JP7433868B2 - Control device and its control method - Google Patents

Description

The present invention relates to driving a focus lens included in an electronic still camera or the like having a focus adjustment function.

2. Description of the Related Art Some imaging devices such as digital cameras perform focus detection using a phase difference detection method using an output signal from an image sensor for capturing a subject image. Further, there is known a technique related to focus lens drive control for focusing on a moving subject using the result of focus detection using a phase difference detection method. The imaging device disclosed in Patent Document 1 calculates a subject image plane velocity and calculates a correction amount that correlates with the subject image plane velocity. This correction amount is added to the latest defocus amount detected by the phase difference detection method to calculate the focus lens drive amount for tracking servo, and the actual movement amount of the focus lens is detected. Then, servo driving is performed to drive the focus lens to the in-focus position according to the focus lens driving amount and the actual movement amount of the focus lens. Accumulation of the photoelectric conversion element included in the image sensor and servo driving are performed one after another in an overlapping manner.

Japanese Unexamined Patent Publication No. 4-133016

In the method disclosed in Patent Document 1, the calculation of the object image plane velocity is used to correct the defocus amount, and the lens drive is performed by servo driving according to the focus lens drive amount based on the defocus amount. . In this configuration in which the focus lens is driven strictly according to the focus lens drive amount, the drive speed of the focus lens changes depending on the focus lens drive amount. For this reason, it may be difficult to maintain a focused state while driving the focus lens to focus on a moving object. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control device and a control method thereof that can better maintain a focused state while driving a focus lens on a moving object.

In order to achieve the above object, the present invention provides a focus detection means for calculating the amount of defocus of a subject, an acquisition means for acquiring information regarding the position of the lens, information regarding the amount of defocus, the information regarding the position of the lens, and a time. , a prediction means for predicting the future image plane position of the subject based on the plurality of data stored in the storage means, and a prediction means for predicting the driving amount of the lens based on the image plane position. a first calculating means for calculating, a second calculating means for calculating a driving speed of the lens based on the driving amount, and controlling the driving of the lens at the driving speed calculated by the second calculating means. a first value corresponding to the upper limit and a second value corresponding to the lower limit of the lens drive speed based on the image plane speed of the subject calculated based on the plurality of data stored in the storage means. and a third calculation means for setting the lens drive speed, and is configured to limit the lens driving speed based on the first value and the second value calculated by the third calculation means. shall be.

According to the present invention, it is possible to better maintain a focused state while driving a focus lens on a moving object.

Block diagram of interchangeable lens camera system Flowchart diagram of servo mode processing Flowchart diagram of focus detection processing Flowchart diagram of focus lens drive speed calculation Image plane position history and image plane predicted position diagram Relationship diagram between the image plane speed of the subject and the speed limit Relationship diagram 2 between the image plane speed of the subject and the speed limit Flowchart of focus lens drive speed calculation Figure 2 History of lens drive speed

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an example of a functional configuration of an interchangeable lens camera (also referred to as an imaging device) as an example of a control device according to a first embodiment of the present invention.

The imaging device of this embodiment includes an exchangeable lens unit 10 and a camera body 20. The lens control section 106, which controls the entire operation of the lens, and the camera control section 212, which controls the operation of the entire camera system including the lens unit 10, can communicate with each other through a terminal provided on the lens mount.

First, the configuration of the lens unit 10 will be explained. The fixed lens 101, the aperture 102, and the focus lens 103 constitute a photographing optical system. The aperture 102 is driven by an aperture drive unit 104, and controls the amount of light incident on the image sensor 201, which will be described later. The focus lens 103 is driven by a focus lens drive unit 105, and the focal length of the imaging optical system changes depending on the position of the focus lens 103. The aperture drive unit 104 and focus lens drive unit 105 are controlled by a lens control unit 106, and determine the aperture amount of the aperture 102 and the position of the focus lens 103.

The lens operation unit 107 is a group of input devices for the user to make settings regarding the operation of the lens unit 10, and includes, for example, the following input devices. Switching between AF (autofocus)/MF (manual focus) mode, adjusting the position of the focus lens using MF, setting the operating range of the focus lens, setting the image stabilization mode, etc. When the lens operation section 107 is operated, the lens control section 106 performs control according to the operation.

The lens control unit 106 controls the aperture drive unit 104 and the focus lens drive unit 105 according to control commands and control information received from the camera control unit 212, which will be described later, and also transmits lens control information to the camera control unit 212. .

Next, the configuration of the camera body 20 will be explained. The camera body 20 is configured to be able to obtain an imaging signal from the light beam that has passed through the imaging optical system of the lens unit 10.

