JPH10239579A - Automatic focus device for video camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power consumption. SOLUTION: The evaluation value corresponding to the high-frequency component of the intensity signal caused by a slight shift of a focus lens in one direction and another direction is received, and the shift quantity (focus shift quantity) of the focus lens for focusing is calculated (ST1-ST4). The focus shift quantity of the present field is stored in a buffer in the non-wobbling field except during a zooming action, during low-speed shuttering, and when the focus position is not located near a focal position (ST5-ST7), and the focus shift quantity is set to 0. The sum of the shift quantity of the focus lens on wobbling (wobbling quantity), the present focus shift quantity, and the focus shift quantity of the previous field stored in the buffer is used as the focus lens shift quantity to control the shift of the focus lens in the wobbling field (ST9-ST14). The moving time of the focus lens is shortened, and power consumption is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automatic focusing device for a video camera. More specifically, a video that reduces power consumption by intermittently performing the movement of the focus lens for focusing in synchronization with the movement of the focus lens to obtain focus information The present invention relates to an autofocus device for a camera.

[0002]

2. Description of the Related Art FIG. 4 shows a configuration example of a conventional video camera 20. The video camera 20 includes a lens block 21 including a focus lens 22 and the like, and a C in which a subject image is formed on an imaging surface by the lens block 21.
A CD (Charge Coupled Device) solid-state image sensor 23,
A signal processing unit 24 that performs a sampling process and a YC separation process on an image signal output from the image sensor 23 to obtain a luminance signal Y and a color signal C (a color difference signal, a primary color signal, and the like); The luminance signal Y output from 24
And output terminals 29a and 29 for outputting color signals C, respectively.
9b.

The video camera 20 includes a signal processing unit 2
4 to extract a high frequency component of the luminance signal Y output from
A detector 25 for rectifying and detecting the rectified signal to obtain an evaluation value required for autofocusing; and a C for controlling the entire system.
PU (Central Processing Unit) 26 and this CPU
26, an autofocus module 26a for taking in the evaluation value obtained by the detection unit 25 and controlling the movement of the focus lens 22 so that the value becomes the maximum value, and an autofocus module 26a for moving the focus lens 22. It has a motor 28 and a motor driver 27 that drives the motor 28 according to a control signal from the autofocus module 26a.

Next, the operation of the video camera 20 shown in FIG. 4 will be described. Image sensor 23 by lens block 21
An image of a subject is formed on the imaging surface of the imaging device 23, and an imaging signal corresponding to the subject is output from the imaging device 23. This image pickup signal is supplied to the signal processing unit 24, where it is subjected to sampling processing and Y
The C separation process is performed to obtain a luminance signal Y and a chrominance signal C. These luminance signal Y and color signal C are output from output terminals 29a and 29b, respectively. The luminance signal Y output from the signal processing unit 24 is
And a high-frequency component is extracted from the luminance signal Y, rectified and detected, and an evaluation value is obtained. Then, the evaluation value is supplied to an autofocus module 26a formed in the CPU 26, and the movement of the focus lens 22 is controlled so that the evaluation value becomes the maximum value, thereby realizing the autofocus operation.

Here, the evaluation value and the control operation of the autofocus module 26a will be described in more detail.

FIG. 5 shows an example of a change in the evaluation value output from the detector 25.

In FIG. 1, the horizontal axis (x-axis) indicates the focus position, and the vertical axis (y-axis) indicates the evaluation value. As the focus position moves from the far direction to the near direction, the evaluation value takes the maximum value a at a certain position. This is called an “evaluation value peak”, and the focus position at which the evaluation value takes the maximum value “a” is the in-focus position of the subject.

Therefore, as described above, the autofocus module 26a captures the evaluation value output from the detection unit 25 and performs the “hill climbing control” of moving the focus lens 22 so that the evaluation value becomes the maximum value. Is going. At this time, in the auto focus module 26a, the focus position is slightly vibrated to check in which direction the focus position is from the current focus position, and the differential component d of the evaluation value obtained at that time is obtained.
The direction to the in-focus position is estimated based on the sign of y / dx. This minute vibration at the focus position is called wobbling.

FIG. 6A shows wobbling on a time axis. In this case, the focus position is controlled on a field basis. The movement of the focus position by the wobbling described above is performed in the far direction and the near direction every other field during the stop period of one field.
It is controlled to move alternately in the r direction. The autofocus module 26a checks the differential component dy / dx of the evaluation value obtained at this time, and moves the focus lens 22 so as to bring the focus position closer to the focus position, thereby realizing autofocus.

FIG. 7 is a flowchart showing the operation of controlling the movement of the focus lens 22 by the autofocus module 26a. The operation of the flowchart in FIG. 7 is repeatedly performed in one field cycle.

