JPS60143070A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To widen the operating range by increasing amount of fog optically and periodically when an object is at a low illuminance or a low contrast so as to improve the stability at focusing. CONSTITUTION:When the amplitude of a high frequency component is small with the object at a low illuminance or a low contrast, the signal is amplified at a gain control circuit 8 so as to attain a prescribed dynamic range. If a motor 14 is driven as it is, however, the circuit is sensitive to noise by the share of the gain of the circuit 8 to be increased. Then the gain of a gain control circuit 17 is decreased by a control circuit 15 to a degree that the motor 14 is not deflected by the noise component. Thus, the gain of a gain control circuit 16 is increased by the share of the decreased gain of the circuit 17 so as to increase the amount of fog optically and periodically thereby preventing the deterioration of a loop gain.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention detects high frequency components of a video signal obtained from an image sensor of a video camera, and adjusts the focus of a lens so that the amplitude of the high frequency components is maximized. The present invention relates to an automatic focusing device that drives an aligning device.

2. Description of the Related Art Structures of Conventional Examples and Their Problems In recent years, demand for video cameras has been rapidly increasing along with portable video tape recorders.

Automatic focusing devices simplify the handling of video cameras and contribute to their further widespread use.

As a type of conventional automatic focusing device, it emits infrared rays toward the subject, receives the infrared rays reflected from the subject, and
The distance to the subject is calculated from the light receiving angle, and the lens focusing device is driven to a predetermined position based on the calculated value. The above-mentioned method works regardless of the illuminance and contrast of the subject, but in order to accurately measure the distance to the subject and drive and stop the lens focusing device to a predetermined position based on the measurement result, a high lens assembly is required. Precision is required. Furthermore, since infrared rays are emitted towards the subject and the reflected light is received, they tend to malfunction when shooting distant subjects, and still consume a lot of power.

In addition, as a method that does not require high assembly precision for the lens and solves the above-mentioned problems, a closed loop is formed including the lens focusing device, and the focusing is performed using the video signal itself obtained from the image sensor. There is a way to get it. That is, the subject image formed on the light receiving surface of the image sensor is periodically and optically focused, the amount of blur is detected, and the lens is adjusted so that the high frequency component of the video signal obtained from the image sensor is maximized. This is a method for driving a focusing device.

An automatic focusing device that forms a closed loop including the conventional lens focusing device described above will be described below.

FIG. 1 shows a block diagram of a conventional automatic focusing device, in which 1 is a lens, 2 is an image sensor that converts the subject image formed on the optical surface into an electrical signal, and 3 is an image sensor 2. a preamplifier for amplifying the output signal of the preamplifier 3; 4 is a process circuit that processes the output signal of the preamplifier 3 to produce a television signal; 5 is a synchronization signal generator that supplies various synchronization signals, blanking signals, etc.; Reference numeral 6 denotes an image sensor driving circuit that drives the image sensor 2. 7 connects the output of the image sensor 2 to the preamplifier 3
A high frequency component detection circuit that detects high frequency components from a video signal amplified by, for example, a center frequency of 1 [MHz
] bandpass filter. A gain control circuit 8 detects whether the high frequency component is within a predetermined dynamic range using a high frequency level detection circuit 9, and controls the gain of the high frequency component based on the detection result. 10 supplies the reference frequency to the synchronous detection circuit 12, and also supplies the motor drive circuit 13.
This is a reference frequency generator that uses a motor 14 to slightly vary the focusing device of the lens 1. Reference numeral 12 denotes a reference frequency component detection circuit that detects a reference frequency component from high frequency components of a video signal obtained from an image sensor. 12 synchronously detects the reference frequency component at the reference frequency to detect the amplitude and phase, and connects the motor drive circuit 13 so that the high frequency component is maximized.
This is a synchronous detection circuit that drives the focusing device of the lens 1 using the motor 14 and the motor 14.

The operation of the automatic focusing device configured as above will be described below.

The focusing device of the lens 1 varies slightly at the reference frequency, and the focus changes by a degree that is imperceptible to the eye.

Therefore, the high frequency component of the video signal undergoes amplitude modulation at the reference frequency and has a reference frequency component. The reference frequency component is detected by a reference frequency component detection circuit 11. Further, the amplitude and phase are detected by the synchronous detection circuit 12, and the focusing device of the lens 1 is driven so that the high frequency component is maximized.

