JPH05122582A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To enable a high-speed and exact focusing operation without being affected by a change in the brightness of an object or an iris value by obtaining focus information from the divided result of an output in proportion to the contrast and brightness of an image. CONSTITUTION:A luminance signal YH of an image signal picked-up by a CCD is supplied through a process circuit to a contrast detection part 55. The output in proportion to the contrast of the photographed image is extracted from the luminance signal YH through a high-pass filter 551 and a rectifier circuit 552. The output in proportion to the brightness is extracted through a low-pass filter 553, and these outputs proportional to the contrast and the brightness are divided by a division circuit 554. Then, the focusing position of the CCD to the object is adjusted by controlling a focus driving circuit with a main controller. Thus, the high-speed and exact focus operation can be realized without being affected by a time constant or time lag.

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. 3 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 the maximum, so-called It is designed to achieve contrast autofocus.

Here, when the ambient brightness 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. A malfunction may occur in AF. Therefore, in order to prevent such a malfunction, the brightness signal extracted by the image pickup circuit 6 is integrated by the integrating circuit 10 to detect the brightness value, which is then detected.
The aperture driving circuit 11 adjusts the aperture of the aperture 2 so that the brightness value obtained from the integration circuit 10 is constant, thereby preventing malfunction caused by contrast autofocus brightness change. I have to.

[0006]

However, in the autofocus device using such a contrast, it is a premise of the operation that the brightness is constant in the state where the contrast autofocus operation is completed. However, in this case, the integrating circuit 10 for obtaining the brightness value has a relatively large time constant, and the diaphragm 2 that is adjusted so that the brightness is constant includes a time lag due to the drive mechanism. However, there is a drawback that an operation delay is likely to occur and, as a result, a high-speed autofocus operation cannot be obtained. Further, in the case of shooting in a dark place or shooting of a subject whose contrast is not clear, it becomes difficult to adjust the focus by the lens system 1 so as to maximize the contrast voltage, so that accurate autofocus operation cannot be obtained. There were also drawbacks. Furthermore, if you try to use the manual aperture, it will be in the same state as when the brightness of the subject has changed,
The autofocus AF may malfunction.

The present invention has been made in view of the above circumstances, and provides an autofocus device capable of realizing high-speed and accurate autofocus operation without being affected by changes in the brightness and aperture value of a subject. With the goal.

[0008]

An autofocus device of the present invention extracts an output proportional to the contrast of a photographed image and an output proportional to the brightness of a photographed image from a luminance signal of an image signal photographed by an image pickup means. , The output proportional to the contrast of the photographed image and the output proportional to the brightness of the photographed image are divided, and the focus position of the image pickup unit with respect to the subject is adjusted so that the division result has the maximum value. I am configuring.

[0009]

As a result, according to the present invention, the focus information is obtained from the division result of the output proportional to the contrast of the photographed image and the output proportional to the brightness of the photographed image. It does not depend on the absolute value of the luminance signal, but only on the focus position as long as the same subject is imaged, and it is possible to eliminate the influence of changes in subject brightness and aperture value. ..

[0010]

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, the data of the luminance signal YH for each line is 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 is 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
It is for creating an RGB signal from H and the 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, and
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 high-pass filter, which is adapted to extract a signal of a high frequency component from the luminance signal YH given from the process circuit 24. Then, the high frequency component signal extracted by the high pass filter 551 is rectified by the rectifier circuit 552 and is generated as an output A proportional to the contrast of the captured image. on the other hand,
The luminance signal YH from the process circuit 24 is also given to the low-pass filter 553. This low pass filter 553
The signal of the low frequency component is extracted from the luminance signal YH and is generated as an output B proportional to the brightness of the captured image. Then, the output A proportional to the contrast of the captured image from the rectifier circuit 552 and the output B proportional to the brightness of the captured image from the low-pass filter 553 are sent to the division circuit 554, respectively. The division circuit 554 calculates A / B from these outputs A and B, and outputs the calculation result as a contrast signal X.

