JPH0534871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device for a video camera.

Traditionally, automatic focusing devices for video cameras detect the definition of the screen using high-frequency components in the video signal, and then control the rotation of the lens focusing ring (hereinafter referred to as helicoid) to maximize the definition. So-called mountain climbing control is known. This method is based on the NHK Technical Research Report No. 17, 1963.
No. 1, Volume 86, page 21, it is described in detail by Ishida et al. as ``Automatic focus adjustment of television cameras using mountain-climbing servo method.''
This will be briefly explained using FIGS.

FIG. 1 is a block diagram showing the configuration of an automatic focusing device (hereinafter referred to as AF device) using a hill climbing method. 1 is a lens, 2 is a camera circuit, 3 is a video signal output terminal, 4 is a high-pass filter, 5 is a detector, 6 is a differential hold circuit, 7 is a motor drive circuit, and 8 is a motor for rotating the helicoid of the lens. It is.

The operation of the configuration shown in FIG. 1 will be explained below using the characteristic diagram shown in FIG. 2.

Light from a subject that enters a lens 1 is converted into an electrical signal by a camera circuit 2, and outputted to a terminal 3 as a video signal. Only the high-frequency components of the video signal are extracted by the high-pass filter 4, detected by the detector 5, and then appear at the terminal 51. What should be noted here is that the voltage corresponding to the high-frequency component of the video signal appearing at the terminal 51 (hereinafter referred to as focal voltage) corresponds to the definition of the photographed image, so as shown in FIG. The voltage will be maximum if the helicoid position of lens 1 (referred to as A) matches the distance to the subject;
The value decreases as the value deviates from the original value.

What can be determined from FIG. 2 is that if the helicoid position is controlled by some means so that the focus voltage, which is the output of the terminal 51, is maximized, automatic focusing can be achieved. This means is achieved by the differential hold circuit 6 to motor 8 shown in FIG. That is, the differential hold circuit samples and holds the focal voltage appearing at the terminal 51 at fixed time intervals as shown in FIG.
This circuit generates a negative voltage if the focal voltage decreases over time, and the motor drive circuit 7
If the output voltage of the differential hold circuit 6 appearing at the terminal 61 is positive, the motor 8 is rotated in the forward direction to move the helicoid position in the forward direction, and if the same output voltage is negative, the motor 8 is rotated in the reverse direction to move the helicoid position. Move in the direction of the backlight.

The differential hold circuit output voltage in Figure 2 shows the case where the helicoid is rotated from close range to infinity, but it is easily understood that the same applies when the helicoid is rotated from infinity to close range. .

In this way, the helicoid position control loop of the motor 8 climbs the mountain created by the focal voltage using the output voltage of the differential hold circuit 6, and finally reaches a steady state at the top of this mountain while vibrating in small increments. It is understood that automatic focusing is possible.

The above is an automatic focusing device for a video camera using the mountain climbing method.

Although the above-mentioned device has sufficient performance as an automatic focusing device, it has the following drawbacks.

In other words, if the subject to be photographed changes due to movement, panning of the camera, or camera shake, the focal voltage will also respond to this change, so the straightforward focal voltage characteristic shown in Figure 2 will not work. This has the disadvantage that a plurality of peaks and troughs occur in the focal voltage, resulting in incorrect focusing, resulting in malfunctioning hill-climbing operation and large out-of-focus. In order to eliminate this drawback, the present applicant previously proposed the method shown in FIG. 3 (see Japanese Patent Application No. 56-9370).

In FIG. 3, blocks 1 to 9 are the same as in FIG. 10 is a subject change detection circuit;
1 indicates a gate circuit.

If there is no change in the subject, as described above, the mountain climbing circuit 9 moves the lens 1 using the motor drive circuit 7 and the motor 8 to perform a hill climbing operation using the output of the camera circuit 2. When the subject is changing, the subject change detection circuit 10 detects the change from the output of the camera circuit 2, and the gate circuit 1 detects the change from the output of the camera circuit 2.
1 separates the mountain climbing circuit 9 from the motor drive circuit 7 and stops the mountain climbing operation, thereby preventing defects in the mountain climbing operation due to changes in the subject. Furthermore, a circuit shown in FIG. 4 has been proposed as an example of a single circuit configuration of the subject change detection circuit 10.

