JP2016114683A - Filter and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter capable of nearly completely removing infrared light, with a simple configuration.SOLUTION: An image sensor 20 includes a filter 21 used for a solid-state imaging element 24, the single plate color imaging system solid-state imaging element 24, and a package 25 sealing the solid-state imaging element 24. The filter 21 includes a sealing glass 23 arranged on the optical path of incident light made incident on the solid-state imaging element 24 and transmitting the incident light and a dielectric multilayer 22 formed on one surface of the sealing glass 23 and removing the infrared light having a wavelength of at least 680nm and less than 1100nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a filter that removes infrared rays, and an imaging apparatus including the filter.

  In general, a photographing camera uses a three-plate color imaging method in which incident light is split into three colors of RGB using an optical prism and an image of each color is photographed by an individual imaging device. At this time, light rays other than visible light necessary for photographing, particularly infrared light having a long wavelength, adversely affects the captured image. For this reason, the photographing camera is provided with an infrared light cut filter (hereinafter referred to as “IR cut filter”) for removing (cutting) infrared light contained in incident light by absorbing or reflecting (for example, “IR cut filter”). Patent Documents 1 and 2).

Here, in the three-plate color imaging method, it is possible to use a trimming filter that performs spectral separation with an optical prism whose spectral characteristics can be designed relatively freely and adjusts the spectral characteristics for each color. Furthermore, an IR cut filter is installed in front of the trimming filter. For this reason, the IR cut filter is not required to have a filter characteristic in which the transmittance sharply decreases near the wavelength of 680 nm, and a filter characteristic in which the transmittance gradually decreases as shown in FIG. 11 is sufficient. As a result of using these IR cut filters, optical prisms, and trimming filters, the broadcast camera can realize spectral characteristics that almost completely remove infrared light having a wavelength of 680 nm or more, as shown in FIG.
Note that “[au]” in FIG. 12 represents an arbitrary unit.

  In addition, a single camera color imaging system that acquires RGB signals (color signals) with a single imaging device is also used in the photographing camera. In this single-plate color imaging method, an organic material on-chip color filter is formed on the imaging element. As shown in FIG. 13, the filter characteristics are determined by the spectral characteristics of the on-chip color filter.

  In the single-plate color imaging method, similarly to the three-plate color imaging method, an IR cut filter is disposed on the optical path to remove infrared light. At this time, in order to simplify the configuration of the photographing camera, an IR cut filter is also used as a glass lid for sealing the image sensor (for example, Patent Document 3).

JP 2009-217138 A JP 2013-50593 A Japanese Patent Laid-Open No. 7-281021

  In general, in the single-plate color imaging method, the spectral characteristics of the on-chip color filter have a lower degree of design freedom than the spectral characteristics of the dichroic film in the optical prism, and it is difficult to obtain the required filter characteristics. Further, in the single-plate color imaging method, the trimming filter that can be applied to each color in the three-plate color imaging method cannot be used due to the structure.

  For these reasons, in the single-plate color imaging method, as in the case of the three-plate color imaging method, when an IR cut filter having a filter characteristic in which the transmittance gradually decreases, the image quality is adversely affected. Specifically, in the single-plate color imaging method, a part of infrared light that has passed through the IR cut filter causes a phenomenon in which red pixels are reacted and a red signal is increased. In particular, this phenomenon becomes prominent when some ND filters for film that transmit infrared light are used.

  The IR cut filter that also serves as the sealing glass is an absorption type filter formed of a material that absorbs infrared light. This absorption type filter has its filter characteristics determined by its material, and it is difficult to remove infrared light almost completely without impairing the sensitivity in the visible light region. Therefore, in the single plate color imaging method, the absorption filter cannot be adopted, and the configuration of the photographing camera cannot be simplified.

  Therefore, an object of the present invention is to provide a filter and an imaging device that can remove infrared light almost completely with a simple configuration.

In view of the above-described problems, a filter according to the present invention is an optical member that is disposed on an optical path of light incident on an image sensor and transmits the light in a filter used in an image sensor of a single-plate color imaging system, And a dielectric multilayer film that is formed on one plane of the optical member and that removes infrared light that removes infrared light having a wavelength of 680 nm or more and less than 1100 nm.
According to such a configuration, the filter can combine the function of the optical member that seals the imaging element and the function of the IR cut filter that removes infrared light.

