JP2004219881A - Automatic focus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focus system capable of quickly moving a lens to a detected focal point, for quick focusing. <P>SOLUTION: A focal point voltage is detected from a high-frequency component of the video signal obtained from an imaging element 2. A lens 1 is driven to a specified position based on a differential voltage between specified fields of the focal point voltages, so that the differential voltage comes to be minimum. Thus, focusing of image light to the imaging element 2 is performed in hill-climbing method. An FIFO20 for storing lens position data is provided, and if the minimum value of the differential voltage is detected, a drive signal is generated based on the lens position data, read from the FIFO20, which proceeds for the time period required for the process to acquire the drive signal for driving the lens from the imaging element 2, to move the lens 1 to the position specified by the lens position data. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an autofocus apparatus for video recording equipment such as a movie, and more particularly to an autofocus apparatus suitable for quickly reaching an appropriate focus position using a hill-climbing servo system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an autofocus apparatus using a hill-climbing control (servo) method has been known (for example, see Patent Document 1).
Describing this, the high frequency component included in the video signal of the captured image corresponds to the degree of focus (focus) and shows the maximum value at the focal point.
FIG. 7 is an explanatory diagram showing the basic operation of the hill-climbing servo system, and shows the state thereof.
In the figure, the horizontal axis represents the lens position, and the vertical axis represents the focal voltage which is a high frequency component. Since the point at which the focal voltage is maximized is the appropriate peak (focus point) PF, the focus adjustment (focusing) is performed by moving the focusing lens so that the focal voltage is maximized (see arrow FA in the figure). .
[0003]
FIG. 4 shows a configuration of a conventional autofocus device 10.
In FIG. 1, a lens 1 for focus adjustment is provided on a light incident side of an imaging device 2 such as a CCD. A video process circuit 3 is provided on the charge signal output side of the image sensor 2. The video signal is also connected so as to be output also to the focus voltage detection circuit 4. A microcomputer 6 is connected to an output side of the focus voltage detection circuit 4 via an A / D converter 5, and a focus control output side is connected to a drive circuit 7.
[0004]
Of the above components, the lens 1 can be shifted by a motor 8 so that focus adjustment is performed. The video process circuit 3 includes well-known circuits such as a preamplifier, a color separation circuit, and a γ correction circuit, and outputs a video signal of R (red), G (green), B (blue) or a color difference. It has become so. The focus voltage detection circuit 4 is for extracting a focus voltage, which is a high-frequency component, from an input video signal, and includes a filter and a sample-and-hold circuit.
[0005]
The microcomputer 6 has a function of repeatedly performing the operation shown in FIG. 5 based on the focus voltage data extracted by the focus voltage detection circuit 16.
FIG. 5 is a flowchart showing the operation of the conventional autofocus device.
The focus control signal obtained by the microcomputer 6 is supplied to the drive circuit 7, and the drive circuit 7 drives the motor 8 based on the focus control signal. The synchronization generation circuit 9 is a circuit for outputting a clock signal and a synchronization signal required for each unit.
[0006]
Next, the operation of the conventional autofocus device 10 will be described with reference to the flowchart of FIG. 5 and the graph of FIG. The image sensor 2 captures an input image and outputs a charge signal C to the video process circuit 3. The video processing circuit 3 performs desired processing such as amplification and color separation on the input signal, and outputs a video signal. This video signal is supplied to a video tape or a display device as needed.
[0007]
This video signal is also supplied to the focus voltage detection circuit 4, where the high-frequency component is detected as the focus voltage F. The detected focus voltage F is converted into a digital signal by the A / D converter 5 and taken into the microcomputer 6.
The microcomputer 6 detects the point at which the focus voltage F changes from an increase to a decrease by observing the change in the focus voltage F, and outputs a control signal S so as to reverse the movement of the lens in the opposite direction.
The microcomputer 6 compares how the focus voltage F of the latest field has changed with the focus voltage F of the immediately preceding field (step S1).
As a result, if it is determined that the peak is appropriate, the process is stopped (step S2).
If the peak is not appropriate, the change in the focus voltage F is checked (step S3).
If the change in the voltage increases, the control signal S is output to the drive circuit 7 to continue the process in the same direction (step S4).
If the change in the voltage decreases, a control signal S is output to the drive circuit 7 so that the moving direction of the focus lens 1 is reversed (step S5).
[0008]
In the drive circuit 7, the motor 8 is driven based on the control signal S input from the microcomputer 6, and the focus lens 1 is shifted. Such an operation is repeatedly executed until a proper peak is detected (step S2).
