JPH0595517A - High resolution image pick-up device - Google Patents

Abstract

PURPOSE:To perform a simple and stable operation without decreasing the light incident quantity to an image pick-up surface and to statically vary the displacement quantity with many steps. CONSTITUTION:An electric optical element group 28 consisting of a pair of electronic optical elements 22 and 24 capable of controlling the degree of double refraction according to the applied voltage and a deflection surface rotary element 26 rotating the deflection surface by 90 deg. while being held between a pair of electric optical elements 22 and 24 is arranged in front of an image pickup element 20. By changing the double refraction characteristic of a pair of the electric optical elements 22 and 24 at every image picking-up of the image pick-up element 20, the image picking-up is performed by repeating the '0' and '1/2' pitch shifts when an image is made incident on the image pick-up surface of the image pick-up element 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high definition of an image capturing device, and more particularly to high resolution of an image pickup device having a finite aperture.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made in order to achieve high resolution of an image pickup device having a finite aperture.

For example, as disclosed in Japanese Patent Laid-Open No. 61-247168, an electro-optical element whose polarization characteristic can be controlled according to a voltage and a birefringence means are arranged in front of an image pickup means, and It has been proposed to provide voltage switching means for controlling the electro-optical element.

Also, as disclosed in Japanese Patent Laid-Open No. 62-26984, there has been proposed a device using a magneto-optical element instead of the electro-optical element.

[0005]

However, in the former, the position of the optical image is controlled by a pair of the electro-optical element and the birefringence means, and a polarizer (only one of the independent polarization components is selected on the front surface is selected. However, there is a problem that a double image is directly captured unless an analyzer (polarizer) is provided on the rear surface.

Further, since both of them selectively transmit only one of the independent polarization components, the amount of light on the image pickup surface is ½.
If the aperture is opened to compensate for it, the depth of field of the copy becomes shallow, and if the exposure time is increased, the problem of image blur occurs due to the high resolution.
There is a problem that the S / N is deteriorated.

Further, since the polarization characteristic of the incident light is controlled electrically or magnetically, the relative positional relationship between the incident light image and the pixel of the image pickup means is switched in several steps (higher resolution). In such a case, there is no choice but to construct a pair of optical elements by stacking them by the number of switching steps as disclosed above. That is, in such a case, there is a problem that the configuration becomes complicated.

Further, as disclosed in Japanese Patent Laid-Open No. 60-18958, a method of mechanically vibrating an image pickup device by a half pixel pitch by a piezo element has been proposed, but the piezo vibration cycle is limited. However, there was a problem that there were multiple mechanisms.

The present invention has been made in view of the above points, and performs a simple and stable operation without reducing the amount of light incident on the image pickup surface, and statically changes the displacement amount (steps). It is an object of the present invention to provide a high resolution image pickup device that can be changed.

[0010]

In order to achieve such an object, in the high resolution image pickup device according to the present invention, a pair of electro-optical devices capable of controlling the magnitude of birefringence according to an applied voltage. An element and a polarization plane rotating element for sandwiching the electro-optical element between the pair of electro-optical elements to rotate the plane of polarization by 90 °, and a light beam received through the pair of electro-optical elements and the polarization plane rotating element. Image pickup means, and voltage control means for changing the birefringence characteristics of the pair of electro-optical elements for each image pickup of the image pickup means.

Here, the voltage control means controls the pair of electro-optical elements so that voltages having different polarities are applied for each image pickup.

Further, a plurality of electro-optical means composed of the pair of electro-optical elements and the polarization plane rotating element may be arranged so that the deviation directions of the outgoing light rays with respect to the incident light rays are different from each other. good.

[0013]

That is, in the high-resolution image pickup device according to the present invention, a pair of electro-optical elements capable of controlling the magnitude of birefringence according to an applied voltage, and a polarized light sandwiched between the pair of electro-optical elements. Electro-optical means including a polarization plane rotating element for rotating the surface by 90 ° is arranged in front of the image pickup means, and the birefringence characteristics of the pair of electro-optical elements are picked up by the image pickup means by the voltage control means. Change every time.

