JPH08317126A - Image input optical system - Google Patents

Abstract

PURPOSE: To obtain the image input optical system with excellent color reproducibility. CONSTITUTION: Light from a white light source section 61 is emitted to a slit 62. The light passing through the slit 62 is projected onto a color original 3 via a cylindrical lens 63 and a prism 64. An image forming optical system 81 forms an image of the color original 3 onto an image sensor 82 with nonmagnification. The slit 62 and each of line light receiving elements LB, LG, LR are conjugated independently in each color. Thus, only a spectral light corresponding to each color individually reaches each line light receiving element provided on the image sensor 82. Thus, even when the spectral characteristics of the image sensor 82 itself is insufficient, the image of the color only is received accurately by each color and then the color reproducibility of the image is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input optical system, and more particularly to an image input optical system for color-separating and inputting an image of a color original using a line type image sensor.

[0002]

2. Description of the Related Art Conventionally, an image recorded on a color original is input to a line type image sensor (for example, a line CCD) to obtain an image which is separated into three colors. Is used.

The first input method is to illuminate a color document with monochromatic illumination light and switch the color of the illumination light each time the document is scanned and input. Therefore, three scans are required to capture an image of three colors.

The second input method is that the illumination light is white and three line type image sensors are used independently. Then, by adding light splitting means (for example, a dichroic mirror or a dichroic prism) corresponding to the colors R, G, and B in the imaging optical system, a monochromatic image is formed for each line image sensor. It is what makes me.

In the third input method, the illumination light is white, but a line type color image sensor is particularly used as an input means for separating and detecting the input light projected from the imaging optical system for each color. Is. In this line type color image sensor, three input lines are closely arranged in parallel on the detection surface, and color filters corresponding to colors R, G, B to be separated are added to each input line. It is a thing.

In these input methods, a slit and an illumination optical system are arranged between a white light source for illumination and a color original, and a slit image is formed on the color original to form a color original. Illumination of areas other than the image input portion is prevented and flare is also reduced.

[0007]

The above-mentioned first input method has a problem that the productivity of image input is lowered because the original has to be scanned three times.

In the second input method, it is difficult to prevent the relative positions of the three line-type image sensors from shifting.
As a result, there is a problem that an image with a color shift is captured.

On the other hand, the third input method does not have these drawbacks, but has another problem as described below. That is, since the filter added in the line type color image sensor needs to be created by using a fine processing technique, the spectral characteristic is not so good, and therefore only the image by blue light should be extracted originally. The problem is that even with an input line, an image due to red light or infrared light is captured although it is slight. As described above, when infrared light or an infrared light image is added to the blue image, the color reproducibility of the image is significantly deteriorated.

Of these, infrared light can be removed by inserting an infrared cut filter in the white light source or the illumination optical system. However, the red light cannot be removed from the illumination light because it is necessary to detect the red light on the input line that originally captures the red image.

There is a possibility that an image of blue light will be taken into the input line where only an image of red light should be extracted. In this case, the color reproducibility of the image is remarkably deteriorated as in the above case.

From the above circumstances, as long as the third input method is adopted, the color reproducibility of the image cannot be avoided.

Therefore, according to the present invention, three scans can be made by scanning the original once.
An object of the present invention is to provide an image input optical system capable of obtaining a color-separated image, causing no color shift, and further accurately capturing an image of each color.

[0014]

In order to solve the above-mentioned problems, an image input optical system according to the present invention comprises a white light source, a slit irradiated with light from the white light source, and a light source passing through the slit. An illumination optical system that projects light to the document position as illumination light, an image forming optical system that forms an image of a color document arranged at the document position, and an image formed by this image forming optical system is projected. At least the first to the third
In the image input optical system including the image sensor including the line type light receiving element, the spectroscopic means is arranged between the slit and the document position, and the first to third line type light receiving elements are independent for each wavelength. And is conjugate to the slit.

[0015]

In the image input optical system according to the present invention, since the spectroscopic means is arranged between the slit and the document position, the spectral image of the slit is formed at the document position. Further, since the first to third line type light receiving elements are independently conjugated with respect to each slit for each corresponding wavelength, an image of a color document whose spectral image of the slit is illumination light is used for each wavelength. The images are independently projected onto the first to third line type light receiving elements. Therefore, not only a three-color separated image can be obtained by scanning the color original once, but also any one line type light receiving element of the first to third line type light receiving elements can be used for other line type light receiving elements. Since it is possible to prevent the projection of images of other wavelengths, it is possible to accurately separate and capture the image corresponding to the required color. Further, since a common optical system is used when projecting an image of a color original on each line type light receiving element for each wavelength,
The problem of color shift between the obtained images is unlikely to occur.

