JPH0463074A - Image shift type image pickup device - Google Patents

Abstract

PURPOSE:To improve the resolution in both of the horizontal direction and the vertical direction by constituting an optical system of a normal lens system, a polarizer, and two liquid crystal panels and crystal plates arranged at the rear of the polarizer and two-dimensionally shifting an image. CONSTITUTION:When the light going from an object toward an image sensor 5 passes first liquid crystal panel 31 and crystal plate 41 after passing a polarizer Z and having the direction of polarization uniformized in a certain direction, the optical path is shifted to the direction determined by the direction of the optical axis of the crystal plate by turning-on/off of the voltage applied to the liquid crystal panel. Next, the light passes second liquid crystal panel 32 and crystal plate 42. The optical path is shifted in the same manner. If directoions of optical axes of two crystal plates are shifted from each other by 90 deg., shift directions are different from each other by 90 deg. in the X direction. Consequently, thickness of crystal plates are so checked that the shift width in each direction is 1/2 of the picture element pitch of an image sensor, thereby improving the resolution two-dimensionally.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is an image sensor type imaging device ML using a solid-state image sensor used in a TV camera, an image scanner, etc., in which a subject image is captured on the image sensor. The present invention relates to a technique for capturing high-resolution images by shifting the pixel pitch by an integer of 2 or more.

[Prior art]

Solid-state image sensors (hereinafter referred to as image sensors) have characteristics such as small size and low power consumption, and are therefore widely used in TV cameras, image scanners, and the like. However, the resolution of the 400,000 pixel image sensor currently in practical use is considerably lower than that of an image pickup tube, and therefore higher resolution is desired.

Recently, 2 million pixel image sensors have been developed for HDTVs, but the resolution is still insufficient for use as input for printing manuscripts, etc., and even higher resolution is required. .

Conventionally, attempts have been made to increase the resolution by increasing the number of pixels as described above, but increasing the number of pixels requires increasing the chip size or reducing the pixel area. Among these, increasing the chip size lowers the manufacturing yield and increases costs, so attempts have been made to increase the resolution by exclusively reducing the pixel area. However, when the pixel area is reduced, the signal becomes smaller and the S/N ratio deteriorates. When this reduction in S/N is taken into account, the number of pixels of 2 million is already close to its limit, and it is currently difficult to further increase the number of pixels and improve resolution.

In order to overcome the above limitations in increasing resolution, methods have been devised to improve resolution without increasing the number of pixels. This method increases the spatial sampling area by temporally changing the relative positional relationship between the subject image and pixels for each field by 1/2 of the pixel pitch, and increases the resolution without increasing the number of pixels (hereinafter referred to as , image shift method).

Three methods have been proposed so far to implement the image shift method. The first method is to mount an image sensor on top of a piezoelectric element with an amplitude of 172 pixels pitch and 1 field per field, as described in the document ED736 (1986), Technical Report of the Television Society of Japan. This is a method of vibrating in the direction.

However, in this method, high-speed mechanical vibrations with a period of several tens of milliseconds (msec) are continuously applied to the image sensor, so there is a problem that the long-term reliability of the device is reduced. Furthermore, in addition to the drive system for the image sensor, a drive system for the piezoelectric element synchronized with the drive system for the piezoelectric element is required, making the structure complicated. Furthermore, since the image shift is in one direction, there is a problem in that the resolution can only be increased in one direction, either the horizontal direction or the vertical direction.

The second method is SID '83 Technical
As described in the document by Digest (1983), this method involves shaking a thin glass plate placed in front of the image sensor at a small angle to shift the subject image on the image sensor.

This method requires a complicated mechanical system to vibrate the glass plate at a minute angle, and also has the problem that high-speed vibration is difficult and the time required for imaging is long.

The third method, as described in Japanese Patent Application No. 63-204145, consists of adding an optical system to a normal lens system, a polarizer, a liquid crystal panel, and a quartz plate, and utilizes the birefringence effect of the quartz plate. This is the way to do it.

