JP3098144B2 - Auto focus device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera autofocus apparatus, and more particularly, to a signal processing type autofocus apparatus.

[0002]

2. Description of the Related Art In a signal processing type autofocus apparatus, the high frequency component of an image luminance signal when a focus lens is moved forward and backward draws a mountain shape having a peak at a focus position. After integrating the high frequency component of the signal, the signal is input to a microcomputer, and the microcomputer performs hill climbing control using the high frequency component.

FIG. 3 shows an example of a circuit block diagram of a conventional autofocus device.

[0004] The autofocus device photoelectrically converts the light S7 passing through the lens 8 into an electric signal S8.
D9, a signal processing unit 10 for processing the electric signal S8 as a video signal, and a band-pass filter (BPF)
It comprises a high frequency component detector 11 having an integrator 11-1 and an integrator 11-2, a microcomputer 12 for performing hill-climbing control, and a lens control 13 for controlling a lens position based on a control signal from the microcomputer 12.

The light S7 passing through the lens 8 is photoelectrically converted by the CCD 9 into an electric signal S8, which is processed as a video signal by the signal processing unit 10. The processed video signal S9 is output to the next processing unit. The luminance signal S10 from the signal processing unit is input to the high-frequency component detector 11.

In the high frequency component detector 11, a BPF 11-
In step 1, only the necessary band is extracted from the luminance signal S10, and the integrator 11-2 performs integration. The result of this integration is input to the microcomputer 12 as high frequency component data Sll, and is used as autofocus data.

The microcomputer 12 controls the focus through the lens control 13 by performing hill-climbing control using the obtained data.

[0008]

According to the conventional method, when a subject is photographed in a state where the focus is fixed and camera shake occurs, or when the subject moves even when the camera is fixed, as shown in FIG. Time change of the high frequency component. Also, when the camera shake or the subject moves during the hill-climbing control, the change of the high-frequency component is as shown in FIG. In these cases, a false peak will be present before reaching the focus position.
The high-frequency component in the actual video signal changes to create a fake peak in response to camera shake and the movement of the subject,
Such a change is not desirable as a high-frequency component for autofocus.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention relates to an autofocus apparatus, comprising: means for detecting a high-frequency component of an image luminance signal; It is characterized by comprising means for detecting the amount, means for normalizing the high-frequency component by the amount of motion, and means for controlling the hill-climbing of the focus by the normalized high-frequency component.

Preferably, the means for detecting the high-frequency component comprises a band-pass filter and an integrator. Similarly, the means for detecting the amount of motion comprises an absolute value of a previous field and a current field for a plurality of representative points. It is desirable to have a means for calculating the difference and an integrating means for integrating the absolute value difference results for the plurality of representative points.

[0011]

The means for detecting the high frequency component of the luminance signal extracts only the high frequency component by the BPF from the luminance signal from the signal processing section and outputs the result of integration to the normalizing means. The means for detecting the motion amount of the video detects the motion amount at each point of the video, and outputs the motion amount data to the normalizing means. The motion amount data is obtained by integrating the absolute value difference between the luminance data of the previous field and the luminance data of the current field of several tens of representative points. Ideally, a stationary subject is 0, and a subject with more movement has larger data. . The normalizing means normalizes the high frequency component by multiplying the motion amount data by a certain coefficient and performing an operation on the high frequency component data. By normalizing the high-frequency component by the amount of movement at each point, the reliability of the high-frequency component as data for autofocus can be improved.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an automatic focusing apparatus according to the present invention.

FIG. 1 is a circuit block diagram of the autofocus device. The autofocus device photoelectrically converts the light S1 passing through the lens 1 and outputs an electric signal S
2, a signal processing unit 3 for processing the electric signal S2 as a video signal, a high frequency component detector 4 including a BPF 4-1 and an integrator 4-2, and a microcontroller for performing hill-climbing control. The computer includes a computer 6 and a lens control 7 for controlling a lens position based on a control signal from the microcomputer 6.

The autofocus device of the present embodiment further includes a motion detector 5 to which a luminance signal S4 from the signal processor 3 is input, in addition to the above configuration. The motion amount detector 5
A signal S6 obtained by integrating the absolute value difference between the luminance data of the previous field and the luminance data of the current field at several tens of representative points.
, A D flip-flop 5-1 to which the luminance signal S4 is input, an absolute value differentiator 5-2, and an absolute value differentiator 5 to which the luminance signal S4 and the output from the D flip-flop 5-1 are input. -2 to which the output from -2 is input
-3.

