JPH03268671A - Image forming adjustment system of color reader - Google Patents

Abstract

PURPOSE:To obtain a read picture at a photodetector face with high accuracy by controlling a driving means so as to adjust a color resolving means in an image forming optical path and a color aberration correcting means simultaneously. CONSTITUTION:Both of a color resolving means 11 resolving a reflecting light lto red, green and blue colors provided in an image forming optical path and a color aberration correcting means 12 correcting color aberration caused by difference of wavelengths of each color and a deviation of an optical path length caused by the color resolving means 11 are simultaneously adjusted by driving means 13, 14 based on the control of a control means 15. The color resolving means 11 is a color glass filter, whose thickness is adjusted in response to the wavelength of each color resolved and the internal transmission rate, the color aberration correcting means 12 is parallel glass transmission plates whose thickness and refractive index are set corresponding to each resolved color. Through the constitution above, the out of focus and the color aberration caused in the lens image forming system are suppressed and high color accuracy is warranted and the color reading with high accuracy is attained.

Description

[Detailed Description of the Invention] [Summary] Regarding an image formation adjustment method in a color reading device, it is an object of the present invention to improve color accuracy (color reproducibility) by simultaneously adjusting both a color separation means and a chromatic aberration correction means. In a color reading device, an image formation adjustment method is provided in which light reflected by a light source from a document is imaged on a light receiving surface of a light receiving element via a lens, and the reflected light is transferred to a red, red, green,
A color separation means for separating into each color of blue, and a chromatic aberration correction means for correcting a chromatic aberration caused by a deviation in optical path length caused by the color separation means and a difference in wavelength of each color, the color separation means and the chromatic aberration correction means The configuration is such that an optimal image is formed on the light-receiving surface by adjusting both simultaneously by a driving means under the control of a control means.

[Industrial application field]

The present invention relates to an image formation adjustment method for improving color accuracy in a color reading device.

In recent years, color reading devices used as image input devices for facsimile machines and computers have significantly developed. In general, color reading devices color-separate the three-color light of red (R), green (G), and blue (B) reflected from the document surface and form an image, for example, to form a line image using a charge-coupled device (CCD device). A method of reading using an image sensor is used.

[Conventional technology]

FIG. 5 is a block diagram of the main parts of a conventional filter switching type color reading device. In FIG. 5, a reading line 6 on a document 1 is illuminated by an illumination device 2, and an image on this reading line 6 is read.

That is, the reflected light from the reading line 6 is CC-coded by the lens 4.
An image is formed on the line image sensor 5 by the D element.

In order to perform color reading, R is placed between the lens 4 and the sensor 5.
, G, and B. Three color separation filters 9 corresponding to each color component.
a, 9b, and 9c are provided.

The color separation filters 9a, 9b, 9c are held by linear motors 10a, 10b, 10c, respectively, and can be moved to a position where the optical path from the reading line 6 to the sensor 5 is blocked by the operation of the linear motors 10a, 10b, 10c. It has become.

FIGS. 6(a), 6(a) and 6(c) are explanatory diagrams of the color reading operation of the apparatus having the structure shown in FIG. First, when reading the red component (R component) of the color image on the reading line 6, (a
), an R filter 9a that transmits the red component among the three color separation filters is driven by a linear motor 10a and placed in the optical path. 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 color image is read.

When reading the green component (G component) of a color image, (
As shown in b), when reading the blue component (B component), as shown in (C), a G filter 9bSB filter 9C that transmits each component is sequentially arranged in the optical path. Then, when one line of RGB reading is completed,
The document is fed a predetermined length in the direction of the arrow in the figure, and the next line is read.

Such equipment uses small, lightweight color separation filters,
By combining a high-speed linear motor, the color separation filters 9a, 9b, and 9c are switched in a time comparable to the time required to read one line of the sensor, thereby realizing color reading.

[Problem to be solved by the invention]

As mentioned above, in color reading devices that perform color separation,
A color image is obtained by separating the image information of the subject into three colors (R, G, and B components) and combining them. This type of reading device often uses an imaging lens system.

However, in such an imaging lens system, since the thickness of each color separation filter and the wavelength of each separated color are different, the refractive index of the lens changes, and as a result, the focal length of each color differs.

In addition, defocus (blurring of the image) and chromatic aberration occur in accordance with the difference in focal length on the imaging plane.

