JPH05191708A - Automatic focus device - Google Patents

Abstract

PURPOSE:To quicken the focus speed in the automatic focusing by using a depth of field of a lens system so as to move a lens system of focal point set ting. CONSTITUTION:A process circuit 24 extracts a luminance signal and a chrominance signal from a picture signal picked up by a CCD 23 via a lens system 21, and a contrast detection section 55 detects a contrast of each pint from the luminance signal YH. Then a focus drive circuit 57 forwards a position of a lens system 21 in a close end direction by a movement in response to a depth of field and when the contrast is larger than a value at a point before the movement, the circuit 57 retracts the lens system position in the infinite end direction and uses a point at which a focus point is placed within a range of a depth of field as a focal position by the lens system 21. Thus, the movement of the lens system per once is set large and the focus speed in the automatic focusing is quickened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device used in electronic cameras and the like.

[0002]

2. Description of the Related Art The development of electronic cameras has been remarkable, and those adopting an autofocus device as seen in recent cameras are being put to practical use. Therefore, conventionally, there is an autofocus device configured as shown in FIG. 5 as an autofocus device applied to such an electronic camera.

In the figure, reference numeral 1 denotes a lens system, a CCD 3 is arranged on an optical axis of the lens system 1 through a diaphragm 2, and a photographed image of a subject is taken by the CCD 3 through the lens system 1 and the diaphragm 2. The image is formed on the surface. In this case, the lens system 1 is provided with a focus motor 4 for moving the lens system 1 in the optical axis direction thereof to enable focus adjustment of image formation, and for the diaphragm 2, the opening of the diaphragm 2 is adjusted. A diaphragm motor 5 for controlling is provided.

Then, the image signal picked up by the CCD 3 is given to the image pickup circuit 6, a luminance signal is extracted from the image pickup circuit 6, and this luminance signal is given to a high-pass filter 7 so that a high frequency component contained in the luminance signal is obtained. To detect. Further, the high frequency component in the luminance signal is given to the rectifier circuit 8, and the direct current voltage proportional to the contrast of the photographed image is obtained as the contrast voltage by rectifying it here, and this contrast voltage is supplied to the autofocus drive circuit 9. give. As a result, the autofocus drive circuit 9 drives the focus motor 4 by the contrast voltage at this time to adjust the focus by the lens system 1. In this case, the lens system 1 is moved to move the focus position. Then, the contrast of the captured image changes and reaches the maximum at the in-focus position. Therefore, the autofocus drive circuit 9 drives the focus motor 4 so that the contrast voltage becomes maximum, so that the so-called It is designed to achieve contrast autofocus.

Here, when the brightness of the surroundings changes while shooting the same image, the contrast of the image changes even though the focus position does not change, and the contrast voltage fluctuates to cause autofocus. May malfunction. Therefore, in order to prevent such malfunctions,
The brightness signal extracted by the image pickup circuit 6 is integrated by the integrating circuit 10 to detect the brightness value, which is given to the diaphragm driving circuit 11, and the brightness value obtained by the integrating circuit 10 by the diaphragm driving circuit 11. The aperture of the diaphragm 2 is adjusted so that the aperture ratio becomes constant, thereby preventing a malfunction due to a change in brightness of contrast autofocus.

By the way, in order to drive the focus motor 4 with such an autofocus device so that the contrast value becomes the maximum, that is, the in-focus position M, for example, as shown in FIG. On the other hand, when the in-focus position M is close to the point B, first, as shown in FIG.
Is moved from point A on the infinity ∞ side to point B, and points A and B
Compare the contrast values of the points. Here, since A <B, the contrast values are compared by moving from the point B to the point C on the short distance MOD side. Then, since B> C here, the moving amount of the lens system 1 is halved and the moving direction is reversed to move from the point C to the point D, and the contrast values are compared. In this case, C <D, so that the contrast value is further moved from the D point to the E point and compared. Then, since D> E here, the moving amount is halved, and the moving direction of the lens system 1 is reversed again to move from point E to point F. Similarly, if the contrast value of the point before moving is smaller than the contrast value of the point after moving, move in the same direction, and move if the contrast value of the point before moving is higher than the contrast value of point after moving. The movement amount of the lens system 1 is increased to 1/2 and the focal length is maximized.
When the aperture of the lens is open and the focal position of the lens is half the depth of field in front of the lens at the short distance end, and the in-focus position M is within this range of movement, The position M is determined.

