JP2925172B2 - Automatic tracking device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic tracking device suitable for use in video equipment such as a video camera and an electronic still camera.

2. Description of the Related Art Conventionally, there are various types of automatic focus adjusting devices for cameras. Devices having an image capturing means for photoelectrically converting a subject image to obtain a video signal, such as a video camera and an electronic still camera, are used. In this method, a method of detecting the definition of a subject image from a video signal and performing focus adjustment so that the definition is maximized is used.

In this type of apparatus, a focus detection area is set in a part of a normal photographing screen, and focus detection is performed on a subject image in the area. A device with an automatic subject tracking function that can move the object following the movement of the subject image and keep focusing on the moving subject has been proposed. (For example, JP-A-60-249477).

Various types of such subject tracking methods have been proposed. For example, a peak value of a high-frequency component in a focus detection area is detected as a feature point of a subject image for each field (or one frame). Thus, the moving position of the subject is known, the focus detection area is reset to a position substantially centered on the moving position of the subject, and the focus can be kept on the moving subject. .

(Problems to be Solved by the Invention) However, in the above-described apparatus, the subject image is tracked by moving the focus detection area having the same size and the same response speed in each field regardless of the shooting conditions. For example, when considering a device that tracks a subject by detecting a feature point of the subject based on a peak value of a high-frequency component or the like, when the depth of field is deep, it is possible to distinguish a main subject from a surrounding background. Difficulties, causing perspective conflicts,
There is a risk of malfunction such as unstable movement of the focus detection area regardless of the subject.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above problems, and according to the invention described in claim 1,
An automatic tracking device capable of moving a detection area for detecting information relating to a subject image formed on a shooting plane by a shooting optical system within the imaging screen, wherein a position for detecting a subject position within the detection area is provided. Detecting means; calculating means for calculating a set position of the detection area based on information of the position detecting means; and moving the detection area based on an output of the calculating means and simultaneously changing a depth of field of the photographing optical system. The automatic tracking device includes a control unit that variably controls a moving range and / or a moving response speed of the detection area based on information.

According to the second aspect of the present invention, there is provided an automatic tracking apparatus capable of moving a detection area for detecting information on a subject image formed on an imaging surface by an imaging optical system within the imaging screen. A position detecting means for detecting a position of a subject in the detection area; a calculating means for calculating a set position of the detection area based on information of the position detecting means; and Control means for moving the detection area and variably controlling the movement range and / or movement response speed of the detection area based on the depth-of-field information of the photographing optical system; The automatic tracking device includes a display unit for displaying a position in the photographing screen.

(Operation) By this, the operation characteristics such as the size, the moving range, and the response speed of the tracking detection area can always be optimally controlled without being affected by factors that change depending on the shooting state such as the depth of field. The movement of the area can be tracked naturally and the intended subject image can be accurately tracked.

(Embodiment) One embodiment of the automatic focusing apparatus according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a case where the automatic focusing apparatus of the present invention is applied to a video camera or the like.

In FIG. 1, reference numeral 1 denotes a focusing lens for performing focus adjustment, and 2 denotes a zoom lens for performing a zoom operation, which are moved in the optical axis direction via motors 19 and 20 and their motor drive circuits 16 and 17, respectively. Thus, focus adjustment and zoom operation are performed.

Reference numeral 3 denotes a stop for adjusting the amount of incident light, which is driven and controlled via an ig meter 21 for driving the stop and a drive circuit 18.

Reference numeral 4 denotes an imaging lens, reference numeral 5 denotes an imaging element such as a CCD which photoelectrically converts a subject image formed on an imaging surface through the lenses 1, 2, aperture 3, and lens 4 and outputs a video signal; Denotes a preamplifier for amplifying a video signal output from the image sensor 5 to a predetermined level, and 7 denotes a standard that performs predetermined processing such as gamma correction, blanking processing, and addition of a synchronization signal on the video signal output from the preamplifier 6. This is a process circuit that converts the signal into a standardized television signal and outputs it from a video output terminal. The television signal output from the process circuit 7 is supplied to a monitor such as a video recorder (not shown) or an electronic viewfinder.

8 inputs the video signal output from the preamplifier 6,
An aperture control circuit that automatically controls the drive circuit 8 and the ig meter 21 so that the level of the external video signal is kept at a predetermined level.

