JPH01160263A - Automatic focusing device for video camera - Google Patents

Abstract

PURPOSE:To reduce the time of a focusing device controlled remarkably by an erroneous signal by detecting the moving quantity of a camera or an object by means of two-dimensional correlation operation between two fields, discriminating the degree of the reliability depending on the quantity of detection and not using the focus when the reliability thereof is low. CONSTITUTION:The correlation operation of a correlation arithmetic unit 22 is executed for lots of number of times while deviating a data corresponding to the midpoint of the pattern among data stored in the 1st storage device 20 and the position of the midpoint of the pattern stored in the 2nd storage device little by little. A microcomputer 11 finds out the correlation value having a maximum value among lots of correlation values to be read, obtains the deviated quantity between two sets of data when the correlation is calculated to operate it as the quantity of an object moved on the pattern from the preceding field till this field, that is, the object moving quantity. If the the object moving quantity is extremely large, the quantity is not used for the control of a motor 4. Furthermore, if the correlation value does not reach a prescribed value, the value is not used to control the motor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focus adjustment device for a video camera, and in particular drives a lens so that the high frequency component of a video signal obtained from an image sensor is maximized. The present invention relates to an automatic focus adjustment device.

2. Prior Art As an example of the prior art of the above-mentioned autofocus device for a video camera, the "
A method known as the "mountain climbing method" is known. In this method, the focusing device is first driven in one direction and the resulting increase or decrease in the high frequency components of the video signal is detected.
The configuration is such that the focus adjustment device is further driven in the same direction if the number increases, and in the opposite direction if the number decreases.

Normally, a motor is used as the drive device to drive this focus, but since the response speed of the motor is slow, there is also a method that uses a piezo element to detect the focus direction and a motor to drive the focus. It is being

In other words, this uses a piezo element with a fast response speed to shorten the time required for direction detection.

The configuration of a conventional automatic focus adjustment device using this piezo element will be explained using the block diagram of FIG. Reference numeral 1 denotes an imaging lens, and a focus adjustment motor 4 is attached to the front group of this lens. By driving this motor 4, the focus of the image of the imaging lens l formed on the light receiving surface of the image sensor 2 is adjusted. do.

Further, this motor 4 is connected to a microcombinator 11 via a motor drive circuit 13, so that it can be freely controlled by the microcombinator 111.

The image sensor 2 has a structure supported by a piezo vibrator 5, and when the piezo vibrator 5 vibrates, it vibrates in the optical axis direction on the imaging plane of the image pickup lens 1.

This piezo vibrator 5 is connected to a microcomputer 11 via a piezo driver 12.

On the other hand, the video signal obtained from the image sensor 2 is processed by the video camera circuit 3, and the obtained luminance signal is supplied to the bypass filter 6. Furthermore, the video camera circuit 3
, a vertical synchronization signal and a horizontal synchronization signal synchronized with the scanning of the image sensor 2 are supplied to the micro combi coater 11 . The luminance signal supplied to the bypass filter 6 passes only the high frequency component and is supplied to the detector 7, where it is rectified and detected. The signal rectified by the detector 7 is supplied to the angle of view gate 8, where only the effective component in the detection area at the center of the screen passes through and is transmitted to the integrator 9. Here, a control signal for opening and closing the view angle gate 8 is supplied from a microcomputer 11.

A reset signal is supplied to the integrator 9 at the beginning of each field. Therefore, the integrator 9 integrates the high frequency component at the center of the screen during the l field. The output of the integrator 9 is a signal that increases or decreases depending on the degree of focus, and is called a focal amount. This focal amount is supplied to the AD converter 10,
At the end of each field, the data is AD converted and read into the microcomputer 11.

