JPH0691601B2 - Image input device using solid-state image sensor - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an image input device using a solid-state image sensor in which the resolution of the solid-state image sensor is increased by optical image shifting.

(Background of the Invention) Conventionally, the resolution when an optical image is captured by a solid-state imaging device such as a CCD is determined by the number of pixels of the CCD. Therefore, in order to improve the resolution, it is conceivable to increase the degree of integration to increase the number of pixels, but in the case of CCD, it is necessary to make a light receiving part and a charge transfer part, so if the integration degree is increased, The area of one light receiving pixel is reduced, and the sensitivity is reduced.

As a method to solve this, C without changing the integration degree of CCD
A pitch corresponding to half the horizontal pixel pitch of the CD itself, that is, 1 /
A swing method has been proposed in which the resolution is doubled by mechanically moving by two pixel pitches.

That is, the CCD is placed on the two bimorph piezoelectric elements, the charge of the odd field is transferred at the reference position, and then the driving voltage is applied to the bimorph piezoelectric element to move the CCD by 1/2 pixel pitch from the reference position. Only horizontally,
After that, the electric charge is transferred in the even field, so that the number of pixels is equivalently increased to increase the resolution.

(Problems to be Solved by the Invention) However, in the method of mechanically swing-driving the solid-state image pickup device by the bimorph piezoelectric element, the solid-state image pickup element is provided on the bimorph piezoelectric element. There is a drawback in that the thickness is extremely increased as the size of the pixel and the amount of displacement by the bimorph piezoelectric element changes depending on the ambient temperature, so that there is a drawback in that the pixel cannot be accurately shifted.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and has a very simple structure because it has no mechanical drive portion and is not affected by external conditions. It is an object of the present invention to provide an image input device for a solid-state image pickup device, which optically realizes accurate pixel shift to increase the resolution of the solid-state image pickup device.

(Summary of the Invention) In order to achieve this object, in the present invention, focusing on the point that the incident light of a parallel plate crystal filter is separated by the direction of linearly polarized light, light from an image input medium such as a negative film is considered. Is alternately linearly polarized in two directions orthogonal to each other and is incident on the crystal filter, and is refracted by the crystal filter so as to be displaced by a half pitch of the light receiving pixel so as to be incident on the solid-state image sensor.

(Embodiment) FIG. 1 is an explanatory view showing an embodiment of the present invention, and shows an example of inputting a positive image from a film negative.

First, the configuration will be described. 1 is a solid-state image sensor in which light-receiving pixels are two-dimensionally arranged in a direction orthogonal to each other. For example, a CCD having a two-dimensional array can be used. Reference numeral 2 denotes a pixel shift unit that optically shifts pixels, and is configured by sequentially arranging a crystal filter 3, a liquid crystal 4, and a polarizing plate 5 from the solid-state image sensor 1 side.

6 is a projection lens, 7 is a negative film as an image input medium, 8 is a diffusion plate, and 9 is a light source.

Next, the principle for optically performing pixel shift with the crystal filter 3 provided in the pixel shift unit 2 will be described.

First, the birefringence of the crystal filter 3 will be described with reference to FIG.

In FIG. 2, 3 is a parallel plate crystal filter,
As shown in FIG. 2 (a), 10 is an optical axis determined by the crystal structure of quartz, and the optical axis 10 intersects the front and back entrance / exit surfaces at an angle θ, for example, θ = 45 °.

When a spot light 11 of natural light is made to enter the crystal filter 3 having an optical axis 10 having an angle θ with respect to such a light input / output surface perpendicularly from the front surface, the light passing through the crystal filter 3 has an opposite surface depending on the polarization direction. Is split into spot lights 12 and 13.

Here, the light that travels straight with respect to the incident light is called an ordinary ray, and light that is linearly polarized in the vertical direction appears in the illustrated state.
On the other hand, the light refracted with respect to the incident light is called an extraordinary ray, and light linearly polarized in the lateral direction comes out. Further, a separation width 1 of an ordinary ray that becomes vertically polarized light and an extraordinary ray that becomes horizontally polarized light when passing through the crystal filter 3 is proportional to the thickness D of the crystal filter 3.

Next, as shown in FIG. 2 (b), considering the spot light 14 that is linearly polarized in the vertical direction as incident light, in this case, since there is no component in the horizontal direction, no extraordinary ray appears, and an ordinary ray that travels straight. Only the spot light 14a comes out. Also, FIG. 2 (c)
Considering the spot light 15 that is linearly polarized in the horizontal direction as the incident light as shown in Fig. 5, in this case, the ordinary ray does not appear because there is no vertical component, only the spot light 15a refracted as an extraordinary ray. Come out.