In this figure, 12 is a gate circuit, 13 is a low-pass filter, 14 is an amplifier, 15 is a differential circuit, 16 is a monostable multivibrator, 17 is a pulse number counting circuit, and 18 is a fluctuation detection circuit. First, a specific portion of the screen is extracted from the video signal 3 which is the output of the camera circuit 2 by the gate circuit 12 using the view angle gate signal 122, and is made into a signal 121. Furthermore, in order to prevent the output from being affected even if the camera is out of focus, the waveform is blunted through a low-pass filter 13 with a cutting frequency of several hundred KHz, and then the amplifier 14 outputs a preset gray value or input signal. The average value of is set as a threshold value, and the output signal of the low-pass filter exceeding this threshold value is amplified until it is saturated and becomes a pulse train 141. This pulse train 141 is differentiated by a differentiating circuit 15 and converted into a pulse train 161 with a constant pulse width by a monostable multivibrator 16.
An analog output 171 is generated by the pulse count circuit 17. In this way, analog output 1
At 71, a voltage corresponding to the picture being photographed is obtained. Note that at this time, the angle of view gate signal 12
By resetting the count for each pattern using the reset signal 172 corresponding to 2, it is possible to respond even to instantaneous fluctuations in the pattern. By detecting variations in the analog output 171 by the variation detection circuit 18, it is possible to identify that the subject has changed.

As explained above, in the configuration of the prior application, the number of pulses of brightness change in each image is counted, and the fluctuation detection circuit 18 detects a change in the number of contours and identifies that the subject has changed. ing. However, although the configuration example shown in FIG. 4 can reduce defects in mountain-climbing motion due to changes in the subject in many situations, it has the following drawbacks. That is, near the in-focus point (near the top of the mountain in FIG. 2), only the change in the number of contours due to pattern variation can be faithfully identified, and there is no problem even if the lens position moves slightly near the in-focus point.
However, if the lens position deviates significantly from the in-focus point for some reason, the significant reduction filter characteristics of the lens (for example, the cutoff frequency
(approximately 30KHz), the signal from the subject's camera circuit is completely distorted, and it is no longer possible to accurately count the number of contours the subject has, and the counted value changes as the lens position moves. This may result in erroneous counting, where the subject is not moving, but the variation detection circuit 18 generates a variation detection signal due to the movement of the lens position, and the lens climbs a mountain. This causes the inconvenience of stopping the operation and stopping at a blurred area, making it impossible to perform a good focusing operation. And as shown in Figure 4,
This requires a pulse circuit and a linear circuit, making the circuit scale considerably complicated.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above and simply provide a circuit that more faithfully generates a fluctuation detection signal only when the subject changes, thereby reducing malfunctions caused by subject changes and improving the video signal. The objective is to realize a better automatic focusing device using

The gist of the present invention is to compare the DC levels of video signals of different fields, and to detect changes in the subject based on the comparison results, as a method for accurately detecting changes in the subject from video signals.

FIG. 5 shows a subject change detection circuit 10 according to the present invention.
This is an example showing a circuit configuration of. 3 is a video signal input terminal from the camera, and 19 is a reduction filter set to a cutoff frequency lower than the cutoff frequency f _CL (20 to 30KHz) when the image reaches the blurred position, which is the equivalent reduction filter characteristic of the lens. The circuit (for example, cut-off frequency f _CC 30Hz to 100Hz, f _CC <<f _CL ), 20, an amplifier circuit 18, is a fluctuation detection circuit as shown in FIG. When the video signal from the camera that photographs the current object and is obtained at the terminal 3 is passed through the reduction filter 19 and amplified by the amplifier circuit 20, a signal waveform as shown in the solid line in FIG. 6 is obtained at the terminal 171. . As mentioned above, this signal waveform is the cutoff frequency f _CL of the equivalent reduction filter characteristic of the lens when it reaches the blurred position.
Since the cut-off frequency f _CC is passed through the reduction filter circuit 19, which is sufficiently low compared to Minor. However, when the subject or picture changes, the frequency spectrum of the picture changes from the reduced frequency component (brightness, gradation component, signal component indicating the brightness of the picture) to the high frequency component (i.e., the distance between the pictures or Even if only the reduced frequency component is extracted, the appearance of the waveform changes greatly as shown by the dashed line in FIG. 6. Therefore, terminal 171
The fluctuation detection circuit 18 detects the level fluctuation of the waveform (for example, detects the level fluctuation at the timing A for each picture) due to the change in the object obtained, and obtains the object fluctuation detection signal terminal 181.

FIG. 7 is an example of the fluctuation detection circuit 18 in FIG. 5, and FIG. 8 is a diagram for explaining its operation. The output signals of the amplifier circuit 20 are different in phase by one field period T _F1 (vertical period),
The signal is then input to sample-and-hold circuits 22 and 23, which respectively sample and hold the signal using sampling pulses P _S1 and P _S2 having a period T _F2 of two fields. The output signals of the sample and hold circuits 22 and 23 are input to a voltage comparison circuit 24 for voltage comparison.
The voltage comparator circuit 24 generates a pulse voltage at the output terminal only during the period T _P during which a predetermined voltage difference or more is generated (or for a predetermined period after a predetermined voltage difference or more is generated). This is the object variation detection signal, and with the configuration shown in FIG. 7, it is possible to detect variations for each picture (every vertical period).

