JPH01125065A - Automatic focussing device - Google Patents

Abstract

PURPOSE:To decrease mal-actions in judging focussing/defocussing by determining the reference signal level of a focussing judging means to judge a focussing point corresponding to the special frequency component level of a video signal from an image pickup means at the time of closing an iris. CONSTITUTION:A focussing signal detecting circuit 12 detects the special high-frequency component level in a video signal from the image pickup element 2. And a focussing reference level control circuit 16, during a period when the closing of an iris does not cause any harm such as a time immediately after the turning-on of a power source, transmits a command to an iris drive circuit 15 to close the iris. Depending on the magnitude of a level detected by the circuit 12, the output of a focussing reference level generating circuit 14 is set. After finishing this setting, the closing of the iris is released, and the device is returned to its normal image pickup state. Thereafter, the focussing judging circuit 13 compares a corrected output from the circuit 14 with an output from the circuit 12, and thus judges the focussing/defocussing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device, and particularly to an automatic focusing device suitable for a video camera.

Conventional technology As an automatic focusing device that takes advantage of the characteristics of video cameras, it detects the definition of the screen using the high-frequency components of the video signal being shot, and adjusts the focusing lens to maximize the definition. A method of controlling the entire position is being considered. One of the above methods, the so-called mountain climbing control method, will be explained. FIG. 3 is a block diagram of the configuration of an automatic focusing device based on the Yamato system. 1 is a lens, 2 is an image sensor, 3 is a camera circuit, 4 is an output terminal for a video signal, 5 is a bypass filter, 6 is a detector, 7 is a differential hole/read circuit, 10 is a motor drive circuit, 11 is a lens A motor for moving the position of the focusing lens 1 (hereinafter referred to as lens position), 12 a focus signal detection circuit, 13 a focus judgment circuit, 14 a focus reference level voltage, 8 a bypass filter 6, and a detection circuit. This is a mountain climbing circuit that collectively represents the blocks of the circuit 6 and the differential hold circuit 7. The operation of the configuration shown in FIG. 3 will be described below using the characteristic diagram shown in FIG. 4.

Light from the subject entering through the lens 1 forms an image, is processed into a stain completion signal by the image sensor 2, processed by the camera circuit 3, and outputted to the terminal 4 as a video signal. After only the high-frequency components of the video signal are extracted by the bypass filter 5 and detected by the detector 6, the voltage corresponding to the high-frequency components of the video signal that is applied to the terminal 9 (hereinafter referred to as focal voltage) is: If the position of the lens 1 is changed for the same object, the voltage will be as shown by curve A in FIG. 4. Since this focal voltage corresponds to the definition of the captured image, it is at the maximum when the lens position of the lens 1 (referred to as A) coincides with the in-focus position of the lens 10, and decreases as it deviates from this position.

While moving the lens position by the motor 11, the differential hold circuit samples and holds the focal voltage appearing at the terminal 9 at fixed time intervals, and if the focal voltage is increasing over time, it is a positive voltage, and it is decreasing. If it is in the direction, a negative voltage is output.

In the motor drive circuit 10, when the voltage of the differential hold circuit 7 appearing at the terminal 9 as shown at the curved line in FIG. 4 is positive,
The direction of rotation of the motor 11 is kept as it is to continue climbing the mountain 9, and when the rotation direction is negative, the direction of rotation is reversed and returned to the direction of climbing the mountain. In this way, the lens position control circuit shown in FIG. By vibrating in small increments at the top and reaching a steady state), automatic focusing is possible.

The above is the basic operation of the mountain climbing method, but this alone causes many malfunctions, and in general, the following focus/out-of-focus judgments are used to stop or start the motor. It has a judgment device.

Reference numeral 12 denotes a focus signal detection circuit that detects the level of a specific high frequency component in the video signal of the image sensor 2.

