JP3726399B2 - Autofocus device for video camera - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an autofocus device for a video camera. Specifically, the movement of the focus lens for focusing is intermittently performed in synchronization with the movement of the focus lens for obtaining focus information, and the intermittent movement of the focus lens for focusing is stopped. The present invention relates to an autofocus device for a video camera that is designed to reduce power consumption while suppressing deterioration in autofocus followability by adding the movement amount of the minute .
[0002]
[Prior 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, a CCD (Charge Coupled Device) solid-state imaging device 23 on which an object image is formed on the imaging surface by the lens block 21, and an output from the imaging device 23. The signal processing unit 24 that obtains the luminance signal Y and the color signal C (color difference signal, primary color signal, etc.) by performing sampling processing and YC separation processing on the captured image signal, and the luminance output from the signal processing unit 24 Output terminals 29a and 29b for outputting the signal Y and the color signal C, respectively.
[0003]
In addition, the video camera 20 takes out a high-frequency component of the luminance signal Y output from the signal processing unit 24, and rectifies and detects it to obtain an evaluation value necessary for autofocus, and controls the entire system. CPU (Central Processing Unit) 26, and an autofocus that is configured in this CPU 26, takes in an evaluation value obtained by the above-described detection unit 25, and controls the movement of the focus lens 22 so that the value becomes the maximum value. It has a module 26a, a motor 28 for moving the focus lens 22, and a motor driver 27 for driving the motor 28 in accordance with a control signal from the autofocus module 26a.
[0004]
Next, the operation of the video camera 20 shown in FIG. 4 will be described. A subject image is formed on the imaging surface of the image sensor 23 by the lens block 21, and an imaging signal corresponding to the subject is output from the image sensor 23. This imaging signal is supplied to the signal processing unit 24, and sampling processing and YC separation processing are performed to obtain a luminance signal Y and a color signal C. The luminance signal Y and the color signal C are output from output terminals 29a and 29b, respectively. Also, the luminance signal Y output from the signal processing unit 24 is supplied to the detection unit 25, and a high frequency component is extracted from the luminance signal Y and subjected to rectification detection to obtain an evaluation value. Then, this evaluation value is supplied to an autofocus module 26a configured in the CPU 26, and the movement of the focus lens 22 is controlled so that this evaluation value becomes the maximum value, thereby realizing an autofocus operation.
[0005]
Here, the evaluation value and the control operation of the autofocus module 26a will be described in more detail.
[0006]
FIG. 5 shows an example of a change in the evaluation value output from the detection unit 25.
[0007]
In this figure, the horizontal axis (x-axis) is the focus position, and the vertical axis (y-axis) is the evaluation value. When the focus position is moved from the far direction to the near direction, the evaluation value takes the maximum value a at a certain position. This is called “evaluation value peak”, and the focus position where the evaluation value has the maximum value a is the in-focus position on the subject.
[0008]
Therefore, as described above, the autofocus module 26a performs “mountain climbing control” in which the evaluation value output from the detection unit 25 is taken and the focus lens 22 is moved so that the evaluation value becomes the maximum value. . At this time, the autofocus module 26a slightly vibrates the focus position in order to check in which direction the in-focus position is from the current focus position, and the positive / negative of the differential component dy / dx of the evaluation value obtained at that time Thus, the direction to the in-focus position is estimated. This minute vibration at the focus position is called wobbling.
[0009]
FIG. 6A shows wobbling on the time axis. In this case, the focus position is controlled in field units. The movement of the focus position by the wobbling described above is controlled so as to alternately move in the far direction and the near direction every other field during the stop period of one field. In the autofocus module 26a, the differential component dy / dx of the evaluation value obtained at this time is examined, and the focus lens 22 is moved so as to bring the focus position closer to the in-focus position, thereby realizing autofocus.
[0010]
The flowchart of FIG. 7 shows the movement control operation of the focus lens 22 by the autofocus module 26a. The operation of the flowchart of FIG. 7 is repeatedly performed in one field cycle.