In step ST20, when the control operation by the autofocus module 26a is started, first, in step ST21, an evaluation value is fetched from the detection unit 25, and in step ST22, a differential component of the evaluation value obtained by wobbling is extracted, and focusing is performed. Guess the position direction. Then, in step ST23, the movement amount (focus movement amount) of the focus lens 22 for moving the focus position closer to the focus position based on the evaluation value, that is, for focusing, is calculated. Then, in step ST24, it is determined whether or not the field is a field in which the focus position related to wobbling is moved. If the field is a field in which the focus position related to wobbling is moved, the process proceeds to step ST26 to start wobbling. The movement amount (wobbling amount) of the focus lens 22 is calculated, and if it is not a field where the movement of the focus position related to wobbling is performed, the process proceeds to step ST25 and the wobbling amount is set to 0.

In step ST27, the motor driver 27 is controlled by setting the amount of movement of the focus lens 22 to the sum of the amount of focus movement and the amount of wobbling. And
In step ST28, the auto focus module 26
The control operation according to a ends.

[0013]

FIG. 6B shows an example of the state of movement of the focus lens 22 during the autofocus of the video camera 20 described above.

In this figure, the movement for wobbling is performed once in two fields, and the movement for focusing is performed irrespective of the movement for wobbling. It is controlled to move almost every field. Therefore, there is a problem that power consumption increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic focusing device for a video camera capable of reducing power consumption.

[0016]

According to the present invention, there is provided a lens block including a focus lens, an image sensor for forming a subject image on an image pickup surface by the lens block, and an image signal output from the image sensor. A signal processing unit for processing to obtain a luminance signal and a chrominance signal; first focus lens moving means for finely moving the focus lens alternately in one direction and another direction during a fixed stop period; Focus information obtaining means for obtaining focus information based on a change in a high-frequency component of a luminance signal caused by the first focus lens, and second focus lens moving means for moving a focus lens based on the focus information so that a focus position approaches a focus position. Movement of the focus lens by the second focus lens moving means,
It is characterized in that it is performed in synchronization with the movement of the focus lens by the first focus lens moving means.

According to the present invention, during a certain stop period, the focus position changes to the in-focus position based on a change in the high-frequency component of the luminance signal due to the slight movement of the focus lens in one direction and the other direction. It is determined whether or not there is, and when it is not at the in-focus position, focus information such as in which direction the in-focus position is located is obtained. And
Based on this focus information, the focus lens is controlled to move so that the focus position approaches the focus position, thereby realizing autofocus.

In this case, the movement of the focus lens is controlled so that the focus position approaches the focus position. The movement intermittently moves in synchronization with the movement of the focus lens for obtaining the focus information. To be. Accordingly, the time during which the focus lens is moving is shortened, and power consumption can be reduced.

Note that the focus lens is intermittently moved so that the focus position approaches the focus position. By adding the movement amount for the stop period to the movement amount, the followability of the auto focus is improved. Degradation is suppressed.

Further, during zoom operation, when the shutter speed of the image sensor is low, or when the focus position is far from the in-focus position, it is not preferable that the follow-up performance of the autofocus is impaired. Therefore,
In such a case, the focus lens is continuously moved to bring the focus position closer to the focus position, thereby preventing the follow-up of autofocus from being reduced.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a video camera 10 as an embodiment.

The video camera 10 has a lens block 11 including a focus lens 12 and the like, and a CCD in which a subject image is formed on the image pickup surface by the lens block 11.
A solid-state imaging device 13 and a signal processing unit 14 that performs a sampling process and a YC separation process on an imaging signal output from the imaging device 13 to obtain a luminance signal Y and a color signal C.
And output terminals 19a and 19b for outputting a luminance signal Y and a color signal C output from the signal processing unit 14, respectively.
And

The video camera 10 includes a signal processing unit 1
4 to extract a high frequency component of the luminance signal Y output from
A detector 15 for rectifying and detecting the rectified signal to obtain an evaluation value necessary for autofocusing, and a C for controlling the entire system.
A PU 16, an autofocus module 16 a configured in the CPU 16, which captures the evaluation value obtained by the above-described detection unit 15 and controls the movement of the focus lens 12 so that the value becomes the maximum value, and a focus lens 12. A motor 18 for moving and a motor 18 according to a control signal from the autofocus module 16a.
And a motor driver 17 for driving the motor.

Next, the operation of the video camera 10 shown in FIG. 1 will be described. Image sensor 13 by lens block 11
An image of a subject is formed on the imaging surface of the imaging device, and an imaging signal corresponding to the subject is output from the imaging device 13. This image pickup signal is supplied to the signal processing unit 14, and is subjected to sampling processing and Y
The C separation process is performed to obtain a luminance signal Y and a chrominance signal C. These luminance signal Y and color signal C are output from output terminals 19a and 19b, respectively. The luminance signal Y output from the signal processing unit 14 is
And a high-frequency component is extracted from the luminance signal Y, rectified and detected, and an evaluation value is obtained.