Reference numeral 9 denotes a band pass filter (BPF) for extracting a high-frequency component necessary for performing focus detection from the video signal output from the preamplifier 6, and reference numeral 10 denotes a gate of the output signal of the BPF 9, and A gate circuit for passing only a video signal corresponding to a predetermined designated area; 11 a gate circuit based on a command from a control micro computer 14 described later
A gate pulse generation circuit that opens and closes 10 to generate a gate pulse for setting the designated area in the video screen. The gate circuit 10 passes only a signal corresponding to a designated area in the video signal for one field according to the gate pulse from the gate pulse generation circuit 11, thereby extracting a high-frequency component at an arbitrary position in the imaging screen. In this case, it is possible to set a passing area, that is, a focus detection area for performing focus detection.

The gate pulse output from the gate pulse generation circuit 11 is subjected to predetermined signal processing via the display circuit 15 and is then superimposed on the television signal output from the process circuit 7 and focused on the monitor screen. The detection area is superimposed.

Numeral 12 detects a high-frequency component in the video signal corresponding to the focus detection area on the imaging screen extracted by the gate circuit 10, and detects the peak level of the high-frequency component and the peak detection position in the screen of one field. This is a peak position detection circuit that detects each coordinate in the horizontal direction and the vertical direction. Here, regarding the detection of the peak position coordinates, for example, the imaging screen is divided into a plurality of blocks in the vertical and horizontal directions, and in the video signal for one field,
This was realized by a method of detecting the horizontal and vertical position coordinates of the block where the peak point was detected. The peak value detected within the peak position 12 is held and output by the sample and hold circuit 13 for each field. Then, these peak position coordinates and peak levels are supplied to a control microcomputer 14 described later.

Reference numeral 23 denotes a focus encoder that detects information on the movement position of the focusing lens 1, reference numeral 24 denotes a zoom encoder that detects the movement position of the zoom lens 2, that is, information on the focal length.
Reference numeral 25 denotes an aperture encoder for detecting the aperture value of the aperture 3,
The detection information is supplied to a control microcomputer 14 described later.

Reference numeral 14 denotes a control microcomputer for controlling the entire system. In addition to the CPU, an input / output port (not shown), an A / D converter, and a read-only memory (RO)
M), and random access memory (RAM).

The control microcomputer detects the moving position of the subject based on the peak detection position information detected by the peak position detecting circuit 12, calculates the set position of the focus detection area following the subject, and detects the focus. The area control signal is supplied to the gate pulse generation circuit 11. The gate pulse generation circuit 11 supplies a gate pulse that allows only the video signal corresponding to the focus detection area set by the focus detection area control signal to the gate circuit 10, and controls the opening and closing of the gate pulse.

The focus detection area is set at a position such that the detected peak position is the center.

Further, it calculates the depth of field from the outputs of the zoom encoder 24 and the aperture encoder 25, and controls the size, moving range, and moving response speed of the focus detection area based on the calculated depth of field.

Also, the drive circuit is controlled so that the peak level of the high-frequency component output from the sample-and-hold circuit 13, that is, the level of the signal indicating the degree of focus of the captured image is maximized.
A control signal such as the rotation direction, rotation speed, rotation / stop, etc. of the motor 19 is sent to 16 to control the movement of the focusing lens 1 to the focal point.

Further, a zoom operation switch (not shown) is controlled to control the drive circuit 17 in accordance with a zoom operation command to drive the motor 20 for driving the zoom lens, thereby driving the zoom lens 20.

The configuration of the automatic focusing apparatus according to the present invention is as described above. Next, the control of the focusing detection area by the control microcomputer 14 will be described with reference to the flowchart shown in FIG.

In FIG. 2, a step S1 is a routine for A / D converting an analog signal of the aperture value inputted from the aperture encoder 25 and reading the analog signal into a memory in the micro computer 14 for each field.
Routine for reading the input digital signal indicating the focal length to the memory in the microcomputer 14 for each field (A / D conversion and storage for analog output), step S3 detects the peak position for each field A routine for reading the information of the horizontal and vertical coordinates of the peak position of the screen output from the circuit 12 into the memory in the microcomputer 14, and the step S4 includes the aperture value information and the focal length information obtained in the steps S1 and S2 in advance. The third memory stored in the ROM in the microcomputer 14 (not shown)
This is a routine for determining the depth of field with reference to the information table shown in the figure.

Steps S5, S6, and S7 are routines for determining the depth of field determined in step S4 and determining the size of the focus detection area, the latitude range, and the response speed.