[0011]
When the control operation by the autofocus module 26a is started in step ST20, first, an evaluation value is fetched from the detection unit 25 in step ST21, a differential component of the evaluation value obtained by wobbling is extracted in step ST22, and the in-focus position direction is determined. Infer. In step ST23, a movement amount (focus movement amount) of the focus lens 22 for calculating the focus position close to the focus position, that is, focusing is calculated based on the evaluation value. Then, in step ST24, it is determined whether or not the field is the field where the focus position related to wobbling is moved. If the field is the field where the focus position related to wobbling is moved, the process proceeds to step ST26 and wobbling is performed. The movement amount (wobbling amount) of the focus lens 22 is calculated, and when the field is not a field where the focus position movement related to wobbling is performed, the process proceeds to step ST25 and the wobbling amount is set to zero.
[0012]
In step ST27, the motor driver 27 is controlled with the movement amount of the focus lens 22 as the sum of the focus movement amount and the wobbling amount. In step ST28, the control operation by the autofocus module 26a is terminated.
[0013]
[Problems to be solved by the invention]
FIG. 6B shows an example of the moving state of the focus lens 22 when the video camera 20 is autofocused.
[0014]
In this figure, the movement related to wobbling is performed once every two fields, and the movement for focusing is performed regardless of the movement related to wobbling. It is controlled to move with. For this reason, there is a problem that power consumption increases.
[0015]
Accordingly, an object of the present invention is to provide an autofocus device for a video camera that can reduce power consumption while suppressing deterioration in followability of autofocus.
[0016]
[Means for Solving the Problems]
In the present invention, a lens block including a focus lens, an image sensor on which an object image is formed on the imaging surface by the lens block, an image signal output from the image sensor, and a luminance signal and a color signal are processed. A signal processing unit to obtain, a first focus lens moving unit that slightly moves the focus lens in one direction and the other in a certain stop period, and a change in the high-frequency component of the luminance signal due to the slight movement A focus information obtaining unit that obtains focus information based on the focus information, and a second focus lens moving unit that moves the focus lens so that the focus position approaches the in-focus position based on the focus information. The focus lens is moved by the focus by the first focus lens moving means. Is performed in synchronization with the movement of the lens, the amount of movement of the second focusing lens after stopping period and is characterized that you and those obtained by adding the amount of movement of the stop period.
[0017]
In the present invention, whether or not the focus position is at the in-focus position based on a change in the high-frequency component of the luminance signal caused by a slight movement of the focus lens in one direction and the other direction during a certain stop period. If it is not in the in-focus position, focus information such as in which direction the in-focus position is located is obtained. Based on this focus information, the focus lens is controlled to move so that the focus position approaches the in-focus position, thereby realizing autofocus.
[0018]
In this case, the focus lens is controlled to move so that the focus position approaches the in-focus position, but the movement is intermittently performed in synchronization with the movement of the focus lens for obtaining the focus information described above. The Further, the movement amount for the stop period is added to the movement amount when the focus lens moves intermittently so that the focus position approaches the in-focus position. As a result, the time during which the focus lens is moving is shortened, power consumption can be reduced , and deterioration in autofocus followability can be suppressed .
[0020]
Further, when the zoom operation is performed or the shutter speed of the image sensor is low, or when the focus position is far away from the in-focus position, it is not preferable that the autofocus followability is impaired. Therefore, in such a case, the focus lens is moved continuously to bring the focus position closer to the in-focus position, thereby preventing a decrease in autofocus followability.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of a video camera 10 as an embodiment.
[0022]
The video camera 10 includes a lens block 11 including a focus lens 12 and the like, a CCD solid-state imaging device 13 on which an object image is formed on an imaging surface by the lens block 11, and an imaging signal output from the imaging device 13. The signal processing unit 14 that obtains the luminance signal Y and the color signal C by performing sampling processing and YC separation processing on the output, and the output terminal 19a that outputs the luminance signal Y and the color signal C output from the signal processing unit 14, respectively. , 19b.
[0023]
In addition, the video camera 10 takes out a high-frequency component of the luminance signal Y output from the signal processing unit 14, and rectifies and detects it to obtain an evaluation value necessary for autofocus, and controls the entire system. A CPU 16 for controlling the movement of the focus lens 12 so as to take in an evaluation value obtained by the detection unit 15 and control the movement of the focus lens 12 so that the value becomes a maximum value. And a motor driver 17 that drives the motor 18 in response to a control signal from the autofocus module 16a.