  Since the filter according to the present invention combines the sealing function of the image sensor and the function of the IR cut filter, infrared light can be removed almost completely with a simple configuration. As a result, the filter according to the present invention can achieve good color reproducibility with a single-panel color photographing camera.

1 is a schematic configuration diagram of an imaging optical system according to a first embodiment of the present invention. It is a block diagram of the dielectric multilayer film of FIG. It is a graph showing the filter characteristic of the filter of FIG. It is a schematic block diagram of the imaging camera which concerns on 2nd Embodiment of this invention. It is a flowchart showing operation | movement of the imaging camera of FIG. It is a graph showing the filter characteristic in Example 1 of this invention. In Example 2 of this invention, it is a graph showing the spectral characteristic of the reflected light of sunlight by a lawn. In Example 2 of this invention, it is a graph showing the light attenuation characteristic of an ND filter. It is a table showing the experimental result in a comparative example. It is a table showing the experimental result in Example 2 of this invention. It is a graph showing the filter characteristic of the IR cut filter used with the conventional 3 plate color imaging system. It is a graph showing the spectral characteristic of the imaging | photography camera using the conventional 3 plate color imaging system. It is a graph showing the spectral characteristic of the imaging | photography camera using the conventional single plate color imaging system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In each embodiment, means having the same function are denoted by the same reference numerals and description thereof is omitted.

(First embodiment)
[Configuration of imaging optical system]
With reference to FIG. 1, the structure of the imaging optical system 1 which concerns on 1st Embodiment of this invention is demonstrated.
As shown in FIG. 1, the imaging optical system 1 is used as an optical system of the photographing camera 100 (imaging device) in FIG. 4, and includes a photographing lens 10 and an image sensor 20.

  The photographing lens 10 is a lens group including a plurality of lenses including an objective lens. Since the photographic lens 10 has a general configuration that is not directly related to the present invention, further explanation is omitted. In FIG. 1, the photographic lens 10 is shown as a single lens for easy viewing of the drawing.

  The image sensor 20 captures a subject (not shown) via the photographing lens 10 and generates an RGB signal (captured image). The image sensor 20 includes a filter 21, a solid-state image sensor (image sensor) 24, and a package 25.

  The filter 21 combines the sealing function of the solid-state imaging device 24 and the function of the IR cut filter, and includes a dielectric multilayer film 22 and a sealing glass (optical member) 23.

The dielectric multilayer film 22 is formed on the flat surface (incident surface) on the photographing lens 10 side with the sealing glass 23. As shown in FIG. 2, the dielectric multilayer film 22 is formed on the sealing glass 23 by alternately vapor-depositing the first reflective layer 22A and the second reflective layer 22B. The first reflective layer 22A and the second reflective layer 22B have different refractive indexes.
In FIG. 1, the dielectric multilayer film 22 is shown by hatching.

  The sealing glass 23 is disposed on the optical path of incident light that has passed through the photographing lens 10 and seals the opening of the package 25. Here, the sealing glass 23 is disposed on the optical axis LF of the photographing lens 10. For example, the sealing glass 23 may be an optical glass such as a general glass lid that transmits incident light.

  The solid-state imaging device 24 receives incident light that has passed through the photographing lens 10 and generates RGB signals from the received incident light. In the present embodiment, the solid-state imaging device 24 is a single-plate color imaging type imaging device. For example, as the solid-state image sensor 24, a CCD (Charge Coupled Device) sensor and a CMOS (Complementary Metal Oxide Semiconductor) sensor can be used.

  The package 25 accommodates the solid-state image sensor 24 in the internal space. Further, the opening of the package 25 is sealed with a sealing glass 23. In this way, the sealing glass 23 and the package 25 can prevent air exposure and dust adhesion of the solid-state imaging device 24.

[Filter characteristics]
The filter characteristics of the filter 21 will be described with reference to FIG. 3 (see FIGS. 1 and 2 as appropriate).
In FIG. 3, the vertical axis represents the transmittance, and the horizontal axis represents the wavelength of the incident light. Further, in FIG. 3, the range included in the filter characteristics of the filter 21 is illustrated by hatching.

  The filter 21 includes the dielectric multilayer film 22 and thus has filter characteristics as shown in FIG. Specifically, the dielectric multilayer film 22 has a transmittance of less than 1% at a wavelength of 350 nm or more and less than 370 nm. That is, the dielectric multilayer film 22 almost completely removes ultraviolet rays having a wavelength of 350 nm or more and less than 370 nm.