FIG. 4 is a graph of the focal amount for a typical subject, with the vertical axis representing the focal amount and the horizontal axis representing the amount of displacement from the in-focus position. Here, 27 is the focal amount curve;
28, 30, and 32 show the displacement due to vibration of the piezo element 5, and 29, 31, and 33 are graphs showing how the focal amount changes due to the vibration. 2 of these
8.29 is a graph when the focus adjustment device is far out of focus, 30.31 is a graph almost at focus, 3
2.33 is a graph when moving out of focus in the opposite direction. From this graph, it can be understood that the phase of the fluctuation component of the focal amount due to the vibration of the piezo element changes depending on the direction of deviation from the focal point. Here, the microcomputer 11 calculates the phase of the variable component from the read focus amount, detects the focusing direction from the phase, and drives the focusing system such as the motor 4 in the detected direction.

Problems to be Solved by the Invention However, in the conventional automatic focusing device having such a configuration, since focus is determined only by increasing/decreasing the focal amount, it is difficult to determine the focus by driving the focusing device such as the piezo element 5 or the motor 4. It is important to distinguish between fluctuations in focus and fluctuations in focus caused by other causes, such as changes in the position of the subject relative to the video camera, such as when the video camera is moved or the subject moves during recording. This has the disadvantage of causing malfunctions as it is used directly to determine the focus direction.

Normally, in order to eliminate this drawback, if the fluctuation in the amount of focus is extremely large and cannot be considered to be due to the drive of the piezo element or motor, it is determined that the fluctuation is due to a change in the subject itself, as described above, and the Countermeasures have been taken, such as stopping the focusing device and waiting until the change in the amount of focus becomes small.

However, such a measure can only be used when the fluctuation in the amount of focus is extremely large, and is not a measure that can sufficiently solve the problem. Furthermore, with this measure, the focusing device is stopped during the period when a malfunction is expected as described above, resulting in a new drawback that the response speed is slow.

The present invention was developed in view of these drawbacks, and it does not malfunction even when there is a change in the subject itself, such as movement of the camera or subject, and furthermore, it does not cause any sacrifice in response speed. The purpose is to provide an automatic focus adjustment device that does not require any automatic focusing.

Means for Solving the Problems The present invention includes a binarizer that samples a video signal and binarizes it with an appropriate threshold value, and a binarizer that samples the video signal and binarizes the binarized data while keeping timing with the horizontal and vertical synchronizing signals supplied from the camera circuit. a first storage device that arranges and stores the data two-dimensionally; a second storage device that stores this data until the next field;
A correlation calculator uses the data in these two storage devices as a human input signal, and a large number of correlation values obtained from this correlation calculation are read and determined to control the focus amount detection device, and focus adjustment is performed based on the obtained focus amount. This is an automatic focus adjustment device that is comprised of a microcomputer that controls the device.

Here, the focus amount detection device includes an AD converter that receives a high frequency component of a video signal and converts it into a digital signal, a third storage device that stores the digital signal, and a direct signal from the AD converter and a third storage device. It consists of an absolute value calculator which receives both signals from the absolute value calculator as input signals, and an adder which adds the signals from the absolute value calculator and outputs the result to the computer.

In the present invention, by obtaining and storing binary images of two frames and performing a correlation calculation between the two images, the degree of correlation between frames and the amount of movement of the camera or subject are determined. Since the reliability of the focusing signal is determined in real time based on the degree of correlation and the magnitude of the amount of movement, it is possible to significantly reduce the chance of malfunction in controlling the focus adjustment device.

In addition, in the present invention, as described above, the amount of movement of the camera or the subject can be obtained by the correlation calculation, a new detection inclination/area corrected by the amount of movement is set, and the new area is stored in the data. By applying this method, the focal amount can be detected even in that new area. The amount of focus obtained from the corrected disconnection detection area can eliminate the effects of subject movement, making it possible to determine correct focus even when the camera or subject is moving, significantly improving response speed. be done.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. 1st
The figure is a block diagram showing one embodiment of the present invention. Here, among the elements in the figure, the elements common to those of the prior art shown in FIG. 3 are given the same numbers, and the explanation thereof will be omitted. The difference in configuration from the conventional technology is that the AD converter 14 and below, which process the output signal of the bypass filter 6, have been changed, and the video signal output from the video camera circuit 3 has been newly installed in addition to the bypass filter 6. It is also supplied to the band-pass filter 18, and each element necessary to execute the following correlation calculation is added.