[0016]

EXAMPLE An image input optical system of Example 1 will be described below. The image input optical system of the first embodiment uses a prism as a means for forming a spectral image of the slit at the document position.

FIG. 1 is a perspective view showing the overall structure of an optical device section 2 as an image input optical system provided in an image input device (not shown). The optical device section 2 is provided with a color original 3
An illumination unit 6 that supplies illumination light to the document position where
A detection unit 8 for detecting the color-separated image of the color original 3 is provided.

The former illumination unit 6 includes a white light source unit 61 forming a line-shaped light source and a line-shaped slit 62 irradiated with white light source light emitted from the white light source unit 61.
And a cylindrical lens 63 that projects the light source light that has passed through the slit 62 as illumination light onto the color original 3 in a linear manner, and is arranged between the cylindrical lens 63 and the color original 3 and And a prism 64 for pre-splitting the illumination light projected on the.

The latter detecting section 8 forms an image of an image of the color original 3 on which the spectrally illuminated linear illumination light from the illuminating section 6 is projected, and an image forming optical system 81 for forming this image. An image formed by the optical system 81 is projected, and an image sensor 82 for individually detecting the projected image for each of the three colors B, G, and R is provided.

The color original 3 is fixed in the x-axis direction perpendicular to the longitudinal direction of the spectral images IB, IG, and IR of the slit 62 projected as illumination light on the color original 3 by a conveying mechanism (not shown). Move at speed.

The illumination unit 6 will be described in more detail.
A halogen lamp with an umbrella 61a is used as a light emitting source of the white light source unit 61. The white light from the halogen lamp 61a is introduced from one end side of a rod 61b whose back side is coated with a diffusion material in a line shape. The white light introduced into the rod 61b is scattered on the back surface side of the rod 61b, and as a light emission from the band-shaped light source surface OS on the front surface of the rod 61b, a surface including the central axis of the rod 61b parallel to the y axis and the optical axis OA1. Emit almost along. The linear light source O of the rod 61b
The illumination length by S is 100 mm.

The slit 62 has a width of 20 μ in the center of the light shielding plate.
A gap having a length of m and a length of 70 mm is provided.

The cylindrical lens 63 has a focal length of 2
It is 0 mm and is arranged at a distance of 30 mm from the slit 62. The size of the slit image formed on the color original 3 by the cylindrical lens 63 is 40 μm wide and 70 mm long for light of a specific wavelength.

The prism 64 is a cylindrical lens 6
Before the illumination light emitted from 3 is projected on the color original 3, it is spectrally separated. The spectrally separated illumination light is projected as a band-shaped region extending in the y-axis direction on the color original 3 in order from the short wavelength side to the long wavelength side in the −x axis direction. That is, the line-shaped spectral images IB, IG, and IR of the slit 62 are projected on the color original 3 in parallel in the −x direction in order from the short wavelength to the long wavelength. The central wavelengths of the three colors to be separated and detected by the prism 64 are 4
55 nm (B), 550 nm (G), 650 nm (R)
In this case, the material of the prism 64 is BK7, and by appropriately adjusting the apex angle, the distance between the centers of the projected positions of the pair of colors G and B on the color original 3 becomes 55 μm, and the pair of colors R , G, the distance between the centers of the projected positions is 45 μm.

The image forming optical system 81 is a lens having a focal length of 40 mm and forms an image of the color original 3 on the image sensor 82 at the same size. Therefore, the spectral images IB, IG, I
Each image area on the color original 3 illuminated by R is also
Input images IB ', IG', I of the same size are formed on the image sensor 82.
Projected as R '.

The image sensor 82 is a line type color image sensor in which a plurality of line CCDs are formed in parallel on a single substrate and different color filters are attached to the respective line CCDs. Therefore, although not shown, three line type light receiving elements extending in the y-axis direction are formed on the light receiving surface 82a of the image sensor 82. The line type light receiving elements are arranged with a mutual pitch in the x-axis direction of 50 μm. Therefore, the input images IB ′, IG ′, and IR ′ of the slits are projected almost exactly on the three line type light receiving elements of the image sensor 82 in a band shape.

FIG. 2 is a side view of the optical device section 2 shown in FIG. As shown, from the front of the rod 61b, the optical axis O
The white light emitted along A 1 passes through the slit 62 and then enters the cylindrical lens 63. The white light emitted from the cylindrical lens 63 is dispersed by the prism 64 and projected on the color original 3 as illumination light.

At this time, the light beam of the short wavelength of color B which is split by the prism 64 illuminates the color original 3 through the optical path PB. Then, the input image of the color B corresponding to the illumination position is projected by the imaging optical system 81 onto the line type light receiving element LB of the image sensor 82. The light beam of the intermediate wavelength of color G, which is split by the prism 64, illuminates the color original 3 through the optical axis OA2. Then, the input image of the color G corresponding to the illumination position is projected by the imaging optical system 81 onto the line type light receiving element LG of the image sensor 82.