Such an operation will be described with reference to FIG. First, while climbing the hill (movement of arrow FA), the focus position gradually approaches, so that the focus voltage F gradually increases in each new field. When the peak voltage exceeds the proper peak PF, the focal voltage decreases (movement of arrow FB). When the decrease in the focal voltage is detected, the direction of movement of the lens is reversed, and the aim is to reach the proper top PF (movement of arrow FC). Finally, the inversion is repeated before and after the proper top PF. Desired.
[0009]
[Patent Document 1]
Utility Model Registration No. 2603535 (Page 2-3, FIG. 1-5)
[0010]
[Problems to be solved by the invention]
By the way, as described above, the conventional autofocus device is configured to obtain an appropriate top PF by using overrun after focusing. Is not a value obtained from the image at the current lens position, but is an image delayed by arithmetic processing in the image sensor 2 and the focus voltage detection circuit 4. Is the value obtained from Also, it takes a certain time for the microcomputer 6 to determine the focus.
[0011]
As an example, in the case of a movie, imaging by the image sensor (CCD) 2 requires one field time. The focus voltage F is obtained in the focus voltage output circuit 4 from the charge signal C output from the image sensor 2, and this requires one field time. Further, it takes one field time for the microcomputer 6 to determine whether the focus voltage F has increased or decreased and to output the control signal S.
[0012]
That is, when it is detected that the focus voltage has started to reach the focal point PF and the control voltage S is output to the drive circuit 7 accordingly, even if an appropriate focal point is detected quickly, The position of the lens 1 at this time is three fields ahead of the position at which the focus is actually focused and the focus voltage starts to decrease.
[0013]
FIG. 6 shows this relationship. FIG. 6 is a diagram showing a time relationship among a lens position, an output of an image sensor, an output of a focus voltage detection circuit, and a drive signal in a conventional autofocus device.
In the figure, n represents time, and n + 1 represents time one field later than time n.
As shown in the figure, at time n + 3, the position P of the lens is at _{Pn + 3} . The output C of the imaging device at this time (CCD) is the output C _{n + 2} by the position P _{n + 2} of the previous field of the lens, the output (focusing voltage) F of the focal voltage output circuit according to the position P _{n + 1} of two fields before the lens an output _{F n + 1} obtained by the CCD output _{C n + 1,} with _{S n} control signal S outputted from the microcomputer 6 is output from the output _{F n} obtained from the CCD output _{C n} of the lens position _{P n} of the previous three fields is there.
[0014]
Therefore, when the focus voltage is detected to decrease after reaching the focal point PF and the direction of movement of the lens 1 is reversed, the position of the lens 1 has already exceeded the focal point and has been lowered by three fields. It takes more time to reach the peak focus point PF again, so that several trials and errors are required to obtain a focus position, and an extra time until focus is required accordingly. There is.
[0015]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems and to provide an auto-focusing device that enables a lens to be immediately moved to a detected focus position, thereby enabling quick focus.
[0016]
[Means for Solving the Problems]
As a means for achieving the above object, the present invention is obtained by processing a lens 1 for condensing image light on an image sensor 2 and an electric signal corresponding to the image light output from the image sensor 2. A focus voltage detecting means (circuit) 4 for detecting a focus voltage from a high-frequency component of a video signal; and a drive for generating a drive signal for driving the lens to a predetermined position based on a difference voltage between predetermined fields of the focus voltage. A signal generating means (microcomputer) 6A, and a driving unit 7 for driving the lens by the driving signal, and by moving a lens position of the lens with respect to the image sensor so that the differential voltage is minimized. In an autofocus apparatus for performing focus adjustment of the image light to the image sensor by a hill-climbing method,
A memory (FIFO) 20 for storing lens position data indicating a position of the lens in each field between the predetermined fields, wherein when the minimum of the differential voltage is detected, the image sensor read from the memory; The drive signal is generated by the drive signal generation means based on the lens position data at a time preceding the predetermined field by a time required for processing until the drive signal is obtained from the drive signal, and the lens is moved by the drive unit to the lens. An autofocus device moves to a position specified by position data.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings by way of preferred examples. For the sake of simplicity, the same components as those of the conventional example are denoted by the same reference characters, and description thereof is omitted.
[0018]
<Example>
FIG. 1 is a configuration diagram showing an embodiment of the autofocus device of the present invention.
