JPH0983858A - Image pickup device and image pickup method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a 2-dimension spatial frequency limit characteristic being a variable and excellent characteristic with a simple configuration in the image pickup device. SOLUTION: An image pickup optical system 2 is moved by a lens drive means 8 so that a focal position of an object image varies with a prescribed range nearly around a photosensing face of an image pickup element 4 during exposure of the image pickup element 4. Thus, the 2-dimension spatial frequency characteristic with a low pass characteristic is obtained. The characteristic is used for the 2-dimension spatial frequency limit characteristic to eliminate loopback distortion.

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 still images and moving images using an image pickup element, and more particularly to removing aliasing distortion.

[0002]

2. Description of the Related Art In an image pickup apparatus using a solid-state image pickup element, a subject image formed on the image pickup element is spatially sampled by the image pickup element. For this reason, when a subject having a spatial frequency component equal to or higher than the Nyquist frequency determined by the number of pixels of the image pickup device is photographed, aliasing distortion occurs, and moire occurs in an image obtained from the image pickup device, which significantly deteriorates the image quality.

Conventionally, there has been proposed a method of optically reducing this by using an optical low pass filter. The optical low-pass filter is, for example, a filter that double-blurrs the subject image by using the birefringence effect of the crystal and limits the spatial frequency characteristic. By placing this between the image pickup optical system and the image pickup element, folding back is performed. The components are reduced to prevent the image quality from being deteriorated due to moire.

[0004]

However, in the conventional optical low-pass filter using a crystal or the like, the spatial frequency limiting characteristic is a characteristic represented by a COS function, so that the aliasing distortion can be completely removed. Absent. Further, in order to obtain the two-dimensional spatial frequency limiting characteristic, it is necessary to stack a plurality of quartz plates, which increases the thickness of the optical low pass filter and increases its cost.
Furthermore, when a plurality of spatial frequency limiting characteristics are obtained, it is difficult to change the characteristics instantaneously by only inserting and removing the optical low-pass filter for replacement, and there is a problem that the characteristics cannot be variously changed. The present invention overcomes the above-mentioned problems, has a simple structure, is variable, and has good characteristics.
An object of the present invention is to provide an imaging device that can obtain a dimensional spatial frequency limiting characteristic.

[0005]

In order to achieve the above object, in the present invention, an image pickup device is constructed as in the following (1) to (4) and an image pickup method is constructed in the following (5). To do.

(1) Photographing optical system, photographing means for photographing a subject image formed by the photographing optical system, and photographing optical system for moving at least a part of the photographing optical system in the optical axis direction of the photographing optical system. An image pickup apparatus comprising: a system moving unit; and a control unit that operates the photographing optical system moving unit during exposure of the image pickup device so that a desired spatial frequency limiting characteristic can be obtained.

(2) The photographic optical system moving means moves at least a part of the photographic optical system so that the in-focus position of the subject image changes within a predetermined range with the photosensitive surface of the image pickup device as the approximate center. The imaging device according to (1) above.

(3) A photographing optical system, an image pickup device for picking up a subject image formed by this photographing optical system, an image pickup device moving means for moving the image pickup device in its optical axis direction, and a desired spatial frequency. An image pickup apparatus comprising: a control unit that operates the image pickup device moving unit during exposure of the image pickup device so that a limiting characteristic can be obtained.

(4) The image pickup device moving means moves the image pickup device so that the in-focus position of the subject image changes within a predetermined range with the photosensitive surface of the image pickup device as a center. ) The imaging device described above.

(5) During the exposure of the image pickup device, the focus position of the object image is moved in the optical axis direction of the photosensitive face near the photosensitive face of the image pickup device so that a desired spatial frequency limiting characteristic can be obtained. Image pickup method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a video camera capable of capturing moving images, in the form of a video camera capable of capturing both moving images and still images, and an electronic still camera (also referred to as a still video camera) capable of capturing still images. Can be implemented in the form of.

The present invention will be described in detail below with reference to an embodiment of a video camera.

[0013]

【Example】

(Embodiment 1) FIG. 1 is a diagram showing a configuration of a main part of a "video camera" which is Embodiment 1.

