JPH08223473A - Imaging device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an imaging device with improved image quality. [Structure] The polarization means 3 transmits only the imaging light of which the polarization direction is one direction among the imaging light. The ferroelectric liquid crystal cell 4 is
The polarization direction of the imaging light from the polarization means 3 is rotated and emitted according to the polarity of the applied voltage. The driving means 5 drives the ferroelectric liquid crystal cell 4 so as to switch the polarity of the applied voltage so that the optical axis of the ferroelectric liquid crystal cell 4 is switched to a symmetrical position with respect to the propagation axis of the polarization means 3. The birefringence means 6 converts the imaged light into an ordinary ray and an extraordinary ray according to the polarization direction of the imaged light from the ferroelectric liquid crystal cell 4, and emits the ray. Image sensor 7
Receives the ordinary ray and the extraordinary ray emitted from the birefringent means 6, respectively, performs photoelectric conversion to form and output an image pickup signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for picking up an image while controlling the polarity of a voltage applied to a liquid crystal plate to electrically shift the relative position between the image pickup element and the image pickup light. The present invention relates to an image pickup device suitable for use in a video camera device, an image scanner, or the like that picks up an image of a subject using an image pickup element.

[0002]

2. Description of the Related Art In recent years, a high-resolution television receiver (H
high Definition Television
With the spread of (n), it is required to improve the resolution of the image pickup apparatus. Therefore, an image pickup device that electrically performs image shift is known as an image pickup device that achieves high resolution.

This image pickup device includes, for example, a solid-state image pickup device (CCD: Charge Coupled Device).
A crystal plate is provided as an optical element exhibiting a so-called birefringence phenomenon between the (e image sensor) and the lens, and a voltage-driven liquid crystal plate is provided in front of the lens.

Further, for example, the liquid crystal plate is a twisted nematic liquid crystal (TN: Twisted Ne) as shown in FIG.
matic) cell 101 and polarizing film 102. The polarizing film 102 converts incident light into linearly polarized light, but in general, polarized light can be decomposed into two linearly polarized light components vibrating in directions perpendicular to each other in a plane perpendicular to the traveling direction. Therefore, the polarizing film 102 is
Of the two linearly polarized light components, E indicated by the arrow in the figure
Only the linearly polarized light component that vibrates in the ₀ direction is transmitted. Here, the E ₀ direction denotes the direction of the electric field vector, the vibration direction of linearly polarized light component vibrating in the E ₀ direction say E ₀ direction of the incident light.

Such a polarizing film 102 is attached to the TN cell 101, and the incident light passes through the polarizing film 102 so that the light entering the TN cell 101 has an oscillation direction of E ₀ direction. Becomes

When image pickup is started by such an image pickup device, first, the vibration direction is E ₀ from the polarizing film 102.
Only the imaging light in the direction is emitted to the TN cell 101. Here, for example, an AC voltage is applied to the TN cell 101 for each field. AC voltage is TN cell 10
When the voltage is applied to 1, the TN cell 101 directly transmits the image pickup light whose vibration direction is the E ₀ direction from the polarizing film 102 and emits the image pickup light whose vibration direction is the E ₁ (= E ₀ ) direction. When no AC voltage is applied to the TN cell 101, the TN cell 101 has a vibration direction of E ₂ direction having a polarization angle difference of 90 ° with respect to the imaging light of which vibration direction from the polarizing film 102 is E ₀ direction. It is converted into imaging light and emitted.

Therefore, the quartz plate is irradiated with the image pickup light whose vibration direction is the E ₁ direction and the image pickup light whose vibration direction is the E ₂ direction, respectively. When the image pickup light whose vibration direction is the E ₁ direction is irradiated, the crystal plate irradiates the CCD image sensor as ordinary light without changing its optical path, and the image pickup light whose vibration direction is the E ₂ direction is irradiated. In that case, the CCD image sensor is irradiated with abnormal light shifted downward by a 1/2 pixel pitch, for example, in the optical path.

As a result, the CCD image sensor is irradiated with the ordinary light and the abnormal light shifted downward by 1/2 pixel pitch with respect to the irradiation position of the ordinary light for each field. As a result, the spatial sampling area can be increased, and high resolution can be achieved without increasing the number of pixels.

The above-described image pickup device uses a TN cell as a liquid crystal plate, but instead of the TN cell, a ferroelectric liquid crystal (FLC: Ferroelectric Liquid) is used.
Crystal) cell, and this FLC cell is 1 /
An imaging device used as a two-wavelength (λ) plate is also known. In this case, as shown in FIG. 8, the fast axis F of the SSFLC cell 103 is switched for an arbitrary angle (= θ). As a result, from the FLC cell 103,
The imaging light whose vibration direction is E ₀ is the same as the vibration direction E
The image pickup light is emitted in the ₁ (= E ₀ ) direction, or the image pickup light whose vibration direction is the E ₀ direction is converted into the image pickup light whose vibration direction is the E ₂ direction and is emitted.

