JP2002199171A - Color image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent color mixture (crosstalk) from occurring in the subscanning direction in a color picture reader having a color-separating optical system. SOLUTION: In the color image reader having the color separating optical system, the image formation magnification in the subscanning direction is made higher than that in the main scanning direction.

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 in particular, reads out color image information of a document by forming color image information of the document on an image reading means (monolithic three-line sensor) by an image forming means. The present invention relates to a color image reading apparatus as described above.

[0002]

2. Description of the Related Art Conventionally, color image information of a document or the like is line-scanned in the sub-scanning direction, and the color image information is formed on a monolithic three-line sensor surface as image reading means (light receiving means) via an imaging lens. Various color image reading apparatuses have been proposed in which an image is read and color image information of the document or the like is read using an output signal obtained from the three-line sensor.

FIG. 4 is a schematic view of a main part of a color image reading apparatus of this type. In the figure, a light beam from a color image on the surface of the document 41 illuminated by an illumination means (not shown) is condensed by an imaging lens, and the size of a single element is 8 μm × 8 μm or 10 μm × 10.
When an image is formed on a line sensor (solid-state image sensor) having a thickness of about μm, the light beam is split into two color-separating beam splitters 42 a and 42 b to which a wavelength selective transmission film (dichroic film) having dichroism is added. Via, for example, R. G.
The color is separated into three light beams (color light) corresponding to the three colors B.

Then, a color image based on the three color lights is converted into a color image.
An image is formed on each of the line sensors 44a, 44b, and 44c of a so-called monolithic three-line sensor (hereinafter, also referred to as "three-line sensor") in which two line sensors are provided on the same substrate surface. Thus, a color image is line-scanned to read each color light.

However, in FIG. 1, after the color image information at point A on the upper surface 41 of the document is color-separated into three color lights by two color-separating beam splitters 42a and 42b,
Line sensors 44a, 44b, 44c corresponding to the three color lights
When condensing light on the surface, point B (AB
The distance between lines is obtained by dividing the line interval of the line sensor by the imaging magnification). For example, as shown by a dotted line in FIG. , 42b, and other R (red) line sensors 44 that do not correspond to the G (green) image information.
There was a problem that light was collected on a. This is generally called crosstalk (color mixing) in the sub-scanning direction, and is one of the causes of image disturbance when reading color image information.

Therefore, conventionally, as shown in FIG. 5, a narrow slit 45 for blocking the light beam from point B is arranged near the surface of the original 41, thereby preventing crosstalk in the sub-scanning direction, and Color image information of 3 line sensor 44
There has been proposed a color image reading apparatus that reads images by using a color image reading apparatus.

As another color image reading apparatus method, for example, as shown in FIG. 6, a three-line sensor 54 is used as an image reading means, and a reflection type one-dimensional blazed diffraction grating 52 is used as a color separating means in an image forming optical path. Is arranged away from the exit pupil of the imaging lens 53 in the direction of the three-line sensor 54, and color separation is performed using reflection diffraction (for example, G, 1
R for primary light, B for primary light B) Color image information of one line on original 51 is color-separated and imaged in the sub-scanning direction on the surface of three-line sensor 54 to form color image information. A color image reading apparatus has been proposed.

In this case as well, the crosstalk in the sub-scanning direction occurs. Reflective color image from point A 1
When a color image is read using a two-dimensional blazed diffraction grating and separated into 0th-order light (G), 1st-order light (R), and -1st-order light (B), a color image from point B near point A, for example, 0 The next light (G) is collected on the R line sensor that does not correspond to the color. Therefore, even in a color image reading apparatus having a color separation optical system using a blazed diffraction grating, it is necessary to arrange the narrow slit 55 near the document surface in order to prevent crosstalk in the sub-scanning direction.

[0009]

However, each of the above-described color image reading apparatuses has the following various problems.