The image sensor 201 is composed of a CCD or CMOS sensor. A light flux incident from the photographing optical system of the lens unit 10 forms an image on the light receiving surface of the image sensor 201, and is converted into a signal charge according to the amount of incident light by photodiodes provided in pixels arranged in the image sensor 201. Ru. The signal charge accumulated in each photodiode is sequentially read out from the image sensor 201 as a voltage signal corresponding to the signal charge by a drive pulse outputted by the timing generator 214 in accordance with a command from the camera control unit 212.

Each pixel of the image sensor 201 used in this embodiment is composed of two (pair) photodiodes A and B and one microlens provided for the pair of photodiodes A and B. . Each pixel splits incident light with a microlens to form a pair of optical images on a pair of photodiodes A and B, and from the pair of photodiodes A and B, a pair of optical images used for AF signals, which will be described later, are generated. Outputs pixel signals (A signal and B signal). Furthermore, by adding the outputs of the pair of photodiodes A and B, an imaging signal (A+B signal) can be obtained.

A plurality of A signals output from a plurality of pixels are combined with each other, and a plurality of B signals are combined with each other. As a result, a pair of image signals are obtained as AF signals (in other words, focus detection signals) used in AF using the imaging surface phase difference detection method (hereinafter referred to as imaging surface phase difference AF). The AF signal processing unit 204, which will be described later, performs a correlation calculation on the pair of image signals, calculates a phase difference (hereinafter referred to as the amount of image shift), which is the amount of shift between the pair of image signals, and further calculates the amount of image shift. The defocus amount (and defocus direction) of the photographing optical system is calculated from

The CDS/AGC/AD converter 202 performs correlated double sampling, gain adjustment, and AD conversion on the AF signal and imaging signal read out from the image sensor 201 to remove reset noise. The converter 202 outputs the processed imaging signal and AF signal to the image input controller 203 and the AF signal processing section 204, respectively.

The image input controller 203 stores the imaging signal output from the converter 202 in the SDRAM 209 via the bus 21 as an image signal. The image signal stored in the SDRAM 209 is read out by the display control unit 205 via the bus 21 and displayed on the display unit 206. Further, in a recording mode in which an image signal is recorded, the image signal stored in the SDRAM 209 is recorded on a recording medium 208 such as a semiconductor memory by the recording medium control unit 207.

The ROM 210 stores control programs and processing programs executed by the camera control unit 212 and various data necessary for executing these programs. The flash ROM 211 stores various setting information regarding the operation of the camera 20 set by the user.

The AF signal processing unit 204 as a focus detection device performs a correlation calculation on a pair of image signals, which are AF signals output from the converter 202, and calculates the amount of image shift and reliability of the pair of image signals. . Reliability is calculated using the degree of agreement between the two images and the steepness of the amount of correlation change. Further, the AF signal processing unit 204 sets the position and size of a distance measurement area, which is an area where focus detection and AF are performed within the imaging screen. The AF signal processing unit 204 outputs the image shift amount (detection amount) calculated in the distance measurement area and reliability information to the camera control unit 212.

The AF control unit 2121 in the camera control unit 212 instructs the lens control unit 106 to move the focal position based on the converted defocus amount. Further, the motion determination section 2122 performs motion determination based on the subject image plane position calculated from the photographing time and the defocus amount stored in the memory circuit 215 by the storage section 2123. The AF control unit 2121 predicts the future image plane position using the prediction unit 2124, calculates the lens drive amount necessary for the focus lens 103 to come to the predicted image plane position, and instructs the lens control unit 106. I do.

The camera control section 212 controls each section within the camera body 20 while exchanging information with them. In addition, the camera control unit 212 performs user operations such as turning on/off the power, changing various settings, imaging processing, AF processing, and playback processing of recorded images in response to input from the camera operation unit 213 based on user operations. Perform various corresponding processes. Furthermore, the camera control section 212 transmits control commands for the lens unit 10 (lens control section 106) and information about the camera body 20 to the lens control section 106, and acquires information about the lens unit 10 from the lens control section 106. do. The camera control unit 212 is configured by a microcomputer, and controls the entire camera system including the interchangeable lens 10 by executing a computer program stored in the ROM 210.

The camera control unit 212 calculates a defocus amount using the image shift amount in the ranging area calculated by the AF signal processing unit 204, and controls the focus lens 103 through the lens control unit 106 based on the defocus amount. Control the drive.

The processing performed by the camera body 20 will be described below. The camera control unit 212 performs the following processing according to an imaging processing program that is a computer program.

FIG. 2 is a flowchart showing the photographing processing of the camera body 20, particularly the processing in the servo mode performed by the AF control section 2121. S means step.

First, in S201, the camera control unit 212 determines the state of SW1 (shooting start switch), and if the switch is on, the process moves to S202, and if the switch is off, the servo mode processing ends.

