JPH07261019A - Image reader - Google Patents

Abstract

PURPOSE:To provide a color image reader using an unmagnified image forming type optical system which can separate a clear color signal at a high speed without complicating a circuit system for a signal processing system. CONSTITUTION:The color image reader is provided with a bluish white fluorescent tube 7 whose spectroscopie intensity characteristic becomes low in the order of a short wavelength area having a peak value near 500nm, an intermediate wavelength area and a long wavelength area, a lens column 5 forming the image of light reflected on the surface of an original as an erected unmagnified image, an image sensor 4 whose spectroscopic sensitivity characteristic becomes low in the order of the long wavelength area, the intermediate wavelength area and the short wavelength area and a color separation filter 41 separating the color of the light reflected on the surface of the original. Then, when the white original is read, the outputs of the respective cells of the sensor 4 are balanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus capable of efficiently separating color signals when performing color image pickup.

[0002]

2. Description of the Related Art Image reading apparatuses are being made faster, higher in resolution, higher in function and more economical with the development of solid-state image sensors. Recently, various efforts have been made to develop a color image pickup device for a television, and to improve the performance of a solid-state image pickup device, in particular, a single-plate color image pickup device. As the first of the basic problems to be solved in improving these performances, it is necessary to improve the utilization efficiency of imaging light. In the conventional color imaging device,
The basic method is to read color signals in a dot-sequential manner from each pixel of the solid-state image pickup plate using color separation filters of red (R), green (G), and blue (B). In order to increase the luminance signal component, a method of using a complementary color filter for at least one of a red color pass filter and a blue color pass filter has been proposed (for example, JP-A-57-2697).
No. 8). On the other hand, as a method of reading a color document image using a single linear image sensor, for example, a CCD
(Charge Coupled Device) A linear image sensor may be configured to perform dot-sequential color coding in a form in which red, green, and blue color separation filters are on-chip in a mosaic pattern. FIG. 1 is a diagram schematically showing a conventional example of a facsimile optical system for reading an original by such a system. The optical system according to this drawing has a configuration in which an original 1 is illuminated by a white light source (fluorescent tube) 2 and is read by a linear image sensor 4 via an imaging lens 3, and is used in a facsimile. Reference numeral 30 in the figure is a slit. In such an optical system, the color separation filter 41 formed on the image sensor 4 by the on-chip method is shown in FIG.
As shown in b, if three primary color filters of red, green, and blue are used, color separation, color separation, and hue correction processing become easy. However, in general, the spectral sensitivity of a solid-state image sensor has a peak value in a long wavelength region near 700 (nm) and an intermediate wavelength region near 600 (nm) of 500 (n) as shown in FIG.
m) near the short wavelength region, the wavelength gradually decreases, and if the red, green, and blue wavelength regions are defined during this period, red,
Since the wavelengths of green and blue are lower in order, it is difficult to achieve white balance. When the spectral transmittance of the color filter is controlled, the amount of light used is extremely reduced (about 1/10) as compared with the case of reading white. This is because in addition to the spectral sensitivity of the image sensor 4 as described above, the spectral intensity distribution of the white fluorescent tube is high in red and green and low in blue as shown in FIG. This is because we have to suppress the green. In view of this situation, a measure is taken to improve the light utilization efficiency by using a complementary color filter as described above, but FIG. 4 shows a design example when cyan (Cy) is used as a complementary color filter. .

[0003]

However, according to such a configuration, signal processing for separating each of the red, green, and blue color components is required, which complicates the circuit system for that and makes delicate color tone adjustment. However, there is an inconvenience that color mixing becomes difficult. Such a problem arises from the fact that the conventional image pickup device is designed mainly for an object under the illumination of natural light or a so-called "daylight color" light source, and the spectral sensitivity characteristics of the light source and the sensor. It is derived from the idea of constructing an optical system with reference to.

The present invention has been made by paying attention to such a conventional problem, and an object thereof is to separate a color signal at high speed and sharply without complicating a circuit system for signal processing. It is to provide a color image reading device that enables the color image reading device.

[0005]

In order to achieve the above object, the present invention provides a blue-white luminescent material having a spectral intensity characteristic having a peak value in the vicinity of 500 nm, which decreases in the order of a short wavelength region, an intermediate wavelength region and a long wavelength region. A single light source for illuminating a document, an imaging lens for forming the reflected light from the document surface as an erecting equal-magnification image, and spectral sensitivity characteristics of a long wavelength region, an intermediate wavelength region, and a short wavelength region. It is characterized by comprising a solid-state image sensor which becomes lower in order, and a color separation filter which has a predetermined spectral characteristic and color-separates the reflected light from the document surface.

