JPH06311412A - Auto focus video camera - Google Patents

Abstract

PURPOSE:To prevent the completion of a focusing operation before a lens reaches a focusing location by monitoring whether the changed amount of a focus evaluation value in accordance with a diaphragm operation exceeds a prescribed value or not. CONSTITUTION:A diaphragm control circuit 81 transmits a diaphragm completion signal TG to a fifth comparator 83 when the diaphragm of prescribed amount is completed by an optical diaphragm mechanism 82. This fifth comparator 83 immediately monitors whether the difference of the focus evaluation value at the time of a focus operation completion which is stored in a fourth memory 11, the latest focus evaluation value obtained also after a focusing operation completion and the latest focus evaluation value exceeds a third threshold or not when the signal TG is inputted. The diaphragm of prescribed amount is performed when the difference exceeds the third threshold or just after focusing operation is completed, and when the rise width of the focus evaluation value by this disphragm is so large as it exceeds the third threshold, a non-focus signal NS showing that the lens location does not reach the focusing location is outputted to a focus motor control circuit 110 and the focus motor control circuit 110 performs the focusing operation again from the beginning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus video camera which performs a focusing operation by using a high frequency component of a picked-up video signal.

[0002]

2. Description of the Related Art In an autofocus device for a video camera, a method of using a picked-up image signal obtained from an image pickup device itself for evaluating a focus control state is essentially free of parallax and has a depth of field. It has many advantages such as being able to focus accurately even when the subject is shallow or at a distance. Moreover, no special sensor for autofocus is required, and the mechanism is extremely simple.

JP-A-63-215268 (H04
N5 / 232) discloses an example of the autofocus device as described above. The essence of this prior art will be described below with reference to FIGS.

FIG. 2 is a circuit block diagram of the entire autofocus device. An image formed by the incident light formed on the image pickup element by the lens 1 becomes an image pickup video signal by the image pickup circuit 4 including the image pickup element and is input to the focus evaluation value generation circuit 5.

The focus evaluation value generating circuit 5 is shown in FIG.
It is configured as shown in. The picked-up video signal passes through a high-pass filter (HPF) 5c to separate only high-frequency components, and amplitude detection is performed by a detection circuit 5d at the next stage. The detected output is sequentially converted into digital values while being sampled by the A / D conversion circuit 5e, only the information in the focus area at the center of the screen is extracted by the gate circuit 5f, and integrated by each field by the integration circuit 5g. That is, the A / D conversion circuit 5e in the focus area obtained in one field period
Digital integration is performed to add all the outputs, and this integrated value is output as the focus evaluation value of the current field.

At this time, the vertical sync signal and the horizontal sync signal separated from the picked-up video signal by the sync separation circuit 5a are input to the gate control circuit 5b in order to set the focus area. The gate control circuit 5b sets a rectangular focus area in the central portion of the screen based on the vertical synchronizing signal, the horizontal synchronizing signal, and the fixed oscillator output, and passes the digital value of the high frequency component of the luminance signal only in this area. Is supplied to the gate circuit 5f.

The focus evaluation value generation circuit 5 configured as described above always outputs the focus evaluation value for one field, and each circuit in the subsequent stage starts the focusing operation using this focus evaluation value. Immediately after starting the focusing operation, the first focus evaluation value is held in the maximum value memory 6 and the initial value memory 7. After that, the focus motor control circuit 10 rotates the focus motor 3 in a predetermined direction to rotate the focus ring 2 that supports the lens 1, and displaces the lens 1 in the optical axis direction. Monitor the output.

The second comparator 9 compares the focus evaluation value obtained after driving the focus motor with the initial evaluation value stored in the initial value memory 7, and outputs the magnitude.

The focus motor control circuit 10 rotates the focus motor 3 in the first direction until the second comparator 9 outputs a large or small output, and the current focus evaluation value is larger than the initial evaluation value. If it is judged that the current evaluation value is smaller than the initial evaluation value, the rotation direction of the focus motor is reversed and the moving direction of the lens is changed. Is reversed and the output of the first comparator 8 is monitored.