In FIG. 1, reference numeral 1 is a subject, and 2 is a photographic optical system, which is composed of, for example, lenses 201, 202, 204 and a diaphragm 203. Reference numeral 3 is an infrared cut filter, and 4 is an image sensor. An infrared cut filter 3 removes unnecessary infrared light from the subject image formed by the photographing optical system 2, and forms an image on the image sensor 4. Reference numeral 5 is a signal processing circuit, 6 is a CPU, 7 is a low-pass control circuit, 8 is a lens driving means, and 9 is an AF (autofocus) control circuit. The output signal of the image sensor 4 is subjected to various processing by the signal processing circuit 5 to generate an image signal. The image signal is output to an output device such as a monitor (not shown) or a storage device such as a magnetic disk. In order to automatically focus on the subject, the AF control circuit 9 controls the lens driving means 8 composed of, for example, a motor based on the focus information, and moves the photographing optical system 2 in the optical axis direction. Therefore, the subject image is formed on the image sensor 4 in a focused state. The focus information can be calculated by, for example, a method of calculating from the high frequency component of the image signal, a method of calculating from the phase difference of the subject image that has passed through the pupil positions of different optical systems, or the like. The CPU 6 calculates the amount of movement of the optical system for obtaining a desired spatial frequency limiting characteristic from various information of the photographing optical system 2, for example, the value of the aperture and the sensitivity of the lens. The low-pass control circuit 7 controls the image sensor 4 during one exposure period.
Based on the calculated amount of movement, the lens driving means 8 is controlled to move the photographing optical system 2 in the optical axis direction to obtain a desired spatial frequency limiting characteristic.

2, 3 and 4 are views showing the principle of the present invention. When the photographic optical system 2 is at the position B, the point P of the subject is focused on the photosensitive surface of the image sensor 4 at the position B '. When the photographic optical system 2 is at the A or C position, the point P of the subject is imaged at the A'and C'positions, respectively, so that the photosensitive surface of the image sensor 4 is blurred.

For example, if the photographing optical system 2 is moved from the position A to the position B during one exposure period of the image pickup device 4,
The image of the point P formed on the image sensor 4 is represented by the sum of the image forming times at the respective positions of the moved photographing optical system 2. Therefore, for example, when the image pickup optical system 2 is moved at a constant speed, the point P forms an image on the image pickup element as shown in FIG. Therefore, the spatial frequency characteristic is obtained by Fourier transforming FIG. 3, and is as shown in FIG. Although FIG. 3 shows the one-dimensional direction on the image sensor for simplicity,
It is a dimension. Therefore, the obtained spatial frequency characteristic is also 2
It is a dimension.

The spatial frequency characteristic can be changed by changing the moving amount of the photographing optical system 2 or the moving speed thereof. In this embodiment, the spatial frequency characteristic thus obtained is used as the spatial frequency limiting characteristic for eliminating aliasing distortion.

Although the moving range of the photographing optical system 2 during the exposure period is arbitrary, in order to photograph the subject image in the image signal so as to be most focused, the focus position of the subject image is set to the image pickup element. It is desirable to move the photosensitive surface of No. 4 substantially forward and backward about the center.

The reason will be described with reference to FIGS.
When the photographing optical system 2 is at the position B, the point P of the subject is
An image is focused on the photosensitive surface of the image pickup device 4 at the position B '. When the photographic optical system 2 is moved from A to B, the image of the point P formed on the image pickup element 4 is represented by the sum of the image forming times at the respective positions of the moved photographic optical system 2. It becomes like the solid line of 6. At this time, it is slightly closer to the image pickup element 4 than the point P, that is, A ′ by the photographing optical system 2.
The image of the point N at the position where the image is formed at the midpoint between B and B ′ is shown in FIG.
It becomes like the dashed line. Therefore, in the image signal obtained from the output signal of the image pickup device 2, what appears to be most focused is an image of the point N on the photosensitive surface of the image pickup device 4 with a small spread. Therefore, the imaging optical system 2 is moved in the optical axis direction so that the in-focus position of the subject image is approximately in front of and behind the photosensitive surface of the image sensor 4, so that the desired subject is best focused. An image signal of the state is obtained.

In the structure of the image pickup apparatus shown in FIG.
Although the entire photographing optical system 2 is moved in the optical axis direction, a part of the photographing optical system 2 may be moved in the optical axis direction. In this case, the weight of the object to be moved becomes lighter,
The load on the lens driving means 8 is reduced and the power consumption can be reduced. It is also advantageous for downsizing. In addition, the shooting optical system 2
In addition to the single focus lens shown in the figure, a zoom lens can be used. In that case, the focus lens is moved.