Here, the electro-optical element has a birefringence characteristic by itself, and controls the different refractive indices of the independent polarization components by the voltage level applied from the voltage control means, so that the inter-images of the output double light image can be controlled. The amount of deviation is variably controlled. Further, the polarization plane rotation element rotates the polarization (light) plane of the double image light made up of the ordinary ray and the extraordinary ray incident from the first electro-optical element on the front side by 90 ° and emits it. The second electro-optical element on the rear surface of the polarization plane rotating element is controlled by the voltage control means so as to have the same birefringence characteristic as the first electro-optical element, and the ordinary light becomes extraordinary light by the polarization plane rotating element. The extraordinary light changes the double image light converted into the ordinary light into the single image light. When the image light incident on the first electro-optical element in this process changes the polarity of the voltage output from the voltage control means with time inversion (or ON, OFF) while synchronizing with the image pickup timing of the image pickup means, When entering the image pickup surface, 0 and ½ pixel pitch shifts are repeatedly taken to pick up an image, and the pixel pitch of the image data is doubled by combining in a buffer memory or a frame memory in the subsequent stage.

Therefore, it is possible to provide a high-resolution image pickup device which can perform a simple and stable operation without reducing the amount of light incident on the image pickup surface and can change the displacement amount statically in many steps. Like

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block configuration diagram of a high resolution image pickup apparatus according to a first embodiment of the present invention. The system controller 10 is for controlling various parts, which is SS
It is driven by the timing clock from the G (sync signal generator) 12.

An optical system 18 including a lens 14 and a diaphragm 16.
And a CCD 20 as an image pickup element, a pair of electro-optical elements 22, 24, which is a characteristic part of the present invention.
And a polarization plane rotating element 26 sandwiched between them and an electro-optical element group 28. The electro-optical elements 22 and 24 and the polarization plane rotating element 26 are, for example,
It is a liquid crystal (LC). When the LC driver 30 receives an optical image shift command from the system controller 10 (whether the image is to be shifted or not), the LC driver 30 synchronizes with the shift start timing signal from the SSG 12 and outputs the electro-optical element 22. , 24 are controlled.

SSG 12 and system controller 10
After the time when the shift of the optical image is completed,
The control and driving clock signal for image pickup are transmitted to the driver 32, and image pickup and reading of the CCD 20 are performed. Sample / hold circuit (S / H) from CCD 20
The signal read by 34 is amplified by a preamplifier 36 and then converted into a digital signal by an A / D conversion circuit 38. Then, it is stored in the temporary buffer memory 40 and appropriately read by the digital video process unit 42. The digital video process unit 42 performs color separation, conversion processing, and correction processing (γ, WB, gain control, aperture, etc.) on the digital signal read from the buffer memory 40. Then, the result is an I / F (interface) 4 as a captured image signal.
It is transferred to the multimedia filing system 48 via 4, 4, and processed and recorded.

Of course, the recording medium (HD, MO, FD, memory card, etc.) may be directly recorded.
Image data may be transferred to a remote place using a communication line such as ISDN, ISDB, INS, and RAN.

Further, in FIG. 1, the data compression unit (ADC
(T, ADPCM, AVQ, etc.) is not specified, but the image data compressed by the data compression unit with an appropriate compression rate and format is sent to the receiving side in response to the request from the receiving side. Depending on the transfer rate of transmission / reception, the data is temporarily stored in the frame memory 50, and the data is sequentially read according to the transfer rate. In FIG. 1, reference numeral 5
Reference numeral 2 is a memory controller that controls the frame memory 50, and 54 is a lens and diaphragm driver that drives the optical system 18.

FIG. 2A shows the structure of the electro-optical element group 28. The electro-optical element group 28 is configured such that two nematic (N) liquid crystals 22a and 24a as the electro-optical elements 22 and 24 sandwich the TN liquid crystal 26a as the polarization plane rotating element 26.

Each N liquid crystal 22a, 24a has a transparent electrode 56.
It is configured such that the liquid crystal is sandwiched between thin glass plates 58 to which is attached. By applying a voltage between the electrodes 56,
The alignment of the liquid crystal (index ellipsoid 60) can be controlled.

The TN liquid crystal 26a is the thin glass plate 5 as well.
The liquid crystal (refractive index ellipsoid) array is fixed so that the plane of polarization is rotated by 90 ° (circularly polarized light). Further, the electrodes 56 on the side in contact with the TN liquid crystal 26a are both grounded or 0 V, and the TN liquid crystal 26a
No electric potential is generated on both sides.