  The dielectric multilayer film 22 has a transmittance of less than 10% at a wavelength of 370 nm or more and less than 380 nm. Further, the transmittance of the dielectric multilayer film 22 at a wavelength of 380 nm or more and less than 390 nm is not limited (that is, arbitrary between 0% and 100%). The dielectric multilayer film 22 has a transmittance of 75% or more at a wavelength of 390 nm or more and less than 500 nm. The dielectric multilayer film 22 has a transmittance of 80% or more at a wavelength of 500 nm or more and less than 640 nm.

  The dielectric multilayer film 22 has a transmittance of 40% or more at a wavelength of 640 nm or more and less than 650 nm. Further, the dielectric multilayer film 22 has a transmittance at a wavelength of 650 nm that falls within 10% before and after a half value of a maximum transmittance at a wavelength of 390 nm or more and less than 640 nm. The dielectric multilayer film 22 has a transmittance of less than 60% at a wavelength exceeding 650 nm and less than 680 nm.

  The dielectric multilayer film 22 has a transmittance of less than 2% at a wavelength of 680 nm or more and less than 690 nm, a transmittance of a wavelength of 690 nm or more and less than 1050 nm is less than 1%, and a transmittance at a wavelength of 1050 nm or more and less than 1100 nm is 2%. Is less than. That is, the dielectric multilayer film 22 can almost completely remove infrared light having a wavelength of 680 nm or more and less than 1100 nm.

[Action / Effect]
As described above, since the filter 21 serves both as the sealing function of the solid-state image sensor 24 and the function of the IR cut filter, infrared light can be almost completely removed with a simple configuration. Further, the filter 21 can almost completely remove ultraviolet rays. Thus, the filter 21 can realize good color reproducibility with the photographing camera 100 of the single plate color method.

(Second Embodiment)
[Camera configuration]
With reference to FIG. 4, the structure of the photographing camera 100 according to the second embodiment of the present invention will be described (see FIGS. 1 and 2 as appropriate).
For example, the photographing camera 100 is a single-plate color broadcasting camera, and includes a photographing optical system 1, a signal processing circuit (signal processing means) 30, and an output circuit 40.

The photographing optical system 1 has the same configuration as that in FIG. 1 and includes a photographing lens 10 and an image sensor 20. The photographing optical system 1 outputs the RGB signal generated by the image sensor 20 to the signal processing circuit 30.
In FIG. 4, a part of the configuration is omitted for easy understanding of the drawing.

  The signal processing circuit 30 performs various signal processing on the RGB signals input from the photographing optical system 1. For example, the signal processing circuit 30 performs linear matrix processing for multiplying the RGB values generated by the image sensor 20 by a matrix of 3 rows and 3 columns (linear matrix) in order to correct an error of the color signal.

  Here, the linear matrix processing is defined by the following equation (1). In this equation (1), R, G, and B represent the R signal value, G signal value, and B signal value of the RGB signal input from the image sensor 20. Further, a to f represent preset linear matrix coefficients. R ′, G ′, and B ′ represent the R signal value, G signal value, and B signal value after linear matrix processing.

Thereafter, the signal processing circuit 30 outputs the RGB signal subjected to the linear matrix processing to the output circuit 40.
The signal processing circuit 30 may perform white balance adjustment and gamma correction as signal processing in addition to linear matrix processing.

  The output circuit 40 outputs the RGB signal input from the signal processing circuit 30 to the outside (for example, a computer or a display). Further, the output circuit 40 converts the RGB signal input from the signal processing circuit 30 into a storage device (for example, a hard disk) provided in advance in the photographing camera 100 or a storage medium (for example, SD) inserted in the photographing camera 100. Card).

[Camera operation]
The operation of the photographing camera 100 in FIG. 4 will be described with reference to FIG. 5 (see FIG. 4 as appropriate).
As shown in FIG. 5, the photographing camera 100 generates RGB signals by the image sensor 20 (step S1).
The photographing camera 100 performs linear matrix processing on the RGB signal generated in step S1 by the signal processing circuit 30 (step S2).
The photographing camera 100 outputs the RGB signal subjected to the linear matrix processing in step S3 to the outside by the output circuit 40 (step S3).

[Action / Effect]
As described above, the photographing camera 100 can obtain more accurate RGB values by performing linear matrix processing in addition to the same effects as those of the first embodiment. Thereby, the photographing camera 100 can further improve the color reproducibility.