In S202, focus detection processing is performed. Details of the processing will be described later using FIG. 3.

In S203, moving object determination processing is performed. Although details of the process will be omitted, there is a method of determining whether the subject image plane position calculated from the photographing time and defocus amount stored in the memory circuit 215 continuously changes by a predetermined amount or more.

In S204, it is determined whether the result of the moving object determination process in S203 is a moving object. If it is a moving object, the process advances to S205, and if not, the process advances to S206.

In S205, predictive calculation processing is performed using the subject image plane position calculated from the photographing time and the defocus amount, which is stored in the memory circuit 215 by the storage unit 2123, to calculate a future image plane position. Although the details of the prediction method will be omitted, a known prediction method can be used. Further, a quadratic curve may be used as a prediction function, or only the latest two points may be obtained and predicted using a linear curve. Furthermore, the prediction formula f(t) as shown in equation (1) may be obtained by statistical calculation using the least squares method.
f(t)=α+βt+γtn...Formula (1)

In S206, it is determined whether or not the camera is in focus. If it is in focus, the process advances to S201, and if it is not in focus, the process advances to S207.

In S207, it is determined whether or not the focus detection process has ended. If it is determined that the focus detection process has ended, the servo mode processing ends, and if it has not ended, the process advances to S208. An example of determining whether the focus detection process has been completed is when it is determined that the focus lens cannot be brought into focus even if the focus lens is moved any further, such as when the focus lens has scanned the entire drivable range.

In S208, based on the image plane position calculated in S205, the difference between the current lens image plane position and the lens drive amount is calculated.

In S209, in order to drive the lens so that the image plane position of the lens matches the image plane position of the subject, the lens drive speed is calculated by dividing the lens drive amount calculated in S208 by the lens drive time. . Details of the speed calculation method will be described later using FIG. 4.

In S210, lens drive control is performed by specifying the lens drive amount calculated in S208 and the lens drive speed calculated in S209.

Next, an example of the operation of the focus detection process will be described based on the flowchart of FIG. 3.

First, the AF signal processing unit 204 acquires a pair of image signals as AF signals from a plurality of pixels included in the distance measurement area of the image sensor 201 (S301). Next, the AF signal processing unit 204 calculates the amount of correlation between the pair of acquired image signals while relatively shifting them one pixel (one bit) at a time (S302). Subsequently, the AF signal processing unit 204 calculates a correlation change amount from the correlation amount calculated in S302 (S303). Next, the AF signal processing unit 204 calculates an image shift amount using the correlation change amount calculated in S303 (S304).

Next, the AF signal processing unit 204 calculates the defocus amount of the distance measurement area using the image shift amount of the distance measurement area calculated in S304 (S305). Then, in S306, the obtained focus detection information is stored in the memory circuit 215. Here, the defocus amount and photographing time of each focus detection area are stored.

Next, focus lens drive speed calculation will be explained using the flowchart of FIG. 4 and FIG. 5. FIG. 5 shows the predicted image plane position p _i +1 at a future time t _i+1 using a prediction formula calculated based on the image plane positions p _i to p i- _{5 acquired at times t i to t i- 5 .} It is something that

First, in S401, the lens drive amount D calculated in S208 is obtained. Next, in S402, the lens drive time T _Dif is acquired. In S403, the lens driving speed V _Lens is calculated from the lens driving amount acquired in S401 and the lens driving time acquired in S402. In the example of FIG. 5, D=p _i+1 -p _i, T _Dif =t _i+1 -t _{i, and} V _Lens =D/T _Dif . Incidentally, in the case where the lens continues to move when acquiring each image plane position, T _Dif = t _{i +1} − t _{i ′} (t _{i <} t _{i ′} ). (t _i ' corresponds to the current time when the focus lens driving speed is being calculated)

Next, in S404, the image plane velocity V of the subject is acquired, and in S405, speed limits V _{Max and} V _Min based on the image plane velocity V are calculated, respectively.
V _Max = αV (α>1) ...Formula (2)
V _Min =βV (β<1) ...Formula (3)

FIG. 6 shows the relationship between the speed limits V _{Max and} V _Min calculated based on the image surface velocity V calculated at a certain time t. Furthermore, the ratios of the coefficients α and β may be the same, such as ±20%, or may be different, such as α=150% and β=80%. Furthermore, as shown in FIG. 7, the numerical values of α and β may be changed at a certain image surface velocity V _th . Alternatively, a plurality of V _th may be provided and the numerical values of α and β may be changed in stages.

In S406, the lens driving speed V _Lens calculated in S403 is compared with V _Max and V _Min calculated in S405. As a result of the comparison, if the speed is within the speed limit, V _Lens is directly set as the lens drive speed in S210, and if it is not within the speed limit, the speed limit V _Max or V _Min is set as the lens drive speed.