By the way, Japanese Patent Application Laid-Open No. 61-284162 by the same applicant
In order to solve the above-mentioned conventional problems, the publication discloses that a parallel plane transparent plate made of a glass plate is inserted in each color separation filter, and the change in refractive index due to the thickness of this glass plate is utilized. The focal length is adjusted for each color separation. As a result, the optical path length can be forcibly changed, and defocus and chromatic aberration can be corrected.

In this conventional method, a glass plate whose thickness is adjusted according to the color separation filter to be switched as described above is inserted into the optical path together with each color separation filter. In this way, the position where the out-of-focus with respect to the refractive index and the wavelength of each color is the smallest is set to be the sensor imaging plane, so that the out-of-focus is minimized on average.

On the other hand, the above methods are not sufficient to achieve highly accurate reading in order to reproduce colors as close to those of the original as possible, and adjustments cannot be made by adjusting the thickness or refractive index of the glass plate alone. This is because in order to improve color accuracy, it is also necessary to consider the optical characteristics of each color separation filter. This is because in the optical system of a color reading device, color accuracy is influenced by the spectral characteristics of the color separation filter, that is, the relationship between the transmitted output and the wavelength of the transmitted light.

A commonly used method for adjusting spectral characteristics is to adjust the thickness of a color separation filter.

However, the transmitted output varies greatly along the wavelength due to variations in the filter itself, and this increases the chromatic aberration of the imaging optical system, so there is still a problem in achieving high color accuracy. Furthermore, even if the conventional method corrects the out-of-focus and chromatic aberrations, deterioration in color accuracy due to out-of-focus and chromatic aberrations, especially near the edges of the document, remains unsolved.

Another option is to reduce the F value of the lens system, but this cannot be used because the spread of focus for each wavelength will become narrower and the color accuracy at the average focus position will further deteriorate. .

The object of the present invention is to set the thickness of the color separation filter to be optimized according to the wavelength of each color, and to further correct the optical path length by disposing a transparent plate made of a parallel plane plate in the optical path. An object of the present invention is to provide an image formation adjustment method in a color reading device that makes use of changes in refractive index and simultaneously adjusts them to correct out-of-focus and chromatic aberration, thereby obtaining a highly accurate read image.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. The present invention provides a color reading device in which a light source 2 reflects light from a document 1.
This is an image-forming adjustment method in which the reflected light is imaged on the light-receiving surface of the light-receiving element 5 via the lens 4, and the reflected light is
The color separation means 11 includes a color separation means 11 that separates green and blue colors, and a chromatic aberration correction means 12 that corrects chromatic aberration caused by a deviation in optical path length caused by the color separation means 11 and a difference in wavelength of each color. 11 and the chromatic aberration correction means 12 are driven by driving means 13.14 under the control of the control means 15.
The color separation means 11 is a colored glass filter, and the wavelength and internal transmission of each color separated are The thickness of the colored glass filter is set according to the color separation ratio, and the chromatic aberration correcting means 12 is a parallel plane glass transparent plate, and the thickness of the transparent plate is set according to each color separated. , The refractive index of the transparent plate α is set corresponding to each separated color.

[For production]

As shown in FIG. 2, in the present invention, first, the arrangement of optical system elements such as light sources, mirrors, lenses, originals, glass, etc. other than color separation filters are determined, and second, the color separation filter In order to optimize the characteristics, the optical characteristics, ie, the thickness of the color separation filter, the refractive index, the selected wavelength, etc., are determined. moreover,
Third, the optical characteristics of the plane-parallel transparent plate for correcting chromatic aberration, that is, the thickness and refractive index of the plane-parallel transparent plate, are determined based on the overall imaging characteristics of the imaging optical system. Basically, these steps perform highly accurate image formation adjustment on the sensor surface.

〔Example〕

FIG. 3 is a diagram showing the main part of an embodiment of a color reading device according to the present invention. Same as the color separation filter 11 of the present invention in which three package components R1G and B are arranged on a flat plate;
, G, and B are placed in the imaging optical path β, and when reading the original, the two are adjusted by different and independent drive sources 13 and 14 to operate. Color separation of three colors is performed.