Hereinafter, as Example 1, a specific example of the dielectric multilayer film 22 and the filter characteristics of the filter 21 will be described (see FIGS. 1 and 2 as appropriate).
36 layers of the first reflective layer 22A and the second reflective layer 22B are deposited on the electric multilayer film 22. Here, as a material of the first reflective layer 22A, SiO ₂ can be cited. In addition, for example, TiO ₂ can be used as the material of the second reflective layer 22B.

  In FIG. 6, the measurement result of the spectral characteristic of the filter 21 in Example 1 was illustrated. FIG. 6 shows that the filter 21 almost completely removes ultraviolet rays and infrared rays. Therefore, it is considered that good color reproducibility can be realized by using the filter 21 of the first embodiment.

In the following, the influence of infrared light on RGB signals will be described with reference to an example of a captured image including sunlight reflected by a lawn.
Chlorophyll, which is contained in plant leaves and is involved in photosynthesis, has a feature of well absorbing red light having a wavelength of around 660 nm and blue light having a wavelength of around 450 nm. Also, unabsorbed green light and infrared light tend to be scattered or reflected. Here, the spectral characteristics of sunlight reflected by the lawn were measured, and the measurement results are shown in FIG. From FIG. 7, it can be seen that a large amount of green light and infrared light are included in the reflected light of sunlight from the lawn. Therefore, in a photographing camera, when there are many opportunities to photograph outdoors, it is effective in improving characteristics to cut a wavelength of 680 nm or more.

As shown in FIG. 8, an ND filter for film (hereinafter referred to as an ND filter) having a characteristic of transmitting infrared rays is known. Therefore, a photographing camera (Example 2) provided with the filter 21 of the first embodiment and a photographing camera (Comparative Example) provided with a conventional IR cut filter were prepared, and the lawn was photographed with both photographing cameras. At this time, both the photographing cameras were not only photographed with the ND filters having different densities, but also photographed without the ND filters.
In FIG. 8, the numerical value described after ND represents the density (dimming characteristic) of the ND filter.

  The experimental results of Example 2 and the comparative example are shown in FIGS. FIG. 9 shows the experimental results of the comparative example, and FIG. 10 shows the experimental results of the second example. 9 and 10 show the R signal value and the B signal value with respect to the G signal value. That is, the R signal value and the B signal value are relative values when the G signal value is 1.

  In the comparative example of FIG. 9, as the ND filter's light attenuation rate increases, infrared light affects the R signal, and the ratio of the R signal to the G signal increases. The R signal value at ND 1.6 is increased by about 1.7 times compared to the R signal value without ND. On the other hand, in Example 2 of FIG. 10, since the filter characteristic in which the transmittance sharply decreases near the wavelength of 680 nm can be obtained, the influence of infrared light transmitted through the ND filter can be suppressed. As a result, the R signal value at ND 1.6 is suppressed to an increase of about 1.2 times compared to the R signal value without ND.

  Furthermore, in Example 2, since the filter characteristic in which the transmittance sharply decreases in the vicinity of the wavelength of 680 nm is obtained, it can be seen that the effective signal amount as the R signal component in the visible light is increased. This also increases the R signal value itself, which is considered effective for improving the S / N.

DESCRIPTION OF SYMBOLS 1 Imaging optical system 10 Shooting lens 20 Image sensor 21 Filter 22 Dielectric multilayer film 22A 1st reflection layer 22B 2nd reflection layer 23 Sealing glass (optical member)
24 Solid-state imaging device (imaging device)
25 Package 30 Signal processing circuit (signal processing means)
40 output circuit 100 photographing camera (imaging device)

Claims (3)

In a filter used for an image sensor of a single plate color imaging system,
An optical member disposed on an optical path of light incident on the image sensor and transmitting the light;
A dielectric multilayer film that is formed on one plane of the optical member and removes infrared light having a wavelength of 680 nm or more and less than 1100 nm;
A filter comprising:   The dielectric multilayer film has a transmittance of less than 1% at a wavelength of 350 nm to 370 nm, a transmittance of less than 2% at a wavelength of 680 nm to 690 nm, a transmittance of less than 1% at a wavelength of 690 nm to 1050 nm, and a wavelength of 1050 nm. 2. The filter according to claim 1, wherein the transmittance at less than 1100 nm is less than 2%. A filter according to claim 1 or claim 2;
An image sensor of a single-plate color imaging system that generates RGB signals by the light transmitted through the filter;
Signal processing means for performing linear matrix processing on the RGB signals generated by the image sensor;
An imaging apparatus comprising:

Images