JP2000047094A - Autofocus control method for digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform appropriate focus control processing even when camera shake is caused by obtaining the difference value of plural acquired contrast signal values and selectively switching a succeeding focus control method in accordance with the difference value. SOLUTION: The camera is composed of a zoom lens 1, an AF lens 2, a CCD 3, a motor driving circuit 4 for the zoom lens, a motor driving circuit 5 for the AF lens, an MPU 6 and a stepping motor 7. In such constitution, while a photographing lens is moved from a closest distance to infinity, it is stopped at plural points and a contrast signal at that position is obtained. At such a time, a difference from the contrast signal at the previous position is calculated to obtain the difference value and whether it is equal to or above a specified value or whether it is positive or negative are judged. By repeating such operation at each point, the contrast signal is acquired again, When the signal level is a value near to the value at the previous focusing position, the position is finally recognized as the focusing position and automatic focus control is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an automatic focus control method for a photographing lens of a digital camera.

[0002]

2. Description of the Related Art In a conventional automatic focusing control method for a photographic lens by a hill-climbing servo system, a maximum value is detected by measuring a contrast signal while moving the photographic lens along its optical axis. At this time, when the change of the contrast signal changes from increase to decrease, a contrast signal having a value larger than this peak value within a predetermined distance before and after the position of the taking lens indicating the peak value during the increase and decrease is obtained. If not found, the photographing lens is set at a position indicating the peak value. On the other hand, when a contrast signal having a value larger than the peak value is obtained, the photographing lens is further moved from the position according to the hill-climbing servo method (for example, Japanese Patent Publication No. 3-21892).

[0003]

However, in the prior art, when a camera shake or the like occurs, the position of the photographing lens showing the peak value changes, and it is necessary to perform automatic focus control again from the beginning. Would. Also,
Therefore, there is a problem that the processing time of the automatic focus control takes a long time.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems of the prior art, and to provide an automatic focusing lens for a digital camera capable of performing an appropriate focus control process according to the state of camera shake even when camera shake occurs. A focus control method is provided.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to an automatic focusing control method for a photographing lens using a hill-climbing servo system. The imaging lens is moved to the position of the maximum value, the contrast signal is measured and obtained again at that position, the difference value between the obtained contrast signal value and the previously obtained contrast signal value is obtained, and the difference value of this difference value is obtained. There is provided an automatic focus control method for a digital camera, characterized in that a subsequent focus control method is selectively switched according to the size.

In the above automatic focus control method, if the difference value is within a specified value range, it is determined that a camera shake has occurred, and the photographing lens is moved again within a certain range to obtain a contrast signal. Then, the in-focus position is corrected.

[0007] According to the above method, an appropriate automatic focus control method can be selected according to the deviation of the camera shake.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration around a lens of an automatic focus control device according to the present invention. FIGS. 2 and 3 are graphs showing a change of a contrast signal with respect to a photographing lens position. FIG. 3 is a graph for explaining a change due to camera shake. FIG. 4 is a flowchart showing the procedure of the automatic focus control method of the present invention.

In FIG. 1, 1 is a zoom lens, 2 is A
A photographing lens for automatic focus control by an F lens, 3 an image sensor such as a CCD, 4 a drive circuit of a zoom lens drive motor,
Reference numeral 5 denotes a driving circuit of an AF lens driving motor, 6 denotes an MPU for controlling the control, and 7 denotes a stepping motor for driving each lens. Since the present invention does not involve a zoom lens system, description thereof will be omitted.

In FIG. 2, the horizontal axis represents the position of the taking lens, the vertical axis represents the magnitude of the contrast signal, and the circles in the figure represent the positions of the taking lens for measuring and acquiring the contrast signal. . In the figure, denotes a photographing lens movement point when a contrast signal is obtained. Is the focus point, which is the peak point in the contrast signal obtained by moving the photographing lens, and once the focus position is recognized, it returns to that position again for confirmation, and the contrast signal is obtained. 5 shows the level of the contrast signal when the display is turned on.

[0011] The same applies to the case where the level of the contrast signal is lower and different. Here, indicates the locus of the contrast signal obtained by moving the taking lens.

FIG. 3 shows a locus of a contrast signal obtained by first moving the photographing lens in one way.
Indicates the locus of the contrast signal when camera shake occurs. Indicates a photographing lens movement range when the camera shake is recognized and the photographing lens is moved again within a certain range.

Next, based on the flowchart of FIG.
The automatic focus control method of the present invention will be described. In the figure, the photographing lens is moved from the closest point to infinity, and the lens is stopped at a plurality of points in the meantime to obtain a contrast signal at that position. At this time, a difference from the contrast signal at the previous position is calculated to obtain a difference value (current value b-previous value a), and it is determined whether the difference is equal to or greater than a specified value and whether the value is positive or negative. Here, if the difference value is equal to or smaller than a specified value, it is determined that there is no change. If the difference value is equal to or larger than the specified value, the difference is determined to be increased, and if the difference value is negative, it is determined to be decreased.

This is repeated at each point, and when the increase and the decrease are recognized, the in-focus position can be determined. In order to confirm that the in-focus position is really correct, return to the in-focus position from the reduced position and acquire a contrast signal again (in FIG. 2,...), And this signal level is higher than the previous in-focus position. If the value is close to the value, the position is finally recognized as the in-focus position, and the automatic focus control ends.

In the case of the signal level at the time of confirming the in-focus position, it is determined that camera shake has occurred to a small extent, and the photographing lens is moved again within a certain range as described above.
A focus position correction process is performed on a subject shifted due to camera shake.

That is, as shown in FIG. 3, the solid line is the original locus of the contrast signal, but the locus becomes like the locus of the signal due to camera shake. Therefore, if the level of camera shake is small, it is sufficient to move the photographing lens only within a certain range and detect the in-focus position again.

If the signal level deviates to the signal level at the time of confirming the in-focus position, it is determined that significant camera shake has occurred, and a retry process for performing automatic focus control is performed from the beginning.

[0018]

As described above, according to the present invention, even when camera shake occurs, appropriate automatic focus control can be performed, and by performing processing at the time of confirming the in-focus position, it is possible to prevent defocusing and stabilize. Automatic focus control can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration around a lens of an automatic focus control device according to the present invention.

FIG. 2 is a graph showing a change of a contrast signal with respect to an imaging lens position in the automatic focus control method of the present invention.

FIG. 3 is a graph showing a change of a contrast signal for explaining a shift due to camera shake with respect to a photographing lens position.

FIG. 4 is a flowchart showing a procedure of an automatic focus control method of the present invention.

[Explanation of symbols]

 2 AF lens (photographing lens) 3 Image sensor (CCD) 5 AF lens drive motor drive circuit 6 MPU 7 Stepping motor

Claims (2)

[Claims] In an automatic focusing control method for a photographing lens using a hill-climbing servo method, a photographing lens is moved to a position of a maximum value of a contrast signal when detecting a focus point, and the photographing lens is moved again to that position. A contrast signal is measured and acquired, a difference value between the acquired contrast signal value and the previously acquired contrast signal value is obtained, and a focus control method is selectively switched according to the magnitude of the difference value. An automatic focus control method for a digital camera. 2. When the difference value is within a specified value range, it is determined that a camera shake has occurred, and the photographing lens is moved again within a certain range to obtain a contrast signal, thereby correcting the in-focus position. 2. The method according to claim 1, wherein the automatic focus control is performed.