First, in the color image reading apparatus shown in FIGS. 5 and 7, in order to prevent crosstalk in the sub-scanning direction, the length of the document 41 is the same as the length in the main scanning direction and the width in the sub-scanning direction. It is required that a very narrow narrow slit 45 be attached near the surface of the document 41 with high accuracy. When reading color image information by line scanning in the sub-scanning direction, if the narrow slit 45 is arranged near the surface of the document 41,
Synchronization due to an error such as parallelism between the surface of the document 41 and a guide rail for guiding a scanning mirror unit (not shown) causes a problem such as vignetting of a light beam.

According to the present invention, the crosstalk is prevented by making the imaging magnification of the imaging means different in the main scanning direction and the sub-scanning direction, and setting the imaging magnification of the sub-scanning to be larger than that of the main scanning. It is an object of the present invention to provide a color image reading apparatus which eliminates a narrow slit for the above purpose and can reduce or prevent crosstalk in the sub-scanning direction.

[0012]

According to the present invention, there is provided a color image reading apparatus comprising: (1) color separation in which color image information of a document placed on a document table is color-separated by an image forming means into an incident light beam into a plurality of color lights; A color image reading apparatus for forming an image on a surface of an image reading means in which a plurality of line sensors are arranged in parallel on the same substrate surface via means, and reading color image information of the original by the image reading means; The imaging magnification of the means is made different in the main scanning direction and the sub-scanning direction, and the imaging magnification of the sub-scanning is set to be larger than the imaging magnification of the main scanning.

In particular, (1-1) the imaging magnification of the sub-scanning has the following relational expression:

[Outside 2] W: width of one pixel of the line sensor in the sub-scanning direction (μm) n: number of lines between adjacent lines of the line sensor β ′; imaging magnification of the image forming unit in the sub-scanning direction m; If the resolution (dpi) is satisfied, the same or better effects can be obtained. (1-2) the color separation means may be composed of a reflection type or transmission type blazed diffraction grating or (1-3) the color separation means is a plurality of beams to which a wavelength selective transmission film having at least dichroism is added It is characterized by comprising a splitter, (1-4) using a cylindrical lens having power in the sub-scanning direction, and setting the imaging magnification in the sub-scanning direction to be larger than the imaging magnification in the main scanning direction.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a drawing that best illustrates the features of the present invention, in which 11 is a document, 12 is an imaging lens, 13 is a monolithic three-line sensor, and 14 is color separation. A one-dimensional blazed diffraction grating which is an optical system, 15 is a convex cylindrical lens having power in the sub-scanning direction, 16 is a concave cylindrical lens having power in the sub-scanning direction, and is a concave / convex cylindrical lens having power in the sub-scanning direction. The imaging magnification in the sub-scanning direction is set to be larger than the imaging magnification in the main scanning direction.

FIG. 2 is a diagram showing a relationship between a mixed color pixel and a chart for explaining the effect of the present invention. In the present embodiment, the color image reading apparatus has a resolution of 600 dpi in the main scanning direction. In an ordinary image reading apparatus, the resolutions of the main and sub optical units are optically identical. If the resolution is 600 dpi, the image forming magnification is -0.18898 when one pixel of the document sensor is 42.3 μm and one pixel of the line sensor is 8 μm. Therefore, the imaging magnification in the sub-scanning direction is set to 3
When the magnification is set to twice (β '=-0.56693) and the line sensor line spacing is 4 lines, the monolithic 3-line sensor's farthest line spacing on the document surface is 127 μm. Become. This value corresponds to one pixel of 200 dpi. The reading in the sub-scanning direction is performed by scanning a mirror or the like (not shown) and moving the original and the monolithic three-line sensor relative to each other. Do with.

Since there is no narrow slit, the mixed color pixels 24a and 24b
Although the information light of the read pixel 23 is disturbed by the information light from the image reader, color mixing does not occur for an image up to 200 dpi. In this embodiment, a monolithic three-line sensor having a main scanning of 600 dpi, one pixel of 8 μm, and a line interval of four lines is used. However, if the following relational expression is satisfied, the same or higher effects can be obtained.