The long-wavelength light beam of color R separated by the prism 64 illuminates the color original 3 through the optical path PR. Then, the input image of the color R corresponding to the illumination position is projected by the imaging optical system 81 onto the line type light receiving element LR of the image sensor 82.

As is apparent from the above, in the optical device section 2 of the first embodiment, only the corresponding spectral lights individually reach the respective line type light receiving elements LB, LG, LR provided in the image sensor 82. As described above, the slits 62 and the line type light receiving elements LB, LG, and LR have an optical arrangement in which the respective colors B, G, and R are independently conjugated. Therefore,
Each line type light receiving element LB, LG, L of the image sensor 82
Even if the spectral characteristic of the filter added for each R is insufficient, it is possible to accurately capture only the image of that color for each color.

This point will be described in more detail. FIG.
In the optical device section 2 shown in FIG. 2, the spectral image of the slit 62 is evenly spaced on the color original 3 by about 50 μm in the x-axis direction by the function of the prism 64 arranged between the slit 62 and the color original 3. Will be projected at.

On the other hand, it can be considered that the image forming optical system 81 forms an image of the light receiving surface 82a of the image sensor 82 on the color original 3. The image sensor 82
Since the line type light receiving elements LB, LG, and LR corresponding to the respective colors are arranged in parallel and close to each other at equal intervals of 50 μm in the x-axis direction on the light receiving surface 82a of the line type light receiving elements LB, LG, It can be considered that the LR conjugate image is also projected on the color original 3 at each wavelength at equal intervals of 50 μm in the x-axis direction.

Therefore, the spectral image of the slit 62 projected on the color original 3 and the line type light receiving elements LB, LG, LR that can be considered to be formed on the color original 3 are obtained.
It is possible to substantially match the conjugate image of each color for each color.

This means that the line type light receiving elements LB, LG,
This means that LR, the slit 62, and the color original 3 are substantially conjugate for each color with respect to the xz plane. Therefore, for example, only the blue light reaches the line type light receiving element LB to which a filter transmitting the blue light is added, and unnecessary light such as red light does not reach. Similarly, a line type light receiving element L to which a filter for transmitting green light is added
Only green light arrives on G, and only red light arrives on the input line to which the line type light receiving element LR that transmits red light is added. Therefore, it is possible to provide an image input device having excellent color reproducibility of an image. According to the apparatus of the first embodiment, the image obtained by separating the color original 3 into three colors by scanning the color original 3 once is the line type light receiving element L.
Obtained by B, LG, LR.

Furthermore, since no method such as providing a dedicated image forming means for each color is adopted, the problem of color misregistration hardly occurs in the obtained image. Although the illumination position on the color original 3 differs for each color, this positional deviation is easily compensated by adjusting the scanning speed of the color original 3 and the read timing of each line type light receiving element LB, LG, LR. can do.

The image input optical system of the second embodiment will be described below. The second embodiment is a modification of the first embodiment. Therefore, the same parts are designated by the same reference numerals and the description thereof is omitted.

In the image input optical system according to the second embodiment, optical decentering is used instead of the prism 64 as shown in FIG. 1 as means for forming the spectral image of the slit on the color original.

FIG. 3 is a side view of the optical device section 2 as an image input optical system in the second embodiment. Slit 62
A rod lens 68 is disposed between the color document 3 and the color original 3. The rod lens 68 is arranged such that its central axis extends in the y-axis direction perpendicular to the optical axis OA1 and is decentered from the optical axis OA1 in the substantially x-axis direction. As a result,
The rod lens 68 serves not only as an illumination optical system that projects the light source light that has passed through the slit 62 onto the color original document 3 but also as a spectroscopic means that disperses the illumination light that is projected onto the color original document 3. Also has the role of.

More specifically, the rod lens 68
Has a diameter of 40 mm and is arranged such that its optical axis is eccentric from the optical axis OA1 by d = 4 mm. Therefore, the luminous flux of the illumination light emitted from the slit 62 is projected on the color original document 3 as slit images at substantially equal intervals in the x-axis direction due to the chromatic aberration projected at the magnification of the rod lens 68.

FIG. 4 shows the states of the spectral images IB, IG, and IR projected on the color original 3 obtained by simulation. Since the emission characteristics of the halogen lamp 61a, which is the light source, is a continuous spectrum, the actual spectral image I
B, IG, and IR are also continuous in the wavelength dispersion direction. Here, for convenience of explanation, in order to clarify the state of spectroscopy,
The case where the slit 62 is illuminated with a plurality of monochromatic lights having central wavelengths of 455 nm, 550 nm, and 650 nm is shown. According to this simulation, the spectral images IB, IG,
It can be seen that IR is formed on the color original 3 with a pitch of about 50 μm.

