JPH0614700B2 - Automatic focusing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a high frequency component of a video signal obtained from an image pickup device of a video camera and drives a lens focus matching device so that its amplitude is maximized. The present invention relates to an automatic focusing device.

Configuration of Conventional Example and Problems Thereof In recent years, the demand for video cameras along with portable video tape recorders is rapidly increasing. The automatic focus adjustment device simplifies the handling of the video camera and contributes to its further spread.

The conventional automatic focusing device will be described below. As a conventional automatic focus matching device, it emits infrared rays toward a subject, receives the infrared rays reflected from the subject, measures the distance to the subject from the light receiving angle, and the focus adjustment device of the lens is set at a predetermined position according to the distance. There is a method to drive to. Although the above method has a fast response speed, the distance to the object can be accurately measured, and the result of the measurement ensures that the lens focus matching device can be driven to a predetermined position with high assembly accuracy of the focus matching device. Was needed. Furthermore, since infrared rays are emitted and the reflected light from the subject is used, the subject having a long distance is not good and the power consumption is not small.

Further, as a means for solving the above-mentioned problems that do not require the assembling accuracy of the matching device, a closed loop including the focus matching device of the lens is used by using the video signal obtained from the image pickup device of the video camera. There is an autofocusing device formed. That is, the subject image formed on the light receiving surface of the image sensor is periodically and optically blurred, and the signal corresponding to the blur is detected from the video signal obtained from the image sensor, and the high frequency band of the video signal is detected. The focus matching device of the lens is driven so that the signal amplitude of the frequency component is maximized. Hereinafter, a conventional example of an automatic focusing device in which the above-described lens is placed in a closed loop will be described with reference to the drawings.

FIG. 1 is a block diagram of a conventional automatic focusing device. In FIG. 1, 1 is a lens, 2 is an image pickup device for converting optical information of an object into an electric signal, 3 is a preamplifier for amplifying an electric signal obtained from the image pickup device 2, and 4 is an output of the preamplifier 3. A process circuit 5 for converting a signal into a television signal is a sync signal generator for supplying various sync signals to the process circuit 4 and the image pickup device drive circuit 6. The image sensor drive circuit 6 drives the image sensor 2. Reference numeral 7 denotes a high frequency component detecting circuit for detecting a high frequency component from the output signal of the preamplifier 3, which is, for example, a band pass filter having a center frequency of 1 [MHz]. 8 is a high frequency level detection circuit 9
It is a gain control circuit that changes the gain according to the output signal of. The high frequency level detection circuit 9 detects whether the level of the output signal of the high frequency component detection circuit 7 is within the dynamic range of the circuit and outputs the result. Reference numeral 10 is a reference frequency generation circuit, and 11 is a reference frequency component detection circuit for detecting a reference frequency component included in the high frequency component, which is, for example, a bandpass filter having the reference frequency as the center frequency. Reference numeral 12 is a synchronous detection circuit that synchronously detects the output signal of the reference frequency component detection circuit 11 at the reference frequency, 13 is a motor drive circuit that drives the motor with the reference frequency and the output signal of the synchronous detection circuit 12, and 14 is the focus matching of the lens 1. A motor that drives the device.

The operation of the conventional automatic focus adjusting device configured as described above will be described below.

The focus matching device for the lens 1 slightly moves by the motor 14 at the reference frequency generated by the reference frequency generation circuit 10, and changes the focus of the lens to such an extent that it cannot be detected by the eye. The high frequency component of the video signal obtained from the image sensor 2 includes a change component corresponding to the slight fluctuation of the focus,
High frequency component detection circuit 7, reference frequency component detection circuit 1
Detected by 1. The synchronous detection circuit 12 detects the amplitude and phase of the detected reference frequency component, and in addition to the motor drive circuit 12, the motor 14 so that the amplitude of the high frequency component of the video signal obtained from the image sensor 2 becomes maximum. To drive. This point will be described in more detail with reference to FIG.

