JP2018017864A - Imaging device - Google Patents

Abstract

An imaging apparatus capable of acquiring good polarization information with a simple configuration is provided. An imaging device that receives light from a subject, a first retardation plate that gives a relative phase difference of π / 2 between polarization components in the slow axis direction and the fast axis direction, and a slow axis Relative phase difference between the second retardation plate capable of changing the relative phase difference applied between the polarization component in the direction and the fast axis direction, the polarizer extracting the polarization component guided to the image sensor, and the second retardation plate A setting unit configured to set a phase difference; and a processing unit configured to generate an image based on an output of the image sensor. The first retardation plate, the second retardation plate, and the polarizer are provided from the subject side. Arranged in order toward the image sensor side, the second retardation plate is set such that the slow axis direction or the fast axis direction is inclined with respect to the slow axis direction or the fast axis direction of the first retardation plate. The means changes the relative phase difference of the second retardation plate according to the polarization component of the light from the subject, and the processing unit But to generate a 0.01fps bigger picture. [Selection] Figure 1

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that can observe the outside world by image processing using polarization information.

  In recent years, surveillance cameras such as in-vehicle cameras for observing road conditions, security cameras for detecting intruders, and disaster prevention cameras for disasters such as fires and earthquakes have been used. In these surveillance cameras, it is widely known that the object identification capability is improved by using the polarization information of the captured image.

  Patent Document 1 discloses an intruder detection monitoring camera that acquires polarization information by rotating a polarizing filter attached to the front surface of the camera. Patent Document 2 discloses a vehicle-mounted camera including two polarization filters in the vertical direction and horizontal direction, a beam splitter, or a polarization array in order to acquire two orthogonal polarizations.

JP 2011-13965 A Japanese Patent No. 5664152

  However, in Patent Document 1, since it takes time to rotate the polarization filter, a time lag occurs in the time for acquiring each polarization image. In Patent Document 2, when two polarizing filters and beam splitters in the vertical direction and the horizontal direction are used, an image pickup device is required for each polarized light, so that the apparatus becomes large. Also, when using a polarizing array, the resolution is lost.

  In view of such a problem, an object of the present invention is to provide an imaging apparatus capable of acquiring good polarization information with a simple configuration.

An imaging apparatus according to an aspect of the present invention provides a relative phase difference of π / 2 between an imaging element that receives light from a subject and a polarization component in a slow axis direction and a polarization component in a fast axis direction. A first retardation plate, a second retardation plate capable of changing a relative phase difference applied between a polarization component in the slow axis direction and a polarization component in the fast axis direction, and a polarization component guided to the image sensor And a setting unit that sets a relative phase difference of the second retardation plate, and a processing unit that generates an image based on the output of the imaging device,
The first retardation plate, the second retardation plate, and the polarizer are arranged in order from the subject side to the imaging element side, and the second retardation plate has a slow axis direction. Alternatively, the fast axis direction is inclined with respect to the slow axis direction or the fast axis direction of the first phase difference plate, and the setting means determines the first phase according to the polarization component of light from the subject. The relative phase difference between the two phase difference plates is changed, and the processing unit generates an image having a frame rate greater than 0.01 fps.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can acquire favorable polarization information with a simple structure can be provided.

It is a block diagram of the surveillance camera of Example 1. FIG. It is a block diagram of a variable phase difference plate. It is a figure which shows an example of the orientation dependence of the polarization state of incident light, and light intensity. It is a figure which shows the transmittance | permeability dependence of the polarization | polarized-light acquisition means with respect to the polarization direction of incident light. It is a figure which shows the transmittance | permeability dependence of the polarization | polarized-light acquisition means with respect to the polarization component of the incident light for every phase difference of a variable phase difference. It is a state change figure of the polarization component of the maximum transmission angle corresponding to the phase difference of a variable phase difference plate. It is a figure which shows the light intensity dependence of the polarization component of a polarization | polarized-light acquisition means. It is a block diagram of the surveillance camera of Example 2. It is a block diagram of the vehicle-mounted camera of Example 3. FIG. 10 is a configuration diagram of a network camera according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  The surveillance camera of the present invention is a camera system (imaging) comprising an imaging unit used for the purpose of monitoring, that is, an information collecting activity for detecting changes in surrounding conditions and states, and a main body unit for performing calculations and the like. Device). For example, a security camera installed inside or outside a site for recognizing an intruder or a suspicious person, an in-vehicle camera installed in a vehicle for checking a road condition while traveling, and the like are used as a monitoring camera. Note that the frame rate, which is an index representing the smoothness of the display of the moving image of the surveillance camera, is preferably 0.01 fps (frames per second) or more, and more preferably 0.1 fps or more.