By utilizing the separation action between the ordinary ray and the extraordinary ray in such a crystal filter, the thickness D of the crystal filter is set so that the separation width l of the ordinary ray and the extraordinary ray becomes half the pixel pitch of the fixed image pickup device. If a polarizing plate is disposed on the front surface of the crystal filter and the polarization of the light entering the crystal filter is controlled as shown in FIGS. 2 (b) and 2 (c), optical pixel shifting is possible.

As shown in FIGS. 2B and 2C, the crystal filter 3
A liquid crystal 4 and a polarizing plate 5 as shown in FIG. 1 are used as means for inputting light that has received linearly polarized light in the vertical direction and linearly polarized light in the horizontal direction.

That is, when a liquid crystal cell having a TN (Twisted Nematic) structure is used as the liquid crystal 4, the polarization direction of light entering the crystal filter 3 can be electrically controlled.

FIG. 3 shows the principle of pixel shifting using the polarizing plate 5 and the liquid crystal 4 having the TN structure.

First, FIG. 3 (a) shows a case where a drive voltage is applied to the liquid crystal 4, and natural light incident from the left side is linearly polarized in the vertical direction by the polarizing plate 5 and is incident on the liquid crystal 4 to which the drive voltage is applied. . The light that has received the linearly polarized light in the vertical direction is not polarized because the drive voltage is applied to the liquid crystal 4, passes through the liquid crystal 4 as it is, and enters the crystal filter 3. In this case, similarly to the case shown in FIG. 2B, the incident light goes straight on and goes out of the crystal filter 3.

On the other hand, as shown in FIG. 3B, when the drive voltage is not applied to the liquid crystal 4, the natural light incident from the left side is similarly linearly polarized in the vertical direction by the polarizing plate 5. Then liquid crystal 4
When entering, the light linearly polarized in the vertical direction is rotated by 90 degrees because no driving voltage is applied to the liquid crystal 4, and emerges as linearly polarized light in the horizontal direction. When the light linearly polarized in the lateral direction enters the crystal filter 3, the incident light is refracted in the lateral direction as in FIG.
Come out of.

Therefore, it is possible to optically shift the pixels with respect to the solid-state image sensor 1 by turning on and off the drive voltage of the liquid crystal 4.

FIG. 4 is an explanatory view schematically showing the light receiving surface of the solid-state imaging device 1, in which a plurality of light receiving pixels 1a shown by solid lines are two-dimensionally arranged in a direction orthogonal to each other. In addition, the light receiving pixel 1b indicated by the broken line
The portion is actually a charge transfer portion of each light receiving pixel 1a and does not have a function as a light receiving pixel.

However, in the present invention, since the pixel shift is performed by turning on / off the drive voltage applied to the liquid crystal 4 by a half pixel pitch of the light receiving pixel 1a, it is apparent that the light receiving pixel 1b is also at a position indicated by a broken line. Is equivalent to being provided.

FIG. 5 is a circuit block diagram showing a device configuration for extracting image information from a color negative film by using the image input device of the present invention for performing the optical pixel shift of FIG.

First, the structure will be described. Reference numeral 20 is a take-in switch for starting image recording, and 22 is a timing control section for controlling timing of each section. The drive control unit of the solid-state imaging device 1 uses the horizontal transfer and vertical transfer clocks φh and φv based on the vertical and horizontal synchronization signals from the synchronization signal generation unit 23.
There is provided a timing generation section 24 for generating the signal, a driver 26a and a ROM 26 for storing data for controlling the drivers 25a and 25b, and the timing generation section 24. A sample hold circuit 27, an auto iris control circuit 28, a low-pass filter 29 are provided as a processing system for the image information read from the solid-state image sensor 1.
And a signal processing circuit 30. An analog image signal for monitoring is taken out from the B / Wsig terminal 21 provided at the output of the signal processing circuit 30. Further, as a digital processing system of the image signal, an A / D converter 31 for converting the output of the sample hold circuit 27 into a digital signal, a ROM 32 for performing γ correction, and
A frame memory 33 that stores image information is provided for each PGB. Further, in order to reproduce the RGB image information recorded in the frame memory 33, D / A converters 34a to 34c and low pass filters 35a to 35c are provided, and further, RY, BY and Y signals for still video floppy. Matrix circuit for obtaining 3
6 and encoder 3 to get NTSC signal for video output
7 is provided.

Next, the image input operation according to the embodiment shown in FIG. 5 will be described.

First, the image is not recorded until the capture switch 20 is turned on, only the video operation is performed, the video signal from the B / Wsig terminal 21 is displayed on the monitor, and the negative film 7 is trimmed.

When trimming is decided, the capture switch 20 is turned on to record an image.