As shown in the figure, an autofocus device 10A of the present embodiment includes a lens 1, an image sensor 2, a video process circuit 3, a focus voltage detection circuit 4, an A / D converter 5, a microcomputer 6A, and a memory (FIFO). 20), a drive circuit 7 and a motor 8.
[0019]
A lens 1 for focus adjustment is provided movably in the front-rear direction on the light incident side of the imaging device 2 composed of a CCD.
A video process circuit 3 is provided on the charge signal output side of the image sensor 2, and a charge signal C corresponding to an image formed by the lens 1 is supplied from the image sensor 2 to the video process circuit 3.
The video process circuit 3 converts the input charge signal C into a video signal and outputs the video signal. A focus voltage detection circuit 4 is connected to the video process circuit 3, and a video signal is also output to the focus voltage detection circuit 4.
[0020]
A microcomputer 6A is connected to the output side of the focus voltage detection circuit 4 via an A / D converter 5.
A memory (FIFO) 20 for storing lens position data P is separately connected to the microcomputer 6A. The FIFO 20 is for first-in, first-out data, and may be provided inside the microcomputer 6A.
A control signal SA is supplied from the microcomputer 6A to the drive circuit 7, and the drive circuit 7 rotates the motor 8 according to the control signal SA.
[0021]
Of the above components, the lens 1 can be shifted by the rotation of the motor 8 by a moving mechanism (not shown) connected to the motor 8, whereby the focus adjustment of the image light incident on the image sensor 2 is performed. It is configured as follows. The video process circuit 3 includes well-known circuits such as a preamplifier, a color separation circuit, and a γ correction circuit, and outputs a video signal of R (red), G (green), B (blue) or a color difference. It has become so. The focus voltage detection circuit 4 is for extracting a focus voltage F, which is a high frequency component, from an input video signal, and includes a filter and a sample and hold circuit.
[0022]
The microcomputer 6A stores the focus voltage F output from the focus voltage detection circuit 4, outputs the data of the lens position at which the focus voltage F is obtained (lens position data P) to the FIFO 20, and outputs the advance data of the FIFO 20 And supplies a control signal SA to the drive circuit 7. The drive circuit 7 drives the motor 8 based on the input control signal SA. The synchronization circuit 9 is for outputting a clock signal and a synchronization signal required for each unit.
The lens position data P is a numerical value indicating the position or movement of the lens. An example in which a stepping motor is used for the lens driving circuit will be described. The signal given to the stepping motor is information on how many move from the current position. When the telephoto direction is set to + and the closest direction is set to-, the lens is moved in the telephoto direction by two pulses from the current position, when +2 is moved by four pulses in the close direction, -4 is recorded in the FIFO 20.
[0023]
Next, the operation of the autofocus device of the present embodiment will be described with reference to FIG.
FIG. 2 is a flowchart showing the operation of the embodiment of the autofocus device of the present invention.
The autofocus device 10A performs a hill-climbing operation for focusing, the lens 1 is at a predetermined position, the image sensor 2 captures an input image, and the charge signal C is output to the video process circuit 3. You. The video processing circuit 3 performs desired processing such as amplification and color separation on the input signal, and outputs a video signal. This video signal is supplied to a video tape or a display device as needed.
[0024]
This video signal is also supplied to the focus voltage detection circuit 4, where the high frequency component is detected as the focus voltage F. The detected focus voltage F is converted into a digital signal by the A / D converter 5 and taken into the microcomputer 6A.
In the microcomputer 6A, as described above, the focus voltage F of the latest field is stored in its memory (FIG. 2, step S11). Here, the lens position data P is calculated and output to the FIFO 20. The FIFO 20 sequentially stores the lens position data P.
[0025]
The generation of the charge signal C in the image sensor 2, the generation of the focus voltage F in the focus voltage detection circuit 4, and the generation of the control signal SA in the microcomputer 6 each require a time corresponding to one field. The time relationship is as shown in FIG.
FIG. 3 is a diagram showing the time relationship among the lens position, the output of the image sensor, the output of the focus voltage detection circuit, and the drive signal in the embodiment of the autofocus device of the present invention.
As shown in the figure, when indicating the time t of the n fields and _the time _{t n,} ((n + 1) becomes a time _{t n + 1} in the field), the control signals SA _n output at time _{t n + 3,} the time _{t n + 2} is obtained from the focus voltage _{F n + 1} of the focus voltage _{F n} and time _{t n + 3,} these focus voltage _F n _{to F n + 1,} respectively, the charge of the time _{t n + 1} of the charge-voltage _{C n} and time _{t n + 2} voltage _{C n + 1} are those more obtained, the lens position at that time are those corresponding from time t _n at time t _{n + 1.}
Here, lens position data corresponding to time t _n is displayed as P _n .