The above is a method for calculating the driving speed of the focus lens, but if the driving speed is limited using such a simple method, the ability to follow the focus may be impaired depending on conditions such as the subject.

A calculation method with better control for reducing these influences will be explained using FIG. 8. A description of the same processing as that described in FIG. 4 will be omitted.

In S804, it is determined whether the subject is moving in a close direction, and if so, the process advances to S804, and if not, the process ends.

In S806, it is determined whether the image plane velocity of the subject is greater than or equal to a predetermined value, and if it is greater than or equal to the predetermined value, the process proceeds to S807, and if not, the process is terminated.

In S807, it is determined from the history of past lens drive speeds whether the lens is currently accelerating or decelerating. Using FIG. 9 as an example, the section from V1 is under acceleration, the section from V1 to V2 is under deceleration, and the section from V2 to V3 is under acceleration. Depending on this result, only the upper limit value can be set if it is determined that the vehicle is accelerating. Further, when it is determined that the vehicle is decelerating, only the lower limit value can be set. If the upper limit value calculated during acceleration is smaller than the previous lens drive speed, and if the lens is controlled at that speed limit, the lens will start decelerating, it is possible to not limit the speed. .

Further, it is also possible to add determinations to the history of lens drive speeds shown in FIG. For example, if V3 is the latest lens driving speed, the local maximum value V1 and local minimum value V2 are determined from the history excluding the latest lens driving speed. Further, the restriction is performed when the difference value Dif2 in the acceleration section is equal to or greater than a predetermined ratio of the difference Dif1 in the extreme value.

Based on the above acceleration/deceleration determination results, it is determined in S808 whether or not to perform speed restriction. If so, the process advances to S809, and if not, the process ends.

As explained above, according to the present invention, by performing the above-described control, it is possible to prevent the hunting phenomenon of the lens and provide a stable and highly responsive automatic focus adjustment operation. .

103 Focus lens 105 Focus lens drive section 106 Lens control section 20 Camera main body 204 AF signal processing section 212 Camera control section 2121 AF control section 2122 Motion determination section 2123 Storage section 2124 Prediction section

Claims (7)

a focus detection means for calculating the amount of defocus of the subject; an acquisition means for acquiring information regarding the position of the lens;
a storage means for storing data of the defocus amount, information regarding the position of the lens, and time;
prediction means for predicting a future image plane position of the subject based on the plurality of data stored in the storage means;
a first calculation means for calculating a driving amount of the lens based on the image plane position;
a second calculation means for calculating a driving speed of the lens based on the driving amount;
When controlling the driving of the lens at the driving speed calculated by the second calculation means,
a first value corresponding to an upper limit and a second value corresponding to a lower limit of the driving speed of the lens based on the image plane speed of the subject calculated based on the plurality of data stored in the storage means; 3 calculation means,
A control device that limits a lens drive speed based on the first value and the second value calculated by the third calculation means. 2. The control device according to claim 1, wherein the lens driving speed is controlled based on the first value and the second value only when the image plane speed of the subject is equal to or higher than a predetermined value. 3. The control device according to claim 1, wherein the lens driving speed is controlled based on the first value and the second value only when the direction of movement of the subject is a close-up direction. 4. A ratio of the first value and the second value based on the image surface velocity is different between the first value and the second value. The control device described in . Claim 1, wherein it is determined from the history of the lens driving speed whether the lens driving speed is accelerating or decelerating, and if it is determined that the lens driving speed is accelerating, the first value is set. 5. The control device according to any one of 4 to 4. 2. The lens driving speed is determined from the history of the lens driving speed to determine whether the lens driving speed is accelerating or decelerating, and if it is determined that the lens driving speed is decelerating, the second value is set. 5. The control device according to any one of 4 to 4. A control method for a control device, the method comprising:
a focus detection step for calculating the amount of defocus of the subject;
an obtaining step of obtaining information about the position of the lens;
a storing step of storing data of the defocus amount, information regarding the position of the lens, and time in a storage means ;
a prediction step of predicting a future image plane position of the subject based on the plurality of data stored in the storage means ;
a first calculation step of calculating a driving amount of the lens based on the image plane position;
a second calculation step of calculating a driving speed of the lens based on the driving amount;
When controlling the drive of the lens at the drive speed calculated in the second calculation step, the lens drive is controlled based on the image plane speed of the subject calculated based on the plurality of data stored in the storage means. a third calculation step of setting a first value corresponding to the upper limit of the driving speed and a second value corresponding to the lower limit;
A method for controlling a control device, further comprising: limiting a lens driving speed based on the first value and the second value calculated in the third calculating step.

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