FIG. 2 is a diagram for explaining the principle of detecting the driving direction of the motor 14. The vertical axis represents the level of the high frequency component of the video signal obtained from the image sensor 2, and the horizontal axis represents the position of the focus matching device of the lens 1. Now, when the subject is located at the distance D ₁ , the level of the high frequency component is maximum when the focus matching device of the lens 1 focuses at a position corresponding to the distance to the subject, and is closer to the far side and far side. Even if there is a deviation, it becomes a mountain-shaped characteristic that decreases, as shown in FIG. On the other hand, a ₁ and a ₂ are motors 1.
4 shows a slight change at the reference frequency of 4. a ₁ is the case where the focus matching device of the lens 1 is closer than the position corresponding to the distance to the subject, and at this time, the high frequency component is b ₁
Undergoes amplitude modulation. Also, a ₂ is on the far side, and at this time, it undergoes amplitude modulation like b ₂ . As described above, the high frequency component is amplitude-modulated at the reference frequency due to the slight fluctuation of the motor 14. The phase of the reference frequency component included in the high frequency component due to the amplitude modulation is inverted by 180 ° on the short distance side and the long distance side, as is clear from b ₁ and b ₂ . Therefore, the reference frequency component is detected from the high frequency component subjected to the amplitude modulation like b ₁ ,
If the motor 14 is driven in the direction of the arrow c ₁ by a signal obtained by synchronously detecting the reference frequency component with the reference signal, in the case of b ₂ , the motor 14 moves in the direction of the arrow c ₂ .
The motor 14 is always stable where the high frequency component is maximum. As described above, the closed loop can be formed by including the focus adjusting device of the lens, and the precision of the focus adjusting device can be roughened. However, the level of the high frequency component obtained from the image pickup device 2 has a very large dynamic range and requires gain control. This point will be described with reference to FIG.

Now, for the sake of simplification of the explanation, consider a pattern of right half dark and left half bright as shown in FIG. At this time, the video signal obtained by scanning ee 'is as shown in (b). When the illuminance of the portion corresponding to the bright portion is I _max and the illuminance of the dark portion is I _min , the contrast C is And C changes from 0 to 1. Contrast C = 0
Has uniform brightness over the entire pattern and has no contrast. Also,
When the illuminance in the dark part is 0, the contrast C is 1. A high frequency component obtained by imaging such a subject is proportional to the contrast C. Furthermore, the brightness of light and dark I _max
Is also proportional to However the amplitude of the video signal obtained from the imaging element is proportional to the illuminance, eventually, amplitude V _max of the high frequency component V _H video signal for each illuminance, V When V _{min H} αC · V _max ... … (1) ∝V _max -V _min …… (2) Satisfies the relation. When configuring an autofocusing device,
The dynamic range of the contrast C needs to be guaranteed up to the detection limit of humans, and is more than 20 [dB]. On the other hand, in the case of a video camera, the dynamic range of the maximum value V _max of the amplitude of the video signal is wider than the dynamic range of the contrast C and is 30 [dB] or more. After all, the dynamic range of the high frequency component V _H is 60.
[DB] It will be necessary near. This is not only difficult to realize in the circuit, but also becomes equivalent to the loop gain changing by nearly 60 [dB], which makes the system very unstable. Because
This is because the fundamental frequency component included in the high frequency component is proportional to the level of the high frequency component. Further, if the circuit is saturated and the peak part of the high frequency component is suppressed, the amplitude modulation component of the high frequency is lost. This makes it impossible to detect the reference frequency component, and the automatic focusing device does not operate at all, which is fatal. For this reason, the gain control is indispensable for the automatic focusing device, and the gain control circuit 8 performs it. The gain control circuit 8 detects whether the level of the high frequency component is within a predetermined dynamic range by the high frequency level detection circuit 9 and changes the gain stepwise according to the result. An AGC loop method that makes the envelope of the high frequency component a constant value is also conceivable as a means for controlling the gain, but having another loop in one loop makes the response,
It is difficult to realize in terms of stability, and the stepwise gain control as described above is simple and effective. The gain control circuit 8 requires about five stages of gain control in order to prevent the circuit from being saturated and to suppress the extreme fluctuation of the loop gain.

