JPH0230486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device for a video camera.

Traditionally, automatic focusing devices for video cameras detect the definition of the screen using high-frequency components in the video signal, and then control the rotation of the lens focusing ring (hereinafter referred to as helicoid) to maximize the definition. So-called mountain climbing control is known. This method is published in the NHK Technical Research Report, Volume 17, 1963.
No. 1, Volume 86, page 21, it is described in detail by Ishida et al. as ``Automatic focus adjustment of television cameras using mountain-climbing servo method.''
This will be briefly explained using FIGS.

FIG. 1 is a block diagram showing the configuration of an automatic focusing device (hereinafter referred to as AF device) using a hill climbing method. 1 is a lens, 2 is a camera circuit, 3 is a video signal output terminal, 4 is a high-pass filter, 5 is a detector, 6 is a differential hold circuit, 7 is a motor drive circuit, and 8 is a motor for rotating the helicoid of the lens. It is. Further, 9 is a mountain climbing circuit, and 51 and 61 are terminals.

The operation of the configuration shown in FIG. 1 will be explained below using the characteristic diagram shown in FIG. 2.

Light from a subject that enters a lens 1 is converted into an electrical signal by a camera circuit 2, and outputted to a terminal 3 as a video signal. Only the high-frequency components of the video signal are extracted by the high-pass filter 4, detected by the detector 5, and then appear at the terminal 51. What should be noted here is that the voltage corresponding to the high-frequency component of the video signal appearing at the terminal 51 (hereinafter referred to as the focal voltage) corresponds to the definition of the captured image, so the focal voltage as shown in FIG. The voltage will be maximum if the helicoid position of lens 1 (referred to as A) matches the distance to the subject;
The value decreases as the value deviates from the original value.

What can be determined from FIG. 2 is that if the helicoid position is controlled by some means so that the focus voltage, which is the output of the terminal 51, is maximized, automatic focusing can be achieved. This means is achieved by the differential hold circuit 6 to motor 8 shown in FIG. That is, the differential hold circuit samples and holds the focal voltage appearing at the terminal 51 at fixed time intervals as shown in FIG.
This circuit generates a negative voltage if the focal voltage decreases over time, and the motor drive circuit 7
If the output voltage of the differential hold circuit 6 appearing at the terminal 61 is positive, the motor 8 is rotated in the forward direction to move the helicoid position in the forward direction, and if the same output voltage is negative, the motor 8 is rotated in the reverse direction to move the helicoid position. Move in the opposite direction.

The differential hold circuit output voltage in Figure 2 shows the case where the helicoid is rotated from close range to infinity, but it is easily understood that the same applies when the helicoid is rotated from infinity to close range. .

In this way, the helicoid position control loop of the motor 8 climbs the mountain created by the focal voltage using the output voltage of the differential hold circuit 6, and finally reaches a steady state at the top of this mountain while vibrating in small increments. It is understood that automatic focusing is possible.

The above is an automatic focusing device for a video camera using the mountain climbing method.

Although the above-mentioned device has sufficient performance as an automatic focusing device, it has the following drawbacks.

If the subject to be photographed changes due to movement, panning of the camera, or camera shake, the focal voltage will fluctuate, making it impossible to obtain the focal voltage shown in FIG. 2. Therefore, there is a drawback that the hill-climbing operation may malfunction, resulting in a large loss of focus. Furthermore, even if the subject changes, the focal voltage may not change. In this case, even if the subject moves and becomes blurred after being focused, the camera cannot be activated and remains stuck.

Furthermore, if the subject moves rapidly, the focal voltage may fluctuate greatly, and the mountain-climbing motion may not be completed completely and the subject may stop at a blurred point.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-described drawbacks of the prior art and to provide an automatic focusing device using a video signal that is less likely to malfunction due to a change in subject.

The gist of the present invention is to prevent malfunctions in the mountain climbing motion due to movement of the subject by detecting changes in the subject from the video signal and stopping and restarting the mountain climbing motion.

FIG. 3 shows an embodiment of the present invention. 1 to 9 are the same as in FIG. Reference numeral 10 indicates a subject change detection circuit, and reference numeral 11 indicates a gate circuit.

If there is no change in the subject, as described above, the output of the camera circuit 2 is used to move the lens 1 by the motor drive circuit 7 and the motor 8 by the mountain climbing circuit 9 to perform a mountain climbing operation. When the subject is changing, the subject change detection circuit 10 detects the change from the output of the camera circuit 2, and the gate circuit 11 disconnects the mountain climbing circuit 9 from the motor drive circuit 7 to stop the mountain climbing operation. do.

Further, a more detailed embodiment of the subject change detection circuit 10 is shown in FIG. 4, and waveforms of various parts thereof are shown in FIG. 1
2 is a gate circuit, 13 is a low pass filter, 14
15 is an amplifier, 15 is a differential circuit, 16 is a monostable multivibrator, 17 is a pulse count circuit, and 18 is a fluctuation detection circuit.

