JPH07298119A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To correctly discriminate a moving direction of a lens even when automatic focusing is implemented under the lighting with flicker. CONSTITUTION:A high frequency component of a video signal obtained from an image pickup element 2 through an amplifier 3 is detected by a BPF 5 and a detection circuit 6 and a flicker period detection section 10 detects a period of flicker based on a level change of the video signal. A microcomputer 7 controls a motor drive circuit 8 and a motor 9 to implement wobbling of a lens 1 synchronously with the period of flicker. After the moving direction of the lens 1 is decided based on a change in the detected high frequency component obtained by the wobbling, the lens 1 is moved up to a position at which the detected value is maximized to obtain the focusing state. Thus, erroneous discrimination of the moving direction of the lens due to disturbance in the change of the detected value resulting from flicker is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device for automatically focusing the focus of an image pickup device such as a video camera.

[0002]

2. Description of the Related Art Conventionally, as an automatic focusing device of this kind, a high frequency component included in a video signal obtained from an image pickup device is extracted by a bandpass filter or the sharpness of an edge portion of a subject is extracted by a differentiating circuit or the like. There is known a method in which the focus state of the subject image is determined by doing so and the lens is moved so that the extracted amount, that is, the focus value is maximized, to obtain the focus state of the subject image. Next, an automatic focusing device according to this method will be described with reference to FIGS.

FIG. 3 is a block diagram showing the structure of a conventional image pickup apparatus. Reference numeral 1 is a lens, 2 is an image pickup element such as a CCD, and 3 is a lens.
Is a preamplifier, 4 is a process circuit, 5 is a bandpass filter (hereinafter abbreviated as “BPF”), 6 is a detection circuit, 7 is a logic control unit (hereinafter referred to as “microcomputer”), 8 is a motor drive circuit, 9 Is a motor for moving the lens.

Next, the operation will be described. The image of the subject is projected on the image pickup surface of the image pickup device 2 by the lens 1, and a video signal converted into an electric signal is obtained by the image pickup device 2. This video signal is amplified to a proper level by the preamplifier 3 and then converted into a standardized video signal such as NTSC by the process circuit 4. The output of preamplifier 3 is B
A high frequency component included in the video signal is extracted by the PF 5, and the detection circuit 6 obtains an output corresponding to the absolute amount of the high frequency component.

As shown in FIG. 4, the output of the detection circuit 6 changes depending on the amount of movement of the lens 1 at a certain position (point B).
Has a maximum value at. This is because when the amount of extension of the lens 1 changes, the focus state of the subject image projected on the image pickup surface of the image pickup element 2 changes, and when this is in focus, the sharpness of the projected image becomes maximum and the image pickup element This is because the absolute amount of the high frequency component contained in the signal becomes maximum when the signal is converted into the electric signal in 2.

The microcomputer 7 outputs the output of the detection circuit 6 to A /
D-convert and take in the lens 1 in the direction that maximizes this.
The rotation direction of the motor 9 is controlled via the motor drive circuit 8 so as to move. Then, by stopping the motor 9 at the position where the output of the detection circuit 6 is maximum, a focused state can be obtained.

In the above process, for example, first in FIG.
If the lens 1 is extended to the position shown by the dot,
First, an auxiliary vibration called a wobbling is performed to determine the direction of the point B, which is the in-focus position. In this method, the lens 1 is reciprocated back and forth several times with a very short width around the point A, and the direction of inclination of the point A is detected from the output of the detection circuit 6 during this time. By this operation, the direction of the point B is discriminated, and then the lens 1 is moved to the point B and stopped at the position where the output of the detection circuit 6 becomes maximum.

The principle of inclination detection by the wobbling operation will be described below. First, when the lens 1 is at the position shown in FIG. 4A, when the wobbling operation is performed at this position, a slightly higher focus value is detected as shown in S ₁ when the lens 1 is shaken in the direction shown in a, and b When the lens shakes in the direction indicated by (4), a slightly lower focus value is detected as indicated by S ₂ . On the other hand, when the lens 1 is at the position indicated by point C in FIG. 4, when the lens is shaken in the direction C, a slightly lower focus value is detected as shown in S _3, and when it is shaken in the direction d. A slightly higher focus value as shown at S ₄ is detected. By detecting the change of the focus value depending on the wobbling vibration direction in this way, the direction of the tilt at each lens position, that is, the direction of the point B, which is the focus position, can be determined.

Here, the cycle of the vibration of the lens 1 due to wobbling is the cycle of the video signal output from the image pickup device is 1
Since it is every vertical synchronization period (hereinafter abbreviated as “1V”),
In synchronism with this, as shown in FIG. 5A, the lens 1 is alternately oscillated every 1 V between the close-up side and the infinity side, that is, oscillated in a 2 V cycle, or when it is desired to increase the oscillation width, As shown in FIG. 2B, wobbling is generally performed such that the lens 1 is swung in a 4V cycle with the driving period of the lens 1 in between.