Then, the evaluation value is supplied to an autofocus module 16a formed in the CPU 16,
The focus lens 1 is set so that this evaluation value becomes the maximum value.
2 is controlled, and an autofocus operation is realized.

Here, the autofocus module 16
The control operation a will be described in more detail.

In the auto focus module 16a,
The evaluation value output from the detection unit 15 is fetched, and the hill-climbing control of moving the focus lens 12 so that the evaluation value takes the maximum value is performed. At this time, the autofocus module 16a slightly vibrates the focus position in order to check the direction of the focus position from the current focus position, and determines whether the differential component dy / dx of the evaluation value obtained at that time is positive or negative. Is used to estimate the direction to the in-focus position.

FIG. 2A shows wobbling, which is a minute vibration of the focus position, on a time axis. In this case, the focus position is controlled on a field basis. The movement of the focus position by the above-described wobbling is performed during the stop period of one field.
It is controlled to alternately move in the far direction and near direction every other field.

Then, the autofocus module 16
Within a, the differential component dy /
dx is checked, and the autofocus lens 12 is moved so that the focus position approaches the focus position, thereby realizing autofocus.

In the present embodiment, the movement control of the focus lens 12 related to the wobbling described above is the same as the conventional one, but the movement of the focus lens 12 for focusing is performed by the focus lens 1 related to the wobbling.
2 is performed intermittently so as to synchronize with the movement of No. 2.

FIG. 3 is a flowchart showing the operation of controlling the movement of the focus lens 12 by the autofocus module 16a. The operation of the flowchart of FIG. 3 is repeatedly performed in one field cycle.

When the control operation by the autofocus module 16a is started in step ST1, first, in step ST2, the evaluation value is fetched from the detection unit 15, and in step ST3, the differential component of the evaluation value obtained by wobbling is extracted, and the focusing position is obtained. Guess the direction. Then, in step ST4, the movement amount (focus movement amount) of the focus lens 12 for moving the focus position closer to the focus position based on the evaluation value, that is, for focusing, is calculated.

Then, in a step ST5, it is determined whether or not the zoom operation is being performed. At this time, when it is determined that the zoom operation is being performed, the process proceeds to step ST10 without synchronizing with the focus movement by wobbling in order to quickly follow the auto focus, and the focus movement amount is calculated based on the calculated current field. It is calculated as the sum of the focus movement amount and the focus movement amount in the previous field stored in the buffer. Then, the focus movement amount of the previous field stored in the buffer is set to 0.

If it is determined in step ST5 that zooming is not being performed, the process proceeds to step ST6, where the image pickup device 1
It is determined whether or not the shutter speed of No. 3 is low, that is, whether or not a low-speed shutter is being performed. When it is determined that the low-speed shutter is being performed, step ST1 is performed as described above.
The focus shift amount is calculated as the sum of the focus shift amount in the current field and the focus shift amount in the previous field stored in the buffer in order to shift to 0 and quickly follow the autofocus. Then, the focus movement amount of the previous field stored in the buffer is set to 0.

If it is determined in step ST6 that the low-speed shutter is not being performed, the process proceeds to step ST7 to compare the calculated focus movement amount in the current field with the threshold value _DTH . At this time, when it is determined that the focus movement amount is larger than the threshold value D _TH , that is, when it is determined that the focus position is not in the vicinity of the focus position, the process proceeds to step ST10 and the auto focus is quickly followed as described above. Therefore, the focus movement amount is calculated as the sum of the focus movement amount in the current field and the focus movement amount in the previous field stored in the buffer.
Then, the focus movement amount of the previous field stored in the buffer is set to 0.

When it is determined in step ST7 that the focus movement amount is equal to or less than the threshold value D _TH , that is, when it is determined that the focus position is near the focus position,
The process proceeds to step ST8 to determine whether or not the field is a field in which the focus position related to wobbling is moved. If it is the field in which the focus position related to wobbling is to be moved, step ST
The process proceeds to step 10, where the focus movement amount is calculated as the sum of the focus movement amount in the current field and the focus movement amount in the previous field stored in the buffer. Then, the focus movement amount of the previous field stored in the buffer is set to 0.

If it is determined in step ST8 that the field is not a field in which the focus position related to wobbling is to be moved, the process proceeds to step ST9 to store the focus movement amount in the current field in a buffer, and to focus on the current field. The moving amount is set to 0.