The advantage of this structure is that in one embodiment, the color separation filter 11 and the parallel plane transparent plate (glass plate) 12 for correction are provided independently, and the driving sources are also independent, so that there is no change in one of them. It is easy to readjust when necessary.

FIG. 4 is a block diagram of main parts of another embodiment of the present invention.

As shown in the figure, a color separation filter 11 and a transparent plate 12 for correcting chromatic aberration are laminated together to form an integral structure. in this case,
Drive sources 13,14 work together to drive the integral structure. Therefore, it is necessary to adopt such a structure after completely adjusting the color separation filter 11 and the glass plate for correcting chromatic aberration.

Next, the optical characteristics of the color separation filter according to the present invention and the method for determining the parallel plane transparent plate for correction will be explained below.

In the color separation filter 11, the thickness is t. , the internal transmittance τ at a certain wavelength. When using a color separation filter having a color separation filter as a reference, the internal transmittance τ at a certain wavelength has a thickness of 1.
is t,=to (logτ,/log τ0)...(
It can be expressed as 1).

Therefore, using equation (1), first, the thickness t of the color separation filter for the R component is calculated based on the optimum value (approximately 650 nm) of the wavelength of the R component. Determine. Regarding the G and B components, the relationship between the wavelength λ and the internal transmittance τ is clear according to Lambert's law, so the internal transmittance τ of the R component is
0, the respective thicknesses t of the G and B components are determined by formula (1) based on the internal transmittance τ1 for the wavelength of the G and B components.
Determine l.

On the other hand, in the correction parallel plane transparent plate 12, when the imaging magnification of the imaging optical system is m and a parallel plane glass plate with a thickness of 1S and a refractive index of n is arranged in the optical path, the amount of defocus Δ is 1 △=m” [: (n-1)/n):] ・t(
2) Therefore, the change in focal length due to the thickness t of the transparent plate can be calculated from equation (2), and the thickness 1. and the thickness t of the transparent plate based on the amount of defocus Δ obtained from equation (2),
Under the control of the control means 15, the focal length for each color is adjusted. In this case, the refractive index changes somewhat due to the difference in the wavelengths of R, G, and B, but this is a value that can be ignored.

〔Effect of the invention〕

As explained above, according to the image formation adjustment control method of the color reading device of the present invention, defocus and chromatic aberration for each wavelength that occur in the lens imaging system can be suppressed, and high color accuracy (color reproducibility) can be achieved. Therefore, highly accurate color reading becomes possible.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention; Fig. 2 is an explanatory diagram of the basic procedure of the invention; Fig. 3 is a diagram showing the main part of an embodiment of the invention; Fig. 4 is a diagram showing another embodiment of the invention. Main part configuration diagram FIG. 5 is a main part configuration diagram of a conventional color reading device, and FIG. 6 is an explanatory diagram of the operation of FIG. 5. (Explanation of symbols) 1... Original, 2... Light source, 3... Mirror 4... Lens, 5... Line image sensor, 6... Reading line, 9a, 9b, 9c...・Color separation filter, 10a, 1
0 b, l0C-=motor, 11... color separation means, 12... chromatic aberration correction means, 13, 14... drive source, 15... control means.

Claims (1)

[Claims] 1. In a color reading device, a light source (
2) is an image formation adjustment method in which the reflected light (l) is imaged on the light receiving surface of the light receiving element (5) via the lens (4),
In the imaging optical path, a color separation means (for separating the reflected light into red, green and blue colors) is provided.
11), and a chromatic aberration correction means (12) for correcting chromatic aberration caused by a deviation in optical path length caused by the color separation means (11) and a difference in wavelength of each color, the color separation means (11) and chromatic aberration correction means. Both of the means (12) are driven by the drive means (13) under the control of the control means (15).
, 14) An image forming adjustment method in a color reading device, characterized in that an optimum image is obtained on the light receiving surface by simultaneously adjusting the above. 2. The imaging adjustment method according to claim 1, wherein the color separation means (11) is a colored glass filter, and the thickness of the colored glass filter is set according to the wavelength and internal transmittance of each color separated. . 3. The imaging adjustment method according to claim 1, wherein the chromatic aberration correcting means (12) is a parallel plane glass transparent plate, and the thickness of the transparent plate is set corresponding to each color separated. 4. The image formation adjustment method according to claim 3, wherein the refractive index of the transparent plate (12) is set corresponding to each separated color.