Further, as shown in FIG. 7A, when the in-focus position M is close to the point C with respect to the contrast value curve,
As shown in FIG. 6B, first, the focus motor 4 moves the lens system 1 from the point A on the infinity ∞ side to the short distance MO.
Move to point D to point B, and compare the contrast values at points A and B. Here, since A <B, the contrast values are compared by moving from the point B to the point C on the short distance MOD side. Since B <C also here, the contrast values are compared by moving from point C to point D. Then, here C>
Since it becomes D, the moving amount of the lens system 1 is halved, the moving direction is reversed and the lens system 1 is moved from the point D to the point E, and the contrast values are compared. Then, in this case as well, if the contrast value of the point before the movement is smaller than the contrast value of the point after the movement in the same manner as described above, the point is moved in the same direction, and the contrast value of the point before the movement is equal to that of the point after the movement. If it is larger than the contrast value, the movement amount is halved, and the operation of reversing the movement direction is repeated. Finally, the movement amount of the lens system 1 has the maximum focal length, the lens diaphragm is opened, and the lens When the focal position is half the depth of field in front of the lens at the short distance end, and the in-focus position M is within the range of this movement amount,
The focus position M is determined.

[0008]

However, when the amount of movement of the lens system 1 has the maximum focal length, the aperture of the lens is open, and the focal position of the lens is at the close-range end, the depth of field in front of the lens is as described above. The focus motor is repeatedly rotated in the normal direction and the reverse direction until the in-focus position M falls within the range of this movement amount, and the in-focus point is obtained by switching the moving direction of the lens system 1. There was a problem that it took time until.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an autofocus device capable of increasing the focusing speed during the autofocus operation and shortening the time until focusing. To aim.

[0010]

An autofocus device according to the present invention comprises an image pickup means for picking up an image of a subject, and a contrast detecting means for detecting an output corresponding to the contrast of a picked-up image from a luminance signal of an image signal picked up by the image pickup means. A focus drive means for adjusting the position of the lens system with respect to the image pickup means, and the focus drive means moves the position of the first lens system in the near end direction or the infinite direction by a movement amount according to the depth of field of the lens system. When the contrast value at each point detected by the contrast detection means is moved forward and becomes larger than the contrast value at the point before the movement, this time, the focus drive means moves the lens system position according to the depth of field. The point at which the in-focus position is located within the depth of field by retracting to the infinity direction or the close-up direction is determined as the in-focus position by the lens system. It is configured to control the focus driving means so that.

[0011]

As a result, according to the present invention, the amount of movement of the lens system per movement can be set according to the depth of field of the lens system, and when the lens system is retracted toward the infinite end, Since the point where the in-focus position is located within the depth of field is determined as the in-focus position by the lens system, there is no operation that frequently switches the moving direction of the lens system,

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of an electronic camera to which the autofocus device of the embodiment is applied.
In the figure, 21 is a lens system, and this lens system 21 is
The focus motor 22 allows movement along the optical axis. The CCD is placed on the optical axis of the lens system 21.
23 is arranged so that a photographed image of the subject is formed on the image pickup surface of the CCD 23 via the lens system 21. Here, the CCD 23 has its image pickup operation controlled by a CCD driver 232 whose operation timing is measured by a timing generator 231.

The image signal picked up by the CCD 23 is given to the process circuit 24. The process circuit 24 extracts the luminance signal YH and the color signal C from the image signal.

