JPH0666631A - Infrared image sensor - Google Patents

Abstract

PURPOSE:To obtain an infrared image sensor producing an image where noise is suppressed. CONSTITUTION:An image correcting filter alpha9 and a filter having thickness different from that of the filter alpha9 are interposed between an optical system 1 and a solid state image sensor 3 such that they can be replaced through a replacing mechanism. Light receiving amount to be accumulated in the solid state image sensor 3 can be equalized for each pixel through the use of the image correcting filter alpha9 and the filter beta10 and thereby the sensitivity is corrected correctly resulting in an image where noise is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an infrared image pickup device for picking up an image by a solid-state image pickup device.

[0002]

2. Description of the Related Art FIG. 5 shows an example of the configuration of a conventional infrared imaging device. In the figure, 1 is a lens system and 2 is the lens system 1.
Is a solid-state image sensor that receives the light rays that are transmitted by the lens system 1 and that is transmitted through the filter 2, and 4 is an electric signal that is output from the solid-state image sensor 3. An amplifier 5 for amplification, a storage device for storing the electric signal amplified by the amplifier 4, a processing device 6 for processing the electric signal output from the amplifier 4 and the electric signal stored by the storage device 5, Reference numeral 7 is a display device for displaying an electric signal processed by the processing device 6 as an image, and 8 is a shutter located on the front surface of the solid-state imaging device 3.

The conventional infrared imaging device is constructed as described above and operates as follows. The light beam condensed by the lens system 1 and transmitted through the filter 2 is received by the solid-state image sensor 3, and the image is output to the outside as an electric signal. The output electric signal is amplified by the amplifier 4 and then displayed as an image by the display device 7. The output value of the solid-state image sensor 3 varies from pixel to pixel even when a uniform light beam is incident. Therefore, sensitivity correction for correcting this variation is performed as follows. First, the shutter 8 installed on the front surface of the solid-state image sensor 3 is closed to cause a uniform light beam to enter the solid-state image sensor 3, and the output signal for each pixel at that time is stored in the storage device 5 in advance. Next, when the target object is imaged, the shutter 8 is opened and the light beam from the target object is received by the solid-state image sensor 3 and an electric signal is output. In the processing device 6, the electric signal stored in the storage device 5 in advance is subtracted from the output electric signal to perform sensitivity correction, and the image is displayed on the display device 7 as an image.

[0004]

In the conventional infrared image pickup device as described above, a uniform light beam is obtained by using the shutter 8 when sensitivity correction is performed, but this light beam is different from the image pickup target luminance. In addition, the temperature of the shutter 8 rises during use of the infrared image pickup device, so that this light ray becomes different from the image pickup target brightness. Therefore, the sensitivity is not sufficiently corrected, and there is a problem that noise is generated in the image displayed by the display device 7.

The present invention has been made in order to solve the above-mentioned problems, and equalizes the amount of light received by each pixel of the solid-state image pickup device from the image pickup target and accumulated in each pixel,
It is an object of the present invention to obtain an image with less noise by performing appropriate sensitivity correction by storing the output value of each pixel at that time in a storage device and performing sensitivity correction.

[0006]

In the infrared image pickup device according to the present invention, the filter located between the lens system and the solid-state image pickup device is replaced with a filter having a different thickness.

An infrared imaging device according to another invention is
The filter located between the optical system and the solid-state image sensor is replaced with a filter having a different refractive index.

[0008]

In the infrared image pickup device according to the present invention, the amount of light received by the solid-state image pickup element from the image pickup target is made equal for each pixel by exchanging with a filter having a different thickness, and sensitivity correction is performed based on the output signal. Output image noise is reduced.

In the infrared image pickup device according to another aspect of the present invention, the amount of light received by the solid-state image pickup device from the image pickup target is made equal in each pixel by replacing with a filter having a different refractive index, and sensitivity correction is performed based on the output signal. Since this is done, the noise in the output image is reduced.

[0010]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 and 3 to 7 are portions having the same names and functions as those of the conventional example, and 9 is a first filter (hereinafter referred to as a filter α) located on the optical path of the light beam condensed by the optical system 1.
10 is a second filter (hereinafter referred to as filter β) that can be replaced with the filter α9 by a filter replacement mechanism.