[0026]
As shown in FIG. 2, the microcomputer 6A compares with the focus voltage one field before, and outputs a control signal for moving the lens position according to the result (step 11). At this time, the lens position data P is output and stored in the FIFO 20, respectively. Note that the FIFO 20 can store three lens position data P, and the leading memory that holds the data further holds data three fields before. For example, at time t _{n + 3} , the FIFO 20 holds the lens position data P _n to P _{n + 2} . The data in the FIFO 20 is sequentially updated when new data is input.
[0027]
In the drive circuit 7, the motor 8 is driven based on the control signal input from the microcomputer 6A, and the focus lens 1 is moved. Such an operation is repeatedly executed until a proper peak is detected (step S12).
Next, when an appropriate peak is detected and the focus voltage F starts to decrease, the microcomputer 6A generates a control signal SA based on the lens position data P held at the head of the FIFO 20, and generates a control signal SA. , And the lens 1 is moved to an appropriate in-focus position (step 13).
If it is detected that the focus voltage F _{n + 1} corresponding to the lens position P _{n + 1} has decreased, the result appears at the control signal SA _n at time t _{n + 3} . Therefore, the microcomputer 6A outputs the control signal SA _n so that the lens position becomes P _n at time t _{n + 3} . As a result, the lens 1 is immediately moved to an appropriate top.
[0028]
In this embodiment, when the lens reaches the proper peak, the lens position is immediately returned to the stored lens position. Therefore, when the lens moves beyond the peak as in the conventional example, the lens moves. It is possible to reach the in-focus point earlier than in the method of reversing the direction and finding the proper peak.
[0029]
Note that the present invention is applicable to an autofocus apparatus having a configuration in which a focal point can be determined by comparing focus voltages of at least front and rear fields.
[0030]
【The invention's effect】
As described above, according to the first aspect, the autofocus device of the present invention has a memory that stores lens position data indicating a position of a lens in each field between predetermined fields, and minimizes the difference voltage. If it is detected, the drive signal is read by the drive signal generation means based on the lens position data at the time preceding the predetermined field by the time required for processing until the drive signal is obtained from the image sensor, read from the memory. By generating and moving the lens to a position specified by the lens position data by the driving unit, the lens can be immediately moved to the detected focusing position, and an autofocus device that enables quick focusing is provided. There is an effect that it can be provided.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of an autofocus device of the present invention.
FIG. 2 is a flowchart showing an operation of the embodiment of the autofocus device of the present invention.
FIG. 3 is a diagram illustrating a time relationship among a lens position, an output of an image sensor, an output of a focus voltage detection circuit, and a drive signal in the embodiment of the autofocus apparatus of the present invention.
FIG. 4 is a configuration diagram illustrating a conventional autofocus device.
FIG. 5 is a flowchart showing an operation of a conventional autofocus device.
FIG. 6 is a diagram illustrating a time relationship among a lens position, an output of an image sensor, an output of a focus voltage detection circuit, and a drive signal in a conventional autofocus apparatus.
FIG. 7 is an explanatory diagram showing a basic operation of the hill-climbing servo system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Image sensor (CCD), 3 ... Video process circuit, 4 ... Focus voltage detection circuit, 5 ... AD converter, 6, 6A ... Microcomputer, 7 ... Drive circuit, 8 ... Motor, 9 ... Synchronization Signal generating circuit, 10, 10A: autofocus device, 20: FIFO.

Claims (1)

A lens that focuses image light on an image sensor, and a focus voltage detector that detects a focus voltage from a high-frequency component of a video signal obtained by processing an electric signal corresponding to the image light output from the image sensor, A drive signal generation unit that generates a drive signal for driving the lens to a predetermined position based on a difference voltage between predetermined fields of the focus voltage, and a drive unit that drives the lens by the drive signal, By moving a lens position of the lens with respect to the image sensor so that the differential voltage is minimized, in an autofocus apparatus that performs focus adjustment on the image sensor of the image light in a hill-climbing method,
A memory for storing lens position data indicating a position of the lens in each field between the predetermined fields, and when the minimum of the differential voltage is detected, the drive signal from the image sensor read from the memory; The drive signal is generated by the drive signal generation means based on the lens position data at a time preceding the predetermined field by a time required for processing until obtaining the lens, and the lens is designated by the lens position data by the drive unit. An auto-focusing device that moves to a position to be moved.

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