That is, also with the optical device unit 2 of the second embodiment, the optical device unit 2 of the first embodiment shown in FIGS. 1 and 2 is used.
The same effect as can be obtained. The optical device unit 2 of the second embodiment has fewer components than the first embodiment, and the device can be manufactured at low cost. On the other hand, the illumination optical system also serves as the spectroscopic means. So the slit 62
Therefore, there is little design freedom between the imaging magnification and the wavelength dispersion of the spectral images IB, IG, and IR.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments.
For example, each line type light receiving element L of the image sensor 82
The color filters provided in B, LG, and LR are not always necessary. However, in order to enhance the spectral performance of the optical device unit 2, it is desirable to use a color filter as an auxiliary.

In the second embodiment, the rod lens 6 is used.
Although 8 is decentered, other imaging means for forming a one-dimensional image, for example, the cylindrical lens 63 shown in FIG. 1 is replaced with a rod lens 68 shown in FIG. 3 to decenter it. By doing so, the same effect can be obtained. The eccentricity in this case means the optical axis OA connecting the slit 62 and the position on the color original 3 where the spectral image is to be formed.
1, OA2 does not match the optical axis of the cylindrical lens 63. Therefore, both axes may be arranged parallel to each other with an appropriate distance, or may have an appropriate inclination in the xz plane.

Further, the line type light receiving elements LB, LG, LR provided in the image sensor 82 do not need to have the same pitch. However, when illuminating the color original 3 using the prism 64, practical problems will occur even if the line type light receiving elements LB, LG, and LR are of equal pitch, as long as a prism material having a normal refractive index dispersion is used. Absent.

Further, the image forming optical system 81 does not need to be a lens having a fixed focal length, but may be a lens having a variable magnification. When the variable magnification is used as described above, it becomes necessary to adjust the pitch of the spectral images IB, IG, and IR projected on the color original 3. For example, in the case of the first embodiment, by moving the cylindrical lens 63 along the optical axis OA1, it is possible to adjust the pitch of the spectral images IB, IG, and IR without substantially changing the center positions thereof. Further, in the case of the second embodiment, the rod lens 68 is set to the optical axis OA.
By moving along 1 and adjusting the amount of eccentricity in the x-axis direction appropriately, the pitch can be adjusted appropriately without substantially changing the center positions of the spectral images IB, IG, and IR.

[0046]

According to the image input optical system of the present invention, since the first to the third line type light receiving elements are independently conjugated to the slit for each corresponding wavelength, the spectral image of the slit is obtained. The image of the color original with illuminating light is projected on the first to third line type light receiving elements independently for each wavelength. Therefore, not only a three-color separated image can be obtained by scanning the color original once but
Since it is possible to prevent an image of another wavelength corresponding to another line type light receiving element from being projected on any one line type light receiving element of the third line type light receiving element, an image corresponding to the required color Can be accurately separated and captured. Therefore, when the first to third line type light receiving elements in the image sensor are not provided with a spectral filter,
Even if the spectral characteristics of the filters provided in the first to third line type light receiving elements are insufficient, the color reproducibility of the image can be made excellent. In addition, since a common optical system is used when projecting an image of a color original on each line type light receiving element for each wavelength, the problem of color misregistration between the obtained images is unlikely to occur, and individual optical systems are used. There is no need for complicated position adjustment as in the case of capturing an image for each wavelength in an individual image sensor.

[Brief description of drawings]

FIG. 1 is a perspective view showing an image input optical system of Example 1. FIG.

FIG. 2 is a side view of the image input optical system shown in FIG.

FIG. 3 is a side view showing an image input optical system of a second embodiment.

FIG. 4 is a diagram illustrating a spectral image projected on a document.

[Explanation of symbols]

 2 Optical device section 3 Color original 6 Illumination section 8 Detection section 61 White light source section 62 Slit 63 Cylindrical lens 64 Prism 68 Rod lens 81 Imaging optical system 82 Image sensor LB, LG, LR Line type light receiving element

Claims (1)

[Claims] 1. A white light source, a slit for irradiating the light source light from the white light source, an illumination optical system for projecting the light source light passing through the slit as illumination light to a document position, and the document position. An image including an image forming optical system for forming an image of a color original and an image sensor including at least first to third line type light receiving elements on which the image formed by the image forming optical system is projected. In the input optical system, a spectroscopic unit is arranged between the slit and the document position, and the first to third line type light receiving elements are independently conjugated to the slit for each corresponding wavelength. An image input optical system characterized by the above.