JPH0377481A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To obtain high object tracking information and focusing accuracy by controlling at least one of a size of focus sensing area, a moving range and a moving reply speed in response to the depth of focus of an object of an image pickup optical system. CONSTITUTION:A control microcomputer 14 detects a moving position of an object based on peak detection position information detected by a peak position detection circuit 12, calculates the setting position of a focus sensing area in following to the object, supplies a gate pulse picking up only a video signal corresponding to inside of the focusing sensing area to a gate circuit 10, which is switching controlled. Moreover, the depth of field is calculated from an output of a zoom encoder and an aperture encoder, and the size of focus sensing area, moving range and moving reply speed are controlled based thereon. Thus, the movement of the focus sensing area is made natural and the object image is traced accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an automatic focusing device suitable for use in video equipment such as video cameras and electronic still cameras.

(Prior Art) Conventionally, there are various types of automatic focus adjustment devices for cameras, but there are devices such as video cameras, electronic still cameras, etc. that have an imaging means that photoelectrically converts a subject image to obtain a video signal. In this method, the definition of the subject image is detected from the video signal, and the focus is adjusted so that the definition is maximized.

This type of device is usually configured to set a focus detection area in a part of the imaging screen and perform focus detection on the subject image within that area. A device has been proposed that has an automatic subject tracking function that allows the camera to follow the movement of the subject image and maintain focus even on a moving subject. (For example, Japanese Patent Application Laid-Open No. 60-249477).

Various methods have been proposed for such object tracking methods, but for example, the peak value of a high frequency component within the focus detection area is detected as a feature point of the object image for each l field (or one frame). There is a camera that is capable of keeping the moving subject in focus by knowing the moving position of the subject and resetting the focus detection area to a position approximately centered on the subject's moving position.

(Problems to be Solved by the Invention) However, in the above-mentioned apparatus, the subject image is tracked by moving a focus detection area of the same size at the same response speed in each field, regardless of the shooting situation. Therefore, for example, if we consider a device that tracks a subject by detecting the feature points of the subject using peak values of high-frequency components, etc., if the depth of field is deep, it may be difficult to distinguish the main subject from the surrounding background. This may result in conflict between distance and distance, and there is a risk of malfunctions such as the focus detection area moving unstablely regardless of the subject.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and is characterized by the object image formed on the imaging screen by the imaging optical system. An automatic focusing device capable of moving a focus detection area for detecting the degree of focus within the imaging screen, comprising: a position detection means for detecting a subject position within the focus detection area; and a position detection means for detecting a subject position within the focus detection area. a calculation means for calculating a set position of the focus detection area based on the information of the calculation means; and a calculation means for moving the focus detection area based on the output of the calculation means and based on depth of field information of the photographing optical system. and a control means for variably controlling at least one of the size of the focus detection area, the movement range, and the movement response speed.

Another feature of the present invention is an automatic focusing device further comprising display means for displaying a subject position within the imaging screen using the focus detection area.

(Function) As a result, operating characteristics such as the size of the focus detection area, movement range, and response speed can be optimally controlled at all times without being affected by factors that change depending on the shooting condition such as depth of field.
It is possible to naturally track the movement of the focus detection area and to accurately track the desired subject image.

<Embodiment> Hereinafter, an embodiment of the automatic focusing device according to the present invention will be described in detail with reference to the respective figures.

FIG. 1 is a block diagram showing a case where the automatic focusing device of the present invention is implemented in a video camera, etc. 6 In the same figure, 1 is a focusing lens for adjusting the focus, and 2 is a zoom lens for performing a zoom operation. motors 1920 and their motor drive circuits 16 and 17 respectively in the lenses;
Focus adjustment and zooming operations are performed by moving the lens in the optical axis direction via the lens.

Reference numeral 3 denotes an aperture that adjusts the amount of incident light, and its drive is controlled via an ig meter 21 and a drive circuit 18 for driving the aperture.

4 is an imaging lens, 5 is a lens 1.2. An image sensor such as a CCD that photoelectrically converts a subject image formed on an imaging surface through an aperture 3 and a lens 4 and outputs a video signal, and 6 adjusts the video signal output from the image sensor 5 to a predetermined level. The amplifying preamplifier 7 converts the video signal output from the preamplifier 6 into a standardized standard television signal by performing predetermined processing such as gamma correction, blanking processing, and adding a synchronization signal, and outputs it from the video output terminal. This is a process circuit that outputs. The television signal output from the process circuit 7 is then supplied to a monitor such as a video recorder (not shown) or an electronic viewfinder.