The principle of detecting the driving direction of the motor 14 will be explained in more detail with reference to FIG. The vertical axis is the amplitude of the high frequency component, and the horizontal axis is the position of the focusing device of the lens, where "near" is the position where a close object is in focus, and "far" is the position where a long distance object is in focus. Now, if the subject is at a distance D1, when the focusing device is at a position corresponding to the distance, the high frequency component will be at its maximum, and it will be a mountain shape that decreases when moving toward either the far side or the near side. Becomes a characteristic. al and a2 indicate slight fluctuations in the reference frequency of the focusing device caused by the motor 14. The high frequency component undergoes amplitude modulation at the reference frequencies indicated by bl and b2 due to the change in focus due to the slight fluctuation. As is clear from FIG. 2, the amplitude modulation has a phase difference of 180° between the near and far sides of the in-focus position. Therefore, if the reference frequency component is detected from the high frequency component subjected to amplitude modulation such as bl, and synchronous detection is performed at the reference frequency to drive the motor 14 in the direction of 01, in the case of b2, the motor 14 is driven in the direction of C2. As a result, the amplitude of the high frequency component is always the maximum. In this way, a closed loop including the lens focusing device is formed, so the focusing device does not require high assembly precision, and the video signal itself is used to obtain focusing, so infrared rays are emitted. It has features such as no power consumption. By the way, in order to operate the system normally from low illuminance to high illuminance and from low contrast to high contrast, the high frequency component has a very large dynamic range and requires gain control. The gain control is performed by the gain control circuit 8 after the high frequency level detection circuit 9 detects whether the high frequency component is within a predetermined dynamic range.

However, with the above configuration, when the subject is in low illuminance or low contrast, the stability of the focusing system becomes a problem. That is, since the motor 14 drives the focusing device of the lens 1, its response is not fast. Therefore, to speed up the time to focus, the loop gain of the system is increased. However, if the subject is of low illuminance or low contrast, the gain of the gain control circuit 8 becomes large, and the loop gain becomes extremely high.

On the other hand, when the image is out of focus and the image is blurred, the noise component is masked by the reference frequency component and the system operates normally, but when the focus is focused, the amplitude of the reference frequency component decreases and the noise component becomes dominant. . If the loop gain of the system is extremely high at this time, the noise component will cause the motor to oscillate, causing the image to become blurred, resulting in poor stability and being very unsightly, and greatly restricting operation in low-light or low-contrast conditions. was. If the loop gain is still low, the response will be slow, and if the gain of the gain control circuit 8 is made small, there is a problem that the system will not operate if the subject has low contrast or low illuminance.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object thereof is to provide an automatic focusing device that has a quick response and operates stably even when an object has low illuminance or low contrast.

Structure of the Invention The present invention periodically and optically focuses a subject image formed on a light receiving surface of an image sensor, detects the amount of blur, and detects the high frequency of a video signal obtained by the image sensor. means for driving a focusing device of the lens so that the component is maximized; and (b) automatic means for increasing the amount of periodic optical blur when the subject is in low illumination or low contrast. It is a focusing device that makes it possible to reduce the gain of the circuit by increasing the amount of periodic and optical blurring during low illumination or low contrast, which greatly improves stability during focusing. It is possible.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows a block diagram of an automatic focusing device in a first embodiment of the present invention.

In FIG. 3, the gain of the gain control circuit 8 is controlled by the output of the high frequency level detection circuit 9 which detects whether the high frequency component is within a predetermined dynamic range. When the gain of the gain control circuit 8 becomes large due to illuminance or low contrast, the gain control circuit 16
This is a control circuit that increases the gain of the gain control circuit 17 and further decreases the gain of the gain control circuit 17 by the increased gain of the gain control circuit 16. 16 is a gain control circuit that controls the gain of the reference frequency by the control circuit 16 so that the amount of variation in the reference frequency of the motor 14 becomes large when the subject is in low illuminance or low contrast; , is a gain control circuit that is controlled by the control circuit 15 so that the output gain of the synchronous detection circuit 12 is reduced by the increase in the gain of the gain control circuit 16.