The first comparator 8 compares the maximum focus evaluation value up to now held in the maximum value memory 6 with the current evaluation value, and compares the current focus evaluation value with the contents of the maximum value memory 6. Is large (first mode) and has decreased below a preset first threshold value M (second mode), two comparison signals S1;
Outputs S2. Here, the maximum value memory 6 is the first comparator 8
If the current evaluation value is larger than the content of the maximum value memory 6 based on the output of, the value is updated and the maximum focus evaluation value up to the present is always held.

A lens position 13 indicates a position (lens position) in the optical axis direction of the lens 1 output from a motor position detection circuit 30 for detecting the rotational position of the motor based on the rotation amount of the focus motor 3. It is a lens position memory for storing signals, and like the maximum value memory 6, the first comparator 8 output S
Based on 1, the lens position is updated so as to always hold the lens position when the maximum evaluation value is reached.

The focus motor control circuit 10 monitors the output of the first comparator 8 while rotating the focus motor 3 in the direction determined based on the output of the second comparator 9, and the focus evaluation is performed as shown in FIG. At the same time as instructing the second mode in which the value is smaller than the preset first threshold value M as compared with the maximum evaluation value, the focus motor 3 is reversed. Due to the reverse rotation of the focus motor 3, the moving direction of the lens 1 is changed, for example, from a direction approaching the image sensor to a direction away from the image sensor, or vice versa.

After this reverse rotation, the contents of the lens position memory 13 and the current lens position signal are compared by the third comparator 14, and when they match, that is, the lens 1 returns to the position where the focus evaluation value is maximum. When this happens, the focus motor control circuit 10 functions to stop the focus motor 3. At the same time, the focus motor control circuit 10 outputs a lens stop signal LS.

Reference numeral 11 denotes a fourth focus value which is held at the same time when the focus operation by the focus motor control circuit 10 is completed and the lens stop signal LS is issued.
This is a memory, and the content held in the fourth memory 11 is compared with the latest focus evaluation value after the focusing operation by the fourth comparator 12 in the subsequent stage, and the latest focus evaluation value is compared with the content of the fourth memory 11. When it becomes smaller than the preset second threshold value, it is determined that the subject has changed, and the subject change signal is output. When the focus motor control circuit 10 receives this signal, the focus motor control circuit 10 performs the focusing operation again to follow the change of the subject.

[0015]

The autofocus system is excellent in focusing accuracy and adaptability to a wide range of subjects, but has the following drawbacks. That is, when the focus evaluation value falls below the first threshold value due to factors such as an obstacle crossing between the camera and the subject or the state of the subject itself changing while the lens is moving in the focusing direction, There is a possibility of stopping the focusing operation by setting the wrong lens position as the focusing position. Further, even if the focus state is already in focus before the focus operation, there is a problem that the lens is displaced to perform an unnecessary focus operation.

[0016]

According to the present invention, an image pickup video signal is created from incident light which is imaged on an image pickup element through a lens, and a high frequency component amount of the image pickup video signal is output as a focus evaluation value. A focus control unit that changes the position and executes a focusing operation that stops the lens when the focus evaluation value reaches a maximum value, and an optical diaphragm mechanism that performs a diaphragm operation that reduces the amount of incident light by a predetermined amount. A monitoring means for monitoring whether or not the amount of change in the focus evaluation value due to the diaphragm operation exceeds a predetermined value, and after the focusing operation ends and the lens stops, the diaphragm operation is executed to focus by the monitoring means. When it is determined that the amount of change in the evaluation value exceeds a predetermined amount, restart the focusing operation, or execute the diaphragm operation before the start of the focusing operation to monitor the amount of change in the focus evaluation value. Determined not to exceed the prescribed amount Occasionally, and inhibits the focusing operation.

