JPS6069612A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To stabilize an automatic focus matching by reducing a driving gain of a focus matching means against a sudden variation of an object to be photographed. CONSTITUTION:An output signal of a photodiode is amplified and applied to a delaying circuit 18 and an operating circuit 19. The circuit 19 subtracts a delayed signal and an undelayed original signal, and detects a variation quantity of an infrared ray. A level discriminating circuit 21 drives a timer 20 when the detected variation quantity exceeds some quantity reduces a gain of a driving circuit 11 or stops it. Accordingly, an unnatural response of a picture against a sudden variation of an object to be photographed can be improved without delaying a response time of driving of a motor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device for automatically driving a lens focusing device of a television camera so that the object being imaged is brought into focus.

Problems with the configuration of the conventional example In the conventional technology, infrared rays are emitted toward the subject, the infrared rays reflected from the subject are received, the distance to the subject is measured, and the lens focusing device is fully activated based on that distance. There is a method. In addition, the lens is equipped with a focusing system that detects all high-frequency components of the signal obtained from the image sensor and maximizes the amplitude. There is also a method of driving &. Because these systems respond to rapid changes in the subject, the resulting image on a television receiver is unsightly.

The present invention provides a stable automatic focusing device by reducing the drive gain of the focusing device or completely stopping the driving for a certain period when the subject being imaged changes suddenly! All that is offered.

The conventional example will be explained in detail below. Figure 1 shows the method of emitting all infrared rays and measuring the distance to the subject.

In the figure, 1 is a light emitting diode that emits infrared light, and 2
is a lens that focuses infrared rays, 3.subject, 46''i is a lens that fully focuses infrared rays reflected by object 3, and 5j is a photodiode that receives infrared rays, which is moving in the direction of the arrow. The light receiving position differs depending on the distance as shown by the solid line and the broken line. Therefore, the distance to the subject 3 can be measured depending on the position of the photodiode 6. The focusing device of the lens is fully driven based on the distance.

FIG. 2 shows an example of this device used in a FITK television camera. 6 is a lens, 7 is an image pickup tube that converts the optical information of the subject into an electric signal, 8 is a preamplifier that amplifies the electrical signal obtained from the image pickup tube 7, and 9 is a gamma correction, blanking process, and a synchronization signal ( This is a process circuit that performs addition of SYNC). 12 is a distance measuring device shown in FIG. Based on the distance measured by the distance measuring device 12, the drive circuit 11 drives the motel 10 to adjust the focusing device of the lens 6.

Here, when the subject being imaged suddenly changes, for example, when a whole person crosses the television camera, the focusing device of the lens is activated in response, causing the image to become blurred or Return to original state. This is very unsightly. To improve this, the response speed has been slowed down. Therefore, when a subject approaches at a certain speed, such as when a person approaches while running, the camera cannot respond adequately.

As described above, improvements in unsightliness and response speed in response to sudden changes in the subject have conventionally been contradictory. Furthermore, this method requires a highly accurate focusing device.

In order to improve the accuracy of a warped alignment device, some prior art techniques place the alignment device in the feedback loop of an autofocus system. Next, this will be explained using FIG. 3. In the figure, numbers 6 to 10 are the same as in the second diagram and perform the same operations. 1e
is a circuit for detecting high frequency components, and is, for example, a bandpass filter with a center frequency of 1. The lens focusing device is slightly moved by the motor 10 using the signal obtained from the reference frequency generation circuit 14, and the focus of the lens is changed to such an extent that it cannot be detected by the eye.As a result, the output signal of the high frequency component detection circuit 13 changes the focus. 17 is a circuit for detecting the reference frequency component, a synchronous detection circuit 15 detects the polar amplitude of the reference frequency component signal, and in addition to the motor drive circuit 13, The motor 10 is driven so that the amplitude of the high frequency component of the output signal of the image pickup tube 7 becomes equal to 1.

Detection of the driving direction of the motor 10 will be explained using FIG. 4. When the lens focusing device is driven from a short distance to a long distance and the object is located at a distance D1, the amplitude of the high frequency component signal becomes as shown in FIG. a 1 * a 2
indicates slight fluctuations in the motor. When the distance is adjusted to be closer than the subject, the output of the reference frequency detection circuit 17 is a waveform signal such as bl.

When tuned to a long distance, all waveform signals like b2 are obtained. When the motor 10 is driven in the direction of the arrow 01 with the signal obtained by synchronously detecting the signal bl, the signal b2 drives the motor 10 in the direction of the arrow C2, so that the amplitude is stabilized at the maximum value.