The principle of image shifting according to this third method is shown in FIG. In the fifth @, 4 is a crystal plate, and in this crystal plate 4, due to the birefringence effect, when the polarization direction is oriented in a specific direction, the transmitted light ray deviates from the extension line of the incident light ray, and If the polarization direction differs by 90 degrees from the light in which this shift occurs, there is no shift and the transmitted light ray travels on an extension of the incident light ray.The birefringence effect of such a crystal plate,
Furthermore, the image shift is realized by utilizing two physical phenomena: the polarization direction of light after passing through the liquid crystal depends on the presence or absence of an electric field in the liquid crystal. That is, the light from the subject is made to enter the polarizer after the lens, and only the light in a specific polarization direction is allowed to pass through. The polarization direction is such that the polarization direction can be rotated by 90 degrees by passing through the liquid crystal panel when no voltage is applied to the liquid crystal panel through which the light is subsequently passed. With this arrangement of the polarizer and the liquid crystal panel, it is possible to cause light whose polarization direction differs by 90° to be incident on the crystal plate depending on whether a voltage is applied to the liquid crystal panel or not. If two types of light with 906 different polarization directions are used, a difference will occur in the optical path after passing through the crystal plate 4 between the two types of light due to the above-mentioned birefringence effect of the crystal plate 4. Therefore, the position of the subject image formed on the image sensor is different.

In other words, in this type of image shift type image sensor, the voltage at both ends of the liquid crystal panel is turned ON or OFF, and the polarization direction of the light incident on the crystal plate 4 is changed by 90 degrees, so that the optical path after passing through the crystal plate is shifted in parallel. , performs an image shift. Therefore, image shifting can be performed electrically, and the image sensing device differs greatly from other types of image-shifting imaging devices in that it does not use any moving parts that require a complicated mechanical system.

As a result, the structure is simple, manufacturing is easy, and the cost is therefore low, making it the most practical method.

[Problem to be solved by the invention]

However, in the third method, the direction of image shift is either the horizontal direction or the vertical direction, so the improvement in resolution is also limited to one direction. It is possible to increase the definition of images as long as the human eye can see them.

However, in recent years, it has become increasingly common for machines, that is, computers, to view scanned images and perform various processing and judgments instead of humans. For example, in character recognition devices and factory inspection devices, a computer views images read by an image input device and performs various processes and judgments.

In such a case, the effect will be halved unless the image resolution is increased two-dimensionally. Therefore, in the third method, the resolution is improved only in one direction, which limits its use, and improving the resolution two-dimensionally is a future challenge.

The present invention has been made to solve the above problems.

An object of the present invention is to provide an image sensor type imaging device,
The object of the present invention is to provide a technology that can improve resolution two-dimensionally.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

In order to achieve the above object, the present invention includes an optical system that includes a polarizer, two liquid crystal panels arranged behind the polarizer, and two crystal plates in addition to a normal lens system. The method of arranging these optical components is to arrange the polarizer closest to the subject, followed by the liquid crystal panel, crystal plate, liquid crystal panel, and crystal plate in this order. These optical components may be placed anywhere along the optical path from the subject to the image sensor, and other components such as lenses may be inserted along the way. It is most desirable that the optical axis directions of the two crystal plates be shifted by 90'.

[Effect]

According to the above-mentioned means, in the configuration of the optical system, after the light traveling from the subject to the image sensor passes through the polarizer and the polarization direction is aligned in a certain direction, when it passes through the first liquid crystal panel and the crystal plate, The direction in which the optical path is determined by the optical axis direction of the crystal plate by turning on or off the voltage applied to the liquid crystal panel (
Shift in the X direction). Next, the light passes through the second liquid crystal panel and the crystal plate, but here as well, the optical path is shifted in the direction determined by the optical axis direction of the crystal plate by turning on or off the voltage applied to the liquid crystal panel. If the optical axis directions of the two crystal plates are shifted by, for example, 90 degrees, the shift direction here will be a direction (referred to as the Y direction) that is 90' different from the X direction.

By the above means, the voltage applied to the two liquid crystal panels is
It becomes possible to shift N10 F F independently.

As a result, two-dimensional high resolution can be achieved by selecting the thickness of the crystal plate so that the shift width in each direction is exactly 172, which is the pixel pitch of the image sensor.

[Example 1] Hereinafter, an example of the present invention will be specifically described using the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of an image sensor type imaging device of the present invention.