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

When a subject is photographed in low illumination or low contrast, the images obtained by a video camera have many noise components and the clarity deteriorates. Therefore, there is no practical problem even if the amount of periodic optical blurring of the object image formed on the light-receiving surface of the image sensor when the object is in low illuminance or low contrast is larger than in the normal case. On the other hand, increasing the amount of periodic and optical blurring increases the amplitude of the reference frequency component,
Since the reference frequency component is synchronously detected at the reference frequency to drive the motor, this is equivalent to increasing the loop gain of the system.

Therefore, even if the gain of the circuit is reduced by increasing the periodic and optical blurring amount, the loop gain of the system will equivalently remain the same.

The automatic focusing device of this embodiment utilizes the above-mentioned points. That is, when the amplitude of the high frequency component becomes small when the subject is in low illumination or low contrast, the high frequency component is amplified by the gain control circuit 8 so that it is within a predetermined dynamic range where circuit nonlinearity etc. do not become a problem. Ru.

A reference frequency component is detected from the gain-controlled high frequency components, and the amplitude and phase are detected by a synchronous detection circuit.

However, if the motor is driven as it is, as described above, the gain of the gain control circuit 8 has increased, making it vulnerable to noise components. Therefore, the gain of the gain control circuit 17 is
It is lowered by the control circuit 15 to such an extent that the motor does not swing due to noise components. Then, the gain control circuit 1
7, the gain of the gain control circuit 16 increases by an amount corresponding to the decrease in the gain of 7. This increases the periodic and optical blurring amount to prevent a decrease in the loop gain. Therefore, it is possible to improve the stability of the system during focusing when the subject is in low illuminance or low contrast, without lowering the loop gain of the system and slowing down the response.

As described above, according to this embodiment, by increasing the amount of periodic optical blurring of the subject image formed on the light receiving surface of the image sensor when the subject is in low illumination or low contrast, The gain of the circuit can be lowered without reducing the loop gain of the circuit, making it more resistant to noise components, and the stability during focusing can be significantly improved. Therefore, the usable range of the system can be dramatically expanded for subjects with low illuminance or low contrast.

In the embodiment, the gain control circuit 17 is provided after the synchronous detection circuit 12, but if the nonlinearity of the circuit does not become a problem when the amplitude of the high frequency component becomes small, the gain control circuit 17 may not be provided. , in place of the gain control circuit 170 during low illumination or low contrast, the gain control circuit 8 is made resistant to noise components without increasing the gain, and the deficiency in loop gain is compensated for by increasing the gain of the gain control circuit 16. Good too.

However, it is also possible to detect the amplitude of the video signal, detect that the subject is under low illumination based on the magnitude of the amplitude, increase the amount of periodic optical blur, and lower the gain of the circuit. .

Furthermore, the amount of periodic and optical blurring is increased and the gain of the circuit is lowered when the subject is in low illumination, low contrast, low illumination or low contrast, and low illumination and low contrast. Similar effects can be obtained in either case.

Effects of the Invention The automatic focusing device of the present invention periodically and optically focuses the subject image formed on the light receiving surface of the image sensor, detects the amount of blur, and adjusts the image signal obtained from the image sensor. The method further includes means for driving a focusing device of a lens so that a high frequency component of the object is maximized, and the amount of periodic optical blurring is increased when the object is in low illuminance or low contrast. As a result, the stability during focusing can be greatly improved, and the range of use for low illuminance and low contrast can be dramatically expanded, and its practical effects are significant.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional automatic focusing device, Fig. 2 is a diagram for explaining the principle of detecting the driving direction of a motor, and Fig. 3 is a block diagram of an automatic focusing device in an embodiment of the present invention. It is a diagram. 1...Lens, 2...Image sensor, 7.
...High frequency component detection circuit, 8...Gain control circuit, 9...High frequency level detection circuit, 1o...Reference frequency generator, 11・・・・・・
- Reference frequency component detection circuit, 12... Synchronous detection circuit, 15... Control circuit, 16... Gain control circuit, 17... Gain control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person wk
Figure iFigure 2

Claims (2)

[Claims] (1) The subject image formed on the light receiving surface of the image sensor is periodically and optically focused, the amount of blur is detected, and the high frequency component of the video signal obtained from the image sensor is maximized. An automatic focusing device comprising a means for driving a focusing device of a lens, and periodically increasing the amount of optical blur when the subject is in low illuminance or low contrast. Device. (2) The automatic focusing device according to claim 1, characterized in that the circuit gain of the system is reduced when the periodic optical blur amount is increased.