JPS61284162A - Color reader - Google Patents

Abstract

PURPOSE:To improve the read precision by inserting a light-transmissive plate, which corrects the difference of the distance between an image and an object for insertion of one of filters inserted in time division to the optical path through which the reflected light from the surface of an original is incident on an image sensor, together with the other. CONSTITUTION:The optical path where the reflected light from the surface of an original 1 is incident on an image sensor 5 through a lens 4 is formed. Filters 9a, 9b, and 9c are inserted to the optical path in time division, and color signals of two colors are read divisionally. The distance between the original 1 and the sensor 5 is set to a value for insertion of the filter 9a having a maximum optical path length. When the filter 9b is inserted, a light- transmissive plate 11 which corrects the difference of the distance between the original 1 and the sensor 5 is put on the filter 9b and they are inserted to the optical path. When the filter 9c is inserted, a light-transmissive plate 12 which corrects the difference is put on the filter 9c and they are inserted to the optical path. Thus, the read precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention is capable of reducing the deviation in optical path length between each filter due to the insertion of the filter by inserting a different transparent plate into the optical path together with the filter for each color reading. The optical path length shift due to the chromatic aberration of the lens is corrected, and no matter which filter is inserted, an image is accurately formed on the image sensor, so that reading is performed without out-of-focus.

[Industrial application field]

The present invention relates to a color reading device used in a facsimile machine and the like, and more particularly to a color reading device improved to prevent out-of-focus caused by insertion of a color filter.

[Conventional technology]

FIG. 4 is a perspective view of a conventional fillet switching type color reading device.

In the figure, a reading line 6 on a document 1 is illuminated by an illumination device (not shown), and an image on this line 6 is read. The reflected light from the reading line 6 is imaged by a lens 4 onto a sensor (such as a CCD line image sensor) 5. In order to perform color reading, 83 R, G filters 9a, 9 are installed between the lens 4 and the sensor 5.
b, 9c are provided. Fields 9a, 9b, 9c
are linear motors 10a, 10a, 10c, respectively.
It can be moved to a position where it blocks the optical path from the reading line 6 to the sensor 5.

The color reading operation is shown in FIGS. 5(a)-(c). First, when reading the R(#) component of the color image on the reading line 6, as shown in (a), among the three
The R line 9a is placed into the optical path by driving the linear motor 10a. The other two filters are held in positions where they do not block the optical path. As a result, of the reflected light from the reading line 6, only the red light can reach the sensor 5, and the R component of the image is read.

When reading the G (green) and B (blue) components of an image, use the same figure (
As shown in (b) and (c), a G filter 9b and a B filter 9c are inserted into the optical path and read. When the reading of one line of KGB is completed, the original l is sent a predetermined length in the direction of the arrow in FIG. 1, and the next line is read.

[Problem that the invention seeks to solve]

It is well known that when an object such as a field is inserted into the optical path of an optical system as shown in Figure 1, the optical path length changes and the imaging position of the lens changes. There is.

For example, when there is no filter, the original 1. Lens 4. and sensor 5 are arranged, and the distance between the document and the sensor, that is, the optical path length is set to 4. The surrounding area is air (refractive index 1).

If a filter with thickness tl and refractive index n1 is inserted into this optical path, the optical path length t will be L'' 4-tl+n, tl = 4+tl (nl-1), and the imaging position will shift from the top of the sensor. Therefore, it is necessary to take this deviation into account and determine the distance between the document and the sensor.

In the case of a color reading device, there are a plurality of filters to be switched (for example, three types of KGB), and it is difficult to make them all the same in thickness and refractive index.

The reason for this is that the spectral characteristics of the filter are important in color reading, and in order to give priority to these spectral characteristics, the thickness and refractive index of the filter are restricted and cannot be determined freely.

As a result, if an optical system is configured so that an image is formed on the sensor when a certain filter is inserted, there is a problem that the image will be out of focus when another filter with a different thickness and refractive index is inserted into the optical path.

In addition, chromatic aberration (the same object has a different refractive index depending on the wavelength of light), especially chromatic aberration when light passes through a lens, causes the focal position of each color to shift, resulting in out-of-focus.

When read in such an out-of-focus state, the reproduced color image naturally has a disadvantage of poor image quality.

The purpose of the present invention is to change the light transmitting plate according to the filter to be changed.
By inserting the filter into the optical path of the optical system,
To provide a field switching type color reading device capable of performing color reading with high precision and no out of focus.

[Means for solving problems]

nine Oh.

In the figure, an optical path is formed so that the light reflected from the reading line 6 of the original 1 is incident on the surface of the sensor 5 via the lens 4. Filter 9 that transmits different colors into this optical path
A, 9b, and 9e are inserted in order, and transparent plates 11 and 12 having interesting optical properties are bonded to each of the films 9b and 9c.