  FIG. 1 is a configuration diagram of a monitoring camera 100 according to the present embodiment. The monitoring camera 100 includes an imaging device unit 101 and a main body unit 102. The imaging device unit 101 is disposed on the optical system 1 that forms an image of light from the subject 500 on the imaging device 2, the imaging device 2 that acquires image information of the subject, and the optical path between the optical system 1 and the imaging device 2. The polarized light acquisition means 6 is provided. The main body unit 102 includes a control unit (setting unit) 103 that controls imaging of the imaging device unit 101, a processing unit 104 that processes image information of the imaging element 2, and a display unit 105 that displays images and videos according to usage. Have

  In the present embodiment, the polarization acquisition means 6 is disposed on the optical path between the optical system 1 and the image sensor 2, but the present invention is not limited to this. The polarization acquisition unit 6 may be disposed on the light incident side (subject side) from the imaging device 2. For example, when the light incident side from the optical system 1 or the optical system 1 is formed of a plurality of optical elements, You may arrange | position in the middle of several optical element.

  The polarization acquisition means 6 includes a λ / 4 plate (first retardation plate) 3, a variable retardation plate (second retardation plate) 4, and a polarizing plate (polarizer) 5. The λ / 4 plate 3, the variable phase difference plate 4, and the polarizing plate 5 are arranged so that each axis is in a plane perpendicular to the optical axis of the optical system 1. The λ / 4 plate 3, the variable phase difference plate 4, and the polarizing plate 5 are disposed adjacent to each other.

  The λ / 4 plate 3 is composed of a stretched film, and gives a relative phase difference of π / 2 (rad) between orthogonally polarized components of incident light. The relative phase difference of π / 2 given by the λ / 4 plate 3 is unchanged (fixed). In this embodiment, a λ / 4 plate is used, but a 3λ / 4 plate or a variable phase difference plate may be used as long as a relative phase difference of π / 2 can be given.

Similar to the λ / 4 plate 3, the variable phase difference plate 4 gives a changeable relative phase difference (hereinafter referred to as a phase difference of the variable phase difference plate 4) between the orthogonal polarization components of incident light. In this embodiment, the variable phase difference plate 4 is an element using liquid crystal, and changes the phase difference of the variable phase difference plate 4 in accordance with an applied voltage. FIG. 2 is a configuration diagram of the variable retardation plate 4, and a circular portion in the drawing is an enlarged view of the liquid crystal layer. The variable retardation plate 4 is configured so that the liquid crystal layer 11 is sandwiched between the substrate 8, the electrode layer 9, and the alignment film 10. The liquid crystal layer 11 is a VA liquid crystal layer (VA liquid crystal layer), and the liquid crystal molecules 12 are aligned so as to follow the alignment film 10. When the applied voltage is changed to 0 [V], A [V], B (> A) [V], the alignment angle (tilt angle) of the liquid crystal molecules 12 reaches the maximum value from the minimum value θ _min through the intermediate value θ. It changes to θ _max . In the present embodiment, the control unit 103 applies a voltage to the variable retardation plate 4 and controls the tilt angle θ of the liquid crystal molecules 15, that is, the refractive index anisotropy, thereby changing the phase difference of the variable retardation plate 4. Change. The configuration of the variable phase difference plate 4 in FIG. 2 is an example, and the present invention is not limited to this. For example, liquid crystal elements having different driving methods in which the orientation direction changes instead of the tilt angle may be used. Further, a configuration using a change in refractive index due to the electro-optic effect, a configuration in which the grating height and interval of the birefringence due to a fine structure are precisely controlled, or a configuration combining them may be used. Further, the variable phase difference plate 4 may not be configured to uniformly change the phase difference within the plate surface, but may be configured to generate different phase differences in different regions within the plate surface.

  The polarizing plate 5 transmits (extracts) a component in the transmission axis direction (transmission polarization direction) among the polarization components of incident light. Since the polarization acquisition means 6 is used in the imaging device unit 101, it is desirable that the polarizing plate 5 be a type of polarizing plate that absorbs unnecessary light. If a polarizing plate such as a wire grid polarizer, which reflects unnecessary light, is used, the polarized light on the cut side is reflected and the light becomes stray light or ghost, which adversely affects the image. This is not desirable. More preferably, in order to suppress the influence on the ghost, it is desirable that the polarizing plate 5 has a characteristic of absorbing 50% or more of the polarized light that vibrates in the direction orthogonal to the transmission axis in the entire use wavelength range. Examples of such a polarizing plate include a film obtained by stretching a resin member containing an iodine compound. However, the polarizing plate is not limited to such a material, and any absorbing polarizing plate may be used.

