KR950007031B1 - Auto-focus controlling circuit for camera - Google Patents

Abstract

a counter for receiving a horizontal synchronous signal from an image signal processor and dividing it into signals of a designated duty ratio; a switch for generating an image signal through a selective path by switching by means of the control of the counter; a peak detector for receiving the alternatively applied image signal from the switch in every period of the horizontal synchronous signal and detecting the peak thereof; an A/D converter for converting the output analog signal of the peak detector to a digital signal; and a micon for generating the control signal to automatically adjusting focus by regulating the lens of the camera according to the change of the estimated focus value from the A/D converter.

Description

Camera auto focusing circuit

1 is a conventional camera focus automatic adjustment circuit diagram.

2A and 2B show a relationship between a subject, an image signal, and a high frequency component.

3 is an automatic focus adjustment circuit of the camera of the present invention.

4 is an operation timing diagram of a horizontal synchronization signal and a counter of FIG.

5 is a flowchart of control performed by the microcomputer of FIG.

* Explanation of symbols for main parts of the drawings

1: lens 2: aperture

3: CD 4: auto gain control unit

5: Image signal processor 20: Counter

21: switch 22 to 24: peak detector

25: A / D converter 26: Micom

TECHNICAL FIELD The present invention relates to the adjustment of the autofocus of a camera, and more particularly, to an automatic focus adjustment circuit of a camera that is suitable for automatically adjusting the focus on a subject having a horizontal pattern.

In general, the conventional camera automatic focus adjustment circuit is used as shown in Figure 1, the image signal input through the lens (1), the aperture (2) and the CD (3) is the automatic gain control unit (4) The high-pass filter unit 6 is input to the high-pass filter unit 6, and the high-pass filter unit 6 extracts the high-band components of the video signal and uses the focus evaluation value to determine whether the focus is correct or not.

That is, when the focus is correct, the high frequency component of the video signal is large, and the value of the focus evaluation value is increased. On the contrary, when the focus is not focused, the high frequency component of the video signal is decreased.

The focus evaluation value is analog-digital converted and the value is transmitted to the microcomputer 9 to rotate the motor (not shown) in the direction of increasing the focus evaluation value, thereby automatically adjusting the focus of the camera.

Referring to the operation and problems with respect to the automatic focusing device configured as described above in detail as follows.

First, the image signal passing through the lens 1, the aperture 2, the CD 3, and the automatic gain adjusting unit 4 in FIG. 1 is input to the signal recording circuit through the image signal processing unit 5. In addition, the video signal passing through the automatic gain control unit 4 is input to the high pass filter unit 6 to extract the high pass component.

The high frequency component of the video signal is converted into a digital signal by the analog / digital converter 7 and digital integration is performed at intervals of one field. The integrated value is transmitted to the microcomputer 9 to be used as the evaluation value of the automatic focus, and the microcomputer 9 performs the automatic focus by driving the motor in the direction in which the focus evaluation value increases.

However, when the autofocus adjustment circuit extracts the focus evaluation value using a high-frequency motor, the high-frequency component exists in the image signal for the subject as shown in FIG. There is a problem that causes a malfunction because the high frequency component does not exist in the auto focus cannot be performed.

Accordingly, the present invention was conceived in order to provide a camera driving circuit capable of performing auto focus on a subject having a horizontal pattern in view of the deficiencies caused by the conventional auto focus control circuit as described above. As follows.

FIG. 3 is an automatic focusing circuit diagram of the present invention. As shown in FIG. 3, three peak detectors are used in place of the high pass filter in the conventional circuit of FIG. The counter 20, the counter 20 for dividing the horizontal synchronizing signal from the counter 20, and the output signal of the automatic gain control unit 4 according to the control signal from the counter 20. A switch 21 for performing a switching operation to output to another path, peak detectors 22 and 23 for holding the maximum value in an image signal input from the switch 21, and the peak detectors 22 and 23; A peak detector 24 for holding the maximum value by comparing the value of the held video signal, an A / D converter 25 for converting the analog signal of the peak detector 24 into a corresponding digital value, and Output data of the A / D converter 25; It consists of a microcomputer 26 that automatically adjusts the focus of the camera by controlling the motor driver 10 coupled to the outside by inputting and interpreting it.

Referring to the operation and effect of the circuit of the present invention configured as described above in detail as follows.

That is, in FIG. 3, the image signal passed through the lens 1, the iris 2, the CD 3, and the automatic gain control unit 4 is output to the signal recording circuit through the image signal processing unit 5. As shown in FIG.

The horizontal synchronization signal generated by the image signal processor 5 is divided in two by the counter 20, and then the switch 11 is turned on / off according to the level of the divided signal to alternate the horizontal scanning time. Switch to.

4A and 4B are timing diagrams of the horizontal synchronization signal and the output of the counter 20. During the first horizontal scanning period, the peak detector 22 is selected to detect the maximum value of the image signal, and the counter 20 is output. By resetting the peak detector 23 at the falling edge of and resetting the peak detector 22 between the second and horizontal syringes, the difference in the maximum value of the video signal is always output during the adjacent horizontal scanning period.

This value is input to the peak detector 24 to detect the maximum value within one field period, and this value is again converted into a digital signal through the A / D converter 25 and then input to the microcomputer 16 to focus It is used as an evaluation value.

On the other hand, the vertical synchronizing signal generated by the image signal processing unit 5 generates an interrupt to the microcomputer 26 every field to read the focus evaluation value from the A / D converter 25 every field period. .

After reading the focus estimate, the microcomputer 26 immediately resets the peak detector 24 and performs the most optimal automatic focusing by an algorithm such as FIG. When one field has elapsed, the evaluation value of the focus is obtained, and then the peak detector 24 is reset, and if the evaluation value of the focus is not increased, the focusing in the camera is automatically adjusted by reverse rotation of the motor.

As described above, the present invention makes it possible to automatically adjust the focus accurately even on a subject having a horizontal pattern from the difference of the maximum value of the image signal during the adjacent horizontal scanning period in the camera.

Claims (1)

A counter 20 for inputting a horizontal synchronous signal from the image signal processor 5 and dividing it into a signal having a certain duty ratio, and controlled by the counter 20 to selectively route the video signal through a switching action. Peak detectors 22 and 23 for inputting a switch 21 to be output through the image signal, an image signal applied alternately from the switch 21 for each period of the horizontal synchronization signal, and detecting the peak value; A peak detector 24 which compares the outputs of 22 and 23 and detects the peak value thereof, an A / D converter 25 which converts an output analog signal from the peak detector 24 into a digital signal, and the A A micro-computation of the camera, characterized in that the input of the focus evaluation value from the / D converter 25 and outputs a control signal to automatically adjust the focus by adjusting the lens of the camera according to the increase or decrease state. Circuit.