[0010]

However, in the above-mentioned conventional example, when an image is taken with an illumination fixture such as a fluorescent lamp for home use as a light source, the discharge occurs or stops depending on the frequency of the AC power source of the light source. That is, a so-called flicker occurs, which causes a change in the image output of the image sensor, which may result in erroneous direction detection due to the wobbling operation.

FIG. 6 shows flicker and changes in the output of the image pickup device 2 when the frequency of the AC power source is 50 Hz and the output signal standard of the video camera is NTSC system, that is, when the vertical synchronizing frequency is 60 Hz. FIG. 6A shows the change of the absolute voltage of the AC voltage with time. Since the AC power supply waveform is a sine wave, the waveform of the positive part of the sine wave of the absolute voltage is repeated at a 100 Hz cycle.

FIG. 6 (b) shows a repeated phenomenon of discharge of a fluorescent lamp. The fluorescent lamp starts discharging when the absolute value of the power supply voltage exceeds a certain value, that is, Vth shown in FIG. 6A, and stops discharging when the absolute value of the power supply voltage becomes lower than Vth. As shown in FIG. 6B, the light emission amount changes at 100 Hz cycles.

FIG. 6C shows a change in the amount of charge accumulated in the image pickup device 2 for each 1V. Image sensor 2 is 1V
The charge is repeatedly stored every 60 Hz. Therefore, while the fluorescent lamp is discharged almost twice in the period of V ₁ shown in FIG. 6C, once in the period of V ₂ and 2 /
The light quantity changes three times, once and ⅓ times during the period of V ₃ , and thus the accumulated charges also change as shown in FIG. 6C.

The output level of the image signal of the image pickup device 2 changes in the same manner because it is proportional to the accumulated charge amount, and the high frequency component and the focus value extracted by this change also change. When the wobbling operation is performed in such a state, for example,
It suffices to obtain a relatively large focus value change like wobbling at point A in FIG. 4, but in the case of wobbling at point C, it is possible to determine whether it is a focus change due to wobbling or a focus value change due to flicker. Therefore, the moving direction may be erroneously detected. For example, if the charge accumulation period at the point C in FIG. 4 when swung in the direction c is V ₁ shown in FIG. 6C, the lower focus value as shown in S ₃ in FIG. If no change is obtained, the value becomes higher on the contrary, and when it is further swung in the direction of d during the period of V ₃ shown in C of FIG. 6, the higher focus value as shown in S ₄ of FIG. The change is low. In such a case, the direction determination by wobbling is mistaken, the lens is driven in the direction opposite to the direction of the point B in FIG. 4, which is the in-focus point, the focusing operation time becomes extremely long, and, for example, the shooting timing is lost. There was a problem such as inconvenience.

The present invention has been made in order to solve the above problems, and an automatic movement in which the lens moving direction is not erroneous even when wobbling is performed in a state where flicker occurs due to a change in the amount of illumination light on a subject. The aim is to obtain a focusing device.

[0016]

According to a first aspect of the invention, a high frequency component of a video signal obtained from an image pickup device for photographing a subject through a lens is detected, and the lens is moved to a position where the detected value is maximum. By doing so, the in-focus state of the lens is obtained, at which time wobbling is performed to vibrate the lens back and forth, and the direction of movement of the lens is changed based on the change in the detected value of the high frequency component obtained by this wobbling. In the automatic focusing device configured to determine, the lens driving means for wobbling the lens, the flicker cycle detecting means for detecting a cycle of flicker due to a change in illumination light with respect to the subject, and the flicker cycle detecting means. The lens driving means is arranged so that the detected flicker cycle and the wobbling cycle are synchronized. Are provided and Gosuru control means.

According to the second aspect of the present invention, in the automatic focusing device having the above-mentioned configuration, the flicker period detecting section for detecting the flicker period is provided.

According to a third aspect of the present invention, in the automatic focusing device having the above-mentioned configuration, a flicker period detecting section for detecting the flicker period based on the level change of the video signal is provided.

[0019]

According to the first and second aspects of the invention, the wobbling operation is performed in synchronization with the detected flicker period, so that the moving direction of the lens can be correctly determined even under illumination with flicker.

According to the third aspect of the invention, the wobbling operation is performed in synchronization with the change in the output level of the video signal due to the flicker, so that the moving direction of the lens can be correctly determined even under the illumination with the flicker.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, parts 1 to 9 are substantially the same as the parts having the same reference numerals in FIG.

In FIG. 1, reference numeral 10 denotes a flicker period detecting section for detecting a flicker period. As the flicker cycle detection unit 10, a unit that detects a periodic level fluctuation from a change in the output level of the image sensor 2 and the flicker cycle is detected by the microcomputer 7 is used. Alternatively, the flicker may be detected optically, or the flicker cycle may be detected from the power supply frequency of the lighting equipment. Further, when the area where the product is used is limited, a flicker cycle which is known to occur in advance may be written in the memory.

The motor drive circuit 8 and the motor 9 constitute a lens drive means, and the microcomputer 7 constitutes a control means and a part of the flicker cycle detection section 10.