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

9 is a band pass filter (BPF) for extracting high frequency components necessary for focus detection from the video signal output from the preamplifier 6; 10 is a band pass filter (BPF) that applies a gate to the output signal of BPF 9, A gate circuit 11 allows only a video signal corresponding to a predetermined designated area to pass through, and a gate circuit 11 generates a gate pulse that opens and closes the gate circuit IO based on instructions from a control microcomputer 14, which will be described later, to set the designated area within the imaging screen. This is a gate pulse generation circuit that generates a gate pulse. The gate circuit 10 includes a gate pulse generation circuit 11
According to the gate pulse from 1 field, only the signal corresponding to the specified area in the video signal of 1 minute is passed, and thereby the passing area, that is, the focus detection, is performed to extract the high frequency component at an arbitrary position within the imaging screen. A focus detection area can be set.

Further, the gate pulse output from the gate pulse generation circuit 11 is subjected to predetermined signal processing via the display circuit I5, and then superimposed on the television signal output from the process circuit 7, and focused on the monitor screen. The detection area is superimposed.

12 detects high frequency components 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 within the screen of one field and the horizontal direction of the peak detection position. , a peak position detection circuit that detects each coordinate in the vertical direction. Here, detection of the peak position coordinates is realized by, for example, dividing the imaging screen into multiple blocks vertically and horizontally, and detecting the horizontal and vertical position coordinates of the block where the peak point is detected in the video signal of 8 minutes of l-feel. be able to. Further, the peak value detected within the peak position 12 is held and output for each field by the sample and hold circuit 13. These peak position coordinates and peak levels are then supplied to a control microcomputer 14, which will be described later.

Further, 23 is a focus encoder that detects the movement position information of the focusing lens l, 24 is a zoom encoder that detects the movement position of the zoom lens 2, that is, focal length information, and 25 is an aperture encoder that detects the aperture value of the aperture 3. The detection information is supplied to a control microcomputer 14, which will be described later.

Reference numeral 14 denotes a control microcomputer that centrally controls the entire system.In addition to the CPU, the microcomputer 14 includes an input/output board (not shown), an A/D converter, a read-only memory (ROM), and a random access memory (RAM). ).

This control microcomputer detects the moving position of the subject based on the peak detection position information detected by the peak position detection circuit I2, and calculates the set position of the focus detection area by following the subject and detects the focus. A region control signal is supplied to the gate pulse generation circuit 11. Then, the gate pulse generation circuit 11 supplies a gate pulse to the gate circuit 10 to control the opening and closing of the gate circuit 10, which allows only the video signal corresponding to the focus detection area set by the focus detection area control signal to pass through.

This focus detection area is set at a position with the detected peak position as its center.

Also, the zoom encoder 24. Aperture 1) The depth of field is calculated from the output of the encoder 25, and based on this, the size, movement range, and movement response speed of the focus detection area are controlled.

In addition, the drive circuit 16 controls the rotational direction, rotational speed, and rotational speed of the motor 19 so that the peak level of the high frequency component output from the sample hold circuit 13, that is, the level of the signal representing the degree of focus of the image being photographed, is maximized. A control signal such as /stop is sent to bring the focusing lens 1 to the in-focus point.

In addition, a zoom operation switch (not shown) is controlled, and a drive circuit 17 is controlled in accordance with a zoom operation command to drive a zoom lens driving motor 20.
0 can be driven.

The configuration of the dynamic focusing device according to the present invention is as described above.Next, the control of the focus detection area by the control microcomputer 14 will be explained using the flowchart shown in FIG.

In FIG. 2, step S1 is a routine for l\/D converting the analog signal of the aperture value input from the aperture encoder 25 and reading it into the memory in the microcomputer 14 for each field, and step S2 is a routine that similarly converts the analog signal of the aperture value input from the aperture encoder 25 into the memory in the microcomputer 14. A routine that reads a digital signal indicating the focal length input from the microcomputer 14 for each field into the memory in the microcomputer 14 (for analog output, A/
Step S3 is a routine that reads information on the horizontal and vertical coordinates of the peak position of the screen output from the peak position detection circuit 12 for each field into the memory in the microcomputer 14, and Step S4 is a step Sl, the aperture value information and focal length information obtained in step S2, and the microcomputer 1 (not shown) in advance.
This is a routine for determining the depth of field by referring to the information table shown in FIG. 3 stored in the ROM in the camera.

Step S5. S6. S7 determines the depth of field determined in step S4, and determines the size of the focus detection area,
This routine determines the latitude range and response speed.

Step S8 is a routine that calculates the peak position based on the response speed of the focus detection area determined in steps 85 to S7, and step S9 is a routine that limits the movement range of the focus detection area also determined in steps 35 to S7. routine,
Step SIO 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 85 to S7.

Step Sll is each step mentioned above, ! This is a routine for actually updating the focus detection area by supplying a control signal for setting the focus detection area to the gate pulse generation circuit 11 based on the i-calculated setting conditions for the focus detection area. be.

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 explained step by step.

When the flowchart in Fig. 2 is started, step S
1, the aperture value of the analog voltage manually input from the aperture encoder 25 is stored in a predetermined area of the RAM by the A/D converter in the microcomputer, for example, 8 bits (25
6 stages) data is stored.

Subsequently, in step S2, the digitized focal length information from the zoom encoder 24 is stored in a predetermined area of the RAM.

In step S3, the horizontal and vertical position coordinates of the peak position within the digitized one-field screen detected and outputted by the peak position detection circuit 12 are stored in the RAM.

In step S4, the aperture value F+ (i=1,
2. −−−・−, n), lens focal length information f, (i
=1.2. Depth of field DP is determined from . . . , n).

Here, the magnitude relationship of each focal length is f + > f 2>
...>f, where f is the longest focal length in the device of this embodiment. The relationship between this longest focal length and any focal path 1ift f can be expressed as (1>).

Also, the size relationship of the aperture value F is Fl<F2<...
KuF. , Fl is the smallest aperture value (open aperture) in the device of this embodiment. The relationship between this minimum aperture value F and any aperture value is F + = 2 '-' F l (i = 2.-, n)
・・・・・・・・・・・・(2) It becomes. In general, the depth of field DP when the aperture value is F and the focal length f1 is expressed by the following formula (i=1...
., 2n) ...... (3) Here, D P + is the depth of field at the maximum aperture and the longest focal length.

An arbitrary depth of field D P + can be determined using these equations (1), (2), and (3). Here DP,
is the shallowest depth, DP.

DP, it goes without saying that the more you yell, the deeper it becomes.

Next, step S5. S6. The process advances to S7, a routine for determining the setting conditions for the focus detection area, and the focus is determined by referring to the information table for determining the focus detection area shown in FIG. 4, based on the depth of field DP obtained in step S4. The size W of the detection area, the vertical movement range X, and the movement response speed SP are determined. This information table is stored in advance in the ROM in the control microcomputer 14.

In FIG. 4, the depth of field DP is DP<ppx<
...... DP2n, and the size W of the focus detection area is W l< W t <...<W2. ,,
The vertical movement range X is X,>X! ＞・・・・・・
X2. ,, response speed sp is SPI >SP, >・-・・
・>SP, n.

As the depth of field becomes deeper, the size of the focus detection area becomes larger, the vertical movement range becomes smaller, and the response speed becomes slower.

In other words, when the depth of field is deep, it becomes difficult to focus on many points on the image capture screen regardless of the main subject, so the peak point of the high frequency component of the image changes drastically and becomes highly dispersive, making it difficult to focus on the normal peak. Point tracking becomes difficult.

In other words, when the depth of field is deep and it is easy to focus, there is less need for a subject tracking operation for focusing. Therefore, in such a case, the size of the focus detection area is made as large as possible to increase the probability that the main subject will be located within the focus detection area, and more natural subject tracking operation can be performed.

In addition, especially when zooming in the direction where the depth of field increases from the telephoto side to the wide side, the angle of view becomes substantially wider and the movement of the subject becomes relatively slower. The range also becomes narrower, especially in the vertical direction. Therefore, in such cases, it is better to limit the vertical movement range of the focus detection area and slow down the response speed to reduce unnecessary tracking operations and achieve natural and smooth tracking without malfunctions. It can be realized.

Conversely, when the depth of field is shallow, the level difference in high frequency components between the subject and the background is large, and the peak position can be clearly obtained, so the focus detection area can be made smaller to capture the subject. In addition to making it possible to accurately set the focus detection area at the feature points of It is controlled so that it can follow even large changes in the subject.

When the movement conditions of the focus detection area are determined by the above operations, the process proceeds to the peak position calculation routine of step S8, and the response speed SP obtained in the above steps S5 to S7 is
Based on this, calculate the peak position coordinates set in the next field.

Here, the peak position coordinates are calculated using multiple peak position coordinates that differ in time, for example, in order to prevent the position accuracy from decreasing due to factors such as variations in the peak position within the same subject, noise, and complex fluctuations in the peak position due to movement of the subject. It is determined by calculations such as averaging the peak position coordinates detected in the field.

For example, variations in the position of the peak point within the subject image are averaged and removed by determining the center of gravity of the horizontal and vertical position coordinates of the peak position in each of N fields, and further variations in the peak position due to movement of the subject are removed. For example, a method can be used to remove the difference by using the so-called exponential averaging method.

This exponential averaging method is a type of moving average method, and it is an averaging method that reduces weighting exponentially as you go back into the past.It has the advantage of being able to smooth data without remembering past peak position coordinates. have.

Specifically, it is expressed by the following formula.

・・・・・・・・・・・・・・・・・・ (4)N ・
Specified number of times (number of fields) Xn: nth data Xs: nth average result The above-mentioned calculation will be specifically explained using FIG. 6.

Now, looking at the case where the peak position is determined by the average of three fields, (x++y1) indicates the coordinates of the current horizontal and vertical peak position in the current field,
(XI-+1.Y), (XI-21yl-a)
indicate the peak position coordinates of the previous field and the field before the previous field, respectively.

First, the positional degree fl (X, , Y, ), which is the center of gravity of these three peak position coordinates, is determined from the following equation.

(Xi+ x, -, + Xl-2) xI= ...
・ (51) (y++ yl-, + yl-2) Y, = ・・・・
・(52) Furthermore, the peak position coordinates (PH1, □, ,
pv) and equation (4), the calculated blur position i (PH,, PV, ) for setting the focus detection area in the field is determined as follows.

...... (6l) ...... (62) Here, N is the number of times specified in equation (4), and this represents the degree of weighting, so the larger the number, the more the weighting goes back in the past. , the average effect is large, but the delay time is increased by 6 (by changing this value according to the aperture, focal length, degree of focus, etc. at each time, tracking of the subject can be made appropriate).

In the peak position setting calculation using the above Exponential method, the above-mentioned weighting, that is, N
By appropriately changing the value of , the change in peak position coordinates between fields, that is, the movement response speed is controlled, and the focus detection area in the next field is set.

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

FIG. 5(a) shows the movement locus of the focus detection area and the peak position when the focus detection area is moved using the beak maneuvering position information of each field as is when calculating the peak position coordinates. Figure 5(b) shows peak position information in each field using the exponential averaging method, etc., as is done in this embodiment. 1ii
Figure 6 shows the locus of movement of the focus detection area and the peak position coordinate when the focus detection area is moved based on the peak position coordinate smoothed by calculating i.

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 imaging screen of that field, and the section at the top of the figure is the number of fields representing the time elapsed as the peak position moves. This is what we are expressing.

In other words, when detecting the peak position of a high-frequency component of a subject with low contrast, such as a person, there are often many peak values of the same degree, and even if the subject does not move, the peak position fluctuates wildly from field to field. do. When the subject moves, the fluctuation becomes even more severe.

Therefore, when the peak value is detected as a feature point of the subject and the focus detection area is made to follow it, as shown in Fig. 5(a).
As shown in FIG. 1, the position of the first focusing area fluctuates drastically, and as a result, it becomes difficult to stably track the subject, and the tracking accuracy decreases.

Furthermore, when the focus detection area is displayed on a monitor screen such as an electronic viewfinder, the focus detection area appears to vibrate violently, degrading the quality of the screen and resulting in an extremely unsightly screen.

By setting the focus detection area around the horizontal and vertical peak position coordinates (PH, PV,) obtained in this way, the peak point of the subject and its movement can be adjusted.
As shown in Fig. 5(b), the focus is stably focused on the subject and smoothly and reliably even when the subject moves, without drastically changing the focus detection area as shown in Fig. 5(a). This means that the area can be tracked.

Returning to the flowchart, in step S9 to determine the movement range of the first focus detection area, based on the movement range X in the vertical direction obtained in steps S5 to S7, step S8
The vertical coordinate value of the focus detection area determined by (actually the peak position set to be located in the center of the focus detection area U) is monitored so that it does not exceed the movement range, and if it does , control is performed to reset the vertical position coordinates to the limit value of the movement range.

In step S10 of 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.

Then, in step Sll, setting data for setting one focus detection area based on the setting conditions for the focus detection area calculated as described above is outputted to the gate pulse generation circuit, and the opening/closing of the gate circuit is performed. By controlling the operation and actually updating the focus detection area, it is possible to always achieve a natural and optimal subject tracking operation regardless of the depth of field.

Thereafter, the process returns to step Sl again and the above-described flow is repeated.

In addition, in the above-mentioned flowchart, for convenience of explanation,
In order to conceptually show that the size, movement range, and response speed of the focus detection area are varied depending on the depth of field, the depth of field is determined to be large or small in step S5, and step S6
, and branch to S7, but as is clear from the above explanation, it is not variable in two stages, but in fact, detailed settings are made by the control microcomputer using the information table shown in Figure 4. .

Furthermore, since FIG. 7 conceptually shows the focus detection area on the imaging screen, in the same figure, 101 indicates the focus detection area, and l*2 indicates the moving range of the focus detection area.

Further, according to the above embodiment, when setting the focus detection area, E is used as a means for changing the response speed of the focus detection area.
Although we have shown an example in which the weighting of the xponential average is varied, the method is not limited to this method. For example, the update of the focus detection area that is performed every field may be changed to an update interval such as every 2 fields or every 3 fields. Even if it is made variable, the apparent response speed can be made slower, and the same effect as in the above-mentioned embodiment can be obtained.

Furthermore, in the above embodiment, the case was explained in which the three parameters of the focus detection area size, movement range, and response speed were all varied according to the depth of field. Even if there is no mode, the effect can be obtained by selecting and varying at least one of them, depending on the cost of the device, or by setting and using multiple modes depending on the condition of the subject. , the computational burden on the control microcomputer can be reduced.

(Effects of the Invention) As described above, according to the automatic focusing device of the present invention, the automatic focusing device is configured to follow the focus detection area according to the movement of the subject and keep the subject always in focus. In the focusing device, by controlling at least 61 of the size, movement range, and movement response speed of the focus detection area according to the depth of field of the photographing optical system, the subject tracking operation is adapted to the depth of field. As the depth of field changes depending on the aperture and zoom operation, and the conditions of the subject change, the subject can always be stably captured within the focus detection area, resulting in a high It is possible to perform a practical subject tracking operation that can obtain a subject tracking accuracy of 1 focusing performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic focusing device according to the present invention, FIG. 2 is a flowchart for explaining the setting operation of a focus detection area in the automatic focusing device according to the present invention, and FIG. 3 is a block diagram showing the configuration of an automatic focusing device according to the present invention. Figure 4 is a diagram showing an information table for determining the depth of field, Figure 4 is a diagram showing an information table for determining the setting parameters of the focus detection area, and Figure 5 is a diagram showing calculations for smoothing the subject tracking operation. FIG. 6 is a diagram for explaining the smoothing of the movement of the subject according to the present invention. FIG. 7 is a diagram conceptually showing a focus detection area on the imaging screen. Be← 輛41 狐韇→÷ Fig. 5 (O-) Fig. 5 (1)) Ei← → Possess (P)-Il, PVl) (xi, Yi) Hi-kui standing 31 za 1 deshi ← ψfuki f treasure) fame/5i0
・C ise 41 no 1 fence,

Claims (2)

[Claims] (1) An automatic focusing device capable of moving within the imaging screen a focus detection area that detects the degree of focus of a subject image formed on the imaging screen by a photographing optical system, a position detection means for detecting the position of the subject within the detection area; a calculation means for calculating a set position of the focus detection area based on information of the position detection means; and a calculation means for calculating the focus detection area based on the output of the calculation means. A control means for moving the area and variably controlling at least one of the size, movement range, and movement response speed of the focus detection area based on depth of field information of the photographing optical system. Automatic focusing device. (2) An automatic focusing device capable of moving within the imaging screen a focus detection area for detecting the degree of focus of a subject image formed on the imaging screen by the imaging optical system, a position detection means for detecting the position of the subject within the detection area; a calculation means for calculating a set position of the focus detection area based on information of the position detection means; and a calculation means for calculating the focus detection area based on the output of the calculation means. a control means for moving the area and variably controlling at least one of the size, movement range, and movement response speed of the focus detection area based on depth of field information of the photographing optical system; and display means for displaying a subject position within the imaging screen.