Hereinafter, in such a structure, when a control signal (voltage) as shown in FIG. 2B is applied from the LC driver 30 to the electro-optical element group 28 using the liquid crystal. Will be explained. In addition, in FIG.
The vertical sync signal (VD) is also shown.

That is, when a voltage of V is applied to the electrode v1 of the electro-optical element 22, the molecules (refractive index ellipsoid) of the N liquid crystal 22a are oriented by + θ1. Then, in the incident light, the ordinary light travels straight with almost no refraction, but the extraordinary light is refracted along the long axis direction of the molecule, and the course is bent. Therefore, when the light passes through the N liquid crystal plate having the thickness D, it is separated into ordinary light and extraordinary light by the alignment of the liquid crystal, and due to the difference in the refractive index between them, when it is emitted, the light is displaced with a position of d (liquid crystal Birefringence).

The optical image formed into a double image by the N liquid crystal 22a maintains the plane of polarization (linearly polarized light), and is the TN liquid crystal 26a.
Incident on. In the TN liquid crystal 26a, since the liquid crystal is arranged so that the plane of polarization is rotated by 90 °, each light is
By passing through the TN liquid crystal 26a, its polarization plane is 90 °.
The normal light of the first N liquid crystal 22a rotates, and the light of the extraordinary light changes its plane of polarization into the ordinary light and enters the second N liquid crystal 24a.

In the second N liquid crystal 24a, the first N liquid crystal 2
In the same process as in the case of 2a, the extraordinary light converges in the direction of ordinary light due to the birefringence.

Here, the first and second N liquid crystals 22a, 24
When the thicknesses D ₁ and D _{2 of a} are D ₁ = D ₂ , the orientation angles θ ₁ and θ
_{If 2} is θ ₁ = θ ₂ and the applied voltage v ₁ = −v ₂ ,
And the second N liquid crystals 22a and 24a are both the lens 1
When viewed from the 4 side, they have the same orientation, refractive index, and optical path length. Therefore, the light that has entered the first N liquid crystal 22a is refracted on the way in the first or second N liquid crystal 22a, 24a at a refractive index with respect to the extraordinary light, changes its position, and is emitted again as one unit.

The applied voltage is adjusted (that is, the orientation angle is adjusted), and the shift amount in the electro-optical element group 28 is changed by the image pickup element 2.
When the pixel pitch is set to 1/2 of the pixel pitch of 0 (the pitch between the light receiving elements 20a), the light that has passed through the lens 14 has a 1/2 pixel pitch from the position of the imaging surface that originally reaches,
The image is displaced (case (I), see FIG. 2C). Further, when the applied voltage is set to v ₁ = v ₂ = about 0 V,
The N liquid crystal molecules are vertically aligned in both the first and second directions, and the incident light goes straight (case (II), see FIG. 2D).

Therefore, as shown in the time chart of FIG. 2B, when the applied voltage is switched to V ₁ and V ₀ (about 0 V) every other frame, the image light reaching the image pickup device 20 becomes
An image is captured with a 1/2 pixel pitch shift for each frame.

When the image signals picked up for two frames are overlapped with each other in the buffer memory 40 or the frame memory 50 of FIG. 1 so as to interpolate with each other, the resolution as a whole is doubled.

The optical path length is naturally different when the voltage is applied and when the voltage is not applied. However, this difference in optical path length is a constant value. Therefore, for example, the image pickup device 20 is arranged at the focal position when no application is applied, and when applied, the optical system 18 is moved in a direction to cancel the movement amount of the focal position caused by the difference in optical path length.
Correct the focus position of. That is, a focus correction signal is applied to the lens / aperture driver 54 in synchronization with the application of the control voltage, and the lens 14 is subjected to focus correction so as to focus on the surface of the image sensor.

FIG. 3A shows a timing chart in the second embodiment of the present invention. In the second embodiment, the applied voltage is V, -V. The operation is basically the same as that of the first embodiment described above, but when −V is applied (case (I)), the first and second N liquid crystals 22 are provided.
a, the orientation of 24a is reverse (-θ _1, -θ ₂₎ it becomes.
Therefore, in the case of V, -V of the second embodiment, the amount of shift of the image light is doubled as compared with V, 0 of the first embodiment (see FIG. 3B).

