JPS6398285A - Automatic focus device - Google Patents

Abstract

PURPOSE:To attain the focusing even to a horizontal stripe pattern and to realize a highly speedy automatic focus by providing a means to synchronize with a focus adjusting means and change an aperture position in the accumulating time of one frame and moving a lens to a focus adjusting position when a two-dimensional spatial frequency is the highest. CONSTITUTION:A moving aperture plate 2 to be able to synchronize with a focus adjustment and move an aperture position is provided. At the time of the position in which a lens 1 is located, a first exposure is executed at a certain position on a photoelectric converting surface 13. Next, the lens 1 is moved at a high speed up to certain step by a focus adjusting means 11. At this time, an instruction judgement means 9 instructs the effect to the means 11 and an aperture control means 10 and the aperture is dislocated to the position different from the above-mentioned and exposed. These actions are repeated several times and one frame of about 33 m-seconds is completed. This information is once accumulated to a frame memory 7. A discrete Fourier transformation of the part equivalent to the above-mentioned aperture is executed in the memory 7, the frequency component of respective aperture areas is analyzed by an area frequency analyzing means 8, an instruction/judgement means 9 instructs the means 11 to return to the focus adjusting position when the highest spatial frequency component is obtained and moves the lens 1 to a focusing position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device that automatically adjusts the focus of an imaging device such as a video camera.
- Prior Art In recent years, automatic focus devices have been required to automatically adjust the focus when the position of the subject is uncertain or when a camera is attached to a robot's hand.

An example of the above-mentioned conventional autofocus device will be described below with reference to the drawings.

FIG. 4 shows a functional block diagram of a conventional autofocus device. In FIG. 4, 22 is a lens. 23 is an image sensor that converts light into an electrical signal;
24 is a preamplifier for the electrical signal, and 26 is a horizontal signal superimposed on the electrical signal.

It separates the vertical synchronizing signal and converts it into a DC signal with a black level of zero, and 26 is an A/D converter that digitizes the DC signal. 27 is a bandpass filter that passes only a certain frequency band of the electrical signal output from the preamplifier, 28 is a peak detector that detects the peak level of the output, and 29 is a peak detector. This is a control circuit that controls the rotational direction and speed of the motor based on the output of the motor, and 3o is a motor that drives the lens once to bring it into focus.

The autofocus device configured as above will be explained.

First, an object forms an image on the image sensor 23 through the lens 22. The electrical signal containing the image information is sent to the preamplifier 2.
Amplified by 4. Then 21viHz ~ 3MHz
It passes through a bandpass filter 27 centered at
Do step 8. Now, if the image is not in focus, high frequencies among the frequency components output from the preamplifier 24 are not very strong, so the output of the peak detector 28 becomes small. Therefore, the control circuit 29 drives the motor 30 to perform focusing. If the direction of rotation of the motor 29 is wrong and the high frequency components are reduced, the motor 29 should be rotated in the opposite direction. Then, the motor 3o continues to be moved until the output of the peak detector 28 reaches the maximum, and the motor 3Q is stopped at the maximum point. At this time, focusing is completed, and the electric signal containing the current information of the subject is synchronously separated, passed through a DC reproduction 25, and digitized by an AD converter 26 for image processing.

Problems to be Solved by the Invention However, with the above configuration, the focus is adjusted by checking the frequency components of the electrical signal when scanning in the horizontal direction. If there is a horizontal striped pattern, there is a problem in that focusing is not possible at all. Therefore, as a method to enable focusing in such cases, an image for one frame is stored in a frame memory, and two-dimensional frequency analysis is performed based on this image to correspond to one frame. There is a method of focusing by knowing the frequency characteristics and repeating similar operations to compare frequencies. However, there are problems in that it takes at least 1/3 Q seconds to scan and store an image for one frame in a frame memory, and that focusing takes a long time, resulting in inefficiency.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an automatic focusing device that can detect changes in the vertical direction even if there are no changes in the horizontal direction, and perform focusing at high speed.

Means for Solving the Problems In order to solve the above problems, the automatic focusing device of the present invention has the following features:
Means for changing the aperture position in front of the imaging unit in synchronization with the focus adjustment means within the accumulation time of one frame, and two-dimensional frequency analysis of the images of each aperture area to determine which one contains the highest frequency component. and a means for returning focus adjustment to the position where the image was obtained.