  The used wavelength range is a wavelength range acquired by the imaging device unit 101 and can be selected depending on the application and the wavelength characteristics of the imaging element 2. In this embodiment, the used wavelength range is the visible range (400 nm to 700 nm). Based on the configuration of the imaging device unit 101, the used wavelength range is selected from at least one of the visible range (400 to 700 nm), the near infrared range (700 to 1100 nm), and the near ultraviolet range (200 to 400 nm). What should I do? Further, the design wavelength λ (nm) of the variable phase difference plate 4 may be selected according to the used wavelength range acquired by the imaging device unit 101 so as to have appropriate characteristics.

  The monitoring camera 100 acquires a plurality of images with different polarization states by fixing the transmission axis direction of the polarizing plate 5 and imaging while changing the phase difference of the variable retardation plate 4 with time. The control unit 103 sets (changes) the phase difference of the variable phase difference plate 4 in synchronization with the image sensor 2. With this setting, the polarization component of the light from the subject received by the image sensor 2 changes, and the control unit 103 acquires an image having the polarization information of the subject. The control unit 103 acquires polarization information of the subject 500 based on the acquired plurality of images. The processing unit 104 performs predetermined processing based on the image information and polarization information acquired from the image sensor 2, and generates an image or video. The display unit 105 displays the image or video generated by the processing unit 104.

  Hereinafter, a method of acquiring a plurality of images having different polarization states by imaging while changing the phase difference of the variable retardation plate 4 while fixing the transmission axis direction of the polarizing plate 5 will be described.

  First, referring to FIG. 3, the orientation dependency of light intensity from a general subject will be described. The ellipse shown in FIG. 3 (a) shows the orientation dependence of the amplitude of an exemplary polarization state. φ is an azimuth angle (degree) with respect to the x-axis direction of the polarization direction. 3B is a diagram in which the azimuth angle φ is the horizontal axis, and the light intensity I (φ) that is the square of the elliptical radius of FIG. 3A when the azimuth angle φ is the vertical axis. Each arrow having a different line type in FIG. 3A corresponds to an arrow having the same line type in FIG. In FIG. 3, the light intensity of the polarization component having the azimuth angle φ of 45 degrees is the strongest. Therefore, by extracting a polarization component having an azimuth angle φ of 45 degrees or 135 degrees orthogonal thereto, it is possible to acquire an image in which the characteristics of the subject are most emphasized.

  Next, referring to FIG. 4, the behavior of the incident light incident on the polarization acquisition means 6 when the transmission axis direction of the polarizing plate 5 is fixed and the phase difference of the variable retardation plate 4 is set to be constant. explain. FIG. 4 is a diagram showing the transmittance dependency of the polarization acquisition means 6 with respect to the polarization direction of incident light. In FIG. 4, the phase difference of the variable phase difference plate 4 is set to λ / 4. The directions and lengths of the arrows before and after transmission of the polarization acquisition means 6 are the polarization direction and the intensity, respectively. The broken line arrows on the λ / 4 plate 3 and the variable phase difference plate 4 indicate the slow axis direction, and the broken line arrows on the polarizing plate 5 indicate the transmission axis direction.

  The λ / 4 plate 3 and the polarizing plate 5 are arranged so that the slow axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5 are parallel to each other. However, it is not necessary to be strictly parallel, and even if it is shifted by several degrees, it is regarded as substantially parallel (substantially parallel). Further, the variable phase difference plate 4 is arranged such that the slow axis direction is inclined by 45 degrees counterclockwise with respect to the slow axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5. However, it is not necessarily strictly 45 degrees, and even if it is shifted by several degrees, it is regarded as substantially 45 degrees (approximately 45 degrees).

  In this embodiment, the azimuth angle φ (degree) with respect to the x-axis direction of the slow axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5 is 90 degrees. However, it is not necessarily strictly 90 degrees, and even if it is shifted by several degrees, it is regarded as substantially 90 degrees (substantially 90 degrees). Further, the azimuth angle φ of the variable retardation plate 4 with respect to the x-axis direction in the slow axis direction is 45 degrees. However, it is not necessarily strictly 45 degrees, and even if it is shifted by several degrees, it is regarded as substantially 45 degrees (approximately 45 degrees).