Step S8 is a routine for calculating the peak position based on the response speed of the focus detection area determined in steps S5 to S7, and step S9 controls the moving range of the focus detection area similarly determined in steps S5 to S7. Routine, step S1
0 is a routine for varying the size of the focus detection area based on the size information of the focus detection area determined in steps S5 to S7.

Step S11 supplies a control signal for setting the focus detection area to the gate pulse generation circuit 11 based on the focus detection area setting conditions calculated in each of the above-described steps, and actually performs focus detection. This is a routine for updating the area.

Next, the flow of the control operation of the focus detection area by the control microcomputer 14 shown in the flowchart of FIG. 2 will be described step by step.

When the flowchart of FIG. 2 starts, the steps
At S1, the aperture value of the analog voltage input from the aperture encoder 25 is stored in a predetermined area of a RAM by an A / D converter in the microcomputer, for example, as 8 bits (256 steps) of data.

Subsequently, the focal length information from the zoom encoder 2 digitized in step S2 is stored in a predetermined area of the RAM. In step S3, the digitized 1 detected and output from the peak position detection circuit 12 is output. The horizontal and vertical position coordinates of the peak position in the field screen are stored in the RAM.

In step S4, the aperture values F _i (i = 1, 2,...) Stored in steps S1 and S2 are stored in accordance with the information table for calculating the depth of field stored in the ROM shown in FIG. , n) and the depth of field from the lens focal length information f _i (i = 1,2,..., n)
Ask for DP.

Here, the magnitude relationship between the focal lengths is f ₁ > f ₂ >...> F _n , and f ₁ is the longest focal length in the present embodiment. The relationship between the longest focal length and an arbitrary focal length f _i is Can be represented by

The relationship between the aperture _values F is F ₁ <F ₂ <... <F _n and F ₁ is the smallest aperture value (open aperture) in the present embodiment.
The relationship between the minimum aperture value F ₁ and any aperture ^{_{value, F i = 2 i-1}} F 1 (i = 2, ..., n) a ... (2). Generally, when the aperture value is F _i and the focal length is f _i , the depth of field D
P _i can be expressed by the following equation.

Here DP ₁ is open aperture, a depth of field at the longest focal length.

These (1), (2), (3) makes it possible to obtain an arbitrary depth of field DP _i. Here, it goes without saying that DP ₁ has the shallowest depth and becomes deeper as it becomes DP ₂ and DP ₃ .

Then, the process proceeds to a routine for determining the setting conditions of the focus detection areas in steps S5, S6, and S7. From the depth of field DP obtained in step S4, information for determining the focus detection areas shown in FIG. The size W of the focus detection area, the vertical movement range X, and the movement response speed SP are determined with reference to the table. This information table is stored in the ROM in the control micro computer 14 in advance.

In FIG. 4, the depth of field DP is DP ₁ <DP ₂ <... <
DP _2n , and the size W of the focus detection area is W ₁ <W ₂ <...
<W _2n , the vertical movement range X is X ₁ > X ₂ >... X _2n , and the response speed SP is SP ₁ > SP ₂ >...> SP _2n .

As the depth of field increases, the size of the focus detection area increases, the moving range in the vertical direction decreases, and the response speed decreases.

That is, when the depth of field is deep, it becomes easy to focus at many points on the shooting screen regardless of the main subject, so the peak point of the high-frequency component of the image changes drastically, the variation becomes large, and the normal peak Point tracking operation becomes difficult.

In other words, in a state where the depth of field is deep and focusing is easy, the necessity of the subject tracking operation for focusing is reduced. Therefore, in such a case, the size of the focus detection area is increased as much as possible to increase the probability that the main subject is located within the focus detection area, so that a more natural subject tracking operation can be performed. I do.

In particular, when the zoom operation is performed in a direction in which the depth of field is increased from the tele side to the wide side, the angle of view is substantially widened, and the movement of the subject is relatively slow. In particular, it becomes narrower in the vertical direction. Therefore, in such a case, if the response speed is reduced by limiting the vertical movement range of the focus detection area, unnecessary tracking operation is reduced, and natural and smooth tracking without malfunction is performed. Can be realized.

Conversely, if the depth of field is shallow,
Since the level difference between the high-frequency components of the subject and the background is large and the peak position is clearly obtained, the focus detection area is reduced so that the focus detection area can be set accurately at the feature point of the subject. Is also relatively large within the angle of view, so that the moving range of the focus detection area and the response speed of the movement are both large, and control is performed so as to follow large changes in the subject.