In this way, since the lens focusing device can be included in the entire feedback loop, the accuracy of the focusing device may be rough. However, if the response speed is slowed down so as not to respond to sudden changes in the subject being imaged, the system becomes unstable. That is, since the amplitude of the signal of the high frequency component of the object changes in various ways, the loop gain of the system changes. If the response time is slowed down and the loop gain becomes high, the system will oscillate or the response will become unstable.

OBJECTS OF THE INVENTION The present invention improves the response time under normal conditions without slowing down the response time.
An object of the present invention is to provide an automatic focusing device that can improve image unnaturalness even when a subject being imaged changes suddenly.

Structure of the Invention The present invention detects a sudden change in the subject, reduces the control of motor drive, and! ! Alternatively, the drive may be stopped and the device may not respond for a certain period of time.

DESCRIPTION OF EMBODIMENTS One embodiment of the present invention is shown in FIG. 5 and will be described below. Fifth
6 to 12 in the figure are the same as 6 to 12 in FIG. 2, and perform the same operations. The output signal of the photodiode 5 is amplified and applied to a delay circuit 18 and a subtraction circuit 19. Since the subtraction circuit 19 completely subtracts the delayed signal and the undelayed original signal, it detects the entire amount of change in the amount of infrared rays reflected from the subject. A level discrimination circuit 21 discriminates the amount of change, and when the change exceeds a certain amount, a timer 20i is driven, and when this timer is operating, the gain of the drive circuit 11 is reduced or stopped. In this way, the response time of the motor drive can be shortened, and the unnatural response of the image to sudden changes in the subject can be completely improved.

Next, an automatic focusing device detects all the high frequency components of the signal and drives the lens focusing device so that the amplitude of the high frequency components is maximized. A practical example of the present invention is shown in FIG. 6 and will be described below. 6 to 17 in FIG. 6 are the same as 6 to 17 in FIG. 3, and perform the same operations. The averaging circuit 22 averages all the luminance signals,
The signal passed through the delay circuit 23 and the original signal are subtracted by the total subtraction circuit 24 to detect the entire amount of change in the subject. A level determination circuit 26 determines whether the amount of change is above a certain level, and if it is above a certain level, the gain of the drive circuit 13 of the motor 10 is reduced or the motor 1o is stopped. In this way, when the distance to the subject normally changes, the response time is determined so that the system is stable and responds quickly, and when the subject changes suddenly, the loop gain of the system is reduced or the motor 10 is adjusted. By stopping the drive, the unnatural response can be eliminated. The period for decreasing the loop gain may be performed using a timer method as shown in FIG.

Effects of the Invention As described above, the present invention reduces the motor drive gain or
By stopping the system, the unnaturalness of the response is corrected, and when the distance to the object changes, the response time can be determined to match the change, so the system operates very stably. Also, the circuit configuration is simple. As described above, the present invention has extremely outstanding effects.

[Brief explanation of the drawing]

Figure 1 shows the principle of distance measurement using an infrared distance meter. Figure 2 is a block diagram showing a conventional example of an automatic focusing device using a distance measuring method. Figure 3 shows an automatic focusing device that uses a motor to completely change the focus. Figures 1, 2 and 3 showing the conventional example are principle diagrams for explaining the entire principle of detecting the driving direction of the motor, and Figures 5 and 6 are diagrams of the automatic focusing device in each sister example of the present invention. It is a block diagram. 6...lens, 7...imaging tube, 10.
...Motor, 18.23...Delay circuit,
21.25...Level discrimination circuit. Figure 1? Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] (1) A system for automatically driving a focusing means of a lens of a television camera that is imaging a subject so that the subject is in focus, An automatic focusing device, characterized in that the driving gain of the focusing means is reduced when the focusing device suddenly changes. (2) The automatic focusing device according to claim 1, characterized in that the drive gain is reduced over a predetermined period of time. (3) The automatic focusing device according to claim 1, characterized in that the reduction in drive gain is performed for a period of time when the rate of change when the object being imaged changes rapidly is greater than or equal to a certain value. ( 4) The automatic focusing device according to claim 1, characterized in that the drive gain is reduced when an electric signal obtained from an image sensor of a television camera changes rapidly. (5) Drive gain 2. The automatic focusing device according to claim 1, wherein the automatic focusing device stops driving the focusing means of the lens when the object being imaged changes rapidly, including a decrease of zero.