Now, let us consider a change in the high frequency component after gain control when the focus matching device of the lens 1 is driven from the near side to the in-focus position from the in-focus position. Initially, the gain control circuit 8 has a large gain so that the output of the high frequency component detecting circuit 7 falls within a predetermined dynamic range because the high frequency component is small because the image is out of focus and the image is blurred. The high frequency components increase as the focus matching device is driven and brought into focus. When the high frequency component exceeds the upper limit of the predetermined dynamic range, the high frequency level detection circuit 9 detects it and the gain control circuit 8 lowers the gain by one step. When the high frequency component further increases and exceeds the upper limit of the dynamic range, the gain control described above is repeated to reach the in-focus position. . Video cameras are used from indoors to outdoors and capture a wide range of subjects. Therefore, the number of times of gain control inevitably increases. By the way, the output of the high frequency component detecting circuit 7 shows a sudden change before and after the gain control. The reference frequency component detection circuit 11 is a bandpass filter having the reference frequency as the center frequency as described above, and its Q is set high in order to detect the reference frequency component with good S / N. For this reason, the response to the rapid change in the level of the high frequency component accompanying the gain control is poor, and an unnecessary ringing component is output for a considerably long period. This automatic focus matching apparatus synchronously detects the output signal of the reference frequency component detection circuit 11 with the reference signal and detects the motor 14
, The unnecessary ringing component described above causes a malfunction of the system. In order to prevent malfunctions, the loop must be cut or the motor must be stopped each time gain control is performed.If the gain control is performed frequently, the response time from driving the motor to obtaining focus is very slow. Become. This is a fatal problem as an automatic focusing device for a video camera that often captures images of a moving subject.

As described above, in the above-described configuration, the number of gain control times from driving the motor to obtaining the focus is large, and the motor is stopped each time the gain control is performed to prevent malfunction. It had a problem that it could not stand.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an automatic focusing device which can sufficiently follow an object having a fast response speed.

According to the present invention, there is provided an automatic focus matching device for detecting a high frequency component of a video signal obtained from an image sensor and driving a lens focus matching device so that the amplitude of the high frequency component is maximized. An automatic focusing device that detects the amplitude of a video signal, that is, the level of brightness, and controls the gain based on the detection result. By detecting the brightness level of the video signal and controlling the gain, the gain control until the in-focus state is obtained. The number of times can be greatly reduced and the response speed can be dramatically improved.

Description of Embodiments FIG. 5 is a block diagram of an automatic focusing device according to a first embodiment of the present invention. In FIG. 5, 1
Reference numeral 5 denotes a brightness gain control circuit that changes the gain so that the amplitude of the video signal, that is, the brightness level, falls within a predetermined dynamic range by the output of the brightness level detection circuit 16. The brightness level detection circuit 16 detects the brightness level, and is a brightness level detection circuit configured to detect V _max in the formula (1), and is a peak detection circuit, for example. 17
Is a gain control circuit that changes the gain by the output of the high frequency frequency level detection circuit 9 like the gain control circuit 8 in FIG. 1, but the number of control stages is small.

The operation of the automatic focusing device of this embodiment constructed as described above will be described below.

The level of the high frequency component is proportional to the amplitude of the video signal, that is, the brightness level, as described above. The brightness level is constant if the subject is the same regardless of whether the subject is in focus. The amplitude of the video signal, that is, the brightness level is 30 [d
B) The above dynamic range is a major factor in increasing the number of stages of gain control, but as described above, even if the image is blurred, the brightness level is detected in advance and gain control is performed. However, the result does not change until the focus is obtained. Therefore, after the luminance level is detected and the gain control is performed, the high frequency component has only 20 dynamic range [dB] due to the contrast. With this dynamic range, there is no gain control or 1
It can be realized in steps. The high frequency gain control circuit 17 controls the gain of this portion. Now, it is assumed that the high frequency gain control circuit 17 has one control stage.

According to the present embodiment, the number of times of gain control is at most once, no matter what kind of object in a wide range is picked up from the blurred state to the focused state. With such a gain control circuit, the response speed does not deteriorate even if the motor is stopped during the gain control, and the response speed is dramatically improved as compared with the conventional automatic focusing device.

As described above, according to the present embodiment, the level of the high frequency component is detected and the gain is controlled, and the brightness level is detected and the gain is controlled, thereby significantly reducing the gain control circuit until the focus is obtained. , The response speed is significantly improved. In addition, the image is greatly blurred and a sufficient high frequency component cannot be obtained. For example, when searching a lens focus matching device, a small high frequency component that cannot obtain a sufficient reference frequency component by controlling the gain at the brightness level. It is possible to prevent switching with ingredients.

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

FIG. 6 is a block diagram of an automatic focusing device showing a second embodiment of the present invention.