In Figure 1, 1 is a lens, 2 is a polarizer, 31 and 3
2 is a liquid crystal panel, 41 and 42 are crystal plates, 5 is a CCD sensor as an image sensor, 61 is a signal processing circuit, 6
2 is a driving circuit for the CCD sensor and the liquid crystal panel; 14 is an image signal storage section; and 15 is an address control section for the image signal storage section.

The image sensor type imaging device of Example 1 uses a commercially available CCD camera, and as shown in FIG. 1, a polarizer 2 is arranged in front of a lens 1 of the CCD camera.
Two sets of liquid crystal panels 3 are placed between the lens 1 and the CCD sensor 5.
1 and a crystal plate 41, and a liquid crystal panel 32 and a crystal plate 42 are arranged. The liquid crystal panels 31 and 32 are driven by drive pulses from a drive circuit 62 provided in the camera body.

Here, the CCD sensor 5 used in the CCD camera
is an interline type CCD sensor with approximately 420,000 pixels and a pixel pitch of 11 μm.

Further, the liquid crystal used in the liquid crystal panels 31 and 32 was of a twisted nematic type. In this type of liquid crystal, when the applied voltage is ON, the long axis of the molecules of the liquid crystal is aligned in the electric field direction (Z-axis direction), so that incident light passes through without changing the polarization direction.

On the other hand, when the applied voltage is OFF, the electric field in the liquid crystal disappears, the liquid crystal molecules are arranged in a twisted manner with the long axis twisted by 90', and the polarization direction of the light passing through the liquid crystal panel changes by 90'.

The crystal plates 41 and 42 were those in which the angle (direction angle) between the optical axis and the polished surface was 45 degrees, and the plate thickness was 0 degrees and 9 mm.

With the crystal plates 41 and 42 having this thickness, the optical path difference of the transmitted light due to the difference in the polarization direction of the incident light is 5.5 μm, which is exactly 1/2 of the pixel pitch of the CCD sensor 5 used in the first embodiment. The optical axes of the two crystal plates 41 and 42 are such that light whose polarization direction is in the X direction (direction perpendicular to the plane of the paper in FIG. 1) travels straight as ordinary rays. Therefore, light whose polarization direction is in the Y direction (vertical direction in Fig. 1) becomes an extraordinary ray, and its optical path is shifted by passing through the crystal plates 41 and 42, but this shift direction is the crystal plate on the lens side (
The first crystal plate) 41 is set in the X direction (the front direction in Figure 2), and the crystal plate (second crystal plate) 4 is located on the CCD sensor 5 side.
2, the arrangement direction of the two crystal plates 41° and 42 was determined so as to be in the Y direction (downward in FIG. 2).

In the first embodiment, a method of shifting an image and reading a high-definition image using the optical system will be described with reference to FIG.

In FIG. 2 (,), 7 is the optical path of the light emitted from one point of the subject until it enters the crystal plate 41, 71.72 is the optical path of the light after passing through the first crystal plate 41, and 73 ,74
, 75 and 76 are the optical paths of the light after passing through the second crystal plate 42.

In Fig. 2(a), a polarizer 2 placed in front of the lens
Although omitted, the arrangement is such that only light whose polarization direction is in the X direction shown in FIG. 2 passes through.

FIG. 2(b) is a timing chart showing the timing of voltages applied to each liquid crystal panel 31, 32. Here, vl and V2 indicate voltages applied to the first and second liquid crystal panels 31 and 32, respectively.

In the first embodiment, four frames (or fields,
(omitted below) to import one image. First, in the first frame, both vl and ■2 are turned ON. ■1 is O
When N, the polarization direction does not change when passing through the first liquid crystal panel 31, so the light polarized in the X direction passes through the first crystal plate 4.
1 and no shift of the optical path occurs. That is, it proceeds along the optical path 71 shown in FIG. 2(a). Furthermore, v2 is also O
Since the polarization direction is N, the polarization direction does not change even when passing through the second liquid crystal panel 32, so the light polarized in the X direction passes through the second crystal plate 42, and no shift of the optical path occurs. That is, the second
It travels along the optical path 73 shown in FIG. 7(a) and reaches point A on the surface of the CCD sensor 5.