  The λ / 4 plate 3 and the polarizing plate 5 may be arranged so that the fast axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5 are parallel to the y-axis direction. In this case, the variable retardation plate 4 is arranged such that the fast axis direction is inclined by 45 degrees clockwise with respect to the fast axis direction of the λ / 4 plate 3 and the transmission axis direction of the polarizing plate 5.

  FIG. 4A shows a case where a polarization component having an azimuth angle φ of 90 degrees is incident. In this case, since the polarization direction is parallel to the slow axis direction of the λ / 4 plate 3, the incident light is transmitted through the λ / 4 plate 3 without undergoing a phase change. Since the light transmitted through the λ / 4 plate 3 is converted into right circularly polarized light by the variable phase difference plate 4, when passing through the polarizing plate 5, it becomes linearly polarized light having an intensity of about 50% with respect to the incident light.

  FIG. 4B shows a case where a polarized component having an azimuth angle φ of 45 degrees is incident. In this case, incident light is converted into left circularly polarized light by the λ / 4 plate 3. The light transmitted through the λ / 4 plate 3 is converted into linearly polarized light having an azimuth angle φ of 90 degrees in the polarization direction by the variable retardation plate 4 and parallel to the transmission axis direction of the polarizing plate 5. Transmits without loss.

  FIG. 4C shows a case where a polarized component having an azimuth angle φ of 0 degrees is incident. In this case, since the polarization direction is orthogonal to the slow axis direction of the λ / 4 plate 3, the incident light is transmitted through the λ / 4 plate 3 without undergoing a phase change. Since the light transmitted through the λ / 4 plate 3 is converted into left circularly polarized light by the variable phase difference plate 4, when it passes through the polarizing plate 5, it becomes linearly polarized light having an intensity of about 50% with respect to the incident light.

  FIG. 4D shows a case where a polarized light component having an azimuth angle φ of 135 degrees is incident. In this case, incident light is converted into right circularly polarized light by the λ / 4 plate 3. The light transmitted through the λ / 4 plate 3 is converted into linearly polarized light having an azimuth angle φ of 0 degree in the polarization direction by the variable retardation plate 4 and is orthogonal to the transmission axis direction of the polarizing plate 5. do not do.

  Therefore, when the phase difference of the variable retardation plate 4 is λ / 4, the transmittance of the polarization component having the azimuth angle φ of 45 degrees among the polarization components of the incident light to the polarization acquisition means 6 is maximized. Hereinafter, the angle (maximum transmission angle) with respect to the x-axis direction of the polarization component having the maximum transmittance among the polarization components of the incident light to the polarization acquisition means 6 is defined as φo (degree).

  In the present embodiment, the monitoring camera 100 changes the maximum transmission angle φo of the component having the maximum transmittance among the polarization components of the incident light by changing the phase difference of the variable phase difference plate 4 by electrical control. . Thereby, polarization information about a plurality of polarization components can be acquired while fixing the transmission axis of the polarizing plate 5.

  FIG. 5 is a relationship diagram between the azimuth angle φ of the polarization component of incident light for each phase difference of the variable phase difference plate 4 and the transmittance T (φ) of the polarization acquisition means 6. Lines (A) to (D) in the figure show cases where the phase difference of the variable phase difference plate 4 is set to 0, λ / 4, λ / 2, and 3λ / 4, respectively. For example, in the line (A), when the azimuth angle φ is 90 degrees, the transmittance T (φ) is 100%, and the maximum transmission angle φo is 90 degrees.

  FIG. 6 is a state change diagram of the polarization component of the maximum transmission angle φo corresponding to the phase difference of the variable phase difference plate 4. The broken line arrows on the λ / 4 plate 3 and the variable phase difference plate 4 indicate the slow axis direction, and the broken line arrows on the polarizing plate 5 indicate the transmission axis direction. In FIG. 6A, the phase difference of the variable phase difference plate 4 is set to 0, and the maximum transmission angle φo is 90 degrees. In FIG. 6B, the phase difference of the variable phase difference plate 4 is set to λ / 4, and the maximum transmission angle φo is 45 degrees. In FIG. 6C, the phase difference of the variable phase difference plate 4 is set to λ / 2, and the maximum transmission angle φo is 0 degree. In FIG. 6D, the phase difference of the variable phase difference plate 4 is set to 3λ / 4, and the maximum transmission angle φo is 135 degrees.