[Effect]

In FIG. 1, the optical path length is set so that an image is formed on the sensor 5 surface with the filter 9a inserted, and when the filters 9b and 9c are inserted, the focal point due to the thickness and circumferential ratio of the filters is set. The optical path length is j by correcting the positional deviation.
The optical characteristics of the transparent plate are selected so that a.

〔Example〕

The optical system to which the present invention is applied is shown in FIGS. 3(a) to 3(c). In FIG. 3 (&), the illumination light distance (not shown) for the original 1 is Lo.

Now, the thickness of 4n/9m, 9b, 9c is ta,
tb, tc.

Letting the refractive index be na, nb, nc, the optical path length when each filter is inserted is mu 1ty +
ta(na-1), tb-#+tb(nb-IL
tc-7a+tc(ne-1). In this, tI
L! Assuming that the value of &+ta (na-1) is the maximum, this length M is set as the distance between the document 1 and the sensor 5. Therefore, when the fiery pulp is inserted into the optical path, the image will be correctly formed on the sensor 5 (FIG. 3(b)).

However, when the filter 9b is inserted, the image will be formed in front of the sensor 5 (FIG. 3(C)). Similarly,
Although not shown, even when the filter 9c is inserted, the image is formed in front of the sensor 5 and becomes out of focus on the sensor 5 surface.

FIG. 1 shows an embodiment of the present invention.

Note that the same parts as in FIG. 4 are given the same reference numerals, and the motors that drive the filters 9a, 9b, and 9c are omitted.

As shown in FIG. 1, the distance between the document and the sensor is set to the value when the filter 9a having the maximum optical path length is inserted.

Next, a transparent plate 11 having a thickness tx and a refractive index ■ is superimposed on the filter 9b and inserted into the optical path. At this time 1m -1o
+ tb (nb -1) + tx (13x-1)
-Convex+tx(nx-1) Transparent plates for tx and nx are selected so that the following relationship holds.

Similarly, the filter 9c is a transparent plate 1 having a thickness ty and a refractive index V.
2 and insert it into the optical path. At this time M = to
+tc(nc-1)+ty(ny-1)If such transparent plates 11 and 12 are inserted at the same time as the fields 9b and 9c, the image will be accurately formed on the sensor 5, and the image will always be accurate and out of focus. No reading can be done.

Furthermore, Honda did not only use the method of time-divisionally reading the three filters as described above, but also, for example, the read signals St and So when the R filter and G filter are inserted separately, and the read signal when no filter is inserted. , that is, a method of obtaining R, G, and B signals by calculating the read signal S1 of white light respectively (Japanese Patent Application No. 61,649/1989).
reference). Even when reading without inserting a filter in this way, it is possible to prevent out-of-focus by inserting a transparent plate with an appropriate refractive index and thickness into the optical path.

Further, in this embodiment, a line sensor is used as the sensor, but an area sensor may also be used.

Next, the case of correcting the chromatic aberration of the lens will be explained using FIG. 2.

The refractive index of light in the same medium changes depending on the wavelength. Generally, light with a longer wavelength has a smaller refractive index. For example, when red light is imaged at point 13b shown in FIG. 2, blue light is imaged at point 131L near the lens side, and chromatic aberration can also be corrected. If the transparent plates 11 and 12 are selected, even more accurate reading can be performed.

The transparent plate may be attached to each filter in advance as described above, but it goes without saying that it may be inserted in synchronization with the insertion of the filters by a separate drive mechanism.

〔Effect of the invention〕

According to the present invention, by inserting a transparent plate corresponding to each filter into the optical path together with the filter, it is possible to correct changes in the optical path length due to each filter and chromatic aberration of the lens, thereby achieving highly accurate color reading without blurring. be able to.

[Brief explanation of drawings]

Figure 1 is a plan view of a color reading device of the present invention, Figure 2 is a diagram for explaining chromatic aberration, Figure 3 is a diagram showing an optical system for explaining the present invention, and Figure 4 is a diagram of a conventional color reading device. A perspective view of the reading device, No. 5rIA is an explanatory view of the reading operation in FIG. 4. In the drawing, l is the original, 2 is the imaging position, 4 is the lens, 5 is the image sensor, 6 is the reading line, 9m, 9b, 9c are filters, 10a, 10b, 10c are linear motors, 11.12 is a transparent light Each board is shown. 4 bases θ ＄ 777-R missing 13
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Claims (1)

[Claims] An optical path is formed in which reflected light from the surface of the original (1) is incident on the image sensor (5) via the lens (4), and at least two types of filters (9a, 9b, 9c) is inserted in a time-division manner and reads color signals of at least two colors separately, in which the image when the other filter (9a) is inserted is paired with at least one of the filters (9b, 9c). A color reading device characterized in that a transparent plate (11, 12) is inserted to correct the difference in distance between objects.