The focus determination circuit 13 compares the focus reference level voltage 14 with the output of the focus signal detection circuit 12 and determines whether the focus signal detection circuit 1
If the output of 2 is larger than the focus reference level voltage 14, it is determined that the focus is in focus, and a stop command is issued to the motor drive circuit 1o.
The mountain climbing operation is stopped, and if it is small, it is determined that the focus is out of focus, a driving command is issued, and the mountain climbing operation is started.

According to the above operation υ, the mountain climbing circuit is 1. near the top of the mountain.
When searching for mountains and hunting more than necessary, the output of the focus signal detection circuit 12 becomes the focus reference level voltage 1.
Since it is larger than 4, the mountain climbing operation is stopped, thereby preventing hunting.

Furthermore, due to camera shake or the like, the focal voltage may change, causing a false peak in the focal voltage, which may be mistaken for an actual peak, causing the lens to stop. In that case, the focus signal detection circuit 12
Due to the low output of the lens, a restart is required to prevent the lens from stopping at an out-of-focus position.

The above is an example of a conventional automatic focusing device using a video signal.

Problems to be Solved by the Invention However, with the above configuration, the output of the focus signal detection circuit 12 is affected by noise in the video signal, so it is easy to misjudge in-focus/out-of-focus. .

The relationship between the lens position and the output of the focus signal detection circuit 12 is the curve shown in FIG. 6A. The focusing reference level voltage 14 is
In the diagram a, when the curve a is higher than the level a, the motor 11 stops. That is, when the lens is moved from close range, the motor 11 stops at the position shown in FIG. 5B.

When noise is superimposed on the focus signal detection circuit 12, the fifth
At this time, when the curve edge exceeds the level shown in Figure 6 a, it is determined that the focus is in focus, and the motor 11 stops, so that the curve is moved from the focus position (Figure 5 A). It stops at a large distance (position C in Figure 5).

The noise superimposed on the focus signal detection circuit 12 may include noise in the image sensor output, noise in the electronic circuit from the image sensor 2 to the focus signal detection circuit 12, etc.
In particular, the noise in the image sensor output is large.

Image sensor noise varies depending on the image sensor.
In addition, even in the same image sensor, it changes depending on the ambient temperature. Particularly in the case of a solid-state image sensor, when the temperature rises, the dark current increases and the noise rises significantly.

The level of noise superimposed on the curve in Figure 5 A changes,
In some cases it will be similar to the curve at the mouth of Figure 6, and in other cases it will be higher.

Therefore, in the conventional configuration, the lens position determined to be in focus changes depending on the level of the superimposed noise, and there is a problem in that the lens position determined to be in focus changes when it is out of focus.

In view of the above-mentioned problems, the present invention provides an automatic focusing device that is less prone to errors in determining focus/out-of-focus due to the influence of noise in a video signal.

Means for Solving the Problems In order to solve the above problems, the automatic focusing device of the present invention has a reference signal level μ of the focus 1 determining means for determining the in-focus position.
is determined in accordance with the specific frequency component level of the video signal of the imaging means when the iris is closed.

Effect According to the above configuration, the level of noise superimposed on the video signal has a strong correlation with the video signal level when the iris is closed, so the level of the video signal when the iris is closed is By correcting the reference level of the determination circuit, it is possible to reduce malfunctions in determining focus/out-of-focus.

Embodiment Hereinafter, an automatic focusing device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the configuration of an automatic focusing device in an embodiment of the present invention.

In Fig. 1, 1 is a lens, 2 is an image sensor, 3 is a camera circuit, 4 is an output terminal for a video signal, and 5 is a bypass filter.
6 is a detector, 7 is a differential horn circuit, 10 is a motor drive circuit, 11 is a motor, 12 is a focusing signal detection circuit,
13 is a focus judgment circuit; 14 is a focus reference level generation circuit;
15 is a ° iris drive circuit, 8 is a bypass filter 6,
The detector 6 and the differential hold circuit 7 are collectively represented by a Yamato circuit; 16 is a focusing reference level control circuit.

Regarding the automatic focusing device configured as above, the following is
The operation will be explained using FIGS. 1 and 2.