As described above, according to this embodiment, it is possible to provide a video camera which can be varied with a simple structure and which can obtain a two-dimensional spatial frequency limiting characteristic with good characteristics.

Further, by making the moving means of the image pickup optical system common to the AF mechanism already mounted on the video camera as in the present embodiment, there are advantages such as simplification of the apparatus and reduction of the number of parts. .

(Embodiment 2) In Embodiment 1, the spatial frequency limiting characteristic is realized by moving the photographing optical system in the optical axis direction. However, as shown in FIG. It may be configured to move in the direction. This example will be described as a second embodiment. 7, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.
Reference numeral 10 is an image pickup device moving means including a motor or the like. The CPU 6 calculates the amount of movement of the image pickup device 4 to obtain a desired spatial frequency limiting characteristic from various information of the photographing optical system 2, such as aperture value and lens sensitivity. The low-pass control circuit 7 controls the image pickup device moving means 10 based on the calculated movement amount to move the image pickup device 4 in the optical axis direction during one exposure period of the image pickup device 4 to obtain a desired spatial frequency. Get the limiting property.

FIG. 8 is a diagram showing the principle of moving the image pickup device. By the photographic optical system 2, the point P of the subject
Is focused on the photosensitive surface of the image sensor 4 at the position B '. The photosensitive surface of the image sensor 4 is A'or C '.
In the position of, the image of the object point P is in a blurred state. Therefore, the two-dimensional spatial frequency limiting characteristic can be obtained as in the case where the photographing optical system 2 is moved. By thus moving the image pickup device 4, the spatial frequency limiting characteristic can be controlled independently of the AF control. Further, the image pickup device moving means 10 may be of any type. For example, if a piezoelectric device having a good response is used, the spatial frequency limiting characteristic can be changed at a higher speed.

In the present invention, the image pickup optical system is preferably a telecentric system in order to reduce the shift of the off-axis image forming point.

[0026]

As described above, according to the present invention,
A two-dimensional spatial frequency limiting characteristic with good characteristics can be obtained with a simple configuration, and image moire due to aliasing distortion can be significantly reduced, and image quality can be improved.

Further, the spatial frequency limiting characteristic can be arbitrarily changed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a first embodiment.

FIG. 2 is a diagram showing the principle of the present invention (No. 1)

FIG. 3 is a diagram showing the principle of the present invention (No. 2)

FIG. 4 is a diagram showing the principle of the present invention (No. 3)

FIG. 5 is a diagram (part 1) explaining an optimum movement range of a lens.

FIG. 6 is a diagram (part 2) explaining an optimum movement range of a lens.

FIG. 7 is a diagram showing a configuration of a second embodiment.

FIG. 8 is an explanatory view of a second embodiment.

[Explanation of symbols]

 1 subject 2 image pickup optical system 4 image pickup device 6 CPU 7 low-pass control circuit 8 lens driving means

Claims (5)

[Claims] 1. A photographing optical system, an image pickup means for photographing a subject image formed by the photographing optical system, and a photographing optical system for moving at least a part of the photographing optical system in an optical axis direction of the photographing optical system. An image pickup apparatus comprising: a moving unit and a control unit that operates the photographing optical system moving unit during exposure of the image pickup device so that a desired spatial frequency limiting characteristic can be obtained. 2. The photographic optical system moving means moves at least a part of the photographic optical system so that the focus position of the subject image changes within a predetermined range with the photosensitive surface of the image pickup device as a center. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is provided. 3. An image pickup optical system, an image pickup device for picking up a subject image formed by this image pickup optical system, an image pickup device moving means for moving the image pickup device in its optical axis direction, and a desired spatial frequency limit. An image pickup apparatus comprising: control means for operating the image pickup element moving means during exposure of the image pickup element so that characteristics can be obtained. 4. The image pickup device moving means moves the image pickup device so that a focus position of a subject image changes within a predetermined range with the photosensitive surface of the image pickup device as a center. The imaging device according to claim 3. 5. The focus position of the subject image is moved in the optical axis direction of the photosensitive surface near the photosensitive surface of the image sensor during exposure of the image sensor so that desired spatial frequency limiting characteristics can be obtained. An imaging method characterized by imaging.