[0024]
Next, the operation of the video camera 10 shown in FIG. 1 will be described. A subject image is formed on the imaging surface of the imaging device 13 by the lens block 11, and an imaging signal corresponding to the subject is output from the imaging device 13. This imaging signal is supplied to the signal processing unit 14, and sampling processing and YC separation processing are performed to obtain a luminance signal Y and a color signal C. The luminance signal Y and the color signal C are output from output terminals 19a and 19b, respectively. The luminance signal Y output from the signal processing unit 14 is supplied to the detection unit 15, and a high frequency component is extracted from the luminance signal Y and rectified and detected to obtain an evaluation value.
[0025]
Then, this evaluation value is supplied to an autofocus module 16a configured in the CPU 16, and the movement of the focus lens 12 is controlled so that this evaluation value becomes the maximum value, and an autofocus operation is realized.
[0026]
Here, the control operation of the autofocus module 16a will be described in more detail.
[0027]
The autofocus module 16a performs “mountain climbing control” in which the evaluation value output from the detection unit 15 is taken and the focus lens 12 is moved so that the evaluation value takes a maximum value. At this time, the autofocus module 16a slightly vibrates the focus position in order to check in which direction the in-focus position is from the current focus position, and the positive / negative of the differential component dy / dx of the evaluation value obtained at that time Thus, the direction to the in-focus position is estimated.
[0028]
FIG. 2A shows the wobbling, which is the minute vibration of the focus position, on the time axis. In this case, the focus position is controlled in field units. The movement of the focus position by the wobbling described above is controlled so as to alternately move in the far direction and the near direction every other field during the stop period of one field.
[0029]
In the autofocus module 16a, the differential component dy / dx of the evaluation value obtained at this time is examined, and the autofocus lens 12 is moved so as to bring the focus position closer to the in-focus position, thereby realizing autofocus. .
[0030]
In the present embodiment, the movement control of the focus lens 12 related to wobbling described above is the same as the conventional one, but the movement of the focus lens 12 for focusing is synchronized with the movement of the focus lens 12 related to wobbling. It is done intermittently.
[0031]
The flowchart of FIG. 3 shows the movement control operation 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.
[0032]
When the control operation by the autofocus module 16a is started in step ST1, first, an evaluation value is fetched from the detection unit 15 in step ST2, and a differential component of the evaluation value obtained by wobbling is extracted in step ST3 to estimate the in-focus position direction. To do. In step ST4, the amount of movement of the focus lens 12 (focus amount of movement) for calculating the focus position close to the in-focus position, that is, focusing is calculated based on the evaluation value.
[0033]
In 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, in order to follow the autofocus quickly, the process moves to step ST10 without synchronizing with the focus movement by wobbling, and the focus movement amount is calculated for 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 zero.
[0034]
When it is determined in step ST5 that the zoom is not being performed, the process proceeds to step ST6, and it is determined whether or not the shutter speed of the image sensor 13 is low, that is, whether or not the shutter is in low speed. When it is determined that the shutter is in low speed, the process moves to step ST10, and the focus movement amount is stored in the buffer and the focus movement amount in the current field in order to quickly follow the autofocus as described above. Calculated as the sum of the focus movement amount in the previous field. Then, the focus movement amount of the previous field stored in the buffer is set to zero.
[0035]
If it is determined in step ST6 that the shutter is not in low shutter speed, the process proceeds to step ST7, and the calculated focus movement amount in the current field is compared 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 in-focus position, the process proceeds to step ST10 in the same manner as described above to quickly follow autofocus. 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 zero.
[0036]
In step ST7, when it is determined that the focus movement amount is equal to or less than the threshold value _DTH , that is, when it is determined that the focus position is in the vicinity of the in-focus position, the process proceeds to step ST8 and the focus position related to wobbling is determined. It is determined whether the field is to be moved. If it is a field where the focus position is moved for wobbling, the process proceeds to step ST10, and the focus movement amount is changed to the focus movement amount in the current field and the focus movement amount in the previous field stored in the buffer. As the sum of Then, the focus movement amount of the previous field stored in the buffer is set to zero.
[0037]
If it is determined in step ST8 that the field of focus position movement related to wobbling is not performed, the process proceeds to step ST9, the focus movement amount in the current field is stored in the buffer, and the focus movement amount in the current field is set. 0.
[0038]
Next, the process proceeds to step ST11, where it is determined whether or not the field is the field where the focus position related to wobbling is performed. When the field is the field where the focus position related to wobbling is performed, the process proceeds to step ST13. Thus, the movement amount (wobbling amount) of the focus lens 12 related to wobbling is calculated, and when the focus position movement related to wobbling is not performed, the process proceeds to step ST12 and the wobbling amount is set to zero. In step ST14, the motor driver 17 is controlled using the movement amount of the focus lens 12 as the sum of the focus movement amount and the wobbling amount. In step ST15, the control operation by the autofocus module 16a is terminated.