Next, in the second frame, v2 is turned off while vl remains on. In this case, the optical path does not shift in the first crystal plate 41 as in the first frame. However, the polarization direction changes to the Y direction when passing through the second liquid crystal panel, and the optical path shifts in the horizontal direction when passing through the second crystal plate 42. Then, it reaches point B, which is 55 μm away from point A in the horizontal direction.

Next, in the third frame, Vl is turned OFF.

Turn on v2. In this case, the first liquid crystal panel 32
The polarization direction changes to the Y direction by passing through the first crystal plate 41.
The passage of the light causes a downward shift of the optical path. That is,
It proceeds along the optical path 72 shown in FIG. 2(a). Next, v2
is ON, the polarization direction does not change when passing through the second liquid crystal panel 32, so the light polarized in the Y direction passes through the second crystal plate 42, causing a horizontal shift of the light. That is, it travels along the optical path 75 shown in FIG.
The point 0 is reached on the surface of the CD sensor 5 at a distance of 0.55 μm downward from point B.

Next, in the fourth frame, both vl and v2 are OF
Make it F. In this case, as in the third frame, the polarization direction changes to the Y direction when the light passes through the first liquid crystal panel 31, and the optical path shifts downward when it passes through the first crystal plate 41. That is, it proceeds along the optical path 72 shown in FIG. 2(a).

Next, since v2 is OFF, the polarization direction is rotated by 90 degrees by passing through the second liquid crystal panel, and returns to the X direction again. Therefore, the polarization direction does not shift when the light passes through the second crystal plate 42. That is, it travels along the optical path 76 shown in FIG.
．． It reaches point D, which is 55 μm away.

The above description has been about one light path emitted from one point on the object, but the light emitted from all points on the object is shifted in the same way, and eventually the entire image is shifted sequentially as described above.

FIG. 3 shows how the subject image shifts on the CCD sensor 5 for each frame.

In Fig. 3, 8 is a pixel, 9 is a photosensitive part, 10 is the subject image in the first frame, 11 is the subject image in the second frame, 12 is the subject image in the third frame, and 13 is the subject image in the fourth frame. The image of the subject is shown. In FIG. 3, the pixels 8 arranged two-dimensionally are numbered in the format (II j) for convenience.

As shown in Figure 3, from the first frame to the second frame, the position of the subject image shifts to the left by 1/2 of the pixel pitch, and from the second frame to the third frame, the position of the subject image shifts to the left by 1/2 of the pixel pitch. Furthermore, from the third frame to the fourth frame, it is shifted to the right by 1/2 of the pixel pitch, and then returns to the original position again in the next first frame. In this way, the pixel pitch is 1 for each frame.
A subject image shifted by /2 can be captured, and an image shift type imaging device can be realized.

In this way, the image is read while shifting 4
We will explain how to synthesize a high-definition image from multiple images.

Here, the image signal storage section 14 (FIG. 1) has addresses four times as many as the number of pixels of the CCD sensor 5, and each address has an 8-bit capacity corresponding to 256 gradations.

First, in accumulating the image signal read in the first frame, the signal read by the (xpj) pixel 8 of the CCD sensor 5 is stored in (2i-1, 2j) of the memory of the image signal accumulation section 14.
-1) Accumulate at address.

Next, in the case of the second frame, the CCD sensor 5 (it
The signal read by the pixel 8 of J) is stored in the image signal storage section 14.
The data is stored at address (2i-1, 2j) in the memory of

In the case of the third frame, the signal read by the (1°j) pixel 8 of the CCD sensor 5 is stored at address (2x*2j) in the memory of the image signal storage section 14.

Furthermore, in the case of the fourth frame, (i,
The signal read by the pixel 8 of pixel 8 of pixel 8 is accumulated at address (2i, 2j-1) of the memory of the image signal accumulation section 14.

The above address designation is performed by the address control section 15. When outputting the image signal accumulated in this way to a display or recording device, it can be output as a single high-definition image by reading it out in the order of the addresses in the memory. It is possible to do so.

[Embodiment 2] FIG. 4 is a block diagram showing a schematic configuration of Embodiment 2 of the image sensor type imaging device of the present invention.