  In other words, in any state of FIG. 6A to FIG. 6D, the incident light passes through the λ / 4 plate 3 and the variable phase difference plate 4, so that the desired polarization component of the incident light is The linearly polarized light becomes parallel to the transmission axis direction of the polarizing plate 5 and passes through the polarizing plate 5 with almost no loss. In other words, the polarization acquisition means 6 rotates the direction of the desired polarization component of the polarization components of the incident light in the direction of the transmission axis of the polarizing plate 5 and guides the desired polarization component to the image sensor 2 with almost no loss.

  In addition, since the slow axis of the λ / 4 plate 3 and the variable phase difference plate 4 and the slow axis of the variable phase difference plate 4 and the transmission axis of the polarizing plate 5 are each 45 degrees, the phase of the incident light The impact of information is minimal. For example, when complete circularly polarized light is incident, the λ / 4 plate 3 becomes linearly polarized light having an azimuth angle of 45 degrees parallel to the slow axis of the variable phase difference plate 4, and thus the transmittance of the polarization acquisition means 6 is variable. Regardless of the phase difference of the phase difference plate 4, the transmittance of the polarization acquisition means 6 is constant. In the case of elliptically polarized light, a value corresponding to the orientation dependency of the intensity of incident polarized light is obtained, so that information on the intensity can be acquired.

In addition, the control unit 103 uses the input value from the image sensor 2 as the polarization component intensity to determine the polarization component that maximizes the light intensity of the incident light, and is appropriate for the orientation dependency of the light intensity of the incident light. Analysis with a simple function (for example, Sin function). The transmittance T _ij of the polarization acquisition means 6 at the phase difference Δj (nm) of the variable phase difference plate 4 with respect to the light intensity I (φ _i ) and the light intensity I (φ _i ) of the polarization component at the azimuth angle φi (degree), The transmitted light intensity T _j of all the polarization components of the incident light at the phase difference Δj satisfies the following determinant (1).

  The subscript j of the transmitted light intensity Tj corresponds to the phase difference Δj, and each phase difference corresponds to a polarization component in one direction of the incident light. Further, the transmittance Tij is uniquely obtained if the vibration direction of the incident linearly polarized light and the configuration of the polarization acquisition means 6 are determined. Therefore, the control unit 103 obtains the transmittance Tij in advance and analyzes the transmitted light intensity Tj that can be obtained by changing the phase difference Δj as a transmitted light intensity plot with respect to the vibration direction of the polarization component of the incident light. The orientation dependency of the light intensity of light can be obtained.

  Using the above method, the monitoring camera 100 can acquire information on the azimuth dependence of light intensity by electrically driving the variable retardation plate 4 without rotationally driving the element.

Hereinafter, the configuration of the present embodiment will be described by applying specific data. Regarding the phase difference between the λ / 4 plate 3 and the variable retardation plate 4, λ is set to a wavelength of 550 nm with high visibility. The variable phase difference plate 4 gives four phase differences Δ (0, λ / 4, λ / 2, 3λ / 4) (nm). Table 1 shows the transmittance for linearly polarized light having different vibration directions corresponding to each phase difference of the variable retardation plate 4, that is, the transmittance [T _ij ] of the equation (1). Φi in Table 1 represents an angle formed by the vibration direction of the incident polarized light with respect to the x-axis direction. The numerical value is a value near the center of the image display element, and is a value obtained by averaging the polarization characteristics of the incident light flux with an incident angle of 15 degrees. Get as. The maximum transmission angle φ ₀ of each phase difference Δ is shown in the bottom row of Table 1. For example, the polarization state after passing through the variable retardation plate 4 having a phase difference Δ of λ / 4 is the state shown in FIG. Therefore, the highest transmittance is obtained when the angle φi is 45 degrees, and the smallest transmittance is obtained when the angle φi orthogonal to the angle φi is 135 degrees. The relationship between the maximum transmission angle φ ₀ and the phase difference ψ (degrees) at a wavelength of 550 nm can be expressed as φ ₀ = −ψ / 2 + 90. For other wavelengths, the maximum transmission angle φo changes according to the chromatic dispersion of the variable phase difference plate 4. However, if the dispersion characteristics of the variable phase difference plate 4 are known, for any wavelength, The maximum transmission angle φo can be obtained.