Next, the operation of the above configuration will be described. The process of converting the subject image projected by the lens 1 in FIG. 1 into an electric signal and obtaining a focus value is the same as in the conventional example of FIG. The output of the detection circuit 6 changes as shown in FIG. 4 as in the conventional example. The position of the lens 1 is shown in FIG.
If it is at point C, the wobbling operation is performed around this point C.

At this time, flicker due to a fluorescent lamp or the like occurs,
This is detected by the flicker period detector 10. At this time, when the output of the image pickup element 2 changes in a 3V cycle as shown in FIG. 2A, the wobbling cycle is synchronized with this and vibrated in a 6V cycle. FIG. 2B shows changes in the position of the lens 1 and changes in the focus value when the lens is swung in this manner.

As shown in FIG. 2 (a), even if flicker occurs due to a fluorescent lamp, the output of the image pickup device 2 changes in a cycle of 3V. Therefore, the vertical synchronization period shown by V ₁ , V ₄ , V ₇ , and V ₁₀ is obtained. Is constant if the lens position does not move. Lens in the direction of C of FIG. 4 to V ₁ period by wobbling operation 1
When the lens shakes, a slightly lower focus value is obtained as shown in S _3, and when the lens 1 shakes in the direction of d during the V ₄ period, S
_A slightly higher focus value is obtained as shown in ₄ . Since this change is purely due to the wobbling operation, even if the movement direction of the lens 1 is discriminated based on this change, no mistake will be made.

The timing at which the lens 1 is swung in the directions c and d in FIG. 4 by wobbling is particularly the maximum change in the output of the image sensor 2 due to flicker such as V ₁ , V ₄ , V ₇ , and V ₁₀ described above. The timing does not have to be. For example, as shown in FIG. 2C, V ₃ , V ₆ ,
The timing may be such that the output change of the image sensor 2 is the minimum such as V ₉ and V ₁₂ , and as shown in FIG. 2D, as in V ₂ , V ₅ , V ₈ , and V ₁₁ . The timing may be an intermediate timing between (b) and (c).

Furthermore, the period during which the lens 1 is shaken by wobbling may be a 2V period as shown in FIG. If it is fast, 3V as shown in Fig. 2 (f)
It may be a period. In such a case, for example, FIG.
In the case of the fluctuation of 2V period shown in (e), V ₁ , V ₂ , and V ₄
The direction may be determined based on the sum of the focus values of the respective periods such as V ₅ and V ₅ .

In the above, the wobbling operation is performed at a cycle twice the cycle 3V of the change in the video signal output due to flicker, that is, a 6V cycle. However, this is not particularly limited to the 6V cycle, and a triple 9V cycle or It may be an integral multiple, such as four times the 12V cycle.

[0030]

As described above, the invention of claim 1 is configured to detect the flicker cycle and perform the wobbling operation in synchronization with the flicker cycle.

Further, the invention of claim 3 is configured such that the wobbling operation is performed in synchronization with the change of the output level of the video signal due to the flicker.

Therefore, according to the present invention, the moving direction of the lens can be correctly discriminated even in the case of photographing under the flicker illumination such as a fluorescent lamp, and there is an effect that a good focusing operation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the embodiment.

FIG. 3 is a block diagram showing a conventional imaging device.

FIG. 4 is a graph for explaining a focusing operation.

FIG. 5 is a timing chart for explaining a focusing operation.

FIG. 6 is a timing chart for explaining a focusing operation.

[Explanation of symbols]

 1 Lens 2 Image Sensor 5 Band Bass Filter 6 Detection Circuit 7 Microcomputer 8 Motor Drive Circuit 9 Motor 10 Flicker Cycle Detection Section

Claims (3)

[Claims] 1. A focused state of the lens is obtained by detecting a high frequency component of a video signal obtained from an image pickup device for photographing a subject through the lens and moving the lens to a position where the detected value is maximum. In this case, wobbling is performed to vibrate the lens back and forth, and automatic movement is performed to determine the moving direction of the lens based on the change in the detected value of the high frequency component obtained by this wobbling. The focusing device is provided with a lens driving means for wobbling the lens, and a control means for controlling the lens driving means so that a cycle of flicker and a cycle of the wobbling due to a change in illumination light with respect to the subject are synchronized. Automatic focusing device. 2. The automatic focusing device according to claim 1, wherein:
Further, the flicker detection means for detecting the flicker is provided, and the control means is configured to control the lens driving means by synchronizing the flicker cycle detected by the flicker detection means and the wobbling cycle. Automatic focusing device characterized by. 3. A focused state of the lens is obtained by detecting a high frequency component of a video signal obtained from an image pickup device for photographing a subject through the lens and moving the lens to a position where the detected value is maximum. In this case, wobbling is performed to vibrate the lens back and forth, and automatic movement is performed to determine the moving direction of the lens based on the change in the detected value of the high frequency component obtained by this wobbling. In the focusing device, a lens driving means for wobbling the lens, a flicker cycle detecting means for detecting a flicker cycle due to a change in illumination light for the object from a level change of the video signal, and a flicker cycle detecting means for detecting the flicker cycle. The lens driving means is controlled so that the flicker cycle and the wobbling cycle are synchronized. An automatic focusing device having a control means.