The high frequency component of the video signal output from the bypass filter 6 is AD converted by the AD converter 14, one of which is input to the adder 17 through the absolute value calculator 15, and the other is supplied to the third storage device 16 and stored therein. Ru.

This absolute value calculator 15 corresponds to the detector 7 in the prior art shown in FIG. 3, and functions to obtain an absolute value from positive and negative data input from the AD converter 14. Adder 17
corresponds to the integrator 9 in the prior art, and functions to perform addition operations on signals within the detection area among the signals output from the absolute value calculator 15, and to integrate high frequency components within the area.

These two elements, the absolute value calculator 15 and the adder 17, are
Two types of operations are performed: one is to operate in real time every time a signal is output from the AD converter 14, and the other is to process data stored in the third storage device 16 during idle time of the real-time operation. When operating in real time, calculations are performed on data in a fixed area at the center of the screen, and when data from the latter storage device 16 is supplied and operating, the detection area is newly set, and the data in the new detection area is calculated. only are calculated. Control of each of these elements is performed by outputting control signals from the microcomputer 11 to each element. In this way, two types of focal amounts having different detection areas for each field are output from the adder 17 and read into the microcomputer 11.

On the other hand, the video signal output from the video camera circuit 3 is also supplied to the bandpass filter 18, and in this bandpass filter 18, only the frequency components in the intermediate range of the signals included in the video signal are passed to the next stage binarizer. 19. The reason why this bandpass filter 18 is used is as follows.
If the signal used for correlation calculation contains a high frequency component, it will increase or decrease sensitively due to the movement of the focus adjustment device and the degree of correlation will decrease, so errors may occur in the calculation of the amount of movement of the subject performed using this correlation value. This is because

The signal input to the binarizer 19 is sampled at an appropriate sampling period, further binarized using an appropriate threshold value, and converted into a binary signal. This sampling frequency is
Usually, a frequency approximately twice the high-frequency cutoff frequency of the bandpass filter is selected, which is approximately I MHz. The time-series binary signal output from the binarizer 19 is input to the first storage device 20, synchronized by the control signal output from the microcomputer 11, and is displayed two-dimensionally like a video screen. placed and stored. The data stored in this first storage device 20 is stored in the correlation calculator 2
After that, only the data corresponding to the center part of the screen is transferred to the second storage device 21 and stored therein until the data of the next field is entered manually.

Here, the correlation calculation of the correlation calculation unit 22 is performed by the first storage device 2.
0, the data stored in the second storage device 21 corresponding to the center part of the screen and the data stored in the second storage device 21 are treated as data having a two-dimensional distribution. This is repeated a number of times while gradually shifting the position of the central portion of the screen stored in the second storage device 21. FIG. 2 is a diagram explaining the operation of the correlation calculator 22, where 23 represents the binary data of the current field stored in the first storage device 20 as having a two-dimensional distribution, and 24 .25 and 26 represent the binary data in the previous field stored in the second storage device 21 as having the same two-dimensional distribution.

In FIG. 2, 24 indicates the most shifted field of the correlation calculations performed a large number of times, 25 is the field at the reference position, and 26 is the field when the most shifted to the opposite side. As shown in the figure, this correlation calculation is repeated many times starting with the data in the second storage device placed at position 24 in the figure, little by little in the vertical and horizontal directions from 25 to 26. Further, this correlation calculation is performed during free time in each field, and as a result, a set of correlation data consisting of a large number of correlation values is output for each field and read into the microcomputer 11.

The microcomputer 11 finds the correlation value with the largest value from among the many read correlation values, and calculates the amount of shift between the two sets of data when that correlation value is calculated. This is calculated as the amount by which the subject moved on the screen between the previous field and the current field, that is, the amount of subject movement. Here, if the amount of movement of the subject is extremely large, it is thought that the subject or camera moved at a very fast speed, and the motor 4
It is not used for control. Also, when the correlation value does not reach a predetermined value, the correlation between the two compared screens is small.
At this time as well, the focal amount obtained from the adder 17 is not used for controlling the motor 4 because the reliability is low.