First, the gate circuit 12 extracts a specific portion of the screen from the video signal 3 which is the output of the camera circuit 2 using the view angle gate signal 122 to generate a signal 121 .
It is desirable that the position of this view angle gate correspond to the position of the video signal used for the mountain climbing operation. Furthermore, in order to prevent the output from being affected even if the camera is out of focus, the waveform is passed through a low-pass filter 13 to blunt it, and then the amplifier 14 uses a preset gray value or the average value of the input signal as a threshold until it reaches saturation. Amplify and pulse train 141
Make it. This pulse train 141 is differentiated by a differentiating circuit 15, converted into a pulse train 161 with a constant pulse width by a monostable multivibrator 16, and converted into an analog output 171 by a pulse number counting circuit 17. In this way, the analog output 171 can obtain a voltage corresponding to the picture pattern being photographed. At this time, by resetting the count at the period of the vertical synchronization signal using the reset signal 181 corresponding to the view angle gate signal 122, it is possible to respond even to instantaneous fluctuations in the image pattern. By detecting variations in the analog output 171 by the variation detection circuit 18, it is possible to identify that the subject has changed. Conceptually, this object change detection method counts the number of contrast changes (changes from black to white and changes from white to black) in the image being shot, and converts the counted value into a value unique to that image. Therefore, for example, with the above configuration, the differential circuit 15 and the monostable multivibrator 1
It is also possible to remove 6.

Further, the pulse number counting circuit 17 can also be configured using a low-pass filter.

Furthermore, FIG. 6 shows an example in which the present invention is implemented in a system in which the mountain climbing is stopped until the conditions change after the mountain climbing operation is completed. 19 in the figure is a focal length detection device;
20 is an aperture value detection device, 21 is a mountain climbing control circuit,
22 indicates a starting circuit.

First, a conventional case without the subject change detection circuit 10 will be described. The starting circuit 22 receives the focal voltage from the mountain climbing circuit 9, the focal length from the lens 1 from the focal length detection device 19, and the aperture value from the aperture value detection device 20. When any of these three inputs fluctuates, the starting circuit 22 activates the mountain climbing control circuit 2.
1, the mountain climbing operation is started. The mountain climbing control circuit 21 performs a mountain climbing operation and stops the mountain climbing operation after moving the helicoid to the top of the mountain. This method has the advantage that the helicoid does not vibrate in small increments after focusing because the hill-climbing motion is not always performed, but it also ensures that the hill-climbing motion is activated when refocusing is necessary. difficult to do.

Here, as shown in FIG. 6, the output of the subject change detection circuit 10 is connected to a gate circuit 11 to prohibit mountain climbing while the subject is changing, thereby preventing malfunctions in mountain climbing. Further, in order to obtain the same effect as the example shown in FIG. 3, the output of the subject change detection circuit 10 is connected to the starting circuit 22, and the mountain climbing operation is started when the subject stops changing.

As described above, by detecting a change in the subject from the video signal and stopping or restarting the mountain climbing operation, malfunctions in the mountain climbing operation due to changes in the subject can be prevented.

Note that although we have described the mountain climbing method reported by NHK, other mountain climbing methods, for example, after completing the mountain climbing motion once, refocusing may be necessary as the subject moves or the light source changes. This is even more effective in a system in which the hill-climbing operation is stopped until the operation is required. In other words, it can be used not only to prevent malfunctions by stopping mountain climbing while the subject is changing, but also to restart mountain climbing when the subject has finished changing.

Note that in the above explanation, the mountain climbing operation is always stopped when a change in the subject is detected, but even if a change in the subject is detected, if the amount of change is small, the mountain climbing operation is not canceled as long as the mountain climbing operation does not malfunction. This may ensure smoothness of operation.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional hill-climbing automatic focusing device, Fig. 2 is a waveform diagram for explaining the operation of the configuration shown in Fig. 1, and Fig. 3 is an embodiment of an automatic focusing device according to the present invention. FIG. 4 is a block diagram showing one embodiment of the object change detection circuit, and FIG. 5 is a waveform diagram for explaining the operation of the structure shown in FIG. 4. FIG. 6 is a block diagram showing another embodiment according to the present invention. 1: Lens, 2: Camera circuit, 7: Motor drive circuit, 8: Motor, 9: Mountain climbing circuit, 10: Subject change detection circuit, 16: Monostable multivibrator, 17: Pulse number counting circuit, 1
8: Fluctuation detection circuit, 21: Hill climbing control circuit, 2
2: Starting circuit.

Claims (1)

[Claims] 1. A focusing voltage is created by extracting a high frequency component of a video signal of an object photographed through a lens, and focusing is performed by moving the position of the lens using a motor so that the value of the focusing voltage is maximized. In an automatic focusing device that performs An automatic focusing device characterized in that it sometimes includes a motor drive prohibiting means for prohibiting driving of the motor and stopping focusing. 2. A lens, a motor that moves the position of the lens, a camera circuit that converts the optical image of the subject incident through the lens into a video signal, and a focal voltage that extracts high frequency components included in the video signal and generates a focal voltage. In an automatic focusing device equipped with a generating means and a motor drive circuit that is supplied with a focus voltage and drives a motor so that the value of the focus voltage is maximized, the low frequency component of the video signal is extracted and the subject changes. an object change detection means for generating a change detection signal for detecting that the object has changed; an automatic focusing device comprising: a driving means for restarting the driving of the motor when the automatic focusing device is activated;