Next, a method for estimating the azimuth dependency of the intensity of incident polarized light will be described by taking as an example the case where light of the polarization component shown in FIG. 3 is incident. First, from FIG. 3B, the intensity of the polarized light in each azimuth φ is I (0) = 0.75, I (45) = 1.0, I (90) = 0.75, I (135) = 0. .5. Taking the product of the intensity of these four incident polarized lights as [I (φ _j )] and the transmittance [T _ij ] in Table 1 according to equation (1), [T _j ] is as follows. T (j = 0, Δ = 0) = 1.500, T (j = 1, Δ = λ / 4) = 1.746, T (j = 2, Δ = λ / 2) = 1.500, T (J = 3, Δ = 3λ / 4) = 1.250. When normalized by the maximum value, T ′ (j = 0) = 0.858, T ′ (j = 1) = 1.000, T ′ (j = 2) = 0.661, T ′ (j = 3) = 0.716.

Here, since the maximum transmission angles φo for j = 0, 1, 2, and 3 are 90 degrees, 45 degrees, 0 degrees, and 135 degrees, respectively, the transmitted light intensity T after normalization after j is corrected to φo A graph in which '(φo) is superimposed on the light intensity I (φ) and plotted is shown in FIG. The plot indicated by □ in FIG. 7A shows the light intensity obtained when the transmission axis direction of the polarizing plate 5 is the maximum transmission angle φo, and the plot indicated by ◯ is the light intensity obtained by the polarization acquisition means 6. Indicates. From both data, the fact that the azimuth angle of the polarization component with the maximum light intensity is 45 degrees indicates that A, B, φ by the least square method or the like as I (φ) = A + B * Sin ² (φ−φ ₀ ). Obtained from _zero fitting. However, the plot indicated by ○ has more offset than the light intensity. This offset amount is due to a decrease in the extinction ratio in the polarization information acquisition process. For example, after subtracting the minimum value of the transmittance T ′ after normalization from T (φ), it is normalized again. It is possible to easily cancel to some extent. FIG. 7B shows a graph similar to FIG. 7A after this processing. Each plot of FIG.7 (b) is based on Fig.7 (a). In FIG. 7B, data reflecting a plot of incident intensity is obtained as compared to FIG. 7A.

  In this embodiment, the phase difference of the variable phase difference plate 4 is set to four values from 0 to 3λ / 4 in increments of λ / 4. However, according to the polarization information to be acquired, a single value, 2 A value or a ternary value may be set. For example, when the polarization information is acquired once in a state where the imaging device is fixed, or when the orientation of the polarization-dependent maximum intensity and minimum intensity is known to some extent, only that state needs to be imaged. An image having necessary polarization information may be obtained even with a value. However, it is desirable to pick up an image so that the phase difference of the variable retardation plate 4 is an integral multiple of λ / 4 for ease of analysis.

  Further, the image acquired by the monitoring camera 100 may be output as it is without undergoing arithmetic processing such as image processing. The phase difference of the variable phase difference plate 4 may be set so that, for example, a polarization component of light from the subject guided to the image sensor 2 is acquired in advance and an appropriate polarization state is acquired. Even if the polarization state of the subject is not acquired in advance, the specific (one or more) polarization state may be acquired in advance.

  Further, by performing arithmetic processing between images having different polarization information, it is possible to acquire an image in which the characteristics of the subject are more emphasized in units of pixels. For example, when an image is generated using only the smallest value of the acquired data, reflected light from the water surface or road surface is excluded from the generated image. In-vehicle cameras have a problem of image degradation due to the movement of the windshield, but prevent misrecognition of road surface conditions by displaying an image with the optimal polarization direction that excludes reflected light based on the acquired polarization information. Can do. Note that the value of the light intensity of the polarized light may be a direct value of the image obtained by the polarization acquisition unit 6 or may be an interpolation value or an extrapolation value from the polarization analysis. Interpolation and extrapolation mean using an estimated value from an analysis result so as to emphasize or suppress the difference in polarization intensity obtained.

  Also, by acquiring the degree of polarization defined by the P-polarized light component that is parallel to the incident light surface and the S-polarized light component that is perpendicular, the difference in material (boundary part) in the plane is recognized. And the image accuracy of the monitoring object can be improved. The degree of polarization is a value that varies depending on the incident angle and the refractive index, and is defined by Expression (2).

Polarization degree = (P polarization component−S polarization component) / (P polarization component + S polarization component) (2)
As described above, by acquiring the object information of the subject optically, it is possible to generate an image in which the feature amount is emphasized or suppressed. Moreover, it becomes possible to produce | generate the image suitable for a photographer's intention by these combinations. Furthermore, you may produce | generate the image which gave different polarization | polarized-light information or the emphasis effect for every area | region of an image. For example, by combining images of different polarization states with respect to the main subject and the background (for example, the sky), it is possible to acquire an image with a uniform background color or an image in which the background and the main subject are emphasized. In addition, an image in accordance with the purpose can be acquired by performing various processes using the polarization intensity dependency of the subject.