That is, when the acquisition switch 20 is turned on, the timing control unit 22
First, a driving voltage is applied to the liquid crystal 4, and at the same time, a red filter is inserted into the optical system. The insertion position of this red filter is either between the light source 9 and the diffusion plate 8 in FIG. 1 or between the negative film 7 and the projection lens 6.

Then, the auto iris by the auto iris control circuit 28
The amount of light is adjusted by the operation of 28a, and thereafter, digital recording of image information is performed by reading out odd fields.

In the digital recording by reading the odd field, the driving voltage is applied to the liquid crystal 4,
As shown in FIG. 3 (a), the light from the negative film 7 travels straight through the crystal filter 3 in the pixel shift section 2 and enters the solid-state image sensor 1, and the odd field (o The light-receiving signal obtained by the light-receiving element is recorded in the frame memory 33.

When the digital recording of this odd field (o) is completed, the drive voltage applied to the liquid crystal 4 is turned off, and as a result, as shown in FIG. The image is shifted by 1/2 pixel pitch in the horizontal operation direction. In this state, when digital recording is performed by reading from the even field (e) shown in FIG. 6, by shifting the pixel by 1/2 pixel pitch, the information of the light receiving position indicated by the shaded area in the even field (e) is obtained. The light-receiving pixels in the even field (e) are read.

Subsequently, a green filter is inserted into the optical system to perform similar digital recording of the odd field (o) and the even field (e), and a blue filter is further inserted to digitally record the odd field (o) and the even field (e). Make a record.

Next, regarding the reproduction of the image digital information for each RGB recorded in the frame memory 33, the signal of the even field (e) is spatially shifted by 1/2 pixel pitch from the signal of the odd field (o). Since it has a corresponding time shift, the correction of this time shift is corrected by the D / A converters 34a to 34a.
Do with c. Specifically, by inverting the phase of the continuous clock that determines the D / A conversion timing between the odd field (o) and the even field (e), there is a time shift, and the light reception shown by the shaded area in FIG. The image is reproduced with the spatial arrangement of information.

Therefore, the reproduced image from the frame memory 33 is about 2
It is obtained as a positive image with double the horizontal resolution. Although the above-mentioned embodiment has been described by taking the input device of the image information of the negative film as an example, the present invention is not limited to this, and when a still image or a subject image with slow movement is input as an image. It can be applied to high resolution as it is, and it can also be applied to electronic still cameras and VTR cameras using solid-state imaging devices.

Further, in the above embodiment, the crystal filter was taken as an example of the optical element for shifting the pixel, but not only the crystal filter but also an optical element having a similar optical shifting action, for example, a parallel plate filter made of calcite. May be.

(Effect of the Invention) As described above, according to the present invention, since the pixels are optically shifted, the mechanical configuration is not provided, the device configuration is simple, and the sensor unit can be made small. it can.

In addition, since the pixel shift amount is determined depending on the thickness of the crystal filter that performs optical pixel shift, the pixel shift amount is highly accurate and is not affected by ambient conditions such as temperature. The effect that the MTF of the captured image is also good is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of an optical system showing an embodiment of the present invention, FIG. 2 is an explanatory view of an optical action of a crystal filter used in the embodiment of FIG. 1, and FIG. 3 is a liquid crystal shown in FIG. FIG. 4 is an explanatory view of polarization control, FIG. 4 is an explanatory view of a light-receiving surface of a solid-state image pickup element schematically showing an action by optical pixel shift, and FIG. 5 is a circuit block diagram of a device for storing image information of a negative film. FIG. 6 is an explanatory view showing the image information obtained in the embodiment of FIG. 5 on a schematic light receiving surface of a solid-state image sensor. 1: Solid-state image sensor 2: Pixel shift part 3: Crystal filter 4: Liquid crystal 5: Polarizing plate 6: Projection lens 7: Negative film 8: Diffuser 9: Light source 20: Capture switch 21: B / Wsig terminal 22: Timing control 23: Sync signal generator 24: Timing generator 25a, 25b: Driver 26, 32: RPM 27: Sample and hold circuit 28: Auto iris control circuit 29, 35a to 35c: Low pass filter 30: Signal processing circuit 31: A / D Converter 33: Frame memory 34a to 34c: D / A converter 36: Matrix circuit 37: Encoder

Claims (1)

[Claims] 1. A solid-state image sensor in which light-receiving pixels are arranged two-dimensionally, a polarizing means for alternately linearly polarizing light from an image in two directions orthogonal to each other, and refraction of light from the polarizing means different depending on the polarization direction. An image input device using a solid-state image sensor, comprising: a refraction unit that shifts the light-receiving pixels by a half pitch and alternately enters the solid-state image sensor with a path.