[0017]

Since the present invention is configured as described above, it is possible to prevent the lens from being stopped at an out-of-focus position and to execute an unnecessary focusing operation.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the entire circuit block of the first embodiment device, and the same parts as those in FIG.

In the present embodiment, when the lens stop signal LS is input from the focus motor control circuit 10, the fourth memory 11 stores the focus evaluation value at the time of this input, as in the conventional example. Fourth memory 1 in comparator 121
The operation of comparing the stored content of 1 with the latest focus evaluation value is different from the conventional example in that it is not executed until a focus completion signal GS issued from a fifth comparator 83 described later is issued.

Reference numeral 82 denotes a diaphragm mechanism that adjusts the amount of incident light that enters the image sensor through the lens 1. The diaphragm amount is adjusted by driving the iris motor 84, and the iris motor 84 commands the diaphragm control circuit 81. Is controlled by.

Upon receiving the lens stop signal LS issued from the focus motor control circuit 110, the aperture control circuit 81 drives the iris motor 84 for a certain period to narrow down the optical aperture mechanism 82 by a predetermined amount to reduce the amount of incident light.

The depth of field becomes deeper in conjunction with the diaphragm operation, and the relationship between the lens position and the focus evaluation value changes from the curve A showing the state before the diaphragm operation to the state after the diaphragm operation as shown in FIG. It changes to the curve B shown. Comparing these two curves, the maximum values, that is, the focus evaluation values at the in-focus position both maintain substantially the same value, but as the distance from the in-focus position increases, m1,
As indicated by m2, the amount of increase in the focus evaluation value on the curve B is larger than that on the curve A, and the curve B has a gentler slope than that on the curve A.

When the aperture control circuit 81 completes the aperture of a predetermined amount by the optical aperture mechanism 82, it outputs an aperture completion signal TG to the fifth comparator 83. The fifth comparator 83 outputs the signal TG
The inoperative state is maintained until is input, and when the signal TG is input, the focus evaluation value at the time of the completion of the focusing operation, which is immediately stored in the fourth memory 11, and the focus evaluation value after the completion of the focusing operation are obtained. The latest focus evaluation values are compared in level, and the fourth memory 1
It is monitored whether the difference between the focus evaluation value of 1 and the latest focus evaluation value exceeds the third threshold value.

When the difference exceeds the third threshold value, that is, when the focusing operation is performed by a predetermined amount immediately after the focusing operation is completed and the increase range of the focus evaluation value by the diaphragm is large enough to exceed the third threshold value,
A non-focus signal NS indicating that the lens position has not reached the focus position is output to the focus motor control circuit 110, and the focus motor control circuit 110 restarts the focus operation from the beginning.

If the difference is within the third threshold value, it is determined that the focus position has been reached, and the focus completion signal GS is sent to the fourth comparator 12.
Output to 1. As described above, when the fourth comparator receives the focusing completion signal GS, the value stored in the fourth memory 11 and the latest focus evaluation value enter a monitoring operation for subject change by level comparison, and at the same time, the aperture is stopped. The control circuit 81 issues a command to return the diaphragm state to the original state. The third threshold corresponds to the difference between the focus evaluation values of the curves A and B at the in-focus state and the allowable lens position (position extremely close to the in-focus position) in the curves A and B of FIG. The amount of increase in the focus evaluation value due to the diaphragm at the limit of the lens position that can be allowed as the focused state is calculated by an experiment, and this amount of increase is calculated as
Is set as the threshold value of.

The focus motor control circuit 110 is shown in FIG.
The focus motor control circuit 10 functions as a non-focus signal N
A measure for receiving S is added.

In the above-described embodiment, the predetermined operation using the diaphragm is performed immediately after the focusing operation to determine whether or not the lens has reached the in-focus position. When an obstacle crosses over and the focusing action is performed on this obstacle, or the subject itself changes during the focusing action and the focusing action is performed on the old subject, the focusing action is performed. Immediately after the operation is completed, out-of-focus can be detected immediately, and the in-focus operation can be redone.