Next, if the correlation value is greater than a predetermined value and the amount of subject movement is not extremely large in the above case, but exceeds the predetermined value, the focus amount output from the adder 17 in real time is Assuming that the influence of movement is large, the third storage device 16, absolute value calculator 15, and adder 17 are newly activated to detect the focal amount again. At this time, micro combination tool - evening 1
1 sets a new detection area corrected by the amount of movement of the subject and outputs it to the adder 17 in the form of a control signal for control. At this time, the adder 17 detects the correct focal amount in which the amount of movement of the subject, that is, the movement of the camera or the subject is corrected.

Effects of the Invention In the present invention, the movement and amount of the camera and subject are detected by two-dimensional correlation calculation between two fields, and the degree of reliability is determined based on the magnitude of the detection result, and the focus amount when reliability is low is determined. Take measures to control it so that it is not used. Compared to conventional methods, this method is less affected by the condition of the subject or the focus adjustment device and can be detected at all times, which greatly reduces the time the focus adjustment device is controlled by incorrect signals and reduces malfunctions. Furthermore, if the amount of movement is small and the reliability is high, it becomes possible to immediately return to normal control, so the response speed can also be significantly improved.

Furthermore, the amount of movement of the camera or subject can be detected in real time, the detection area can be changed by the amount of movement, and the focus amount can be detected again, making it possible to determine the correct focusing direction. However, it has become possible to control the focus adjustment device, and the response speed has been greatly improved, which has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an automatic focus adjustment device for a video camera according to the present invention, and FIG.
Graph diagram explaining the operation of the correlation calculator shown in 2, 3rd
The figure is a block diagram of a conventional automatic focus adjustment device for a video camera, and FIG. 4 is an explanatory diagram of the operation of the conventional example. DESCRIPTION OF SYMBOLS 1...Photographing lens, 2...Imaging element, 3...Video camera circuit 4...Motor, 6...Bypass filter, 11...Microcombinator 13...Piezo driver, 15 ...Absolute value calculator, 16...Third storage device, 20...First storage device, 21...Second storage device, 22...Correlation calculator. Figure 4

Claims (4)

[Claims] (1) By varying the optical path length between the imaging lens and the imaging element disposed on its imaging plane, and detecting the high frequency component of the effective part at the center of the screen of the video signal obtained from the imaging element, In an automatic focus adjustment device for a video camera that drives a focus adjustment device that determines a focusing direction based on a direction of variation in optical path length and an increase or decrease in a detected high-frequency component, the video signal is binarized using an appropriate threshold value. a first storage device that arranges and stores the binarized time series data two-dimensionally, and a second storage device that stores the stored data up to the next field. A two-dimensional correlation operation between the binarized data of the previous field stored in the second storage device and the binarized data of the current field stored in the first storage device is performed between the two sets of data. A large number of correlation values are obtained by performing the experiment many times while shifting the relative positions of the As the reliability of the obtained focusing direction is low,
An automatic focus adjustment device for a video camera, characterized in that the automatic focus adjustment device is excluded from a control signal of the focus adjustment device. (2) The displacement between the position where the maximum correlation value is obtained among the many calculated correlation values and the reference position is defined as the amount of movement of the subject on the imaging plane, and this calculated amount of movement is determined as a predetermined amount. When the value is larger than the above value, the reliability of the determination of the focusing direction obtained from the increase/decrease of the high frequency component is considered to be low, and it is excluded from the control signal of the focus adjustment device. Automatic focus adjustment device for video cameras. (3) Move the detection area for detecting the high frequency component of the video signal by the calculated amount of movement of the subject, detect a new high frequency component in the set area, and detect the newly detected high frequency component. The automatic video camera according to claim 1 or 2, characterized in that a high frequency component in a previous field is compared with the high frequency component in the previous field, a focusing direction is determined based on the increase or decrease, and a focus adjustment device is controlled. Focusing device. (4) Claims 1 to 3 are characterized in that a bandpass filter is disposed before the binarization converter, and only intermediate frequency components of the video signal are extracted and binarized. The automatic focus adjustment device for a video camera according to any one of the items.