The infrared imaging device according to the present invention is constructed as described above and operates as follows. When performing the sensitivity correction, the filter β10 is inserted between the lens system 1 and the solid-state imaging device 3 with the imaging target placed within the field of view of the lens system 1. In the above state, the solid-state image sensor 3 receives the light beam from the imaging target and stores the output value of each pixel in the storage device 5. Next, the filter α9 is replaced with the filter β10, and the filter α9 is inserted between the lens system 1 and the solid-state imaging device 3. In this state, the light beam from the imaging target is received by the solid-state imaging device 3 and an electric signal is output. In the processing device 6, the electric signal stored in the storage device 5 in advance is subtracted from the output electric signal to perform sensitivity correction, and the image is displayed on the display device 7 as an image.

When the image pickup target is imaged with the filter α9 inserted between the lens system 1 and the solid-state image pickup device 3, the light beam from the image pickup target forms an image on the light receiving surface of the solid-state image pickup device 3 as shown in FIG. When the image pickup target is picked up with the filter β10 inserted between the lens system 1 and the solid state image pickup device 3, the light rays from the image pickup target are not formed on the light receiving surface of the solid state image pickup device 3 as shown in FIG. The thickness of the filter α9 is set to dα filter β1
When the thickness of 0 is dβ, the refractive indices of the filters α9 and β10 are n, and parallel rays perpendicular to the light receiving surface of the solid-state imaging device 3 are incident on the lens system 1, the filters α and β
When the maximum angle of incidence of the light ray on is i, the difference between the imaging positions when the filter α9 and the filter β10 are used is
Absolute value of the difference between the values obtained from equation (7) and equation (8) |
−ζβ |.

[0013]

[Equation 7]

[0014]

[Equation 8]

Assuming that the depth of focus of the optical system is ε, if the expression (9) is satisfied, if the image pickup target is put in the visual field of the optical system while the filter β10 is used, and the received light beam is accumulated,
By blurring the image, the light intensity distribution of the image is made uniform, and the amount of received light accumulated in each pixel of the solid-state image sensor 3 becomes equal.

[0016]

[Equation 9]

Since the output value for each pixel stored in the storage device 5 is a value in which each pixel equally receives a light beam from the image pickup target by a fixed amount, when the image is picked up using the filter α9, the stored output signal is used as a basis. An output image with less noise for which sensitivity correction is performed can be displayed on the display device 7. When the filter α9 and the filter β10 do not satisfy the expression (9), when the sensitivity correction is performed, the output value for each pixel of the solid-state image sensor 3 stored in the storage device 5 has an uneven light intensity distribution of the image. Will be remembered. When sensitivity correction is performed based on the output value,
The non-uniform light intensity distribution stored in the storage device 5 is generated as an afterimage in the output image, which rather deteriorates the output image. Therefore, it is necessary to prepare the filter β10 that satisfies the relationship of the expression (9). The operation is similar to that of the conventional infrared imaging device except that the sensitivity correction is performed by the above method.

Example 2. Next, another embodiment of the present invention will be described with reference to the drawings. In FIG. 3, 1 and 3 to 7 are portions having the same names and functions as those of the conventional example, 11 is a first filter (hereinafter referred to as a filter γ) located on the optical path of the light beam condensed by the optical system 1. Reference numeral 12 is a second filter (hereinafter referred to as filter δ) that can be replaced with the filter γ11 by a filter replacement mechanism.

The infrared imaging apparatus of the embodiment shown in FIG. 3 is constructed as described above and operates as follows. When performing the sensitivity correction, the filter δ12 is inserted between the lens system 1 and the solid-state image sensor 3 with the imaging target in the field of view of the lens system 1. In the above state, the solid-state image sensor 3 receives the light beam from the imaging target and stores the output value of each pixel in the storage device 5. Next, the filter γ11 is replaced with the filter δ12 and is inserted between the lens system 1 and the solid-state image sensor 3. In this state, the light beam from the imaging target is received by the solid-state imaging device 3 and an electric signal is output. In the processing device 6, the electric signal stored in the storage device 5 in advance is subtracted from the output electric signal to perform sensitivity correction, and the image is displayed on the display device 7 as an image.

When the image pickup target is imaged with the filter γ11 inserted between the lens system 1 and the solid-state image pickup device 3, the light beam from the image pickup target forms an image on the light-receiving surface of the solid-state image pickup device 3 as shown in FIG. When the same imaging target is imaged with the filter δ12 inserted between the lens system 1 and the solid-state imaging device 3, the light rays from the imaging target do not form an image on the light-receiving surface of the solid-state imaging device 3 as shown in FIG. Filter γ11 and filter δ1
When the thickness of 2 is d, the refractive index of the filter γ11 is nγ, the refractive index of the filter δ12 is nδ, and parallel rays perpendicular to the light receiving surface of the solid-state image sensor 3 are incident on the lens system 1, the filter γ11 and the filter δ12. Where i is the maximum incident angle of the ray on the filter, the difference between the imaging positions when the filter γ11 and the filter δ12 are used is the absolute value of the difference between the values obtained from the equations (10) and (11) | ζγ −ζδ |.

