JPS63177650A - Image reader/recorder - Google Patents

Abstract

PURPOSE:To correct a chromatic aberration on of image forming surface by forming a spectral filter by a means for varying an optical path length in accordance with each spectral color. CONSTITUTION:Reflected light from an original surface 1 phases through an optical system 2 and forms an image on an image forming surface 3. Between the optical system 2 and the image forming surface 3, a spectral filter 4 is provided, and the thickness of this filter 4 is different in R, G and B. In general when a parallel plate 4 such as a filter, etc., is inserted into an optical path, an image forming position, namely, an optical path length is varied. Accordingly, by setting the thickness of the filter 4 in accordance with the correction quantity of conjugate length of each color, the image forming position can be made equal to each color. In such a way, a chromatic aberration on the image forming surface can be corrected. In this regard, by equalizing the thickness of an optical filter to each other, and also, inserting a transparent parallel plate 5, and setting suitably its plate thickness, the optical path length can also be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a technique for correcting chromatic aberration in color image reading devices such as color scanners and color video cameras.

(Prior art) When performing color separation of a color original, for example, R (red)
, G (green), and B (blue) spectral filters to read the color information of the image. At that time, as shown in Figure 1(a), R light (wavelength around 600 nm), G light
The values of the conjugate length TC are different between light (wavelength around 530 nm) and B light (wavelength around 45 Onm). This is so-called chromatic aberration.

Therefore, when a color document is read using an image reading scanner or the like, a phenomenon occurs in which some colors are in focus, but other colors are blurred.

Therefore, in the past, lenses were designed with little chromatic aberration. However, no matter how good the lens is, chromatic aberration can be reduced to 0.
It's almost impossible to do so. In addition, there is no flexibility in designing such lenses, and lens configuration and precision become stricter.
There were constraints such as high cost, miniaturization, and lens brightness (F value). Therefore, chromatic aberration of the lens usually occurs.

As a solution to this problem, we focus on matching the magnification of each color and adjust the lens position, sensor position, etc.
This resulted in a decrease in resolution (focus). Also, R, G,
In order to match both magnification and resolution for each color of B,
The sensor position, lens position, mirror position, etc. had to be switched for each color, requiring a very complicated mechanism.

(Objective of the Invention) In view of the above-mentioned drawbacks of the prior art, the present invention provides a method for reading a color image in which the image of each spectral filter has no deviation in magnification between each color and has good resolution (focus) using a simple mechanism.・The purpose is to provide recording devices.

(Structure of the Invention) In order to achieve the above object, the present invention provides an optical device that performs color separation using a spectral filter and reads or records image information on an imaging plane via an optical system. It is characterized in that it is configured by means for varying the optical path length depending on the color, and corrects chromatic aberration on the imaging plane.

Examples of the present invention will be described below.

FIG. 1(a) shows a principle diagram of the present invention.

The reflected light from the document surface 1 passes through the optical system 2 and is directed to the imaging surface 3.
image is formed. There is a spectral filter 4 between the optical system 2 and the imaging surface 3, and the thickness of this filter is different for R, G, and B.

In general, a parallel plate 4 such as a filter is placed in the optical path in FIG. 9(a).
When inserted into the optical path as shown in FIG. 9 (bl), the imaging position, that is, the optical path length changes by bl in the following equation.

Here, t: thickness of the filter, n: refractive index of the filter, then Δ1=t (1-1/n)...
(1) That is, the filter 4 with a thickness t is connected to the optical system 2 and the imaging surface 3.
By inserting it between the two, the distance to the imaging section becomes longer by bl.

From this, if the filter thickness t is set according to the amount of correction of the conjugate length of each color, the imaging position can be made the same for each color. In this case, in order to change the optical path length, in addition to changing the thickness of the spectral filter, the spectral filter thickness is kept the same, another transparent parallel plate is inserted, and the thickness of the plate is set according to the correction amount. It is also possible to change the optical path length by doing this. In addition, since it is only necessary to change the value of Δ2, (in equation 11, by changing the material of the spectral filter or the transparent parallel plate to change the refractive index n, or by combining the plate thickness t and the refractive index n) By doing so, it is also possible to correct the desired optical path length.