The light S1 having passed through the lens 1 is photoelectrically converted by the CCD 2 into an electric signal S2, which is processed as a video signal by the signal processing section 3. The processed video signal S3 is output to the next processing unit. Also, the luminance signal S from the signal processing unit
4 is input to the high frequency component detector 4 and the motion amount detector 5.

In the high-frequency component detector 4, only a necessary band is extracted by a band-pass filter (hereinafter, BPF) 4-1.
The integration is performed by the integrator 4-2. This integration result is input to the microcomputer 6 as high frequency component data S5,
Used as autofocus data.

On the other hand, the motion amount detector 5 calculates the absolute value difference between the previous field and the current field for a certain number of 10 representative points of the luminance signal S4. In the case of a temporally continuous image, the luminance signal has some correlation between consecutive fields. Therefore, comparing the luminance signals at the same point in consecutive fields, if there is no difference, the point is stationary, and it can be considered that the larger the difference, the greater the movement. This is obtained for 10 representative points in the field, and by integrating them all, the motion amount of the video can be detected. The D flip-flop 5-1 stores the representative point of the previous field. The absolute value differentiator 5-2 obtains the absolute value difference between the two fields. The integrator 5-3 integrates the results of the absolute value difference at several tens of points. The integration result is input to the microcomputer 6 as motion amount data S6.

The microcomputer 6 calculates Equation 1 from the high-frequency component data and the motion amount data to obtain normalized data.

Normalized data = F (high-frequency component data, motion amount data) Equation 1 Here, the function F is, for example, as shown in Equations 2 and 3.

F (A, B) = A + α · B (α is a coefficient) Equation 2 F (A, B) = A · (β · B) (β is a coefficient) Equation 3 Equations 2 and 3 are as follows. The purpose is to correct high-frequency component data that decreases in a certain case with the amount of motion. Which correction is appropriate is determined experimentally, including the coefficients α and β.

The microcomputer 6 controls the focus through the lens control 7 by performing hill-climbing control using the obtained normalized data.

FIG. 2 shows an example of the results of the implementation of the present invention.
The high frequency component when there is no camera shake is constant, but when there is camera shake, the high frequency component rises and falls due to camera shake. In addition, the amount of motion shows a change opposite to that of the high-frequency component due to camera shake. According to Equation 2, the normalized data shown in the figure is obtained.

[0023]

As described in detail above, the present invention comprises means for detecting the amount of motion at each point of an image, and means for normalizing high-frequency components with the amount of motion. It can suppress the occurrence of spurious peaks for subjects with noisy spots, improving reliability as data for autofocus, thereby improving focus performance for camera shake and moving subjects. I can do it.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an autofocus device according to the present invention.

FIG. 2 shows a temporal view of a high-frequency component in a case where a camera shake is caused by photographing a stopped subject in a state where the focus is fixed and a case where the subject moves even when the camera is fixed in the auto focus apparatus according to the embodiment. It is a figure showing a change.

FIG. 3 is a block diagram of a conventional autofocus device.

FIG. 4 shows a temporal change of a high-frequency component in a case where camera shake occurs when a subject to be stopped is photographed in a state where the focus is fixed by a conventional autofocus device or when the subject moves even when the camera is fixed. FIG.

FIG. 5 is a diagram illustrating a change in a high-frequency component when a camera shake or a subject moves during hill-climbing control by a conventional autofocus device.

[Explanation of symbols]

 1, 8 lens 2, 9 CCD 3, 10 signal processing unit 4, 11 high-frequency component detector 4-1, 11-1 BPF 4-2, 11-2 integrator 5 motion detector 5-1 D flip-flop 5 -2 Absolute value difference unit 5-3 Integrator 6,12 Microcomputer 7,13 Lens control unit S1, S7 Optical signal S2, S8 CCD output signal S3, S9 Signal processing unit output signal S4, S10 Luminance signal S5, S11 High frequency Component data S6 Motion data

Claims (3)

(57) [Claims] A means for detecting a high-frequency component of a luminance signal of an image; a means for detecting an amount of motion at each point of the image;
An autofocus apparatus comprising: means for normalizing a high-frequency component by a motion amount; and means for performing focus hill-climbing control using the normalized high-frequency component. 2. The auto-focusing device according to claim 1, wherein the means for detecting the high-frequency component comprises a band-pass filter and an integrator. 3. The method according to claim 2, wherein the means for detecting the amount of motion includes means for calculating an absolute value difference between luminance signals of a previous field and a current field for a plurality of representative points, and integrating the absolute value difference results for the plurality of representative points. The autofocus device according to claim 1, further comprising an integrating means.