[0006]

With the above-described structure, the present invention makes it possible to balance the outputs from the solid-state image sensor when a white original is read in an equal-magnification imaging type optical system using a large image sensor.

[0007]

EXAMPLES An example of the present invention will be described below.
5 and 6 show spectral transmittance characteristics (hereinafter, simply referred to as spectral characteristics) of a color separation filter used in a color image reading apparatus according to an embodiment of the present invention and spectral intensity characteristics of a blue-white fluorescent tube that serves as a light source. FIG. 6 is a graph showing respective (hereinafter, simply referred to as spectral characteristics). That is, in the present invention, an optical system having the same basic structure as that shown in FIG.
Spectral sensitivity characteristics of the image sensor 4 of this optical system (hereinafter,
2) is set as shown in FIG. 2, and the image sensor 4 is combined and arranged in a mosaic pattern so that color separation signals in the order of red, green, and blue dots are obtained on the opening surface of the image sensor 4.
Moreover, a color separation filter 41 having the spectral characteristic shown in FIG. 5 is arranged. At this time, instead of the white fluorescent tube 2, a blue-white fluorescent tube 7 (see FIG. 9) having a spectral characteristic as shown in FIG. 6 is used as the light source.

When a color image is read by such an optical system, the red, green, blue and white screens corresponding to the respective pixels of the color separation filter 41 on the image sensor 4 as shown in FIG. 7A are output. As can be seen from FIG. 11, almost balanced components are obtained as shown in FIG. In the present embodiment, (1) the spectral sensitivity of the image sensor 4 is set as shown in FIG. 2, and (2) the spectral characteristics desired in the case of the three primary color separations of red, green, and blue are used as a basis, and further white A color separation filter 41 having a spectral (transmittance) characteristic as shown in FIG. 5 in which the balance is taken into account is additionally used, and (3) the light source has a wavelength of around 500 (nm) as shown in FIG. It has a peak value in the short wavelength range, an intermediate wavelength range near 600 (nm), and 700 (n
The object of the invention is achieved by using a single bluish white light-emitting lamp 7 having a spectral characteristic that gradually decreases in the long wavelength region near m), but in addition to such an aspect,
When an infrared cut filter having a spectral characteristic as shown in FIG. 8 is used as the color matching filter in combination with the color separation filter 41, the white balance can be further corrected.

In the color separation filter 41 shown in FIG. 7a, photoelectric conversion outputs S (j) (j = 1, 2, 3, ...) Corresponding to the pixel aperture columns 411, 412, 413 ,.
...) indicates the maximum value with respect to the reference white screen. In this embodiment, the optical system is arranged so that the saturation output level E (mV) of the image sensor 41 with respect to red, green, and
The light quantity is designed so that the maximum output of each blue color component is about 0.7E (mV), and the signal component ratio (that is, S / N ratio) to the noise component of the image sensor 41.
Is to maximize.

In the above embodiment, a lens reduction type optical system is constructed as shown in FIG. 1 to read a color image, but the present invention is not limited to this, and other types of optical systems may be used. Good. FIG. 9 is a diagram showing a second embodiment of the present invention in which an equal-magnification image-forming optical system is prepared by using a large image sensor.

In this embodiment, reference numeral 5 is a lens array forming an erecting equal-magnification image. For the lens array 5, a distributed index type rod lens array, a planar microlens array, or a spherical microlens array can be appropriately used. The rest of the configuration is the same as that of the first embodiment, and the original 1 is irradiated with illumination light from a light source composed of a blue-white fluorescent tube 7, and the reflected light is condensed by the lens array 5 and then the slit 30 is formed. Through the image sensor 4, photoelectric conversion is performed. The image sensor 4 is
A row of apertures 411, 4 with a color filter arrangement as in FIG. 9b.
12, ... The mosaic pattern of the three-color separation filter 41 in the aperture array 411 and the like is shown in FIG.
It is not limited to the repeating pattern of red, green, and blue as shown in FIG. 2, but the density of each of the red and blue components (pitch: P ₂ ) is 1/2 that of the green component (pitch: P ₁ ) (P in FIG. 9b). ₂ = 2P ₁ ) may be arranged.