On the contrary, if the image light shift amount is the same 1/2 pixel pitch, the first and second N liquid crystals 22 are reversed.
It is shown that the thickness of a and 24a may be 1/2. As a result, the thickness of the electro-optical element group 28 is reduced to about 1/2, which leads to a margin of installation space. Further, since the amount of light absorption (loss) in the electro-optical element group 28 is also reduced to about 1/2, exposure time is shortened, the diaphragm can be narrowed by that amount, or S / N can be improved.

Others are the same as in the first embodiment. In addition,
3C shows the alignment of the liquid crystal when -V is applied (case (I)), and FIG. 3D is when V is applied (case (II)). Shows the orientation of the liquid crystal.

Next, a third embodiment of the present invention will be described.
In the third embodiment, the voltage applied to the electro-optical element group 28 is, as shown in FIG.
It has three states of V, 0, and -V. Basically, the operation is the same as in the first and second embodiments described above, but the orientation angle is θ ₁ (θ ₂ ), 0 (0) by sequentially switching the applied voltage to V, 0, -V. changes - [theta] ₁ and (- [theta] _2). Therefore, the shift of the optical image is also shown in FIGS. 4C and 4D.
As shown in, the three values of A, A ', and A "are taken.
4C shows the case viewed from the incident light, and FIG. 4D shows the case viewed from the image sensor 20 side.

When the shift amount of the optical image when V _in = V and −V is set to 1/3 pixel pitch, finally, as shown in FIG. Will be obtained. Further, since the shift amount is 2/3 as compared with the above-described first embodiment, the shift amount can be made thinner than that of the electro-optical element group 28 of the first embodiment, and the space transmittance can be improved.
Alternatively, the values of the applied voltages V and -V can be lowered to 2/3.

As a fourth embodiment, the electro-optical element group 28
The electro-optical element group 28 is set so that the image pickup element 20 and the image pickup element 20 are rotated by 90 ° with respect to the optical axis. In such a structure, when an applied voltage is applied, the image light moves in the direction perpendicular to the pixel array of the image sensor 20. That is, the above-mentioned first
In the third to third embodiments, the horizontal resolution is improved, so that the horizontal resolution is improved to 2 to 3 times, but in the fourth embodiment, the vertical resolution is improved to 2 to 3 times ( (See FIG. 5B).

Similarly, as a fifth embodiment, the electro-optical element group 28 may be installed so that the electro-optical element group 28 and the image pickup element 20 are rotated by 45 ° with respect to the optical axis.
In this case, when an applied voltage is applied, the image light is emitted from the image sensor 2
The pixel array of 0 is moved diagonally (see FIG. 5C). In the fifth embodiment, the same effect as the sub-Nyquist sampling is obtained, and the horizontal and vertical bidirectional resolution is improved by a factor of 2 to 3.

Further, FIG. 6A shows the arrangement of the electro-optical element group of the sixth embodiment of the present invention. In the sixth embodiment, the image light is shifted in the respective image pickup elements 20. On the other hand, two electro-optical element groups in the horizontal direction and the vertical direction are combined. Here, for example, the first for horizontal shift
The electro-optical element group 28a and the vertical-shifting electro-optical element group 28a are referred to as second electro-optical element group 28b. Of course, the reverse arrangement is also possible.

Next, the operation of the sixth embodiment will be described with reference to FIGS. 6 (B) and 6 (C). First, in the first frame, an image is taken without applying a voltage to either of the two electro-optical element groups 28a and 28b ((B) in FIG. 6).
Pixels). Then, the pixel signal is stored in the buffer memory 40.
Temporarily store in.

Next, in the second frame, as shown in FIG. 6C, the control voltage is applied only to the first electro-optical element group 28a. Then, the image light is imaged with a 1/2 pixel pitch shift in the horizontal direction (Δ in FIG. 6B).
Then, the pixel signal is temporarily stored in the buffer memory 40.

In the third frame, a control voltage is applied to the first and second electro-optical element groups 28a and 28b. Then,
The image light is imaged with a 1/2 pixel pitch shift in the diagonal direction (x in FIG. 6B). Then, the pixel signal is temporarily stored in the buffer memory 40.