[0010]

However, the above-mentioned TN
Since the cell 101 is easily affected by the ambient temperature and depends on the wavelength of the image pickup light incident on the TN cell 101, the image pickup light whose vibration direction is the E ₀ direction from the polarizing film 102 remains in the vibration direction E ₁ (= The light amount of the image pickup light applied to the CCD image sensor when it is emitted as the image pickup light in the E ₀ ) direction, and the image pickup light whose vibration direction is the E ₀ direction is converted into the image pickup light whose vibration direction is the E ₂ direction and is emitted. In this case, the balance with the light amount of the image pickup light with which the CCD image sensor is irradiated is lost. Further, in the above-described FLC cell 103, the state change when switching the fast axis F is the wavelength of the imaging light incident on the FLC cell 103, and
Since it is easily affected by the ambient temperature, the polarizing film 102
If it vibration direction imaging light vibrating direction E ₀ direction of emitted as E ₁ (= E ₀₎ direction of the imaging light from, and the vibration direction of the imaging light in the oscillation direction is E ₀ direction E ₂ Direction It was not possible to stabilize the light amount of the image pickup light applied to the CCD image sensor when converted into the image pickup light and emitted.

As described above, in the conventional image pickup apparatus, the MTF (Mdu) in two states, that is, when the voltage is applied to the liquid crystal cell and when the voltage is not applied to the liquid crystal cell.
(Lation Transfer Function)
However, the image quality could not be improved.

Therefore, the present invention has been made in view of the conventional circumstances as described above, and has the following objects.

That is, it is an object of the present invention to provide an image pickup apparatus with improved image quality.

[0014]

In order to solve the above-mentioned problems, an image pickup apparatus according to the present invention comprises a polarizing means for transmitting only the image pickup light having one polarization direction among the image pickup light, and the polarity of an applied voltage. The ferroelectric liquid crystal cell for rotating the polarization direction of the image pickup light from the polarizing means to emit the polarized light, the driving means for driving the ferroelectric liquid crystal cell by switching the polarity of the applied voltage, and the ferroelectricity Birefringent means for converting the imaged light into ordinary rays and extraordinary rays according to the polarization direction of the imaged light from the liquid crystal cell, and emitting the ordinary rays and extraordinary rays emitted from the birefringent means. An image pickup device for performing photoelectric conversion to form and output an image pickup signal, wherein the drive means
The driving is performed so that the optical axis of the ferroelectric liquid crystal cell is switched to a symmetrical position with respect to the propagation axis of the polarization means.

Further, in the image pickup apparatus according to the present invention, the driving means is driven so as to be in an elliptically polarized state which is rotated by 45 ° with respect to the image pickup light incident on the ferroelectric liquid crystal cell through the polarizing means. It is characterized by doing.

[0016]

In the image pickup apparatus according to the present invention, the polarization means transmits only the image pickup light whose polarization direction is one direction among the image pickup light.
The ferroelectric liquid crystal cell rotates the polarization direction of the imaging light from the polarization means and emits the imaging light according to the polarity of the applied voltage. The driving means drives the ferroelectric liquid crystal cell so that the polarity of the applied voltage is switched and the optical axis of the ferroelectric liquid crystal cell is switched to a symmetrical position with respect to the propagation axis of the polarizing means. The birefringence means converts the imaged light into ordinary rays and extraordinary rays according to the polarization direction of the imaged light from the ferroelectric liquid crystal cell, and emits the rays. The image pickup device receives the ordinary ray and the extraordinary ray emitted from the birefringent means, respectively, performs photoelectric conversion to form an image pickup signal and outputs the image pickup signal.

Further, in the image pickup device according to the present invention, the driving means is driven so as to be in an elliptically polarized state which is rotated by 45 ° with respect to the image pickup light incident on the ferroelectric liquid crystal cell through the polarizing means. To do.

[0018]

An embodiment of the present invention will be described below with reference to the drawings.

The image pickup device of the present invention shown in FIG. 1 has an image pickup lens 2, a polarizer 2 as a polarizing means, and the polarization direction of the image pickup light from the polarizer 2 is rotated and emitted in accordance with the polarity of an applied voltage. Ferroelectric liquid crystal (FLC) cell 4 and FLC cell 4
Is provided with a driving means 5 for driving the element according to the polarity of the applied voltage, a crystal plate 6 as a birefringent means, and an image pickup element 7. The polarizer 2 converts the imaging light of the subject 1 emitted through the imaging lens 2 into linearly polarized light, and, for example, as shown in FIG.
Of the imaged light converted into the linearly polarized light, only the imaged light whose light oscillation direction is the direction of the electric field vector (= E ₀ direction) is transmitted.