In the figure, reference numeral 18 is a gain control circuit that controls the gain by the output of the brightness level difference detection circuit 19. The brightness level difference detection circuit 19 detects the difference in brightness level change, that is,
A brightness level difference detection circuit that detects a value corresponding to V _max -V _min in the equation (2), for example, detects a maximum value and a minimum value and obtains the difference.

The operation of the automatic focusing device of the second embodiment constructed as described above will be described below.

As described above, the brightness level difference detection circuit 19 uses the V of the equation (2).
_Max- V _min is detected, and if gain control is performed based on the detection result, no other gain control is required as is apparent from the equation (2). On the other hand, as described above, the brightness level has nothing to do with the focus adjustment state. Therefore, according to this embodiment, the required gain control can be performed in advance, and the gain control is not performed until the motor is driven and the focus adjustment state is obtained. The response speed is significantly improved because the motor does not stop due to gain control.

As described above, according to the present embodiment, by detecting the difference in the change in the brightness level and controlling the gain, no other gain control is required while driving the motor for focus matching, and the response speed is increased. It will be improved.

According to the present invention, the subject image formed on the light receiving surface of the image pickup device is periodically and optically blurred, and a signal corresponding to the blur is detected from a video signal obtained from the snow image device. To maximize the amplitude of the high frequency components of the signal,
The automatic focus matching device for driving the lens focus matching device has been described, but the invention is not limited thereto, and detects a high frequency component of a video signal obtained from an image sensor,
The present invention can be applied to all automatic focusing devices that drive a lens focusing device so that its amplitude is maximized.
For example, even in a hill-climbing control automatic focus matching device that drives a lens focus matching device in a direction in which the high frequency component increases, and detects a point where the high frequency component reaches a peak, the high frequency component naturally has a wide range. It has a wide dynamic range and requires gain control. In order to detect the peak quickly and without malfunction, it is better that the gain control is smaller from the start of driving the motor to the in-focus position. Therefore, the present invention plays an effective role.

Further, the method of periodically and optically blurring the subject image formed on the imaging surface is not limited to the conventional example.

In the first embodiment, the brightness gain control circuit 15 is located after the preamplifier 3 and the high frequency gain control circuit 17 is located after the brightness gain control circuit 15. However, the circuits saturate at these positions. As long as the system does not operate normally due to such reasons, there is no restriction and these may be combined into one.

Further, although the brightness level detection circuit 16 detects the maximum value of the brightness level before receiving the gain control, the same effect can be obtained by detecting whether the brightness level after receiving the gain control is within a predetermined dynamic range. can get.

Further, the high band frequency level detection circuit 9 may also detect the level of the high band frequency component which is not subjected to the high band frequency gain control or gain control.

The automatic focusing device of the present invention is capable of dramatically improving the response speed by receiving the amplitude detection circuit of the video signal, that is, the luminance level detection circuit, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional automatic focusing device, FIG. 2 is a principle diagram for explaining a principle of detecting a driving direction of a motor, and FIG. 3 is a dynamic range of high frequency components. FIG. 4 is a diagram showing a change in a high frequency component due to gain control when the motor is driven in a focusing direction, and FIG. 5 is a diagram showing an automatic focusing device according to the first embodiment of the present invention. A block diagram and FIG. 6 are block diagrams of an automatic focusing device according to a second embodiment of the present invention. 1 ... Lens, 2 ... Image sensor, 3 ... Preamplifier, 7
...... High frequency component detection circuit, 9 …… High frequency level detection circuit, 11 …… Reference frequency component detection circuit, 12 ……
Synchronous detection circuit, 14 ... Motor, 15 ... Luminance gain control circuit, 16 ... Luminance level detection circuit, 17 ... High frequency gain control circuit, 18 ... Gain control circuit, 19 ... Luminance level difference detection circuit .

Claims (2)

[Claims] 1. An optical path length varying means for periodically changing the optical path length of an image pickup optical system at a reference frequency, and a high frequency component whose gain is controlled stepwise by the level of a high frequency component in a video signal. The high frequency component amplifier has a signal amplifier and lens driving means for detecting the reference frequency component from the output of the high frequency component signal amplifier and driving a lens focus matching device by the reference frequency component signal. An automatic focusing device characterized in that it has a wide-band amplifier in which the video signal level is detected and the gain is controlled stepwise in the preceding stage. 2. The automatic focusing device according to claim 1, wherein a video signal obtained by horizontal scanning or a vertical difference signal is used as the input video signal.