JPH039677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention periodically and optically changes the imaging state of a subject that is imaged on the imaging surface at a reference frequency in a television camera, and this change causes the high frequency components of the video signal to be reduced. The present invention relates to an automatic focusing device that adjusts the focus by changing the focus.

As a conventional technology, a signal obtained from an image sensor is passed through a single bandpass filter to detect a high frequency component, a modulation component due to a periodic optical change in the imaging state included in this signal is detected, and this signal is used to detect a high frequency component. There is a method of driving a focusing device so that high frequency components are maximized.

However, if there is a large degree of defocus, the high frequency component becomes small and is lost in the noise component, resulting in malfunction.

The present invention provides a highly accurate automatic focusing device that prevents the above-mentioned malfunctions.

First, the prior art will be explained using FIG. 1. 1 is a lens with a focusing device, and 12 motors drive this device. 2 is an image pickup tube that converts the optical information of the subject into an electrical signal; 3 is a preamplifier that amplifies the output signal of the image pickup tube 2; 4 is a gamma correction;
A process circuit that performs blanking processing, addition of synchronization signals, etc. converts the electrical signal into a television signal. 6 is a synchronization signal generator which generates a synchronization signal, a blanking signal, a vertical drive signal, a horizontal drive signal, etc. A deflection circuit 5 deflects the beam from the image pickup tube 2. 7 is a band pass filter (BPF) for extracting high frequency components of the video signal; 10 is a reference frequency generation circuit for periodically slightly changing the focus of the lens 1; a motor drive circuit 11;
2, the focusing device of the lens 1 is slightly moved to slightly change the focus to the extent that it cannot be detected by the eye. As a result, the output of the BPF 7 slightly changes with the period of the reference frequency. The reference frequency component detection circuit 8 detects only the reference frequency component included in the output signal of the BPF 7. This signal and the reference frequency signal of the reference frequency generating circuit 10 are synchronously detected to detect the driving direction of the motor 12, and a feedback loop is constructed so that the amplitude of the output signal of the BPF 7 is maximized.

Next, the driving direction of the motor 12 will be explained with reference to FIG. FIG. 2 shows the amplitude characteristics of the output signal of the BPF 7 when the focus adjustment device is changed to a short distance when the object is at a distance of _D1 . When the distance is adjusted to be closer than D ₁ , if the slight change in the focusing device caused by the motor 12 is a ₁ , then the change in amplitude is
b Becomes ₁ . This signal is synchronously detected and the output signal is used to move the focusing device in the direction of the arrow _c1 . Then, when adjusted to a distance farther than D ₁ , if the focusing device changes as a ₂ , the output signal of BPF 7 will change as b ₂ , so the synchronous detection output will have the opposite polarity than above. , the focusing device moves in the direction of the arrow c ₂ and as a result stabilizes at the point D ₁ where the output signal of BPF 7 is maximum. Like this,
When the focus is slightly changed, the direction in which the image is always out of focus is quickly created due to changes in the high frequency components of the video signal, and by feeding this back to the focusing device of the lens, an automatic focusing device with quick response can be obtained. It will be done. The lens system is also in a feedback loop, so the accuracy of focusing is very high. However, if the distance to the subject and the distance at the lens focusing device deviate, the output of BPF 7 becomes very small, which causes noise. As the frequency becomes larger, the reference frequency component indicating the driving direction of the lens focusing device also becomes extremely small and is lost in noise, resulting in malfunction.

In the present invention, when the focus adjustment of the lens is greatly deviated, by calculating the output signals of the BPF with a high center frequency and the BPF with a low center frequency,
Find out the driving direction of the lens focusing device,
This reduces errors in lens focus adjustment and drives the BPF with a high center frequency to maximize its output signal, eliminating malfunctions. Figure 3 shows the characteristics of the output signals of BPF1 with a low center frequency and BPF2 with a high center frequency.

Since the output signal of BPF1 is very broad, the detection range is very wide. Therefore, when the output signal of BPF2 is small, the output of BPF1 forms an autofocus feedback loop, and when the amplitude of the output signal of BPF2 exceeds a certain value and a sufficient reference frequency component is obtained, the output Create an autofocus feedback loop.

A basic embodiment of the invention is shown in FIG.

1 to 6 and 8 to 12 operate in the same way as the same numbers in FIG. That is, the motor is caused to move slightly at the reference frequency, and the high frequency component of the electrical signal obtained by the image pickup tube 2 is changed to an invisible degree. Then, high frequency components are detected by two bandpass filters 13 and 14 having different center frequencies. One bandpass filter 13 has a low center frequency, for example, a band of 200 KHz to 1 MHz, and has characteristics as shown in BPF 1 in FIG. 3. That is, the detection range is very wide, but the detection sensitivity is poor. The other bandpass filter 14 has a high center frequency, for example, a band of 15 MHz to 25 MHz, and has characteristics as shown in BPR2 in FIG. 3. In other words, the detection range is narrow, but the detection sensitivity is excellent.