In FIG. 4, parts having the same functions as those in FIG.

As shown in FIG. 4, the image sensor type imaging device according to the second embodiment includes multiple frame memories 16 to 19 in the image signal storage section 14 according to the first embodiment. That is, the configuration of the optical system and the method of image shifting are the same as in the first embodiment.

In this embodiment, images read in four frames are stored in four frame memories 16 to 19.

That is, the image signal read in the first frame is stored in the frame memory 16, the image signal read in the second frame is stored in the frame memory 17, and the image signal read in the third frame is stored in the frame memory 19. do. and,
When outputting to a display or a recording device, the image signals are sequentially read out while switching the frame memory read out every other pixel according to instructions from the address control unit 15, thereby outputting one high-definition image.

The present invention has been specifically explained above based on examples, but
It goes without saying that the present invention is not limited to the above embodiments, and can be modified in various ways without departing from the spirit thereof.

For example, in the above embodiment, the polarizer is placed in front of the lens, but it can also be placed between the lens and the first liquid crystal panel. Furthermore, in this example.

Although a quartz plate was used as a material having a birefringence effect, any transparent plate having a birefringence effect can be used regardless of its type. Furthermore, the 0N10FF combinations of voltages v1 and v2 applied to the 52 sets of liquid crystal panels can be implemented by performing the four combinations in any order.

〔Effect of the invention〕

As described above, according to the present invention, since image shifting can be performed two-dimensionally, resolution can be increased in both the horizontal and vertical directions.

Furthermore, since this image shift can be performed electrically, it is possible to eliminate moving parts, improve reliability, and eliminate mechanical vibration noise.

Furthermore, the parts used are simple and inexpensive parts such as polarizers, liquid crystal panels, and crystal plates, and the size is 1~2A++ when used immediately after the lens.
Because it can be made small, it can be stored inside a regular camera, making it possible to create a compact and inexpensive high-definition image input device.

Furthermore, in devices that use multiple image sensors that share one lens, such as a three-lens camera, the conventional method of mechanically vibrating the image sensor itself requires the installation of a driving element for each image sensor. However, in the present invention, images on all image sensors can be shifted by simply installing one set in the optical path before division, such as immediately after the lens.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of an image sensor type imaging device of the present invention. FIG. 2 is a diagram for explaining the principle of a method of shifting images and reading high-definition images. FIG. 3 is a schematic diagram showing how a subject image shifts on an image sensor, FIG. 4 is a block diagram showing a schematic configuration of a second embodiment of an image sensor type imaging device of the present invention, and FIG. This is a diagram for explaining the principle of image shift due to birefringence phenomenon.6 In the diagram, 1...lens, 2...polarizer, 31, 32...
・Liquid crystal panel, 41.42...Crystal plate, 5...Image (CCD) sensor, 61...Signal processing port/path, 6
2... Image sensor and liquid crystal panel drive circuit,
7... Optical path of light emitted from a certain point on the subject until it enters the crystal plate, 71.72... Optical path of light after passing through the first crystal plate, 73, 74, 75, 76... - Optical path of light after passing through the second crystal plate, 8...pixel, 9...photosensitive section,
10... Subject image in the first frame, 11... Second frame
Subject image in frame, 12... Subject image in third frame, 13... Subject image in fourth frame, 14...
. . . Image signal storage unit, 15 . . . Address control unit of the image signal storage unit, 16, 17, 18, 19 . . . Frame memory. Figure 1 v2 Figure 2 (a) (b) Figure 4 Figure 3 r-ゝ-1

Claims (1)

[Claims] In an image shift type imaging device that increases resolution by an image shift operation that temporally changes the relative positional relationship between the subject image and pixels on a solid-state image sensor, the polarization direction is specified in the optical system from the subject to the solid-state image sensor. A polarizer that allows light to pass in only one direction, and two liquid crystal panels that can rotate the polarization direction of the transmitted light by applying or blocking a voltage.When the incident light is polarized in a specific direction, the transmitted light A two-dimensional image shift is performed by providing two transparent plates having a birefringence effect that causes a deviation from the extension line of incident light, and means for applying or cutting off a driving voltage to the two liquid crystal panels. An image shift type imaging device characterized by: