KR950007868B1 - Automatic focus control apparatus of a camcorder - Google Patents

Abstract

The automatic focusing control circuit performs an accurate focusing function regardless of the color combination of the subject. The circuit includes: (a) a high-pass filter(6) which filters out the brightness component of the input image signal; (b) an absolute value computing unit(7) which protects the negative signal of the high pass filter output from the loss; (c) an A/D converter(8) which converts analog input signal into digital signal; (d) a micro computer(10) which controls the focusing motor to move the lens(1) into correct position using a generated focusing evaluation value.

Description

Camcorder Auto Focus Control

(A) of FIG. 1 is an exemplary diagram in which the subject is black and white, (b) is a waveform diagram of an image signal for (a), and (c) is a waveform diagram of a signal obtained by high-pass filtering (b).

(A) of FIG. 2 is an exemplary diagram in which the subject is white and black, (b) is a waveform diagram of the video signal for (a), and (c) is a waveform diagram of the signal obtained by high pass filtering of (b).

3 is a block diagram of an autofocus control device of the camcorder.

* Explanation of symbols for main parts of the drawings

1: lens 2: aperture

3: CD 4: Automatic gain control unit

5: Image signal processor 6: High pass filter

7: Absolute value calculation unit 8: A / D conversion unit

9: adding unit 10: microcomputer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for automatically adjusting the focus of a camcorder. In particular, in an autofocus control apparatus, when a focus evaluation value is acquired using a high pass filter, a negative voltage generated at a falling edge of an image signal is not lost. The present invention relates to an autofocus control apparatus of a camcorder which enables an autofocus function to be performed on any subject.

In a conventional autofocus apparatus of a camcorder, when a subject is black and white as shown in FIG. 1 (a), the corresponding video signal is as shown in FIG. 1 (b), and the high-pass filtered signal is shown in FIG. As shown in (c), the normal focusing function can be normally performed. However, when the subject is white or black as shown in (a) of FIG. 2, the corresponding video signal is as shown in (b) of FIG. Since the filtered signal becomes as shown in (c) of FIG. 2, i.e., a negative differential pulse is generated and the focus function cannot be performed.

In order to solve such a defect, the present invention has been invented to always perform a normal focal point function regardless of how the color of a subject is configured, which will be described in detail with reference to the accompanying drawings.

3 is a block diagram of an automatic focus control apparatus of a camcorder according to the present invention, in which a focus is input through a lens 1, an aperture 2, and a CD 3 in the camera focusing apparatus. An automatic gain control unit 4 for controlling gain of an image signal for a subject, an image signal processing unit 5 for processing the output signal of the automatic gain control unit 4 to be output to the outside, and the CD 3 A high pass filter 6 for filtering the luminance signal from the output video signal of the subfield, an absolute value calculating unit 7 for calculating an absolute value so that negative voltage is not lost among the output signal components of the high pass filter 6, and Focus evaluation value data by receiving the output signal of the analog (A) / digital (D) converter 8 and the A / D converter 8 which converts the analog output signal of the absolute value calculating part 7 into a digital signal. In addition to dividing the screen to calculate the digital signal The division unit 9 and the microcomputer 10 for moving the lens 1 to the home position by controlling the focus motor in order to achieve autofocus by receiving the focus evaluation value output from the adder 9. The present invention configured as described above will be described in detail with reference to FIGS. 1 and 2 as follows.

First, the general focus control process will be described. The image signal incident from the subject through the lens 1, the aperture 2, and the CD 3 is supplied to the automatic gain control unit 4 to adjust the gain, and then again. The output signal of the CD 3 is supplied to the high pass filter 6, and the high frequency luminance signal corresponding to the preset cutoff frequency is supplied. It is filtered out.

Then, the high-frequency luminance signal output to the high-pass filter 6 is supplied to the absolute value calculating section 7 to calculate the absolute value of the luminance signal, which is in turn supplied to the A / D converter 8, where the digital signal is obtained. Is converted and then supplied to an adder 9, and the adder 9 accumulates and outputs the luminance signal, and the focus evaluation data output from the adder 9 is microcomputer 10. Is supplied to the microcomputer 10 to grasp the current focus state based on this, and then control the focal length of the lens 1 through the motor drive to find the position of the focal point.

For example, when the subject is black and white as shown in (a) of FIG. 1, the image signal is as shown in (b) of FIG. 1, and the high-pass filtered signal is as shown in (c) of FIG. Therefore, it is possible to perform the normal focal point function normally, and when the subject is made of white and black as shown in FIG. 2A, the corresponding video signal is as shown in FIG. 2B. Since it becomes as (c) of FIG. 2, that is, negative differential pulse generate | occur | produces.

However, the signal as shown in (c) of FIG. 2 is supplied to the absolute value calculating section 7 again, so that the negative pulse is calculated as an absolute value, so that the signal is not lost, which is the A / D converter 8 Since the focus evaluation value is normally calculated through the summation unit 9 and the summation unit 9, the microcomputer 10 controls the focal length of the lens 1 through the motor driving unit (not shown) as described above based on the position of the focal point. You will find.

As described in detail above, the present invention has the advantage that it is always possible to normally perform the focal point function regardless of how the color of the subject is configured by calculating the absolute value of the luminance signal of the subject.

Claims (1)

A focus adjusting apparatus of a camera, comprising: a high pass filter (6) for filtering a luminance signal from an image signal input through a lens (1), an aperture (2) and a CD (3), and an output of the high pass filter (6) An absolute value calculating section 7 for calculating an absolute value so that no negative voltage is lost in the signal component, an A / D converter 8 for converting the analog output signal of the absolute value calculating section 7 into a digital signal, A summation section 9 for dividing the screen and integrating a digital signal to receive the output signal of the A / D converter 8 to calculate the focus evaluation value data, and to output the summation section 9. It is composed of a microcomputer 10 which moves the lens 1 to the correct position by controlling the focus motor to receive the focus evaluation value and to realize the auto focus. Control unit.