JPH0443475B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic focusing device in a TV camera.

Conventional configuration and its problems In recent years, the autofocus function of TV cameras has become important in terms of improving operability.

As a conventional technique, a high frequency component is detected by passing a video signal obtained from an image sensor through a band pass filter, and the peak value of this detection signal is maximized within, for example, one field or one frame.
There is a method of driving a lens focusing device.

First, the prior art will be explained using FIG. 1. 1 is a lens with a focusing device, and 14 motors drive this device. 2 is an image sensor, 3 is a preamplifier that amplifies the image sensor output signal, and 4 is a standard
5 is a synchronizing signal generator; 6 is a scanning drive circuit for the image sensor; 7 is a bandpass filter (hereinafter referred to as BPF) that passes the high frequency component of the video signal; 8 is the BPF. Out of the output, a gate circuit passes only the signal corresponding to the screen range (hereinafter referred to as the angle of view) to be focused when displayed on a TV receiver, etc., 9 is within one field or one frame period of the gate circuit output. 11 is a reference frequency generation circuit that generates a reference frequency of 1/N (N: an integer of 1 or more) of the frame frequency; 10 is a detector that detects the reference frequency component from the output of the detector 9; 12 is a synchronous detection circuit that synchronously detects the reference frequency component detected by 10 with a reference frequency signal generated by 11; 13 is a motor 14;
The output signal of the reference frequency generation circuit 11 for slightly moving the motor 14 to periodically slightly change the focus of the lens 1 (hereinafter referred to as wobbling) and the synchronous detection circuit 1
2 output signals are input.

Next, automatic focusing operation will be explained using FIG. 2. Figure 2 shows the focus position of the focus matching device for a subject at a distance D1 from the focus position to a short distance.
It represents the output level of the detection circuit 9 when moved to the far side. First, when the focal position is closer than D1, wobbling A1 based on the reference frequency causes
A reference frequency component A2 is detected from the detection output, and when this is synchronously detected with the reference frequency, a positive polarity signal A3 is obtained. This signal causes the focal position of the focusing device to move in the direction of arrow A4.
Next, when the distance is longer than D1, a reference frequency component B2 having an opposite phase to A2 is detected by wobbling B1, and a negative polarity signal B3 is obtained by synchronous detection. Since this has the opposite polarity to A3, the focal point moves in the direction of arrow B4. In other words, in both far and near situations, it moves in the direction of the in-focus position, and at the in-focus point there is no reference frequency component, so it stops moving and stabilizes at the in-focus point.

In this way, the lens system is also included in the return loop, so the focusing accuracy is very high, but since the image signal itself is detected, it is necessary to photograph objects at different distances on the same screen, and parts with contrast may be included in the screen. Inconveniences arise when photographing a subject that only has a portion of it.

This will be explained with reference to FIG. As shown in Figure 3 a), there are objects OBJ 1 and OBJ ₁ at different distances within the same screen.
If you have OBJ ₂ and use it to focus at a wide angle of view a, it is uncertain whether OBJ ₁ or OBJ ₂ will be in focus. This phenomenon is considered to be a malfunction. One possible way to prevent this is to narrow the angle of view and focus only on the subject in the center of the screen. However, as shown in Figure 3 b), this method has the disadvantage that it becomes impossible to focus if there is no object with contrast within the narrow angle of view b. This is a serious drawback as it frequently moves outside the narrow field of view when moving. In other words, both wide and narrow angles of view have advantages and disadvantages, and unless these are resolved, it will be difficult to put autofocus based on image contrast into practical use.

OBJECTS OF THE INVENTION An object of the present invention is to eliminate the above-described inconvenience caused by setting the angle of view and to provide a practical automatic focusing device.

Structure of the Invention The present invention uses both a narrow angle of view and a wide angle of view as the above-mentioned angle of view for focusing, and if the high frequency component within the narrow angle of view exceeds a specified level, priority is given to focusing using the signal within the narrow angle of view. (This is abbreviated as narrow angle of view loop.)