Furthermore, it is also possible to adopt another arrangement configuration without arranging the three-color separation filters in a mosaic pattern as shown in FIGS. 7a and 9b. FIG. 10 is a diagram showing a third embodiment of the present invention in which the structure of the filter is changed. In this embodiment, the filter 6 is composed of a shaft portion 64 and a disc portion 65 that extends outward in the radial direction from the shaft portion 64. The disc portion 65 matches the optical path of the image reading apparatus, and 6 is arranged so as to rotate about the rotation center axis 0. A dielectric multilayer film 60 is formed on the back surface of the disc portion 65 of the filter 6, and the dielectric multilayer film 60 is formed.
As shown in FIG. 10B, fan-shaped color separation filter regions 61, 62 and 63 having predetermined spectral characteristics are formed as needed. Of these color separation filter regions, for example, the region 61 is divided into red, the region 62 is green, and the region 63 is divided into blue, and as the filter 6 rotates around the rotation center axis 0, the red, green, and blue regions are separated. The three color separation filter regions 61, 62, 63 are sequentially inserted into the path of the optical system,
It is designed to read in a frame-sequential manner.

In the third embodiment, the image reading optical system is a rotary cylinder 10 on which the original 1 is provided.
And a bluish white fluorescent tube 7 for irradiating the surface of the original 1 with light, an imaging lens 3 for converging the reflected light from the original 1 that has passed through the filter 6, and an image sensor 4. The surface of the original 1 is illuminated by a blue-white fluorescent tube 7 serving as a light source, and the optical system constitutes a scanner for reading the image information, which is similar to the conventional black-and-white image reading optical system. Since the optical system according to the third embodiment reads color image information, the motion of the rotary cylinder 10 holding and fixing the color original document 1 is controlled, and the red, green, and blue three-color separation filter regions 61, By switching between 62 and 63, the image signals are sequentially read.

[0014]

As described above, according to the present invention,
In high-speed reading of color images using the same-magnification optical system, the spectral intensity characteristics of the light source, the spectral sensitivity characteristics of the image sensor, and the spectral characteristics of the color separation filter are matched to produce a white screen output corresponding to each color. Uniform correction is ensured mainly by the spectral intensity characteristics of the light source within the range on the long wavelength side from the spectral intensity peak value of the light source, and is supplemented by the spectral characteristics of the color separation filter and color matching filter to obtain a color image. When reading, the light utilization rate can be maximized, and the S / N ratio in the image sensor can be maximized.
Furthermore, since the red, green, and blue color signals can be read almost faithfully, it is not necessary to use a complicated color signal processing circuit, and clear color image information can be obtained with a simple configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a general color image information reading device using a white light source and an image sensor having a three-color separation filter on-chip. (A) A diagram showing the configuration of an optical system (b) Color Diagram showing the structure of the decomposition filter

FIG. 2 is a diagram showing spectral characteristics of an image sensor used in an image reading apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing spectral characteristics of a white light source used in a conventional image information reading device.

FIG. 4 is a diagram showing spectral characteristics of a complementary color filter used for improving light utilization efficiency in the image information reading device.

FIG. 5 is a diagram showing spectral characteristics of a color separation filter.

FIG. 6 is a diagram showing spectral characteristics of a blue-white light source.

7A is a diagram showing a configuration of a color separation filter and FIG. 7B is a diagram showing a light amount conversion output corresponding to a pixel aperture row of the color separation filter. FIG. 7B is a diagram showing a configuration of the color separation filter and its color separation filter. The figure which shows the light quantity conversion output corresponding to the pixel aperture row

FIG. 8 is a diagram showing spectral characteristics of an infrared cut filter that can be used together with a color separation filter.

FIG. 9A is a schematic configuration diagram of an image reading device according to a second embodiment of the present invention and a diagram showing a configuration of a color separation filter. FIG. 9B is an image reading device according to a second embodiment of the present invention. Schematic configuration diagram and diagram showing the configuration of the color separation filter

FIG. 10A is a schematic configuration diagram of an image reading device according to a third embodiment of the present invention and a diagram showing a configuration of a color separation filter. FIG. 10B is an image reading device according to a third embodiment of the present invention. Schematic configuration diagram and diagram showing the configuration of the color separation filter

[Explanation of symbols]

 1 Original 2 White Fluorescent Tube 3 Imaging Lens 4 Image Sensor 5 Lens Row 6 Filter 7 Blue White Fluorescent Tube 41 Color Separation Filter 60 Dielectric Multilayer Film 61, 62, 63 Color Separation Filter Area

Front page continuation (72) Inventor Tadashi Aoki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kazumasa Nomi, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A single light source for illuminating a document, which comprises a blue-white illuminant whose spectral intensity characteristics have a peak value in the vicinity of 500 nm and decreases in the order of a short wavelength region, an intermediate wavelength region and a long wavelength region, and the document surface. It has an imaging lens that forms the reflected light from the image as an erecting equal-magnification image, a solid-state image sensor whose spectral sensitivity characteristics gradually decrease in the long wavelength range, intermediate wavelength range, and short wavelength range, and the specified spectral characteristics. An image reading apparatus comprising: a color separation filter that separates light reflected from the document surface.