In the fourth frame, the control voltage is applied only to the second electro-optical element group 28b. Then, the light image is captured with a 1/2 pixel pitch shift in the vertical direction (FIG. 6).
▽ in (B) of. Then, the pixel signal is temporarily stored in the buffer memory 40.

In this way, when the image signals for the first to fourth frames stored in the buffer memory 40 are synthesized so as to be interpolated by the digital video processing unit 42, finally, in the horizontal, vertical, and diagonal directions. Resolution 2
Doubled. That is, the same resolution as that obtained by the image pickup device having four times the number of images can be obtained ((B) in FIG. 6).
reference).

[0046]

As described in detail above, according to the present invention,
It is possible to provide a high-resolution image pickup device that can perform a simple and stable operation without reducing the amount of light incident on the image pickup surface and can statically change the displacement amount in multiple steps.

Therefore, a high-resolution (high-resolution) image pickup device can be obtained by using a low-resolution (small number of pixels) inexpensive image pickup element.

Further, instead of mechanically moving the optical system or the image pickup device, the image light can be electrically and statically shifted. Therefore, the structure is simple and the accuracy is high, and mechanical vibration, noise, etc. do not occur. In addition, the device can be downsized and the control is simple.

Furthermore, a conventional polarization filter (polarizer,
All of the incident light can be effectively used (the amount of light is improved by a factor of 2) as compared with a combination with an analyzer. Therefore, it is possible to minimize the setting of the shutter speed and the aperture and the deterioration of the S / N due to the decrease of the exposure amount.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a high resolution image pickup apparatus according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a configuration of an electro-optical element group,
(B) is a waveform diagram of a control signal (voltage) applied to the electro-optical element group, (C) is a schematic diagram for explaining the operation of the electro-optical element group when a voltage of V is applied, (D) [Fig. 3] is a schematic diagram for explaining the operation of the electro-optical element group when a voltage of 0 is applied.

FIG. 3A is a waveform diagram of a control signal (voltage) applied to the electro-optical element group according to the second embodiment of the present invention, and FIG.
Is a schematic diagram for explaining the operation of the electro-optical element group when a voltage is applied, (C) is a schematic diagram showing the orientation of the electro-optical element group when a voltage of V is applied, and (D) is It is a schematic diagram which shows the orientation of an electro-optical element group when a voltage of -V is applied.

4A and 4B are waveform diagrams of a control signal (voltage) applied to the electro-optical element group according to the third embodiment, and FIG. 4C is electro-optical when voltage is applied. Schematic diagram when viewed from the incident light for explaining the operation of the element group,
FIG. 3D is a schematic diagram for explaining the operation of the electro-optical element group when a voltage is applied, as viewed from the image pickup element.

5A is a diagram for explaining the resolution in the third embodiment, FIG. 5B is a diagram for explaining the resolution in the fourth embodiment, and FIG. 6 is a diagram for explaining the resolution in the embodiment of FIG.

FIG. 6A is a diagram showing an arrangement of electro-optical element groups in a sixth embodiment of the present invention, FIG. 6B is a diagram for explaining resolution in the sixth embodiment, C) is a waveform diagram of a control signal (voltage) applied to the electro-optical element group in the sixth example.

[Explanation of symbols]

20 ... Imaging device (CCD), 22, 24 ... Electro-optical device, 22a, 24a ... Nematic (N) liquid crystal, 26 ... Polarization plane rotating device, 26a ... TN liquid crystal, 28, 28a, 28
b ... Electro-optical element group, 30 ... LC driver.

Claims (3)

[Claims] 1. A pair of electro-optical elements capable of controlling the magnitude of birefringence according to an applied voltage, and a pair of electro-optical elements sandwiched between the pair of electro-optical elements, and a polarization plane of 9
A polarization plane rotating element for rotating by 0 °, an image pickup means for receiving a light beam through the pair of electro-optical elements and the polarization plane rotating element, and a birefringence characteristic of the pair of electro-optical elements. A high-resolution image pickup device, comprising: 2. The high-resolution imaging according to claim 1, wherein the voltage control unit controls the pair of electro-optical elements so that voltages having different polarities are applied for each imaging. apparatus. 3. A plurality of electro-optical means composed of the pair of electro-optical elements and the polarization plane rotating element are arranged so that the deviation directions of the outgoing light rays with respect to the incident light rays are different from each other. The high-resolution image pickup device according to claim 1.