When the high frequency component within the narrow field of view falls below the specified level in the state of the narrow field of view loop, and the high frequency component within the wide field of view exceeds the specified level, the focusing operation is performed using the signal within the wide field of view. (abbreviated as wide-angle loop)
If the high-frequency component within the wide angle of view is also below the specified level, it is considered to be largely blurred, and the focal position of the lens is continuously changed until the high-frequency component can be detected (this is abbreviated as search mode). ).

In the search mode, even if the high frequency component within the wide angle of view exceeds a specified level, the system does not immediately switch to the wide angle of view loop, but instead searches the entire range of the lens focal position (from near to far). When it does not transition to the narrow angle loop, it transitions to the wide angle loop.

When in the wide-angle loop state, even if the subject becomes another object due to panning or telt, if the high frequency component happens to be above a specified level, a problem will occur in which the wide-angle loop state will continue to be maintained. Therefore, in order to give priority to the narrow angle of view loop, a reset function is provided for forcibly transitioning to the search mode by, for example, inputting a signal indicating that a large change in brightness has occurred or by inputting an external manual switch.

This is a practical automatic focusing device that uses judgment control functions such as the above to focus preferentially on the center of the screen, and is capable of focusing not only on the center but also on a wide area of the screen.

DESCRIPTION OF THE EMBODIMENT FIG. 4 shows an embodiment of the present invention. In the figure, 1 to 14 are the same as the elements shown in the conventional example shown in FIG. 1, and the same functions are designated by the same numbers. There is. However, the circuits 8 and 9 are divided into a gate circuit 8a and a detection circuit 9a for a narrow angle of view, and a gate circuit 8b and a detection circuit 9b for a wide angle of view. 9 is a controller that performs judgment and control, and uses a microcomputer to reset the output of the AD converter 16, lens position data indicating whether the lens focal position is at the near end or far end, and the wide angle loop state. An external reset signal is input for this purpose. 15 is an analog switch for sequentially inputting the detection outputs of the narrow-angle gate side 9a and the wide-angle gate side 9b, which are held until the next frame period, to the AD converter; 17 is the narrow-angle gate side and the wide-angle gate side; an analog switch 18 for switching one of the detection outputs on the gate side to the input of the reference frequency detection circuit 10;
is the input of the motor drive circuit 13, the output of the synchronous detection circuit 12 for driving the lens in a feedback loop, the positive voltage V _M ′ for driving the lens at high speed in search mode, the negative voltage −V _M ′, and the voltage for stopping. This is an analog switch that switches to one of the ground voltages G, and the switching of the analog switches 15, 17, and 18 is all controlled by the controller 19.

Next, the operation of this embodiment will be explained using the flowchart shown in FIG. In this embodiment, the detection of high frequency components in the video signal is performed on a frame-by-frame basis, and therefore the operations in each flowchart are performed on a frame-by-frame basis. Further, the presence or absence of a high frequency component is determined by determining whether the detected output is equal to or higher than a predetermined level.

First, when the detection output is less than the specified level for both the narrow and wide angle of view, the mode changes to search mode, and by switching the analog switch 18 in Fig. 4 to +V _M or -V _M , the lens can be moved to the near or far side. to drive. Then, the detection output on the narrow field of view side is read by the A/D converter 16 for each frame, and when it is above the specified level, the transition is made to the narrow field of view loop, and when it is below the specified level, the detection output on the wide field of view side is determined. conduct. However, at this time, the level is above the specified level and the controller 19
When the lens moves to the near end or far end according to the lens position data input to transition to wide-angle loop only when . When there is no transition to either the narrow angle of view loop or the wide angle of view loop, lens edge detection is performed to detect whether the lens has moved to the far end or the near end as described above. At this time, the number of lens end times is counted up and the direction of lens movement is reversed.