15 is an arithmetic processing circuit; when the focus of the lens is shifted and the image is blurred, the output of the bandpass filter 14 is very small, so the output of the bandpass filter 13 forms a feedback loop; If the output of the filter 14 is above a certain level, the output forms a feedback loop. In addition, in this case, when the focus gradually shifts from the stage where the focus is largely shifted and the image is blurred and the output of the bandpass filter 14 increases, the reference frequency component obtained from the output also increases. The configuration may be such that the bandpass filters forming the feedback loop are changed depending on the magnitude of the reference frequency component. Next, a specific example of the arithmetic processing circuit 15 is shown in FIG. In the figure, D ₁ ,
D ₂ is a diode, and C ₁ and C ₂ are capacitors, which constitute a peak rectifier circuit that rectifies the peak values of the output signals of band pass filters BPF1 and BPF2, and changes with the reference frequency signal of circuit 10 in Fig. 4. This component has a time constant that is not smoothed.
17 is a comparator, and when the output of BPF2 exceeds a certain amplitude, the output signal _C0 becomes high level. 16 is an analog switch; when the output signal C ₀ becomes high level, the input signal I ₂ becomes the output signal of the analog switch; when C ₀ becomes low level, the input signal I ₁ becomes the output signal of the analog switch 16. becomes. In this way, when the output signal of BPF2 is small, the output signal of BPF1 forms the feedback loop of the automatic focusing device, and when the output signal of BPF2 exceeds a certain amplitude, the output signal forms the feedback loop. It becomes like this.

Next, FIG. 6 shows a specific example of a means for achieving focus matching with even higher precision. 18, 19, 2 in the diagram
0 and 21 are bandpass filters having different center frequencies and overlapping bands, and the center frequencies increase in the order of 18, 19, 20, and 21. 22, 23, and 24 are comparators, and the output signals of the bandpass filters 21, 20, and 19 are
When I ₆ , I ₅ , and I ₄ exceed a certain level, the output signal
C ₃ , C ₂ and C ₁ become high level. 25 is a discrimination circuit, so that when _C3 is at a high level, _C2 is given priority; no matter what level _C1 is, if _C3 is at a low level and _C2 is at a high level, priority is given to _C2 no matter what level of _C1 is. It drives 26 analog switches. In other words, when a signal with a higher frequency component exceeds a certain level, priority is given to it and a feedback loop is formed.

Another example of a method for detecting high frequency components is shown in FIG. Similar to FIG. 6, 18 to 21 are band pass filters having different center frequencies, and their outputs are added by resistors R ₃ , R ₄ , R ₅ , and R ₆ . At this time, output signals with high center frequencies are weighted and added together so that they become larger. In the specific example above, the bandpass filters that make up the feedback loop change depending on the magnitude of the output signal of each bandpass filter. When the signal becomes large, the magnitude of the reference frequency component obtained from the signal also exceeds a certain level, so it goes without saying that the above specific example can also be constructed by detecting the reference frequency component and using the detected signal. As described above, according to the present invention, the detection range is expanded to detect high-frequency components of the image, and the focusing device of the lens is also included in the feedback loop, so the formed image can be periodically rotated with extremely high precision. Since out-of-focus is constantly detected by optical blurring, an automatic focusing device with quick response can be constructed. In other words, even if the precision of the focusing device is rough, or even if the focus varies slightly due to temperature, as with a plastic lens, the focusing device remains stable as a system. In addition, since the feedback loop is configured with a signal detected as a high-frequency component signal with good focusing accuracy, it has extremely outstanding functions and effects, such as becoming a highly accurate automatic focusing device.

An example of the present invention has been described using a method in which the focusing device of the lens is slightly moved by a motor to slightly blur the image formed on the image sensor, but other methods, such as using glass between the subject and the image sensor, have been described. It is also possible to apply a method in which the optical path length is varied by inserting a glass and varying the degree of inclination of the glass.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional automatic focusing device, FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1, and FIG. 3 is a characteristic diagram of the BPF used in the present invention.
FIG. 4 is a block diagram of an automatic focusing device according to an embodiment of the present invention, and FIGS. 5, 6, and 7 are block diagrams showing specific examples of essential parts of the present invention. DESCRIPTION OF SYMBOLS 1... Lens with a focusing device, 2... Image pickup tube, 10... Lens, 2... Image pickup tube, 10... Reference signal generation circuit for finely moving the focusing device of the lens at low frequency, 12... . . . A motor for driving a lens focusing device, 13, 14 . . . Band pass filter for obtaining a high frequency component signal, 15 . . . Arithmetic processing circuit.

Claims (1)

[Scope of Claims] 1. means for generating a reference frequency signal, means for periodically and optically changing the imaging state of a subject imaged on the imaging surface of an image sensor at the frequency, and the image sensor If the level of the signal of a plurality of bandpass filters having different bands or center frequencies into which video signals obtained from the above are inputted, and the bandpass filter having a higher center frequency among the output signals of the bandpass filters exceeds a certain level, means for prioritizing the signal; means for detecting a periodic or optical change component of the imaging state from the output signal of the means; means for comparing the change component with the phase or amplitude of the reference frequency signal; An automatic focusing device comprising means for driving a lens focusing device based on a comparison result. 2. A patent claim characterized in that, when the output signal of the bandpass filter with the highest center frequency among the plurality of bandpass filters exceeds a certain level, the output signal is used to drive a lens focusing device. The automatic focusing device according to the range 1.