  In the present embodiment, a monitoring camera 200 that takes into account the influence that occurs when an optical low-pass filter or the like is arranged will be described with reference to FIG. FIG. 8 is a configuration diagram of the monitoring camera 200 of the present embodiment. The monitoring camera 200 includes an imaging device unit 201 that includes the optical system 1, the imaging device 2, and the polarization acquisition unit 6, and a main body unit 202 that includes a control unit 103, a processing unit 104, and a display unit 105. The description of the same components as those in the first embodiment is omitted.

  In general, in an imaging apparatus such as a digital single-lens reflex camera, an optical low-pass filter is disposed in the vicinity of the imaging element in order to prevent moire and false colors. Even when the configuration described in the first embodiment is used, when an optical low-pass filter is disposed in front of the image sensor 2 or when there is polarization dependency in the autofocus unit, the polarization information of the subject may not be acquired correctly. . If the polarization acquisition unit 6 is simply disposed between the optical low-pass filter and the lens, a desired effect as the optical low-pass filter may not be obtained due to the influence of the polarization acquisition unit 6.

  The imaging device unit 201 includes an optical low-pass filter 17. As the optical low-pass filter 17, a multi-layered birefringent medium or a polarizing diffraction element or the like using polarization characteristics is used.

  In the present embodiment, in contrast to the adverse effects caused when the above-described optical low-pass filter or the like is arranged, in this embodiment, an achromatic λ / 4 plate 16 (achromatic phase difference plate, second optical plate) is provided between the polarizing plate 5 and the optical low-pass filter 17. 3 retardation plate) is inserted and converted into circularly polarized light. A normal λ / 4 plate may be inserted, but the λ / 4 plate has wavelength dispersion and does not become uniform circularly polarized light over the entire visible light range, and the phase shift due to the wavelength may appear in the image as a color change. There is sex. Therefore, as the λ / 4 plate to be inserted, an achromatic λ / 4 plate designed so as to minimize the phase difference in the visible wavelength band that is the used wavelength is desirable.

  In addition to the above effects, in the present embodiment, stray light reflected by the imaging element 2 can be cut by inserting the achromatic λ / 4 plate 16. Therefore, the polarization information of the subject can be acquired with higher accuracy.

  As another countermeasure, the light separation direction of the layer (in the case of a laminated structure) closest to the polarization acquisition means 6 of the optical low-pass filter 17 and the transmission axis direction of the polarizing plate 5 form 45 degrees. You may arrange. Also in this case, the characteristics of the optical low-pass filter, the characteristics of the polarization acquisition means 6, and the stray light suppressing effect can be achieved. Either measure can be used, but the latter is simpler.

  FIG. 9 is a perspective view of a vehicle equipped with an in-vehicle camera 300 that is one form of the surveillance camera 100 or the surveillance camera 200 of the present invention. The in-vehicle camera 300 includes an imaging device unit 301 including the optical system 1, the imaging element 2, and the polarization acquisition unit 6, and a main body unit 302 including the control unit 103, the processing unit 104, and the display unit 105. The in-vehicle camera 300 can realize a safe driving environment by acquiring polarization information without accurately reducing resolution and color information and accurately detecting a surrounding situation during traveling.

  FIG. 10 is a perspective view showing a network camera (monitoring network camera) 400 which is an embodiment of the monitoring camera 100 or the monitoring camera 200 of the present invention. The network camera 400 includes an imaging device unit 401 that includes the optical system 1, the imaging device 2, and the polarization acquisition unit 6, and a main body unit 402 that includes a control unit 103, a processing unit 104, and a display unit 105. The network camera 400 acquires polarization information without reducing resolution and color information, and accurately detects the surrounding situation to be monitored (detection of intruders and suspicious persons, detection of accidents and disasters) It is effective for disaster prevention.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. In the present embodiment, the in-vehicle camera and the monitoring network camera have been described as examples of the monitoring camera, but the present invention is not limited to these.

  Note that λ indicated by the phase difference of the variable phase difference plate 4 is a visible wavelength (400 to 700 nm) in a general imaging apparatus, and therefore may be such a wavelength. For example, the center wavelength is 550 nm. And it is sufficient. Or when a use wavelength range is an infrared region (700 nm-1100 nm), what is necessary is just a wavelength in an infrared region, for example, what is necessary is just to be wavelength 900nm. When both are included, the wavelength may be in the visible range or the infrared range, for example, the wavelength may be 750 nm.