Next, if a correction plate 5 is provided between the original surface 1 and the optical system 2 as a highly transparent parallel plate with a different thickness for each spectral filter, the optical path length will change, and the original will be The distance to the lens can be made the same distance as corrected by each spectral filter. This correction plate 5 may be a spectral filter, but it is not necessary, and a transparent parallel plate is sufficient. Alternatively, other spectroscopy using an infrared cut filter or the like may be performed. Generally, the material used for the filter has a refractive index of 1 or more with respect to air, so the thickness is R≦G≦B. By doing this, for each spectral filter,
An optical device with good focus and magnification can be obtained.

FIG. 2 shows an embodiment in which the correction plate 5 in FIG. 1 is not provided. If the document surface is now the same, the focused position of each spectral filter will be shifted as shown in FIG. 2(a). Also, the magnification is different for each color. This is shown in Figure 2 (b
), if you correct by changing the thickness of each spectral filter,
The focus position can be made the same. However, since the distance from the document surface l to the optical system 2 is not corrected, the magnification is different for each color. This difference in magnification can be corrected by interpolation or thinning through electrical signal processing, so in the case of a digital reading device, the effects of the present invention can be sufficiently obtained without a correction plate.

Next, other embodiments will be described. 3 to 7 show other embodiments of the present invention.

FIG. 3(a) is a schematic diagram of a digital image reading scanner. The original is set on the contact glass 6,
This is illuminated by the lighting device 7, and the first. 2nd and 3rd mirror 8
, 9.10 and the optical system 2, the image is formed on the image sensor 11. In addition, the spectral filter 4 and the correction plate 5, which have different thicknesses depending on each color, are located between the third mirror lO and the optical system 2, and between the optical system 2 and the image sensor 1, as shown in the figure.
1. First, when reading the R light, the light is separated using the spectral filter 4 and the first stage of the correction plate 5.
Spectroscopy is performed using the second stage for light and the third stage for B light. As a result, an image of the original on the contact glass ■ is formed on the image sensor 11 with the same focus and magnification for each color, and it is possible to prevent out-of-focus (blur) due to color, which has been a problem in the past. can.

FIG. 3(b) shows a self-hock lens array 12 in the optical system.
(manufactured by Nippon Sheet Glass) is used. Since the self-hock lens array 12 has a shallow depth of focus, a slight deviation will cause blurring, so the effects of the present invention are significant. Moreover, this cell-hock lens array 12 has a conjugate length T
Since C is short, the filter or correction plate of the present invention may not be able to be inserted. As a countermeasure for these, a material with a large refractive index is used, provided that formula (1) is satisfied.
By reducing its thickness, it becomes possible to insert a spectral filter and a correction plate.

FIG. 4 shows an embodiment in which the present invention is applied to an analog color copying machine. The originals on the contact glass 6 are
The image is formed on the photoreceptor 14 via the mirrors 8, 9, 10 and the optical system 2. The spectral filter 4 and the correction plate 5, which have different thicknesses, are rotatable around axes 4a and 5a, respectively.
It is provided between the third mirror 10 and the optical system 2 and between the reflecting mirror 13 and the photoreceptor 14. In this way, the photoreceptor 14
The electrostatic latent image formed thereon is developed by the developing section 15 of each color.

FIG. 5 shows an embodiment in which the correction plate 5 is not used in the embodiment of FIG. 3(a). As mentioned above, in the case of a digital reading device, the effects of the present invention can be sufficiently obtained even without a correction plate.

FIG. 6 shows an embodiment in which a variable magnification mechanism is provided. For example, when the magnification ratio is 100%, 75%, and 50%, the distance from the lens 2 to the contact glass surface 6, the lens 2
Since the distance from the image sensor 11 or the photoreceptor to
, the thickness of the correction plate 5 must be changed. Therefore, as shown in FIG. 6, three sets of R, G, and H filters and three sets of correction plates are provided, and they are used depending on each magnification.

FIGS. 7(a) and 7(b) are examples in which the image sensor itself has a spectral filter. A sensor 17 is fixed to a substrate 16 and protected by a dustproof glass 18. Spectral filters 19 corresponding to R, G, and B are alternately attached to the sensor 17 as shown in FIG. 7 [b]. By changing the thickness of this spectral filter 19 according to each of R, G, and H, the optical path length can be changed, and the effects of the present invention can be obtained.