In FIG. 1, a lens 1, an image sensor 2, a camera circuit 3
, bypass filter 6, detector 6, differential hold circuit 7
, motor drive circuit 10. The mountain-climbing operation through the motor 11 is the same as in the conventional example, and will therefore be omitted.

The focus signal detection circuit 12 detects the level of a specific high frequency component in the video signal of the image sensor 2.

The relationship between the lens position and the output of the focus signal detection circuit 12 is as shown in the curve shown in FIG. 2A.

If the output of the reference level generation circuit 14 is at the level ~ in Figure 2a, and if it goes from the lens position (closest in Figure 2) to the in-focus lens position (Figure 2A), then the curve A and It stops at the lens position of intersection B of level 7kfi. point B and A
The points are close and within the depth of field there is no problem.

However, when noise is superimposed on curve A in Figure 2, the second
The intersection of the curved line and the reference level a is at the lens position C.
Move away from focal point A.

Incidentally, the level of the superimposed noise has a correlation with the output level of the focusing signal detection circuit 1.2 when the input optical signal from the lens 1 is blocked and darkened.

That is, when the noise level is high, the level of the focus signal detection circuit 12 during unattended operation is high, and when the noise level is low, the level is low.

In addition, immediately after the power is turned on, or when the video camera is in playback mode, there is no problem even if it is dark, so in this embodiment, the focus reference level control circuit 16
Immediately after N, a command is sent to the iris drive circuit 16 during a period when no problem will occur even if the iris is closed, the iris is closed, and the focus signal detection circuit 12 at that time is sent.
Depending on the magnitude of the level, the focusing reference level generation circuit 14
Set the output of After completing this setting, the iris is unclosed and the normal shooting state is restored.

Thereafter, the focus determination circuit 13 compares the corrected output of the focus reference level generation circuit 14 and the output of the focus signal detection circuit 12 to determine in-focus/out-of-focus.

That is, when noise is superimposed as shown in Figure 2, the output of the focusing reference level generation circuit 14 is equal to the level zvb in Figure 2, and the intersection thereof is the level B in Figure 2. position. That is, if no correction is applied, the lens position C will move to the lens position B and will be in focus.

Further, in this embodiment, an example of a mountain climbing method has been described, but the invention is not limited to the mountain climbing method, but can be applied to an automatic focusing method that focuses based on the definition of a video signal.

Effects of the Invention As described above, the automatic focusing device of the present invention is configured to set the reference level of the focus determination means for determining in-focus/out-of-focus according to the level of the video signal when the iris is closed. Therefore, it is possible to reduce malfunctions of the automatic focusing device in determining in-focus/out-of-focus due to noise superimposed on the video signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic focusing device in an embodiment of the present invention, and FIG. 2 is a characteristic diagram for explaining the operation of the embodiment.
Figure 3 is a block diagram of a conventional automatic focusing device; Figure 4;
FIG. 6 is a characteristic diagram of the conventional example. 1...Lens, 2...Image sensor, 3.
... Camera circuit, 4 ... Video signal output terminal, 6 ... Bypass filter, 6 ...
・Detector, 7...Differential ho tk F circuit, 8
...Yamatobi multi-circuit, 9...Focus voltage, 1
0... Motor drive circuit, 11... Motor, 12. Old... Focusing signal detection circuit, 13...
Focus determination circuit, 14...Focus reference level generation circuit, 16...Iris drive circuit, 16...
...Focusing reference level control circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure to CBA No Lens position

Claims (1)

[Claims] a first driving means for changing the relative distance between the optical lens system and the imaging device according to a control signal; and extracting a high frequency component of a video signal output from the imaging device, and increasing the level of the high frequency component. control signal generating means for generating the control signal in the direction; detecting the level of a predetermined frequency component extracted from the video signal; and only when the detected level is equal to or higher than the reference signal level, Automatic focusing comprising: a focus detecting means for stopping the first driving means; and a means for setting the reference level according to the detection level of the detecting means when an iris provided in the optical lens system is closed. Device.