As shown in FIG. 3, the FLC4 cell 4 has F
The LC44 has a symmetrical seven-layer structure so as to sandwich the LC44 in the center, and in order from the outside, the substrates 41a and 41b, the transparent electrodes 42a and 42b, the alignment films 43a and 43b, and the F
It is composed of LC44. As the FLC 44, for example, a chiral smectic C liquid crystal exhibiting ferroelectricity is used. F using this chiral smectic C liquid crystal
The LC cell 4 is excellent in high-speed response and memory property, and the polarization direction of the chiral smectic C liquid crystal is controlled by the magnetic field.

As shown in FIG. 4, the driving means 5 is located at a position where the fast axis F of the FLC cell 4 is symmetric with the vibration direction (= E ₀ ) of the imaging light emitted from the polarizer 2 as the symmetry axis P. Depending on the polarity of the applied voltage, the FLC cell 4 is switched.
Drive. That is, when driving the FLC cell 4,
The electric field in the (−) direction and the electric field in the (+) direction are switched for each field and applied to the FLC cell 4, whereby the fast axis F of the FLC cell 4 is switched.

For example, an electric field in the (-) direction is applied to the FLC cell 4 so that the fast axis F of the FLC cell 4 switches to a position forming + θ (= + 22.5 °) with respect to the symmetry axis P. In this case, the imaging light from the polarizer 2 whose vibration direction is the E ₀ direction is converted into the imaging light whose vibration direction having a polarization angle difference of + 2θ (= 45 °) is the E ₁ direction.

On the contrary, the fast axis F of the FLC cell 4 is -θ (= -22.5 °) with respect to the symmetry axis P.
(+) On the FLC cell 4 so that it switches to the position
An electric field in the direction is applied. In this case, the imaged light from the polarizer 2 whose vibration direction is the E ₀ direction is converted into the imaged light whose vibration direction having a polarization angle difference of −2θ (= −45 °) is the E ₂ direction.

Therefore, the FLC cell 4 functions as a ½ wavelength (λ) plate, and the imaging light emitted from the FLC cell 4 with respect to the imaging light incident on the FLC cell 4 via the polarizer 2. The elliptically polarized light is rotated by 45 °. The imaged light in the elliptically-polarized state whose vibration direction is the E ₁ direction and the imaged light whose vibration direction is the E ₂ direction are emitted to the quartz plate 6 provided in the next stage of the FLC cell 4.

The crystal plate 6 is an optical element exhibiting a so-called birefringence phenomenon, and when the image pickup light whose vibration direction is the E ₁ direction is incident from the FLC 4, the optical path of the image pickup light is output as it is as ordinary light without changing it. To do. When the imaging light whose vibration direction is the E ₂ direction is incident from the FLC 4, the optical path of the imaging light is changed from the optical path of the imaging light whose vibration direction is the E ₁ direction, for example,
The abnormal light shifted in the horizontal direction by 1/2 pixel pitch is emitted. Here, as described above, the imaging light whose vibration direction from the FLC 4 is the E ₁ direction and the imaging light whose vibration direction from the FLC 4 is the E ₂ direction are switched for each field, and are switched to the crystal plate 6. Is emitted. Therefore, the ordinary light is emitted from the crystal plate 6 as the subject image of the first field,
The extraordinary light whose pixel pitch is shifted by 1/2 pixel with respect to the ordinary light is emitted to the image sensor 7 as a subject image of the second field.

The image pickup device 7 is, for example, a solid-state image pickup device (C
CD (Charge Coupled Device image sensor), which captures subject images of the first and second fields from the quartz plate 6, respectively. When the image pickup surface of the image pickup device 7 at this time is schematically represented, for example, as shown in FIG. 5, the state in which the subject image is shifted on the image pickup device 7 for each field is the subject image 10 in the first field. And the position of the subject image 11 in the second field is 1 of the pixel pitch.
It is in the state of being horizontally shifted by / 2. In FIG. 5, 8 indicates a pixel and 9 indicates a photosensitive portion. In this way, the imaging of one frame is completed by the imaging of the first and second fields.

Then, the first obtained by the image pickup device 7,
The image pickup signals of the second field are combined in a signal processing unit (not shown) to generate an image pickup signal for one frame.