When the moving condition of the focus detection area is determined by the above operation, the process proceeds to a peak position calculation routine in step S8, and the next field is calculated based on the response speed SP obtained in the above steps S5 to S7. Calculate the peak position coordinates set by.

Here, the peak position coordinates are, for example, time-based in order to prevent a decrease in position accuracy due to factors such as variations in the peak position within the same subject, noise, and complicated fluctuations of the peak position due to the movement of the subject. It is obtained by an operation such as averaging the coordinates of peak positions detected in a plurality of different fields.

For example, the variation in the position of the peak point in the subject image is averaged and removed by obtaining the barycenter of the horizontal and vertical position coordinates of the peak position in each of the N fields, and further, the variation in the peak position due to the movement of the subject. Can be removed by, for example, the so-called Exponential averaging method.

The Exponential averaging method is a type of moving average method, and is an averaging method in which the weighting decreases exponentially as it goes back to the past. It has the advantage that data can be smoothed without storing past peak position coordinates. have.

 Specifically, it is represented by the following equation.

Here, the above-described calculation will be specifically described with reference to FIG.

Looking at the case where the peak position is obtained by averaging three fields, (x _i , Y _i ) indicates the coordinates of the horizontal and vertical current peak positions in the current field.
(X _i−1 , Y _i−1 ) and (X _i−2 , Y _i−2 ) indicate the peak position coordinates of the previous field and the field immediately before the field, respectively.

Here, first, position coordinates (X _i , Y _i ) serving as the center of gravity of these three peak position coordinates are obtained from the following equation.

Further, (X _i , Y _i ) obtained here and E
Using the peak position coordinates (PH _i−1 , PV _i−1 ) calculated by the xponential averaging method and equation (4), a calculated peak for setting the focus detection area in the field as follows: Find the position coordinates (PH _i , PV _i ).

Here, N is the number of designations in the equation (4), and represents the degree of weighting. The larger the weighting, the more the weighting goes back in the past, and the greater the average effect, but the larger the line delay time. By changing the aperture, the focal length, the degree of focusing, and the like, it is possible to appropriately follow the subject.)

In the above-described peak position setting calculation by the exponential method, the above-mentioned weighting, that is, the value of N is appropriately changed based on the response speed of the focus detection area obtained in steps S5 to S7, thereby obtaining the coordinates of the peak position. The change between fields, that is, the movement response speed is controlled to set the focus detection area in the next field.

 The effect of the above average calculation will be further described.

FIG. 5A shows the locus of movement of the focus detection area and the peak position when the focus detection area is moved using the peak replacement position information of each field as it is in calculating the peak position coordinates. FIG. 5 (b) shows the case where the focus position information in each field is moved based on the peak position coordinates calculated and smoothed by the Exponential averaging method or the like, and the focus detection area is moved. It shows the focus detection area and the movement locus of the peak position coordinates.

In each figure, 100 is the horizontal and vertical position of the peak point in each field, 101 is the focus detection area on the shooting screen of the field, and the upper section of the figure is the number of fields indicating the time elapsed along with the movement of the peak position. It is a representation.

That is, when the peak position of the high-frequency component of a subject having a small contrast such as a person is detected, many peak values of the same level are often present, and the peak position fluctuates greatly in each field even if the subject does not move. I do. When the subject moves, the fluctuation becomes more intense.

Therefore, the peak value is detected as the feature point of the subject,
When the focus detection area is followed, the position of the focus area also fluctuates drastically as shown in FIG. 5 (a), and as a result, it becomes difficult to stably track the subject. Accuracy also decreases.

When the focus detection area is displayed on a monitor screen such as an electronic viewfinder, the focus detection area appears to vibrate violently, degrades the quality of the screen, and makes the screen extremely unsightly.

By setting the focus detection area centered on the horizontal and vertical peak position coordinates (PH _i , PV _i ) obtained in this way, the fifth point with respect to the peak point of the subject and its movement can be obtained.
As shown in FIG. 5 (b), the in-focus area can be stably positioned with respect to the subject and smoothly and reliably with respect to the movement of the subject without drastically changing the focus detection area as in FIG. It can be tracked.

Returning to the flowchart, in step S9 for determining the movement range of the focus detection area, the vertical coordinates of the focus detection area obtained in step S8 based on the vertical movement range X obtained in steps S5 to S7. The value (actually, the peak position set so as to be located at the center of the focus detection area) is monitored so as not to exceed the moving range, and if it does, the vertical position coordinates are set to the limit value of the moving range. Is set again.