The means for changing the position of the aperture on the front surface of the imaging section is constituted by a liquid crystal shutter provided on the front surface of the imaging section, which adapts patterns in which the shape, arrangement, and number of aperture areas vary depending on the shape of the subject, and is synchronized with the focus adjustment means. Preferably, the liquid crystal shutter is provided with means for changing its pattern.

Effect of the Invention With the above-described configuration, the present invention performs frequency analysis on the two-dimensional image to detect the highest frequency component in the two-dimensional aperture area, even if the subject does not change in the horizontal direction, such as a horizontal striped pattern. Since the focus adjustment position can be set to the obtained focus adjustment position, the above problem can be avoided compared to the conventional example in which only one-dimensional horizontal scanning frequency components are investigated, and multiple focus adjustments can be made within the accumulation time of one frame. It is fast because different images can be obtained and processed.

Furthermore, with the configuration described in claim 2, an aperture area suitable for any shape of the object can be formed arbitrarily using the liquid crystal shutter, so that the aperture can obtain a high two-dimensional spatial frequency component. can be adapted to perform high-speed autofocus independent of the subject.

EXAMPLE A first example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a functional block diagram of an automatic focusing device in a first embodiment of the present invention. In FIG. 1, 1 is a lens, and 2 is a movable aperture plate whose aperture position, shown later in FIG. 2, can be moved in synchronization with focus adjustment. 3 is an image sensor that converts light into an electrical signal (C); 4
is a preamplifier that amplifies the electrical signal with low noise.
6 is a synchronization separator and value current regenerator that separates the horizontal and vertical synchronization signals superimposed on the electrical signal and converts them into a DC signal with a black level of zero, and 6 samples and quantizes the DC signal. 7 is a frame memory that stores a digital image quantized on finite grid points within the image. Reference numeral 8 denotes a region frequency analysis means for determining the two-dimensional spatial frequency of each apertured region, and 9 a region frequency analysis means 8 which gives a command to move in synchronization with the aperture control and focus adjustment control. Determining and commanding means determines which region has the highest spatial frequency component based on the result and commands to return to the focusing position at that time, and 10 drives the movable aperture plate to complete focusing. 11 is an aperture control means that sometimes opens the front surface of the image sensor 3; 11 is a focus adjustment means that can move the lens 1 stepwise in the optical axis direction in synchronization with the aperture control; 12; is a motor that can move the lens 1 step by step in the direction of the optical axis at high speed. FIG. 2 is a detailed explanatory diagram of the movable aperture plate 2, where 13 is the photoelectric conversion surface of the image sensor, 14 is the barrier plate, and 16 is the barrier plate 1.
4 is an aperture formed at a specific position, and 16 is a slide drive mechanism that moves the aperture-equipped shielding plate 14 at high speed so that it can be opened at several specific positions on the photoelectric conversion surface 13 of the image sensor for a certain period of time. It is.

The operation of the automatic focus adjustment configured as described above will be described below with reference to FIGS. 1 and 2.

First, FIG. 2 shows a movable aperture plate, and when the lens 1 is at a certain position, the first exposure is performed at a certain position on the photoelectric conversion surface 13. Next, the lens 1 is moved rapidly along the optical axis to a certain stage by the focusing means 11. At this time, the command/control means 9 instructs the focus adjustment control means 11 and also the aperture control means 10 to shift the aperture to another position on the photoelectric conversion surface so as not to overlap with the first time. Exposure for a certain period of time. These operations are repeated several times to complete the accumulation time of one frame of about 33 msec. The electrical signals of the image accumulated by shifting the aperture while adjusting the focus are amplified through a preamplifier 4, further passed through a synchronous separation/DC regeneration 6, and then sampled and quantized by an A/D converter 6 to form a frame. It is temporarily stored in the memory 7. In the frame memory 7, a discrete 7-lier transform is first performed on the portion corresponding to which exposed aperture, and the frequency component of each aperture area is analyzed by the area frequency analysis means 8. Area frequency analysis means 8
Based on the results obtained by , the command determining means 9 commands the focus adjustment control means 11 to return to the focus adjustment position when the highest spatial frequency component is obtained. In response to this command, the focus adjustment control means 11 operates the motor 12 to move the lens 1 to a position where a focused image can be obtained. At this time, the second
The base plate 14 shown in the figure is moved by a slide mechanism 16 so as to open the photoelectric conversion surface 13 of the image sensor 3.