Next, the process proceeds to step ST11, where it is determined whether or not the field is a field in which the focus position related to wobbling is moved. If the field is a field in which the focus position related to wobbling is moved, step ST13 is performed. , The amount of movement (wobbling amount) of the focus lens 12 related to wobbling is calculated, and if it is not the field where the movement of the focus position related to wobbling is performed, the process proceeds to step ST12 to set the amount of wobbling to 0. . Then, step ST14
Then, the motor driver 17 is controlled by using the movement amount of the focus lens 12 as the sum of the focus movement amount and the wobbling amount. Then, in step ST15, the control operation by the autofocus module 16a ends.

As described above, according to the flowchart shown in FIG. 3, when the control operation by the autofocus module 16a is performed, the focus lens 12 of the video camera 10 is in the zoom operation, during the low-speed shutter, and when the focus position is in the in-focus position. FIG. 2B, except when not in the vicinity
As shown in (1), the movement of the focus lens 12 for focusing is performed intermittently (every other field) in synchronization with the focus movement related to wobbling. For this reason, the time during which the focus lens 12 moves is shortened, and power consumption can be reduced. For example, when the zoom is at the wide angle (WIDE) end and an image of a wide area of the subject is taken, the focus lens 1 is used.
Since the range of movement of the line 2 becomes narrow, it can greatly contribute to reduction of power consumption.

Also, during the zoom operation, during the low-speed shutter, and when the focus position is not in the vicinity of the in-focus position, the movement of the focus lens 12 for focusing is continuously performed. Is prevented from decreasing.

Further, when the movement of the focus lens 12 for focusing is performed intermittently, the movement of the focus lens 12 is controlled by adding the focus movement amount of the previous field where the movement is not performed. In addition, the deterioration of the followability of the auto focus can be suppressed.

In the present embodiment, the cost can be increased because the control method by the current autofocus module 16a can be achieved only by changing the program, and there is no need to change or modify peripheral circuits at all. Nothing to do.

Further, in the above-described embodiment, the unit of the field, which is the cycle at which the control operation of the autofocus module 16a starts, is considered. You may.

[0044]

According to the present invention, the movement of the focus lens for focusing is performed intermittently in synchronization with the movement of the focus lens for obtaining focus information. Time is reduced, and power consumption can be reduced. Further, since only the control method of the autofocus module is changed, there is an advantage that the conventional focus lens can be used without changing the peripheral circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a video camera as an embodiment.

FIG. 2 is a diagram illustrating a relationship between wobbling and movement of a focus lens.

FIG. 3 is a diagram illustrating an example of movement control of a focus lens as an embodiment.

FIG. 4 is a block diagram showing a configuration of a conventional video camera.

FIG. 5 is a diagram illustrating an example of a change in an evaluation value obtained from a luminance signal.

FIG. 6 is a diagram showing a relationship between wobbling and movement of a conventional focus lens.

FIG. 7 is a diagram illustrating an example of conventional movement control of a focus lens.

[Explanation of symbols]

11: Lens block, 12: Focus lens, 13: Image sensor, 14: Signal processing unit, 15
... Detection unit, 16 ... CPU, 16a ... Autofocus module, 17 ... Motor driver, 1
8 ... motor, 19a, 19b ... output terminal

Claims (5)

[Claims] A lens block including a focus lens; an image sensor configured to form a subject image on an imaging surface by the lens block; and an image signal output from the image sensor to process a luminance signal and a color signal. A first focus lens moving means for finely moving the focus lens alternately in one direction and another direction during a fixed stop period; and a high frequency component of the luminance signal due to the fine movement. A focus information obtaining unit that obtains focus information based on the change of the focus information; and a second focus lens moving unit that moves the focus lens based on the focus information so that a focus position approaches a focus position. The movement of the focus lens by the second focus lens moving means is performed by the first focus. An autofocus apparatus for a video camera, wherein the autofocus apparatus is performed in synchronization with movement of the focus lens by a lens moving unit. 2. The moving amount of the focus lens by the second focus lens moving means after the stopping period is obtained by adding a moving amount for the stopping period. Video camera autofocus device. 3. A zoom operation determining means for determining whether or not a zoom operation is being performed, wherein during the zoom operation, the operation performed in synchronization with the first focus lens moving means is canceled. The video camera autofocus apparatus according to claim 1, wherein: 4. The apparatus according to claim 1, further comprising a shutter speed determining unit configured to determine whether a shutter speed of the image sensor is lower than a predetermined speed, wherein the first focus lens is moved when the shutter speed is lower than the predetermined speed. 2. The video camera auto-focusing device according to claim 1, wherein the operation performed in synchronization with the means is canceled. 5. A focus position determining means for determining whether or not a focus position is near a focus position based on a movement amount of the focus lens calculated based on the focus information, wherein the focus position is determined. 2. The video camera auto-focusing device according to claim 1, wherein when it is not near the in-focus position, the operation performed in synchronization with said first focus lens moving means is canceled.