When transitioning to the narrow angle of view loop, the analog switch 17 in FIG. 4 is first set to the narrow angle of view detection output side, and the analog switch 18 is set to the output side of the synchronous detection circuit 12, resulting in a narrow angle of view loop state. This state is maintained as long as the detection output on the narrow angle of view side is equal to or higher than the specified level. When the level falls below the specified level, the detection output on the wide-angle side is first read, and if this output is equal to or higher than the specified level, a transition is made to the wide-angle loop, and when it is less than the specified level, the mode is changed to search mode.

In the wide-angle loop, first, when transition occurs, the analog switch 17 is set to the wide-angle detection output side, and the analog switch 18 is set to the output side of the synchronous detection circuit 12, resulting in a wide-angle loop state. In this state, the narrow field angle side detection output is always read, and when this reaches a specified level or higher, the narrow field angle loop is preferentially entered. Also, even if the subject changes due to panning, tilting, etc., only the detection output on the wide-angle side happens to be above the specified level, and the detection output on the narrow-angle side is greatly blurred, so if it is less than the specified level, it is a wide-angle loop. This state is maintained, and this results in a malfunction in preferentially focusing on subjects within a narrow angle of view. For this purpose, a reset function is provided to cancel the wide-angle loop state and transition to search mode. This can be realized by using a signal indicating that a large luminance change has occurred between frames or a manual switch input as an external reset input of the controller 19. Similarly to the narrow view angle loop, when the wide view angle side detection output becomes less than a specified level, a transition is made to the search mode.

Effects of the Invention As described above, according to the present invention, the center of the screen can be focused preferentially, and even if the subject moves away from the center of the screen, it is possible to focus on a wider screen area. The inconvenient phenomenon that is considered to be a malfunction by the user as described in the example is eliminated, and a practical automatic focusing device can be realized.

The present invention is applicable not only to the lens wobbling method, but also to a method using a variable optical path length element as described in patent application S57-72109, and to an automatic focusing method such as a mountain climbing servo method. Needless to say, it can also be applied.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of a conventional example;
The figure is an explanatory diagram of the operation in the conventional example, Figures 3a and b are explanatory diagrams of drawbacks in the conventional example, Figure 4 is a block diagram showing the configuration of an embodiment of the present invention, and Figure 5 is the operation of the same embodiment. It is a flowchart diagram. DESCRIPTION OF SYMBOLS 1...Lens with focus matching device, 2...Imaging element, 7...Band pass filter, 8a, 8b...
Gate circuit, 9a, 9b...Detector, 10...Reference frequency component detection circuit, 11...Reference frequency generation circuit, 12...Synchronized detection circuit, 13...Motor drive circuit, 14...Motor, 15, 17 ,18...
Analog switch, 16...AD converter, 1
9... Controller.

Claims (1)

[Scope of Claims] 1. A bandpass filter that passes high frequency components of a video signal obtained from an image sensor, and a narrow image that passes a signal corresponding to the angle of view at the center of the imaging screen among the outputs of the bandpass filter. It has an angle gate circuit and a wide angle gate circuit that allows a signal corresponding to a wider angle of view to pass through, and when the output of the narrow angle gate circuit is equal to or higher than a specified level, the output of the narrow angle gate circuit is given priority. When the output of the narrow-angle gate circuit is less than a specified level and the output of the wide-angle gate circuit is above a specified level, the focus matching device is driven so that the output of the wide-angle gate circuit is maximized. An automatic focusing device characterized by: 2. A patent claim characterized in that when both the outputs of the narrow-angle and wide-angle gate circuits are below a specified level, the focus state of the focusing device is put into a lens search mode that changes the focus state from short distance to long distance. The automatic focusing device according to item 1. 3 In search mode, when only the wide-angle gate output is above the specified level, search from short to long distances, and when the narrow-angle gate output is below the specified level, the wide-angle gate output is maximized. 3. The automatic focusing device according to claim 2, wherein the focusing device is driven in accordance with the present invention. 4. Claim 3, characterized by having a function of forcibly canceling the state in which the focusing device is driven so that the wide-angle gate output is maximized, and transitioning to the search mode state. automatic focusing device.