[0021]

[Equation 10]

[0022]

[Equation 11]

When the focal depth of the optical system is ε, (12)
If the expression is satisfied, when the image pickup target is placed in the field of view of the optical system while the filter δ12 is used and the received light rays are accumulated, the image is blurred and the light intensity distribution of the image is made uniform. The amount of received light accumulated in each pixel of 3 becomes equal.

[0024]

[Equation 12]

Since the output value for each pixel stored in the storage device 5 is a value in which the light rays from the image pickup target are equally received by each pixel by a fixed amount, when the image is picked up using the filter γ11, the sensitivity is based on the output signal. When correction is performed, an output image with less noise can be displayed on the display device 7. When the filters γ11 and γ12 do not satisfy the expression (12), when sensitivity correction is performed, the output value for each pixel of the solid-state image sensor 3 stored in the storage device 5 has an uneven light intensity distribution of the image. Will be remembered. When sensitivity correction is performed based on the output value,
The non-uniform light intensity distribution stored in the storage device 5 is generated as an afterimage in the output image, which rather deteriorates the output image. Therefore, it is necessary to prepare the filter δ12 that satisfies the relationship of the expression (12). The operation is similar to that of the conventional infrared imaging device except that the sensitivity correction is performed by the above method.

[0026]

As described above, according to the present invention, by exchanging filters having different thicknesses by the exchanging mechanism,
The amount of light received by the solid-state image sensor from the imaging target is made equal for each pixel, and the output value of each pixel at that time is stored. Since the sensitivity correction is performed based on the stored output value, an output image with less noise can be obtained.

As described above, according to another aspect of the present invention, by exchanging the filters having different refractive indexes by the exchanging mechanism, the amount of light received by the solid-state image pickup device from the image pickup target is made equal in each pixel, and in that case. The output value of each pixel is stored.
Since the sensitivity correction is performed based on the stored output value, an output image with less noise can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an infrared imaging device showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an infrared imaging device showing Embodiment 1 of the present invention.

FIG. 3 is a configuration diagram of an infrared imaging device showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an infrared imaging device showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing an embodiment of a conventional infrared imaging device.

[Explanation of symbols]

 1 Lens System 2 Filter 3 Solid-state Image Sensor 4 Amplifier 5 Storage Device 6 Processing Device 7 Display Device 8 Shutter 9 Filter α 10 Filter β 11 Filter γ 12 Filter δ

Claims (2)

[Claims] 1. A lens system for condensing light rays reflected or radiated by an external target, a first filter located on the optical path of the light rays condensed by the lens system, the lens system and the first filter. In an infrared imaging device including a solid-state imaging device at a position where a light beam that has passed through a filter forms an image on a light receiving surface, a second thickness different from that of the first filter is provided.
And a mechanism for inserting the first filter and the second filter by exchanging the first filter and the second filter. The first filter and the second filter have a thickness of the first filter of dα and a second filter of the second filter.
The thickness of the filter is dβ, the refractive indices of the first filter and the second filter are n, and when a parallel light beam perpendicular to the light receiving surface of the solid-state image sensor enters the lens system, And the maximum angle of incidence of the ray on the second filter is i,
When the depth of focus of the optical system is ε, equations (1) and (2)
An infrared imaging device characterized by satisfying the relationships of equation (3) and equation (3). [Equation 1] [Equation 2] [Equation 3] 2. A lens system for condensing light rays reflected or radiated by an external target, a first filter located on the optical path of the light rays condensed by the lens system, the lens system and the first lens system. In an infrared imaging device including a solid-state imaging device at a position where a light beam that has passed through a filter forms an image on a light receiving surface, a second refractive index different from the refractive index of the first filter is used.
And a mechanism capable of replacing and inserting the first filter and the second filter. The first filter and the second filter both have a thickness d and a refractive index of the first filter. Nγ, the refractive index of the second filter is nδ, and when a parallel light ray perpendicular to the light receiving surface of the solid-state image sensor is incident on the lens system, the maximum incidence of the light ray on the first filter and the second filter An infrared imaging device, characterized in that, when an angle is i and a depth of focus of the optical system is ε, the relationships of expressions (4), (5), and (6) are satisfied. [Equation 4] [Equation 5] [Equation 6]