the imaging magnification in a direction perpendicular to the pixel arrangement direction of the line sensor is smaller than in the arrangement direction of the pixels of the line sensor. Image reading device. (3) The color image reading device according to claim 2, wherein the pixels of the line sensor have a smaller dimension in a direction perpendicular to the arrangement direction than in the arrangement direction of the pixels. (4) The color image reading device according to claim 3, wherein the detection means has three line sensors, and the diffraction grating is a one-dimensional blazed diffraction grating.