Contrast detection section 5 thus constructed
The contrast signal X of 5 is sent to the main controller 56. The main controller 56 controls the focus drive circuit 57 so that the contrast signal X of the contrast detector 55 becomes maximum. The focus drive circuit 57 drives the focus motor 22 under the control of the main controller 56 to realize the contrast autofocus for adjusting the image forming position on the CCD 23, that is, the focus position. Next, the operation of the embodiment configured as described above will be described.

Now, the CCD 23 is replaced by the CCD driver 232.
When a subject is imaged through the lens system 21, the captured image signal is given to the process circuit 24, and the luminance signal YH and the color signal C are extracted.

The luminance signal YH of the process circuit 24 is supplied to the high-pass filter 551 of the contrast detection section 55, and the high frequency component signal is extracted. Then, this high frequency component signal is rectified by the rectifier circuit 552 and obtained as an output A proportional to the contrast of the captured image. On the other hand, the luminance signal YH from the process circuit 24 is supplied to the low pass filter 5
The signal of the low frequency component is also supplied to 53, and is obtained as an output B proportional to the brightness of the captured image.

These outputs A and B are given to the division circuit 554, where A / B is calculated, and the result of this calculation is given to the main controller 56 as the contrast signal X. Main controller 56
Then, the focus drive circuit 57 is controlled so that the contrast signal X at this time is maximized, and accordingly, the focus drive circuit 57 drives the focus motor 22 to move the lens system 21 in the optical axis direction. As a result, the contrast autofocus for adjusting the focus position of the CCD 23 with respect to the subject is realized.

In this case, the output A proportional to the contrast of the photographed image obtained by the rectifying circuit 552 and the output B proportional to the brightness of the photographed image obtained from the low-pass filter 553 are respectively proportional to the magnitude of the luminance signal YH. The output A / B of the division circuit 554 obtained by dividing these
Does not depend on the absolute value of the luminance signal YH, but depends only on the focus position as long as the same subject is imaged, so it is not affected by changes in subject brightness or aperture value. It becomes possible to realize a contrast autofocus operation that is faster and more reliable than the conventional one, and it is also possible to manually change the aperture.

Then, with the contrast autofocus set to the optimum focus position,
The image signal picked up by the CCD 23 is the process circuit 2
4, the luminance signal YH and the color signal C are extracted, and A /
It is supplied to the D converter 25, digitized here, and then used for the above-mentioned video through and still image pickup.

The present invention is not limited to the above-mentioned embodiments, but can be carried out by appropriately modifying it within the scope of the invention.
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.

[0026]

According to the present invention, the focus information does not depend on the absolute value of the luminance signal of the photographed image signal, but can depend on only the focus position as long as the same subject is imaged. It is possible to obtain an autofocus device that is not affected by the brightness and aperture value of a subject, can realize a high-speed and accurate autofocus operation, and can change the aperture manually.

Further, for example, even when the automatic exposure (AE) operation is also used, the autofocus operation can be independently performed without waiting for the end of the AE operation, so that a higher speed camera operation can be realized.

[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 block diagram showing an example 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 ... High-pass filter, 552 ... Rectifier circuit, 553
... low-pass filter, 554 ... division circuit, 56 ... main controller, 57 ... focus drive circuit.

Claims (2)

[Claims] 1. An image pickup unit for picking up an image of a subject, a unit for extracting an output proportional to a contrast of a picked-up image from a luminance signal of an image signal picked up by the image pickup unit, and a picked-up image of a picked-up image from a luminance signal of the image signal. Means for extracting an output proportional to the brightness; means for dividing the output proportional to the contrast of the photographed image and the output proportional to the brightness of the photographed image; and the division result of this means becomes the maximum value. An autofocus device comprising: a focus driving unit that adjusts a focus position of the image pickup unit with respect to the subject. 2. A means for extracting an output proportional to the brightness of a captured image from a luminance signal of the image signal, a high-pass filter for extracting a high-frequency component from the luminance signal, and rectifying the high-frequency component extracted by the high-pass filter. Has a rectifying circuit to
An autofocus device, wherein the means for extracting an output proportional to the brightness of a captured image from the brightness signal of the image signal has a low-pass filter for extracting a low-frequency component from the brightness signal.