By the way, if the operation of monitoring the change in the focus evaluation value by the diaphragm is carried out immediately before the start of the focusing operation and it is judged whether or not it is in the focusing state, it is already in the focusing state before the focusing operation. In this case, unnecessary focusing operation can be prevented. This embodiment will be described below as a second embodiment.

FIG. 6 is a circuit block of the second embodiment.
The point different from FIG. 1 of the first embodiment is that the start timing of the monitoring operation involving a predetermined amount of diaphragm started by a command issued from the diaphragm control circuit 81 is the same as the start timing of the focusing operation in the first embodiment. Although the lens stop signal LS to be issued is used, instead of this, the monitoring start signal SS issued from the focus control circuit 210 in synchronism with the power-on timing of the video camera is used. Also,
The focus control circuit 210, unlike the first embodiment or the conventional example, does not perform the focusing operation when the power is turned on. Simultaneously with the input of the monitoring start signal SS, the aperture control circuit 81 controls the operations of the iris motor 84 and the optical aperture mechanism 82 so as to perform the aperture of a predetermined amount, and when the aperture of the predetermined amount is finished, the aperture completion signal TG is output. The sixth comparator 90 is supplied.

In the sixth memory 91, the focus evaluation value obtained at the time when the monitoring start signal SS is input, that is, at the same time when the power is turned on, the iris motor 84 is not in operation and a predetermined amount of aperture is still executed by the optical aperture mechanism 82. The focus evaluation value obtained in the non-executed state is stored.

In the sixth comparator 90, the focus evaluation value obtained after input of the diaphragm completion signal TG issued by executing the diaphragm operation of a predetermined amount after the data storage in the sixth memory 91 is completed, and the sixth memory 90. The levels of the focus evaluation values stored in are compared, and it is monitored whether the difference between the two exceeds a third threshold value. The focus motor control circuit 210 determines whether to start the focusing operation based on the comparison result of the sixth comparator 90. That is, if it is found as a result of comparison by the sixth comparator 90 that the difference between the two exceeds the third threshold value, it is judged that the lens 1 is not in the in-focus state and the in-focus operation is necessary. The camera is moved to start the above-mentioned hill climbing focusing operation. Further, if it is found as a result of the comparison that the difference between the two is within the third threshold value, it is already in focus and the focus is not required again, and the focus operation is not performed and the lens stop signal LS is set. After the output, the fourth comparator 12 monitors the change of the subject. By configuring in this way,
Focusing is determined in advance before the focusing operation is performed, and if the focusing state is already in focus at the start of imaging when the power of the video camera is turned on, the lens 1 is displaced to perform an unnecessary focusing operation. Can be prevented.

The focus motor control circuit 210 is
Except that the monitoring start signal SS is output when the power of the video camera is turned on, and the focusing operation is prohibited until the sixth comparator 90 obtains a comparison result that the focusing operation needs to be started. It has the same function as the focus control circuit 10 of FIG.

Needless to say, the operation of each of the above embodiments can be processed by software using a microcomputer. In addition, the first and second embodiments are summarized,
That is, it is possible to perform the focus determination before and after the focus operation. Further, instead of displacing the lens itself during the focusing operation, it is possible to change the relative positional relationship between the lens and the image sensor by displacing the image sensor in the optical axis direction without moving the lens.

In addition to the focusing operation for confirming the focus, the iris motor 84 and the optical diaphragm mechanism 82 adjust the diaphragm so that the brightness signal level of the picked-up image signal over the entire screen matches the target value, so-called exposure. Although the adjustment operation is also performed, this exposure adjustment operation is performed by the fifth comparator 8 in the first embodiment.
3 is executed after the focusing completion signal GS or the non-focusing signal NS is output, that is, after the comparison result is output by the fifth comparator 83, and in the second embodiment, the sixth comparator. It is executed after the comparison result is output at 90.