2 Image sensor 3 λ / 4 plate (first retardation plate)
4 Variable phase difference plate (second phase difference plate)
5 Polarizing plate (polarizer)
100 monitoring camera 103 control unit (setting means)
104 processing unit 200 surveillance camera 300 vehicle-mounted camera 400 network camera 500 subject

Claims (19)

An image sensor that receives light from the subject;
A first retardation plate that provides a relative phase difference of π / 2 between the polarization component in the slow axis direction and the polarization component in the fast axis direction;
A second retardation plate capable of changing a relative phase difference applied between the polarization component in the slow axis direction and the polarization component in the fast axis direction;
A polarizer for extracting a polarization component guided to the image sensor;
Setting means for setting a relative phase difference of the second retardation plate;
A processing unit that generates a video based on the output of the imaging device,
The first retardation plate, the second retardation plate, and the polarizer are sequentially arranged from the subject side to the imaging element side,
In the second phase difference plate, the slow axis direction or the fast axis direction is inclined with respect to the slow axis direction or the fast axis direction of the first phase difference plate,
The setting means changes a relative phase difference of the second retardation plate according to a polarization component of light from the subject,
The image processing apparatus, wherein the processing unit generates an image having a frame rate greater than 0.01 fps.   The said setting means acquires image information from the said image sensor for every relative phase difference of the said 2nd phase difference plate, and acquires the polarization information of the said object from the acquired image information. The imaging device described.   The imaging apparatus according to claim 2, wherein the processing unit generates a video based on the image information and the polarization information.   The slow axis direction or the fast axis direction of the second retardation plate is inclined by 45 degrees with respect to the polarization direction extracted by the polarizer. The imaging device according to item.   5. The imaging according to claim 1, wherein a slow axis direction or a fast axis direction of the first retardation plate is parallel to a polarization direction extracted by the polarizer. apparatus.   When the slow axis direction of the first retardation plate is arranged in parallel with the direction in which the polarizer extracts, the slow axis direction of the second retardation plate is from the direction in which the polarizer extracts. The imaging apparatus according to claim 5, wherein the imaging apparatus is arranged to be inclined by 45 degrees counterclockwise.   When the fast axis direction of the first retardation plate is arranged in parallel with the direction in which the polarizer extracts, the fast axis direction of the second retardation plate is from the direction in which the polarizer extracts. The imaging apparatus according to claim 5, wherein the imaging apparatus is arranged to be inclined by 45 degrees clockwise.   The setting means has a relative phase difference of the second retardation plate so that a polarization component of light from the subject is parallel to a direction in which the polarizer extracts after passing through the second retardation plate. The imaging apparatus according to any one of claims 1 to 7, wherein: The second retardation plate is composed of one retardation plate,
The imaging device according to any one of claims 1 to 8, wherein the first retardation plate, the second retardation plate, and the polarizer are arranged adjacent to each other. The second retardation plate is a retardation plate using liquid crystal,
The imaging apparatus according to claim 1, wherein the setting unit sets a voltage to be applied to the second retardation plate.   11. The imaging apparatus according to claim 1, wherein the setting unit sets a relative phase difference of the second retardation plate to an integral multiple of λ / 4. An optical low-pass filter composed of a plurality of layers is further provided between the imaging element and the polarizer, and the light separation direction by the layer closest to the polarizer of the optical low-pass filter is a direction in which the polarizer extracts. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is tilted by 45 degrees.   The imaging apparatus according to claim 12, wherein the optical low-pass filter is a system using birefringence or a polarization diffraction element. An optical low-pass filter is further provided between the image sensor and the polarizer,
A third retardation plate that provides a relative phase difference of π / 2 between the polarization component in the slow axis direction and the fast axis direction between the optical low-pass filter and the polarizer;
The slow axis direction or the fast axis direction of the third phase difference plate is inclined by 45 degrees from the direction of extraction by the polarizer, according to any one of claims 1 to 11. The imaging device described.   The imaging apparatus according to claim 14, wherein at least one of the first retardation plate and the third retardation plate is an achromatic retardation plate.   The said polarizer absorbs 50% or more of the polarization component of the direction orthogonal to the direction which the said polarizer extracts in a visible wavelength band, The any one of Claims 1-15 characterized by the above-mentioned. Imaging device.   The imaging apparatus according to claim 1, further comprising a display unit that displays an image generated by the processing unit.   The imaging apparatus according to claim 1, wherein the imaging apparatus is a surveillance camera. The imaging apparatus according to claim 1, wherein the imaging apparatus is an in-vehicle camera.