The luminance signal YH and the chrominance signal C from the process circuit 24 are given to the A / D converter 25, where they are digitized. Then, the digitized luminance signal YH
Are applied to one input terminals of the adders 26 and 27, respectively. The adder 26 gives the addition output to the field memory 29 via the switch 28, and the output of the field memory 29 is given to the other input terminal. Also,
The adder 27 gives the addition output to the field memory 31 via the switch 30, and the field memory 31
Output is applied to the other input terminal. In this case, as the data of the luminance signal YH for each line, A, B, C, D,
Given E, F, ..., Field memory 2
9 stores the field data having the contents of A + B, C + D, E + F, ... And the field memory 31 stores the field data having the contents of B + C, D + E, F + G ,.

Here, in the case of video through (when viewing an image from the CCD in the viewfinder), the output of the field memory 31 is taken out through the switch 32, and after being gamma-corrected by the gamma correction unit 33, The outline is emphasized by the enhancer unit 34 and output through the switch 35. On the other hand, at the same time, the color signal C digitized by the A / D converter 25 is given to the color difference generation unit 38 via the switch 36 and the synchronization unit 37 for adjusting the timing with the luminance signal YH, and R The color difference signals of -Y and BY are generated and stored in the field memories 41 and 42 via the switches 39 and 40, respectively. Then, RY and B- fetched from these field memories 41 and 42.
The Y color difference signal is applied to the color viewfinder ROM table 43 together with the luminance signal YH output through the switch 35. As a result, the corresponding display data is output from the ROM table 43 under the control of the driver 44 and displayed as a video through image on the color viewfinder 45. This ROM table 43 has a luminance signal Y
RGB signals are created from H, color difference signals RY and BY.

Further, in the case of still image pickup, the output of the field memory 29 is given to the 1H memory 46.
The output of the H memory 46 is given to one input terminal of the adder 47. The adder 47 receives the output from the field memory 29 at the other input terminal and outputs the addition result. Then, the output of the adder 47 is taken out via the switch 32, gamma-corrected by the gamma-correction unit 33, contour-emphasized by the enhancer unit 34, and returned to the field memory 29 again. At the same time, the color signal C digitized by the A / D converter 25 is supplied to the field memory 48 and also to one input terminal of the adder 49. The adder 49 receives the output from the field memory 48 at the other input terminal and outputs the addition result. Then, the output of the adder 49 is
It is given to the color difference generation unit 38 via the switch 36 and the synchronization unit 37, and is generated as color difference signals of RY and BY,
Field memories 41, 4 via switches 39, 40
2 are stored respectively. Then, the luminance signal YH of these field memories 29 and the field memories 41, 4 and
The two color difference signals RY and BY are stored in the external memory 50 as a frame still image.

In the case of image reproduction, the external memory 50
The luminance signal YH is written to the field memory 31 via the switch 30, and the color difference signals RY and BY are written to the field memories 41 and 42 via the switches 39 and 40. Then, the output of the field memory 31 is taken out through the switches 32 and 35 and is given to the ROM table 51 together with the outputs from the field memories 41 and 42. As a result, the corresponding display data is output from the ROM table 51 under the control of the encoder / timing generator 52, converted into an analog signal by the D / A converter 53, and output as a video reproduction signal via the amplifier / buffer 54. Like

On the other hand, a contrast detector 55 is connected to the process circuit 24 described above. The contrast detection section 55 is supplied with the luminance signal YH output from the process circuit 24, and detects the imaging contrast from the luminance signal YH.

FIG. 2 shows such a contrast detector 5
5 shows the configuration of No. 5. In the figure, reference numeral 551 is a bandpass filter, which extracts a signal in a predetermined band from the luminance signal YH given by the process circuit 24.
Then, the signal in the predetermined band extracted by the bandpass filter 551 is rectified by the rectifier circuit 5 via the switch 552.
Given to 53. Here, the switch 552 is switched by a timing signal given from the main controller 56, which will be described later, and rectifies only the signal in the predetermined band output from the bandpass filter 551 that corresponds to the predetermined range of the captured image. It is applied to the circuit 553. Then, the signal rectified by the rectifying circuit 553 is integrated by the integrating circuit 554, and this is integrated into the A / D converter 55.
The signal is output via 5 as a signal indicating the contrast value. Then, such a contrast signal of the contrast detection unit 55 is given to the main controller 56. The main controller 56 responds to the output from the contrast detection unit 55 by the focus drive circuit 57.
Are controlled as described later.

The focus drive circuit 57 drives the focus motor 22 under the control of the main controller 56 and moves the lens system 21 from the ∞ end to the closest end to adjust the focus position with respect to the CCD 23. In this case, the control of the focus drive circuit 57 by the main controller 56 is performed based on the following idea. Generally, the depth of field of a lens is expressed by the following equation. t1 = δFa ² / (F ² + ΔFa) t2 = δFa ² / (F ² −δFa)

Where t1 is the depth of field in front of the lens,
t2 is the depth of field behind the lens, a is the focal position of the lens, f is the focal length of the lens, F is the brightness (aperture value) of the lens, and δ is the minimum scattering circle. In the present invention, the lens system 2
The depth of field is calculated for the position of 1 from the above equation, and the in-focus position M is determined using the calculated depth of field.

Now, as shown in FIG. 3A, when the in-focus position M is close to the point B with respect to the contrast value curve,
As shown in FIG. 7B, first, the infinite end A of the lens system 21
The depth of field at the point is obtained from the above formula, and the lens system 21 is moved to the point B toward the closest end with a movement amount that is twice the depth of field fA in front of the lens at this time. Then, the contrast values at points A and B are compared. Here, A <B, so B
The depth of field at the point is obtained from the above equation, and the lens system 21 is further moved to the point C with a movement amount twice the depth of field fB in front of the lens at this time, and the contrast values are compared. Then, since B> C here, it is determined that the peak value of the contrast value is before the point C, and the depth of field at the point C is obtained from the above formula. Then, this time, the lens system 1 is retracted in the infinite end direction to the point B with a movement amount that is twice the depth of field fC behind the lens. In this case, the depth of field fC ′ behind the lens at point C and the depth of field fB before the lens at point B are equal.

Then, the depth of field at the point B is obtained again from the above equation. In this case, the depth of field at the point B is the depth of field fB before the lens and the depth of field fB ′ behind the lens.
(= Depth of field fA in front of the lens at point A),
Since the in-focus position M is located in the range of the depth of field fB in front of the lens, the point B is determined as the in-focus position by the lens system 21.

Next, as shown in FIG. 4A, when the in-focus position M is close to the point C with respect to the contrast value curve,
As shown in (b) of the figure, first, the depth of field at the point A of the lens system 21 is obtained from the above formula, and the depth of field fA in front of the lens at this time is moved by a distance twice as close as possible. The lens system 1 is moved to the point B in the end direction. Then, the contrast values at points A and B are compared. Here, since A <B, the depth of field at the point B is obtained from the above equation, and the lens system 2 is further moved to the point C by a moving amount that is twice the depth of field fB before the lens at this time.
Move 1 to compare the contrast values. Then, since B <C also here, the depth of field at the point C is obtained from the above equation, and the lens system 21 is further moved to the point D with a movement amount twice the depth of field fC in front of the lens at this time. To move. Then, the contrast values at points D and C are compared. Here, since C> D, the peak value of the contrast value is
It is determined that it is before the point D, and the depth of field at the point D is calculated from the above formula. Then, this time, the lens system 21 is retracted in the infinite end direction to the point C with a movement amount that is twice the depth of field fD behind the lens. In this case, the depth of field fD 'behind the lens at point D and the depth of field fC in front of the lens at point C are equal.

Then, the depth of field at the point C is obtained again from the above equation. The depth of field at the point C in this case is the depth of field fC in front of the lens and the depth of field fC ′ in the rear of the lens.
(= Depth of field fB in front of the lens at point B),
Since the in-focus position M is located in the range of the depth of field fC ′ behind the lens, the point C is determined as the in-focus position by the lens system 21.

Therefore, in this way, first, the contrast value at each point before and after the movement is advanced while the lens system 21 is moved forward in the direction of the close end by a movement amount twice the depth of field in front of the lens. If the contrast value of the point before the movement is smaller than the contrast value of the point after the movement, the same operation is repeated, and when the contrast value of the point before the movement becomes larger than the contrast value of the point after the movement, This time lens system 2
1 is moved backward toward the infinite end by a movement amount that is twice the depth of field behind the lens, and a point at which the in-focus position M is located within the depth of field is searched for. Therefore, the movement amount of the lens system 21 per movement can be set according to the depth of field.
As a result, the conventional lens system is sequentially moved from the predetermined movement amount to 1 /
When the lens system movement amount is reduced by 2 and the lens system movement direction is frequently changed, the final lens system movement amount is the maximum focal length, the lens diaphragm is open, and the lens focal position is at the near end. The depth of field in front of the lens is halved, and the focus speed M jumps compared to the one in which the focus position M is determined when the focus position M enters the range of this movement amount. Therefore, it is possible to significantly shorten the time until focusing.

In the present invention, the focusing operation is performed from the infinity end to the infinity end, but it can be performed conversely from the infinity end to the infinity end. Further, the present invention is not limited to the above-mentioned embodiments, and can be carried out by appropriately modifying it without changing the gist. For example, in the above-described embodiment, the example in which the present invention is applied to the electronic camera is described, but the present invention can also be applied to a video camera or the like.

[0029]

According to the present invention, by moving the lens system for setting the in-focus position using the depth of field information of the lens system, the movement amount of the lens system per movement can be reduced. Since it can be set large, and the point where the in-focus position is located in the range of the depth of field of the lens system is determined as the in-focus position, it is possible to speed up the in-focus speed during the auto-focus operation. It is possible to shorten the time until focusing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a contrast detection section used in the embodiment shown in FIG.

FIG. 3 is a diagram for explaining the operation of the embodiment shown in FIG.

FIG. 4 is a diagram for explaining the operation of the embodiment shown in FIG.

FIG. 5 is a block diagram showing an example of a conventional autofocus device using contrast detection.

FIG. 6 is a diagram for explaining the operation of a conventional autofocus device.

FIG. 7 is a diagram for explaining the operation of a conventional autofocus device.

[Explanation of symbols]

21 ... Lens system, 22 ... Focus motor, 23 ... CC
D, 231 ... Timing generator, 232 ... CCD driver, 24 ... Process circuit, 25 ... A / D converter 26, 2
7, 47, 49 ... Adder, 29, 31, 41, 42, 4
8 ... Field memory, 33 gamma correction section, 34 ... Enhancer section, 37 ... Synchronization section, 38 ... Color difference generation section, 43 ...
Color viewfinder ROM table, 44 ... Driver, 45 ... Color viewfinder, 46 ... 1H memory, 50 ... External memory, 51 ... ROM table, 52 ...
Encoder / timing generator, 53 ... D / A converter,
54 ... Amplifier / buffer, 55 ... Contrast detection unit,
551 ... Bandpass filter, 552 ... Switch, 55
3 ... Rectifier circuit, 554 ... Integrator circuit, 555 ... A / D converter, 56 ... Main controller, 57 ... Focus drive circuit.

Claims (1)

[Claims] 1. An image pickup means for picking up a subject, a contrast detection means for detecting an output corresponding to a contrast of a picked-up image from a luminance signal of an image signal picked up by the image pickup means, and a position of a lens system with respect to the image pickup means. And a focus drive means for adjusting the lens system position, and the focus drive means advances the lens system position in the near end direction or infinite direction by a movement amount according to the depth of field of the lens system, and is detected by the contrast detection means. When the contrast value at each point becomes larger than the contrast value at the point before the movement, the focus driving means retracts the lens system position toward the infinite end or the close-up direction by the movement amount according to the depth of field. The focus is set so that the point where the in-focus position is located in the range of the depth of field is determined as the in-focus position by the lens system. An autofocus device comprising: a control unit that controls a drive unit.