Further, in the above-mentioned embodiment, the focus state determination operation using the comparator, that is, the fifth comparator 83 of the first embodiment is carried out.
Alternatively, the comparison of the sixth comparator 90 of the second embodiment has been described only once, but if the comparison operation is performed a plurality of times, the reliability of the determination is further improved. That is, a predetermined amount of aperture of the optical aperture mechanism 82 is intermittently repeated a plurality of times, and each time the intermittent aperture operation is executed, the comparison operation is performed in each comparator, and the number of apertures is compared according to the number of apertures. Focus determination based on the result,
For example, a predetermined amount of aperture is intermittently repeated five times, and the focus evaluation values before and after the sequential aperture operation are compared each time each aperture is completed, and the majority of the five comparison results obtained is obtained. In the case where three or more of the above indicate the same result, the influence of noise or the like can be suppressed by making this result the final determination output.

In addition to the above-mentioned both embodiments, while the lens is moved while the focus evaluation value is updating the maximum value,
The aperture value is changed to extract the variation in the evaluation value, the degree of focusing is detected from this variation, and when the variation becomes small, the lens is considered to be in focus and the lens is stopped. Given this, it is possible to reduce the drive speed of the focus motor to reduce the amount of displacement of the lens per field.

[0037]

As described above, according to the present invention, it is possible to easily judge whether or not the lens is at the in-focus position by monitoring the variation of the focus evaluation value with the diaphragm without specifically displacing the lens. It is possible to prevent the lens from completing the focusing operation before the lens reaches the in-focus position by performing this change monitoring after completion of the focusing operation. By doing so, unnecessary focusing operation can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a first embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional example.

FIG. 3 is a circuit block diagram of a main part of a conventional example.

FIG. 4 is a diagram showing a relationship between a lens position and a focus evaluation value associated with a focusing operation.

FIG. 5 is a diagram showing a change in focus evaluation value associated with a diaphragm operation.

FIG. 6 is a circuit block diagram of a second embodiment of the present invention.

[Explanation of symbols]

 1 Lens 4 Imaging Circuit 5 Focus Evaluation Value Generation Circuit 110 Focus Motor Control Circuit 210 Focus Motor Control Circuit 82 Optical Aperture Mechanism 83 Fifth Comparator 90 Sixth Comparator

Claims (2)

[Claims] 1. An image pickup means for creating an image pickup video signal from incident light imaged on an image pickup element through a lens, and a focus evaluation value generation means for outputting a high frequency component amount of the image pickup video signal as a focus evaluation value. A focus control unit that executes a focusing operation that changes a lens position that is a relative position of the lens with respect to the image sensor and fixes the lens position when the focus evaluation value reaches a position where the focus evaluation value reaches a maximum value. An optical diaphragm mechanism for performing a diaphragm operation for reducing the light quantity of the incident light by a predetermined amount, and a monitoring means for monitoring whether or not the amount of change in the focus evaluation value before and after the diaphragm operation exceeds a predetermined value. When the focusing operation is once ended and the lens position is fixed, the diaphragm operation is executed, and when the change amount of the focus evaluation value exceeds the predetermined amount by the monitoring means,
An autofocus video camera characterized by restarting the focusing operation. 2. An image pickup means for forming an image pickup video signal from incident light formed on an image pickup element through a lens, and a focus evaluation value generation means for outputting a high frequency component amount of the image pickup video signal as a focus evaluation value. A focus control unit that executes a focusing operation that changes a lens position that is a relative position of the lens with respect to the image sensor and fixes the lens position when the focus evaluation value reaches a position where the focus evaluation value reaches a maximum value. An optical diaphragm mechanism for performing a diaphragm operation for reducing the light quantity of the incident light by a predetermined amount, and a monitoring means for monitoring whether or not the amount of change in the focus evaluation value before and after the diaphragm operation exceeds a predetermined value. The autofocusing is characterized in that the focusing operation is prohibited when the diaphragm operation is executed before the focusing operation is started and the change amount of the focus evaluation value does not exceed a predetermined amount by the monitoring means. Camcorders.