Also, the difference between the image with the highest frequency component and the images before and after it is checked, and if the difference is large, the range in which the lens 1 is moved is narrowed and the above operation is performed again to converge the focus.

As described above, according to this embodiment, by providing means for changing the aperture position in synchronization with the focus adjustment means within the accumulation time of one frame, the focus adjustment position when the highest two-dimensional spatial frequency can be obtained is obtained. By moving the lens, it is possible to focus even on subjects with horizontal stripes. Also, since the time required to accumulate while moving the lens is extremely small, the lens can be driven quickly, resulting in high-speed shooting. Automatic focus is possible.

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

FIG. 3 is a diagram showing a liquid crystal shutter portion of an automatic focusing device showing a second embodiment of the present invention. In the same figure, 17 is
The portion 18 blocked by the liquid crystal shutter is an elongated shape captured on the photoelectric conversion surface of the image sensor, and the numeral 19 similarly has a round shape. 20
is one area when a specific area of the liquid crystal display is opened, and 21 is the same, but the sizes of these areas may be different. This liquid crystal shutter is the first
It serves as a substitute for the movable aperture plate 2 of FIG. 1 explained in the embodiment, but its function is great.

The operation of the automatic focus adjustment device configured as described above will be described below. Focusing by changing the aperture position in synchronization with focus adjustment using the liquid crystal shutter is based on exactly the same principle as in the first embodiment, but the aperture of the liquid crystal shutter and the fact that it can be set to any area are utilized. For the elongated shape 18 as shown in FIG. 3(a), by moving the aperture in its longitudinal direction, an opening pattern is created in which the highest possible frequency component is obtained when the focal point is located. Adapt. Furthermore, for a round object 19 as shown by K in FIG. 3, a pattern in which openings are arranged on the circumference is provided to enable detection of high frequency components.

As described above, by changing the pattern of the aperture shape, number, arrangement, etc. according to the subject, it is possible to avoid obtaining a large aperture area, and to set as many aperture areas as possible at the edges of the shape. It is possible to increase the two-dimensional spatial frequency component.

Effects of the Invention As described above, according to the present invention, two-dimensional spatial frequency components are detected even when the subject has a horizontal striped pattern, so changes in the vertical direction can be investigated and focused. Due to the function of the means for changing the aperture position in front of the imaging unit, there is very little time to move the lens during the accumulation time, so the lens can be moved at high speed, resulting in high-speed focusing, which is very effective. It is something.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic focusing device according to a first embodiment of the present invention, FIG. 2 is a diagram explaining the movable aperture plate of FIG. 1 in detail, and FIG. 3 is a diagram of a second embodiment of the present invention. FIG. 4 is a block diagram of a conventional autofocus device. 1...lens, 2...movable aperture plate, 3
...Group/imaging device, 8... Area frequency analysis means, 9... Command/determination means, 10... Aperture control means, 11... Focus Adjustment control means, 2o
......Liquid crystal shutter opening area. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 figure
t-L Shimata 2-Town movement opening V Wolf

Claims (2)

[Claims] (1) A means for changing the aperture position in front of the imaging unit in synchronization with the focus adjustment means within the accumulation time of one frame, and a two-dimensional frequency analysis of the image of each aperture area to determine which one has the highest frequency component. An automatic focusing device comprising means for determining whether the image is contained, and means for returning focus adjustment to the position where the image was obtained. (2) The means for changing the aperture position on the front surface of the imaging section is composed of a liquid crystal shutter provided on the front surface of the imaging section, and the shape, arrangement, and number of aperture areas are adapted to different patterns depending on the shape of the subject, and the means for adjusting the focus is Claim 1, wherein means for changing the pattern in synchronization is attached to the liquid crystal shutter.
Autofocus device as described in section.