[0039]
As described above, when the control operation by the autofocus module 16a is performed according to the flowchart shown in FIG. 3, the focus lens 12 of the video camera 10 is in the zoom operation, in the low-speed shutter, and the focus position is not in the vicinity of the focus position. Except for the case, as shown in FIG. 2B, the focus lens 12 for focusing is moved intermittently (every other field) in synchronization with the focus movement related to wobbling. For this reason, the time during which the focus lens 12 is moving is shortened, and power consumption can be reduced. For example, when the zoom is at the wide angle (WIDE) end and the subject is in a wide range, the range of movement of the focus lens 12 is narrowed, which can greatly contribute to the reduction of power consumption.
[0040]
Further, when the zoom operation, the low-speed shutter, and the focus position are not in the vicinity of the focus position, the focus lens 12 is continuously moved for focusing. Is prevented.
[0041]
Further, when the focus lens 12 is moved intermittently for focusing, the movement of the focus lens 12 is controlled by adding the focus movement amount in the previous field where the movement is not performed. Deterioration of follow-up performance is suppressed.
[0042]
Further, in the present embodiment, it can be achieved only by a control method using the current autofocus module 16a, that is, a program change, and there is no need to change or modify the peripheral circuit at all, which may increase the cost. Absent.
[0043]
Further, in the above-described embodiment, the field is a unit that is a cycle at which the control operation by the autofocus module 16a is started. However, the unit may not be a field unit as long as the autofocus module 16a starts. .
[0044]
【The invention's effect】
According to the present invention, the movement of the focus lens for focusing is intermittently performed in synchronization with the movement of the focus lens for obtaining focus information, and the time during which the focus lens is moving is shortened. Thus, power consumption can be reduced. In addition, intermittent movement of the focus lens for focusing is performed by adding the amount of movement for the stop period, and deterioration of autofocus followability can be suppressed. Further, since only the control method of the autofocus module is changed, there is an advantage that it can be used without changing the peripheral circuit of the conventional focus lens.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a video camera as an embodiment.
FIG. 2 is a diagram showing a relationship between wobbling and movement of a focus lens.
FIG. 3 is a diagram illustrating an example of focus lens movement control 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]
DESCRIPTION OF SYMBOLS 11 ... Lens block, 12 ... Focus lens, 13 ... Imaging device, 14 ... Signal processing part, 15 ... Detection part, 16 ... CPU, 16a ... Auto-focus module, 17 ... Motor driver, 18 ... Motor, 19a, 19b ... Output terminal

Claims (4)

A lens block including a focus lens;
An image sensor on which an object image is formed on the imaging surface by the lens block;
A signal processing unit that obtains a luminance signal and a color signal by processing an imaging signal output from the imaging element;
First focus lens moving means for minutely moving the focus lens alternately in one direction and the other direction during a fixed stop period;
Focus information obtaining means for obtaining focus information based on a change in a high-frequency component of the luminance signal due to the minute movement;
Second focus lens moving means for moving the focus lens so that the focus position approaches the in-focus position based on the focus information;
The movement of the focus lens by the second focus lens moving means is performed in synchronization with the movement of the focus lens by the first focus lens moving means , and the second focus lens moving means after the stop period. moving amount of the focus lens by the autofocus device of a video camera, characterized in that shall be the ones obtained by adding the amount of movement of the stop period. Zoom operation determining means for determining whether or not the zoom operation is in progress;
2. The video camera autofocus device according to claim 1, wherein during the zoom operation, cancellation of the operation performed in synchronization with the first focus lens moving unit is canceled. Shutter speed determining means for determining whether or not the shutter speed of the image sensor is lower than a constant speed;
2. The video camera autofocus device according to claim 1, wherein when the shutter speed is lower than a constant speed, the operation performed in synchronization with the first focus lens moving unit is canceled. A focus position determining means for determining whether or not the focus position is in the vicinity of the in-focus position from the amount of movement of the focus lens calculated based on the focus information;
2. The video camera autofocus device according to claim 1, wherein when the focus position is not in the vicinity of the in-focus position, the synchronization with the first focus lens moving unit is canceled.

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