[0017]

[Outside 3] W: width of one pixel of the line sensor in the sub-scanning direction (μm) n: number of lines between adjacent lines of the line sensor β ′; imaging magnification of the image forming unit in the sub-scanning direction m; Resolution (dpi)

(Second Embodiment) FIG. 3 is a drawing showing a second embodiment. The main scanning resolution is 400 dpi (1
When a monolithic three-line sensor with a pixel interval of 2 μm and a line interval of 2 μm is used, and the sub-scanning imaging magnification is set to −0.6299 (main scanning: −0.12598), the monolithic three-dimensional sensor on the document surface All three lines of the line sensor fit at 63.5 μm per pixel at 400 dpi. So 40
If the image is up to 0 dpi, it does not mean that the colors are mixed. In this case, since the resolution of the main scanning is 400 dpi, it is sufficient to read the sub-scanning to the same resolution. That is, this embodiment corresponds to completely preventing crosstalk.

[0019]

As described above, according to the present invention,
By setting the imaging magnification of the imaging means different in the main scanning direction and the sub-scanning direction and setting the imaging magnification of the sub-scanning on the enlargement side of the imaging magnification of the main scanning, a color image is read using the color separation means. It is possible to achieve a color image reading apparatus in which narrow slits for preventing crosstalk in the sub-scanning direction, which are generated at the time, are eliminated, and crosstalk in the sub-scanning direction can be reduced.

[Brief description of the drawings]

FIG. 1 is a sub-scan sectional view of a color image reading apparatus for explaining a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a relationship between a mixed-color pixel and a chart according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a relationship between a mixed-color pixel and a chart according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating crosstalk of a conventional color image reading apparatus using a beam splitter.

FIG. 5 is a cross-sectional view of a conventional color image reading apparatus using a beam splitter in the sub-scanning direction.

FIG. 6 is a diagram illustrating crosstalk of a conventional color image reading apparatus using a reflective one-dimensional blazed diffraction grating.

FIG. 7 is a sub-scan sectional view of a color image reading apparatus using a reflection type one-dimensional blazed diffraction grating as a conventional example.

[Explanation of symbols]

 11 Original 12 Imaging lens 13 Monolithic 3-line sensor 14 Color separation optical system 15 Convex cylinder lens 16 Concave cylinder lens 21, 31, Original surface 22 600dpi black and white line chart 32 400dpi black and white line chart 23, 33 Reading pixels 24a, 24b, 34a, 34b Mixed pixels 25, 35 One-dimensional blazed diffraction grating 26, 36 Monolithic three-line sensor 41, 51 Documents 42a, 42b Beam splitter 52 Reflective one-dimensional blazed diffraction grating 43, 53 Imaging lens 44, 54 Monolithic three-line sensor 45, 55 Narrow slit A Reading image point B Mixed color image point

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B047 AA01 AB04 BB03 BC05 BC30 CA17 CB10 5C051 AA01 BA03 DA03 DB01 DC02 EA01 5C072 AA01 BA02 BA17 DA02 DA06 DA20 DA23 EA04 FA07 QA02 QA20 RA20

Claims (5)

[Claims] 1. A plurality of line sensors are arranged in parallel on the same substrate surface via color separation means for separating color image information of a document placed on a document table into a plurality of color lights by an image forming means. In a color image reading apparatus in which an image is formed on an image reading means surface arranged in the image reading means and color image information of the document is read by the image reading means, the imaging magnification of the image forming means is changed in the main scanning direction and the sub-scanning direction. A color image reading apparatus wherein the imaging magnification of the sub-scanning is set to be larger than the imaging magnification of the main scanning. 2. The relationship according to claim 1, wherein: W: width of one pixel of the line sensor in the sub-scanning direction (μm) n: number of lines between adjacent lines of the line sensor β ′; imaging magnification of the image forming unit in the sub-scanning direction m; Color image reader that satisfies resolution (dpi). 3. The color image reading apparatus according to claim 1, wherein said color separation means comprises a reflection type or transmission type blazed diffraction grating. 4. The apparatus according to claim 1, wherein said color separation means comprises a plurality of beam splitters to which a wavelength selective transmission film having at least dichroism is added.
The color image reading device according to any one of the above. 5. An imaging magnification in the sub-scanning direction is designed on the enlargement side by an imaging magnification in the main scanning direction using a cylindrical lens having power in the sub-scanning direction.
The color image reading device according to any one of the above.