As described above, in the present embodiment, the vibration axis (= E ₀ ) of the imaging light emitted from the polarizer 2 is the symmetry axis P, and the fast axis F of the FLC cell 4 is ± 22.5 °. Since the FLC cell 4 is driven so as to be switched to the formed position, it is possible to accurately switch the imaging light emitted from the polarizer 2 with the vibration direction of E ₀ direction to the position of ± 45 ° with respect to the symmetry axis P. . As a result, the imaging light with the vibration direction E _{1 and} the imaging light with the vibration direction E ₂ emitted from the FLC cell 4 are elliptically polarized light symmetrical with respect to the symmetry axis P, as shown in FIG. Because of the state, the wavelength of the incident light,
Alternatively, the MTFs in these two polarization states can be made equal regardless of the ambient temperature. Further, since the image pickup light whose vibration direction is the E ₁ direction and the image pickup light whose vibration direction is the E ₂ direction are radiated to the image pickup element 7 through the crystal plate 6 as the ordinary light and the abnormal light. It is possible to stabilize the respective amounts of ordinary light and extraordinary light with which the image pickup device 7 is irradiated. As described above, it is possible to balance the MTFs during normal light irradiation and during abnormal light irradiation. That is, the MTFs of the image generated by the imaging light whose vibration direction is the E ₁ direction and the MTF of the image generated by the imaging light whose vibration direction is the E ₂ direction can be made equal, and the image quality can be improved. .

Further, in this embodiment, the liquid crystal cell is a FLC cell 4 which uses a stable FLC which has a fast response, is easy to manufacture.
Therefore, the cost can be reduced.

In the embodiment described above, the driving means 5 is
Although the fast axis F of the FLC cell 4 is switched, the slow axis of the FLC cell 4 may be switched.

[0031]

In the image pickup device according to the present invention, the polarization means transmits only the image pickup light whose polarization direction is one direction out of the image pickup light. The ferroelectric liquid crystal cell rotates the polarization direction of the imaging light from the polarization means and emits the imaging light according to the polarity of the applied voltage. The driving means drives the ferroelectric liquid crystal cell so that the polarity of the applied voltage is switched and the optical axis of the ferroelectric liquid crystal cell is switched to a symmetrical position with respect to the propagation axis of the polarizing means. The birefringence means converts the imaged light into ordinary rays and extraordinary rays according to the polarization direction of the imaged light from the ferroelectric liquid crystal cell, and emits the rays. The image pickup device receives the ordinary ray and the extraordinary ray emitted from the birefringent means, respectively, performs photoelectric conversion to form an image pickup signal and outputs the image pickup signal. As a result, the MTFs of the states of the image pickup signals generated by the ordinary ray and the extraordinary ray can be balanced, so that the image quality can be improved.

Further, in the image pickup apparatus according to the present invention, the driving means is in an elliptically polarized state which is rotated by 45 ° with respect to the image pickup light incident on the surface-stabilized ferroelectric liquid crystal cell through the polarizing means. To drive. Thereby, the image quality can be further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a vibrating direction of imaging light transmitted through a polarizer of the imaging device.

FIG. 3 is a diagram showing a configuration of a ferroelectric liquid crystal cell of the image pickup device.

FIG. 4 is a diagram for explaining switching of the first axis of the ferroelectric liquid crystal cell.

FIG. 5 is a diagram showing how a subject image shifts on an image sensor of the image pickup apparatus.

FIG. 6 is a diagram showing an elliptically polarized state.

FIG. 7 is a diagram for explaining conversion of a vibration direction of imaging light when a twisted nematic liquid crystal cell is used in a conventional imaging device.

FIG. 8 is a diagram for explaining conversion of a vibration direction of imaging light when a ferroelectric liquid crystal cell is used in a conventional imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Subject 2 Imaging lens 3 Polarizing plate 4 Ferroelectric liquid crystal cell 5 Driving means 6 Quartz plate 7 Imaging element

Claims (2)

[Claims] 1. A polarization means for transmitting only the imaging light of which the polarization direction is one direction among the imaging light, and a ferroelectric for rotating and emitting the polarization direction of the imaging light from the polarization means according to the polarity of an applied voltage. Liquid crystal cell, driving means for driving the ferroelectric liquid crystal cell by switching the polarity of the applied voltage, and the ordinary and extraordinary rays of the imaging light depending on the polarization direction of the imaging light from the ferroelectric liquid crystal cell. And a birefringent means for converting the light into an ordinary ray and an extraordinary ray emitted from the birefringent means, and photoelectrically converting the ordinary ray and the extraordinary ray to form and output an image pickup signal. Is driven so that the optical axis of the ferroelectric liquid crystal cell is switched to a symmetrical position with respect to the propagation axis of the polarization means. 2. The drive means is 45 ° with respect to the imaging light incident on the ferroelectric liquid crystal cell via the polarization means.
The image pickup apparatus according to claim 1, wherein the image pickup apparatus is driven so as to be in an elliptically polarized state of optical rotation.