Next, Fig. 8 shows an example of a concrete implementation of the present invention.
This will be explained based on FIG. 10 (al, (b)).

Figure 8 shows the self-hock lens array used in the optical system (
It is a graph showing the chromatic aberration of Nippon Sheet Glass (Japanese Sheet Glass), that is, the relationship between the wavelength of light and the conjugate length TC. When a TC54 lens is used, the conjugate length TC for each color is as follows.

B light (blue) 450 nm: conjugate length 53.3 t*G light (green) 550 nm: conjugate length 54.5 tmR light (red) 650
nm: conjugate length 55.4 am Using this and formula (11),
After correction, the thickness of each spectral filter (■) and correction plate (■) is as follows: B filter: 3.81 m, G filter: 2.5 m, R filter: 0.751. However, as the refractive index of the spectral filter and correction plate, n=
Using a glass material of 1.52mm, filters and correction plates are installed on both sides of the optical system as shown in Figure 10 (al).

The conjugate lengths of G and R are corrected to be almost the same.

When correcting only one side of the lens to obtain almost the same conjugate length as shown in Figure 10 (bl), a filter twice as thick as the one above is required. B filter Near, 63 Tsuru G filter: 5. 0 Tsuru R film: 1.501 rin The above example is an example of the thickness of the filter and the correction plate, and can be arbitrarily selected depending on the combination of the refractive index n and the thickness t.

This is particularly effective in cases where attempting to correct based on thickness alone would result in a problem in terms of space due to the increase in thickness.

(Effects of the Invention) According to the present invention, when color separation is performed using a spectral filter, the resolution can be maximized without changing the magnification depending on each color. Therefore, it is possible to read an image with excellent resolution, gradation, color reproducibility, and magnification error. In addition, the parallel plate that changes the optical path length can also be used as a spectral filter.
It can be made into a simple mechanism. Furthermore, since the chromatic aberration of the lens can be sufficiently corrected, various restrictions on lens selection are eliminated, leading to cost reduction.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a schematic diagram showing a difference in conjugate length based on a difference in wavelength, a schematic diagram of an embodiment of the present invention, and FIG.
Figures (a) and (b) are schematic diagrams of an embodiment of the present invention that does not use a correction plate, and Figures 3 (a) and (b) are schematic diagrams of an embodiment in which the present invention is applied to a digital image reading scanner. 4 is a schematic diagram of an embodiment in which the present invention is applied to an analog color copying machine. FIG. 5 is a schematic diagram of another embodiment in which the present invention is applied to a digital image reading scanner. 7 is a schematic diagram of an embodiment in which the present invention is applied to a variable magnification device, FIGS. 7(a) and 7(b) are a side view and a front view when a spectral filter is provided in the image sensor itself, and FIG. ,
Graphs showing the relationship between conjugate length (TC) and wavelength of a self-hock lens, Figures 9 (a), (b), and 10 (a) and (b), respectively, show the change in optical path length when a parallel plate is inserted. FIG. 1... Original, 2... Optical system, 3... Image forming surface, 4...
...Spectral filter, 5...Correction plate. (a) (b) Figure 1 (a) (b) Figure 2 Factor 4 Figure 8 Figure 9

Claims (6)

[Claims] (1) In an optical device that performs color separation using a spectral filter and reads or records image information on an imaging plane via an optical system, the spectral filter is configured by means for changing the optical path length according to each spectral color. An image reading/recording device that corrects chromatic aberration on an imaging plane. (2) Claim 1, characterized in that, in contrast to the spectral filter provided on the imaging surface side, a transparent parallel flat plate having different optical path lengths depending on each spectral color is provided on the document surface side. Image reading/recording device. (3) The image reading/recording apparatus according to Claims 1 and 2, wherein the means for varying the optical path length varies the thickness depending on the magnitude of the wavelength. (4) The image reading/recording apparatus according to claim 1 or 2, wherein means for varying the refractive index depending on the magnitude of wavelength is used as the means for varying the optical path length. (5) The image reading/recording device according to item 2, wherein the transparent parallel plate is an infrared cut filter. (6) The image reading/recording apparatus according to claim 2, characterized in that a number of spectral filters and transparent parallel plates having different optical path lengths are provided in accordance with the variable magnification stage.