In step S10 for changing the size of the focus detection area,
Similarly, the size of the focus detection area is set based on the size W obtained in steps S5 to S7.

In step S11, setting data for setting the focus detection area is output to the gate pulse generation circuit in accordance with the focus detection area setting conditions calculated as described above, and the gate circuit is opened and closed. By controlling the operation, the focus detection area is actually updated, and the natural and optimal subject tracking operation can be always realized regardless of the depth of field.

Thereafter, the flow returns to step S1, and the above flow is repeated.

In the above-described flowchart, for convenience of explanation, the size of the focus detection area according to the magnitude of the depth of field,
In order to conceptually show that the moving range and the response speed are variable, the step S5 determines whether the depth of field is large or small, and
Although it is branched to S6 and S7, as is clear from the above description, it does not change in two steps, but in fact, it is finely set by the control microcomputer according to the information table shown in FIG. Have been.

FIG. 7 conceptually shows a focus detection area on the photographing screen. In FIG. 7, reference numeral 101 denotes a focus detection area, and reference numeral 102 denotes a moving range of the focus detection area.

Further, according to the above-described embodiment, as a means for changing the response speed of the focus detection area when setting the focus detection area,
The example of changing the weight of Exponential average was shown,
The method is not limited to this method. For example, even if the update of the focus detection area performed every field is changed every two fields or every three fields, the apparent response speed may be reduced. This can be delayed, and the same effect as in the above-described embodiment can be obtained.

Further, in the above-described embodiment, the case has been described in which the three parameters of the size of the focus detection area, the moving range, and the response speed are all changed according to the depth of field.
Even if they are not all changed at the same time, the effect can be obtained even if at least one of them is appropriately changed, and a plurality of modes can be obtained depending on the cost of the apparatus or the state of the subject. By setting and using different values, it is possible to reduce the computational burden on the control microcomputer.

(Effect of the Invention) As described above, according to the automatic tracking device of the present invention, the tracking detection area is made to follow the movement of the subject,
In an automatic tracking device configured to always keep focusing on a subject, at least one of a size movement range of a tracking detection area and a movement response speed according to a depth of field of an imaging optical system.
By controlling one of them, the subject tracking operation adapted to the depth of field can be performed, so that the depth of field changes due to the aperture and zoom operations, and the condition of the subject changes. However, the subject can always be stably captured in the tracking detection area, and a practical subject tracking operation capable of obtaining high subject tracking accuracy and focusing accuracy can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an automatic focusing apparatus according to the present invention, FIG. 2 is a flowchart for explaining an operation of setting a focus detection area in the automatic focusing apparatus according to the present invention, and FIG. FIG. 4 is a diagram showing an information table for determining a depth of field, FIG. 4 is a diagram showing an information table for determining a setting parameter of a focus detection area, and FIG. 5 is a diagram showing a calculation for smoothing a subject tracking operation. FIG. 6 is a diagram for explaining a case where the process is not performed and a case where the process is performed, and FIG. 6 is a diagram for explaining smoothing of the movement of the subject in the present invention. FIG. 7 is a diagram conceptually showing a focus detection area on the imaging screen.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Suda 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Prefecture Inside the Tamagawa Office of Canon Inc. (72) Inventor Masamichi Toyama 770 Shimonoge, Takatsu-ku, Kawasaki, Kanagawa Prefecture (56) References JP-A-61-10372 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 7/28-7/40 H04N 5/232

Claims (2)

(57) [Claims] An automatic tracking device capable of moving a detection area for detecting information on a subject image formed on an imaging surface by an imaging optical system within the imaging screen, wherein the object is located within the detection area. Position detecting means for detecting a position; calculating means for calculating a set position of the detection area based on information of the position detecting means; and moving the detection area based on an output of the calculating means and the photographing optical system Control means for variably controlling a moving range and / or a moving response speed of the detection area based on the depth of field information of the automatic tracking apparatus. 2. An automatic tracking device capable of moving a detection area for detecting information relating to a subject image formed on an imaging surface by an imaging optical system within the imaging screen, wherein the object is located within the detection area. Position detecting means for detecting a position; calculating means for calculating a set position of the detection area based on information of the position detecting means; and moving the detection area based on an output of the calculating means and the photographing optical system Control means for variably controlling a moving range and / or a moving response speed of the detection area based on depth of field information of
Display means for displaying the position of the subject in the imaging screen by displaying the detection area.