Its operational functions will be explained in detail using FIG. Now, if the object changes or the camera pans, and the stationary picture a changes to the picture b, then the output signal of the amplifier circuit 20 will be the signal V _L shown in A in the figure. When the signal V _L is sampled and held by the sample and hold circuits 22 and 23, the signal shown by the chain line is obtained at the output of the sample and hold circuit 22, and the voltage shown by the solid line is obtained at the output of the sample and hold circuit 23.

The difference voltage between these two voltages is shown in Figure B. If the difference voltage exceeds a predetermined voltage V _TH , the voltage comparator circuit 2
4 generates a pulse signal during this period or a predetermined period. The purpose of setting the predetermined voltage V _TH is to prevent voltage drift in the circuit from being sensitive to extremely small voltages.

FIG. 9 is a circuit diagram of another invention, which is a further improvement of the invention of FIG. In other words, in Fig. 6, depending on the picture content, even at timing A, as shown at timing B, even if the picture changes, a level change cannot be detected, although it is rare, and in such cases, the subject This means that it will not be possible to detect fluctuations in . FIG. 9 is an improvement on this, in which the waveform shown in FIG. 6 obtained at the terminal 171 is double-wave rectified and smoothed by the circuit 21, and is applied to the terminal 172 for each picture (every vertical period). The DC voltage obtained by resetting with the reset signal obtained at the terminal 173 is obtained at the terminal 173, and the variation detection circuit 18 detects the change in the DC voltage for each picture due to the change of the subject obtained at the terminal 173. Detection is performed to obtain a subject change detection signal. Figure 10 shows terminal 1
73, and are the waveforms obtained by rectifying, smoothing, and resetting the waveforms in FIG. 6 for each vertical period. That is, the circuit 21 is as shown in FIG.
Since the low frequency components of the video signal are double-wave rectified,
The peak values in both the positive and negative directions shown in Figure 6 are aligned on one polarity side, and as a result, the number of peak values on one polarity side increases, and the smoothing effect for converting to DC is reduced by a smaller time constant. realizable. Therefore, it is possible to convert the DC current for each pattern, that is, for each field. As shown in this figure, as in the description of the first embodiment, the level does not change much as the lens position moves, as shown by the solid line and the broken line. On the other hand, if the pattern changes, the level changes as shown by the dashed line, and the level remains constant within one vertical period (corresponding to one pattern) excluding the reset period, so the problem described in the first embodiment occurs. Sufficient points will be further improved.

As described above, the object change detection circuit according to the present invention can generate a detection signal corresponding only to a change in the object without generating an erroneous detection signal due to movement of the lens position. By stopping the mountain climbing operation by this signal,
Defects in mountain climbing motion due to changes in the subject can be effectively prevented. Furthermore, compared to the conventional method of counting the number of outlines of a pattern, it can be realized using a simpler circuit.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a hill-climbing automatic focusing device, Figure 2 is a waveform diagram to explain the operation of the configuration shown in Figure 1, and Figure 3 is an automatic focusing device with the function of a subject change detection circuit. 4 is a block diagram of the apparatus, FIG. 4 is a configuration diagram of the subject change detection circuit of the prior application, FIG. 5 is an embodiment of the present invention, FIGS. 6 and 8 are diagrams for explaining the present invention, and FIG. 7 is a diagram for explaining the main part of FIG. 5, FIG. 9 is a diagram showing another embodiment of the present invention, and FIG. 10 is a diagram for explaining the embodiment of FIG. 9. 1... Lens, 2... Camera circuit, 3... Terminal, 4... High pass filter, 5... Detector, 6
...Differential hold circuit, 7...Motor drive circuit,
8...Motor, 9...Mountain climbing circuit, 51...Terminal, 61...Terminal, 10...Subject change detection circuit, 11...Gate circuit, 12...Gate circuit,
13...Low pass filter, 14...Amplifier, 1
5...differentiation circuit, 16...monostable multivibrator, 17...pulse number counting circuit,
18... Fluctuation detection circuit, 19... Reduction filter,
20...Amplifier, 21...Rectification, smoothing, reset circuit.

Claims (1)

[Claims] 1. A lens, a motor that moves the lens, a camera circuit that converts an optical image formed through the lens into an electrical signal and generates a video signal, and an image output from the camera circuit. a focus voltage generation circuit that generates a focus voltage signal from a high frequency component of the signal; a motor driving means that drives the motor using the focus voltage signal generated by the focus voltage generation circuit; and a subject variation detecting means for generating a detection signal and controlling the operation/non-operation of the motor driving means using the detection signal, and the subject variation detecting means converts a signal component indicating the brightness of the picture into the video signal. a generating means that generates signal components based on the signal generating means; a comparing means that compares signal components obtained by the generating means in different fields; An automatic focusing device comprising: detection signal generating means for generating a detection signal. 2. The automatic focusing according to claim 1, wherein the generating means generates a DC voltage in which a low frequency component of a video signal is converted into a DC voltage as a signal indicating the brightness of a picture. Device.